Tabriz University of Medical Sciences Journal of Dental Research, Dental Clinics, Dental Prospects 2008-210X 11 1 2017 03 30 Effect of nano-hydroxyapatite toothpaste on microhardness of artificial carious lesions created on extracted teeth 14 17 10.15171/joddd.2017.003 EN Asghar Ebadifar Mohammad Nomani Sayed Ali Fatemi Journal Article 10.15171/joddd.2017.003 2016 08 14 2017 03 01 Background. Many types of toothpastes contain substances that can remineralize initial enamel caries. This study aimed to assess the effect of nano-hydroxyapatite (NHA) on microhardness of artificially created carious lesions. Methods. In this in vitro study, NHA was prepared using sol-gel technique and added to the toothpaste with 7% concentra-tion. A total of 80 extracted sound teeth were collected. The crowns were polished using 500-grit abrasive paper. The spe-cimens were randomly coded from 1 to 80. Number 1 to 40 were assigned to group A and numbers 41 to 80 to group B. The microhardness was measured using HVS-1000 Vickers microhardness tester. The specimens were demineralized using 37% phosphoric acid for 3 minutes in order to create artificial carious lesions and then were rinsed with water, air-sprayed for 3 minutes and dried. Microhardness was measured again. Next, the specimens were brushed for 15 days, twice daily, for 15 seconds. After 15 days, microhardness was measured again. Toothpaste A contained NHA and fluoride and toothpaste B contained fluoride alone. Data were analyzed using SPSS 16, with one-sample Kolmogorov-Smirnov test and ANOVA at a significance level of P<0.05. Results. The microhardness of specimens significantly decreased following acid exposure (P<0.01) but increased again in both groups after exposure to toothpastes. The increase in microhardness was significantly greater in group A (P<0.01). Conclusion. The toothpaste containing NHA was more effective than the toothpaste without NHA for the purpose of re-mineralization.