Effect of different boron contents within boron-doped hydroxyapatite-chitosan nano-composite on the microhardness of demineralized enamel

Dental caries is a prevalent chronic disease globally, arising from an imbalance between tooth remineralization and demineralization. Early detection of lesions is crucial, with non-invasive methods preferred in the initial stages of caries for enamel remineralization and demineralization prevention. This study aimed to assess the impact of varying contents of boron-doped hydroxyapatite-chitosan nano-composite on the microhardness of demineralized enamel.

Boron-doped hydroxyapatite-chitosan nano-composites at concentrations of 0%, 5%, 10%, and 15% were prepared using the sol-gel method. Thirty intact human premolars were collected to evaluate tooth remineralization. The teeth were divided into buccal and lingual halves, subjected to pH cycling for 14 days to demineralize the enamel surface. Subsequently, the specimens were randomly divided into four groups (n = 15) based on the application of remineralizing materials: Group 1 - Hydroxyapatite-chitosan nano-composite (HApC); Group 2 - Boron-doped hydroxyapatite-chitosan nano-composite (B@HApC) with 5% boron concentration; Group 3 - Boron-doped hydroxyapatite-chitosan nano-composite (B@HApC) with 10% boron concentration; and Group 4 - Boron-doped hydroxyapatite-chitosan nano-composite (B@HApC) with 15% boron concentration. Microhardness was measured at three points using a Vickers hardness test (300 g force for 10 s).

The study revealed a significant difference between the nano-composite groups containing 5%, 10%, and 15% boron compared to the control group (p < 0.001). The highest microhardness was observed in the 15% boron group (49.42), with the control group showing the lowest microhardness (20.15). Pairwise comparisons of microhardness indicated a significant difference between Group 4 and the control group (p < 0.05). However, no significant differences were found between Groups 2 and 3, Groups 2 and 4, and Groups 3 and 4 (p > 0.05). Scanning electron microscope (SEM) results supported the microhardness findings, showing a mineral layer covering the porous structure resulting from enamel surface demineralization in the intervention groups, highlighting the effectiveness of boron in enhancing the microhardness of demineralized enamel.

The study demonstrated that a content of 15% boron in B@HApC and higher led to increased microhardness of demineralized enamel. Additionally, content of 5% and 10% boron in the nano-composite also improved microhardness, although not to a statistically significant extent.