Abnormalities of teeth

• Developmental defects of the teeth include opacity/hypomineralisation, hypoplasia, discoloration, fluorisis, amelogenesis imperfecta and dentinogenesis imperfecta
• Opacity is also called hypomineralisation, describes a defect in the quality and mineral content of the enamel, resulting in a softer and more porous enamel
• Opacity: incomplete mineralisation of enamel results in a change in porosity; the defect is located below the intact enamel surface
• Hypoplasia refers to a defect in the quantity of enamel (rather than the quality)
• Hypoplasia results in a breach in the surface continuity; there may be pits, grooves, and a reduced thickness of the enamel/missing enamel
• Hypoplasia is caused by failure of enamel matrix formation during development
• Discoloration can be extrinsic (superficial, occurs after tooth eruption so it is not really a developmental defect) or intrinsic
• Extrinsic discoloration may be due to poor oral hygiene, smoking, drinking coffee, etc.
• Intrinsic discoloration results from a developmental defect of enamel or internal staining of teeth that causes changes in enamel color
• Discoloration: the actual pigmented substance is usually in the dentine, but will affect the appearance of enamel (e.g. a necrotic tooth after trauma)
• Fluorosis results from consuming too much fluoride during tooth development
• Fluorosis effects range from tiny white flecks on the tooth (manifests as hypomineralisation) to confluent opacities, which make the entire crown lack translucency
• Amelogenesis imperfecta is when enamel formation is disturbed with regard to the mineralisation stage of the matrix formation stage
• In amelogenesis imperfecta, enamel on all the teeth in the dentition are affected to the same extent
• Dentinogenesis imperfecta is also called opalescent dentition, where the enamel might appear more translucent to give the teeth a glassy appearance
• Dentinogenesis imperfecta: due to the underlying dentine defects, the overlying enamel may appear discolored and can chip/wear away easily as the enamel cannot properly adhere
• Dentinogenesis imperfecta may occur in isolated or be associated with a systemic disorder such as osteogenesis imperfect, and results from failure of odontoblasts to differentiate properly
• Supernumerary/hyperdontia teeth are additional teeth than the normal dentition
• Mesiodens: extra tooth in premaxilla, between the two central incisors
• Paramolar: extra tooth in the premolar/molar area
• Distomolar: extra tooth distal to third molars
• Supplementary teeth: extra tooth but with the same appearance as normal dentition
• Supernumerary teeth may resemble a tooth of the normal series (supplementary teeth) or present as a conical (pointed, peg-like) or tuberculate (cylindrical, rounded) form
• Supernumerary teeth are commonly found in patients with cleidocranial dysplasia or Gardner syndrome
• Hypodontia refers to having less teeth than normal, usually congenital
• Anodontia: complete absence of one or both dentitions
• Hypodontia is commonly found in patients with ectodermal dysplasia, clefting, and Down syndrome
• Microdontia refers to one or more teeth being smaller than normal, mostly affects the maxillary third molars and lateral incisors
• Macrodontia/megadontia is a condition where the teeth are larger than normal, often occurs with central incisors
• Macrodontia may be associated with facial hemihyperplasia
• Dens invaginatus/dens in dente is a condition characterised by the invagination of the enamel and dentine into the pulp chamber
• Dens invaginatus usually occurs on the incisors and canines
• Dens evaginatus/evagination/Leong’s premolar refers to when an enamel-covered tubercle projects from the occlusal surface, usually on the premolars
• Dens evaginatus usually occurs bilaterally and is common among Asians, especially Chinese
• Germination: a single tooth bud attempts to divide, resulting in a single tooth with a large, bifid crown with typically a single root and pulp chamber
• Fusion: two adjacent tooth buds unite during development, forming a single large tooth with two distinct crowns/roots and possibly separate pulp chambers
• Talon cusps are horn-like projections of the cingulum of maxillary incisor teeth, which may reach and contact the incisal edge of the tooth
• Mulberry teeth/Hutchinson's teeth have tapered crowns and medial notching of the incisal edge, very rare as it is associated with congenital syphilis
• Taurodontism is characterised by an enlarged pulp chamber and short roots
• Taurodontism results from the failure of the proper invagination of Hertwig’s epithelial root sheath during odontogenesis