The Microhardness of Enamel and Dentin

Abstract

THE hardness of enamel and dentin has been determined by a variety of methods including abrasion," 2 pendulum,' scratch,4-7 and indentation" teehnics. Since the hardness of enamel and dentin has been shown to have considerable local variations, the methods using a microscratch or microindentation have been preferred. One of the more common types is the Knoop diamond indenter14 which has been used by a number of investigators. ', 12, 15, 16 It should be mentioned, however, that in spite of the fact that the indentations are extremely small, they still represent a macroindentation when compared to the microstructure of enamel and dentin.The majority of the published hardness data for enamel and dentin has been measured on ground sections, although several papers'0 13 reported the hardness of intact enamel surfaces. The conclusions in regard to the difference in hardness from one section of a tooth to another are at times in variance with each other. This study of dentin and enamel was undertaken in an attempt to establish any trends in hardness existing from one area of a tooth to another or between different types of teeth. With this purpose in mind, this research did not attempt to relate the hardness values to the histologic tooth structure, but a sufficiently large number of hardness measurements were made so that the data could be treated on a statistical basis. EXPERIMENTAL Specimen Preparation.-Mature, freshly extracted, noncarious teeth were imbedded in Ward's Bio-Plastic by suspending them in a Vaughn ring containing the polymer mixed with the catalyst and accelerator. The incorporated air was removed by degassing in a vacuum chamber, after which the polymerization was hastened by placing the ring in an oven at 500 C. for 4 hours or more.The imbedded teeth were sectioned by using a water-spray cooled carborundum wheel, 0.33 mm. thick. The specimens were cut so that the sections were 1 to 2 mm. thick, the first cut being made at or slightly below the ocelusal surface or incisal edge. Specimens cut in a direction mesial to distal or buccal to lingual were cut so that the first section was the lingual or mesial surface, respectively. The thickness of each section was measured with a micrometer and the surfaces to be tested were

Microhardness of dentine underlying ART restorations in primary molars: an in vivo pilot study

“…Other studies using that test also made a large number of identations. 7,16,17 The microhardness values of the dentine found in this work differ from those reported in the literature. 14,17 The figures obtained are below the range proposed by Craig 14 and Meredith et al 17 which vary from 50 to 70 KHN, showing the different conditions under which this research was done, when it was sought to evaluate the carious dentine left under the ART.…”

“…A fact that was also noted by Craig and Peyton. 16 Post-restoration time influenced zones 1 and 2, although zone 3 did not show any statistically significant difference (p=0.549) among the four groups, suggesting that the dentine closest to the pulp and farther from the restoration was not affected as to hardness, either by incorporation of elements released by the restorative material or by a process of physiological reparation.…”

“…7 The load used to make the identations in that study was 10 g, which is very small if compared with other experiments that used 50 g for testing enamel and/or dentine. 7,16,17 However, the compared to the G3 teeth (90 days). It is necessary to consider two situations to explain that finding.…”

Microhardness of superficial and deep sound human dentin

“…The calculated mean value for Knoop hardness is also similar to previously reported values, ranging from 50 to 70. [15][16][17] The similarity of reported values is certainly due to the reproducible microindentation techniques employed. 1 Although a hardness-load dependence sometimes exists for brittle materials, no significant hardnessload dependence was detected for either the Vickers or Knoop tests within the test load ranges.…”

The effect of prism orientation on the indentation testing of human molar enamel

“…It consists of mineral-rich prisms embedded in a matrix consisting of water, organic material, and non-prismatic material. The individual prisms are bundles of similarly oriented calcium hydroxyapatite (HA) crystals (Ca 10 (PO 4 ) 6 (OH) 2 ) that are both carbonated and defective. The prisms measure 3-6 μm in cross-sectional diameter while the crystallites are approximately 200 nm in diameter and reach 100 μm in length.…”