Evaluation of implant-supported connecting crowns fabricated by optical and conventional impression methods.

Purpose To investigate the accuracy of implant-supported connecting crowns fabricated with digital definitive casts and conventional definitive casts.Methods Using a master model with two implant bodies inserted into the right mandibular molar area, 10 digital definitive casts were fabricated. Additionally, 10 conventional definitive casts were fabricated. The distance and angle between the two abutments of each definitive cast were compared. To compare the amount of lift of the incisal pin, each of the 10 superstructures was fabricated via computer-aided design/computer-aided manufacturing and then returned to the master model.Results No significant difference was observed for either the angle or the distance between the two abutments. The amount of lift of the incisal pin when the superstructure obtained via the optical method was returned to the master model was significantly larger than that when the superstructure obtained via the conventional method was returned to the definitive cast and the master model. No significant difference was observed after occlusal adjustment of the superstructures obtained using the conventional method.Conclusions The precision of definitive casts obtained via the optical method was virtually equal to that of definitive casts obtained via the conventional method. The accuracy of implant-supported connecting crowns fabricated using the optical method was significantly lower than that of implant-supported connecting crowns fabricated using the conventional method. This is attributed to the alignment of the maxillary and mandibular digital definitive casts.

Application of alumina coping to porcelain laminate veneered crown: part 1 masking ability for discolored teeth.

A densely sintered high-purity alumina has been successfully utilized as a coping for all-ceramic crown. In order to apply the alumina coping to the porcelain laminate veneer restoration for the discolored teeth, the present study evaluated its masking ability when it was thinner than the proposed thickness for the crown. Colorimetric examination was performed on white and black backgrounds for the 0.7 mm thick porcelain laminate veneer with 0.40 or 0.25 mm thick alumina coping and 0.7 mm thick porcelain without coping. With the presence of the coping, the porcelain appeared significantly lighter. Judging from the calculated color differences delta E and the literature, it was suggested that the masking ability of the alumina coping would be sufficient with a 0.25 mm thickness for the porcelain laminate veneer for heavily discolored teeth.

The effects of abutment taper, length and cement type on resistance to dislodgement of cement-retained, implant-supported restorations.

PURPOSE: The purpose of this study was to compare the effect of 20 degrees and 30 degrees of total occlusal convergence (TOC), the occlusocervical dimension, and the type of cement on the tensile resistance to dislodgement of cement-retained, implant-supported restorations. MATERIALS AND METHODS: Cylindrical preparations with TOC angles of 20 degrees and 30 degrees and occlusocervical dimensions of 4 mm (S) and 8 mm (L) were made through a machining process. The cylinders had a shoulder finish line of 1.0 mm in depth. Eight impressions were made of each machined cylinder and poured in type IV dental stone, for a total of 32 dies. Die spacer was applied to each die. A master wax pattern was designed, and the 32 wax patterns were marginated, invested, and cast in type IV gold alloy (n = 8). The gold crowns were cemented with Fleck's cement (zinc phosphate cement), Temp-Bond (zinc oxide eugenol cement), Temp-Bond plus Vaseline (30% by weight), and IMProv temporary cement (acrylic/urethane cement) under a 10-kg load and placed in a humidor at 37 degrees C for 1 hour before testing. A uniaxial tensile force was applied to the crown using an Instron machine with a crosshead speed of 5 mm/min until cement failure occurred. Analysis of variance models were fit to determine the effect of TOC, occlusocervical dimension, and cement type of the restorations on the mean tensile strength. RESULTS: For each type of cement, the mean tensile strengths were significantly higher at 20 degrees of TOC and 8 mm of occlusocervical dimension compared with the other preparations. At this preparation, IMProv had the highest mean tensile resistance to dislodgement (47.7 +/- 8.4 kg), followed by Fleck's (38.2 +/- 8.8 kg), Temp-Bond (35.9 +/- 4.4 kg), and Temp-Bond plus Vaseline (8.2 +/- 2.2 kg). No statistically significant difference was observed between Temp-Bond and Fleck's zinc phosphate cement when 20 degrees of TOC and 8 mm of occlusocervical dimension was used. There was no statistical difference in the mean tensile resistance to dislodgement for Temp-Bond plus Vaseline with different preparation designs (p > 0.05) except when 20 degrees of TOC and 8 mm of occlusocervical dimension was used. The mean tensile strength was significantly different between Temp-Bond and Temp-Bond plus Vaseline for each of the 4 preparation designs (p < 0.05). Among the cements tested, IMProv exhibited higher values, which were statistically different (p < 0.05). Restorations with greater occlusocervical dimension and less TOC exhibited higher tensile resistance to dislodgement. CONCLUSIONS: Preparations with 20 degrees of TOC and 8 mm of occlusocervical dimension had significantly higher mean retentive values for all of the cements tested. Significant differences in mean tensile strength were observed, with the highest tensile resistance seen with IMProv, followed by Fleck's cement, and the lowest tensile resistance seen with Temp-Bond plus Vaseline.

A multicenter interracial study of facial appearance. Part 2: A comparison of intraoral parameters.

PURPOSE: This article compares interracial or gender differences of six intraoral dental parameters among six racial groups (African American, Caucasian, Chinese, Hispanic, Japanese, and Korean). MATERIALS AND METHODS: The same 253 patients participating in part 1 were included in this portion of the study to evaluate six intraoral parameters. The data were collected and analyzed using a one-way analysis of variance, followed by the Tukey-Kramer test for honestly significant difference when statistically significant differences were found (P < .05). RESULTS: Women displayed significantly more gingival tissue in four of the six races, and African Americans displayed significantly more gingival tissue than any other race. Women had significantly more missing teeth than men in three of the six races studied. Japanese subjects had significantly fewer missing teeth and smaller maxillary central incisors than all other groups except Caucasians. Women had significantly narrower maxillary central incisors in three of the races. There was a significantly higher prevalence of Angle Class III relationships in Chinese subjects. The Japanese had significantly more Class II molar relationships than other races. CONCLUSION: Racial and gender differences were found in gingival tissue display, the number of missing teeth, maxillary right central incisor crown width, and Angle molar classification, but not in the amount of vertical or horizontal overlap of the anterior teeth.

A multicenter interracial study of facial appearance. Part 1: A comparison of extraoral parameters.

PURPOSE: This study was undertaken to compare the facial appearance of patients from six racial groups (African American, Caucasian, Chinese, Hispanic, Japanese, and Korean) for interracial and/or gender differences and to determine if "norms" existed. MATERIALS AND METHODS: A total of 253 subjects (144 men and 109 women) ranging in age from 18 to 41 years (mean age 26.5 years) were evaluated using a standardized protocol. The data were collected and analyzed to establish reference ranges for seven frontal and six profile extraoral parameters. Mean scores were compared by race and gender using a one-way analysis of variance, followed by the Tukey-Kramer test for honestly significant difference when statistically significant differences were found (P < .05). RESULTS: There were no significant differences for any of the seven frontal or six profile extraoral parameters between men and women. No significant differences were found between racial groups for five of the seven frontal and one of the six profile extraoral parameters. CONCLUSION: Most of the frontal facial parameters and one profile extraoral parameter might be considered norms for male and female patients of different ethnic origins. Additional research with larger patient populations would be needed to confirm or refute these trends.