Streptococcus mutans is one of the more significant pathogens involved in the development of dental caries in humans. The purpose of this research was to design a $TiO_2-coated$ dental instrument and to determine the bactericidal effects of the instrument on S. mutans. $TiO_2$ photocatalytic films were prepared by the low-pressure metal-organic chemical vapor deposition (LPMOCVD) method using titanium tetraisopropoxide (TTIP) as precursor. The photocatalytic reaction was carried out on a $TiO_2-coated$ pyrex petri dish with an ultraviolet (UV) light emitting diode (LED) illuminator or a fluorescent lamp light source. Our data indicates that the relative survival ratio of S. mutans when plated onto $TiO_2$ photocatalytic films and under exposure to UV-A light for 15 min was 0.01%. In addition, a fluorescent lamp light source also had bactericidal effects on the S. mutans plated $TiO_2$ photocatalytic films. These results indicate that $TiO_2-coated$ dental materials or devices may be useful in dental treatments for the prevention of carious or enamel demineralization.