Relationship between the Occlusal Plane corresponding to the Lateral Borders of the Tongue and Ala-tragus Line in Edentulous Patients

Definitions of the ala-tragus line (ATL) cause confusion, because the exact points of reference for this line do not agree. This study determined the relationship between the prosthetic occlusal plane (OP) corresponding to the lateral borders of the tongue and ATL which was established by using the inferior border of the ala of the nose and (1) the superior border of the tragus (ATL 1), (2) the tip (ATL 2) and (3) the inferior border of the tragus (ATL 3).Neutral zone moldings using phonation and autopolymerizing acrylic resin were recorded and leveled with the lateral borders of the tongue. Lateral cephalometric radiographs were taken of each subject by a standard method. Tracings were obtained on acetate paper to show the prosthetic OP and the three ATLs. The relationship between the prosthetic 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).Significant difference was found between the three mean angles (p = 0.001). There was no significant difference between the mean angle (5.00° ± 4.38) formed by OP and ATL 2, and the mean angle (4.90° ± 3.50) formed by OP and ATL 3 (p = 1.00) which revealed the smallest.The findings of this study indicated that ATLs, extending from the inferior border of the ala of the nose to (1) the tip of the tragus of the ear, and (2) the inferior border of the tragus presented the closest relationship to the prosthetic OP corresponding to the lateral borders of the tongue.When the ATL is used for orientation of the OP in denture construction, it would seem preferable to define it as running from the inferior border of the ala of the nose to the tip or to the inferior border of the tragus of the ear.