Abstract: Tooth agenesis is the most common craniofacial malformation. Its prevalence in permanent dentition reaches 20% and its expressivity ranges from only one tooth, usually a third molar, to the whole dentition. Genetic linkage and molecular biology studies have allowed, in the last decade, the identification of mutations responsible for some patterns of syndromic and non-syndromic tooth agenesis. The molecular basis of the defect is not completely understood, despite identification of several mutations in muscle segment homeobox gene（msx）-1 and pax-9 genes that seem to be crucial for tooth agenesis, and mutations in the axin-2 gene that cause oligodontia together with a predisposition to colorectal cancer. The main purpose of this article was to summarize the clinical cases and laboratory tests of mutated msx-1 to find out its relationship with the non-syndromic congenital absent teeth, and to provide a reference for the future research of hypodontia.