Morphological abnormaly of tooth and/or root anatomy may not only adversely influence the effort of instrumentation in periodontal therapy, but adversely become a high risk areas for microbial dental plaque retention. Therefore, it is important for understanding the knowledge concerning the variations of tooth morphology and root anatomy. This text, reviewing a seral research data on the tooth morphology and comparative literatures related to clinical significance in localized periodontal and pulpal disease, is addressed.