Orthodontic treatment with a series of vacuum-formed removable appliances-case report

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1 Case Reports Orthodontic treatment with a series of vacuum-formed removable appliances-case report EDDIE HSIANG-HUA LAI CHUNG-CHEN JANE YAO YI-JANE CHEN JENNY ZWEI-CHIENG CHANG School of Dentistry, College of Medicine, National Taiwan University, Taipei, Taiwan, ROC. Division of Orthodontics, Department of Dentistry, National Taiwan University Hospital, Taipei, Taiwan, ROC. This case report focuses on the treatment of a patient with moderate crowding and a maxillary right lateral incisor crossbite. A treatment plan of moving the teeth through the use of setup models and vacuum-formed plastic appliances manually fabricated for the tooth movements was proposed to the patient. Resin attachments were bonded to the labial surface of the maxillary right lateral incisor to facilitate extrusive movement. A desktop mechanical 3D digitizer was used to measure the amount of movement of the maxillary and mandibular teeth during each stage. Evidence showed that these plastic appliances could move a tooth at most 1 mm in each stage, and that resin attachments combined with elastics could achieve complex extrusion within 3 weeks. (J Dent Sci, 3(3): , 2008) Key words: vacuum-formed orthodontic appliances, resin attachment, 3D digitizer. The practice of orthodontics is facing new trends. Adults are increasingly aware of the influence of appearance in their personal and professional lives 1. Two determinants of receiving orthodontic treatment for adult patients are esthetics and speed. Lingual brackets and clear brackets have met the esthetic demands to a certain extent, but some patients want even less-visible treatment modalities 2. Teeth movement being conducted without the use of bands, brackets, or wires was described as early as 1945 by Kesling 3, who reported on the use of a flexible tooth-positioning appliance. Later, Nahoum 4 and others 5-8 wrote about various types of clear plastic overlay appliances such as invisible retainers. Minor tooth movements can be achieved by manually setting up the teeth on a plaster model and fabricating an Received: June 16, 2008 Accepted: August 13, 2008 Reprint requests to: Dr. Jenny Zwei-Chieng Chang, Division of Orthodontics, Department of Dentistry, National Taiwan University Hospital, No.1, Chang-Te Street, Taipei, Taiwan 10048, ROC. overlay appliance for each stage of treatment. The major limitation of these described methods is perceived as only relatively small magnitudes of possible changes because of the technical difficulty of evenly dividing larger overall movements into small, precise stages manually 9. Align Technology (Santa Clara, CA, USA), developed the Invisalign system in Invisalign takes the principles of Kesling, Nahoum, and others using 3-dimensional (3D) digital technologies combined with laboratory techniques to fabricate a series of custom appliances that are esthetic and removable, and that can move teeth from beginning to end in a series of precise movements of 0.15~0.25 mm. The Invisalign system does have some limitations. Severe rotations, complex extrusions, and large translations are less predictable with Invisalign alone and might require auxiliary treatment 9. The model setup and fabrication of vacuumformed plastic appliances can be done with manual labor to carry out the planned tooth movement. For more than 5 years, we have successfully applied this type of treatment to treat patients who need minor tooth movement. Herein, we present the treatment of J Dent Sci 2008 Vol 3 No 3 167

2 E. H.H. Lai, C.C. J. Yao, Y.J. Chen, et al. an adult patient with moderate anterior tooth crowding and a palatal crossbite of the upper right lateral incisor. CASE PRESENTATION The patient was a 22-year-old female whose chief concern was upper and lower anterior tooth crowding. Her medical history was noncontributory. She had an overall well-proportioned and balanced facial pattern with a straight profile (Figure 1). The maxillary right lateral incisor was in crossbite with the mandibular right lateral incisor. Both the upper and lower dental midlines were slightly deviated to the right side. Crowding was moderate with 4 mm in the maxillary arch and 6 mm in the mandibular arch. She had a Class I molar and canine relationship on both sides. A panoramic radiograph revealed symmetric condylar heads and no sign of pathology. Fixed restorations were evident on many posterior teeth. Treatment was aimed at expanding the upper and lower arches, especially in the canine and premolar regions, to relieve anterior crowding. Interproximal reduction was not planned due to the slender crown shape. Local treatment with a conventional fixed appliance was proposed to the patient. However, she preferred more-esthetic means. Fixed lingual appliance treatment was proposed. However, she was concerned about the difficulty with hygiene care and interference with pronunciation. Thus, tooth movements were planned through the use of plastic appliances fabricated on setup models by a pressure molding machine. Alginate impressions were taken of the upper and lower dental arches. After the dental casts were poured and trimmed, they were occluded and checked for any rotations or other dental irregularities. The anterior teeth were cut and reset into the proposed position. Only 0.50~1.0 mm of dental movement for each tooth in each stage was allowed. A Biostar positive-pressure thermal forming machine (Great Lakes Orthodontic Products, Tonawanda, NY, USA) was used to fabricate the aligners. The appliance was thermoformed according to the manufacturer s instructions. The patient was asked to wear the appliance 24 hours a day except during meals, brushing, and flossing. Since greater tooth movements (0.5~1.0 mm) in each stage were designed than those proposed by Invisalign (0.15~0.25 mm), the patient was aware that each appliance would only become fully seated in place in 3~4 days after delivery. The appointment Figure 1. Pretreatment photographs. 168 J Dent Sci 2008 Vol 3 No 3

3 Vacuum-formed orthodontic appliance interval was 2 weeks. Impressions were taken, and a new appliance was fabricated until the ideal tooth position was achieved. With good compliance in wearing the appliances, this patient achieved properly aligned maxillary teeth after 5 sets of consecutive appliances worn as instructed (Figure 2). Lower teeth alignment was achieved after 7 sets of consecutive appliances. A slight anterior open-bite of the upper right lateral incisor occurred. The sixth appliance for the upper arch was designed and combined with composite resin attachments to correct this localized vertical problem. The resin attachment was bonded to the upper right lateral incisor near the cervical region as the active component (Figure 3A), and on the appliance near the incisive portion of the upper right central incisor and upper right canine as the reactive component (Figure 3B). A reservoir space was intentionally provided between the appliance and the upper right lateral incisor to facilitate extrusion of this tooth with the use of elastics. Three weeks later, a positive overbite was achieved (Figure 3C). The wearing of elastics was reduced to nighttime only for retention. The overall orthodontic treatment time for this patient was 6 months, and the appliances used consisted of 6 maxillary aligners and 7 mandibular aligners. The final treatment result was satisfactory. Class I molar and canine relationships were maintained, and the anterior teeth were aligned. Mild lip incompetence remained. Fixed lingual retainers were bonded onto the maxillary and mandibular anterior teeth (Figure 4). Upper and lower vacuum- formed retainers were fabricated to maintain the transverse correction. At 1.5 years after treatment, the fixed retainers are still intact. The results appear to be very stable, and the long-term prognosis is good. Three-dimensional tooth movements on maxillary and mandibular casts of this patients were analyzed with a desktop mechanical digitizer (Microscribe 3DX, Immersion Corporation, San Jose, CA, USA), which collects 3D data of dental casts through a stylus tip 10,11. The Rhinoceros software program (National Instruments, Austin, TX, USA) was used to read the serial port communications from the digitizer and compute the X, Y, and Z coordinate locations. Maxillary and mandibular pretreatment and posttreatment casts were fixed to the flat desktop work surface with fixture putty. In total, 32 points were digitized for each maxillary cast and 30 points for each mandibular cast. The 3D data from the study models were oriented in a spatial coordinate system for easier perception of tooth movements. Pretreatment and posttreatment study casts were placed in the same coordinate system via superimposition to analyze changes in tooth positions during treatment. Palatal ruga points and mandibular molars were used as the registration landmarks. Results revealed that during the alignment period, Figure 2. Intraoral photographs after initial alignment. J Dent Sci 2008 Vol 3 No 3 169

4 E. H.H. Lai, C.C. J. Yao, Y.J. Chen, et al. Figure 3. (A)Attachments bonded onto the maxillary right lateral incisor and the aligner. (B) Reservoir space was provided and elastics were worn for extrusion of the upper right lateral incisor. (C) A total of 2.5 mm of extrusion was achieved. Figure 4. Posttreatment photographs. 170 J Dent Sci 2008 Vol 3 No 3

5 Vacuum-formed orthodontic appliance mesial-outrotation with 3.1 mm of labial movement at the mesial aspect of the incisal edge and 1.7 mm at the distal edge were noted for the maxillary right lateral incisor (Figure 5). The maxillary central incisors were slightly retracted by about 0.6 mm. The upper left canine and premolars were buccally expanded. The upper dental midline was moved to the left side by about 1 mm and became more coincident with the facial midline. The maxillary right lateral incisor extruded about 2.5 mm, while the maxillary central incisors and canine maintained their original vertical positions. Buccal expansion was achieved in the mandibular canine and premolar areas, thus creating space to relieve the mandibular anterior crowding without proclining the lower incisors (Figure 6). The lower left canine was moved buccally and distally about 2.4 mm. Distal-outrotation with 2.7 mm of labial movement at the distal aspect of the incisal edge and 1.8 mm at the mesial aspect were noted for the mandibular right canine. The lower dental midline was moved 1 mm to the left side and was brought into coincidence with the upper dental midline. DISCUSSION In 1945, Kesling published the first article on the use of clear plastic overlays to achieve minor tooth movements 3. Although the results of those devices were satisfactory, manual work is required, which is thought to be impractical due both to laboratory costs and technical difficulties of evenly dividing a larger overall movement into small, precise stages manually. To reduce manual labor, we allowed 0.50~1.0 mm of tooth movement for each stage, which allowed the treatment to progress more efficiently. With this modality, the treatment cost was far less than that using the Invisalign system. Align Technology sequences tooth movements into a series of evenly divided, 0.15~0.25-mm movements, because they propose that this threshold of movement reflects the maximum amount of activation possible, given the virtual tooth position, modulus of elasticity of the material, and thickness 9. We found that satisfactory results could be achieved even with 0.5~1.0 mm of movement in each step, although the appliance would not completely fit initially, due to the larger dental movements planned. The patient was educated to always fully seat the posterior portion of the appliance, which served as the anchorage portion of the appliance. The anterior portion of the appliance could be fully seated in place within a few days. Comparative cases treated with Invisalign took a longer time because smaller tooth Figure 5. Superimposition of the pretreatment and posttreatment maxillary dental casts. Red dots indicate the initial position and blue dots the final position. J Dent Sci 2008 Vol 3 No 3 171

6 E. H.H. Lai, C.C. J. Yao, Y.J. Chen, et al. Figure 6. Superimposition of pretreatment and posttreatment mandibular dental casts. Red dots indicate the initial position and blue dots the final position. movements (0.15~0.25 mm) were planned for each step 12. The total treatment time for this patient was only 6 months with 6 appliances for the upper arch and 7 for the lower arch. The orthodontic treatment duration was far less than treatment with Invisalign. Currently complex extrusions are less predictable with the Invisalign system alone and might require auxiliary treatment 1,9. Attachments are required to be bonded onto teeth to facilitate extrusive movements. The Invisalign system should always engage the undercut area of the attachment, and should always be fully seated to achieve extrusive movement, which is rather difficult due to the nature of the material of the appliance. Therefore, only a small amount of tooth movement can be planned to allow full engagement of the attachment. In our treatment regimen, we bonded attachments onto the appliance and the tooth that required extrusion. The appliance did not have to fully engage the undercut area of the attachments; instead, it had to be trimmed away from the attachment on the tooth, and a reservoir was intentionally provided to allow continuous vertical tooth movement until the reservoir space was eliminated. Although this might be less esthetically pleasing, it proved to be quite efficient for extruding the teeth. Results showed that as much as 2.5 mm of extrusion could be achieved within 3 weeks. Using clear removable appliances to treat patients is advantageous because it eliminates the difficulty of bonding fixed appliances to multiple crowns. In addition, the bulk of tooth movement can be concentrated in a specific region while minimizing unwanted tooth movements in other regions. As in this case, unilateral expansion of the left upper canine and premolar area was achieved without alteration of the right upper posterior segment. One major disadvantage of the Invisalign system is that once treatment has begun, changes to the treatment may require additional time and documentation. Alteration of the original restorations may cause a poor fit of the Invisalign appliances leading to treatment failure. Orthodontic tooth movements achieved by plastic appliances fabricated on setup models eliminate this problem. Since a new alginate impression is taken to fabricate the subsequent aligner, alterations of the previous dental restorations will not interrupt the original treatment sequence. It is important to note that some conditions can be difficult to treat with clear removable appliances. Such conditions include centric-relation and centricocclusion discrepancies, large skeletal anteriorposterior discrepancies, and severely rotated teeth. Thus, careful case selection is mandatory. The present case had a solid Class I molar relationship and a 172 J Dent Sci 2008 Vol 3 No 3

7 Vacuum-formed orthodontic appliance stable posterior occlusion with no centric-relation or centric occlusion discrepancies, and thus would benefit from treatment with clear removable appliances. In this case report, a patient with moderate crowding and a maxillary lateral incisor crossbite was treated with a series of removable plastic appliances, which were fabricated on consecutive setup models. For each stage, 0.5~1.0 mm of tooth movement was achieved. Specially designed resin attachments with the wearing of elastics achieved complex extrusion within 3 weeks. Three-dimensional data obtained from selected landmarks on serial dental models were superimposed to detect tooth movements during treatment. Crowding was relieved and midlines corrected via differential expansion of both arches instead of interproximal reduction. REFERENCES 1. Womack WR, Ahn JH, Ammari Z, Castillo A. A new approach to correction of crowding. Am J Orthod Dentofacial Orthop, 22: , Owen AH. Accelerated Invisalign treatment. J Clin Orthod, 35: , Kesling HD. The philosophy of the tooth positioning appliance. Am J Orthod, 31: , Nahoum HI. The vacuum formed dental contour appliances. NY State Dent J, 9: , Pontiz RJ. Invisible retainers. Am J Orthod, 59: , McNamara JA Jr, Kramer KL, Jeunker JP. Invisible retainers. J Clin Orthod, 19: , Sheridan JJ, LeDoux W, McLinn R. Essix retainers: fabrication and supervision for permanent retention. J Clin Orthod, 27: 37-45, Rinchuse DJ. Active tooth movement with Essix-based appliances. J Clin Orthod, 31: , Boyd RL, Vlaskalic V. Three-dimensional diagnosis and orthodontic treatment of complex malocclusions with the Invisalign appliances. Sem Orthod, 7: , Ashmore JL, Kurland BF, King GJ, Wheeler TT, Ghafari J, Ramsay DS. A 3-dimensional analysis of molar movement during headgear treatment. Am J Orthod Dentofacial Orthop, 121: 18-30, Yao CC, Lee JJ, Chen HY, Chang ZC, Chang HF, Chen YJ. Maxillary molar intrusion with fixed appliances and mini-implant anchorage studied in 3-D. Angle Orthod, 75: , Chenin DA, Trosien AH, Fong PF, Miller RA, Leem RS. Orthodontic treatment with a series of removable appliances. JADA, 134: , J Dent Sci 2008 Vol 3 No 3 173