Experimental design of FPD made of all-ceramics and fibre-reinforced composite.

OBJECTIVES: This study was carried out to combine flexural properties of FRC materials with aesthetic values of ceramics. METHODS: The bonding strength of fibre-reinforced composite to ceramic was determined. Afterwards, 8 three unit and 8 four unit FPDs (fixed partial dentures) were manufactured based on the experimental design and were then adhesively luted onto human molars. After thermal cycling and mechanical loading in an artificial environment, the fracture strength and marginal adaptation was determined. FPDs made of FRC (fibre-reinforced composite) materials were used as a control. RESULTS: The most reliable bonding strength of ceramic to FRC material was achieved using acid etching in combination with adhesive luting techniques. Median fracture strength values of 575 N for three unit FPD and 876 N for four unit FPD were established. More than 85% of the experimental FPDs showed a perfect margin while less than 15% revealed a marginal gap, even after thermal cycling and mechanical loading (TCML). The strongest influence of TCML on the marginal adaptation of the experimental design FPD was determined within the four unit system showing approximately a 10% change in marginal gap and perfect margin. SIGNIFICANCE: Assuming an improvement in adhesive bonding between the ceramic and the FRC material and, in addition, an enhancement of the contact surface between pontic and abutment, the hybrid technique could represent an interesting procedure for further investigations and, eventually, clinical implication.     

Approach for valuating the significance of laboratory simulation

OBJECTIVE: The aim of this investigation was to compare the clinical survival rate of all-ceramic FPDs with failures during in vitro simulation. METHODS: 40 anterior FPDs were manufactured from lithiumdisilicate ceramic and alumina-oxide ceramic. The FPDs were adhesively bonded to human teeth and artificially aged to investigate the survival rate during thermal cycling and mechanical loading (TCML(1); 3.6 Mio*50 N ML). Survival rates were compared to available clinical data, and the TCML parameter 'mastication force' was adapted accordingly for a second TCML run (TCML(2); 3.6 Mio*25 N/35 N ML). The fracture resistance of the FPDs that survived TCML was determined. Data were statistically analysed by means of Mann-Whitney U-test, and survival rates were determined by curve fitting/regression analysis. RESULTS: TCML decreased survival rates by 30-50%, depending on the type of material used. Failures during TCML included cracking, chipping or fracture. Increased masticatory loading during TCML caused a higher decrease in the fracture resistance of FPDs. Fracture results were 403 N (278/453) and 426 N (317/538) for Empress 2 and 325 N (164/584) and 405 N (344/558 N) for Inceram. CONCLUSIONS: Despite the limitations of this study, the results indicate that TCML with 1,200,000*25/35 N provide a sufficient prognosis of probable clinical failures. Longer TCML-time with higher mastication forces may help to exclude catastrophic clinical failures.     

In vitro study of fracture strength and marginal adaptation of polyethylene-fibre-reinforced-composite versus glass-fibre-reinforced-composite fixed partial dentures

This in vitro study was carried out in order to estimate the clinical usability of adhesively luted three-unit posterior fixed partial dentures (FPD) made of a polyethylene-fibre-reinforced-composite system (PFRC) in comparison with a glass-fibre-reinforced-composite system (GFRC). Therefore the fracture strength and marginal adaptation were examined. A total of 16 FPDs of each material combination were manufactured and adhesively luted to human molars. Before and after an artificial ageing process by thermal cycling and mechanical loading (TCML) the quality of the marginal adaptation was examined by evaluating epoxy replicas in a scanning electron microscope (SEM). After TCML the fracture strength of eight FPDs of each series was tested by mechanical loading them to failure. With the remaining eight FPDs the quality of deeper layers of the luting was examined with a dye penetration technique. The calculated median fracture strength values (25/75% percentiles) were 830 N (643/982) for the PFRC and 884 N (684/1,113) for the GFRC. The SEM analysis showed at least 80% of perfect marginal areas for both material combinations in dentine as well as in enamel before and after TCML. Looking at the cement-tooth interfaces the dye penetration technique showed statistically significant better results for the enamel finishing lines than for those in dentine. With finishing lines in dentine the two material combinations showed statistically significant differences for this interface. Fracture force results as well as marginal quality encourage further clinical investigations on both systems although the GFRC performed slightly better than the PFRC.     

Fracture behavior of straight or angulated zirconia implant abutments supporting anterior single crowns

The aim of the study was to evaluate the influence of artificial aging on the fracture behavior of straight and angulated zirconia implant abutments (ZirDesign?; Astra Tech, Mölndal, Sweden) supporting anterior single crowns (SCs). Four different test groups (n?=?8) representing anterior SCs were prepared. Groups 1 and 2 simulated a clinical situation with an ideal implant position (left central incisor) from a prosthetic point of view, which allows for the use of a straight, prefabricated zirconia abutment. Groups 3 and 4 simulated a situation with a compromised implant position, requiring an angulated (20°) abutment. OsseoSpeed? implants (Astra Tech) 4.5 mm in diameter and 13 mm in length were used to support the abutments. The SCs (chromium cobalt alloy) were cemented with glass ionomer cement. Groups 2 and 4 were thermomechanically loaded (TCML?=?1.2?×?10⁶; 10,000?×?5°/55°) and subjected to static loading until failure. Statistical analysis of force data at the fracture site was performed using nonparametric tests. All samples tested survived TCML. Artificial aging did not lead to a significant decrease in load-bearing capacity in either the groups with straight abutments or the groups with angulated abutments. The restorations that utilized angulated abutments exhibited higher fracture loads than the restorations with straight abutments (group 1, 280.25?±?30.45 N; group 2, 268.88?±?38.00 N; group 3, 355.00?±?24.71 N; group 4, 320.71?±?78.08 N). This difference in load-bearing performance between straight and angulated abutments was statistically significant (p?=?0.000) only when no artificial aging was employed. The vast majority of the abutments fractured below the implant shoulder.     

Fracture load of fixed partial dentures anchored by composite inlays

PURPOSE: To evaluate in vitro the fracture load of fixed partial dentures (FPDs) anchored by use of composite inlays. The effects of span length, silica-coating, mechanical loading and framework material were also tested. METHODS: Defined box inlay cavities were made on a mandibular molar and a premolar. Fifty-six FPDs were manufactured using a polymer composite material and received an industrial prefabricated polymethylmethacrylate (PMMA) frame for stabilization. All FPDs underwent thermal cycling. The FPDs were divided into test groups simulating the effect of different span length (7 or 12 mm), tribochemically silicoating (yes or no) and mechanical loading (yes or no). The load to fracture was measured and fracture sites were evaluated. As a control group for the PMMA frame, a metal alloy frame was used, and evaluated under the most unfavorable conditions. The Mann-Whitney U-test followed by the Bonferroni correction was used for statistical analysis. RESULTS: The span length significantly affected the fracture load. Values ranged from 413 N for the 12 mm span length to 706 N for the 7 mm span length. Thermal cycling and mechanical loading significantly reduced fracture load values for FPDs with the 12 mm span length, but there were no significant effects for FPDs with 7 mm span length. Silicoating pretreatment of the metal abutments significantly reduced fracture load values. Replacement of the PMMA frame with a metal frame increased fracture load values up to 1,075 N.     

Influence of the preparation design and artificial aging on the fracture resistance of monolithic zirconia crowns

PURPOSE

The aim of this study was to evaluate the fracture resistance and fracture behavior of monolithic zirconia crowns in accordance with the preparation design and aging simulation method.

MATERIALS AND METHODS

An upper first molar was prepared sequentially with three different preparation designs: shoulderless preparation, 0.4 mm chamfer and 0.8 mm chamfer preparation. For each preparation design, 30 monolithic zirconia crowns were fabricated. After cementation on Cr-Co alloy dies, the following artificial aging procedures were performed: (1) thermal cycling and mechanical loading (TCML): 5000 cycles of thermal cycling 5℃–55℃ and chewing simulation (1,200,000 cycles, 50 N); (2) Low Temperature Degradation simulation (LTD): autoclave treatment at 137℃, 2 bar for 3 hours and chewing simulation; and (3) no pre-treatment (control group). After artificial aging, the crowns were loaded until fracture.

RESULTS

The mean values of fracture resistance varied between 3414 N (LTD; 0.8 mm chamfer preparation) and 5712 N (control group; shoulderless preparation). Two-way ANOVA analysis showed a significantly higher fracture loads for the shoulderless preparation, whereas no difference was found between the chamfer preparations. In contrast to TCML, after LTD simulation the fracture strength of monolithic zirconia crowns decreased significantly.

CONCLUSION

The monolithic crowns tested in this study showed generally high fracture load values. Preparation design and LTD simulation had a significant influence on the fracture strength of monolithic zirconia crowns.     

Approach for valuating the influence of laboratory simulation

ObjectiveThe aim of this investigation was to determine the fracture resistance of zirconia fixed partial dentures (FPDs) after laboratory simulation. Failure type and failure rates during simulation were compared to available clinical data for estimating the relevance of the simulation.Methods32 FPDs were fabricated of a zirconia ceramic and a corresponding ceramic veneer. The FPDs were adhesively bonded on human molars and artificial aging was performed for investigating the survival rate during thermal cycling and mechanical loading (TCML1; 3.6 Mio × 50 N ML). Survival rates were compared to available clinical data and the TCML parameter “mastication force” was adapted accordingly for a second TCML run (TCML2; 3.6 Mio × 100 N ML). The fracture resistance of the FPDs which survived TCML was determined. FPDs were examined without TCML (control) or after TCML according to literature (1.2 Mio × 50 N ML). Data were statistically analyzed (Mann–Whitney U-test) and curve fitting/regression analysis of the survival rates was performed.ResultsTCML reduced survival rates down to 63%. Failures during TCML were chipping off of the veneering ceramic, no zirconia framework was damaged. Under clinical conditions comparable failures (chipping) are reported. The clinical survival rate (～10%) is lower compared to TCML data because of the short period of observation. The fracture resistance after TCML was significantly reduced from 1058 N (control) to values between 320 and 533 N.ConclusionThe results indicate that TCML with 1.2 Mio × 50 N provides a sufficient explanatory power. TCML with prolonged simulation time may allow the definition of a mathematical model for estimating future survival rates.     

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 × 50 N, 1.6 Hz) 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 1173.5 N (#4) and 1316.0 N (#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.     

Glass fiber-reinforced abutments for dental implants. A pilot study

Titanium abutments in dental implants shine through all-ceramic crowns and therefore limit excellent esthetic results. Prototypes of tooth-colored fiber-reinforced abutments were investigated to avoid the shining-through effect. In vitro, the fracture strength was determined after thermal cycling and mechanical loading of all-ceramic single crowns and four-unit bridges made of a fiber-reinforced composite. The suprastructures were adhesively fixed onto fiber-reinforced implant abutments and compared with those fixed on standard titanium abutments. The median of the fracture strength of the titanium-supported all-ceramic crowns was significantly higher than the median of crowns fixed onto the prototypes. But this value was still more than twice as high as the maximum loading force under oral conditions. No statistical difference was found between four-unit bridges made by fiber-reinforced composite inserted onto titanium abutments and those inserted onto fiber-reinforced abutments. Fiber-reinforced abutment prototypes for dental implants avoided the shining-through effect associated with metal abutments. Their load-bearing capacity after in vitro stress simulation was higher than the maximum oral loading force. With some improvements, the fiber-reinforced implant abutments are therefore a promising alternative to titanium abutments.     

Fracture behaviour of implant–implant- and implant–tooth-supported all-ceramic fixed dental prostheses utilising zirconium dioxide implant abutments

This in vitro study investigated the fracture behaviour of implant–implant-supported and implant–tooth-supported all-ceramic fixed dental prostheses (FDP) using zirconium dioxide implant abutments (FRIADENT® CERCON® abutments, DENTSPLY Friadent). Six different test groups (n?=?8) were prepared. Groups 1, 2, 4, and 5 represented an implant–implant-supported FDP condition, whereas groups 3 and 6 simulated an implant–tooth-supported FDP condition. The second right premolar of the mandible was replaced with a pontic tooth. In groups 2 and 5, implant abutments were individualised by circumferential preparation. XiVe® S plus screw implants (DENTSPLY Friadent) that were 4.5 mm (first molar) and 3.8 mm (first premolar) in diameter and 11 mm in length and metal tooth analogues with simulated periodontal mobility, representing the first right premolar, were mounted in a polymethyl methacrylate block. The FDPs were cemented with KetacCem (3 M Espe GmbH, Germany). Groups 4, 5, and 6 were thermomechanically loaded (thermal and mechanical cycling (TCML)?=?1.2?×?10⁶; 10,000?×?5°/55°) and subjected to static loading until failure. Statistical analysis of data obtained for the force at fracture was performed using non-parametric tests. All samples tested survived TCML. In the implant–implant-supported groups, circumferential abutment preparation resulted in a tendency to lower fracture forces compared to groups with unprepared abutments (group 1, 472.75?±?24.71 N; group 2, 423.75?±?48.48 N; group 4, 647.13?±?39.10 N; group 5, 555.86?±?30.34 N). The implant–tooth-supported restorations exhibited higher fracture loads (group 3, 736.25?±?82.23 N; group 6, 720.75?±?48.99 N) than the implant–implant-supported restorations which did not possess circumferentially individualised abutments. Statistically significant differences were found when comparing the non-artificially aged groups. Implant–tooth-supported FDP restorations did exhibit an increased fracture load compared to implant–implant-supported FDP restorations.     

Load-bearing capacity of all-ceramic posterior four-unit fixed partial dentures with different zirconia frameworks

The aim of this in vitro study was to compare the load-bearing capacity of posterior four-unit fixed partial dentures (FPDs) produced with two different yttria-stabilized polycrystalline tetragonal zirconia (Y-TZP) ceramics, one being a presintered material, the other a fully sintered, hot isostatically pressed material. Additionally, as a novel approach, the influence of preliminary mechanical damage upon the fracture force of an FPD has been investigated. A total of 20 frameworks each were milled from presintered zirconia and from fully sintered zirconia. Prior to veneering, 10 frameworks of each material were 'damaged' by a defined saw cut similar to an accidental flaw generated during shape cutting. Before fracture testing, all FPDs were subjected to thermal and mechanical cycling. Additionally, scanning electron microscopy was used to investigate fracture surfaces. Statistical analysis showed that FPDs milled from fully sintered zirconia had a significantly higher fracture resistance compared with specimens made from presintered material, whereas preliminary damage did not have a significant effect. After aging, FPDs made from both materials were capable of withstanding occlusal forces reported in the literature. Therefore, both types of Y-TZP may be suitable for posterior four-unit all-ceramic FPDs, although further prolonged aging experiments and prospective clinical trials are required to prove their fitness for clinical use.     

An analysis of stress around abutment teeth and periodontium in three-unit fixed partial dentures--photoelastic analysis with simulated periodontal ligament

The mechanical characteristics of zirconia, hybrid hard resin and dental metal for crowns and fixed partial dentures (FPD) have been researched for clinical applications. However, for these kinds of restorations, the distribution of mechanical stress around the abutment teeth and periodontium during function has not been sufficiently assessed. The aim of this study was to clarify the influence of these materials upon abutment teeth and periodontium through a two-dimensional photoelastic method. Two-dimensional simulation models of three-unit FPDs were constructed from these materials. By applying a force of 400 N vertically to these FPDs, the stress distribution around the abutment teeth and alveolar bone was analyzed and the fringe orders were recorded with a transmission polariscope. As a result, the fringe order values at the root dentin around the marginal area of the pontic joint were the highest in zirconia, and the smallest in hybrid hard resin. The spread of internal stress around the marginal area was larger in the hybrid hard resin model and dental metal model than in the zirconia model. This study suggested that differences in stress distribution within the abutment teeth and around the alveolar bone were related to differences in elastic coefficients of the materials used in FPDs.     

Fracture resistance of the veneering on inlay-retained zirconia ceramic fixed partial dentures

AIMS: The aim of this in vitro study was to evaluate the fracture load of zircon frames veneered with a polymer glass holding box inlay-retained fixed partial dentures (FPDs). The influence of the position of the frame and the span length was tested. Additionally, the fracture load values of zircon frames veneered with a press ceramic were evaluated. MATERIAL AND METHODS: Box inlay cavities were prepared on mandibular molars and premolars. Forty-eight FPDs were manufactured using industrially prefabricated zircon frames veneered with the polymer glass Artglass. Sixteen FPDs received individually manufactured CAD/CAM zircon frames veneered with a press ceramic. All FPDs underwent thermal cycling and mechanical loading (ML). The load to fracture was measured and fracture sites were evaluated. RESULTS: Four polymer veneered FPDs showed fractures in the veneering material after ML. The mean fracture resistance ranged from 531 N to 727 N. No significant influence of frame localization could be observed. Significantly greater fracture resistance values were found in the ceramic veneered FPDs (1276 N to 1413 N). There was no significant effect of span length in the polymer veneered group or in the all-ceramic group, with the exception of a significant peak in fracture load value for intermediate span lengths in the polymer group with a localized occlusal zircon frame. CONCLUSIONS: Polymer veneered FPDs with Y-TZP frames showed acceptable fracture resistance values, but they cannot yet be unreservedly recommended for clinical use. Fracture values for CAD/CAM manufactured Y-TZP frames combined with a press ceramic deserve further clinical investigation.     

Influence of core material on fracture resistance and marginal adaptation of restored root filled teeth

Aim To investigate ex vivo the influence of direct placement core materials on the fracture strength and marginal adaptation of root filled maxillary central incisors restored with glass fibre‐reinforced posts, various core materials and all‐ceramic crowns. Methodology Forty‐eight human maxillary incisors were root filled. Posts were placed and teeth restored with composite cores and crowns (n = 8). Six core materials were examined after thermal cyclic and mechanical loading (TCML). Fracture force was determined under static loading. The marginal adaptation at the interfaces between cement‐tooth and cement‐crown were categorized as ‘intact margin’ or ‘marginal gap’ using scanning electron microscopy. Statistical analysis was undertaken with the Mann–Whitney U‐test (α = P ≤ 0.05). Results Median fracture strength varied between 204 N (low viscous experimental core) and 1094 N (Multicore). No difference in fracture resistance was found with varying viscosity of the core material. The layering technique improved the fracture performance (P = 0.059) to a minor degree. Crowns with dedicated core materials (Rebilda 1063 N; Multicore 1094 N) had a significantly higher fracture resistance than crowns with a conventional restorative material (Tetric Ceram 509 N). Significantly poorer marginal adaptation before TCML was found for the layering technique at the tooth–cement interface and for all experimental cores after TCML. At the crown–cement interface significant differences in marginal adaptation could be determined between Multicore‐layered core (P = 0.002) and Multicore‐Rebilda (P = 0.001) after TCML. Conclusions The fracture strength of post and core restorations was dependent on the core material and bonding system. Marginal adaptation was influenced by the method of application of the core material and by TCML.     

Stability of prototype two-piece zirconia and titanium implants after artificial aging: an in vitro pilot study

Background: Zirconia oral implants are a new topic in implant dentistry. So far, no data are available on the biomechanical behavior of two‐piece zirconia implants. Therefore, the purpose of this pilot investigation was to test in vitro the fracture strength of two‐piece cylindrical zirconia implants after aging in a chewing simulator. Materials and Methods: This laboratory in vitro investigation comprised three different treatment groups. Each group consisted of 16 specimens. In group 1, two‐piece zirconia implants were restored with zirconia crowns (zirconia copings veneered with Triceram®; Esprident, Ispringen, Germany), and in group 2 zirconia implants received Empress® 2 single crowns (Ivoclar Vivadent AG, Schaan, Liechtenstein). The implants, including the abutments, in the two zirconia groups were identical. In group 3, similar titanium implants were reconstructed with porcelain‐fused‐to‐metal crowns. Eight samples of each group were submitted to artificial aging with a long‐term load test in the artificial mouth (chewing simulator). Subsequently, all not artificially aged samples and all artificially aged samples that survived the long‐term loading of each group were submitted to a fracture strength test in a universal testing machine. For the pairwise comparisons in the different test groups with or without artificial loading and between the different groups at a given artificial loading condition, the Wilcoxon rank‐sum test for independent samples was used. The significance level was set at 5%. Results: One sample of group 1 (veneer fracture), none of group 2, and six samples of group 3 (implant abutment screw fractures) failed while exposed to the artificial mouth. The values for the fracture strength after artificial loading with 1.2 million cycles for group 1 were between 45 and 377 N (mean: 275.7 N), in group 2 between 240 and 314 N (mean: 280.7 N), and in the titanium group between 45 and 582 N (mean: 165.7 N). The fracture strength results without artificial load for group 1 amounted to between 270 and 393 N (mean: 325.1 N), for group 2 between 235 and 321 N (mean: 281.8 N), and between 474 and 765 N (mean: 595.2 N) for the titanium group. The failure mode during the fracture testing in the zirconia implant groups was a fracture of the implant head and a bending/fracture of the abutment screw in the titanium group. Conclusions: Within the limits of this pilot investigation, the biomechanical stability of all tested prototype implant groups seems to be – compared with the possibly exerted occlusal forces – borderline for clinical use. A high number of failures occurred already during the artificial loading in the titanium group at the abutment screw level. The zirconia implant groups showed irreparable implant head fractures at relatively low fracture loads. Therefore, the clinical use of the presented prototype implants has to be questioned.     

Influence of the fabrication process on the in vitro performance of fixed dental prostheses with zirconia substructures

Chipping of the applied veneering ceramic is reported to be a main clinical failure type of computer-aided design/computer-aided manufacturing- or manually copy-milled zirconia restorations. The aim of this in vitro study was to investigate whether different substructure designs and veneering processes done by different dental technicians do significantly influence chipping in zirconia-based all-ceramic fixed dental prostheses during simulated oral service. Five groups (n = 8 per group) of three-unit zirconia substructures were fabricated in three different laboratories using copy-milling technique. Three series were veneered with identical porcelain (groups 1–3) and one with a second different porcelain (group 4). The fifth group was milled to final contour design without veneering. Dimensions of the connector areas were determined. All fixed partial dentures (FPDs) were adhesively boned on human teeth and thermally cycled and mechanically loaded (1.2 × 10⁶ × 50 N; 6,000 × 5°C/55°C) using human antagonists. Restorations were monitored during thermal cycling and mechanical loading (TCML). FPDs which survived were loaded to fracture. FPDs which failed during TCML were investigated with fractographic means. During TCML, chipping took place in groups 1 (two times), 2 (four times) and 3 (five times) (Table 1). Chipping areas varied between 2.3 mm² (group 3) and 58.7 mm² (group 2). Groups 4 and 5 provided no failures during TCML. Failure in all cases started from contact points, where superficial wear and disruption of the porcelain were found. No significant correlation could be determined between connector thickness and number of failures. Median fracture results varied between 1,011 N (group 3) and 2,126 N (group 2). The results show the necessity of considering individual design and manufacturing of restorations as well as contact situation. Advanced technical training on zirconia-based restorations is recommended.     

Glass–fibre-reinforced-composite fixed partial dentures on dental implants

The objective was to investigate the fracture strength and marginal fit of implant suprastructures made of fibre-reinforced composite which were fixed onto the implants using cementation or screws. A sample (n=8) of 4-unit bridges, made of the fibre-reinforced composite Vectris/Targis, were adhesively cemented onto titanium conical implant abutments. The second sample consisted of eight screwable Vectris/Targis bridges which were based on prototypes of titanium crown bases. After a 5 year simulation of thermal cycling and mechanical loading (TCML), all specimen were loaded to fracture. Marginal fit was investigated using a semiquantitative SEM analysis. The cemented 4-unit bridges showed a fracture strength of 1553 N (Q1=1498 N, Q3=1825 N) and the screw-fixed bridges had a median of 1457 N (Q1=1223 N, Q3= 1781 N). The analysis of the marginal adaptation showed similar results of cemented and screwed bridges. The bond between the Targis facing-material and the composite cement was significantly deteriorated after TCML. CONCLUSION: Suprastructures made of glass-fibre-reinforced composite could become an alternative to reconstructions with a metal-framework. Both, fixation onto the implants with screws or cementation, are possible.     

Fracture resistance of PMMA and resin matrix composite-based interim FPD materials

PURPOSE: The aim of this study was to compare the fracture strength of several commercial interim fixed partial denture (FPD) materials in an artificial oral environment. MATERIALS AND METHODS: Twenty identical three-unit FPDs of the PMMA materials Trim and Cronsin and the composite-based materials Protemp 3 Garant, Protemp Garant, Luxatemp, and Tempofit were cemented on Co-Cr alloy dies. Ten FPDs of each material were stored for 14 days in distilled water and artificially aged. Ten FPDs of each material were stored for 24 hours in distilled water as a control group. Fracture resistance was determined using a testing machine. RESULTS: The tested interim materials showed initial fracture values between 484 and 1,081 N. During artificial aging, the PMMA FPDs failed because of irreversible deflection. All Tempofit FPDs, four Luxatemp FPDs, two Protemp Garant FPDs, and one Protemp 3 Garant FPD failed because of fracture during artificial aging. The remaining FPDs showed fracture values of 759 N (Luxatemp), 772 N (Protemp Garant), and 956 N (Protemp 3 Garant). CONCLUSION: The PMMA FPDs and the composite Tempofit FPDs showed poor stability during artificial aging, whereas the highest strength values in combination with low fracture rates were found for the Protemp 3 Garant composite FPDs.     

Composite veneering of metal based fixed partial dentures

The aim of this in vitro study was to determine the thermal mechanical properties of veneering composites after polymerization with the appropriate polymerization device. Fracture tests were performed to investigate the effect on fixed partial dentures (FPDs). Dynamic mechanical thermal analysis was used to determine the temperature-dependent mechanical properties. To approximate the clinical situation, the fracture resistance of three-unit metal-based FPDs with different composite veneering was investigated after a simulated 5-year oral wearing period. The restorations were made of a high gold alloy and veneered with three different composites. To determine the influence of fabrication, one composite was used in a light-polymerizing and a heat/pressure-curing version and, in addition, a newly developed heat protection paste was used. After a 5-year simulation period, the fracture resistance was determined. The storage modulus varied between 14268 N mm(-2) (Belleglass) and 6616 N mm(-2) (Sinfony). Adoro showed no significant differences between light curing (9155 N mm(-2)) and heat curing (8184 N mm(-2)) variations. The Adoro-veneering with the heat protection paste showed the highest median fracture strength (1700 N), followed by Adoro LC (1555 N), Belleglass (1051 N), Adoro HP (1150 N) and Sinfony (909 N). The most common failure type occurring in all FPDs was a cracking of the composite, exposing the metal framework. All FPDs showed stress cracking of the composite. The heat protection paste seemed to reduce the crack formation after fabrication and increased the fracture resistance of the composite veneering. Stress cracking after thermal cycling and mechanical loading affected all composites, but all veneered three-unit alloy FPDs showed a fracture resistance sufficient for posterior application.