The formation of secondary palate starts with the growing of tissues vertically and mesially forming the right and left lateral palatal shelves. On the week 8, the tongue will be withdrawn downwards and the right and left lateral palatal shelves will be rapidly elevated, flipped into a horizontal orientation and fuse together from the front to the back two. The right and left lateral palatal shelves contact or fuse with each other at the midline to form the secondary palate two.A lot of growth factors are actively involved in the signalling to the tissues during craniofacial development. These growth factors function to control the cells proliferation, survival and apoptosis. Some of the growth factors that can be implicated in the facial development resulting in craniofacial defect are BMP, FGF, Shh, Wnt and endothelins. One of the environmental factors that has been identified in mice study to have link to cleft lip is teratogen which can interfere the molecular signalling between the growth factors. However, the exact mechanism is still not clear. Another environmental factors that has been actively involved in studies to prevent cleft lip and palate occurrences is the intake of folic acid during pregnancy. 0.4 mg folic acid intake per day has been shown to reduce one third risk of cleft lip (with or without cleft palate) in babies. However, it seems had no apparent effect on the risk of cleft palate alone.
They allow for the appraisal of shape and size of jaws and teeth. This can be valuable for the long-term evaluation of development and for the follow up of treatment results. Depending on the type of jaw abnormality, a face bow record for transfer on to the articulator, can sometimes be appropriate for the patient. Radiographs - Radiographic investigations should be based on individual needs and used in conjunction to the clinical examination. As with all other dental radiographs, the benefit gained for the patient with the radiograph must be weighed against the radiation dosage of taking it. In the assessment of jaw abnormalities, the most common radiographs taken used to be the dental panoramic tomography and lateral cephalometry. With the advancement in technology, the use of 3D imaging e.g. Cone Beam Computed Tomography (CBCT) has gained popularity for the use of radiographic examinations of facial bones for purpose of planning complex orthognathic surgery, especially involving significant facial asymmetry. A 3D facial construction model can be utilised in more complex malocclusion to help plan management. Classification
Size
MicrognathiaMandibular micrognathia is the condition when lower jaw is smaller than normal. Failure of the ramus to develop will give rise to micrognathia. Micrognathia can be classified as either congenital or acquired. Clinical appearance of some patients with congenital type of mandibular micrognathia can have a severe retrusion of the chin but by actual measurements, the mandible maybe be found to be within the normal limits of variation.