Effects of inter-implant distance on the accuracy of intraoral scanner: An in vitro study

PURPOSE@#. Several studies focused on the accuracy of intra-oral scanners in implant dentistry, but the data of inter-implant distances were not widely mentioned. Therefore, this study aimed to evaluate the effect of distance between two implants on the surface distortion of scanned models generated by intra-oral scanners. MATERIALS AND METHODS. Three models with the distances between two fixed scan bodies of 7, 14, and 21 mm were fabricated and scanned with a highly precise D900L dental laboratory scanner as reference models. Fifteen scans were performed with TRIOS3 and CEREC Omnicam intra-oral scanners.Trueness, precision, and angle deviation of the test models were analyzed (α=.05). @*RESULTS@#. There was a significant difference among inter-implant distances in both intraoral scanners (P <.001). The error of trueness and precision increased with the increasing inter-implant length, while the angle deviation did not show the same trend. A significant difference in the angle deviation was found among the inter-implant distance. The greatest angle deviation was reported in the 14-mm group of both scanners (P <.05). In contrast, the lowest angle deviation in the 21-mm group of the TR scanner and the 7-mm of the CR scanner was reported (P <.001). CONCLUSION. The inter-implant distance affected the accuracy of intra-oral scanner. The error of trueness and precision increased along with the increasing distance between two implants. However, the distortions were not clinically significant. Regarding angle deviation, the clinically significant angle deviation may be possible when using intra-oral scanners in the partially edentulous arch.

Effects of inter-implant distance on the accuracy of intraoral scanner: An in vitro study

PURPOSE@#. Several studies focused on the accuracy of intra-oral scanners in implant dentistry, but the data of inter-implant distances were not widely mentioned. Therefore, this study aimed to evaluate the effect of distance between two implants on the surface distortion of scanned models generated by intra-oral scanners. MATERIALS AND METHODS. Three models with the distances between two fixed scan bodies of 7, 14, and 21 mm were fabricated and scanned with a highly precise D900L dental laboratory scanner as reference models. Fifteen scans were performed with TRIOS3 and CEREC Omnicam intra-oral scanners.Trueness, precision, and angle deviation of the test models were analyzed (α=.05). @*RESULTS@#. There was a significant difference among inter-implant distances in both intraoral scanners (P <.001). The error of trueness and precision increased with the increasing inter-implant length, while the angle deviation did not show the same trend. A significant difference in the angle deviation was found among the inter-implant distance. The greatest angle deviation was reported in the 14-mm group of both scanners (P <.05). In contrast, the lowest angle deviation in the 21-mm group of the TR scanner and the 7-mm of the CR scanner was reported (P <.001). CONCLUSION. The inter-implant distance affected the accuracy of intra-oral scanner. The error of trueness and precision increased along with the increasing distance between two implants. However, the distortions were not clinically significant. Regarding angle deviation, the clinically significant angle deviation may be possible when using intra-oral scanners in the partially edentulous arch.

Tensile strength of bilayered ceramics and corresponding glass veneers

PURPOSE: To investigate the microtensile bond strength between two all-ceramic systems; lithium disilicate glass ceramic and zirconia core ceramics bonded with their corresponding glass veneers. MATERIALS AND METHODS: Blocks of core ceramics (IPS e.max(R) Press and Lava(TM) Frame) were fabricated and veneered with their corresponding glass veneers. The bilayered blocks were cut into microbars; 8 mm in length and 1 mm2 in cross-sectional area (n = 30/group). Additionally, monolithic microbars of these two veneers (IPS e.max(R) Ceram and Lava(TM) Ceram; n = 30/group) were also prepared. The obtained microbars were tested in tension until fracture, and the fracture surfaces of the microbars were examined with fluorescent black light and scanning electron microscope (SEM) to identify the mode of failure. One-way ANOVA and the Dunnett's T3 test were performed to determine significant differences of the mean microtensile bond strength at a significance level of 0.05. RESULTS: The mean microtensile bond strength of IPS e.max(R) Press/IPS e.max(R) Ceram (43.40 +/- 5.51 MPa) was significantly greater than that of Lava(TM) Frame/Lava(TM) Ceram (31.71 +/- 7.03 MPa)(P<.001). Fluorescent black light and SEM analysis showed that most of the tested microbars failed cohesively in the veneer layer. Furthermore, the bond strength of Lava(TM) Frame/Lava(TM) Ceram was comparable to the tensile strength of monolithic glass veneer of Lava(TM) Ceram, while the bond strength of bilayered IPS e.max(R) Press/IPS e.max(R) Ceram was significantly greater than tensile strength of monolithic IPS e.max(R) Ceram. CONCLUSION: Because fracture site occurred mostly in the glass veneer and most failures were away from the interfacial zone, microtensile bond test may not be a suitable test for bonding integrity. Fracture mechanics approach such as fracture toughness of the interface may be more appropriate to represent the bonding quality between two materials.

Gap comparison between single crown and three-unit bridge zirconia substructures

PURPOSE: To compare marginal and internal gaps of zirconia substructure of single crowns with those of three-unit fixed dental prostheses. MATERIALS AND METHODS: Standardized Co-Cr alloy simulated second premolar and second molar abutments were fabricated and subsequently duplicated into type-III dental stone for working casts. After that, all zirconia substructures were made using Lava(TM) system. Marginal and internal gaps were measured in 2 planes (mesial-distal plane and buccal-palatal plane) at 5 locations: marginal opening (MO), chamfer area (CA), axial wall (AW), cusp tip (CT) and mid-occlusal (OA) using Replica technique. RESULTS: There were significant differences between gaps at all locations. The mean +/- SD of marginal gap in premolar was 43.6 +/- 0.4 microm and 46.5 +/- 0.5 microm for single crown and 3-unit bridge substructure respectively. For molar substructure the mean +/- SD of marginal gap was 48.5 +/- 0.4 microm and 52.6 +/- 0.4 microm for single crown and 3-unit bridge respectively. The largest gaps were found at the occlusal area, which was 150.5 +/- 0.5 microm and 154.5 +/- 0.4 microm for single and 3-unit bridge premolar substructures respectively and 146.5 +/- 0.4 microm and 211.5 +/- 0.4 microm for single and 3-unit bridge molar substructure respectively. CONCLUSION: Independent-samples t-test showed significant differences of gap in zirconia substructure between single crowns and three-unit bridge (P<.001). Therefore, the span length has the effect on the fit of zirconia substructure that is fabricated using CAD/CAM technique especially at the occlusal area.

The relationship of maxillary canines to the facial anatomical landmarks in a group of Thai people

PURPOSE: The objective was to evaluate canine positions, intercanine tip width (ICTW) and width of distal surface of canine (WDC), related to facial landmarks including interalar width (IAW), intercommissural width (ICoW), and distance between left and right projection lines drawn from inner canthus of eyes to alae of the nose (DPICa) in a group of Thai. MATERIALS AND METHODS: One hundred Thai subjects aged 18-35 years were selected. IAW and ICoW were measured on subject's face using digital vernier caliper. Irreversible hydrocolloid impression of the upper arch was taken, and a cast was poured with dental stone. Silicone impression material was used to take imprint of the incisal edge of upper six anterior teeth. DPICa was obtained from the subject's face using custom-made measuring equipment and marked on the silicone incisal imprint. The marks were then transferred from the imprint to the stone cast and measured with digital caliper. The ICTW and WDC were also measured on the stone cast. Pearson's correlation was used to determine the correlation. RESULTS: The results revealed that the correlation between ICTW-ICoW was 0.429 and ICTW-DPICa was 0.573. The correlation between WDC-ICoW was 0.426 and WDC-DPICa was 0.547. However, IAW did not show any correlation with ICTW or WDC (P>.05). CONCLUSION: The correlation between canine position and facial landmarks was found. ICTW and WDC had relationship with ICoW and DPICa. DPICa showed stronger correlation with the position of maxillary canine than that of ICoW.