The effect of filler loading and morphology on the mechanical properties of contemporary composites,☆☆,,★★

https://doi.org/10.1067/mpr.2002.125179Get rights and content

Abstract

Statement of Problem. Little information exists regarding the filler morphology and loading of composites with respect to their effects on selected mechanical properties and fracture toughness. Purpose. 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. Material and 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 × 2.5 × 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. Conclusion. 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. (J Prosthet Dent 2002;87:642-9.)

Section snippets

Filler morphological and elemental analysis

Table I lists the 14 commercial composites evaluated in this study.

. Composites examined in this study

GroupProductManufacturerLot numberFiller morphology
1Metafil CXSun Medical, Shiga, Japan70301Pre-polymerized particles
Silux Plus3M, St. Paul, Minn.5702XL
Heliomolar RadiopaqueVivadent, Schaan, Liechtenstein818828
Palfique EsteliteTokuyama Soda, Tokyo, Japan282
2AelitefilBisco, Itasca, Ill.089294Irregular-shaped particles
CharismaKulzer, Friedrichsdorf, Germany032
Herculite XRKerr, Orange, Calif.710552

Results

Figures 1 through 4 are representative SEM micrographs of the composites evaluated in this study.

. Group 1 composites contained prepolymerized filler particles. Metafil CX: 30- to 60-μm round particles (a1), 5- to 10-μm irregular-shaped particles (a2), and <50-nm spherical particles (a3). Silux Plus: 5- to 30-μm prepolymerized particles of various shapes (b1 and b2) and 100- to 200-nm spherical particles (b3). Heliomolar Radiopaque: 30-μm round particles and <10-μm irregular-shaped prepolymerized

Discussion

Factors that affect the characteristics of composites include the resin monomer, filler, and coupling agents. Filler content has been correlated with depth of polymerization, color stability, hardness, compressive strength, and stiffness. Increased filler loading has been shown to result in lower water absorption and higher resistance to both toothbrush abrasion and wear by hydroxyapatite.26 Thus, filler loading has been considered an important factor for determining the mechanical properties

Conclusions

Within the limitations of this study, composites could be classified by their filler morphology. Composites that contained prepolymerized filler particles had the lowest filler loading and therefore the lowest flexural properties and hardness. Composites that contained round filler particles had the highest filler loading, resulting in the highest flexural properties and hardness. Composites that contained either irregular-shaped or a mixture of prepolymerized and irregular-shaped filler

Supplementary Files

References (32)

  • New American Dental Association specification no. 27 for direct filling resins. Council on Dental Materials and Devices

    J Am Dent Assoc

    (1977)
  • ISO 4049

    Dental resin-based restorative materials

    (1985)
  • G Willems et al.

    Composite resins in the 21st century

    Quintessence Int

    (1993)
  • H St Germain et al.

    Properties of microfilled composite resins as influenced by filler content

    J Dent Res

    (1985)
  • M Braem et al.

    Mechanical properties and filler fraction of dental composites

    Dent Mater

    (1989)
  • FF Lange

    Fracture energy and strength behavior of a sodium borosilicate glass-Al2O3 composite system

    J Am Ceram Soc

    (1971)
  • Cited by (382)

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    aProfessor and Chairman, Department of Dental Biomaterials, College of Dentistry and Institute of Biomaterials Research and Development, Kyungpook National University.

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    bAssociate Professor, Department of Restorative Dentistry, Division of Biomaterials, University of Texas Health Science Center at San Antonio, Texas.

    cProfessor, Division of Dental Biomaterials, Department of Oral Rehabilitation and Materials Science, Graduate School of Dentistry, Tohoku University.

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    Reprint requests to: Dr Kyo-Han Kim, Department of Dental Biomaterials, College of Dentistry and Institute of Biomaterials Research and Development, Kyungpook National University, Taegu 700-422, Korea, Fax: (82)53-422-9631, E-mail: [email protected]

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