Depth of light-initiated polymerization of glass fiber-reinforced composite in a simulated root canal

PURPOSE: The possibility of polymerizing glass fiber-reinforced composite (FRC) material into the root canal was preliminarily evaluated by determining the depth of light-initiated polymerization of FRC. MATERIALS AND METHODS: The material used was polymer-preimpregnated E-glass fiber reinforcement, which was further impregnated with light-polymerizable dimethacrylate monomer resin. The same resin without fiber reinforcement was used as a control. Six different lengths (range 4 to 24 mm) of light-protected cylinders filled with the test materials were light polymerized from one end. The degree of monomer conversion was determined from the other end by FT-IR spectrometry. Infrared spectra were recorded at six time points from the beginning of polymerization. The microhardness of the test materials was measured from the light-exposure surface toward the other end of the cylinder. RESULTS: Both groups showed a reduction in the degree of conversion with increased lengths of the cylinder. The FRC group showed a higher degree of conversion in the longest sample group compared to the resin group. Microhardness measurement confirmed the constant reduction of the degree of conversion by the reduced Vickers hardness values with increased cylinder length of the FRC. CONCLUSION: Generally, the glass FRC showed an almost equal degree of conversion after light curing as monomer resin without fibers. However, in the longest cylinders, FRC showed a slightly higher degree of conversion compared to resin only; this might be due to the fibers' ability to conduct light.     

The effect of adding a new monomer “Phene” on the polymerization shrinkage reduction of a dental resin composite

Objective

A new photocurable monomer, “Phene” (N-methyl-bis(ethyl-carbamate-isoproply-α-methylstyryl)amine) was synthesized and incorporated into Bis-GMA/TEGDMA with the aim of reducing polymerization shrinkage swithout detriment to the physical properties and wearing of the resin composites.

Strength of adhesive-bonded fiber-reinforced composites to enamel and dentin substrates

PURPOSE: To compare in vitro the bond strength of a particulate filler composite and two brands of fiber-reinforced composite (FRC) to teeth with or without the addition of flowable composite at the adhesive interphase. Physicomechanical properties that might contribute to the bonding were also evaluated. MATERIALS AND METHODS: Two hundred extracted human molars were used as substrates with a standard acid-etch and adhesive technique. FRC material [everStick (EV) or Stick (SC)] was applied on the substrate either directly or with a thin layer of flowable composite resin [Tetric Flow (TF)] and light cured for 40 s. As a control, particulate filler composite was used. The specimens (n = 10) were water stored for 24 h or thermocycled for 6000 cycles and subjected to shear bond strength testing. Fracture surfaces were analyzed with SEM and the microhardness and thermal expansion behavior of the materials at the adhesive interface were also evaluated. Multifactorial ANOVA and Tukey's post hoc tests were used at a significance level of p < 0.05. RESULTS: ANOVA showed that storage condition and substrate type (p < 0.05) had a significant effect on the bond strength values. Bond strengths of FRC did not show a significant difference compared to the control (p > 0.05). For enamel, the mean bond strengths in MPa (SD) after thermocycling were: control 19.4 (3.8); EV 22.3 (3.6); SC 16.9 (4.9); EV-TF 22.8 (3.2); SC-TF 16.7 (2.7); and for dentin they were: control 15.3 (5.57); EV10.2 (2.2); SC 14.4 (4.5); EV-TF 8.85 (1.1); SC-TF 15.6 (3.6). Thermocycling increased the bond strength values typically by 10%. The presence of flow composite resin did not produce any significant effect (p > 0.05). CONCLUSION: The bond strength of FRC did not differ from that of particulate filler composite, and the addition of flowable composite did not improve bond strength values.     

Direct composite resin restoration of an anterior tooth: effect of fiber-reinforced composite substructure

The aim of the study was to determine the static load-bearing capacity of fractured incisal teeth restored with the conventional adhesive-composite technique or by using fiber reinforced composites (FRC). Upper incisal teeth were prepared by cutting the incisal part of the crown horizontally. Restorations were made by three techniques. Group A (control group) was restored by reattaching the original incisal edge to the tooth. Group B was restored using composite resin. Group C was restored with composite and FRC. Restored teeth were statically loaded until fracture. Results suggest that an incisally fractured tooth restored with a combination of composite resin and FRC-structure provide the highest load bearing capacity.     

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 x 5-55 degrees 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.     

Mechanical properties of denture base resin cross-linked with methacrylated dendrimer

Objectives

The aim of this study was to investigate the mechanical properties of denture base resin cross-linked with methacrylated dendrimer.

Methods

The test specimens (3 mm × 10 mm × 65 mm) were fabricated from autopolymerizing resin with the powder/liquid ratio of 10 g/7 ml. The monomer liquid of resin was applied with the mixture of methylmethacrylate and crosslinker dendrimer (DD1) or crosslinker ethyleneglycol dimethacrylate (EGDMA) with five different volume percentages (vol%). The dendrimer crosslinker in this study is a methacrylated molecule (MW = 3617 g/mol) with 12 methacrylate groups. Quantity of crosslinkers varied from 1.1 to 9.1 vol%. The specimens (n = 8/group) were polymerized in distilled water maintained at 55 °C under pressure of 0.4 MPa for 20 min. Test specimens were stored dry at room temperature before testing. The flexural strength (MPa) and flexural modulus (GPa) was measured with three-point bending test at a crosshead speed of 5 mm/min. Surface microhardness (MHN) of matrix area of polymer (n = 8/group) was measured with a load of 245.3 mN by 10 s. Data were analyzed with two-way ANOVA.

Results

ANOVA showed that the addition of DD1 had a significantly higher effect (p < 0.05) on flexural modulus and hardness of matrix area than EGDMA but on flexural strength (p > 0.05). The effect of quantity differences of crosslinker was statistically significant only on flexural strength (p < 0.05).

Significance

The results of this study suggest that dendrimer-crosslinked resin gives better stiffness than that of EGDMA.     

Interface shear strength and fracture behaviour of porous glass-fibre-reinforced composite implant and bone model material

Glass-fibre-reinforced composites (FRCs) are under current investigation to serve as durable bone substitute materials in load-bearing orthopaedic implants and bone implants in the head and neck area. The present form of biocompatible FRCs consist of non-woven E-glass-fibre tissues impregnated with varying amounts of a non-resorbable photopolymerisable bifunctional polymer resin with equal portions of both bis-phenyl-A-glycidyl dimethacrylate (BisGMA) and triethyleneglycol dimethacrylate (TEGDMA). FRCs with a total porosity of 10-70 vol% were prepared, more than 90 vol% of which being functional (open pores), and the rest closed. The pore sizes were greater than 100?μm. In the present study, the push-out test was chosen to analyse the shear strength of the interface between mechanically interlocked gypsum and a porous FRC implant structure. Gypsum was used as a substitute material for natural bone. The simulative in vitro experiments revealed a significant rise of push-out forces to the twofold level of 1147 ±?271?N for an increase in total FRC porosity of 43%. Pins, intended to model the initial mechanical implant fixation, did not affect the measured shear strength of the gypsum-FRC interface, but led to slightly more cohesive fracture modes. Fractures always occurred inside the gypsum, it having lower compressive strength than the porous FRC structures. Therefore, the largest loads were restricted by the brittleness of the gypsum. Increases of the FRC implant porosity tended to lead to more cohesive fracture modes and higher interfacial fracture toughness. Statistical differences were confirmed using the Kruskal-Wallis test. The differences between the modelled configuration showing gypsum penetration into all open pores and the real clinical situation with gradual bone ingrowth has to be considered.