Evaluation of Parallelism Between Ala-Tragus Line and Occlusal Plane in Natural Dentition Among Young Dentate North Indian Subjects: A Photographic Study Manu Rathee 1 Mohaneesh Bhoria 2 M.D.S, D.N.B M.D.S. Department of Prosthodontics, Post Graduate Institute of Dental Sciences, Pt. B.D Sharma University of Health Sciences Rohtak, Haryana, India. Corresponding Author: Professor Dr. Manu Rathee, Head of Department of Prosthodontics Post Graduate Institute of Dental Sciences, Pt. B.D Sharma University of Health Sciences, Rohtak, Haryana, India. PIN 124001. Email: ratheemanu@gmail.com Abstract Purpose: Establishment of the lost natural occlusal plane is must for developing an occlusion especially in complete denture prosthodontics. However, obvious controversies have been observed in the literature regarding the posterior reference point of the ala-tragus line, precisely parallel to which the occlusal plane can be established in complete denture prosthodontic practice. The aim of this study was to determine the parallelism of the occlusal plane in natural dentition to ala-tragus line among young dentate North Indian subjects. Method: A total of one hundred young participants (50 male, 50 female) with full complement of teeth and Angel s Class I occlusal relationship were included for standard facial photograph with Fox plane held between teeth. Digital tracing on photographs was carried out and the angles between the natural occlusal plane (Fox plane) and the ala-tragus line with superior, middle, inferior border of tragus as posterior reference point were measured. Descriptive statistics, one sample t-test and independent t-test were used. Results: In lateral view, no parallelism was observed as one sample t-test showed angle varied significantly from zero with three posterior reference points. In general, lowest mean angle noted was with middle reference point. However, among male and female subjects, the lowest mean angle noted was with the middle reference point and inferior reference point, respectively. The t-test for independent samples showed no statistically significant difference on right and left side. Conclusion: There was no parallelism between the natural occlusal plane and the ala-tragus line with three posterior reference points namely superior, middle and inferior border of the tragus; however, the middle reference point on tragus had stronger tendency to be parallel to the Fox plane with lowest mean angle. Key words: Ala-tragus line; Camper s line; Fox plane; Occlusal plane; Prosthetic plane. How to cite this article: Rathee M, Bhoria M. Evaluation of parallelism between ala-tragus line and occlusal plane in natural dentition among young dentate North Indian subjects: A photographic study. J Pak Prosthodont Assoc 2014; 02 (02): 80 85. Introduction The establishment of orientation of occlusal plane is one of the most important clinical procedures in prosthetic rehabilitation of edentulous patients. As it affects aesthetics, function and denture stability, it should be reconstructed as near as possible to the occlusal plane of lost natural teeth. [1] Also to proceed clinical and laboratory phases simultaneously, it is necessary to precisely record the occlusal plane to orient dental casts on the articulator. 80
Various techniques have been evolved as well as several intraoral and extraoral landmarks for orientation of the occlusal plane. [2] [3] Consequently, under consensus of many opinions the most common extraoral landmarks used to establish the occlusal plane is the use of the ala-tragus line. [4] [5] However, difference in view of many authors on best position of posterior reference point raises controversies on the exact point of reference on the tragus of the ear. The defined posterior reference points on the tragus of the ear are superior, middle and inferior point. Hence, it is not precisely defined and variation has been observed. This study aimed to evaluate the parallelisms between the occlusal plane in natural dentition and ala-tragus line among the young dentate North Indian population. Materials and Methods One hundred young adults (50 male, 50 female) with full complement of teeth and Angel s Class I occlusal relationship were selected. Subjects with previous orthodontic and prosthodontic treatment, history of aesthetic surgery, facial asymmetry and craniofacial anomaly, over-jet and overbite more than 2 mm, previous craniofacial trauma or temporomandibular disorders were excluded. Ethical approval was obtained from the Institutional Ethics Committee (PGIDS/2014/IEC/116). Written consent was obtained from all selected subjects and they were asked to gently hold Fox s Occlusal Plane Device between the teeth while standing in natural head position (Figure 1). Figure 1. Subject in Natural Head Position with Fox plane clenched between natural teeth. Fox Plane permitted the extra-oral view of occlusal plane orientation. Standard facial photographs were taken using a digital camera (Canon 600D camera, Canon 80-135 mm Macro lens), and a macro ring lite flash (DIGIPRO DP690) on an adjustable tripod (Tanner TR303) elevated to the height of the Fox Plane for digital documentation. Digital tracing of the photographs was carried out by marking a line joining the anterior and posterior reference points. Anterior reference point was marked at the lower border of the ala of the nose and posterior reference points were marked on the tragus of the ear at its superior, middle and inferior border. Following lines were drawn using the software: A line parallel to superior border of Fox plane (FxP), A line from the inferior border of the ala of the nose to superior border of the tragus (ATs), A line from the inferior border of the ala of the nose to middle border of the tragus (ATm), A line from the inferior border of the ala of the nose to inferior border of tragus (ATi). The Digimizer Image analysis (MedCalc Software, version 4.2.5.0) was used for angle measurements between these reference lines. (Figure 2). 81
Figure 2. Digital planes drawn on the lateral standard photograph and measurements recorded. Results One sample t-test showed that the angles between the occlusal plane and ala-tragus line with three different posterior reference points varied significantly from zero. Hence, no parallelism was observed between these planes. The lowest mean angle noted was with middle reference point on tragus of ala-tragus line i.e. 3.6 0 and 3.5 0 on right and left side respectively. (Table 1) Descriptive statistics, one sample t-test and independent t-test were used. P value less than 0.05 was considered significant. Hypothetical population mean value was considered zero in one sample t-test, as it was supposed that the occlusal plane and the ala-tragus line are parallel to each other. Table 1. Angle (mean and standard deviation) between Fox plane and Ala-tragus line with three posterior reference points on right and left side Angle Right (n=100) Left (n=100) SD t p SD t p FxP-ATs 5.5 3.36 16.27 <.0001 5.1 3.04 16.86 <.0001 FxP-ATm 3.6 2.63 13.72 <.0001 3.5 2.77 12.55 <.0001 FxP-ATi 4.6 3.55 12.94 <.0001 4.6 3.81 11.97 <.0001 Angle: 1. FxP- fox plane. 2. ATs, ATm, ATi Ala-tragus line with superior, middle, inferior posterior reference point on tragus, respectively. 82
Table 2. Angle ( mean and standard deviation) between Fox plane and Ala-tragus line with three posterior reference points in female and male subjects Female (n=50) Male (n=50) Angle Right Left Right Left SD t p SD t p SD T p SD t p FxP-ATs 3.4 2.48 9.8 <.0001 3.6 2.5 10.3 <.0001 7.5 2.88 18.4 <.0001 6.6 2.81 16.7 <.0001 FxP-ATm 3.3 2.66 8.7 <.0001 3.3 3.2 7.3 <.0001 3.9 2.58 10.8 <.0001 3.6 2.26 11.3 <.0001 FxP-ATi 6.5 3.78 12.2 <.0001 6.4 4.1 11.2 <.0001 2.6 1.86 10.05 <.0001 2.7 2.31 8.1 <.0001 Angle: 1. FxP- Fox plane 2. ATs, ATm, ATi Ala-Tragus line with superior, middle, inferior posterior reference point on tragus, respectively. In female subjects, the middle reference point of alatragus line showed lowest mean angle 3.3 0 on both right and left side. Whereas in male subjects the inferior reference point of ala-tragus line showed lowest mean angle 2.6 0 and 2.7 0 on right side and left side respectively. (Table 2) The t-test for Independent samples showed no statistical significant difference on right and left sides. (Table 3) Table 3. Angle (mean and standard deviation) between Fox plane and Ala-tragus line with three posterior reference points on right and left side. FxP-ATs FxP-ATm FxP-ATi difference t p difference t p Right 5.5 3.7 4.59-0.32-0.72 0.47-0.19-0.52 0.6 Left 5.1 3.5 4.61 difference t p 0.01 0.04 0.9 Angle: 1. FxP- fox plane 2. ATs, ATm, ATi Ala-tragus line with superior, middle, inferior posterior reference point on the tragus, respectively. Discussion Occlusal plane is the missing determinant in the edentulous patients. Orientation of occlusal plane using ala-tragus line is in practice for compete denture fabrication. A common method of establishing the orientation of missing occlusal plane clinically is to make it parallel to ala-tragus line, a line running from the inferior border of the ala of the nose to some defined point on the tragus of the ear, 83 usually considered is the tip of the tragus. It is frequently used, with a third point on the opposing tragus, for establishing the ala-tragus plane. Ideally the ala-tragus plane is considered to be parallel to the occlusal plane. It is also called Camper s line.6 However, investigations into the clinical reliability of Camper s line serve only to compound the confusion, as Augsburger 7 detected deviations in the angle of occlusal plane from Camper s line (3.2-7.85 degree) in
dentate patients of different facial types. Whereas, Karkazis and Polyzois 8 did not detect correlation between Camper s line and the occlusal plane of natural teeth (average angle 2.84) or artificial teeth (average angle 3.25). Later, Petricevic et a 9, reported angle between the occlusal plane and the Camper s line to be 3.94. In this photographic study with North Indian young subjects, the ala-tragus line with middle posterior reference point on the tragus of the ear showed lowest mean angle of about 3.6 0 and 3.5 0 on right and left side, respectively. Whereas, lowest mean angle observed was 3.3 0 with middle reference point in female subjects, and 2.6 0-2.7 0 with inferior reference point in male subjects. The angle between the occlusal plane and Camper s plane (3.5 0-3.6 0 ) was found comparable to that observed in similar studies by Augeburger, Ismail and Bowman 10, Karkazis & Polyzois, Petricevic et al. Variation between the results of the present study and the other studies could be explained by the use of different methods of study and points of measurement. Van Niekerk et al 11 used the inferior border of the tragus as the posterior reference point of the ala-tragus line and result found were comparable as in case of male subjects of this present study. Whereas Ismail and Bowman, Karkazis and Polyzois used the centre of the tragus as the posterior reference for Camper s plane with the occlusal plane of natural teeth and concluded that dentures constructed accordingly would have an occlusal plane set far too low posteriorly. The results of this study indicate that the middle border of the tragus is the most acceptable point to orient the occlusal plane in the population studied, which complies with Ismail and Bowman, Karkazis and Polyzois who suggested the use of the middle part of the tragus. On the other hand, the result obtained in this study are not in accordance with the findings of other studies on selecting superior point as posterior reference point such as the Glossary of Prosthodontic Terms, Trapozzano 12 and Lahori 13 Conclusion Within the limitation of this study, the results showed that the ala-tragus line corresponding to centre of the tragus of the ear had the lowest mean value and had stronger tendency to be parallel to the natural occlusal plane among young adults. However, female subjects showed that the middle reference point on tragus of ala-tragus line is a reliable landmark and in male subjects the inferior reference point on tragus of ala-tragus line proved as a reliable landmark for orientation of occlusal plane for prosthetic rehabilitation. No precise parallelism was observed between the natural occlusal plane and the ala-tragus line with three posterior reference points on the tragus of the ear in the young dentate subjects from North Indian population. References 1. Roraff AR: Arranging artificial teeth according to anatomic landmarks. J Prosthet Dent 1977; 28: 120-30. 2. Celebic A, Valentic-Peruzovic M, Kraljevic K, Brkic H. A study of the occlusal plane orientation by intra-oral method (retromolar pad). J Oral Rehabil 1995;22:233 36. 3. Foley PF, Latta GH Jr. A study of the position of the parotid papilla relative to the occlusal plane. J Prosthet Dent 1985; 53:124-26. 4. Abrahams R, Carey PD. The use of ala-tragus for occlusal plane determination in complete dentures. J Dent 1979; 7:339-41. 5. Kazanoglu A, Unger JW. Determining the occlusal plane with the Camper s plane indicator. J Prosthet Dent 1992; 67:400 501. 6. Glossary of prosthodontic terms. J Prosthet Dent 2005; 94:10-92. 7. Augsburger RH. Occlusal plane relation to facial type. J Prosthet Dent 1953; 3:53-65. 8. Karkazis HC, Polyzois GL. Cephalometrically predicted occlusal plane: Implications in removeable prosthodontics. J Prosthet Dent 1991; 65:258-64. 9. Petricevic N, Celebic A, Celic R, Baucic-Bozic M. Natural head position and inclination of craniofacial planes. Int J Prosthodont 2006;19: 279-80. 84
10. Ismail YH, Bowman JF. Position of the occlusal plane in natural and artificial teeth. J Prosthet Dent 1968; 20:407-11. 11. Van Niekerk FW, Miller VJ, Bibby RE. The alatragus line in complete denture prosthodontics. J Prosthet Dent 1985; 53:67-69. 12. Trapozzano V. Occlusal records. J Prosthet Dent 1955; 5:325-33. 13. Manesh L, Nagrath R, Malik N. A Cephalometric Study on the relationship between the occlusal plane, ala-tragus and Camper's lines in subjects with Angle's Class I, Class II and Class III occlusion. J Indian Prosthodont Soc 2013; 13:494-98. 85