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Mecanismos de formação da face: o que ocorre é nivelamento, e não fusão, dos processos
... All evidence has shown that the face is formed by leveling of the embryonic processes, except at a very specific and central point of the hard palate, from which anterior and posterior leveling is also established. 6 These concepts, of face formation mechanisms, and their evolution -from the fusion to the leveling -have been meticulously reviewed, described and presented in an article published in 2017 6 (Figs 2 and 3). ...
... But there is a most important point: the first signs of formation of this successional lamina that will give rise to permanent teeth only begin to appear after the eleventh week of embryonic life. 6,13 As mentioned before, the deciduous teeth ...
... The fact that the deciduous maxillary lateral incisor arises from one or another facial embryonic process does not distinguish or modify its embryonic origin or its nature, especially if we consider that the mechanism of fusion of embryonic processes is not scientifically supported: There is no evidence of these fusions, obtained by means of any analysis or methodology. 6 All evidence shows that leveling of embryonic pro- ...
Introduction:
Supernumerary teeth in cases of cleft lip and palate do not result from the division of normal germs before the formation of hard tissue. Deciduous and permanent teeth odontogenesis begins after the face has formed, either with or without the cleft.
Discussion:
The most acceptable hypothesis to enable understanding of the presence of supernumerary teeth on one or both sides of the cleft palate is hyperactivity of the dental lamina in its walls. This hyperactivity, with the formation of more tooth germs, must be attributed to mediators and genes related to tooth formation, under strong influence of local epigenetic factors, whose developmental environment was affected by the presence of the cleft.
Conclusion:
The current concepts of embryology no longer support the fusion of embryonic processes for the formation of the face, but rather the leveling of the grooves between them. All human teeth have a dual embryonic origin, as they are composed of ectoderm and mesenchyme/ectomesenchyme, but this does not make it easy for them to be duplicated to form supernumerary teeth.
... 6 In the anterior region, it levels with the primary palate, preserving the incisive foramen and canal in the midline, which are derived from the primary and secondary palates and contain vessels, nerves, glands and segments or remnants of the nasopalatine duct. 7 In the first years of postnatal life, cranial growth predominates over facial growth. 8,9 During this period, mandibular growth is exuberant, while the growth of the maxillary complex is limited. ...
... 12 Comprehension of the mechanism of formation and the causes of orofacial developmental disorders requires full knowledge of embryology and anatomy. 7 The understanding of premaxillary development and how it is associated with the maxilla may: ...
... These are two independent phenomena, especially in relation to the time when they occur. 7 Cleft position does not always coincide with the premaxillary-maxillary suture, 12,15,19 because bone development does not match primary facial development. Face formation lines are not identical to those where bone growth centers meet in all sutures, including the premaxillary-maxillary suture. ...
Objective:
To evaluate topographic and temporal aspects of premaxillary bone and premaxillary-maxillary suture, since they are fundamental anatomical elements little explored clinically.
Methods:
1,138 human dry skulls were evaluated, of which 116 (10.19%) of the specimens were children, and 1,022 (89.81%) were adults. The skulls were photographed and the percentage of premaxillary-maxillary suture opening was determined. Subsequently the data were tabulated and submitted to statistical analysis, adopting a level of significance of 5%.
Results:
The progression of premaxillary suture closure from birth to 12 years of age was 3.72% per year. In 100% of the skulls up to 12 years, the premaxillary-maxillary suture open in the palatal region was observed, while 6.16% of adults presented different degrees of opening.
Conclusions:
The premaxilla exists in an independent way within the maxillary complex and the presence of the premaxilla-maxillary suture justifies the success of anteroposterior expansions to stimulate the growth of the middle third of the face, solving anatomical and functional problems.
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