**Abstract**

Dental caries is among the most prevalent chronic diseases of childhood, affecting larger part of children and adults. Non-treated enamel caries can lead to destruction and then spreads into the underlying softer and sensitive dentine layer. Dental restorative materials are applied to treat and reconstruct damaged teeth clinically and recover their functions. Currently, there are various dental restorative materials available, and many appropriate materials are used to restore dental carious teeth. The applicability of biomimetic principles can elicit innovations in restorative dentistry for tooth conservation and preservation. There are three types of materials commonly used in dental restorations: resin, alloys, and ceramic. During the past decade, zirconia-based ceramics have been successfully introduced into the clinic due to acceptable biocompatibility, lower price compared with gold restorations, and better appearance than traditional metal-ceramic restorations. Recently, zirconia restoration is an acceptable treatment option in restorative dentistry and a developing trend in esthetic dentistry.

**Keywords:** dental caries, dental restorative materials, biomimetic principles, resin, zirconia

#### **1. Introduction**

Human teeth have a complex structure with an inner core of highly vascular, soft, and delicate pulp surrounded by the highly mineralized enamel and dentin tissues (**Figure 1**) [1]. The structure of teeth can be altered by diet, age, or diseases such as caries and sclerosis. Currently, dental caries is among the most prevalent chronic diseases of childhood, affecting 60–90% of school-aged children and the larger part of adults [2]. Non-treated enamel caries can lead to destruction and then spreads into the underlying softer and sensitive dentine layer. Dental caries could attack the cement of the root and cause gum recession and periodontitis [3]. Dental enamel is composed of long and parallel mineralized crystals containing 90–92% hydroxyapatite, 1–2% organic matrix proteins, and 4–12% water [4]. In addition, the thickness of enamel is different in different anatomical parts of different teeth. For instance, the enamel thickness at the cementum-enamel junction (CEJ) is thinner than the occlusal/incisal surface. Further, the average enamel thickness of incisal edge, premolar cusp, and molar cusp are 2 mm, 2.3–2.5 mm, and 2.5–3 mm, respectively [5]. Dentin is composed of inorganic (50% by volume) and organic material (30% by volume; 90% of which is type 1 collagen and 10%

#### **Figure 1.**

*Structure of human tooth. Human teeth have a complex structure with an inner core of highly vascular, soft, and delicate pulp surrounded by the highly mineralized enamel and dentin tissues.*

non-collagenous proteins) [6]. Dentin covers most of the tooth structure, and it is externally covered by enamel and cementum.

Unfortunately, dental caries is non-avoidable disease. The tooth's hard tissue, included the enamel and dentin, is typically damaged by dental caries. The shape and function of the teeth are also impaired. In spite of much effort in oral health promotion and preventive methods, dental restorations are still needed. Natural teeth are always considered to be a reference while employing biomimetic approaches to restore diseased or fractured dental tissues [7]. The main goal of restorative dentistry is to create a restoration that can mineralize initial enamel and dentinal lesions in native form. Besides, restorative dentistry aims to develop material that can mimic natural teeth' structural, functional, and biological properties.

Dental restorative materials are applied to treat and reconstruct damaged teeth clinically and recover their functions [8]. Currently, there are various dental restorative materials available, and many appropriate materials are used to restore dental carious teeth. At a macrostructural level, various biomimetic restorative materials can be applied to achieve the teeth' biomechanical, structural, and aesthetic integrity. For this purpose, materials scientists take natural teeth as a reference during the development of dental restorative materials. The widespread application of bionic principles in the field of dentistry can also promote the innovation of restorative dentistry, especially in the field of protection and preservation of teeth. For example, when restoring damaged parts of teeth, dentists should pay more attention to factors, such as color tone, internal coronal anatomy, mechanics, and tooth position in the dental arch [9]. There are three types of materials commonly used in dental restorations: resin, alloys, and ceramic [10]. In dental clinical, resin dental composites and glass-ionomer cements are commonly used to restore features depending on the extent of damage and aesthetic requirement. While alloy and ceramic materials are mainly used for fixed restorations (e.g., fixed dentures), removable restorations mainly use nano-resins and alloys. Recently, the most prevalent clinical materials in oral restorations are ceramics and nano-resins.
