Static strength of molar region direct technique glass fibre-reinforced composite fixed partial dentures

The aim of this study was to determine static fracture force of fibre-reinforced composite (FRC) fixed partial dentures (FPD) with different retainer designs. The fabrication simulated the process to make directly made 3-unit maxillary molar FPD. Four types of retainers were tested (n = 5): conventional crown preparation (1.2 mm axially and 2.0 mm occlusally), slot preparation (3.5 mm high x 3.5 mm wide x 1 mm deep), no preparation with broad fibre abutment contact, and combination of the slot and broad fibre contact were performed. The FPD contained unidirectional E-glass FRC veneered with particulate reinforced composite. Dimensions of the FPDs were homogenized. FPDs were stored at 1 week 37 degrees C deionized water, thermocycled between 5 degrees C and 55 degrees C (5000 cycles, dwell time 10 s) and statically loaded to failure. The slot retainer design yielded the lowest mean load to initial and final failure (FF) (1284 and 1313 N, respectively), the crown retainer the highest mean load to initial failure at 1755 N, and the combination retainer resulted in the highest mean load to FF (1836 N) (anova, P < 0.001; Tukey multiple comparisons, 0.05 significance level). The results of this study suggest that the fabrication of direct FRC FPD does not necessarily require extensive preparation for the retainers.     

Structural optimization of the fibre-reinforced composite substructure in a three-unit dental bridge

IntroductionFailures of fixed partial dentures (FPDs) made of fibre-reinforced composites (FRC) have been reported in many clinical and in vitro studies. The types of failure include debonding at the composite-tooth interface, delamination of the veneering material from the FRC substructure and fracture of the pontic. The design of the FRC substructure, i.e. the position and orientation of the fibres, will affect the fracture resistance of the FPD.ObjectivesThe purpose of this study was to find an optimal arrangement of the FRC substructure, by means of structural optimization, which could minimize the failure-initiating stresses in a three-unit FPD.MethodsA structural optimization method mimicking biological adaptive growth was developed for orthotropic materials such as FRC and incorporated into the finite element (FE) program ABAQUS. Using the program, optimization of the fibre positions and directions in a three-unit FPD was carried out, the aim being to align the fibre directions with those of the maximum principal stresses. The optimized design was then modeled and analyzed to verify the improvements in mechanical performance of the FPD.ResultsResults obtained from the optimization suggested that the fibres should be placed at the bottom of the pontic, forming a U-shape substructure that extended into the connectors linking the teeth and the pontic. FE analyses of the optimized design indicated stress reduction in both the veneering composite and at the interface between the veneer and the FRC substructure.SignificanceThe optimized design obtained using FE-based structural optimization can potentially improve the fracture resistance of FPDs by reducing some of the failure-initiating stresses. Optimization methods can therefore be a useful tool to provide sound scientific guidelines for the design of FRC substructures in FPDs.     

Fiber-reinforced composite in fixed prosthodontics

Fiber reinforced composite (FRC) is composed of resin matrix and fibers filler. Common types of fibers: polyethylene, carbon and glass. Fibers can be continuous and aligned, discontinuous and aligned, discontinuous and randomly oriented. The architecture of the fibers is unidirectional, woven or braided. The two main types are: dry fibers or impregnated. Inclusion of fibers to resin composite increased its average flexural strength in 100-200 MPa. FRC can be utilized by the dentist in direct approach (splinting, temporary winged bridge) or indirect approach (laboratory made fixed partial denture). Laboratory fixed partial denture (FPD) is made from FRC substructure and Hybrid/Microfill particulate composite veneer. Main indications: interim temporary FPD or FPD in cases of questionable abutment teeth, in aesthetic cases where All Ceram FPD is not feasible. Retention is attained by adhesive cementation to minimally prepared teeth or to conventionally prepared teeth; other options are inlay-onlay bridges or hybrid bridges. Contraindications are: poor hygiene, inability to control humidity, parafunction habits, and more than two pontics. Survival rate of FRC FPD over 5 years is 75%, lower compared to porcelain fused to metal FPD which is 95%. Main reasons for failure are: fracture of framework and delamination of the veneer. Part of the failures is repairable.     

Effect of fiber position and orientation on fracture load of fiber-reinforced composite

OBJECTIVES: The aim of this study was to determine the effect of fiber position and orientation on the initial and final fracture loads of fiber-reinforced composite (FRC). METHODS: Test specimens made of two indirect particulate composites (BelleGlass HP, Kerr, Orange, CA) or (Targis, Ivoclar Vivadent, Amherst, NY) were reinforced with ultra high molecular weight polyethylene (UHMWPE) fiber ribbon (Connect, Kerr, Orange, CA), woven E-glass fibers (Vectris Frame, Ivoclar Vivadent, Amherst, NY) or unidirectional R-glass fibers (Vectris Pontic, Ivoclar Vivadent, Amherst, NY). Fibers were placed with different positions, orientations or geometry into the rhombic test specimens (2 x 2 x 25 mm3). Control specimens did not contain fiber reinforcement. The test specimens (n=6) were stored in distilled water for 1 week at 37 degrees C before testing in a three-point loading test to determine the initial and final fracture load values. RESULTS: Initial failure loads varied from 22.6 to 172.1 N. The lowest value resulted from one UHMWPE reinforcement fiber located in diagonal orientation and the highest from two unidirectional glass fiber reinforcements, one located on the tension side and the second on the compression side. SIGNIFICANCE: Position and fiber orientation influenced the load to initial and final failure, and specimen deflection. Tension side reinforcement was most effective in increasing the load to initial and final fracture.     

Fracture strength of fiber-reinforced surface-retained anterior cantilever restorations

PURPOSE: This study compared the fracture strength of direct anterior cantilever fiber-reinforced composite (FRC) fixed partial dentures (FPD) reinforced with 3 types of E-glass fibers preimpregnated with either urethane tetramethacrylate, bisphenol glycidylmethacrylate/polymethyl methacrylate, or bisphenol glycidylmethacrylate monomers and 1 ultrahigh molecular weight polyethylene fiber. Failure types were also evaluated. MATERIALS AND METHODS: A total of 40 caries-free, human maxillary central incisors (n = 10 per group) received surface-retained direct cantilever restoration (1 pontic) after etching and application of bonding agent. Four FRC materials were used (FRC1 = EverStick; FRC2 = BR-100; FRC3 = Interling; FRC4 = Ribbond), and pontics were built up using 1 particulate filler composite (Clearfil Photo Posterior). After the fracture test, failure types were analyzed. RESULTS: No significant difference was found between the 4 FRC types veneered with particulate filler composite (893 +/- 459 N to 1326 +/- 391 N) (P = .1278). Complete pontic fracture at the connector area was most prominent for FRC4 (90%), followed by FRC3 (70%). Only FRC2 (10%) showed some fiber fractures, with half of the fiber remaining attached on the enamel surface of the abutment. CONCLUSION: The fracture strengths of cantilever FPDs made of 4 FRC materials with different monomer matrices and architectures, veneered with particulate filler composite, did not show significant differences. However, failure behavior varied between groups.     

Short fiber reinforced composite in restoring severely damaged incisors

Abstract

Objective. To evaluate the static-load-bearing capacity of severely damaged endodontically-treated incisors restored with short fiber composite (SFC) as a direct post-core-crown complex and to investigate the effect of SFC on the failure mode of the restorations. Materials and methods. The clinical crowns of 40 maxillary incisors were prepared by cutting 2/3 parts of the crown horizontally. Five groups were fabricated (n = 8) using the direct technique; Group A: Crown restorations from conventional composite (CC); Group B: FRC-posts with core-crown restorations from CC; Group C: Crown restorations from SFC; Group D: FRC-posts and core-crown restorations from SFC; Group E: Post–core-crown restorations from SFC. The posts were cemented with dual-cure resin cement. The restorations were polymerized with a hand-light curing unit. All restored teeth were stored in distilled water at 37°C for 5 days before they were statically loaded. Initial fracture (IF) and final fracture (FF) were recorded. Failure modes were visually examined. Results. ANOVA revealed that SFC restorations had greater IF (469.8 N) and FF load values (515.8 N) (p < 0.05) than the CC restorations (164.8 N). No significant difference for both IF and FF was observed among groups C, D and E. Group E revealed a more favorable fracture mode than any other material combination used. Conclusion. The use of SFC as a restorative material for fabricating the direct composite post-core-crown restorations of severely damaged incisors provided improved load-bearing capacity than CC used alone or with FRC post reinforcement.     

In Vitro Evaluation of Shear Bond Strength and Mode of Failure of the Interface between an Indirect Composite Bonded to Fiber-Reinforced Composite Substructures

Purpose: Failures of fixed partial dentures (FPDs) fabricated with fiber-reinforced composites (FRCs) have been attributed to veneering fractures. The aim of the present study was to investigate the shear bond strength and mode of failure between an indirect composite and FRC substructures. Material and Methods: SR Adoro indirect composite was bonded to the following substructures: (a) flat surface made of unidirectional glass fibers (group A), (b) retentive sticks made of unidirectional glass fibers (group B), (c) flat surface made of fiber net (group C), (d) retentive sticks made of fiber net (group D), (e) nickel-chromium dental alloy (control, group E). For every group, 13 specimens were fabricated. All specimens were hydrothermocycled (5000 cycles, 5°C/30sec, and 55°C/30sec). A bond test was performed in a testing machine at a 0.5 mm/min crosshead speed according to ISO 10477. The failure mode was determined by examination of the fractured surfaces under an optical microscope. Selected specimens were examined with scanning electron microscope and with energy dispersive spectroscopy for compositional determination. The morphology (flat-sticks) and the type (unidirectional-net) of fibers on the bond strength were estimated. Results: The mean shear bond strength was significantly different between groups E and A (p= 0.044), and groups A and B (p= 0.010). All FRC specimens showed cohesive failure. Group E showed predominantly adhesive failure. The bond strength was higher when sticks or fiber nets were used. Conclusions: Fiber nets and retentive sticks increase the shear bond strength between FRCs and indirect composite. Clinical implications: In FPDs, the morphology and type of FRC substructures might influence the shear bond strength between the FRC substructure and the indirect veneering composite. With the proper design of these substructures, the number of veneering fractures may be decreased.     

Fiber-reinforced composite substructure: load-bearing capacity of an onlay restoration and flexural properties of the material

AIM: The aim of this study was to determine the static load-bearing capacity of composite resin onlay restorations made of particulate filler composite (PFC) with two different types of fiber-reinforced composite (FRC) substructures. In addition, flexural properties of the material combination and the effect of polymerization devices were tested. METHODS AND MATERIALS: Specimens were prepared to simulate an onlay restoration, which consisted of 2 to 3 mm of FRC layer as a substructure (short random and continuous bidirectional fiber orientation) and a 1 mm surface layer of PFC. Control specimens were prepared from plain PFC. In Group A the specimens were incrementally polymerized only with a hand-light curing unit for 40 s, while in Group B the specimens were post-cured in a light-curing oven for 15 min before they were statically loaded with a steel ball. Bar-shaped test specimens were prepared to measure the flexural properties of material combination using a three-point bending test (ISO 10477). RESULTS: Analysis of variance (ANOVA) revealed all specimens with a FRC substructure have higher values of static load-bearing capacity and flexural properties than those obtained with plain PFC (p<0.001). CONCLUSION: The load-bearing capacity of all the specimens decreased after post-curing and water storage. Restorations made from a material combination of FRC and PFC showed better mechanical properties than those obtained with plain PFC.     

Fiber-reinforced composite substructure: load-bearing capacity of an onlay restoration

OBJECTIVE: To determine the static load-bearing capacity of composite resin onlay restorations made of particulate filler composite (PFC) with two different types of fiber-reinforced composite (FRC) substructures. MATERIAL AND METHODS: Specimens were prepared to simulate an onlay restoration, composed of a 2 to 3 mm FRC layer as the substructure (short random and continuous bidirectional fiber orientation) and a 1 mm surface layer of PFC. Control specimens were prepared from plain PFC. The specimens were incrementally polymerized with a hand-light curing unit for 40 s and then post-cured in a light-curing oven for 15 min. The specimens were cemented on dentin substrate of extracted human molars using a standard adhesive resin cementation technique. The specimens (n=8/group) were water stored either for 24 h at room temperature or for 4 weeks at 37 degrees C before they were statically loaded until fracture using a universal testing machine. Failure modes were visually examined. RESULTS: ANOVA revealed that all specimens with FRC substructures had higher values of static load-bearing capacity than those obtained with plain PFC (p<0.001). The load-bearing capacity of all the specimens decreased after water storage (p<0.001). CONCLUSIONS: Restorations made from a combination of FRC and PFC showed better load-bearing capacity than those obtained with PFC alone.     

Fracture strength of direct surface-retained fixed partial dentures: effect of fiber reinforcement versus the use of particulate filler composites only

This study compared the fracture strengths and analyzed the failure types of direct, surface-retained, anterior fixed-partial-dentures (FPD), reinforced with four types of fiber-reinforced composites (FRC) versus non-fiber-reinforced FPDs made of three particulate filler composites (PFC). To this end, surface-retained anterior FPDs (N = 70, 10 per group) were prepared and divided into seven experimental groups, where Group 1: FRC1 (everStick) + PFC1 (Clearfil Photo Posterior); Group 2: FRC2 (BR 100) + PFC1; Group 3: FRC3 (Interling) + PFC1; Group 4: FRC4 (Ribbond) + PFC1; Group 5: PFC1 only; Group 6: PFC2 only (Sinfony); and Group 7: PFC3 only (Estenia). Fracture strength test was performed after water storage at 37 degrees C for three days (universal testing machine, 1 mm/min). No significant differences were found among the four FRC types veneered with PFC1 (1490 +/- 548--1951 +/- 335 N) (p < 0.05) (ANOVA, Tukey's test). Among all the experimental groups, PFC1 presented a significantly higher mean value (2061 +/- 270 N) than PFC2 (1340 +/- 395 N) (p < 0.05) and all the other FRC-reinforced groups (p < 0.05). Complete pontic fracture was 100% and 70% for PFC2 and PFC3 respectively.     

Reinforcement effect of adhesively luted fiber reinforced composite versus titanium posts.

OBJECTIVE: The aim of the present study was to investigate the influence of the rigidity of different post materials (titanium versus glass fiber reinforced composite [FRC]) on the fracture resistance of endodontically treated teeth (ETT). METHOD: Forty-eight caries-free maxillary central incisors were randomly assigned to six groups (n=8). After endodontic treatment, teeth of four groups were flattened 2mm above and two groups at the cemento-enamel junction (CEJ). As control, specimens of one group received neither composite build-up nor post, and teeth were left empty (E). In another group only a resin composite build-up was placed (C). In two groups, both titanium and FRC posts were inserted. One group with titanium (2/T) and FRC (2/FRC) post received a 2mm deep ferrule preparation. For one group with titanium (0/T) and FRC (0/FRC) post no ferrule design was provided. All-ceramic crowns were adhesively luted on all specimens. Specimens were exposed to thermomechanical loading and finally statically loaded until failure. RESULTS: The median fracture load values (min-max) were: E=317 (242-404); C=387 (335-475); 0/FRC=352 (0-440); 2/FRC=502 (326-561); 0/T=420 (0-548), 2/T=517 (416-653). Statistically significant differences were computed between E, C, 2/FRC, 0/T and 2/T; between C, 2/FRC and 2/T; between 0/FRC, 2/FRC and 2/T; between 0/T and 2/T regarding maximum fracture load. SIGNIFICANCE: Fracture resistance of ETT is not influenced by the rigidity of the post material. The combination of ferrule preparation and endodontic post results in higher load resistance after TML than any other build-up design.     

Load bearing capacity of fibre-reinforced and particulate filler composite resin combination

OBJECTIVES: Longevity of particulate filler resin (PFR) is controversial for large restorations with high occlusal-stresses. The aim of this study was to reinforce PFR with fiber reinforced composite (FRC) and to evaluate the effect of thickness of FRC substructure and thickness of overlaying PFR, on the static load-bearing capacity of the material combination. METHODS: A total of 336 test specimens having a FRC substructure (short random or continuous bidirectional fibre orientation) and layer of restorative PFR were prepared for this study. In Group A, the specimens contained short random oriented fibres (length: 2-3mm) and in Group B, there were continuous bidirectionally oriented fibres. The specimens (n = 12/group) were polymerized with a hand light-curing unit and were either dry-stored or thermocycled before they were statically loaded with a steel ball until fracture, using a universal testing machine. RESULTS: Increase the volume fraction of the short random FRC versus the fraction of PFR, the load-bearing capacity of the specimen increased (p < 0.001). Short random FRC revealed significantly different behavior than the bidirectionally oriented FRC (p < 0.001). By combining the FRC layer of 0.5mm in thickness with a layer of 2.5mm of PFR gave load values of 1462N and 1196N, which were considerably higher than values for plain PFR of 3mm in thickness (782N and 729N). CONCLUSION: The results suggest that by adding a FRC substructure under the PFR, the load-bearing capacity of the material combination was increased.     

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.     

Does the thickness of the resin cement affect the bond strength of a fiber post to the root dentin?

This study aimed to evaluate the influence of cement thickness on the bond strength of a fiber-reinforced composite (FRC) post system to the root dentin. Eighteen single-rooted human teeth were decoronated (length: 16 mm), the canals were prepared, and the specimens were randomly allocated to 2 groups (n = 9): group 1 (low cement thickness), in which size 3 FRC posts were cemented using adhesive plus resin cement; and group 2 (high cement thickness), in which size 1 FRC posts were cemented as in group 1. Specimens were sectioned, producing 5 samples (thickness: 1.5 mm). For cement thickness evaluation, photographs of the samples were taken using an optical microscope, and the images were analyzed. Each sample was tested in push-out, and data were statistically analyzed. Bond strengths of groups 1 and 2 did not show significant differences (P = .558), but the cement thicknesses for these groups were significantly different (P < .0001). The increase in cement thickness did not significantly affect the bond strength (r2 = 0.1389, P= .936). Increased cement thickness surrounding the FRC post did not impair the bond strength.     

The effect of box preparation on the strength of glass fiber-reinforced composite inlay-retained fixed partial dentures

STATEMENT OF PROBLEM: Nonstandardized box dimensions for inlay-retained fixed partial dentures (FPDs) may result in uneven distribution of the forces on the connector region of such restorations. PURPOSE: The objective of this in vitro study was to evaluate the effect of box dimensions on the initial and final failure strength of inlay-retained fiber-reinforced composite (FRC) FPDs. MATERIAL AND METHODS: Twenty-one inlay-retained FPDs were prepared using FRC (everStick) frameworks with unidirectional fiber reinforcement between mandibular first premolars and first molars. Boxes were prepared using conventional inlay burs (Cerinlay), and small and large ultrasonic tips (SONICSYS approx). Box dimensions were measured after preparation with a digital micrometer. All restorations were subjected to thermal cycling (6000 cycles, 5 degrees C-55 degrees C). Fracture testing was performed in a universal testing machine (1 mm/min). Acoustic emission signals were monitored during loading of the specimens. Initial and final fracture strength values (2-way ANOVA, Bonferroni post hoc tests, alpha =.05) and failure types (Fisher exact test) were statistically compared for each group. RESULTS: Significant differences (P =.0146 and P =.0086) were observed between the groups in the dimensions of the boxes prepared using conventional burs buccolingually (2.8-3.0 mm in molars, 3.1-4.3 mm in premolars) and the small size (2.5-2.9, 2.9-3.8 mm) or large size (2.6-3.8, 3.2-4.9 mm) ultrasonic tips for the premolars and the molars, respectively. No significant differences were found at the initial and final failures between the conventionally prepared group (842 +/- 267 N, 1161 +/- 428 N) and those prepared with either small (1088 +/- 381 N, 1320 +/- 380 N) or large ultrasonic tips (1070 +/- 280 N, 1557 +/- 321 N), respectively. The failure analysis demonstrated no significant difference in failure types but predominant delamination of the veneering resin (85%) in all experimental groups. According to acoustic emission tests, a higher energy level was required for final failure of the FRC FPDs with boxes finished using small ultrasonic tips. CONCLUSION: Standardized box dimensions showed no significant effect on fracture strength at either initial or final failure of the fiber-reinforced FPDs. The FRC FPDs with boxes refined with small ultrasonic burs required a greater energy level before failure. The type of failure observed after the fracture tests was primarily delamination of the veneering resin.     

Comparison of Repair Methods for Ceramic-Fused-to-Metal Crowns

PURPOSE: The objective of this study was to evaluate the effect of four repair methods on the fracture load of repaired ceramic-fused-to-metal crowns. MATERIALS AND METHODS: Metal-ceramic crowns were fractured, and the failure load was measured. The fractured metal-ceramic crowns (n = 9) were assigned randomly to the following treatment groups: (1) hydrofluoric acid (9.5%) etching, (2) air-particle abrasion (50 microm Al(2)O(3)), (3) silica coating (30 microm SiO(x)), and (4) the application of a layer of glass fiber-reinforced composite (FRC) (thickness: 0.12 mm) on the repair surface. The crowns were repaired with a highly filled resin composite and subjected to 3 repair cycles (n = 27). All specimens were stored in water at 37 degrees C for 24 hours and then thermocycled (6000 cycles, 5 degrees C to 55 degrees C). The fracture load values for final failure of intact and repaired crowns were measured with a universal testing machine, and failure types were recorded. RESULTS: No significant differences (p > 0.05) were found between the final failure values for the groups treated with 9.5% hydrofluoric acid (376 N) and airborne particle abrasion with either Al(2)O(3) (432 N) or SiO(x) (582 N) followed by silanization, respectively. Significantly, higher (p < 0.0001) final failure values (885 N) were obtained with the use of the FRC layer when compared with the other repaired groups. There was no significant difference (p > 0.05) between the final fracture load of intact crowns (872 N) and those repaired with FRC (885 N) (One-way ANOVA with repeated measures, Bonferroni test). No significant difference in fracture loads was found between the 1st, 2nd, and 3rd repair cycles (558 N, 433 N, 485 N, respectively). Failure sites were predominantly at the alloy/veneering resin interface in Group 1; Groups 2 and 3 both showed more cohesive failures than Group 1. In the case of FRC, the failure pattern was exclusively cohesive between the two laminates of FRC layer. CONCLUSIONS: The conditioning methods (Groups 1 to 3) of the repair surfaces did not show differences between each other; each resulted in mean fracture loads at lower levels than that of the intact crowns. Addition of an FRC layer increased the fracture load to the level of intact crowns. This suggests that the use of FRC in repairs of metal-ceramic crowns might be a viable option.     

Acoustic emission analysis of fiber-reinforced composite in flexural testing.

OBJECTIVES: The aim of this study was to examine the emission of acoustic signals from six commercially available fiber-reinforced composites (FRC) used in the frameworks of fixed partial dentures in material bending. METHODS: FRC test specimens were made of six commercially available fiber products of polyethylene or glass and five light-curing resins. FRC test specimens were polymerized with a hand light-curing unit or with a light-curing oven. The flexural test for determination of ultimate flexural strength of test specimens (n = 6) was based on the ISO 10477 standard after the specimens were stored in air or in water for two weeks. The acoustic emission (AE) signals were monitored during three-point loading test of the test specimens using a test with increasing loading levels until the specimens fractured. RESULTS: Generally, stress level required for the AE activity initiation ranged from 107 MPa (Ribbond) to 579 MPa (everStick). The ultimate flexural strength of FRC specimens were higher, ranging from 132 to 764 MPa, being highest with everStick and Vectris FRC, and lowest with Ribbond FRC. ANOVA showed a statistically significant difference between the initiation of AE activity and the ultimate flexural strength according to the brand (p < 0.001) storing conditions (p < 0.001) and polymerization procedure (p < 0.001). AE activity and ultimate flexural strength correlated significantly (p < 0.010, r = 0.887). SIGNIFICANCE: The result of this study suggested that AE activity in FRC specimens started at a 19-32% lower stress level than occurred at final fracture.     

Static and fatigue compression test for particulate filler composite resin with fiber-reinforced composite substructure.

OBJECTIVES: The aim of this study was to determine static load-bearing capacity and compressive fatigue limits (CFL) of laboratory particulate filler composite resin (PFC) with three different types of fiber-reinforced composite (FRC) substructures. METHODS: A total of 420 test specimens were prepared having 1.0mm of FRC layer as substructure (short random, continuous unidirectional and bidirectional fiber orientations), and a 2.0-mm thick surface layer of PFC. Control specimens were prepared from plain FRC or PFC. The specimens (n=15) were either dry stored or water stored (37 degrees C for 2 weeks) before they were loaded with a steel ball (? 3.0mm) under static load until fracture and cyclic load with maximum controlled regimen following a staircase approach with maximum 10(3) cycles. The decrease in CFL compared to static load was calculated and data were analyzed using ANOVA and Weibull statistics. RESULTS: The highest static loads were registered for plain FRC specimens [short random 1842 N(205), continuous bidirectional 2258 N(233) and unidirectional fiber orientation 538 N(254)]. The specimens with FRC substructure and PFC coverage gave load values of 1517 N(249), 1670 N(241) and 677 N(240), respectively. The specimens made of PFC only, failed with 1047 N(230) load. The CFL for 10(3) cycles ranged between 19 and 39% of the static load values. ANOVA revealed that all factors significantly affected the load bearing capacity (p<0.001). SIGNIFICANCE: The results suggested that the material combination of continuous bidirectional or random FRC and PFC, gave higher CFL and static load-bearing capacity than that obtained with plain particulate filler composite resin.     

The effect of alveolar bone loss on the load capability of restored endodontically treated teeth: a comparative in vitro study

OBJECTIVES: The aim of the present investigation was to study the influence of a reduced bone support on the fracture resistance of endodontically treated teeth restored with glass fibre-reinforced posts (FRC). METHODS: 30 caries-free maxillary central incisors were divided into 3 groups (n=10). Endodontic treatment was performed. Teeth were flattened 2 mm above the cemento-enamel junction. Group I (control) simulated a clinical situation without horizontal bone loss. In group II a horizontal bone loss of 25% and in group III of 50% was simulated. All specimens received FRC posts and composite core restorations. All-ceramic crowns were adhesively cemented. Specimens were exposed to thermal cycling and mechanical loading (TCML) and finally statically loaded until failure in a universal testing machine (v=1 mm/min). Non-parametric tests were used to compare median fracture loads between groups. Fracture modes were compared using Fisher's exact test. RESULTS: The median fracture load values (min/max) in [N] were: group I=501 (326/561), group II=422 (323/495); group III=352 (266/406), p=0.004. Two specimens in each group II and III failed during TCML. Statistical analysis revealed statistically significant differences between all test groups regarding maximum fracture load and mode of fracture. CONCLUSIONS: The fracture resistance of endodontically treated teeth restored adhesively with a FRC post, composite core, and all-ceramic crown is dependent on the level of surrounding supporting periodontal bone. Loss of alveolar bone loss due to periodontal disease may lead to an increased risk of failure.     

Bonding of fibre-reinforced composite post to root canal dentin

OBJECTIVE: The aim of this study was to determine bonding properties of two types of fibre-reinforced composite (FRC) posts cemented into root canals of molars. Serrated titanium posts served as reference. METHODS: Prefabricated carbon/graphite FRC posts with cross-linked polymer matrix and individually formed glass FRC posts with interpenetrating polymer network (IPN) polymer matrix were compared. The crowns of extracted third molars were removed and post space (diameter: 1.5mm) was drilled, etched and bonded. The posts were treated with dimethacrylate adhesive resin, light-polymerized and cemented with a dual-polymerizing composite resin luting cement. After thermocycling (6000x) the samples were cut into discs of thicknesses: 1, 2 and 4mm (n=12/group). Push-out force was measured by pushing the post from one end. Assessment of failure mode was made under a stereomicroscope (1, adhesive failure between post and cement; 2, cohesive failure of post-system; 3, adhesive failure between cement and dentin). RESULTS: The push-out force increased with increased height of dentin disc in all groups (ANOVA, p<0.001). In the 4mm thick dentin discs the individually formed glass FRC posts showed highest push-out force and the difference to that of the titanium posts was significant (ANOVA, p<0.001). The other differences were not statistically significant. None of the individually formed glass FRC posts showed adhesive failures between the post and the cement. CONCLUSIONS: Contrary to the other posts, there were no adhesive (post-cement) failures with the individually formed glass FRC posts, suggesting better interfacial adhesion of cement to these posts.