Influence of space size of abutment screw access channel on the amount of extruded excess cement and marginal accuracy of cement-retained single implant restorations.

STATEMENT OF PROBLEM: The detrimental effect of extruded excess cement on peri-implant tissue has been well documented. Although several techniques have been proposed to reduce this effect by decreasing the amount of extruded cement, how the space size of the abutment screw access channel (SAC) affects the amount of extruded cement and marginal accuracy is unclear. PURPOSE: The purpose of this in vitro study was to evaluate the effect of the size of the unfilled space of the abutment SAC on the amount of extruded excess cement and the marginal accuracy of zirconia copings. MATERIAL AND METHODS: Twelve implant replicas and corresponding standard abutments were attached and embedded in acrylic resin blocks. Computer-aided design and computer-aided manufacturing (CAD-CAM) zirconia copings with a uniform 30-µm cement space were fabricated by 1 dental technician using the standard method. The copings were temporarily cemented 3 times at different sizes of the left space of the SAC as follows: the nonspaced group (NS), in which the entire SAC was completely filled, the 1-mm-spaced group (1MMS), and the 2-mm-spaced group (2MMS). Abutments and crowns were ultrasonically cleaned, steam cleaned, and air-dried. The excess cement was collected and weighed. To measure the marginal accuracy, 20 measurements were made every 18 degrees along the coping margin at ×300 magnification and compared with the pre-cementation readings. One-way ANOVA was calculated to determine whether the amount of extruded excess cement differed among the 3 groups, and the Tukey test was applied for multiple comparisons (α=.05). RESULTS: The mean weights (mg) of extruded excess cement were NS (33.53 ±1.5), 1MMS (22.97 ±5.4), and 2MMS (15.17 ±5.9). Multiple comparisons showed significant differences in the amount of extruded excess cement among the 3 test groups (P<.001). The mean marginal discrepancy (µm) of the pre-cemented group (29.5 ±8.2) was significantly different (P<.01) from that of the NS (72.3 ±13.7), the 1MMS (70.1 ±19), and the 2MMS group (70.1 ±18.8). No significant differences were found in marginal accuracy among the 3 test groups (P=.942). CONCLUSIONS: Within the limitations of this in vitro study, leaving a 2-mm space in the SAC reduced the amount of extruded excess cement by 55% in comparison with the nonspaced abutments. However, no effect was found on the marginal accuracy of zirconia copings.

Influence of framework design on the cervical color of metal ceramic crowns.

STATEMENT OF PROBLEM: The replication of natural teeth, especially for single tooth restorations in patients with high esthetic needs, represents a challenge. PURPOSE: The purpose of the study was to analyze the color of the cervical portion of single metal ceramic crowns fabricated with different metal framework designs. MATERIAL AND METHODS: The color, as measured on the CIELAB color scale, of 3 different groups of restorations (n=10) fabricated with a high noble metal alloy (V-Deltaloy) and feldspathic porcelain (Noritake Super Porcelain) was analyzed with a colorimeter. Conventional metal ceramic crowns with metal facial margins were compared to metal ceramic crowns with porcelain facial margins and a horizontal reduction of the metal framework (1.0 mm reduction) or an additional vertical reduction (1.0 mm reduction). In all specimens, the finish line was positioned at a subgingival or equigingival level. The 6 groups obtained by the combination of the levels of the 2 factors (framework extension and finish line location) were examined with an ANOVA Fisher's F-test and a post hoc Tukey's HSD test (α=.05). RESULTS: The mean color difference for all the groups was clinically acceptable (ΔE<3.7). Conventional metal ceramic crowns showed higher differences in relation to finish line location (ΔE=2.34), while a vertical reduction of the framework was related to lower values (ΔE=0.96). Mean Lab* values were reported for all the groups of crowns. Statistically significant differences were present for L*, a*, and b* values when related to framework extension. Considering each value in relation to the interaction between framework extension and finish line location factors, significant differences were present only for L* and a* values. CONCLUSIONS: No significant differences in base shade were present among the investigated crowns. Nevertheless metal ceramic crowns with vertical cut-back and porcelain facial margins presented more consistent results that tended to be closer to those of natural teeth.