The effect of filler loading and morphology on the mechanical properties of contemporary composites.
BACKGROUND
Little information exists regarding the filler morphology and loading of composites with respect to their effects on selected mechanical properties and fracture toughness.


OBJECTIVE
The objectives of this study were to: (1) classify commercial composites according to filler morphology, (2) evaluate the influence of filler morphology on filler loading, and (3) evaluate the effect of filler morphology and loading on the hardness, flexural strength, flexural modulus, and fracture toughness of contemporary composites.


METHODS
Field emission scanning electron microscopy/energy dispersive spectroscopy was used to classify 3 specimens from each of 14 commercial composites into 4 groups according to filler morphology. The specimens (each 5 x 2.5 x 15 mm) were derived from the fractured remnants after the fracture toughness test. Filler weight content was determined by the standard ash method, and the volume content was calculated using the weight percentage and density of the filler and matrix components. Microhardness was measured with a Vickers hardness tester, and flexural strength and modulus were measured with a universal testing machine. A 3-point bending test (ASTM E-399) was used to determine the fracture toughness of each composite. Data were compared with analysis of variance followed by Duncan's multiple range test, both at the P<.05 level of significance.


RESULTS
The composites were classified into 4 categories according to filler morphology: prepolymerized, irregular-shaped, both prepolymerized and irregular-shaped, and round particles. Filler loading was influenced by filler morphology. Composites containing prepolymerized filler particles had the lowest filler content (25% to 51% of filler volume), whereas composites containing round particles had the highest filler content (59% to 60% of filler volume). The mechanical properties of the composites were related to their filler content. Composites with the highest filler by volume exhibited the highest flexural strength (120 to 129 MPa), flexural modulus (12 to 15 GPa), and hardness (101 to 117 VHN). Fracture toughness was also affected by filler volume, but maximum toughness was found at a threshold level of approximately 55% filler volume.


CONCLUSIONS
Within the limitations of this study, the commercial composites tested could be classified by their filler morphology. This property influenced filler loading. Both filler morphology and filler loading influenced flexural strength, flexural modulus, hardness, and fracture toughness.
Kim
Kyo-Han
KH
Department of Dental Biomaterials, College of Dentistry and Institute of Biomaterials Research and Development, Kyungpook National University, Taegu, Korea. kyohan@knu.ac.kr
Ong
Joo L
JL
Okuno
Osamu
O
D000180:Acrylic Resins / Q000737:chemistry; D000704:Analysis of Variance; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D003188:Composite Resins / Q000032:analysis / Q000737:chemistry* / Q000145:classification; D003764:Dental Materials / Q000032:analysis / Q000737:chemistry* / Q000145:classification; D003799:Dental Stress Analysis / Q000295:instrumentation; D004548:Elasticity; D004577:Electron Probe Microanalysis; D006244:Hardness; D006801:Humans; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D018583:Pliability; D011140:Polyurethanes / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry; D012821:Silanes / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry; D013223:Statistics as Topic; D013314:Stress, Mechanical; D013499:Surface Properties; D016474:Weight-Bearing; D015040:Zirconium
D000180:Acrylic Resins; C098721:Aelitefil; C084111:Charisma composite resin; C029012:Composite Dental Resin; D003188:Composite Resins; D003764:Dental Materials; C090891:Metafil Ex; D008689:Methacrylates; C079764:Pertac hybrid; D011140:Polyurethanes; D019279:Resin Cements; D012821:Silanes; C113300:TPH hybrid; C083568:Z100 composite resin; C086113:palfique estelite; C074046:Photo Clearfil A; C065770:Herculite XR; C074741:Silux Plus; D017438:Bisphenol A-Glycidyl Methacrylate; D012822:Silicon Dioxide; D015040:Zirconium