title: Adhesion of resin materials to S2-glass unidirectional and E-glass multidirectional fiber reinforced composites: effect of polymerization sequence protocols.
abstract: OBJECTIVE
  To evaluate the effect of different polymerization sequences employed during application of bis-GMAbased particulate filler composites (PFC) or a flowable resin (FR) on fiber-reinforced composite (FRC).
  
  
  METHODS
  Unidirectional, pre-impregnated S2-glass fibers (Dentapreg) and multidirectional preimpregnated E-glass fibers (Dentapreg) (length: 40 mm; thickness: 0.5 mm) were obtained (N = 144, n = 12 per group) and embedded in translucent silicone material with the adhesion surface exposed. The resulting specimens were randomly divided into 12 groups for the following application sequences: a) FRC+PFC (photopolymerized in one step), b) FRC+FR (photopolymerized in one step), c) FRC+PFC (photopolymerized individually), d) FRC+FR (photopolymerized individually), e) FRC (photopolymerized)+intermediate adhesive resin and PFC (photopolymerized in one step), f) FRC (photopolymerized)+intermediate adhesive resin and FR (photopolymerized in one step). The sequences of unidirectional (groups a to f) were repeated for multidirectional (groups g to l) FRCs. PFCs were debonded from the FRC surfaces using the shear bond test in a universal testing machine (1 mm/min). On additional specimens from each FRC type, thermogravimetric analysis (TGA) was performed to characterize the fiber weight content (Wf) (N = 6, n = 3 per group). After debonding, all specimens were analyzed using SEM to categorize the failure modes. The data were statistically analyzed using 3-way ANOVA and Tukey's tests (α = 0.05).
  
  
  RESULTS
  Significant effects of the FRC type (S2 or E-glass) (p < 0.01), resin type (PFC or FR) (p < 0.01) and polymerization protocol (p < 0.05) were observed on the bond strength (MPa). Interaction terms were also significant (p < 0.05). The multidirectional FRC groups (g to l) showed significantly lower bond strengths (2.3 ± 0.2 to 7.3 ± 0.3 MPa) than did the unidirectional FRC groups (a to f) (10.7 ± 0.6 to 24.4 ± 0.8 MPa). Among the unidirectional FRC groups, the highest values were obtained with protocol f (24.4 ± 0.8), followed by protocol e (18.6 ± 0.4). PFC adhesion to unidirectional FRC was lower when FRC and PFC were polymerized in one step (protocol a: 11.3 ± 0.5) than individual polymerization (protocol c: 14.1 ± 0.5). The opposite situation was true for FR (protocol b: 17.5 ± 0.4; protocol d: 10.7 ± 0.6). Groups a to f presented exclusively mixed failures (a combination of partial cohesive failure in the PFC and adhesive failure between the FRC and PFC) and groups g to l demonstrated only adhesive failure (intact FRC no cohesive failure of PFC). TGA revealed 55 ± 3 wt% fiber content for multidirectional and 60 ± 3 wt% for unidirectional FRCs tested.
  
  
  CONCLUSIONS
  Multidirectional pre-impregnated E-glass fibers cannot be recommended in combination with the PFC and FR materials tested in this study. Application of an intermediate adhesive resin layer increases the adhesion of both PFC and FR to unidirectional FRC. FRC and FR can be polymerized in one step, but FRC and PFC combinations should be polymerized individually.
authors.forename: Petr
authors.initials: P
authors.lastname: Polacek
authors.forename: Vladimir
authors.initials: V
authors.lastname: Pavelka
authors.forename: Mutlu
authors.initials: M
authors.lastname: Ozcan
mesh_terms: D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry*; D001840:Dental Bonding; D003764:Dental Materials / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D005898:Glass / Q000737:chemistry*; D006801:Humans; D008027:Light; D008855:Microscopy, Electron, Scanning; D058105:Polymerization; D033081:Shear Strength; D012828:Silicones / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013818:Thermogravimetry; D014783:Viscosity
chemical_list: D003188:Composite Resins; D003764:Dental Materials; D012828:Silicones; C009753:fiberglass; D017438:Bisphenol A-Glycidyl Methacrylate