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

To determine the differences in various linear and angular measurements between erupted and impacted lower third molar group on conventional panoramic radiographs.

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.

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 +/- 2.51 mm 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 degrees whereas 34.56 +/- 27.89 degrees in Group B.

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.