Measurement of cement thickness under lithium disilicate crowns using an impression material technique.

According to the literature, marginal gaps below 120 µm are recommended for conventionally cemented crown restorations. Therefore, the null hypothesis tested was as follows: the upper bound of the 95% confidence interval of the marginal accuracy of chair-side generated lithium disilicate crowns lies below 120 µm. Prior to definite insertion, the accuracy of 20 lithium disilicate crowns (e.max CAD LT) was evaluated by a replica technique. A light-body silicone was used to document the gap between crown and abutment. The thickness of the light-body silicone layer was examined under microscope (MM40, Nikon Corp., Tokyo, Japan; magnification, ×50) at four different landmarks (LM): LM1 = marginal discrepancy, LM2 = mid-axial discrepancy of the inner crown surface, LM3 = axio-occlusal discrepancy, and LM4 = mid-occlusal discrepancy. At LM1, the mean marginal discrepancy revealed 100 µm (SD, ±61 µm); the median was 81 µm. The lower bound of the 95% confidence interval was 90 µm, and the upper bound was 110 µm. The means of internal gaps at LM2, LM3, and LM4 showed 148 µm (SD, ±61 µm), 227 µm (SD, ±83 µm), and 284 µm (SD, ±95 µm), respectively. The lower bounds of the 95% confidence interval revealed values between 137 µm (LM2) and 269 µm (LM4). The upper bounds were between 158 µm (LM2) and 300 µm (LM4). The null hypothesis was not rejected. Within the limits of the study, the chair-side generated lithium disilicate crowns exhibited a sufficient clinical accuracy.

A preliminary study on the short-term efficacy of chairside computer-aided design/computer-assisted manufacturing- generated posterior lithium disilicate crowns.

The purpose of this preliminary study was to evaluate the clinical performance of chairside-generated crowns over a preliminary time period of 24 months. Forty-one posterior crowns made of a machinable lithium disilicate ceramic for full-contour crowns were inserted in 34 patients using a chairside computer-aided design/computer-assisted manufacturing technique. The crowns were evaluated at baseline and after 6, 12, and 24 months according to modified United States Public Health Service criteria. After 2 years, all reexamined crowns (n = 39) were in situ; one abutment exhibited secondary caries and two abutments received root canal treatment. Within the limited observation period, the crowns revealed clinically satisfying results.

In vitro analysis of laboratory-processed and CAD/CAM-generated occlusal onlay surfaces.

The purpose of this study was to evaluate the occlusion of all-ceramic onlay surfaces generated with a laboratory (LAB) and computer-aided design/computer-assisted manufacturing (COMP) system. The treatment of the mandibular left first molar was simulated on 16 casts. A minimum of three static contacts and their localization were defined beforehand (MIN3). The occlusal contacts obtained (CORR) were analyzed and the mean quotients (MIN3/CORR) for COMP- and LAB-processed restorations were calculated (1.06 +/- 0.17 and 1.03 +/- 0.13, respectively). The Wilcoxon signed ranks test revealed no significant differences (P <.05).

Marginal fit of heat-pressed vs. CAD/CAM processed all-ceramic onlays using a milling unit prototype.

The composite luting gap between ceramic and dental hard tissue can be termed an "Achilles heel". Therefore, one major goal of luting ceramics focuses on minimizing the inter-marginal gap area. This study evaluated the marginal accuracy of two all-ceramic systems. The null hypothesis was that there is no statistical difference between the marginal accuracy of the IPS Empress and Cerec 3D all-ceramic systems. On 16 casts, representing different clinical situations, the left first mandibular molar was prepared to receive large onlays (MOD and replacement of the distobuccal and distal cusps). For each cavity, one laboratory heat-pressed (IPS Empress) and one chairside CAD/CAM restoration (Cerec 3D) were manufactured. A newly developed milling unit was used for CAM processing. The restorations were placed in their respective cavities and die replicas were taken and examined under SEM for quantitative gap measurement. The gap width was measured at 11 defined landmarks by two different examiners. An overall gap width of 56 microm (+/- 31 microm) was measured for IPS Empress, compared to the significantly increased value of 70 pm (+/- 32 microm) for Cerec 3D. From a clinical viewpoint, the statistically significant difference between the two systems is not relevant, since both systems still exhibit a clinically acceptable gap width of less than 100 microm.