Differences in various measurements on panoramic radiograph among erupted and impacted lower third molar groups

Objective: to determine the differences in various linear and angular measurements between erupted and impacted lower third molar group on conventional panoramic radiographs. methods: the quasi-experimental study based on non-probability convenience sampling and done at the national institute of oral diseases, karachi, comprised 140 patients having full dentition with bilaterally present mandibular third molars varying between ages of 18-30 years. after clinical examination, 280 lower third molars were divided into two groups; group a had erupted, while group b comprised impacted mandibular third molars. all radiographs were traced and measured for five variables to compare the two groups. for statistical purpose, spss version 10, and t test were used. results: retromolar space measured from xi (centre of ramus) was 31.60±3.33 mm in group a and 27.02±4.17mm in group b. retromolar space measured from anterior edge of ramus (aer) was 16.30±2.51mm in group a and 11.21±3.69 in group b. mesiodistal width was 13.39±1.44mm in group a and 13.80±1.58 in group b. retromolar space/width ratio was 1.22±0.20 for group a and 0.82±0.34 for group b. mean angulations in group a was 5.98±5.9° whereas 34.56±27.89°in group b. conclusion: the probability of eruption of the lower third molar increases if retromolar space measured from anterior edge of ramus (aer-7) and centre of rumus point (xi-7) is 13mm and 25mm respectively, provided the space/width ratio is greater than 1 and angulation is also vertical. mesiodistal width of the tooth has no significant role in impactions.