60 completely edentulous patients desirous of seeking complete denture treatment were selected for the study. The patients were informed about the study through participant information sheet and signed consent was obtained. The patients enrolled for the study were within the age group of 40 to 90 years, of which 21 were women and 39 were men. This study was performed in the Department of Prosthodontics and Crown and Bridgework in collaboration with the Department of Oral Medicine and Radiology and the Department of Orthodontics and Dentofacial Orthopaedics, Dharmsinh Desai University, Nadiad. The study was carried out with the approval from the Institutional Ethical panel.
Two pairs of occlusal rims were fabricated for each patient using Modelling wax (Y-Dents, MDM Corp., Lalkuan, Delhi, India), while recording jaw relations (Fig. 1). One pair of occlusal rim was adjusted intraorally, in order to orient the occlusal plane parallel to the inter-pupillary line anteriorly and ala-tragus line posteriorly with the help of a Fox plane (Fox-Plane; ZahnSply, Ghaziabad, Uttar Pradesh, India) and a metallic scale (Steel Scale; Pelican Industries, Rajkot, Gujarat, India) (Fig. 3,4). The other pair of occlusal rim was modified in such a way that the occlusal plane coincides with the corner of mouth anteriorly and anterior two-thirds of the retromolar pad posteriorly (Fig. 4,5). Vertical dimension was kept constant while adjusting each pair of occlusal rims using the Niswonger’s technique.29
Barium sulfate (Barium Sulfate Oral Suspension IP; Eskay Speciality Chemicals, Worli, Mumbai, India) was painted on the occlusal plane of the wax rims (Fig. 6), which were placed intraorally and lateral cephalograms were recorded (Fig. 7). For making lateral cephalograms, all the subjects were instructed to remove jewelleries from the head and neck region to avoid artefacts. All the cephalometric films were exposed keeping a standard distance of five feet between the x-ray target and mid-sagittal plane of patient’s head. Patient’s head was positioned in the Cephalostat (CS 8100SC; Carestream Health, Inc., Rochester, NY USA) with the Frankfort’s Horizontal plane parallel to the floor without any motion during exposure.
Two lateral cephalograms were recorded with each pair of occlusal rim placed intraorally. These lateral cephalograms were traced digitally using Dolphin Imaging Software (Dolphin 3D Imaging 11.5; Patterson Technology, Effingham, Illinois, USA) (Fig. 8,9). The skeletal landmarks traced on the lateral cephalogram were:
a) Porion (Po) :- point at the superior border of the ear rod shadow of the lateral cephalogram.
b) Nasion (N) :- anterior point at the junction of suture of frontal and nasal bones.
c) Anterior nasal spine (ANS) :- point on the lower contour of the anterior nasal spine where thickness of bone is 3 mm.
d) Orbitale (O) :-lowest point on the inferior margin of orbit
e) PoNANS angle (X) :-angle formed by porion, nasion and anterior nasal spine.
f) Frankfort’s Horizontal plane (FH- plane) :- formed by joining porion and orbitale.
g) Ymx :- occlusal plane angle formed by radio-opaque line visible on the occlusal wax rims and FH-plane, wherein occlusal rim was adjusted using inter-pupillary and ala-tragus line.
h) Ymn :- occlusal plane angle formed by radio-opaque line visible on the occlusal wax rims and FH-plane, wherein occlusal rim was adjusted using corner of mouth and anterior two-thirds of the retromolar pad.
The value for PoNANS angle(X) was derived by calculating the mean value of X1 and X2, which was obtained through tracing the PoNANS angle from both the lateral cephalograms. The value of PoNANS angle (X) thus obtained was plotted in the mathematical equation derived for Indian population, in order to calculate occlusal plane angle (Y). For male group, the equation was Y = -0.511 5(X) + 48.1 and for female group, Y = -0.7434(X) + 65.27.5 The occlusal plane angle obtained through clinical methods (Ymx and Ymn) was measured by tracing the radio-opaque line (occlusal plane) and the FH-plane on lateral cephalograms. The occlusal plane angle obtained through various methods such as the mathematical entity (Y), using inter-pupillary and ala-tragus lines (Ymx) and using corner of mouth and anterior two-thirds of the retromolar pad (Ymn) was compared and evaluated through statistical analysis.
OBSERVATION AND RESULTS
The lateral cephalograms obtained for each subject were traced by using Dolphin Imaging software and the measurements were calculated with the measuring tools of the software (Table -1). The mean occlusal plane angle by clinical method Ymx was 10.90 ± 3.96, The mean occlusal plane angle by clinical method Ymn was 10.07 ± 4.49, Mean PoNANS angle (X) was 78.30±3.50 and the mean occlusal plane angle derived by mathematical formula was 7.78 ± 2.21 (Table-2). Pearson’s correlation coefficient was calculated for the PoNANS angle (X) and the occlusal plane angle (Y). There was a negative correlation present between the PoNANS angle and the Occlusal plane angle, which indicates that when the PoNANS angle increases occlusal plane angle definitely decreases (Table-3).
There was a statistically significant difference present in the occlusal plane angle obtained by various methods (p