| Background and objectiveThe residual roots and crowns caused by caries of deciduous anterior teeth are common in clinic.How to treat and repair the residual roots and crowns of deciduous anterior teeth is a key and difficult problem faced by children’s dentists.Due to the particularity of deciduous teeth,polylactic acid(PLA)material has been gradually used in the research and development of absorbable root canal posts of deciduous teeth,and tried to be used in clinic,but the application of polylactic acid root canal posts are mostly reported in individual cases.At present,there is no manufacturer to produce absorbable root canal posts specially for deciduous teeth,so it still needs a lot of experimental research to make polylactic acid material into absorbable root canal posts of deciduous teeth.Hydroxyapatite(HA)is the main component of teeth and is often used as a filling material of polylactic acid.At present,the application of polylactic acid and hydroxyapatite in the restoration of deciduous anterior teeth has not been reported,so this study is to find a suitable mass ratio of polylactic acid and hydroxyapatite composite materials,and to explore the feasibility of polylactic acid composite root canal post in the restoration of deciduous anterior teeth from the point of view of mechanics,so as to lay a foundation for the application of polylactic acid composite root canal post.Methods1.Poly-L-lactic acid/hydroxyapatite(PLLA/HA)composites with different proportions were prepared by melt blending.According to the different mass fraction of HA,the composites were divided into five groups:PLLA,PLLA-1%HA,PLLA-3%HA,PLLA-5%HA and PLLA-7%HA.The tensile and bending properties were tested by electronic universal testing machine,and the impact properties were tested by pendulum impact tester.The bending modulus and impact strength of the five groups were compared by one-way ANOVA,the tensile strength and bending strength were compared by Welch test,pairwise comparison was conducted by Games-Howell method,and the test level was bilateral α=0.05.2.Sixteen isolated deciduous anterior teeth were collected,the compression modulus and compressive strength of root dentin were measured by electronic universal testing machine,and the mechanical properties of the root dentin were compared with those of PLLA-1%HA,PLLA-3%HA and PLLA-5%HA composites.3.20 isolated deciduous anterior teeth with single root canal and similar shape were randomly divided into 4 groups with 5 teeth in each group,which were fixed with PLLA-1%HA root canal post,PLLA-3%HA root canal post,PLLA-5%HA root canal post and composite resin short post respectively,and were restored with post-core crown,and the fracture resistance of each group was tested by electronic universal testing machine,and the fracture types were observed.One-way ANOVA was used to compare the fracture resistance of the four groups of teeth,LSD test was used for pairwise comparison,and Fisher exact probability method was used to analyze and compare the fracture types of the four groups of teeth.Results1.There was no significant difference in bending modulus and impact strength among the five groups of PLLA/HA composites(P>0.05).There were significant differences in tensile strength and bending strength of PLLA/HA composites among the five groups(P<0.05).The tensile strength and bending strength of PLLA-1%HA,PLLA-3%HA,PLLA-5%HA and PLLA-7%HA groups were lower than those of PLLA group,and the tensile strength of PLLA-7%HA group decreased most obviously.However,there was no significant difference in tensile strength and bending strength among PLLA-1%HA,PLLA-3%HA and PLLA-5%HA(P>0.05).2.The average compressive modulus and compressive strength of 16 deciduous anterior teeth were 3.63GPa and 128.03MPa respectively.The results of t test showed that there was no significant difference in the compression modulus between the root dentin of deciduous anterior teeth and the bending modulus of PLLA-1%HA,PLLA-3%HA and PLLA-5%HA composites(P>0.05).The compressive strength of root dentin of deciduous anterior teeth was higher than tensile strength of PLLA-1%HA,PLLA-3%HA and PLLA-5%HA composites,and the difference was statistically significant(P<0.05).3.There was no significant difference in fracture resistance of deciduous anterior teeth after restoration of deciduous anterior teeth with PLLA-1%HA,PLLA-3%HA and PLLA-5%HA root canal post groups(P>0.05),and they were all higher than those of composite resin short post groups,the P values were 0.009,0.009 and 0.034,respectively.Most of the fracture types of the four groups were repairable,and there was no significant difference among the four groups(P>0.05).Conclusion1.PLLA/HA composites are successfully prepared in this experiment,PLLA-1%HA,PLLA-3%HA and PLLA-5%HA composites have better mechanical properties.2.Considering the bending modulus of the material,the composite materials of PLLA-1%HA,PLLA-3%HA and PLLA-5%HA are suitable for the manufacture of root canal posts of deciduous anterior teeth.3.The fracture resistance of PLLA-1%HA,PLLA-3%HA and PLLA-5%HA root canal posts in repairing residual roots of deciduous anterior teeth are higher than that of composite resin short posts,and can meet the needs of children’s daily masticatory function. |
