Clinical Assessment of Dynamic and Static Occlusal Contacts in Direct and Indirect Posterior Restorations

The study was conducted on patients who applied to the undergraduate and postgraduate clinics of the Department of Restorative Dentistry, Marmara University Dentistry Faculty. The number of teeth to be included in the study was determined by Statistical Power Analysis (G-Power Analysis). With 90% confidence (1-α), 85% test power (1-β), and an effect size of f =0.276, the total number of teeth to be included in the study for 3 groups was determined to be a minimum of 90. Patients aged between 17 and 45 requiring restoration of maxillary or mandibular first molar teeth were included in the study. The teeth with mesial-occlusal-distal (MOD) cavity preparation encompassing 50% of the intercuspal distance for direct restorations and overlay preparation for indirect restorations were included. The ones having asymptomatic root canal treatments were also included. Those who had caries, crowns, amalgam restorations, fractures, pathological wear, or severe periodontal problems on their maxillary or mandibular first molar teeth were excluded from the study. The patients who had active temporomandibular disorders, missing teeth, primary dentition, posterior disocclusion, posterior crossbite, and anterior openbite were also excluded. Those who were undergoing active orthodontic treatment were excluded from the study. Finally, total of 90 maxillary or mandibular first molars were selected from 45 patients. All the included patients were informed about the study procedures and provided written informed consent before the study.

The restorations were performed using standardized equipment and techniques for the study groups either by a 5th-grade undergraduate clinician or a postgraduate clinician with 5 years of clinical experience. Three application groups were determined according to the type of posterior restoration and clinician. The postgraduate clinician performed 30 direct posterior MOD restorations and 30 indirect overlay restorations, and the undergraduate clinician performed 30 direct posterior MOD restorations.

Intraoral scans of the final direct and indirect restorations were obtained at immediately after and one month recall periods using the Element 5D intraoral scanner. To prevent any unintended change in occlusion, the dental procedures were prohibited for the patients between the first and second intraoral scans. For each patient, full maxillary and mandibular arches and the interocclusal records were scanned and recorded by the postgraduate clinician, and the acquired scan data were exported as polygon file format (.PLY). Then 3D digital models of the jaws were transferred to a specific software program (ChairsideCAD 3.1, Exocad, Align), in which the static and dynamic occlusal contacts with the opposing dentition could be visualized. To evaluate static and dynamic occlusal contacts, two different methods were followed.

For static occlusal contacts, after importing .PLY files into ChairsideCAD software program, the tightness of the occlusal contact surfaces was visualized and evaluated by eight occlusal distance grades: 10, 50, 100, 150, 200, 250, 300, and 350 μm. High resolution .PNG images of upper or lower jaws' 3D models were generated from the occlusal plane when the entire occlusal surface and occlusal contact areas were visible. Therefore, 8 different 2D images representing each grade were recorded in high-resolution of 90 teeth immediately after the restorations and one month after the restorations.

For the dynamic occlusal contact surface evaluation, .PLY files were imported to ChairsideCAD 3.1 software program, then 3D models were mounted on a fully adjustable Arcon type virtual articulator (Artex CR, Amann Girrbach) integrated with the software. For the mounting of the maxillary arch model to the articulator, the mesio-incisal embrasure of the upper central teeth and the mesio-buccal tubercle of the left and right upper first molars were selected respectively. The virtual articulator was adjusted to the average value parameters: Bennett angle was set at 10 degrees, immediate side shift was set at 0.5 mm, condylar angle was set at 30 degrees, and incisal table angle was set at 30 degrees as described in a previous research. In the articulator tool of the software program, the lateral movements of 0.5, 1, 2, and 3 mm were set gradually to the working side. The tightness of the occlusal contact surfaces was defined by the same occlusal distances as in static occlusal contacts (10, 50, 100, 150, 200, 250, 300, and 350 µm). The occlusal surface dynamic contacts were assessed as positive (+) or negative (-) for each lateral movement step, for all occlusal distances, immediately after the restorations and one month after the restorations.