Lippo V.J. Lassila

Flexural properties of fiber reinforced root canal posts

OBJECTIVES Fiber-reinforced composite (FRC) root canal posts have been introduced to be used instead of metal alloys and ceramics. The aim of this study was to investigate the flexural properties of different types of FRC posts and compare those values with a novel FRC material for dental applications. METHODS Seventeen different FRC posts of various brands (Snowpost, Carbopost, Parapost, C-post, Glassix, Carbonite) and diameters, (1.0-2.1 mm) and a continuous unidirectional E-glass FRC polymerized by light activation to a cylindrical form (everStick, diameter 1.5 mm) as a control material were tested. The posts (n=5) were stored at rooms humidity or thermocycled (12.000 x, 5 degrees C/55 degrees C) and stored in water for 2 weeks before testing. A three-point bending test (span=10 mm) was used to measure the flexural strength and modulus of FRC post specimens. RESULTS Analysis of ANOVA revealed that thermocycling, brand of material and diameter of specimen had a significant effect (p<0.001) on the fracture load and flexural strength. The highest flexural strength was obtained with the control material (everStick, 1144.9+/-99.9 MPa). There was a linear relationship between fracture load and diameter of posts for both glass fiber and carbon fiber posts. Thermocycling decreased the flexural modulus of the tested specimens by approximately 10%. Strength and fracture load decreased approximately 18% as a result of thermocycling. SIGNIFICANCE Considerable variation can be found in the calculated strength values of the studied post brands. Commercial prefabricated FRC posts showed lower flexural properties than an individually polymerised FRC material.

The semi-interpenetrating polymer network matrix of fiber-reinforced composite and its effect on the surface adhesive properties

This aim of this study was to examine the effect of further-impregnation time of polymer pre-impregnated fiber-reinforcement on polymer matrix structure of the fiber-reinforced composite (FRC) used in dental applications. In addition, shear bond strength between the FRC and veneering composite after various length of further-impregnation was studied. Polymethyl methacrylate (PMMA) pre-impregnated glass fiber-reinforcement was further-impregnated with a diacrylate monomer resin by using five lengths of further-impregnation from 10 min to 24 h. The test specimens (n=5) from each five groups were treated with the solvent tetrahydrofuran and examined with a scanning electron microscope (SEM) to determinate the existence of linear PMMA in the polymer matrix of the FRC. The same lengths of further-impregnation were used to form an adhesive substrate for veneering composite and to measure the shear bond strength (n=8). The SEM examination showed that linear PMMA-polymer and cross-linked diacrylate polymer formed two independent networks for the polymer matrix of FRC. The highest mean shear bond strength value (18.7±2.9 MPa) was achieved when the fiber reinforcement was further-impregnated for 24 h. The shortest further-impregnation, 10 min, resulted in the lowest mean shear bond strength (12.7±2.9 MPa). A correlation between increased shear bond strength and longer further-impregnation was found (0.689, p<0.001). The results revealed that linear PMMA network of the polymer matrix of the FRC remained in the structure regardless of the various lengths of the further-impregnation with diacrylate resin.

Physical properties and depth of cure of a new short fiber reinforced composite

OBJECTIVES To determine the physical properties and curing depth of a new short fiber composite intended for posterior large restorations (everX Posterior) in comparison to different commercial posterior composites (Alert, TetricEvoCeram Bulk Fill, Voco X-tra base, SDR, Venus Bulk Fill, SonicFill, Filtek Bulk Fill, Filtek Superme, and Filtek Z250). In addition, length of fiber fillers of composite XENIUS base compared to the previously introduced composite Alert has been measured. MATERIALS AND METHODS The following properties were examined according to ISO standard 4049: flexural strength, flexural modulus, fracture toughness, polymerization shrinkage and depth of cure. The mean and standard deviation were determined and all results were statistically analyzed with analysis of variance ANOVA (a=0.05). RESULTS XENIUS base composite exhibited the highest fracture toughness (4.6MPam(1/2)) and flexural strength (124.3MPa) values and the lower shrinkage strain (0.17%) among the materials tested. Alert composite revealed the highest flexural modulus value (9.9GPa), which was not significantly different from XENIUS base composite (9.5GPa). Depth of cure of XENIUS base (4.6mm) was similar than those of bulk fill composites and higher than other hybrid composites. The length of fiber fillers in XENIUS base was longer (1.3-2mm) than in Alert (20-60μm). CONCLUSIONS The new short fiber composite differed significantly in its physical properties compared to other materials tested. This suggests that the latter could be used in high-stress bearing areas.

Dentin moisture conditions affect the adhesion of root canal sealers.

INTRODUCTION The purpose of this study was to evaluate the effects of intraradicular moisture conditions on the push-out bond strength of root canal sealers. METHODS Eighty root canals were prepared using rotary instruments and, thereafter, were assigned to 4 groups with respect to the moisture condition tested: (1) ethanol (dry): excess distilled water was removed with paper points followed by dehydration with 95% ethanol, (2) paper points: the canals were blot dried with paper points with the last one appearing dry, (3) moist: the canals were dried with low vacuum by using a Luer adapter for 5 seconds followed by 1 paper point for 1 second, and (4) wet: the canals remained totally flooded. The roots were further divided into 4 subgroups according to the sealer used: (1) AH Plus (Dentsply-Tulsa Dental, Tulsa, OK), (2) iRoot SP (Innovative BioCeramix Inc, Vancouver, Canada), (3) MTA Fillapex (Angelus Indústria de Produtos Odontológicos S/A, Londrina, Brasil), and (4) Epiphany (Pentron Clinical Technologies, Wallingford, CT). Five 1-mm-thick slices were obtained from each root sample (n = 25 slices/group). Bond strengths of the test materials to root canal dentin were measured using a push-out test setup at a cross-head speed of 1 mm/min. The data were analyzed statistically by two-way analysis of variance and Tukey tests at P = .05. RESULTS Irrespective of the moisture conditions, iRoot SP displayed the highest bond strength to root dentin. Statistical ranking of bond strength values was as follows: iRoot SP > AH Plus > Epiphany ≥ MTA Fillapex. The sealers displayed their highest and lowest bond strengths under moist (3) and wet (4) conditions, respectively. CONCLUSIONS The degree of residual moisture significantly affects the adhesion of root canal sealers to radicular dentin. For the tested sealers, it may be advantageous to leave canals slightly moist before filling.

Bonding of resin composite luting cements to zirconium oxide by two air-particle abrasion methods.

OBJECTIVE This study evaluated the shear bond strength of two resin composite luting cements to zirconium oxide ceramic substrate using two air-particle abrasion methods. METHODS Two resin composite cements, RelyX Unicem (3M ESPE) and Panavia F (Kuraray), each with an acidic composition, were used in combination with a zirconium oxide (DCS Dental AG) substrate containing Al2O3 and SiO2 (Rocatec system, 3M ESPE) and two air-particle abrasion methods. The shear bond strength of the resin composite cement to the substrate was tested after the samples were either water-stored for one week or thermocycled following 24 hours of water storage. RESULTS The RelyX Unicem resin composite cement specimens with the Rocatec treatment (20.9 +/- 4.6 Mpa and 20.1 +/- 4.2 MPa, respectively, n = 12) demonstrated the highest shear bond strength. Alternatively, the lowest values were obtained for the Panavia F resin cement samples, with Al2O3 air-particle abrasion in both storage conditions, water storage for one week (17.7 +/- 8.9MPa) or thermocycling after 24 hours of water storage (16.3 +/- 4.9 MPa). Neither storage condition or particle abrasion system significantly affected shear bond strengths (ANOVA, p > 0.05). CONCLUSION It was concluded that two different surface conditioning methods and storage conditions did not significantly affect the bonding properties of Panavia F and RelyX Unicem resin composite luting cements to Zirconia.

The effect of fiber orientation on the thermal expansion coefficients of fiber-reinforced composites

OBJECTIVES The aim of this study was to characterize the thermal expansion and dimensional changes of fiber-reinforced composite (FRC) according to the fiber orientation, brand of FRC product and polymerization conditions. METHODS Cubic specimens (n=5) were prepared from different brands of FRC and particulate filler composites and dimethacrylate monomer resin. The specimens were polymerized with a light-curing device for 40 s or additionally with prolonged polymerization in the light-curing oven for 15 min. Linear coefficients of thermal expansion (LCTE) values for different materials and for FRC with different fiber orientations were determined using a thermomechanical analyzer. RESULTS All specimens exhibited linear increase in the value of LCTE between 37 and 67 degrees C. The analysis of ANOVA revealed that orientation of fiber and brand of material had significant effect (P<0.001) on LCTE values for 37-67 degrees C interval. Some interaction between factors also existed. Also, temperature interval 110-150 degrees C had significant effect on the LCTE values according to the curing unit, brand and orientation of fibers. SIGNIFICANCE The results of this study suggest that the anisotropic nature of FRC exists also with regard to thermal expansion. The variation of LCTE of FRC compared to that of particulate filler composites might influence the interfacial adhesion of FRC appliances.

The effect of length and concentration of glass fibers on the mechanical properties of an injection- and a compression-molded denture base polymer

STATEMENT OF PROBLEM Fiber-reinforcement has been used to overcome the mechanical limitations of denture base polymers. One major difficulty in the use of fiber reinforcement has been the addition of fibers during conventional processing methods. PURPOSE This study evaluated the effect of various lengths and concentrations of chopped E-glass fiber-reinforcement on the transverse strength, modulus of elasticity, and impact strength of injection and compression-molded polymethyl methacrylate based denture base polymer. MATERIALS AND METHODS Test specimens (n=10) of 4-, 6-, and 8-mm fiber length and 1%, 3%, and 5% weight fiber concentrations were prepared with either an injection or a compression-molded processing method. Denture base polymer specimens without any fiber reinforcement were used as control for both processing methods. Transverse strength test specimens (65 x 10 x 2.5 mm) were stored in water bath at 37 degrees C for 2 weeks. The transverse strength (MPa) and modulus of elasticity (GPa) was measured with the 3-point bending test. Impact strength (kJ/m(2)) test specimens (60 x 7.5 x 4 mm) were tested with the Charpy-type pendulum impact test setup. The data were analyzed with multifactorial analysis of variance and Tukey post hoc tests (alpha=.05). RESULTS Injection-molded fiber-reinforced groups showed significantly higher transversal strength, elastic modulus, and impact strength compared with compression-molded groups (P <.001). In the injection-molded groups, fiber concentration increased all mechanical properties tested (P <.05), but fiber length only increased transverse strength and modulus of elasticity (P <.05). In the compression molded groups, fiber concentration affected modulus of elasticity and impact strength significantly (P <.05), but fiber length did not show any significant effect on the mechanical properties tested (P >.05). CONCLUSION The transverse strength, elastic modulus and impact strength of injection-molded denture base polymer increased significantly with the use of chopped E-glass fibers, whereas the effect was not significant with the compression-molded polymer.

Five-year survival of 3-unit fiber-reinforced composite fixed partial dentures in the anterior area

OBJECTIVES The purpose of this clinical study was to evaluate the long-term outcome of 3-unit anterior fixed partial dentures (FPDs) made of fiber-reinforced resin composite (FRC), and to identify design factors influencing the survival rate. METHODS 52 patients (26 females, 26 males) received 60 indirectly made FRC FPDs, using pre-impregnated unidirectional glass fibers, requiring manual wetting, as framework material. FPDs were surface (n=48) or hybrid (n=12) retained and mainly located in the upper jaw. Hybrid FPDs had a combination of retainers; i.e. crown at one and surface retention at the other abutment tooth. Surface FPDs were either purely adhesively retained (n=29) or with additional mechanical retention (n=19). Follow-up period was at minimum 5 years, with check-ups every 1-2 years. Six operators were involved, in three centers in the Netherlands, Finland and Sweden. Survival rates, including repairable defects of FPDs, and success rates were determined. RESULTS Kaplan-Meier survival rate at 5 years was 64% (SE 7%). For the level of success, values were 45% (SE 7%) and the estimated median survival time 58 (SE 10.1) months. For surface FPDs, additional mechanical retention did not improve survival significantly. There was a trend towards better survival of surface FPDs over hybrid FPDs, but differences were not significant. Main failure modes were fracture of the FPD and delamination of veneering composite. SIGNIFICANCE A success rate of 45% and a survival rate of 64% after 5 years was found. Fracture of the framework and delamination are the most prevalent failure modes, especially for surface FPDs.

Effect of operating air pressure on tribochemical silica-coating

Objective. Alumina and zirconia are inert to conventional etching and need to be initially conditioned with, for example, silicatization. The aim of the present study was to evaluate the effect of operating air pressure of tribochemical silica-coating method on the shear bond strength of composite resin to ceramic substrates. Material and methods. Alumina (Procera Alumina, Nobel Biocare) and zirconia (LAVA; 3M ESPE and Procera Zirconia; Nobel Biocare) were airborne particle silica-coated (CoJet; 3M ESPE) using selected, clinically available air pressures of 150, 220, 300, and 450 kPa. The surfaces were silanized with silane coupling agent (ESPE Sil; 3M ESPE) and coated with adhesive resin (3M Multipurpose resin; 3M ESPE). Particulate filler resin composite (Z250; 3M ESPE) stubs (diameter 3.6 mm, height 4.0 mm) were added onto ceramics and light-cured for 40 s. The test specimens (n=18/group) were thermocycled (6000×5–55°C) and shear bond strengths were measured with a cross-head speed of 1.0 mm/min. Fracture surfaces were examined with SEM, and an elemental analysis (EDS) was carried out to determine silica content on the substrate surface. Results. The highest bond strengths were obtained with the highest pressures. ANOVA showed significant differences in bond strength between the ceramics (p<0.05) and between the specimens treated at various air pressures (p<0.05). Conclusions. Clinically, the operating air pressure of silicatization may have a significant effect on bond strength to non-etchable ceramics.

Pilot evaluation of resin composite cement adhesion to zirconia using a novel silane system.

Objective. In this study, we evaluated the effect of two silane coupling agents and their blends with a cross-linker silane on the bond strength of a dimethacrylate-based resin composite cement to surface-conditioned zirconia. Material and Methods. A total of 40 planar zirconia specimens were used for 8 test groups. After alumina particle abrasion, followed by tribochemical silica-coating, the specimens were randomly assigned to four silanizations: with 1.0 vol% 3-methacryloyloxypropyltrimethoxysilane or 1.0 vol% 3-mercaptopropyltrimethoxysilane or their blends with 1.0 vol% 1,2-bis-(triethoxysilyl)ethane (all in ethanol/water). The resin composite (RelyX™ ARC, 3M ESPE) stubs (n=10/group) were light-polymerized onto zirconia specimens. Four test groups were tested without water storage and 4 thermo-cycled at 6000 cycles (5±1°C to 55±1°C), with a dwelling time of 30 s. The shear bond strength of the cement stubs to zirconia was measured using a universal testing machine at a constant cross-head speed of 1 mm/min. Scanning electron microscopy was employed for imaging the zirconia surface after conditioning and testing. Failure mode was evaluated visually. A surface chemical analysis was carried out with the EDXA system. Results. The highest shear bond strength was 21.9±8.7 MPa, obtained with a blend of 3-mercaptopropyltrimethoxysilane and 1,2-bis-(triethoxysilyl)ethane (dry storage), and 16.0±1.5 MPa, with 3-methacryloyloxypropyltrimethoxysilane (thermo-cycled). Thermo-cycling decreased the bond strengths significantly (ANOVA, p<0.01), and the silanes differed significantly (p<0.005). Some specimens suffered from spontaneous debonding during thermo-cycling. Conclusions. The luting cement adhesion might be promoted to silica-coated zirconia with 1.0 vol% 3-methacryloyloxypropyltrimethoxysilane and with a blend of 1.0 vol% 3-mercaptopropyltrimethoxysilane and 1.0 vol% 1,2-bis-(triethoxysilyl)ethane.