Pasi Alander

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.

Evaluation of some properties of two fiber-reinforced composite materials

Objective. Water sorption, flexural properties, bonding properties, and elemental composition of photopolymerizable resin-impregnated fiber-reinforced composite (FRC) materials (everStick C&B and BR-100) (FPD) were evaluated in this study. Material and methods. Bar-shaped specimens (2×2×25 mm) were prepared for water sorption and flexural strength testing. The specimens (n=6) were polymerized either with a hand light-curing unit for 40 s or, additionally, in a light-curing oven for 20 min and stored in water for 30 days. Water sorption was measured during this time, followed by measurements of flexural strength and modulus. A shear bond strength test was performed to determine the bonding characteristics of polymerized FRC to composite resin luting cement (Panavia-F), (n=15). The cement was bonded to the FRC substrate and the specimens were thermocycled 5000 times (5–55°C) in water. SEM/EDS were analyzed to evaluate the elemental composition of the glass fibers and the fiber distribution in cross section. Results. ANOVA showed significant differences in water sorption according to brand (p<0.05). Water sorption of everStick C&B was 1.86 wt% (hand-unit polymerized) and 1.94 wt% (oven polymerized), whereas BR-100 was 1.07 wt% and 1.17 wt%, respectively. The flexural strength of everStick C&B after 30 days’ water storage was 559 MPa (hand-unit polymerized) and 796 MPa (oven-polymerized); for BR-100, the values were 547 MPa and 689 MPa, respectively. Mean shear bond strength of composite resin cement to the FRC varied between 20.1 and 23.7 MPa, showing no statistical difference between the materials. SEM/EDS analysis revealed that fibers of both FRC materials consist of the same oxides (SiO2, CaO, and Al2O3) in ratios. The distribution of fibers in the cross section of specimens was more evenly distributed in everStick C&B than in BR-100. Conclusion. The results of this study suggest that there are some differences in the tested properties of the FRC materials.

Repair of bone segment defects with surface porous fiber‐reinforced polymethyl methacrylate (PMMA) composite prosthesis: Histomorphometric incorporation model and characterization by SEM

Background and purpose Polymer technology has provided solutions for filling of bone defects in situations where there may be technical or biological complications with autografts, allografts, and metal prostheses. We present an experimental study on segmental bone defect reconstruction using a polymethylmethacrylate‐(PMMA‐) based bulk polymer implant prosthesis. We concentrated on osteoconductivity and surface characteristics. Material and methods A critical size segment defect of the rabbit tibia in 19 animals aged 18–24 weeks was reconstructed with a surface porous glass fiber‐reinforced (SPF) prosthesis made of polymethylmethacrylate (PMMA). The biomechanical properties of SPF implant material were previously adjusted technically to mimic the properties of normal cortical bone. A plain PMMA implant with no porosity or fiber reinforcement was used as a control. Radiology, histomorphometry, and scanning electron microscopy (SEM) were used for analysis of bone growth into the prosthesis during incorporation. Results The radiographic and histological incorporation model showed good host bone contact, and strong formation of new bone as double cortex. Histomorphometric evaluation showed that the bone contact index (BCI) at the posterior surface interface was higher with the SPF implant than for the control. The total appositional bone growth over the posterior surface (area %) was also stronger for the SPF implant than for controls. Both bone growth into the porous surface and the BCI results were related to the quality, coverage, and regularity of the microstructure of the porous surface. Interpretation Porous surface structure enhanced appositional bone growth onto the SPF implant. Under load‐bearing conditions the implant appears to function like an osteoconductive prosthesis, which enables direct mobilization and rapid return to full weight bearing.

Bonding of ceramic insert to a laboratory particle filler composite

The push-out bond strength of cylindrical ceramic inserts (CI) to particulate filler resin composite (VC) was evaluated in this study. Various surface treatments to improve the adhesion of CI to resin composite were tested. Additionally, the effect of fiber-reinforced composite (FRC) laminate encapsulation around CI was tested. Feldspathic porcelain CI with a diameter of 3.1 mm was bonded to VC. Adhesive resin was used for bonding. In group 1, no surface treatment of CI was done. In group 2, CI was encapsulated with a thin layer of woven glass FRC. In group 3, the surface of the CI was tribochemically silica coated and silanized. In group 4, the surface of the CI was grit-blasted with 50 μm aluminum oxide and etched with hydrofluoric acid. In group 5, the grit-blasted CI was encapsulated with a layer of FRC. The specimens (n=6/group) were either dry stored or thermocycled in water (6000×5–55°C). The push-out test was carried out with a universal material testing machine. The highest push-out strength was achieved in group 5 (20.4 MPa) and the lowest in group 2 (11.5 MPa). ANOVA revealed that both surface treatment and storage condition had a significant effect on push-out strength (p<0.05). We conclude that the additional glass FRC encapsulation can be used to increase the bond strength of insert to composite.