X-ray  methods of diagnostic.Method oftelerentgenography (straight and lateral)

 

ROENTGENOLOGIC METHODS OF INVESTIGATION

Radiologic investigation is necessary for diagnosis clarification, defining the plan and prognosis of treatment, studying changes that take place in the process of child's growth under the influence of medical procedures. It is important, depending on the aim, to choose the most effective method of radiologic investigation correctly. These methods fall into intraoral and extraoral.

Intraoral Roentgenography

Intraoral roentgenography (Fig. 64) is carried out with the help of dental devices of different construction. Intraoral roentgenogram allows studying the state of hard tooth tissues, periodontal tissues, alveolar processes and jawbones with the purpose of finding out destructive changes, cysts, new formations, congenital and acquired de­fects, and also the clarification of teeth germs position anomalies, the degree of their crowns and roots formation, teeth retention, their form anomalies, correlation of milk teeth roots and permanent teeth crowns.

Intraoral roentgenogram of the median palatine suture is needed to study its structure, the degree of ossification, changes that take place at slow or rapid suture opening in the process of upper jaw dilation, specifying indications to surgical plasty of the frenulum of the upper lip, if its fibers interweave into the median palatine su­ture and promote diastem formation.

Extraoral Roentgenography Methods

 

Extraoral roentgenography methods include panoramic radiography, orthopanto-mography, TMJ tomography, and teleroentgenography.

 Fig. 64. Intraor al roentgenogram:

a — dental; b - of the median palatine suture

 

 

 

Fig. 65. Panoramic ra­diograph

Fig.  66.  Orthopanto-mogram\

Panoramic Radiography of Jaws

In a panoramic radiograph of the upper jaw the images of its dental, alveolar, and basal arches, the vomer, nasal cavity, maxillary sinuses, zygomatic bones are ob­tained; in a panoramic radiograph of the lower jaw — the images of its dental, alveo­lar and basal arches, lower jaw margin, angles and wings (Fig. 65).

In comparison with intraoral roentgenograms, at obtaining a panoramic radiograph the distance object—film increases. Due to this at the expense of a big area of investiga­tion and image magnification by 1.8—2 times valuable diagnostic data can be obtained.

Orthopantomograpliy

Orthopantomography, or panoramic tomography, provides obtaining a flat image of the arched surfaces of volumetric areas. Orthopantomograms (Fig. 66) are obtained with the help of this method; they make possible studying the degree of teeth roots and crowns mineralization, the degree of milk teeth roots resorption and their cor­relation with permanent teeth germs, inclination of erupted teeth and the teeth re­tained relative to the neighboring teeth and the median plane, dentoalveolar height in the frontal and lateral parts of jaws, overbite, the symmetry of the right and left parts of face, of the middle and lower parts of the facial skeleton.

TMJ Tomography

There are at least 30 methods of studying TMJ functions in roentgenology. In Ukraine TMJ tomography is extensively used — sectional roentgenography, at which Chapter 4. Auxiliary Methods of Examining Patients with Dentognathic Anomalies...

the definition and sharpness of the image of the anatomical formations of the layer, which is marked out, improve. A tomogram (Fig. 67) enables to get the most impor­tant indices of the glenoid cavity form, width, depth, and the evidence of the articu­lar tubercle, the form of the articular head and the size of the joint space between the head and the glenoid cavity in its anterior, middle, and posterior parts. At physiologi­cal occlusion the articular heads usually locate in the middle of the glenoid cavity. At occlusion anomalies three main positions of articular heads are observed: they may be in the middle of glenoid fossae, displaced backwards and up or forward and down­wards.

There are a couple of methods of TMJ tomograms calculation. At the Chair of Orthodontics and Children's Prosthetics of MMSI N.A. Rabukhina's technique of tomogram interpretation is applied in I.E. Androsova, A.A. Anikiyenko, and L.I. Ka-mysheva's modification (Fig. 68).

The apex of the articular tubercle joins with the lower margin of the foramen of the external acoustic duct. From the top point (L) of the glenoid cavity a per­pendicular drops on this line (the point of intersection is marked K). From the point Kat the angle of 45° straight lines are drawn to the right and left to the inter­section with the glenoid cavity, thus distances a and c are obtained; the distance b is obtained by means of drawing a perpendicular from the point K. From the bot­tom point of the mandible incisure a perpendicular drops on the continuation of the LN line.

Tomograms are used to measure:

•   the length of the coronoideus process (NM);

•   the height of the lower jaw head (KM);

•   the width of the lower jaw head AfBj,

•   joint space width:

 

-   by the aperture in the anterior part AAr

-   by the aperture in the posterior part BBr

Fig. 68. TMJ tomogram interpretation

Fig. 67. Copied tomogram of the TMJ (anterior position of the articular head)

-           at an angle of 45° in the anterior part (a),
— at an angle of 45° in the posterior part (c),

-        in the superior part (b).

Teleroentgenography (Cephalometry)

Teleroentgenography is an X-ray photograph of the skull, made at a distance, which reflects the craniofacial skeleton and circuits of the soft tissues of face. Tele-roentgenogram helps to detect the peculiarities of the growth and development of the facial skeleton, the localization of its modified growth; to have a clear idea of the structure and correlation of the bony matrix with the soft tissues of face; to choose the most efficient method of treatment (Fig. 69).

Anatomical variants of the facial skeleton structure were studied by L. De Coster, G. Korkhaus, C.H. Tweed, A. Bjork, W.B. Downs, V. Sassouni, G. Maj, H.P. Bim-ler, R.M. Ricketts, A.M. Schwarz, A.A. El-Nofeli, R. Frankel, A.P. Kolotkov, Stein-hauser, Legan, Burstone, Harvold, Steiner and others.

One of the first registered roentgenograms of head was made in 1896; in 1919 Ketchman published first lateral roentgenograms of head; in 1921 Brown designed a head fixation device for conducting X-ray imaging of face. First scientific papers on roentgenologic anthropometry of skull were the publications of Pacini in 1922. In the same year in the Angel's College of Orthodontics Spencer Atkinson exhibited a lateral roentgenogram of head with references to the correlation of the jaws and skull base. Before Holly Broadbent (elder) designed the roentgenographic craniometer in 1924, cephalometry did not have its present form.

In 1931 the works of H. Hofrat and B.H. Broadbent Jr. on studying the changes in the process of skull growth and development were published. In 1935 the first work of Schwarz was published; it supplemented the main principles of "gnathostatics" of Simon and was widely used in orthodontic diagnostics. B.H. Broadbent Jr. and later Bjork (1947) noted that the type efface does not change with age.

Now more than 200 methods of analyzing lateral teleroentgenograms of head and numerous supplements to them are well-known. Various methods differ from one another by measurement types, points for linear and angle measurements, planes of references, which change slightly in the process of facial skeleton growth and development.

The methods of analyzing lateral teleroentgenograms by measurement types are the following:

• detecting linear dimensions bet­ween certain points and their correla­tion (methods of De Coster, Kork­haus, Moorrees, Wylie);

Fig. 69. Teleroentgenogram in lateral pro­jection

•    angles measurement (methods of Bjork, Downs, Graber);

•    detecting the proportionality of the dimensions of the facial skeleton bones
(methods of Maj, Luzy);

•        combined — detecting linear and angle dimensions and the proportionality of
the facial skeleton structure (methods of Sassouni, Schwarz, A.A. El-Nofeli, Frankel,
A.P. Kolotkov and others).

The most widespread method of interpreting lateral teleroentgenograms of head in Ukraine is the technique offered by Schwarz with supplements of other authors.

During the analysis of teleroentgenograms Schwarz divides linear and angle mea­surements into craniometric, gnathometric, and profile metric.

Craniometric investigations aim at detecting the position of jaws relative to the plane of the anterior part of the cranium base — detecting the type efface and finding out the deviations from average dimensions, characteristic of neutrocclusion at the same type of face. The purpose is to get the natural patient's profile without any pa­thology. The difference between the "right" and real profiles is caused by pathology.

Gnathometric investigations aim at detecting the morphological peculiarities of different types of occlusion anomalies and deformations. At that, measurements con­cern the dentognathic complex, located between SpP — the spinal plane, or the plane of the upper jaw base, and MP — the mandibular plane, or the plane of the lower jaw base. On the basis of gnathometry anomalies caused by jaws dimensions inadequacy, teeth position anomalies, and by alveolar process shape anomalies are detected; the influence of jaws dimensions and position, and also of teeth position anomalies on the form of face profile is found out; the degree of the inclination of OcP — occlusal plane — to N—Se is evaluated, which is important for the prognosis of treatment from the esthetic point of view.

Profilometric investigations aim at studying the form of face profile and clarifying the influence of craniometric ratios on the profile form. Schwarz recommends estimat­ing the form of jaw profile by the position of lips, by the relation of the mouth tangent Tto Pn and Po, by the proportionality efface parts, and by the profile angle T.

Basic points used to interpret lateral teleroentgenograms (Fig. 70)

A (ss) — subspinale — the subspinal point of Downs, the most posteriorily lo­cated on the anterior circuit of the apical basis of the upper jaw;

B (sm) — submentale — the submental point of Downs, the most posteriorily located on the anterior circuit of the apical basis of the lower jaw;

Ba — basion — the lowest point of the anterior margin of the great occipital fora­men in the medium-sagittal plane;

Ar — articulate — the intersection of the anterior surface of the basilar part of the occipital bone with the posterior surface of neck;

C — condylen — the point on the apex of the articular heads circuit;

TV — nasion — the union of the coronal and nasal bones in the medium-sagittal plane; the position of the point may be different depending on the degree of frontal sinus development;

Fig. 70. Lines and angles used for lateral tele-          *~

roentgenograms interpretation    "

Se — sellia turcica — the point in the middle of the opening into the Turkish saddle;

S — sella — the point in the middle of the Turkish saddle;

O (A—I) -- the point formed by a perpendicular on SpP from the point A;

Or — orbital — the lowest located point of the inferior orbit margin; is lo­cated on the ocular margin of the zygo-matic bone;

Sna (ANS) — spina nazalis anterior — the apex of the anterior nasal spine; is located on the plane of the upper jaw base;

Snp (PNS) — spina nazalis posterior— posterior nasal spine; the posterior bound­ary of the upper jaw base;

sp — the highest point on the inferior palate circuit;

Pt (FPM) — ptergomaxillare — the superior distal point of the ptergomaxillary fissure, on the intersection of the foramen rotunda with the posterior wall of ptergoma­xillary fossa; forms a loop behind and above the point Snp (PNS), its posterior point corresponds to the point Snp (PNS);

Gn — gnation — the place of the union of the posterior lower jaw margin and external symphysis margin; the anterior point on the posterior circuit of the lower jaw body;

Go — gonion — on the external lower jaw margin at its intersection with the bi­sectrix of the angle formed by the tangent to the inferior margin of the body and the posterior margin of the jaw branch; the posterior point on the inferior circuit of the lower jaw body;

Pg — pogonion — the most anterior point of the mental protuberance;

Me — menton — the most inferior point on the lower jaw symphysis;

Po — porion — is located on the superior circuit of the external acoustic duct, touches the Frankfort horizontal;

Ocpl — anterior occlusive point — the middle of the vertical of overbite between the cutting edges of central incisors; the middle of the vertical and sagittal fissures between the central incisors;

Ocp2 — posterior occlusive point — the middle of the surface of the 1st upper and lower molars occlusion;

AOc — the projection of the point A on OcP',

BOc — the projection of the point B on OcP;

Pr — prostnion — the most inferior and anterior point of the alveolar process of the upper jaw;

is — incision superius — the middle point of the scalprum of the most protruding upper central incisor;

aps — apex superius — the middle point of the apex of the scalprum of the most protruding upper central incisor;

ms — molar superius — the distal-buccal tubercle of the upper 1st molar;

id — infradentale — the most superior and anterior point on the surface of the alveolar process of the lower jaw;

» — incision inferius — the middle point of the scalprum of the most protruding lower central incisor;

api — apex inferius — the middle point of the apex of the scalprum of the most protruding lower central incisor;

mi — molar inferius — the distal-buccal tubercle of the lower 1st molar;

g — glabella — the most prominent point of the soft tissues of the frontal part;

n — cutaneous nasion (the point of n—Se intersection with skin circuit);

sn — subnasale — the cutaneous point, the most posteriorily located on the place of the transition of the inferior nasal circuit to the upper lip;

pr (EN) — pronasale — the most prominent point of the tip of nose;

tr — trichion — the point of the anterior boundary of the pilary part of head on the median sagittal plane;

// — the most prominent point of the circuit of the red border of the lower lip;

ul — the most prominent point of the circuit of the red border of the upper lip;

st — stomion — the middle point between the upper and lower lips;

pg (DT) — cutaneous pogonion — the most prominent point on the chin profile.

Basic lines used to interpret lateral teleroentgenograms

(see Fig. 70):

N—Se (NSL) — the cranial plane (Schwarz), the plane of the anterior part of the cranium base; joins nasion and sellia turcica;

H(FH) — the Frankfort horizontal (Simon), the otoorbital plane; joins the orbi­tal and condylen;

SpP (NL) — the spinal plane, the nasal line, the plane of the upper jaw base; joins spina nazalis anterior and spina nazalis posterior,

OcP — the occlusal plane; is drawn in such a way that it is touched by not less than three tubercles of molars; divides the middle of incisors overbite and the overbite of the tubercles of last teeth, located in contacts; in the period of temporary occlusion it goes through the middle of the overbite of temporary central incisors and the tu­bercles of 2nd temporary molars, in the period of transitional dentition — through the middle of permanent central incisors and tubercles of the 1st or 2nd permanent molars located in occlusive contact;

MP (ML) — the mandibular plane, the plane of the lower jaw base, the plane of the lower jaw body; joins gnation and the most superiorly located point of the infe­rior circuit of the lower jaw body;

MT1 — the tangent to the inferior circuit of the lower jaw; goes along the infe­rior circuit of the lower jaw base beginning from the point formed by the perpen­dicular on MP from pogonion to the point of intersection with the tangent vertical A; real length \Ist\ of the lower jaw body;

 

 

OK — real length \Ist\ of the upper jaw body; is taken between the points A-1 (perpendicular from the point A on SpP) and Snp;

Pn — the nasal vertical (Dreyfus); perpendicular, dropped on TV—Se in the point of cutaneous nasion;

Po — the orbital vertical (Dreyfus); drawn from the point orbital; perpendicular to N~Se, parallel to Pn;

(Note: The space between Pn and Po is named Dreyfus'jaw profile field.)

N—A — the facial vertical (Downs); joins nasion and subspinale;

A—B — joins subspinale and submentale;

A~Pg — joins subspinale and pogonion;

A — the tangent vertical, the vertical of the posterior circuit of the lower jaw branch;

MT2 — the tangent to the posterior circuit of the lower jaw branch; from the point of intersection of Hand A, and the point of intersection of MP and A; the real length \Ist\ of the olower jaw branch;

T— the tangent to the points sn—subnasale and pg (DT) — cutaneous pogonion;

oi — the longitudinal axis of the upper central incisor, joins is and aps;

ui — the longitudinal axis of the lower central incisor, joins /'/' and api (the axes of other single-rooted teeth are drawn similarly);

ami — the longitudinal axis of the upper 1SI molar, is drawn through the middle of the distance between the medial and distal roots and intertubercular fissure;

uml — the longitudinal axis of the lower 1st molar, is drawn through the bifurca­tion of teeth roots and intertubercular fissure (the axes of other double-rooted and multirooted teeth are drawn similarly).

Basic angles and lines used to interpret lateral teleroentgenograms

(see Fig. 70):

Facial angle (angle /) is formed at the intersection of N—Se and N—A. The mean value of this angle makes 85±5°. Its value characterizes the location of the lower jaw relative to the cranium base: forward dislocation in comparison with the "average face" — anteposition; backward dislocation in comparison with the "average face" — retroposition (by Schwarz).

At posterior occlusion the mean value of the angle may be both bigger and smaller of the mentioned mean value; the analyses of other parameters allows detect­ing different kinds of posterior occlusion, conditioned not only by the anterior loca­tion of the upper jaw (prognathism), but also by the underdevelopment of the lower jaw body, its branches, decrease of the value of lower jaw angles. At mesial occlusion the mean value of the angle is less than the mean value pointing at the retroposition of the upper jaw basis.

Inclination angle, or the angle of spinal length inclination (angle I) is formed at the intersection of Pn and SpP. The mean value of the angle makes 85+5°.

If the angle value is bigger than the mean value, the jaws are inclined more for­ward than in the "average face" — anteinclination; if the value is smaller than the mean value, the jaws are inclined more backwards — retroinclination.

At anterior or posterior inclination the direction of the occlusive and mandibular planes and the direction of incisors axes change.

Different combinations of facial and inclination angles characterize the type of face, resulting from the genetic conditions of development. Depending on the value of facial and inclination angles and combination of their values 9 types are differenti­ated by Schwarz (Table 14). The profile is characterized by three angles: F, /, T.

Table 14. Types of Face according to Schwarz

 

 

Anteface

Average face

Retroface

Straight

Angle > 85°

Angle F = 85°

Angle F < 85°

 

Angle I = 85°

Angle I = 85°

Angle I = 85°

 

Angle T = 10°

Angle T = 10°

Angle T = 10°

Slant backwards

Angle F > 85°

Angle F = 85°

Angle F < 85°

 

Angle I < 85°

Angle I < 85°

Angle I < 85°

 

Angle T < 10°

Angle T > 10°

Angle T > 10°

Slant forward

Angle > 85°

Angle F = 85°

Angle F < 85°

 

Angle I > 85°

Angle I > 85°

Angle I > 85°

 

Angle T < 10°

Angle T < 10°

Angle T < 10°

SeNB angle is formed at the intersection of N—Se and N—B. The mean value of the angle makes 83±5°.

Its value characterizes the location of the apical basis of the lower jaw in the sagittal direction relative to the plane of the cranium base.

Posterior occlusion is more often conditioned by the retroposition of the apical basis of the lower jaw, and the angle is less than the norm. Mesial occlusion is more often conditioned by the anteposition of the apical basis of the lower jaw, and the angle is bigger than the norm.

ANB angle is formed at the intersection of N—A and N—B\ is detected by the correlation of the apical bases of jaws. The mean value of the angle makes 3°.

At sagittal occlusion anomalies the angle value differs form the norm. At poste­rior occlusion possible changes of the angle are within the limits from + 1° to +11°, at mesial — from +5° to —11°, which emphasizes the inadequacy in the location of the apical bases of jaws.

The angle of the Frankfort horizontal (angle H) is formed at the intersection of H and Pn. The mean value of the angle makes 90°.

Its value characterizes the location of the articular heads of the lower jaw relative to the cranium base, which influences the face profile form; characterizes TMJ loca­tion in the vertical direction. According to Schwarz' data, there is a correlation of the middle cranial fossa depth and TMJ location: the flatter the fossa, the higher the joints location, and vice versa.

If the angle's value is less than the mean value, the articular heads are in supra-position, i.e. closer to the cranium base than in the "average face"; if the angle's value is bigger than the mean value, the articular heads are in infraposition, i.e. lower from the cranium base than in the "average face". Every 2 mm of depth or height equal to 3° of the angle, and vice versa.

At articular heads supraposition or normal location of the lower jaw the chin is dislocated backwards, at infraposition — forward. Because of this, articular heads su­praposition influences the form of jaw profile as retroinclination, and infraposition -as anteinclination. The chin location might level at the expense of the growth of the lower jaw branches, mandibular angles increase.

Studying the Profile Type of the Facial Skeleton by A.H. Hasund

A.H. Hasund modified the analysis of jaws position in the sagittal and vertical directions depending on the basal angle value and charted a metric table of the profile type of the lower part efface: retrognathic, orthognathic, prognathic. For this purpose the angles F (SeNA), SeNB, SeNPg, N-Se-SpP, N-Se-MP are studied (Table 15).

Table 15. Detecting the Profile Type of Face

 

Position

Angle

Profile, °

Position

 

 

Retrognathic

Normal

Prognathic

 

Retroposition

F

74-78

79-85

86-90

Anteposition

Retroinclination

N-Se-SpP

16.5-11.5

11.5-5.5

5.5-0.5

Anteinclination

Retroinclination

N-Se-MP

48-40

38-26

25-21

Anteinclination

Retroposition

Se-NB

72-76

77-83

84-88

Anteposition

The metric field is divided into three parts. If all the values lie in one plane — close to one vertical line — this testifies to harmonious face structure, which, as a rule, does not need orthodontic correction of jaw bodies, and only points at conduct­ing dentoalveolar compensation (dentoalveolar form of anomalies). Deviation of val­ues of one or a couple of angles from mean values testifies to the tendency to dishar­mony caused by irregular position and inclination of jaws in the cranium, namely — rel­ative to the cranium base (gnathic form of anomaly).

Estimation of the Type of Jaws Growth (J. Jaraback, Ricketts) of "Growing" Patients

The type of jaws growth is estimated. The degree of osseous and dentognathic systems formation may be detected in the roentgenogram of hand in the pubertal period and by the anthropometric values of the teleroentgenogram of head in the lateral projection: having estimated the ratio of the posterior and anterior heights of the facial cranium part (Se—Go : N—Me), the angle of the inclination of the lower jaw body plane to the plane of the anterior cranium part (N—Se (NSL)—MP (ML)), the angle of the total of three angles (NSeAr + SeArGo + ArGoMe), the inferior gonial angle (NGoMe), the facial angle by Ricketts (N—Ba—Se—Gri), the intermaxillary angle (formed at the intersection of SpP and MP). There are differentiated the following types of growth: neutral, vertical, horizontal.

The analysis of substantial values, obtained by measurements and teleroentgeno-gram analysis, shows a tendency to the vertical or horizontal type of growth. The tendency is the more evident, the farther the marked fields are located from the middle (normofacial) area (Table 16).

Table 16. Estimating the Type of Jaws Growth of "Growing" Patients

 

 

Angle, °

 

Se-Go: N-Me, %

Angle N-Se-MP

Angle NSeAr + angle SeArGo + angle ArGoMe

Angle NGoMe

Angle N-Ba-Se-Gn

Angle SpP-MP

Growth type

75

17

381

62

99

13

Horizontal

71

22

386

65

96

18

Horizontal

67

27

391

68

93

23

Horizontal

62-65

32

396

70-75

90

26±4

Neutral

58

37

401

78

87

33

Vertical

54      -

42

406

82

84

38

Vertical

50

47

411

86

81

43

Vertical

1. The ratio of the posterior face height to its anterior height Se—Go: N—Me
normally makes 62—65 %. Little value of the index points at the vertical type of
growth, big — at horizontal.

2. The angle of lower jaw body inclination to the plane of cranium base (N~Se
(NSL)—M (ML)) at the neutral tendency of jaws growth makes 32°. Angle value in­
crease is characteristic of patients with the vertical type of jaws growth, decrease —
with horizontal.

3. The summary angle NSeAr + SeArGo + ArGoMe. Its value bigger than 396°
testifies to the vertical growth of jaws, its decrease — to horizontal.

4. The value of the inferior gonial angle NGoMe more than 75° is characteristic
of patients with the vertical type of growth, less than 70° -- with horizontal.

5. The facial angle by Ricketts N—Ba—Se—Gn at the neutral type of jaws growth
makes 90±2°. Angle value increase is observed at the horizontal type of jaws growth,
decrease — at vertical.

6. The change of the height of the facial cranium part is closely connected with
the change of the intermaxillary angle SpP—MP. Its mean value is 26±4°. The in­
crease of the intermaxillary angle testifies to the tendency to the vertical jaws growth
and lengthening of the lower part efface, decrease — to the tendency to the horizon­
tal type of jaws growth.

At the vertical type of growth there is observed the favorable prognosis of treating mesial and deep occlusion, deep incisive disocclusion, and at the same time the prog­nosis of treating posterior occlusion and vertical incisive disocclusion is unfavorable.

At the horizontal type of growth the prognosis of treating mesial occlusion and deep incisive disocclusion is unfavorable, and the prognosis of treating posterior oc­clusion and vertical incisive disocclusion is favorable.

The angle of occlusal plane inclination (PnOcP) is formed at the intersection of Pn and OcP, reflects the position of incisors and molars in the vertical direction. The mean value of the angle makes 75—80°.

If the angle is smaller than the mean value, the occlusal plane is more inclined upwards relative to the cranium base than in the "average face", and this influences the esthetic prognosis of treating sagittal occlusion anomalies. If the angle is bigger than the mean value, after treating sagittal occlusion anomalies the improvement of face profile may be expected.

At the orientation at the position of the 1st and 6th teeth (transitional dentition occlusion) the mean value of the angle is bigger than at the orientation at the position of the 1s1 and 7th teeth (permanent occlusion).

SpP OcP angle is formed at the intersection of SpP and OcP. The mean value of the angle makes 8-10°; it reflects the vertical position of frontal and lateral teeth.

At the orientation at the position of the 1st and 6th teeth (transitional dentition occlusion) the mean value of the angle is bigger than at the orientation at the position of the 1s1 and 7th teeth (permanent occlusion).

OcP MP angle is formed at the intersection of OcP and MP. The mean value of the angle makes 10—12°.

At the orientation at the position of the 1st and 6lh teeth (transitional dentition occlusion) the mean value of the angle is bigger than at the orientation at the position of the 1st and 7th teeth (permanent occlusion).

The angle of the mandibular plane (Pn MP) is formed at the intersection of Pn and MP. The mean value makes 60—65°.

Angle value changes as a result of ante- and retroinclination of jaws, infra- and supraocclusion of the articular lower jaw heads, at anomalies of the position and de­velopment of the lower jaw.

Basal angle (E) is formed at the intersection of SpP and MP, the mean value makes 20±5°; characterizes the vertical position of jaws. Its value depends on the lateral teeth height, the value of mandibular angles, the length of the lower jaw branches, the height of TMJ location, the inclination of the upper jaw base to the plane of the cranium base.

Mandibular (gonial) angle (go) is measured between MT1 and MT2. The mean value makes 123±10°.

Decrease or increase of the angle increases the severity of dentognathic deforma­tions.

Ricketts' facial angle (N-Ba-Se-Gn) is formed at the intersection of the lines joining the points N and Ba, and the lines joining the points Se and Gn, the infe­rior posterior angle. At the neutral type of jaws growth the mean value of the angle makes 90±2°.

Length Relationship of Jaws

When interpreting teleroentgenograms the following terms are used: the real /Ist/ length of jaws, i.e. the one present in the patient, and the required one /Sol/, i.e. the one which should be.

The required length is calculated compared to the length of the anterior cranial base, i.e. the distance N-Se. According to Schmuth Tigelkamp, the length of the lower jaw body relates to the length of the anterior cranial base as 20:21 or 60:63.

 

The length of the lower jaw body at its normal development is compared to the length of the anterior cranial fossa base. Under 11 years: MT1 = N—Se + 7 mm. After 11 years: MTl = N—Se + 3 mm.

The ratio of the lower jaw body length to the length of its wings. The length of the lower jaw body is measured from the intersection point of the perpendicular dropped from the point Pg on the plane MT1 to the point Go.

The height of the lower jaw branches is measured from the intersection point of MT1 and MT2 to the intersection point of MT2 and H.

Normally, MT1: MT2 ratio makes 7:5.

o the 3rd degree — 50° and less.

Interincisor angle (ii) is formed at the intersection of incisors axes; the mean value makes 140°±5°. Positional relationship of incisors is influenced by the value of basal angle.

Wlst-value is the degree of disproportion of the development of frontal areas of jaws apical bases (by Jacobson); is detected as the distance AOc—Boc on the occlusal plane (OcP). From the points A and B perpendiculars are dropped on OcP. The AOc—Boc distance is to equal 1 mm.

The correlation of the apical bases of upper and lower jaws in sagittal direction is detected by the A—B—SpP angle. At the intersection of the A—PG and SpP lines the MM angle forms (maxillomandibular). The mean value of the angles makes 90°.

At regular correlation of dental arches in a person with the average face the points A, Pg, B are on the line, which forms a right angle intersecting with SpP. These points often deviate from one another, more often — the point Pg. At that, not one but two angles form: A—B—SpP and A—Pg—SpP.

Human face is divided into several parts. Legan and Burstone estimate two parts of face: g—sn / sn—Me. The ratio of the upper part of face to the lower one makes 1.

Schwarz estimates three parts of face: frontal — from the point tr to the point «; nasal — from the point n to the point sn; maxillary — from the point sn to the point gn.

Profile form depends on soft tissues thickness. Soft tissue might both compensate irregular profile and worsen it. Therefore soft tissues thickness is to be always taken into consideration. It is especially important during choosing the method of treatment.

The following average data of soft tissues thickness are known: in the area «—N it makes 6 mm on average in a child and adult; in the area sn—A it makes 12—14 mm in children and 15—17 mm in adults (the deviation of soft tissues by 2 mm to this or that side reflects on the position of the point sn); in the area of the upper and lower lips — 12 mm; in the pg area — 10 mm.

At the location of sn in front of Pn the distance is marked with "+", at location behind - with "-".

The labial angle is formed between the labial tangent, which joins the most pro­truding points of the lips and Pn. If the angle equals 0, the lips are on one level; if it is formed on the left of Pn, it is considered negative, on the right — positive.

Lips position is detected by their relation to the nine: if the nine halves the red border of the upper lip and touches the external surface of the red border of the lower lip — lips position is medial. If the lips (one or both) are in front of the T line — lips position is positive, if behind — negative.

Lips position relative to esthetic convexity is estimated (by Ricketts). On the basis of this convex, concave, and straight face profiles are differentiated.

Face profile is characterized by means of estimating the position of the upper lip (ut) and the lower lip (II) relative to the plane (jE-plane), drawn through the points pr (EN) and pg (DT). The point ul is on the plane, and the point // is behind it by 2 mm — straight face profile. Lower lip projecting from the esthetic plane by 1—2 mm — convex face profile. Lower lip coming off the esthetic plane by more than 2 mm — concave face profile.

 

Ratio of the upper jaw body length to the lower jaw body length normally makes OK: MT1 =2:3. The size of the upper jaw does not depend on the type of face.

Detecting the sagittal correlation of the apical bases and dimensions of jaws (ac­cording to Weet). The estimation of the dimensions, position, and proportionality of the jaws bases is conducted by means of detecting the correlation of the apical bases and jaws dimensions, and also the vertical-basal ratio. The correlation of the apical bases of jaws is detected by the ANB angle. Its value is not identical in persons with different profiles. For the retrognathic type of profile the angle value makes 0°, for orthognathic type — 2°, for prognathic — 4°.

Individual standard of the ANB angle can be found by Weet's formula:

ANB angle = -35.16 + 0.4 x angle F (SeNA) + 0.2 x angle N-Se-MP

Teeth height correlation. The measurement of teeth height allows judging about the peculiarities of jaws growth in the vertical plane. It is recommended to measure the teeth height with a perpendicular from the occlusal planes of teeth to their basal planes.

According to Schwarz, the central upper incisor relates to the central lower inci­sor as 2 : 3; the central upper incisor to the 1st lower molar as 5 : 4.

The required jaws height is detected by the formulae:

oi: ui = oml: uml =2:3;

oi: oml = ui: uml = ui: um2 =5:4;

oi: om2 =4:3,

where oi — central upper incisor, oml — upper 1st permanent molar, ui — central lower incisor, uml — lower 1st permanent molar.

The angle of teeth axes inclination to the planes of jaws bases for.

ISpP angle = 70°,

3SpP = 80°,

4SpP angle = 90°,

IMP angle = 90°,

3MP angle = 90°, with the difference ±5°.

The angles are measured outside, i.e. vestibularly. If the axial inclination of upper incisors makes 65°, they are in the position of protrusion, more than 75° - in the position of retrusion.

Schwarz singles out three degrees of upper central incisors protrusion:

o the 1s1 degree — from 65° to 55°,

o the 2nd degree — from 55° to 50°,