This week I have a case of some very large mandibular third molars. The right mandibular third molar appears as if it’s two molars stuck together. This is due to gemination or twinning. Gemination is when a single developing tooth germ attempts to divide but is unable to completely divide resulting in one massively large tooth. With gemination there is an overall tooth count of 16 in the associated arch. This is not to be confused with fusion (which also results in a massively large tooth) but will only have 15 teeth present in the associated arch. In this case it appears that there is also gemination of the left mandibular third molar as well.