New teeth from old: IN BRIEF • Raises awareness of the incidence of retained deciduous teeth and common PRACTICE causes, particularly for GDPs. treatment options for • Outlines treatment options for such patients. • Describes situations where retention retained primary teeth of the deciduous tooth/teeth may be preferable. S. Robinson1 and M. F. W-Y. Chan2 VERIFIABLE CPD PAPER Retention of primary teeth beyond their expected exfoliation date is encountered relatively frequently. Most commonly this is due to absence of the permanent successor. In this article patient assessment and the restorative treatment options are discussed with particular emphasis on retention of the primary tooth/teeth in the medium to long-term. The restorative techniques that may be used to improve aesthetics and function of retained primary teeth are illustrated. Consideration of this minimally invasive approach is commended in such cases. Introduction Many of these problems can be overcome anomalies.9 It is essential that practition- Primary teeth may be retained for a with orthodontic and/or surgical interven- ers monitor the developing dentition and variety of reasons, the most common tion, a discussion of which is beyond the there should be a high index of suspicion being developmental absence of the per- scope of this article. if eruption of permanent tooth is more manent successor. While agenesis of pri- Agenesis of some permanent teeth is than one year later than expected, or has mary teeth is rare (0.1-0.9%),1 absence of more common than others. Third molars not commenced within six months of the permanent teeth is encountered relatively excepted, mandibular second premolars emergence of the contra-lateral tooth. frequently with a prevalence of 2.5-6.9%.2 are most frequently missing (2.9-3.2%), Particular attention should be paid to max- Variations between racial groups have followed by maxillary lateral incisors illary canines which should be palpable been noted as has a female predilection - (1.6-1.8%), maxillary second premo- buccally by the age of ten in most cases.10 a female: male ratio of 1.37:1 reported.2 lars (1.4-1.6%) and mandibular incisors Should concerns arise, early referral to a Various terms have been used to classify (0.2-0.4%)2 while the absence of other multidisciplinary team, often including the number of missing permanent teeth. teeth is relatively rare. It should be noted paediatric, restorative and orthodontic The absence of 1-5 teeth (except third when treatment planning that patients specialists, is advised. molars) is described as ‘hypodontia’ while with one missing permanent tooth are Careful assessment is essential for all severe hypodontia or oligodontia is the likely (83%)2 to have at least one other patients with retained primary teeth. absence of six or more teeth. Anodontia missing tooth however, the absence Following consideration of general issues describes the complete absence of of six or more teeth (oligodontia) is such as the patient’s health, motivation, permanent teeth.3 rare (0.14%).2 expectations and oral health, a local Even when the permanent tooth is The aetiology of dental agenesis has yet assessment should be made. Clinically present it may fail to erupt leaving the to be fully explained. There is undoubtedly this should focus on the coronal shape, primary tooth in situ. This can be a con- a genetic component5,6 with an autosomal colour and structural integrity of the pri- sequence of crowding, ankylosis of the dominant pattern of inheritance, variable mary teeth. The gingival level of these primary tooth or the presence of supernu- expression and incomplete penetrance.3 teeth and their relationship to the occlusal meraries or other obstructions.3 Maxillary Certain syndromes such as ectodermal plane should be noted as it is often coro- canines may become ectopic if the adja- dysplasia are associated with develop- nal to that of the permanent teeth. Inter- cent lateral incisor is diminutive or absent.4 mental absence of large numbers of teeth7 occlusal space may be reduced if primary and even anodontia.8 Environmental teeth have worn allowing over-eruption of factors may also be implicated such opposing teeth (Fig. 1). 1*Specialist Registrar in Restorative Dentistry, 2Consult- as trauma, infection, irradiation and Conversely, the gingival and occlusal ant in Restorative Dentistry, Leeds Dental Institute, 2 Restorative dentistry, Clarendon Way, Leeds, LS2 9LU endocrine disorders. levels may be apically located and inter- *Correspondence to: Dr Stephen Robinson occlusal space increased. This is com- Email: [email protected] Assessment of retained monly referred to as ‘infra-occlusion’ primary teeth Refereed Paper and is frequently caused by ankylosis. Accepted 22 June 2009 DOI: 10.1038/sj.bdj.2009.855 Often the general dental practitioner Ankylosis is fusion of the cementum to ©British Dental Journal 2009; 207: 315–320 will be fi rst to encounter developmental the alveolar bone thus preventing normal BRITISH DENTAL JOURNAL VOLUME 207 NO. 7 OCT 10 2009 315 © 2009 Macmillan Publishers Limited. All rights reserved. PRACTICE adaptive changes as facial growth carries Prognosis of retained primary teeth the adjacent occlusal plane coronally. If Among the most important considerations this progresses, it may appear that the pri- when managing patients with retained pri- mary tooth is ‘submerging’ or later it may mary teeth is their prognosis. Several stud- become completely ‘submerged’. Another ies have shown mandibular and maxillary cause of infra-occlusion is tipping of adja- primary canines and second molars have cent permanent teeth resulting in impac- a much better prognosis than incisors and tion of the primary tooth. Infra-occlusion fi rst molars.13,14 Primary mandibular sec- has been detected in 55% of retained ond molars have attracted most attention mandibular second molars11 though severe in the literature. Due to frequent absence Fig. 1 Worn primary teeth (62, 63) with loss of inter-occlusal space and low gingival level infra-occlusion, where the occlusal level is of the permanent second premolar, they below the gingival margin of the adjacent are commonly retained into adolescence teeth, is much less common affecting only and adulthood. Bjerklin,11 in a longitudinal 2.5-8.3% of retained primary molars.12 study, assessed the fate of retained lower In patients with several missing teeth, second molars from the age of 11-12 into there may be considerable derangement adulthood. Of 59 teeth in 41 subjects only of the occlucal plane - reduced occlusal seven were lost, none of which were after vertical dimension and inter-maxillary the age of 20. Infra-occlusion tended to space are frequently observed (Fig. 2). The progress very slowly and was absent in occlusion should therefore be carefully almost half the sample. Root resorption assessed particularly the vertical dimen- was described as slow and the authors Fig. 2 Oligodontia with irregular occlusal plane and reduced vertical dimension sion, retruded contact position, intercuspal concluded that if primary lower second position and excursive contacts. In patients molars are retained until the age of 20, with more challenging occlusal schemes, their prognosis is good. Other studies have articulated study casts are invaluable and found similar results15,16 (see Fig. 3). trial tooth adjustment and/or diagnostic Concerns have been raised with regard wax-up are often helpful. Additive proce- to periodontal bone loss on the mesial dures can be demonstrated to the patient by aspect of permanent molars when the applying orthodontic wax, uncured com- adjacent primary tooth is retained and posite or a temporary crown and bridge infra-occluded. Kurol17 studied this risk acrylic intra-orally. An aesthetic preview is in 68 individuals with 119 infra-occluded often more helpful in agreeing the desired primary molars and found only two cases aesthetics than a wax-up on a model, of signifi cant bone loss. These authors Fig. 3 A 74-year-old with an asymptomatic lower left second primary molar. Had although reductive procedures cannot be therefore concluded that there is minimal such a tooth been extracted and replaced trialled in the same way. The structure of associated periodontal risk. in adolescence or early adulthood, the adjacent teeth that may serve as possible restoration would almost certainly have bridge abutments should be assessed clini- Treatment options for required replacement on more than one occasion over the ensuing fi ve or six decades cally as should the alveolar bone volume. retained primary teeth The alveolus often ‘necks in’ apical to Retain – if the root and coronal structure retained primary teeth – a factor that can are good, the tooth is functionally and composite may be added, with or with- complicate implant placement. aesthetically acceptable, and there is no out the guidance of a diagnostic wax-up Radiographic assessment should include compelling orthodontic need for extrac- and silicone index. While some have sug- the length and form of the remaining root tion, a primary tooth may be retained gested poorer bond strengths of compos- structure, apical status, periodontal sup- intact. The benefi t of this approach is that ite to primary enamel,18 the authors have port and, if previous fi lms are available, minimal maintenance will be required and not found this to be a problem clinically the rate of root resorption. Vertical bone the primary tooth is likely to preserve the (see Figs 4a-g). height and inter-radicular space should bone and soft tissue architecture. If the pri- Indirect restorations such as compos- be considered, particularly if implant mary tooth does fail however, there may be ite, porcelain or gold onlays have been replacement is a proposed. If extraction insuffi cient space for an adult sized pros- described.19,20 In previously un-restored and replacement of the primary tooth with thetic replacement.