Relationship between occlusal plane and ala-tragus line in dentate individuals: A Clinical pilot study.

Many methods have been used to establish the occlusal plane in complete denture prosthodontics. However, no single method seems to be fully accepted. Anteriorly, esthetic considerations help define the occlusal plane, and posteriorly the tongue, retromolar pad, and Stenson's duct are considered. Some dentists bisect the space between the residual ridges. The technique of using the ala-tragus line (Camper's line) to establish the occlusal plane is well documented. However, definitions of the ala-tragus line cause confusion, because the exact points of reference do not agree. For example, the glossary of prosthodontic terms states that the ala-tragus line runs from the inferior border of the ala of the nose to the superior border of the tragus of the ear while Spratley' describes it as running from the center of the ala to the center of the tragus. This article concerns us the exact relationship between the occlusal plane and ala-tragus line in dentate individuals.

To establish occlusal plane while recording maxillomandibular relation during fabrication of complete denture, many methods have been tried in the past. However, none of these methods proved its accuracy to perfection. Correct orientation of the occlusal plane plays a vital role in providing optimal esthetic and functional satisfaction. Improper orientation of this plane jeopardizes the coordination between the components of oro-facial articulatory complex[12] The plane of occlusion is formed after joining the incisal edges of the mandibular central incisors to the disto-buccal cusps of the mandibular first molars. The occlusal plane is defined as the common plane established by the incisal and occlusal surfaces of the teeth (GPT-8).[3] It is not a plane in the true sense of the word but represents the mean of the curvature of the inciso-occlusal surfaces of teeth. Various landmarks and techniques had been used over the years by clinicians and researchers for establishing this plane, which include: Orientating the occlusal plane with the buccinator grooves and the commissure of the lips[45] Terminating the occlusal plane posteriorly at the middle or upper third of the retromolar pad,[6] positioning the occlusal plane on the same level as the lateral border of the tongue[7] and many more concepts have been reported in literature.

Objective

The aim of this study was to correlate the best posterior reference point of ala-tragus line for orientation of the occlusal plane in dentate individuals.

Materials and Methods

In this cross-sectional study 50 dental students (35 females, 15 males) [Graph 1] with complete natural dentition and angles class I occlusion was selected between the age groups of 20–25 years. With the following exclusion criteria:

Graph 1

Gender distribution

No previous orthodontic or prosthodontic treatment

History of any esthetic surgery

Facial asymmetry and craniofacial anomaly

Overjet and overbite over 2 mm.

Following this, the subjects were asked to hold a Fox plane, covered with dental wax, between their teeth [Figure 1]. Left profile photographs were taken with a digital camera, with the subjects standing in natural head position. An adjustable tripod was used for adjusting the camera with the height of the Fox plane in the subjects, Then the photographs were traced [Figure 2].

Figure 1

Fox pane in position

Figure 2

Traced photographs

After tracing photographs, angle between Fox plane and superior border of ala-tragus, Fox plane and inferior border of ala-tragus and Fox plane and middle borders of ala-tragus line was measured and statistical analysis was performed using SPSS and CAD software, version 13. (IBM SPSS Statistics Ltd. (USA)).

Results

After statistical analysis, the results were tabulated and following results were drawn [Graph 2]: The angles between the occlusal plane and ala-tragus superior, ala-tragus middle, ala-tragus inferior, are significantly different from zero. It means no parallelism exists between the occlusal plane and the ala-tragus line. There is also no parallelism between the Fox plane and the ala-tragus with three posterior point locations in males and females; however, the results showed that in both sexes the inferior border of the ala-tragus line had the lowest mean value and stronger tendency to be parallel to the Fox plane.

Graph 2

Ala Trarus line in degrees

Discussion

There is a controversy for the orientation of the occlusal plane during complete denture fabrication. Some of the existing concepts regarding orientation of the occlusal plane in the edentulous patients are of the opinion that the occlusal plane has relation with Camper's line. It is the oldest, simplest and most commonly used method. It would seem desirable to locate it accurately and propagate its use while establishing the occlusal plane. The definitions of the ala-tragus line have created confusion. The exact points of references on tragus and ala are not categorically specified. Spratley described it as running from the center of the ala to the center (middle) of the tragus.[8] Boucher defines it as “The line is running from the inferior border of the ala of the nose to the superior border of the tragus of the ear.[9]” van Niekerk et al. used the inferior border of tragus as the posterior end of the ala-tragus line because it could provide sufficient space for the arrangement of maxillary posterior teeth.[10] Karkazis and Polysois showed in a cephalometric study that natural and artificial occlusal planes are not parallel to the ala-tragus line.[11] Dentulous individuals were evaluated to establish the definite correlation between camper's plane and occlusal plane so that a similar relation could be established in edentulous individuals. The average angles for natural and artificial teeth were 2.84° (3.45) and 3.25° (4.69), respectively. They used the center of the tragus as the posterior point for the ala-tragus line. Petricevic et al. reported a mean of 3.94° between the occlusal plane and the Camper plane,[12] which is consistent with the results of the present study.

Conclusion

According to the results of the present study, the inferior border of the tragus is suggested as the posterior reference for the ala-tragus line. Positioning of the occlusal plane depends on mature clinical judgment and must ultimately satisfy esthetics, function, and denture stability.