Assessment and determination of human mandibular and dental arch profiles in subjects with lower third molar impaction in Port Harcourt, Nigeria

AIM: The aim of this study was to determine the normal size of the mandible and the difference in dental arch length and total teeth size space that is necessary to prevent lower third molar impaction. BACKGROUND: The mandible is an important component of facial skeleton and its morphology is relevant to the determination of acceptable aesthetics. In addition, function of the dentition is dependent on the available space for positioning of all the teeth including the third molar, and for enough space to be created, the sizes of the mandible and dental arch must be within normal ranges. MATERIALS AND METHODS: Impaction of the lower third molar was assessed by clinical evaluation and radiography. The total length of the mandible is determined by adding the distance between the midpoint of the tragus and soft tissue around the angle of the mandible to the distance between the angle and the soft tissue in the region of the chin. Mandibular width is the distance between the two angles of the mandible. The teeth sizes of the three anterior teeth, the two premolars, and the two molars were measured with a divider/ruler and recorded. The anterior-posterior distance of the arch from the midline to the retromolar pad was also measured. RESULTS: There were 44 (53%) females and 39 (47%) males. Eighty-one (97.6%) of the participants were between 16 and 23 years old, while 2 (2.4%) were in the fourth decade. There were 38 (45.8%) cases of impaction and 45 (54.2%) cases of unimpacted mandibular third molar. The means/standard deviation values for mandibular length for males in each group are 18.20 ± 0.98 and 18.20 ± 1.13 cm, respectively. The values for mandibular length for females in each group are 17.20 ± 0.76 and 17.60 ± 1.07. There are significant differences between the genders for mandibular length (P < 0.05, 95% CI). The means/standard deviation values for mandibular width for both genders in each group are also shown. There are also significant differences between the genders for mandibular width (P < 0.05, 95% CI). Normal sized mandible should have a length within or above 17.22–19.33 cm in males and 16.44–18.67 cm in females, while normal dental arch-total teeth size difference range should be within or above 0.71–1.20 cm in males and 0.76–1.10 cm in females in order to accommodate a properly erupting third molar. CONCLUSIONS: Based on these figures, clinicians may be justified to perform a preventive or therapeutic surgical removal of the impacted lower third molars of the postpubertal patients whose parameters fall below these set values. This study is also useful for evaluation of patients who would need orthognathic and reconstructive surgeries.