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

Abstract

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 +/- 2.51 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.

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.