Contrary to the conventional detection method like radiography, the near infrared light source has been demonstrated to be suitable for dental imaging due to different reflectivity among enamel, dentin, and caries lesion. In this paper, three light sources with different bandwidths based on a transillumination method are compared. The contrast among enamel, dentin, and caries lesion is calculated in different situations. The experimental results show that the random fiber laser has the best comprehensive quality in dental imaging due to its high spectral density, low coherence, and deep penetration. This work provides a guidance for light source selection in dental imaging.