3-unit Fixed Dental Prostheses Research Articles

Marginal Fit and Internal Adaptation of Monolithic Zirconia 3-Unit Fixed Dental Prosthesis: In Vitro Study.

To compare the marginal and internal fit of monolithic zirconia (MZ) 3-unit fixed dental prostheses (FDPs) fabricated using two CAD/CAM workflows: full-chairside (FCH) and lab (LAB). The right maxillary first premolar and first molar were prepared for MZ 3-unit FDPs on a typodont. CEREC Primescan digitized the typodont model 15 Omes. A total of 30 FDPs was fabricated using two processes: FCH (n = 15) and LAB (n = 15). FCH and LAB FDPs were designed using CEREC SW 4.5.1 and Exocad and milled using CEREC MC X and Zirkonzhan 600/V3, respectively. A fast-sintering protocol was used in both groups. A dual-scan technique was used to assess the cement space at the occlusal surface (OC), axial wall (AX), and margin (MA). Statistical analysis of the results was performed using univariate ANOVA with Scheff. post hoc test (a = .05). Measurements in the FCH and LAB groups were within the clinically acceptable marginal and internal fit. The fit of FCH FDPs at MA, AX, and OC was 77.50 ± 29.99 μm, 99.67 ± 21.58 μm, and 150.03 ± 30.78 μm, respectively. The fit of LAB FDPs at MA, AX, and OC was 100.27 ± 27.06 μm, 116.53 ± 17.90 μm, and 142.30 ± 19.00 μm, respectively. The difference between the two groups was not statistically significant. MZ 3-unit FDPs fabricated using FCH have clinically acceptable marginal and internal fit. This result verifies the ability of FCH workflow to fabricate MZ mulOunit FDPs in a single visit.

Evaluation of photopolymer resins for dental prosthetics fabricated via the stereolithography process at different polymerization temperatures. Part II: Dimensional accuracy and fracture load of fixed dental prostheses

Prostheses printed on a 3-dimensional (3D) printer need to undergo the postpolymerization process, which can increase the working time. However, it has been not suggested for reducing workload and improving the properties of prostheses in dental clinical practice. The purpose of this in vitro study was to evaluate how the printing temperature impacts the dimensional accuracy and fracture load of 3D printed fixed dental prostheses (FDPs). Dental prostheses were printed at room temperature (RT), 50°C, and 70°C using a stereolithography 3D printer. Subsequently, after rinsing away residual monomer, the printed parts underwent the green condition (it was not subjected to any postprocessing) and postpolymerization. The mechanical properties of the printed FDPs were determined by loading to fracture (n=6). To evaluate their clinical applicability, the dimensional accuracy and fit of FDPs fabricated at various resin polymerization temperatures were measured (n=6). The 1-way analysis of variance was used to perform statistical comparisons, followed by the Tukey honestly significant difference test (α=.05). The specimens printed at RT and 50°C were better than those printed at 70°C in terms of dimensional accuracy and fit (P<.05). Nonetheless, the dimensional accuracy and fit of the specimens printed at 70°C were clinically acceptable. The fracture load of the 3-unit FDPs depended significantly on the printing temperature. The dimensional accuracy and fracture load of the 70°C group were acceptable for FDP fabrication. Thus, the temperature of 70°C without postprocessing may help make the procedure more efficient.

Failure Load and Fatigue Behavior of Monolithic and Bi-Layer Zirconia Fixed Dental Prostheses Bonded to One-Piece Zirconia Implants.

No evidence-based prosthetic treatment concept for 3-unit fixed-dental-prostheses (FDPs) on ceramic implants is currently available. Therefore, the aim of this in vitro study was to investigate the failure load and fatigue behavior of monolithic and bi-layer zirconia FDPs supported by one-piece ceramic implants. Eighty 3-unit FDPs supported by 160 zirconia-implants (ceramic.implant; vitaclinical) were divided into 4 groups (n = 20 each): Group Z-HT: 3Y-TZP monolithic-zirconia (Vita-YZ-HT); Group Z-ST: 4Y-TZP monolithic-zirconia (Vita-YZ-ST); Group FL: 3Y-TZP zirconia (Vita-YZ-HT) with facial-veneer (Vita-VM9); Group RL (Rapid-layer): PICN “table-top” (Vita-Enamic), 3Y-TZP-framework (Vita-YZ-HT). Half of the test samples (n = 10/group) were fatigued in a mouth-motion chewing-simulator (F = 98 N, 1.2 million-cycles) with simultaneous thermocycling (5−55 °C). All specimens (fatigued and non-fatigued) were afterwards exposed to single-load-to-failure-testing (Z010, Zwick). Statistical analysis was performed using ANOVA, Tukey’s post-hoc tests and two-sample t-tests (p < 0.05, Bonferroni-corrected where appropriate). All specimens withstood fatigue application. While the effect of fatigue was not significant in any group (p = 0.714), the choice of material had a significant effect (p < 0.001). Material FL recorded the highest failure loads, followed by Z-ST, Z-HT and RL, both with and without fatigue application. Taken together, all tested FDP material combinations survived chewing forces that exceeded physiological levels. Bi-Layer FL and monolithic Z-ST showed the highest resilience and might serve as reliable prosthetic reconstruction concepts for 3-unit FDPs on ceramic implants.

Clinical outcomes of single crown and 3-unit bi-layered zirconia-based fixed dental prostheses: An upto 6- year retrospective clinical study: Clinical outcomes of zirconia FDPs

ObjectivesThe aim of this retrospective clinical study was to evaluate the survival and the occurrence of technical and biological complications in bi-layered zirconia-based (Zi) single crown and 3-unit fixed dental prostheses (FDPs). Also, the study aimed to analyze the effects of tooth vitality (vital versus non-vital), abutment location (anterior versus posterior), and luting cement (self-adhesive resin versus resin-reinforced glass ionomer) on clinical outcomes. MethodsA total of 147 prostheses (in 94 patients) placed by undergraduate dental students in a university dental center during the period 2015–2021 were examined clinically using modified United States Public Health Service (USPHS) and California Dental Association (CDA) criteria. The mean duration of follow-up was 37 months (range, 6 - 63 months) for the single crowns (n = 77) and 25 months (range, 6 - 68 months) for the 3-unit FDPs (n = 70). Data were descriptively analyzed to determine the types and rates of complications based on USPHS and CDA criteria. The Kaplan-Meier survival estimation method was used to determine the cumulative survival and success rates of the prostheses (α=0.05). Differences in clinical outcomes (survival or failure) according to tooth vitality, luting cement, and location were statistically analyzed using cross-tabulations and Х2 test (α=0.05). ResultsThe Kaplan-Meier cumulative survival rate was estimated as 96% for the Zi 3-unit FDPs after 5.5 years, and 90% for the Zi single crowns after 4.8 years. The 5-year estimated success rate was 68% for both 3-unit FDPs and single crowns. Seven (9.1%) 77Zi single crowns and 70 2 (2.9%) Zi 3-unit FDPs were recorded as failures with occlusal roughness being the most commonly-observed complication (crowns: 4 [5.6%]; 3-unit FDPs: 8 [11.4%]). In terms of clinical outcomes, statistically significant differences were found between all included vital and non-vital teeth (p = .006), and cement types (p = .028). Taking single crowns alone, significant differences in clinical outcomes according to tooth vitality were noted (p = .036), but not for PFDPs. The location of the prostheses did not produce any significant differences in the clinical outcomes, for both prostheses types independently or combined (p > .05). ConclusionsThe estimated cumulative survival rates in this study for single crowns and 3-unit Zi FDPs concurred with the ranges reported in systematic reviews. Zi-based prostheses on vital teeth produced better clinical outcomes than those placed on non-vital teeth, and type of luting cement influenced the final clinical outcome. Clinical significanceZi crowns and 3-unit PFDPs fabricated using the specific CAD-CAM system used in the controlled environment of this study showed good clinical performance with minimal veneer porcelain chipping. Root canal treated teeth seem to be at higher risk for failure of Zi prostheses compared with vital teeth.

Marginal and internal fit and fracture resistance of three-unit provisional restorations fabricated by additive, subtractive, and conventional methods.

To compare the marginal and internal fit and fracture resistance of three-unit provisional fixed dental prostheses (FDPs) fabricated by additive, subtractive, and conventional methods. Eighty 3-unit FDPs were fabricated on metal dies of the maxillary right second premolar and second molar by four different techniques (n = 20): The direct method by using autopolymerizing polymethyl methacrylate (PMMA), indirect method by the compression molding technique, subtractive manufacturing by using PMMA blocks, and additive manufacturing by using digital light processing technology. The adaptation of restorations at the marginal, axial, cuspal, and fossa areas was assessed by using the silicone replica technique. After thermocycling and cyclic loading, the fracture resistance was measured by a universal testing machine. Data were analyzed by atwo-wayanalysis of variance (ANOVA), ANOVA, and Tukey test (α = .05). The mean gap measured in the additive group was lower than that in all other groups at all points (p < .05); however, the difference in the marginal gap with the subtractive group was not significant (p = .995). The mean marginal and axial gaps in the subtractive group were significantly lower than the corresponding values in both conventional groups (p < .05). A significant difference existed between all groups regarding the mean cuspal and fossa gaps (p < .05). The mean fracture resistance of the additive group was significantly higher than that of indirect (p = .018) and direct (p < .001) groups, and the fracture resistance of the subtractive group was significantly higher than that of the direct group (p = .020). The digitally fabricated provisional FDPs showed superior marginal and internal fit and higher fracture resistance than the conventionally fabricated FDPs. Between the digital methods, the additive technique yielded superior internal fit.

Mechanical Properties of Additively Manufactured and Milled Interim 3-Unit Fixed Dental Prostheses.

To investigate the survival and mechanical properties of 3-unit interim fixed dental prostheses (FDPs) made with additive manufacturing (AM) technology compared to milled and conventional manual fabrication. Sixty 3-unit interim FDPs replacing the first left mandibular molar were divided in 6 groups (n = 10): manual (Man) (Protemp 4), milled (Mil) (Telio-CAD Multi), and 4 additive manufacturing (AM) groups were subdivided into 4 AM technology subgroups: direct light positioning (DLP) (Rapidshape P30 [RS]), and stereolitography (SLA) (Formlabs 2 [FL]) and the type of printed interim polymer (P Pro C&B [St] and SHERAprint-cb [Sh]) (RS-St, RS-Sh, FL-St, and FL-Sh). Survival and complications were assessed after thermomechanical aging. The surviving samples were tested for fracture resistance. Kaplan-Meier test followed by log-rank test to show differences between groups was used to calculate the survival and complication rates. For fracture strength, one-way ANOVA and Tukey-b post hoc test were used to compare groups. Descriptive statistics was used for failure modes and Pearson chi-square to compare groups (α = 0.05). Survival rates among groups varied from 100% (Man, Mil and FL-Sh), 70% (FL-St), 50% (RS-Sh), and 20% (RS-Sh) (p < 0.001), respectively. Additional events were observed in 50% to 80% in FL-St, RS-St, and RS-Sh groups (p < 0.001). Man, FL-St, and RS-S showed lower mean static load resistance (p < 0.001). Fracture through the connector between tooth 35 and the pontic was the most prevalent type of failure. The manufacturing method, type of resin, and the printing mode had a significant influence on the mechanical properties of AM interim 3-unit FDPs.

Editorial: Dental Ceramics: From Science and Technology to Clinical Application

Editorial: Dental Ceramics: From Science and Technology to Clinical Application

Effect of mastication simulation on the phase transformation of posterior 3-unit monolithic zirconia fixed dental prostheses

Statement of problemMonolithic zirconia restorations are directly exposed to cyclic loads and temperature changes in the oral cavity after cementation. These stresses may reduce the long-term success of the material by causing uncontrolled phase transformations within the zirconia. PurposeThe purpose of this in vitro study was to evaluate the effect of mastication simulation and different measurement points on the phase transformation of posterior 3-unit monolithic zirconia partial fixed dental prostheses (FDPs) in the posterior region. Material and methodsPosterior 3-unit FDPs of monolithic yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP), including BruxZir Shaded (group B), FireZr (group F), and Upcera (group U) (n=10), were machined from presintered blocks. All specimens were exposed to mastication simulation (240 000 cycles/1.7 Hz/50 N). The monoclinic phase content was evaluated by X-ray diffraction (XRD). Phase transformation was measured at the mesial connector (group M), distal connector (group D), and pontic regions (group P) before and after mastication simulation. The relative monoclinic phase amount (Xm) was calculated for all specimens. The data were analyzed by ANOVA and post hoc tests (α=.05). ResultsAccording to XRD analysis, Xm for all groups and regions showed higher results after aging than before aging (P<.05). Group B has the lowest Xm among the groups. Group B showed a statistically significant difference compared with both group F and group U (P<.05). There was no significant difference between group F and group U (P>.05). When the regions were evaluated regardless of brand and the groups were evaluated in terms of regions, no statistically significant difference was observed between connectors and the pontic region (P>.05). ConclusionsMastication simulation causes an increase in the Xm. However, this increase was unlikely to be clinically significant. There may be differences in phase transformation depending on the contents of the brands and sintering procedures. Variations in the phase quantity were independent of the connector regions and pontic for FDPs.

Marginal and internal fit of three-unit fixed dental prostheses fabricated from translucent multicolored zirconia: Framework versus complete contour design

Statement of problemTranslucent multicolored zirconia materials enable more esthetic complete contour zirconia fixed dental prostheses (FDPs) than conventional zirconia, which exhibits low translucency and high opacity and is monochromatic. However, how the marginal and internal fit of translucent multicolored zirconia FDPs compare with those of traditional frameworks that require veneering is unclear. PurposeThe purpose of this in vitro study was to compare the marginal and internal fit of frameworks and complete contour 3-unit FDPs fabricated from translucent multicolored zirconia. Material and methodsFrameworks with a thickness of 0.5 mm and complete contour FDPs with a thickness of 0.8 to 1.5 mm were manufactured by using a workflow similar to one from a zirconia master model (mandibular left second premolar-mandibular left second molar). Two polyvinyl siloxane replicas were made for each specimen to measure the marginal and internal fit. Measurement locations were mesial, lingual, buccal, and distal for each abutment. In these locations, the marginal opening (MO), chamfer area (CA), axial wall (AW), and occlusal area (OC) were measured. The data were analyzed with 2-way ANOVA and the Bonferroni post hoc test (α=.05). ResultsFrameworks showed significantly better mean ±standard deviation fit values than complete contour 3-unit FDPs at measurement areas MO (frameworks: 112 ±22 μm, complete contour FDPs: 144 ±37 μm) (P=.013), CA (frameworks: 89 ±12 μm, complete contour FDPs: 110 ±22 μm) (P=.006), and OC (frameworks: 182 ±36 μm, complete contour FDPs: 244 ±64 μm) (P=.008). At the measurement area AW (frameworks: 47 ±7 μm, complete contour FDPs: 50 ±9 μm of each location, no significant difference was observed between frameworks and complete contour FDPs (P=.361). ConclusionsDesign differences in 3-unit FDPs fabricated from translucent multicolored zirconia influenced the marginal and internal fit. Frameworks had smaller marginal fit than complete contour FDPs for translucent multicolored zirconia.

A Prospective Clinical Cohort Investigation on Zirconia Implants: 5-Year Results.

Mid-term data on zirconia oral implants is very rare. Therefore, the aim of this prospective clinical investigation was to evaluate the survival rate and the marginal bone loss of a one-piece zirconia implant after five years. Patient-reported outcomes were also recorded. Zirconia implants to support single crowns (SC) or a 3-unit fixed dental prosthesis (FDP) were placed and subsequently restored. After the insertion of the implants, at prosthetic delivery, and after five years, standardized radiographs were taken to evaluate marginal bone loss (MBL). For bone tissue evaluation, linear mixed models with random intercepts were fitted. Twenty-seven patients received one implant for an SC and 13 patients received two implants for a 3-unit FDP. Three patients each lost one implant for an SC before prosthetic delivery. Thirty-five patients were seen after five years, and no further implant was lost. The cumulative five-year implant survival rate was 94.3%. The MBL from implant installation up to five years was 0.81 mm. The MBL from implant installation to prosthetic delivery was statistically significant (p < 0.001). Patients perceived a significant improvement in function, esthetics, sense, speech, and self-esteem from pretreatment up to the five-year follow-up. The present findings substantiate the clinical applicability of this implant system.

Evaluation of Stress Distribution in Tooth-Supported Fixed Dental Prostheses Made of Translucent Zirconia with Variations in Framework Designs: A Three-Dimensional Finite Element Analysis.

To evaluate the influence of the framework designs on the stress distribution within tooth-supported partially veneered fixed dental prostheses (FDPs) made of translucent zirconia under simulated loads using a three-dimensional finite element analysis (3D-FEA). For a linear 3D-FEA, simplified 3D solid models of prepared abutment teeth (first premolar and first molar) with different 3-unit FDPs were created. The models with different FDP designs-monolithic zirconia (control); semi-monolithic zirconia with 0.3 mm veneer thickness (SM0.3); semi-monolithic zirconia with 0.5 mm veneer thickness (SM0.5); semi-monolithic zirconia with 0.5 mm veneer thickness supported with cap design (SMC), and semi-monolithic zirconia with 0.5 mm veneer thickness supported with wave design (SMW)-were analyzed using 3D-FEA. The elastic properties of the components (bone, dentine, cement, translucent zirconia, and veneering porcelain) were obtained from the published data for FEA. Simulated static loading forces (300 N) were applied at 10° oblique direction over six points in the occlusal surfaces of the FDPs. Maximum principal stress, shear stress, and safety factor were calculated and analyzed among the different models. Semi-monolithic with cap design showed the smallest maximum principal stress levels in the veneering porcelain compared to all other models (SM0.3, SM0.5, SMW). The SM0.3 had lower maximum principal stress levels in the veneering porcelain compared to SM0.5. Regarding stresses in the zirconia framework, all models had comparable results in maximum principal tensile stresses, except SMW had a lower value. Maximum principal stress levels were located in the veneer component of SM0.3, SM0.5, and SMW, whereas, such levels were observed in the cervical areas of the zirconia frameworks of SMC and control. The SM0.3 had the highest maximum shear stress levels at the zirconia-veneer interface, while SMW had the lowest shear values. The 3D-FEA models with different FDP designs showed different minimum safety factor levels. Framework and veneer designs play a significant role in the stress distribution of the partially veneered zirconia FDPs under loading. The FDPs with zirconia frameworks with cap design minimize the maximum principal tensile stress in the veneering porcelain. The FDPs with 0.3-mm-veneering porcelain show low maximum principal tensile stress in the veneering porcelain, but highest maximum shear stress at the zirconia-veneer interface. The FDPs with wave design of zirconia frameworks minimize the maximum shear stress considerably.

A Comparative Study of the Fitness and Trueness of a Three-Unit Fixed Dental Prosthesis Fabricated Using Two Digital Workflows

The purpose of this study was to measure and correlate the fitness and trueness of a 3-unit fixed dental prosthesis (FDP) fabricated using two digital workflows. The 3-unit FDPs were fabricated using two digital workflows (N = 15). The digital workflows were divided into chairside (closed type) and in-lab (open type) groups. The scanning, computer-aided design (CAD), and computer-aided manufacturing (CAM) processes were conducted with 3shape E1 scanner, exocad CAD software, and DDS EZIS HM, respectively, in the in-lab group; and with CEREC omnicam intraoral scanner, CEREC CAD software, and CEREC MC XL, respectively, in the chairside group. The fitness of the fabricated 3-unit FDPs was evaluated by scanning the silicone replica of the cement space and analyzing the thickness of the silicone replica in the three-dimensional (3D) inspection software (Geomagic control X). The trueness of the milling unit was analyzed by 3D analysis of the CAD reference model, which is the design file of the 3-unit FDP, and the CAD test model, which is the scanned file of the 3-unit FDP. In the statistical analysis, comparison of the two groups was conducted by Mann–Whitney U test, and the correlation between the fitness and trueness was conducted by Pearson correlation test (α = 0.05). The marginal and internal fit were significantly lower in the in-lab group at all measurement positions (p &lt; 0.001). The trueness of the milling unit was significantly higher in the in-lab group compared to the chairside group (p &lt; 0.001). There was a positive correlation between the trueness and internal fit (correlation coefficient = 0.621) in the in-lab group (p = 0.013). The use of appropriate equipment in an in-lab (open type) digital workflow enables a better fabrication of 3-unit FDPs than a chairside (closed type) digital workflow, and poor trueness on the inner surface of the crown adversely affects the internal fit.

Financial costs comparison between replacing a tooth with a dental implant or with a fixed dental prosthesis or saving the tooth with endodontic therapy in Riyadh and Al-Hasa

Background: Extracting a decayed tooth and replacing it or trying to save it is one of the most common chief complaints, and every patient is given a variety of viable treatment options. Cost of each option plays a major role in the patient's decision. Aim: The aim was to compare the costs of three treatment modalities in the private dental clinics in Riyadh and Al-Hasa, dental implants placement to replace a missing tooth or to replace a missing tooth with a fixed dental prosthesis (FDP), or to save the tooth with endodontic treatment and crown lengthening and an FDP. Materials and Methods: An interview-based survey was done in the private dental clinics in both Riyadh and Al-Hasa. Convenience sampling was used to choose the clinics. Results: A total of 52 clinics were surveyed. Average costs of a single ceramo-metal, all ceramic and zirconium FDP were 589, 857, and 1241 S. R., respectively. Average costs of a 3-unit ceramo-metal, all ceramic, and zirconium FDP were 1595, 2329, and 3402 S. R., respectively. Average costs of randomized control trials of anterior and posterior teeth were 507 and 733 S. R., respectively. The average cost of the crown lengthening surgical procedure was 411 S. R. Average baseline cost for a single dental implant was 3907 S. R., and the average cost for placing an immediate dental implant was 2972 S. R. Moreover finally, the average cost for replacing the anterior and posterior teeth with dental implants were 3199 and 3176 S. R., respectively. Patients nowadays are faced with a variety of treatment options to replace or save a tooth, one of the most important factors in this decision-making process in the financial factor. This research's results revealed that the highest discrepancy margin in the price was for the treatment with implant therapy, followed by the replacement with a 3-unit FDP and finally the procedures to try and save the tooth. Conclusion: Treatment with implant therapy in both Riyadh and Al-Hasa is still the costliest treatment modality compared to the other modalities, but by a smaller cost margin compared to what it used to be in previous years.

Residual stress of porcelain-fused to zirconia 3-unit fixed dental prostheses measured by nanoindentation

ObjectiveTo evaluate the residual stress (nanoindentation based on hardness) of fatigued porcelain-fused to zirconia 3-unit fixed dental prostheses (FDP) with different framework designs. MethodsTwenty maxillary 3-unit FDP replacing second-premolar (pontic) were fabricated with conventional framework-design (even-thickness of 0.5mm and 9mm2 connector area) and modified framework-design (thickness of 0.5mm presenting lingual collar connected to proximal struts and 12mm2 connector area). Connector marginal ridges were loaded and the fractured and suspended FDPs were divided (n=3/each) into: (1) Fractured zirconia even-thickness (ZrEvenF); (2) Suspended zirconia even-thickness (ZrEvenS); (3) Fractured zirconia with modified framework (ZrModF); (4) Suspended zirconia with modified framework (ZrModS); (5) Non-fatigued FDP with conventional framework design (Control). The FDPs were nanoindented at 0.03mm (Region of Interest (ROI) 1), 0.35mm (ROI 2) and 1.05mm (ROI 3) distances from porcelain veneer outer surface with peak load 4000μN. The Linear Mixed Analysis of Variance (ANOVA) Model on ranks and Least Significant Difference Test on ranks (95%) were used. ResultsHighest rank hardness values were found for Control group and ZrModS, whereas the lowest values were found in ZrModF. Statistical differences (p=0.000) were found among all groups except for comparison between ZrModS and Control group (p=0.371). Hardness between ROIs were statistically significant different (p<0.001) where ROI 1 presented the lowest values. SignificanceFramework-design modification did not influence the residual stress of porcelain-fused to zirconia fatigued 3-unit FDP. Whereas fractured FDPs showed the highest residual stress compared to suspended and control FDPs. Residual stress increased as nanoindented away from framework.

Fracture behavior of all-ceramic, implant-supported, and tooth-implant-supported fixed dental prostheses.

In vitro investigation of the effects of fixed dental prosthesis (FDP) support and loading conditions on the fracture behavior of all-ceramic, zirconia-based FDP veneered with computer-aided design/computer-aided manufacturing (CAD/CAM)-manufactured lithium disilicate ceramic. Based on a model for a 3-unit FDP in the molar region (tooth in region 15, implant in region 17), 16 identical zirconia frameworks were fabricated and veneered with milled lithium disilicate ceramic. Another 16 FDPs were manufactured similarly, using a model in which the tooth was replaced by an implant. The specimens underwent 10,000 thermal cycles between 6.5 and 60°C and 1,200,000 chewing cycles with a force magnitude of 100N. All were then subsequently loaded until fracture in a universal testing device. Half of the FDPs were subjected to centric and axial loading on the pontic, the others to eccentric and oblique loading on one cusp of the pontic. No failures were observed after artificial aging. Fracture loads of tooth-implant-supported restorations were 1636±158 and 1086±156N for axial and oblique loading, respectively; implant-supported FDPs fractured at 1789±202 and 1200±68N, respectively. Differences were significant for load application (P<0.001) and support type (P=0.020). For the two types of load application, fracture mode differed substantially: complete fracture was observed for centric and axial loading whereas mixed cohesive/adhesive failure was observed for many FDPs loaded eccentrically and obliquely. The high incidence of chipping of manually veneered implant-supported all-ceramics restorations might be reduced by use of CAD/CAM-manufactured lithium disilicate veneers. FDPs veneered with lithium disilicate resist occlusal forces of 500N, irrespective of load application and support type. The fracture resistance of implant-supported FDPs was, however, higher than that of combined tooth-implant-supported FDPs. Their clinical use seems to be justified.

Clinical Results and Technical Complications of Posterior Implant-Supported Modified Monolithic Zirconia Single Crowns and Short-Span Fixed Dental Prostheses: A 2-Year Pilot Study.

The purpose of this clinical trial was to investigate the clinical outcomes of implant-supported modified monolithic zirconia single crowns (SCs) and short-span fixed dental prostheses (FDPs) after a follow-up of 2 years. Twenty-seven patients in need of implant-supported SCs or 3-unit FDPs in the posterior maxilla or mandible were consecutively selected for this study. A total of 56 modified monolithic zirconia prostheses including 44 SCs (8 screw-retained, 36 cement-retained) and twelve 3-unit FDPs (5 screw-retained, 7 cement-retained) were included in this study. All patients were followed at 6 months, 12 months, 18 months, and 2 years after placement of the modified monolithic zirconia prostheses. During the follow-up period, all prostheses were evaluated with clinical and radiographic examinations. The following technical parameters were assessed: framework fracture, fracture of veneering porcelain, screw loosening, loss of retention because of prosthesis de-cementation and opposing tooth fracture. No implant was lost during the follow-up period, yielding a 2-year implant survival of 100%. One FDP failed because of framework fracture. The overall prosthesis survival rate was 98.2% after 2 years of clinical service. During the study, 5 complication events were observed in 3 SCs and one FDP, including one fracture of veneering porcelain and 2 screw loosenings in 3 SCs, and loss of retention and opposing tooth fracture in the same FDP. Therefore, the complication-free rate of prostheses was 91.1%. According to the results of this study, the modified monolithic zirconia design used in this study resulted in a favorable short-term outcome for posterior implant-supported SCs and 3-unit FDPs.

Three-dimensional finite element analysis of occlusal splint and implant connection on stress distribution in implant–supported fixed dental prosthesis and peri-implantal bone

The aim of this study was to investigate the influence of occlusal splint therapy on the stress distribution of implant-supported fixed dental prosthesis (FDP) and peri-implantal bone structures using three-dimensional (3D) finite element analysis (FEA). The system consisted of two implants (positioned on region of second premolar and second molar) as retainers of fixed porcelain-fused-to-metal 3-unit FDP (first molar as pontic element). Two implant connections systems (external and internal hexagon) were tested. Static axial loads simulating functional (100N) and overloaded (300N) chewing were applied on the occlusal surface of the FDP covered or not with the occlusal splint. Maximum von Mises stress and bioperformance were accessed for the implants and bone tissues (cortical and cancellous) models. Analytic results indicated that independently of the load condition, implant region, and connection type, the presence of the occlusal splint decreased the stress developed in the implants. Both bone tissues showed increased levels of von Mises stress, and the bioperformance index was far from their maximum yield strength. The internal hexagon implants presented lower stress on premolar and molar regions than external hexagon implants under functional load and overload. The presence of the occlusal splint device over implant-supported FDP may be clinically useful for forwarding stresses towards the bone structure to maintain implants for long term.

Effects of two grading techniques of zirconia material on the fatigue limit of full-contour 3-unit fixed dental prostheses

ObjectiveThis study evaluated the effects of two grading techniques of zirconia material on the fatigue limit of full-contour 3-unit fixed dental prostheses (FDPs). MethodsPresintered blocks of 3Y-TZP were milled to obtain sixty-nine 3-unit FDPs, which were divided into three groups (n=23). The control group (CTL) was sintered and glazed following manufacturer’s instructions. In the two experimental groups presintered FDPs received a surface silica/glass infiltration treatment before the sintering process. Silica sol–gel group (SSG) was graded by the sol–gel processing route, while the glass-zirconia-glass group (GZG) was graded by an enameling technique. Graded groups did not receive a glaze layer after sintering. All FDPs were then luted with a dual-curing resin cement on composite abutments, embedded in polyurethane and stored in water for five days. The initial load of the fatigue test was calculated based on the results of the monotonic testing applied on three specimens of each group. To determine the fatigue limit, 20 samples of each group were subjected to staircase testing (100,000 cycles/5Hz). ResultsThe fatigue limits (in Newtons) were CTL=1607.27, SSG=1824.31, and GZG=2006.57, and the Dixon and Mood test indicated statistically significant differences among groups (95% confidence interval) (GZG > SSG > CTL). SignificanceThe infiltration of silica and glass on bulk zirconia, by two different grading methods, increased the fatigue limits of monolithic zirconia FDPs.

Effect of Cyclic Fatigue Tests on Aging and Their Translational Implications for Survival of All-Ceramic Tooth-Borne Single Crowns and Fixed Dental Prostheses.

The objective of this systematic review was to elaborate the aging effect of cyclic fatigue tests on mechanical durability of all-ceramic single crowns and fixed dental prostheses (FDP). Original scientific papers published in the MEDLINE (PubMed) database in English between 01/01/1950 and 12/31/2013 on cyclic loading on all-ceramics were included in this systematic review. The following MeSH terms, search terms, and their combinations were used: "in vitro," "stress mechanical," "crowns," "denture, partial, fixed," "dentistry," "fatigue," "all-ceramic," "zirconia," "fixed dental prosthesis," "FDP," "bridges," and "cyclic loading." Two reviewers performed screening and analyzed the data. Only the studies that reported on both static fracture strength and static fracture after fatigue of all-ceramic single crowns and FDPs that allowed comparison of aging effect through cyclic loading were included. The selection process resulted in a final sample of 14 journal articles. In total, 9 articles were identified related to all-ceramic single crowns, 3 of which were on anterior and 6 on posterior crowns, and 5 articles on 3-unit FDPs, all of which were on posterior FDPs. Fatigue cycles varied between minimum of 1000 to maximum 1,200,000 cycles for crowns and 10,000 to 2,000,000 cycles for 3-unit FDPs. The applied force during cyclic loading varied between 20 to 300 N for single crowns and 49 to 200 N for 3-unit FDPs. For the 3-unit FDPs, fracture strength results showed slightly decreased values after cyclic loading (659 ± 182 to 2333 ± 183 N) compared to static loading only (841 ± 244 to 2434 ± 154 N). For crowns similar trends were not observed, but cyclic loading decreased the fracture strength in only some materials after cyclic loading (659 ± 182 to 2333 ± 183 N) compared to static loading only (395 ± 96 to 2726 N). An inclination for decreased static fracture strength could be observed after cyclic loading of all-ceramic single crowns and FDPs, but this was material specific. Due to the heterogeneity of data such as aging, loading conditions, and fewer experimental groups, statistical analysis could not be performed. Cyclic loading tests require more standardized guidelines for testing and reporting.

Marginal fit and photoelastic stress analysis of CAD-CAM and overcast 3-unit implant-supported frameworks

Statement of problemSeveral studies have shown the superiority of computer-assisted design and computer-assisted manufacturing (CAD-CAM) technology compared with conventional casting. However, an advanced technology exists for casting procedures (the overcasting technique), which may serve as an acceptable and affordable alternative to CAD-CAM technology for fabricating 3-unit implant-supported fixed dental prostheses (FDPs). PurposeThe purpose of this in vitro study was to evaluate, using quantitative photoelastic analysis, the effect of the prosthetic framework fabrication method (CAD-CAM and overcasting) on the marginal fit and stress transmitted to implants. The correlation between marginal fit and stress was also investigated. Material and methodsThree-unit implant-supported FDP frameworks were made using the CAD-CAM (n=10) and overcasting (n=10) methods. The frameworks were waxed to simulate a mandibular first premolar (PM region) to first molar (M region) FDP using overcast mini-abutment cylinders. The wax patterns were overcast (overcast experimental group) or scanned to obtain the frameworks (CAD-CAM control group). All frameworks were fabricated from cobalt-chromium (CoCr) alloy. The marginal fit was analyzed according to the single-screw test protocol, obtaining an average value for each region (M and PM) and each framework. The frameworks were tightened for the photoelastic model with standardized 10-Ncm torque. Stress was measured by quantitative photoelastic analysis. The results were submitted to the Student t test, 2-way ANOVA, and Pearson correlation test (α=.05). ResultsThe framework fabrication method (FM) and evaluation site (ES; M and PM regions) did not affect the marginal fit values (P=.559 for FM and P=.065 for ES) and stress (P=.685 for FM and P=.468 for ES) in the implant-supported system. Positive correlations between marginal fit and stress were observed (CAD-CAM: r=0.922; P<.001; overcast: r=0.908; P<.001). ConclusionsCAD-CAM and overcasting methods present similar marginal fit and stress values for 3-unit FDP frameworks. The decreased marginal fit of frameworks induces greater stress in the implant-supported system.