Manual of Laboratory Testing Methods for Dental Restorative Materials. Paromita Mazumdar

tooth tissues.Saturationsaturation is the purity of a color. It is the color of an area judged in proportion to its brightness.Sensitivityability of a test to correctly identify those with the disease (true positive).Shear strengthShear stress at the point of fracture.Shear stressRatio of shear force to the original cross‐sectional area parallel to the direction of the applied force.Specificityability of a test to correctly identify those without the disease (true negative).Spectral reflectanceThe reflectance spectrum or spectral reflectance curve is the plot of the reflectance as a function of wavelength.Surface tensionA measurement of the cohesive energy present at an interface.Tensile strength (ultimate tensile strength)Tensile stress at the instant of fracture.Tensile stressRatio of tensile force to the original cross sectional area perpendicular to the direction of applied force.Teratogenicitycapacity of a substance to cause foetal abnormalities when administered during pregnancy.TransmissionTransmission of light is the moving of electromagnetic waves (whether visible light, radio waves, ultraviolet, etc.) through a material.Toxicityadverse effects that a chemical or physical agent may produce within a living organism.ViscosityResistance of a fluid to flow.

      About the Companion Website

      The companion website for this book is at

      www.wiley.com/go/mazumdar/dental‐restorative‐materials

      The website contains –

       All figures from the book as downloadable PowerPoint slides

       A video demonstrating a universal testing machine

      Scan this QR code to visit the companion website.

Introduction

      Dental materials are a wide variety of materials which have been used in preventive and restorative dentistry in order to preserve and enhance oral health. Different materials such as ivory, sea shells, ceramic, and metals have been used historically, and some of them are still in use. There is a constant search for a material that fulfills the requirements of an ideal restorative material.

      The requirements for an ideal restorative material are as follows:

       Biocompatibility

       Ability to bond to tooth structure and other restorative materials

       Ability to mimic the natural appearance of the tooth

       Has properties similar to dental tissues

       Ability to repair and regenerate damaged tissue

      Studying the properties of these materials along with their interaction in the oral environment allows clinicians to predict the clinical performance in the oral cavity.

      Several in vitro tests are proposed to evaluate different properties of dental materials, to study the tooth restoration or tooth substitute material and the intervention system. Each test has its design and evaluates specific properties. In order to seek for standardized testing protocols, an international organization was created to act in that direction. The main guidance for dental materials laboratory testing recommended by International Organization for Standardization (ISO) is tabulated as follows.

Table 1 ISO specifications to guide dental tests.

1559:1995	Dental materials – alloys for dental amalgam
1564:1995	Dental aqueous impression materials based on agar
1942‐2:1989	Dental vocabulary – part 2: dental materials
6876:2001	Dental root canal sealing materials
7405:1997	Dentistry – preclinical evaluation of biocompatibility of medical devices used in dentistry test methods for dental materials
7491:2000	Dental materials – determination of colour stability
9333:1990	Dentistry – brazing materials
10271:2001	Dental metallic materials – corrosion test methods
11245:1999	Dental restorations – phosphate‐bonded refractory die materials
TS 11405:2003	Dental materials – testing of adhesion to tooth structure
TS 14569‐1:1999	Dental materials – guidance on testing of wear – Part 1: wear by toothbrushing

      The following chapters present the different techniques of testing the dental restorative materials which have been categorized based on the different properties.

1 Assessment of Mechanical Properties of Dental Restorative Materials

      KEY CONCEPTS

       Knowledge of properties of dental restorative materials.

       Ability to differentiate between each type of mechanical properties.

       Understanding of the type of sample preparation required for the different testing modalities.

       Working principle of the equipment used.

       Different applications of the universal testing machine.

      In the oral environment, restorations are subjected to stresses from mastication. These forces act on teeth and/ or material producing different reactions that lead to deformation, which can ultimately compromise their durability over time [1–5].When a specific force or load is applied to a body, a reaction of the same intensity and with opposite direction is produced which causes an internal tension. Hence, it is possible to quantify the reaction that resulted by the applied external load. Since shape and dimensions of specimens under test can be measured, one can calculate stress by the reason between force and unit area.

Depending on the applied load characteristics and consequent stress, different reactions from the tested material may occur. The stress can result in structural alteration of original dimensions. The rate between this alteration by the original dimension results in deformation, that is defined as strain. The stress–strain ratio of a material is relevant to determine its mechanical behavior. For each material, there is a stress–strain proportional relationship, establishing a stress–strain curve. If there is a stress relief during loading and no permanent deformation occurs, it demonstrated its elasticity. This proportion occurs until a limit point that is defined as proportional limit and deformation as elastic deformation. In this point, the maximum stress of a material will withstand without permanent deformation. As stress–strain is proportional until this point, there is a constant proportionality. It determines the elasticity of a material and is calculated by the ratio of stress–strain curve within the elastic limit. This proportionality is defined as modulus of elasticity or Young's modulus. This value will measure the stiffness of such material. However, when the applied load exceeds this point, irreversible deformation occurs, resulting in permanent or plastic deformation. Each