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Overview of orthodontic implants for the correction of Class II malocclusion
Section V: Orthodontic implants for the treatment of Class II malocclusion
19
Overview of orthodontic implants for the correction of Class II malocclusion Gero Kinzinger, Heiner Wehrbein, Friedrich K. Byloff and Moschos A. Papadopoulos
almost always observed after non-compliance maxillary molar distalization. In addition, the temporary partial coverage of the palate causes oral hygiene problems. To avoid these problems, anchorage can be provided for example by osseointegrated implants inserted in the palate. This chapter will discuss anchorage designs using orthodontic implants and maxillary molar distalization appliances or approaches.
INTRODUCTION Maxillary molar distalization is intended to gain or restore space for the teeth in the arch. This can be achieved by molar distalization, dental arch expansion or extraction of teeth. Among others, the following criteria should be considered when assessing available treatment options: ■ ■ ■ ■ ■ ■ ■
the size of the maxillary apical base the functional tongue space third molar formation potential tooth agenesis patient’s growth pattern patient’s soft tissue profile patient’s oral hygiene and their susceptibility to caries patient’s compliance patient’s perception of esthetics.
■ ■
IMPLANTS FOR ORTHODONTIC ANCHORAGE Orthodontic implants of reduced diameter or length inserted in the palate can serve as absolute or auxiliary types of anchorage modalities, providing either direct or indirect anchorage (see Chapter 3):
■
Intraoral non-compliance distalization appliances allow correction of Class II malocclusion with a variety of active components delivering the distalization force (see Chapter 2). Depending on the location of the incorporated force module, they can be classified as appliances with vestibular or palatal force application:
■
■
vestibular force application: ♦ magnetic modules ♦ loaded coil spring systems: Wilson Distalizing Arch, Ni-Ti springs, Jones Jig, Lokar Distalizing appliance palatal force application ♦ pendulum appliances ♦ loaded coil spring systems: Distal Jet, Keles Slider, First Class Appliance.
■
■
■
DIMENSIONS OF ORTHODONTIC IMPLANTS Conventional dental implants have large dimensions and may only be suitable for orthodontic anchorage in patients who have spaces after extraction of teeth, where they may provide viable options not only for the prosthetic rehabilitation of the missing teeth but also to act as absolute anchorage for various orthodontic movements including distalization of molars prior to the prosthetic restoration (Fig. 19.1). Further, endosseous titanium implants of reduced length inserted in the palate can provide adequate stationary anchorage (see Chapter 7).
These appliances are anchored on the maxillary anterior teeth, usually by means of bands or occlusal wire rests on the premolars, as well as on the anterior palate by means of modified acrylic resin Nance buttons. However, this type of anchorage is not always adequate to withstand the reciprocal forces, and anchorage loss of the anterior teeth, in terms of mesial movement of the premolars and canines and proclination of the incisors are
A
B
direct anchorage: the active component is fitted by support elements or special constructions to the implant and applies force directly on the tooth or group of teeth to be moved during treatment indirect anchorage: the teeth that act as reactive units are indirectly stabilized by the skeletal device via a transpalatal bar connected to the implant absolute anchorage: only the orthodontic implant resists the reciprocal forces of the distalization systems auxiliary anchorage: a number of teeth, or more often other anchorage modalities (e.g. a modified acrylic resin Nance button), form part of the anchoring system.
C
D
Fig. 19.1 A dental implant used to support maxillary molar distalization and asymmetrical anterior teeth retraction prior to the final prosthetic restoration. (A) Occlusal view immediately after insertion of a dental implant with provisional crown for the second premolar to provide orthodontic anchorage control. Push–pull biomechanics were used (coil spring and elastic chain, respectively) to distalize the molars and move the midline towards the implant simultaneously. (B) In progress occlusal view of the maxillary arch close to the final result. The space mesial to the second premolar is closed and a distal space has opened. (C) Post-treatment radiograph after molar distalization. The left canine was retracted as much as possible, almost touching the implant. (D) Post-treatment lateral view following the final restoration of the left second premolar with the molars in Class I occlusion.
104
Overview of orthodontic implants for the correction of Class II malocclusion
A
B
105
C
Fig. 19.2 The Mainz Implant Pendulum (MIP). (A) Occlusal view of the maxillary arch after paramedian insertion of an endosseous palatal implant of reduced length (Orthosystem) and placement of the MIP for non-compliance maxillary molar distalization. (B) Occlusal view after distalization of the first molars and drifting of the premolars. (C) Occlusal view following replacement of the MIP with a modified transpalatal bar attached to the molar bands and the palatal implant, providing further stationary anchorage for the anterior teeth retraction. (From Kinzinger et al., 2005,10 with permission of Springer.)
INSERTION LOCATION In many patients requiring maxillary molar distalization, the most suitable area for implant insertion is the palate and the issues of palatal insertion are discussed in detail in Chapters 7 and 12. The degree of obliteration of the median palatal suture increases with age but is still very variable and this must be taken into consideration when considering implant position in adolescents.
APPLIANCES FOR NON-COMPLIANCE MAXILLARY MOLAR DISTALIZATION AND IMPLANT-SUPPORTED ANCHORAGE The two types of appliances used most frequently for non-compliance maxillary molar distalization are pendulum appliances and palatal coil spring systems (e.g. the Distal Jet), which rely basically on two different biomechanical concepts. Pendulum appliances attempt to achieve maxillary molar distalization by distalizing the maxillary molars along a pendulum arc. To counteract this pendulum type of movement, certain modifications of the appliance as well as specific preactivations of the pendulum springs are essential.1–4 Uprighting activation at the horizontal arm of the pendulum springs is vital to exert an intrusive force and an uprighting moment on the molars while at the same time it applies a reciprocal moment in the opposite direction and an extrusive force on the anchoring unit.1,4 The anchorage unit should be firm enough to resist this reciprocal distalization force, which can best be achieved using endosseous palatal implants of reduced length5 or subperiosteal osteosynthetic plates fixed with miniscrews and supported by push-on palatal buttons.6 In contrast, in palatal coil spring systems the line of force application determined by the active components runs almost through the center of resistance of the first molars; since the maxillary molars are forced to move on a line parallel to the occlusal plane of the maxillary arch, and no vertical forces and moments are exerted on the anchoring unit, uprighting activations are not needed. The most commonly used non-compliance distalization approaches in combination with stationary anchorage provided by orthodontic implants are presented below.
THE MAINZ IMPLANT PENDULUM The Mainz Implant Pendulum (Fig. 19.2) is a skeletonized K-Pendulum appliance with a distal screw that is firmly anchored by means of an endosseously positioned palatal implant of reduced length (Orthosystem, Institut Straumann, Waldenburg, Switzerland).1,3,5,7 As this is stationary anchorage, there is no need for occlusal wire rests for additional dental anchorage or for an acrylic resin palatal button, which facilitates maintenance of good oral hygiene of the palatal area, particularly around the implant. The
anterior part of the distal screw is attached directly to the soldered or welded cap of the implant by laser welding. The distal part of the screw in which the retentive elements of the pendulum springs are located is coated with plastic. Before insertion of the appliance in the mouth, the arms of the pendulum springs have to be bent to avoid unwanted effects: (1) uprighting activation of the springs results in an uprighting of the molar roots and counteracts the tendency for distal molar crown tipping, which could occur because the distalization force is applied more occlusally in relation to the center of resistance of the molars; and (2) a toe-in of the pendulum springs avoids undesirable distobuccal rotation of the molars. Regular adjustment of the distal screw allows a larger amount of bodily maxillary molar distalization.1,2,4,8,9 Since an orthodontic implant is used as anchorage, the reactive forces are absorbed exclusively by bone and there are no effects on the anterior dentition in terms of mesial movement and proclination. In addition, since no occlusal wire rests are used to anchor the appliance on the teeth, spontaneous distal drifting of the premolars and canines takes place. Thus, the severity of the initial malocclusion is reduced and the total time needed for the retraction of the anterior teeth is less. Following distalization, the appliance is removed and the molars are connected by a new fabricated transpalatal bar to the palatal implant, providing for further stationary anchorage for the retraction of the anterior teeth (Fig. 19.2C). Thus, anchorage loss of the molars during this stage of treatment is avoided.
THE AACHEN IMPLANT PENDULUM The Aachen Implant Pendulum (Fig. 19.3) consists of a Quad Pendulum anchored solely to an endosseously placed palatal orthodontic implant of reduced length (Orthosystem).5 This implant-supported Pendulum appliance is an interesting option, particularly for the treatment of adults where the preservation of anchorage is usually very challenging owing to significant periodontal involvement. The four pendulum springs allow a sequential distalization of the first and second molars, distalizing initially the second molars by applying a rather low force. The first molars are not incorporated in the anchoring system at this stage so that they can drift freely distally under the pull of the transeptal fibers. When the second molars are sufficiently distalized, their pendulum springs are deactivated. This way the second molars are kept in place, reinforcing the anchorage unit for the subsequent distalization of the first molars. The pendulum springs of the Quad Pendulum are removable components, while lingual sheaths originally designed for molar bands are incorporated into the acrylic resin button to ensure a firm hold when they are activated and prevent any slippage out of the acrylic resin. By replacing these springs with longer ones, it is possible to displace the horizontal and sagittal centers of rotation of molars. Prior to the insertion of the appliance, uprighting activation and a toe-in have to be performed at the ends of the pendulum springs, as described above.
106 SECTION V: ORTHODONTIC IMPLANTS FOR THE TREATMENT OF CLASS II MALOCCLUSION
A
B
C
D
Fig. 19.3 The Aachen Implant Pendulum (AIP). (A) Occlusal view of the maxillary arch after median insertion of an endosseous palatal implant of reduced length (Orthosystem). (B) Occlusal view of the maxillary arch after insertion of the palatal implant and placement of the AIP, initially with two pendulum springs for second molar distalization. (C) Occlusal view of the maxillary arch after distalization of the second molars. Stabilization of the second molars with “active anchorage” and placement of one further pendulum spring to distalize the left first molar. (D) Occlusal view of the maxillary arch after removal of the AIP and placement of a transpalatal bar connected to the first molars to support retraction of the lateral and the anterior teeth.
The modified acrylic resin Nance button serves for the incorporation of the sheaths that hold the pendulum springs and is firmly attached to the neck of the implant through a clamping cap with an octagonal design to resist rotation. Although the acrylic resin has surface contact with the palatal mucosa, it does not provide any additional anchoring capacity to the system. Consequently it can be very thin and slim to decrease discomfort for the patient. Occlusal wire rests on the premolars and canines are not needed. Following completion of distalization, supporting the distalized molars with a transpalatal bar prevents loss of posterior anchorage (in terms of mesial movement of the molars) during the subsequent stage of Class II treatment involving the retraction of the anterior teeth (Fig. 19.3D). Compatibility of the Aachen Implant Pendulum with other Pendulum appliances is possible in general. All these exclusively implant-supported appliances are fitted with only one screw, and, therefore, they can be easily removed during treatment by the clinician for reactivations or for ultrasound cleaning.
THE IMPLANT-SUPPORTED DISTAL JET Although some applications of the Distal Jet appliance in conjunction with palatal implants have been described,11 most uses of the Distal Jet are associated with miniscrew implants. These applications are presented in detail in Chapters 31 and 32.
THE IMPLANT-SUPPORTED KELES SLIDER The implant-supported Keles Slider consists of a modified Keles Slider appliance (see Fig. 2.9) attached to a stepped screw titanium palatal implant (diameter, 4.5 mm; length, 8 mm; Frialit-2 Implant System, Friadent, Mannheim, Germany), which is positioned either on the midpalatal suture or in the paramedian area. This modification eliminates the need to use palatal soft tissues, first premolars or anterior teeth to support anchorage, thus avoiding the side effects of maxillary molar distalization using the conventional Keles Slider with a Nance button. To construct the appliance, the maxillary first molars are banded, and tubes (diameter, 0.045 inch; Leone, Firenze, Italy) are soldered on the palatal side of the first molar bands. A SS wire (diameter, 0.040 inch) is then attached to the palatal implant, positioned approximately 5 mm apical to the gingival margin of the first molars, passing through the tube and oriented parallel to the occlusal plane. A Ni-Ti open coil spring (length, 2 cm; diameter, 0.045 inch; thickness, 0.010 inch; Leone) is placed between the lock on the wire and the tube in full compression in order to exercise the appropriate force for molar distalization. The amount of force generated following full activation of the coil springs is approximately
200 g per side. After appliance insertion, there is a 3-month healing period to allow completion of osseointegration before the palatal implant is loaded with orthodontic forces. The patient is seen at 1-month intervals for regular checks as well as to activate the appliance by compressing the coil springs using the Gurin locks (3M Unitek, Orthodontic Products, Monrovia, CA, USA), which are attached to the SS wire. This system allows the application of a consistent force close to the center of resistance of the first molars, resulting in an almost bodily distal movement of the molars. In addition, because stationary anchorage is used, no anchorage loss of the anterior segment with maxillary incisor proclination or increase of the overjet is observed after molar distalization. Furthermore, since no occlusal rests are used, first and second premolars drift distally during maxillary molar distalization. When molar distalization is completed, the coil springs are removed and the Gurin locks are tightened and fixed to the mesial side of the molar tubes, converting the appliance into a passive anchorage device that can be used to reinforce posterior anchorage during the subsequent stage of anterior teeth retraction with fixed orthodontic appliances. Either some months before the end of the total orthodontic treatment or during the removal of the fixed orthodontic appliances, the palatal implant is easily removed by loosening it with a hollow drill. The implant site heals rapidly, usually within 5 days. The implant-supported Keles Slider is effective in correcting Class II malocclusion and in resolving maxillary crowding. Maxillary molars are distalized almost bodily without or with minimal crown tipping and without loss of anchorage of the anterior teeth. No patient cooperation is required beyond maintenance of a good oral hygiene.
IMPLANT-SUPPORTED TRANSPALATAL BAR AND COIL SPRINGS An efficient indirect orthodontic implant anchorage for molar distalization can be constructed relatively simply in terms of appliance design and without extensive laboratory work. A combined tooth–implant anchoring system can be constructed with a transpalatal bar anchored on a palatal implant and connected to the first or second premolars. When the Orthosystem implant (length, 4.0 mm; diameter, 3.3 mm) is used, the individually manufactured transpalatal bar is attached to the implant by means of a clamping cap featuring an eccentric slot and a fastening screw. Alternatively, the cap and the bar may also be soldered or laser welded. In either case, the transpalatal bar is anchored three dimensionally on the palatal implant and bonded on the palatal surfaces of the first or second premolars bilaterally, incorporating these teeth in the anchorage unit. The distalization force is provided by open coil springs, which are attached on sectional or full archwires positioned vestibularly (Fig. 19.4) or palatally (Fig. 19.5).
Overview of orthodontic implants for the correction of Class II malocclusion
A
B
C
107
D
Fig. 19.4 Combination of implant-supported transpalatal bar with vestibular mechanics. (A) Occlusal view of the maxillary arch after median insertion of an endosseous palatal implant of reduced length (Orthosystem). (B) Distalization of the second molars by Nitinol coil springs supported by indirect stationary anchorage. (C) Stabilization of the distalized second molars with a new transpalatal bar attached to the implant and the second molars, and retraction of the first molars with elastomeric chains. (D) Distalization of the first premolars and canines. (Parts B,D from Kinzinger et al., 2005,10 with permission of Springer.)
A
B
C
D
Fig. 19.5 Combination of implant-supported transpalatal bar with palatal mechanics. (A) Occlusal view after median insertion of an endosseous palatal implant of reduced length (Orthosystem). Distalization of the second molars by means of Nitinol coil springs attached to palatal archwires using indirect anchorage. (B) Stabilization of the distalized second molars with composite interlocking. Distalization of the first molars by open coil springs attached between the second molars and first molars. (C) Occlusal view of the maxillary arch after placement of a transpalatal bar with the new one connected to the first molars to support retraction of the lateral teeth. (D) Occlusal view of the maxillary arch during retraction of the anterior teeth. (Parts C,D from Kinzinger et al., 2005,10 with permission of Springer.)
Table 19.1 Appliance designs for non-compliance maxillary molar distalization featuring orthodontic implants, with their specific characteristics Appliance
Design and features
Main indications
Mainz Implant Pendulum
Stationary anchorage; skeletonized K-Pendulum appliance and endosseous palatal implant of reduced length Paramedian/median insertion No occlusal rests needed Compatible with various Pendulum appliances Pendulum appliance can be replaced with a TPA after molar distalization
All ages
Aachen Implant Pendulum
Stationary anchorage; Quad Pendulum with an endosseous palatal orthodontic implant of reduced length, supported by a reduced palatal acrylic button Median insertion No occlusal rests needed Compatible with various Pendulum appliances Pendulum appliance can be replaced with a TPA after molar distalization
Adults
Implant-supported Keles Slider
Stationary anchorage; modified Keles Slider with endosseous palatal orthodontic implant Median/paramedian insertion No occlusal rests needed Can be converted into a passive anchorage device after molar distalization
All ages
Implant-supported transpalatal bar with coil springs
Indirect anchorage; endosseous palatal implant connected to the bar Median insertion Transpalatal bar attached (palatally) to first or second premolars bilaterally Compatible with various loaded spring systems Original transpalatal bar can be replaced with a new one after molar distalization
Adults
When the maxillary second molars are erupted, sequential distalization is recommended. Initially, the second molars are distalized while the reciprocally acting forces are absorbed by the anchorage unit incorporating the anchoring teeth and the palatal implant. Following distalization of the second molars, their position is stabilized with a new transpalatal bar connected again with the palatal implant to reinforce posterior anchorage during the subsequent phase of the retraction of the anterior teeth. The initial transpalatal bar is removed and the new one is constructed and attached to the implant and bonded to the distalized second molars. Alternatively, the second molars may be stabilized by composite interlocking,
which has the advantage that no transpalatal bar replacement is needed. Finally, the first molars and afterwards the teeth anterior to them can be moved distally along the archwires by means of elastomeric chains or closed coil springs.
CONCLUSIONS Table 19.1 summarizes the appliances designed for use with orthodontic palatal implants for maxillary molar distalization. Endosseous implants of
108 SECTION V: ORTHODONTIC IMPLANTS FOR THE TREATMENT OF CLASS II MALOCCLUSION
reduced length inserted into the anterior region of the hard palate provide anchorage that does not result in unwanted mesial proclination of the anterior teeth, which is evident when conventional non-compliance distalization appliances are used. In particular, the combination of palatal implants with Pendulum appliances can be considered as an alternative anchorage design that presents several advantages:
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treatment outcome is not dependent on patient’s cooperation treatment is possible even with a reduced number of teeth (i.e. with limited dental anchoring capacity of the supporting zone) there is no anchorage loss of the anterior dental unit since the anterior teeth are not incorporated in the anchorage unit spontaneous distal drifting of the premolars and canines takes place during molar distalization, as well as afterwards, under the pull of the transeptal fibers, since there are no occlusal rests on these teeth following molar distalization, the construction of an “active anchorage” of the posterior teeth to support anterior teeth retraction is possible, but usually the appliances connected to the palatal implants are replaced with newly fabricated transpalatal bars connected to molars in order to reinforce posterior anchorage during that stage of treatment.
The disadvantages are that insertion and removal of palatal implants are associated with more complicated and invasive surgical procedures and a higher cost is incurred. In conclusion, the use of orthodontic implants in conjunction with intraoral non-compliance maxillary molar distalization approaches is a feasible and efficient treatment option that can be applied not only in children and adolescents but also in adults. For this purpose, the use of anchorage designs with orthodontic implants of reduced length seems to be very advantageous compared with use of conventional dental implants.
REFERENCES 1. Kinzinger G, Fuhrmann R, Gross U, et al. Modified pendulum appliance including distal screw and uprighting activation for non-compliance therapy of Class II malocclusion in children and adolescents. J Orofac Orthop 2000;61:175–90. 2. Kinzinger GSM, Wehrbein H, Diedrich PR. Molar distalization with a modified pendulum appliance: in vitro analysis of the force systems and in vivo study in children and adolescents. Angle Orthod 2005;75:484–93. 3. Kinzinger GSM, Diedrich PR. Biomechanics of a modified pendulum appliance: theoretical considerations and in vitro analysis of the force systems. Eur J Orthod 2007;29: 1–7. 4. Kinzinger G, Syree C, Fritz U, et al. Molar distalization with different pendulum appliances: in vitro registration of orthodontic forces and moments in the initial phase. J Orofac Orthop 2004;65:389–409. 5. Kinzinger G, Wehrbein H, Diedrich P. Pendulum appliances with different anchorage modalities for non-compliance molar distal movement in adults. Kieferorthopädie 2004;18:11–24. 6. Byloff FK, Kärcher H, Clar E, et al. An implant to eliminate anchorage loss during molar distalization: a case report involving the Graz implant-supported pendulum. Int J Adult Orthod Orthognath Surg 2000;15:129–37. 7. Brender D, Thole M, Wehrbein H. Skelettale Verankerung in der Kieferorthopädie. Freie Zahnarzt 2004;48:22–8. 8. Kinzinger GSM, Fritz UB, Sander FG, et al. Efficiency of a pendulum appliance for molar distalization related to second and third molar eruption stage. Am J Orthod Dentofacial Orthop 2004;125:8–23. 9. Kinzinger GSM, Gross U, Fritz UB, et al. Anchorage quality of deciduous molars versus premolars for molar distalization with a pendulum appliance. Am J Orthod Dentofacial Orthop 2005;127:314–23. 10. Kinzinger G, Wehrbein H, Byloff FK, et al. Innovative anchorage alternatives for molar distalization: an overview. J Orofac Orthop 2005;66:397–413. 11. Jung BA, Harzer W, Wehrbein H, et al. Immediate versus conventional loading of palatal implants in humans: a first report of a multicenter RCT. Clin Oral Invest 2011;15:495–502.
19
Overview of orthodontic implants for the correction of Class II malocclusion Gero Kinzinger, Heiner Wehrbein, Friedrich K. Byloff and Moschos A. Papadopoulos
almost always observed after non-compliance maxillary molar distalization. In addition, the temporary partial coverage of the palate causes oral hygiene problems. To avoid these problems, anchorage can be provided for example by osseointegrated implants inserted in the palate. This chapter will discuss anchorage designs using orthodontic implants and maxillary molar distalization appliances or approaches.
INTRODUCTION Maxillary molar distalization is intended to gain or restore space for the teeth in the arch. This can be achieved by molar distalization, dental arch expansion or extraction of teeth. Among others, the following criteria should be considered when assessing available treatment options: ■ ■ ■ ■ ■ ■ ■
the size of the maxillary apical base the functional tongue space third molar formation potential tooth agenesis patient’s growth pattern patient’s soft tissue profile patient’s oral hygiene and their susceptibility to caries patient’s compliance patient’s perception of esthetics.
■ ■
IMPLANTS FOR ORTHODONTIC ANCHORAGE Orthodontic implants of reduced diameter or length inserted in the palate can serve as absolute or auxiliary types of anchorage modalities, providing either direct or indirect anchorage (see Chapter 3):
■
Intraoral non-compliance distalization appliances allow correction of Class II malocclusion with a variety of active components delivering the distalization force (see Chapter 2). Depending on the location of the incorporated force module, they can be classified as appliances with vestibular or palatal force application:
■
■
vestibular force application: ♦ magnetic modules ♦ loaded coil spring systems: Wilson Distalizing Arch, Ni-Ti springs, Jones Jig, Lokar Distalizing appliance palatal force application ♦ pendulum appliances ♦ loaded coil spring systems: Distal Jet, Keles Slider, First Class Appliance.
■
■
■
DIMENSIONS OF ORTHODONTIC IMPLANTS Conventional dental implants have large dimensions and may only be suitable for orthodontic anchorage in patients who have spaces after extraction of teeth, where they may provide viable options not only for the prosthetic rehabilitation of the missing teeth but also to act as absolute anchorage for various orthodontic movements including distalization of molars prior to the prosthetic restoration (Fig. 19.1). Further, endosseous titanium implants of reduced length inserted in the palate can provide adequate stationary anchorage (see Chapter 7).
These appliances are anchored on the maxillary anterior teeth, usually by means of bands or occlusal wire rests on the premolars, as well as on the anterior palate by means of modified acrylic resin Nance buttons. However, this type of anchorage is not always adequate to withstand the reciprocal forces, and anchorage loss of the anterior teeth, in terms of mesial movement of the premolars and canines and proclination of the incisors are
A
B
direct anchorage: the active component is fitted by support elements or special constructions to the implant and applies force directly on the tooth or group of teeth to be moved during treatment indirect anchorage: the teeth that act as reactive units are indirectly stabilized by the skeletal device via a transpalatal bar connected to the implant absolute anchorage: only the orthodontic implant resists the reciprocal forces of the distalization systems auxiliary anchorage: a number of teeth, or more often other anchorage modalities (e.g. a modified acrylic resin Nance button), form part of the anchoring system.
C
D
Fig. 19.1 A dental implant used to support maxillary molar distalization and asymmetrical anterior teeth retraction prior to the final prosthetic restoration. (A) Occlusal view immediately after insertion of a dental implant with provisional crown for the second premolar to provide orthodontic anchorage control. Push–pull biomechanics were used (coil spring and elastic chain, respectively) to distalize the molars and move the midline towards the implant simultaneously. (B) In progress occlusal view of the maxillary arch close to the final result. The space mesial to the second premolar is closed and a distal space has opened. (C) Post-treatment radiograph after molar distalization. The left canine was retracted as much as possible, almost touching the implant. (D) Post-treatment lateral view following the final restoration of the left second premolar with the molars in Class I occlusion.
104
Overview of orthodontic implants for the correction of Class II malocclusion
A
B
105
C
Fig. 19.2 The Mainz Implant Pendulum (MIP). (A) Occlusal view of the maxillary arch after paramedian insertion of an endosseous palatal implant of reduced length (Orthosystem) and placement of the MIP for non-compliance maxillary molar distalization. (B) Occlusal view after distalization of the first molars and drifting of the premolars. (C) Occlusal view following replacement of the MIP with a modified transpalatal bar attached to the molar bands and the palatal implant, providing further stationary anchorage for the anterior teeth retraction. (From Kinzinger et al., 2005,10 with permission of Springer.)
INSERTION LOCATION In many patients requiring maxillary molar distalization, the most suitable area for implant insertion is the palate and the issues of palatal insertion are discussed in detail in Chapters 7 and 12. The degree of obliteration of the median palatal suture increases with age but is still very variable and this must be taken into consideration when considering implant position in adolescents.
APPLIANCES FOR NON-COMPLIANCE MAXILLARY MOLAR DISTALIZATION AND IMPLANT-SUPPORTED ANCHORAGE The two types of appliances used most frequently for non-compliance maxillary molar distalization are pendulum appliances and palatal coil spring systems (e.g. the Distal Jet), which rely basically on two different biomechanical concepts. Pendulum appliances attempt to achieve maxillary molar distalization by distalizing the maxillary molars along a pendulum arc. To counteract this pendulum type of movement, certain modifications of the appliance as well as specific preactivations of the pendulum springs are essential.1–4 Uprighting activation at the horizontal arm of the pendulum springs is vital to exert an intrusive force and an uprighting moment on the molars while at the same time it applies a reciprocal moment in the opposite direction and an extrusive force on the anchoring unit.1,4 The anchorage unit should be firm enough to resist this reciprocal distalization force, which can best be achieved using endosseous palatal implants of reduced length5 or subperiosteal osteosynthetic plates fixed with miniscrews and supported by push-on palatal buttons.6 In contrast, in palatal coil spring systems the line of force application determined by the active components runs almost through the center of resistance of the first molars; since the maxillary molars are forced to move on a line parallel to the occlusal plane of the maxillary arch, and no vertical forces and moments are exerted on the anchoring unit, uprighting activations are not needed. The most commonly used non-compliance distalization approaches in combination with stationary anchorage provided by orthodontic implants are presented below.
THE MAINZ IMPLANT PENDULUM The Mainz Implant Pendulum (Fig. 19.2) is a skeletonized K-Pendulum appliance with a distal screw that is firmly anchored by means of an endosseously positioned palatal implant of reduced length (Orthosystem, Institut Straumann, Waldenburg, Switzerland).1,3,5,7 As this is stationary anchorage, there is no need for occlusal wire rests for additional dental anchorage or for an acrylic resin palatal button, which facilitates maintenance of good oral hygiene of the palatal area, particularly around the implant. The
anterior part of the distal screw is attached directly to the soldered or welded cap of the implant by laser welding. The distal part of the screw in which the retentive elements of the pendulum springs are located is coated with plastic. Before insertion of the appliance in the mouth, the arms of the pendulum springs have to be bent to avoid unwanted effects: (1) uprighting activation of the springs results in an uprighting of the molar roots and counteracts the tendency for distal molar crown tipping, which could occur because the distalization force is applied more occlusally in relation to the center of resistance of the molars; and (2) a toe-in of the pendulum springs avoids undesirable distobuccal rotation of the molars. Regular adjustment of the distal screw allows a larger amount of bodily maxillary molar distalization.1,2,4,8,9 Since an orthodontic implant is used as anchorage, the reactive forces are absorbed exclusively by bone and there are no effects on the anterior dentition in terms of mesial movement and proclination. In addition, since no occlusal wire rests are used to anchor the appliance on the teeth, spontaneous distal drifting of the premolars and canines takes place. Thus, the severity of the initial malocclusion is reduced and the total time needed for the retraction of the anterior teeth is less. Following distalization, the appliance is removed and the molars are connected by a new fabricated transpalatal bar to the palatal implant, providing for further stationary anchorage for the retraction of the anterior teeth (Fig. 19.2C). Thus, anchorage loss of the molars during this stage of treatment is avoided.
THE AACHEN IMPLANT PENDULUM The Aachen Implant Pendulum (Fig. 19.3) consists of a Quad Pendulum anchored solely to an endosseously placed palatal orthodontic implant of reduced length (Orthosystem).5 This implant-supported Pendulum appliance is an interesting option, particularly for the treatment of adults where the preservation of anchorage is usually very challenging owing to significant periodontal involvement. The four pendulum springs allow a sequential distalization of the first and second molars, distalizing initially the second molars by applying a rather low force. The first molars are not incorporated in the anchoring system at this stage so that they can drift freely distally under the pull of the transeptal fibers. When the second molars are sufficiently distalized, their pendulum springs are deactivated. This way the second molars are kept in place, reinforcing the anchorage unit for the subsequent distalization of the first molars. The pendulum springs of the Quad Pendulum are removable components, while lingual sheaths originally designed for molar bands are incorporated into the acrylic resin button to ensure a firm hold when they are activated and prevent any slippage out of the acrylic resin. By replacing these springs with longer ones, it is possible to displace the horizontal and sagittal centers of rotation of molars. Prior to the insertion of the appliance, uprighting activation and a toe-in have to be performed at the ends of the pendulum springs, as described above.
106 SECTION V: ORTHODONTIC IMPLANTS FOR THE TREATMENT OF CLASS II MALOCCLUSION
A
B
C
D
Fig. 19.3 The Aachen Implant Pendulum (AIP). (A) Occlusal view of the maxillary arch after median insertion of an endosseous palatal implant of reduced length (Orthosystem). (B) Occlusal view of the maxillary arch after insertion of the palatal implant and placement of the AIP, initially with two pendulum springs for second molar distalization. (C) Occlusal view of the maxillary arch after distalization of the second molars. Stabilization of the second molars with “active anchorage” and placement of one further pendulum spring to distalize the left first molar. (D) Occlusal view of the maxillary arch after removal of the AIP and placement of a transpalatal bar connected to the first molars to support retraction of the lateral and the anterior teeth.
The modified acrylic resin Nance button serves for the incorporation of the sheaths that hold the pendulum springs and is firmly attached to the neck of the implant through a clamping cap with an octagonal design to resist rotation. Although the acrylic resin has surface contact with the palatal mucosa, it does not provide any additional anchoring capacity to the system. Consequently it can be very thin and slim to decrease discomfort for the patient. Occlusal wire rests on the premolars and canines are not needed. Following completion of distalization, supporting the distalized molars with a transpalatal bar prevents loss of posterior anchorage (in terms of mesial movement of the molars) during the subsequent stage of Class II treatment involving the retraction of the anterior teeth (Fig. 19.3D). Compatibility of the Aachen Implant Pendulum with other Pendulum appliances is possible in general. All these exclusively implant-supported appliances are fitted with only one screw, and, therefore, they can be easily removed during treatment by the clinician for reactivations or for ultrasound cleaning.
THE IMPLANT-SUPPORTED DISTAL JET Although some applications of the Distal Jet appliance in conjunction with palatal implants have been described,11 most uses of the Distal Jet are associated with miniscrew implants. These applications are presented in detail in Chapters 31 and 32.
THE IMPLANT-SUPPORTED KELES SLIDER The implant-supported Keles Slider consists of a modified Keles Slider appliance (see Fig. 2.9) attached to a stepped screw titanium palatal implant (diameter, 4.5 mm; length, 8 mm; Frialit-2 Implant System, Friadent, Mannheim, Germany), which is positioned either on the midpalatal suture or in the paramedian area. This modification eliminates the need to use palatal soft tissues, first premolars or anterior teeth to support anchorage, thus avoiding the side effects of maxillary molar distalization using the conventional Keles Slider with a Nance button. To construct the appliance, the maxillary first molars are banded, and tubes (diameter, 0.045 inch; Leone, Firenze, Italy) are soldered on the palatal side of the first molar bands. A SS wire (diameter, 0.040 inch) is then attached to the palatal implant, positioned approximately 5 mm apical to the gingival margin of the first molars, passing through the tube and oriented parallel to the occlusal plane. A Ni-Ti open coil spring (length, 2 cm; diameter, 0.045 inch; thickness, 0.010 inch; Leone) is placed between the lock on the wire and the tube in full compression in order to exercise the appropriate force for molar distalization. The amount of force generated following full activation of the coil springs is approximately
200 g per side. After appliance insertion, there is a 3-month healing period to allow completion of osseointegration before the palatal implant is loaded with orthodontic forces. The patient is seen at 1-month intervals for regular checks as well as to activate the appliance by compressing the coil springs using the Gurin locks (3M Unitek, Orthodontic Products, Monrovia, CA, USA), which are attached to the SS wire. This system allows the application of a consistent force close to the center of resistance of the first molars, resulting in an almost bodily distal movement of the molars. In addition, because stationary anchorage is used, no anchorage loss of the anterior segment with maxillary incisor proclination or increase of the overjet is observed after molar distalization. Furthermore, since no occlusal rests are used, first and second premolars drift distally during maxillary molar distalization. When molar distalization is completed, the coil springs are removed and the Gurin locks are tightened and fixed to the mesial side of the molar tubes, converting the appliance into a passive anchorage device that can be used to reinforce posterior anchorage during the subsequent stage of anterior teeth retraction with fixed orthodontic appliances. Either some months before the end of the total orthodontic treatment or during the removal of the fixed orthodontic appliances, the palatal implant is easily removed by loosening it with a hollow drill. The implant site heals rapidly, usually within 5 days. The implant-supported Keles Slider is effective in correcting Class II malocclusion and in resolving maxillary crowding. Maxillary molars are distalized almost bodily without or with minimal crown tipping and without loss of anchorage of the anterior teeth. No patient cooperation is required beyond maintenance of a good oral hygiene.
IMPLANT-SUPPORTED TRANSPALATAL BAR AND COIL SPRINGS An efficient indirect orthodontic implant anchorage for molar distalization can be constructed relatively simply in terms of appliance design and without extensive laboratory work. A combined tooth–implant anchoring system can be constructed with a transpalatal bar anchored on a palatal implant and connected to the first or second premolars. When the Orthosystem implant (length, 4.0 mm; diameter, 3.3 mm) is used, the individually manufactured transpalatal bar is attached to the implant by means of a clamping cap featuring an eccentric slot and a fastening screw. Alternatively, the cap and the bar may also be soldered or laser welded. In either case, the transpalatal bar is anchored three dimensionally on the palatal implant and bonded on the palatal surfaces of the first or second premolars bilaterally, incorporating these teeth in the anchorage unit. The distalization force is provided by open coil springs, which are attached on sectional or full archwires positioned vestibularly (Fig. 19.4) or palatally (Fig. 19.5).
Overview of orthodontic implants for the correction of Class II malocclusion
A
B
C
107
D
Fig. 19.4 Combination of implant-supported transpalatal bar with vestibular mechanics. (A) Occlusal view of the maxillary arch after median insertion of an endosseous palatal implant of reduced length (Orthosystem). (B) Distalization of the second molars by Nitinol coil springs supported by indirect stationary anchorage. (C) Stabilization of the distalized second molars with a new transpalatal bar attached to the implant and the second molars, and retraction of the first molars with elastomeric chains. (D) Distalization of the first premolars and canines. (Parts B,D from Kinzinger et al., 2005,10 with permission of Springer.)
A
B
C
D
Fig. 19.5 Combination of implant-supported transpalatal bar with palatal mechanics. (A) Occlusal view after median insertion of an endosseous palatal implant of reduced length (Orthosystem). Distalization of the second molars by means of Nitinol coil springs attached to palatal archwires using indirect anchorage. (B) Stabilization of the distalized second molars with composite interlocking. Distalization of the first molars by open coil springs attached between the second molars and first molars. (C) Occlusal view of the maxillary arch after placement of a transpalatal bar with the new one connected to the first molars to support retraction of the lateral teeth. (D) Occlusal view of the maxillary arch during retraction of the anterior teeth. (Parts C,D from Kinzinger et al., 2005,10 with permission of Springer.)
Table 19.1 Appliance designs for non-compliance maxillary molar distalization featuring orthodontic implants, with their specific characteristics Appliance
Design and features
Main indications
Mainz Implant Pendulum
Stationary anchorage; skeletonized K-Pendulum appliance and endosseous palatal implant of reduced length Paramedian/median insertion No occlusal rests needed Compatible with various Pendulum appliances Pendulum appliance can be replaced with a TPA after molar distalization
All ages
Aachen Implant Pendulum
Stationary anchorage; Quad Pendulum with an endosseous palatal orthodontic implant of reduced length, supported by a reduced palatal acrylic button Median insertion No occlusal rests needed Compatible with various Pendulum appliances Pendulum appliance can be replaced with a TPA after molar distalization
Adults
Implant-supported Keles Slider
Stationary anchorage; modified Keles Slider with endosseous palatal orthodontic implant Median/paramedian insertion No occlusal rests needed Can be converted into a passive anchorage device after molar distalization
All ages
Implant-supported transpalatal bar with coil springs
Indirect anchorage; endosseous palatal implant connected to the bar Median insertion Transpalatal bar attached (palatally) to first or second premolars bilaterally Compatible with various loaded spring systems Original transpalatal bar can be replaced with a new one after molar distalization
Adults
When the maxillary second molars are erupted, sequential distalization is recommended. Initially, the second molars are distalized while the reciprocally acting forces are absorbed by the anchorage unit incorporating the anchoring teeth and the palatal implant. Following distalization of the second molars, their position is stabilized with a new transpalatal bar connected again with the palatal implant to reinforce posterior anchorage during the subsequent phase of the retraction of the anterior teeth. The initial transpalatal bar is removed and the new one is constructed and attached to the implant and bonded to the distalized second molars. Alternatively, the second molars may be stabilized by composite interlocking,
which has the advantage that no transpalatal bar replacement is needed. Finally, the first molars and afterwards the teeth anterior to them can be moved distally along the archwires by means of elastomeric chains or closed coil springs.
CONCLUSIONS Table 19.1 summarizes the appliances designed for use with orthodontic palatal implants for maxillary molar distalization. Endosseous implants of
108 SECTION V: ORTHODONTIC IMPLANTS FOR THE TREATMENT OF CLASS II MALOCCLUSION
reduced length inserted into the anterior region of the hard palate provide anchorage that does not result in unwanted mesial proclination of the anterior teeth, which is evident when conventional non-compliance distalization appliances are used. In particular, the combination of palatal implants with Pendulum appliances can be considered as an alternative anchorage design that presents several advantages:
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treatment outcome is not dependent on patient’s cooperation treatment is possible even with a reduced number of teeth (i.e. with limited dental anchoring capacity of the supporting zone) there is no anchorage loss of the anterior dental unit since the anterior teeth are not incorporated in the anchorage unit spontaneous distal drifting of the premolars and canines takes place during molar distalization, as well as afterwards, under the pull of the transeptal fibers, since there are no occlusal rests on these teeth following molar distalization, the construction of an “active anchorage” of the posterior teeth to support anterior teeth retraction is possible, but usually the appliances connected to the palatal implants are replaced with newly fabricated transpalatal bars connected to molars in order to reinforce posterior anchorage during that stage of treatment.
The disadvantages are that insertion and removal of palatal implants are associated with more complicated and invasive surgical procedures and a higher cost is incurred. In conclusion, the use of orthodontic implants in conjunction with intraoral non-compliance maxillary molar distalization approaches is a feasible and efficient treatment option that can be applied not only in children and adolescents but also in adults. For this purpose, the use of anchorage designs with orthodontic implants of reduced length seems to be very advantageous compared with use of conventional dental implants.
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