Maxillary Lateral Incisor Agenesis (MLIA)

In the permanent dentition, the type of congenital missing teeth varies from author to author and the demographic and geographic profiles. In Europeans, the mandibular second premolar is the most frequently absent tooth, followed by the maxillary lateral incisor and the maxillary second premolars (Bergstrom, 1977; Rolling, 1980; O'Dowling & McNamara, 1990; Aasheim & Øgaard, 1993; Nordgarden et al., 2002). In the Malaysian (Nick-Hussein & Majid, 1996), Israeli (Chosack et al., 1975) and American populations (Muller et al., 1970), the most frequently missing teeth are the maxillary lateral incisors. Focusing on MLIA the prevalence varies between 0.8 and 4.25% (Horowitz, 1966; Muller et al., 1970; Thilander & Myrberg, 1973; Magnusson, 1977; Rolling, 1980; Aasheim & Øgaard, 1993; Johannsdottir et al., 1997; Tavajohi-Kermani et al., 2002). In the Portuguese population a prevalence of 1.3 per cent was estimated, with a slightly higher frequency in females and also a unilateral occurrence more common than the bilateral occurrence (Pinho et al., 2005). Unilateral agenesis is often associated with dysmorphia or microdontia of the corresponding contralateral tooth (Pinho et al., 2009). This discovery led to the presumption that maxillary lateral incisors microdontia may represent a different expression of these molecular changes that lead to a defective development of the maxillary lateral incisors and it should therefore be considered with particular emphasis in the clinical diagnosis or in family history, allowing us to suspect of tooth agenesis (Pinho et al., 2010a). Hypodontia in the temporary dentition is a rare occurrence (0.4–0.9 per cent) and, when present, occurs more frequently in the incisor region, generally including an upper lateral incisor or a lower central or a lateral incisor (Ravn, 1971; Bennett & Ronk, 1980; Järvinen & Lehtinen, 1981; Johannsdottir et al., 1997; Pinho et al., 2005). When hypodontia occurs in the temporary dentition, most authors report 100 per cent absence of the permanent successor (Ravn, 1971; Bennett & Ronk, 1980; Järvinen & Lehtinen, 1981; Johannsdottir et al., 1997; Pinho et al., 2005) (Figure 1).