Evaluation of the relationship between occlusal contact areas and chewing efficiency in patients who underwent orthodontic treatment with premolar extractions

Extraction and non-extraction treatment methods for borderline cases in orthodontics have always been a subject of debate. The aim of this thesis is to evaluate the potential effects of premolar extraction on masticatory performance by comparing the occlusal contact areas and masticatory performance of patients who underwent fixed orthodontic treatment with and without premolar extraction to those of untreated individuals. Furthermore, the correlation between the masticatory performance, the occlusal contact areas, the retention duration, and the post- treatment quality will also be evaluated. The null hypothesis is that premolar extraction does not affect the occlusal contact areas nor the masticatory performance. In this study, data from 320 patients were evaluated based on the archive records of the Department of Orthodontics, Faculty of Dentistry, Bezmialem Vakif University. Data from a control group of 31 people without a history of orthodontic treatment were compared with data from 75 patients between the ages of 18 and 40 who had received orthodontic treatment between 2011 and 2024, had finished treatment at least six months earlier, and had no missing teeth other than premolars and third molars. The study sample was formed of 4 groups. The participants included 4 premolar extraction cases (Group 1: 15 females, 7 males), 2 upper premolar extraction cases (Group 2: 18 females, 3 males), non-extraction treatment cases (Group 3: 19 females, 12 males), and untreated individuals (Group 4: 18 females, 13 males). Dental impressions and panoramic radiographs were obtained from the patients. Orthodontic diagnostic models derived from the impressions and panoramic radiographs were evaluated according to ABO-OGS criteria to assess the quality of treatment completion. 3D intraoral scans were taken with the iTero Element 5D (Align Technologies, San Jose, California, USA) system. The digital models were transferred to the OrthoCAD (Cadent, Fairview, New Jersey, USA) software to identify occlusal contact areas in maximum intercuspation. Average contact areas for mandibular molars and premolars were measured using ImageJ (Macintosh, NIH, Bethesda, Maryland, USA) software. The two-colored chewing gum mixing method was used to evaluate masticatory performance. Vivident Fruit Swing (Perfetti van Melle, Turkey) chewing gum (watermelon and acai grape flavors) was chewed by participants with 20 strokes and then flattened to a 1 mm thickness. The gum samples were scanned at 300 DPI using a color desktop scanner, and color mixing was analyzed using ViewGum (dhal, Kifissia, Greece) software. The collected data were analyzed using the SPSS software. In the intergroup comparisons, a statistically significant difference was observed in age between Group 2 and Group 4 (p<0.05) and in gender within Group 2 (p<0.05). A significant difference in ABO-OGS scores was found between Group 2 and Group 4 (p<0.05), while no significant difference was observed among the groups in terms of time elapsed since treatment completion (p>0.05). There was no significant difference among the groups in heavy occlusal contact areas (p>0.05), whereas moderate contact areas showed a significant difference between Group 2 and Group 3 (p<0.05), and between Group 2 and Group 4 (p<0.001). No significant difference was found among the groups in masticatory performance (p>0.05). The gender parameter had no significantly effect on the masticatory performance, nor the occlusal contact areas. No statistically significant correlation was observed between ABO-OGS scores and occlusal contact areas, masticatory performance, or the time elapsed since treatment completion. Likewise, no significant correlation was found between masticatory performance and occlusal contact areas or time elapsed since treatment completion. However, a moderate positive correlation was found between the occlusal contact areas and the retention time (moderate contact r=0.440; heavy contact r=0.429). Although variations in occlusal contact areas were noted among individuals who underwent extraction of two maxillary premolars, those treated without extractions, and untreated controls, these differences did not translate into statistically significant changes in masticatory performance. Similarly, in patients who had four premolars extracted, no significant differences were observed in either occlusal contact areas or masticatory performance when compared to non-extraction treatment group and untreated individuals. Furthermore, no significant associations were found between occlusal contact areas and masticatory performance. However, a correlation was identified between the duration since treatment completion and the extent of occlusal contact areas.