ABSTRACT
BACKGRoUND:The clinical manipulation properties of light-cured composite resin,such as flowing property.filling capacity,shaping and stability has not unified definition in dental materials notwithstanding more studies of rheological behaviors were undertook.OBJECTIVE:To explore the dynamic viscoelasticity difference of unpolymerized light.cured composite resins with retentive filler or normal filler,and to investigate effect on the clinical manipulation properties of rheological behaviors in two light-cured composite resins to define an ideal resin.DESIGN,TIME AND SETTING:This controlled study is a correlation study of integrating the base study and clinical use.Basic study was performed in January 2003 at Key Laboratory of Engineering Plastics of Chinese Academy of Sciences in Beijing.The clinical observation study was conducted at the Stomatology Center,Haikou People's Hospital until December 2006.MATERIALS:Light-cured composites employed in this study were reinforced with RF(experimental composite resin I,ECR-Ⅰ)or NF(experimental composite resin Ⅱ,ECR-Ⅱ),which were supplied by Dental Materials Laboratory.Medical College of Stomatology of Peking University.They contained different types of fillers,but had the same resin matrix and volume percent of filler.METHODS:The dynamic viscoelastic properties of ECR-Ⅰ or ECR-Ⅱ were measured respectively with the dynamic stress rheometer DSR-200 in a room maintained 25℃.Flowing property,filling capacity,shaping and stability property were employed to assess the clinical manipulation property of ECR.MAIN OUTCOME MEASURES:Viscoelasticity(G',G",tan δ)and clinical manipulation of two kinds of compound resins.RESULTS:The dynamic viscoelastic behavior of the two composites was sensitive to changes in frequency.ECR-Ⅰhad significantly higher G'than ECR-Ⅱ.ECR-Ⅰ had a greater ability of stability and shaping.and a lower potential for deformation clinically.ECR-Ⅱ had significantly higher G"than ECR-Ⅰ.and ECR-Ⅱ had a higher flowing ability clinically.ECR-Ⅱ had significantly higher tan δ than ECR-Ⅰ.ECR-Ⅱ was found to be more viscous and better filling capacity,with a good adaptation to the cavity of the tooth clinically.CONCLUSION:The dynamic viscoelasticity(G',G",tan δ)and clinical manipulation properties of ECR-ⅠI or ECR-Ⅱ are compared.The ideal composites should have higher G'and lower tan δ
ABSTRACT
Objective To evaluate the dynamic viscoelasticity of unpolymerized light-cured composite resins reinforced with retentive filler(RF)or normal filler(NF),and the effect of dynamic viscoelasticity on clinical manipulation.Methods The dynamic viscoelastic properties of two light-cured composite resins reinforced with RF or NF were measured respectively with the dynamic stress rheometer.Flowing property,filling capacity,shaping and stability were designed to describe the clinical manipulation of the composites.Results The dynamic viscoelastic behavior of the composites is sensitive to changes in frequency,composite resin reinforced with RF had significantly higher shear storage modulus(G')and shear loss modulus(G″)than composite resins reinforced with NF,and had significantly lower loss tangent(tan?).The former was found to be more viscous,and the latter was found to be more elastic.Clinically,composite resin reinforced with RF has a greater ability of stability and shaping,and a lower potential for deformation;composite resin reinforced with NF has a higher flowing ability,and with a good adaptation to the cavity of the tooth.Conclusions The ideal composites should have high G' and low tan?.
ABSTRACT
<p><b>OBJECTIVE</b>To inspect the directionality of adhesive strength between composite resins and dental hard tissues.</p><p><b>METHODS</b>Two kinds of composite resins were bonded with their luting kits to the enamel and dentin surfaces of bovine teeth separately. The dead load shear and impact shear testing were performed from both of root apex direction and cutting edge direction.</p><p><b>RESULTS</b>The shear adhesive strength between the enamel and two kinds of composite resins was on the same behavior, that the shear adhesive strength of root apex direction was greater than that of cutting edge direction. In the dead load shear testing, the former was about two to three times of the latter (P < 0.05). In the impact shear testing, the former was about three to four times of the latter (P < 0.001). The effect of the direction of acting force was small on the shear adhesive strength between the dentin and two kinds of composite resins. In the both dead load shear testing and impact shear testing, there was no statistically significant difference between the datum of two directional loadings (P > 0.05, P > 0.5).</p><p><b>CONCLUSION</b>The shear adhesive strength between the composite resins and enamel of bovine teeth is related to the acting direction of the shear force.</p>