The effect of nano-hydroxyapatite on white spot lesions: A systematic review and meta-analysis

Objectives To assess the effect of nano-hydroxyapatite (nano-HAP) either with or without fluoride on white spot lesions (WSLs) in terms of remineralisation and colour change. Data sources An electronic search was carried out in MEDLINE via PubMed, Scopus, Web of Science, LILACS, Embase, Cochrane Library, Google Scholar, Grey literature, and hand search. There were no limitations in terms of language and date (till August 2024) and all studies meeting the inclusion criteria were included. The outcome variables were enamel surface microhardness, enamel remineralisation rate, mineral content, and colour change. Different risk of bias tools were employed according to the study design. The level of evidence was graded using the GRADE profiler. Study selection A total of 14 out of 422 studies met the inclusion criteria. Three out of 14 studies were in vivo, one was in situ, while ten of them were in vitro. All 14 studies investigated the nano-HAP effects on WSLs. Following the full-text reviews and statistical analysis, 12 out of 14 studies were only included in the meta-analysis, since the remaining two studies lacked comparable data (mean +/- SD). Results Different forms of delivery for nano-HAP were reported in the included studies. Pure nano-HAP showed promising effects on enamel surface microhardness (MD = 9.29, 95 % CI [7.74, 10.84], p < 0.00001), and mineral gain (MD = 0.09, 95 % CI [0.05, 0.13], P < 0.0001) when compared to fluoride alone. In addition, nano-HAP and fluoride demonstrated similar remineralisation abilities based on the DIAGNOdent (TM) readings (MD=0.09, 95 % CI [0.05, 0.13], p < 0.0001) There were no colour improvements within the WSLs following the application of nano-HAP (MD = -2.76, 95 % CI [-6.79, 1.27], p = 0.18). Conclusion The intervention containing pure nano-HAP showed a promising remineralisation effect on WSLs in comparison to fluoride alone. However, there were no colour changes within WSLs following the use of nano-HAP. Limited number of clinical studies, high risk of bias, quality of the available studies, and relatively short follow-up periods failed to result in concrete evidence. Clinical significance The intervention containing pure nano-HAP showed a promising remineralisation effect in comparison to fluoride alone. Therefore, it might be an effective alternative to fluoride-containing agents.