PURPOSE: The purpose of this study was to evaluate the proper axial thickness of zirconia abutment applied to implant in the anterior region. MATERIALS AND METHODS: Zirconia abutments were prepared at different axial wall thickness by processing pre-sintered zirconia blocks via CAD/CAM to obtain equal specimens. The abutments were each produced with a thickness of 0.5 mm (Group 1), 0.8 mm (Group 2), 1.2 mm (Group 3), or 1.5 mm (Group 4). The implant used in this study was a external connection type one (US, Osstem, Pussan, Korea) product and the zirconia abutment was prepared via replication of a cemented abutment. The crowns were prepared via CAM/CAM with a thickness of 1.5 mm and were cemented to the abutments using RelyX(TM) UniCem cement. A universal testing machine was used to apply load at 30 degrees and measure fracture strength of the zirconia abutment. RESULTS: Fracture strength of the abutments for Group 1, Group 2, Group 3, and Group 4 were 236.00 +/- 67.55 N, 599.00 +/- 15.80 N, 588.20 +/- 33.18 N, and 97.83 +/- 98.13 N, respectively. Group 1 showed a significantly lower value, as compared to the other groups (independent Mann-Whitney U-test. P<.05). No significant differences were detected among Group 2, Group 3, and Group 4 (independent Mann-Whitney U-test. P>.05). CONCLUSION: Zirconia abutment requires optimal thickness for fracture resistance. Within the limitation of this study, > 0.8 mm thickness is recommended for zirconia abutment in anterior implants.
Crowns

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Crowns*

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Crowns*

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Crowns*

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Crowns*

PURPOSE: To compare and analyze trueness and precision of provisional crowns made using stereolithography apparatus and subtractive technology. MATERIALS AND METHODS: Digital impressions were made using a master model and an intraoral scanner and the crowns were designed with CAD software; in total, 22 crowns were produced. After superimposing CAD design data and scan data using a 3D program, quantitative and qualitative data were obtained for analysis of trueness and precision. Statistical analysis was performed using normality test combined with Levene test for equal variance analysis and independent sample t-test. Type 1 error was set at 0.05. RESULTS: Trueness for the outer and inner surfaces of the SLA crown (SLAC) were 49.6±9.3 µm and 22.5±5.1 µm, respectively, and those of the subtractive crown (SUBC) were 31.8±7.5 µm and 14.6±1.2 µm, respectively. Precision values for the outer and inner surfaces of the SLAC were 18.7±6.2 µm and 26.9±8.5 µm, and those of the SUBC were 25.4±3.1 µm and 13.8±0.6 µm, respectively. Trueness values for the outer and inner surfaces of the SLAC and SUBC showed statistically significant differences (P < .001). Precision for the inner surface showed significance (P < .03), whereas that for the outer surface showed no significance (P < .58). CONCLUSION: The study demonstrates that provisional crowns produced by subtractive technology are superior to crowns fabricated by stereolithography in terms of accuracy.
Crowns

BACKGROUNDFor esthetic consideration, dentin color post core materials were normally used for all-ceramic crown restorations. However, in some cases, clinicians have to consider combining a full ceramic crown with a metal post core. Therefore, this experiment was conducted to test the esthetical possibility of applying cast metal post core in a full ceramic crown restoration.

METHODSThe color of full ceramic crowns on gold and Nickel-Chrome post cores was compared with the color of the same crowns on tooth colored post cores. Different try-in pastes were used to imitate the influence of a composite cementation on the color of different restorative combinations. The majority of patients could not detect any color difference less than DeltaE 1.8 between the two ceramic samples. So, DeltaE 1.8 was taken as the objective evaluative criterion for the evaluation of color matching and patients' satisfaction.

RESULTSWhen the Empress 2 crown was combined with the gold alloy post core, the color of the resulting material was similar to that of a glass fiber reinforced resin post core (DeltaE = 0.3). The gold alloy post core and the try-in paste did not show a perceptible color change in the full ceramic crowns, which indicated that the color of the crowns might not be susceptible to change between lab and clinic as well as during the process of composite cementation. Without an opaque covering the Ni-Cr post core would cause an unacceptable color effect on the crown (DeltaE = 2.0), but with opaque covering, the color effect became more clinically satisfactory (DeltaE = 1.8).

CONCLUSIONSIt may be possible to apply a gold alloy post core in the Empress 2 full ceramic crown restoration when necessary. If a non-extractible Ni-Cr post core exists in the root canal, it might be possible to restore the tooth with an Empress 2 crown after covering the labial surface of the core with one layer of opaque resin cement.

OBJECTIVETo access the effects of post's diameter on the retention of post-core restorations.

METHODSThirty-three simulant roots with same length,taper and different diameter (1.305 mm, 1.830 mm, 2.175 mm and 2.700 mm respectively) were made of polymethylmethacrylate and were divided into 4 groups. The wax patterns of post-cores were manufactured and cast. The post-cores were cemented. After that, the adhesion, frictional force and restriction of the post-core restorations were measured.

RESULTSWhen the proportion of length and diameter was smaller than 4.372, the linear regression between the post's diameter and the retention of post-core crown system was F = 107.98 + 72.08D. The linear regression between the post's diameter and the adhesion was P = 9.60 + 2.22D. The linear regression between the post's diameter and the frictional force and restriction was Q = 98.37 + 69.87D. The statistical analysis of the results indicated significant difference (P < 0.05). When the proportion of length and diameter was lager than 4.372, the retention of post-core crown system increased although the post's diameter decreased.

CONCLUSIONWhen the proportion of length and diameter was smaller than 4.372, the retention of post-core crown system increased with the decrease of the post's diameter. While the proportion was lager than a certain value, this rule did not exist.

OBJECTIVETo evaluate the clinical effect of indirect cast post core by two different impression methods between silicone rubber impression and agar/alginate combination impression.

METHODS389 massive destruction teeth after root canal therapy were randomly divided into two groups (group A and group B). The teeth of group A was treated by silicone rubber impression material for making indirect post core impression. The teeth of group B was treated by agar/alginate combination impression for making indirect post core impression. The effect of two different impression methods was evaluated.

RESULTSThe success rate of making indirect post core impression by silicone rubber impression method was higher than that of making impression by agar/alginate combination impression method. Significant difference was found in making indirect post core impression between premolars and molars by two different impression methods (P<0.05), while there was no significant difference in making indirect post core impression of anterior teeth by two different impression methods (P>0.05).

CONCLUSIONThe clinical effect of making indirect post core impression by silicone rubber impression method is better than that of making impression by agar/alginate combination impression method.

Many patients with large-area tooth defect need cast post-core crown restoration. However, the color defect of the cast post-core will affect the final restorative result, especially that of the anterior teeth. A new technology of color masking by applying CERAMAGE polymeric porcelain to the cast metal post-core surface improves the color of a full-ceramic restoration of anterior teeth and may provide a new alternative for the aesthetic repair of anterior teeth with a large area of defective tooth.
Ceramics ; Crowns ; Dental Porcelain ; Esthetics, Dental ; Humans ; Post and Core Technique