# Prevalence of lower second premolar agenesis and study of rhizolysis of primary second molars without permanent successor with 2 methods

## TL;DR

This study examines how often lower second premolars are missing and how the roots of baby teeth before them break down using two methods.

## Contribution

The study introduces two methods to assess root resorption in primary molars with no permanent successor.

## Key findings

- The prevalence of lower second premolar agenesis was found to be 3.4%.
- Root resorption in primary molars begins at age 9 and remains stable afterward.
- Healthy primary molars with no infraocclusion experience less root resorption.

## Abstract

The aims of this study were to estimate the prevalence of lower second premolar (2Pr) agenesis and to quantify rhizolysis of the preceding primary molars.

A descriptive and cross-sectional study was carried out to quantify root resorption of lower primary second molar (p2m) with permanent successor agenesis in panoramic radiographs using 2 methods: Bjerklin–Bennett method (graphical method by fractions) and ratios’ method (proportions).

3206 panoramic radiographs were reviewed. The final sample consisted of 174 p2m. With the graphical method, it was found that half of the sample had both roots without resorption. With the numerical method, it was observed that root length decreased with age. Almost half of them have infraocclusion and greater infraocclusion led to greater resorption. Healthy p2m showed less resorption.

The prevalence of 2Pr in the present study was 3.4%. The p2m with agenesis of the successor begin to resorb from the age of 9 years, remaining stable from this age. Those p2m without infraocclusion and healthy suffer less resorption. We consider both methods used to measure root resorption to be valid without the need for multiple sequential radiographs. We consider new studies necessary, expanding the sample and studying more variables that affect rhizolysis.