Influence of water storage and thermal cycling on the fracture strength of all-porcelain, resin-bonded fixed partial dentures

Structural Integrity of Anterior Ceramic Resin-Bonded Fixed Partial Denture: A Finite Element Analysis Study

This study was conducted as a means to evaluate the stress distribution patterns of anterior ceramic resin-bonded fixed partial dentures derived from different materials and numerous connector designs that had various loading conditions imposed onto them through the utilization of the finite element method. A finite element model was established on the basis of the cone beam computed tomography image of a cantilevered resin-bonded fixed partial denture with a central incisor as an abutment and a lateral incisor as a pontic. Sixteen finite element models representing different conditions were simulated with lithium disilicate and zirconia. Connector height, width, and shape were set as the geometric parameters. Static loads of 100 N, 150 N, and 200 N were applied at 45 degrees to the pontic. The maximum equivalent stress values obtained for all finite element models were compared with the ultimate strengths of their materials. Higher load exhibited greater maximum equivalent stress in both materials, regardless of the connector width and shape. Loadings of 200 N and 150 N that were correspondingly simulated on lithium disilicate prostheses of all shapes and dimensions resulted in connector fractures. On the contrary, loadings of 200 N, 150 N, and 100 N with rectangular-shaped connectors correspondingly simulated on zirconia were able to withstand the loads. However, two of the trapezoidal-shaped zirconia connectors were unable to withstand the loads and resulted in fractures. It can be deduced that material type, shape, and connector dimensions concurrently influenced the integrity of the bridge.

An infection-induced oxidation site regulates legumain processing and tumor growth

Oxidative stress is a defining feature of most cancers, including those that stem from carcinogenic infections¹. Reactive oxygen species (ROS) can drive tumor formation^2–4, yet the molecular oxidation events that contribute to tumorigenesis are largely unknown. Here we show that inactivation of a single, redox-sensitive cysteine in the host protease legumain, which is oxidized during infection with the gastric cancer-causing bacterium Helicobacter pylori, accelerates tumor growth. By using chemical proteomics to map cysteine reactivity in human gastric cells, we determined that H. pylori infection induces oxidation of legumain at Cys219. Legumain oxidation dysregulates intracellular legumain processing and decreases the activity of the enzyme in H. pylori-infected cells. We further show that the site-specific loss of Cys219 reactivity increases tumor growth and mortality in a xenograft model. Our findings establish a link between an infection-induced oxidation site and tumorigenesis while underscoring the importance of cysteine reactivity in tumor growth.

Comparison of Fracture Resistance for Chairside CAD/CAM Lithium Disilicate Crowns and Overlays with Different Designs

PURPOSE

To determine the fracture resistance of chairside computer-aided design and computer-assisted manufacturing (CAD/CAM) lithium disilicate full coverage crowns and two different designs of overlay restorations for premolars.

MATERIALS AND METHODS

CAD/CAM lithium disilicate (IPS e.max CAD for CEREC/HT A1 C14, Ivoclar Vivadent) restorations (15 specimens/group) with 1.5 mm occlusal thickness and 1.0 mm chamfer were designed and fabricated with a chairside CAD/CAM system (CEREC, Dentsply Sirona). The restorations were prepared in three different designs: (1) full coverage crowns, (2) overlays with the margin located 2 mm above the gingiva, and (3) overlays with the margin located 4 mm above the gingiva. Restorations were cemented using conventional resin luting cement (Multilink, Ivoclar Vivadent) with primer system (Monobond Plus, Ivoclar Vivadent) to resin printed dies, load cycled (2,000,000 load cycles at 1 Hz with 275 N force), and then finally loaded with a steel indenter until failure. Scanning electron microscopy observations of fractured surfaces were also conducted. Group results were analyzed with one-way analysis of variance, and the medians were evaluated independently with Kruskal-Wallis.

RESULTS

The fracture force of CAD/CAM lithium disilicate restorations was significantly different (p < 0.001) depending on the design of the restoration. Full coverage crowns showed significantly higher force to fracture (1018.8 N) than both types of overlays (p = 0.002 for overlay 2.0 mm and p < 0.001 for overlay 4.0 mm above gingiva). Among the two overlays, the restoration with the margin located 2 mm above the gingiva showed significantly higher fracture force (813.8 N) than the overlay with margin at 4 mm above the gingiva (436.1 N; p < 0.001). The fracture appearance of the crowns was much more complex than that of the overlay restorations.

CONCLUSIONS

Full coverage chairside CAD/CAM lithium disilicate premolar crown showed higher fracture resistance than overlay restorations. Overlays with the margin located 2 mm above the margin demonstrated higher resistance than those with the margin located 4 mm above the gingiva.

Shear bond strength evaluation of metallic brackets bonded to a CAD/CAM PMMA material compared to traditional prosthetic temporary materials: an in vitro study

INTRODUCTION

Orthodontic treatment for adults is currently increasing, and therefore the need to bond brackets to restorations and temporary crowns. The use of CAD/CAM PMMA provisional restorations for orthodontic purposes have not yet been described, and there is currently insufficient information regarding the strength of bracket adhesion.

OBJECTIVE

This study aimed at evaluating the effects of thermocycling (TC) and surface treatment on shear bond strength (SBS) of brackets to different provisional materials.

METHODS

Forty specimens were made from each material [PMMA (Telio Lab), bis-acryl (Telio CS C&B), and PMMA CAD/CAM (Telio CAD)], sandpapered, and divided according to surface treatment (pumiced or sandblasted) and TC (half of the samples = 1,000 cycles, 5°C/55°C water baths) (n = 10/group). Stainless-steel brackets were bonded to the specimens (using Transbond XT), and SBS testing was performed. Data were analyzed by three-way ANOVA and LSD post-hoc tests (α = 0.05). Failure types were classified with adhesive remnant index (ARI) scores.

RESULTS

SBS values ranged from 1.5 to 14.9 MPa. Sandblasted bis-acryl and sandblasted auto-curing PMMA groups presented similar values (p> 0.05), higher than the CAD/CAM material (p< 0.05), with or without TC. When thermocycled, pumiced bis-acryl showed higher SBS than pumiced acrylic (p= 0.005) and CAD/CAM materials (p= 0.000), with statistical difference (p= 0.009). TC showed negative effect (p< 0.05) for sandblasted bis-acryl and pumiced acrylic groups. ARI predominant score was mostly zero (0) for CAD/CAM, 1 and 2 for bis-acryl, and 1 for acrylic groups.

CONCLUSION

In general, bis-acryl material showed the highest SBS values, followed by acrylic and CAD/CAM materials, which showed SBS values lower than an optimum strength for bonding brackets.

Displacement of teeth without and with bonded fixed orthodontic retainers: 3D analysis using triangular target frames and optoelectronic motion tracking device

PURPOSE

The objective of this study was to evaluate the anterior tooth movement without and with bonded fixed orthodontic retainers under incremental loading conditions.

MATERIALS AND METHODS

Six extracted mandibular anterior human teeth were embedded in acrylic resin in True Form I Arch type and 3D reconstruction of Digital Volume Tomography (DVT) images (0.4 mm³ voxels) were obtained. The anatomy of each tooth was segmented and digitally reconstructed using 3D visualization software for medical images (AMIRA, FEI SVG). The digital models of the teeth were repositioned to form an arch with constant curvature using a CAD software (Rhinoceros) and a base holder was designed fitting the shape of the roots. The clearance between the roots and their slot in the holder was kept constant at 0.3 mm to replicate the periodontal ligament thickness. The holder and the teeth were then manufactured by 3D printing (Objet Eden 260VS, Stratasys) using a resin material for dental applications (E = 2-3 GPa). The 3D-printed teeth models were then positioned in the holder and the root compartments were filled with silicone. The procedure was repeated to obtain three identical arch models. Each model was tested for tooth mobility by applying force increasing from 5 to 30 N with 5 N increments applied perpendicular on the lingual tooth surface on the incisal one third (crosshead speed: 0.1 mm/s). The teeth on each model were first tested without retainer (control) and subsequently with the bonded retainers (braided bonded retainer wire; Multi-strand 1 × 3 high performance wire, 0.022″ × 0.016″). Tooth displacement was measured in terms of complicance (F/Δ movement) (N/mm) using custom-built optoelectronic motion tracking device (OPTIS) (accuracy: 5 µm; sampling rate: 200 Hz). The position of the object was detected through three LEDs positioned in a fixed triangular shape on a metal support (Triangular Target Frame). The measurements were repeated for three times for each tooth. Data were analyzed using mixed model with nesting (alpha = 0.05).

RESULTS

The use of retainer showed a significant effect on tooth mobility (0.008 ± 0.004) compared to non-bonded teeth (control) (0.014 ± 0.009) (p < 0.0001). The amount of displacement on the tooth basis was also significantly different (p = 0.0381) being the most for tooth no. 42 (without: 0.024 ± 0.01; with: 0.012 ± 0.002) (p = 0.0018). No significant difference was observed between repeated measurements (p = 0.097) and the incremental magnitude of loading (5-30 N: 0.07 ± 0.01-0.09 ± 0.02) (p > 0.05).

CONCLUSION

Mandibular anterior teeth showed less tooth mobility when bonded with stainless steel wire as opposed to non-bonded teeth but the tooth mobility varied depending on the tooth type. Intermittent increase in loading from 5 to 30 N did not increase tooth displacement.

Shear bond strength of orthodontic metal brackets to aged composite using three primers

BACKGROUND

This study aimed to assess the effect of surface preparation with sandblasting and diamond bur along with the use of three primers on shear bond strength (SBS) of metal brackets to aged composite.

MATERIAL AND METHODS

In this in vitro, experimental study, 60 Filtek Z250 composite discs were fabricated (10×2mm), immersed in distilled water for 24 hours and subjected to 5000 thermal cycles. They were randomly divided into two groups (n=30) of sandblasting with aluminum oxide particles for 10 seconds and surface roughening with bur. Each group was randomly divided into three subgroups (n=10) for use of Transbond XT, Assure Plus and Composite Primer. Metal brackets were bonded and the samples were stored in distilled water for 24 hours followed by 2000 thermal cycles. The SBS of brackets was measured and the adhesive remnant index (ARI) score was calculated. The data were analyzed by one-way ANOVA, t-test and Chi square test.

RESULTS

The difference in the mean SBS was not significant among the six subgroups.

CONCLUSIONS

All combinations of primers and surface preparation methods provided adequately high SBS between brackets and aged composite surfaces. Considering the ARI scores, surface roughening by bur is superior to sandblasting. Key words:Shear strength, composite resins, orthodontic brackets, aged composite, surface preparation.

Minimally invasive preparation and design of a cantilevered, all-ceramic, resin-bonded, fixed partial denture in the esthetic zone: a case report and descriptive review

Resin-bonded, fixed partial dentures have the potential to offer a minimally invasive, fixed-prosthetic approach to tooth replacement in patients who may not be candidates for implant therapy. However, traditional preparation protocols often recommend extensive preparation designs on two abutment teeth, thereby potentially compromising the long-term health of the adjacent abutments and often resulting in unilateral debonding of one of the retainers in the long term. In light of advances in high-strength ceramic systems capable of being reliably bonded to tooth structure and offering improved esthetic outcomes, as well as clinical and case-series research demonstrating improved survivability of cantilevered resin-bonded fixed partial dentures, new preparation designs and methodologies can be advocated. The following case report demonstrates the clinical application of sonoabrasion, coupled with a dental operating microscope, to minimally prepare a single abutment for a cantilevered, all-ceramic resin-bonded fixed partial denture. Relevant historic and contemporary literature regarding double versus single-retainer resin-bonded fixed partial dentures are reviewed, as well as clinical conditions that are most favorable for such restorations to have an optimal long-term prognosis.

CLINICAL SIGNIFICANCE

If appropriate clinical conditions exist, a cantilevered, all-ceramic, resin-bonded, fixed partial denture may be the most conservative means of tooth replacement in a patient who is not a candidate for an endosseous implant.

The influence of support properties and complexity on fracture strength and fracture mode of all-ceramic fixed dental prostheses

Abstract Objective. When a new material is released, clinical studies are indicated. For the clinical studies to be defensible, in-vitro studies, which are as clinically relevant as possible, must be performed. The aim of this study was to investigate how the choice of material used for supporting tooth analogues and support complexity influences test results concerning the fracture strength of fixed dental prostheses (FDPs) made from a brittle material: Y-TZP. Material and methods. Twenty-four FDPs were produced in Y-TZP. The FDP cores were subjected to heat treatment to simulate veneering and then thermocycled for 5000 cycles to simulate ageing. The FDPs were divided into three groups and were cemented on tooth-supporting analogues made from aluminium, polymer and DuraLay( ). The FDPs were preloaded for 10,000 cycles and finally loaded to fracture. Results. There were no significant differences in load to fracture or fracture mode between the groups cemented on polymer and DuraLay tooth analogues. The FDPs cemented on aluminium tooth analogues showed a significantly higher load at fracture and a different fracture mode. Conclusions. Within the limitations of this in-vitro study, the following could be concluded. To achieve mutually comparable results there is a need for a standardized, simple test set-up for in-vitro testing of all-ceramic FDPs intended for cementation upon natural teeth. Resilient, non-complex and resilient, complex tooth analogues give comparable test results when the test set-up is unchanged in all other aspects. Non-resilient (with an elastic modulus equivalent to or higher than that of aluminium) tooth analogues give high and unrealistic load-at-fracture values together with adverse fracture modes compared to FDPs failing in clinical situations.

Dynamic fatigue and fracture resistance of non-retentive all-ceramic full-coverage molar restorations. Influence of ceramic material and preparation design

OBJECTIVES

The purpose of the study was to evaluate the influence of preparation design, and ceramic material, masticatory fatigue and fracture resistance of non-retentive all-ceramic full-coverage restorations luted on human mandibular molars.

METHODS

Full-coverage occlusal restorations were laboratory fabricated from leucite reinforced glass-ceramic (IPS Empress Esthetic) or lithium disilicate glass-ceramic (IPS e.max Press). For each ceramic material four groups with eight specimens each were randomly assigned. Groups had either a non-retentive, occlusal preparation with chamfer finishing line or straight-beveled finishing line and the preparation was either completely within enamel or within dentin with a finishing line in enamel. Restorations were adhesively luted to the teeth using composite resin. After storage in water for 1 week specimens were cyclic loaded 600,000 times with a weight of 10kg and additionally, thermocycled 3500 times (5/55 degrees C) in a masticatory simulator. Surviving specimens were loaded until, fracture in a universal testing machine. Statistical analysis was done using three-way ANOVA.

RESULTS

All specimens survived the masticatory fatigue. Mean fracture resistance ranged from 2895 to 4173N. Influence of ceramic material on fracture resistance was significant (p=0.0001). Lithium disilicate glass-ceramic restorations had higher fracture resistances than leucite reinforced glass-ceramic restorations. Different preparation designs showed no significant influence on fracture resistance (p=0.0969). The design of the finishing line did not influence the fracture resistance (p=0.9461).

SIGNIFICANCE

The fracture resistance of adhesively luted non-retentive full-coverage molar restorations, made of lithium disilicate or leucite reinforced glass-ceramic is promising and seems to permit clinical application.

The influence of internal surface treatments on tensile bond strength for two ceramic systems

STATEMENT OF THE PROBLEM

The ceramic composition and surface microstructure of all-ceramic restorations are important components of an effective bonding substrate. Hydrofluoric acid and sandblasting are well-known procedures for surface treatment; however, surface treatment for high alumina-containing and lithium disilicate ceramics have not been fully investigated.

PURPOSE

This in vitro study evaluated the tensile bond strength of resin cement to two types of ceramic systems with different surface treatments.

METHODS AND MATERIALS

Thirty specimens of each ceramic system were made according to the manufacturer's instructions and embedded in polyester resin. Specimens of In-Ceram Alumina [I] and IPS Empress 2 [E] were distributed to three groups with differing surface treatments (n = 10): sandblasting with 50 microm aluminum oxide (APA); sandblasting with 110 microm aluminum oxide modified with silica particles (ROCATEC System-RS); a combination of sandblasting with APA and 10% hydrofluoric acid etching (HA) for two minutes on In-Ceram and for 20 seconds for IPS Empress 2. After the respective surface treatments, all the specimens were silanated, and Rely-X resin cement was injected onto the ceramic surface and light polymerized. The specimens were stored in distilled water at 37 degrees C for 24 hours and thermally cycled 1,100 times (5 degrees C/55 degrees C). The tensile bond strength test was performed in a universal testing machine at a 0.5 mm/minute crosshead speed.

RESULTS

The mean bond strength values (MPa) for IPS Empress 2 were 12.01 +/- 5.93 (EAPA), 10.34 +/- 1.77 (ERS) and 14.49 +/- 3.04 (EHA). The mean bond strength values for In-Ceram Alumina were 9.87 +/- 2.40 (IAPA) and 20.40 +/- 6.27 (IRS). All In-Ceram specimens treated with 10% hydrofluoric acid failed during thermal cycling.

CONCLUSION

The Rocatec system was the most effective surface treatment for In-Ceram Alumina ceramics; whereas, the combination of aluminum oxide sandblasting and hydrofluoric acid etching for 20 seconds worked more effectively for Empress 2 ceramics.

Orthodontic bonding to several ceramic surfaces: are there acceptable alternatives to conventional methods?

INTRODUCTION

The objectives of this study were to determine the effects of various surface conditioning methods on 3 types of ceramic materials (feldsphatic, leucite-based, and lithia disilicate-based) in orthodontic bonding.

METHODS

A total of 210 ceramic disk samples were fabricated and divided into 3 groups. In each group, 5 subgroups were prepared by sandblasting; sandblasting and hydrofluoric (HF) acid; sandblasting and silane; sandblasting, HF acid, and silane; and tribochemical silica coating and silane. Mandibular incisor brackets were bonded with light-cured adhesive. The samples were stored in water for 24 hours at 37 degrees C and then thermocycled. Shear bond tests were performed, and the failure types were classified with adhesive remnant index scores.

RESULTS

In all 3 ceramic groups, the lowest shear bond strength values were found in the sandblasted-only samples. For the feldspathic and lithia disilicate-based ceramic, the highest bond strength values were obtained with silica coating (15.2 and 13.2 MPa, respectively). For the leucite-based ceramic, HF without silane produced the highest bond strength value (14.7 MPa), but comparable values were obtained with silicatization also (13.4 MPa).

CONCLUSIONS

The silica-coating technique could replace the other conditioning techniques in bonding brackets to ceramic. However, debonding must be done carefully because of the risk of porcelain fracture.

Partial coverage restoration systems on molars – comparison of failure load after exposure to a mastication simulator

This in vitro study evaluated the failure load of partial coverage restorations (PCR) made of various materials cemented on natural molars after exposure to the mastication simulator. Sixty-four maxillary molars were divided into four groups of 16 test specimens each. The specimens in one group remained unprepared (group NP); the teeth in the other groups were prepared equally according to standardized guidelines and restored with the following PCR: Group GO (Gold-Pontor-MPF; Metaux Precieux SA, Metalor, Neuchatel, Switzerland), group TA (Targis; Ivoclar Vivadent AG, Schaan, Liechtenstein) and group EM (IPS-Empress; Ivoclar Vivadent AG). The restorations in group GO were cemented conventionally, while those in groups TA and EM were luted adhesively. Groups NP and GO served as control groups. All test specimens were subjected to 1.2 million cycles (F = 49 N) in a mastication simulator. Subsequently, all test specimens were loaded occlusally until fracture occurred using an universal testing machine. All specimens withstood the masticating simulation. The median (IQR = x(0.25)-x(0.75)) failure loads were as follows: group NP: 1960.3(1480.5-2227.5) N, group TA: 1478.6(1293.4-1856.7) N and group EM: 1400.1(1043.1-1721.6) N. All test specimens of group GO achieved fracture strength values which exceeded a fracture load of 5500 N. The values of group GO were statistically significantly higher than those of groups NP, TA and EM (P < 0.00001). Furthermore, the results of group NP were significantly higher (P = 0.0226) than those of group EM. The results of groups NP and TA (P = 0.2022) as well as of groups TA and EM (P = 0.5340) did not differ significantly. The median values of all PCR systems obtained were within the limits of clinical acceptance. Long-term clinical investigations which take additional parameters into consideration are required before the composite-based Targis(R) (Ivoclar Vivadent AG) material can be recommended for indirect PCR.

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 storage solution on enamel demineralization submitted to pH cycling

Extracted human teeth are frequently used for research or educational purposes. Therefore, it is necessary to store them in disinfectant solutions that do not alter dental structures. Thus, this study evaluated the influence of storage solution on enamel demineralization. For that purpose, sixty samples were divided into the following groups: enamel stored in formaldehyde (F1), stored in thymol (T1), stored in formaldehyde and submitted to pH cycling (F2), stored in thymol and submitted to pH cycling (T2). All samples were evaluated by cross-sectional microhardness analysis and had their percentage of mineral volume versus micrometer (integrated area) determined. Differences between groups were found up to 30-µm depth from the enamel surface (p < 0.05), where samples from group T2 were more demineralized. It was concluded that the storage solution influenced the reaction of a dental substrate to a cariogenic challenge, suggesting that formaldehyde may increase enamel resistance to demineralization, when compared to demineralization occurring in enamel stored in thymol solution.

Flexural strength of Cerec 2 machined and jointed InCeram-Alumina and InCeram-Zirconia bars

OBJECTIVE

The flexural strength of Cerec 2 InCeram-Alumina and InCeram-Zirconia bars is evaluated. The focus of the in vitro study is to identify a jointing procedure for InCeram which may be used for producing full-ceramic fixed-partial-denture frameworks.

METHODS

Six groups (n=15) of machined and jointed InCeram-Alumina (T1-T5) and InCeram-Zirconia (T6) bars (3x4x13mm(3)), respectively, were examined using a 3-point-bending test. InCeram-Alumina joint-free controls were: machined (C1), slip cast (C2, C3) and cut from the block (C4) bars. Machined joint-free InCeram-Zirconia bars were used as controls (C5). InCeram-Alumina slip was used for jointing T1-T5 and InCeram-Zirconia slip for bars T6. Bars were jointed in groups T1 and T2 using butt joint (S1), in T3 and T4 oblique (S2, S3) and in T5 and T6 rounded (S4) joint shapes.

RESULTS

Two-way analysis of variance showed significant differences between materials (p<0.001) and jointing shapes (p<0.001). The rounded (S4) shape showed the highest flexural strength of 434 (65) MPa of InCeram-Alumina (T5) and 475 (54) MPa of InCeram-Zirconia (T6) bars, respectively but machined/joint-free InCeram-Alumina (511 (59) MPa, C1) and machined/joint-free InCeram-Zirconia (624 (58) MPa, C5) were significantly (p<0.01/p<0.001) stronger. No significant differences (p>0.05) were found between machined/jointed InCeram-Zirconia (475 (54) MPa, T6), joint-free InCeram-Alumina slip cast (498 (125) MPa, C2) and joint-free InCeram-Alumina machined bars (511 (59) MPa, C1).

SIGNIFICANCE

Compared to conventional slip cast InCeram-Alumina the flexural strength of machined/jointed InCeram-Zirconia appears to be adequate for fixed-partial-denture frameworks.

Influence of design and mode of loading on the fracture strength of all-ceramic resin-bonded fixed partial dentures: an in vitro study in a dual-axis chewing simulator

STATEMENT OF PROBLEM

In a clinical study, all-ceramic resin-bonded fixed partial dentures showed a high rate of fractures within the first years of service but remained in function as cantilevered restorations. No data are available on the fracture strength of such cantilevered restorations.

PURPOSE

This in vitro study evaluated the influence of design and mode of loading on the fracture strength of all-ceramic resin-bonded fixed partial dentures.

MATERIAL AND METHODS

Forty-eight frameworks were copy milled using the aluminum-oxide ceramic In-Ceram, glass-infiltrated, and circularly veneered with feldspathic porcelain to replace a maxillary incisor on a test cast. The airborne particle-abraded restorations were bonded to acid-etched human abutments using composite. Twenty-four restorations used a conventional 2-retainer design and another 24 restorations used a cantilevered single-retainer design. Subgroups of 8 specimens were subjected to a quasi-static load in the direction of the long axis of the abutments (0 degrees) or in an angle of 45 degrees. Additional subgroups were subjected to dynamic loading under 45 degrees with either 50 or 25 N in a dual-axis chewing simulator until fracture.

RESULTS

Mean fracture strengths, under 45-degree quasi-static loading, were between 134 and 174 N and under 0-degree loading about 233 N. Samples subjected to dynamic loading fractured after 25 to over 200,000 loading cycles.

CONCLUSION

Direction of loading exhibited a significant influence on the fracture strength, regardless of the retainer design. The applied dynamic loading force, regardless of the retainer design, had a significant influence on the loading cycles until fracture.

The fatigue strength of the interface between Ag-Pd alloy and hydrothermal ceramic

OBJECTIVE

The purpose of this paper was to investigate the fatigue strength of a hydrothermal ceramic fused to Ag-Pd alloy. This study compared the values with those of other metal-ceramic systems previously reported by other authors.

METHODS

This investigation was performed on 48 specimens made of Ag-Pd alloy frames (45 x 12 x 4 mm) on which the hydrothermal ceramic was fused (25 x 12 x 2 gmm). The specimens were divided into two groups. The first group of specimens was dynamically loaded immediately after casting and fusing, while the other group of specimens was thermocycled (1000 times at 0 degree C and 55 degrees C) before dynamic loading. The dynamic loading tests were carried out by using a modified three-point load method in a universal testing machine.

RESULTS

The determined dynamic loading limit was up to 550 N for thermocycled, and up to 850 N for non-thermocycled specimens. These results are very respectable in comparison with other metal-ceramics. A statistically significant difference between maximal dynamic forces and number of loading cycles for thermocycled and non-thermocycled samples was determined.

SIGNIFICANCE

From the data obtained in this study and current literature profiles, it is concluded that the tested metal-ceramic system is more durable than other metal-ceramic systems.

Bonding to alumina ceramic in restorative dentistry: clinical results over up to 5 years

OBJECTIVES

The purpose of this clinical pilot study was to evaluate the resin bond to alumina ceramic in vivo when using a bonding method which had been shown to be successful in laboratory testing.

METHODS

Seventeen resin-bonded all-ceramic bridges and splints fabricated from a glass-infiltrated alumina ceramic were tribochemically silica coated and resin bonded to their abutment teeth. The patients were recalled every 6 months to evaluate the restorations with regard to function and possible failures.

RESULTS

Over a mean observation time of 3.8 +/- 1.6 years some ceramic fractures occurred. However, the resin bond between the teeth and the alumina ceramic always remained stable.

CONCLUSIONS

Silica coating of alumina ceramic resulted in a durable resin bond over up to 5 years.

Perspectives on strength

Strength values are often relied upon as indicators of structural performance for brittle dental materials. Strength, however, is more of a "conditional" than an inherent material property, and strength data alone cannot be directly extrapolated to predict structural performance. Strength data are meaningful when placed into context via knowledge of material microstructure, processing history, testing methodology, testing environment and failure mechanism(s). Structure failure is determined by additional failure probability variables (in concert with strength) that describe stress distributions, flaw size distributions, and that can account for either single or multiple failure modes. Lifetime predictions require additional information about the time dependence of slow crack growth. Basic fracture mechanics principles and Weibull failure modeling will be reviewed for the perspective they provide in understanding strength and the data obtained using various laboratory tests. Examples will be given to demonstrate how failed specimens can provide crucial information to either validate or question the failure mechanisms invoked during laboratory testing. The role of interfacial stresses is discussed as applied to dental structures of current interest. Overall, it is emphasized that an understanding of actual clinical failure modes is absolutely necessary before results of in vitro strength testing can be considered to have clinical validity.