as double teeth)
Fusion: union of two normally separated tooth buds resulting in a joined tooth with confluent dentine (clinically seen as double teeth) and separate root canals
Concrescence: union of two teeth by cementum without confluence of dentine
1.4.2 Frequency
Varies; approximate prevalence rates are:Gemination: 0.22%Fusion: 0.19%Concrescence: 0.8% in permanent teeth and 0.2–3.7% in deciduous teeth
1.4.3 Aetiology/Risk Factors
Gemination and fusion: evolution, trauma, heredity and environmental factors
Concrescence: inflammation around roots
1.4.4 Clinical Features
Tooth count:Individuals with gemination have a normal tooth count. Clinically seen as double teeth but radiograph shows common root canal (Figure 1.4a,b)Individuals with fusion show a missing tooth due to the union of two teeth. Clinically seen as a large tooth crown (Figure 1.4c)Individuals with concrescence have a normal tooth count. Roots of two teeth are joined by cementum (Figure 1.4d)
Gemination: more common in the maxilla
Fusion: more common in the mandible
Concrescence: common in posterior maxillary region. Often, second molar roots are joined with adjacent impacted third molar roots
Gemination and fusion in deciduous teeth may cause crowding, abnormal spacing or delayed eruption of permanent teeth
1.4.5 Radiographical Features
Gemination: common root, common root canal
Fusion: separate roots and root canals
Concrescence: roots joined at cementum of two adjoining teeth. CBCT is useful for concrescence (gives a three‐dimensional image)
1.4.6 Diagnosis
History
Clinical examination
Radiography
1.4.7 Management
Depends on patient requirement
Usually not indicated unless symptomatic due to other causes, such as extensive caries, periodontal pathology or interference with tooth eruptionFigure 1.4 (a) Gemination; mandibular right incisors show gemination. Note the presence of all incisors. (b) Radiograph of bilateral gemination in maxillary central incisors. Note incisal notch and common root and root canal. (c) Fusion; shows left maxillary lateral incisor fused with the central incisor. (d) Concrescence; roots of two teeth are joined by cementum.(sources: a–c, by kind permission of Professor Charles Dunlap, Kansas City, USA); d, by kind permission of Dental Press Publishing, Brazil.)
1.5 Taurodontism and Dilaceration
1.5.1 Definition/Description
Taurodontism refers to an enlarged pulp chamber, apical displacement of the pulpal floor and no constriction at the level of the cementoenamel junction
Dilaceration refers to abnormal angulation or bend in the root
1.5.2 Frequency
Range:Taurodontism: 0.5–4.6% in general populationDilaceration: 0.3–15% in general population
1.5.3 Aetiology/Risk Factors
Taurodontism:Failure of Hertwig's epithelial root sheath diaphragm to invaginate at the proper horizontal levelNo genetic association
Dilaceration:IdiopathicInjury that displaces the calcified portion of the tooth germ from the uncalcified portion resulting in an abnormal angle of the root
1.5.4 Clinical Features
Taurodontism:May be unilateral or bilateralPermanent teeth are frequently affectedNo gender predilectionMay occur as a part of syndromes such as Klinefelter syndrome, Mohr syndrome and McCune–Albright syndromeIncreased frequency in patients with cleft lip, cleft palate and those with hypodontia.Increased chances of pulp exposure in decayed teeth with taurodontismDegree of taurodontism:hypotaurodontism (mild form)mesotaurodontism (moderate form)hypertaurodontism (severe form)
Dilaceration:Mandibular third molars are frequently involved followed by maxillary second premolars and mandibular second molarsRare in deciduous dentitionAsymptomatic in most casesAssociated with syndromes (e.g. Ehlers–Danlos syndrome)
1.5.5 Radiographical Features
Taurodontism:Commonly detected on routine radiographyInvolved teeth presume a rectangular shapeThe pulp chamber is exceedingly large with a greater apical–occlusal height than normalThe tooth lacks the usual constriction at the cervical regionRoots are exceedingly short and trifurcation or bifurcation may be seen a few millimetres above the apices of the roots (Figure 1.5a)
Dilaceration:Radiographically, detected as mesial or distal bend in the root (Figure 1.5b)Periodontal ligament space is normalDetected on routine radiographyFigure 1.5 (a)Taurodontism of the mandibular first molar shows abnormally large pulp chamber and short roots. (b) Dilaceration of an extracted tooth shows abnormal bend in the roots.(source: by kind permission of Professor Charles Dunlap, Kansas City, USA.)
1.5.6 Management
Taurodontism:No specific treatment required
Dilaceration:No treatment for mild dilacerationIf symptomatic due to gross dilaceration, tooth requires surgical extraction
1.6 Amelogenesis Imperfecta
1.6.1 Definition/Description
A group of inherited disorders caused by defects in the genes that encode enamel matrix proteins, resulting in defective structure of the enamel involving both dentitions
1.6.2 Incidence/Prevalence
Global prevalence: 0.5%
1.6.3 Aetiology/Risk Factors
Caused by mutations or altered expression in five genes:AMEL (amelogenin)ENAM (enamelin)MMP20 (matrix metalloproteinase‐20)KLK4 (kallikrein‐4)FAM83H. 6–16
Inheritance