Under-bite

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Alternative names
Micrognathia; Receding chin

Definition
Micrognathia is a relative term describing the small size of the lower jaw.

Considerations
In true micrognathia, the jaw is small enough to interfere with feeding of the infant. Infants with micrognathia may require special nipples in order to feed adequately.

Micrognathia may be the only abnormality in a child, and is often self-correcting during growth, especially at puberty when the jaw grows significantly. It may also be associated with certain inherited disorders and syndromes.

Micrognathia is one cause of abnormal alignment of the teeth. This can be seen by noticing the closure of the teeth. Often there will not be enough room for the teeth to grow and an orthodontist should be consulted when the adult teeth come in. At times, the child can outgrow micrognathia and it makes sense to wait until they are older.

Common Causes

• Pierre Robin syndrome
  
• Hallerman-Streiff syndrome
  
• Trisomy 13
  
• Trisomy 18
  
• X0 syndrome (Turner syndrome)
  
• Progeria
  
• Treacher-Collins syndrome
  
• Smith-Lemli-Opitz syndrome
  
• Russell-Silver syndrome
  
• Seckel syndrome
  
• Cri du chat syndrome
  
• Marfan syndrome

Home Care
If micrognathia interferes with feeding, special feeding techniques and equipment will be required. Techniques can be learned through special programs at most hospitals .

Call your health care provider if

• Your child seems to have a very small jaw.
  
• Your child has difficulty feeding properly.

What to expect at your health care provider’s office
The medical history will be obtained and a physical examination performed.

Medical history questions documenting micrognathia in detail may include:

• When did you first notice that the jaw was small?
  
• How severe is it?
  
• Is there difficulty eating?
  
• What other symptoms are also present?

The physical examination will include a thorough examination of the mouth.

Diagnostic tests that may be performed are:

• Dental x-rays
  
• Skull x-rays

If there are other symptoms present that indicate an inherited condition, testing for that condition may be recommended.

Intervention:
Surgery or orthodontic appliances may be recommended.

After seeing your health care provider:
You may want to add a diagnosis related to micrognathia to your personal medical record.

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