Issue 10.2

Virtual Journal of Orthodontics

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Virtual Journal of Orthodontics - Issue 10.2 -

Corticotomy Assisted OrthodonticsAUTHORS:

1. Dr. Deepti Govindankutty! Postgraduate student,

2. Dr. Prashanth Kamath, MDS! Professor and Head of Department,

3 . Dr. Arun Kumar B.R, MDS! Senior Lecturer,

4. Dr. Rajat Scindhia D, MDS! Senior Lecturer,

5. Dr. Raghuraj M.B, MDS! Senior Lecturer,

Department of Orthodontics and Dentofacial Orthopaedics,Dr. Syamala Reddy Dental College Hospital and Research Centre,Bangalore,India-560037.

Abstract

The use of orthodontic treatment in adult patients is becoming more common and these patients have different requirements especially regarding duration of treatment and facial and dental aesthetics. Theories to increase the rapidity of tooth movement are always being suggested. One such theory is Corticotomy assisted orthodontic treatment. Alveolar corticotomy is an effec-tive means of accelerating orthodontic treatment. This literature review includes an historical background, biological and orthodontic fundamentals and clinical appli-cation and contraindications of this techni-que. Orthodontic treatment time is redu-

ced with this technique to one-third of that in conventional orthodontics. Corticotomy facilitated orthodontics is promising proce-dure . Controlled clinical and histological studies are needed to understand the bio-logy of tooth movement with this procedu-re, the effect on teeth and bone, post-reten-tion stability, quantifying the volume of ma-ture bone formation, and determining the status of the periodontium and roots after treatment.

Key words: Corticotomy, osteotomy, acce-lerated orthodontics.

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Address of Correspondence:

Department of Orthodontics and Dento-facial Orthopaedics,Dr. Syamala Reddy Dental College, Ho-spital and Research centre,111/1 SGR College main road, Munne-kolala, Marathahalli Post,Bangalore, Karnataka , India- 560037Mobile no: +918892968340E- mail: deeptigk@hotmail.com

Introduction

One of the main disadvantages of ortho-dontic treatment is time. Most of the con-ventional orthodontic treatments require more than twelve months to complete. Un-fortunately many potential orthodontic pa-tients jeopardize their dental health and de-cline treatment, due to long treatment time. This is especially encountered in ca-se of adult patients.

Corticotomy-assisted or corticotomy-facili-tated orthodontics is a therapeutic proce-dure that helps orthodontic tooth move-ment by accelerated bone metabolism due to controlled surgical damage. This is not a new procedure, although it was initially ba-sed more on techniques using osteotomy instead of approaches with corticotomy. It is said to harness the regional acceleratory phenomenon (RAP). It is considered an in-termediate therapy between orthognatic surgery and conventional orthodontics.The procedure has several advantages, such as reduced treatment time and facilitation of dental arch expansion . This article pre-sents a review of the literature, including the historical background, biological and orthodontic fundamentals based on experi-mental studies, and the most significant cli-nical applications and contraindications ba-sed on recently published clinical studies.

Historical background

Corticotomy facilitated orthodontics has been employed in various forms over the past to speed up orthodontic treatments. It was first introduced in 1959 by Kole1 as a means for rapid tooth movement. It was believed that the main resistance to tooth movement was the cortical plates of bone and by disrupting its continuity, orthodon-tics could be completed in much less time than normally expected. Koleís procedure involves the reflection of full thickness flaps to expose buccal and lingual alveolar bone, followed by interdental cuts through the cortical bone and barely penetrating the medullary bone (corticotomy style). The subapical horizontal cuts connecting the interdental cuts were osteotomy style, penetrating the full thickness of the alveo-lus. He suggested that since the blocks of bone was being moved rather than the indi-vidual teeth, the root resorption would not occur and retention time will be minimized. Because of the invasive nature of Koleís technique it was never widely accepted.

Duker2 (1975) used Koleís basic technique on beagle dogs to investigate how rapid tooth movement with corticotomy affects the vitality of the teeth and the marginal pe-

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riodontium. The health of the periodontium were preserved by avoiding the marginal crest bone during corticotomy cuts. It was concluded that neither the pulp nor the pe-riodontium was damaged following ortho-dontic tooth movement after corticotomy surgery . The results helped to substantia-te the belief regarding the health of crestal bone in relation to the corticotomy cuts. Design of the subsequent techniques has taken this into consideration; the interden-tal cuts are always left at least 2 mm short of the alveolar crestal bone level.

Suya3 (1991) reported corticotomy-assi-sted orthodontic treatment of 395 adult Ja-panese patients. Suyaís technique differed from Koleís with the substitution of a suba-pical horizontal corticotomy cuts in place of the horizontal osteotomy cut beyond the apices of the teeth. Suya contrasted his technique with conventional orthodontics in being less painful, producing less root resorption, and exhibiting less relapse. Out-standing results and extreme patient sati-sfaction with corticotomy procedures were reported. He believed that the tooth move-ments were made by moving blocks of bo-ne using the crowns of the teeth as han-dles. Completing tooth movement in 3-4 months were recommended, after which time the edges of the blocks of bone would begin to fuse together.

These initial approaches included some ty-pes of alveolar osteotomy alone or combi-ned with corticotomy, called ëbone block movementí. Traditionally, vertical and hori-zontal osteotomies have had an increased risk of postoperative tooth devitalization or even bone necrosis, depending on the se-verity of injury to the trabecular bone. The-re is also an increased risk of periodontal damage, mainly in cases in which the inter-radicular space is less than 2 mm . Cortico-tomy has many advantages compared with osteotomy. It prevents injury of the pe-riodontium and pocket formation, and also prevents devitalizing of a single tooth or a group of teeth. The nutritive function of the bone is maintained through the spongiosa, although the bone is exposed, avoiding the possibility of bone aseptic necrosis. Ta-king into account these advantages and drawbacks, procedures based on cortico-tomy are gradually replacing those using osteotomy.

Recent Techniques

A more recent surgical orthodontic therapy was introduced by Wilcko4-7 et al. which in-cluded the innovative strategy of combi-ning corticotomy surgery with alveolar graf-ting in a technique referred to as Accelera-

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ted Osteogenic Orthodontics (AOO) and more recently to as Periodontally Accelera-ted Osteogenic Orthodontics (PAOO) (Wilc-ko7 et al., 2008). This technique advocated for comprehensive fixed orthodontic ap-pliances in conjunction with full thickness flaps and labial and lingual corticotomies around teeth to be moved. Bone graft con-sisting of demineralized freeze-dried bone and bovine bone with clindamycin was ap-plied directly over the bone cuts and the flap was sutured in place. Tooth movement was initiated two weeks after the surgery, and every two weeks there after by activa-tion of the orthodontic appliance. Wilcko et al. reported that this technique will reduce treatment time to one-third the time of con-ventional orthodontics. Alveolar augmenta-tion of labial and lingual cortical plates we-re used in an effort to enhance and strengt-hen the periodontium, reasoning that the addition of bone to alveolar housing of the teeth, using modern bone grafting techni-ques, ensures root coverage as the dental arch expanded. They advocated using the PAOO for treatment of moderate to seve-rely crowded Class I and Class II. Several reports indicated that this technique is sa-fe, effective, extremely predictable, asso-ciated with less root resorption and redu-ced treatment time, and can reduce the need for orthognathic surgery in certain si-tuations.

Regional acceleratory phenomenon

First coined by Frost8, the regional accele-ratory phenomenon (RAP) is a collection of physiological healing events. Some of the features of RAP include accelerated bone turnover and decreased bone density. Yaf-fe9 et al, suggest that RAP in humans be-gins within a few days of surgery, typically peaks at 1 to 2 months and may take from 6 to more than 24 months to subside. They characterized the initial phase of RAP as an increase in cortical bone porosity becau-se of increase osteoclastic activity and spe-culated that bone dehiscence might occur after periodontal surgery in an area where cortical bone is initially thin. They surmised that RAP might be a contributing factor to increased mobility of teeth after periodon-tal surgery. There is a strong indirect evi-dence that the physiologic evidence asso-ciated with RAP following surgery, ie cal-cium depletion and diminished bone densi-ties, result in rapid tooth movement. Frost stated that the duration and intensity of the RAP are proportional to extent of injury and soft tissue involvement in the injury.

An interesting observation made by some authors is the rapidity of tooth movement following orthognathic surgery. Although anecdotal, they surmised that RAP may be the biological mechanism behind their abili-

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ty to treat cases quickly following a surgi-cal procedure. It is clear that further re-search in this area is required.

The CAO Technique

Case selection is a very important step; both the orthodontist and the periodontist should agree upon the need for cortico-tomy, treatment plan and the extent and lo-cation of the decortication cuts. The PAOO technique described by Wilcko is as fol-lows: full-thickness flaps are reflected la-bially and lingually using sulcular releasing incisions. The releasing incision can also be made within the thickness of the gingi-val attachment or at the base of the gingi-val attachment (mucogingival junction). Ver-tical releasing incisions can be used, but they should be positioned at least one tooth away from the ìbone activation". Flaps should be carefully reflected beyond the apices of the teeth to avoid damaging the neurovascular complexes exiting the alveolus and to allow adequate decortica-tion around the apices. Selective alveolar decortication is performed in the form of decortications cuts and at points up to 0.5 mm in depth, combined with selective me-dullary penetration to enhance bleeding. This poses little threat to tooth vitality and makes PAOO much safer than the osteo-tomy technique, in which cuts extend into

the medullary bone around the teeth that are to be moved. Adequate bio-absorbab-le grafting material is placed over the inju-red bone. Flaps are then repositioned and sutured into place. Sutures should be left in place for a minimum of two weeks. Tooth movement should start one or two weeks after surgery. Unlike conventional orthodontics, the orthodontic appliance should be activated every two weeks until the end of treatment after PAOO .

Indications and Clinical Applications

Several clinical applications for CAOT have been reported. Corticotomy was used to facilitate orthodontic tooth movement and to overcome some shortcomings of con-ventional orthodontic treatment, such as the long required duration, limited envelo-pe of tooth movement and difficulty of pro-ducing movements in certain directions. These applications include the following:

1. Resolve Crowding and Shorten Treat-ment Time[d1]

Corticotomy and osteotomy were used in orthodontics primarily to resolve crowding in a shorter period of time. It has been shown that corticotomy is efficient in redu-cing the treatment time to as little as one

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fourth the time usually required for conven-tional orthodontics. Wilcko6 et al published a report about two adult patients with seve-re crowding who were treated via AOO in just 6.5 months . Wilcko7 also reported a case of an adult female who was treated in only 4.5 months. Hajji10 studied the effects of resolving mandibular anterior dental crowding by comparing non-extraction ,ex-traction , and corticotomy-facilitated non-extraction orthodontic treatments in a clini-cal trial. The mean active treatment time for the corticotomy-facilitated group was 6.1months, versus 18.7 months required for non-extraction orthodontics and 26.6 months for extraction therapy. A reduced chance of root resorption , less oral hygie-ne related enamel decalcification and bet-ter patient cooperation and acceptance are possible advantages when lengthy ort-hodontic treatment is avoided.

2. Accelerate Canine Retraction after Pre-molar Extraction

Canine retraction after premolar extraction is a lengthy step during the extraction sta-ge of orthodontic treatment. Canine retrac-tion was accelerated by corticotomy in two animal studies. Both studies demonstrated faster canine retraction when compared to

conventional orthodontic retraction of the canines11-12. Miniscrew implant-suppor-ted maxillary canine retraction with cortico-tomy-facilitated orthodontics was to clini-cally evaluated by Ela SM13 et al. The average daily rate of canine retraction was significantly higher with corticotomy than without corticotomy.

3. Enhance Post-Orthodontic Stability

Stability after treatment has always been an important concern after orthodontic treatment. Thinner mandibular cortices are a risk feature for bony dehiscence after de-crowding orthodontic treatment. Techni-ques that increase alveolar volume with grafts may resolve this situation; thus, whe-re 5 mm of crowding was considered the limit for traditional orthodontics without ex-traction, this may be extended to 10-12 mm without risk of dehiscence. Retention and stability with CAO are better that with conventional orthodontics10,14. The impro-ved stability was attributed to the increa-sed turnover of tissues adjacent to the sur-gical site. However, there have been no long-term prospective longitudinal studies supporting these initial results.

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4. Facilitate Eruption of Impacted teeth

Surgical traction of impacted teeth, espe-cially the canines, is a frustrating and lengthy procedure. A study by Fischer15 showed that under the same periodontal conditions, the corticotomy-assisted appro-ach produced faster tooth movement du-ring traction of palatally impacted canines compared to conventional canine traction methods at the end of either treatment. In an adult female patient, an impacted se-cond premolar was facilitated to erupt spontaneously using corticotomy after creating enough space as a part of an overall fixed orthodontic treatment, which included extraction of the first premolars and bilateral corticotomy assisted expan-sion. Spontaneous eruption was comple-ted in three months without any orthodon-tic traction.

5. Facilitate Slow Orthodontic Expansion

A limited number of successful techniques is available for the treatment of maxillary arch constriction; these include surgically-assisted rapid palatal expansion (SARPE) and slow palatal expansion. These techni-ques are aggressive in nature and less ac-cepted by patients. The presence of non-growing alveolar bone that confines the

teeth in the predetermined space available in the alveolus limits transverse tooth mo-vement16 . Yen17 et al. reported a cleft pa-tient with palatal constriction in the upper arch who was treated via corticotomy assi-sted expansion (CAE) after surgical closure of a palatal fistula . CAE is an effective technique for the treatment of maxillary transverse deficiency in adults and is assu-med to provide greater stability and better periodontal health than conventional ex-pansion, which can be less effective, dan-gerous and unstable in many patients. In addition, CAE allows differential expansion as well as unilateral expansion in a more controlled way than conventional expan-sion. Figs present a case of severely con-stricted maxilla that was expanded using a quad-helix appliance assisted by bilateral buccal and palatal decortication. Suc-cessful expansion of the upper arch was achieved; the inter-molar distance was in-creased by 5 mm, and the inter-canine di-stance was increased by 4 mm.

CAE can be a good alternative to conven-tional orthodontic mechanics in the treat-ment of unilateral cross-bites in adults, which are either less efficient, patient-de-pendent, or accompanied by unnecessary side effects such as overexpansion on the normal side, canting of the occlusal plane and compromised vertical dimension. Per-

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forming corticotomy on only the con-stricted side helps to overcome these un-necessary side effects. The decorticated side is assumed to exhibit reduced resi-stance to expansion and faster tooth move-ment, making the effect of any bilateral ex-pansion appliance unilateral.

6. Molar Intrusion and Open Bite Correc-tion

CAOT has also been used in the treatment of severe anterior open bite in conjunction with skeletal anchorage18-19 . Moon19 et al. achieved sufficient maxillary molar intru-sion (3.0 mm intrusion in two months) using corticotomy combined with a skele-tal anchorage system with no root resorp-tion and with no patient compliance requi-red. Olivieria20 et al. also reported 4 mm of molar intrusion in 2.5 months using corti-cotomy in one patient and 3 to 4 mm in 4 months in another patient. Hawang and Lee21 demonstrated intrusion of supra-e-rupted molars using corticotomy

7. Manipulation of Anchorage

CAOT was used in the treatment of bimaxil-lary protrusion as an adjunct to manipulate skeletal anchorage without any adverse side effects in only one-third of the regular

treatment time22 . CAOT was also used to achieve molar distalization23. After perfor-ming segmental corticotomy around the molars, the anchorage value and resistan-ce of the molars to distal movement were effectively reduced without the use of any extra anterior anchorage devices .

Contraindications

Despite an increasing number of reports on the use of alveolar corticotomies as an aid to orthodontic treatment, few studies have reported setbacks when employing this combined treatment. Recently, howe-ver, Wilcko et al gave an objective account of scenarios where the use of ACS-ortho-dontics should be avoided, i.e., (1) patients showing any sign of active periodontal di-sease, (2) individuals with inadequately treated endodontic problems, (3) patients making prolonged use of corticosteroids, (4) persons who are taking any medica-tions that slow down bone metabolism, such as bisphosphonates and NSAIDs

Conclusion

CAO is a promising adjuvant technique, in-dicated for many situations in the orthodon-tic treatment of adults. It has been used in some limited cases to avoid secondary ef-fects of conventional orthodontics, such as root resorption in molar intrusion or pe-

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riodontal dehiscence in slow tooth expan-sion. However, its main advantages are re-duction of treatment time and postortho-dontic stability, which may allow its genera-lized use in many adult patients without ac-tive periodontal pathology. The biological principle of this method is based on tempo-rary reduction of medullar bone density (transitory osteopenia) within a 3-4-month window, which allows more physiological tooth movement inside the alveolar bone (less hyalinization period of PDL).

References

1) Kˆle H. Surgical operations on the alveolar ridge to correct occlusalabnormalities. Oral Surg Oral Med Oral Pathol. 1959;12:515-29.

2) Duker, J., 1975. Experimental animal research in-to segmental alveolar movement after corticotomy. J. Maxillofac. Surg. 3, 81-84.

3) Suya, H., 1991. Corticotomy in orthodontics. In: Hosl, E., Baldauf, A. (Eds.), Mechanical and Biolo-gical Basis in Orthodontic Therapy. Huthig Buch Ver-lag, Heidelberg, Germany, pp. 207-226.

4) Wilcko, W.M., Wilcko, M.T., Bouquot, J.E., Fergu-son, D.J., 2000. Accelerated orthodontics with alveo-lar reshaping. J. Ortho. Practice 10, 63-70.

5) Wilcko WM, Wilcko T, Bouquot JE, Ferguson DJ. Rapid orthodonticswith alveolar reshaping: two case reports of decrowding. Int J Periodont Resto-rat Dent. 2001;21:9-19.

6) Wilcko, M.W., Ferguson, D.J., Bouquot, J.E., Wilc-ko, M.T., 2003.Rapid orthodontic decrowding with

alveolar augmentation: case report. World J. Ort-hod. 4, 197-205.

7) Wilcko, M.T., Wilko, W.M., Bissada, N.F., 2008. An evidence-based analysis of periodontally accelera-ted orthodontic and osteogenic techniques: a synt-hesis of scientific perspective. Seminars Orthod. 14, 305-316.

8) Frost, H.M., 1983. The regional acceleratory phe-nomenon: a review. Henry Ford Hosp. Med. J. 31, 3-9.

9) Yaffe A, Fine N, Bindermann I. Regional accelera-ted phenomenon in the mandible following mucope-riosteal flap surgery. J Periodontol. 1994;65:79-83

10) Hajji SS. The influence of accelerated osteoge-nic response on mandibular de- crowding [thesis]. St Louis: St Louis Univ, 2000.

11) Ren A, Lv T, Zhao B, Chen Y, Bai D. Rapid ortho-dontic tooth movement aided by alveolar surgery in beagles. Am J Orthod Dentofacial Orthop 2007; 131: 160.e1-10.

12) Mostafa YA, Fayed MM, Mehanni S, ElBokle NN, Heider AM. Comparison of corticotomy-facilitated vs standard tooth-movement techniques in dogs with miniscrews as anchor units. Am J Orthod Den-tofacial Orthop 2009; 136: 570-7.

13) Ela SM, El-Beialy AR, El-Sayed KM, Selim EM, El-Mangoury NH, Mostafa YA. Miniscrew implant-supported maxillary canine retraction with and wit-hout corticotomy-facilitated orthodontics. Am J Ort-hod Dentofacial Orthop. 2011 Feb;139(2):252-9. doi: 10.1016/j.ajodo.2009.04.028

14) Nazarov AD, Ferguson DJ, Wilcko WM, Wilcko MT. Improved retention following corticotomy

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using ABO objective grading system. J Dent Res 2004; 83: 2644.

15) Fischer TJ. Orthodontic treatment acceleration with corticotomyassisted exposure of palatally im-pacted canines. Angle Orthod 2007; 77: 417-20.

16) Vanarsdall RL Jr. Transverse dimension and long-term stability.Semin Orthod 1999; 5:171-80.

17) Yen SL, Yamashita DD, Kim TH, Baek HS, Gross J. Closure of an unusually large palatal fistula in a cleft patient by bony transport and corticotomy-assisted expansion. J Oral Maxillofac Surg 2003;61: 1346-50.

18) Kanno T, Mitsugi M, Furuki Y, Kozato S, Ayasa-ka N, Mori H. Corticotomy and compression osteogenesis in the posterior maxilla for treating se-vere anterior open bite. Int J Oral Maxillofac Surg 2007; 36: 354-57.

19) Moon CH, Wee JU, Lee HS. Intrusion of overe-rupted molars by corticotomy and orthodontic ske-letal anchorage. Angle Orthod 2007; 77: 1119-25.

20) OliveiraDD, de Oliveira BF, de Ara˙jo Brito HH, de Souza MM, Medeiros PJ. Selective alveolar corti-cotomy to intrude overerupted molars. Am J Orthod Dentofacial Orthop 2008; 133: 902-8.

21) Hwang H, Lee K. Intrusion of overerupted mo-lars by corticotomy and magnets. Am J Orthod Den-tofacial Orthop 2001; 120: 209-16.

22) Iino S, Sakoda S, Miyawaki S. An adult bimaxilla-ry protrusion treated with corticotomy-facilitated ort-hodontics and titanium miniplates. Angle Orthod 2006; 76: 1074-82.

23) Spena R, Caiazzo A, Gracco A, Siciliani G. The use of segmental corticotomy to enhance molar di-stalization. J Clin Orthod 2007; 41:693-9.

Name and complete mailing address of the aut-hor†to contact for more information or suggestions:

Dr. Deepti Govindankutty

Post graduate , Department of Orthodontics and Dentofacial Orthopaedics,

Dr. Syamala Reddy Dental College, Hospital and Re-search centre,

111/1 SGR College main road, Munnekolala, Marat-hahalli Post,

Bangalore, Karnataka , India- 560037

Mobile no: +918892968340

E- mail: deeptigk@hotmail.com

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Virtual Journal of Orthodontics - Issue 10.2 -

Evaluation of Shear Bond strength between Acid etching, Air Abrasion and Bur abrasion Technique An in vitro Study.

Abstract

The present study was to evaluate the shear bond strength of straight wire brac-kets bonded to pre treated enamel surface prepared by 37% phosphoric acid, air abra-sion and bur abrasion. Sixty human premo-lars extracted for orthodontic purposes we-re randomly assigned to three groups ba-sed on conditioning method: Group 1- con-

ventional etching with 37% phosphoric acid; Group 2- Air abrasion with 50 µm alu-minium oxide; and Group 3- Bur abrasion with diamond fissure bur (#330, MANI, Dia-Burs, New jersy). The specimens were fixed in a self cure acrylic blocks and were bonded on prepared enamel using a light-cured composite. Shear bond strength we-re measured using a uni- versal testing ma-chine with a crosshead speed of 0.5 mm

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AUTHORS:

1. Dr. Anila Charles, Reader, Department of orthodontics, Madha Dental College, Dr. MGR Medical University, Madha Nagar, Somangalam Road, Kundrathur, Chen-nai – 600069, Tamilnadu, India.Email ID: cs_anila@yahoo.co.in

2. Dr. Senkutvan Rathnam sapabathy, Prof and Head, Department of orthodontics, Madha Dental College, Dr. MGR Medical University,Madha Nagar, Somangalam Road, Kun! !drathur, Chennai – 600069, Tamilnadu, India.

3. Dr. Sivaram SubbiahM.D.S, M.Orth RCS (Edinburgh) Assistant Professor, Department of orthodontics Penang International Dental College NB Towers - Level 18, Jalan bagan Luar But-terworth, Penang. Malaysia-12000 H/P:0060124510502

4. Dr. Sanjay JacobReader, Department of orthodontics, Madha Dental Col-lege, M.G.R University, Kundrathur, Chennai – 600069, Tamilnadu, India

Address of Correspondence:

Dr. Anila Charles, Reader, Department of Orthodon-tics, Madha Dental College, Dr. MGR Medical University, Madha Nagar, Somangalam Road, Kun-drathur, Chennai – 600069, Tamil-nadu, India.Email ID: cs_anila@yahoo.co.in

per second. The statistical comparison of different group was carried out by One-way analysis of variance was used to com-pare shear bond strengths The results showed that the bond strength of the sandblasted groups was significantly lower than that of the etching groups. It was con-cluded that sand blasting was favourable than conventional bur preparing enamel surface for bond strength. The result of the study proved acid etching to be acceptab-le for bonding procedures.

Introduction

The late nineteenth century paved way for innovation of materials in material science and bonding technique was widely accepted due to its simplicity, efficacy and providing more es-thetic qualities.1 Before its advent, large amount of sound tooth structure were sacrificed to meet the physi-cal demands of the material were as acid-etch bonding, allowed maximum preserva-tion of tooth structure in the field of ortho-dontics. This technology has resulted in si-gnificant treatment improvements, inclu-ding more esthetic and hygienic appliance, elimation of post treatment band space, ea-sier caries detection and treatment, less soft tissue irritation, and decreased possibi-lity of enamel decalcification.

Another novel technology introduced before acid-etch bonding was air abrasion by Dr. Robert Black in the 1940s. Its popu-larity decline as it effect was viewed as the disadvantage in the late 1950s in restorati-ve dentistry. Today it is viewed as an advantage in terms of protecting the oral soft tissues with typical tooth surface pre-paration times ranging from 0.5 to 3 se-conds without the additional step of rin-sing in orthodontic bonding. Air abrasion technique uses the kinetic energy of Al oxi-de particles for cutting and abrading tooth surface.

In recent years, in addition to conventional acid etch and air abrasion technique bur abrasive techniques has been used for pre-paration of enamel surfaces.  As surface roughness created by diamond burs cau-ses an increased surface area the mechani-cal retention is increased. Since various techniques are available to enhance the bonding performance the most reliable technique was evaluated by this in vitro study. Scanning electron microscopic ob-servations were also conducted.

Materials and Methods

Preparation of specimen

A total of sixty freshly extracted teeth for orthodontic purpose (maxillary and mandi-

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bular premolars) were collected. All the teeth used in this study were extracted over the course of three months. They had undamaged buccal enamel with no caries, cracks and no pre-treatment by any chemi-cals. Following extraction, residue on the teeth was removed and washed away with tap water. They were then stored in normal saline at room temperature to prevent dehydration and changed weekly to pre-vent bacterial growth.

To mount the teeth in universal testing ma-chine (Lloyd Universal testing machine-Mo-del No.L.R 100K) they were fixed in a self cure acrylic blocks with dimension by 35mm x 9mm. The teeth were mounted on acrylic blocks such that the roots were completely embedded into the acrylic up to the cemento-enamel junction leaving the crown exposed. The teeth were ran-domly divided into three groups as shown in the Figure 1

The blocks were colour coded for easy identification. Prior to the bonding procedu-re, the enamel surface were polished with oil and fluoride free fine pumice, using a brush and a slow-speed hand piece, rin-sed again and dried with an air syringe. The method specified for each experimen-tal group was then followed.

Bonding System

For the acid-etching procedure (Group 1) the enamel surfaces were etched with 37% phosphoric acid gel for 20 seconds, rinsed with air-water spray for 15 seconds, and dried to a chalky-white appearance. Conventional Transbond adhesive primer by 3M Unitek was applied on the enamel surface to it a Premolar metal bracket 3M Jammuna International with a mesh an average base area of 10.5mm2 was pla-ced, excess was removed using a probe and was cured using A 3M ESPE, Elipar 2500-Halogen -curing unit emitting light at wavelength of 480nm was used for polyme-rization for 40 sec

For air abrasion procedure (Group 2) the enamel was surfaces was air blasted for five second with 50μm Al2O3 particles at 80 psi , It was accomplished at a distance of approximately 2 mm using the KCP 2000 unit (AmericanDental Technologies,

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Southfield, MI) and at an angle of 45°. The application of the aluminium oxide jet was accomplished inside a closed transparent acrylic box, to avoid particle aspiration by the operator as shown on Figure 2

After the blasting, oil free compressed air was used to clean the surface on it a thin film of bonding agent was applied and bon-ding was done as per manufactures in-struction.

For Bur abrasion procedure (Group 3) the enamel was surfaces was abraded mecha-nically using a thin diamond fissure bur sli-ghtly (#330, MANI, Dia-Burs, Japan). Air and water spray from the hand piece was adjusted to a level of 85% air and 85% wa-ter for 2 W during abrasion procedure the bur was placed parallel to the buccal surfa-

ce of teeth. The tooth surface was dried and bonding agent was applied and the bracket was secured with adhesive on the buccal surface and cured.

Bond strength testing

After storing the specimens for 24 h in di-stilled water at 37ºC,Shear bond strength was measured with universal testing machi-ne (Lloyd Universal testing machine-Model No. L.R 100K) The specimen mounted in its acrylic block was secured to the lower grip of the machine. To maintain a consi-stent debonding force a jig was embedded on to an acrylic block was fixed in the mo-vable head and positioned in such a way that it touches the bracket as shown in Fi-gure 3

16

A cross-head speed of one mm/min was used. The computer recorded the force to debond the bracket in Newtons (N) and converted into megapascals using the for-mula

Shear strength = load failure (newtons) --------------------------------------------Surface area of bond specimen (mm)

Results were recorded and analyzed using SPSS 14.0.0 for Windows (SPSS Inc., Chi-cago, IL, USA). We compared the mean bond strengths using a one-way analysis of variance and Tukey’s post-hoc tests

RESULT

The descriptive statistics for shear bond strength of the various groups tested were presented in Table 1.

The results of the analysis of variance (ANOVA)Table 2 described that there was a significant difference in shear bond strength among the group 1 X = 9.4 + 2.0 Mpa, the group 2 X =2.7 +1.1 Mpa, and the group 3 X= 3.5 + 2.2 Mpa tested groups(p=0.0001)

Based on individual 95% confidence inter-vals, the group 1 showed significant higher shear bond strength (9.4+2.0 Mpa) than group 2 and Group 3. The group 2 and

group 3 shows lower shear bond strength 2.7 + 1.1 Mpa; 3.5 +2.2 Mpa respectively. The group 3 shear bond strength values were slightly higher than group II and stati-cally significant. The bar chart depicting the shear bond strength can be seen

DISCUSSION

One of the most significant developments in the field of orthodontics over the past two decades has been the successful bon-ding of the attachment to the teeth, re-placing the age old system of cementing bands. A key factor that influences bong strength is the nature of enamel prepara-tion. The bond strength attachment must be able to withstand the forces applied du-ring orthodontic treatment. While on the ot-her hand, an easy debonding and clean up procedure at the end of treatment is desi-rable to avoid iatrogenic damage such as scratches and loss of enamel.

Prophylaxis of the tooth surface helps to removal of surface debris/ plaque and constitutes an important step in the direct bonding procedures. Rubber cup prophy-laxis was found to be less destructed to enamel surface than bristle brush. The ena-mel loss with the rubber cup prophylaxis 6.9 micrometers as against bristle brush which was 14.38 micrometers2 the present

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study employed rubber cup pumice pro-phylaxis. Enamel preparation has traditio-nally been done with phosphoric acid. The-re has been resurgence of interest in other methods of enamel preparation which in-cludes employment of different etching so-lutions and the uses of air propelled abrasi-ves. While several investigations have be-en conducted to evaluate the bond strength with the conventional acid etching, literature is scant with regard to Air and Bur abrasion for preparing enamel prior to bonding in Orthodontics Hence the study was conceived and comparison of the enamel surface after surface prepara-tion with phosphoric acid , air abrasion and bur abrasion has been done.

Normally, phosphoric acid at a concen-tration between 30-40% provided retentive enamel surfaces3. The process involves di-screte etching of the enamel in order to provide selective dissolution of prism co-res or peripheries, with resultant micro po-rosity into which resin can flow and can be polymerized to form a mechanical bond to the enamel. This procedure practically eli-minated micro leakage at the tooth/restora-tion interface 4 Etching of enamel with H3PO4 result in superficial etched zone and sub surface quantitative and qualitati-ve porous zone. The enamel from the su-perficial etch zone is permanently lost but

the porous zones establishes a mechanical bond to etched enamel. 5

Most commonly the use of etching procols employs the use of 30% phosphoric acid, with an etching time of 60 seconds.6 While the concentration of phosphoric acid employed for enamel pre-paration has been standardized, literature is replete with recommendation bone by various authors on different etch times. Oli-ver reported that etch times of 20 seconds and more would produce similar degrees of surface irregularity and types of etch pat-t e r n . 7

Barkmeir, Gwinnett,and Shaffer compare the shear strength of bond achieved with 50 seconds and 60 seconds etch with pho-sphoric acid and found no stastistically si-gnificant difference between the two groups.8 However, Marbaga and Sha-nomm proved that in vitro study 37% H3PO4 for 30 seconds provided good bond strength. Despite its popularity the acid etching technique has inherent limita-tions like loss of enamel structure, toxicity of acid to oral soft tissue and time required to obtain the desired dissolution. The ena-mel loss with acid etching ranges from 3-10 micrometer (Levitt and Zachrisson) the-se limitation has lead to the search newer, enamel friendly technique preparation.

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Air abration technology has been exami-ned for enamel surface preparation prior to bonding the orthodontic attachments. This technology was introduced by Dr.Robert Black in 1940s.9 Air abrasion of enamel the depth of etch on the type of acid used, the acid concentration, the duration of etching and the chemical composition of enamel.

Air abrasion technology can prepare enamel and dentin for bonding, similar to etching by acidic gels and solution. It can also be used in cavity preparation and pro-phylaxis. Air abrasion technology uses a strem of high speed aluminium oxide parti-cles , propelled air pressure. Air abrasion is based on the law of kinetic energy which states that harder the substances, faster the cutting speed, softer the substance, slower the cutting speed10 Hence enamel cuts must faster than dentin. This is due to energy being lost to a substance individual resilience.Air abrasion offers a conservati-ve approach as it requires only 0.5 -3 se-conds time to prepare enamel surface and with minimal oral soft tissue damage.11 In-herent drawbacks of air abrasion procedu-re like its inability to used in respiratory di-sease, Such patient may not be an ideal choice for orthodontic treatment also.

In recent years, in addition to conventional bur abrasive techniques, air abrasion tech-

nique has been used for preparation of ena-mel surfaces. Sengum et in a study sugge-sted that the surface roughness created bur the diamond burs increase the surface area and aiding in better retention.12

Since the bur abrasion technique is faster and avoids damage to soft tissue it could be consider as in alternate method of enamel preparation for direct bonding procedure. Further very few studies have been reported in the literature assessing the usefulness of this method when compa-red to aviod etching technique.

Wang and Meng reported that bong strength of transbond was superior to that of chemically cured concise, when trans bond was cured for 40 or 60 seconds.13 Trans bond has higher bond strength due to its filler content (80-82%) and filler type than chemically cured resins

Visible light system was used, suggested by Douglas et al. This system as curing units with the blue filters and emanates light at 420-450 micro millime-tres. The advantage of visible light uv, being the depth of cure of the composite resin that is cured is more and less time is required to cure. Maijer and Smith found that the best resin penetration and bond strength were obtained with the mesh brac-

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ket bases. The bracket base area was mea-sured by screw gauge and found to be 13.96 millimetres square.

The bonded tooth was stored in wa-ter at room temperature for 48 hrs to ensu-re complete polymerization of all the resin material and achieve max bond strength. The bond between enamel and orthodon-tic bracket is unique in dentistry in that it is intended to be temporary. The bond is re-quired to remain intact for about 2 years, withstanding both orthodontic forces of oc-clusion, but then must be broken with mini-mum amount of trauma to the tooth and patient on completion of treatment.

In the present study ,group 1 (acid etch) show higher bond strength (9.4+ 2.0 Mpa) than the air abraded group and bur abra-sion group (group 2 and group 3) sugge-sting that the acid etch treatment of ena-mel is more favourable than the air abra-sion method, and bur abrasion method in providing better bond strength. The depth of etched enamel surface created by pro-sphoric acid may be a contributing factor to the higher shear bond strength.

In group 2 (50 µm Al2O3) and group 3(Bur abrasion) mean shear bond strength va-lues were 2.7+1.1 and 3.5 +2.2 Mpa re-spectively. Group 2 (50 µm Al2O3) showed

decrease in bond strength than group 3 (Bur abrasion), this was due to the finer alu-minium particles size that cause a smoot-her surface, and result in less mechanical retention.These two group values were be-low the optimal bond strength between 5.9 and 7.8 Mps to with stand normal ortho-dontic forces.

The increased bond strength in the pho-sphoric acid group when compared to the air abraded group as observed in this study was in conformity with previous work done by Reinser,Olsen,Bishara,Ea-kle,but there were not in agreement with Laurell.Lord and Beck study. An alternative method to increase bond strength with ena-mel preparation is by using sandblasting alone with acid etch procedure.

SUMMARY AND CONCLUSION

The present study was undertaken to com-pare the usefulness of three different types of enamel preparation by using shear bond strength .The shear bond strength values of acid etched samples were higher than the tooth air abraded and bur abraded. Air abrasion by 50 µm aluminium oxide parti-cles showed higher shear bond strength than bur abrades. Enamel preparation plays a vital role in the strength of bonded orthodontic attachment. Air abrasion and

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Bur abrasion compliments the acid etch procedure, but by itself is not suitable for optimal enamel preparation for routine ort-hodontic use. Further clinical trials are nee-ded to exemplify the same.

It was concluded that sand blasting was favourable with the conventional bur prepa-ring enamel surface for bond strength. Still conventional etching of enamel surfaces with phosphoric acid was found to be pre-ferable procedure.

REFERENCES

1. Fernandez L, Canut JA. In vitro compari-son of the retention capacity of new aesthetic brackets. Eur J Orthod 1999 Feb; 21(1):71-7.

2. Thompson RE, Way DC..Enamel loss due to prophylaxis and multiple bonding/debonding of orthodontic attachments. Am J Orthod. 1981 Mar;79(3):282-95

3. Silverstone LM: Fissure sealants: Labora-tory studies. Caries Res 8: 2-26, 1974

4. Retief DH, Woods E, Jamison HC: Effect of cavosurface treatment on marginal leakage in class V composite resin restora-tions. J Prosthet Dent 47: 296-501, 1982.

5.Sarah Mehdi, Marie-Charlotte Mano, Oli-vier Sorel, Guy Cathelineau Orthod Fr 2009;80:179–192

6. Mardaga WJ, Shannon IL.Decreasing the depth of etch for direct bonding in ort-hodontics. J Clin Orthod 1982 Feb; 16(2):130-2.

7.Oliver, R. G. (1986) The effects of diffe-ring concentrations, techniques and etch time on the etch pattern of erupted and unerupted human teeth examined using the Scanning Electron Microscope, British Journal of Orthodontics, 14, 105–107.

8.WWBarkmeier,AJGwinnett,SEShaffer.Effects_of_reduced_acid_concentratio..etching time on bond strength and enamel morphology Journal of clinical orthodon-tics: 1987; 21(6):395-8

9. Vivek S Hegde and Roheet A Khatavkar-Conserv Dent. 2010 Jan-Mar; 13(1): 4–8.

10. Vipin Arora,Pooja Arora, S.K. Jawa In-ternational Journal of Scientific and Re-search Publications, Volume 2, Issue 11, November 2012; 1:1-7Microabrasive Technology for Minimal Restorations

11.Damon PL, Bishara SE, Olsen ME et al] Effects of fluoride application on shear

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bond. strength of ... Orthop.1997; 112: 666-669.

12. Abdulkadir Sengun, Hasan Orucoglu, Ilknur Ipekdal, Fusun Ozera. Adhesion of Two Bonding Systems to Air-Abraded or Bur-Abraded Human Enamel Surfaces .Eur J Dent. 2008 July; 2: 167–175

13. Wang WN, Meng CL..A study of bond strength between light- and self-cured ort-hodontic resin. Am J Orthod Dentofacial Orthop. 1992 Apr; 101(4):350-4

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