The concept of the norm in orthodontics

The concept of the norm in orthodontics.Ortohnatychnyy bite, his characterization. Keys occlusion by Engle and E. Andrews. Physiological and pathological types of malocclusion. Periods formation bite. Meaning symptom Tsylinskoho in the formation of permanent occlusion. Final plane on LJ Boume and A.M.Schwarz.

 NORM NOTION IN ORTHODONTICS

Orthodontics is a complex many-sided discipline, which is engaged not only in the correction of teeth, dental arches, and occlusion, but also studies jaws growth, corrects the facial skeleton form, normalizes dentognathic apparatus functions, re­stores the esthetic harmony of face.

During the development of orthodontic diagnostics the authors tried to word the notion of norm and pathology of the development, structure, and functioning of the dentognathic apparatus.

The norm in orthodontics is a generalized notion, characterised by extra- and intraoral signs (morphologic functional balances of the dentognathic apparatus and esthetic harmony efface on the whole).

There are facial and jaw extraoral signs.

Facial signs: characteristics of cutaneous coverings (color, absence of pathologi­cal damages, scars, new formations, swellings, etc.).

The esthetic harmony of face was based on the studying of the head in coordinate system, founded by Van Loon (1916) and followed by P. Simon (1922). On the basis of the obtained results the scientists detected the proportionality, symmetry, and in­terrelation of the parts of face sizes.

•    Face proportionality is conventionally divided into three equal parts: from the
scalp to the superciliary arches, from the superciliary arches to the nose base, from
the nose base to the chin.

•    The right and left parts of face were found to be symmetrical.

•    The idea of harmonious interrelation between separate parts of body was bor­
rowed by orthodontists from anatomy, art, and architecture, and developed into the
hypothesis of the proportional structure of separate parts of the dentognathic appara­
tus. The facial skeleton should be viewed as a whole, as a structural unity, taking into
account racial, family, and individual peculiarities.

Jaw signs: correct harmonious development of the branch and body of the lower and upper jaws; the lower jaw angle iewborns makes 164°, in adults — 117—124°;

full value and harmonious face profile. The credit of introducing the concept of the dentognathic apparatus normal position in the facial skeleton is given to V. Andresen (1925, 1930).

Intraoral signs. In 1939 Y. Katz introduced the notion “functional norm of den­tal arches”. This is the pathologic function correction to the transition of quantitative changes into qualitative and formation of correlation between the form and function in the dentognathic apparatus. The main parameter for their characteristics became the type of dental arches closure — occlusion. Orthognathic occlusion is considered normal, it provides the optimal functioning of the dentognathic apparatus.

PHYSIOLOGICAL TYPES OF OCCLUSION

In the clinical picture of orthodontics there are distinguished four forms of physio­logical occlusion: orthognathic, straight, biprognathic, and opisthognathic (Fig. 14). All these occlusions have identical signs of closure in the region of molar and premo-lar teeth, and different signs — in the region of incisors and canine teeth.

The sign of the correct sagittal occlusion of molar teeth is the position of the anterior buccal tubercle of the 1^st upper molar in the transverse sulcus of the similar lower tooth.

Orthognathic bite of permanent teeth in central occlusion is characterised by the following:

•    the upper frontal teeth cover the lower ones by 1/3 length of the lower teeth
crowns;

•    the tubercle of the upper canine tooth crown is located between the lower
canine tooth and the 1^st premolar;

•    the centerline between the central incisors of the upper and lower jaws coin­
cides;

•    the mesial-buccal tubercle of the upper 1^s1 molar is located in the transverse
sulcus of the similar lower tooth;

•    every tooth of the upper jaw has two antagonists — similar and standing be­
hind (except for the lower central incisors and upper wisdom teeth);

•    the buccal tubercles of the upper lateral teeth cover the buccal tubercles of the
lower ones, and the palatine tubercles of the upper teeth are located between the buc­
cal and lingual tubercles of the lower teeth;

•    the upper dental arch is semielliptical, the lower — parabolic; in temporary
occlusion — a semicircle on both jaws;

•    the dental arches of the upper and lower jaws are symmetrical;

•    in the state of central occlusion there is a full occlusive contact between all
teeth (except for unerupted ones);

•    in the state of physiological rest an interocclusive space varying within 2 mm
arises between dental arches.

The highest esthetic optimum, the highest indexes of mastication function, the best conditions for the formation of somatic swallowing, and full value tongue func­tion are characteristic of this occlusion.

Fig. 14. Physiological oc­clusion types:

a — orthognathic; b — straight;

c — biprognathic; d — opisthognathic

At straight occlusion all the listed above correlations are kept, except for the oc­clusion character of frontal teeth, which contact with the lower sculpri.

Physiological biprognathism — all the listed above correlations are kept, except for the character of frontal teeth occlusion — they have a vestibular inclination of the upper and lower incisors and canine teeth at minor covering of the lower teeth by the upper ones.

At opisthognathic occlusion the canine teeth and incisors on both jaws are in­clined into the oral cavity, contacting with each other by means of covering the lower teeth by the upper ones at the level of teeth tubercles or by means of marginal occlusion; all the listed above occlusive correlations are preserved.

Fig. 15. The 1^st Andrews’ occlusion key:

a — regular inclination of the 6^th tooth axis, its mesial-buccal tubercle is in the intertubercular fissure of the 6^th

lower tooth; the distal-buccal tubercle contacts regularly with the mesial-buccal tubercle; b~d — variants of molars

closure in case of the 1^st Angle’s class: irregular inclination of the 6^th tooth axis violating its closure

of the 1^st permanent molar mesial-buccal and distal-buccal tubercles on the right and on the left of dental arches relative to the intertubercular fissure of the lower 1^s‘ per­manent molar and the clivus of the mesial-buccal tubercle of the 2^nd molar.

• The 2″¹ key (crown angulation) — regular angulation in degrees (mesiodistal inclination) of the longitudinal axis of all teeth crowns. It is characterised by the size of the angle formed at the intersection of the tangent to the clinical crown of every tooth and the perpendicular to the occlusal plane. At optimal occlusion angulation is positive in case the occlusion segment of the tangent to the medial line of the tooth crown vestibular surface is mesial relative to the gingival margin, and negative — at reverse correlation. The latter is characterised as abnormality (Fig. 16, 17). At optimal occlusion every tooth has the angulation, characteristic of it.

Fig. 16. Incisors angulation (the 2^nd Andrews’ occlusion key): a — normal; b — positive violated; c — negative violated

Fig. 17. Angulation of the up­per and lower frontal and lat­eral teeth (the 2^nd Andrews’ occlusion key)

•    the mesial-buccal tubercles of the upper 1^st molar teeth are to be located in the
intertubercular fissure of the lower molar teeth;

•    the distal-buccal tubercles of the upper 1^st molar teeth are to tightly contact
with the distal-buccal tubercles of the lower 1^st molar teeth and the mesial clivus of
the buccal tubercles of other lower molar teeth.

Andrews’ occlusion keys (optimal occlusion). In 1972 L. Andrews described 6 keys characterizing optimal occlusion. Some of them had been known before, but their pooled estimate is important for clinical practice.

•        The 1^st key — regular tubercle-fissure contacts between the lower and upper 1^st
permanent molar teeth at the right inclination of their longitudinal axes to the oc­
clusal plane; the mesial-buccal tubercles of the upper 1^st molars are to be located in
the intertubercular fissure of the lower molars. The distal-buccal tubercles of the up­
per molars are to contact tightly with the distal-buccal tubercles of the lower 1^st mo­
lars and the mesial clivus of the buccal tubercles of other lower molars (Fig. 15).

The l^sl key allows to detect occlusion violations of the 1^st permanent molars in the mesiodistal direction taking into account the location and contacts of the apices

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phc. 18. Teeth torque (the 3^ri Andrews’ occlusion key):

a — positive of incisors; b — negative of incisors; c, d — correct of other teeth

•        The 3^rd key (torque) — vestibulooral inclination of the crowns and roots of
teeth. It is characterised be the size of the angle formed at the intersection of the
tangent to the medial line of the tooth crown vestibular surface and the perpendicular
to the occlusal plane. At normal position of the incisors’ crowns their occlusive part
is located vestibularly relative to the gingival part. Normally, the lingual inclination
of the occlusive part of the upper lateral teeth crowns increases in the direction from
canine to molar teeth (Fig. 18).

If to place a direct arch in the horizontal direction parallel to the tooth occlusion surface (interdental line direction) and draw a tangent to its fascial tubercles there will be an angle equal to 10° on average. The knowledge of its size is important for the calculation of the curve of the third order on the arch in the region of every upper 1^st permanent molar. Such curves are made when using the standard edgewise-tech­nique.

•        The 4^h key (rotations) — the teeth located in dental arches should not be
turned round. Frontal teeth, which are turned round, take less space in the dental
arch causing its flattening and shortening. Turned round premolars and molars take
more space in the dental arch causing its deformation and lengthening, and thus oc­
clusion violation (Fig. 19).

When a tooth is turned round the vertical axis, dental arch length changes. If frontal teeth, being in the dental arch, are turned round, the arch flattens and short­ens; if lateral teeth — it lengthens, which violates dental arches correlation.

•        The 5^:h key — the presence of tight contact between the teeth of every dental
arch without diastems and diaereses. Not infrequently gaps arise at the violation of
the myodynamic balance of the muscles surrounding dental arches from external and
internal surfaces. Such anomaly is observed at nonoclosure of lips, infantile swallow­
ing, bad habits — sucking of fingers, tongue, lips, different objects. Spaces between
teeth can be conditioned by excessive jaw growth, more often of the lower one, at
gnathic varieties of mesial occlusion.

Fig. 19. Teeth torsion around the vertical

axis (the 4^th Andrews’ occlusion key): a — a turned frontal tooth takes less space in the dental arch, a turned lateral one — more; b — the absence of place for the 5^th tooth as a result of the 6^th tooth torsion and mesial shift; c — correct posi­tion of the 6^th tooth provides space increase in the dental arch for the 5′^h tooth

• The 6″¹ key — the concavity of Spec’s curve should not exceed 2 mm, which is detected at measuring the biggest distance between the plane, tangent to the lower central incisors scalprum and to the last permanent molars distal tubercles, and the most low located occlusion surface of lateral teeth. The shorter the dental arch and the longer the apical arch are, the deeper Spee’s curve is, which causes irregular teeth position and the deviation of their longitudinal axis.

Spee’s curve reflects the teeth-alveolar height in the anterior and posterior re­gions of the dental arches of both jaws and normally makes up to 2 mm (Fig. 20). The curve is interdependent with the length of dental arches and their apical basis. It can be concave, flat or convex (Fig. 21).

Fig. 20. The Spee’s curve:

a — shortened at pronounced Spee’s curve; b — length increases after the nor­malization of the Spee’s curve form

Fig. 21. Spee’s curve types (the 6^lh Andrews’ occlusion key): a — concave; b — straight; c — convex

According to L. Andrews, the most common treatment errors are:

•    irregular position of the incisors’ axes in the mesiodistal and vestibular-oral
directions, which was observed at the distal transfer of incisors to the place of the 1^st
permanent premolars, extracted by orthodontic indications;

•    unclosed spaces between teeth after the distal transfer of incisors to the place
of the extracted 1^st premolars;

•    preserved rotation of teeth round the vertical axis;

•    mesial angulation of supporting molars.

The errors, especially the irregular angulation and inclination of teeth, lead to the recurrence of dentognathic anomalies with age, functional overload of some teeth, change of their position, increase of the overbite depth.

Spaces in the dental arch, left after teeth extraction (more often of the 1^st premo-lar teeth), are eliminated without any intervention with age, but not in all patients. Contacts between teeth form at the eruption of the 3^rd molars after the orthodontic treatment of the neutral pathologic occlusion combined with the irregular position of the frontal teeth and extraction of the 1^st premolars on both jaws; after the orthodon­tic treatment of posterior occlusion and extraction of the 14^th and 24^th teeth, and also of mesial occlusion after extracting the 34^th and 44^lh teeth, when the treatment was finished with the presence of tubercular (but not tubercular-fissure) contacts of the 1^st and 2^nd permanent molars.

. PATHOLOGICAL TYPES OF OCCLUSION

Occlusions characterised by the anomalous position of individual teeth, deformed dental arches and their anomalous interrelation (a shift in the sagittal, vertical or transversal direction) are named anomalous or pathologic.

There are distinguished such types of main anomalous occlusions:

l)prognathic (distal);

2)progenic (mesial);

3)open;

4)deep;

5)cross;

6)neutral with anomalous position of individual teeth.

Each type can have a number of variants, resulting from a characteristic position of the 1^st molars (neutral, distal or mesial), a peculiarity of alveolar crests develop­ment and jaws position (dentoalveolar and gnathic varieties), basic anomaly signs combined with the signs of other occlusion types, presence of dental arches deforma­tions (narrowing, compression or dilation, lengthening or shortening), incomplete or excessive teeth quantity.