Revista Australiana de Ortodoncia (1)

ContentsOriginal articles1 The dimensions of the roots of the human permanent dentition as a guide to the selection of optimal orthodontic forces

Brian Lee10 Amorphous calcium phosphate-containing orthodontic composites. Do they prevent demineralisation around orthodontic

brackets?Tancan Uysal, Mihri Amasyali, Alp Erdin Koyuturk, Suat Ozcan and Deniz Sagdic

16 Cytotoxicity of orthodontic separating elasticsMatheus Melo Pithon, Rogrio Lacerda dos Santos, Fernanda Otaviano Martins, Maria Teresa Villela Romanos andMnica Tirre de Souza Arajo

21 Porcelain brackets during initial alignment: are self-ligating cosmetic brackets more efficient?Peter Miles and Robert Weyant

27 Display of the incisors as functions of age and genderAndrea Fonseca Jardim da Motta, Margareth Maria Gomes de Souza, Ana Maria Bolognese, Clarice Jlia Guerraand Jos Nelson Mucha

33 McNamara norms for Turkish adolescents with balanced faces and normal occlusionNihat Kilic, Glhan Catal and Hsamettin Oktay

38 Assessment of slot sizes in self-ligating brackets using electron microscopyNidhi B. Bhalla, Sarah A. Good, Fraser McDonald, Martyn Sherriff and Alex C. Cash

42 Space planning sensitivity and specificity: Royal London Space Planning and Korkhaus AnalysesRania Dause, Martyn Cobourne and Fraser McDonald

49 Response of the expanded inter-premaxillary suture to intermittent compression. Early bone changesTancan Uysal, Huseyin Olmez, Mihri Amasyali, Yildirim Karslioglu, Atilla Yoldas and Omer Gunhan

56 Associations between upper lip activity and incisor positionNihat Kilic

61 Effects of levelling of the curve of Spee on the proclination of mandibular incisors and expansion of dental arches: a prospective clinical trialNikolaos Pandis, Argy Polychronopoulou, Iosif Sifakakis, Margarita Makou and Theodore Eliades

66 A comparison of dental changes produced by mandibular advancement splints in the management of obstructive sleepapnoeaHui Ching Ang and Craig Dreyer

73 Does ozone water affect the bond strengths of orthodontic brackets?Matheus Melo Pithon and Rogerio Lacerda dos Santos

78 Incremental effects of facemask therapy associated with intermaxillary mechanicsGuilherme Thiesen, Juliana de Oliveira da Luz Fontes, Michella Dinah Zastrow and Naudy Brodbeck May

84 Bond strengths of different orthodontic adhesives after enamel conditioning with the same self-etching primerRogelio J. Scougall-Vilchis, Chrisel Zrate-Daz, Shusuke Kusakabe and Kohji Yamamoto

Case report90 Multidisciplinary treatment of a fractured root: a case report

Osmar Aparecido Cuoghi, lvaro Francisco Bosco, Marcos Rogrio de Mendona, Pedro Marcelo Tondelli andYsselin Margot Miranda-Zamalloa

Editorial95 Can an optimal force be estimated?

Michael Harkness

General97 Book reviews 107 Calendar102 Research reviews 108 ASO Directory106 New products

AustralianOrthodontic JournalVolume 26 Number 1, May 2010

Australian Orthodontic Journal Volume 26 No. 1 May 2010

Introduction

In 1952 Storey and Smith showed that orthodonticforces above a certain level produced lower rates oftooth movement than forces below that level.1They named the lower forces optimal forces. Thisdefinition has been extended to include the proviso oflittle or no permanent damage to the root and/or the tissues surrounding the root. Importantly, it wassuggested that it was the pressure exerted by the root on the surrounding tissues rather than the actualnumeric value of the force that was a critical factor intooth movement.1 Almost coincidentally, Begg pub-lished results of cases with dramatically short treat-ment times treated entirely by using round wires withsmall cross-sectional areas which seemed to supportthe notion of differential force, which is the use oflight and heavy forces to control the speed of toothmovement.2

Various authors have investigated root dimensionssuch as the surface area;312 root volume,13,14 the relation between root length and crown diameter14and the projected area of the roots,15,16 that may beimportant for tooth movement. It has been arguedthat the relative size of the root(s) may indicate atooths resistance to an orthodontic force or theanchorage value.17 High forces are required to moveteeth with large root surface areas. If it were possibleto determine the optimal force levels for tooth move-ment prior to the commencement of treatment,appliances would function with greater efficiency.Our attention was thus focused on the areas of theroots of the permanent dentition.

In this study the lengths, widths and projected areasof the roots of the upper and lower permanent teeth,including the third molars, were measured. Ourintention was to gain an insight into the relations

Australian Society of Orthodontists Inc. 2010 Australian Orthodontic Journal Volume 26 No. 1 May 2010 1

The dimensions of the roots of the human permanent dentition as a guide to the selection of optimal orthodontic forces

Brian LeeBonnet Hill, Tasmania, Australia

Background: The dimensions of the roots of the teeth are important in the assessment of orthodontic anchorage and to estimatethe forces to be used during orthodontic tooth movement. Aims: To investigate the relations between the lengths, widths and projected areas of the roots of the permanent teeth.Methods: Intact, extracted human permanent teeth were photographed and the lengths, widths and projected areas of selectedsurfaces measured. Descriptive statistics and associations between selected linear dimensions and root areas were calculated.Results: The data showed significant kurtosis and skewness. Neither exponential nor polynomial transformations improved thegoodness of fit, and there was no a priori reason to use other than linear regression. When the lengths of all teeth were multiplied by the respective widths of the mesial, distal and lingual surfaces, the correlations between the product of length andwidth and area improved in 28 out of 30 surfaces. In the lower arch the correlation coefficients ranged from r = .343 (mesialsurface first premolar) to r = .845 (mesial surface of the canine). The correlations in the upper arch ranged from r = .201(mesial surface of the second molar) to r = .847 (mesial surface lateral incisor).Conclusions: For clinical purposes, root length may be an acceptable indicator of root area. Low correlations were attributed tovariations in root shape.(Aust Orthod J 2010; 26: 19)

Received for publication: January 2009Accepted: February 2010

Brian Lee: [email protected]

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Table I. Upper teeth, lengths and projected areas of selected surfaces.

Surface Tooth N Minimum Q25 Median Q75 Maximum r R2

Distal length (cm) 1 32 1.10 1.38 1.50 1.57 1.65 .714 0.5112 32 1.36 1.50 1.61 1.68 1.84 .762 0.5813 32 1.20 1.56 1.83 1.95 2.05 .838 0.7024 30 1.04 1.28 1.39 1.49 1.73 .715 0.5125 27 0.98 1.28 1.36 1.46 1.59 .611 0.3736 31 0.80 1.13 1.23 1.29 1.54 .524 0.2747 32 0.90 1.16 1.27 1.39 1.72 .299 0.090

Distal area (cm2) 1 32 0.43 0.60 0.65 0.70 0.822 32 0.56 0.66 0.71 0.77 0.883 32 0.62 0.82 0.98 1.06 1.544 30 0.64 0.74 0.83 0.89 1.155 27 0.48 0.66 0.72 0.77 0.936 31 1.18 1.47 1.54 1.66 2.087 32 0.69 1.00 1.12 1.26 1.62

Lingual length (cm) 1 32 1.08 1.20 1.28 1.37 1.48 .499 0.2492 32 1.12 1.20 1.32 1.43 1.59 .731 0.5353 32 1.08 1.49 1.66 1.80 1.90 .746 0.557

Lingual area (cm2) 1 32 0.42 0.45 0.50 0.56 0.702 32 0.32 0.38 0.45 0.49 0.623 32 0.34 0.56 0.60 0.64 0.84

Mesial length (cm) 1 32 1.09 1.41 1.53 1.64 1.74 .803 0.6452 32 1.29 1.50 1.59 1.73 1.86 .847 0.7173 32 1.20 1.69 1.87 1.99 2.20 .566 0.3204 30 1.08 1.29 1.36 1.49 1.71 .713 0.5085 27 1.00 1.30 1.39 1.45 1.61 .558 0.3126 31 1.06 1.22 1.34 1.41 1.66 .730 0.5337 32 1.06 1.20 1.25 1.38 1.62 .201 0.0408 12 0.83 0.93 0.99 1.10 1.15 .456 0.208

Mesial area (cm2) 1 32 0.50 0.59 0.67 0.74 0.852 32 0.54 0.65 0.69 0.74 0.863 32 0.61 0.97 1.00 1.09 1.834 30 0.48 0.73 0.85 0.94 1.135 27 0.48 0.70 0.74 0.79 0.966 31 1.10 1.56 1.68 1.81 2.347 32 0.84 1.14 1.23 1.31 1.758 12 0.77 0.97 1.19 1.27 1.36

ROOT DIMENSIONS AS A GUIDE TO 0PTIMAL ORTHODONTIC FORCES

Australian Orthodontic Journal Volume 26 No. 1 May 2010 3

Table II. Lower teeth, lengths and projected areas of selected surfaces.

Surface Tooth N Minimum Q25 Median Q75 Maximum r R2

Distal length 1 30 1.16 1.31 1.39 1.47 1.68 .441 0.1952 25 1.20 1.34 1.48 1.57 1.73 .518 0.2693 26 1.44 1.61 1.74 1.79 2.17 .835 0.6964 39 1.16 1.44 1.50 1.60 2.00 .375 0.1415 23 1.21 1.42 1.60 1.64 1.79 .485 0.2366 27 0.86 1.19 1.26 1.39 1.70 .608 0.377 27 1.00 1.12 1.20 1.37 1.60 .820 0.672

Distal area 1 30 0.46 0.53 0.57 0.61 0.762 25 0.48 0.58 0.62 0.68 0.843 26 0.64 0.80 0.97 1.12 1.514 39 0.67 0.85 1.02 1.20 1.535 23 0.64 0.70 0.76 0.80 0.956 27 0.98 1.30 1.40 1.50 2.247 27 0.71 1.10 1.30 1.50 1.71

Lingual length 1 33 1.02 1.18 1.28 1.37 1.65 .529 0.2772 47 1.10 1.32 1.40 1.48 1.60 .665 0.4423 28 1.36 1.61 1.67 1.77 2.01 .717 0.514

Lingual area 1 33 0.22 0.27 0.29 0.38 0.482 47 0.26 0.31 0.34 0.37 0.513 28 0.49 0.61 0.64 0.74 0.93

Mesial length 1 33 1.31 1.34 1.42 1.51 1.75 .566 0.3212 19 1.20 1.45 1.57 1.60 1.78 .594 0.3533 22 1.40 1.68 1.78 1.94 2.30 .845 0.7144 39 1.16 1.41 1.48 1.56 2.04 .343 0.1185 23 1.17 1.45 1.58 1.60 1.84 .582 0.3386 27 1.16 1.26 1.40 1.48 1.78 .807 0.6517 27 1.02 1.08 1.30 1.41 1.55 .812 0.6618 12 1.03 1.28 1.35 1.39 1.73 .554 0.307

Mesial area 1 33 0.53 0.57 0.63 0.67 0.882 19 0.54 0.60 0.64 0.70 0.923 22 0.64 0.80 0.96 1.11 1.574 39 0.66 0.82 1.02 1.15 1.535 23 0.48 0.70 0.80 0.83 1.066 27 1.11 1.32 1.46 1.55 2.337 27 0.87 1.11 1.38 1.50 1.888 12 0.65 0.70 0.83 1.03 1.50

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between the lengths and widths to the areas of corresponding root surfaces in the hope that thisinformation may be of value to clinicians planningorthodontic anchorage and selecting appropriateforces for tooth movement.

Materials and methods

Measurements were made of the root surfaces ofapproximately 580 extracted human permanentteeth, including the third molars. Intact and fullyformed permanent teeth were collected in the period196365 and measured using the methods describedbelow. The age, gender and ethnicity of the subjectswere not recorded.

The teeth were cleaned of attached soft tissue, dried,labelled and numbered. Multi-rooted teeth were sec-tioned through the furcation(s) in order to obtain aclear view of the root surfaces and each root was pho-tographed and measured separately. The four surfacesof the teeth (mesial, distal, buccal, lingual) were photographed alongside a metric rule. The film planewas parallel to the long axis of each tooth. The photo-graphic images were enlarged x10 and the outline ofeach root surface traced on paper. The lengths andwidths of the roots were measured on the tracings.The length of the proximal surface of a root was thedistance from the root apex to the peak of the curveof the cemento-enamel junction on the proximal sur-face, and the length of a lingual surface was the distance from the apex to the lowest point on thecurve of the cemento-enamel junction. Root widthwas measured at the cemento-enamel junction. The dimensions of the same surfaces were added.Data for corresponding right and left teeth were combined.

The area of each root surface was then measureddirectly with a planimeter (Allbrit 37595 Fixed Armplanimeter, Stanley, London, UK). The accuracy ofthe planimeter was tested before use by tracing a circle using the radius arm provided with the instru-ment to determine if the area of the traced circle coincided with the nominated area. Before analysis,the planimeter measurements were converted to theactual sizes by dividing the linear measurements by10 and the area measurements by 100. All linear andwidth measurements are in centimetres (cm) and theareas in centimetres squared (cm2).

Descriptive statistics and skewness and kurtosis werecalculated for the distal, mesial and lingual lengths,

widths and projected areas of the upper and lowerteeth. Pearsons correlation coefficients and regressionequations between the lengths and projected areas ofcorresponding root surfaces, and associations betweenroot length and the calculated area (the product oflength and width) to the projected area of correspon-ding surfaces were also calculated for teeth with widthand length measurements.

Results

The results are given in Tables I and II and Figures 1and 2. The tables contain the sample sizes, minimumand maximum values, quartile values, medians, corre-lations of length to the projected areas of selected per-manent teeth and coefficients of determination (R2

values). The measured and calculated values of thevarious surfaces of selected upper and lower teeth areshown in Figure 1. Regression lines of the relationsbetween projected root length and area of the distal,mesial and lingual surfaces of the upper and lowerteeth are given in Figure 2.

The median length of the distal surface of the uppercentral incisor root was 1.50 cm and for the uppercanine it was 1.83 cm (Table I). The median areas ofthe distal surfaces of the upper canine and first molarwere 0.98 and 1.54 cm2, respectively. The palatal sur-face of the upper lateral incisor (Median: 1.32 cm)was slightly longer than that of the upper central inci-sor (Median: 1.28 cm), but shorter than the uppercanine (Median length: 1.66 cm). The median areasof the palatal surfaces of the upper central incisor,upper lateral incisor and upper canine were 0.50,0.45 and 0.60 cm2, respectively. Although the mesialsurface of the upper first molar was shorter than allother teeth in the upper arch except the second andthird molars, it had the largest mesial area (Median:1.68 cm2). The mesial areas (medians) of all upperteeth were larger than the distal areas (medians) ofcorresponding teeth, except for the lateral incisors.

The canine was the longest tooth in the lower arch,but the areas of the mesial and distal root surfaces(Distal surface area median: 0.97 cm2; Mesial surfacearea median: 0.96 cm2) were less than the corres-ponding areas (Distal area median: 1.40 cm2; Mesialarea median: 1.46 cm2) of the first molar (Table II).The distal surface of the lower first premolar wasshorter than the same surface of the canine, but themedian area of the distal surface of the first premolarwas greater than the median area of the canine.



Length: y = 1.1851x + 0.6068 R2 = 0.7022Width: y = 0.1838x + 0.6022 R2 = 0.3644Calculated area: y = 1.273x + 0.1395 R2 = 0.8378

(a) Upper canine distal.

Length

Width

Calculated

2.5

2

1.5

1

0.5

00 0.5 1 1.5 2 2.5

Measured area cm2

Length: y = 0.7085x + 0.8334 R2 = 0.3119Width: y = 0.9536x + 0.369 R2 = 0.6159 Calculated area: y = 0.3104x + 0.5616 R2 = 0.3256

(d) Upper second premolar mesial.

LengthWidthCalculated

2.5

2

1.5

1

0.5

00 0.5 1 1.5 2 2.5

Measured area cm2

Length: y = 0.5239x + 0.465 R2 = 0.533Width: y = 0.2651x + 0.6938 R2 = 0.3841Calculated: y = 0.9501x + 0.0614 R2 = 0.7864

(e) Upper first molar mesial.

2.5

2

1.5

1

0.5

00 0.5 1 1.5 2 2.5

Measured area cm2


(f) Lower canine distal.


2.5

2

1.5

1

0.5

00 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Measured area cm2

Figure 1. Plots derived from raw data. Individual data are indicated and regression lines for length, width and calculated area (length x width) with the projected(measured) area are given.

Length

Leng

th/W

idth

/Cal

cula

ted

area

(cm

/cm

/cm

2 )

Leng

th/W

idth

/Cal

cula

ted

area

(cm

/cm

/cm

2 )Le

ngth

/Wid

th/C

alcu

late

d ar

ea(c

m/c

m/c

m2 )

Leng

th/W

idth

/Cal

cula

ted

area

(cm

/cm

/cm

2 )

1.6

1.4

1.2

1

0.8

0.6

0.4

0.2

00 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Calculated area cm2

Length: y = 0.7647x + 0.8948 R2 = 0.2495

(b) Upper central incisor lingual.

Length1.81.6

1.4

1.2

1

0.8

0.6

0.4

0.2

00 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Measureed area cm2

Length: y = 1.2694x + 0.7516 R2 = 0.5349

(c) Upper lateral incisor lingual.


Leng

th/W

idth

/Cal

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area

(cm

/cm

/cm

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Leng

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In the upper arch, the coefficients range from .847between the length and area of the mesial surface ofthe lateral incisor to .201 between the length and areaof the mesial surface of the second molar. The corre-lation coefficient between the distal surface and distalarea of the upper canine was .838 and between thelength and area of the mesial facing root surfaces ofthe upper first molar it was .730. In the lower arch,the coefficients for the distal surface of the canine andthe mesial surface of the first molar were .835 and.807, respectively.

There was significant kurtosis and skewness in thedata (more than two standard deviations) indicatingthat the distributions were not normal, but there wasno apparent relationship between skewness and thecoefficients of determination, nor was there any con-sistency in the sense or direction of the skew.However, neither exponential nor polynomial trans-formations improved the goodness of fit, and there isno a priori reason to use other than linear regression.Coefficients of determination (R2) for selected teethare given in Tables I and II. The coefficient of deter-mination indicates the degree to which the variationamongst projected areas can be accounted for by rootlength.

When the lengths of the upper teeth were multipliedby the respective widths the correlations with the cor-responding root surface lengths increased in 28 of 30surfaces. Only the correlations between the lengthsand calculated areas of the distal surfaces of the upperfirst and second molars, and the mesial lengths andcalculated areas of the lower lateral incisor and distalsurface of the lower central incisor did not improve.

DiscussionThis study set out to determine if clinically usefulassociations existed between the lengths and areas ofthe roots of the upper and lower teeth, however laterin the study, root width was included to determinewhether that dimension was of any value in estimat-ing projected area. A strong association (>.8) wouldenable a clinician to use the product of root lengthand width as a predictor of root area and select anappropriate force to obtain optimal tooth movementand/or estimate the anchorage value of a tooth orgroup of teeth.

The coefficients for the distal surfaces of the uppercanines and the mesial surfaces of the lower firstmolars accounted for approximately 70 and 65 percent of the variations in root area, respectively, whenthe root lengths were known. The coefficients ofdetermination were relatively high for several otherteeth, notably the mesial surfaces of the upper lateralincisor and the lower first and second molars. Thecoefficient of determination for the lingual surface ofthe upper central incisor was only .249, possiblybecause an incisor with a short, wide root can havethe same area as one with a long, slender root. For theupper central incisor, root length alone is not a goodpredictor of root area. We succeeded in improving thepredictability of root length by using a calculated area(length x width) in our calculations. Data for thesecalculations are available on the Journal website. In all but two cases, this quantity accounted for morevariance than using length alone.

Estimation of optimal forces needs to take intoaccount teeth with unusual variations in the axes of

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Length: y = 0.657x + 1.0277 R2 = 0.3383

(g) Lower second premolar mesial.

Length2

1.81.61.41.2

10.80.60.40.2

00 0.2 0.4 0.6 0.8 1 1.2

Measured area


(h) Lower first molar mesial.


21.81.61.41.2

10.80.60.40.2

00 0.5 1 1.5 2 2.5

Measured area cm2

Figure 1 (Continued). Plots derived from raw data. Individual data are indicated and regression lines for length, width and calculated area (length x width) with theprojected area are given.

Leng

th/W

idth

/Cal

cula

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area

(cm

/cm

/cm

2 )

Leng

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(cm

/cm

/cm

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Upper 1Upper 2Upper 3Upper 4Upper 5Upper 6Upper 7

Dis

tal a

rea

(cm

2 )

2.5

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1.5

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Distal length (cm)

Upper 1Upper 2Upper 3Upper 4Upper 5Upper 6Upper 7Upper 8

Mes

ial a

rea

(cm

2 )

2.5

2

1.5

1

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00 0.5 1 1.5 2 2.5

Mesial length (cm)

Lower 1

Lower 2

Lower 3

Lower 4

Lower 5

Lower 6

Lower 7

Dis

tal a

rea

(cm

2 )

2.5

2

1.5

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Distal length (cm)

Lower 1Lower 2Lower 3Lower 4Lower 5Lower 6Lower 7Lower 8

Mes

ial a

rea

(cm

2 )

2.5

2

1.5

1

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00 0.5 1 1.5 2 2.5

Mesial length (cm)

Lower 1

Lower 2

Lower 3

Ling

ual a

rea

(cm

2 )

2.5

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Lingual length (cm)

Upper 1

Upper 2

Upper 3

Ling

ual a

rea

(cm

2 )

2.5

2

1.5

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00 0.5 1 1.5 2

L:ingual length (cm)

(a) Regression lines showing the relations between distal lengths and areasfor the upper teeth.

(f) Mesial lengths and areas for the lower teeth.

(c) Mesial lengths and areas for the upper teeth.

(e) Lingual lengths and areas for the lower teeth.

(d) Distal lengths and areas for the lower teeth.

(b) Lingual lengths and areas for the upper teeth.

Figure 2. Regression lines for the length and areas of the upper and lower teeth.

the crowns and roots and/or root bends or curves.18,19Also the shape of the cemento-enamel junction on aproximal surface varies according to the labio-lingualwidth of the root.18 In a wide tooth the curve of thecemento-enamel junction has a somewhat flattenedshape, whereas in a narrow tooth the junction issomewhat angular in shape.

Limitations in this study that should be consideredare our methods of measuring length and area: bothmeasurements were made parallel to the long axis ofthe root and were influenced to a certain degree by the angle between the root surface and the longaxis of the tooth, and the shape of the root. Some teeth had pyramidal roots and other teeth hadcurved roots. These variations, although small, maycontribute to the variability in tooth movementencountered by a clinician using root length to estimate root area and an optimal force. For someteeth the projected length, for example of the upperlateral incisor, would be less than the actual length.When, however, the width (at right angles to the rootsurface of interest) and the projected length of a rootare known, the actual length of the root can be cal-culated. Bucco-lingual widths are difficult to measure using traditional radiographs. To overcomethis, we designed a caliper to measure the width at the cemento-enamel junction and have used thisinstrument to estimate projected areas and haveobtained results consistent with other workers (Figure 3).16,20,21 Finally, the strengths of this studyare the size of the samples and our use of teeth withfully developed roots.

How can the results be applied to estimate the optimum force for tooth movement or anchorage? To

use the graphs, first decide on a treatment plan andthe directions of tooth movement. Estimate the rootlength of a particular tooth from a radiograph orfrom an already extracted tooth and use the appro-priate regression line to obtain an estimate of rootarea. As the mean peak velocity of movement of thecanines in both humans and dogs occurred when amean pressure of 200 cN/cm-2 was exerted, multiplythis estimated area by 200 (as force equals pressure xarea) to determine the force required.20 When thisfigure is applied to the median projected area of thedistal surface of the upper canine (0.98 cm2) themean optimum pressure is 196 cN/cm-2. Thisapproximates reported estimates of 197 cN/cm-2

based on experimental data from humans.1,16,21,22Using this approach it is now possible to estimate theforces required to obtain optimal rates of tooth move-ment and, by using higher forces, a stable anchorunit. Eventually, other root dimensions, such as volume and bone density may improve estimates of atooths resistance to orthodontic movement than eitherroot length or the product of root length and width.12,13

Conclusions

The following conclusions were drawn:

1. For clinical purposes, root length may be anacceptable indicator of root area.

2. The product of root length and width resulted inhigher coefficients of determination. A method ofmeasuring bucco-lingual width is described.

2. Low correlations between root length and areawere attributed to variations in root shape.

Acknowledgments

I would like to thank Professor Shen Gang for hisassistance in collating the data for this study andDesmond Fitzgerald and Geoffrey Fenn for theirassistance with the statistics and my wife Joanna forhelp with the preparation of this report.

Corresponding author

Dr Brian W. Lee3 Lynden RoadBonnet Hill, Tasmania 7053AustraliaTel: (+61 3) 6229 9468Email: [email protected]

LEE


Figure 3. Caliper designed to measure tooth dimensions at the cemento-enamel junction.

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16. Lee BW. The force requirements for tooth movement. PartIII: The pressure hypothesis tested. Aust Orthod J 1996;14:937.

17. Chen SK, Pan JH, C CM, Jeng JY. Accuracy of supportedroot ratio estimation from projected length and area usingdigital radiographs. J Periodontol 2004;75:86671.

18. Taylor RMS. Variation in form of human teeth: I. Ananthropologic and forensic study of maxillary incisors. JDent Res 1969; 48:516.

19. Taylor RMS. Variation in form of human teeth: I. Ananthropologic and forensic study of maxillary canines. JDent Res 1969; 48:17382.

20. Ren Y, Maltha J, Vant Hof MA, Kuijpers-Jagtman AM.Optimum force magnitude for orthodontic tooth move-ment: a systematic literature review. Am J OrthodDentofacial Orthop 2004;125:717.

21. Lee BW. The force requirements for tooth movement. Part I:Tipping and bodily movement. Aust Orthod J 1995;13:23848.

22. Smith R, Storey E. The importance of force in orthodontics.Design of cuspid retraction springs. Aust J Dent 1952;56:291304.



IntroductionPoor oral hygiene following placement of a bondedorthodontic appliance can result in unsightly whitespot lesions on the labial surfaces of the anteriorteeth.1,2 Although a white spot lesion is the first visi-ble sign of enamel softening, measurable deminerali-sation can occur around orthodontic brackets as earlyas one month after an appliance has been placed.36Overall management of white spot lesions involvesmethods of both preventing demineralisation andencouraging remineralisation of existing lesions.7 The

former includes good oral hygiene and the latter mayinclude the application of materials, such as caseinphosphopeptide amorphous calcium phosphatenano-complexes (CPP-ACP) that enhance remineral-isation of enamel.8 A recent development has beenthe addition of amorphous calcium phosphate (ACP)to orthodontic composites with the intention ofenhancing enamel remineralisation around bondedbrackets. This area is particularly prone to deminer-alisation because plaque readily accumulates onorthodontic composites.

Australian Orthodontic Journal Volume 26 No. 1 May 2010 Australian Society of Orthodontists Inc. 201010

Amorphous calcium phosphate-containing orthodontic composites. Do they prevent demineralisation around orthodontic brackets?

Tancan Uysal,* Mihri Amasyali, Alp Erdin Koyuturk,+ Suat Ozcan,and Deniz SagdicDepartment of Orthodontics, Erciyes University, Kayseri, Turkey and King Saud University, Riyadh, Saudi Arabia,* Department ofOrthodontics, Glhane Military Medical Academy, Ankara, Turkey, Department of Pediatric Dentistry, Ondokuz Mayis University, Samsun,Turkey,+ and the Department of Conservative Dentistry and Endodontics, Gazi University, Ankara, Turkey

Background: A preliminary study using laser fluorescence suggested that amorphous phosphate-containing orthodontic composites may prevent demineralisation around bonded orthodontic brackets. Objective: To compare the microhardness of the enamel around brackets bonded with an amorphous calcium phosphate-containing orthodontic composite (ACP-containing) with the microhardness of the enamel around brackets bonded with a conventional composite resin.Methods: Forty extracted upper premolars were used. Orthodontic brackets were bonded to the teeth with either an ACP-containing composite resin (N = 20) or a conventional composite resin (N = 20). The latter were used as the control. Thecrowns of all teeth were painted with an acid resistant varnish, leaving a 2 mm ring of exposed enamel around the brackets.The teeth were then subjected to a daily cycle of demineralisation for 6 hours and remineralisation for 18 hours for 21 days.Each tooth was sectioned and the microhardness of the enamel determined 25, 50, 75, 100 and 150 m from the surface.Results: The enamel was significantly harder 25 m (p = 0.000) and 50 m (p = 0.001) from the enamel surface in the teethwith brackets bonded with the ACP-containing composite resin as compared with the control teeth.Conclusion: ACP-containing orthodontic composite resins may reduce the enamel decalcification found in patients with poororal hygiene.(Aust Orthod J 2010; 26: 1015)

Received for publication: April 2009Accepted: July 2009

Tancan Uysal: [email protected] Amasyali: [email protected] Koyuturk: [email protected] Ozcan: [email protected] Sagdic: [email protected]

DO ACP-CONTAINING COMPOSITE RESINS PREVENT DEMINERALISATION?


In a preliminary study we used a laser fluorescencedevice to compare enamel demineralisation aroundorthodontic brackets bonded with either an ACP-containing composite or a resin-modified glassionomer cement.9 We found that ACP-containingorthodontic composites provided the highest reduc-tions in enamel demineralisation when comparedwith a resin-modified glass ionomer cement and thecontrol. However, Diniz et al. recently reported thatlaser fluorescence devices for detecting in-vitro demineralisation are unreliable.10 Thus, we decidedto determine the extent of demineralisation aroundorthodontic brackets bonded with either an ACP-containing composite resin or a conventional composite resin by measuring enamel microhardness:one of the traditional methods of determining earlydemineralisation.46,10 The method, which has beenwidely used in caries research, correlates deminerali-sation with microhardness.4

The aim of this in-vitro study was to compare themicrohardness of the enamel around brackets bondedwith an amorphous calcium phosphate-containingorthodontic composite (ACP-containing) with theenamel around brackets bonded with a conventionalcomposite resin after the teeth had been exposed toacid attack.

Materials and methodsPreparation of the teethForty caries-free human upper premolars, extractedfor orthodontic reasons, were used in this study.Before use the teeth were stored in 0.1 per cent thymol for periods no longer than one month. Teethwith hypoplastic areas, cracks and/or gross irregulari-ties of enamel structure or treated with chemicalagents such as alcohol, formalin or hydrogen per-oxide were excluded from the study. Soft tissue rem-nants and calculus were removed from the teeth andthe crowns cleaned with fluoride-free pumice and arubber cup. The teeth were then stored in StreckTissue Fixative (Streck Laboratories, Inc., Omaha,NE, USA) for two weeks. This solution has anantimicrobial action and does not compromise histo-logical examination of the enamel following artificialdemineralisation.11 The teeth were randomly distrib-uted into the control (Group 1) and the experimentalgroup (Group 2) equally. The buccal surface of eachpremolar was etched with 37 per cent ortho-phosphoric acid gel (3M Dental Products, St. Paul,

MN, USA) for 15 seconds, rinsed with water for 15seconds and dried with oil-free air for 10 secondsuntil the enamel appeared frosty-white.

In Group 1, Transbond XT primer (3M Unitek,Monrovia, CA, USA) was applied to the etched sur-face in a thin film and not cured. Transbond XT com-posite paste was applied to the base of the stainlesssteel bracket (Dyna-Lok series, 100-gauge mesh, 3MUnitek, USA). Each bracket was positioned at themaximum contour mesio-distally in the middle onethird of the buccal surface occluso-gingivally and parallel to the long axis of the tooth, and pressedfirmly into place. The excess composite was removedwith a scaler.

In Group 2, a thin layer of ACP-containing ortho-dontic composite (Aegis Ortho, Harry J BosworthCo., IL, USA) was applied to the etched enamel andthe base of the bracket. The bracket was pressed ontothe buccal surface of the tooth in an identical positionto that used in Group 1. Following the manufac-turers recommendations, excess composite was notremoved.

A light-emitting diode curing unit (Elipar Freelight 2,3M-ESPE, St. Paul, MN, USA) was applied to themesial and distal edges of the brackets in both groupsfor 10 seconds per side (Total time: 20 seconds).Following curing, the crowns of the teeth were paint-ed with an acid-resistant varnish, leaving a 2 mm ringof exposed enamel around the brackets. The speci-mens were stored in 100 per cent humidity for 12hours at 37 C.

Demineralisation procedureThe baseline mineralisation of the enamel aroundeach bracket was measured with a portable battery-powered laser fluorescence device (Diagnodent Pen,KaVo, Germany). The scores in both groups were under 13, indicating that the enamel was notdemineralised and all teeth had the same risk of caries(Figure 1).

The demineralisation procedure was adapted fromthe method described by Hu and Featherstone.12 Thedaily procedure of pH cycling included a deminerali-sation period of 6 hours (09001500 hours) and aremineralisation period of 18 hours (15000900hours). The crown of each tooth was immersed in 60mL of demineralisation solution containing 2.0mmol/L calcium, 2.0 mmol/L phosphates, and 75

mmol/L acetate at pH 4.3 for 6 hours at 37 C.Specimens were then removed from the demineralisa-tion solution, rinsed with deionised water andimmersed in 40 mL of the remineralisation solutionat 37 C overnight (18 hours), to simulate the rem-ineralising stage of the caries process. The reminerali-sation solution consisted of 1.5 mmol/L calcium, 0.9mmol/L phosphates, 150 mmol/L potassium chlo-ride, and 20 mmol/L cacodylate buffers at pH 7.0.This cycling procedure was repeated daily for 21 days.On day 21, the presence of demineralised enamel wasconfirmed with the laser fluorescent device and, visu-ally, the enamel appeared frosty-white when the teethwere dried. The teeth were removed from the solutionand the brackets removed.

Microhardness analysisThe roots of the teeth were removed with a water-cooled diamond disk. The crowns were hemi-sectioned vertically into mesial and distal halves witha large 15 HC wafering blade in an Isomet low-speedsaw (Buehler, Lake Bluff, IL, USA). The hemi-sections were cut into a cervical portion and anocclusal portion. Both portions were embedded inself-curing epoxy resin (Epo-Kwick, Buehler, Lake

Bluff, IL, USA), leaving the cut face exposed. Thehalf crown sections were polished with abrasive paperdiscs (320, 600, and 1200 grit) and polished with a 1 m diamond spray and a cloth polishing disc(Buehler, Lake Bluff, IL, USA). A microhardnesstester (HMV-700, Shimadzu, Kyoto, Japan) under a2N load for 15 seconds was used for the microhard-ness analysis. In the occlusal and cervical regions,indentations were made at the edge (0 m) of thecomposite and 25, 50, 75, 100, 125, and 150 mfrom the external surface of the enamel.

Statistical analysisData analysis was performed by using StatisticalPackage for Social Sciences, (SPSS, Vers.13.0, SPSSInc. Chicago, IL, USA) and Excel 2000 (MicrosoftCorporation, Redmond, WA, USA). Descriptive statistics were calculated for both groups. TheShapiro-Wilks normality test and Levenes variancehomogeneity test were applied to the microhardnessdata. The data were normally distributed and therewas homogeneity of variances between the groups.Occlusal and cervical microhardness scores at thesame depths in matching half crown specimens werecompared with the paired t-test. Students t-test wasused to compare the effect of the materials(Transbond XT and Aegis Ortho) 25, 50, 75, 100,125, and 150 m from the enamel surface. For multiple comparisons, the analysis of variance(ANOVA) and Tukey Honestly Significant Differ-ence (HSD) post-hoc test were used. A significancelevel of p < 0.05 was used for all tests.

To determine the intra- and inter-observer agree-ment, the microhardness of the enamel was measuredby two investigators using the same instrument at twoseparate times, and Cohens Kappa scores were determined.

UYSAL ET AL


Figure 1. Measurement of the demineralisation on the occlusal side of the bracket by Diagnodent Pen.

Table I. Intra- and inter-examiner agreement for the microhardnessscores.

Observation Kappa score (K)

Intra-examiner agreement (Examiner 1) 0.83Intra-examiner agreement (Examiner 2) 0.88Inter-observer agreement 0.81

Cohen's Kappa:K < 0.40 poor agreement K = 0.41 - 0.60 moderate agreement K = 0.61 - 0.80 substantial agreement K > 0.80 - almost perfect agreement



Results

The intra- and inter-examiner Kappa scores forassessment of microhardness exceeded 0.80 (Table I).

There were no statistically significant differencesbetween the enamel microhardnesses in the occlusaland cervical sections in each group (p > 0.05). Themean microhardness scores in the Transbond XTgroup (Group 1) increased steadily from 185.80Vickers Hardness Number (VHN) at the 25 m,234.70 VHN at 50 m, 253.70 VHN at 75 m,271.35 VHN at 100 m, 295.95 VHN at 125 m to300.50 VHN at 150 m (Table II). The mean micro-hardness scores in the Aegis Ortho group (Group 2)also increased steadily from 223.35 VHN at 25 m to302.85 VHN at 150 m. Although the mean differ-ences between the two groups fell from 37.55 VHNat 25 m to 2.35 VHN at 150 m, only the micro-hardness values at the 25 and 50 m levels were sig-nificantly different. The enamel was significantlyharder in Group 2 (Aegis Ortho) than in Group 1(Transbond XT) 25 and 50 m from the enamel sur-face. There were no significant group differences inenamel microhardness from 75 to 150 m from theenamel surface.

The microhardness scores in both groups at the 25and 50 m were approximately twice as variable asthe microhardness scores at the 75, 100 and 150 mlevels, but not at the 125 m level. For example, therange in enamel microhardness 25 m from the

surface was 49 VHN in the Transbond XT group(Range: 160209 VHN) and 44 VHN in the AegisOrtho group (Range: 201245 VHN). Similar varia-tion in the ranges occurred at the 50 m level.

Discussion

We subjected teeth with stainless steel orthodonticbrackets bonded with either an ACP-containing com-posite resin or a conventional composite resin tocycles of demineralisation and remineralisation andmeasured the microhardness of the enamel surround-ing the brackets. The enamel was significantly harder25 m and 50 m from the enamel surface in theteeth with brackets bonded with the ACP-containingcomposite resin, suggesting that ACP-containingcomposite resins may lessen the risk of demineralisa-tion in patients with poor oral hygiene.

In this in-vitro study we attempted to simulate theprocesses of acid attack that occurs beneath plaque invivo and subsequent remineralisation by minerals inthe saliva over 21 days.12,13 Whereas Hu andFeatherstone12 cycled the teeth in their study through demineralisation and remineralisation solu-tions for 14 days, we extended our study to 21 daysbecause we found no visual evidence of demineralisa-tion after 14 days exposure to the solutions. By 21days, however, the enamel surrounding the bracketsin the control group appeared frosty-white whendried.

Table II. Comparisons of enamel microhardness.

Microhardness (VHN)

Depth Composite N Mean SD SEM Minimum Maximum p

25m Transbond XT 20 185.80 9.95 2.22 160 209 0.000Aegis Ortho 20 223.35 11.03 2.47 201 245






Significant values in bold

We assessed mineral loss from the teeth by deter-mining the microhardness of the enamel at selected depths. This is a proven and widely-usedmethod to determine the loss of mineral that is a feature of early carious lesions. A strong correlation (r = .91) was reported by Featherstone and co-workers between enamel microhardness scores andthe percentage loss of mineral in the carious lesions.13While others have reported that the demineral-isation of the enamel around orthodontic bracketscan extend as far as 75 m below the enamel sur-face, Gorton and Featherstone4 and Pascotto et al.5reported that enamel demineralisation extended to only 30 m from the enamel surface in vivo. They allowed their subjects to brush their teeth which presumably removed some/all of the plaque and micro-organisms responsible for deminer-alisation.

We used a portable battery-powered laser fluores-cence device to determine the levels of mineralisationat the start of the study and after 21 days. Althoughthe device confirmed that the groups had similarbaseline levels of mineralisation at the start of thestudy and that they were demineralised after 21 daysexposure to the solutions, these results should beregarded with caution as it has recently been reportedthat this method of determining the level of mineralisation is unreliable.10

Bioactive materials, such as ACP or CPP-ACP havebeen added to several materials used in dentistry toincrease the concentrations of calcium and phosphateions in dental plaque and replace minerals lost fromthe enamel during the demineralisation process.1417CPP-ACP has been added to various products, suchas sugar-free chewing gum, mints, topical gels,mousse, tooth paste, sports drinks and glass ionomercements and remineralisation of already deminer-alised enamel lesions has been reported.8,12,18 Theseinnovations are ideal for the prevention of enameldemineralisation in vivo as the material is in closeproximity to the enamel, and there appears to be aninverse relationship between calcium and phosphatelevels in dental plaque and caries experience.17Sodium fluoride either alone or in combination withCPP-ACP will also prevent enamel demineralisationadjacent to orthodontic brackets.7 The consensus isthat ACP-containing materials have higher reminer-alising potential than the conventional compositeresins and cements.8,16

Conclusion

ACP-containing orthodontic composite resins mayreduce the enamel decalcification found in patientswith poor oral hygiene.

Acknowledgments

The authors thank Ertan Sekin of Guney Dental forproviding the Diagnodent Pen and for supportingthis project.


Dr Tancan UysalErciyes UniversitesiDis Hekimligi FacultesiOrtodonti Anabilum Dall, 38039MelikgaziKayseriTurkeyEmail: [email protected]

References1. Smales RJ. Plaque growth on dental restorative materials. J

Dent 1981;9:13340.2. Vorhies AB, Donly KJ, Staley RN, Wefel JS. Enamel dem-

ineralization adjacent to orthodontic brackets bonded withhybrid glass ionomer cements: an in vitro study. Am JOrthod Dentofacial Orthop 1998;114:66874.

3. OReilly MM, Featherstone JD. Demineralization and rem-ineralization around orthodontic appliances: an in vivostudy. Am J Orthod Dentofacial Orthop 1987;92:3340.

4. Gorton J, Featherstone JD. In vivo inhibition of demineral-ization around orthodontic brackets. Am J OrthodDentofacial Orthop 2003;123:1014.

5. Pascotto RC, Navarro MF, Capelozza Filho L, Cury JA. Invivo effect of a resin-modified glass ionomer cement onenamel demineralization around orthodontic brackets. Am JOrthod Dentofacial Orthop 2004;125:3641.

6. de Moura MS, de Melo Simplcio AH, Cury JA. In-vivoeffects of fluoridated antiplaque dentifrice and bondingmaterial on enamel demineralization adjacent to orthodon-tic appliances. Am J Orthod Dentofacial Orthop 2006;130:35763.

7. Sudjalim TR, Woods MG, Manton DJ, Reynolds EC.Prevention of demineralization around orthodontic bracketsin vitro. Am J Orthod Dentofacial Orthop 2007;131:705e19.

8. Kumar VL, Itthagarun A, King NM. The effect of caseinphosphopeptide-amorphous calcium phosphate on reminer-alization of artificial caries-like lesions: an in vitro study.Aust Dent J 2008;53:3440.

9. Uysal T, Amasyali M, Koyuturk AE, Sagdic D. Efficiency ofamorphous calcium phosphate-containing orthodontic com-posite and resin modified glass ionomer on demineralizationevaluated by a new laser fluorescence device. Eur J Dent2009;3:12734.

10. Diniz MB, Leme AF, Cardoso KD, Rodrigues JD, CordeiroRD. The efficacy of laser fluorescence to detect in vitro

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demineralization and remineralization of smooth enamelsurfaces. Photomed Laser Surg 2009;27:5761.

11. Shapiro S, Meier A, Guggenheim B. The antimicrobial activ-ity of essential oils and essential oil components towards oralbacteria. Oral Microbiol Immunol 1994;9:2028.

12. Hu W, Featherstone JD. Prevention of enamel demineraliza-tion: an in vitro study using light-cured filled sealant. Am JOrthod Dentofacial Orthop 2005;128:592600.

13. Featherstone JB, ten Cate JM, Shariati M, Arends J.Comparison of artificial caries-like lesion by quantitativemicroradiography and microhardness profiles. Caries Res1983;17:38591.

14. Dunn WJ. Shear bond strength of an amorphous calcium-phosphate-containing orthodontic resin cement. Am JOrthod Dentofacial Orthop 2007;131:2437.

15. Uysal T, Ulker M, Akdogan G, Ramoglu SI, Yilmaz E. Bondstrength of amorphous calcium phosphate-containing ortho-dontic composite used as a lingual retainer adhesive. AngleOrthod 2009;79:11721.

16. Shen P, Cai F, Nowicki A, Vincent J, Reynolds EC.Remineralization of enamel subsurface lesions by sugar-freechewing gum containing casein phosphopeptide-amorphouscalcium phosphate. J Dent Res 2001;80:206670.

17. Reynolds EC, Cai F, Shen P, Walker GD. Retention inplaque and remineralization of enamel lesions by variousforms of calcium in a mouthrinse or sugar-free chewinggum. J Dent Res 2003;82:20611.

18. Rose RK. Binding characteristics of streptococcus mutansfor calcium and casein phosphopeptide. Caries Res 2000;34:42731.

Introduction

Recent studies have been concerned with the bio-compatibility of different types of orthodontic materials.1,2 Separating elastics made from naturalrubber and non-latex materials are commonly usedprior to orthodontic treatment. Allergic reactionscaused by latex proteins have been well-documented,but little is known if latex and non-latex products arecytotoxic to oral mucosal cells.39

Cell lines, such as L-929 mouse fibroblasts, have beenshown to behave similarly to human gingival fibrob-lasts and, therefore, are a suitable in-vitro model totest the toxicity of products used intra-orally during

orthodontic treatment.1014 The objective of this in-vitro study was to determine if latex and non-latexorthodontic separating elastics are cytotoxic.

Materials and methods

Fifteen blue-coloured elastics (Diameter: 4.4 mm)from four manufacturers were assigned to the follow-ing groups: Group M, silicone (non-latex) modularelastics (Masel, Bristol, PA, USA); Group D, naturallatex modular elastics (Dentaurum, Ispringen,Germany); Group A, natural latex bulk pack elastics(Aditek, Cravinhos, So Paulo, Brazil); Group O,natural latex bulk pack elastics (OrthoSource, North

Australian Orthodontic Journal Volume 26 No. 1 May 2010 Australian Society of Orthodontists Inc. 201016

Cytotoxicity of orthodontic separating elastics

Matheus Melo Pithon, Rogrio Lacerda dos Santos, Fernanda Otaviano Martins,Maria Teresa Villela Romanos and Mnica Tirre de Souza AraujoFederal University of Rio de Janeiro-UFRJ, Rio de Janeiro, Brazil

Background: Separating elastics may be cytotoxic to the interdental gingival tissues. Both latex and non-latex separating elasticsare widely used and both types should be biocompatible.Objective: To determine if latex and non-latex orthodontic separating elastics are cytotoxic. Methods: The cytotoxicity of natural latex (Groups A, D and O) and non-latex (Group M) orthodontic separating elastics weredetermined by incubating 15 elastics of each type in Eagles essential medium (MEM), removing the supernatant after 24, 48,72 and 168 hours and adding it to cultures of L-929 mouse fibroblasts in growth medium (MEM plus glutamine, garamicine,fungizone, sodium bicarbonate, buffered saline and foetal calf serum). To verify the cell response in extreme situations, threeadditional groups were included: Group CC (cell control), consisting of L-929 cells not exposed to supernatants from the main-tenance medium with the elastics; Group C+ (positive control), consisting of Tween 80; Group C- (negative control), consistingof phosphate buffered saline solution. The positive and negative controls were incubated in MEM maintenance medium for 24,48, 72 and 168 hours and the extracted elutes were added to L-929 line cells incubated in the growth medium. The viabilityof the cells was determined with neutral red (dye-uptake method) at 24, 48, 72 and 168 hours. The data were analysed withthe analysis of variance (ANOVA) and Tukeys multiple comparison test. The significance level was p 0.05. Results: The elastics in Groups A, D and O induced greater cell lysis at 72 hours compared to the other experimental times.There were statistically significant differences between the cytotoxicity of the elastics in Groups A, D and O in relation to Group CC for experimental times of 24, 48, 72 and 168 hours (p > 0.05). There was not, however, a statistically significantdifference between Groups D and CC at 24 hours.Conclusion: The latex and non-latex orthodontic separating elastics tested were considered to be biocompatible.(Aust Orthod J 2010; 26: 1620)

Received for publication: June 2009Accepted: August 2009

Matheus Melo Pithon: [email protected] Lacerda dos Santos: [email protected] Otaviano Martins: [email protected] Teresa Villela Romanos: [email protected] Tirre de Souza Arajo: [email protected]

CYTOXICITY OF ORTHODONTIC SEPARATING ELASTICS


Hollywood, CA, USA) (Figure 1). All samples hadrecent manufacturing dates, were from the same pro-duction lot and came in sealed plastic packages.Before testing, the powder coating was removed bywashing the elastics for 15 seconds with deionisedwater in a Milli-Q purification system (Millipore,Bedford, MA, USA). The elastics were then sterilisedby exposure to ultraviolet light (Labconco, Kansas,MO, USA) for 30 minutes.15,16

Volumes of 100 l L-929 line cells (American TypeCulture Collection ATCC, Rockville, MD, USA)and growth medium consisting of Eagles minimumessential medium (MEM, Cultilab, Campinas,Brazil) plus 0.03 mg/ml of glutamine (Sigma, St.Louis, MO, USA), 50 g/ml of garamicine (ScheringPlough, Kenilworth, NJ, USA), 2.5 mg/ml of fungi-zone (Bristol-Myers-Squibb, New York, NY, USA),0.25 per cent sodium bicarbonate solution (Merck,Darmstadt, Germany), 10 mmol of HEPES (Sigma,St. Louis, MO, USA) and 10 per cent bovine foetalserum (Cultilab, Campinas, Brazil) were distributedinto 96-well microplates and incubated for 48 hours

at 37 C. This ensured that the cells adhered to the microplates. After 48 hours, the growth mediumwas replaced with 100 l of MEM in which the elastics had been incubated for 24, 48, 72 and 168hours.

To verify the cell response in extreme situations, threeadditional groups were included in the study: GroupCC (cell control), consisting of L-929 cells notexposed to supernatants from the elastics; Group C+(positive control), consisting of Tween 80(Polyoxyethylene-20-sorbitan, Sigma, St. Louis, MO,USA); Group C- (negative control), consisting ofphosphate-buffered saline (PBS) solution (Table I).The positive and negative controls were incubated inMEM maintenance medium for 24, 48, 72 and 168hours and the extracted elutes were added to L-929line cells incubated in the growth medium.

Dye uptake The cytotoxicity of the orthodontic elastics was deter-mined with the dye-uptake method, which is basedon the uptake of neutral red by living cells.17 After 24hours incubation, 100 l of 0.01 per cent neutral reddye (Sigma, St. Louis, MO, USA) was added to eachwell in the microplates and incubated for 3 hours at37 C. Following this period of time, 100 l of 4 percent formaldehyde solution (Vetec, Rio de Janeiro,Brazil) in PBS (130 mmol of NaCl; 2 mmol of KCl;6 mmol of Na2HPO4 2H2O; 1 mmol of K2HPO41 mmol; pH 7.2) were added to each well to promotecell attachment to the plate. After 5 minutes, 100 lof 1 per cent acetic acid (Vetec, Rio de Janeiro, Brazil)and 50 per cent methanol (Vetec, Rio de Janeiro,Brazil) were added in order to remove the dye nottaken up by the cells. After 20 minutes, a spectro-photometer (BioTek, Winooski, VT, USA) set at a

Table I. Experimental and control groups used for the assays.

Groups Trademark/Firm Composition External Reference Batchdiameter number number

(mm)

M Masel Non-latex 4.4 4108-720 132864D Dentaurun Natural latex 4.4 774-200-01 401783A Aditek Natural latex 4.4 159341 081126O OrthoSource Natural latex 4.4 00424-625 205874C+ Tween 80C- PBS solution

Figure 1. Intra-oral separating elastics tested: M (Masel), D (Dentaurum), A(Aditek) and O (OrthoSource).

wavelength of 492 nm was used to determine the dyetaken up by the cells. This test was repeated threetimes and each test used samples of the mediaobtained by incubating 15 new elastics from eachgroup for 24, 48, 72 and 168 hours. Because separat-ing elastics can be in the oral cavity for up to 7 days(168 hours) cell viability was determined after exposure to MEM in which the elastics had beenincubated for 24, 48, 72 and 168 hours.

Data were compared with an analysis of variance(ANOVA) and Tukeys multiple comparison test wasused to identify statistically significant differencesbetween the groups. The significance level was set atp 0.05.

Results

There were no statistically significant differencesbetween the viability of the cells in Groups CC, Mand D at 24 hours or between Groups CC and M at48, 72 and 168 hours. Nor were there any statistic-ally significant differences between the viability of thecells in Groups D, A and O at 24, 48 and 72 hours,between Groups M, D and O at 48 hours or GroupsM, D, A and O at 168 hours (Table II). No statistic-ally significant differences were observed betweenGroups M and CC at any experimental time and

between M and D groups at 24, 48 and 168 hours (p > 0.05). There were fewer viable cells in Groups D, A and O at 72 hours compared to the other experimental times (Table II, Figure 2).

At 24 hours the percentage of viable cells variedbetween 97.2 per cent in Group M with the siliconepolymer separator to 92.9 per cent in Group A witha natural rubber latex separating elastic. The percent-age of viable cells fell slightly over the following 24hours in Groups M, A and O, continued to fall inGroups D, A and O between 48 and 72 hours andincreased between 72 and 168 hours.

Discussion

In this cross-sectional study we evaluated the cyto-toxic effects of latex and non-latex separating elasticson cultures of mouse fibroblasts. We used the vitaldye neutral red, which stains viable cells only, andmeasured the optical density of the cells with a spectro-photometer. We determined the percentage of viablecells by comparing the mean optical density of thecells in the control group, which had no contact withthe elastics, with the mean optical densities of thecells in contact with supernatants in which the elastics had been incubated for varying periods oftime. The supernatants from the groups with latex

SANTOS ET AL


Table II. Cell viability at 24, 48, 72 and 168 hours.

Groups N Mean Median SD Cell viability Mean Median SD Cell viability(Per cent) (Per cent)

Time 24 hours Time 48 hours

CC 15 0.680 a 0.710 0.08 100.0 0.720 a 0.735 0.08 100.0C+ 15 0.061 0.078 0.01 9.1 0.059 0.070 0.01 8.3M 15 0.660 a 0.668 0.04 97.2 0.697 ab 0.710 0.052 96.9D 15 0.642 ab 0.658 0.04 94.5 0.681 bc 0.698 0.07 94.6A 15 0.631 b 0.650 0.07 92.9 0.66 c 0.682 0.04 92.6O 15 0.634 b 0.646 0.07 93.3 0.670 bc 0.678 0.08 93.1

Time 72 hours Time 168 hours

CC 15 0.660 a 0.664 0.08 100.0 0.694 a 0.708 0.08 100.0C- 15 0.653 0.710 0.05 99.0 0.682 0.698 0.03 98.4C+ 15 0.060 0.068 0.01 9.1 0.061 0.074 0.01 8.9M 15 0.642 a 0.658 0.08 97.3 0.676 ab 0.690 0.08 97.5D 15 0.608 b 0.622 0.07 92.2 0.659 b 0.666 0.06 95.0A 15 0.594 b 0.604 0.06 90.1 0.645 b 0.658 0.05 93.0O 15 0.605 b 0.616 0.08 91.7 0.653 b 0.670 0.08 94.1

Values followed by same letters are not significantly different (p > 0.05) for the same time.

CYTOXICITY OF ORTHODONTIC SEPARATING ELASTICS


elastics had lower cell viabilities compared to thegroup with silicone polymer separating elastics. Therewas no significant variation in cell viability in the latter group over the experimental period, althoughthe cell viability in all groups increased slightly at 168hours.

The cytoxicity of the supernatants may be due to by-products from the latex elastics or the colourants inthe separating elastics. The latter appears to be anunlikely cause for cell death as Holmes et al.18 reported that the colourants in orthodontic elasticshad low toxicity and could be regarded as clinic-ally inoffensive. Short-term studies are needed to

investigate further whether colourants affect cell via-bility as they appear to have leached from the surfacelayers of the elastics in the first 24 hours. How-ever, by-products from latex elastics are known to becytotoxic.3,14,19

Spectrophotometric assay is a rapid and reliablemethod of determining cell viability. We used neutralred dye as it is widely used to check L-929 cell viabil-ity. Dead or damaged cells did not take up the vitalstain and were not recognised by the assay.Spectrophotometry does not, however, distinguishdead and damaged cells.

Although L-929 mouse fibroblasts behave similarly toprimary human gingival fibroblasts, the cell cultureresults are only a guide to the human response.12,13

Protocols for direct contact cytotoxicity tests varywidely. Assays using L-929 mouse fibroblasts havebeen shown to give comparable results to cultures ofhuman gingival fibroblasts, and are considered to bean acceptable model for testing the toxicity of sub-stances to gingival fibroblasts in vitro.1013 There are,however, some limitations to the method: cyotoxicityassays of the same material can give different resultsbecause of differences in production of the cytotoxicsubstance(s) and different cell surface/volumes in theculture medium. Internationally standardised proto-cols are obviously needed to obtain comparableresults and to further develop cytotoxicity screeningtests for the dental materials used in patients.13

Silicone separating elastics were shown to have similar cytotoxicity to the latex separating elastics. Weremoved the powder coating from the elastics before-hand in order to standardise the samples and ensurethat it did not influence the results. We could notdetermine if the powder was cytotoxic or if it con-tributed to the cytotoxicity of the elastics. Accordingto Schmalz,14 potentially cytotoxic intra-oral elastics could release harmful substances that mightaccumulate in the body and over time initiate a disease process. It is known that latex is not entirelybiocompatible and it may interact with certainfoods5,20 and medications.21

The natural latex separating elastics induced more celllysis at 72 hours than at 24, 48 and 168 hours, sug-gesting that toxic substances were released after 72hours. These substances could be due to degradationproducts and/or the release of harmful proteins fromthe latex itself. Our finding that the process was not

Figure 2. Percentage viability of tested elastics obtained by spectrophotometry.

continuous is supported by Holmes et al. whoreported that natural latex elastics were biocompat-ible after 3 days intra-oral use.18 As these materials arewidely used in clinical orthodontics and are in inti-mate contact with the gingival tissues, they should beused sparingly or replaced by proven biocompatiblematerials.

The elastics we tested showed over 90 per cent cellviability after 3 days. Other investigators have reported that latex elastics cause more cell death (upto 50 per cent) than non-latex elastics, but concludedthat both types of elastic (latex and non-latex) couldbe used in orthodontics.22 We conclude that the latexand non-latex orthodontic separating elastics we tested have acceptable biocompatibilies, but elasticswith cell viabilities less than 50 per cent should beavoided.14


Dr Mnica Tirre de Souza ArajoUniversidade Federal do Rio de Janeiro - UFRJFaculdade de Odontologia - Departamento deOrtodontiaAv. Prof. Rodolpho Paulo Rocco325 Ilha do FundoRio de Janeiro RJ Brasil CEP: 21941-617Email: [email protected]

References 1. Vande Vannet BM, Hanssens JL. Cytotoxicity of two bond-

ing adhesives assessed by three-dimensional cell culture.Angle Orthod 2007;77:71622.

2. Kao CT, Ding SJ, He H, Chou MY, Huang TH.Cytotoxicity of orthodontic wire corroded in fluoride solution in vitro. Angle Orthod 2007;77:34954.

3. Fiddler W, Pensabene J, Sphon J, Andrzejewski D.Nitrosamines in rubber bands used for orthodontic pur-poses. Food Chem Toxicol 1992;30:3256.

4. Hwang CJ, Cha JY. Mechanical and biological comparisonof latex and silicone rubber bands. Am J Orthod DentofacialOrthop 2003;124:37986.

5. Turjanmaa K, Alenius H, Makinen-Kiljunen S, Reunala T,Palosuo T. Natural rubber latex allergy. Allergy 1996;51:593602.

6. Tomazic VJ, Withrow TJ, Fisher BR, Dillard SF. Latex-asso-ciated allergies and anaphylactic reactions. Clin ImmunolImmunopathol 1992;64:8997.

7. Everett FG, Hice TL. Contact stomatitis resulting from theuse of orthodontic rubber elastics: report of case. J Am DentAssoc 1974;88:103031.

8. Wakelin SH, White IR. Natural rubber latex allergy. ClinExp Dermatol 1999;24:2458.

9. Palosuo T, Alenius H, Turjanmaa K. Quantitation of latexallergens. Methods 2002;27:528.

10. Schmid-Schwap M, Franz A, Konig F, Bristela M, Lucas T,Piehslinger E et al. Cytotoxicity of four categories of dentalcements. Dent Mater 2009;25:3608.

11. Franz A, Konig F, Lucas T, Watts DC, Schedle A. Cytotoxiceffects of dental bonding substances as a function of degreeof conversion. Dent Mater 2009;25:2329.

12. Schedle A, Samorapoompichit P, Rausch-Fan XH, Franz A,Fureder W, Sperr WR et al. Response of L-929 fibroblasts,human gingival fibroblasts, and human tissue mast cells tovarious metal cations. J Dent Res 1995;74:151320.

13. Franz A, Konig F, Skolka A, Sperr W, Bauer P, Lucas T et al.Cytotoxicity of resin composites as a function of interfacearea. Dent Mater 2007;23:143846.

14. Schmalz G. Use of cell cultures for toxicity testing of dentalmaterials advantages and limitations. J Dent 1994;22Suppl 2:S611.

15. Santos RL, Pithon MM, Oliveira MV, Mendes GS, RomanosMT, Ruellas AC. Cytotoxicity of intraoral orthodontic elastics. Braz J Oral Sci. 2008;7:15205.

16. Santos RL, Pithon MM, Mendes GS, Romanos MT, RuellasAC. Cytotoxicity of intermaxillary orthodontic elastics ofdifferent colors: An in vitro study. J Appl Oral Sci 2009;17:3269.

17. Neyndorff HC, Bartel DL, Tufaro F, Levy JG. Developmentof a model to demonstrate photosensitizer-mediated viralinactivation in blood. Transfusion 1990;30:48590.

18. Holmes J, Barker MK, Walley EK, Tuncay OC. Cytotoxicityof orthodontic elastics. Am J Orthod Dentofacial Orthop1993;104:18891.

19. Perrella FW, Gaspari AA. Natural rubber latex proteinreduction with an emphasis on enzyme treatment. Methods2002;27:7786.

20. Carey AB, Cornish K, Schrank P, Ward B, Simon R. Cross-reactivity of alternate plant sources of latex in subjects withsystemic IgE-mediated sensitivity to Hevea brasiliensis latex.Ann Allergy Asthma Immunol 1995;74:31720.

21. Towse A, OBrien M, Twarog FJ, Braimon J, Moses AC.Local reaction secondary to insulin injection. A potentialrole for latex antigens in insulin vials and syringes. DiabetesCare 1995;18:11957.

22. Hanson M, Lobner D. In vitro neuronal cytotoxicity of latexand nonlatex orthodontic elastics. Am J Orthod DentofacialOrthop 2004;126:6570.

SANTOS ET AL


Introduction

Although self-ligating (SL) brackets have been avail-able for many years they have recently become popular with clinicians because of claims that theyresult in shorter treatment times. There is some evi-dence that these brackets can be ligated quickly andhave less friction than conventional brackets.13Many of these claims have been based on evidencefrom retrospective clinical studies, which may be con-founded by factors such as the proficiency of the clinician(s), the treatment mechanics used and/orobserver bias.4,5 Randomised clinical trials attempt toovercome the shortcomings of retrospective trials, butthey may have limitations also, such as the use ofarchwires with different dimensions.6 Prospectiveclinical trials that have used identical wire sequencesfound no difference in the ability to align anterior teethbetween SL brackets and conventional brackets.713

There is little doubt that the latches on SL bracketscan be unfastened and closed more quickly than elasto-meric modules or wire ligatures can be removed andplaced on conventional brackets. Time savings of upto 1012 minutes per patient for SL brackets com-pared with tying steel ligatures and 23 minutes compared with elastomeric modules have beenreported.1,5,14,15 Many patients would like their treat-ment to be as short and as inconspicuous as possible,and for these reasons they prefer to have porcelain orplastic brackets bonded on their upper anterior teeth.

The aims of this study are to compare the effective-ness of SL porcelain brackets with conventional porce-lain (CP) brackets tied with ligatures for initial alignment in the upper arch, to compare the discomfortof both bracket archwire combinations and to com-pare the times taken (both assisted and unassisted) tountie and ligate both bracket archwire combinations.

Australian Society of Orthodontists Inc. 2010 Australian Orthodontic Journal Volume 26 No. 1 May 2010 21

Porcelain brackets during initial alignment: areself-ligating cosmetic brackets more efficient?

Peter Miles* and Robert WeyantPrivate practice, Caloundra, Queensland, Australia* and the Division of Pediatric and Developmental Dental Sciences, School of DentalMedicine, University of Pittsburgh, Pittsburgh, U.S.A.

Objective: To compare the effectiveness of a self-ligating (SL) porcelain bracket with a conventional porcelain (CP) bracket tiedwith ligatures for initial alignment in the upper arch, to compare the discomfort of both bracket archwire combinations and tocompare the times taken (both assisted and unassisted) to untie and ligate both bracket archwire combinations.Methods: Sixty nonextraction patients were randomly assigned to either a group with CP brackets on the upper six anteriorteeth and conventional metal brackets on the premolars and first molars, or a group with SL porcelain brackets on the anteriorteeth and SL metal brackets on the posterior teeth. The CP brackets were tied with coated ligatures. The irregularity index wasmeasured at the start of treatment and at the first recall 10.7 weeks later. Discomfort was recorded over the first week with aLikert scale and the times to untie and ligate the six anterior porcelain brackets (assisted and unassisted) were recorded.Results: There were no differences in irregularities at the start of treatment (p = 0.91) or 10.7 weeks later (p = 0.12). No sig-nificant difference in discomfort was found between the bracket types (p = 0.90). The porcelain SL brackets were significantlyfaster (p < 0.001) to untie and ligate than the CP brackets with ligatures.Conclusion: Porcelain SL brackets were faster to untie and ligate by 22 seconds per bracket, but there were no significant differences in the alignment achieved or discomfort experienced.(Aust Orthod J 2010; 26: 2126)

Received for publication: September 2009Accepted: October 2009

Peter Miles: [email protected] Weyant: [email protected]

MILES AND WEYANT


Subjects and methods

Sixty-eight consecutive subjects, scheduled for non-extraction treatment in the upper arch, were drawnfrom the senior authors private orthodontic practice.All subjects agreed to participate in the study after thepurpose had been explained to them. The subjectswere not informed which bracket was the newerdesign.

The subjects were randomly allocated to one of twogroups. In Group 1, SL porcelain 0.018 inch In-Ovation C brackets (GAC International, Bohemia,NY, USA) were indirectly bonded to the upper incisors and canines and metal In-Ovation bracketswere indirectly bonded on the upper premolars andfirst molars. In Group 2, conventional porcelain (CP)0.018 inch Clarity brackets (3M/Unitek, Monrovia,CA, USA) were bonded indirectly to the upper incisors and canines and Victory brackets (3M/Unitek, Monrovia, CA, USA) were bonded to theupper premolars and first molars.

Of the 68 patients enrolled in the study, follow-upimpressions were missed for two subjects in Group 1and four subjects in Group 2 (Figure 1). Two sub-jects, matched for age, gender and incisor irregularitywith two subjects in Group 2, were dropped fromGroup 1 to keep the same number of subjects in eachgroup. At analysis both groups had 19 female subjectsand 11 male subjects. The overall mean age at theconclusion of the trial was 13.5 + 1.5 years.

Alginate impressions for study models were takenprior to bonding. Immediately after bonding a 0.014inch G4 heat-activated NiTi wire (G & H WireCompany, Franklin, IN, USA) was placed in eachsubject. To prevent the archwire from sliding aroundthe arch and interfering with the incisors duringalignment, V-bends were placed distal to each centralincisor. The six anterior CP brackets were ligated withcoated ligatures while elastomeric modules (3MUnitek, Monrovia, CA, USA) were used on the pre-molars. The SL In-Ovation brackets were ligatedusing the clip mechanism in the bracket. The first

Randomised(N = 68)

Group 1Allocated to In-Ovation C (N = 34)

Received allocated intervention (N = 34)

Group 2Allocated to Clarity (N = 34)

Received allocated intervention (N = 34)

Lost to follow-up (N = 0)Impression missed (N = 4)

Analysed (N = 30)Excluded from analysis (N = 0)

Lost to follow-up (N = 0)Impression missed (N = 2)

Analysed (N = 30)Excluded from analysis (N = 2)

Enr

olm

ent

Allo

catio

nFo

llow

-up

Ana

lysi

s

Figure 1. Flow chart showing the progress of patients through the trial.

wire change was scheduled approximately 10 weeksafter bonding, at which time a second alginateimpression and photographs were taken of the upper arch.

The alginate impressions were poured up in dentalstone for later measurement of the irregularityindex.16 The irregularity index, defined as the summeddisplacement of adjacent anatomical contact pointsof the six anterior teeth, was measured using a digitalcaliper to the nearest 0.1 mm with the operator blinded to the identity of each cast.

The irregularity data before the start of the trial (T1)and after approximately 10 weeks (T2) were com-pared with a one-way analysis of variance (ANOVA).The irregularity data were also divided into two sub-groups: subjects with an initial irregularity score < 5.0mm and subjects with an initial irregularity score 5.0 mm.6

To assess the accuracy of measuring the irregularityindex, 10 models were randomly selected and remeasured one month after the first set of measure-ments. Pearsons correlation coefficient and a paired t-test were used to assess the accuracy and repro-ducibility of the method. There was no significantdifference between the two sets of measurements(Mean difference: 0.06 mm, p = 0.76, r = .98) indicating that the irregularity measurements werereliable.

To assess the discomfort with each type of bracket,the subjects were asked to record the levels of dis-comfort in the upper arch on a 7-point Likert scale 4 hours, 24 hours, 3 days and 1 week after placementof the initial archwire. They were also asked to returnthe questionnaires at the following visit. The 4-, 24-hour, 3-day and 1-week and total discomfort scoreswere compared with a one-way ANOVA and withpost-hoc Tukeys HSD test for multiple comparisons.

The times taken by the senior author to untie and ligate 10 consecutive cases from each group, and the

times taken by the senior author assisted by a staffmember to untie and ligate the CP brackets in 10consecutive subjects were compared with a one-wayANOVA.

ResultsThere were no statistically significant differencesbetween the irregularity scores in the groups eitherpretreatment (T1) or 10.7 weeks later (T2). At T2 the anterior teeth in the self-ligating group wereslightly less irregular than the anterior teeth in theClarity group, but the difference was not statisticallysignificant (Table I).

When the irregularity data were subdivided into thelow irregularity (< 5 mm) and high irregularity ( 5 mm) subgroups, there were no statistically significant group differences at T1 (Low irregularitysubgroup: SL vs CP, p = 0.92; High irregularity sub-group: SL vs CP, p = 0.63) or T2 (Low irregularitysubgroup: SL vs CP, p = 0.95; High irregularity sub-group: SL vs CP, p = 0.11).

Of the 60 patients who completed the study, 42 (70per cent) returned the discomfort questionnaires. Todetermine if there was any difference in the irregular-ity scores of those who returned the questionnaires

ARE SELF-LIGATING COSMETIC BRACKETS MORE EFFICIENT?


Table I. Irregularity scores for each bracket type, in millimetres.

Time In-Ovation C Clarity pMean (SD) Mean (SD)

T1 7.0 (3.4) 7.1 (3.0) 0.91T2 2.3 (1.0) 2.7 (1.1) 0.12

T1, pretreatment; T2, recall at approximately 10.7 weeks

Table III. Times taken to untie and ligate six porcelain brackets unassist-ed and assisted by a staff member, in seconds.

In-Ovation C Clarity ClarityMean (SD) Assisted Unassisted

Untying 9.2 (2.5) a,b 31.5 (10.2) a 32.2 (12.9) bLigating 12.4 (6.3) a,b 91.2 (5.8) a,c 119.6 (8.7) b,cTotal 21.6 (7.5) a,b 122.7 (10.1) a,c 151.8 (16.3) b,c

The letters indicate groups significantly different at p < 0.001 withTukeys HSD test.

Table II. Ratings of upper arch discomfort for each bracket type.

Time In-Ovation C Clarity pMean rating (SD) Mean rating (SD)

4-hours 2.8 (1.5) 2.4 (1.1) 0.421-day 3.4 (1.8) 3.9 (1.7) 0.333-days 2.5 (1.5) 2.4 (0.9) 0.877-days 1.6 (1.1) 1.3 (0.6) 0.29Total 10.2 (5.2) 10.1 (3.2) 0.90

MILES AND WEYANT


and those who did not, the T2 irregularity scores ofthese two subgroups were compared. There were nostatistically significant differences between the irregul-arity scores of the SL subjects either with or withoutpain scores (p = 0.85) or for the CP subjects with orwithout pain scores (p = 0.19). There were no statis-tically significant group differences in the subjectsratings of discomfort at any of the time intervals or inthe total rating (Table II).

The times to untie and ligate the six anterior SLbrackets unassisted and the six anterior CP bracketsunassisted and assisted, are given in Table III. The SLbrackets could be untied and ligated significantlyfaster than the CP brackets either assisted or unassisted(p < 0.001). On average, the SL brackets could beuntied and ligated 1 minute 41 seconds (assisted) or2 minutes 10 seconds (unassisted) less than the CPbrackets. The help of an assistant saved no time whenuntying the CP bracket (p = 0.89), but tying ligatureswith the help of an assistant saved 29 seconds for thesix CP brackets (p < 0.001).

Discussion

We found that SL and CP brackets with 0.014 inchNiTi archwires were equally effective at aligning theupper six anterior teeth and that our subjects consid-ered both bracket archwire combinations equallyuncomfortable. We did, however, find significant savings in the times required to untie and ligate theSL brackets over the CP brackets, which is hardly sur-prising as the SL brackets were closed with a latch,whereas the CP brackets were ligated with coated lig-atures. An assistant significantly reduced the timerequired to ligate the CP brackets.

Coated ligatures were used on the CP brackets as elastomeric modules could not be tied in a figure-8on these ceramic brackets. The ligatures ensured thatthe archwire was seated in the bracket slots. Small,but statistically significant, improvements in align-ment have been reported for conventional metalbrackets tied with either modules in a figure-8 patternor steel ligatures over passive SL brackets.7,8 On theother hand, no statistically significant differences inlower arch alignment were found between SL bracketsand metal conventional brackets,911 or betweenactive and passive SL brackets in upper arch aligment.17In addition to the method of ligation, factors such astooth shape, slot dimensions, bracket width andbracket position may influence alignment. We

limited the variation due to bracket position by using an indirect bonding technique and randomlyassigning the subjects to both groups.

As we found no difference in alignment, the smalldifferences reported in previous studies could be due to the use of a passive rather than an active SLbracket. The bracket geometry may also be a factor assome SL brackets are narrower than conventionalbrackets and offer less rotational control. A recentstudy comparing an active SL bracket with a passiveSL bracket in the upper arch found no significant dif-ference in the time required to attain alignment,17and a study comparing plastic/metal Damon 3 SLbrackets with conventional metal brackets ligatedwith elastomeric modules also found no differenceduring initial alignment in the lower arch.9

In agreement with previous studies we found no sig-nificant difference in the ratings of discomfortbetween the different brackets.1820 In other words,the SL bracket archwire combination was no moreuncomfortable during initial alignment than the CPbracket archwire combination. On four out of fiveoccasions the Clarity group ratings were slightly less,but not significantly so, than the ratings by the In-Ovation C group. The lack of significant findingscould also be due to the lack of sensitivity of theLikert rating scale, because the raters had differentframes of reference or because they were influencedby what they thought was the purpose of the scale.The Likert scale was used in this study to enable ourresults to be compared with other studies using thesame method.

A previous study reported that SL brackets were nomore efficient in terms of the time required to alignincisors with high irregularity scores ( 5 mm) thanconventional brackets, but incisors with low irregul-arity scores (< 5 mm) were aligned more quickly withSL brackets.6 In that study two different wiresequences were used for each bracket type: the secondarchwire in the conventional bracket group was around wire whereas a rectangular archwire was usedin the SL bracket group. Use of archwires with differ-ent cross-sections may have accounted for the differ-ent results. We used identical archwires in bothgroups and found no significant difference betweenthe subjects with low irregularity scores (< 5 mm) andthose with high scores ( 5 mm).Anecdotal reports have suggested that high caninesrespond more favourably to the lesser friction of SL

brackets. We subjectively assessed the subjects in ourstudy and found four with high canines: two subjectsin each group. The mean irregularities reduced from12.0 mm to 1.8 mm in the subjects with CP bracketsand from 11.4 mm to 1.2 mm in the subjects with SLbrackets (Figure 2). In both cases the mean improve-ment in alignment was identical at 10.2 mm. This isnot unexpected as displacement of the archwire intothe bracket on a high canine can result in the arch-wire binding and notching, which are the major contributors to resistance to sliding.

In the present study, untying and ligating SL bracketson the upper anterior teeth saved a small, but statisti-cally significant, amount of time over the timerequired to untie and ligate the CP brackets. Withouthelp from an assistant the time saved with six anter-ior SL brackets averaged 2 minutes 10 seconds or 22seconds per bracket compared with a ligature tie oneach CP bracket. Extrapolating this time saving to 20SL brackets in both arches could save approximately7 minutes 20 seconds over CP brackets tied with ligatures. This time saving is less than the saving of 1012 minutes reported by others when using ligatures.14 Although the time savings were small, apotential saving of 2 minutes 10 seconds at each visit

could add up to approximately 32 minutes over thecourse of 15 visits if ligatures were replaced at everyvisit.

During initial alignment it is important to engage thewire completely to gain the maximal correction ofrotations and vertical alignment. Once alignment hasbeen achieved, elastomeric modules, which can beplaced more quickly, can be used to maintain the cor-rection and time savings would be less. The time savings of SL brackets compared with modules are inthe order of one minute for both arches.5,15 This rep-resents only a portion of the actual chair time duringan orthodontic adjustment and, depending upon theutilisation of staff and flow of patients in the office,may have little impact upon practice efficiency. Insome circumstances small gains in efficiency may bepossible if the orthodontist works unaided. However,if an auxiliary ligates the archwire and the orthodon-tist is not available to check the patient, efficiency willdepend upon the availability of the orthodontistrather than the method of ligation. In some cases,such as using chain or a long ligature to close or con-solidate space closure or prevent spaces opening, having to close a clip or gate on an SL bracket as wellas tying a chain or ligature could actually add a small

ARE SELF-LIGATING COSMETIC BRACKETS MORE EFFICIENT?


Figure 2. Subjects with high canines. Both subjects had 0.014 inch heat-activated NiTi archwires.Top left, Group 1 subject at T1; Top centre, the same Group 1 subject at T1; Top right, the same Group 1 subject at T2 (CP and metal brackets).Bottom left, Group 2 subject at T1; Bottom centre, the same Group 2 subject at T1; Bottom right, the same Group 2 subject at T2 (SL porcelain and SL metal brackets).

amount of time compared with a conventional bracket. Finally, the bracket and ligation mechanismneed to be reliable throughout the course of treat-ment. If a clip or gate locks and cannot be opened,or distorts or breaks during treatment, then this canaff

Revista Australiana de Ortodoncia (1)

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