An Evaluation of the Relation Between Variation in Arch Forms and Relative Parallelism of the Occlusal Plane to the Line Joining the Inferior Border of Ala of the Nose With Different Tragal Levels of the Ear in Dentulous Subjects: An In Vivo Study

Introduction The purpose of this study was to evaluate which of the three positions on the tragus (superior, middle, and inferior), when connected to the inferior border of the ala of the nose, was the most parallel to the natural occlusal plane in dentate patients, to correlate the level of the naturally existing occlusal plane with the ala-tragal line when the tragus was divided into three portions (superior, middle, and inferior), and to determine which position in the tragus occlusal plane is the most parallel. The study also evaluated the correlation between the variation of arch forms and the relative parallelism of the occlusal plane to the ala-tragal line at different tragal levels. Methods This study included 1405 subjects between the ages of 18 and 35 years. A custom-made occlusal plane analyzer was used to check the relative parallelism between the existing occlusal plane and the ala-tragal line when the tragus was divided into the superior, middle, and inferior portions. The Fox plane of the occlusal plane analyzer was placed on the occlusal plane and the paralleling rod was adjusted till parallelism was obtained. The point on the tragus (superior, middle, or inferior) at which parallelism existed was recorded. The study also measured the inter-canine and intermolar distance to find the type of arch form and related it to the position (superior, middle, or inferior) at which the ala tragal line was parallel to the occlusal plane. The assessment was done on both the right and left sides of the subjects. Results Out of the 2810 tragi, the most common location at which parallelism was established was the inferior part of the tragus, which accounted for 47% of the total. Seventy-one percent (71%) of the subjects showed ovoid arch form. When the variation of arch forms was compared to the level of occlusal plane, 46.8% of the subjects with tapered arch form, 54.5% of subjects with square arch form, and 46.0% of subjects with ovoid arch form had the level of the occlusal plane at the inferior portion of the tragus. Conclusion The result of the study indicated that in the majority of the tragi studied, 47% of the subjects had the occlusal plane parallel to a line joining the inferior border of the ala of the nose to the inferior part of the tragus. Irrespective of the arch form, the occlusal plane was found parallel to a line joining the inferior border of the ala of the nose and the inferior part of the tragus. Thus the tragal position did not show any correlation to the variation of arch forms.