Applying intraoral scanner to residual ridge in edentulous regions: in vitro evaluation of inter-operator validity to confirm trueness.

BACKGROUND: The 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. METHODS: Both 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. RESULTS: In 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. CONCLUSIONS: The present study demonstrated satisfactory trueness of intraoral scanning of the residual ridge in edentulous regions during in vitro evaluation of inter-operator validity.

Determinant Factors in Locating Main Occluding Area on Dental Arch.

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.

Newly designed gustatory test based on the number of chewing strokes required for recognition of the taste.

PURPOSE: The purpose of this study was to examine the usefulness of a new gustatory test based on the progress of mastication by counting the number of chewing strokes required for recognizing tastes. METHODS: Thirty-nine subjects (20 males and 19 females, 25.3±6.4 years old) without missing teeth were selected. Four types of newly designed test materials made from 15% gelatine were prepared, containing sucrose, sodium chloride, tartaric acid, or quinine hydrochloride. Five or six concentrations, representing weak to strong tastes, were prepared for each tastant. Subjects were instructed to chew the food, and the number of chewing strokes necessary to recognize the taste was counted. RESULTS: Female subjects recognized the sweet taste more accurately than male subjects (Friedman test: p<0.05). For each tastant of the test materials, the average number of chewing strokes (recognition threshold) was approximately 10. The frequency of correct responses and the average number of chewing strokes tended to be higher and lower, respectively, as the concentration of the taste in the test material increased (Kruskal-Wallis test: sweet p<0.01, salty p<0.01, sour p<0.01 and bitter p<0.01). CONCLUSIONS: Using the newly designed test materials, counting the number of chewing strokes necessary for recognizing the taste would be a useful index of a new gustatory test to investigate taste sensation.