From Volume 41, Issue 9, November 2014 | Pages 811-815
Patients with hypodontia present clinical challenges in relation to function and aesthetics. In this two part series we will explore the clinical features of hypodontia in part 1 and will move on to discuss the inter-disciplinary management of hypodontia in part 2.
The term hypodontia refers to the developmental absence of one or more primary or secondary teeth, excluding third permanent molars.1 Hypodontia is a common dental anomaly with a prevalence that ranges from 2.6–11.3% worldwide.2 In the UK, however, studies are relatively consistent and suggest a prevalence rate of 4–4.5%.2,3 It is generally accepted that hypodontia occurs as a result of both genetic and environmental factors. Females tend to be more frequently affected than males.4 Mandibular second premolars are most commonly absent, followed by maxillary lateral incisors and second premolars.4 The primary dentition tends to be less affected with a prevalence of only 0.1–0.9%.5
Whilst hypodontia may occur in isolation, likely as a result of genetic mutation, it is also commonly associated with conditions such as cleft lip and palate, Down's syndrome and ectodermal dysplasia.6 Patients with absent teeth are referred to as having hypodontia and this can be classified as simple (one or two absent teeth), moderate (one or more absent teeth per quadrant) and severe (more than one absent tooth in all quadrants).7 Historically, the term anodontia refers to complete absence of teeth and oligodontia to when six or more teeth are missing. Regardless of the type, however, treatment aims are the same – to provide patients with a healthy, functional and aesthetic outcome throughout life.6
Absence of primary or permanent teeth can have a significant effect on facial aesthetics, which may have a negative psychological impact in some cases. A study of 451 patients reported that dissatisfaction with facial aesthetics was a major concern for patients with congenitally missing teeth.8 Following from this, a more recent qualitative study confirmed that child patients became increasingly concerned by their dental appearance as they grew older. Participants confessed to modifying their behaviour to conceal their teeth. Participants generally felt self-conscious and were uncomfortable in social surroundings. From this study, the main motivator for receiving current and future care was aesthetics.6 In cases of anodontia, or where a large number of teeth are missing, the situation is further complicated with a reduced lower face height which ultimately leaves the patient with an aged appearance.9
Individuals with hypodontia experience aesthetic, functional and psychological morbidity. Child patients may initially present with problems associated with mastication and speech.6 A study by Wong and co-workers looked at the oral health-related quality of life in 11–15-year-olds, affected by severe hypodontia (four or more absent teeth), and reported that 88% experienced functional limitations.10 These results were similar to those of Locker and co-workers,11 in whose study over three quarters of subjects reported experiencing functional limitations on a regular basis. These limitations included difficulty chewing and taking longer to complete a meal compared to others. In some cases, a restricted diet was necessary. The same study also reported that 8% of patients suffered speech difficulties as a result of hypodontia.11
It is important to note that hypodontia patients often do not simply have ‘missing teeth’ and there are several other associated features that impact on aesthetics and function. These will be considered prior to discussing hypodontia per se.
Patients with hypodontia of permanent teeth often present with retention of the primary predecessor. This should be an early warning sign to the practitioner that the permanent successor may be absent and the appropriate investigations completed.
One of the commonest scenarios is retention of a primary second molar tooth with hypodontia of the second mandibular premolar.12 Infra-occlusion of these teeth has been reported at 55%12 with up to 8.3%13 suffering from significant infra-occlusion (occlusal level below gingival level of adjacent teeth). Any marked infra-occlusion should be managed to prevent over-eruption of the opposing teeth and resultant occlusal derangement, leading to potential functional issues. This can impinge on the space for planned restorations (Figure 1). Any occlusal adjustments should be planned with the help of articulated study models, diagnostic wax-ups and orthodontic planning models (Keslings set-up) as necessary. These records aid patient understanding and allow the clinician to develop a treatment strategy and assess possible tooth movements and space requirements. Of course care should be taken to ensure that the result is achievable; whilst it is easy to move and re-shape plaster teeth, it will be much more challenging and time consuming in the clinical setting.
Retained primary teeth should be scrutinized in relation to coronal shape, root form and length, shade and structural integrity. They often have short clinical crown heights leading to suboptimal aesthetics, which can be compounded by over-eruption of the worn teeth giving a step in the gingival margin. Treatment options for these teeth include onlays, which help maintain tooth form and prevent food packing. The lifespan of retained primary teeth is uncertain, although several studies have suggested that canines and second molars have the best prognosis. Bjerklin and Bennett12 concluded that, if mandibular primary second molars were still present at age 20, then they had a good prognosis, with infra-occlusion and root resorption progressing slowly. Haselden et al suggest only primary canine teeth are predictable.14 Deciduous lateral incisors are rarely kept for the long term owing to their poor root profile.
Early removal of infra-occluding primary second molars should be considered. Future implant placement can be complicated if extraction of these ankylosed teeth is delayed due to the bony vertical defect present. Advocates of early removal suggest that vertical alveolar growth is not impeded and will allow the alveolar height to develop as adjacent teeth erupt during growth.15 The alveolar ridge may still be deficient in a horizontal plane but bony augmentation procedures are much more predictable in a horizontal rather than vertical direction.16 Opting to remove these teeth at an early stage can sometimes be a difficult decision but can be most effective when made early. Options such as space closure should also be considered.
Hypodontia has been associated with diminutive teeth, in particular peg-shaped lateral incisors.17 A peg lateral has been defined as an ‘undersized, tapered maxillary lateral incisor’(Figure 2).18 If the prognosis of these teeth is poor, then they are often extracted as part of the interdisciplinary treatment plan. If they are to be maintained, they are restored to normal tooth morphology by direct or indirect methods. Direct application of resin composite is an attractive option as it can be completed in a single visit, does not require any tooth reduction and is relatively economical, often not involving any lab work other than a diagnostic wax-up (Figure 3). Additionally, the composite can be easily adjusted, reshaped and repaired as required and is not highly abrasive, unlike poorly polished ceramic.
Composite resin restorations can be technically challenging, especially in the aesthetic zone. Peg-shaped laterals have specific challenges, including the often inevitable formation of an acute emergence angle; having to increase the diameter from the small size of the microdont tooth to aesthetically optimum size of a normal incisor, which can often be twice the width. Maintaining moisture control close to the gingival margin is difficult and the patient's oral hygiene regime should be excellent.
Indirect options include porcelain veneers and crowns. Depending on their precise position, diminutive teeth may only require minimal preparation, often resembling dentine crown preparations with removal of any sharp edges and the addition of a finishing line. Enamel is preserved to allow maximum bond strength and pulpal health is maintained.
Another consideration is the high prevalence of impacted maxillary canine teeth in patients with hypodontia. Peck et al reported 37% of patients with palatally displaced canines to have congenitally absent or diminutive lateral incisors.19 A more recent study found that 16% of subjects with palatally displaced canines had missing or diminutive lateral incisors or absent second premolar teeth.20 It has been hypothesized that the guidance of the permanent canine is influenced by the lateral incisor root. Therefore, a diminutive root or absent lateral incisor may cause canines to be ectopically positioned. It is the responsibility of the practitioner to monitor canine position through palpation.
Where canines are not palpable at 10 to 11 years of age, radiographic localization should be carried out.21 Patients should be referred for an orthodontic opinion where there is concern over canine position.
Figure 4 illustrates some of the challenges commonly associated when treatment planning hypodontia cases. This patient is a 13-year-old female who presented with congenitally absent UR2 and UL2 and a retained URC. The UR3 and UL3 have erupted into the lateral incisor position. A number of questions require consideration in order to advise the patient on her treatment options appropriately:
This case illustrates that often the answer does not lie in one field of dentistry but a collaborative team approach.
This paper has highlighted challenges faced by patients and clinicians in the management of hypodontia. The specific problems have been identified and discussed, such as missing teeth, diminutive teeth, retained primary teeth and ectopic canines. The second part of this paper will discuss the management of these issues.
