Mezialny bite – the anomaly of occlusion which is characterized by promotion forward of the lower tooth alignment in relation to top at close position of jaws. As external manifestations of a mezialny bite serve the massive, acting chin, a concave profile of the face, the sinking-down upper lip; oral signs include mezialny occlusion of painters and canines, a straight line or the return reztsovy occlusion; functional changes – violations of chewing and the speech. Diagnostics of a mezialny bite is helped by data of anthropometrical measurements, to a telex-ray analysis, an orthopan-tomography, the analysis of diagnostic models, VNChS X-ray analysis. Correction of a mezialny bite includes miofunktsionalny gymnastics, massage of an alveolar shoot, orthodontic treatment.
Mezialny bite – the kind of the wrong bite caused by shift of the lower jaw forward in relation to top. Along with a disteel bite (prognatiya), mezialny occlusion of tooth alignments belongs to anomalies of a bite in sagittalny napravleyoniya. Prevalence of a mezialny bite in population fluctuates from 1 to 12%. Among other zubochelyustny anomalies the specific weight of a mezialny bite makes 2-6%. In stomatology the mezialny bite is also designated by the concepts "the III class of a smykaniye across Engl", "pro-genius", "the progenichesky bite", "the lower prognatiya", "an anterialny bite", etc. the Mezialny bite can be combined with an open and cross bite.
Reasons of a mezialny bite
The Mezialny bite is formed under the influence of the genetic, congenital and acquired factors. Genetic forms of a mezialny bite are connected with hereditary features of a structure of a facial skull and are registered in 20-40% of cases of anomaly. During antenatalny ontogenesis diseases of the pregnant woman, patrimonial injuries of the newborn, a hypoplasia of an intermaxillary bone, etc. can lead to a mezialny bite. Among the factors promoting formation of a mezialny bite, the large role is played by the accompanying anomalies of teeth and an oral cavity: accessory teeth on the lower jaw, a partial and multiple edentia in the top jaw, a mikrodentiya of upper teeth or a mikrodentiya of the lower teeth, a short bridle of language, a makroglossiya.
Among prichinno significant post-natal factors it should be noted artificial feeding of the child, a disease of early age (rickets), oral breath owing to LOR-pathology (a curvature of a nasal partition, a hypertrophy of palatal almonds), etc. The separate group of the reasons is made by various behavioural factors promoting emergence of a mezialny bite: sucking of a verkhyony lip, fingers and various objects; a dream with the head hung on a breast; a habit to enclose a fist or a hand under a chin in a sitting position. To development of a mezialny bite can give violations in terms and the sequence of a teething, namely – a retention of upper teeth and an early teething of the lower jaw.
The underdevelopment of the top jaw and formation of a mezialny bite can be promoted in some cases by osteomyelitis of jaws, consequences of correction of a palatal crevice, a tumor of jaws, an akromegaliya.
Classification of a mezialny bite
Taking into account the sizes and position of jaws allocate the following types of a mezialny bite:
1. The Mezialny bite caused by the lower makrognatiya:
- at the normal sizes of the top jaw
- at an underdevelopment or disteel position of the top jaw
2. The Mezialny bite caused by the lower prognatiya:
- at increase in basal department of the lower jaw
- at increase in podborodochny department of the lower jaw
3. The Mezialny bite caused by the top mikrognatiya
4. The Mezialny bite caused by the top retrognatiya
5. The Mezialny bite caused by a combination:
- top mikrognatiya and lower makrognatiya;
- top retrognatiya and lower prognatiya;
- top mikrognatiya and lower prognatiya;
- top retrognatiya and lower makrognatiya.
The first and second options of a mezialny bite in orthodontics are regarded as true the pro-genius; the third and fourth option – as false the pro-genius at which the lower jaw has the normal sizes and a mezialny bite is caused by an underdevelopment of the top jaw or its retroposition.
Taking into account violation of occlusion in the sagittalny direction and size and a mandibular corner allocate three degrees of a mezialny bite:
The I degree - a sagittalny crack between foreteeth to 2 mm; violation of a ratio between the first painters in the sagittalny direction to 5 mm; a mandibular corner to 131 °.
The II degree – a sagittalny crack between foreteeth to 10 mm; violation of a ratio between the first painters in the sagittalny direction to 10 mm; a mandibular corner to 133 °.
The III degree - a sagittalny crack between foreteeth is more than 10 mm; violation of a ratio between the first painters in the sagittalny direction of 11-18 mm; a mandibular corner to 145 °.
Also distinguish a zuboalveolyarny and gnatichesky form of a mezialny bite: in the first case perhaps any shift of the lower jaw back before achievement of the correct occlusion of boyokovy teeth; at the second form shift is impracticable.
Symptoms of a mezialny bite
At a mezialny bite the combination of these or those front and intra oral signs, and also various functional violations caused by them can be noted. Externally mezialny bite is shown by promotion of a chin and lower lip forward, a zapadeniye of an upper lip, is frequent – a gaping of an oral crack. At the same time the midface in a profile looks sunk down, bent. In general the look of the patient with a mezialny bite is characterized as "angry".
Intra oral signs of a mezialny bite are characterized by the return reztsovy overlapping or direct occlusion of teeth in forward department; existence of a mezialny step at a smykaniye of chewing teeth. The oral inclination of teeth on the lower jaw is possible, education diasty and we rub, existence of dihundred-pyrobathing teeth. Dense position of teeth on the lower jaw can cause adjournment of a scale, development of a gingivit and prisheechny caries.
Functional violations at a mezialny bite can include defects of the speech (an interdental sigmatizm – a kind of a mechanical dislaliya), difficulties of a nibble and a chewing of food, VNChS dysfunction. The wrong distribution of chewing loading in foreteeth is followed by an overload of fabrics of a parodont, development of periodontosis and early loss of teeth. The Mezialny bite can interfere with performing prosthetics and dental implantation.
Diagnostics of a mezialny bite
Consultation of the orthodontist is necessary for recognition of a mezialny bite, the correct assessment of its look and degree. Inspection of the patient begins with survey of the person full face and a profile, removals of anthropometrical indicators, visual assessment of occlusion in an oral cavity, conducting the functional test allowing to distinguish true to the pro-genius from false.
Degree of a vyrazhenyonost of a mezialny bite is estimated by results of definition of a bite by means of prikusny rollers, studying of diagnostic models, an ortopantomografiiya, a telex-ray analysis in a side projection, a X-ray analysis and a tomography of VNChS. The electromyography of chewing and temporal muscles is made for identification of functional violations; consultation of the logopedist and otolaryngologist.
Treatment of a mezialny bite
At preschool age when jaws of the child are in process of growth, for correction of a mezialny bite the miofunktsionalny gymnastics and massage of an alveolar shoot of the top jaw is appointed; if necessary plasticity of a bridle of language is carried out. For the child's breaking from harmful oral habits use of vestibular plates is recommended. Orthodontic treatment at this stage according to indications can be carried out by means of Bryukl's device, Bynin's kappa. There is an opinion that the best results of treatment of a mezialny bite in the period of a dairy and early replaceable bite are reached in case of use of a front mask.
In the period of a replaceable bite treatment of mezialny occlusion is carried out with use of aktivayotor of Andrezena-Goypl, Klammt, Frenkel, Vunderer or Persin's devices. With establishment of a constant bite the fixed orthodontic equipment – breket-systems is used to correction of abnormal occlusion. Along with an orthodontic stage logopedic classes are given in correction of a dislaliya.
Protetichesky treatment of a mezialny bite can include a selective prishlifovyvaniye of teeth, removable or fixed prosthetics for normalization of okklyuzionny contacts. Sometimes at excessive development of the lower jaw there is a need of preliminary surgical treatment - removals of teeth, an osteotomiya of a branch of the lower jaw.
Forecast and prevention of a mezialny bite
The best results of correction of a mezialny bite are achieved at an initiation of treatment in the period of a dairy or replaceable bite. Despite all difficulties, correction of esthetic and functional violations is possible even at adult age. However in this case treatment terms increase, stage-by-stage treatment with participation of stomatologists-surgeons, orthodontists, orthopedists quite often is required.
An important role from the point of view of prevention of a mezialny bite is played by the normal course of pregnancy and childbirth, breastfeeding, the child's breaking from addictions, the correct situation during sleep. Timely treatment of the diseases which are slowing down or breaking growth of maxillary bones, correction of anomalies of separate teeth is necessary.