Third-generation zirconia was developed to address the esthetic concerns present in the first and second generations. Higher yttria content (4 mol% or 5 mol%) was incorporated to partially stabilize dental zirconias with increased cubic phase content and, consequently, improve the translucency of these materials [1]. The 4 mol% partially stabilized zirconia (4Y-PSZ) is an intermediary material, which comprises ∼70 w% cubic and ∼30 % tetragonal grains [2]. The clinical indications of this material are usually monolithic anterior and posterior full crowns and 3-unit bridges [2], [3].

Monolithic restorations are commonly glazed to achieve a smooth and aesthetic appearance. On the other hand, the defects created by occlusal contact on glazed surfaces can serve as crack initiators and ultimately degrade the material’s strength [4]. Hence, novel glass coating or infiltration methods for dental zirconia have been developed to enhance mechanical and surface properties, such as smoothness and flexural strength [4], [5], [6]. However, the impact of these alternative glass coatings or infiltration approaches on third-generation zirconia has been explored only to a limited extent [7], [8].

One should note that biological failures or complications (e.g. secondary caries) are frequently reported in clinical studies of ceramic restorations [9], [10], [11]. Oral biofilms are structured communities of microorganisms that adhere to teeth, restorative materials, and soft tissues [12]. The oral cavity undergoes constant fluctuations in pH and temperature as a result of dietary intake. Furthermore, regions beneath the gingival margin often exhibit low oxygen levels or even an absence of oxygen [12], [13], where the cervical margins of ceramic restorations are frequently placed. These conditions render the oral environment conducive to the proliferation of both aerobic and anaerobic microorganisms[12], [13]. Although factors such as fitting accuracy and patients' oral hygiene habits play a key role in biofilm formation and related biological complications, incorporating antimicrobial agents may help prevent or inhibit biofilm growth.

In an attempt to decrease the number of biological failures and complications, antimicrobial actives have been added to resin cements [14], adhesives [15], [16], or restorative materials [17], [18]. In addition, glasses with antimicrobial effect have been explored for dental purposes [5], [18], [19]. The incorporation of silver in glasses [5], [18], [20] has been of particular interest due to the silver’s broad spectrum of activity against different microorganisms [18], [21]. It is suggested that the Ag+ ions are released and act by binding to biological molecules of microorganisms (e.g., DNA, RNA, proteins), which disrupt their functions [21], [22]. Other formulations of biocide glasses have been described [19], [23]. A previous study demonstrated that soda-lime glass powders with CaO content ranging from 15 to 20 w% are potent biocidal agents against both gram-positive and gram-negative bacteria, as well as yeasts [24]. These glasses release Ca2+ ions in saliva. When the microorganism cells come into contact with the material, the leached Ca2+ raise the pH of their membranes, resulting in membrane depolarization [25] and/or calcium uptake into the cytoplasm. The alkalinization might internally spread and ultimately lead to cell death [24].

Given the context above, two soda-lime glass powders were developed: one containing 19.5 wt% of CaO and the other containing 17.6 wt% of CaO and 10 wt% of Ag. These glasses were processed and fused onto a 4Y-PSZ zirconia. Thus, this study aimed to evaluate the effect of two biocidal soda-lime glasses on the mechanical and optical behavior of a third-generation zirconia. The initial and prolonged antimicrobial effects of these glasses against Candida albicans, Streptococcus sanguinis, and Streptococcus mutans were also assessed. All analyses were performed using a commercial glaze as the control. The tested hypotheses were that both experimental glasses would provide an antimicrobial effect (1) and improve flexural strength (2) without affecting translucency (3) when compared to the commercial glaze.