Effect of sintering time on the marginal and internal fit of monolithic zirconia crowns containing 3-4 mol% Y2O3.

BACKGROUND: Short-term sintering may offer advantages including saving time and energy but there is limited evidence on the effect that altering sintering time has on the accuracy of monolithic zirconia crowns. The purpose of this in vitro study was to investigate the effect of shortened sintering time on the marginal and internal fit of 3Y-TZP and 4Y-TZP monolithic crowns. METHODS: Sixty monolithic zirconia crowns were fabricated for the maxillary first molar tooth on the prefabricated implant abutment. Groups were created according to the material composition: 3Y-TZP Generation 1, 3Y-TZP Generation 2 and 4Y-TZP. Two different sintering protocols were performed: same final sintering temperature (1500 °C) and various rates of heating (10 °C/min and 40 °C/min), cooling down speed (- 10 °C/min and - 40 °C/min), holding time (45 and 120 minutes), and total sintering time (approximately 2 and 7 hours, respectively). The marginal and internal fit of the crowns were determined using the silicone replica technique. Comparisons between groups were analyzed using two-way ANOVA. Pairwise multiple comparisons were performed using t-test (p < 0.05). RESULTS: The mean marginal gap values of 4Y-TZP zirconia revealed statistically significant increase for the short-term sintering protocol (p < 0.0001), while no difference was observed between the sintering protocols for the mean marginal gap values of 3Y-TZP groups. Although all groups showed clinically acceptable gap values, altering the sintering time had an effect on marginal fit of the crowns manufactured from 4Y-TZP zirconia. CONCLUSIONS: Shortening the sintering time may lead to differences within clinically acceptable limits. The manufacturer's recommendations according to material composition should be implemented with care.

Effect of Anti-Rotational Abutment Features and Novel Computerized Fabrication Techniques on the Marginal Fit of Implant-Supported Metal Copings.

PURPOSE: An in vitro study to compare the marginal fit of cobalt-chromium (Co-Cr) metal copings fabricated with selective laser melting (SLM), computer-aided design and computer-aided manufacturing (CAD/CAM) milling, and lost-wax (LW) techniques, on abutments with two different antirotational features. MATERIALS AND METHODS: A total of 60 stainless steel abutments with the same length and convergence angles were fabricated using a numerical control machining. Half of the abutments had one flat plane, while the other half had three grooves as an antirotation feature. Thirty abutments of each kind were then divided into three subgroups, and metal copings were fabricated with SLM, CAD/CAM milling, or the LW technique (n = 10). The metal copings were cemented with polycarboxylate cement. Marginal gap measurements were performed using a stereomicroscope at a magnification of × 45 and data were analyzed with two-way analysis of variance (ANOVA) tests. RESULTS: The LW (p = 0.002) and CAD/CAM (p < 0.001) techniques exhibited increased marginal gaps on the abutments with a three groove antirotational feature; however, no significant difference was detected with the SLM technique (p = 0.259). The copings fabricated with the SLM technique demonstrated significantly lower gap values in both abutment types (p < 0.001). CONCLUSION: While all marginal gap values were within the clinically acceptable range (<120 µm), abutments with more antirotational grooves exhibited wider marginal gaps with the LW and CAD/CAM techniques.

Effect of manufacturing techniques on the marginal and internal fit of cobalt-chromium implant-supported multiunit frameworks.

STATEMENT OF PROBLEM: Subtractive and additive computer-aided design and computer-aided manufacturing (CAD-CAM) systems have been used in the fabrication of cobalt-chromium (Co-Cr) long-span restorations. However, the accuracy of fit of multiunit frameworks is unclear. PURPOSE: The purpose of this in vitro study was to compare the marginal and internal fit of implant-supported, cement-retained 3-unit, 4-unit, and 5-unit Co-Cr metal frameworks fabricated by the lost wax (LW), CAD-CAM milling, and selective laser melting (SLM) techniques. MATERIAL AND METHODS: A total of 90 Co-Cr metal frameworks were fabricated for 3-unit, 4-unit, or 5-unit implant-supported cement-retained restorations on stock abutments with 3 different manufacturing technique subgroups (LW, CAD-CAM milling, and SLM). The silicone replica technique was used to evaluate the marginal and internal discrepancy values. By using a light microscope at ×45 magnification and a digital measurement program, the thickness of the silicone layer was measured at 16 reference points on each abutment for a total of 3360 measurements. The effect of manufacturing techniques and number of units (groups) on discrepancy values was evaluated using a full factorial ANOVA model. Group and manufacturing technique effects were analyzed separately by 1-way ANOVA in case of significant interactions. Pairwise comparisons were evaluated using the Tukey post hoc test (α=.05). RESULTS: The mean marginal discrepancy of 3-unit frameworks showed no statistically significant differences in the LW (35 µm) and SLM (25 µm) techniques; however, the frameworks manufactured by CAD-CAM milling (68 µm) had the highest marginal discrepancy values (P<.001). The mean marginal discrepancy values were 40 µm (LW), 33 µm (CAD-CAM milling), and 25 µm (SLM) for 4-unit frameworks, and no significant differences were found among the manufacturing techniques. For 5-unit frameworks, CAD-CAM milling techniques had the widest mean marginal discrepancy values (85 µm), and copings manufactured by the LW technique had the lowest mean marginal discrepancy values (36 µm). For all manufacturing techniques, axial discrepancy values were not affected with respect to the unit number (P=.526). The highest internal discrepancy values were measured at the occlusal area in all groups. CONCLUSIONS: CAD-CAM milling had the poorest marginal fit values for 5-unit frameworks, whereas the LW technique demonstrated the best results. Unit number had no significant influence on the marginal and internal fit of the LW manufactured frameworks.

Mechanical Failure of Endocrowns Manufactured with Different Ceramic Materials: An In Vitro Biomechanical Study.

PURPOSE: To evaluate the effect of different silica-based ceramic materials on the mechanical failure behavior of endocrowns used in the restoration of endodontically treated mandibular molar teeth. MATERIALS AND METHODS: Thirty-six intact mandibular molar teeth extracted because of a loss of periodontal support received root canal treatment. The teeth were prepared with a central cavity to support the endocrowns, replacing the occlusal surface with mesial-lingual-distal walls. Data acquisition of the prepared tooth surfaces was carried out digitally with a powder-free intraoral scanner. Restoration designs were completed on manufactured restorations from three silicate ceramics: alumina-silicate (control), zirconia-reinforced (Zr-R), and polymer-infiltrated (P-I). Following adhesive cementation, endocrowns were subjected to thermal aging, and then, each specimen was obliquely loaded to record the fracture strength and define the mechanical failure. For the failure definition, the fracture type characteristics were identified, and further analytic measurements were made on the fractured tooth and ceramic structure. RESULTS: Load-to-fracture failure did not differ significantly, and the calculated mean values were 1035.08 N, 1058.33 N, and 1025.00 N for control, Zr-R, and P-I groups, respectively; however, the stiffness of the restoration-tooth complex was significantly higher than that in both test groups. No statistically significant correlation was established in paired comparisons of the failure strength, restorative stiffness, and fractured tooth distance parameters. The failure mode for teeth restored with zirconia-reinforced glass ceramics was identified as non-restorable. The resin interface in the control and P-I groups presented similar adhesive failure behavior. CONCLUSION: Mechanical failure of endocrown restorations does not significantly differ for silica-based ceramics modified either with zirconia or polymer.

Comparison of implant versus tooth-supported zirconia-based single crowns in a split-mouth design: a 4-year clinical follow-up study.

OBJECTIVES: This study aims to evaluate the 4-year clinical performance of tooth versus implant-supported single-unit zirconia crowns (LAVA™) placed on posterior region. MATERIALS AND METHODS: Twenty-four patients (10 men and 14 women) who had received 48 single crowns (24 implant-supported and 24 tooth-supported) from January 2007 to December 2009, were included. California Dental Association (CDA) quality assessment system, plaque and gingival index scores were used to evaluate the performance of the crowns at baseline and at all follow-up examinations. RESULTS: During the follow-up period, no fracture of zirconia coping has occurred. Major complication was chipping in three patients that required a new crown fabrication. Except for the failure ones, all crowns in both groups were rated as satisfactory at the follow-up examinations based on the CDA quality assessment criteria. There were no statistically significant differences between tooth and implant-supported crowns in terms of periodontal parameters. CONCLUSIONS: The present 4-year follow-up clinical study demonstrates that single-unit tooth- and implant-supported zirconia crowns have similar prosthetic and periodontal outcomes. CLINICAL RELEVANCE: Single-unit implant or tooth-supported zirconia crowns may be considered acceptable treatment modalities for restoration of either missing or compromised posterior teeth.

Effect of digitizing techniques on the fit of implant-retained crowns with different antirotational abutment features.

STATEMENT OF PROBLEM: The development of computer-aided design/computer-aided manufacturing technology has enabled the fabrication of implant-retained restorations. However, information on the marginal and axial accuracy of restorations fabricated by different digitizing techniques with different antirotational abutment features is not sufficient. PURPOSE: The purpose of this in vitro study was to evaluate the influence of digitizing techniques on the fit of implant-retained crowns with 2 antirotational features. MATERIAL AND METHODS: An experimental working cast housing a tissue-level dental implant was created. Resin-retained abutments with different antirotational features were connected to the implant. Optical impressions of 2 abutment types were obtained separately with 1 chairside and 2 laboratory approaches. Alumina silicate restorations were milled from chairside optical impressions, and ceramic oxide cores were milled from laboratory optical impressions. Restoration fit was evaluated from axial sections of restorations with silicone materials representing the marginal and axial gaps. Axial and marginal fits were measured on digital photographs of the sectioned specimens with a computer program. Two-way ANOVA was used to compare differences between abutments with 2 different antirotational features and digitizing techniques separately for the marginal and axial fits of single implant-retained crowns. A post hoc least significant difference test was used to compare digitizing techniques (α=.05). RESULTS: Significant differences in the marginal fit of single-implant-retained crowns were found among digitizing techniques (P=.011) and between antirotational features (P<.001). No significant difference in the axial fit of single-implant-retained crowns was found among digitizing techniques (P=.905) or between antirotational features (P=.075). CONCLUSIONS: Within the limitations of this in vitro study, the marginal fit of single-implant-retained crowns was affected by antirotational abutment features. Furthermore, digitizing techniques were found to play an important role in the marginal fit of single-implant-retained restorations.

Effect of different implant locations and abutment types on stress and strain distribution under non-axial loading: A 3-dimensional finite element analysis.

Background/purpose: Dental implants have been a popular treatment for replacing missing teeth. The purpose of this study was to investigate the impact of engaging (hexagonal) and non-engaging (non-hexagonal) abutments in various six-unit fixed prosthesis on the stress distribution and loading located in the implant neck, implant abutment, and surrounding bone. Materials and methods: Three implants were digitally designed and inserted parallel to each other in edentulous sites of the maxillary right canine, maxillary right central incisor, and maxillary left canine. Titanium base engaging abutments, non-engaging abutments and connecting screws were designed. Five distinct models of 6-unit fixed dental prosthesis were created, each featuring different combinations of various abutments. Forces (45-degree angle) were applied to the prosthesis, allowing for the analysis of the stress distribution on the implant neck and abutments, and the maximum and minimum principal stress values on the cortical and trabecular bone. Results: Von Mises stress values and stress distributions located in the implant neck region due to the applied loading forces were analyzed. The overall stress values were highest while employing the hexagonal abutments. The maxillary left canine with a hexagonal abutment (model 5) reported the highest von mises value (64.71 MPa) while the maxillary right canine with a non-hexagonal abutment (model 4) presented lowest von mises value (56.69 MPa). Conclusion: The results suggest that both the various abutment combinations (engaging and non-engaging) on five different models have a similar influence on the distribution of stress within the implant system.

Effects of different cavity designs on fracture load of fiber-reinforced adhesive fixed dental prostheses in the anterior region.

PURPOSE: To evaluate the fracture strength of inlay-retained, surface-retained, and cantilevered fiber-reinforced adhesively fixed dental prostheses (FRA-FDPs) in the anterior region. MATERIALS AND METHODS: Thirty-two sound human right central incisors and canines were divided into four groups. Test groups were as follows: group 1, both teeth had deep cavity preparation; group 2, both teeth had shallow cavity preparation; group 3, only the canine teeth had deep cavity preparation; group 4, no preparation was made on the abutment teeth. Lateral pontics were restored with FRA-FDPs. All restorations were subjected to fracture loading from the lateral pontic. The restorations were tested in a universal testing machine (LRX Material Testing Machine) with a crosshead speed of 1 mm/min. One-way ANOVA was used for statistical analyses. Fracture modes were examined visually. RESULTS: The highest (667.3 ± 90.4 N) and the lowest (409.3 ± 158.1 N) debonding values were found for groups 4 and 3, respectively. CONCLUSIONS: Different preparation designs (inlay-retained, surface-retained) had no significant effect on fracture strength of FRA-FDPs in the anterior region. However, a cantilever design exhibited significantly lower fracture strength. Delamination of the veneering composite was observed as the primary failure type after fracture tests.

Performance of high-translucent zirconia CAD/CAM fixed dental prostheses using a digital workflow: A clinical study up to 6 years.

Background/purpose: Zirconia has recently become a popular material for fixed restorations. The purpose of this study was to use a digital workflow to fabricate monolithic zirconia fixed dental prostheses (FDPs) and assess the connection between variable connector sizes compared to their clinical performance. Materials and methods: Clinicians evaluated monolithic zirconia FDPs in 58 patients. After definitive impressions were made, stone casts were obtained. The stone casts were scanned to a standard triangle language (STL) file. A digital wax up was fabricated, and corresponding provisional restorations were milled. Final FDPs were fabricated from a high-translucent zirconia material. During digital fabrication, the connector area of each FDP was recorded while meticulous attention was paid to ensure that the connector cross-sectional area was ≥9 mm2 for the 3-unit restorations (pontic to retainer) and ≥12 mm2 for the 4-unit restorations (pontic to pontic). Biological an technical outcomes of the FDPs were performed at 1 week, 6 months and then annually for 6 consecutive years. Results: A total of 23 men and 35 women received a total of 63 full-contour zirconia FDPs in the posterior regions and were observed for a time period ranging between 50 and 70 months. No decementation occurred and no caries were detected during the observation period, however signs of gingivitis were detected in 4 patients. The dimension of the connector areas was 12 mm2 in the two broken 4-unit FDPs. Conclusion: The results of this study suggest that the use of digital scanning and milling to fabricate monolithic zirconia FDPs of posterior regions may be an acceptable alternative restorative approach to traditional metal-ceramic restorations.

A Randomized Clinical Trial of Monolithic Single-Tooth Crowns: 1-Year Preliminary Results.

PURPOSE: To investigate the clinical results of single-tooth ceramic crowns in the posterior region produced from three different monolithic materials. MATERIALS AND METHODS: A total of 36 posterior single-tooth crowns were fabricated from lithium silicate glass-ceramic (LSGC; n = 12), lithium disilicate glass-ceramic (LDGC; n = 12), and polymer-infiltrated ceramic network (PICN; n = 12) in 27 patients. Restorations were evaluated for prosthetic and periodontal criteria at baseline (0) and after 6 and 12 months. Prosthetic evaluation was performed according to the modified United States Public Health Service (USPHS) criteria, and probing depth (PD), clinical attachment level (CAL), gingival bleeding time index (GBTI), and gingival (GI) and periodontal indices (PI) were evaluated in the periodontal assessment. Friedman and Kruskal-Wallis tests were used for statistical analyses (P = .05). RESULTS: All restorations were evaluated according to survival and success rates. No dropouts occurred. The survival rate of all three materials was 100% after 1 year. However, in the PICN group, a statistically significant difference was found between baseline and 12 months for color match (from A to B) and surface texture (from A to C; P < .001). CONCLUSIONS: Although long-term clinical follow-up periods are needed, all three ceramics showed clinically acceptable survival and success rates over 1 year. The ceramics evaluated in the present study could be preferred for single-tooth full-crown restorations in the posterior region.

Influence of the implant scan body modifications on trueness of digital impressions.

Background/purpose: Effects of implant angulation on digital impression accuracy remain controversial. The purpose of this study was to assess the relationship between the alteration of implant scan bodies and the trueness of digital impressions. Materials and methods: A maxillary typodont without the right premolars and first molar was scanned with a laboratory scanner and saved as a standard triangular language (STL) file. A model from the STL file was fabricated with a 3-dimensional printer. Two implants were placed into the first premolar and first molar sites of the model, followed by the insertion of two scan bodies onto the implants. These scan bodies were divided into four test groups, based on the surface modifications. A digital impression of each typodont was made with three different intraoral scanners. An abutment was digitally seated on each implant. 120 STL files (30 for each group) of the typodont with two implants and two corresponding abutments were used for statistical analysis. Results: A total of 240 values (two implants for each typodont) were obtained after each sample (4 groups) was scanned 10 times by utilizing three intraoral scanners. The overall linear and angular discrepancies were analyzed. Group 1 showed the lowest linear discrepancy of 14.9 ± 5.4 µm while Group 4 reported the highest linear discrepancy of 137.5 ± 41.7 µm, yielding a statistical significance (P < 0.05). Conclusion: It has been concluded that the more adjustments made to the scan bodies, the greater the linear and angular deviations occur, compromising the trueness of the digital implant impression.

Fit of High-Translucency Zirconia Fixed Dental Prostheses Using Two Different Intraoral Scanners.

PURPOSE: To assess the marginal and internal fit of monolithic zirconia fixed dental prostheses (FDPs) comparing two different intraoral scanners (IOSs) and assessment methods. MATERIALS AND METHODS: A maxillary typodont with three prepared teeth allowed fabrication of five-unit high-translucency monolithic zirconia FDPs. The typodont was scanned with two IOSs: Cerec Omnicam and 3Shape TRIOS 3. In total, 30 FDPs were milled from presintered high-translucency zirconia blocks. Dual-scan and silicone replica assessments were used to determine marginal and internal gaps. RESULTS: A statistical significance was observed for marginal gaps (3Shape [74.27 ± 10.4 µm] and Cerec [86.45 ± 14.3 µm]) and for internal gaps (3Shape [126.12 ± 12.7 µm] and Cerec [112.38 ± 17.2 µm]). CONCLUSIONS: The outcomes of this study showed that the 3Shape TRIOS 3 produced a better overall marginal fit, while the Cerec Omnicam created a better internal fit. Additionally, a greater overall marginal and internal gap was noted with the silicone replica method over the dual-scan method.

Analysis of the impact of various finish line designs and occlusal morphologies on the accuracy of digital impressions.

Background/purpose: Recent advancements in dental technology has led clinicians to convert from traditional methods to digital workflows. The purpose of this study was to analyze the effect of various finish line designs and occlusal morphologies on the accuracy of digital impressions. Materials and methods: Six maxillary molar crown preparations were designed by using a digital sculpting software program. The samples differed in finish line design and occlusal surface morphology. Three different finish line designs (shoulder, chamfer, and shoulder with internal round angle) and two different occlusal morphologies (sharp and rounded) were used, giving six groups. Using three different intraoral scanners, each group was scanned and compared with a reference scan obtained from an industrial scanner. The accuracy of each scan was studied, and the data were statistically analyzed. Results: A total of 180 scans were acquired by utilizing three different intraoral scanners. The reference scan was compared with the scans from each group and overall differences (marginal, axial, and occlusal) were assessed. A crown preparation with a chamfer finish line showed the lowest marginal discrepancy of 13.2 ± 4.18 µm while preparation with a shoulder finish line reported the highest discrepancy of 34.8 ± 7.9 µm (P < 0.05). Also, the occlusal discrepancies of the samples with rounded and sharp occlusal morphologies were 12.55 ± 3.09 µm and 19.13 ± 2.3 µm, respectively (P < 0.05). Conclusion: It has been suggested that chamfer finish line design and rounded occlusal anatomy may produce more accurate digital impression for single crown restorations.

Effects of Surface Treatments and Cement Type on Shear Bond Strength between Titanium Alloy and All-Ceramic Materials.

This study aimed to evaluate the effects of surface treatments and resin cement on the adhesion of ceramic and ceramic-like materials to titanium. A total of 40 specimens (5 mm diameter) of each material (lithium disilicate glass ceramic (LDGC-IPS e.maxCAD), lithium silicate glass ceramic (LSGC-VITA Suprinity) and a polymer-infiltrated ceramic network (PICN-Vita Enamic)) were fabricated using CAD/CAM technologies. In total, 120 titanium (Ti) specimens were divided into 12 groups, and half of the titanium specimens were tribochemically coated using CoJet. The titanium and all-ceramic specimens were cemented using either Self-curing adhesive cement (SCAC-Panavia 21) or a Self-curing luting composite (SCLC-Multilink Hybrid Abutment). After 5000 cycles of thermal aging, the shear bond strength (SBS) test was conducted using a universal testing machine. The failure modes of the specimens were analyzed using stereomicroscopy, and additionally, the representative specimens were observed using Scanning Electron Microscopy. ANOVA was used for the statistical analysis (p < 0.05). The post-hoc Duncan test was used to determine significant differences between the groups. The mean SBS values (mean ± STD) ranged from 15 ± 2 MPa to 29 ± 6 MPa. Significantly higher SBS values were acquired when the titanium surface was tribochemically coated (p < 0.05). The SCLC showed higher SBS values compared to the SCAC. While the LDGC showed the highest SBS values, the PICN presented the lowest. The tribochemical coating on the cementation surfaces of the titanium increased the SBS values. The specimens cemented with the SCLC showed higher SBS values than those with the SCAC. Additionally, the SCLC cement revealed a more significant increase in SBS values when used with the LDGC. The material used for restoration has a high impact on SBS than those of the cement and surface conditioning.

Accuracy of digital impressions for implant-supported complete-arch prosthesis when using an auxiliary geometry device.

Background/purpose: Digital impressions using intraoral scanners have recently gained popularity. The aim of the present study was to evaluate the fit of full-arch screw-retained cobalt-chromium frameworks fabricated via two different digital impression methods. Materials and methods: An edentulous resin master model with four dental implants was fabricated. Forty cobalt-chromium superstructures were fabricated and evaluated according to four groups. In Group 1, the superstructures were evaluated using an intraoral scanner to generate digital impressions. Group 2 relied on the help of an auxiliary geometric appliance in generation of digital impressions via intraoral scanner. The traditional method of splinted open-tray conventional impressions was designated for Group 3. Finally, the control group (Group 4) relied on scanning of the master model directly with a laboratory scanner. Vertical marginal discrepancy was evaluated, and data obtained were statistically analyzed. Results: The highest mean vertical marginal gap value (80.86 ± 50.06 µm) was observed for Group 1 and statistically higher than Group 2, 3, and 4 (P < 0.05). The lowest mean vertical marginal gap value (41.98 ± 26.33 µm) was measured from Group 4 and statistically similar to Group 2 and 3 (P > 0.05). Conclusion: It has been suggested that the use of auxiliary geometric appliances yields increased scanning accuracy. Frameworks fabricated using the traditional splinted open-tray technique were more reliable compared to those frameworks from digital impressions.

Comparison of marginal and internal fit of 5-unit zirconia fixed dental prostheses fabricated with CAD/CAM technology using direct and indirect digital scans.

BACKGROUND/PURPOSE: Advancements in digital dentistry and the development of intraoral scanners (IOS) have provided clinicians with an accurate and efficient alternative to analog impressions. The aim of this study was to assess the accuracy of the marginal and internal fit of 5-unit monolithic zirconia fixed dental prostheses (FDPs) fabricated with CAD/CAM technology using direct and indirect digitalization methods. MATERIAL AND METHODS: Three teeth in a maxillary typodont model were prepared to receive a 5-unit zirconia FDP. Six different groups were created according to the type of scanner (intraoral and extraoral) and the type of workflow. For direct workflow, the typodont was scanned with two different IOS (3Shape Trios 3 [3S-IOS] and Cerec Omnicam [C-IOS]). For indirect workflow, after conventional impressions were obtained, the impressions (IMP) were scanned with two different laboratory scanners (3S-IMP and C-IMP). After the impressions were poured, the stone (STN) casts were scanned with the same laboratory scanners (3S-STN and C-STN). Sixty 5-unit monolithic zirconia FDPs (10 in each group) were designed and milled. The marginal and internal fit was assessed. RESULTS: The mean marginal gap values were 78.2±9 µm in the IOS group, 82.6± 9 µm in the IMP group, and 82.6±9 µm in the STN group, indicating no statistically significant differences among groups (p > 0.05). The mean axial gap values were 77.7 ± 10 µm in IOS group, 83.61 ± 15 µm in the IMP group, and 84.5±9 µm in the STN group, indicating no statistically significant differences among groups (p > 0.05). CONCLUSION: The marginal and internal fit of 5-unit monolithic zirconia FDPs fabricated with direct and indirect digital scans were similar. The smallest gap values were observed at the marginal region while the greatest gap values were detected at the occlusal region.

Clinical, Technical, and Radiologic Outcomes of 182 Implant-Supported Zirconia Single Crowns Using Titanium-Base Abutments: A Retrospective Study.

PURPOSE: To evaluate the biologic, technical, and radiographic outcomes of CAD/CAM-milled bilayer and monolithic zirconia crowns using implants and Ti-base abutments with up to 5 years of follow-up. MATERIALS AND METHODS: A total of 182 implant-supported "screw-mentable" (hybrid screw/cement retention) single crowns were evaluated in 118 patients. Ti-base abutments were selected according to the chimney (3.5 or 5 mm) and gingival (1, 2, or 3 mm) heights in the virtual model. Zirconia crowns were designed using CAD/CAM software and then milled from partially stabilized zirconia blocks. After all crowns were cemented onto Ti-base abutments, they were clinically screwed onto the implants. Both implants and crowns were followed up for up to 5 years, and their clinical, technical, and radiologic results were recorded. RESULTS: A total of 118 patients (86 women and 32 men) who received 182 implant-supported screw-mentable crowns were included in this study. The mean follow-up period was 32 ± 18 months (range: 24 to 60 months) for all implants and crowns. No implant was lost during the follow-up period, yielding a cumulative implant survival rate of 100%. Two technical complications were observed in two bruxer patients, yielding a cumulative restoration survival rate of 98.9%. The marginal bone loss was 0.7 ± 0.5 mm from the baseline radiograph to the radiograph taken at the final recall visit. No implants were diagnosed with peri-implantitis. CONCLUSION: The outcomes of this study suggest that Ti-base abutments are a feasible and affordable alternative to CAD/CAM abutments and that they can successfully support single zirconia crowns.

Scanning electron microscopy assessment of the load-bearing capacity of cad/cam-fabricated molar crowns.

Although fiber-reinforced composites are commonly used in dental practice, whether fiber-reinforced crowns and fixed partial dentures can be used as definitive prostheses remains to be determined. This study used scanning electron microscopy to evaluate the load-bearing capacity of non-reinforced and fiber-reinforced composite (FRC) molar crowns prepared by computer-aided design/computer-aided manufacturing (CAD/CAM). The crowns were fabricated from three empirical FRC blocks, one empirical composite block, and one commercial ceramic block. The FRC resin was prepared by mixing BaO silicate particles, E-glass fiber, and dimethacrylate resin. Specimens were divided into five groups (n = 10), differing in the amounts of filler, resin, and fiber. Crowns were statically loaded until fracture. One-way analysis of variance and Tukey's post hoc multiple comparison tests were used for statistical analyses. The groups showed significant differences in load-bearing capacity; empirical bidirectional FRC resin blocks had the highest capacity, while commercial ceramic blocks had the lowest capacity. Molar crowns formed from FRC resin blocks had higher load-bearing capacity compared to non-reinforced composite resin and ceramic blocks. These results show that fiber reinforcement increased the load-bearing capacity of molar crowns.

Scanning electron microscopy assessment of the load-bearing capacity of cad/cam-fabricated molar crowns

Abstract Although fiber-reinforced composites are commonly used in dental practice, whether fiber-reinforced crowns and fixed partial dentures can be used as definitive prostheses remains to be determined. This study used scanning electron microscopy to evaluate the load-bearing capacity of non-reinforced and fiber-reinforced composite (FRC) molar crowns prepared by computer-aided design/computer-aided manufacturing (CAD/CAM). The crowns were fabricated from three empirical FRC blocks, one empirical composite block, and one commercial ceramic block. The FRC resin was prepared by mixing BaO silicate particles, E-glass fiber, and dimethacrylate resin. Specimens were divided into five groups (n = 10), differing in the amounts of filler, resin, and fiber. Crowns were statically loaded until fracture. One-way analysis of variance and Tukey's post hoc multiple comparison tests were used for statistical analyses. The groups showed significant differences in load-bearing capacity; empirical bidirectional FRC resin blocks had the highest capacity, while commercial ceramic blocks had the lowest capacity. Molar crowns formed from FRC resin blocks had higher load-bearing capacity compared to non-reinforced composite resin and ceramic blocks. These results show that fiber reinforcement increased the load-bearing capacity of molar crowns.

Effect of colouring green stage zirconia on the adhesion of veneering ceramics with different thermal expansion coefficients.

This study evaluated the adhesion of zirconia core ceramics with their corresponding veneering ceramics, having different thermal expansion coefficients (TECs), when zirconia ceramics were coloured at green stage. Zirconia blocks (N=240; 6 mm×7 mm×7 mm) were manufactured from two materials namely, ICE Zirconia (Group 1) and Prettau Zirconia (Group 2). In their green stage, they were randomly divided into two groups. Half of the specimens were coloured with colouring liquid (shade A2). Three different veneering ceramics with different TEC (ICE Ceramic, GC Initial Zr and IPS e.max Ceram) were fired on both coloured and non-coloured zirconia cores. Specimens of high noble alloys (Esteticor Plus) veneered with ceramic (VM 13) (n=16) acted as the control group. Core-veneer interface of the specimens were subjected to shear force in the Universal Testing Machine (0.5 mm⋅min(-1)). Neither the zirconia core material (P=0.318) nor colouring (P=0.188) significantly affected the results (three-way analysis of variance, Tukey's test). But the results were significantly affected by the veneering ceramic (P=0.000). Control group exhibited significantly higher mean bond strength values (45.7±8) MPa than all other tested groups ((27.1±4.1)-(39.7±4.7) and (27.4±5.6)-(35.9±4.7) MPa with and without colouring, respectively) (P<0.001). While in zirconia-veneer test groups, predominantly mixed type of failures were observed with the veneering ceramic covering <1/3 of the substrate surface, in the metal-ceramic group, veneering ceramic was left adhered >1/3 of the metal surface. Colouring zirconia did not impair adhesion of veneering ceramic, but veneering ceramic had a significant influence on the core-veneer adhesion. Metal-ceramic adhesion was more reliable than all zirconia-veneer ceramics tested.