

Year : 2013  Volume
: 24
 Issue : 6  Page : 669673 

A cephalometric study to determine the plane of occlusion in completely edentulous patients 

Amit D Hindocha^{1}, Vikas N Vartak^{1}, Aruna J Bhandari^{2}, Mohit T Dudani^{1}
^{1} Department of Prosthodontics, Sinhgad Dental College and Hospital, Pune, Maharashtra, India ^{2} Department of Prosthodontics, Rural Dental College, Loni, Maharashtra, India
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Date of Submission  23Nov2011 
Date of Decision  11Jun2013 
Date of Acceptance  08Jul2013 
Date of Web Publication  20Feb2014 




Abstract   
Aim: Determination of the plane of occlusion in completely edentulous patients with the help of the alatragus line (Camper's plane) may be questioned. An attempt to devise an alternative method to determine the orientation of the plane of occlusion was made. Materials and Methods: Cephalometric analysis was used to identify whether a correlation exists between the plane of occlusion of dentulous Indian individuals and other stable cranial landmarks. Results: A negative correlation was found to exist between the occlusal PlaneFH plane angle and the porionnasionanterior nasal spine (PoNANS) angle. Conclusions: From the derived mathematical correlation, it was concluded that the angulation of the occlusal plane in completely edentulous subjects may be determined by taking a cephalogram at the diagnostic stage. Further, the clinical applicability of the derived mathematical formula (while determining the plane of occlusion) was tested on completely edentulous patients. Keywords: Cephalograms, edentulous, plane of occlusion
How to cite this article: Hindocha AD, Vartak VN, Bhandari AJ, Dudani MT. A cephalometric study to determine the plane of occlusion in completely edentulous patients. Indian J Dent Res 2013;24:66973 
How to cite this URL: Hindocha AD, Vartak VN, Bhandari AJ, Dudani MT. A cephalometric study to determine the plane of occlusion in completely edentulous patients. Indian J Dent Res [serial online] 2013 [cited 2022 Aug 19];24:66973. Available from: https://www.ijdr.in/text.asp?2013/24/6/669/127606 
Considerable debate exists within the prosthodontic community over the exact definition of the alatragus or Camper's line. ^{[1],[2],[3]} Most of the controversy revolves around which part of the tragus should be considered as a posterior landmark during orientation of the plane of occlusion. Through a review of literature, it was concluded that no single tragal reference could safely be considered as a posterior landmark. ^{[2],[4],[5],[6],[7],[8],[9]} Hence, empirical use of the alatragus line (Camper's plane) to determine the plane of occlusion in completely edentulous patients (at the jaw relation stage) is cautioned against by the authors. It would be desirable that a more reliable method be developed to determine the plane of occlusion in order to reduce the interoperator variation commonly observed within the profession.
Cephalometric analysis is an important diagnostic tool in dentistry and is widely used in the fields of orthodontics and dental research. In prosthodontics, the significance of cephalometrics lies in the ability to reestablish the spatial position of lost structures (such as the teeth). This is achieved by identifying predictable relationships between the teeth and other cranial landmarks that are not subject to postextraction changes. It is therefore quite plausible that a correlation may exist between the plane of occlusion of dentulous patients and stable cranial landmarks (as determined by a cephalogram). If scientifically determined, such a correlation could help in determining the plane of occlusion in completely edentulous patients.
A review of literature on this subject highlights the work of Monteith (1984). ^{[10]} His cephalometric study revealed that an intimate correlation (i.e. a mathematical formula) existed between the PoNANS angle (encompassed by the Cephalometric points  porion, nasion, and the anterior nasal spine) on the one hand and the angulation of the occlusal plane relative to the Frankfort plane on the other. This finding assumes particular importance in completely edentulous patients where the angulation of the plane of occlusion may be mathematically derived from the PoNANS angle based on a diagnostic cephalogram. It should also be noted that the work of Monteith was based on the analysis of a sample population of female Caucasian subjects. A review of the orthodontic literature reveals that different races have different cephalometric norms, thus indicating the need to collect data specifically of our Indian population. ^{[11]}
The aim of this cephalometric study was therefore to determine whether a similar correlationship (in the form of a mathematical formula) exists between the PoNANS angle and the occlusal planeFrankfort horizontal (FH) plane angle in a study population of Indian subjects. In the event of a mathematical formula being derived, it was decided to further test its clinical application through a pilot study.
Materials and Methods   
A total of 105 dentulous subjects (65 male and 40 female) were selected for the study. The main criterion for inclusion in the study was absence of derangement of the plane of occlusion due to longstanding extraction of teeth and no history of Orthodontic treatment. Lateral cephalograms of these subjects were obtained.
All the cephalometric films were exposed keeping a standard distance of 5 feet between the Xray target and midsagittal plane of the head of the subject. The midsagittal plane to film distance was standardized at 15 cm. The cephalograms were taken with the subject closing in maximal intercuspation position [Figure 1]. The same cephalostat and Xray technician were used for all the subjects. After developing, the cephalograms were mounted on an Xray viewer and traced using acetate films [Figure 2].
The cephalometric points Nasion (N  the anterior point of the intersection between the nasal and frontal bones), Orbitale (Or  the lowest point on the inferior margin of the orbit), Anterior Nasal Spine (ANS  point on the lower shadow of the anterior nasal spine where the projecting spine is 3mm thick), and Porion (Po  the midpoint of the upper contour of the metal rod of the cephalometer) were determined on the tracings using accepted scientific criteria. ^{[12]} The point Porion (Po) was plotted to coincide with the earrods of the cephalostat rather than with its more correct but less frequently visible bony counterpart. ^{[10]}
The plane of occlusion was then drawn extending from the midincisal point of the maxillary central incisors to the mesiopalatal cusp of the maxillary first molar (Line d in Figure 2). The FH plane was also traced extending from the porion to orbitale points (Line c in [Figure 2]. The Porion and Nasion points were connected with a straight line (Line a in Figure 2), and so were the Nasion and the Anterior Nasal Spine points (Line b in Figure 2).  Figure 2: Tracing of a cephalogram showing PoNANS angle and occlusal planeFH plane angle
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In the next phase of cephalometric analysis, the porionnasionanterior nasal spine angles, that is, the PoNANS angle denoted as 'X' (Angle 1 in Figure 2) and the occlusal planeFrankfort horizontal plane angles denoted as 'Y' (Angle 2 in Figure 2) were measured to the nearest degree with a protractor (the angle of intersection of the occlusal and FH planes was measured) and noted.
Observations and Results   
[Table 1] shows the means of the PoNANS angles ('X') and the occlusal planeFH plane angles ('Y') measured and their standard deviations for the male subjects.
Karl Pearson's correlation coefficient (r) was then calculated with the help of these values. A negative correlation was found between these two variables [Graph 1]. A ttest was applied for determining the significance of the correlation coefficient and it was found to be significant. Regression analysis was then performed and an equation was obtained with the help of which the value of 'Y' could be obtained if the value of 'X' is known (Equation 1).
Equation 1. (Male group)
Regression analysis
To estimate Y (occlusal planeFH plane angle) when X (PoNANS angle) is known:
Y = 0.5115 (X) + 48.1
[Table 2] shows the means of the PoNANS angles ('X') and occlusal planeFH plane angles ('Y') and their standard deviations for the female subjects.
Karl Pearson's correlation coefficient (r) was then calculated with the help of these values. A negative correlation was found between these two variables [Graph 2]. A ttest was applied for determining the significance of the correlation coefficient and it was found to be significant. Regression analysis was then performed and an equation was obtained with the help of which the value of 'Y' could be obtained if the value of 'X' is known (Equation 2).
Equation 2. (Female group)
Regression analysis
To estimate Y (Occlusal planeFH plane angle) when X (PoNANS angle) is known:
Y = 0.7434 (X) + 65.27
Pilot study
The possible clinical application of the above derived mathematical formulae was then tested clinically on two completely edentulous subjects (1 male and 1 female) as part of a pilot study. A lead wire was attached to the tragus of the patient and the base of the ala of the nose was marked with barium sulfate. Lateral cephalograms were then made.
The cephalograms were then traced [Figure 3] and [Figure 4] and the following points were identified:
 Porion (Po): Plotted to coincide with the midpoint of the upper contour of the metal rod of the cephalometer
 Nasion (N): Plotted to coincide with the anterior point of the intersection between the nasal and frontal bones
 Anterior nasal spine (ANS): Plotted to coincide with the point on the lower shadow of the anterior nasal spine where the projecting spine is 3mm thick
 Orbitale (Or): Plotted to coincide with the lowest point on the inferior margin of the orbit
 The radiopaque markings of the lead wire at tragus and the barium sulfate mark at the base of the ala of the nose.
The Po, N, and ANS points were joined and the resultant PoNANS angle ('X') was measured to the nearest 1°. The obtained value of 'X' was substituted in the previously derived mathematical regression formulae and the occlusal planeFH plane angle ('Y') was calculated for both patients [Table 3].
The next phase of the cephalometric analysis involved establishing a correlation between the computed occlusal plane angle and the tragus of the patient in order to determine a patient specific tragal reference (in order to adjust the plane of occlusion of the maxillary wax occlusion rim).
The Frankfort horizontal (FH) plane was drawn extending from the Porion to Orbitale points. A line was then drawn at the angle 'Y' (computed above) to the FH plane. A line parallel to this line was drawn passing through the base of the ala marking and passing posteriorly through the tragal marking. The position of the line as it crossed the tragus was noted in order to identify which part of the tragus was to be considered as the posterior landmark while determining the plane of occlusion using the alatragus line (Camper's plane). The plane of occlusion of the individual patients was thereby established on the maxillary wax occlusion rim.
Discussion   
A cephalogram reveals areas in the cranial base that are not subject to alteration between certain ages. ^{[13]} Hence, a cephalogram is considered to serve as a very useful diagnostic tool for periodic analysis of alterations in the teeth, jaws, and face. Based on the evaluation of dentate population samples, several authors have suggested that a predictable relationship may exist between certain fixed cranial landmarks and the plane of occlusion. ^{[14],[15],[16]} This finding holds relevance in the field of complete denture therapy since such a correlation could be applied in providing a more accurate method of establishing the plane of occlusion of completely edentulous patients.
Monteith's cephalometric study has revealed that the angulation of the plane of occlusion may be mathematically derived from the PoNANS angle (encompassed by the Cephalometric points  porion, nasion, and anterior nasal spine) based on a diagnostic cephalogram. ^{[10]} According to him, the PoNANS angle was representative of the angular relationship between the cranial base and the vertical axis of the nasomaxillary complex. According to his mathematical formula, an increase in the PoNANS angle (as observed in skeletal Class III patients) could be used to predict a flattening of the plane of occlusion whereas a decrease in the same (as observed in skeletal Class II patients) could be used to predict a steepening of the plane of occlusion, in completely edentulous patients.
This cephalometric study was therefore conducted to test whether such a similar mathematical correlation existed within a sample population of 105 dentulous Indian patients. The results of our study seem to support the findings of Monteith and a mathematical formula correlation (between the PoNANS angle and angulation of the plane of occlusion) was specifically derived for the sample Indian population. A similar negative correlation was found to exist between the PoNANS angle and the angulation of the plane of occlusion.
It may be interesting to note that Monteith's study was based on a sample population of 32 Caucasian female subjects whereas this study comprised 105 Indian subjects, of which 65 were male and 40 were female. It was therefore possible to derive a separate mathematical correlation for both genders in this study. In comparing both formulae, a variation of approximately 1 to 3 degrees in the calculated occlusal planeFH plane angle ('Y') was observed. For example, if the PoNANS angle ('X') were to be considered as 65 degrees, then the computed values of 'Y' for males and females (based on our formulae) would be 15 and 17 degrees respectively. Accordingly, Monteith's formula (based on evaluation of Caucasian female subjects only) would project the occlusal planeFH plane angle ('Y') to be 19 degrees.
Any mathematical formula once derived is of significance only once tested clinically. Monteith (through his subsequent work) demonstrated the use of an Occlusal Plane Projector. ^{[17],[18]} This programmable mechanical device was to be attached to the semiadjustable articulator and the maxillary artificial posterior teeth were to be arranged based on the computed angulation of the plane of occlusion.
In our pilot study, an attempt was made to establish the relation between the computed angulation of the plane of occlusion and the alatragus line (Camper's plane). It was found through our methodology that the formula could be indeed used to project which part of the tragus was to be considered as the posterior landmark. The fact that this information could be made available at the diagnostic stage itself would significantly reduce interoperator variation in using the alatragus line to establish the plane of occlusion. It is a known fact that the use of a semiadjustable articulator by the general dental community is very limited (at least within our country). Many dentures are fabricated on a meanvalue articulator without a face bow transfer and a balanced occlusal scheme. The use of a diagnostic cephalogram (to establish the plane of occlusion) in such a scenario would help to at least introduce some accuracy to complete denture therapy in our country.
Finally, a longterm invivo study on a larger population sample is suggested in order to further evaluate the clinical application of the derived mathematical formulae for both genders. What effect this would have in developing a balanced occlusal scheme is another area which the profession may desire to explore.
Summary and Conclusions   
Following were the results of this study:
 In 105 Indian dentulous subjects (65 male and 40 female), a negative correlation was found to exist between the porionnasionanterior nasal spine (PoNANS) angle ('X') and the occlusal planeFH plane angle ('Y')
 From the above correlation, a mathematical formula (relating both angulations) was derived for both genders. These were
 For males: Y =  0.5115 (X) + 48.1
 For females: Y =  0.7434 (X) + 65.27
 A methodology was developed to apply the formulae clinically on two completely edentulous patients (1 male and 1 female). From the computed occlusal planeFH plane angle ('Y'), it was possible to identify which part of the tragus was to be considered as the posterior landmark while using the alatragus line (Camper's plane) to establish the plane of occlusion.
Following were the conclusions of this study:
 From the derived mathematical correlation, it was concluded that the angulation of the occlusal plane in completely edentulous subjects may be determined by taking a cephalogram at the diagnostic stage
 By using this mathematical formula, it is possible to determine for each completely edentulous patient which part of the tragus should be selected as the posterior landmark for establishing the plane of occlusion.
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Correspondence Address: Amit D Hindocha Department of Prosthodontics, Sinhgad Dental College and Hospital, Pune, Maharashtra India
Source of Support: None, Conflict of Interest: None  Check 
DOI: 10.4103/09709290.127606
[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3] 

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