Dental resin composites containing ceramic whiskers and precured glass ionomer particles.
OBJECTIVE
Glass ionomer, resin-modified glass ionomer, and compomer materials are susceptible to brittle fracture and are inadequate for use in large stress-bearing posterior restorations. The aim of this study was to use ceramic single crystal whiskers to reinforce composites formulated with precured glass ionomer, and to examine the effects of whisker-to-precured glass ionomer mass ratio on mechanical properties, fluoride release, and polishability of the composites.


METHODS
Silica particles were fused onto silicon nitride whiskers to facilitate silanization and to improve whisker retention in the matrix. Hardened glass ionomer was ground into a fine powder, mixed with whiskers, and used as fillers for a dental resin. Four control materials were also tested: a glass ionomer, a resin-modified glass ionomer, a compomer, and a hybrid composite. A three-point flexural test was used to measure flexural strength, modulus, and work-of-fracture. A fluoride ion-selective electrode was used to measure fluoride release. Composite surfaces polished simulating clinical procedures were examined by SEM and profilometry.


RESULTS
At whisker/(whisker + precured glass ionomer) mass fractions of 1.0 and 0.91, the whisker composite had a flexural strength in MPa (mean (SD); n = 6) of (196 (10)) and (150 (16)), respectively, compared to (15 (7)) for glass ionomer, (39 (8)) for resin-modified glass ionomer, (89 (18)) for compomer, and (120 (16)) for hybrid composite. The whisker composite had a cumulative fluoride release of nearly 20% of that of the glass ionomer after 90 days. The whisker composites had surface roughness comparable to the hybrid resin composite.


CONCLUSIONS
Composites filled with precured glass ionomer particles and whiskers exhibit moderate fluoride release with improved mechanical properties; the whisker-to-glass ionomer ratio is a key microstructural parameter that controls fluoride release and mechanical properties.
Paffenbarger Research Center, American Dental Association Health Foundation, Building 224, Room A-153, Gaithersburg, MD 20899-8546, USA. hockin.xu@nist.gov
H H
HH
Xu
F C
FC
Eichmiller
J M
JM
Antonucci
G E
GE
Schumacher
L K
LK
Ives
D000180:Acrylic Resins; D000704:Analysis of Variance; D002516:Ceramics; D020770:Compomers; D003188:Composite Resins / Q000737:chemistry*; D003775:Dental Polishing; D003793:Dental Restoration, Permanent; D004548:Elasticity; D005459:Fluorides / Q000737:chemistry; D005899:Glass Ionomer Cements; D017736:Ion-Selective Electrodes; D008277:Magnesium Oxide; D008422:Materials Testing; D008689:Methacrylates; D008855:Microscopy, Electron, Scanning; D008963:Molar; D018583:Pliability; D011076:Polycarboxylate Cement; D012821:Silanes; D017640:Silicates; D017655:Silicon Compounds; D012822:Silicon Dioxide; D018709:Statistics, Nonparametric; D013314:Stress, Mechanical; D013499:Surface Properties; D013718:Tensile Strength; D015034:Zinc Oxide
D000180:Acrylic Resins; D020770:Compomers; D003188:Composite Resins; C088486:Dyract; D005899:Glass Ionomer Cements; D008689:Methacrylates; D011076:Polycarboxylate Cement; D012821:Silanes; D017640:Silicates; D017655:Silicon Compounds; C113300:TPH hybrid; C084550:Vitremer; C015897:glass ionomer; D008277:Magnesium Oxide; D012822:Silicon Dioxide; C040235:Ketac-cem; D005459:Fluorides; C032734:silicon nitride; D015034:Zinc Oxide