Patterns of mandibular third molar impaction and its relationship to the inferior alveolar canal: retrospective Cone Beam Computed Tomography analysis in a group of Sri Lankan patients

Abstract

Impacted mandibular third molar (IMTM) tooth is one of the most commonly impacted teeth in the dental arch with a frequency of occurrence between 18-32 %. Cone beam computed tomography (CBCT) provides a precise three dimensional analysis of vicinity of IMTM which helps in surgical decision making. Objective of this study was to analyze the pattern of IMTM and the relationship of inferior alveolar canal to the tooth in 68 patients presented in year 2014 to Division of Oral Medicine and Radiology for preoperative CBCT assessment. The study sample included retrospective analysis of 112 IMTM teeth in 68 patients. Sample consisted 54.4 % females and 45.4 % males with average age of 28 years. Pattern of impaction was determined according to Pell and Gregory classification of IMTM and categorization of angulation of IMTM was done in accordance with modified Winter’s classification. Preoperative radiological assessment of IMTM was carried out with the aim of establishing relationship of inferior alveolar canal to the roots of IMTM, analyzing their morphology, predicting anticipated difficulty in exodontia of IMTM and complications such as damaging the inferior alveolar nerve. All the CBCT scans were re-assessed and measurements were done using the tools provided in the CBCT software. Pell and Gregory Class I B pattern of impaction was predominant in the sample with mesioangular impaction being the most commonly occurring angulation of impaction. The inferior alveolar canal was placed on buccal aspect of the root apex in 35.7% cases whereas in 33.9% it was lingually placed. Average depth of impaction was recorded to be 10.23mm and average mesio-distal and bucco-lingual lengths were found to be 11.15mm and 10.18 mm respectively. Two roots were present in 92% of the teeth studied. Pattern of impaction and the morphology of IMTM in current study comply with international norms except in few aspects.