Dental Implants in the Management of Nonsyndromal Oligodontia

This article was published in an Elsevier journal. The attached copy is furnished to the author for non-commercial research and education use, including for instruction at the author’s institution, sharing with colleagues and providing to institution administration. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright Author's personal copy Atlas Oral Maxillofacial Surg Clin N Am 16 (2008) 11–31 Dental Implants in the Management of Nonsyndromal Oligodontia Robert P. Carmichael, DMD, MSc, FRCDCa,b,c,d,*, George K.B. Sándor, MD, DDS, PhD, Dr Habil, FRCDC, FRCSC, FACSa,b,c,d,e,f a Bloorview Kids Rehab, Suite 2E-285, 150 Kilgour Road, Toronto, Ontario M4G 1R8, Canada The Hospital for Sick Children, S-525, 555 University Avenue, Toronto, Ontario M5G 1X8, Canada c University of Toronto, Toronto, Ontario, Canada d Mount Sinai Hospital, Toronto, Ontario, Canada e Regea Institute for Regenerative Medicine, University of Tampere, Biokatu 12, Tampere, Finland f University of Oulu, Oulu, Finland b No consensus concerning the nomenclature of agenesis of teeth exists in the literature. The most frequently used terms to describe tooth agenesis are hypodontia and oligodontia. Hypodontia is usually employed to describe a situation in which only a few teeth are missing, whereas oligodontia is used when a large number of teeth are missing. Nevertheless, The Glossary of Prosthodontic Terms makes no distinction between the two terms with respect to the number of teeth missing. In medicine, the Greek prefix hypo- denotes an abnormally low level of a substance in the body. The prefix oligo-, also Greek, denotes few. Because teeth are structures present in discreet numbers, the authors believe that oligodontia is the most appropriate term to describe the congenital absence of more than one tooth but not all teeth, and that the Tooth Agenesis Code may be used to assign a unique value to the pattern of agenesis. The term anodontia is reserved to describe the total absence of teeth, a use for which there seems to be no dispute. Etiology of oligodontia Oligodontia is thought to have a significant genetic basis because it is associated with mutations in several genes, the protein products of which regulate odontogenesis. Oligodontia may also be associated with environmental influences. Prevalence of oligodontia Oligodontia has been reported to be the most or one of the most common developmental dental anomalies, which probably explains why the prevalence of oligodontia is one of the few topics in the literature for which there is good evidence supported by meta-analyses. The prevalence of agenesis of permanent teeth in a meta-analysis of 28 studies covering Europe, Australia, and whites in North America was found to differ by continent and gender. Overall, oligodontia occurred 1.37 times more frequently in females than in males. Oligodontia was more prevalent in Australia (females: 7.6%; males: 5.5%) and Europe (females: 6.3%; males: 4.6%) than in North American whites (females: 4.6%; males 3.2%). Mandibular second premolars * Corresponding author. Bloorview Kids Rehab, Suite 2E-285, 150 Kilgour Road, Toronto, Ontario, Canada M4G 1R8. E-mail address: [email protected] (R.P. Carmichael). 1061-3315/08/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.cxom.2007.10.002 oralmaxsurgeryatlas.theclinics.com Author's personal copy 12 CARMICHAEL & SÁNDOR were found to be absent more frequently than maxillary lateral incisors or maxillary second premolars (Fig. 1A–T). Moreover, maxillary lateral incisors were found to be absent more frequently bilaterally than unilaterally, whereas the opposite was true for maxillary first and second premolars and mandibular second premolars. Author's personal copy MANAGEMENT OF NONSYNDROMAL OLIGODONTIA 13 : Fig. 1 (continued) Fig. 1. A 13-year-old female with congenital absence of the maxillary lateral incisors and second premolars, and mandibular second premolars. (A) Front facial view. (B) Profile view. Note orthognathic skeletal pattern. (C) Right lateral view of teeth. Note class I molar relationship. Note maxillary canines have erupted into the lateral incisor sites and second primary molars are retained. (D) Frontal view of teeth. Note maxillary canines have erupted mesially into lateral incisor sites. (E) Left lateral view. Note class I molars. Note maxillary canines have erupted into the lateral incisor sites and second primary molars are retained. (F) Panoramic tomography at age 13 years. Note maxillary and mandibular second molars are retained. (G) Maxillary occlusal view at 18 years of age. Note orthodontic alignment has opened space for maxillary lateral incisors and closed down the space for second premolars to approximately 8 mm. (H) Mandibular occlusal view at 18 years of age. Note orthodontic alignment has closed down space for second premolars down to approximately 8 mm. (I) Panoramic tomography at 18 years of age demonstrating implant alignment. (J) Post-treatment front facial view at 19 years of age. (K) Post-treatment profile view. (L) Post-treatment frontal view of teeth demonstrating implant supported maxillary lateral incisor crowns. (M–P) Maxillary right and left and mandibular right and left occlusal close-up views. Prosthetic second premolar crowns are larger than natural first premolars to avoid interdental spacing, a result of mild microdontia of anterior teeth. (Q–S) Maxillary anterior, right lateral, and left lateral close-up views. (T) View of smile. Author's personal copy 14 CARMICHAEL & SÁNDOR Fig. 1 (continued) Most patients with oligodontia are missing only one or two teeth, fewer than 10% are missing four or more, and less than 1% are missing six or more. Estimates of the prevalence of oligodontia involving the absence of six or more teeth, third molars excluded, range from about 0.1% to 0.3%, whereas the prevalence of eight or more missing teeth has been reported to range from 0.01% to 0.03%. Consequences of oligodontia Concomitant with oligodontia, there are often positional, morphologic, and size differences associated with the teeth that are present. Patients with ostensibly nonsyndromal oligodontia may also have signs or symptoms in other ectodermally derived tissues, such as low salivary secretion and impaired structure or function of the sweat glands, hair, or nails. The more severe the oligodontia, the more likely it is to be associated with a syndrome. The subjective need for the replacement of missing teeth may be perceived by the patient as being undermined cosmetics, poor mastication, or malocclusion and spacing. In fact, 60% of patients with oligodontia present for treatment with these or other complaints. Other more objective findings in patients with oligodontia include the following: malocclusion involving a deep bite, crossbite, spacing, rotations, ectopic eruptions and transpositions; reduced orthodontic anchorage; cone-shaped incisors and canines; ankylosis and submergence of retained primary teeth; disruption of the growth of alveolar bone around ankylosed teeth; agenesis of edentulous regions of the alveolar process; resorption of the alveolar process following the exfoliation of primary teeth without succedaneous replacements; attrition and pulp exposure of retained primary teeth; attrition of permanent teeth, especially misaligned incisors; extrusion of unopposed teeth; and pneumatization of the maxillary sinuses. Oligodontia may also be accompanied by taurodontism and reduced length of teeth, left–right asymmetry of tooth dimensions, and delayed tooth eruption. The severity and pattern of oligodontia has also been shown to affect craniofacial morphology, a situation with obvious implications for preprosthetic orthodontic treatment. Author's personal copy MANAGEMENT OF NONSYNDROMAL OLIGODONTIA 15 For example, patients with oligodontia may demonstrate shorter anterior and overall cranial base lengths, shorter maxillary and mandibular lengths, greater retroclination of maxillary incisors, greater retroclination and elongation of mandibular incisors, a larger interincisal angle, a more prognathic mandible, a more counterclockwise-rotated occlusal plane, and a shorter upper and lower anterior face height than normal. It has been suggested that oligodontia may be an indicator of susceptibility to colorectal cancer. Moreover, calcification of the interclinoid ligament of the sella turcica may be associated with congenital absence of the mandibular second premolars. More recent evidence shows that at least some children with oligodontia may also have previously unassociated white matter diseases. The nature of the relationships between molecular mechanisms regulating the development of epithelial derivatives, such as teeth, skin, and hair, and of neural structures and those involved in the regulation of colorectal carcinogenesis are just now being elucidated. Given the associations between developmental pathways and tissue homeostasis, it is fascinating that oligodontia may be used as a marker for malignancy and hitherto unreported congenital malformations. Treatment of oligodontia The authors subscribe to a holistic approach to the care of patients with oligodontia that integrates clinically relevant scientific evidence within the context of the patient’s history, growth, development, needs, and psychosocial preferences. A multidisciplinary team approach to the treatment of oligodontia has been recommended because management requires the collaboration of at least a pediatric dentist, orthodontist, oral and maxillofacial surgeon, and prosthodontist. In most cases, patients should be referred to the team soon after the diagnosis of oligodontia is made. Clinical documentation should include at least a clinical assessment, preoperative intraoral and extraoral photographs, study casts of the teeth, panoramic tomographs, and intraoral radiographs and lateral cephalograms as required for orthodontic treatment planning and the determination of skeletal maturity. Follow-up to treatment should be ongoing and documented appropriately. Patients should be evaluated for the appropriateness of providing no treatment or at least no prosthetic treatment if an alternative therapy such as orthodontic space closure can be considered. As a general guiding principle, dental implants are employed to safely replace missing teeth when removable prostheses are unacceptable to the patient, when fixed toothsupported bridgework would involve an unconscionable sacrifice of virgin or minimally restored tooth structure, or when an edentulous span is judged to be too long to meet Ante’s law for tooth-supported bridgework. Occasionally, healthy isolated permanent teeth are removed if they are judged to be likely to impede the establishment of a satisfactory prosthodontic outcome or to undergo intrusion following the restoration of adjacent implants. Preprosthetic orthodontic treatment is usually necessary and is planned for and initiated at the age appropriate time. Generally, the goals of orthodontic treatment should include, if feasible, establishing a Class I canine and molar relationship, establishing correct midlines and alignment, optimizing the dimensions of the edentulous gaps, and achieving root parallelism adjacent to edentulous gaps. Whenever possible, orthodontic treatment should employ a strategy to minimize or consolidate missing tooth spaces to reduce the number of dental implants required to restore the dentition to an acceptable level of function, as long as that strategy is unlikely to compromise the facial profile, dental esthetics, or function (Fig. 2A–D). For example, substitution of a canine for a missing maxillary lateral incisor would be considered if a reasonable esthetic outcome could be expected (Fig. 3A–C). Alignment of the teeth is usually established with the same goals for implant-supported restorations, resin-bonded bridges, or removable partial dentures. Exceptions to this strategy include instances when orthodontic tooth movement is used to promote development of alveolar bone, when teeth are positioned remotely from their native sites to minimize orthodontic treatment time (Fig. 4A–D), or when an attempt is made to consolidate arch space in fewer edentulous gaps to minimize the numbers of implants required to restore the arch. Author's personal copy 16 CARMICHAEL & SÁNDOR Fig. 2. An 18-year-old man with agenesis of the mandibular central incisors. (A) Space was closed orthodontically to accommodate a single implant-supported central incisor crown. (B) Occlusal view. (C) Periapical radiograph. (D) Space closure affected neither esthetics nor function adversely. The facial profile may govern decisions to close or fill space. If space closure would adversely affect the facial profile, missing teeth should be replaced. For example, if a patient presents with maxillary retrusion, retraction of anterior teeth to close spaces would exaggerate the poor upper lip support and must be avoided (Fig. 5A–C; Fig. 6A–C; Fig. 7A–C). Similarly, tooth size discrepancies may dictate whether to close or fill spaces. Microdontia is commonly associated with oligodontia and may necessitate extra replacement teeth over and above the missing teeth when space closure would be inappropriate or unfeasible, especially when the facial profile stands to be adversely affected (Fig. 8A–D). Moreover, following space closure, the potential for relapse with reopening of space is high; therefore, prolonged retention is necessary. Missing anterior teeth The treatment of young patients with a unilateral or bilateral congenital absence of the lateral incisors is often a contentious issue in the literature and clinically among treating specialists. The question invariably arises whether to close the space orthodontically or to open it and replace the tooth, usually with a dental implant. In the absence of a lateral incisor, the canine usually erupts into the site of the missing lateral incisor (see Fig. 7B). Distalization of a canine into its native site can be a difficult and lengthy procedure (Fig. 7C) and is usually easier to accomplish if initiated early on. Once accomplished, the tooth alignment must be maintained until the cessation of skeletal growth, when a dental implant may be placed. During this time, temporization can be a problem, the relapse potential is high if fixed appliances are removed, and the residual alveolar ridge may atrophy to the point beyond which the site will have to be Author's personal copy MANAGEMENT OF NONSYNDROMAL OLIGODONTIA 17 Fig. 3. A 21-year-old female carrier of hypohydrotic ectodermal dysplasia following orthodontic consolidation of spaces in the maxillary arch. (A) The maxillary right central incisor is conically shaped. The left maxillary canine has been mesialized to the site of the ipsilateral lateral incisorda so-called ‘‘canine-lateral’’ substitution. (B) Occlusal view. (C) A good esthetic outcome is achieved by direct bonding of composite resin on the three maxillary anterior teeth. The size, shape, and color of the left canine are conducive to substitution for a lateral incisor. Fig. 4. An 18-year-old woman with congenital absence of all premolars. The maxillary canines have erupted distally into the sites of the first premolars. (A) Frontal view of post-orthodontic alignment. The maxillary canines were left to substitute for first premolars. (B) Frontal view of completed implant-supported restorations. (C) Occlusal view of implant restorations. Note bilateral canine-premolar substitutions. (D) View of smile demonstrates that bilateral maxillary canine-premolar substitutions result in an acceptable esthetic outcome. Author's personal copy 18 CARMICHAEL & SÁNDOR Fig. 5. A 22-year-old man with maxillary retrusion and congenital absence of the maxillary first premolars. The decision was made to replace the missing teeth rather than close spaces orthodontically to not worsen the facial profile and dental relationship. (A) Profile view demonstrates poor support of upper lip. (B) Occlusal view of the teeth demonstrates replacement of maxillary premolars with implant-supported crowns. (C) Lateral view of teeth illustrates how replacement of maxillary first premolars instead of orthodontic space closure maintains anterior dental edge-to-edge relationship. Fig. 6. A 20-year-old man with maxillary retrusion and congenital absence of the maxillary lateral incisors. The decision was made to replace the missing teeth rather than close spaces orthodontically to not worsen the facial profile and negative overjet. (A) Profile view demonstrates poor support of upper lip. (B) Occlusal view of the teeth demonstrates replacement of maxillary lateral incisors with implant-supported crowns. (C) Lateral view of teeth illustrates how replacement of maxillary lateral incisors instead of orthodontic space closure and canine substitution prevents worsening of negative overjet. Author's personal copy MANAGEMENT OF NONSYNDROMAL OLIGODONTIA 19 Fig. 7. A 16-year-old adolescent boy with congenital absence of the maxillary lateral incisors, mandibular central incisors, and first premolars. Decision was made to replace maxillary lateral incisors because large, yellow canines were thought unlikely to permit acceptable esthetic outcome if substituted for laterals, and because of borderline maxillary retrusion. (A) Profile view shows straight profile with poor lip support. (B) Panoramic tomograph at age 13 years demonstrates space maintainers and eruption of maxillary canines mesially into lateral incisor sites. (C) Frontal view of teeth demonstrates orthodontic hardware used to distalize maxillary canines and open lateral incisor spaces. Progress was slow, and the procedure was aborted in favor of canine substitution. augmented before or together with implant placement. Increased cost and prolongation of treatment may be potent disincentives for parents and their affected child to consent to implant treatment for a congenitally missing lateral incisor. In order for a canine substitution to provide an acceptable result, several factors should be favorable, such as the skeletal pattern, occlusal relationships, tooth size and arch length coordination, and the size, shape, and color of the canine relative to the central incisor (canines are usually darker and less translucent than lateral incisors) (Fig. 9A–C). Orthodontic space closure in the anterior maxilla can be considered for patients with maxillary crowding, or in some cases with Class II malocclusions where retraction of the maxillary anterior teeth to close the lateral incisor space would also improve the malocclusion by reducing overjet. It is generally contraindicated in patients with a Class III malocclusion (see Fig. 6A–C). If the crown of the canine is too large or too dark in color to masquerade as a lateral incisor without invasive modification, or if the shape of the gingival margin is too highly scalloped or receded, substitution with space closure should be reconsidered carefully (Fig. 10A–C; Fig. 11A–D). Several studies have documented that canine substitution has produced results that were deemed satisfactory by the patient, at least in the context of the times 40 to 50 years ago when the patients in these studies received treatment. Dental implant treatment offers many advantages over conventional prosthodontic treatments that have been available in the past to replace missing lateral incisors, and patients’ expectations of esthetics have heightened, both of which justify additional clinical research comparing space closure with replacement with dental implants in the treatment of congenitally missing lateral incisors (Fig. 12A–C; Fig. 13A–C). A strategy to avoid the need for ridge augmentation at the site of the missing lateral incisor is to postpone distalization of the canine until near the end of skeletal growth. As the tooth is moved distally, it can lay down bone, leaving in its wake an alveolar ridge of sufficient thickness to accommodate a dental implant. A similar strategy can be applied to other teeth in other parts of the mouth. For example, where an alveolar defect has developed at the site of a congenitally Author's personal copy 20 CARMICHAEL & SÁNDOR Fig. 8. A 21-year-old man with oligodontia missing the maxillary laterals and canines and mandibular incisors and canines. A tooth size/arch length discrepancy caused by the associated microdontia and the skeletal pattern necessitated extra replacement teeth over and above the missing teeth to avoid disturbing the facial profile. (A) Profile view. (B) Maxillary occlusal view. (C) Mandibular occlusal view. (D) Frontal view. Fig. 9. A 19-year-old man with congenital absence of the maxillary right central incisor and both lateral incisors. The skeletal pattern, occlusal relationships, tooth size/arch length coordination, and size, shape, and color of the canine relative to the left central incisor were all favorable; therefore, bilateral canine substitution was employed, and implants were placed at the sites left vacant by the mesially erupted canines. (A) Frontal view following implant placement. (B) Frontal view following restoration of implants and modification of canines using direct bonding of composite resin. (C) View of smile demonstrates satisfactory esthetic outcome. Author's personal copy MANAGEMENT OF NONSYNDROMAL OLIGODONTIA 21 Fig. 10. An 18-year-old woman with congenital absence of the maxillary left lateral incisor, lateralization of the left canine, and restoration of an implant placed in the space opened up behind the canine. (A) Frontal view. (B) Left lateral view. Note the absence of attached gingiva and gingival recession at the distobuccal margin of the canine and exposure of the implant shoulder. (C) Occlusal view. missing first premolar, the second premolar can be mesialized into the first premolar site, leaving behind an alveolar ridge with adequate dimensions to permit the placement of a dental implant safely out of the way of the mental foramen (Fig. 14). Dental substitutions other than canines for lateral incisors can often facilitate treatment of patients with oligodontia. An infrequent substitution is the use of a lateral or a canine for Fig. 11. A 20-year-old man with congenital absence of the maxillary lateral incisors and eruption of the canines into the lateral incisor sites. (A) Frontal view. The shape, size, and gingival contours of the canines did not favor canine substitution for lateral incisors. Nevertheless, the patient refused orthodontic treatment. (B) Occlusal view. (C) Panoramic tomography demonstrates placement of implants at canine sites. (D) Despite satisfactory lateralization of the canines with direct application of bonded composite resin, the overall esthetic outcome improved but remained poor. Author's personal copy 22 CARMICHAEL & SÁNDOR Fig. 12. A 21-year-old man with congenital absence of the maxillary left lateral incisor. (A) Placement of an implant at the site of the missing lateral incisor. (B) Restoration of implant. (C) View of smile reveals a satisfactory esthetic outcome. a missing central incisor. Either approach can be an elegant solution if clinical conditions are favorable. In most instances, the narrower lateral incisor will have to be positioned in the center of the central incisor gap made wide enough to accommodate a porcelain restoration with dimensions mirroring the contralateral central incisor. Care must be exercised to intrude the lateral incisor sufficiently so that its gingival margin is level with the gingival margin of the central incisor. Fig. 13. An 18-year-old woman with implant-supported crowns at sites of congenitally missing maxillary lateral incisors. (A) Frontal view of teeth. (B) Occlusal view of teeth. (C) View of smile. Author's personal copy MANAGEMENT OF NONSYNDROMAL OLIGODONTIA 23 Fig. 14. Mesialization of the second premolar into the hypoplastic site of a congenitally missing first premolar leaves behind an alveolar ridge with adequate dimensions to permit the placement of a dental implant safely out of the way of the mental foramen. Canines that erupt distally into the site of a congenitally missing first premolar can be left to substitute for the premolar while the vacancy left at its native site can be filled with an implantsupported crown. The size, shape, and color of the two teeth are usually sufficiently close to achieve an adequate esthetic result (see Fig. 4A–D; Fig. 15A, B). Conversely, a premolar can be used occasionally with impunity to substitute for a missing canine unless it is too short or its lingual cusp would interfere with the opposing dentition and could not be reduced without aggressive enameloplasty. Missing premolars As is true for decisions to employ dental substitutions in the anterior part of the mouth, decisions to close or fill spaces left by missing premolars are also governed by factors such as the skeletal pattern, occlusal relationships, tooth size, arch length, and facial esthetics. In oligodontia characterized by patterns of agenesis of both anterior and posterior teeth, canine substitution or other variations of anterior tooth substitutions are avoided to establish a Class I canine relationship when possible (Fig. 16A–E). This approach has the twofold result of enabling the establishment of canine guidance, which reduces potentially damaging lateral forces on posterior implants, and enhancing the probability of obtaining acceptable esthetics. Usually, situations in which one premolar is missing in the upper or lower arch or both can be corrected orthodontically without adversely affecting the facial profile. An elegant way to close space created by the absence of a mandibular premolar in a patient with a dental Class I relationship and an orthognathic profile is to treat that side of the jaw to achieve a Class I canine and a Class III molar. Conversely, a situation involving a missing maxillary premolar can be treated to achieve a Class I canine and a Class II molar. When one premolar is missing from the Fig. 15. A 19-year-old woman with congenital absence of the maxillary lateral incisors and first and second premolars. The canines have erupted distally into the first premolar sites and have been left to substitute for them. (A) Frontal view. The color, size, and shape of the canines are sufficiently close to that of the missing premolars to permit substitution with preservation of a natural appearance. (B) Occlusal view. Author's personal copy 24 CARMICHAEL & SÁNDOR Fig. 16. An 18-year-old woman with congenital absence of the maxillary lateral incisors, second premolars, and mandibular second premolars. Arches were aligned with canines and molars in a Class I relationship. Missing teeth were habilitated with their respective prosthetic counterparts. (A) Frontal view. (B) Maxillary occlusal view. (C) Mandibular occlusal view. (D) View of smile. (E) Right lateral view. (F) Left lateral view. same side of each arch, it should be possible to close both spaces and maintain the Class I canine and Class I molar. Because it is harder to close space resulting from the absence of both premolars on one side, it may not be possible to eliminate the need for prosthetic intervention in a situation involving two missing premolars on one side of one or each arch; however, closing gaps down from two premolar spaces to one halves the number of spaces to fill. In a patient with a Class I canine and Class I molar with a straight profile missing one maxillary premolar and both mandibular premolars on the same side, it should be possible to close the maxillary premolar space and one of the two missing mandibular premolar spaces while preserving the Class I canine and slipping the molars into a Class III. Instead of needing three implants to replace the missing three premolars, the patient needs only one implant to replace the single missing mandibular premolar. The corollary is also possible. In a patient with a Class I dental relationship and a straight profile missing both maxillary premolars and one mandibular premolar on the same side, it should be possible to close one of the maxillary premolar spaces and the mandibular premolar space while preserving the Class I canine and creating a Class II molar. Again, instead of needing three implants to replace the missing three premolars, the patient needs only one implant to replace the single missing maxillary premolar. These approaches are helpful strategies to use in the treatment of patients with oligodontia and normal skeletal and dental relations; obviously, many more combinations and permutations exist (Fig. 17A–D; Fig. 18A–D). In cases in which complex underlying jaw relationships exist, Author's personal copy MANAGEMENT OF NONSYNDROMAL OLIGODONTIA 25 Fig. 17. The 18-year-old woman shown in Fig. 13. In addition to missing maxillary lateral incisors, she is also missing the right maxillary second premolar, the space of which has been closed, and the right mandibular second premolar, which has been replaced by an implant-supported crown. In addition, she is missing the left mandibular second premolar, which has been replaced. (A) Frontal view. (B) Maxillary occlusal view. (C) Mandibular occlusal view. (D) Left lateral view. (E) Right lateral view. variations of the same strategies can be employed to advantageously manipulate the canine and molar relationships in an effort to minimize the need for prosthetic intervention. Missing molars The need to replace missing molars is debatable. The World Health Organization has recommended the lifelong retention of a natural dentition of not less than 20 teeth, the implication being that adequate oral function can be maintained in the absence of molars. Nevertheless, clinical experience suggests that functional and esthetic demands vary from patient to patient; therefore, the minimum number of teeth required by any one individual cannot be prescribed. When planning the treatment of a patient with oligodontia, it may be appropriate to aim for habilitation of all molars in some instances, but it is more than likely that such a goal may be neither practicable nor necessary. The extent to which the prescription of a full complement of first and second molars is executed is governed by a synthesis of elements specific to each individual patient, including finances, occlusion, anatomy, and medical status. Although many studies support the functionality of a shortened dental arch, that is, one comprising anterior and premolar teeth only, in the authors’ experience, it is a concept that few parents of children with oligodontia embrace. Young patients and their parents often perceive Author's personal copy 26 CARMICHAEL & SÁNDOR Fig. 18. An 18-year-old woman with congenital absence of the maxillary lateral incisors and premolars, right mandibular first premolar, and both mandibular second premolars. (A) Frontal view. (B) Maxillary occlusal view. Note retained palatal implant. (C) Mandibular occlusal view. (D) Right lateral view demonstrates class I canine relationship and class II molar relationship. (E) Left lateral view demonstrates Class I canine and molar relationships. and complain about the adverse effects of missing molars on esthetics and function; therefore, when priorities are set, restorative treatment planning should take into account the patient’s perceptions. In addition, objective parameters specific to the clinical management of oligodontia may support a decision to replace missing molars. Such parameters include clinicians’ opinions about the deleterious consequences of missing molars on individual esthetics and function (Fig. 19A–D), the need to inhibit potential overeruption of opposing teeth (Fig. 20A, B), the need for skeletal orthodontic anchorage, the need for intermaxillary fixation during orthognathic surgery beyond what can be obtained from the natural teeth alone, and the need to effect an increase in the vertical dimension of occlusion. Temporary implant-supported molars are also useful for increasing the bite and for disengaging the bite to retract a bimaxillary protrusion or an anteriorly splayed and spaced anterior/premolar dentition. Contrary to some opinions, placement of molar implants in a patient with oligodontia should not necessarily be considered overtreatment. Just as there are valid reasons to habilitate missing molars, there are valid reasons not to. Agenesis of alveolar bone associated with tooth agenesis heightens the risk of implant failure and the risk of implant placement causing injury to vital structures such as the trigeminal nerve. Agenesis of alveolar bone may also necessitate sinus floor elevation and augmentation, a procedure the patient may wish to avoid. Author's personal copy MANAGEMENT OF NONSYNDROMAL OLIGODONTIA 27 Fig. 19. An 18-year-old woman with congenital absence of all maxillary posterior teeth, mandibular second lateral incisors, second premolars, and first and second molars. Mandibular incisor spaces were closed, and missing premolars and first molars were habilitated. (A) Facial view. (B) Right lateral view. (C) Frontal view of teeth. (D) Left lateral view. Temporary anchorage devices In general, orthodontic treatment is more difficult the greater the number of missing teeth, primarily owing to the relative lack of anchorage. Consequently, treatment times for patients with oligodontia usually exceed the average, and outcomes are sometimes non-ideal. Several methods can be employed to obtain skeletal anchorage that can facilitate the treatment of severe oligodontia. These methods include the use of temporary anchorage devices such as osseointegrated palatal implants (see Fig. 18B), immediately loaded mini-implants, and temporary crowns and bridges placed on conventional dental implants located within the dental arch (Fig. 21), which are converted to definitive prostheses following the completion of orthodontic therapy. Fig. 20. A 23-year old man with congenital absence of the maxillary lateral incisors and right maxillary molars. (A) Maxillary occlusal view. (B) Right lateral view demonstrates prevention of overeruption of the mandibular first and second molars by an implant-supported maxillary first molar crown. Author's personal copy 28 CARMICHAEL & SÁNDOR Fig. 21. Implant-supported temporary crowns at the sites of a congenitally missing mandibular right second premolar and left first premolar are used as temporary anchorage devices to obtain skeletal anchorage and facilitate orthodontic treatment of oligodontia. Temporary anchorage devices facilitate treatment by means of increasing orthodontic anchorage, reducing the need for patient compliance vis-à-vis the wearing of appliances, reducing treatment time, and enabling some orthodontic maneuvers that would otherwise require surgery. Orthognathic surgery Occasionally, orthognathic surgery must be used in combination with orthodontic treatment to correct severe skeletal discrepancies in all three planes of space and to correct significant asymmetries. Dealing with retained primary molars When supervising the care of an adolescent with oligodontia, timing is everything. Retained primary teeth can be ideal space maintainers where the succedaneous tooth is absent. Unfortunately, primary molars can ankylose and, in a growing child, submerge below the occlusal plane and disrupt local alveolar development. If allowed to progress unchecked, this process can result in the creation of a bony defect that, in the future, may compromise implant placement at the site (Fig. 22). Ankylosis of a submerged primary molar can be confirmed clinically by percussing it with the handle of a metal mouth mirror, which elicits a sound like tapping on glass. Radiographically, a discrepancy in the height of the interproximal bone can be identified between an ankylosed primary molar that has started to submerge and the adjacent permanent teeth. Depending on the age and gender of the patient, one should consider extracting an ankylosed primary tooth to prevent creation of a bony defect. The decision to extract will rest on an assessment of the amount of residual skeletal growth. For example, there would be no urgent need to extract an ankylosed primary molar in a 15-year-old girl in whom little residual Fig. 22. Ankylosis of a maxillary left second primary molar in a growing child has submerged below the occlusal plane and disrupted local alveolar development, resulting in the creation of a bony defect that, in the future, may compromise implant placement at the site. Author's personal copy MANAGEMENT OF NONSYNDROMAL OLIGODONTIA 29 jaw growth is anticipated. On the other hand, the same tooth in a 15-year-old boy who may continue growing until 19 or 20 years of age should be extracted to avoid creating a significant bony defect. Great care must be taken to remove an ankylosed primary molar atraumatically without unnecessarily removing alveolar bone. Some degree of residual alveolar ridge resorption is inevitable following extraction. In situations involving the absence of a single premolar, the authors expect about a 25% decrease in alveolar ridge width over the first 3 years or so, after which resorption tapers off. In situations involving the absence of the first and second premolars, greater resorption can be expected. Timely extraction of ankylosed primary molars may have the additional benefit of permitting mesial drift of molars with orthodontic space closure, perhaps obviating the need for a dental implant and associated augmentation procedures. Bone grafting Bone grafting may be used to augment alveolar bone before placing dental implants. Autogenous bone can be harvested from several donor sites. The most common extraoral site is the os ilium, the use of which requires general anesthesia in a hospital or private practice setting. Intraoral bone harvesting may take the form of collecting bone chips from the implant osteotomy with a suction trap. Procedures used to augment the alveolar ridges before, or together with, implant placement include sinus floor elevation, onlay grafting, and guided bone regeneration. Coral granules have been used in some instances to preserve alveolar ridge dimensions in alveolar defects resulting from traumatic tooth loss or from the extraction of ankylosed retained primary molars with no succedaneous teeth. Large continuity defects may be reconstructed using vascularized bone grafts from the fibula. Temporization Temporary prosthetic treatment must be provided when necessary to minimize the impact of impaired cosmetics of missing teeth. Ironically, the cosmetics often worsen with the progress of orthodontic treatment when retained primary teeth, especially incisors, must be extracted to make room for the alignment of permanent teeth, or when alignment opens up edentulous gaps that hitherto had been somewhat camouflaged by the misalignment. During periods of no fixed orthodontic treatment, temporary restorations may take the form of acrylic removable partial dentures or Hawley-type orthodontic appliances furnished with prosthetic teeth and other components designed to effect minor tooth movements. During periods of active orthodontic tooth movement with fixed appliances, and later during retention of the orthodontic alignment, especially during the surgical phases of treatment when the surgical site cannot be loaded by a removable retainer, prosthetic teeth should be attached to the fixed arch wires in the esthetic zone whenever possible (Fig. 23). Transitional therapy may also include recontouring of hypoplastic teeth with composite resin where necessary (see Fig. 3A–C). Fig. 23. Acrylic resin denture tooth suspended from an orthodontic arch wire at the site of a missing maxillary left central maintains an esthetic appearance during periods of active orthodontic tooth movement and later during retention of the orthodontic alignment. Author's personal copy 30 CARMICHAEL & SÁNDOR Prosthodontic habilitation Depending on the location and number of implants to be restored, prosthodontic habilitation may involve the construction of single implant-supported crowns, multi–implant-supported fixed partial dentures, full-arch fixed bridges, and bar-retained complete overdentures. Screwretained restorations are recommended over cement-retained appliances because they allow for retrievability, facilitate maintenance and revision, enhance retention in situations of restricted interocclusal space, and permit shaping and molding of the peri-implant soft tissues during provisionalization. Further readings Altug-Atac AT, Erdem D. 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