Dental burs are commonly used to remove demineralized tooth tissues as a part of routine cavity preparations. However, flaws introduced within dentin and enamel during the material removal process may reduce the structural integrity of the tooth. The influence of flaws on the properties of these tissues has not been adequately addressed. Objectives: To characterize the defects introduced in human dentin using clinically relevant dental burs and assess their influence on the tissue's strength. Methods: Rectangular beams with nominal cross-section of 0.8x0.8mm^2 and 8mm length were obtained from the coronal dentin of unrestored molars. Tungsten carbide or diamond coated burs were used with a high speed handpiece mounted to a Dyna 2400 milling machine to machine each beam (n=15 for each bur type) to a reduced nominal thickness of 0.6mm. After machining, the specimens were tested in 4-point flexure to failure under monotonic displacement control loading. The flexural strength was determined from the load, load-line displacement responses, and compared with that obtained from control beams that were not subjected to the surface treatment with dental burs. Results: Differences in the flexural strength of the control, tungsten carbide bur, and diamond bur prepared specimens were apparent. Removing dentin with carbide and diamond burrs resulted in a reduction of both the minimum and average strength of dentin. The minimum strength was reduced by 36% and 52% when using carbide and diamond burs, respectively. In addition, the use of carbide burs resulted in a 15% reduction in the average strength of dentin, while diamond burs resulted in a 31% reduction in average strength. These differences were found to be statistically significant (p≤0.05). Conclusion: The average and minimum flexural strengths of dentin are reduced significantly by flaws introduced by dental burs. (Supported by the National Science Foundation, BES 0238237).

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