Temporary restoration materials are widely used in dental clinics and are important for predicting the successful prognosis of endodontic treatment including inlay, onlay, crown, and bridge [1,2]. These materials are also used to protect the invasion of external substances and microorganism and to help the recovery of tooth functions, including mastication and esthetics [3,4].
Recently, the introduction of three-dimensional (3D) printing equipment has enabled quick fabrication of dental restoration through the use of an automatized protocol [5]. Unlike conventional fabrication methods of temporary restorations, such as resin curing or CAD/CAM milling, digital dentistry is dominantly driven by 3D printing technology [6,7].
The resin curing method, which is the conventional fabrication method of temporary restorations, adopts the curing reaction of an acrylic resin system, resulting from the reaction of dibutyl phthalate, a plasticizer, due to the interaction between the powder and liquid when mixed. The powder contains poly-methyl methacrylate (PMMA), a reaction initiator, and the liquid contains methyl methacrylate (MMA) and a small amount of inhibitor [8,9]. This manually driven technique has advantages including the ability to create the desired shape, quick hardening, and excellent handling. However, the conditions of the work environment are strict and the process is, thus, time consuming.
3D printing fabrication is classified into several subtypes, including extrusion, wire, granular, and light polymerized, based on the type of the technology used. Temporary restorative resin materials for dental use are treated with the use of digital light processing (DLP) technology, which adopts light polymerized technique to enable the processing of polymers [10,11]. This technology prints the resins layer by layer as it hardens, by projecting light in the desired shape for photo hardening liquid resins [12]. This technology is advantageous, as it is capable of printing without the use of any supporting beam inside the sculpture, and it produces printing products with excellent details and smooth surfaces and has a high printing speed [13]. On the other hand, there are some limitations, such as the colors of applicable materials are limited and the base materials and printer itself are expensive [14]. In addition, the more exquisite the printed product is, the more complicated is the work in creating the printed product [15].
Temporary restorations that are fabricated through such method undergo polishing and cleansing processes and are used until the placement of the permanent restoration for recovery of the function of the lost teeth [16]. Since temporary restorations are placed inside the mouth, temporary restorative resin materials are used based on analyses of their material properties [17]. There is a lack of studies that assess “what kinds of relationships exist between the negative micro influences of the restorations on intraoral living tissues and the restorations applied after the secondary processing following fabrication using such a method.”
According to a previous study, the monomers leached from the temporary restorative resin materials may cause dental pulp injury, oral mucosal irritation, and allergic reaction [18]. Furthermore, these may also cause hypersensitive asthmatic response, conjunctivitis, neurologic response, and epithelial response in dentists and other dental clinic staff [19]. Toxicity of acrylic resins has been reported from in-vitro cell experiments [20].
Hence, the biocompatibility of all dental resin materials used in temporary restoratives that are to be placed in the mouth must be thoroughly studied before and after their clinical use. This study aims to investigate the influence of dental materials fabricated either by 3D printing technology or self-curing technology on fibroblasts. We also assessed the cytocompatibility of dental materials used for temporary restoratives by analyzing and comparing cell adhesion and cell proliferation (Fig. 1).
Figure 1 Dental fabrication process of temporary restorations by DLP 3D printing and Self-curing method cytocompatibility of the fibroblast cell.