Bis-GMA co-polymerizations: influence on conversion, flexural properties, fracture toughness and susceptibility to ethanol degradation of experimental composites.
OBJECTIVE
The aim of this study was to evaluate the influence of monomer content on fracture toughness (K(Ic)) before and after ethanol solution storage, flexural properties and degree of conversion (DC) of bisphenol A glycidyl methacrylate (Bis-GMA) co-polymers.


METHODS
Five formulations were tested, containing Bis-GMA (B) combined with TEGDMA (T), UDMA (U) or Bis-EMA (E), as follows (in mol%): 30B:70T; 30B:35T:35U; 30B:70U; 30B:35T:35E; 30B:70E. Bimodal filler was introduced at 80 wt%. Single-edge notched beams for fracture toughness (FT, 25 mm x 5 mm x 2.5 mm, a/w=0.5, n=20) and 10 mm x 2 mm x 1 mm beams for flexural strength (FS) and modulus (FM) determination (10 mm x 2 mm x 1 mm, n=10) were built and then stored in distilled water for 24 h at 37 degrees C. All FS/FM beams and half of the FT specimens were immediately submitted to three-point bending test. The remaining FT specimens were stored in a 75%ethanol/25%water (v/v) solution for 3 months prior to testing. DC was determined with FT-Raman spectroscopy in fragments of both FT and FS/FM specimens at 24 h. Data were submitted to one-way ANOVA/Tukey test (alpha=5%).


RESULTS
The 30B:70T composite presented the highest K(Ic) value (in MPa m(1/2)) at 24 h (1.3+/-0.4), statistically similar to 30B:35T:35U and 30B:70U, while 30B:70E presented the lowest value (0.5+/-0.1). After ethanol storage, reductions in K(Ic) ranged from 33 to 72%. The 30B:70E material presented the lowest reduction in FT and 30B:70U, the highest. DC was similar among groups (69-73%), except for 30B:70U (52+/-4%, p<0.001). 30B:70U and 30B:35T:35U presented the highest FS (125+/-21 and 122+/-14 MPa, respectively), statistically different from 30B:70T or 30B:70E (92+/-20 and 94+/-16 MPa, respectively). Composites containing UDMA or Bis-EMA associated with Bis-GMA presented similar FM, statistically lower than 30B:35T:35U.


CONCLUSIONS
Composites formulated with Bis-GMA:TEGDMA:UDMA presented the best compromise between conversion and mechanical properties.
Pfeifer
Carmem S
CS
Biomaterials and Oral Biochemistry Department, School of Dentistry, University of São Paulo, Av. Prof. Lineu Prestes, 2227, Sao Paulo, 05508-900, SP, Brazil. pfeifercs@gmail.com
Silva
Laura R
LR
Kawano
Yoshio
Y
Braga
Roberto R
RR
D017438:Bisphenol A-Glycidyl Methacrylate; D003188:Composite Resins / Q000737:chemistry*; D003799:Dental Stress Analysis; D055119:Elastic Modulus; D000431:Ethanol; D006244:Hardness; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing; D008689:Methacrylates; D044367:Phase Transition; D018583:Pliability; D011140:Polyurethanes; D012995:Solubility
D003188:Composite Resins; D008689:Methacrylates; D011140:Polyurethanes; C097103:polyurethane dimethacrylate; C041979:2,2-bis-(4-(2-methacryloxyethoxy)phenyl)propane; D000431:Ethanol; D017438:Bisphenol A-Glycidyl Methacrylate