Treatment Planning Considerations in Congenitally Missing Maxillary Lateral Incisor: The Role of Orthodontics (In Orthodontic Aspect)

Clinicians agree that tooth agenesis regardless of gender or race becomes more prominent in recent societies. The congenital absence of one or more maxillary lateral incisors is a challenge to effective treatment planning for the restorative dentist. The one-sided orthodontic approach of moving canines mesially to eliminate restorative procedures also leads to compromise. Adult patients presenting with malocclusions, missing lateral incisors, and anterior crowding, who request esthetic solutions without proper orthodontic treatment will get compromised results. The avoidance of establishing a stable occlusion, proper alignment and proper axial inclination of the teeth compromises esthetic and periodontal results. Evaluation of anterior smile esthetics must include both static and dynamic evaluations of frontal and profile views to optimize both dental and facial appearance. This article presents how orthodontics is related with other specialties in treating congenitally missing lateral incisor. One case is used to illustrate how orthodontic treatment is progressed in collaboration with other specialists. CLINICAL SIGNIFICANCE Patients with missing teeth, crowding, midline deviation, unesthetic gingival contours, or other restorative needs may require the interaction between different specialists. For the successful treatment of orthodontic-restorative patients, interdisciplinary team management is vital. INTRODUCTION Nowadays demands and expectations of esthetic dentistry are increasingly high. To provide esthetic anterior tooth shape and correct agenesis cases, we must inform patients of their total dental needs, not just those limited specialty. To integrate and coordinate treatment, and not limit treatment to an isolated specialty, we need to present our patients with total treatment approaches, to maximize function, esthetics, and oral health. In many of our routine dental malocclusions, orthodontic treatment alone may be limiting for ideal esthetic and functional dental occlusions. We must evaluate the facial profile, smile line, buccal corridor, black triangles, lip line, and crowding. One-sided approaches to multifaceted problems often produce compromise results. Agenesis of one or more teeth constitutes one of the most common developmental anomalies in man. Familial tooth agenesis is transmitted as an autosomal dominant, recessive or X-linked condition. Reported incidence of permanent tooth agenesis varies from 1.6 to 9.6%, excluding third molars, which occurs in 20% of the population. Studies vary on the second most commonly missing teeth. Some studies 4-8 have shown that it is the maxillary lateral incisor, whereas others believe that mandibular second premolar agenesis has a higher incidence. Muller et al found an interesting correlation that maxillary lateral incisors are the most frequently missing teeth when only 1 or 2 teeth are absent, whereas second premolars are the most frequently missing teeth when more than 2 teeth are absent. Maxillary lateral incisors show the highest genetic component of variability in the general population, whereas the smallest genetic influence on size of an anterior tooth is seen in the canine. Numerous twin studies illustrate hereditary factors in the mesio-distal dimensions of the teeth, and populations with chromosomal aberrations, such as occurs in Down’s syndrome, display a generalized reduction in tooth size and number. Tooth agenesis is more frequent in the parents and siblings of individuals with missing teeth than in the population as a whole, a finding that supports the hypothesis that this condition is genetically determined. TREATEMENT OF THE MISSING ANTERIOR TEETH When examining the esthetics of the anterior teeth and smile, the clinician should be aware of the morphology of the gingival contours, tooth contacts, tooth morphology, and tooth-size problems. To obtain ideal esthetic results, worn incisal edges, tooth shape, incisal contact, the contours of gingival margins, and black triangles should be considered before starting orthodontic treatment. The decision to re-shape or add tooth structure should be evaluated considering the width-to-length ratios of the Golden Proportion. The length of the central incisors should be divided into the width to obtain the proper percentage, with the ideal width being 75-80% of the length. The longer teeth in this range appear more feminine, and shorter teeth appear more masculine. The question of what determines the shape and thickness of the architecture of the scalloped gingiva, the papilla and the thickness of the labial and lingual alveolar bone, is of interest. Clinically, it appears that long tapered triangular maxillary incisors have more delicate thin arched gingival tissue, with longer delicate papilla, thin bone and a smaller more incisal contact point, as opposed to the more rectangular-shaped incisors, with thick gingiva and a flatter, wide, free gingival margin. These latter teeth have broad contacts. As a generalization, the more rectangular the teeth are, the thicker the gingival housing them and the alveolus. The smile line and lip shape also should be evaluated. The position of the lip attachment at the nasolabial junction has a profound effect on the esthetics of the profile. We all need an understanding of facial proportions and facial esthetics to provide our patients with a comprehensive treatment plan. There has been ongoing controversy in orthodontic and restorative dentistry over the treatment of agenesis cases, especially of the lateral incisors. Restorative dentists were opposed to mesial movement of the maxillary canine into the lateral incisor space, since this precluded the potential for developing canine-protected occlusion, because it places the canine in direct opposition to the mandibular lateral incisor. Stuart and Stallard, and D'Amico advocated canine-protected occlusion in all dentitions. However, Nordquist and McNeill justified the mesial movement of canines into lateral incisor space which provided many orthodontists with the rationale for space closure. They stated that no difference existed in adequacy of occlusal function between canine-protected and group function, and no relation with periodontal status existed between the two groups. They also stated that treatment should be designed to eliminate prostheses, which contributed to accumulation of plaque and irritation. Furthermore, studies have shown that two groups did not differ significantly in respect to occlusal function and the prevalence of temporomandibular dysfunction. Many orthodontic studies have shown that reshaping maxillary canines to resemble lateral incisors greatly improves esthetics. When maxillary lateral incisors are missing, there are several factors to consider treating patients with space opening or space closure. The type malocclusion, crowing/spacing, tooth size relationships, canine position, shape and color of canine, and maxillary lip length. The choice between these two modes of treatment should not be made empirically. In most instances the presence or absence of major occlusion problems serves as the primary criterion for either space closure or space opening. Lateral incisor spaces should be closed in cases with malocclusions which require the extraction of permanent mandibular teeth. Mandibular extractions may be indicated to relieve anterior or posterior arch length deficiency, to reduce mandibular dentoalveolar protrusion or to compensate for a Class II molar relationship. In some orthodontic patients may be missing several permanent teeth including maxillary lateral incisors. If teeth have been missing for several years, the remaining teeth may have drifted. In these patients, orthodontists and restorative dentists may not be aware of restorative requirements or eventual restorative treatment plan. For these types of patients, it is recommended to predetermine the final occlusal and restorative outcomes by completing diagnostic wax set-ups. In addition, the trial set-up will allow identification of tooth surfaces which require functional and esthetic reduction so that equilibration may be initiated either at the beginning of or during the orthodontic treatment. Diagnosing and treating growing children who are missing lateral incisors are a problem for many clinicians. If the patient and their parents decide on future implants, it is important to determine that the majority of vertical facial growth and tooth eruption is completed before implant placement. Girls mature faster than boys, and their adolescent growth spurt occurs sooner. After completion of growth in stature (height), sequential cephalometric and hand-wrist radiographs verify the cessation of facial growth over a time-frame of approximately every six months to one year. Explanation of the sequence of treatment in cases of agenesis of anterior teeth must be explained to both the patient and their parents very thoroughly. They must realize that orthodontic treatment is the beginning of the sequence. The sequencing of periodontal therapy and final restorations should all be explained to the parents and patient. All treatment options should be discussed with the interdisciplinary team, just as all the options are explained in the orthodontic treatment phase. ORTHODONTIC CONSIDERATIONS IN TREATMENT OF THE MISSING MAXILLARY LATERAL INCISORS In a long-term clinical and radiographic follow-up study, by Thordarson et al adolescent patients who had extensive remodeling of the permanent canines were evaluated. The canines were ground to the shape of lateral incisors as part of the orthodontic treatment and the patients were recalled after 10-15 years for clinical examination. The study demonstrated that extensive cuspal, labial, lingual, and interproximal recontouring, by the grinding of young teeth associated with orthodontic treatment, can be performed without discomfort to the patient and with only minor or no long-term clinical and radiographic reactions. They stated that this finding is encouraging, since better long-term esthetic results and healthier periodontal conditions may be achieved by recontouring canines, rather than by replacing missing incisors with prosthetic appliances. However, many esthetic dentists disagree with this conclusion. Isler, discussing facial beauty, stated that the bone is the under-structure, the scaffolding, and the major determinant of facial beauty. He also mentioned that a good smile is only partly about the teeth; it is primarily about the way in which the teeth appear to be placed in the face. Therefore, the design foundation of the smile is the very foundation of the teeth themselves, that is, the maxillary alveolar arch. Obviously, if a patient has bilateral agenesis of maxillary lateral incisors, the bone volume of the maxilla will be decreased. By erupting maxillary canines into the lateral incisor space, alveolar bone is developed, and by distalizing the buccal segments for the restoration of the lateral incisors, we can maintain the volume of the maxillary bone. In the canine substitution case, the alveolar canine buttressing of the canine roots is displayed anteriorly where the lateral incisors should be, and the dental arch narrows distally. With space closure, the arch form is condensed and constricted. Obvious gingival and tooth esthetics may be improved with gingival margin recontouring, and the reshaping of the maxillary canines. However, even if the canines esthetically are recontoured, the dentoalveolar arch curvature cannot be changed. The patient in full smile displays buccal corridor, since arch circumference is diminished with closure of the lateral incisor spaces. There is less dentoalveolar bone to work with to create an esthetic smile. Henns reported that the canine eminence is lost from its normal position which canines were used as laterals as the eminence accompanies the canine when it is moved. However, his study showed that the difference of the canine eminence did not exceed a 1.5 mm when the mean arch form recording of the Class I extraction group and the canine substitution group were superimposed. According to his evaluation using the upper study casts, the poor esthetic appearance of the canine eminence may have been exaggerated. CASE REPORT The 38-year-old Japanese female had difficulty in biting and desired to improve her facial esthetics. She had facial symmetry with a convex profile (Figure 1). She presented with an end-on Class II molar relationship on the right side and a mutilated molar relationship on the left side due to the loss of the mandibular left first molar. The missing area was replaced by three-unit bridge. The patient was also missing the maxillary left lateral incisor and the maxillary dental midline was deviated to the left by 3.0 mm relative to the facial midline. Due to the loss of the maxillary left lateral incisor there were severe gingival marginal discrepancies between the maxillary left central incisor and canine. The lingually displaced madibular right lateral incisor also showed gingival marginal discrepancy. The maxillary arch had mild crowding and the mandibular arch had severe anterior crowding. The maxillary left first premolar and madibular left first premolar were in crossbite, and the maxillary right seocnd premolar and the mandibular right second premolar were in Brodie bite. The patient had several restrations in both arches and had 2 mm overjet and 70% overbite. The maxillary left central incisor showed discolarization. The maxillary right lateral incisor and the first premolar exposed metal margins of porcelain-fused-to-metal (PFM) restorations due to gingival recession. The maxillary right first molar also showed gingival recession (Figure 2). The panoramic radiograph showed no caries or pathologies. The patient recevied root canal treatments on the maxillary right and left first molars, maxillary right first premolar, maxillary right lateral incisor, maxillary left central incisor, mandibular central incisors and mandibular right first molar. The maxillary and mandibular third molars were missing (Figure 3A). The cephalometric analysis revealed the patient had a skeletal Class II (ANB= 6.4°). The maxillary incisors were slightly proclined (U1 to FH: 113.5°) and the mandibular incisors showed normal inclination (IMPA: 94.1°). The upper and lower lips were slightly protrusive (Figure 3B). The etiology of the malocclusion was determined to be a combination of heredity and environmental factors. Before orthodontic treatment, the patient was referred to a general dentist for restorative dentistry consultation as well as a periodontist for the evaluation of the existing periodontal condition especially thin attached gingiva on the mandibular canines. One treatment option was to open space to replace the missing maxillary left lateral incisor. However, this treatment plan was not chosen because it can procline the maxillary incisors and increase protrusive lips. Furthermore, the patient was reluctant to undergo a restoration for a single tooth space after orthodontic treatment. The other treatment option was to extract the maxillary right first premolar and mandibular right second premolar which had restorations. In addition, the three-unit bridge on the left posterior segment was planned to be removed to mesialize the left mandibular second molar using the temporary anchorage device (TAD). However, the patient did not want to extract a tooth in the mandibular arch and did not want to install TAD during treatment. The last treatment option was to extract the maxillary right lateral incisor to correct the maxillary dental midline and slenderize the mandibular incisors to relieve the crowding. The patient was explained to replace the mandibular first molar after orthodontic treatment. However, severe gingival marginal discrepancies would result in a compromised gingival architecture. The patient agreed to choose this treatment plan. Full-fixed .022′′ Tip-Edge (TP Orthodontics, Inc., LaPorte, IN) appliances were placed on both arches. Before placing the appliances, the left mandibular three-unit bridge was removed and temporary crowns were delivered. This preadjusted edgewise appliance permits crown tipping in one direction yet creates anchorage through bodily movement in the other. This appliance offers easy rotation and angulation control using auxiliaries like rotating springs and uprighting springs. The Tip-Edge bracket is derived from a single .022′′ straight-wire bracket merely by cutting away two diametrically opposed corners from the archwire slot. The addition of rotation wings and a vertical slot enhances both rotational and tip control. This unique arch slot can close the extraction space without extruding incisors by tipping in the mesiodistal direction in early period of treatment. Brackets have appropriate torque and in-out compensation to assure controlled finishing with rectangular archwires and upright springs. To substitute canines in the position of missing laterals, special bracket placement was necessary for both maxillary canines and the first premolars. The lateral incisor brackets were bonded to the canines and the canine brackets were placed on the first premolars. Before bonding the lateral incisor bracket on the canine, the labial surface was reshaped for the bracket adaptation. It is necessary to position these brackets gingivally to permit the recontouring of the canines required for esthetics and function. To make the canine appear less curved and more like a lateral incisor, the bracket was placed more distally in the center of the canine rather than at the height of contour (Figure 4A). In addition, a canine bracket was placed on the first premolar in the same mesiodistal position (more distally) in which it is placed on the canine. However, to improve the interproximal contact points, offset bonds (in-out) was needed between the central incisor and canine (Figure 4B, C). Maxillary and mandibular arches start with .016′′ high tensile stainless steel archwires with mild bite opening bends mesial to the first molars. To make a room for the lingually displaced mandibular right lateral incisor and to prevent proclination of the mandibular anterior teeth, interproximal reduction was performed in the anterior segment. At the leveling stage, .016′′ nickel titanium archwire was used in conjunction with the main .016′′ high tensile stainless steel archwire to speed the alignment of the mandibular anterior teeth. In the maxillary arch, space was closed using a .022′′ round archwire. While protracting the maxillary right canine, the maxillary dental midline was slightly overcorrected because the patient did not wear elastics (Figure 5). During treatment enamel was recontoured to flatten and create an incisal edge on the canine cusp tip. To eliminate traumatic occlusion of the mandibular lateral incisors with the lingual surfaces of the canines and to establish a balanced occlusion, the lingual cusps the maxillary canines and first premolars were recontoured (Figure 6). At finishing stage, .0215′′ x .028′′ archwires were used for torquing control. At this stage, the patient was referred to the restorative dentist to evaluate space for the threeunit bridge on the left posterior segment. The patient was instructed to elastics all the time to correct dental midline. Uprighting springs were used to exert continuous, uprighting and torquing forces on the anterior teeth to ideal angulations. Total treatment time was 23 months. Following the treatment, a 0.0175 inch twistflex wire fixed retainer was bonded from first premolar-to-first premolar on the mandibular arch. The mandibular central incisors could not be bonded successfully with the fixed retainer due to ceramic crowns which were fabricated after debonding. Mandibular Essix retainer also delivered as removable retainer. On the maxillary arch, Essix retainer was delivered. The patient was instructed to wear them 24 hours per day for one year, and then night time only after one year. Recall visits for retainer checks were given at one, three, and six months for the first year. To ensure continued satisfactory post-treatment alignment of the mandibular and maxillary anterior dentition, the use of fixed or removable retainers is recommended indefinitely. At the end of orthodontic treatment, the patient was referred to her general dentist for the restorative treatment and the periodontist for gingival margin discrepancies. After the treatment, the patient’s profile has been improved (Figure 7). The severe mandibular crowding has been relieved. Dental midlines were aligned with the facial midline, overbite and overjet has been improved (Figures 8 and 9). The panoramic radiograph showed proper space closure and acceptable root parallelism, with no signs of bone or root resorption (Figure 10A). Cephalometric analysis and revealed no significant skeletal changes (ANB= 6.2°). The maxillary incisors showed decent inclination (U1 to FH: 108.9°) and the mandibular incisors showed no significant changes (IMPA: 92.4°). Her upper and lower lip profile has been improved. (Figures 10B and 11, Table I). After six years of retention, the patient showed pretty stable occlusion (Figures 12-14).