Aim: The use of the ala-tragus line (ATL) to orient the occlusal plane (OP) is controversial because there is a lack of agreement on the exact points of reference for this line. This study determined the relationship between the natural OP and ATL which was established by using the inferior border of the ala of the nose and (1) the superior border of the tragus (ATL1), (2) the tip (ATL2), and (3) the inferior border of the tragus (ATL3).
Materials and methods: Lateral cephalometric radiographs were taken of each subject by a standard method and tracings were obtained on acetate paper to show the OP and the three ala-tragus lines. The relationship between the OP and each of ATL was measured for each subject. Mean and standard deviation values were then calculated for the relationship. Statistical analysis was performed using repeated measure analysis of variance followed by Bonferroni pairwise comparisons and Student's t-test (α = 0.05).
Results: Significant differences were noted between the three mean angles (p = 0.046). The mean angle (3.275 degrees ± 2.54) formed by OP and ATL2 was significantly the smallest (p < 0.05).
Conclusion: The ala-tragus line, extending from the inferior border of the ala of the nose to the tip of the tragus of the ear presented the closest relationship to the natural occlusal plane.