Unilateral Lower Second Premolar Hypodontia May Be an Agenesis Subphenotype

Objectives: The etiology of tooth agenesis is still poorly understood. The identification of sub-populations with specific types of hypodontia (subphenotypes) would allow testing the specific hypothesis that certain genetic factors contribute to the specific subphenotype. The aim of this work was assessing a large cohort to verify if preferential tooth agenesis subphenotypes could be identified.

Methods: Panoramic radiographs of 1052 cases were examined and 1034 were used in this study. The presence of tooth agenesis was assessed in the study population.

Results: The frequency of tooth agenesis in the studied population was 3.77%. While bilateral cases did not differ in the frequency of agenesis by arch (p = 0.8), unilateral cases presented more often agenesis on the mandibular arch (p = 0.03). This result was clearly driven by the frequency of second premolar agenesis, which was the most common absent tooth in the studied population. Unilateral lower second premolar agenesis was found more often than bilateral agenesis (p = 0.047). Although not statistically significant, there was a trend for having more mandibular second premolars missing on the right side than on the left side (11 versus 4; p = 0.13).

Conclusions: Our findings that unilateral lower second premolar agenesis is more common than bilateral agenesis, with a trend for unilateral agenesis being more common on the right side, may suggest specific genetic factors may be differentially expressed depending on the side.