DEFINITION/OVERVIEW

• Synonyms: hypovestibulosis mandibularis, reduced mandibular vestibule (the space between the cheeks and the lips and teeth)
  
• Definition: The lower lip folds back and covers the mandibular teeth due to the underdevelopment of or the absence of the lower lip anterior vestibule. This results in an elevated appearance of the lower lip when the mouth is opened. At rest, the lower lip may cover the incisors, canines, or even the premolar teeth depending on the degree of hypovestibulosis.

ETIOLOGY/PATHOPHYSIOLOGY

• Congenital, hereditary, or developmental factors
  
• Systems affected: This syndrome can inhibit the full growth potential of the mandible, resulting in a Class 2 malocclusion. It can also lead to an anterior malocclusion (Class 1 malocclusion) by forcing a distal or lingual displacement of the mandibular incisors and sometimes canine teeth. In addition, the soft tissues of the lower lip are frequently traumatized.

SIGNALMENT/HISTORY

• Tight lip syndrome is seen almost exclusively in Chinese Shar-Pei dogs but can be seen in other canine breeds. Evidence of tight lip can be detected shortly after birth in more severe cases but is usually noticed following eruption of the deciduous teeth. Rarely, tight lip manifests after permanent tooth eruption.

CLINICAL FEATURES

• Tight lip syndrome is classified according to the extent of the condition
  
  
  
  • Type I (mild): lip covers incisors only
    
  • Type II (moderate): lip covers incisors and canines
    
  • Type III (severe): lip covers incisors, canines, and extends over premolars

DIFFERENTIAL DIAGNOSIS

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