Cleft lip (CL) and cleft palate (CP) are common developmental conditions. Each can occur either by itself or in conjunction with the other (CL/P). Clefts involve failure of normal structures to properly unite together. The timing of cleft formation occurs very early in embryonic life. Many misconceptions about clefts exist due to persistence of outdated scientific theories.
Assembly of the human face involves distinct units of soft tissue and bone known as developmental fields. Each field is like a Lego® piece with a unique size, composition and growth potential. Neighboring fields interact with one another. A small or absent field causes changes in the shape or growth pattern of neighboring fields to occur. When defective fields prevent normal structures from correctly fusing, a facial cleft results.
The anatomic site of the cleft lip problem is a faulty developmental field located just inside the nasal cavity. Here, an inadequate amount of bone is produced; this causes the nostril to sit lower than on the non-cleft side. If enough bone is missing the lateral incisor tooth will fail to develop. A cleft in the gum (alveolus) results. The lining of the nose is pulled down into the cleft site. This causes a 30-40% reduction in surface area of the cleft side nasal passage. If this constriction is not released and patched during the initial surgery, the cleft patient is left with an abnormally-shaped nose and is unable to breathe adequately on that side.
Biochemical signals originating from the cleft site can spread outward from the bony nasal rim to affect overlying soft tissues. This process is like an explosion. If small, only the nose is affected; if larger, closure between the lateral lip and the central lip (prolabium) goes wrong: a cleft lip results. Backward extension of the explosion will cause a cleft in the gum (alveolus). Division of the alveolus permits the two sides of the dental arch to drift apart. This can lead to cleft lip-associated cleft palate (see below).
Cleft palate occurs either as an isolated event or in association with a cleft lip. The mechanisms are utterly different. The normal palate is shaped like an upside down letter T. The two sides of the roof of the mouth (palatal shelves) fuse in the midline to a midline vertical bone called the vomer. Fusion occurs like zipper, beginning just behind the gum and continues backward. If the vomer is small it will be out of correct position, the palatal shelves cannot attach to it, and the isolated cleft palate (CP) results. In cleft lip-associated cleft palate (CLP) the vomer field is normal. In CLP, a gum (alveolus) cleft permits a normal-sized vomer to drift away from the midline. When this drift exceeds a critical distance the palatal shelf fails to make contact and a cleft occurs.
Clefts involving the palate are more significant that those affecting the lip alone. Important issues arise regarding feeding, middle ear function, speech and facial growth. These appear at different ages. In infancy and early childhood weight gain and ear infections are problem. Around age two speech development comes into play. In the preteen and adolescence years dental occlusion and facial growth become paramount. For best results a multidisciplinary craniofacial team is essential to provide individualized care for each child.
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