1.5 Dental Anomalies & Developmental Conditions
Key Takeaways
- Hypodontia excluding third molars affects roughly 4 to 6 per cent of the population, most often the lower second premolar and upper lateral incisor; six or more missing teeth is termed oligodontia
- Supernumerary teeth occur in roughly 1 to 3 per cent of the permanent dentition, are commonest as a mesiodens in the anterior maxilla, and are a recognised cause of failure of eruption of a permanent incisor
- Maxillary canine impaction affects about 1 to 3 per cent of people and is palatal in roughly 85 per cent of cases; palpate the buccal sulcus from age 9 to 10 and radiograph if the canine is not palpable by about age 11
- Amelogenesis imperfecta affects enamel only in both dentitions, whereas a Turner tooth is a localised enamel defect on a single permanent tooth caused by infection or trauma to its predecessor
- Multiple supernumerary teeth with delayed eruption suggest cleidocranial dysplasia, and multiple odontomes with osteomas and colorectal polyps suggest Gardner syndrome
Classifying Anomalies
Outcome B1.9 asks for the classification, aetiology, epidemiology and management of dental anomalies. The workable classification is by number, size, shape, structure and eruption.
Anomalies of Number
| Anomaly | Epidemiology | Management |
|---|---|---|
| Hypodontia (developmental absence of one to five teeth, excluding third molars) | About 4–6%; commonest are the lower second premolar, upper lateral incisor and upper second premolar; more common in females | Space management, orthodontic space closure or opening, resin-bonded bridge, denture, implant at skeletal maturity; multidisciplinary planning |
| Oligodontia (six or more missing, excluding third molars) | Around 0.1–0.3%; strongly associated with ectodermal dysplasia | Joint restorative, orthodontic and paediatric care; overdentures in childhood |
| Anodontia | Rare; essentially confined to syndromes | Prosthetic rehabilitation |
| Supernumerary teeth | About 1–3% of the permanent dentition, far less in the primary; male predominance; commonest site is the anterior maxilla | Remove where they obstruct eruption, cause displacement or pathology; observe if asymptomatic and unobstructive |
Supernumeraries are described by form: conical (small, peg-shaped, typically a mesiodens between the upper central incisors), tuberculate (barrel-shaped, often paired and palatal, a classic cause of failed incisor eruption), supplemental (a duplicate of a normal tooth, most often a lateral incisor) and odontome (compound, resembling multiple small tooth-like denticles, or complex, a disorganised mass).
Clinical rule: a permanent central incisor that has not erupted six months after its contralateral partner needs radiographic assessment. A tuberculate supernumerary or an odontome is a common cause, and early removal with space maintenance often allows spontaneous eruption.
Anomalies of Size and Shape
- Microdontia — commonly a peg-shaped upper lateral incisor (about 1–2%), frequently bilateral or paired with a missing contralateral lateral; managed by composite build-up or a veneer once growth is complete.
- Macrodontia — isolated or associated with hemifacial hyperplasia.
- Gemination — a single tooth germ attempts to divide, producing a bifid crown on one root; tooth count is normal.
- Fusion — two adjacent germs unite; tooth count is reduced by one. Counting the teeth is the discriminator between fusion and gemination.
- Concrescence — union by cementum only, usually of adjacent maxillary molars; matters because extraction of one may deliver both.
- Dens invaginatus (dens in dente) — infolding of enamel; a classic cause of early pulp necrosis in an otherwise caries-free upper lateral incisor; seal prophylactically where identified.
- Dens evaginatus and talon cusp — accessory cusps that fracture and expose pulp horns; reduce gradually or seal.
- Taurodontism — enlarged pulp chamber with apically displaced furcation; associated with amelogenesis imperfecta and some syndromes; complicates endodontics.
- Dilaceration — an abrupt bend, classically after intrusion of the primary predecessor; complicates extraction and endodontics.
Anomalies of Structure
| Condition | Tissue affected | Key features |
|---|---|---|
| Amelogenesis imperfecta | Enamel only, both dentitions, generalised | Hypoplastic (thin, hard), hypomineralised or hypomature (normal thickness, soft, chips) types; autosomal dominant, recessive or X-linked; often with anterior open bite and taurodontism |
| Dentinogenesis imperfecta | Dentine, both dentitions | Amber-grey opalescent teeth, bulbous crowns with cervical constriction, obliterated pulps, rapid attrition; type I with osteogenesis imperfecta, type II isolated |
| Dentine dysplasia | Dentine | Normal-looking crowns with rootless teeth (type I) or thistle-tube pulps (type II) |
| Molar-incisor hypomineralisation (MIH) | Enamel of one to four first permanent molars, often with incisors | Demarcated creamy to brown opacities, post-eruptive breakdown, difficult anaesthesia, hypersensitivity |
| Fluorosis | Enamel, generalised and symmetrical | Diffuse white flecking to brown mottling with pitting in severe cases; dose-related exposure before about age 8 |
| Turner tooth | Enamel of a single permanent tooth | Localised hypoplasia from infection or trauma of the primary predecessor — the localisation is the diagnostic clue |
Distinguishing these matters because management differs: MIH molars often need preformed metal crowns or planned extraction with orthodontic space management; amelogenesis imperfecta needs full-coverage protection and long-term multidisciplinary care; fluorosis is usually managed with microabrasion or bleaching.
Anomalies of Eruption and Position
- Ectopic eruption of the first permanent molar against the second primary molar; may resolve or need separation.
- Impaction. Maxillary canine impaction affects about 1–3%, and roughly 85% are palatal. Palpate the buccal sulcus from age 9–10; if the canine is not palpable by about age 11, radiograph and localise. Interceptive extraction of the primary canine in the mixed dentition improves the chance of spontaneous correction. Untreated impacted canines cause resorption of the lateral incisor root.
- Infraocclusion (submerged primary molars) from ankylosis; monitor, and intervene if the tooth falls below the contact point or the successor is displaced.
- Primary failure of eruption — a non-ankylosed tooth fails to erupt with normal follicular structures; orthodontic traction fails, so it is a diagnosis worth making before treatment starts.
- Delayed eruption — think of cleidocranial dysplasia (multiple supernumeraries, retained primary teeth, absent or hypoplastic clavicles), hypothyroidism, Down syndrome, or a local obstruction.
Syndromic Associations Worth Recognising
| Pattern | Consider |
|---|---|
| Multiple supernumeraries + retained primary teeth + clavicular defects | Cleidocranial dysplasia |
| Multiple odontomes + jaw osteomas + colorectal polyps | Gardner syndrome (APC) |
| Oligodontia + sparse hair + reduced sweating | Ectodermal dysplasia |
| Multiple odontogenic keratocysts + basal cell naevi + calcified falx | Gorlin-Goltz syndrome (PTCH1) |
| Hypodontia + cleft lip and palate | Clefting; teeth in the cleft line are frequently absent or malformed |
A 9-year-old has a bifid crown on an upper central incisor. Counting the teeth in the arch shows the normal complement for her age. Which anomaly does this indicate?
A caries-free upper lateral incisor in a 14-year-old is non-responsive to sensibility testing and has a periapical radiolucency. The radiograph shows an infolding of enamel extending into the crown. What is the most likely underlying anomaly?
At what age should the maxillary permanent canine be routinely palpated in the buccal sulcus, and what should prompt radiographic localisation?
A 7-year-old has creamy-brown demarcated opacities with post-eruptive breakdown on three first permanent molars and mild opacities on two incisors. The primary dentition is unaffected. What is the diagnosis?