Investigation of accuracy and reproducibility of abutment position by intraoral scanners.

PURPOSE: We examined the accuracy, including trueness and precision, of the intraoral scanners comparing with laboratory scanner to reveal the error level of intraoral scanners. METHODS: Measurements were performed using a computer numerical control coordinate measuring machine (CNCCMM) of the reference models as a control. Subsequently, intraoral scanners and a laboratory scanner were used for measurements of the reference trueness and precision of the distance were evaluated by image analyzing software. RESULTS: With regard to reference model, there was a significant difference between in the trueness measured by C.O.S. (COS) and that measured by the other scanners. The trueness measured by the second-generation 3M™ true definition scanner (TDS2) and third-generation 3M™ true definition scanner (TDS3) was bigger than the one by TRIOS (TR) and KaVo (KA). With regard to reference model "B," error of the trueness measured by COS was significantly bigger, compared with the one measured by the other scanners. However, error range of intraoral scanners, except for COS, was considerably small and it should be covered with cement space. CONCLUSIONS: The results of this study indicated that an optical impression method with an intraoral scanner could be applied to the implant therapy for multiple teeth missing.

Examination of the Position Accuracy of Implant Abutments Reproduced by Intra-Oral Optical Impression.

An impression technique called optical impression using intraoral scanner has attracted attention in digital dentistry. This study aimed to evaluate the accuracy of the optical impression, comparing a virtual model reproduced by an intraoral scanner to a working cast made by conventional silicone impression technique. Two implants were placed on a master model. Working casts made of plaster were fabricated from the master model by silicone impression. The distance between the ball abutments and the angulation between the healing abutments of 5 mm and 7 mm height at master model were measured using Computer Numerical Control Coordinate Measuring Machine (CNCCMM) as control. Working casts were then measured using CNCCMM, and virtual models via stereo lithography data of master model were measured by a three-dimensional analyzing software. The distance between ball abutments of the master model was 9634.9 ± 1.2 µm. The mean values of trueness of the Lava COS and working casts were 64.5 µm and 22.5 µm, respectively, greater than that of control. The mean of precision values of the Lava COS and working casts were 15.6 µm and 13.5 µm, respectively. In the case of a 5-mm-height healing abutment, mean angulation error of the Lava COS was greater than that of the working cast, resulting in significant differences in trueness and precision. However, in the case of a 7-mm-height abutment, mean angulation errors of the Lava COS and the working cast were not significantly different in trueness and precision. Therefore, distance errors of the optical impression were slightly greater than those of conventional impression. Moreover, the trueness and precision of angulation error could be improved in the optical impression using longer healing abutments. In the near future, the development of information technology could enable improvement in the accuracy of the optical impression with intraoral scanners.

Clinical evaluation of a dental color analysis system: the Crystaleye Spectrophotometer®.

PURPOSE: To evaluate the clinical performance of the Crystaleye Spectrophotometer(®), a dental color analysis system. METHODS: Three color-measuring devices (Crystaleye Spectrophotometer(®), CAS-ID1, MSC-2000) were tested and the differences in color measurements among them were evaluated using Scheffe's F-test. Color measurements with the Crystaleye Spectrophotometer(®) were repeated 10 times by the same operator. The color difference (ΔE) between the first and tenth measurements was calculated. The Crystaleye Spectrophotometer(®) was used to measure the color of the maxillary left central incisor under two conditions (light and dark) and the effect of exterior lighting was analyzed to assess the accuracy of measurements. Furthermore, five different operators performed color measurements, and ΔE among the three devices was calculated. The ΔE between the target tooth and the crown of a single maxillary central incisor crown fabricated using data from the Crystaleye Spectrophotmeter(®) was calculated. Color differences between prebleaching and postbleaching were also analyzed with the Crystaleye Spectrophotometer(®) using the parameters ΔE, ΔL*, Δa*, and Δb*. RESULTS: The data from the three spectrophotometers were not significantly different. The ΔE during repeated color measurements by the same operator was 0.6. The ΔE between light and dark conditions was 0.9. The data from the five operators were not significantly different. The mean ΔE value between the target tooth and the fabricated crown was 1.2 ± 0.4, and the mean ΔE value between prebleaching and postbleaching was 3.7 ± 1.0. CONCLUSIONS: The Crystaleye Spectrophotometer(®) is an easy-to-use color analysis system producing accurate color measurements under clinical conditions.

[Case report of a patient treated with unilateral extension base denture using the altered cast technique].

PATIENT: The patient was a 70-year-old male with a chief complaint of poor adaptation of a mandibular unilateral extension base denture. The diagnosis was missing teeth of the mandibular bilateral second premolars, the first molars and the mandibular left second molar as well as poorly-fitting facing crowns in the mandibular bilateral canines and the first premolars. After inserting the facing crowns, a metal base denture was constructed using the altered cast technique. After 3 years, the metal base denture's masticatory function and appearance were successfully achieved. DISCUSSION: It was considered an achievement in this case to get maximum support from the residual ridge using the altered cast technique. CONCLUSION: The metal base denture was constructed using the altered cast technique and successful masticatory function was gained.