UG Model Analysis Calculation of TTM and Sum of Incisors

The width and the position of the teeth in all the three planes can be tabulated in the following manner (Table 1)

On the basis of the above measurements we come to certain values like

TTM (Total tooth material) – Sum of the measured mesiodistal widths of all teeth. Maxillary and Mandibular TTM are measured separately. 

The normal TTM for the maxillary arch is 91.7 mm and for the mandibular arch is 84mm, these are the values closest to Indian population.

SI (Sum of Incisors) - Sum of mesiodistal widths of upper and lower incisors are measured separately. The normal SI for the maxillary arch is 31.7 mm and for the mandibular arch is 24mm.

Some inferences can be obtained on the basis of these values

·      TTM more than normal indicates wider teeth and less than normal indicates narrower teeth, to be entered in the table as +ve or –ve respectively.                                      

·      SI more than normal indicates wider incisors and less than normal indicates narrower incisors, to be entered in the table as +ve or –ve respectively.

·      If SI is normal and TTM is more it indicates wider posterior teeth and if TTM is less indicates  narrower posterior teeth

·      If TTM is normal and SI is more it indicates that the posterior teeth are narrower and if SI is less it indicates posterior teeth are narrower.

The significance of this reading is that if the SI is more, and then only in such cases slenderisation can be used as a method of gaining space.