A cephalometric study of the effect of extraction of lower first permanent molars.

The sample consisted of 28 patients (16 female: 12 male) from the records of the Orthodontic Department for whom the extraction of both lower first permanent molars was considered due to caries. The age ranged from 8-14 years (mean age 12.4). A cephalometric radiograph was taken prior to the extraction and after a mean of 18 months. No other treatment was done during the observation period. The radiographs were traced arid digitized using the GeLa program. A total of 16 points were digitized yielding 19 measurements (7 angular and 12 linear). The data were analyzed using 't' test and Pearson Correlation Coefficients in SPSS PC and compared to a control group matched for age and sex. Results showed that on average, the lower second molar moved forwards 5.9 mm. On average there was no change in angulation of the incisors to the bases. There was no significant change in the vertical relations of the jaws save that caused by normal growth and development. A significant correlation was found between the change in overbite and original overbite (r = -0.55, P < 0.01), the change in Li/A-Pog (r = 0.41, P < 0.05) and the change in facial proportions (r = -0.59, P < 0.001). The change in overjet was correlated with the change in Li/A-Pog (r = 0.58, P < 0.001) and change in Li/mand (r = -0.55, P < 0.01). The extraction of the lower first molars results in deepening of the overbite on average, but has no effect on the anterior facial height or any other vertical relationship. However, the increase in overbite is associated with lingual positioning of the lower incisor and the change in facial proportions. The change in overjet is related to lingual positioning and retroclination of the lower incisors.