Influence of stress simulation parameters on the fracture strength of all-ceramic fixed-partial dentures.

OBJECTIVES: This in vitro study tested the influence of diverse stress simulation parameters on the fracture strength of all-ceramic three-unit fixed partial dentures (FPDs). METHODS: All-ceramic FPDs made of Empress 2 (Ivoclar-Vivadent, FL) were exposed to thermal cycling and mechanical loading (TCML) with varying loading parameters such as chewing force (amount, frequency), thermal loading, lateral jaw motion, abutment material, artificial periodontium or antagonistic denture. To investigate the influence of the abutment material, human teeth, polymer abutments and alloy abutments were used. Two different TCML devices with pneumatic or weight loading were compared. FPDs without aging were used as a control. RESULTS AND SIGNIFICANCE: Combined thermal and mechanical loading significantly reduced the FPD fracture resistance from 1832N to 410N. Duplication of chewing frequency, phase load increase or additional lateral movement did not effect the results. Increasing chewing force, artificial periodontium, and antagonist or abutment material reduced the fracture resistance of the tested FPDs. Different devices with weight or pneumatic loading had no significant influence on the loading capacity of the FPDs. Artificial aging should be performed combining thermal cycling with mechanical loading. Simulation of the artificial periodontium, human antagonists and abutments should be included to achieve a significant aging.     

Effects of cantilever design and material on stress distribution in fixed partial dentures--a finite element analysis

The purpose of this study was to examine the stress distribution in distal cantilevered fixed partial dentures (FPDs) that are designed with different cantilever morphology and made from different restorative materials. The finite element (FE) method was used to create models of two restoration types; metal-ceramic and an all-ceramic FPDs. Both models were designed with distal cantilevers involving the first and second premolars as abutments and cantilever extension involving at the premolar or molar. The width of connector between the cantilever and the primary abutment restoration was 2.25 mm. The load applied during the FE analysis was positioned at the cusp tips of all teeth. The FE analysis of the models revealed that Von Mises stress values with maximum stress concentrations were observed on connectors of distal cantilevers. Stress concentration sites were also observed at the distal cervical area of the second premolar tooth. Models with premolar cantilever extensions restored with all-ceramic induced lower Von Mises stress values than metal-ceramic restorations, however models with molar cantilever extensions restored with all-ceramic restorations induced higher Von Misses stress values than metal-ceramic restorations. If the distal cantilever length and restorative material is appropriately chosen, the failure frequency may be reduced. All ceramic can be used as restorative material, when the cantilevers length is not more than the mesiodistal dimension of a premolar tooth and metal-ceramic restorations can be used in longer situations.     

All-ceramic surveyed crowns for removable partial denture abutments

All-ceramic restorations may have limitations when used in combinations with other treatment modalities. Removable partial denture (RPD) abutment crowns are typically shaped to provide guide planes, rest seats, and retentive areas. Porcelain-to-metal crowns are routinely fabricated with retentive contours in the veneering porcelain, but until recently, the contours of the other portions of the restoration were developed in metal. This article describes the fabrication of all-ceramic crowns for RPDs with rest seats and guide planes in densely sintered aluminum oxide and retentive areas in veneering porcelain. Within the limitations outlined, this procedure allows the practitioner to use all-ceramic crowns in situations previously reserved for metal or metal-ceramic restorations.     

Evaluation of the fit and strength of an all-ceramic fixed partial denture

A laboratory investigation of the fit and strength of three-unit all-ceramic FPDs was performed with a metal-ceramic FPD control. The conclusions were: 1. No difference was found between the marginal seal of the metal-ceramic and all-ceramic FPDs. 2. The all-ceramic FPDs had a more uniform cement space and their occlusal seat was significantly (99.9%) better than the metal-ceramic restorations. 3. The metal-ceramic FPDs were significantly stronger than the all-ceramic FPDs. 4. Load calculations suggest that short-span all-ceramic FPDs may be strong enough to resist normal masticatory forces for selected patients. However, generalized usage will probably result in an unacceptable failure rate.     

Fracture strength of four-unit Y-TZP FPD cores designed with varying connector diameter. An in-vitro study

Reported clinical success rates of all-ceramic fixed partial dentures (FPDs) made of high-strength oxide ceramics range between 82.5% and 100%. The main cause of all-ceramic FPD failure is fracture in the connector area. There is, however, no consensus on what connector dimensions are adequate. The aim of this in-vitro study was, therefore, to compare the fracture strength of four-unit Y-TZP FPD cores designed with different connector diameters. A total of 40 four-unit FPD cores supported by end abutments and having two pontics were manufactured in Procera Zirconia. Five groups of FPD cores with connector dimensions of 2.0, 2.5, 3.0, 3.5 and 4.0 mm were produced. All FPD cores underwent a firing programme according to the manufacturer's recommendations for the veneering porcelain, a cyclic preload, thermocycling and finally, load until fracture. Fracture strength was significantly higher for each increase in connector diameter except for the 2.0-mm and 2.5-mm diameters where all fractures occurred during preload. All FPD cores fractured in the connector area. Within the limitations of this in-vitro study, a minimum diameter of 4.0 mm is recommended for all-ceramic zirconia-based FPDs with long spans or replacing molars. Clinical studies are, however, needed to determine adequate connector dimensions.     

Effect of Framework Shape on the Fracture Strength of Implant-Supported All-Ceramic Fixed Partial Dentures in the Molar Region

Purpose: The aim of the present study was to clarify the effects of the shape of the zirconium framework of implant-supported, all-ceramic fixed partial dentures (FPDs) on the fracture strength and fracture mode.
Materials and Methods: This study consisted of mechanical strength testing and 3D finite element analysis (FEA). The three framework shapes used in this study were: (1) conventional shape (control); (2) convex shape: 1.0-mm curve in the direction of the occlusal surface; and (3) concave shape: 1.0-mm curve in the direction of the gingival surface. Five frameworks were made for each condition (total: 15). A load (N) was applied until the FPD fractured. For FEA, a 3D model consisting of cortical bone, cancellous bone, implant bodies, and superstructure was constructed.
Results: The results of the mechanical strength test showed that fracture load was 916.0 ± 150.1 N for the conventional shape, 1690.5 ± 205.3 N for the convex shape, and 1515.5 ± 137.0 N for the concave shape. The mean final fracture load for the FPDs with frameworks was the highest for the convex shape; however, a critical crack in the veneer porcelain (736.5 ± 145.2 N) was confirmed during loading for the convex shape. Stress distribution maps for all conditions showed that tensile stress was generated at the veneer porcelain on the gingival side of the mesial and distal connectors of the pontic; however, there were differences in the maximum value and stress distribution within the framework.
Conclusion: The shape of the framework, particularly the shape of the pontic–connector interface, affects the stress distribution, fracture strength, and fracture mode of all-ceramic FPDs, and stress concentration inside a framework may induce cracking of layering porcelain.     

Stress analysis of effects of nonrigid connectors on fixed partial dentures with pier abutments

STATEMENT OF PROBLEM: In some patients, the pattern of missing teeth may require the use of a fixed partial denture (FPD) with an intermediate pier abutment. Information is needed regarding the biomechanical behavior and the position of a nonrigid connector for this treatment option. PURPOSE: The purpose of this study was to evaluate, by means of finite element method (FEM), the effects of rigid and nonrigid design types on stress distribution for 5-unit FPDs with pier abutments. MATERIAL AND METHODS: A 3-dimensional cross-section FEM model (SAP 2000) simulating a 5-unit metal ceramic FPD with a pier abutment with rigid or nonrigid designs (connector location at the mesial region of the second molar, at the distal region of the second premolar, at the mesial region of the second premolar, and at the distal region of the canine) was developed. In the model, the canine, second premolar, and second molar served as abutments. A supporting periodontal ligament and alveolar bone (cortical and trabecular) were modeled. A 50-N static vertical occlusal load was applied on the cusp of each abutment to calculate the stress distributions. Three different types of load were evaluated: loading of all cusps to simulate maximum centric occlusion contacts, loading of the canine to simulate a single anterior contact, and loading of the second molar to simulate a posterior contact. RESULTS: The analysis of the von Mises stress values revealed that maximum stress concentrations were located at the load areas for all models. Also, for all models, the highest stress values were located at connectors and cervical regions of abutment teeth, especially at the pier abutment. CONCLUSIONS: The area of maximum stress concentration at the pier abutment was decreased by the use of a nonrigid connector at the distal region of the second premolar.     

A study on the fracture strength of collarless metal-ceramic fixed partial dentures

PURPOSE

The objective of this study was to evaluate fracture strength of collarless metal-ceramic FPDs according to their metal coping designs.

MATERIALS AND METHODS

Four different facial margin design groups were investigated. Group A was a coping with a thin facial metal collar, group B was a collarless coping with its facial metal to the shoulder, group C was a collarless coping with its facial metal 1 mm short of the shoulder, and group D was a collarless coping with its facial metal 2 mm short of the shoulder. Fifteen 3-unit collarless metal-ceramic FPDs were fabricated in each group. Finished FPDs were cemented to PBT (Polybutylene terephthalate) dies with resin cement. The fracture strength test was carried out using universal testing machine (Instron 4465, Instron Co., Norwood MA, USA) at a cross head speed of 0.5 mm/min. Aluminum foil folded to about 1 mm of thickness was inserted between the plunger tip and the incisal edge of the pontic. Vertical load was applied until catastrophic porcelain fracture occurred.

RESULTS

The greater the bulk of unsupported facial shoulder porcelain was, the lower the fracture strength became. However, there were no significant differences between experimental groups (P > .05).

CONCLUSION

All groups of collarless metal-ceramic FPDs had higher fracture strength than maximum incisive biting force. Modified collarless metal-ceramic FPD can be an alternative to all-ceramic FPDs in clinical situations.     

All-ceramic fixed partial dentures. Studies on aluminum oxide- and zirconium dioxide-based ceramic systems

BACKGROUND: The development of refined, tougher, and stronger ceramic core materials in recent years has led to the wider use of new, strong all-ceramic systems based on oxide ceramics. Results from in-vitro studies investigating the use of oxide ceramics in shorter all-ceramic fixed partial dentures (FPDs) have been positive, but clinical studies and additional in-vitro studies are needed to confirm the advisability of such procedures. AIMS: One aim of this thesis was to investigate whether alumina-based and zirconia-based material systems are adequate for use in shorter (< or = five-unit) FPDs and to evaluate the clinical results. Additional aims were to investigate how to achieve optimal fracture strength in an all-ceramic FPD by varying the try-in procedure, the cervical shape of the abutments, and the support of the FPD (abutment teeth or dental implants). The final aim was to compare the strength of a zirconia material system with that of an alumina equivalent with known long-term clinical performance. MATERIALS AND METHODS: Two clinical studies investigating one alumina-based and one zirconia-based material system were performed. Twenty posterior, three-unit FPDs (glass-infiltrated alumina) were followed for 5 years and 20 three-five-unit FPDs (HIP zirconia) for 2 years. Long-term follow-ups were made after 11 +/-1 (glass-infiltrated alumina) and 3 years (HIP zirconia). In three in-vitro studies, the following variables were investigated: (1a) the flexural strength of porcelain specimens depending on whether they were exposed to saliva before the glaze firing (n=20) or first after the glaze firing (n=20), (1b) the fracture strength of three-unit all-ceramic FPDs (glass-infiltrated alumina) supported by abutments prepared with cervical shoulder preparations (n=9) and abutments with cervical chamfer preparations (n=9), (2) the fracture strength of crowns (n=30) made of a zirconia material system (densely sintered zirconia) and of crowns (n=30) of an alumina material system (densely sintered alumina) that had undergone three different pre-treatment modalities (water storage only; water storage and cyclic pre-loading; water storage, cyclic pre-loading, and thermocycling), (3) the fracture strength of all-ceramic FPDs (densely sintered alumina) supported by simulated teeth (n=12) or by dental implants (n=12). RESULTS: The success rate of the clinical alumina study was 90% after 5 years. Six (+/-1) years later (after a total of 11 +/-1 years), the success/survival rate was 65%. In the second clinical study, the success rates of the 2- and 3-year follow-ups were 100%. In the three in-vitro studies, the following results were found: (1a) the mean flexural strength of the specimens in the group that was exposed to saliva first after glazing was significantly higher (P < 0.001) than that of the specimens in the group that was exposed to saliva before glazing, (1b) the FPDs luted on shoulder preparations resisted higher loads than the FPDs luted on chamfer preparations (P = 0.051), 2) total fractures were more frequent in the alumina than in the zirconia group (P < 0.001), 3) FPDs loaded on implants resisted higher loads (mean = 604 N, SD=184 N ) than FPDs loaded on abutment teeth (mean= 378 N, SD=152 N, P = 0.003). CONCLUSIONS: This thesis justifies the use of shorter alumina- (< or = three-unit) and zirconia-based (< or = five-unit) FPDs as the clinical results are acceptable. The clinical performance of alumina is, however, not as good as that of comparable high-gold alloy based porcelain-fused-to-metal FPDs concerning fracture resistance. Within the limitations of the in-vitro studies: Saliva exposure of porcelain before glaze firing should be avoided to optimize the strength of the porcelain. Shoulder preparations can be beneficial for the strength of all-ceramic FPDs compared to chamfer preparations, as can support by dental implants compared to abutment teeth. The fracture mode of alumina crowns (total fractures) differs from that of zirconia crowns (veneer fractures), suggesting that the zirconia core is stronger than the alumina core.     

Stress distribution of inlay-anchored adhesive fixed partial dentures: a finite element analysis of the influence of restorative materials and abutment preparation design

STATEMENT OF PROBLEM: Indirect composite or ceramic fixed partial dentures (FPDs) have become an alternative to conventional metal-ceramic adhesive fixed partial dentures (AFPDs). Little information about the adequate restorative material and tooth preparation design for inlay-anchored AFPDs is available to the clinician. PURPOSE: The purposes of this simulation study were: (1) to use 2-dimensional finite element modeling to simulate stresses at the surface and interface of 3-unit posterior AFPDs made with 6 different restorative materials, and (2) to investigate the influence of 3 different abutment preparation configurations on the stress distribution within the tooth/restoration complex. MATERIAL AND METHODS: A mesio-distal cross-section of a 3-unit AFPD was digitized and used to create 2-dimensional models of the periodontal membrane, supporting bone, different restorative materials (gold, alumina, zirconia, glass-ceramic, composite, and fiber-reinforced composite), and different abutment preparation configurations (interproximal slots vs. 2-surface [MO, DO] vs. 3-surface [MOD]). A simulated 50-N vertical occlusal load was applied to the standardized pontic element. The principal stress within the restorative materials, stresses at the tooth/restoration interface, and surface tangential stresses at the level of the pontic were calculated in MPa from the postprocessing files and compared to each other. RESULTS: All materials and tooth preparation design exhibited a similar stress pattern, with a definite compressive area at the occlusal side of the pontic, a tensile zone at the gingival portion of the pontic, and tensile stress peaks in the abutment/pontic connection areas. Among isotropic materials, standard non-reinforced composites exhibited better stress transfer and reduced tensile stresses at the adhesive interface than ceramics and gold. Optimized placement of the glass fibers within the composite resulted in similar stress distribution when tested in 2-surface abutment preparation configuration. There was no detectable influence of preparation design on the behavior of the pontic area. Among all 3 preparation designs, only the DO design exhibited almost pure compression at the interface. CONCLUSION: Within the limitations of this simulation experiment, the composite materials tested demonstrated a resilient component that favored stress transfer within the tooth/restoration complex. Their clinical use, however, may be contraindicated due to insufficient strength and fracture toughness. The addition of extremely tough fibers to composites represents the most promising combination. Clinical trials are required to ensure that veneering composite can survive under clinical conditions.     

Biomechanical interactions in tooth-implant-supported fixed partial dentures with variations in the number of splinted teeth and connector type: a finite element analysis.

OBJECTIVE: The aim of this study was to investigate the biomechanical interactions in tooth-implant-supported fixed partial dentures (FPDs) under several loading conditions with different numbers of splinted teeth and connector types (rigid and non-rigid) by adopting the three-dimensional (3D) non-linear finite element (FE) approach. MATERIAL AND METHODS: A 3D FE FPD model was constructed containing one Frialit-2 implant in the mandibular second-molar region splinted to the first and second premolars. Frictional contact elements were used to simulate realistic interface conditions within the implant system and the non-rigid connector function. The main effects for each level of the three investigated factors (loading condition, number of splinted teeth and connector type) in terms of the stress values and dissimilar mobility of the natural teeth and implant were computed for all models. RESULTS: The results indicated that load condition was the main factor affecting the stress developed in the implant, bone and prosthesis when comparing the type of connector and the number of splinted teeth. The stress values were significantly reduced in centric or lateral contact situations once the occlusal forces on the pontic were decreased. However, the prosthesis stress for the non-rigid connections was increased more than 3.4-fold relative to the rigid connections. Moreover, the average tooth-to-implant displacement ratios (R(TID)) with a non-rigid connection were obviously larger than those for rigid connections under axial loading forces. Adding an extra tooth to support a three-unit tooth-implant FPD only exploited its function when the prosthesis withstood lateral occlusal forces. CONCLUSIONS: The load condition is the main factor affecting stress distribution in different components (bone, prosthesis and implant) of tooth-implant-supported FPDs. Minimizing the occlusal loading force on the pontic area through selective grinding procedures could reduce the stress values obviously. A non-rigid connector may more efficiently compensate for the dissimilar mobility between the implant and natural teeth under axial loading forces but with the risk of increasing unfavorable stresses in the prosthesis.     

A new design for all-ceramic inlay-retained fixed partial dentures: a report of 2 cases.

In a previous clinical study, all-ceramic resin-bonded 3-unit inlay-retained fixed partial dentures (IRFPDs) had a significantly worse outcome in the posterior region than did crown-retained 3-unit FPDs made from the same material. Debonding or fractures were causes of failure. To improve the clinical outcome of IRFPDs, a new framework design was developed: (1) The inlay retainers were made out of CAD/CAM-manufactured zirconia ceramic to improve fracture resistance, and additional veneering of the inlays was omitted. (2) The inlay retainers were completed with a shallow occlusal inlay (1-mm minimum thickness) and an oral retainer wing (0.6-mm minimum thickness). The wings were designed to reduce stress on the inlay retainer caused by torsion forces when the FPD is loaded nonaxially and to increase the enamel adhesive surface area. The pontic was circumferentially veneered with feldspathic porcelain. The clinical and laboratory procedures of this new treatment modality are described, and 2 exemplary clinical cases are presented. This new preparation and framework design might improve the clinical outcome of all-ceramic resin-bonded IRFPDs. However, adequate evidence of long-term safety and efficacy is required before this new design can be recommended for general clinical practice.     

The effect of pontic occlusal form on abutment tooth displacement]

The three-dimensional displacements of abutment teeth in fixed partial dentures (FPDs) during mastication were measured while changing the pontic occlusal design, for comparison against those of natural teeth. The purpose of this study was to clarify the influence of pontic occlusal form on the displacements of the abutment teeth, and to decide the optimum pontic occlusal design. Three subjects, who each had a single missing tooth (upper first molar or second premolar), were chosen. After 3-unit FPDs were cemented, abutment tooth displacement during mastication was measured using a three-dimensional tooth displacement transducer Type M-3. The functional or non-functional cusp inclination of the pontic was changed gradually. The flatter the inclination of the functional cusp of pontic became, the more the abutment teeth displaced in the buccal direction. The flatter the inclination of pontic non-functional cusp became, the less the abutment teeth displaced in the buccal direction, and the more the abutment teeth mostly displaced in the palatal direction. If the inclination of the functional cusp of pontic becomes excessively flatter, or the inclination of pontic non-functional cusps becomes as steep as the natural teeth, non-physiological distortion may occur in periodontal tissues of the abutment teeth.     

First two-year complications of fixed partial dentures,eight units or more. Swedish Guarantee Insurance claims

This study is an analysis of fixed partial dentures (FPDs), 8 units or more, that failed or suffered severe complications within the first 2 years after cementation. The material consists of claims to the Swedish Gurantee Insurance for Fixed Prosthodontics. Claim reports, radiographs, etc. were available. Over a 6-month period, 36 FPDs were sampled, 34 of which were made by general practitioners. The sampling resulted in 41 complications in 26 maxillary and 10 mandibular FPDs, 29 of which were made in metal-ceramics. The mean extension was 10.9 units, with an abutment/pontic ratio of 1.4; 40.6% of the abutments were root-canal treated and supplied with root posts. The complications were: metal framework fractures 41%, loss of retention 24%, porcelain fractures 17%, tooth/root fractures 10%, and miscellaneous 7%. The high proportion of metal framework fractures is not in accordance with other studies of FPD complications. No factor that could explain this high frequency could be identified. The fact that the selection of FPD complications applied to the first 2 years only, that the FPDs had been constructed by general practitioners, and that there were many root-canal-treated abutments and distal extension cantilever pontics, might be factors of importance.     

First two-year complications of fixed partial dentures, eight units or more. Swedish Guarantee Insurance claims

This study is an analysis of fixed partial dentures (FPDs), 8 units or more, that failed or suffered severe complications within the first 2 years after cementation. The material consists of claims to the Swedish Guarantee Insurance for Fixed Prosthodontics. Claim reports, radiographs, etc. were available. Over a 6-month period, 36 FPDs were sampled, 34 of which were made by general practitioners. The sampling resulted in 41 complications in 26 maxillary and 10 mandibular FPDs, 29 of which were made in metal-ceramics. The mean extension was 10.9 units, with an abutment/pontic ratio of 1.4; 40.6% of the abutments were root-canal treated and supplied with root posts. The complications were: metal framework fractures 41%, loss of retention 24%, porcelain fractures 17%, tooth/root fractures 10%, and miscellaneous 7%. The high proportion of metal framework fractures is not in accordance with other studies of FPD complications. No factor that could explain this high frequency could be identified. The fact that the selection of FPD complications applied to the first 2 years only, that the FPDs had been constructed by general practitioners, and that there were many root-canal-treated abutments and distal extension cantilever pontics, might be factors of importance.     

Comparison of load-bearing capacity of direct resin-bonded fiber-reinforced composite FPDs with four framework designs

OBJECTIVES: This in vitro study was aimed to compare the fracture resistance of directly fabricated inlay-retained fiber-reinforced composite (FRC) fixed partial dentures (FPDs) with four types of framework designs. METHODS: Forty-eight directly fabricated inlay retained FPDs were made of FRC and particulate resin composite (everStick/Tetric flow and Ceram). Extracted human mandibular first premolars and first molars were as abutments. The following framework designs were tested: in the Group A (control group), the framework was made of two prepregs of unidirectional glass FRC; the Group B, two prepregs in pontic portion were covered with one layer of multidirectional fiber veil FRC; the Group C, the FRC prepregs were covered in pontic portion with four short unidirectional FRC pieces along the main prepregs; in Group D, one short unidirectional FRC prepregs were placed on the main prepregs in 90 degrees angle to the main framework. After thermal cycling, FPDs of each group (n=12) were randomly divided into two subgroups (n=6). Fracture test was performed at the universal testing machine (1mm/min) where FPDs were loaded from the occlusal direction to the occlusal fossa or to the buccal cusp. Failure patterns were observed with stereomicroscope. Median and 25%/75% percentile values were calculated and nonparametric analysis was performed. RESULTS: Compared with three other framework designs, the FPDs in Group D showed the highest resistance when loading to the occlusal fossa, with maximum load of 2,353.8N (25%/75%: 2,155.5/2,500.0) (p=0.000, 0.000, and 0.005 for compared with Group A, B, and C). The same group showed also higher resistance when loaded to the buccal cusp (1,416.3N (1,409.2/1,480.8)) if compared to the FPDs of the Group A and Group C (p=0.044, 0.010). In general the FPDs showed higher resistant to loading at the occlusal fossa (p<0.05). CONCLUSIONS: This in vitro study showed that inlay-retained FRC FPD constructed with direct technique provided high fracture resistance. The framework design that provided support for the veneering composite of the pontic contributed to the highest load-bearing capacity even when loaded to the buccal cusp.     

Fracture resistance of lithium disilicate-, alumina-, and zirconia-based three-unit fixed partial dentures: a laboratory study

PURPOSE: The purpose of this study was to determine the fracture resistance of three-unit fixed partial dentures (FPD) made of new core ceramics. MATERIALS AND METHODS: A base metal three-unit master FPD model with a maxillary premolar and molar abutment was made. Tooth preparation showed 0.8-mm circumferential and 1.5-mm occlusal reduction and a chamfer margin design. FPDs were constructed with a uniform 0.8-mm-thick core ceramic and a porcelain veneer layer. In-Ceram Alumina, In-Ceram Zirconia, and DC-Zirkon core ceramics were machined by a computer-aided design/manufacturing system, whereas IPS Empress 2 core ceramic was indirectly built up using the fabrication technology of waxing and heat pressing. FPDs of IPS Empress were heat pressed as complete restorations without core material. To ensure standardized dimensions, the FPDs were controlled at different points. All FPDs were cemented with ZnPO4 on the master model and loaded on a universal testing machine until failure. The failure load and mode of failure were recorded. RESULTS: The highest failure loads, exceeding 2,000 N, were associated with FPDs of DC-Zirkon. FPDs of IPS Empress and In-Ceram Alumina showed the lowest failure loads, below 1,000 N, whereas intermediate values were observed for FPDs of IPS Empress 2 and In-Ceram Zirconia. Differences in mean values were statistically significant. CONCLUSION: The high fracture resistance evaluated for FPDs made of DC-Zirkon underscores the remarkable mechanical properties of high-performance ceramic, which could be useful for highly loaded all-ceramic restorations, especially in the molar region.     

Use of abutment-teeth vs. dental implants to support all-ceramic fixed partial dentures: an in-vitro study on fracture strength

The aim of the present in-vitro study was to compare the fracture strength of all-ceramic Fixed Partial Dentures supported by tooth-analogues and periodontal membrane with the same supported by dental implants. As ceramics are highly brittle, they cannot withstand deformations of more than 0.1% without fracturing. Hence, when planning an all-ceramic FPD, it is essential to evaluate abutment support, as the fracture strength of all-ceramic constructions depends on the stability of the support to reduce strain in the beam of the prosthesis. The support provided by implants differs, however, from the support provided by natural teeth as the implants are anchored directly in the bone with no intermediate tissue. One question that arises is whether strain and stress in the prosthesis are lower when the prosthesis is loaded on implants compared to natural teeth and hence if all-ceramic FPDs benefit from implant support. Twenty-four three-unit all-ceramic FPDs-12 supported by two dental implants and 12 by two tooth-analogues serving as end abutments-were made. All FPDs were subjected to preloading in a preloading procedure and subsequently subjected to load until fracture occurred. Load at fracture were registered and comparisons between the two groups were made. The loads at fracture were statistically significant higher in the group supported by implants compared to the group supported by tooth-analogues (p = 0.003). Within the limitations of this in-vitro study, the following conclusions can be drawn: All-ceramic fixed partial dentures can be used in combination with dental implants. The solid support gained from implants might thus be beneficial for the outcome of such treatment due to decreased strain and stress levels in the prosthesis when loaded on implants compared to when loaded on natural teeth. Clinical studies are, however, needed to confirm these findings as there are more factors that influence the final clinical outcome.     

All-ceramic resin-bonded bridges A 3-dimensional finite-element analysis study

Resin-bonded fixed partial dentures (FPD) with a metal framework have some disadvantages: a grey shimmer of the metal wings through the abutment teeth, a higher corrosion rate, and an allergenic potential of the non-precious alloys used. The Al²O³, ceramic In-Ceram© seems to be strong enough to serve as a framework for resin-bonded all-ceramic FPDs. Because of the fact that ceramic wings often don't have enough inter-occlusal space, a new preparation design was developed. The objective of this study was to determine the influence of load orientation (45° and 60°) and the design of the interproximal connector on the stress distribution in the bridges. A 3-dimensional finite-element model was developed to simulate the anatomical situation. The biting force was assumed as 250 N and oriented in oro-buccal direction. The loading-point was palatal 1.5 mm beneath the incisal edge. It was found that stress generally increased with an angle of the biting force of 60°. A small interdental connector (3 mm height) and/or strong interdental separation resulted in stresses of up to 455 MPa (45°) or 534 MPa (60°). Less separation with rounded edges and a higher connector (4 mm) reduced the stress to 122 MPa (45°) and 143 MPa (60°). Due to an average tensile strength of In-Ceram at 340–400 MPa. an all-ceramic resin-bonded FPD may only be recommended it the height of the connector could be minimum 4 mm. Rounded edges and little interdental separation are significant for stress reduction.     

All-ceramic inlay-retained fixed partial bridge using a CAD-CAM produced Y-TZP framework and fluoroapatite veneering ceramic: a clinical report

All-ceramic materials have become an excellent option for both anterior and posterior fixed partial dentures (FPDs) due to advances in esthetic and mechanical properties. This clinical report describes the use of an all-ceramic inlay-retained three-unit FPD for replacement of a maxillary second premolar. Prosthetic restorative materials consisted of a CAD-CAM processed presintered yttrium stabilized zirconium oxide (Y-TZP) framework and a fluoroapatite veneering ceramic. The minimally invasive preparation technique and advantages of this highly esthetic and resistant treatment option are discussed.