A Comparison of Stability between Delayed versusImmediately Loaded Orthodontic Palatal Implants

AMY JACKSON, DDS*

ROBERT LEMKE, DDS, MD, PA†

JOHN HATCH, PhD‡

NORMAN SALOME, DDS, MS†

PETER GAKUNGA, BDS, MS, PhD¶

DAVID COCHRAN, DDS, MS, PhD, MMSci.§

ABSTRACT

Introduction: Control of anchorage is a fundamental problem in orthodontics. Conventionalmeans of controlling anchorage are characterized by potential disadvantages and inconve-niences: visibility, compliance dependence, risk of undesirable side effects, and injury. Titaniumimplants have evolved as a potential clinical alternative in overcoming the limits of conven-tional dental orthodontic anchorage.

Methods: This project was designed as a prospective observational study on 20 patients whosetreatment plans required maximum (stable) anchorage during orthodontic treatment. Thepatients received palatal implants (Institut Straumann AG, Waldenburg, Switzerland: length ofimplant 4–6 mm, diameter 3.3 mm), which were placed into the midpalate. The goal of thisstudy was to evaluate if the implant could be loaded immediately, or if time should be allowedfor integration. Patients were randomized into two groups; one group had their implantsloaded immediately with a coil spring, and the second group remained nonloaded, with anannealed coil spring, for the 8-week experimental period. Measurement of implant stability wastaken using resonance frequency analysis on both groups at the time of implant placement andat 8 weeks post-placement.

Results: This study demonstrated that immediate loading of the Straumann orthodonticimplant is possible, based on the clinical success observed in both groups. However, comparedwith the nonloaded group, the stability of the immediately loaded implant was significantly lessat 8 weeks. The mean implant stability quotient (ISQ) of the nonloaded group was 38.7 kHz atbaseline and 47.3 kHz after 8 weeks. The mean ISQ of the loaded group was 42.0 kHz at base-line and 38.4 kHz after 8 weeks. Statistical analysis showed a significant difference between thegroup that was loaded and the nonloaded group after 8 weeks (p < 0.05).

Conclusion: Based on the results of this study, an unloaded healing period provides forincreased stability of the implants compared with immediately loaded palatal implants.

*Resident, Department of Orthodontics, University of Texas Health Science Center,San Antonio Dental School, San Antonio, TX, USA

†Clinical assistant professor, Department of Orthodontics, University of Texas Health Science Center,San Antonio Dental School, San Antonio, TX, USA

‡Professor, Department of Psychiatry and Orthodontics, University of Texas Health Science Center,San Antonio Dental School, San Antonio, TX, USA

¶Assistant professor, Department of Orthodontics, University of Texas Health Science Center,San Antonio Dental School, San Antonio, TX, USA

§Professor, Department of Periodontics, University of Texas Health Science Center,San Antonio Dental School, San Antonio, TX, USA

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CLINICAL SIGNIFICANCEPatients often like to have their orthodontic treatment begin as soon as possible. This studyexamined if palatal implants could be loaded immediately after placement so overall treatmenttime could be decreased. It appears that this is possible based on the results of the study;however, an unloaded healing period results in a more stable implant.

(J Esthet Restor Dent 20:174–185, 2008)

I N T R O D U C T I O N

Orthodontic anchorage can bedefined as the resistance to

unwanted tooth movement. Thegoal of orthodontics is always tomaximize desired tooth movementswhile minimizing undesirableeffects. When stationary anchorageis required in the course of ortho-dontic treatment, a loss of stabilityof the anchoring teeth often leadsto unfavorable occlusal relationsand unsatisfactory outcomes. Con-ventional methods of stabilizinganchorage are with the use ofextraoral and intraoral appliances,such as headgear and elastics.Class II elastics have been associ-ated with some side effects, such asloss of lower anchorage and procli-nation of lower incisors. They havealso been coupled to increased ver-tical dimension and extrusion ofthe upper incisors. Headgear usealso has its inherent disadvantagesrelating to compliance, duration ofwear, unacceptability by adults,and risks of injury.

Orthodontic treatments that do notrely on patient compliance orfoster negative side effects appealto both orthodontists and patients.

Endosseous implants comprise aspecific subgroup of this orthodon-tic armamentarium because theyoffer maximal anchorage by virtueof their osseointegration.1 Faveroand colleagues in 2002 published acomprehensive review of the litera-ture on the theoretical aspects ofsuch fixtures for orthodonticanchorage. In general, orthodonticimplants are indicated when alarge amount of tooth movement isrequired, or dental anchorage isinsufficient because of hypodontia,tooth loss, or periodontal disease.2

Control of anchorage is a funda-mental aspect of orthodontics anddentofacial orthopedics. Osseointe-grated implants have been shownto provide anchorage in a reliablefashion. This has been demon-strated in orthodontics with theuse of prosthodontic implantsinserted for orthodontic purposes.3

More recently, implants have beenintroduced that serve as temporaryanchorage in orthodontics. Oneexample is the Straumann Ortho-system (Institut Straumann AG,Waldenburg, Switzerland). Argu-ably, the most widely availablecommercial palatal orthodontic

implant system, the Orthosystem(Institut Straumann) was developedjointly by the University of Aachenin Germany and the StraumannInstitute in Switzerland.4 This tita-nium implant has three distinctsections. The first is the self-tapping endosseous body, which is3.3 mm in diameter and either 4-or 6.0-mm long. The second is thesmooth cylindrical neck, which hasa 4.1-mm diameter and is either2.5- or 4.5-mm long, and the finalsection is the octagonal head,which is used for intraoral attach-ments. These were the dimensionsof the Orthosystem as used duringthe study. Recently, the dimensionshave been modified slightly toa body of 4.1 and 4.8 mm indiameter, and 6.0 mm in length.The implant relies on primary(mechanical) stability at the time ofinsertion and subsequent integra-tion between its sand-blasted,large-grit, and acid-etched surface(SLA) and the surrounding bone.5

This implant is placed in the mid-sagittal area of the palate. Owingto the reduced bone height avail-able in the palate, only shortimplants (<9 mm) can be consid-ered; surface enlargement by

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texturing and the achievement ofgood primary stability are prereq-uisites for success.6 Minimal surgi-cal treatment, combined withmaximal anchorage, distinguishesthis promising treatment modalityfor the orthodontist collaboratingwith a surgeon.

As implant design has changed andsurface treatments have evolved,the healing time required of animplant has decreased. The tradi-tional Branemark restorativeimplant protocol required a stress-free healing period of 3 to 8months before loading.7 Roberts in2002 showed that “endosseousimplants can be provisionallyloaded at about 18 weeks, but fullmaturation of the interface requiresapproximately 1 year.”8 Hermannand colleagues reported that boneremodeling occurs rapidly duringthe early healing phase afterimplant placement.9 Cochran andcolleagues showed that approxi-mately 6 weeks is consistent forimplant success when an SLAsurface is utilized.10

Implant stability is an importantcriterion for osseointegration, andtherefore, implant treatment suc-cess.11 The methods for assessingstability level are divided into inva-sive methods and noninvasivemethods. The latter is most appli-cable to human cases. Noninvasivemethods include percussion and theOsstell device. Percussion with two

mirror handles is difficult to quan-tify. The Periotest, a percussiondevice, measures mobility of teeth.Teerlinck and colleagues revealedthat the Periotest measurementvalue does not have enough sensi-tivity for detecting the stabilitylevel.12 The Osstell device is a reso-nance frequency analyzer. It is thenewest noninvasive quantitativemeasuring device of stability andpresumed osseointegration ofimplants. Resonance frequencyanalysis (RFA) value was reportedto be correlated with bone-to-implant stability change.13–15 Theseinvestigators showed that the RFAvalue changes are related to theincrease in stiffness of an implantin the surrounding tissues. Thesereports support the RFA as a usefuldevice for assessing changes in thehealing period of an implant.

The Osstell Mentor is the newestRFA device to measure dentalimplant stability in the oral cavity.The Osstell Mentor is a portable,handheld instrument that involvesthe use of the noninvasive tech-nique. The system includes the useof a Smartpeg, which is a magnet,attached to the implant or abut-ment by means of an integratedscrew. The Smartpeg is excited bya magnetic pulse from the mea-surement probe on the handheldinstrument. The resonance fre-quency, which is the measure ofimplant stability, is calculated fromthe response signal. In both in

vitro and in vivo studies, thissystem has proved valuable when itcomes to recording changes inimplant stability.15

The result of a recent histomor-phometric study suggested thatRFA values correlate well with theamount of bone–implant contact.16

These findings support the use ofRFA in assessing changes in thebone healing and osseointegrationprocess following implant place-ment. Gedrange and colleaguesused RFA to determine the primarystability of orthodontic palatalimplants. They examined 4- and6-mm implants placed in thepalatal suture. During their histo-logic and radiologic examination,they found that one can accuratelymeasure implant stability by inves-tigation of the bone available anddensity around the implant. Theyconcluded that the short implant(4 mm) gives sufficient bone fixa-tion, independent of location.17

RFA evaluation in vivo to date hasbeen performed predominantly onimplants placed for restorative pur-poses. It is therefore unknownwhat the pattern is for palatalimplants. Questions that remainunaddressed in the orthodonticimplant field include: Is it possibleto load orthodontic implantsimmediately by virtue of the factthat light forces are used (<300 g)?Will loading the implant immedi-ately influence the healing of the

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implant as judged by RFA? Thegoal of this study was to begin toaddress some of these questionsregarding palatal orthodonticimplant stability and timeof loading.

Implant stability quotient (ISQ) isa measure of implant clinical stiff-ness with a range of 1 to 100. AsISQ values increase, implant stabil-ity increases. Inversely, as ISQvalues decrease, the lower the sta-bility of the implant in the sup-porting bone and soft tissue. TheISQ measurement shows a highdegree of accuracy (�1%).13 Clas-sically, ISQ has been found to varybetween 40 and 80; the higher theISQ, the higher the implant stabil-ity.15 In 2003, Barewal and col-leagues used resonance frequencymeasurements to characterize thestability of 26 unloaded StraumannSLA (sand-blasted, large-grit, andacid-etched) implants placed fortooth restoration. Their findingsdemonstrated that implants placedin type I bone had a small decreasein stability, whereas implantsplaced in type IV bone had thegreatest decrease in stability andhence, the greatest change in ISQ.18

M AT E R I A L S A N D M E T H O D S

This human clinical trial wasdesigned as a randomized prospec-tive study to measure implant sta-bility with an RFA device (OsstellMentor) at the time of implantplacement and 8 weeks post-

placement. The study sample con-sisted of dental patients seekingorthodontic treatment, and thosein which an orthodontic implantwas deemed necessary for treat-ment by their orthodontist. Thetarget was a sample of 20 patientswith both of their maxillary firstmolars erupted and present. At theinitial screening appointment, thepatients’ medical and dental histo-ries were reviewed and inclusion/exclusion criteria confirmed.The Institutional Review Board-approved protocol was explainedto the patient, and informedconsent was obtained from thepatient or parent.

Clinical and radiographic screen-ings were used to limit the study topatients with sufficient bone quan-tity to completely encase a palatalimplant. Implant selection (Strau-mann: length of implant 4 or6 mm, diameter 3.3 mm) for eachpatient was based on the verticalheight of the anterior plate asdetermined by the lateral cephalo-gram taken for the orthodontictreatment planning. The implantlength selection was made by thesurgeon. In certain cases, thesurgeon requested tomograms tohelp determine the appropriatelocation to place the implantwithin the palate.

Preparation of the site for implan-tation was performed according tosurgical procedures prescribed by

the manufacturer: InstitutStraumann AG, Waldenburg,Switzerland. First, intraoperativeprobing of the implant site wasperformed to detect any bony per-foration to the nasal cavity. Afterlocal anesthesia was injected inadequate amounts, a trephine ortissue punch was used to remove a5-mm-diameter area of palatalmucosa (Figure 1). An excavatorwas used to fully release the softtissue. The center of the exposedcortical plate was indented with asmall round bur to help locate theprofile drill. Next, the profile drillwas selected, according to the pre-scribed implant intraosseouslength, and used to prepare theimplant bed (Figure 2). Theselected implant was insertedmanually and rotated clockwiseuntil fully seated, often with theassistance of a ratchet. Thepatients were instructed to use achlorhexidine digluconate mouthrinse perioperatively and thenpostoperatively for 2 weeks.The patients were also asked tonot manipulate the implant withtheir tongue in any way, and toclean their implant with atoothbrush during regularcleanings after the seventhpostoperative day.

Group designation obtained byrandomization was revealed tothe primary investigator on the dayof the surgery. RFA was accom-plished using the Osstell Mentor

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immediately after implant place-ment, and before delivery of thetranspalatal arch (TPA), and thenat the 8-week time point. At each ofthe two time points, the transducerwas calibrated before and after theRFA readings. After the first cali-bration, three RFA readings weretaken at the same angle, with loos-ening and tightening of the Smart-peg between successive readings.

The 5-mm, 200-g nickel titaniumcoil spring, which is designed todeliver constant and continuousforce at any length, was measuredwith an intraoral ruler and acti-vated to 7 mm. Those patients ran-domized to the nonloaded groupreceived a coil spring that had beenannealed, therefore, not applyingany force (Figure 3). After the8-week reading, the TPA wasremoved, and the patient

proceeded with the orthodontictreatment as planned.

Statistical AnalysisAll patients in the study were ran-domized to either immediately

loaded or nonloaded treatmentsusing the method of randomly per-muted blocks. The randomizationscheme was generated by usingthe website Randomization.com,http://www.randomization.com.

Figure 1. Tissue punch used to remove the palatal mucosa. Figure 2. Drill used to prepare the implantbed.

Figure 3. Transpalatal arch, with a nickel titanium coilspring attached to the Orthosystem implant.

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Using the randomization scheme, athird party volunteer sealed thetreatment assignment for eachparticipant in a brown envelope,which was opened immediatelyprior to placement of themidpalatal implant.

The resonance frequency of theimplant/transducer system is calcu-lated by the Osstell Mentor devicefrom the peak amplitude of thesignal, and an ISQ value between 1and 100 was derived via a math-ematical formula that took intoaccount the resonance frequencymeasurement and the calibrationparameters for each transducer.Specification and selection of thetransducer used are availableon the internet: http://www.osstell.com.

SPSS for Windows release 14.0.1(SPSS, Inc., Chicago, IL, USA) soft-ware was used to perform all sta-tistical analyses. Prior to analysis,all data were screened for outliersand for gross departures from nor-mality, and after the final modelfitting, residuals were examinedgraphically and statistically. ISQdata were analyzed using two-way,factorial, mixed models analysis ofcovariance (SPSS mixed modelsprocedure) with one between thepatients’ factor, corresponding totreatment (immediate versus non-loaded), and one within thepatients’ (repeated measures)factor, corresponding to time

(baseline versus 8-week follow-up).Implant length (4 or 6 mm) servedas the covariate. An unstructuredcovariance matrix was assumed.The primary null hypothesis, thatmean change in ISQ (adjusted forimplant length) from baseline to8-week follow-up is unequal underimmediate and delayed loading,was tested by the treatment ¥ timeinteraction effect. Following a sig-nificant result, this interaction wasdecomposed to examine the simpleeffects of time within each treat-ment group and treatment at eachtime. The mean age and the distri-bution of male and female patientswere compared within immediateand delayed treatment groups atbaseline using one-way analysis ofvariance and Fisher’s exact test,respectively. Two-sided tests withstatistical significance defined asp < 0.05 were used for all statisti-cal testing. ISQ measurements werereported as adjusted means � 1standard error.

The within session repeatability ofthe ISQ measurements was esti-mated by calculating the intraclasscorrelation coefficient (ICC) takenover the three measurementsobtained at baseline and at follow-up. A two-way model was usedwith both patients and repeatedISQ measurements modeled asrandom effects. A further assump-tion was made that three repeatedISQ measurements are aggregatedby taking the mean and that

absolute agreement is the repeat-ability standard. The reliability ofthe results was measured at bothbaseline and follow-up. The repeat-ability of readings taken at baseline(ICC = 0.94) and at the 8-weekreading (ICC = 0.98) was excellent.On a scale of 0 to 1.00, this ishighly reliable.

R E S U LT S

Twenty-one patients enrolled in thestudy, with one patient droppingout because of implant failure. Ofthe 23 Straumann orthodonticimplants placed into the midpalate,three implants (13%) failed duringthe 8-week experimental period.Two of the implants were 6 mm inlength, whereas the remainingimplant was 4 mm. Each failedimplant was subsequently removed,and the site was allowed to heal.Of the implants that failed, twowere in the nonloaded group onthe same patient, whereas theremaining one was in the immedi-ately loaded group. The patientwith the two implant failures even-tually completed the study with asuccessful implant. Statisticalanalysis was carried out on the20 successfully osseointegratedimplants over 8 weeks. Seven ofthe 20 implants were 4 mm inlength, five of those were in theloaded group and two in the non-loaded group. The remaining 13implants were 6 mm in length, fivein the loaded group and eight inthe nonloaded group (see Table 1).

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Ten patients were randomized tothe nonloaded group, whereas theother 10 were in the immediatelyloaded category. The age range ofthe patients was 13 to 48, with 12females and 8 males participating.

Initial examination evaluated the20 successfully integrated implants,adjusted for length. Mean ISQvalues for immediately loadedimplants were compared with themean ISQ values for nonloaded

implants at the time of surgery andat the 8-week follow-up. Compar-ing the two groups, there was anaverage increase in ISQ valuesfrom the surgical date to the8-week interval in the nonloadedgroup, and an average decrease inISQ values for the loaded group.Table 2 and Figure 4 illustrate themean change in ISQ values of themidpalatal implants that wereplaced and immediately loaded andthose that were nonloaded fromplacement to 8-weeks later. Thetable illustrates the fact that thetwo groups were very similar intheir mean baseline ISQ and weresignificantly different at8 weeks. Nonloaded implantsshowed about a 15 to 20%increase in stability from the firstto eighth week, which was asignificant change (p < 0.05).In contrast, the loaded implantsdecreased in stability by 10 to15% over this same time period,which was nonsignificant(p > 0.05).

The two implant lengths (Strau-mann Orthosytsem: length ofimplant 4 and 6 mm) were com-pared from surgical placement tothe 8-week interval (see Table 3).The ISQ values of the 4-mmimplants remained practicallyunchanged (p > 0.05), whereas the6-mm implants increased in ISQvalues at the 8-week reading(p < 0.05). Table 3 compares themean ISQ values of the 4- and

Figure 4. The mean implant stability quotient (ISQ) valuesobtained at baseline and at 8 weeks for the loaded andnonloaded groups.

TA B L E 2 . I M P L A N T S TA B I L I T Y Q U O T I E N T ( I S Q ) VA L U E S O F T H E L O A D E D

A N D N O N L O A D E D G R O U P S AT B A S E L I N E A N D AT 8 W E E K S .

Baseline ISQ 8 Weeks ISQ Significance from Baseline

ImplantNonloaded 38.7 � 2.4 47.3 � 1.7 0.000*Loaded 42.0 � 2.4 38.4 � 1.7 0.057

p 0.358 0.002*Significance (p < 0.05); values are given as mean � SD.

*Significant difference (p < 0.05).

TA B L E 1 . D I S T R I B U T I O N O F T H E N U M B E R O F PAT I E N T S , N U M B E R O F

I M P L A N T S , A N D T H E L E N G T H O F I M P L A N T S P L A C E D .

Loaded Nonloaded Total Implants per Length

Implant length4 mm 5 (50%) 2 (20%) 76 mm 5 (50%) 8 (80%) 13

Total implants per group 10 10 20

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6-mm implants. The 6-mmreadings demonstrated an averagehigher reading than the 4-mmimplants. The differencebetween the 4- and 6-mm groupsat 8 weeks was significant(p < 0.05).

D I S C U S S I O N

The results support the hypothesisthat there is a statistically signifi-cant difference in the stability oforthodontic palatal implants thatreceive a constant orthodonticload immediately after placementcompared with implants that arenot loaded until 8 weeks afterplacement. Immediate loading ofmidpalatal implants at the sameappointment as the surgical place-ment had lower RFA readings atthe 8-week time point as com-pared with the nonloaded group(15–20% increase versus 10–15%decrease). However, it does notsupport the hypothesis that thereis a clinically significant differencein the success rate between thetwo groups. Eighty-seven percentof the implants placed exhibitedclinical success. Clinical success

was defined as the ability to usethe implant in the course oforthodontic treatment. However,because the sample size was smalland there was only one patient ineach group with implant failures,the results cannot be interpretedas a recommendation to load theimplants immediately. Further-more, it is not known if theforce delivered throughthe TPA was the same, giventhe difference in implant stabilitybetween groups.

This study was designed toexamine if there was a differencebetween the immediately loadedand the nonloaded groups. In addi-tion, a secondary goal was todetermine if the 12-week healingperiod suggested by the manufac-turer was necessary. This informa-tion coupled with an implant thatwas not clinically usable wouldsupport a longer healing period.First, biologic principles mustbe understood to support thedifferent RFA readings that wereevident between the twoexperimental groups.

Osseointegration is a strain-dependent highly dynamic process.It is defined as a direct and stableanchorage of an implant by theformation of bony tissue withoutgrowth of fibrous tissue at thebone–implant interface.19 Onedefining feature of osseointegrationis that osteoblasts and mineralizedmatrix contact the implant surfaceeven when loads are applied.Cochran and colleagues showedthat an implant is in contact withthe bone when the implant isplaced into the bone.10 This iscalled primary bone contact andrepresented approximately 70% atthe time of implant placement. Thepercentage of the original bonecontact with the implant, primarycontact, decreased over time, from70 to 5%, indicating an increase inthe secondary bone contacts. Thiswas interpreted as a sign ofongoing bone remodeling at thebone–implant interface. This hasbeen reinforced more recently byBuchter and colleagues whoshowed that the bone is in contactwith the implant surface from dayone of implant insertion,as quantified by undecalcifiedhistologic sections.20

Three of the implants placed failedand required removal before thecompletion of the study. Implantfailure can be the result of manyfactors. The first implant thatfailed exhibited good primarystability at surgical placement as

TA B L E 3 . M E A N I M P L A N T S TA B I L I T Y Q U O T I E N T ( I S Q ) VA L U E S F O R T H E

4 - A N D 6 - M M I M P L A N T S AT B A S E L I N E A N D 8 W E E K S .

Mean ISQ Baseline Mean ISQ 8 Weeks Significance from Baseline

Implant length4 mm 36.6 � 7.2 34.0 � 9.3 0.3086 mm 42.4 � 7.3 47.6 � 4.9 0.039*

p 0.105 0.000*Significance (p < 0.05); values are given as mean � SD.

*Significant difference (p < 0.05).

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evidenced by a large RFA reading(ISQ > 40) and the absence ofmobility. However, when thepatient came in for his later RFAreadings, it was loosened by theprimary investigator when unwind-ing the screw that held the healingcap in place. Two days later, thepatient had the implant manuallyremoved by the surgeon because ofexcess mobility. Subsequent to that,a second implant was placed in thesame patient 4 weeks later, with alow initial RFA reading (ISQ < 30).This second implant in the samepatient also failed. It is plausiblethat the palatal bone did not haveenough time to heal between thetwo procedures. The third implantthat failed during the course of theinvestigation also exhibited poorprimary stability as evidenced by alow RFA reading (ISQ < 30) andimplant mobility. One reason forearly implant failure is thought tobe because of excessive mechanicalload applied to the implant,coupled with lower stability atimplant placement.21 It is possiblethat this third implant that failednever attained a good bone toimplant contact and that the orth-odontic appliance undermined theprocess through application of acontinuous load. Insufficientprimary stability is associated withpoor healing and the prematureloss of an implant.22

The results obtained with the twoimplant lengths (4 and 6 mm) were

consistent with a previous publica-tion by Gedrange and colleagues23

that the ISQ values of the 6-mmimplants were higher when com-pared with the 4-mm implants.According to the RFA findings,there was a significant increase inthe 6-mm group from baseline to 8weeks; and a significant differencebetween the 4- and 6-mm groups at8 weeks. Two parameters are par-ticularly useful when evaluatingimplant stability with RFA. Thefirst is the location of the implant inthe bone. The second is thestiffness of the implant in the sur-rounding tissue. There are threefactors that are important for stiff-ness. The first one is the stiffness ofthe implant components them-selves. The second is the stiffness ofthe implant/bone interface, thebond between the surface of theimplant and the surrounding bone.The third is the stiffness of the boneitself, determined by the trabecular/cortical bone ratio and the bonedensity.17 These parameters showthe importance of the length andtype of the implant and the prepa-ration technique depending on bonequality and quantity. It is possiblethat, because of the increasedlength of the 6-mm implants, theywere bicortically stabilized byreaching the cortical layer of thenasal floor. Bicortical placementwould decrease the trabecular/cortical ratio and with the increaseddensity of both cortices, higher RFAvalues would be expected.

C O N C L U S I O N

In summary, this is the first pro-spective clinical trial evaluating thestability patterns of midpalatalimplants under immediate loading.It supports the empirical notionthat orthodontic implants can beloaded immediately because of therelatively light forces that are usedin orthodontics as compared withthe heavy loads that are placed onrestorative implants. It reinforcesearlier findings that the unloadedOrthosystem implants increase instability from surgical placement,which is considered time one(primary stability) to time two(secondary stability)17 and that the6-mm implants have higher ISQvalues compared with the 4-mmimplants, implying higher stability.In addition, the objective of deter-mining the stability of nonloadedmidpalatal implants 8 weeks afterplacement and comparing themwith the immediately loadedimplants for use as orthodonticanchorage was accomplished.These results demonstrate thatdelaying the load on an implant by2 months results in a higher RFAreading, but that loading theimplants immediately did not resultin less implant success. It is pos-sible that a decrease in RFA read-ings, which can be critical forimplants used for tooth replace-ment, is not as critical for orth-odontic implants because of thelight forces that are used duringorthodontic traction (100–200 g).

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Based on the study results, and theclinical success observed in thenonloaded and loaded groups, itsuggests that once primary stabilityis observed at the time of implantplacement, it is possible thatthe implant can be loaded andsuccessfully used for orthodonticpurposes. Primary stability, andtherefore, lack of mobility, appearsto be an important parameter gov-erning the clinical success of thepalatal implants used for orth-odontic purposes. If lack of mobil-ity (good primary stability) isobserved at the time of placement,loading the implants at that timewill allow the orthodontist to savevaluable treatment time and passalong to the patient a cost/timebenefit advantage. However, theclinical success observed in thisstudy will need to be corroboratedwith a larger sample size. Recently,Straumann has introduced palatalimplants with slightly differentdimensions. It is possible that thesenew dimensions may yielddifferent results and warrantfuture investigation.

D I S C L O S U R E A N D

A C K N O W L E D G E M E N T S

A source of support was providedby both the American Academy ofEsthetic Dentistry, in the form of agrant, and Straumann, in the formof equipment. The authors do nothave any financial interest in thecompanies whose materials areincluded in this article.

The authors would like to thankMs. Madge Cluck for her help inpreparing this manuscript. Wewould also like to thank theInstitute Straumann (Basel,Switzerland) for donating theimplants for this study.

R E F E R E N C E S

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2. Favero L, Brollo P, Bressan E. Orthodon-tic anchorage with specific fixtures:related study analysis. Am J OrthodDentofacial Orthop 2002;122(1):84–94.

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Reprint requests: David Cochran, DDS, MS,PhD, MMSci., University of Texas HealthScience Center, San Antonio Dental School,7703 Floyd Curl Drive, San Antonio, TX78229-3900, USA. Tel.: 210-567-3604;email: cochran@uthscsa.edu

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