

ORIGINAL ARTICLE 

Year : 2020  Volume
: 10
 Issue : 3  Page : 166170 

Correlation of interocclusal distance and gonial angle in dentate and edentulous patients in Gujarati population
Miloni Mayank Bhatt, Dipti Shah, Kalpesh Vaishnav, Pankaj Patel, Zeba Harsolia, Richa Dangi
Department of Prosthodontics, Karnavati School of Dentistry, Gandhinagar, Gujarat, India
Date of Submission  27Dec2019 
Date of Decision  27Aug2020 
Date of Acceptance  11Aug2020 
Date of Web Publication  21Sep2020 
Correspondence Address: Miloni Mayank Bhatt Department of Prosthodontics, Karnavati School of Dentistry, Uvarsad, Gandhinagar, Gujarat India
Source of Support: None, Conflict of Interest: None  Check 
DOI: 10.4103/AIHB.AIHB_129_19
Background: The amount of interocclusal distance in any individual is mainly an expression of muscle function, its equilibrium, and gravity. In some medically compromised patients, it is difficult to determine the interocclusal distance. Aim: This study aims to evaluate the correlation of interocclusal distance and corresponding gonial angle on the lateral profile of dentulous individuals in lateral cephalograms in Gujarati population and correlation of these values for edentulous individuals. Material and methods: A total of 100 individuals were involved in this study within age group of 2035 years. Interocclusal distance was determined by the difference between the readings of vertical dimension of rest and vertical dimension of occlusion in dentulous individuals.Gonial angle was calculated with the help of cephalometric radiographs and the two were correlated. Results: Range of gonial angle and interocclusal distance were obtained and the mean of the values was derived. A strong correlation was found to exist.Conclusion: By applying the processes of linear regression to the paired results, a formula was obtained which may be used to predict the best value of one variable for any given value of the other. Thus, in an edentulous case, where the value of the interocclusal distance measurement is unknown and difficult to determine, a method is provided for predicting its best value by the determination of the patient's gonial angle through cephalometric analysis.
Keywords: correlation, dentate, edentulous, gonial angle, interocclusal distance Correlation, dentate, edentulous, gonial angle, interocclusal distance
How to cite this article: Bhatt MM, Shah D, Vaishnav K, Patel P, Harsolia Z, Dangi R. Correlation of interocclusal distance and gonial angle in dentate and edentulous patients in Gujarati population. Adv Hum Biol 2020;10:16670 
How to cite this URL: Bhatt MM, Shah D, Vaishnav K, Patel P, Harsolia Z, Dangi R. Correlation of interocclusal distance and gonial angle in dentate and edentulous patients in Gujarati population. Adv Hum Biol [serial online] 2020 [cited 2021 Apr 17];10:16670. Available from: https://www.aihbonline.com/text.asp?2020/10/3/166/295824 
Aim of the study
This study aims to determine the interocclusal distance for edentulous patients: by using the data of gonial angle and correlating it with the value for dentulous patients, obtained through correlation and regression analysis for dentulous patients.
Introduction   
The interocclusal distance, also commonly known as freeway space, is the distance between the occluding surfaces of the maxillary and mandibular teeth when the mandible is in a physiologic rest position. The interocclusal distance helps in pronunciation and helps to keep teeth disoccluded in rest position of the mandible. This distance varies from person to person. Correct registration of occlusal vertical dimension has a biological importance as it allows the patient to be able to masticate his/her food efficiently, speak without impediment, keep his/her normal appearance and preserve temporomandibular joint function.^{[1],[2]} This freeway space needs to be reestablished while fabricating complete dentures for the patients. In the absence of preextraction records, this freeway space becomes difficult to reestablish with precision. The present methods available can help in reestablishing the interocclusal distance in a generalised approach.
Cephalometric roentgenography is a radiographic aid used for diagnosis purpose. The lateral cephalograms have long been used in the determination of existing interocclusal distance in dentate patients.
This study was done to find a correlation between interocclusal distance and other static reproducible hard tissue landmark, which can help us to derive the interocclusal distance for edentulous patients by using the data of gonial angle for the edentulous patients. Therefore, the present study was conducted to determine the validity of cephalometric approach to determine freeway space.
Materials and Methods   
The study was conducted on 100 dentulous subjects, 45 males and 55 females in the age group of 20–35 years. The minimum age of the subjects was 20 years and the maximum age was 35 years. The minimum age was selected at 20 years because the skeletal maturity is reached at that age.^{[3],[4]} Ethical consideration was taken from the institutional review board. No sex variation was taken into consideration. The subjects selected for the study had facial symmetry and periodontally sound teeth. Variation in the occlusal relationships was not taken into consideration. The radiation dose experienced by the subjects during this procedure is very minimal and does not pose any threat towards the overall health of the patient.
Determination of gonial angle
Lateral cephalometric radiographs were taken for all the cases by cephalostat. 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 angle of the Xray tube was kept at 90°. Just before exposure, the subject was instructed to swallow relax and bring the lips in approximation to secure the rest position of the mandible [Figure 1].
After developing, the cephalographs were mounted on Xray viewer and traced using tracing film. Two reference points were identified in each case [Figure 2]:
 Gnathion, which, as defined by Scott (1967), is the point where the anterior border of the mandible joins the lower border
 Articulare, which is the point of intersection between the posterior border of ramus and the base of the skull.^{[4]}
The following planes were then determined:
 The mandibular plane, which is a line tangent to the lower border of the mandible and which passes through gnathion
 The condylar plane, a line tangent to the posterior border of the mandible, which passes through articulare. The angle formed by the intersection of these two planes was taken as the gonial angle and measured with a protractor to the nearest degree.^{[4]}
Determination of freeway space
The individual was seated in the dental chair comfortably in an erect posture with the head well supported by the head rest.^{[1]} A point was marked on the highest point on the tip of the nose, while another point was marked on the highest prominence of the chin. The subject was instructed to close the mouth with teeth in complete contact (as in chewing). The distance between the marked points was measured with a divider and then measured on a scale. Thus, vertical dimension at occlusion was obtained. The subject was instructed to relax his/her lower jaw and speak the word 'raam'; the distance between two points was measured in similar manner. Thus, the vertical dimension at rest was obtained [Figure 3].  Figure 3: Measuring the distance between two marked points at rest position and in intercuspation. The values are subtracted from each other.
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The difference between these two readings was calculated and the interoclussal distance was obtained.
The value of gonial angle determined cephalometrically in each case was paired with its respective freeway space value measured clinically and was subject to statistical analysis. Pearson's formula was used to determine the coefficient of correlation (r).^{[1],[4],[5]}
Data Analysis and Result
The gonial angle and freeway space values obtained are listed in [Table 1].  Table 1: Master table for data of Gonial Angle and Interocclusal Distance in Dentate Patients.
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The gonial angle ranged from 108° to 135°, with the average of 116.27°. The freeway space ranged from 1 to 4 mm, with the average of 2 mm.
Estimation of correlation
Using Karl Pearson's formula (equation  1), a coefficient of correlation having a value of r = −0.78294 was obtained from the data, which is statistically highly significant.
Pearson's correlation showed a strong negativecorrelation between the variables. Thus as the gonial angle increases, the freeway space decreases, and vice versa.
Karl Pearson's formula is given below:
where x = Gonial angle (in degrees) and y = Interocclusal distance (in millimetre).
The correlation coefficient r value can be positive, zero or negative. The positive value signifies that with increase in x variable, the y variable also increases. The negative value signifies that with increase in x variable, the y variable value decreases, whereas the zero value of r signifies that there is no correlation between the two variables.
Estimate by regression line
As the correlation is significant, a functional relation between x (genial angle) and y (interocclusal distance) can be found by regression coefficient b_{yx}, leading to equation  2.
y = a + b_{y, x}. x(equation  2).
where b_{yx } is given below:
The obtained values of both the variables can be plotted on a graph which shows a regression equation relation. The positive regression coefficient shows a line going upwards, while negative correlation shows the line going downwards (slope/gradient is negative), and if the correlation is zero, highly scattered points are plotted on the graph diagram and no regression line is possible, and thus, no conclusion can be made.
The obtained correlation regression graph of the current data is shown below. The graph shows a negative slope which justifies the results and conclusions of equations 1, 2 and 3. (i.e. a negative correlation).
By applying values of x and y, the value of b_{xy} is derived first (equation  3). As the values of b_{xy}, x and y are known, the value of a is derived using equation  2. Thus, with the help of obtained data, the derived values of a and b are:
a = 12.11.
b = −0.09.
Discussion   
The masticatory apparatus, aesthetics and phonetics of the patient work simultaneously and in harmony like a single unit. Alteration in one of these factors leads to alteration in the other. The maintenance of interocclusal distance provides a balance between surrounding muscle apparatus. Thus, the reestablishment of occlusal vertical dimension and maintenance of interocclusal distance is of prime importance during rehabilitation of removable as well as fixed prosthesis as it functions in harmony with the masticatory apparatus and speech.^{[6],[7]} The most challenging and complex procedure during oral rehabilitation of edentulous patients is the reestablishment of the interocclusal distance because no static guide exists to reproduce the interocclusal distance with accuracy and precision the reestablishment becomes more difficult. It is proven by various studies that if the interocclusal distance is not maintained, it causes variations in anterior facial height, aesthetics of face and speech alterations and change in mandibular positions, ultimately leading to head and cervical spine postures.^{[8],[9]} The decrease of the freeway space can compromise the occlusal vertical dimension, leading to aesthetic and morphologic changes in the complete denture wearers, such as hyperactivity or hypoactivity of the masticatory muscles, increase or decrease in masticatory force, temporomandibular disorders, decreased facial height as a result of mandibular ridge resorption and a downward and forward rotation of the mandible along with soft tissue changes such as angular cheilitis and drooping lips^{[10]} and increasing mandibular prognathism. These complications can significantly affect the function and comfort, as well as the phonetics and aesthetic of the patient.
By finding a correlation between the gonial angle which is static landmark and the interocclusal distance which is a dynamic landmark, we can achieve the balance between the masticatory apparatus, the prosthesis and the orofacial apparatus and reestablish the harmony between these factors. The present study can be applied for patients for whom there is no guidance of the interocclusal distance and who are not able to guide the mandible in a physiologic rest position. The method along with the normal physiologic methods helps to establish the interocclusal distance with more accuracy in patients with muscle and speech disorders.
Significance the study
For n number of values of x, i.e., gonial angle, we can estimate the value of y, i.e., interocclusal distance. Thus, in an edentulous patient, a method can be provided to predict the value of interocclusal distance by determining the patient's gonial angle, through cephalometric analysis. The success of the denture is conditional on there being an adequate interocclusal distance, so incorporation of correct amount of interocclusal distance has long been recognised as a prerequisite for comfort and optimum function.^{[1]}
For any patient in Gujarati population, with a known value of gonial angle (x), applying it in the formula y = a + b_{y, x}. x, the value of interocclusal distance can be determined, where the value of a = 12.11 and b = −0.09.
Example:
The estimated interocclusal distance for an edentulous patient with gonial angle of 120° will be as follows:
y = a + b_{y, x}. x
where x = 120, a = 12.11, and b = −0.09.
Thus,
y = 12.11 + (−0.09). 120
y = 1.31 approximately 1 mm.
Conclusion   
The present study concludes that there is a negative correlation between the gonial angle value (x) and the interocclusal distance (y) for patients of Gujarati population. This means that as the value of gonial angle increases, the value of interocclusal distance will decrease. The study was conducted on dentulous patients to obtain the correlation between the two values and the application of this on edentulous patients was derived. With the help of obtained data, the value of interocclusal distance in edentulous patients can be precisely determined by knowing the value of gonial angle for the patient. The values of constants a = 12.11 and b = −0.09 are applicable for the Gujarati population. The values of the constants might vary with other population groups, and further study needs to be conducted for obtaining correlation amongst other population.
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
Nil.
Conflicts of interest
There are no conflicts of interest.
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10.  Fouda S, Mohamad S AlAttar, Jorma I Virtanen, Aune Raustia et al. Effect of patient's personality on satisfaction with their present complete denture and after increasing the occlusal vertical dimension: A study of edentulous Egyptian patients. Int J Dent 2014; 2014:635943, 17. 
[Figure 1], [Figure 2], [Figure 3]
[Table 1]
