Open Bite

INTRODUCTION-Open bite is a malocclusion that occurs in the vertical plane, characterized by lack of vertical overlap between the maxillary and Mandibular dentition. The anterior open bites particularly skeletal open bites are called as “stigmata of malocclusion”.
Openbites are easy to diagnose but difficult to retain.
CLASSIFICATION - Open bites can be: anterior or posterior
                                                         Skeletal or dental
                                                         Unilateral or bilateral
ANTERIOR OPEN BITE-
ETIOLOGY-Many potential etiologic factors are implicated as causes of open bite including heredity, unfavorable growth patterns, digit-sucking habits, tongue and orofacial muscle abnormal function, orofacial functional matrices and their interaction with the skeletal components , imbalances between jaw posture, occlusal and eruptive forces and head position.

1. Heredity with genetic disposition: Inherited factors such as increased tongue size, and abnormal skeletal size and growth pattern of the maxilla and mandible can also be responsible for open bite malocclusion.
2. Habits: The effect of habits on dentofacial structures is discussed in detail in the chapter of ‘Habits’.
   1. Prolonged thumb-sucking habit is one of the chief etiological factors of open bite. The posture of thumb positioning, the intensity, and the frequency of sucking, all have an influence on the nature and severity of the open bite.
   2. Tongue thrusting is also implicated for some cases of open bite. Tongue thrusting may develop as a complication of thumb sucking habit. Some times tongue thrusting develops as a compensatory mechanism for existing openbite. Thus whether chick comes first or egg is a matter of controversy.
   3. Nasopharyngeal airway obstruction and associated mouth breathing may also result in openbite
3. Skeletal 
   1. An overgrowth or undergrowth of one or more alveolar segments. In anterior openbites there is undergrowth of the anterior segment with excessive growth posterior alveolar portion. In posterior openbites there is undergrowth of the posterior alveolar segment .
   2. Increased anterior and decreased posterior facial height. The posterior face height (Sella -Gonion) and Anterior face height (Nasion –Menton ) are measured on lateral cephalogram with teeth in habitual occlusion to estimate growth directions according to recommendations of JARBAK(JARBAK RATIO). A ratio of less than 62 percent expresses vertical growth pattern and open bite tendency whereas a ratio of more than 65 percent increases the likelihood for horizontal vector and deep bite tendency .
   3. Vertical growth pattern or backward rotation or clock wise rotation of the of the lower jaw
   4. Anticlock wise rotation of the maxillary base.
   5. Divergent jaw bases
   6. Short ramus with long or short body and Increased gonial angle( articulare—gonian –menton )
4. Dental: When there is only dental and dentoalveolar involvement, there is predominance of environmental causes such as thumb or dummy sucking habits, mouth breathing, and tongue or lip thrusting in addition to some local factors such as tooth ankylosis and eruption disturbances that result from over eruption of the posterior teeth or under eruption of the anterior teeth. The periodontal breakdown of anterior teeth may also give rise to anterior openbites with flaring of teeth.

Features of skeletal anterior open bite

 The problem is related to the skeletal bases. A patient having a skeletal anterior open bite is characterized by the following

1. The patient often has a long and narrow face with marked convex profile. A patient with underlying skeletal class III bases may have concave profile.
   1. The patient may have a short upper lip with excessive maxillary incisor exposure
   2. Increase lower anterior facial height and decreased upper anterior facial height
   3. A steep mandibular plane angle( High angle). Thus the angle FMA is increased. There is clock wise rotation or backward rotation of the mandible with increased lower anterior facial height .
   4. Small mandibular body and ramus
   5. Divergent jaw bases 
   6. There is upward rotation of maxillary jaw base

The patient may have a narrow maxillary arch due to lowered tongue posture due to a habit.

Features of dental anterior open bite

Dental anterior open bites do not present with the skeletal complications mentioned above. The following are the features of dental open bite:

1. 1. Proclined upper anterior teeth.
   2. The upper and lower anteriors fail to overlap each other resulting in a mild open bite.
   3. The patient may have a narrow maxillary arch due to lowered tongue posture due to a habit.

POSTERIOR OPEN BITE-

Posterior open bite is a condition characterized by lack of contact between the posteriors when the teeth are in centric occlusion. It mostly occurs in a segment of the posterior teeth.

Causes of posterior open bite

There are two possible causes of posterior open bite:

1. Mechanical interference with eruption, either before or after the tooth emerges from the alveolar bone, or
2. Failure of the eruptive mechanism of the tooth so that the expected amount of eruption does not occur.

Mechanical interference with eruption may be caused by ankylosis of the tooth to the alveolar bone, which can occur spontaneously or as a result of trauma, or by obstacles in the path of the erupting tooth. Examples of such obstructions prior to emergence are supernumerary teeth and non resorbing deciduous tooth roots or alveolar bone. After the tooth emerges from the bone, pressure form soft tissues interposed between he teeth (cheek, tongue, finger) can be obstacles to eruption Ankylosed teeth are usually in infraocclussion and are said to be submerged.The most commonly submerged tooth is retained lower decidous second molar. The second possible cause of eruption failure is a disturbance of the eruption mechanism itself. These patients have no other recognizable disorder, and no mechanical interferences with eruption seem to exist. The condition may be the cause of posterior open-bite which does not respond to orthodontic treatment.