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JIOS 10.5005/jp-journals-10021-1161 CASE REPORT Skeletal Anchorage using Mini-implants in the Maxillary Tuberosity Region Skeletal Anchorage using Mini-implants in the Maxillary Tuberosity Region 1 Sundaram Venkateswaran, 2Ashwin Mathew George, 3MK Anand 4 VR Shobbana Devi, 5Sheelkumar R Vora, 6NR Krishnaswamy ABSTRACT Anchorage conservation has always been a challenge in orthodontics especially in cases requiring group movement of teeth. The drawbacks of conventional anchorage conservation methods like headgears and intermaxillary elastics have been overcome with the advent of skeletal anchorage. Mini-implants which have been proved successful in several intraoral locations for anchorage, can also be successfully placed in the maxillary tuberosity region. However, this site is not commonly used due to the fact that the density of bone in this region is comparably low. But with proper case selection and application of sound biomechanical principles, successful treatment results can be achieved with mini-implants placed in this location. The case reports discussed in the article demonstrates the ability of mini-implants when placed in the maxillary tuberosity for en masse distalization of the entire maxillary dentition, its advantages and biomechanics. Keywords: Skeletal anchorage, Mini-implants, Maxillary tuberosity, En masse retraction. How to cite this article: Venkateswaran S, George AM, Anand MK, Devi VRS, Vora SR, Krishnaswamy NR. Skeletal Anchorage using Mini-implants in the Maxillary Tuberosity Region. J Ind Orthod Soc 2013;47(4):217-224. INTRODUCTION It is a well-established fact that mini-implants have proven itself as a source of absolute anchorage1,2 and it’s benefits are innumerable, especially in biomechanically challenging cases.35 Several sites have been proposed for the placement of miniscrew or microscrew implants. Most frequently recommended sites are the midpalatine area, the alveolar bone between the maxillary second premolars and first molars, and the mandibular first and second molars6 and several case reports with mini-implants placed at these anatomical sites have been successfully reported and published. A relatively new protocol of placing mini-implants in the maxillary tuberosity have kindled interest in the clinician, because of its many biological and biomechanical advantages.7,8 We should also take into consideration or account the varying degrees of difficulty and limitations that could be encountered while using tuberosity implants. The following case reports describe the use of maxillary tuberosity implants for en masse retraction of the upper arch on adult patients, with facial convexity, gummy smile line and a deep bite. It also describes the optimal biomechanics while using tuberosity implants to bring about desired hard and soft tissue esthetics. CASE REPORTS Case 1 An 18-year-old female patient reported with the chief complaint of lip protrusion, gummy smile and spacing between anterior teeth. On extraoral examination, she had a convex profile, Fig. 1A: Pretreatment extraoral photographs 1 2 3 4 5 Former Professor, Professor, Reader, Lecturer, Former Postgraduate Student, 6Professor and Head 1 Department of Orthodontics, Chettinad Dental College and Research Institute, Chennai, Tamil Nadu, India 2-6 Department of Orthodontics, Ragas Dental College and Hospital Chennai, Tamil Nadu, India Corresponding Author: Sundaram Venkateswaran, Former Professor Department of Orthodontics, 2/102 East Coast Road, Uthandi, Chennai600119, Tamil Nadu, India, e-mail: [email protected] Received on: 16/1/13 Accepted after Revision: 9/3/13 Fig. 1B: Pretreatment intraoral photographs The Journal of Indian Orthodontic Society, October-December 2013;47(4):217-224 217 Sundaram Venkateswaran et al Fig. 1C: Pretreatment-lateral cephalogram and OPG posterior divergence and lip incompetence. The interlabial gap was 6 mm at rest and, on smiling, there was 100% incisal showing with a 4 mm of gingival display. The nasolabial angle was acute, mentolabial sulcus was deep, the mandibular plane angle was reduced and the lower facial height was average (Fig. 1A). There were no signs and symptoms of temporomandibular joint problems. Intraoral examination revealed a Class II molar relation on the left side and an end on molar relation on the right side. The overjet and overbite were 7 mm each. The upper and lower incisors were proclined labially. The spacing in the upper arch was 2.5 mm and, in the lower arch, it was 7 mm. The upper midline was coincident with the facial midline, whereas the lower midline was shifted to the left side by about 3.5 mm (Fig. 1B). All the third molars were erupted. The cephalometric analyses revealed a Class II skeletal pattern (ANB-6°), reduced mandibular plane angle (Go GnSN-25°), proclined upper incisors (upper 1 to SN-113°) and proclined lower incisors (IMPA-102°) (Fig. 1C). Treatment Objectives approximately around 150 to 350 Hounsfield units. The bone in this region is typically of poor quality; the cortical layer is thin and irregular and usually merges into the cancellous bone with irregular distribution of lamellae. The patient was also informed of a possible failure of mini-implant, in which case it could to be repositioned. Apart from these inherent disadvantages, the most potent advantage of the maxillary tuberosity implants are that the possibility of root contact during placement of mini-implant is very much reduced due to its anatomical location and there is negligible interference from the roots during tooth movement. Treatment Progress The upper third molars were extracted at the start of treatment in an atraumatic manner taking care to maintain the integrity of the buccal cortical plate to facilitate successful mini-implant placement. Upper and lower arches were strapped up with 022 Roth prescription brackets. A transpalatal arch was fixed in the upper arch to maintain the arch form and arch width and to prevent rotations during retraction of the upper arch. About 5 months after the extraction of the third molars, coinciding with the end of alignment and leveling phase, mini-implants of 1.4 mm diameter and 10 mm length were placed on either side in the tuberosity region. Retraction was started immediately with 250 gm using nickel-titanium closed coil springs extended between the implants and the hooks crimped distal to the canines on a 0.019 × 0.025 inch stainless steel upper archwire (Figs 2A to C). For en masse distalization of maxillary arch using sliding The primary objective of treatment was to correct the lip protrusion and gummy smile by intruding and retracting the upper incisors. The other objectives were to correct the molar relation, increased overjet and overbite, midline shift in the lower arch and close the spaces in the upper and lower arches. Treatment Options The spaces present in the lower arch were sufficient for correction of the tooth size arch length discrepancy, whereas the spaces present in the upper arch were found to be inadequate. The spaces needed for retraction of upper incisors could be obtained by extraction of two upper premolars. However, the disadvantage of extracting premolars in this case is that the gummy smile could get worsened with further increase in overbite. Therefore, it would be preferable to plan for gaining space in the upper arch without premolar extraction. The novel option of third molars extraction and retraction of the entire upper arch using mini-implant anchorage placed in the tuberosity region was suggested and the patient accepted this treatment plan. It is an important criterion to assess the bone with regard to its quantity and density before the decision is made to place the mini-implant. It is a well-established fact that the maxillary tuberosity region belongs to the D4 category as classified by Lekhom and Zarb possessing a density of 218 Fig. 2A: In treatment X-rays (implant placement) Fig. 2B: Diagrammatic representation of en masse distalization using tuberosity implants JIOS Skeletal Anchorage using Mini-implants in the Maxillary Tuberosity Region Fig. 2C: Intreatment intraoral photographs mechanics, it is preferable to solder or crimp the retraction hooks distal to canine. This is advantageous over hooks attached mesial to canines in that a relatively straight path of force application can be obtained. A hook placed mesial to canine could also cause interference with the soft tissue overlying the canine prominence and thereby dissipate some of the force generated by the coil spring. Also the position of hook relatively closer to the center of resistance of maxillary dentition (near the root apex of the maxillary first premolars) reduces the tendency for rotation of the occlusal plane. An accentuated reverse curve of Spee was added to the upper arch wire for correction of deep overbite. Treatment Results The primary objective of correction of lip protrusion and excessive gingival display on smile was achieved by intrusion of the upper incisors and retraction of the entire upper arch (Fig. 3A). The lower incisors were retracted using the spaces available between them. The molar relationship was corrected to Class I by distal movement of the upper arch (Fig. 3B). The Fig. 3A: Post-treatment extraoral photographs Table 1: Cephalometric data Skeletal SNA N perpendicular to point A SNB N perpendicular to Pog ANB Sn to Go-Gn Maxillary dentition U1-NA U1-SN U6 to Ptv Mandibular dentition L1-NB IMPA L1-A Pog Soft tissue S line to upper lip S line to lower lip Lower lip—E plane Nasolabial angle Upper lip angle Overjet Overbite Pretreatment Post-treatment 83° 4 mm 77° 1 mm 6° 28° 81° 2 mm 76° –1 mm 5° 30° 26° 113° 21.5 mm 20° 108° 18 mm 35° 102° 29° 27° 95° 22° 5 mm 6 mm 5 mm 85° 40° 7 mm 7 mm 3 mm 3 mm 2 mm 92° 26° 3 mm 3 mm overjet and overbite were reduced to 3 mm each and the duration of entire treatment took around 18 months. Comparison between pre and post-treatment cephalogram showed marked improvement in the facial balance (Fig. 4A) and the cephalometric superimpositions showed bodily distalization of maxillary molars (Fig. 4B) as also seen in Table 1. Post-treatment OPG revealed good root parallelism between teeth (Fig. 5). Fig. 3B: Post-treatment intraoral photographs The Journal of Indian Orthodontic Society, October-December 2013;47(4):217-224 219 Sundaram Venkateswaran et al Case 2 Fig. 4A: Comparison between pretreatment and post-treatment cephalogram Fig. 4B: Superimpositions: blue—pretreatment, red—post-treatment Fig. 5: Post-treatment OPG An 18-year-old female presented with the chief complaint of proclined upper incisors, protrusive lips and spacing in the lower arch (Figs 6A to C). She reported to be having undergone orthodontic treatment with fixed appliances 2 years earlier, following upper and lower first premolar extractions. However, the patient expressed her dissatisfaction with the treatment results, especially with regard to the lip incompetence and protrusive profile. Clinical examination showed a convex profile, posterior divergence, incompetent lips with incisal exposure of 5 mm at rest, average nasolabial and mandibular plane angles, a deep labiomental sulcus, and a normal lower facial height. Intraoral examination revealed Class II molar and Class I canine relationships on the left side and end-on molar and canine relationships on the right side, with an overjet of 4.5 mm and an overbite of 4 mm. All third molars were erupted. The patient had mesially tipped upper posterior teeth and proclined upper and lower incisors, with residual extraction spaces of 3 mm in the lower left quadrant and 1 mm in the lower right quadrant. There were no signs of TMJ problems. Cephalometric analysis indicated a Class II skeletal pattern. The treatment objectives were to reduce the lip protrusion and improve the soft tissue esthetics, establish Class I molar and canine relationships, upright the mesially tipped upper premolars and molars, and close the residual extraction spaces in the lower arch. These objectives could be achieved by retracting the upper and lower anterior teeth, using one of three options. The first option was to extract the upper and lower first molars. But, the disadvantage of this plan was that the first molar plays an important role in mastication and hence could not be sacrificed. The second option was to extract all four second molars; in this case, however, the positions of the third molars were unfavorable to replace the second molars. The third option was to extract all the third molars and retract the entire maxillary and mandibular dentition into the extraction spaces, using mini-implant anchorage placed in the tuberosity and the retromolar regions. This was the treatment option which was finally accepted by the patient. Roth prescription 0.022" brackets were bonded in both arches. After 2 months of leveling and alignment, the four third molars were extracted. Four months later, titanium mini- Fig. 6A: Pretreatment extraoral photographs 220 JIOS Skeletal Anchorage using Mini-implants in the Maxillary Tuberosity Region Fig. 6B: Pretreatment intraoral photographs Fig. 6C: Pretreatment lateral cephalogram and OPG. Note: Reproduced after taking permission from JCO (J Clin Orthod 2011;45:268-73) implants (AbsoAnchor, 1.4 mm diameter × 10 mm) were inserted into the third molar extraction spaces in the maxillary tuberosity and mandibular retromolar areas, as advocated by Sung et al. The screws were placed about 6 mm apical to the crest of the alveolar bone, so that their lines of force passed through the centers of resistance of the first and second molars. Retraction was initiated immediately using nickel titanium closed-coil springs (12 mm, 200 gm) on both sides of the upper and lower arches, extending from the mini-implant to a retraction hook soldered distal to the canine in each quadrant (Fig. 7A). Similar forces applied in this manner have been shown to be adequate for en masse movement of the maxillary or mandibular arches. Retraction of the entire maxillary and mandibular dentition was completed in 12 months, with a total duration for the completion of the entire treatment being 20 months (Figs 7B and C). Post-treatment facial photographs showed a remarkable improvement in the lip profile and facial esthetics resulting from the retraction of the anterior teeth (Fig. 8A). Class I molar and canine relationships were established, with a 2 mm overjet and a 3 mm overbite. Good intercuspation was also observed in the maxillary and mandibular distalized segment (Figs 8B and C). Cephalometric superimposition showed that the maxillary molars were distalized about 5 mm at the crown level and 3 mm at the apex level; the maxillary incisors were retracted 6 mm, and the mandibular incisors 4 mm (Fig. 9). The upper lip moved backward about 3 mm, and the lower lip about 4 mm, with both in the normal range relative to the Fig. 7A: Miniscrews placed bilaterally in the maxillary tuberosity region and retraction hook placed distal to the maxillary canine Fig. 7B: Intreatment intraoral photographs—occlusal views The Journal of Indian Orthodontic Society, October-December 2013;47(4):217-224 221 Sundaram Venkateswaran et al Fig. 7C: Intreatment lateral cephalogram and OPG Fig. 8C: Post-treatment lateral cephalogram and OPG Table 2: Cephalometric data SNA SNB ANB SN-GoMe U1-SN IMPA Wits appraisal Upper lip to E-line Lower lip to E-line Nasolabial angle Pretreatment Post-treatment Difference 83.0 77.0° 6.0° 32.0° 110.0° 102.0° 2.0 mm –1.5 mm 4.0 mm 92.0° 81.5° 76.0° 5.5° 32.5° 100.0° 98.0° 1.0 mm –4.5 mm 0.0 mm 100.0° 1.5° 1.0° 0.5° 0.5° 10.0° 4.0° 1.0 mm 3.0 mm 4.0 mm 8.0° Fig. 9: Superimpositions (blue—pretreatment; red—post-treatment) DISCUSSION E-line (Table 2). The interlabial gap and incisal display at rest were eliminated. Appropriate nasolabial, labiomental sulcus and interincisal angles were achieved. It took only 12 months to achieve a Class I molar relationship, indicating that the force system and mechanics using mini-implants placed in the tuberosity region, in this patient were efficient, particularly since the maxillary molars were mesially tipped at the beginning of treatment. Fig. 8A: Post-treatment extraoral photographs According to Chen et al, the critical factor for success of orthodontic mini-implants is the initial mechanical stability depending upon the bone quality and quantity.9 Crismani et al observed that placing a mini-implant without loading it immediately could also cause instability.10 In these (two) patients, mini-implant were placed and retraction started only when the arches were completely leveled and aligned thereby preventing any sort of arch wire binding during retraction. Miniimplants were placed in these patients 5 months after extraction of the third molars, coinciding with the end of the leveling and alignment phase. It takes about 4 to 5 months for an extraction socket to remodel enough to become viable for placement of a mini-implant. Placing a screw too soon will lead to instability due to inadequate bone support.11 Sung et al recommend using a relatively long mini-implant with a diameter of 1.3 to 1.5 mm in areas with a predominance of cancellous bone and low bone density,2 such as the maxillary tuberosity.12 Lee and Baek Fig. 8B: Post-treatment intraoral photographs 222 JIOS Skeletal Anchorage using Mini-implants in the Maxillary Tuberosity Region reported that orthodontic mini-implants with a diameter of 1.5 mm or more can cause greater microdamage to the cortical bone, with a negative effect on bone remodeling and miniimplant stability.13 Therefore, we chose a mini-implant with a diameter of 1.4 mm and a length of 10 mm. We did not encounter any failures or fractures during placement or removal. Being an intraoral, extradental device, mini-implants are stationary in nature and this in itself should make one question the considerable variations involved when compared to anchorage using the dentition. The variation in the height of placement of mini-implants, in relation to the center of resistance of the dentition as a whole and, on an individual tooth, is certain to bring about changes in the biomechanical principles. The force system consists of multibanded attachments on all the teeth, including the second molars, adequately leveled and stabilized on a 19 × 25 stainless steel wire. The force used for retraction would be preferably a nickeltitanium closed coil spring of 200 to 300 gm, extending between the two mini-implants placed in the tuberosity regions and retraction hooks placed on a 0.019 × 0.25 inch stainless steel archwire distal to the canines. In any geometry of force vectors, it is important that biomechanical aspects are considered in all the three planes: The horizontal, transverse and vertical planes. • Placement and location of tuberosity implants: Accessibility to place implants in the tuberosity region has always been challenging due to anatomical limitations. In our clinical experience, it is advantageous to use a contraangle driver and a mandrill available in the market. The absence of roots in this region notwithstanding, optimal site selection is essential. The implants may be placed at an angulation of 20o to 40o to the occlusal plane in a vertically directed manner. The placement should allow for sufficient distal movement of the entire upper arch. • Biomechanical considerations in the horizontal plane: For en masse distalization of maxillary arch using sliding mechanics, retraction hooks are soldered or crimped distal to canine and it has following advantages over hooks attached mesial to canines. 1. A straight path of force application—a hook placed mesial to canine would cause interference with the soft tissue overlying the canine prominence and thereby dissipation of some of the force generated by the coil spring. 2. The position of hook relatively closer to the center of resistance of maxillary dentition (near the root apex of the maxillary first premolars). • Biomechanical considerations in the transverse plane: In the transverse plane, the distal driving force that passes from the miniscrew implant to the archwire can causes arch expansion and flaring resulting in buccal crown torque. However, this adverse effect could be overcome by using a transpalatal arch. • Biomechanical considerations in the vertical plane: In the vertical plane, the force system can cause extrusion of incisors and clockwise rotation of the occlusal plane, which can be countered by giving a gentle reverse curve of Spee in the arch wire. The location of the mini-implant in the vertical plane should be at the level of the molar tubes in order to minimize undesirable vertical force vector. Advantages of en masse Retraction of Entire Maxillary Arch using Mini-implant Anchorage Over Molar Distalization followed by Anterior Retraction without Mini-implant Anchorage The most appropriate advantage of mini-implants placed in the tuberosity region is that molar distalization takes place simultaneously along with anterior retraction and some of the many advantages are listed below: • Single stage of retraction • No molar anchorage loss • Bodily movement • No distal tipping of molars • Incisors and premolars not proclined • Better patient comfort than other distalizing appliances • If ideally placed, reduced chance of mini-implant for root contact • No interference with roots or any other anatomic structure during tooth movement compared to mini-implants between premolar and molars or between molars • No need to reposition mini-implants as needed during molar distalization or en masse retraction using mini-implants placed in other locations • Reduced treatment time. CONCLUSION Although the results achieved with mini-implant in the maxillary tuberosity region could lead to a whole new realm of orthodontic treatment options, a proper understanding of the anatomy, implant selection and the force application principles should be gained by the practitioner. The type of implant selected and the vector of force application differs considerably when using tuberosity implants, when compared to mini-implants in other conventional locations and a thorough evaluation must be carried out before making the final decision. As Winston Churchill proclaimed ‘True genius resides in the capacity for evaluation of uncertain, hazardous and conflicting information.’ REFERENCES 1. Costa A, Raffainl M, Melsen B. Miniscrews as orthodontic anchorage: A preliminary report. Int J Adult Orthod Orthog Surg 1998;13:201-09. 2. Sung JH, Kyung HM, Bae SM, Park HS, Kwon OW, McNamara JA Jr. Microimplants in Orthodontics. Dentos, Daegu, Korea 2006;70. 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