The frequency of root canal ramifications in mandibular central and lateral incisors and the efficacy of low-temperature injection thermoplasticized gutta-percha in filling these canals were determined, and any evidence of apical leakage was evaluated. Forty mandibular incisors were instrumented; the external root surfaces were coated with nail polish except for the apical foramen, and the teeth were obturated with injection of gutta-percha and sealer. The teeth were centrifuged in India ink for 20 min at 3000 rpm before being suspended in ink for 30 days and then cleared. Under a stereomicroscope at x30 magnification, 62.5% of the teeth showed a simple main canal, 15.0% a bifurcated canal, 7.5% a lateral canal, and 25% accessory canals. Except for the two lateral and three accessory canals, the thermoplasticized gutta-percha was found to be highly effective in filling the root canal ramifications as well as the main canals. The extent of ink penetration was limited to the main canal in seven teeth showing leakage. However, the reliability of conventional apical leakage assessment by only exposing major foramen to dye needs to be reexamined with regard to the potential presence of multiple foramina on the root surfaces.