This loss would then affect the development of the first molar to a far greater extent that the more posterior molars, enabling a proportionally larger m1.
14, 20, 21 Recently, the existence of fusion of tooth primordia to form a more complex tooth has been experimentally proven during development of the first molar (M1) in the mouse mandible.
The Bionator group presented significantly smaller vertical development of the maxillary molars, mandibular incisors and mandibular molars than the Jasper Jumper group.
Probably, there was restriction of the vertical development of the maxillary molars during the orthopedic phase in the Jasper Jumper and Bionator groups; however, these teeth may have been extruded during the fixed mechanical correction.
This increased vertical development of the mandibular molars was expected since acrylic trimming is performed with this objective, based on Harvold's principle of differential eruption, depending on the need to correct the overbite that normally accompanies class II, division 1 malocclusion [13],[13].
Another process of sequential addition, controlled by a balance of activation and inhibition, is at work in the development of the successive molars.
A key feature of the IC Model is that the changes in size along the molar sequence will be cumulative – in other words, the development of the third lower molar (m3) is affected both by m2 and m1.
For this reason, it is important to reinforce that we found that the position IIIB at beginning of the development of the lower third molar was associated with dental crowding in patients without retainer in the end of their treatment.
Labonne et al.[ 12] demonstrated that loss of the lower fourth premolar in some taxa appeared to remove a spatial constraint on the development of the lower first molar.
The development of the second primary molars starts at around the same time as the development of the first permanent molars and permanent incisors, but the maturation of the permanent teeth occurs more slowly [ 14, 15].
