BackgroundThe purpose of this study was to investigate the trueness of intraoral scanning of residual ridge in edentulous regions during in vitro evaluation of inter-operator validity.MethodsBoth edentulous maxillary and partially edentulous mandibular models were selected as a simulation model. As reference data, scanning of two models was performed using a dental laboratory scanner (D900, 3Shape A/S). Five dentists used an intraoral scanner (TRIOS 2, 3Shape A/S) five times to capture intraoral scanner data, and the “zig-zag” scanning technique was used. They did not have experience with using intraoral scanners in clinical treatment. The intraoral scanner data was overlapped with the reference data (Dental System, 3Shape A/S). Regarding differences that occurred between the reference and intraoral scanner data, the vertical maximum distance of the difference and the integral value obtained by integrating the total distance were analyzed.ResultsIn terms of the maximum distances of the difference on the maxillary model, the means of five operators were as follows: premolar region, 0.30 mm; molar region, 0.18 mm; and midline region, 0.18 mm. The integral values were as follows: premolar region, 4.17 mm2; molar region, 6.82 mm2; and midline region, 4.70 mm2. Significant inter-operator differences were observed with regard to the integral values of the distance in the premolar and midline regions and with regard to the maximum distance in the premolar region, respectively. The maximum distances of the difference in the free end saddles on mandibular model were as follows: right side, 0.05 mm; and left side, 0.08 mm. The areas were as follows: right side, 0.78 mm2; and left side, 1.60 mm2. No significant inter-operator differences were observed in either region.ConclusionsThe present study demonstrated satisfactory trueness of intraoral scanning of the residual ridge in edentulous regions during in vitro evaluation of inter-operator validity.

The mandible exists in a unique mechanical environment subjected to occlusal force and other functional pressures. In dentulous humans, differences in occlusal force and position are believed to be closely linked to the mandible's structural characteristics. The mechanical environment that this bone occupies is difficult to evaluate qualitatively, and it is therefore assessed indirectly by quantitative determination of bone mineral density (BMD). However, in order to understand the loading environment of the human mandible, we must also evaluate local bone quality. In the present study, we therefore sought to identify the structural properties of each tooth in the dentulous human mandible by qualitatively evaluating the crystalline orientation of biological apatite (BAp) as a marker of bone quality. After dividing the area from the alveolar ridge to the apical foramen surrounding the first and second premolar and molar regions of the Japanese dentulous mandible, we measured BAp crystalline orientation and BMD at a total of 4 sites including 2 on the buccal side and 2 on the lingual side. As a result, the orientation of BAp crystallites showed a significant difference between premolar and molar regions, namely preferred orientation in a direction vertical to the occlusal plane (Y-axis) was high for the premolar region and low for the molar region (p < 0.01). These findings indicated that quantitative evaluation of BAp crystallite orientations in the mandibular cortical bone has been revealed to be an effective parameter regarding the local loads that are applied to the human mandible. It was suggested that the distribution map of BAp crystallite orientations in the mandibular cortical bone based on this study would be valuable for planning the prosthodontic treatment in molar and/or premolar regions.

The purpose of this study was to investigate which were the most important factors in determining the location of the main occluding area by comparing its site on the dental arch between patients treated with implant-supported prostheses and those with a shortened dental arch (SDA). Twenty-five patients with Eichner B1 occlusion were enrolled in the study. The molar region in each quadrant was always edentulous. Fifteen patients were treated with implant prostheses, while the remaining 10 patients had SDA. Each patient was instructed to clench a piece of temporary stopping in the occluding area that was preferably used during mastication. The main occluding area was determined by locating the tooth on which the temporary stopping rested during clenching. The main occluding area was located ipsilaterally to the edentulous side in the molar region more often in the implant patients than in the SDA patients. The results of the present study suggest that the most important factor in determining the main occluding area is the presence of bilateral rigid molar occlusal support.