An In Vitro Comparison of the Marginal Adaptation Accuracy of CAD/CAM Restorations Using Different Impression Systems.

PURPOSE: To compare the marginal adaptation of 3-unit zirconia fixed dental prostheses (FDPs) obtained from intraoral digital scanners (Lava True Definition, Cadent iTero), scanning of a conventional silicone impression, and the resulting master cast with an extraoral scanner (3Shape lab scanner). MATERIALS AND METHODS: One reference model was fabricated from intact, non-carious, unrestored human mandibular left first premolar and first molar teeth (teeth #19 and 21), prepared for a three-unit all-ceramic FDP. Impressions of the reference model were obtained using four impression systems (n = 10), group 1 (PVS impression scan), group 2 (stone cast scan), group 3 (Cadent iTero), and group 4 (Lava True Defintion). Then the three-unit zirconia FDPs were milled. Marginal adaptation of the zirconia FDPs was evaluated using an optical comparator at four points on each abutment. The mean (SD) was reported for each group. One-way ANOVA was used to assess the statistical significance of the results, with post hoc tests conducted via Tukey's HSD. p < 0.05 was considered statistically significant. All analyses were done using SPSS 22.0. RESULTS: The mean (SD) marginal gaps for the recorded data from highest to lowest were silicone impression scans 81.4 µm (6.8), Cadent iTero scan 62.4 µm (5.0), master cast scan 50.2 µm (6.1), and Lava True definition scan 26.6 µm (4.7). One-way ANOVA revealed significant differences (p < 0.001) in the mean marginal gap among the groups. The Tukey's HSD tests demonstrated that the differences between all groups (silicone impression scan, master cast scan, Lava True definition scan, iTero Cadent scan) were statistically significant (all p < 0.001). On the basis of the criterion of 120 µm as the limit of clinical acceptance, all marginal discrepancy values of all groups were clinically acceptable. CONCLUSIONS: Within the confines of this in vitro study, it can be concluded that the marginal gap of all impression techniques was within the acceptable clinical limit (120 µm). Group 4 (Lava True Defintion) showed the lowest average gap among all groups followed by group 2 (stone cast scan), group 3 (Cadent iTero), and group 1 (PVS impression scan); these differences were statistically significant.

Effect of different dental ceramic systems on the wear of human enamel: An in vitro study.

STATEMENT OF PROBLEM: The wear of tooth structure opposing different advanced dental ceramic systems requires investigation. PURPOSE: The purpose of this in vitro study was to compare the wear of advanced ceramic systems against human enamel antagonists. MATERIAL AND METHODS: Four ceramic systems (IPS e.max Press, IPS e.max CAD, Noritake Super Porcelain EX-3, and LAVA Plus Zirconia) and 1 control group containing human enamel specimens were used in this study (n = 12). All specimens were fabricated as disks 11 mm in diameter and 3 mm thick. The mesiopalatal cusps of the maxillary third molars were prepared to serve as the enamel styluses. All specimens were embedded individually in 25 mm(3) autopolymerizing acrylic resin blocks. Wear was measured with a cyclic loading machine and a newly designed wear simulator. All enamel styluses (cusps) were scanned using the Activity 880 digital scanner (SmartOptics). Data from the base line and follow-up scans were collected and compared with Qualify 2012 3-dimensional (3D) and 2D digital inspection software (Geomagic), which aligned the models and detected the geometric changes and the wear caused by the antagonist specimen. One-way ANOVA was used to analyze the collected data. RESULTS: After 125,000 bidirectional loading cycles, the mean loss of opposing enamel volume for the enamel disks in the control group was 37.08 µm(3), the lowest mean value for IPS e.max Press system was 39.75 µm(3); 40.58 µm(3) for IPS e.max CAD; 45.08 µm(3) for Noritake Super Porcelain EX-3 system; and 48.66 µm(3) for the Lava Plus Zirconia system. No statically significant differences were found among the groups in opposing enamel volume loss (P=.225) or opposing enamel height loss (P=.149). In terms of opposing enamel height loss, Lava Plus Zirconia system showed the lowest mean value of 27.5 µm. The mean value for the IPS e.max CAD system was 27.91 µm; 29.08 µm for the control enamel; 33.25 µm for the IPS e.max Press system; and 34.75 µm for the Noritake Super Porcelain EX-3 system. CONCLUSIONS: Within the limitations of this in vitro study, no differences were found in the linear and volumetric reduction of enamel cusps abraded against enamel disks and all other ceramic specimens. All ceramic systems exhibited high durability and were wear-friendly to opposing enamel.

An In Vitro Comparison of Fracture Load of Zirconia Custom Abutments with Internal Connection and Different Angulations and Thicknesses: Part II.

PURPOSE: The purpose of part II of this in vitro study was to compare the fracture load of two-piece zirconia custom abutments with different thicknesses and angulations. MATERIALS AND METHODS: Forty zirconia custom abutments were divided into four groups as follows: group A1: 0.7 mm thickness and 0° angulations; group A2: 0.7 mm thickness and 15° angulations; group B1: 1 mm thickness and 0° angulations; group B2: 1 mm thickness and 15° angulations. As in part I, in all groups, implant replicas were mounted in self-cure acrylic jigs to support the abutments. The zirconia custom abutments were engaged in the implant replicas using a manual torque wrench. All jigs were secured and mounted in a metallic vice and subjected to shear stress till failure using a universal testing machine with a 0.5 mm/min crosshead speed with the force transferred to the lingual surface of the zirconia custom abutments 2 mm below the incisal edge. The test specimens used in this study did not include a crown. The universal testing machine was controlled via a computer software system, which also completed the stress-strain diagram and recorded the breaking fracture load. The fracture loads were recorded for comparison among the groups and subjected to statistical analysis (two-way ANOVA and Kolmogorov-Smirnov). RESULTS: The mean fracture load of zirconia custom abutments across the groups (A1 to B2) ranged from 432 ± 97 N to 746 ± 275 N. The angulated zirconia custom abutment exhibited the highest fracture load, which was statistically significant (p = 0.045). The thickness of the zirconia custom abutment also had a positive influence on the strength of the specimens (p = 0.005). CONCLUSIONS: In this study, the 15° angulated zirconia custom abutments showed the highest fracture load of those investigated. The 1 mm thick zirconia custom abutments also exhibited significantly higher fracture load compared to 0.7 mm abutments. CLINICAL IMPLICATIONS: The results of this in vitro study will help dental practitioners with their decision-making process in selecting the type of custom abutment to be used clinically.

Marginal and internal adaptation of ceramic crown restorations fabricated with CAD/CAM technology and the heat-press technique.

STATEMENT OF PROBLEM: The accuracy of chairside computer-aided design and computer-aided manufacturing (CAD/CAM) restorations is questionable, and the effect of the die spacer settings is not well stated in the literature. PURPOSE: The purpose of the study was to evaluate the marginal and internal adaptation of E4D crowns fabricated with different spacer thicknesses and to compare these crowns with those fabricated with the heat-press technique. MATERIAL AND METHODS: The E4D system was used to fabricate 30 crowns for the first 3 groups, with different spacer thickness settings: 30 µm, 60 µm, and 100 µm. In the fourth group, 10 lithium disilicate crowns were fabricated with the heat-press technique. The occlusal gap, axial gap, vertical marginal gap, and absolute marginal discrepancy were evaluated by x-ray microtomography. Statistical significance was assessed with the Kruskal-Wallis test (α=.05). For post hoc analyses, the Mann-Whitney U test was used alongside the Bonferroni correction for multiple comparisons (α=.008). RESULTS: Within the CAD/CAM groups, the 30-µm spacer thickness resulted in the lowest median axial gap (90.04 µm), whereas the 60-µm spacer thickness resulted in the lowest median occlusal gap (152.39 µm). The median marginal gap values of the CAD/CAM-60 group (49.35 µm) and CAD/CAM-100 group (46.65 µm) were lower than those of the CAD/CAM-30 group (55.18 µm). No significant differences among the CAD/CAM groups were observed for absolute marginal discrepancy. The heat-press group had significantly different values than those of the CAD/CAM groups. CONCLUSION: The spacer thickness and fabrication technique affected the adaptation of ceramic crowns. The heat-press group yielded the best marginal and internal crown adaptation results. The 30- or 60-µm spacer settings are recommended for the E4D CAD/CAM system.

An in vitro comparison of fracture load of zirconia custom abutments with internal connection and different angulations and thickness: part I.

PURPOSE: The purpose of this in vitro study was to compare the fracture load of one-piece zirconia custom abutments with different thicknesses and angulations. MATERIALS AND METHODS: Forty zirconia custom abutments were divided into four groups. Group A-1 and group B-1 simulated a clinical situation with an ideal implant position, which allows for the use of straight zirconia custom abutments with two thicknesses (0.7 and 1 mm). Groups A-2 and B-2 simulated a situation with a compromised implant position requiring 15° angulated abutments with different thicknesses (0.7 and 1 mm). Implant replicas were mounted in self-cure acrylic jigs to support the abutments in all groups. The zirconia custom abutments were engaged in the implant replicas using a manual torque wrench. Each jig was secured and mounted in a metallic vice 30° relative to a mechanical indenter. All groups were subjected to shear stress until failure using a universal testing machine with a 0.5 mm/min crosshead speed with the force transferred to the lingual surface of the zirconia custom abutments 2 mm below the top surface. The universal testing machine was controlled via a computer software system that also completed the stress-strain diagram and recorded the breaking fracture load. The fracture loads were recorded for comparison among the groups and subjected to statistical analysis (two-way ANOVA). RESULTS: The mean fracture load of zirconia custom abutments across the groups (A-1 through B-2) ranged from 160 ± 60 to 230 ± 95 N. The straight zirconia custom abutment exhibited the highest fracture load among the groups (p = 0.009); however, the thickness of the zirconia custom abutment had no influence on the strength of any of the specimens (p = 0.827). CONCLUSIONS: There was no statistically significant difference in fracture strength between the 0.7 and 1.0 mm groups; however, angulated zirconia custom abutments had the lowest fracture load. CLINICAL IMPLICATION: The results of this in vitro study will help dental practitioners with their decision-making process in selecting the type of custom abutment to be used clinically.

An in vitro comparison of shear bond strength of zirconia to enamel using different surface treatments.

PURPOSE: The purpose of this in vitro study was to compare the shear bond strength of an airborne-particle abraded zirconia, an acid-etched zirconia (Piranha solution), an Alloy Primer treated zirconia, and a silaned zirconia to enamel, all bonded with a phosphate-methacrylate resin luting agent. MATERIALS AND METHODS: Seventy extracted intact human molars were collected, cleaned, and mounted in autopolymerizing acrylic resin, with the experimental surface of the teeth exposed. The specimens were randomly divided into seven groups of zirconia specimens (4 mm diameter, 2 mm thick). Group 1: Airborne-particle abrasion; group 2: Airborne-particle abrasion and Z-PRIME Plus; group 3: Airborne-particle abrasion and alloy primer; group 4: Piranha solution 7:1; group 5: Piranha solution 7:1 and Z-PRIME Plus; group 6: Piranha solution 7:1 and Alloy primer; group 7: CoJet and silane. All specimens were luted with a phosphate-methacrylate resin luting agent (Panavia F2.0) and stored in distilled water for 1 day, then thermocycled (5°C and 55°C) for 500 cycles and tested for shear bond strength (SBS), measured in MPa, with a universal testing machine at a 0.55 mm/min crosshead speed. All specimens were inspected under a scanning electron microscope to determine mode of failure. The mean values and standard deviations of all specimens were calculated for each group. A one-way ANOVA was performed, and multiple pairwise comparisons were then completed with post hoc Tukey test (alpha = 0.05). RESULTS: The airborne-particle abrasion and Z-PRIME Plus group resulted in a significantly higher SBS than the other groups (21.11 ± 6.32 MPa) (p < 0.001). The CoJet and silane group (15.99 ± 8.92 MPa) and airborne-particle abrasion and alloy primer group (11.07 ± 4.34 MPa) showed high shear bond strength but not statistically significant from the airborne-particle abrasion group (14.23 ± 5.68 MPa). Failure mode was predominately mixed in groups 1, 2, 3, and 7 with islands of retained resin on the zirconia and enamel surfaces; however, groups 4, 5, and 6 showed mostly adhesive failures, which left the zirconia surface free of the adhesive materials. No cohesive failures of the substrates (ceramic, resin, or enamel) were observed. CONCLUSION: Airborne-particle abrasion followed by the application of a zirconia primer produced the highest bond strength to enamel. Therefore, it can be recommended as a promising surface treatment method to achieve a durable bond to densely sintered zirconia ceramics.

Effects of surface treatments and cement types on the bond strength of porcelain-to-porcelain repair.

PURPOSE: The purpose of this in vitro study was to evaluate the effects of four surface treatments and two resin cements on the repair bond strength of a ceramic primer. MATERIALS AND METHODS: Eighty-eight pairs of disks (10 and 5 mm in diameter, 3 mm thickness) were prepared from heat-pressed feldspar ceramics (GC Initial IQ). After being stored in mucin-artificial saliva for 2 weeks, the 10-mm disks were divided into four surface treatment groups (n = 22) and then treated as follows: (1) no treatment (control); (2) 40% phosphoric acid; (3) 5% hydrofluoric acid + acid neutralizer + 40% phosphoric acid; (4) silica coating (CoJet-sand) + 40% phosphoric acid. The 5-mm disks were treated with 5% hydrofluoric acid + 40% phosphoric acid. The two sizes of porcelain disks, excluding the control group, were primed with Clearfil Ceramic Primer. The specimens in each group were further divided into two subgroups of 11 each, and bonded with Clearfil Esthetic Cement (CEC) or Panavia F 2.0 Cement (PFC). The specimens were stored in distilled water at 37°C for 24 hours, thermocycled for 3000 cycles at 5 to 55°C, and stored at 37°C for an additional 7 days. Shear bond strength (SBS) was measured with a universal testing machine at a 0.5 mm/min crosshead speed until fracture. Statistical analysis of the results was carried out with a two-way ANOVA and Tukey HSD test (α = 0.05). Debonded specimen surfaces were examined under an optical microscope to determine the mode of failure. RESULTS: The statistical analysis showed that the SBS was significantly affected by surface treatment and resin cement (p < 0.05). For treatment groups bonded with CEC, the SBS (MPa) values were (1) 2.64 ± 1.1, (2) 13.31 ± 3.6, (3) 18.88 ± 2.6, (4) 14.27 ± 2.7, while for treatment groups cemented with PFC, the SBS (MPa) values were (1) 3.04 ± 1.1, (2) 16.44 ± 3.3, (3) 20.52 ± 2.2, and (4) 16.24 ± 2.9. All control specimens exhibited adhesive failures, while mixed types of failures were observed in phosphoric acid-treated groups. The other groups revealed mainly cohesive and mixed failures. CONCLUSIONS: Combined surface treatment of etching with hydrofluoric acid and phosphoric acid provides the highest bond strengths to porcelain. Also, PFC exhibited higher SBS than CEC did.

The effect of variations in translucency and background on color differences in CAD/CAM lithium disilicate glass ceramics.

PURPOSE: The purpose of this study was to compare the effect of variations in translucency and background on color differences (ΔE) for different shades of computer-aided design and computer-aided manufacturing (CAD/CAM) lithium disilicate glass ceramics. MATERIALS AND METHODS: A pilot study suggested n = 10 as an appropriate sample size for the number of lithium disilicate glass ceramic cylinders per group. High-transparency (HT) and low-transparency (LT) cylinders (diameter, 12 mm; length, 13 mm) were fabricated in three ceramic shades (BL1, A2, C3) using CAD/CAM technology and were cut into specimen disks (thickness, 1.2 mm; diameter, 12 mm) for placement on Natural Die (ND1 and ND4) backgrounds. Four combinations of translucency and background color were evaluated in terms of color differences for the three ceramic shades: group 1 (HT ND1, reference), group 2 (HT ND4), group 3 (LT ND1), and group 4 (LT ND4). A spectrophotometer was used to measure the color differences. Nonparametric tests (Kruskal-Wallis tests) were used to evaluate the color differences among the tested groups, and Mann-Whitney U tests with Bonferroni correction were used as post hoc tests. Furthermore, for each ceramic shade, the HT groups were compared to the LT groups using the Mann-Whitney U test. RESULTS: Significant differences were present among the tested groups of the same ceramic shade (p < 0.001). The highest ΔE values were observed in the HT ND4 group for BL1, while the lowest ΔE values were found in the LT ND1 group for both A2 and C3. Further, the HT groups and the groups with a darker background (ND4) showed increased ΔE values compared with the other groups (p < 0.001). CONCLUSIONS: Within the limitations of this study, the results suggested that the translucency and background color significantly influenced the lithium disilicate glass ceramic color among the BL1, A2, and C3 ceramic shades. Changing the underlying color from a lighter background to a darker background resulted in increased color differences.

An in vitro comparison of the accuracy of implant impressions with coded healing abutments and different implant angulations.

STATEMENT OF PROBLEM: Fabricating implant definitive casts with CAD/CAM technology (Robocasts) from coded healing abutment impressions represents a simpler and innovative alternative to conventional implant impression techniques. However, information about the accuracy of the impressions and the resultant definitive casts is limited. PURPOSE: The purpose of the study was to evaluate the accuracy of the Robocasts and compare them to those definitive casts fabricated with conventional implant impression techniques (open tray with splinted impression copings technique). MATERIAL AND METHODS: A reference epoxy resin cast was fabricated and shaped to simulate a dental arch. Two regular platform implant replicas (Biomet 3i Certain, 4.1 mm diameter and 15 mm length) with internal connections were placed 10 mm apart with a 10-degree convergence for one side of the reference resin cast and a 30-degree convergence for the other. Coded healing abutments (Encode) were placed at 3 different heights above the level of the soft tissue replication material (approximately 1, 2, and 4 mm) and served as test groups (E1, E2, and E4), and open trays with splinted impression copings (OTSC) served as a control group. The control group was compared to the impressions of the coded healing abutments by using a standardized measurement protocol. Impressions were made for each group (n=18) and poured with vacuum mixed (100 g powder/20 mL water) Type IV dental stone. The vertical discrepancy (Z axis) between 2 prefabricated passively fitting titanium reference frameworks and the platforms of the implant replicas was measured with an optical comparator applying the 1 screw test. Data were analyzed with Kruskal-Wallis and post-hoc Mann-Whitney U tests, as well as the Wilcoxon signed-rank tests. The Bonferroni correction was used to account for multiple comparisons. The significance level (α) used in a given set of tests was equal to .05 divided by the number of tests performed in that set. RESULTS: The median vertical discrepancy of each coded healing abutment impression group was higher than the corresponding median of the control group (OTSC) for every combination of angulation and position. Kruskal-Wallis tests indicated a statistically significant difference (P<.001) between groups for each angulation/position combination. All post hoc Mann-Whitney U tests indicated statistically significant differences (all P≤.002) between OTSC and the other groups. Differences between the angulations and positions were not statistically significant when accounting for multiple comparisons. CONCLUSIONS: The implant definitive casts fabricated from the coded healing abutment impressions were found to be less accurate than those fabricated from the open tray with splinted impression copings technique for restoring 2 paired (10 or 30 degrees) convergent internal connection implants with nonengaging screw-retained splinted 2-unit implant restorations. Accuracy of fit was not influenced by the implant angulation or position for either impression technique or by the Encode healing abutment height for the Encode impression technique.

The influence of different convergence angles and resin cements on the retention of zirconia copings.

PURPOSE: This in vitro study aimed to determine the ability of three resin cements to retain zirconia copings under two clinically simulated conditions. MATERIALS AND METHODS: Extracted human molars (72) were collected, cleaned, and divided into two groups. All teeth were prepared with a 15° total convergence angle for group 1 and a 30° total convergence angle for group 2, a flat occlusal surface, and approximately 4-mm axial length. Each group was divided by surface area into three subgroups (n = 12). All zirconia copings were abraded with 50-µm Al(2)O(3), then cemented using Panavia F 2.0 (PAN-1) (PAN-2) Rely X Unicem (RXU-1) (RXU-2), and Clearfil SA (CSA-1) (CSA-2). After cementation, the copings were thermocycled for 5000 cycles between 5°C and 55°C with a 15-second dwell time. Then the copings were subjected to dislodgment force in a universal testing machine at 0.5 mm/min. The force of removal was recorded, and the dislodgement stress was calculated. A Kruskal-Wallis test (nonparametric ANOVA) was used to analyze the data (α= 0.05), and the nature of failure was also recorded. RESULTS: The mean (SD) coping removal stresses (MPa) were as follows: PAN-1: 6.0 (1.3), CSA-1: 4.8 (1.4), RXU-1: 5.5 (2.3), PAN-2: 2.8 (1.1), CSA-2: 3.0 (1.25), and RXU-2: 2.6 (1.2). The Kruskal-Wallis test was significant. Mann-Whitney pairwise comparisons of the subgroups were significant (p < 0.05) for the comparisons between subgroups of group 1 and group 2. Mode of failure was mixed, with cement remaining principally on the tooth for PAN. For CSA and RXU, mode of failure was mixed with cement remaining principally on the zirconia copings. CONCLUSIONS: Retention values of zirconia copings with three different resin cements were not significantly different. Retention of zirconia copings cemented on the teeth with adequate resistance and retention form was higher than that cemented on teeth lacking these forms. The cement remained mostly on the tooth with the adhesive resin cement with a dentin bonding system. The cement remained mostly on the coping with the self-adhesive resin cement.

Color management of the cervical region using different framework materials.

BACKGROUND: Color-matching of the cervical area between natural teeth and different crown prostheses is a common clinical problem. PURPOSE: The purpose of this study was to compare the color of the cervical region of five commercially available crown systems to an extracted natural tooth and to each other. MATERIALS AND METHODS: The color of the cervical region of an extracted maxillary incisor was measured by means of a colorimeter (ShadeVision, X-Rite). Fifty master dies were fabricated, divided into five groups (N=10) according to the framework material; group 1: high-noble gold alloy, group 2: same as group 1 but treated with gold paste material, group 3: precious reinforced alloy, group 4: white zirconium oxide substructure (Lava 3M ESPE), and group 5: shaded zirconium oxide (Lava). A direct comparison of L*, a*, and b* parameters was accomplished between the control natural tooth and the five crown systems, and the mean color differences (ΔE) was calculated. The data were statistically analyzed with one-way analysis of variance and post hoc multiple comparison (α=0.05). RESULTS: Compared to the natural tooth, the mean color differences (ΔE) values were clinically unacceptable for all groups (ΔE > 3.7). The detected color differences, among different porcelain systems, were not visually perceptible (ΔE < 3.7). CONCLUSIONS: Within the limitations of this study, the cervical color of an extracted natural tooth could not be duplicated using different crowns systems. CLINICAL SIGNIFICANCE: Color-matching of the cervical region of different crown systems with natural tooth remains a difficult task.

Latest biomaterials and technology in dentistry.

Navigation technology is applied successfully in oral and maxillofacial surgery. Laser beams are used for caries removal. With nanodentistry, it is possible to maintain comprehensive oral health care. Nanorobots induce oral analgesia, desensitize teeth, and manipulate the tissue. They can also be used for preventive, restorative, and curative procedures. Strategies to engineer tissue can be categorized into 3 major classes: conductive, inductive, and cell transplantation approaches. Several populations of cells with stem cell properties have been isolated from different parts of the tooth.

Digital imaging and fabrication.

Bioceramics have been adopted in dental restorations for implants, bridges, inlays, onlays, and all-ceramic crowns. Dental bioceramics include glass ceramics, reinforced porcelains, zirconias, aluminas, fiber-reinforced ceramic composites, and multilayered ceramic structures. The process of additive manufacturing is ideally suited to dentistry. Models are designed using data from a computed tomography scan or magnetic resonance imaging. Since its development in 2001, direct ceramic machining of presintered yttria tetragonal zirconia polycrystal has become increasingly popular in dentistry. There are wide variety commercially available cements for luting all-ceramic restorations. However, resin cements have lower solubility and better aesthetic characteristics.