Three-unit Fixed Partial Dentures Research Articles

Quality of Fixed Dental Prostheses and Patient Satisfaction in a Sample From Saudi Arabia.

The objective of the study was to retrospectively assess the clinical performance of dental prostheses, single crowns, and three-unit bridges to identify clinical biological and mechanical complications in the Ha'il province of Saudi Arabia. The study was conducted between March 2021 to October 2021 and included 421 patients who underwent crown and tooth-supported fixed partial denture (FPD) procedures at the Dental Polyclinics Center in the Ha'il region of Saudi Arabia from 2010-2020. The planned sampling approach was applied. Patients who underwent crown and FPD placements at the dental center within the scheduled period were identified through clinical assessments. The inclusion criteria were met by patients with three-unit FPDs and a single crown containing a natural contralateral tooth or teeth. A total of six general dentists conducted clinical exams. Patient satisfaction and technical and biological issues were the evaluation criteria for crowns and FPDs. The frequency and percentage of the various characteristics employed in the current investigation were ascertained using cross-tabulation. The Chi-square test was employed to assess the associations between categorical variables, with p-values≤ 0.05 considered significant. Results: Marginal integrity was recorded in 332 participants (78.9%), which was satisfactory for the majority of the restoration. The acceptance morphology was present in 252 (59.9%) restorations. The highest rate of the restorations 274 (66.2%) had satisfactory color. In 86 cases (20.4%), there was visible periodontal depth of at least 5 mm. Three hundred and six (72.7%) of the fixed restorations had gingival bleeding connected to them, and 96 (22.8%) teeth had periapical lesions. A total of 311 patients (73.9%) reported they were satisfied with their fixed restorations. The technical and biological complications noted in the current study were not higher compared with other studies of crowns and fixed dental prostheses. The majority of patients were satisfied with the restoration.

Fracture resistance of 3-unit monolithic ZrO2 ceramics FPDs with different preparation designs of the distal abutment - an in-vitro study

Masticatory pressure increases in the distal areas of the dentition. This should be considered when restoring partially edentulous patients with a metal-free fixed partial denture (FPD). An alternative abutment preparation design can be used in order to increase the materials' volume in the most fracture-prone "connector area" of an FPD. The increased size of the connection might positively influence the constructions' mechanical durability, thereby increasing its success and survivability. The aim of the present study was to investigate the influence of two preparation designs of the distal abutment on the fracture resistance of three-unit, monolithic, ZrO2 FPDs. 3D printed replicas of a partially edentulous mandibular segment and a ZrO2, milled in full-contour, three-unit FPDs were used for this investigation. Two experimental groups (n=10 ) were defined based on the preparation design of the distal abutment tooth - classical shoulder preparation 0.8mm deep, and endocrown preparation with a 2-mm retention cavity. The bridge - mandibular segment replica assembly was done with relyXU200(3M ESPE, USA), light-cured for 10 seconds per side with D-light Duo (GC, Europe). After cementation the test specimens were subjected to loading in a universal testing machine Zwick (Zwick-Roell Group, Germany). Statistical analysis was performed using R and includes descriptive statistics, t-test for quantitative and chi-squared test for qualitative variables. The results showed no difference between the two studied groups in the maximum force required to fracture the test specimens [t=-1.8088 (17.39), p-value=0.087; P>0.05]. 95% of the fracture lines were located in the distal connector. Within the limitations of this study, it can be concluded that both tested preparation designs show similar results in terms of the load required to fracture the test specimens. Furthermore, it is confirmed that the distal connector is the weakest area of an all-ceramic 3-unit FPD in the posterior area.

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.

Accuracy of the Intra- and Extra-Oral Scanning Technique for Transferring the Intaglio Surface of a Pontic of Provisional Restorations to Definitive Restorations.

When taking the final impression for a three-unit fixed partial denture (FPD), the intaglio surface of the pontic of provisional restoration cannot be transferred accurately to that of definitive restoration. The intra- and extra-oral scanning (IEOS) technique, a method for accurately reproducing the submucosal morphology of the superstructure of an implant, has been reported using an intraoral scanner. In the present study, we evaluated the difference between the conventional impression method using impression material and the IEOS technique in reproducing the morphology of the surface of the pontic of a definitive FPD. There was a significant difference in the trueness of the intaglio surface morphology of the pontic between the conventional method and the IEOS technique; however, no significant difference in precision was observed. As a result, the intaglio surface of the pontic of the three-unit FPD could be transferred to definitive restorations more accurately with the IEOS technique than with the conventional method. These results suggest that the IEOS technique can duplicate the intaglio surface of the pontic more reproducibly to the definitive restorations compared with the conventional method.

Zirconium Oxide Three-Unit Fixed Partial Denture Frameworks Supported by Dental Implants in Acceptable and Reduced Interocclusal Space Possibilities: Pilot In Vitro Fracture Strength and Fractographic Analyses.

This study investigated the effect of fracture strength and fracture mode characteristics related to reduced interocclusal space on computer-aided design/computer-aided manufacturing (CAD/CAM). ZrO2 fixed partial denture (FPD) frameworks subjected to quasi-static loads. First, two dental implants (4 × 10 mm) were positioned simulating a three-unit FPD (second premolar and second molar abutments). The implants were distributed into two groups: control group (n = 10), positioned at the same level; and the test group (n = 10), where the interocclusal space corresponding to the second molar was reduced by 3 mm in relation to the second premolar to simulate a clinical situation. After FPD wax-up (25-mm long; connector height = 5 mm; connector width = 3 mm, proximal and lingual collar reinforcement), casting was made in a Co-Cr alloy to serve as a prototype. Upon scanning, screw-retained CAD/CAM ZrO2 FPDs were fabricated for each group. Then, FPDs were subjected to quasi-static axial loading until fracture in the mid-occlusal pontic area using a universal testing machine at the crosshead speed of 0.5 mm/min. Next, the samples were analyzed by scanning electronic microscopy (SEM) to describe the fracture characteristics. The mean fracture strength values for the control group (1,747.4 ± 122.3 N) and test group (1,817.7 ± 158.9 N) showed no significant difference (Student t test, P < .124). The SEM images of the fracture sites revealed two cleavage areas in the test group, providing representative sites with increased fracture energy storage in this group compared with the control group. Within the limitations of this study, the results showed that reduced interocclusal space and reduced length did not decrease the fracture strength of the ZrO2 FPD frameworks.

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.

Assessment of Hypodontia Treatment of Maxillary Lateral Incisors in Adult Patients After 9 Years of Follow-up: A Retrospective Study.

To assess the effects of maxillary lateral incisor hypodontia treatment following the use of implantation procedures, fixed and removable dental prostheses, and change in the shape of the canine. Hypodontia treatment effects were retrospectively evaluated in 129 patients aged 18 to 60 years. The assessment covered esthetic, biologic, and functional aspects of the restored missing teeth within 9 years after treatment. The analysis of the findings took into account the percentage of positive effects of treatment for each method and assessment year and also included statistical tests based on the F statistic, which allowed comparison of the effectiveness of the applied methods of hypodontia treatment. In years 1 to 3, the effects of treatment were wholly positive; in subsequent years, the applied methods differed in terms of effectiveness. After 9 years, there was full clinical success for the implant-prosthetic method and for three-unit porcelain-fused-to-metal (PFM) fixed partial dentures (FPDs), 77.77% success for fiber-reinforced composite (FRC) FPDs, 73.68% for multi-unit PFM FPDs, 67.56% for canine shape change, and 23% for metal-alloy removable partial denture (RPD) prostheses. The results of this study indicate that the use of mini-implants with PFM crowns and three-unit PFM FPDs are the most effective treatment methods. A less favorable clinical effect was obtained with the use of FRC FPDs and multi-unit PFM FPDs. Changing the canine shape led to an acceptable clinical effect in over two-thirds of case histories. Metal-alloy RPD prostheses yielded the weakest effects.

Does the Material Stiffness of Novel High-Performance Polymers for Fixed Partial Dentures Influence Their Biomechanical Behavior?

To investigate the influence of framework materials with different elasticity moduli on the biomechanical performance of fixed partial dentures (FPDs). A tooth-anchored three-unit FPD and surrounding tissues were modeled in two variants (veneered/full anatomical FPD) and loaded on the central unit. Three different framework materials (titanium, zirconia, high-performance polymer) were simulated. The polymer framework resulted in reduced framework stresses and increased veneering stresses. Varying the framework material had minimal influence on the loading of surrounding tissue. Using soft, novel materials as framework for dental FPDs does not negatively influence biomechanical loading of the involved biologic structures.

XFEM Fracture Modelling for Implant-Supported Fixed Partial Dentures

The dental implants have been increasingly used for replacing missing teeth over the past three decades. However, its mechanical strength remains a major concern to dental clinicians and patients. To investigate failure modes and fracture loads of implant-supported fixed partial bridge, eXtended Finite Element Method (XFEM) was employed in this study. The 3D finite element (FE) models simulating full mandibular teeth and implant-supported three-unit fixed partial denture (FPD) were developed to determine the crack initiation and propagation in the dental prostheses. The failure modes and fracture loads are compared for three typical treatment scenarios: namely three-unit FPD supported by two implants at left second premolar and first molar (named as cantilever Model-IIP), second premolar and second molar (bridge Model-IPI), and first and second molars (cantilever Model-PII). The XFEM analyses show that the bridge Model-IPI exhibited considerably high fracture resistance than the other two configurations. Model-IIP displays the worst fracture strength of these three case scenarios. The results provide a basis for clinical assessment of mechanical strength for implant-supported FPD or other restorative devices.

Effect of Connector Design on Fracture Resistance in Zirconia-based Fixed Partial Dentures for Upper Anterior Region.

The purpose of this study was to investigate the influence of the cross-sectional form and area of the connector on fracture resistance in three-unit zirconia fixed partial denture (FPD) frameworks for the upper anterior region. Sixty FPD framework specimens were fabricated using the CAD/CAM system. The cross-sectional form (Type I, II, or III) and area (9.0, 7.0, 5.0, or 3.0 mm(2)) of the connectors differed. The specimens were fixed to a jig capable of applying a load axially to the abutment teeth at an angle of 135 degrees. Each specimen was subjected to fracture load measurements using a universal testing machine and cross-sectional microscopic examination. Fracture load fell significantly with a decrease in cross-sectional area (p <0.01). In terms of cross-sectional form, an isosceles triangle with a gingival base yielded the highest fracture load. These results suggest that the connector of a three-unit zirconia-based FPD framework for the upper anterior region should be triangular, have a gingival base, sufficient height in the loading direction, and a cross-sectional area of >5.0 mm(2).

Basic Finite Element Analysis of Para-periodontal Ligament in All-ceramic Zirconia Fixed Partial Denture.

The purpose of the present study was to investigate the validity of incorporating a para-periodontal ligament in the test mold used in a basic fracture test of a zirconia all-ceramic fixed partial denture (FPD). A simplified three-dimensional finite element analysis model was designed based on the three-unit FPD fracture test. Two types of model, one with and one without a para-periodontal ligament between the abutment and base mold, were fabricated. Microfocus CT of the missing first molar area in a dry human mandible was performed. A three-dimensional model was then fabricated based on the data obtained. A load of 600 N was applied to the center of the pontic and stress distribution observed. The model with the para-periodontal ligament showed stress dispersion to the dental root with rotation of the abutment mold. Stress distribution in the finite element analysis model with a para-periodontal ligament showed greater similarity with that in the mandibular model than with that in the other two models without a para-periodontal ligament.

Effect of different design preparations on the flexural and fracture strength of fiber-reinforced composite fixed partial dentures: an in vitro study.

To determine and compare the flexural and fracture strength of three-unit fiber-reinforced composite (FRC) fixed partial dentures (FPDs) using three abutment design preparations. The flexural and fracture strength of three-unit FRC FPDs were evaluated using three design preparations of the abutments (conventional full crown [group A], box-shaped [group B], and tub-shaped [group C]). Thirty three-unit FRC FPDs were fabricated (10 specimens per group) for the replacement of missing mandibular first molars and were adhesively luted to extracted human teeth. The flexural and fracture strength were determined using a universal testing machine with a steel loading pin of 20 mm diameter with a 3-mm-diameter hardened circular tip. Each specimen was evaluated under SEM to determine mode of failure. Mean fracture strength for group A was 820.00 ± 56.51 N, group B was 536.94 ± 65.62 N, and group C was 501.24 ± 66.71 N. The highest mean flexural strength was found in group A (68.33 ± 4.71 MPa), followed by group B (44.74 ± 5.46 MPa) and lowest in group C (41.77 ± 5.56 MPa). The SEM evaluation showed partial or complete debonding of veneering composite from fiber framework, leaving intact fiber frameworks in all the specimens. Full-coverage design had significantly higher flexural and fracture strengths than box and tub-shaped designs. Since both values were noted to be in the order of masticatory stresses, the full coverage design is a good alternative for the replacement of missing molar teeth; however, the framework veneering composite interface was the weakest phase of FRC FPDs, thus indicating that further improvement in veneering composite or fiber framework is needed to improve the compatibility of veneering composite with that of fiber framework for long-term clinical implications.

A Photoelastic Stress Analysis of Screw‐ and Cement‐Retained Implant Prostheses with Marginal Gaps

The precise fit of an implant prosthesis is considered to be a prerequisite for the success and maintenance of osseointegration. It is unknown how much static stress can be tolerated at the implant-bone interface with ill-fitting prostheses for the two different types of retention (cement vs screw). The purpose of this study was to evaluate the stress pattern and magnitude in the supporting tissues around ITI (Straumann AG, Waldenburg, Switzerland) implants with screw- or cement-retained prostheses with marginal gaps by photoelastic analysis. A photoelastic model of a human mandible, partially edentulous distal to the canine, was made of PL-2 resin. Three ITI implants (4.1 × 10 mm, Straumann AG, Waldenburg, Switzerland) were placed in the posterior edentulous region, and screw- or cement-retained three-unit fixed partial dentures (FPDs) were fabricated. Ill-fitting prostheses were made by placing a 100-μm gap between the abutments and the superstructures on the second premolar or the first molar. A static vertical force of 134 N was applied at three loading points on each prosthesis. Photoelastic stress analysis was carried out to measure the fringe order around the implant-supporting structures. Even in the unloaded condition, low-level stresses were generated around the implants after screw tightening or cementing the three-unit FPDs with marginal gaps. Loading on the terminal implants developed high concentrated stresses around the loaded implant, regardless of the types of restorations or the presence of gaps. However, when the middle implant was loaded, moderate stresses were distributed to the anterior and posterior implants. Screw-retained FPDs with gaps exhibited a wider range of stresses on the interproximal region of adjacent implants than cement-retained FPDs. However, severe misfit in the prosthesis caused the nonaxial stress transfer to the adjacent implants in the cement-retained FPDs with gaps.

Survival Rates of a Lithium Disilicate–Based Core Ceramic for Three-Unit Esthetic Fixed Partial Dentures: A 10-Year Prospective Study

The aim of this prospective study was to evaluate the clinical efficacy and long-term survival rate of three-unit fixed partial dentures (FPDs) made from lithium disilicate-based core ceramic. Twenty-one three-unit FPDs were placed in 19 patients to replace single lost teeth in the esthetic area, following a study protocol that took clinical, esthetic, and radiologic aspects into consideration. Each case was reviewed at 1 week following placement, at 6 months, and then annually for 10 years. Statistical analysis was performed using Kaplan-Meier survival analysis. Out of the 19 patients, 14.3% presented reversible postoperative sensitivity. Recession was observed in 24% of dental posts, and 7.1% presented marginal discoloration. Treatment did not increase either Bleeding or Plaque Index scores at prepared teeth; secondary caries did not appear either. The restorations' survival rate at the 10-year follow-up was 71.4%; six FPDs had fractured and one debonded. Fracture failure rate was 28.6% after 10 years; a high percentage corresponded to connector fractures and occurred during the first 5 years. Lithium disilicate glass-ceramic FPDs present a higher risk of fracture than standard therapies (metal-ceramic) or other more recently developed ceramic materials. The prognosis for survival improves for Class I occlusion and nonparafunctional patients.

Retrospective Analysis of Prosthetic Complications of Implant-Supported Fixed Partial Dentures After an Observation Period of 5 to 10 Years

The purpose of this study was to evaluate the incidence of the most common technical problems with implant-supported fixed partial dentures (FPDs) and to assess the survival and success rates (event-free survival) after 5 to 10 years of function. All of the implants evaluated in this study were from a single manufacturer (Institut Straumann). Follow-up examinations were scheduled 1 week after suprastructure placement, 6 months later, and annually thereafter. Prosthesis-based data on survival/failure rates and technical complications were analyzed. In 95 partially edentulous patients, 231 Straumann implants were placed and restored with 177 implant-supported prostheses (125 single crowns, 18 splinted crowns on two adjacent implants, and 34 three-unit FPDs). One hundred thirty one solid abutments and 100 synOcta abutments were inserted. The survival rate of prostheses supported by implants was 97.7%. The prosthetic success rate (event-free survival) was 96.05%. After an observation period of 5 years, the cumulative incidence of screw loosening was 0%. Fracture of the veneering porcelain occurred in 3.95% of all restorations. Fractures of the superstructure framework were not observed. The overall incidence of complications after 5 years was highest for splinted crowns, which showed the lowest success rate (94.4%), followed by three-unit FPDs (96%) and single crowns (98.4%). Single-unit restorations or short-span FPDs supported by both synOcta and solid abutments on Straumann implants showed low rates of technical complications, the most common being fracture of the veneering porcelain.

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.

Finite element analysis to compare stress distribution of gold alloy, lithium‐disilicate reinforced glass ceramic and zirconia based fixed partial denture

Clinical data indicate that veneer chipping of zirconia core is more likely than with ceramic-fused-to-metal structures. The purposes of this simulation study were to: (a) use two-dimensional finite element modeling to simulate stresses at the interface of three-unit posterior fixed partial dentures (FPDs) made with three different core materials; and (b) to investigate the influence of three different veneer thicknesses on the stress distribution within the veneer-core complex. A mesio-distal cross-section of a three-unit FPD was digitized and used to create two-dimensional models of the teeth, supporting bone, different core materials (gold alloy, zirconia and lithia-disilicate reinforced glass ceramic), and different pontic preparation configurations (occlusal veneer thickness 1.0, 1.5, and 2.0 mm). A simulated 100 N vertical occlusal load was applied to the standardized pontic element. Compression stress and tensile stress values were calculated by finite element analysis along the veneer-core interface and compared. The veneer-core interfacial stress of zirconia-based FPD is greater than that of gold alloy and lithium-disilicate reinforced glass ceramic core. The veneer-core interface stress value decreased with increasing occlusal veneer thickness. Finite element modeling revealed differences in tensile and compressive stresses between different pontic preparation configurations and core materials. In general, gold alloy and lithium-disilicate reinforced glass ceramic core provided more even stress distribution at the connector and pontic of fixed partial denture than a zirconia framework.

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.

A Clinical Comparison of Zirconia, Metal and Alumina Fixed-Prosthesis Frameworks Veneered With Layered or Pressed Ceramic: A three-year report

The authors conducted a randomized controlled clinical trial to determine whether performance differed between metal, zirconia and alumina fixed partial denture (FPD) frameworks veneered with pressed or layered ceramics designed for each framework type. Posterior three-unit FPDs (N = 293) of 10 different framework/veneer ceramic combinations were placed by 115 dentists in 259 patients from their practices according to a masked protocol. Yearly, the clinicians graded the prostheses and the opposing dentition in vivo according to 17 criteria, and two independent scientists graded them in vitro by using gold-sputtered dies, scanning electron micrographs and clinical photographs. Three metal and five zirconia frameworks tested were not statistically different, with zero and two fractures, respectively. Alumina frameworks were statistically worse, with 11 fractures. The veneer ceramics CZR Press (Noritake Dental, Aichi, Japan) and Pulse interface (Jensen Dental, North Haven, Conn.) performed best with zirconia and metal frameworks, respectively. Four nonleucite-containing veneer ceramics used with zirconia frameworks had substantially more fractures. Five zirconia framework brands performed equally well and were statistically comparable with metal frameworks at three years. Two leucite-containing veneer ceramics applied by means of pressing techniques had the statistically lowest number of fractures. Dentists can use metal or zirconia frameworks successfully if they are designed properly, but to avoid veneer ceramic surface crumbling and minimize chipping, use of leucite-containing pressed ceramics is indicated.

Fracture behaviour of zirconia FPDs substructures

The purpose of this study was to evaluate the occurrence of superficial flaws after machining and to identify fracture initiation and propagation in three-unit heat-treated machined fixed partial dentures (FPDs) substructures made of hot isostatic pressed (HIPed) yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) after loaded to fracture. Four three-unit HIPed Y-TZP-based FPDs substructures were examined. To evaluate the occurrence of superficial flaws after machining, the surfaces were studied utilizing a fluorescent penetrant method. After static loading to fracture, characteristic fracture features on both mating halves of the fractured specimens were studied using a stereomicroscope and a scanning electron microscope. Grinding grooves were clearly visible on the surfaces of the machined FPDs substructures, but no other flaws could be seen with the fluorescent penetrant method. After loading to fracture, the characteristic fracture features of arrest lines, compression curl, fracture mirror, fracture origin, hackle and twist hackle were detected. These findings indicated that the decisive fracture was initiated at the gingival embrasure of the pontic in association with a grinding groove. Thus, in three-unit heat-treated machined HIPed Y-TZP FPDs substructures, with the shape studied in this study, the gingival embrasure of the pontic seems to be a weak area providing a location for tensile stresses when they are occlusally loaded. In this area, fracture initiation may be located to a grinding groove.