Abstract | | |
**Aim:** To propose a new technique, based on cephalometrics for determining the vertical dimension of occlusion (VDO). **Methods and Material:** Thirty-five participants in the age range of 20**–**22 years who met the inclusion criteria were recruited. Lateral cephalograms were obtained and tracing done. Five reference landmarks, Nasion (N), Anterior Nasal Spine (ANS), Porion (P), Gonion (G) and Gnathion (Gn) were marked and joined to form four angles, N-ANS-Gn, N-ANS-G, P-G-Gn and P-G-ANS; distance between ANS and Gn was considered as VDO in cephalogram (VDO-Ceph). The angles N-ANS-Gn and N-ANS-G; P-G-Gn, and P-G-ANS were correlated; two simple linear regression models were developed to predict N-ANS-Gn and P-G-Gn, using N-ANS-G and P-G-ANS, as independent variables. Using the formulae, the predicted angles, N-ANS-Gn and P-G-Gn were drawn and intersection marked as 'reconstructed point Gn'. The predicted VDO-Ceph values (distance between ANS and reconstructed Gn) were measured and correlated with actual values. **Results:** The angles N-ANS-Gn and P-G-Gn had a statistically significant positive correlation with N-ANS-G (*r* = 0.77, *P* < 0.001) and P-G-ANS (*r* = 0.83, *P* < 0.001), respectively. Using simple linear regression analysis, the following formulae were obtained: N-ANS-Gn (in degrees) = 1.271 N-ANS-G (in degrees) + 24.83 and P-G-Gn (in degrees) = 0.987 P-G-ANS (in degrees) + 35.93. The predicted and actual VDO-Ceph values showed no statistical significance difference (*P* = 0.92). **Conclusion:** By tracing four cephalometric landmarks, N, ANS, P, G; and using the angular reconstruction, it is possible to predict the location of Gn. Hence, during prosthetic replacement of lost teeth, this can be employed for the estimation of lost dimensions.
**Keywords:** *Cephalometrics, occlusion, vertical dimension*
**How to cite this article:** Vinnakota DN, Kamatham R. Estimation of occlusal vertical dimension using cephalometric angular reconstruction. Indian J Dent Res 2021;32:31-4 |
**How to cite this URL:** Vinnakota DN, Kamatham R. Estimation of occlusal vertical dimension using cephalometric angular reconstruction. Indian J Dent Res [serial online] 2021 [cited 2021 Aug 3];32:31-4. Available from: https://www.ijdr.in/text.asp?2021/32/1/31/321386 |
Introduction | | |
The vertical dimension of occlusion (VDO) is the lower facial height measured between two points when the occluding members are in contact. It is the vertical position of the mandible in relation to the maxilla when the upper and the lower teeth are intercuspated at the closest position.^{[1]} Estimation of lost VDO is a critical step during the fabrication of partial and complete dentures, as the establishment of an appropriate lower facial height plays a significant role in the clinical success of prostheses. In common practice, physiological, metric, phonetic, esthetic, trial and error, telemetric and magnetic methods are employed in the establishment of lower facial height.^{[2],[3],[4],[5],[6],[7],[8],[9],[10],[11],[12]} The use of cephalometric landmarks for the estimation of VDO has been proposed because of the reliability and reproducibility of the bony reference points, that increase the accuracy of measurements.^{[13],[14]} Thus, this method gained more popularity and encouraged further research in this field. The few studies conducted on this topic observed weak to moderate correlations between considered cephalometric dimensions and lower facial height.^{[15],[16],[17],[18],[19]} To compensate for the low values of correlation coefficients, multiple regression analysis, and equations, incorporating abundance of landmarks has been proposed.^{[18]} However, the major drawback of increasing the number of landmarks is the long time taken for completing the analysis and sometimes the difficulty in identifying the landmarks. Hence, there is a need to explore for uncomplicated strategies with strong correlations, to employ simple linear regressions. Therefore, the present study was planned with four cephalometric landmarks that help in the easy determination of the lost vertical dimensions.
Methods | | |
Ethical clearance for the study was obtained from the institutional ethical committee. The inclusion criteria for the selection of participants were: age range of 20**–**27 years with full complement of teeth, well-balanced face, class I skeletal, molar and canine relationship as well as no acute or previous temporomandibular disorder. Individuals who were orthodontically treated previously and those with facial asymmetries were excluded.
The points considered in the present study were [Figure 1]:
Nasion (N): The most anterior point on the frontonasal suture in the midsaggital plane.
Anterior Nasal Spine (ANS): Anterior tip of nasal spine.
Porion (P): The most superiorly positioned point on the external opening of the auditory meatus.
Gonion (G): A point on the curvature of the mandible's angle located by bisecting the angle formed by lines tangent to the posterior ramus and the inferior border of the mandible.
Gnathion (Gn): A point located by taking the midpoint between the anterior and inferior points of the bony chin.
**Procedure**
The cephalogram was placed on the view box with the patient's image facing the right. The four corners of the radiograph were taped to the view box. The matte acetate film was placed over the radiograph and taped securely to the radiograph and the view box (the shiny side is placed down, against the radiograph). With a sharp 3H drawing pencil, employing stepwise tracing, the required reference landmarks were marked and joined to form the following angles [Figure 2] and [Figure 3]:
N-ANS-G: Formed by joining the landmarks nasion, anterior nasal spine and gonion.
N-ANS-Gn: Formed by joining the landmarks nasion, anterior nasal spine and gnathion.
P-G-ANS: Formed by joining the landmarks porion, gonion and anterior nasal spine.
P-G-Gn: Formed by joining the landmarks porion, gonion and gnathion.
VDO in cephalogram (VDO-Ceph): The distance between ANS and Gn was considered as the vertical dimension in cephalogram.
**Sample size determination**
Based on the findings of our pilot study done on five participants (not included in the main study), with the level of significance set at 0.05, power of 80%, a minimal sample size of 28 was determined.
**Reproducibility of angles**
For the above five participants, tracing was done by two investigators (DV and RK) on two occasions. The angles and VDO were measured on the duplicates obtained and tested for intrarater and interrater reliability (cite reliability coefficients).
**Statistics**
All statistical analyses were performed using SPSS 17.0 software (version 17.0, SPSS, Chicago, IL, USA). Cohen's kappa was employed to measure the reliability of the obtained data (both intra-rater and inter-rater). The normality of the data was tested using Shapiro-Wilk test. The correlations between the angles, N-ANS-G and N-ANS-Gn; P-G-ANS and P-G-Gn were determined using Pearson correlation test. For predicting N-ANS-Gn and P-G-Gn angles from N-ANS-G and P-G-ANS respectively, simple linear regression analysis was carried out. The calculated angles were transferred on to tracing, intersection marked as Gn, and VDO constructed which was considered as the predicted value. The actual and predicted VDO values were again analyzed statistically using paired t test.
Results | | |
**Descriptive analysis**
A total of 35 participants were recruited. The mean age of the participants was 21.4 (range of 20**–**22 years). The mean values for the N-ANS-G and N-ANS-Gn angles were 94.2 ± 2.96 (range from 85 to 98) and 145 ± 5.4 (range from 135 to 153), respectively. The mean values for P-G-ANS and P-G-Gn were 90.9 ± 4.5 (range from 84 to 100) and 125.7 ± 5.4 (range from 117 to 137), respectively. The mean VDO-Ceph was 37.7 ± 2.82, with a range between 32 mm and 42 mm.
**Correlations**
The intra-rater and inter-rater reliability of angle determination was found to be 0.99 and 0.98, respectively. The correlation (*r*) between N-ANS-Gn and N-ANS-G was moderately positive and statistically significant (*r* = 0.77, *P* < 0.001) with a determination coefficient (*r*^{2}) of 0.6. Whereas, the correlation between P-G-Gn and P-G-ANS was statistically significant and strong positive (*r* = 0.83, *P* < 0.001) with a determination coefficient (*r*^{2}) of 0.69. Linear regression equations to predict N-ANS-Gn and P-G-Gn were determined using N-ANS-G and P-G-ANS angles as predictors. The equations determined were calculated as y = a + bx where 'y' is the dependent variable, N-ANS-Gn/P-G-Gn, 'x' is the independent variable, N-ANS-G/P-G-ANS, 'a' is the y intercept, and 'b' is the slope of regression. On calculating, for the prediction of N-ANS-Gn, the equation was y = 1.271x + 24.83, N-ANS-Gn (in degrees) = 1.271 N-ANS-G (in degrees) +24.83. For the prediction of P-G-Gn the equation was y = 0.987x + 35.93, P-G-Gn (in degrees) = 0.987 P-G-ANS (in degrees) + 35.93. Applying these equations, the N-ANS-Gn and P-G-Gn were predicted, transferred on to tracing sheet and intersection marked as Gn, to predict VDO-Ceph (VDO on the cephalogram using predicted angles). The mean ± SD (range) of predicted VDO-Ceph was 37.78 ± 1.77 (34 mm-41 mm). The predicted and actual VDO-Ceph for all the participants showed no statistically significant difference (*P* = 0.92).
Discussion | | |
The VDO has been described as the superior limit of rotation closure of mandible around the bicondylar hinge axis.^{[15]} Hence, with loss of posterior teeth, there will be a loss of VDO. The routine clinical determination of rest position and instruments employed for measurement of lower facial height are not accurate for establishing the appropriate lower facial height. Also, the rest position is not fixed or rigid and can be influenced by a variety of extrinsic and intrinsic factors. Hence, there is a need to investigate methods that can guide in the prediction of the lost facial dimensions.
A clear correlation between muscle strength and shape of the face was observed in a study done on children.^{[20]} Thus, the shape and size of facial structures, muscle activity, chewing forces are all interlinked. Therefore, proper establishment of VDO influences the patient's quality of life by improving the function and aesthetics.^{[17]} Therefore, care should be taken to avoid indiscriminate increase or decrease in this value. Standard measurement established through radiographic techniques and cephalometric analyses is needed. These techniques are proved to be easy, accurate, convenient, economical and individualised.^{[15],[16],[17],[18],[19]} In a study done to project radiographic cephalometry as a diagnostic tool in prosthodontics, the maximum correlation between VDO inferior (lower facial angle from the gonion point to the ANS and to the chin point) and the gonial angle was reported.^{[15]} Moreover, regression formulae derived in the study were engaging in this field of Prosthodontics. As the simple regression formulae proposed in that study were based on single cephalometric dimension, it could not claim an accurate measurement.^{[15]} Hence, multiple regression equations derived by considering six angular and four linear cephalometric measurements could surpass these inaccuracies.^{[18]} Despite this alternative, the major drawback is that the dentist needs to invest more time in completing the analysis. As there is a requirement of proposing simple methods with statistical credibility, the present study was planned, which not only simplified the procedure but also increased the accuracy of the measurement.
The facial dimensions follow simple proportions, as stated by various researchers.^{[21],[22]} This concept of harmonic faces can be utilised for the rehabilitation of lost dimensions employing correlation among angles, as done in a previous study. A fixed maxillary relation was transferred to the mandible to determine the maxillomandibular relationship in the vertical plane.^{[17]} Similarly, the statistically significant positive correlations observed in the present study can be due to the fact that human face follows precise dimensions.
The mean difference between the measured and predicted values was 1.6 ± 0.8, which shows the accuracy of the procedure considered. This study projected the fact that correlations are more exciting and relate specifically to the patient. The small dispersion noted is acceptable, because of the 'comfort zone concept', which emphasises VDO to be in a range instead of a fixed point, as dimension varied among individuals at different times, because of the disparity in adaptive capacity.^{[15],[20],[23]} Moderate variations also do not influence muscle activity.^{[23]} The dispersion value in the present study was less, compared to another study^{[15]} done on cephalometrics about VDO determination. Because of the high dispersion in that study, the authors pointed out that cephalometrics using pluralistic method of different regression formulae gives an idea regarding the direction of treatment for the dentists, though not the precise position of VDO.^{[15]}
The landmarks selected in the present study were simple and could be marked easily. Using four cephalometric points, reconstruction of another point, gnathion was done efficiently. Thus, the advantages of the cephalometric reconstruction procedure were strong correlations, ease in calculation, construction and application. As the present study involved participants in the age range of 20–22 years with class I occlusion, the hypothesis proposed has to be tested further, including regression validation. This preliminary data can be used for planning further studies in the application of the formulae for the partially and completely edentulous people. Besides, this technique can also be clinically applied in dentate individuals undergoing orthodontic treatment. The drawback of the present study is the influence of racial differences^{[24]} on the formulae, which can be overcome by using the same theoretical principle and framing separate formulae for other populations.
Conclusion | | |
Cephalometric angular reconstruction, an accurate and convenient tool, can be considered as a reliable method for the estimation of VDO. The considered approach is specific for the age group and race considered. However, further studies on partially and completely edentulous patients are needed for its clinical application.
**Financial support and sponsorship**
Nil.
**Conflicts of interest**
There are no conflicts of interest.
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**Correspondence Address**: Dr. Dileep Nag Vinnakota Department of Prosthodontics, Narayana Dental College, Nellore, Andhra Pradesh India
**Source of Support:** None, **Conflict of Interest:** None
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**DOI:** 10.4103/ijdr.IJDR_783_18
[Figure 1], [Figure 2], [Figure 3] |