Facial growth and lower premolar extraction space closure

The study was undertaken to determine whether the rate of premolar extraction space closure was influenced by vertical growth of the face. Space closure was measured indirectly in 13 subjects using plaster record models. To reduce the influence of spontaneous anterior tooth movement on the size of the extraction space the first model was made at least 12 months after the extraction of the mandibular first premolars. Changes in the facial skeleton were measured by comparing films taken at the same time as the record models. In the sample examined (9 male, 4 female, mean age 13.9 years) mandibular rotation was the single most important explanatory variable (r = 0.81). However, mandibular rotation is merely a measure of the discrepancy in growth in anterior and posterior face heights and once these were included in the multiple regression equation, rotation was not a relevant explanatory variable. Posterior face growth, anterior face growth and length of observation accounted for up to 75% of the variance in the amount of space closure.