Introduction:The development of a self-limiting caries removal technique would be of great clinical importance. Smart bur II is a relatively new bur in the dental market and its manufacturer is claiming that it is the ultimate bur for selective caries removal. Objectives: The aim of this study was to evaluate caries removal time and efficacy of Smart bur II in comparison with conventional carbide bur. Material and methods: Twenty-three children, each with bilateral primary canine showing comparable class V carious lesions were selected for this study. They were randomly divided into two groups. Group I (n=30): caries was removed using the Smart bur II, Group II (n=30): caries was removed using the conventional carbide bur. The efficacy of caries removal was evaluated by "tug-back" sensation. Time needed for caries removal in both groups was recorded in seconds. An additional group of seven extracted carious primary canine were randomly selected for the in vitro study. Teeth were cut into 2 halves through center of the lesion, one half was subjected to caries removal using Smart bur II as in group I and conventional carbide bur was used in the other half as in group II. The specimen were prepared and topographic features of dentin after caries removal was evaluated using the scanning electron microscope. Results: The comparison of caries removal efficiency between smart bur II and carbide bur showed that the smart bur II completely removed caries in 11 cases accounting for 36.6% and incompletely removes caries in 19 cases accounting for 63.4%. While the carbide bur completely removed caries in 28 cases accounting for 93.3% and incompletely remove caries in 2 cases accounting for 6.7%. Caries removal time ranged between 192 seconds to 380 seconds for smart bur II, while caries removal time ranged between 198seconds to 361 seconds for carbide bur (control group). The mean ± SD caries removal time was 271.16± 26.78 for Smart bur II and 235.16± 27.37 for carbide bur. The results of both caries efficiency and caries removal time were significantly different at p ≤ 0.05 and p ≤ 0.05 respectively. Conclusions: The smart bur ΙΙ had significantly lower caries removal efficiency when compared to conventional carbide bur. The smart bur ΙΙ required significantly longer caries removal time when compared to conventional carbide bur.