Irfan Qamruddin, Wasif Qayyum, Syed Mahmood Haider, Seema Wasif Siddiqui, Faisal Rehan.
Differences in various measurements on panoramic radiograph among erupted and impacted lower third molar groups.
J Pak Med Assoc Jan ;62(9):883-7.

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.

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