Citation: Moxon, R.; Xu, Z.; Tettey, F.; Chris-Okoro, I.; Kumar, D. Dental Metal Matrix Composites: The Effects of the Addition of Titanium Nanoparticle Particles on Dental Amalgam. Materials 2024, 17, 1662. https://doi.org/10.3390/ ma17071662 Academic Editors: Manoj Gupta, Pradeep K. Rohatgi and Tirumalai S. Srivatsan Received: 1 March 2024 Revised: 2 April 2024 Accepted: 2 April 2024 Published: 4 April 2024 Copyright: © 2024 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/). materials Article Dental Metal Matrix Composites: The Effects of the Addition of Titanium Nanoparticle Particles on Dental Amalgam Ryan Moxon 1 , Zhigang Xu 1 , Felix Tettey 2,3 , Ikenna Chris-Okoro 1 and Dhananjay Kumar 1, * 1 Department of Mechanical Engineering, North Carolina A & T State University, Greensboro, NC 27411, USA 2 Department of Chemical, Biological and Bioengineering, North Carolina A & T State University, Greensboro, NC 27411, USA 3 Department of Industrial and Systems Engineering, North Carolina A & T State University, Greensboro, NC 27411, USA * Correspondence: dkumar@ncat.edu Abstract: Dental amalgams have been used by dentists for the restoration of posterior human teeth. However, there have been concerns about the release of mercury from amalgams into the oral cavity. The objective of the present research is to study the effect of titanium (Ti) nanoparticles on the microstructural mechanism of the release of mercury vapor in two commonly used brands of dental amalgam (the Dispersalloy: 11.8% Cu; the Sybralloy: 33% Cu). Ti powder was added to both the Dispersalloy and the Sybralloy in increments of 10 mg up to 80 mg. The addition of Ti powder to both brands of dental amalgam has been found to result in a considerable decrease in Hg vapor release. The decrease in the Hg vapor release due to Ti addition has been explained by the formation of strong Hg–Ti covalent bonds, which reduce the availability of Hg atoms for evaporation. The Ti atoms in excess of the solubility limit of Ti in Hg reside in the grain boundaries, which also reduces the evaporation of Hg from the amalgam. The binding of Hg with Ti via a strong covalent bond also results in a significant improvement in mechanical properties such as Vickers hardness. Keywords: mercury vapor concentration; γ-1 phase; γ-2 phase; XRD; SEM/EDS; microstructural mechanism; Vickers hardness; dental amalgams; nanoparticles 1. Introduction Dental amalgam material has been a subject of controversy among the dental commu- nity worldwide due to the release of mercury (Hg) vapor from the material when placed in human teeth during and subsequent to the placement of the material for clinical restorations of posterior human teeth [1–3]. Such material has been utilized by dentists in the United States for the restoration of posterior human teeth since 1833, with additional altercations in material compositions [4–7]. The purpose of the research was to determine and investigate the effects of the addition of titanium powder to dental amalgam constituents and deter- mine how, if any, the mercury vapor released from the dental amalgam is affected by the incremental addition of titanium powder to the alloy. Attempts have been made to reduce the amount of mercury vapor released from dental amalgam, and this research is directed at providing some insights in that direction [8–10]. Titanium is a biocompatible material used in the manufacturing of both dental and medical implants. The material is classified as anti-corrosive and is adaptable to human tissue, thus rendering a good immune response when placed as implants in humans [11–13]. The Dispersalloy (11.8% Cu) is considered a moderately high copper dental amal- gam that releases high levels of mercury vapor initially when condensed in the tooth cavity [14,15]. The alloy composition of the material is approximately 50 wt.% to 57 wt.% silver, 24 wt.% to 26 wt.% tin, 6 wt.% to 10 wt.% copper, and 1.5 wt.% zinc. However, the percentages of metal constituents in the Dispersalloy (11.8% Cu) are not conclusive to Materials 2024, 17, 1662. https://doi.org/10.3390/ma17071662 https://www.mdpi.com/journal/materials