Validity, reliability and reproducibility of retromolar space in predicting third molar eruption in different types of skeletal malocclusions

The purpose of this study was to analyze the reliability of retromolar space as a predictor for lower third molar eruption among subjects with different anteroposterior skeletal patterns. Materials and Methods: The material included orthopantomograms (OPG) and lateral cephalograms (LC) of 90 patients in which a total of 180 lower third molars were studied. The subjects were grouped according to the (ANB) angle and sub grouped according to the level of third molar as compared to the occlusal plane. On the OPG, mesiodistal crown width of third molar, retromolar space, space width ratio, third molar and second molar angulations, inclination between the lower second and third molars and gonial angle were recoded. Angles of maxillary and mandibular prognathism (SNA, SNB), ANB, and various mandibular lengths were calculated using lateral cephalogram. Results: Statistical analysis revealed that there is a strong correlation between the retromolar space and the eruption of mandibular third molar. Also retromolar space, mandibular lengths and third molar angulation were all increased in class III subjects. A strong correlation was found between gonial angle and the molar impaction rate. Conclusion: Retromolar space is the most valid, reliable and reproducible factor for predicting the impaction or eruption of lower third molars. Most of the linear and angular measurements favoring eruption were found in class III skeletal pattern.