The local factors responsible (Etiology of malocclusion) to produce a localized effect confined to one or more adjacent or opposing teeth.
Anomalies in Number of Teeth in etiology of malocclusion
In order to achieve good occlusion, the normal number of teeth should be present. Presence of extra teeth or absence of one or more teeth predisposes malocclusion (etiology of malocclusion).
Supernumerary teeth in etiology of malocclusion
Teeth that are extra to the normal complement are termed supernumerary teeth. These teeth have abnormal morphology and do not resemble normal teeth. Extra teeth that resemble normal teeth are called supplemental teeth.
A frequently seen supernumerary tooth is the mesiodens which occurs in the maxillary midline. They can occur singly or as a pair and are usually conical in shape. Un-erupted mesiodens is one of the causes of midline spacing. Supernumerary teeth can also occur in the premolar or third molar regions (etiology of malocclusion).
Supplemental teeth are most often seen in the premolar and lateral incisor region. It is not uncommon to find an extra lower incisor. The supernumerary and supplemental teeth cause non-eruption of adjacent teeth into abnormal locations. Unerupted supernumerary teeth pose a risk of cystic transformation. This is also responsible for (etiology of malocclusion).
Missing teeth in etiology of malocclusion
Congenitally missing teeth are by far more common than supernumerary teeth and can occur in either of the jaws. The following are some of the commonly missing teeth in decreasing order of frequency:
a. Third Molars
b. Maxillary lateral incisors
c. Mandibular second premolars
d. Mandibular incisors
e. Maxillary second premolars
Absence of teeth can be unilateral or sometimes bilateral. They may occur along with other anomalies such as presence of extra teeth. Absence of one or more teeth predispose to spacing in the dental arch. The adjacent teeth migrate and therefore cause abnormal location and axial inclination of teeth. Absence of a permanent tooth quite often results in over retained deciduous teeth.
Anomalies of Tooth Size in etiology of malocclusion
In order to have normal occlusion, there should be harmony between the tooth size and arch length and also between the maxillary and mandibular tooth size. An increase in size of teeth results in crowding while, smaller sized teeth predispose to spacing.
A commonly seen anomaly is the presence of smaller sized maxillary lateral incisors. Anomalies of size can also occur in the mandibular premolars. Fusion between two adjacent teeth or between a supernumerary tooth and a normal tooth may predispose to malocclusion (etiology of malocclusion).
The size of teeth is to a large extent determined genetically. Thus most of these conditions show a positive family history.
Anomalies of Tooth shape in etiology of malocclusion
Anomalies of tooth size and shape are very often interrelated. Abnormally shaped teeth predispose to malocclusion (etiology of malocclusion). The following are some of the examples of frequently seen tooth shape anomalies:
a. The presence of peg shaped maxillary lateral incisors is often accompanied by spacing and migration of teeth.
b. Another anomaly of tooth shape is the presence of an abnormally large cingulum on a maxillary incisor. The presence of an exaggerated cingulum prevents establishment of normal overbite and overjet. The involved tooth is usually in labioversion due to the forces of occlusion.
c. The mandibular second premolars may rarely have an additional lingual cusp, thereby increasing the mesio-distal dimension of the tooth.
d. Congenital syphilis is often associated with presence of abnormal tooth form. Peg shaped laterals and mulberry molars are classical findings in such patients. Anomalies of shape can occur as a result of developmental defects like amelogenesis imperfecta, hypo plasia of teeth and gemination.
f. Dilaceration is described as a condition characterized by an abnormal angulation between the crown and root of a tooth or angulation within the root. It usually occurs due to a blow to a deciduous tooth which is transmitted to the underlying permanent tooth bud. Dilacerated teeth fail to erupt to normal level and can thus cause malocclusion (etiology of malocclusion).
Abnormal Labial Frenum in etiology of malocclusion
Abnormalities of the maxillary labial frenum are quite often associated with a maxillary midline spacing. Prior to the eruption of teeth, the maxillary labial frenum is attached to the alveolar ridge with some fibers crossing over lingually to the region of the incisive papilla.
As the teeth start erupting, alveolar bone is deposited and the frenal attachment migrates into a more apical position. Rarely, a heavy fibrous frenum is found attached to the interdental papilla region. This type of frenal attachment can prevent the two maxillary central incisors from approximating each other.
This condition is diagnosed by a positive blanch test. When the upper lip is stretched for a period of time, a noticeable blanching occurs over the interdental papilla. A midline intra-oral periapical radiograph usually exhibits notching of the inter-dental alveolar crest.
Midline diastema may also occur due to a number of causes including presence of unerupted mesiodens, anomalies of tooth size and number.
Premature Loss of Deciduous Teeth in etiology of malocclusion
This refers to loss of a tooth before its permanent successor is sufficiently advanced in development and eruption to occupy its place. Early loss of deciduous teeth can cause migration of adjacent teeth into the space and can therefore prevent the eruption of the permanent successor.
Premature loss of an incisor seldom leads to malocclusion (etiology of malocclusion). Loss of a deciduous second molar can cause a marked forward shift of the permanent first molar thereby blocking the eruption of the second premolar, which either gets impacted or is deflected to an abnormal position.
The severity of malocclusion (etiology of malocclusion) caused due to early loss of a deciduous tooth depends on the following factors:
a. Premature loss of deciduous molars predispose to malocclusion due to shifting of adjacent teeth into the space. Early loss of anterior most often do not produce any malocclusion. –
b. The either the deciduous teeth are extracted before the succession teeth are ready to erupt, the greater is the possibility of malocclusion
c. In a person having arch length deficiency or crowding the early loss of deciduous teeth may worsen the existing malocclusion.
Prolonged Retention of Deciduous Teeth in etiology of malocclusion
This refers to a condition where there is undue retention of deciduous teeth beyond the usual eruption age of their permanent successors. A deciduous tooth that fails to undergo resorption will prevent the normal eruption of its permanent successor.
Prolonged retention of deciduous anterior usually results in lingual or palatal eruption of their permanent successors. Prolonged retention of buccal teeth results in eruption of the permanent teeth either bucally or lingually or may remain impacted within the jaws.
Quite often certain parts of the deciduous roots which are away from the path of eruption of the permanent teeth fail to get resorbed thereby leaving small fragments of the root within the jaw These root fragments can deflect or block the adjacent erupting teeth.
The following are some of the reasons for prolonged retention of deciduous teeth:
a. Absence of underlying permanent teeth
b. Endocrinal disturbances such as hypothyroidism
c. Ankylosed deciduous teeth that fail to resorb.
d. Non-vital deciduous teeth that do not resorb.
Delayed eruption of Permanent Teeth in etiology of malocclusion
There are a number of reasons that can delay the eruption of permanent teeth, The following are some of them:
a. Congenital absence of the permanent tooth.
b. Presence of supernumerary tooth can block the erupting permanent tooth.
c. Presence of a heavy mucosal barrier can prevent the permanent tooth from emerging into the oral cavity. A surgical incision in most cases accelerates the eruption.
d. Premature loss of deciduous tooth can result in delayed eruption of the underlying permanent teeth due to formation of bone over the erupting permanent tooth.
e. Endocrinal disorders such as hypothyroidism can cause a delay in eruption of the permanent teeth.
f. Presence of deciduous root fragments that are not resorbed can block the erupting permanent teeth.
Abnormal Eruptive Path in etiology of malocclusion
One of the causes of malocclusion is an abnormal path of eruption which could be due to arch length deficiency, presence of supernumerary teeth, retained root fragments, or formation of a bony barrier.
The maxillary canines develop almost near the floor of the orbit and travel down to their final position in the oral cavity. Thus they are most often found erupting in an abnormal position.
ANKYLOSIS in in etiology of malocclusion
Ankylosis is a condition wherein a part or whole of the root surface is directly fused to the bone with the absence of the intervening periodontal membrane. This most often occurs as a result of trauma to the tooth which perforates the periodontal membrane.
Ankylosis can also be associated with certain infections, endocrinal disorders and congenital disorder such as cleidocranial dysostosis. Clincally, these teeth fail to erupt to the normal level and are therefore called submerged teeth. At times these teeth are totally submerged within the jaw and therefore cause migration of adjacent teeth into the space.
DENTAL CARIES in in etiology of malocclusion
Caries can lead to premature loss of deciduous or permanent teeth thereby causing migration of contiguous teeth, abnormal axial inclination and supraeruption of opposing teeth.
Proximal caries that has not been restored can cause migration of the adjacent teeth into the space leading to a reduction in arch length. A substantial reduction in arch length can be expected if several adjacent teeth involved by proximal caries are left unrestored.
Improper Dental Restorations in etiology of malocclusion
Improper dental restorations may predispose to malocclusion (etiology of malocclusion). Over- contoured occlusal restorations cause premature contacts leading to functional shift of the mandible during jaw closure. Under – contoured occlusal restorations can permit the opposing dentition to supraerupt.
Proximal restorations that are under contoured invariably result in loss of arch length due to drifting of adjacent teeth to occupy the space. Poor proximal contact also causes food lodgement and periodontal weakening of the teeth.