Influence of a specially designed geometric device and modified scan bodies on the accuracy of a maxillary complete arch digital implant scan: An in vitro study.

STATEMENT OF PROBLEM: Capturing accurate complete arch digital implant scans remains a challenging process because of the lack of recognizable anatomic landmarks. The effect of modified scan bodies (SBs) on improving scanning accuracy is unclear. PURPOSE: The purpose of this in vitro study was to evaluate and compare the accuracy of a maxillary complete arch digital implant scan when using a specially designed geometric device with the accuracy of modified scan bodies. MATERIAL AND METHODS: Four implants were placed in an edentulous maxillary model made of porous bone material with polyurethane attached gingiva. Scan bodies were attached to the implants and then digitized with a high precision laboratory scanner to create the reference scan. Round depressions were made on the buccal and palatal surfaces of the scan bodies, and the model was scanned with an intraoral scanner using 4 different scenarios: the model with no geometric device or modified scan bodies (ND-NM), device only without modified scan bodies (D-NM), no device but with modified scan bodies (ND-M), and device with modified scan bodies (D-M). Each group was scanned 10 times for a total of 40 scans. Trueness and precision were evaluated using inspection software to measure the 3D surface deviation. Trueness was measured by superimposing each test scan on the reference scan, and precision was calculated by superimposing the test scans of the same group with each other. Data were analyzed using the GraphPad Prism version 8.0.0 software program. Two-way ANOVA was performed to assess the effect of the device and modifications on trueness and precision (α=.05). RESULTS: Both the geometric device and SB modifications had a significantly significant effect on trueness and precision (P<.001). Regarding trueness, group D-M had the lowest mean and standard deviation (0.158 ±0.028 mm) in contrast with group ND-NM, which had the highest deviation (0.282 ±0.038 mm). In terms of precision, group D-M showed the lowest mean and standard deviation (0.134 ±0.013 mm), while group ND-NM revealed the highest deviation (0.222 ±0.031 mm). However, no statistically significant interaction was found between the device and modifications regarding either trueness or precision (P>.05). CONCLUSIONS: Using a specially designed geometric device improved both the trueness and precision of complete arch digital implant scans. The modified SBs had a positive influence on the scanning trueness and precision, and the best accuracy was achieved when using the geometric device and the modified SBs simultaneously.

Evaluation of the marginal adaptation and debonding strength of two types of CAD-CAM implant-supported cement-retained crowns.

BACKGROUND: In-vitro data from a clinically well-known lithium disilicate ceramic reference was used to assess the expected performance of resin-based materials in implant dentistry. The purpose of the study was to compare the bond strength and marginal adaptation of nano-ceramic hybrid composite crowns cemented to stock cement-retained abutments to lithium disilicate crowns. METHODS: Twenty abutment analogs were embedded into auto-polymerizing acrylic resin blocks. The blocks were divided into 2 groups according to the restorative crown material. The 2 groups were divided as follows: Resin nano-ceramic group and lithium disilicate group. Abutment analogs in both groups were scanned using a laboratory scanner, and the restorations were designed, manufactured, and cemented with resin cement over the corresponding group. All samples were tested for marginal adaptation and bond strength after storage for 24 hours at 37 °C in 100% humidity. Data were collected, tabulated, and statistically analysed using the appropriate tests. Normality was checked using Shapiro Wilk test and Q-Q plots. Data were normally distributed. Variables were presented using mean, 95% Confidence Interval (CI) and standard deviation in addition to median and Inter Quartile Range (IQR). Differences between groups regarding debonding forces was assessed using independent t test. Two Way ANOVA was performed to assess the effect of material and bonding on marginal gap. All tests were two tailed and p value was set at < 0.05. RESULTS: Marginal gap and debonding force values were significantly different according to the type of material used (P < .05). Resin nano-ceramic crowns presented lower marginal gap values before (20.80 ± 8.87 µm) and after (52.11 ± 22.92 µm) bonding than lithium disilicate crowns. The debonding force value for resin nano-ceramic crowns (284.30 ± 26.44 N) was significantly higher than that for lithium disilicate crowns (253.30 ± 33.26 N). Adhesive failure mode was detected in all the specimens in both groups. CONCLUSIONS: The type of material used for implant-supported cement-retained crowns had a statistically significant effect on marginal adaptation and bond strength. Resin nano-ceramic implant-supported cement-retained crowns had better marginal adaptation and higher bond strength than those manufactured using lithium disilicate.

Fit of zirconia fixed partial dentures fabricated from conventional impressions and digital scans: A systematic review and meta-analysis.

STATEMENT OF PROBLEM: Available studies comparing fit accuracy of zirconia fixed partial dentures (FPDs) fabricated from conventional impressions and digital scans provide contradictory results. In addition, studies have been heterogeneous and of a limited number to provide conclusive evidence. PURPOSE: The purpose of this systematic review and meta-analysis was to compare the marginal and intaglio fit of tooth-supported zirconia FPDs fabricated from conventional impressions and digital scans and to investigate the effect of different variables on the fit results. MATERIAL AND METHODS: An electronic search was performed on the National Library of Medicine (NLM), Cochrane Central Register of Controlled Trials, and Scopus databases. In addition, a manual search was carried out. Studies comparing the fit of tooth-supported zirconia FPDs fabricated from conventional impressions and digital scans and reporting sufficient data for qualitative and quantitative analysis were included. Standard mean differences (SMDs) and 95% confidence intervals (CI) were calculated for meta-analysis. Subgroup analysis was performed to study the effect of variables including restoration form (monolithic or framework), units number, intraoral scanner (IOS) type, conventional impression material, spacer thickness, and abutments region. RESULTS: The initial search resulted in a total of 608 articles. Nine articles were included in the analysis (1 clinical and 8 in vitro) evaluating 118 restorations. Digital scan displayed significantly better marginal fit (P<.001; SMD: -0.68; 95% CI: -0.92, -0.09) and intaglio fit (P=.020; SMD: -0.51; 95% CI: -0.94, -0.42). Test for subgroup difference showed a significant influence of only impression material type (P=.008) and units number (P=.030) on marginal fit. Digital scan showed significantly better marginal accuracy for 3-unit FPDs than 4-unit FPDs (P<.001; SMD: -1.02; 95% CI: -1.41, -0.63). In addition, digital scanning had significantly better marginal fit with polyvinyl siloxane than polyether (P<.001; SMD: -0.98; 95% CI: -1.32, -0.64). A cement spacer ≤50 µm improved both marginal and intaglio fit in the digital group. The TRIOS scanner resulted in the best performance in the digital group for marginal fit. CONCLUSIONS: Digital scanning provides significantly better marginal and intaglio fit than conventional impression making for fabricating zirconia FPDs up to 4 units, either in monolithic form or frameworks and at any region of the arch. However, further clinical studies are recommended to obtain more substantial results.

Effect of additional pressing on the color and translucency of pressable ceramic materials: An in vitro study.

STATEMENT OF PROBLEM: Whether reusing the buttons of pressable ceramic materials affects their color or translucency is unclear. PURPOSE: The purpose of this in vitro study was to investigate the effect of additional pressing on the color and translucency of 3 different lithium disilicate ceramic brands. MATERIAL AND METHODS: Seventy-two disk-shaped ceramic specimens (Ø14×1.5 mm) were divided into 2 groups: pressed group and additionally pressed group, each containing 36 specimens. These groups were further divided into 3 subgroups: lithium disilicate (LDS), lithium disilicate with high-density micronization technology (LDS-HDM), and zirconia-reinforced lithium silicate (ZLS). Pressing was performed in the press group yielding 36 pressed specimens. Additional pressing was performed by using the buttons resulting from the press group, yielding 36 additionally pressed specimens. Color differences and translucency between pressed and additionally pressed groups were measured with a portable spectrophotometer (VITA Easyshade Compact). The translucency parameter (TP) was measured on black and white backgrounds. Color differences between the 2 groups were analyzed statistically by using the Kruskal-Wallis nonparametric test followed by the Dunn-Sidek method for individual comparison among means of all groups (α=.05). RESULTS: A statistically significant difference was found in color after additional pressing among the 3 tested materials (P=.005). After additional pressing, color difference (ΔE) values were found between the LDS group (3.78 ±1.11) and the ZLS group (3.03 ±1.44). These ΔE values were beyond the selected clinical perceptible threshold (ΔE=2.6). However, the LDS-HDM group had a ΔE value of 1.80 ±1.22, which is considered clinically not perceivable. Furthermore, LDS showed a statistically significant decrease in translucency after additional pressing (P=.002). However, after additional pressing, ZLS and LDS-HDM showed no statistically significant differences in translucency (P>.05). CONCLUSIONS: The colors of the 3 tested materials were affected by additional pressing. Only LDS-HDM showed color changes below the selected clinically perceptible threshold (ΔE=2.6). Furthermore, only LDS showed a significant decrease in translucency.

Fit of monolithic multilayer zirconia fixed partial dentures fabricated by conventional versus digital impression: a clinical and laboratory investigations.

OBJECTIVES: This study aimed to compare the accuracy of conventional and digital impressions based on the fit of produced three-unit fixed partial dentures (FPDs) in vivo and the trueness and precision of both impression techniques. MATERIALS AND METHODS: Twelve patients received a conventional polyether impression (group C, control, n=12) and a digital impression with CS3500 (group D, test, n=12) for each participant. Monolithic multilayer zirconia FPDs were fabricated, and the internal and marginal fit were assessed using the replica technique. Trueness and precision of both impression methods were assessed in vitro. A master model was used to create a reference scan. The master model received conventional impressions (group C, control, n=5) and digital impressions (group D, test, n=5). The virtual models of both groups were superimposed over the reference scan (5 superimpositions) using a three-dimensional (3D) processing software, and the 3D deviations were measured and averaged to obtain trueness value. For precision, the virtual models of each group were superimposed over each other (10 superimpositions) and the average deviation value was calculated. The data were analyzed using one-tailed Mann-Whitney U test at P ≤ 0.05. RESULTS: Group D resulted in a significantly better marginal and internal fit (30.91±15.15 and 30.86±13.57 µm for group D and 40.02±19.50 and 41.86±18.94 µm for group C). The mean values of trueness and precision for conventional and digital techniques were comparable (trueness: 62.8±5.45 and 62.72±12.01 µm and precision: 56.47±27 and 60.9±14.5 µm, respectively). CONCLUSIONS: No significant difference was found between conventional and digital impressions in 3D datasets accuracy. In addition, both techniques resulted in FPDs with an acceptable clinical fit. However, the FPDs fabricated using the digital technique displayed better internal and marginal fit. CLINICAL RELEVANCE: The applied impression technique as well as the computer-aided processing of the produced virtual models can significantly affect the fit of the final restoration. Direct digital impression is recommended over conventional impression for fabricating accurate monolithic zirconia 3-unit FPDs. TRIAL REGISTRATION: This clinical trial was retrospectively registered on August 11, 2020, in the Pan African Clinical Trial Registry database, and the number for the registry is PACTR202008685699453.

Corrigendum to "Effect of Incisal Porcelain Veneering Thickness on the Fracture Resistance of CAD/CAM Zirconia All-Ceramic Anterior Crowns".

[This corrects the article DOI: 10.1155/2019/6548519.].