Resistance to incipient caries and properties of composite resin containing nano-sized tricalcium phosphate-fluorapatite (TCP-FA) filler

Abstract

Composite resin has been widely used for dental restoration because demand for esthetic application are increased and the properties of materials are improved. However, secondary caries, which is a carious lesion around an existing restoration limit longevity of the restoration and it is a frequent and important reason for the replacement of an existing restoration. Thus it is need to improve materials in order to effectively inhibit it. Tricalcium phosphate [TCP, Ca3(PO4)2], which release calcium and phosphate, has resistance on demineralization and promote remineralization of tooth. Fluorapatite [FA, Ca10(PO4)6F2] releases fluoride and shows aptitude to delay caries process. It also enhances mechanical properties when it is added to TCP. For this reason, the objective of this study was to evaluate resistance on initial caries and was to investigate material properties of composite resin containing TCP-FA filler.Materials and methodsFA with CaHPO4, Ca(OH)2 and CaF2, and TCP with CaHPO4 and Ca(OH)2 were synthesized through dry mechanochemical process. After synthesis, TCP-FA that mixed fluorapatite-tricalcium phosphate mass ratio of 4:6 were developed. Phase analysis of TCP-FA were evaluated with the X-ray diffractometer (XRD) and morphological feature, size of particle and agglomerate distribution were investigate by SEM and TEM.After characteristic analysis, TCP-FA filler were respectively added 0 %, 10 %, 15 %, 20 %, 25 % in resin matrix and resistance on initial caries, mechanical, physical and biological properties were evaluatedTo evaluate resistance on initial caries, resistance of demineralization and acid neutralization were investigated. Resistance of demineralization were evaluated by VHN and QFL-D after 24 and 48 hours demineralization. Acid neutralizing properties were evaluated by pH change per minute for 90 minutes and time to raise pH

from 4.0 to 5.5. Flexural strength for mechanical properties, water sorption and solubility for physical properties and cytotoxicity for biological properties were evaluated. ResultsTCP-FA were identified similar peak with FA and TCP by XRD. Particle with cubic and spheroidal morphology were observed. Particle size of TCP and FA were respectively 19.78±6.4 and 26±7.55 nm.%SMHR (surface microhardness reduction) and △F-value (loss of fluorescence) of composite resin with TCP-FA filler were lower than that without TCP-FA filler. Particularly △F-value of Group 4 with 20 % fo TCP-FA filler and Group 5 with 25 % of TCP-FA filler was respectively the lowest among all groups after 24 hours and 48 hours demineralization respectively (p<0.05). According to add TCP-FA filler, pH change of solution were increased greatly and rapidly. pH was also increased from pH 4.0 to 5.5 in a shorter time by addition of TCP-FA filler. These tendency showed remarkably in Group 5 (p<0.05). As the addition of TCP-FA filler, flexural strength were decreased. Group 5 was especially lowest among all groups (p<0.05) but there were no difference between other groups except 25 % group (p>0.05).Water sorption and solubility of all groups were satisfied requirement ISO 4049 standard and cytotoxicity of all groups except 25 % group showed non-cytotoxic.Conclusion In this study, there were confirmed that nano-sized TCP-FA filler affected on resistance of demineralization, acid neutralizing properties and material properties. Particularly composite resin containing 20 % more of TCP-FA filler were remarkable. However composite resin containing 25 % of TCP-FA filler showed moderate toxic and low flexural strength. Thus composite resin containing 20 % of TCP-FA filler are effective for initial secondary caries-inhibition.