A birth defect in which the upper jaw fails to fuse entirely is called?

The condition where the upper jaw fails to fuse entirely is referred to as a cleft palate. This defect occurs during the early stages of fetal development when the structures forming the roof of the mouth do not fully come together, resulting in an opening or gap in the palate. This can lead to difficulties with feeding, speech, and increased risk of ear infections due to the connection between the oral cavity and the nasopharynx.

Cleft palate specifically refers to the separation affecting the hard and/or soft palate, while cleft lip, indicated in another choice, pertains to a similar but distinct condition affecting the lip. The terms "harelip" and "palatoschisis" are often used interchangeably or as alternative names in certain contexts, but cleft palate is the clinically recognized term that precisely describes the failure of fusion in the upper jaw region. Understanding these distinctions is important in the context of congenital defects and their implications for treatment and management.