The purpose of this research was to create a method for predicting the persistence of primary molars in patients with multiple agenesis. Dental pantomographs (DPTs) from 51 males with agenesis of 5–17 teeth and 54 females with agenesis of 5–21 teeth were investigated. All patients (6 years 9 months to 16 years 7 months) had agenesis of one or both lower second premolars. Patients with ectodermal dysplasia and craniofacial anomalies were not included. The DPTs were classified into two groups according to tooth morphology and agenesis pattern.
Group I—ectodermal symptoms: screwdriver-shaped maxillary central incisors, invaginations in incisors or narrow incisors, taurodontic molar roots, and atypical agenesis. At least two of these ectodermal symptoms had to be present for classification into group I.
Group II: one or none of the criteria for group I.
Each group was subdivided according to the number of missing teeth. The degree of root resorption of the lower second primary molar was analysed and converted to a metric scale for statistical analysis. Ectodermal status (group I versus group II) was analysed as a binary outcome with agenesis and gender as covariates (logistic regression), whereas ordinary multiple regression was performed in order to study the dependency of root resorption score on gender, ectodermal status, and age.
The study showed that subjects with agenesis of more than seven teeth belonged more often to group I than group II, also when correcting for age differences. Root resorption of the primary molars was more severe in group I than in group II.