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A3.1 Introduction

A3.1.1 Structure of human dentition:

The permanent adult human dentition normally consists of 32 teeth, of which 16 are located in the mandible and 16 in the maxilla. There are 4 incisors, 2 canines, 4 premolars and 6 molars for the upper and lower dentition. The incisors are used for cutting food, the canines for tearing, the premolars for grasping, and the molars for grinding (i.e., masticating). There is a generic heterogeneous structure for these teeth, where enamel forms an exterior layer over the underlying dentin. From the cervix to the apex of the root, the exterior of the dentin is covered by cementum to which the periodontal ligament attaches the tooth to alveolar bone. Dental enamel is dense, highly mineralized, hard, and brittle. It contains prism-like structures that span from the enamel surface to the junction of enamel and dentin, the dentino-enamel junction (DEJ). The prisms are comprised of hydroxyapatite crystallites and contain very little organic matrix. These properties make dental enamel an excellent material for cutting and masticating food (i.e., processes that involve friction and wear). In contrast, dentin is not as hard as enamel, but it is tougher. Dentin is a heterogeneous material and can be thought of as a composite structure containing four major components: dentin matrix; dentinal tubules; mineral (i.e., carbonate containing hydroxyapatite); and, dentinal fluid. The dentinal tubules (~45 000 per mm2) are formed during development of the dentin matrix and are distributed throughout the dentin matrix in a somewhat uniform manner. The dentin matrix mineralizes in an anisotropic fashion, where a highly mineralized tissue, peritubular dentin, surrounds the dentinal tubules. The mineralized tissue between the dentinal tubules and peritubular dentin is referred to as intertubular dentin. Histological examination has revealed that intertubular dentin is less mineralized than peritubular dentin. Furthermore, the matrix and mineral content of root dentin is different from coronal dentin. A good review of the structure of teeth can be found in Waters [1].

A3.2 Composition

Table A3.1 Basic Constituents of Human Dentin and Enamel*
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Table A3.2 Major Elemental Composition of Surface and Bulk Dental Enamel
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Table A3.3 Trace Elemental Composition of Surface and Bulk Dental Enamel
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Table A3.4 Significant Differences in Trace Element Composition of Whole Human Enamel for High and Low Caries Populationst†
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Table A3.5 Ca/P Molar Ratio of Human Enamel and Dentin
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Table A3.6 Crystallite Size and Lattice Parameters of the Apatite in Human Enamel and Dentin*
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Table A3.7 Elastic Moduli and Viscoelastic Properties of Human Dentin and Enamel
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Table A3.8 Mechanical Properties of Human Enamel
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Table A3.9 Mechanical Properties of Human Dentin
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Table A3.10 Toughness, Fracture Toughness, and Work of Fracture of Human Dentin and Enamel
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Table A3.11 Hardness of Fracture of Human Dentin and Enamel (see notes for units)
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Table A3.12 Permeabilitya of Human Dentin
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Table A3.13 Wetability of Human Enamel
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Table A3.14 Wetability of Human Dentin [38]
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Table A3.15 Critical Surface Tensions (γc) of Human Enamel and Dentin
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A3.3 Final Comments

The quality of data presented can be inferred from the standard deviations or standard error associated with the mean values. In some cases the error can be attributed to either small sample populations or specimen preparation. Where possible, either the number of specimens used or the number of replications of a measurement was reported. The reader should use this information as a guideline of the quality of data. When data are reported for small sample populations, then these data were usually the only source for a given physical property. In review of the literature, specimen preparation appears to have had the most influence on the precision and accuracy of data. Sample collection and storage conditions (e.g., dehydration, crosslinking agents, exogenous contamination) need to be taken into consideration when utilizing the information tabulated. Additional sources of error are dependent on the analytical technique or test method used to make the measurement. It is more difficult to discern the influence of the instrumentation on the reliability of the measurements. However, confidence of the accuracy was judged based on the use of adequate control samples with known physical properties (e.g., correction of mechanical data). In light of these comments, data in the literature were deemed most accurate and appropriate for this handbook when the following conditions were met: the sample population was large; non-destructive specimen preparation and storage conditions were used; and, multiple replications of measurements on a single sample were performed.

There are significant omissions in the data available in the literature. Most notable, is the lack of quantitative analysis of the organic phase of dentin and enamel, and determination of the viscoelastic properties of dentin. The lack of data is attributed to the technical difficulty required to make such measurements and the heterogeneous nature of the dentin, which imparts large variations in these data depending on anatomical location. Other significance absences are the lack of electrical and thermal properties. Finally, vacancies in the tables provided demonstrate omissions in available data.