*3.2.2 Prevalence*

The prevalence of hypodontia in CLP sample has been reported to range from 31.6–77% [50, 62–64]. In addition, the prevalence of hypodontia also increases with severity of the cleft [3, 44, 61, 65].

Ranta found that in complete cleft cases, almost every fourth (24%) of the upper second premolar was found to be missing [61].

However, other authors found that the maxillary lateral incisor was the most commonly missing tooth (41.7%), followed by the maxillary second premolar (18.3%) [50, 62]. Due to its proximity to the cleft defect, the cleft-sided maxillary lateral incisor is the most vulnerable to maldevelopment and iatrogenic injury, hence explaining its high frequency of being missing [66]. It was similarly reported as the most commonly missing tooth in CLP patients with a frequency ranging from 19.2–39.3% [3, 17, 44–47].

In a non-cleft population, Brook (1984) reported that the prevalence of hypodontia in British school children was 4.4%; the most commonly missing tooth was the mandibular second premolar [67]. The lower second premolar was the most commonly missing tooth in 26.1% of the Singapore Chinese orthodontic population with hypodontia. The lower incisor was the next most commonly missing tooth in 21.6%, followed by the upper lateral incisor in 20.5% of the population [68]. In Caucasians, the next most commonly missing tooth would be the maxillary lateral incisors, followed by the maxillary second premolar [69].

## *3.2.3 Primary vs. permanent dentition*

Hypodontia, in contrast to supernumerary teeth, is found to be more prevalent in the permanent dentition than primary dentition in CLP patients [43, 44, 52, 61].

**9**

*Dental Development and Anomalies in Cleft Lip and Palate*

One hypothesis for hypodontia which explains these findings is the Butler's field theory (1939) that postulated teeth were not individual structures but constituted a series of different morphological classes with the most stable tooth at the mesial

Eerens et al. also demonstrated a higher occurrence of hypodontia in the cleft group and sibling group as compared to the normal, non-cleft control group, hence suggesting some relationship between the genetic factors controlling clefting and

Among the genetic factors involved in craniofacial development are members of the *Msx* homeobox gene family [71] and till date, *Msx1* has shown good evidence of involvement in human orofacial clefting and tooth agenesis [71–76]. A missense mutation resulting in an arginine to proline substitution within the homeodomain of *Msx1* causes selective tooth agenesis in humans, an autosomal dominant phenotype affecting the second premolars and third molars of the

CLP patients present with a higher prevalence of supernumeraries, more commonly found at the lateral incisor region adjacent to the cleft [17, 44, 46, 50, 54, 77–79]. The prevalence of a supernumerary lateral incisor in CLP patients ranged

In contrast, a lower prevalence of supernumeraries is found in normal children, ranging from 0.46–3.4% across all nationalities [80–82]. In a local study carried out on 408 normal Singaporean Chinese patients, the prevalence of hyperdontia was found to be 7.1%, with most of the supernumeraries found in the

It has also been reported that supernumeraries occur more frequently in the primary dentition than in the permanent dentition in CLP patients [44, 46, 47, 49, 61]. However, this finding was disputed in the study by Vichi and Franchi which noted a higher prevalence of supernumerary lateral incisors in the permanent denti-

Some authors attribute this finding of higher prevalence of supernumerary lateral incisor in CLP patients to the close proximity of the lateral incisor tooth bud to the cleft, hence a higher susceptibility to division or modification of the tooth bud or separation of the epithelial remnants, resulting in a supernumerary tooth

togenic regions having the potential to develop lateral incisors [46].

Tsai et al. proposed that there could be two odontogenic origins for the maxillary lateral incisors, one from the maxillary process and one from medial nasal process. The two processes are unable to fuse due to the cleft, resulting in two separate odon-

end. The distal tooth in each class was evolutionarily less stable [70].

*DOI: http://dx.doi.org/10.5772/intechopen.88310*

*3.2.4 Aetiology*

hypodontia [41].

secondary dentition [72].

**3.3 Supernumerary teeth**

from 5.1% – 22.1% [47, 50, 52, 61, 62].

*3.3.2 Primary vs. permanent dentition*

tion (22.1%) than in the primary dentition (19.5%) [52].

*3.3.1 Prevalence*

premaxilla area [83].

*3.3.3 Aetiology*

forming [76, 77].
