Effect of addition of nano-hydroxyapatite on physico-chemical and antibiofilm properties of calcium silicate cements

ABSTRACT Objective Mineral Trioxide Aggregate (MTA) is a calcium silicate cement composed of Portland cement (PC) and bismuth oxide. Hydroxyapatite has been incorporated to enhance mechanical and biological properties of dental materials. This study evaluated physicochemical and mechanical properties and antibiofilm activity of MTA and PC associated with zirconium oxide (ZrO2) and hydroxyapatite nanoparticles (HAn). Material and Methods White MTA (Angelus, Brazil); PC (70%)+ZrO2 (30%); PC (60%)+ZrO2 (30%)+HAn (10%); PC (50%)+ZrO2 (30%)+HAn (20%) were evaluated. The pH was assessed by a digital pH-meter and solubility by mass loss. Setting time was evaluated by using Gilmore needles. Compressive strength was analyzed by mechanical test. Samples were radiographed alongside an aluminum step wedge to evaluate radiopacity. For the antibiofilm evaluation, materials were placed in direct contact with E. faecalis biofilm induced on dentine blocks. The number of colony-forming units (CFU mL-1) in the remaining biolfilm was evaluated. The results were submitted to ANOVA and the Tukey test, with 5% significance. Results There was no difference in pH levels of PC+ZrO2, PC+ZrO2+HAn (10%) and PC+ZrO2+HAn (20%) (p>0.05) and these cements presented higher pH levels than MTA (p<0.05). The highest solubility was observed in PC+ZrO2+HAn (10%) and PC+ZrO2+HAn (20%) (p<0.05). MTA had the shortest initial setting time (p<0.05). All the materials showed radiopacity higher than 3 mmAl. PC+ZrO2 and MTA had the highest compressive strength (p<0.05). Materials did not completely neutralize the bacterial biofilm, but the association with HAn provided greater bacterial reduction than MTA and PC+ZrO2 (p<0.05) after the post-manipulation period of 2 days. Conclusions The addition of HAn to PC associated with ZrO2 harmed the compressive strength and solubility. On the other hand, HAn did not change the pH and the initial setting time, but improved the radiopacity (HAn 10%), the final setting time and the E. faecalis antibiofilm activity of the cement.

摘要 目的 矿化三氧化聚合物（Mineral Trioxide Aggregate，MTA）是一种由硅酸盐水泥（Portland Cement，PC）与氧化铋复配而成的硅酸钙类水门汀。研究表明，添加羟基磷灰石可优化牙科材料的机械性能与生物学性能。本研究旨在评估分别添加氧化锆（zirconium oxide，ZrO₂）及羟基磷灰石纳米颗粒（hydroxyapatite nanoparticles，HAn）的MTA与PC的理化性能、机械性能及抗生物膜活性。
材料与方法 本研究评估了4组试样：巴西Angelus公司生产的白色MTA；70%PC+30%ZrO₂；60%PC+30%ZrO₂+10%HAn；50%PC+30%ZrO₂+20%HAn。采用数字pH计检测各组试样的pH值，通过质量损失率评估其溶解度；使用吉尔莫尔针测定凝结时间；通过力学测试分析抗压强度；将试样与铝梯楔一同进行X线摄影，以评估其射线阻射性。抗生物膜活性测试中，将各组材料与在牙本质块上诱导形成的粪肠球菌（E. faecalis）生物膜直接接触，检测残留生物膜中的菌落形成单位（colony-forming units，CFU mL⁻¹）数量。所有实验数据采用方差分析（ANOVA）与Tukey检验进行统计学分析，检验水准设为5%。
结果 PC+ZrO₂、PC+ZrO₂+HAn（10%）与PC+ZrO₂+HAn（20%）三组试样的pH值无统计学差异（p>0.05），且该三组的pH值均高于MTA组（p<0.05）。PC+ZrO₂+HAn（10%）与PC+ZrO₂+HAn（20%）组的溶解度最高（p<0.05）。MTA组的初凝时间最短（p<0.05）。所有试样的射线阻射性均高于3mm铝当量。PC+ZrO₂组与MTA组的抗压强度最高（p<0.05）。各组试样均无法完全清除细菌生物膜，但在试样制备完成后2天，添加HAn的试样较MTA组与PC+ZrO₂组可实现更显著的细菌减少效果（p<0.05）。
结论 在添加ZrO₂的PC中加入HAn会降低其抗压强度并提升溶解度。但另一方面，HAn不会改变试样的pH值与初凝时间，却可改善该类水门汀的射线阻射性（当HAn添加量为10%时）、终凝时间以及抗粪肠球菌生物膜活性。