Investigating the mechanophysical and biological characteristics of therapeutic dental cement incorporating copper doped bioglass nanoparticles

Highlights

• Copper bioglass nanoparticles incorporated in ZPC (Cu-ZPC) was proposed.

• Cu-ZPC exhibited therapeutic ion releases such as Zn, Cu, Ca and Si.

• Cu-ZPC showed higher odontoblastic differentiation using dental pulp human cells.

• Cu-ZPC inhibited the growth and attachment of E. faecalis.

Abstract

Objective

This study was investigated the mechanophysical properties of zinc phosphate cement (ZPC) with or without the copper doped bioglass nanoparticles (Cu-BGn) and their biological effect on dental pulp human cells and bacteria.

Materials and methods

Cu-BGn were synthesized and characterized firstly and then, the experimental (Cu-ZPC) and control (ZPC) samples were fabricated with similar sizes and/or dimensions (diameter: 4 mm and height: 6 mm) based on the International Organization of Standards (ISO). Specifically, various concentrations of Cu-BGn were tested, and Cu-BGn concentration was optimized at 2.5 wt% based on the film thickness and overall setting time. Next, we evaluated the mechanophysical properties such as compressive strength, elastic modulus, hardness, and surface roughness. Furthermore, the biological behaviors including cell viability and odontoblastic differentiation by using dental pulp human cells as well as antibacterial properties were investigated on the Cu-ZPC. All data were analyzed statistically using SPSS® Statistics 20 (IBM®, USA). p < 0.05 (*) was considered significant, and ‘NS’ represents nonsignificant.

Results

Cu-BGn was obtained via a sol-gel method and added onto the ZPC for fabricating a Cu-ZPC composite and for comparison, the Cu-free-ZPC was used as a control. The film thickness (≤ 25 µm) and overall setting time (2.5–8 min) were investigated and the mechanophysical properties showed no significance (‘NS’) between Cu-ZPC and bare ZPC. However, cell viability and odontoblastic differentiation, alkaline phosphate (ALP) activity and alizarin red S (ARS) staining were highly stimulated in the extracts from the Cu-ZPC group compared to the ZPC group. Additionally, the antibacterial test showed that the Cu-ZPC extracts were more effective than the ZPC extracts (p < 0.05).

Significance

Cu-ZPC showed adequate mechanophysical properties (compressive strength, hardness, and surface roughness) and enhanced odontoblastic differentiation as well as antibacterial properties compared to the ZPC-only group. Based on the findings, the fabricated Cu-ZPC might have the potential for use in the field of dental medicine and clinical applications.

Introduction

Dental types of cement have been widely applied in the field of restorative and orthodontic dentistry such as in cavity linings, sedative filling, temporary or permanent tooth restorations, and the joining of fixed prostheses and orthodontic band [1], [2], [3], [4], [5], [6]. In particular, ‘ideal’ dental cement should have several characteristics: nonirritant, good resistance to dissolution in saliva and oral fluids, high mechanical strength, adequate working and setting time, and low film thickness (≤ 25 µm) for luting agent [7], [8], [9], [10]. Cement that satisfy the aforementioned properties can be classified as zinc phosphate, polycarboxylate, zinc oxide eugenol, glass ionomer, and resin-modified glass ionomer cement [6], [11], [12], [13], [14], [15]. Despite the advent of new cement such as glass ionomers or resin-based cement, many clinicians prefer zinc phosphate cement (ZPC) for luting cast metal prostheses because of its ease of operation, high elasticity and compressive strength, optimum coating degree, ease of excess cement removal, and cost-effectiveness [3], [16], [17]. Moreover, it has been indicated that the high stiffness of ZPC materials could be beneficial for reducing stresses transmitted from the restoration as a base material in the cavity [18]. However, deficiencies of ZPC include low antibacterial activity, the probability of pulp irritation due to the low pH at the beginning of hardening, no chemical adherence to teeth, and relatively high solubility in the oral cavity [3], [19]. Little has been applied to overcome these limitations of ZPC, although many researchers have attempted to improve the properties of cement biomaterials by adding micro/nanoparticles as reinforcements or therapeutic fillers such as graphene oxide, and bioactive glasses [20], [21], [22], [23], [24].

Bioactive glasses (BGs) were first introduced in 1969 by Hench as a promising biomaterial for application in tissue regeneration [25]. A range of bioactive materials with attractive properties, such as biocompatibility and bioactivity, synthesized by novel methods have been investigated [25]. Recently, bioactive glass nanoparticles (BGn) have stood out as excellent candidates for nanostructured composites, as their small size, high surface area to volume ratio and uniformity in shape facilitate a more homogeneous distribution in comparison to their micronsized-counterparts [26], [27], [28]. The addition of BGn to other materials may exhibit synergistic effects combining osteogenic potential and satisfactory mechanical properties through the release of therapeutic metallic ions [26]. Among the variety of therapeutic ions, copper (Cu) ion-containing bioglass nanoparticles (Cu-BGn) have been proven to be able to enhance hard tissue regeneration and vascularization as well as wound healing [29], [30], [31], [32]. Additionally, Cu-BGn is recognized to be antimicrobial, a crucial aspect for effective hard tissue repair under bacterial infection, which can be induced by the release of copper ions from the nanoparticles [33], [34]. As an example, we reported that copper added to bioactive glass nanoparticles or Cu-incorporated bioactive glass nanoparticles (Cu-BGn), not only contributed to angiogenesis but also showed antibacterial activity against E. faecalis, which is frequently accompanied by pulp infections [35].

Recently, Wassmann et al. used commercial Cu-modified zinc phosphate cement (Hoffmann’s copper cement, Hoffmann’s Dental Manufacturer, Germany) to evaluate antimicrobial activities and mechanical properties [19]. They did not find enhanced antimicrobial activities in Cu-modified zinc phosphate cement, probably due to inhomogeneity or the concentration of Cu [36], [37]. To our knowledge, including the above literature, the effect of Cu-modified ZPC has rarely been investigated in terms of odontoblastic differentiation for minimizing pulp irritation. Previously, inorganic cements (e.g., strontium-releasable inorganic, calcium silicate-based, and hydroxyapatite-based cements) have been reported [38], [39], [40]. Unlike commercial Cu-modified zinc phosphate cement, inorganic dental cements have promoted odontogenic differentiation as well as shown antibacterial properties due to the released therapeutic ions.

In this study, we propose a novel Cu-doped bioglass nanoparticles (Cu-BGn) that incorporated onto the ZPC (Cu-ZPC) as a dental cement because Cu-BGn has potential to release therapeutic ions such as Cu, Ca, and Si. To obtain stable Cu-ZPC, the Cu-BGn concentration was optimized based on film thickness and net setting time. The overall characteristics of the optimized Cu-ZPC were compared with those of Cu-free-ZPC by manipulating the mechanophysical properties, such as compressive strength, hardness, and roughness, as well as the biological properties, including cell viability, odontoblastic activities, and antibacterial properties, against dental pulp human cells. The null hypothesis of this study is that there would be no significant differences in the 1) mechanophysical properties and 2) in vitro cellular activations between Cu-ZPC and bare ZPC.