A Study of the Morphology of Deciduous Mandibular Second Molars

Objectives. Variability in tooth morphology plays a significant role in the achievable results of restorative treatment. The purpose of this study was to identify variations in morphology of deciduous mandibular second molars and to compare their crown sizes and shapes in order to provide a detailed description of the morphological characteristics of these teeth.
Methods. The materials consisted of 142 (71 from boys and 71 from girls) dental stone casts of complete deciduous mandibular arches. Standardized photographs of the occlusal surfaces of the stone casts were obtained. The selected reference points on the photographs were digitized by an image analyzer, converted to an X-Y coordinate system, and input into a personal computer for data analysis. Eight linear and eight angular measurements were taken for each deciduous mandibular second molar. The deciduous mandibular second molars were classified as five-, six-, seven- and eight-cusp groups.
Results. Thirty-six percent of the deciduous mandibular second molars were comprised of five cusps, 52% were comprised of six cusps, 11% were comprised of seven cusps, and 1% was comprised of eight cusps. The eight-cusp group had three accessory cusps (ML, MR, and D). The six-cusp group was subdivided into 6ML, 6MB, and 6D types, while the seven-cusp group was subdivided into 7MLD and 7MLMB types according to the positions of the accessory cusp. Most teeth in the six-cusp group were of the 6ML type. Measurements of Ll, L2, L5, and A6 were significantly smalle; in the five-cusp group than in the 6ML type in boys; however, no significant difference was observed in girls.
Conclusions. The crown shape and size of deciduous mandibular second molars might be influenced by the existence of an accessory cusp in Taiwanese boys.