7.2.1 Anomalies of Teeth Positions
Teeth inclination means tilting of a tooth along its longitudinal axis. Its forms are: mesial, vestibular and oral, distal. Vestibular inclination at the front area is often called protrusion, an oral tilt is called retrusion.
Teeth rotation stands for turning a tooth along its longitudinal axis. It is frequent for single-root teeth (incisors, canine teeth) if there is not enough room at the dental arch, or if teeth are jammed.
Supraocclusion - a tooth overhangs the occlusal plane.
Infraocclusion - a tooth does not reach the occlusal plane.
Shift - a tooth changed its position while maintaining its longitudinal axis direction.
Transposition - two teeth exchange their locations.
Dystopia - a tooth cut out of the dental arch at vestibular or oral side.
Retention - a tooth did not cut during a period of physiological teething. The most often cause of retention is horizontal position of the germ or constriction of the dental arch.
These anomalies can be evaluated at sagittal, transversal or vertical directions. At the sagittal plane, the lower dental arch can be positioned by three ways relative to the upper arch: normocclusion - 1st Angle’s class, distocclusion - 2nd Angle’s class, and mesiocclusion - 3rd Angle’s class.
Normocclusion is such relationship of dental arches when at the maximum inter-cuspidation, the mesiobuccal cusp of the first upper molar fits into the inter-cuspate groove of the first lower molar, and the cusp of the upper canine tooth fits between the lower canine tooth and the first premolar.
Distocclusion is characterized by the distal shift of the lower jaw. The first lower molar is shifted relative to the upper molar distally. This group of anomalies can be further divided into the first division - distocclusion is accompanied by protrusion of incisor teeth - and the second division - distocclusion is accompanied by retrusion of incisor teeth.
Mesiocclusion is characterized by the mesial shift of the lower jaw. At this position, the first lower molar is shifted mesially relative to the upper molar. The ventral position of the lower jaw is often accompanied by a reverse bite at the frontal section.
At the transversal plane, the buccal cusps of upper side teeth overlap those of lower teeth, at the maximum inter-cuspidation. A discrepancy between the width of upper and lower dental arches results in anomalies of the bite, designated as buccal nonocclusion, crossed bite, or palatine non-occlusion.
At the vertical plane, mutual position of jaws can be hindered by a deep or an open bite. The deep bite is such a bearing when upper incisor teeth overlap by more than two thirds of the labial surface of lower incisor teeth. The open bite is such an anomaly, where a vertical gap appears between groups of two or more adjacent teeth and their antagonists, at the maximum inter-cuspidation of the teeth. This anomaly may occur at the frontal or lateral sections of the teeth.
7.2.3 Disorders of the Facial Skeleton Structure and Growth
Some of the dental arches mutual position anomalies are determined by deviations in size, position and bearing of the jawbones. These anomalies are often hereditary, although they may be caused by external factors as well.
Prognathia maxillaris is characterized by an excessive growth of the upper jaw in forward direction, while the lower jaw has normal shape and size. The upper frontal teeth do not touch their lower antagonists and protrude out of the mouth, in majority of cases. Chewing of food is difficult, sometimes impossible. The shortened upper lip does not overlap the upper frontal teeth, the lower lip gets inserted between rows of teeth.
Progenia mandibularis is characterized by a large lower jaw, while the upper jaw’s size is at normal range. It is one of the most prominent jaw anomalies and appears at the rate of more than 1% in our population. Hereditary factors play a role at its etiology; although acquired progeniae occur as well, for instance during endocrine glands malfunctions (acromegaly). Increased occlusion and enlarged lower jaw’s body, resulting in the horizontal overlap, are typical for a progenia. Mastication functions of the teeth and speech ability are usually hampered. An altered configuration of the face - enlarged lower third and emphasized chin - does not look nice. That is why this anomaly is often corrected by a surgery after the growth of jaws is completed.
Pseudoprogenia is characterized by a small upper jaw, while the lower jaw’s size is at normal range. This anomaly can be most frequently seen in cases of clefts, that are results of a combination of hereditary causes (insufficient development of the premaxilla) and external factors (consequences of operation scars). It is accompanied by the inverted bite.
Microgenia originates as a result of small lower jaw and is accompanied by distocclusion. The chin projection is absent and the chin changes over to the neck’s upper part almost imperceptibly. The nose and the upper lip, that overlaps the lower lip, protrude from face profile. This disorder may be of hereditary origin, more often it appears after an injury or inflammation of the jaw joint during childhood.
Laterogenia is caused by an increase or reduction in size of one half of the lower jaw, less often by skewing the whole jaw from its normal position. It occurs with the face asymmetry.
7.3 Therapy of Orthodontic Anomalies
The orthodontic therapy is based on the assumption that bone tissues adjust themselves to gradual changes of their functional load. The field can be divided into two basic branches:
1. Conservative orthodontics, that uses effects of forces (orthodontic instruments, functions) and often also the oro-facial system’s growth. Changes in shape of dental arches are initiated by reconstruction of the jaw bone tissue.
2. Surgical orthodontics changes the oro-facial system appearance by surgical operations.
The best time at which the orthodontic therapy should start is the period of mixed teeth, when cutting teeth can be lead to a correct position at the dental arch and when the growth of jaws may affect the teeth development in a positive manner. At the period of temporary dentition, a preventive and prophylactic treatment prevails. Its goal is to enable a natural development of the teeth. A treatment that begins after the dentition change, can be regarded as late therapy, since the main growth of the oro-facial system is over and the dentition development is finished. The period after the growth is finished is suitable for surgical correction of anomalies that require changing the size, the shape, or eventually positions of jawbones (progeniae, prognathiae, open bite). Orthodontic therapy is carried out by several means. Orthodontic instruments, orthodontic extractions, auxiliary surgeries and myotherapy are among the most often used ones.
Orthodontic therapy with the aid of instruments
Fixed appliances are wire arches of various shapes that are connected to the teeth with cemented rings or glued locks. They consist of various springs, elastic tensions and devices that influence the teeth by an external force.
Removable appliances can be divided according to the acting forces into active appliances (acting mechanically), whose elementary example is a plate fitted with active elements (screws, springs etc.), passive and combined appliances. Passive appliances (functional) use muscular functions for correction of an anomaly, they direct the growth and reconstruction of bones. Combined appliances act both mechanically during the therapy - using active elements - and through a muscular function. Treatment with the aid of orthodontic instruments is an exacting one, requiring cooperation of a patient and his/her parents in maintaining the therapeutic regime and oral hygiene.
The basic element of surgical orthodontics are orthodontic extractions that have become a routine part of therapeutic processes today. They enable for faster and more stable incorporation of teeth into the dental arch in case of tightness and lack of space. In case of unequal numbers of teeth at the upper and lower jaws, this method can provide for the correct inter-cuspidation of the teeth. Another reason for extraction may be unfavorable positions of teeth or a tooth’s germ, dental arches asymmetry etc. Extractions also find its application at orthodontic prophylaxis, since well planned extractions of temporary and permanent teeth achieve the correct teeth evolvement.
Surgical therapy of orthodontic anomalies is used mainly for correcting of congenital anomalies of jaws where the orthodontic therapy alone is not sufficient. Surgeries of jawbones are performed after their growth is completed, i.e. around 18 years of age. Until this age, attempts to adjust the teeth positions, height of the bite and mutual positions of jaws should be carried out, so that the best possible conditions for a surgery are achieved. Surgical therapy is most frequently applied in cases of mandibular progenia, open bite, maxillar prognathia, microgenia and laterogenia. A number of surgical techniques have been developed for correction of particular types of anomalies. These are always serious surgical interventions, requiring a patient’s hospitalization.
Myotherapy serves for exercising of particular groups of muscles. It is not very demanding method that should create a proper muscular tonus. Favorable conditions for normal development of the teeth are created by increasing the tonus of flaccid muscles or by releasing a hypertonia.