Evaluating the Relation of Posterior Occlusal Plane to Ala-Tragal Line According to Age and Sex

Evaluating the relation of posterior occlusal plane to ala-tragal line according to


INTRODUCTION
Edentulism is a pervasive problem all around the world. [1] There are various treatment options available for partial or complete edentulism including fixed or removable pros-thetic options. [2] In all the treatment options, the occlusal plane orientation is one of the factors that affects the esthetics, function, and success of prosthesis [3] , and the major reference for maxillary teeth arrangement [4] . The occlusal plane is defined as a hypothetical plane which coincides with the incisal edges of maxillary central incisors and mesiopalatal cusps of first maxillary molars. [3] This plane helps in normal deglutition and respiration, supplies mechanical, esthetic, and phonetic needs [5] , and determines the position and angulation of teeth settlement for prosthetic rehabilitations. Different anatomical landmarks suggested to determine the correct position and orientation of occlusal plane include upper lip, lip commissures [6] , lateral borders of the tongue, retromolar pad [7] , hamular notch, incisal papilla, and parotid papilla. [8,9] However, one of the most prevalent indices is the ala-tragus line [10,11] , which connects the auditory meatus to the ala of the nose [4] . The confusing variations that exist in the ala-tragus line definition go mainly back to disagreement about the exact location of the posterior reference point. [12,13] Some authors believe the superior border of tragus is the correct posterior reference point [14,15] , while the others introduce middle [16][17][18] , or even inferior point as the correct posterior reference. [19] On the other hand, different studies show conflicting results regarding the relationship between occlusal plane and available indices (Table 1). [2,4,12,13,[20][21][22][23][24][25] Meanwhile, the relation between available occlusal plane of dentate patients and ala-tragus line could be the best guide to find the correct orientation of this questionable plane to be used in edentulous patients who missed the predetermined indices relationships.

AIM
The present study aimed to determine which point of tragus plays the best role as the posterior reference of ala-tragus line according to the plane orientation in dentate patient, and evaluate if there are any differences according to age and sex. The null hypotheses were that the mid-tragus point was the best posterior index for ala-tragus line and there was no difference between different age and sex groups for the relation of occlusal plane and ala-tragus line.

MATERIALS AND METHODS
The present descriptive epidemiological study was carried out on 136 participants each giving their informed consent prior to their inclusion in the study. The study protocol was registered and approved in institutional Ethics Committee (IR.JSUMS.REC.1395.483). The study was performed in full compliance with the ethical standards of the revised Helsinki Declaration, and the information and photographs we saved were confidential.
The participants were divided into 2 groups based on their sex. Each group was divided into three subgroups by age: young adults (20-35 years old), middle aged (36-50 years), and old aged (more than 50 years). The inclusion criteria included systemically healthy participant with class-I Angle classification of occlusion, without skin diseases, periodontal diseases, or bone problems; existence of enough posterior maxillary teeth to determine the occlusal plane without interfering supra-eruption or drift; and lack of any history of orthodontic treatments, orthognathic problems, and facial or temporomandibular joint surgery.
A sterilized Fox plane was held in touch with the incisal edge of maxillary central incisors and first molar palatal cusps while the head was stabilized in chin part of panoramic radiographic system, and the Frankfort plane was kept parallel with the horizontal plane. This adjustment was confirmed using a horizontal line traced on the wall behind the patient's head. The Frankfort plane was kept parallel to the line by looking through the camera at the level of the mentioned line. Lateral photographs were taken from 1-meter distance, perpendicular to profile and at proper height for every participant. The position and distance of each patient's head was adjusted by the fixed distance between the chin positioner of panoramic system and the camera. Afterwards, three lines were traced by Auto-cad software (Autodesk Inc., California, USA) connecting inferior border of ala to either inferior, middle, or superior border of tragus on each photograph (Fig. 1). Auto-cad data were analyzed by SPSS (SPSS Inc, Illinois, Chicago) using chi-square test, and one-way ANOVA test (p<0.05).

RESULTS
The study was conducted with 136 participants, 81 men (58.9%) and 55 women (41.1%), with the mean age of 32.5 years (range 18-73 years). Table 2 summarizes the descriptive results on parallelism percentage of occlusal plane and ala-tragus line traced in different orientations. The occlusal plane showed higher percentage of parallelism with ala-tragus line traced to the inferior border of tragus in men. The highest percentage for parallelism in women was seen with superior border of tragus while this position showed the least percentage of parallelism in men. In other words, the parallelism between the occlusal plane and ala-superior border was more prevalent in women, while the men Folia Medica I 2022 I Vol. 64 I No. 5 Nayar [2] AT-S 5.8 No parallelism exists between the occlusal plane and the ala-tragus line, but AT-I was the most parallel line to the occlusal plane. AT-M 4.8

AT-I 4
Quran [21] Camp I 2. Between superior and middle 6.66% Between middle and inferior 8.57% Lahori [22] Sub inferior border The most parallel line to the occlusal plane was ALT2 in Cl I and Cl II participants and ALT3 in Cl III ones. Inferior border Superior border Sheikh [23]

ALT1
There was a significant relationship between age and occlusal plane; inferior border in young adults and superior border in old people is the reference line.

ALT3
Shigli [13] Superior The most parallel line to OP was middle border and the least one was superior border. Middle Inferior Chaturvedi [24] SA plane There was not significant relationship between sex and occlusal plane. The inferior point marked on tragus is the most appropriate point for marking the ala-tragus line.
MA plane

IA plane
Kumar [25] AT 1 16.44±2.08 AT 3 (inferior border) was the most parallel line to the occlusal plane. There was no relationship between sex and occlusal plane AT 2 13.67±1.93  Chi-square test showed a statistically significant difference for parallelism percentages in different genders (p=0.003). The relationship between age and occlusal plane was not statistically significant (p=0.65) (Fig. 2).
This study also evaluated the relationship between ala-tragal line and occlusal plane in different age groups and found no statistically significant difference (p>0.05). Kumar et al. reported no significant relationship between age and the angel between Camper (ala-tragal plane) and occlusal plane [25] ; however, Sheikh et al. reported significant differences between the ala-tragal line orientation and age. [23] Their results suggested the inferior border of tragus as the preferred reference point in young adults while the middle point was preferred in aged individuals.
Occlusal plane redetermination should be based on dynamic functional requirements. The posterior occlusal plane in natural dentition is oriented to coordinate with temporomandibular joint, masticatory muscles, and dynamics of mastication. Static criteria help us to find the lost plane orientation resulting from posterior tooth loss. The determined plane could be used for complete or partial fixed or removable prostheses supported by either teeth or implants. However, different studies suggest possible effects of age, sex, and nationality on plane routine determinants. Comparison by considering only two determinants (age and gender) is one of the limitations of the present study that could be a subject for further study on other determinants. The controversies call for further extensive studies to register special criteria for selecting the best orientation compatible with all available structural and functional determinants.

CONCLUSIONS
Considering the limitation of present study, the following conclusion can be made:

DISCUSSION
Finding the correct orientation of occlusal plane helps to gain an index pattern to arrange the artificial teeth in their natural positions, and consequently provides the best lip support, esthetic, and function in any type of prosthesis. The present study investigated the relationship between occlusal plane and different ala-tragus orientations. The null hypotheses were partially rejected since there was significant difference for the occlusal plane orientation in the different sexes, and the results confirmed higher percentages for parallelism with ala-tragus line traced from inferior border of tragus compared to superior or middle border; the general results were in accordance with the results reported by Shetty et al. [3] , Nayar et al. [2] , Hindocha et al. [12] , Chaturvedi et al. [24] , and Kumar et al. [25] , while in opposition to the results obtained by Priest et al. [4] , Firas [21] , Lahori et al. [22] , Sheikh et al. [23] , and Shigli et al. [13] The variations in the results of these studies could be attributed to race difference that calls for further studies, and using different index points in different race groups.
Considering the participant sex, the difference was also statistically significant (p=0.003); the superior border of tragus was preferred as posterior reference point in women, while the inferior border showed better results in men for tracing the ala-tragus line.