Comprehensive Guide to Dental Anomalies: Size, Shape, and Eruption

Framework of Dental Anomalies and Developmental Etiology

• Developmental Context: Dental anomalies are classified according to the specific stage of tooth development in which the disruption occurs. This begins with the migration of cranial neural crest cells into the brachial arches, resulting in the formation of two dental arches.

• Stages and Associated Conditions:

  • Induction and Proliferation: Anomalies at this stage result in numerical or structural abnormalities, including:

    • Hypodontia: Missing few teeth.

    • Oligodontia: Missing many teeth.

    • Anodontia: Total absence of teeth.

    • Supernumerary teeth: Extra teeth.

    • Double teeth: Fusion or germination.

  • Morphodifferentiation: Disruptions here lead to shape and size anomalies:

    • Macrodontia.

    • Dens invaginatus.

    • Dens evaginatus.

    • Talon cusp.

  • Histodifferentiation: Anomalies at this stage produce conditions such as regional odontodysplasia (covered in separate lectures).

Microdontia: Presentation and Epidemiology

• Definition: The microdontic tooth crown is significantly smaller than the normal dimensions for that specific tooth type.

• Common Locations: This condition most frequently affects the maxillary lateral incisors and maxillary third molars. Notably, these are also the teeth most commonly congenitally missing.

• Scope of Involvement:

  • Can affect a single tooth or multiple teeth.

  • In cases of severe hypodontia, microdontia may be generalized across all tooth types.

• Peg-Shaped Lateral Incisors: An alternative terminology for a microdontic maxillary lateral incisor. The mesial-distal width is narrower than normal, and the crown narrows to a point, often resulting in the complete absence of an incisal surface.

• Diagnostic Distinction: Practitioners must distinguish true generalized microdontia from cases where teeth are of normal width but set in wide, spacious jaws. This creates multiple spacings that give the illusion of small teeth; this is often a result of heredity (e.g., inheriting large jaws from one parent and normal teeth from the other).

• Treatment Strategies:

  • Extraction: May be the optimal choice for small, malformed premolars that cannot be effectively restored.

  • Restoration: Using resin-based composite or all-ceramic crowns to improve width and symmetry. This is common when one lateral incisor is more severely affected than its counterpart.

Macrodontia (Megadontia)

• Definition: The tooth crown is larger than the normal dimensions for that tooth type. Alternative terms include megadont or megadontia.

• Prevalence: Approximately $1.1\%$ in the permanent dentition. Prevalence in the primary dentition is currently unknown.

• Clinical Presentation:

  • Often involves the central incisor when appearing as a single tooth.

  • May occur alongside other anomalies; for example, a child may have a macrodontic tooth $11$ while simultaneously possessing a supernumerary lateral incisor.

  • Generalized Macrodontia: Like microdontia, a small jaw relative to tooth size can create the illusion of generalized macrodontia.

• Case Study Details: A specific patient OPG showed macrodontia in developing teeth $16$, $26$, $36$, $46$, and $47$. In this patient, teeth $36$ and $46$ exhibited extra roots, and several premolars (likely $15$, $25$, $35$, $34$, and $45$) were congenitally missing due to proliferation issues.

• Management Options:

  • Stripping Enamel: Removing enamel to reduce width. This risks exposing the pulp, causing pulpitis or tooth necrosis.

  • Contralateral Build-up: Building up the opposite tooth to create aesthetic balance.

  • Surgical/Orthodontic: Extracting the macrodontic tooth followed by orthodontic bracing (closing spaces, correcting rotations) or replacing the tooth with a bridged prosthesis of normal size.

  • Observation: Acceptance of the aesthetic if function is not impaired.

Double Teeth: Fusion, Gemination, and Concrescence

• Fusion:

  • Definition: The union of two or more teeth via enamel and potentially dentin.

  • Anatomy: Crowns share a groove; roots may be separate with distinct canals.

  • Clinically Significant: Result in a reduced number of teeth in the arch during counting. This is often counted as a single entity.

  • Clinical Implications: If found in primary teeth, there is a risk that only one permanent successor will develop underneath.

• Germination:

  • Definition: The budding of a second tooth from a single tooth germ.

  • Anatomy: Characterized by a single root and a single large canal.

• Concrescence:

  • Definition: Union of teeth via cementum only.

  • Etiology: Believed to result from space restriction during development.

  • Diagnosis: Found incidentally on radiographs because the union occurs below the cemento-enamel junction (CEJ). This is critical for extractions to prevent the accidental removal of an adjacent tooth.

• Prevalence and Treatment:

  • Double teeth prevalence: Primary dentition $(0.5-4.5\%)$; Permanent dentition $0.1\%$.

  • Treatment: Grooves are prone to dental caries. Surgical separation is not possible as cutting cementum results in periodontal defects and non-vital teeth.

  • Monitoring: Primary double teeth are highly correlated with permanent successors being missing, impacted, or double. Monitoring must continue until the permanent teeth successfully erupt.

Dens Invaginatus (Dens in Dente)

• Definition: The invagination of an accessory enamel organ into the dental papilla, creating a tooth-like structure within or adjacent to the pulp chamber.

• Clinical Signs: A pear-shaped invagination of enamel and dentin is visible on radiographs. The invagination is more radiodense than surrounding structures and has a narrow constriction at the tooth surface.

• Pathology: The invagination frequently communicates with the oral cavity. Because the lining is thin and close to the main pulp, caries can quickly penetrate, leading to necrosis of both the dens and the main pulp chamber.

• Location: Most common in maxillary lateral incisors, followed by central incisors, premolars, canines, and molars. Often occurs bilaterally.

• Management:

  • Preventive: Seal deep pits with pit and fissure sealant material immediately after eruption.

  • Endodontic: If necrotic, the tooth requires root canal treatment (RCT), potentially followed by a post-core and crown. A tell-tale sign of a necrotic "dead tooth" is the failure of the root apex to mature or close.

Accessory Cusps: Talon, Carabelli, and Dens Evaginatus

• Talon Cusp:

  • Description: A horn-like projection from the cingulum of a maxillary incisor, reaching toward the incisal edge. It contains enamel, dentin, and sometimes pulp.

  • Prevalence: Permanent dentition $(1-2\%)$.

  • Management: Fissure sealants in the grooves. If it interferes with occlusion, minimal reduction of the height can be performed while monitoring for pulp exposure.

• Cusp of Carabelli:

  • Description: A large accessory cusp on the palatal aspect of maxillary first molars (e.g., tooth $16$).

  • Clinical Note: The size of the cusp can make dental dam clamp placement difficult; however, once placed, the shape prevents the clamp from slipping.

• Dens Evaginatus (Leon’s Premolar):

  • Description: A tubercle protruding from the occlusal surface, predominantly in Asian ethnic groups (Chinese, Thai, Japanese, Indian, Filipino).

  • Risk: Common in mandibular premolars. The horn often fractures, exposing the pulp or dentin.

  • Management: Conservative resin composite over exposed dentin. If the pulp is exposed or the tooth becomes necrotic, root canal treatment is necessary. This is challenging in mixed dentition due to the child's age and potential lack of prior dental experience.

Disruptions in Tooth Eruption

• Infraocclusion and Ankylosis:

  • Ankylosis: The fusion of cementum directly to bone, lacking a periodontal ligament (PDL). This acts as a mechanical obstruction to eruption.

  • Consequences: The primary tooth (e.g., $85$ or $75$) ceases to erupt while adjacent teeth continue. This can cause adjacent teeth (e.g., $36$) to tip over the space.

  • Management: Monitor to see if the tooth sheds naturally within six months. If no resorption occurs, orthodontic consultation is required. If a successor is missing, the space might be used by an orthodontist for crowding relief or held for a future implant.

• Dilacerated Teeth:

  • Definition: A sharp bend or twist in the root or crown.

  • Etiology: Usually caused by previous trauma to a primary predecessor (often between ages $3-5$) which displaces the developing permanent tooth bud.

  • Diagnosis: Suspect dilaceration if there is a 6-month discrepancy in eruption compared to the contralateral tooth.

  • Management: Surgical exposure and orthodontic traction to guide the tooth into the arch.

• Ectopic Eruption:

  • Description: A tooth is physically obstructed by another (e.g., tooth $16$ stuck behind the second primary molar $55$).

  • Prevalence: $2-6\%$ in the maxilla; much rarer in the mandible.

  • Management: The aim is early diagnosis to prevent the premature loss of primary molars and subsequent pain/infection. If the primary molar is lost, the permanent molar (e.g., $16$) must be distalized using braces to regain space for the premolar successor.