|Year : 2017 | Volume
| Issue : 3 | Page : 165-169
Cephalometric study of the position of ala-tragus line in relation to Frankfort horizontal plane and occlusal plane among Ludhiana population
Nitasha Gandhi, Smitha Daniel, Nirmal Kurian
Department of Prosthodontics and Crown and Bridge, Christian Dental College, Ludhiana, Punjab, India
|Date of Web Publication||7-Aug-2017|
Department of Prsothodontia, Christian Dental College, Ludhiana - 141 008, Punjab
Source of Support: None, Conflict of Interest: None
Introduction: The inclination of occlusal plane (OP) is determined by paralleling the OP to ala-tragus line. Inspite of its wide acceptability, the exact location of tragal point on ala-tragus line is unclear. In addition, morphologic features vary among various ethnic groups. Therefore, it is important to evaluate the exact reference point on tragus among Ludhiana population. Aim: The aim of this study is to determine the posterior reference point of the ala-tragus line that forms the most parallel line with the natural OP among Ludhiana population. Methodology: Digital lateral cephalograms were taken in 100 dentulous Angle's Class I subjects of 18–30 age group. Stainless steel balls were attached to ala of the nose (A) and three points that corresponded to superior (S), middle (M), and inferior (I) points on the tragus of ear. The angle formed by each line (SA, MA, and IA planes) with Frankfort horizontal (FH) plane and OP were measured on all tracings of cephalograms. Results: The mean angular value of IFH (angle between IA-FH planes) was the closest to the Cant of OP, and the mean angular value of IOP (angle between IA plane and OP plane) was the least compared to angles MOP (angle between MA-OP planes) and SOP (angle between SA-OP planes). Conclusion: The inferior point marked on tragus is the most appropriate point for marking ala-tragus line among Angle's Class I subjects of Ludhiana.
Keywords: Ala-tragus line, cant of occlusal plane, Frankfort horizontal plane, occlusal plane, tragus
|How to cite this article:|
Gandhi N, Daniel S, Kurian N. Cephalometric study of the position of ala-tragus line in relation to Frankfort horizontal plane and occlusal plane among Ludhiana population. Indian J Dent Sci 2017;9:165-9
|How to cite this URL:|
Gandhi N, Daniel S, Kurian N. Cephalometric study of the position of ala-tragus line in relation to Frankfort horizontal plane and occlusal plane among Ludhiana population. Indian J Dent Sci [serial online] 2017 [cited 2018 Oct 17];9:165-9. Available from: http://www.ijds.in/text.asp?2017/9/3/165/212392
| Introduction|| |
The orientation of occlusal plane (OP) is one of the most indispensable clinical procedures in prosthodontic rehabilitation for edentulous subjects. The position of the OP orientation not only forms the basis for ideal tooth arrangement but also should fulfill the necessary mechanical, esthetic, and phonetic requirements, and aid in respiration and deglutition. While, natural teeth and normal tonus of muscles manipulating the masticatory system are lost in completely edentulous individuals, orientation of OP should be as close as possible to the plane previously occupied by the natural teeth to harmonize with the normal functions of the tongue and cheek muscles.,
A common approach for the orientation of OP is that it is oriented anteriorly to fulfill esthetic and phonetic requirements and posteriorly parallel to ala-tragus line. This line is also known as the Camper's line after Petrus Camper, a Dutch anatomist. He elucidated Camper's line in 1786 as an anthropologic measurement on skulls. Clapp in 1910 was the first to relate Camper's line/plane to OP. According to a study done by Levin and Sauer, this line is the most widely used and frequently taught as a method for determining the OP. However, there is disagreement in the literature concerning which part of tragus has to be used as posterior reference point of ala-tragus line to determine posterior OP.
Standard facial measurements are essential for establishing the level of OP. The basic form, size, and position of the stomatognathic system and variations in the facial morphology arise through differential growth and are controlled by a number of factors which include genetic heritage, climate, and environment in which we live. Data from one ethnic group may be misleading when applied to other ethnic group as anthropometric studies on craniofacial features of different racial groups have shown interregional variations.,
Hence, this study was proposed to determine a reference line most parallel to the natural OP so that this reference on the tragus can be used to determine the OP during the fabrication of complete denture among Ludhiana population. The null hypothesis is that there will be no relation between any reference point of the ala-tragus line and the OP.
| Methodology|| |
The present study was carried out on 100 dentulous subjects in the age group of 18–30. Inclusion criteria for the subjects were both sexes of Ludhiana ethnicity who required lateral cephalograms as part of their diagnosis and treatment plan. They should have straight profile with no skeletal abnormalities, Class I molar relation, and no missing teeth or replacement for the same. Exclusion criteria included subjects treated orthodontically and those presenting the history of temporomandibular disorders. The objectives and method of obtaining cephalogram were explained to each subject, and a signed consent was obtained from them.
The length of the tragus extending from the superior-most point on the tragus up to intertragic notch of external ear was measured using digital Vernier calipers (Rabbit Force Digital Calipers). Three points were marked equidistantly along the double-adhesive tape corresponding to superior (S), middle (M), and inferior (I) points on the measured length of the tragus. Stainless steel balls of 2 mm diameter were attached to these points on the tragus. Another stainless steel ball was attached with the help of double-adhesive tape of about 1 cm × 1 cm to the inferior margin of ala (A) of nose [Figure 1].
|Figure 1: Illustrating placement of steel balls using double-adhesive tape on the subject standing in the cephalostat machineFrankfort|
Click here to view
Digital lateral cephalograms were taken after the patient was positioned within the cephalostat (Vatech PAX-i, Vatech Inc., Delhi, India) using adjustable bilateral ear rods placed within each auditory meatus in the standing position. The subject's Frankfort horizontal (FH) plane was oriented parallel to the floor. A plumb line is suspended in front of the subject to obtain a true vertical. The subject was instructed to look straight and maintain relaxed posture with teeth in centric occlusion during exposure of films and lips should be relaxed. Central ray coincided with the ear rod of the cephalostat. The tube voltage was 84 kVp, current 10 mA, absorbed radiation dose 0.2dGYcm and exposure time was set at 1.8 s. The cephalograms [Figure 2] were traced on X-ray viewer on tracer film using Hb lead pencil (Nataraj Bonded lead, HB, Hindustan Pvt. Ltd., India).
Superior (S), middle (M), and inferior (I) points of the tragus were joined to ala (A) of the nose to form three ala-tragus lines, i.e., SA, MA, and IA lines. The line joining Porion (Po) and Orbitale (Or) gave FH plane. Based on Downs analysis, OP is the line bisecting the overlapping cusps of first molars and first premolars. The true horizontal line (NL) was drawn through bony nasion. The true vertical line (PL) passing through the center of silver chain was drawn. This true vertical line (PL) was perpendicular to the true horizontal line (NL) standardizing the lateral cephalogram. The lines were drawn with the help of scale (Nataraj, Hindustan Pvt. Ltd., India) and set squares (Nataraj, Hindustan Pvt. Ltd., India). Following angles were measured using a protractor (Nataraj, Hindustan Pvt. Ltd., India):
- SFH - angle between SA plane and FH plane
- MFH - angle between MA plane and FH plane
- IFH - angle between IA plane and FH plane
- SOP - angle between SA plane and OP plane
- MOP - angle between MA plane and OP plane
- IOP - angle between IA plane and OP plane
- Cant of OP (COP).
| Results|| |
The data obtained was subjected to statistical analysis to derive mean, median, standard deviation, and Karl Pearson coefficient of correlations of the various angular measurements.
[Table 1] depicted that mean value of IFH was found to be closer to COP compared to SFH and MFH. Mean value of IOP was the least.
|Table 1: Mean, median, standard deviations, and percentiles of the measured angles|
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[Table 2] depicted maximum positive correlation between COP and IFH which was highly statistically significant (P < 0.01). Further, correlation between COP and IOP was positive and highly statistically significant (P < 0.01).
[Table 3] depicted that IFH had the closest angular measurement to COP in 62% individuals.
| Discussion|| |
The design of the OP is acknowledged as one of nature's most beautiful expressions of dynamic harmony among the components of the craniomaxillary complex. Boucher  stated, “It seems to be obvious that if the soft tissue surrounding the denture is to work around as they did around natural teeth, OP should be oriented exactly as it was when the natural teeth were present.” The statement by Boucher is logical since the musculature of the tongue and the cheeks was trained to function normally at this level when the natural teeth were present. This explains the rationale behind assessing the OP orientation in dentulous individuals for determination of OP orientation in edentulous individuals.
In the current study, IOP mean angular measurement was the least (4.3°) among SOP, MOP, and IOP [Table 1]. This observation was similar to the one by Karkazis and Polyzois  and van Niekerk et al., who recorded a 3.45° angle between the OP of the complete denture and the ala-tragus line. The variation in the values of angles of the two studies is due to different populations under study inheriting varied ethnicity. The mean of COP as determined in this study is 11.49°, which is comparable to the widely recognized study done by Downs, which was found to be ranging from +14° to +1.5°, with a mean of +9.5°. Possible reasoning for the wide range of the measured angles can be individual morphological variations. Further, this much variation may be deemed clinically acceptable since Shillingburg et al. stated that up to 8° of difference in angular perception does occur in binocular vision. This is substantiated by Kumar et al. stating that such a difference in vision reinforces a stable relation between FH plane and OP.
The studies by Siefert  and Kumar et al. reinforced that there is a relative consistency in the angle between OP-FH plane in dentulous subjects with Angle's Class I jaw relationship. These findings have a bearing in the arena of complete denture therapy since they can be correlated aiding in establishing an accurate method for OP determination in orthognathic completely edentulous individuals. It was inferred from the current study that angle formed between inferior ala-tragus line and Frankfort plane (IFH) has maximum correlation with COP (r = 0.865, P < 0.01) confirming that inferior point on tragus gives the closest value of IFH (10.7°) that correlated to COP (11.4°) in Angle's Class I jaw relationship.
Thus, it can be inferred from the results of our study that the ala-tragus line passing through inferior point on the tragus is the most suitable plane to orient the OP in orthognathic completely edentulous population of Ludhiana. The null hypothesis which stated that there was no relation between any reference point of the ala-tragus line and the OP was entirely refuted. The results of the present study were backed by the results of the studies by Karkazis and Polyzois, Kumar et al., van Niekerk, Chaturvedi and Thombare, Hindocha et al., Hartono, and Nayar et al. On the contrary, the results of this study were not in agreement with the previous studies done by other researchers Al Quran et al., Gupta and Singh, Augsburger, Jayachandran et al., Sadr and Sadr, Shigli et al. and Nissanet al., who concluded that the line passing through superior and middle border of the tragus were parallel to the OP. This variation may originate from race-related and ethnic population diversities.
In the present study, cephalogram was used, a contemporary and popular diagnostic tool in prosthodontics. It was chosen as the mode for our study as radiographic studies have the potential to examine the relation between various cranial reference lines. The cephalometric analysis makes use of angular measurements which are relatively stable with respect to time, i.e., they are minimally affected by age. They could provide useful information on the orientation of the OP in dentulous and edentulous subjects as they can reestablish the spatial position of lost structures such as teeth. One such universally accepted craniometric landmark, FH plane was taken as a standard reference plane.
Standardization of lateral cephalogram in all the three planes was done to minimize errors. FH plane is kept horizontal to the floor which is confirmed using a plumb line hung from the cephalostat to indicate the true vertical. Both ear rods of cephalostat machine ensured stability of the transverse plane. The nasion holder of the cephalostat stabilized the head in the vertical plane. Angular measurements were used instead of linear measurements in the current cephalometric analysis on the basis of the justification that they are practical, simple and are independent of age and sexual dimorphism.
For the ease of the comparison of the angulations, only orthognathic subjects were selected in this study. The subjects were selected between the age group of 18–30 years. By 18 years growth of the face ceases, and the relationship of camper's plane to the OP remains stable. The upper age limit was restricted to 30 years as at this age a dentition can be expected to remain normal without being subjected to age-related changes such as tooth loss and excessive attrition.
Notable limitations of the current study first are that the age changes within the tragus and ala of the nose were not taken into consideration as it may effect OP orientation in older edentulous patients. Second, reflection on variations in the angular relationships based on gender differences has to be investigated in Punjab population. Third, the results of this study can be applied to only Class I straight profile edentulous patients limiting its use in Class II and Class III profile patients. Backing this limit, Rajawat  observed that COP varied with facial types.
| Conclusion|| |
Based on the results of this study, it can be concluded that:
- Ala-tragus line passing through the inferior part of the tragus is the most parallel line to OP among Punjab population. In this study, the OP was parallel to the ala-tragus line passing through inferior border of the tragus in 53% participants
- It can be used as a guideline for orienting OP among Angles Class I population of Punjab.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]