Co-relation of variables as determined from panoramic radiograph and evaluating their significance in eruption of permanent mandibular third molar

Abstract

Purpose of the Study: Purpose of the study is to investigate whether the variables associated with the permanent mandibular third molar (PMM3) and arch dimensions could be co-related and significantly differentiated between a fully erupted and mesially impacted PMM3 among a set of Indian population. Study Design: A standardized panoramic radiograph was taken of subjects of age 21 years and above. Patients with missing tooth from mandibular arch, subjects undergoing or having history of orthodontic treatment, subjects having disto-angular, horizontal or vertical impacted PMM3 were excluded from the study. Subjects were divided into 2 groups: (1) mesially impacted PMM3 and (2) vertically erupted PMM3. Following measurements were taken from acetate paper tracing of standardized panoramic radiograph: (1) Angulation of long axis of PMM3 to permanent mandibular second molar (theta) (2) Angulation of PMM 3 to base of mandible (theta 2) (3) Gonial angle (theta 3) (4) Mesio-distal width of PMM 3 (5) Retro molar space. From these measurements Ganss ratio (retro molar space /PMM3 crown width.) was calculated. Results and Conclusion: Results revealed that angle theta 1, angle theta 2, retro molar space and Ganss ratio were positively co-related and highly significant variables associated with the mesially and vertically erupted teeth as measured on panoramic radiograph. Using these variables a long-term study can be carried out to predict the ultimate position of lower third molar in the arch so that if there is a probability of the tooth being impacted at a later age, a prophylactic germectomy can be performed at an early age.