polymers Article SEM/EDS Evaluation of the Mineral Deposition on a Polymeric Composite Resin of a Toothpaste Containing Biomimetic Zn-Carbonate Hydroxyapatite (microRepair ® ) in Oral Environment: A Randomized Clinical Trial Andrea Butera 1 , Maurizio Pascadopoli 2, * , Simone Gallo 2, * , Marco Lelli 3 , Fabrizio Tarterini 3 , Federico Giglia 1 and Andrea Scribante 2, *   Citation: Butera, A.; Pascadopoli, M.; Gallo, S.; Lelli, M.; Tarterini, F.; Giglia, F.; Scribante, A. SEM/EDS Evaluation of the Mineral Deposition on a Polymeric Composite Resin of a Toothpaste Containing Biomimetic Zn-Carbonate Hydroxyapatite (microRepair ® ) in Oral Environment: A Randomized Clinical Trial. Polymers 2021, 13, 2740. https:// doi.org/10.3390/polym13162740 Academic Editor: Antonio Gloria Received: 31 July 2021 Accepted: 11 August 2021 Published: 16 August 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Unit of Dental Hygiene, Section of Dentistry, Department of Clinical, Surgical, Diagnostic and Pediatric Sciences, University of Pavia, 27100 Pavia, Italy; andrea.butera@unipv.it (A.B.); federico.giglia01@universitadipavia.it (F.G.) 2 Unit of Orthodontics and Pediatric Dentistry, Section of Dentistry, Department of Clinical, Surgical, Diagnostic and Pediatric Sciences, University of Pavia, 27100 Pavia, Italy 3 Department of Industrial Chemistry “Toso Montanari”, University of Bologna, 40126 Bologna, Italy; lelli.marco1@gmail.com (M.L.); fabrizio.tarterini@unibo.it (F.T.) * Correspondence: maurizio.pascadopoli01@universitadipavia.it (M.P.); simone.gallo02@universitadipavia.it (S.G.); andrea.scribante@unipv.it (A.S.) Abstract: Toothpastes containing biomimetic hydroxyapatite have been investigated in recent years; the behavior of this material in the oral environment has been evaluated directly on dental enamel showing a marked remineralizing activity. To propose microRepair ® -based toothpastes (Zn-carbonate hydroxyapatite) for the domiciliary oral hygiene in patients with dental composite restorations, the aim of this study was to evaluate the deposition of Zn-carbonate hydroxyapatite on a polymeric com- posite resin with Scanning Electron Microscopy/Energy-Dispersive X-ray Spectrometry (SEM/EDS) analysis. Twenty healthy volunteers underwent the bonding of 3 orthodontic buttons on the vestibu- lar surfaces of upper right premolars and first molar. On the surface of the buttons, a ball-shaped mass of composite resin was applied and light-cured. Then, the volunteers were randomly divided into two groups according to the toothpaste used for domiciliary oral hygiene: the Control toothpaste containing stannous fluoride and the Trial toothpaste containing microRepair ® . The buttons were debonded after 7 days (T1—first premolar), after 15 days (T2—second premolar), and after 30 days (T3—first molar) to undergo the SEM/EDS analysis. The deposition of calcium, phosphorus, and silicon was assessed through EDS analysis and data were submitted to statistical analysis (p < 0.05). SEM morphologic evaluation showed a marked deposition of the two toothpastes on the surfaces of the buttons. EDS quantitative analysis showed an increase of calcium, phosphorus, and silicon in both the groups, with a statistically significant difference of calcium deposition at T3 for the Trial group. Therefore, the use of toothpaste containing Zn-carbonate hydroxyapatite could be proposed as a device for domiciliary oral hygiene because the deposition of hydroxyapatite on polymeric composite resin could prevent secondary caries on the margins of restorations. Keywords: biomimetic; dentistry hydroxyapatite; microrepair; toothpaste; composite resin; polymer composite; mineral deposition; remineralization; SEM; EDS 1. Introduction Dental decay is regarded as one of the most frequent conditions affecting people worldwide. This disease arises from a complex interaction over time occurring between acid-producing bacteria and fermentable carbohydrate from the diet. However, many factors play a crucial role for the development of dental decay, among which are physical, biological, environmental, and behavioral ones. In particular, an insufficient fluoride Polymers 2021, 13, 2740. https://doi.org/10.3390/polym13162740 https://www.mdpi.com/journal/polymers