Evaluation of the dislodgement force of splinted restorations with engaging conical abutments over multiple nonparallel implants (in-vitro study).

BACKGROUND: Splinted multiunit cement-retained restorations with screw access channels over engaging abutments are viable implant prosthetic options. However, information regarding the maximum degree of divergence between multiple implants is lacking. The purpose of this in vitro study was to determine the maximum degree of divergence between 2 adjacent implants with conical connections that allows insertion and removal of splinted restorations with engaging preparable abutments or titanium base abutments. METHODS: Two implants were aligned in a stone base, one straight and the other at an angle ranging from 0 to 20 degrees. The implants represented an implant system that had an internal conical connection and a hexed abutment engaging the base of the connection. Two straight preparable engaging cement retained abutments were screwed onto the implants and splinted together using acrylic resin. A total of 11 angles were tested, with 7 specimens for every angle. Evaluation of dislodging force was performed by pulling out the splinted abutments after unscrewing them. This was performed subjectively by 3 blinded investigators who applied a tactile pulling force. A scale of 0-10 was used to estimate the pulling force. Objectively the dislodging force was measured in Newtons using a universal testing machine. A statistical correlation was made between the subjective and objective dislodging force values using Spearman's rank correlation coefficient. RESULTS: The mean subjective values increased gradually from 0 to 16 degrees. A sudden rise was noticed at 18 degrees (9.71 ± 0.23) and, at 20 degrees, the investigators were not able to remove the splinted abutments from the implants. The mean objective dislodgement force values increased gradually from 0 to16 degrees and abruptly from 16 degrees (13.57 ± 0.45 N) to 18 degrees (25.40 ± 0.66 N) and 20 degrees (35.22 ± 0.64). The correlation between the subjective and the objective evaluations assessed using the Spearman's rank correlation coefficient was 0.98 indicating a statistically significant correlation (P < .001). As the objective dislodging force increased, the subjective dislodgement difficulty increased. CONCLUSIONS: Splinting cement retained restorations with screw access channels on engaging abutments is possible when multiple implants with conical connections having an internal flare angle of 8 degrees are used, with implant divergence of up to 16 degrees.

Effect of anodized titanium abutment collars on peri-implant soft tissue: A split-mouth clinical study.

STATEMENT OF PROBLEM: Anodic oxidation of titanium implant abutment collars has been used to mask their unesthetic grayish color. However, the effect of anodic oxidation on the health and appearance of peri-implant soft tissues is unclear. PURPOSE: The purpose of this split-mouth clinical study was to investigate the effect of anodized titanium on the health and esthetics of peri-implant soft tissues. MATERIAL AND METHODS: A total of 60 osseointegrated implants placed in 30 participants were included in the present study. Each participant received 2 randomly allocated abutments, one with a pink anodized collar and the other with an unanodized one to form 2 groups: unanodized group (control group) and anodized group (experimental group). All implants were restored with lithium disilicate restorations. Evaluations of the peri-implant soft tissues were performed at the time of definitive restoration insertion (baseline) and after 3, 6, 12, and 18 months: peri-implant probing depth, soft tissue recession, modified sulcus bleeding index, modified plaque index, and modified gingival index. The esthetics of peri-implant soft tissues were evaluated by using the modified pink esthetic score. The paired t test or Wilcoxon signed-rank test was used for comparing the 2 study groups at each point of time depending on the normality of the variables (α=.05). To compare each variable at different time points within each group separately, repeated measures ANOVA or Friedman tests were used according to the normality of the variables, followed by post hoc pairwise comparisons by using the Bonferroni adjusted significance (α=.05). RESULTS: Five peri-implant soft tissue indices were followed up throughout the study. No statistically significant differences were found among the mean values of the tested indices in the anodized and unanodized groups throughout the evaluation periods (P>.05). The collective mean values of the modified pink esthetic score also showed no statistically significant differences between the groups (P>.05). CONCLUSIONS: Based on this split-mouth clinical study, pink anodized titanium abutment collars do not produce a clinically significant effect on the health or esthetics of peri-implant soft tissues.

Effect of yellow anodization of titanium on the shade of lithium disilicate ceramic with different thicknesses.

STATEMENT OF PROBLEM: The color of the titanium abutment can affect the shade of the definitive restoration. Methods such as anodic oxidation, which changes the gray color of implant abutment to yellow, have been advocated to mask the unesthetic gray color of the abutment. However, whether a yellow anodized titanium abutment can prevent discoloration of translucent ceramic restorations is uncertain. PURPOSE: The purpose of this in vitro study was to evaluate the effect of the yellow anodization of titanium on the shade of lithium disilicate ceramic with different thicknesses by using CIEDE 2000 formulas. MATERIAL AND METHODS: Sixty grade V titanium backgrounds were fabricated and divided into 2 test groups (n=30): group A was anodized to a yellow color, and group U was unanodized. Each group was subdivided into 3 subgroups (n=10) according to the thickness of the lithium disilicate ceramic cemented over it: subgroup 1 with 1-mm-thick lithium disilicate, subgroup 1.5 with 1.5-mm-thick lithium disilicate, and subgroup 2 with 2-mm-thick lithium disilicate. Each titanium background was cemented to its corresponding lithium disilicate block by using translucent resin cement. For the control group, 5-mm-thick lithium disilicate specimens were fabricated. Color measurements of the specimens were made with a spectrophotometer, and differences were calculated by using CIEDE 2000 formulas (ΔE00). Comparisons between the 2 study groups were done by using independent samples t test. Two-way ANOVA was used to assess the effect of anodization and thickness on ΔE00 with calculation of adjusted means and 95% confidence intervals (α=.05). RESULTS: Statistically significant differences were found among the mean values between yellow anodized and unanodized groups in all ceramic thicknesses (P<.001 for 1 mm, P<.001 for 1.5 mm, and P<.046 for 2 mm). Yellow anodization of titanium and increasing the ceramic thickness from 1 to 2 mm decreased the ΔE00 values. CONCLUSIONS: The restoration shade appeared to be improved by titanium anodization to a yellow color and by increasing the thickness of the machinable high-translucent lithium disilicate.