Objectives: The purpose of this study was to compare the ultimate tensile strength (UTS) of sound and caries-affected, mineralized and demineralized human dentin. Methods: Extracted human molars with occlusal carious dentin were vertically sectioned into several 0.7 mm thick slabs. Sound- and caries-affected-containing dentin slabs were obtained from the same tooth and then randomly assigned to be tested either mineralized or demineralized. Each slab was trimmed to a dumbell-shape to reduce the central area to a cross-sectional area of 0.5 mm² located either in sound or carious dentin. Demineralization was obtained by covering the ends of the specimens with nail varnish and immersing in 0.5M EDTA (pH 7.0) for 9 days. Specimens were tested in a Vitrodyne testing machine (0.6 mm/min). Demineralized specimens were tested under water immersion. Comparisons were done by paired t-test (a=5%). Results:  Values are in MPa ± SD (N).

Dentin	Mineralized	Demineralized
Sound	65.1 ± 27.0 (17) a	14.8 ± 6.4 (11) b
Caries-affected	55.5 ± 15.9 (17) a	16.6 ± 9.6 (11) b

There were no significant differences between the UTS of sound and caries-affected dentin, regardless the condition (t=-1.30 for mineralized and t=0.58 for demineralized). Conclusions: No significant differences were found between the UTS of sound vs. caries-affected dentin under both mineralized and demineralized condition. Supported by CNPq 300481/95-0, FAPESP 01/07250-5, Brazil, and CICYT.MAT 2001-2843-C02, Spain.