Zirconia Fixed Partial Dentures Research Articles

Effect of different sintering protocols on the fracture strength of 3-unit monolithic gradient zirconia fixed partial dentures: An in vitro study

Strength-gradient zirconia combining 3 zirconia formulations with different flexural strengths has been reported to have outstanding mechanical properties. However, data concerning the effect of different sintering protocols on the fracture strength of 3-unit monolithic gradient zirconia fixed partial dentures (FPDs) are sparse. The purpose of this in vitro study was to test the effect of different sintering protocols on the fracture strength of 3-unit monolithic gradient zirconia FPDs. Two custom-made stainless-steel master dies were designed to replicate a mandibular right second premolar and second molar prepared to receive a 3-unit monolithic zirconia FPD. Thirty monolithic zirconia FPDs were milled from gradient zirconia blanks and allocated to 3 groups (n=10) according to the sintering protocols: high-speed sintering, speed sintering, and conventional sintering. The FPDs were cemented onto the corresponding dies with traditional glass ionomer cement. All FPDs were cyclic loaded (600 000 cycles/49N/1.7Hz) in a mastication simulator. Fracture load measurements for each FPD were determined by using a universal testing machine. Scanning electron microscopy (SEM) at ×80 magnification was used to examine a fractured FPD from each group. A representative specimen from each group was examined with SEM at ×30 000 magnification to determine the grain size. One-way ANOVA, pair-wise Tukey honestly significant difference (HSD), and Pearson correlation tests were used for statistical analysis of the data (α=.05). The high-speed sintered FPDs recorded the highest statistically significant fracture load mean ±standard deviation value (2526 ±300N), followed by the speed sintered FPDs (2136 ±127N), while the lowest statistically significant fracture load mean value was recorded with the conventionally sintered FPDs (1361 ±181N) (P<.001). In addition, the mean ±standard deviation grain size values were 488 ±272nm for the high-speed sintered specimen, 578 ±409nm for the speed sintered specimen, and 832 ±551nm for the conventionally sintered specimen (P<.001). A significant negative correlation was found between fracture strength and grain size among the 3 groups. The fracture strength of 3-unit monolithic gradient zirconia FPDs sintered by using a high-speed protocol was significantly higher than that of speed and conventionally sintered FPDs (P<.001). The high-speed sintering protocol reduced the mean grain size of gradient zirconia FPDs compared with that of both speed and conventional sintering protocols.

Finite Element Analysis of Occlusal Interferences in Dental Prosthetics Caused by Occlusal Adjustment.

To investigate the influence of occlusal interference using finite element analysis (FEA). The FEA model designed for this study centered on an all-ceramic, bilayered, fixed partial denture (FPD) retained on the maxillary first premolar and first molar, with the second premolar replaced by a pontic. The surrounding structures-such as the neighboring teeth, antagonists, and periodontium-were modeled. Four different loading cases were designed at occlusal interferences of 0, 8, 12, and 24 μm and were loaded by a simulated bite force of 300 N. Principal and von Mises stresses, as well as strain, were evaluated for all included structures. For interferences of 12 and 24 μm, failure-relevant tensile stresses in the veneering layer were observed at the occlusal surfaces. Stress found in the zirconia FPD did not reach fatigue or flexural strength for any test load. Peak tensile stress was observed in close proximity to occlusal contact points, increasing with increasing occlusal interference. The FEA results suggest that the majority of occlusal stress is absorbed by the deformation of the periodontal ligament. Framework failure caused by the simulated interferences was not expected. Surface defects may ultimately lead to failure due to fracture or chipping, especially in cases of weaker ceramics or veneering.

An in vitro trial on the effect of arch form on connector size requirements in long span anterior zirconia fixed dental prostheses.

To test the fracture resistance of maxillary canine to canine fixed partial denture with four missing incisors, with increasing anterior-cantilevers of the pontics and varying connector sizes. Two 3D-printed titanium alloy (Ti6Al4V) models mimicking a maxillary canine to canine fixed partial denture (FPD) with four pontics replacing the incisors were used as master models. Zirconia FPDs were digitally designed and milled with two different connector sizes (9 and 12 mm2 ) each with three different anterior cantilevers (7, 10, and 13mm) accounting for 6 test groups. Seven samples were milled for each group generating a total of 42 samples. The zirconia FPDs were cemented on the titanium model using resin modified glass ionomer cement and the model fixated to a variable angle vice. A sinusoidal cyclic waveform load from 50 to 280N was applied using a universal testing machine at a frequency of 30 cycles per second and a total of 5 million cycles. The results of Fisher's exact tests showed that the difference in the proportion of fractured versus nonfractured fixed partial dentures was not statistically significant when comparing the 9 with the 12 mm2 connector size (p = 1.00), as well as when comparing the six test groups (p = 0.2338); on the other hand, it proved to be statistically significant when comparing the 7mm cantilever with the 10 and 13mm cantilevers combined (p = 0.0407) indicating that a 7mm anterior spread of the pontics showed a significantly greater proportion of fixed partial dentures that fractured. Fracture susceptibility was not a function of cantilever length in this testing configuration for anterior FPDs. Retainer crown thickness seems to be a more important parameter than connector size thickness. Based on the results, a smaller connector size (9 mm2 ) can be used to improve the esthetics of pontics in long span anterior FPDs.

Effect of Sintering Speed and Polishing or Glazing on the Failure Load of Monolithic Zirconia Fixed Partial Dentures.

To evaluate the effect of sintering speed and polishing or glazing on the failure load (FL) of monolithic zirconia fixed partial dentures (FPDs). A total of 40 three-unit FPDs extending from the mandibular first premolar to the first molar were evaluated. The prepared typodont teeth were scanned, and the prostheses were designed. Afterwards, the prostheses were milled from monolithic zirconia blanks. The samples were divided into classic and speed sintering groups (n = 20 each). Half of the samples in each group (n = 10) were polished with an electric handpiece according to the manufacturer's instructions, and the other half (n = 10) were glazed. All of the samples were thermocycled for 3,500 cycles between 5ºC and 55ºC in water baths. The FL was calculated in Newtons with the three-point bending test. The mean ± SD FL values were as follows: classic sintering/polished group = 2,026.5 ± 172.8 N; classic sintering/glazed group = 1,917.58 ± 174.45 N; speed sintering/polished group = 1,787.58 ± 145.81 N; and speed sintering/glazed group = 1,719.6 ± 143.9 N. There was a significant difference in the mean FL between the two sintering methods (P < .001), with the classic sintering group exhibiting the highest FL. Classic sintering of the monolithic zirconia FPDs led to the maximum amount of FL and strength.

Fatigue Resistance of 3-Unit CAD-CAM Ceramic Fixed Partial Dentures: An FEA Study.

To estimate the fatigue life of 3-unit molar fixed partial dentures (FPDs) made from two different monolithic ceramic systems, zirconia cercon (ZC) and lithium disilicate (LD). The effect of the connector size on the fatigue resistance of the monolithic FPD was also investigated. Two models for the FPDs were built, a 3-unit all-ceramic and a porcelain-fused-to-metal. The porcelain-fused-to-metal FPD model was used as the control. Actual 3-unit FPDs (replacing the second lower premolar) were constructed using a computer aided design and computer-aided manufacturing (CAD-CAM) system. Finite element analysis (FEA) was executed. A hemispherical indenter was used to simulate occlusal load. The occlusal load phase of the chewing cycle was applied at the premolar pontic. The failure location for the monolithic FPD was always located at the distal connector. Connector size played a key role in determining the long-term survival of the prosthesis. The fatigue resistance was predicted to be 670 N for the ZC with a connector size 4 × 3 mm, while it was only 226 N for LD. As for porcelain-fused-to-metal (PFM), FEA predicts that fatigue resistance can reach up to 770 N. Under the cyclic load of 670 N, the fatigue life for the zirconia FPD with connector size 4 × 3 mm was 2.23 × 106 cycles while it survived only 3.1 × 105 cycles when the connector was reduced to 3.5 × 2.5 mm. The angle of the oblique load has a significant effect on the stress distribution. 3-unit monolithic FPDs made of ZC have superior fatigue performance compared to those made of LD. The fatigue life of the zirconia FPD was about three times longer than that made of LD with a connector size of 4 mm × 3 mm. The survival rates of ZC FPDs are comparable to porcelain-fused-to-metal. A significant reduction in fatigue strength is predicted for reduced connector size. Therefore, it is necessary to establish general guidelines for the minimum connector size.

Randomized clinical trial comparing monolithic and veneered zirconia three-unit posterior fixed partial dentures in a complete digital flow: three-year follow-up.

ObjectivesTo evaluate and to compare the clinical performance and survival rate of posterior monolithic and veneered zirconia fixed partial dentures (FPDs).Material and methodsSixty 3-unit posterior FPDs were included in the study. The patients were randomly distributed into two groups (n = 30 each) to receive either a monolithic (Zenostar T, Wieland Dental) or veneered zirconia (IPS e.max ZirCAD, Ivoclar Vivadent) FPD. Each patient received only 1 FPD. Tooth preparations were scanned (Trios 3, 3Shape), designed (Dental System 2016, 3 Shape), milled (Zenotec CAM 3.2, Wieland Dental), and cemented with a resin cement. Technical and biological outcomes and periodontal parameters were assessed. Data analysis was made using the Friedman and the Wilcoxon signed-rank tests with the Bonferroni correction and the Mann–Whitney U test.ResultsThe survival rate at 3 years was 100% for veneered and 90% for monolithic zirconia restorations. Three monolithic zirconia FPDs were lost because of biologic complications. The main complication in the veneered zirconia FPDs was the fracture of the veneering ceramic in 4 of the veneered zirconia FPDs. No fracture of the frameworks was observed in any of the groups. All restorations were assessed as satisfactory after 3 years. No differences in periodontal parameters were observed between the groups.ConclusionsThe results of this study suggest that monolithic zirconia and complete digital flow could be a viable alternative to veneered zirconia in the posterior regions.Clinical relevanceThe monolithic zirconia restorations with a digital workflow can be a viable alternative in posterior fixed partial dentures, with good periodontal outcomes.Clinical trial registration numberClinicalTrials.gov (Identifier NCT 04,879,498).

Sintering distortion of monolithic zirconia in 4-unit fixed partial denture: Effect of layered structure and vertical milling area

Layered-type zirconia disks, which offer color gradation from enamel to cervical shade, have been employed in recent years to replicate the shades of natural teeth. The layered structure is effective at replicating colors and has helped popularize monolithic zirconia restorations. However, the sintering shrinkage of zirconia is very large; thus, controlling the sintering distortion is very important. Thus, the objective of this study was to determine the influence exerted by the layered structure of the zirconia disk and the vertical milling area on the sintering distortion. An experimental fixed partial denture (FPD) was designed based on a 4-unit monolithic zirconia FPD. A single-composition (SC)-type disk with no shade and a single-composition-layered (SCL)-type disk with shade gradation were selected for this study. In particular, three milling areas, the top end of the disk (area I), vertical center (area II), and bottom end of the disk (area III), were investigated. Moreover, the sintering distortions generated by the experimental FPDs were measured. Results showed that sintering distortion in 4-unit monolithic zirconia FPDs occurred in all SC and SCL areas. Additionally, the sintering distortions were affected by the layered structure of the zirconia disks, the degree of which depended on the milling area (area I > area II > area III). Thus, when fabricating dental prosthesis using SCL zirconia disks, the milling area must be selected considering both the color adjustment and sintering distortion.

Periodontal outcomes of anterior fixed partial dentures on teeth treated with the biologically oriented preparation technique: A 6-year prospective clinical trial

Statement of problemOne of the most frequent complications in participants with fixed partial dentures (FPDs) is the apical migration of the gingival margin, which may be associated with factors such as fit, gingival margin location, or tooth preparation type. The prevalence of the complication in participants restored with FPDs prepared by using the biologically oriented preparation technique (BOPT) is unclear. PurposeThe purpose of this prospective clinical trial was to evaluate the clinical and biologic outcomes of FPDs on teeth prepared by using the BOPT, over a 6-year follow-up period. Material and methodsTooth-supported zirconia FPDs in the anterior region prepared by using the BOPT were evaluated. Each participant was monitored annually for 6 years by evaluating plaque index, probing depth, vestibular gingival thickness, and gingival margin stability. Biologic and/or mechanical complications were also recorded. Patient satisfaction was measured by using a visual analog scale (VAS). ResultsA total of 25 FPDs supported by 70 teeth in 24 participants were analyzed. Low plaque index values and stable probing depths were observed, whereas the gingival index was 0 for most of the teeth. Teeth treated by using the BOPT presented significant increase in gingival thickness, and the gingival margin was found to be stable in 100% of the treatments. FPD survival was 100%. ConclusionTooth supporting FPDs prepared by using the BOPT presented good periodontal health and gingival margin stability, without recession and with a 100% survival rate during a 6-year follow-up.

Evaluate the Flexural Strength of Zirconia Fixed Partial Denture with Different Connector Designs

Evaluate the Flexural Strength of Zirconia Fixed Partial Denture with Different Connector Designs

Clinical behavior of posterior fixed partial dentures with a biologically oriented preparation technique: A 5-year randomized controlled clinical trial

Statement of problemEvidence of the behavior of the periodontal tissues around anterior teeth restored with the biologically oriented preparation technique (BOPT) is available. However, outcomes of this technique in posterior teeth restored with fixed partial dentures (FPDs) are lacking. PurposeThe purpose of this randomized controlled clinical trial was to evaluate the clinical, mechanical, and biological behavior of posterior 3-unit FPDs placed on teeth prepared with BOPT. Material and methodsForty participants received a 3-unit zirconia FPD in the posterior region of the mandible or maxilla. Twenty FPDs were placed on teeth prepared with BOPT (study group) and 20 on teeth with a horizontal chamfer finishing line (control group). Follow-up examinations were performed 1, 3, and 5 years after treatment to evaluate periodontal responses around the prepared teeth by means of the following parameters: plaque index, gingival index, probing depth, and marginal stability (MS). Mechanical behavior was also assessed, as were any complications. ResultsAfter the 5-year follow-up, 57.9% of the control group and 35% of the BOPT group presented a plaque index of 1. The gingival index was 1 in 68.4% of the control group and 30% of the BOPT group after the follow-up period. In the analysis of probing depth, 26.3% of teeth in the control group had pockets of more than 3 mm in depth, whereas the BOPT group had only 10%. Marginal stability appeared in 100% of the BOPT group, whereas only 10.5% of the control group exhibited gingival stability. Complications during the follow-up period were similar, 20% in the control group and 15% in the BOPT group. ConclusionsPosterior FPDs prepared by using BOPT had a good clinical response over a 5-year follow-up, with a low gingival index, a small increase in pocket depth, and a 100% marginal stability of the surrounding tissues. High survival rates after 5 years indicated that the technique produced predictable outcomes.

Three-year clinical performance of monolithic and partially veneered zirconia ceramic fixed partial dentures.

To compare the 3-year survival and success rates of monolithic (M) and partially veneered (PV) zirconia-fixed partial dentures (FPDs). Sixty-seven FPDs (n = 33 M-FPDs; n = 34 PV-FPDs) were placed in 51 patients (n = 23 males; mean age 61.5 years) and clinically followed up 1 week, 6 months, and then yearly after placement. One hundred per cent (100%) of M-FPDs and 70% of PV-FPDs were located in the posterior region. Ninety-two per cent (92%) of M-FPDs had three units, whereas 50% of PV-FPDs had more than three units. A facial veneer was present in 73% of the PV-FPDs units. Survival and success were calculated using the Kaplan-Meier method and compared using the log-rank test (α = .05). The mean observation period was 3.5 years for M-FPDs and 3.1 years for PV-FPDs. Most complications associated with FPDs were biological in nature. Ceramic defects occurred exclusively among PV-FPDs. Three-year survival was 96.7% for M-FPDs and 93.8% for PV-FPDs (P = .064). Three-year success was 93.8% for M-FPDs and 81.7% for PV-FPDs (P = .039). The use of both M-FPDs and PV-FPDs yielded clinically successful results over a mean period of 3 years. By using monolithic or facially veneered zirconia, ceramic FPDs could be fabricated which showed only a minimum of technical complications over the period of investigation without sacrificing adequate esthetics.

Clinical performance and patient satisfaction obtained with tooth-supported ceramic crowns and fixed partial dentures

Statement of problemStudies reporting survival rates along with patient-centered outcomes are necessary to select the appropriate restorative material for crowns and fixed partial dentures (FPDs). However, studies that report the survival and complication rates of lithium disilicate crowns and the performance of zirconia FPDs compared with metal-ceramic FPDs are lacking. PurposeThe purpose of this clinical study was to assess the failure and complication incidence of tooth-supported ceramic crowns and FPDs in function for at least 5 years. Groups included were pressed lithium disilicate crowns (CP), veneered pressed lithium disilicate crowns (CV), and computer-aided design and computer-aided manufacturing (CAD-CAM) lithium disilicate crowns (CC). Veneered zirconia-based FPDs (FPDC) were compared with metal-ceramic FPDs (FPDM). Outcomes were survival and failure, success and complications, periodontal conditions, and patient satisfaction assessed at 2 examinations (at baseline ≥1 year after delivery and at the follow-up examination ≥5 years of function). Material and methodsEighty-two participants with 158 restorations (CP=39, CV=16, CC=20, FPDM=30, FPDC=53) were examined (2.38 ±0.96 years after delivery) to form the baseline data. For the prospective follow-up examination, 70 participants with 141 restorations (CP=39, CV=15, CC=16, FPDM=28, FPDC=43) were examined 4.08 ±0.36 years later. ResultsAt the follow-up, restorations were in function for a mean of 6.44 ±1.14 years. Survival rates for crowns were 97.1% (CP=97.4%, CV=100%, and CC=93.8%) and 98.6% for FPDs (FPDM=96.4%, FPDC=100%). Among the 68 crowns, 1 technical and 4 biological complications were recorded. FPDs had more biological and technical complications than crowns (15/149 abutment teeth and 11/71 restorations). Technical complications were seen in 9.3% of zirconia FPDs compared with 25% for metal-ceramic FPDs. Complications were commonly observed at the baseline examination (crowns: 12/75 biological and 1/75 technical; FPDs: 40/174 abutment teeth with biological and 8/83 FPDs with technical complications). The periodontal conditions improved significantly after baseline. The patients reported a high level of satisfaction with the esthetics and function of the crowns and FPDs. ConclusionsSurvival rate for ceramic crowns and FPDs was 97.9% after a mean observation time of 6.44 ±1.14 years. Biological complications were more commonly observed than technical complications, and complications were more common in FPDs than in crowns. The complication rate was similar for zirconia FPDs and metal-ceramic FPDs. Adherence to strict maintenance measures may have reduced the risk of biological complications.

Influence of speed sintering on the fit and fracture strength of 3-unit monolithic zirconia fixed partial dentures

Statement of problemSpeed sintering has been introduced to enable single-visit monolithic zirconia prostheses. However, the fit and fracture load of zirconia 3-unit monolithic fixed partial dentures (FPDs) after speed sintering are unknown. PurposeThe purpose of this in vitro study was to test the properties of zirconia 3-unit monolithic FPDs after speed sintering and to compare the properties with conventional sintering. Material and methodsA calibrated operator digitized an in vitro model with a complete coverage preparation of a maxillary right second premolar and second molar (n=12) by using the CEREC AC Omnicam (Dentsply Sirona) scanner. Twelve zirconia FPDs were designed (CEREC SW 4.1.1), and for each data set (n=12), 1 FPD was designed and milled 4 times (MCXL Premium; CEREC Zirconia; Dentsply Sirona), resulting in 4 identical monolithic FPDs (N=48). The FPDs were divided into 2 groups according to the sintering procedure (n=24): speed sintering (group S) by using the SpeedFire (Dentsply Sirona) and the conventional sintering (group C) by using the inFire HTC speed (Dentsply Sirona). All the FPDs were glazed by using glaze-spray and fired according to the sintering group. The SpeedFire (Dentsply Sirona) was used for group S, and the VACUMAT 6000M (VITA Zahnfabrik) was used for group C. The fit of the FPDs was evaluated with the replica technique by using polyvinyl siloxane and analyzed according to the measurement areas: marginal gap, chamfer area, axial wall, and occlusal area. Subsequently, groups S and C were further subdivided, and 12 specimens per group underwent artificial aging by thermomechanical loading in a mastication machine (50 N for 1.2×106 times at a frequency of 1.7 Hz and a thermal change in distilled water from 5 °C to 50 °C every 120 seconds), resulting in additional subgroups: group SA and group CA. For all the FPDs (groups S, C, SA, and CA), a fracture load measurement was conducted. The Kolmogorov-Smirnov test was used to examine the values of the fit and fracture load for normal distribution. The Mann-Whitney U test for the fit and a 2-way ANOVA for the fracture load were used to detect the differences among the groups (α=.05). ResultsGroup S showed a better marginal (P=.018) and occlusal (P<.001) fit than group C. For the fracture load values, no significant difference was found because of the sintering procedure (P=.070) or the interaction of the sintering procedure and artificial aging (P=.484). Artificial aging showed an impact (P=.024) with significantly lower values after aging. ConclusionsSpeed-sintered FPDs had equal and better values for the fit and fracture load than conventional sintering.

Clinical behavior of second-generation zirconia monolithic posterior restorations: Two-year results of a prospective study with Ex vivo analyses including patients with clinical signs of bruxism

ObjectivesThis study aimed to investigate (1) clinical outcomes of second-generation zirconia restorations, including patients with bruxism clinical signs, and (2) the material wear process. MethodsA total of 95 posterior monolithic zirconia tooth-elements in 45 patients were evaluated, 85 on implants and 10 on natural teeth, and 20.3% of restorations being fixed partial dentures (FPDs). Occlusal contact point areas were determined and half of those areas were left unglazed and just polished. Restorations were clinically evaluated following criteria of the World Dental Federation and antagonistic teeth were examined at each evaluation time. Wear ex vivo analyses using SEM and 3D laser profilometry were performed at baseline and after 6 months, 1 year, and 2 years respectively, temporarily removing the prostheses. ResultsThe Kaplan-Meier survival rate of restorations was 93.3% (100% for FPDs) and the success rate was 81.8%, with 4 abutment debondings, 3 tooth-supported crown debondings (provisional cement use), 1 restoration fracture, 1 minor chipping, 1 core fracture, 1 root fracture, and 2 implant losses. 80% of catastrophic failures occurred in patients with clinical signs of bruxism (61.7% of patients). Complications were also observed on antagonistic teeth (3 catastrophic failures). Clinical evaluation of the restorations showed good results from the aesthetic, functional, and biological perspective. Zirconia wear was inferior to 15 μm, while glaze wear was observed on all occlusal contact areas after 1 year. ConclusionsMonolithic zirconia FPDs are promising but the failure rate of single-unit restorations was not as high as expected in this sample including patients with bruxism clinical signs. Clinical significanceWithin study limitations, FPDs showed excellent short-term results but further research is needed for single-unit restorations considering samples, which do not exclude bruxers. The weak link is the restoration support or the antagonist tooth, one hypothesis being that zirconia stiffness and lack of resilience do not promote occlusal stress damping.

Influence of Radius of Curvature at Gingival Embrasure in Connector Area on Stress Distribution of Three-Unit Posterior Full-Contour Monolithic Zirconia Fixed Partial Denture on Various Amounts of Load Application: A Finite Element Study.

Objectives:To test the hypothesis that radius of curvature at gingival embrasure in connector area significantly affects the fracture resistance of full-contour monolithic zirconia three-unit posterior Fixed partial denture (FPD) on various amounts of load application.Materials and Methods:In this study, two types of three-dimensional finite element models of a three-unit posterior full-contour monolithic zirconia FPD with two gingival embrasure radii (rGE I, 0.45 mm and rGE II, 0.25 mm) were constructed. The components modeled through finite element modeling were subjected to 400, 600, and 800 N vertical loads at the central fossa of the pontic, and further analysis was carried out.Results:All the results were displayed by post-processor finite element analysis software (ANSYS). The study revealed that with increase in the amount of load application as well as decrease in the gingival embrasure radii, stress concentration values were increasing gradually for both the full-contour monolithic zirconia FPD.Conclusion:The fracture resistance of the zirconia posterior FPD was significantly affected by the gingival embrasure radii and the mode of load application. When there is a clinical situation of heavier occlusal forces, the fracture resistance can be increased by designing greater gingival embrasure radii in the connector region.

Fatigue resistance of all-ceramic fixed partial dentures – Fatigue tests and finite element analysis

ObjectiveTo estimate the fatigue resistance of a new translucent zirconia material in comparison to lithium disilicate for 3-unit fixed partial dentures (FPDs). MethodsEighteen 3-unit FPDs (replacement of first upper molar) with a connector size of 4mm×4mm were dry milled with a five-axis milling machine (Zenotec Select, Wieland, Germany) using discs made of a new translucent zirconia material (IPS e.max ZirCAD MT, Ivoclar Vivadent). Another 9 FPDs with a reduced connector size (3mm×4mm) were milled. The zirconia FPDs were sintered at 1500°C. For a comparison, 9 FPDs were made of IPS e.max Press, using the same dimensions. These IPS e.max Press FPDs were ground from a wax disc (Wieland), invested and pressed at 920°C. All FPDs were glazed twice. The FPDs were adhesively luted to PMMA dies with Multilink Automix. Dynamic cyclic loading was carried out on the molar pontic using Dyna-Mess testing machines (Stolberg, Germany) with 2×106 cycles at 2Hz in water (37°C). Two specimens per group and load were subjected to decreasing load levels (at least 4) until the two specimens no longer showed any failures. Another third specimen was subjected to this load to confirm the result. All the specimens were evaluated under a stereo microscope (20× magnification). The number of cycles reached before observing a failure, and their dependence on the load and on the material, were modeled, using a Weibull model. This made it possible to estimate the fatigue resistance as the maximum load for which one would observe less than 1% failure after 2×106 cycles. In addition to the experimental study, Finite Element Modeling (FEM) simulations were conducted to predict the force to failure for IPS e.max ZirCAD MT and IPS e.max Press with a reduced cross-section of the connectors. ResultsThe failure mode of the zirconia FPDs was mostly the fracture of the distal connector, whereas the failure mode of the lithium disilicate FPDs observed to be the fracture of the connectors or multiple cracks of the pontic. The fatigue resistance with 1% fracture probability was estimated to be 488N for the IPS e.max ZirCAD MT FPDs (453N for repeated test), 365N for IPS e.max ZirCAD MT FPDs with reduced connector size and 286N for the e.max Press FPDs. All three IPS e.max ZirCAD groups statistically performed significantly better than IPS e.max Press (p<0.001). On the other hand, no significant difference could be established between the two IPS e.max ZirCAD MT3 groups with a 4mm×4mm connector size (p>0.05). The allowable maximum principal stress (σmax) which did not lead to failure during fatigue testing for IPS e.max ZirCAD MT3 was calculated between 208MPa and 223MPa for FPDs with 4mm×4mm connectors for 2×106 cycles. This value could also be verified for the FPDs of the same material with 3mm×4mm connectors. On the other hand fatigue strength in terms of σmax at 2×106 cycles of IPS e.max Press was calculated to be between 78 and 90MPa. SignificanceThe fatigue resistance of the translucent zirconia 3-unit FPDs was about 60–70% higher than that of the lithium disilicate 3-unit FPDs, which may justify their use for molar replacements, provided that a minimal connector size of 4mm×4mm is observed. Even with a limited number of specimens (n=9) per group it was possible to statistically differentiate between the tested groups.

A retrospective evaluation of zirconia-fixed partial dentures in general practices: An up to 13-year study

ObjectivesTo evaluate zirconia-based fixed partial dentures (FPDs) after more than 8 years in clinical service. MethodsPatients treated between 2000 and 2004 with zirconia FPDs were identified from the records of a manufacturer of FPD substructures. Of the 45 patients who met the inclusion criteria 30 attended the appointment and 33 FPDs were evaluated using modified California Dental Association (CDA) criteria. In addition, plaque and the bleeding index were registered. Patient satisfaction with the restorations was evaluated using a 10-point visual analog scale (VAS). ResultsAll the FPDs were made using CAD/CAM and hot isostatic pressed yttria-tetragonal zirconia polycrystal (HIPed Y-TZP) ceramic (Denzir) and were placed within general practices. The mean observation period was 9.6±1.6 years (range 3.0–13.1 years). The CDA rating was 90% satisfactory for the surface. Corresponding figures for anatomic form, color and margin integrity were 94%, 100% and 94%, respectively. Regarding surface three (9.7%) FPDs exhibited veneer chipping and were rated ‘not acceptable’. For margin integrity two (6.5%) were rated ‘not acceptable’ because of caries. For anatomic form two (6.1%) were rated ‘not acceptable’ due to two lost FPDs. No significant differences were seen between the FPDs and controls for plaque and bleeding. The Kaplan–Meier survival rate (still in clinical function) was 94%, the success rate (technical events accounted for) 91% and (biological events accounted for) 73%. Based on the VAS the mean value for patient satisfaction was 9.3±1.2. SignificanceNinety-four percent of the FPDs were still in clinical function. HIPed Y-TZP could serve as an alternative for FPD treatments similar to those in the current study.

Splinted Zirconia Fixed Partial Denture Supported by Small Diameter (Mini Implants) in the Posterior Mandible: A Case Letter

Splinted Zirconia Fixed Partial Denture Supported by Small Diameter (Mini Implants) in the Posterior Mandible: A Case Letter

Marginal fit of anterior 3-unit fixed partial zirconia restorations using different CAD/CAM systems.

PURPOSEFew studies have investigated the marginal accuracy of 3-unit zirconia fixed partial dentures (FPDs) fabricated by computer-aided design/computer-aided manufacturing (CAD/CAM) system. The purpose of this study was to compare the marginal fit of zirconia FPDs made using two CAD/CAM systems with that of metal-ceramic FPDs.MATERIALS AND METHODSArtificial resin maxillary central and lateral incisors were prepared for 3-unit FPDs and fixed in yellow stone. This model was duplicated to epoxy resin die. On the resin die, 15 three-unit FPDs were fabricated per group (45 in total): Group A, zirconia 3-unit FPDs made with the Everest system; Group B, zirconia 3-unit FPDs made with the Lava system; and Group C, metal-ceramic 3-unit FPDs. They were cemented to resin dies with resin cement. After removal of pontic, each retainer was separated and observed under a microscope (Presize 440C). Marginal gaps of experimental groups were analyzed using one-way ANOVA and Duncan test.RESULTSMean marginal gaps of 3-unit FPDs were 60.46 µm for the Everest group, 78.71 µm for the Lava group, and 81.32 µm for the metal-ceramic group. The Everest group demonstrated significantly smaller marginal gap than the Lava and the metal-ceramic groups (P<.05). The marginal gap did not significantly differ between the Lava and the metal-ceramic groups (P>.05).CONCLUSIONThe marginal gaps of anterior 3-unit zirconia FPD differed according to CAD/CAM systems, but still fell within clinically acceptable ranges compared with conventional metal-ceramic restoration.

In vitro failure and fracture resistance of veneered and full-contour zirconia restorations

ObjectivesThis study evaluated the failure and fracture resistance of zirconia-based fixed partial dentures (FPDs) under the influence of different surface treatments and adjustment procedures. MethodsSeven groups (n=8/group) of three-unit zirconia-based FPDs were fabricated in anatomic design (AD) or anatomically reduced design (ARD) and surfaces were prepared according to clinical relevance: #1: AD – sintered; #2: AD – sintered – glazed; #3: AD – sintered – sandblasted – glazed; #4: AD – sintered – polished – grinded (contact points adjusted); #5: AD – sintered – polished – grinded – repolished; #6: ARD – sintered – veneered; #7: control: analogous to #3 but without thermal cycling (TC) and mechanical loading (ML). FPDs were adhesively bonded to polymethylmethacrylate abutment teeth. TCML (TC: 6000×5°/55°; ML: 1.2×106×50N, 1.6Hz) was conducted in a chewing simulator with steatite spheres as antagonists. Failures were monitored and fracture resistance was determined after ageing. Data were analysed statistically with Mann–Whitney U-test (Kolmogorov–Smirnov-test; α=0.05). FPDs were subjected to scanning electron microscopy for fractographic failure analysis. ResultsNone of the FPDs failed during TCML, but showed wear at contact points. Median fracture force ranged between 1173.5N (#4) and 1316.0N (#3) without significant (p=0.910) differences between the groups or in comparison to the control (p>0.462). ConclusionsZirconia restorations showed high resistance to failures and fracture under different surface treatment variations. Full-contour polished or glazed zirconia FPDs might be an alternative to common veneered restorations.