ORTHODONTIC DIAGNOSIS

INTRODUCTION

Orthodontic diagnosis deals with recognition of the various characteristics of the malocclusion.

Orthodontic diagnosis should be based on scientific knowledge combined at times with clinical experience and common sense.

diagnosis include case history, clinical examination and other diagnostic aids such as study casts, radiographs and photographs.

Comprehensive orthodontic diagnosis is established by clinical implementation called diagnostic aids.

Orthodontic diagnostic aids are of two types namely’;

1. Essential diagnostic aids

2. Supplemental diagnostic aids

ESSENTIAL DIAGNOSTIC AIDS

They are clinical aids that are considered very important for all cases.

The following are essential diagnostic aids;

1. Case history

2. Clinical examination

3. Study models

4. Certain radiographs;

Periapical

Bitewing

Panoramic

5. Facial photographs

Supplemental diagnostic aids

They are certain aids that are not essential in all cases. They may require specialized equipments that an average dentist may not possess.

The supplemental diagnostic aids include;

1-Specialized radiographs ex;

a-cephlometric radiographs

b-occlusal intra-oral films

c-selected lateral jaw views

d-cone shift technique

2.Electromyographic examination of muscle activity

3.Hand wrist radiographs to assess bone age or maturation age

4.Endocrine tests

5.Estimation of basal metabolic rate

6.Diagnostic set-up

7.Occlusograms

CASE HISTORY

Case history involves eliciting and recording of relevant information from the patient and parent to aid in overall diagnosis of the case

PERSONAL DETAILS:

NAME :the patient’s name should be recorded for the purpose of communication and identification.

AGE-the patients chronological age should be recorded. Age consideration helps in diagnosis as well as treatment planning.

growth modification procedures using functional and orthopaedic appliances are carried out during growth period.

SEX-patient’s sex should be recorded in case history.

This is important in planing treatment,as the timing of growth events such as growth spurts is different in males and females.

ADDRESS AND OCCUPATION-recording of address and occupation helps in evaluation of socio-economic status of the patient and the parents.

CHIEF COMPLIANT -the patient’s chief compliant should be recorded in his/ her on words.

This help the clinician in identifying the priorities and the desires of the patient.

MEDICAL HISTORY- full medical history is recorded before orthodontic treatment.

Few medical conditions contraindicate the use of orthodontic appliances such as;

• Epilepsy

• History of blood dyscrasias

• Diabetic patient

• Rheumatic fever

• Cardiac anomalies

• Physically and mentally handicapped children

The medical history should include information on drug usage.

The use of certain drugs like aspirin may impede orthodontic tooth movement.

DENTAL HISTORY -it includes information on the age of eruption of the deciduous and permanent teeth,decay,history of extraction, restoration and trauma to dentition.

Past dental history helps in evaluation of patient and parent’s attitude towards treatment.

PRENATAL HISTORY-it include information on the condition of the mother during pregnancy and the type of delivery.

Forceps delivery predispose to TMJ injuries that can result mandibular growth retardation

Drugs like thalidomide or affectation with some infection during pregnancy like german measles can results in congenital deformities of child.

POST NATAL HISTORY -it includes information on the type of feeding, presence of habits and on the milestones of normal development.

FAMILY HISTORY- class 11,class111 malocclusions and congenital conditions such as clefts of lip & palate are inherited.

Family history should record details of malocclusion existing in other members of the family.

GENERAL EXAMIATION

Height and weight-they provide clue to the physical growth and maturation of the patient.

Gait-(way a person walks) abnormalities of gait are usually associated with neuromuscular disorders that may have a dental correlation.

Posture-(way a person stands)abnormal postures can predispose to malocclusion due to alteration in maxillo-mandibular relationship.

Body build-(physique)

A)aesthetic-thin physique and narrow dental arches.

B)plethoric-obese with large square dental arches

C)athletic-normally built, neither thin nor obese. normal sized dental arches.

SHELDEON CLASSIFICATION OF BODY BUILD

A)ECTOMORPHIC-tall and thin physique

B) MESOMORPHIC-average physique

C)ENDOMORPHIC-short and obese physique

EXTRA ORAL EXAMINATION

SHAPE OF THE HEAD: A)MESOCEPHALIC-average shape

of the head. posses normal dental arches

B)DOLICOCEPHALIC-long and narrow head . They have narrow dental arches

C)BRACHYCEPHALIC-broad and short head. broad dental arches

Mesocephalic,dolicocephalic,brachycephalic

FACIAL FORMA)MESOPROSOPIC-average or

normal face formB)EURYPROSOPIC-face is

broad and shortC)LEPTOPROSOPIC-long and

narrow face form

FACIAL SYMMETRY

The patient’s facial symmetry is examined to determine disproportions of the face in transverse and vertical planes. Gross facial asymmetry can occur as a result of:

A. congenital defects B.hemi-facial atrophy/hypertrophy C.unilateral condylar ankylosis and

hyperplasia

FACIAL PROFILE

The facial profile is examined by viewing the patient from the side. the facial profile helps in diagnosing the gross deviation of maxillo-mandibular relationship. the profile is assessed by joining the following two reference lines.

1. A line joining the forehead and the soft tissue point A(deepest point in curvature of upper lip)

2. A line joining point A and the soft tissue pogonion(most anterior part of the chin)

STRAIGHT PROFILE-the two lines form nearly

straight line.

CONVEX PROFILE-the two lines form an angle with concavity facing the tissue.

This kind of profile occurs as a result of prognathic maxilla retrognathic mandible as seen in CLASS 11,DIVISON 1 MALOCCLUSION.

STRAIGHT PROFILE CONVEX PROFILE

COCAVE PROFILE-the two reference lines form an angle with convexity towards tissue.

This type of profile is associated with a prognathic mandible or retrognathic maxilla as in CLASS 11 MALOCCLUSION.

FACIAL DIVERGENCE

Facial divergence is defined as anterior or posterior inclination of the lower face relative to the forehead.

ANTERIOR DIVERGENT-a line drawn between the forehead and the chin is inclined anteriorly towards the chin..

POSTERIOR DIVERGENT

A line drawn between the forehead and chin slants posteriorly towards chin.

STRAIGHT/ORTHOGNATHIC

The line between the forehead and the chin is straight or perpendicular to the floor.

The facial divergence is to a large extend influenced by patient’s ethnic and racial background.

ASSESSMENT OF ANTERO-POSTERIOR JAW RELATIONSHIP

It can be assessed clinically.

Ideally maxillary skeletal base is 2-3 mm ahead of the mandibular skeletal base when the teeth are in occlusion.

Estimation is done by placement of index and middle fingers at the soft tissue point A and point B respectively.

In skeletal CLASS11 PATIENTS, the index finger is anterior to middle finger or the hand points upwards.

In a skeletal CLASS 111 patient, the middle finger is ahead of the forefinger or the hand points downwards.

In a patient with CLASS 1 skeletal pattern the hand is at an even level.

ASSESSMENT OF VERTICAL SKELETAL RELATIONSHIP

The vertical skeletal relationship assessed by studying the angle formed between the lower border of the mandible and the Frankfort horizontal plane(a line between the most superior point of external auditory meatus and inferior border of orbit)

Normally the two planes intersects at the occipital region.

In case the two planes meets beyond the occipital region, it indicates a low angle case or a horizontal growing face.

If two planes meet anterior to occipital region it indicates a high angle case or a vertical growing face.

Assessment of vertical facial height

EVALUATION OF FACIAL PROPORTIONS

A WELL PROPORTIONED FACE CAN BE DIVIDED INTO THREE EQUAL VERTICAL THIRDS USING FOUR HORIZONTAL PLANES AT THE LEVEL OF THE HAIRLINE,THE SUPRA ORBITAL RIDGE, THE BASE OF THE NOSE AND THE INFERIOR BORDER OF CHIN

WITHIN THE LOWER FACE, THE UPPER LIP OCCUPIES A THIRD OF THE DISTANCE WHILE CHIN OCCUPIES THE REST OF THE SPACE.

EXAMINATION OF LIPS

The upper lip covers the entire labial surface of upper anteriors except the incisal 2-3 mm

The lower lip covers the entire labial surface of lower anteriors and 2-3 mm of incisal edge of upper anteriors.

CLASSIFICATION OF LIPS

COMPETENT LIP-THE LIPS ARE IN SLIGHT CONTACT WHEN MUSCULATURE IS RELAXED.

INCOMPETENT LIPS-they are morphologically short lips which do not form a lip seal in a relaxed state.

The lip seal can only be achieved by active contraction of perioral and mentalis muscle.

POTENTIALLY INCOMPETENT LIP-they are normal lips that fails to form a lip seal due to proclaimed upper incisor.

EVERTED LIP-they are hypertrophied lips with weak muscular tonicity.

EXAMINATION OF THE NOSE

The nose to a large extend contributes to the esthetic appearance of a face.

Nose size-normally the nose is one third of the total facial height.

Nasal contour-the shape of the nose can be straight, convex or crooked as a result of nasal in juries.

Nostrils-they are oval and should be bilaterally symmetrical. Stenosis of the nostrils may indicate impaired nasal breathing

EXAMINATION OF CHIN MENTOLABIAL SULCUS-concavity seen below the lower

lip. Deep mentolabial sulcus is seen in CLASS11,DIVISON 1 malocclusion.

MENTALIS ACTIVITY-NORMALY MENTALIS IS NOT ACTIVE AT REST.

Hyperactive mentalis is seen in CLASS 11 DIVISON 1 CASES.

CHIN POSITION AND PROMINENCE-prominent chin is usually associated with class 111 malocclusion.

DEEP MENTOLABIAL SULCUS AND HYPERACTIVE MENTALIS SEEN IN CLASS 11 DIVISON 1 MALOCCLUSION

NASOLABIAL ANGLE

It is the angle formed between lower border of the nose and a line connecting the intersection of nose and the upper lip with the tip of the lip.

This angle is normally 110 degree

It reduces in patients with proclaimed upper incisors prognathic maxilla.

INTRA-ORAL EXAMINATION

EXAMINATION OF TONGUE

ABNORMALITIES OF TONGUE CAN UPSET THE MUSCLE BALANCE AND EQUILIBRIUM LEADING TO MALOCCLUSION.

A PATIENT WHOSE TONGUE CAN REACH THE TIP OF THE NOSE IS SAID TO HAVE A LONG NOSE.

THE LINGUAL FRENUM SHOULD BE EXAMINED FOR TONGUE TIE

EXAMINATION OF THE PALATE

Palate should be examined for the following findings;

1. Dolicofacial patients have deep palate.

2. Presence of swellings in the palate

3. Mucosal ulcerations and indentations are a feature of traumatic deep bite.

4. Presence of cleft in the palate.

5. The third rugae is usually in line with canines. This is useful in the assessment of maxillary anterior proclination.

EXAMINATION OF GINGIVA

GINGIVA SHOULD BE EXAMINED FOR

1. INFLAMMATION

2. RECESSION

3. MUCOGINGIVAL LESIONS POOR ORAL HYGEINE IS ASSOSIATED

WITH ANTERIOR MARGINAL GINGIVITIS. ANTERIOR GINGIVITIS COMMON IN

MOUTH BREATHERS DUE TO DRYNESS OF MOUTH CAUSED BY OPEN LIP POSTURE.

EXAMINATION OF FRENAL ATTACHMENTS

The maxillary labial frenum sometimes be thick fibrous and attached relatively low.

This may lead to midline diastema.

Abnormal frenal attachment are diagnosed by blench test.

EXAMINATION OF TONSILS AND ADENOIDS

ABNORMALY INFLAMED TONSILS CAUSE ALTERATIONS IN TONGUE AND JAW POSTURE THERE BY UPSETTING THE ORO-FACIAL BALANCE LEADING TO MALOCCLUSION

ASSESSMENT OF DENTITION;

Dental system is examined for ;

1. Teeth present in the oral cavity

2. Teeth unerupted

3. Teeth missing

4. Teeth erupted and not erupted

5. Presence of caries,restorations,malocclusions,hypoplasia,wear and dislocation.

6. Check for the occlusion based on ANGLES CLASS 1, 11, 111

7. Record overbite overjet

8. Check for crossbite

9. Individual tooth irregularities such as rotation, displacement ,intrusion and extrusion are noted.

10. Check arch form

FUNCTIONAL EXAMINATION

It is now established that normal function of stomatognathic system promotes normal growth and development of oro-facial complex.

The functional examination should include the following;

1. Assessment of postural rest position and inter occlusal space.

2. Path of closure

3. Assessment of respiration

4. Assessment of TMJ

5. Examination of swallowing

6. Examination of speech

ASSESSMENT OF POSTURAL REST POSITION AND INTER-OCCLUSAL CLEARANCE.

The postural rest position of the mandible at which the muscles that closes the jaw and those that open them are, in state of minimal contraction to maintain the posture of mandible.

At postural rest position, a space exists between the upper and lower jaws.

This space is known as FREEWAY SPACE.

FREEWAY SPACE is 3mm in canine region.

Methods used to record the postural rest position

PHONETIC METHOD; the patient is asked to repeat some consonants “m or c’’ or repeat a word like Mississippi.

The mandible returns to postural rest position 1-2 seconds after the exercise.

The patient is told not to change the jaw, lip or tongue position after phonation, as the dentist parts the lips to study interocclusal space.

COMMAND METHOD

THE PATIENT IS ASKED TO PERFOM CERTAIN FUNCTIONS SUCH AS SWALLOWING.

THE MANDIBLE TENDS TO RETURN TO REST POSITION FOLLOWING THIS ACT.

Non command method

The patient is observed as he speaks or swallows. The patient is no aware that he is being examined.

This is usually being carried out by talking about topics unrelated to the patient while carefully observing him or not

Methods to measure inter-occlusal clearance

VERNIER CALIPERS CAN BE USED DIRECTLY IN THE PATIENT’S MOUTH IN THE CANINE OR INCISAL REGION TO MEASURE FREEWAY SPACE.

THIS IS DIRECT INTRA ORAL METHOD.

EVALUVATION OF PATH OF CLOSURE

The path of closure is the movement of mandible from the rest position to habitual occlusion .

Forward path of closure: a forward path of closure occurs in patients with mild skeletal and prenormalcy or edge to edge incisor contact. In such patients ,the mandible is guided to a more forward position to allow the mandibular incisors to go labial to the upper incisors.

Backward path of closure: class 11 ,division 2 exhibit premature incisor contact due to retroclined maxillary incisors. Thus the mandible is guided posteriorly to establish occlusion

Lateral path of closure : lateral deviation of mandible to left or right side is associated with occlusal prematurities and a narrow maxillary arch

ASSESSMENT OF RESPIRATION

Humans may exhibit three types of breathing: nasal ,oral and oro-nasal

Test to diagnose the mode of respiration: Mirror test : a double sided mirror is held between the

nose and the mouth .fogging on the nasal side of the mirror indicates nasal breathing while fogging towards oral side indicates oral breathing

Cotton test : a butterfly shaped cotton piece is placed over the upper lip below the the nostrils . if the cotton flutters down indicates nasal breathing .this test is used to determine the unilateral nasal blockage

Water test: the patient is asked to fill his mouth with water and retain it for a long period of time .while nasal breathers accomplish this with ease , mouth breathers find it difficult task.

Observation : in nasal breathers the external nares dilate during inspiration .in mouth breathers ,there is either no change in the external nares or they may constrict during inspiration

EXAMINATION OF T.M.J. The functional examination should routinely include

auscultation and palpation of temporomandibular joint and musculature associated with mandibular opening.

The patient should be examined for the symptoms of temperomandibular joint problems like clicking, crepitus , pain of masticatory muscles ,limitation of jaw movement , hyper-mobility and morphological abnormalities.

The maximum mouth opening is determined by measuring the distance between the maxillary and mandibular incisal edges with mouth wide open. The normal inter incisal distance is 40- 45 mm

EVALUVATION OF SWALLOWING In a new born, tongue is relatively large and

protrudes between the gumpads and takes part in establishing the lip seal .this kind of swallow is called infantile swallow and is seen till one and half to two years of age .

Infantile swallow is replaced by mature swallow as the buccal teeth start erupting. The persistence of infantile swallowing can cause malocclusion .thus the swallowing pattern of the individual should be examined.

The persistence of the infantile swallow is indicated by the presence of the following features:

a. Protrusion of the tip of tongue

b. Contraction of perioral muscles during swallowing

c. No contact at the molar region during swallowing

SPEECH

Certain malocclusions may cause defects in speech due to interference with the movement of tongue and lips .this should be observed while talking with the patient .

The patient can be asked to read out from a book or asked to count from 1-20 while observing the speech.

Patients having tongue thrust habit tend to lisp while cleft palate patients may have a nasal tone

ORTHODONTIC STUDY MODELS

Orthodontic study models are accurate plaster reproductions of teeth and their surrounding soft tissues .that are essential diagnostic aid that make it possible to study the arrangement of teeth and the occlusion from all directions .

Uses of study model include:

a) They enable study of occlusion from all aspect

b) Enable accurate measurements to be made in dental arch.they help in the measurement of arch length, arch width ,and tooth size

c) Help in assessment of treatment progress by dentist as well as by patient

d) Help in assessing the nature and severity of malocclusion

e) Helpful in motivation of patient and to explain the treatment plan as weel as progress to patient and parents

f) Makes it possible to stimulate treatment procedures on cast such as mock surgery

g) Useful to transfer records in case patient is treated by another clinician

ORTHODONTIC STUDY MODELS

GNATHOSTATIC MODELS

They are orthodontic study models where the base of the maxillary cast is trimmed to correspond to the Frankfort horizontal plane.

DIAGNOSTIC SET UP It was first propose by H.D. kesling

Diagnostic set up is made from an extra set of trimmed and polished study models .the individual teeth and their associated alveolar processes are sectioned off and replaced on the model base in the desired positions .the diagnostic set up thus help in simulating the various tooth movement s that are planned for patients

USES OF DIAGNOSTIC SET UP1. Useful in visualizing and testing the effect of

complex tooth movements and extractions on the occlusion

2. Patient can be motivated by simulating the various corrective procedures in the cast

3. Tooth size- arch length discrepancies can be visualized

PROCEDURE

The cast is cut using a fretsaw blade to separate the individual teeth.

A horizontal cut is made 3mm apical to gingival margin

Vertical cuts are made to separate the individual teeth

The individual teeth are set in desired position using a red wax

SUPPLEMENTAL DIAGNOSTIC AIDS

FACIAL PHOTOGRAPHS AS A DIAGNOSTIC AID

Facial photographs offers a lot of information on the soft tissue morphology and facial expression.

Both extra-oral as well as intra- oral photographs are useful diagnostic aids.

Three extra-oral views are routinely taken:

a. Frontal view

b. Profile view

c. Oblique facial view

Extra-oral photograph are taken by positioning the patient in such a manner that the F.H.plane is parallel to the floor

The intr-oral photograph taken include:

a. Left and right lateral view.

b. Frontal view.

c. Maxillary and mandibular occlusal view.

USES OF PHOTOGRAPHS

1. Useful in assessment of facial symmetry ,facial type and profile

2. Serve as a diagnostic records

3. Help in assessing the progress of the treatment

ELECTROMYOGRAPHY

Electromyography is a procedure used for recording the electrical activity of muscles the resting potential of a muscle fiber is 85-90mV

Electromyograph is a machine used to receive , amplify and record the action potential during muscle activity . Electromyogram is a record obtained by such procedure . The action potential picked up by the electrodes are of two types

Needle electrodes: used when muscles are placed deep inside e.g. pterygoid muscle

Surface electrodes :used when muscle is superficially placed just below the skin

Having picked up the action potential with surface or needle electrodes it is recorded either with the help of a moving pen in form of a graph or recorded in form o f sound with help of a magnetic tape recorder

Electromyography is used to detect abnormal muscle activity associated with certain forms of malocclusion

a. In severe classII ,division1 malocclusion the upper lip is hypo-funuctionl.Thus during swallowing ,the lower lip extends upwards and forwards to place to force the maxilla labially and a strong mentalis activity is seen .E.M.G .can be used to study such a condition

b. Abnormal buccinator activity in classII ,division1

c. Overclosure of jaw is associated with accentuated temporalis muscle activity

d. Children with cerebral palsy

e. E.M.G . Can be carried out after orthodontic therapy to see if muscle balance is achieved

RADIOGRAPHS USED IN ORTHODONTIC DIAGNOSIS

Radiograph routinely used for diagnosis in orthodontic s are classified into two groups

1. Intra-oral radiograph

2. Extra-oral radiograph

Intra –oral periapical radiographs(I.O.P.A)

They are radiographs that are used to view the teeth and their supporting structures.

Two intra oral techniques are used for periapical radiography. The are;

PARELLEING TECHNIQUE BISECTING ANGLE TECHNIQUEUSES To confirm presence or absence of teeth To establish presence or absence of supernumerary teeth Extend of calcification and root formation of teeth To study alveolar bone & PDL To determine size and shape of unerupted teeth To assess axial inclination of roots

disadvantages Assessment of entire dentition requires too

many radiographs.

They cannot be used in patients with high gag reflex and trismus

Advantages Low radiation dose

Excellent clarity of teeth and their supporting structure

Possible to obtain localized view of area of interest.

BITEWING RADIOGRAPHS

It records the coronal part of upper and lower dentition along with their supporting structure.

1. Used to detect proximal caries

2. Height and contour of inter alveolar bone

3. To detect periodontal changes

4. To detect secondary caries below restorations.

5. To determine inter proximal calculus

OCCLUSAL RADIOGRAPHS

Occlusal radiographs are used in patients who are unable to open their mouth wide enough for periapical radiographs.

Uses1. To locate impacted or unerupted teeth

2. To locate supernumerary teeth

3. To locate foreign bodies in the jaw

4. To diagnose the presence and extend of fractures

EXTRA-ORAL RADIOGRAPHS

THEY ARE USEFUL WHEN LARGE AREAS OF FACE AND SKULL ARE TO BE VISUALIZED

PANORAMIC RADIOGRAPH

It enables viewing of both maxillary and mandibular arches with their supporting structures

USES:

Studying deciduous root resorption and root development of permanent teeth

To study the path of eruption of the teeth

Used to view ankylosed and impacted teeth

To diagnose presence and extend of pathology and fractures of jaw

ADVANTAGES

Broad anatomic area can be visualized

Radiation exposure is low

Can be used in patient who are unable to tolerate intra oral films or unable to open the mouth

DISADVANTAGES

Expensive equipment

Inclination of anterior teeth cannot be visualized

Less clear images as in periapical films

Distortion, magnification and overlapping of the structures occur

CEPHALOMETRIC RADIOGRAPHS

Specialized skull radiograph in which the head is positioned in a specially designed head holder cephalostat.

It is of two types

1. Lateral cephalogram

2. Postero-anterior cephalogram

OTHER RADIOGRAPHS HAND-WRIST RADIOGRAPH

Radiograph of hand and wrist are useful in estimating the skeletal age of a person .the hand and wrist region have number of small bones whose appearance and progress of ossification occur in a predictable sequence. This enables skeletal age of a person they are useful in assessing growth for planning growth modification procedures and surgical resective procedures

RECENT ADVANCES in diagnostic aids

Some of the recently evolved diagnostic aids are :

XERO RADIOGRAPHY

it was invented by Chester f Carlson in 1937

It’s a completely dry non chemical process which makes use of electrostatic process as in Xerox machines

Xerox radiography makes use of a aluminium plate that is coated with layer of vitreous selenium

The selenium particles are given a uniform electrostatic charge

The charge plate is placed in a light tight, air tight cassette

When the film is exposed it causes a selective discharge of selenium depending up on the amount of radiation used and relative density of objects

This pattern of electric discharge on the plate is called latent image

The latent image is converted into visible image by a process called development in a unit called processor

the plate is exposed to charged particle called toner

This particles adhere to the charged areas in amounts proportional to the quantity of the charge present

the image is now transferred on to a special kind of paper called Xerox opaque paper

The unique feature of xero radiography is that its possible to have both positive and negative image

Once latent image is converted into real image on to a paper. The selenium plates can be discharged cleaned and used again.

Difference of xero radiographic image from conventional radiographic image.

I. Exhibit high edge contrast due to a phenomenon called edge enhancement

II. No special illumination is needed for viewing of Xerox radiographic image

III. Choice of negative or positive image is possible

Advantages of Xerox radiographic are:

IV. Reduction in exposure time

V. Ease in manipulation

VI. Ease of viewing

VII. edge enhancement effect

VIII.Cephalometric landmarks are easily identified

DIGI GRAPH

It enables clinician to perform non invasive and non radiographic cephalometric analysis.

Features of digi graph system includes

I. A landmark can be identified as a point in 3d

II. A cephalometric analysis can be made independently of head position

III. Parallelism of x ray in mid sagittal plane and symmetry of anatomic morphology between left and right side is not necessary.

digi graph allows all patients model radiographs, photographs cephalograms and tracing to be stored on one small disk- reducing storage requirements

MRI magnetic resonance imaging

MRI makes use of two fundamental properties of proton ie spin and small magnetic movement

The proton of hydrogen ion which is in water is utilized in MRI

The proton behave like small spinning magnets and when placed in a magnetic field they tend to move parallel to the field.

Because of the spin the proton differently within their axis progressing about the direction of the magnetic field.

If a coil is now wound around a volume of protons ,they now progress at 90 degree around the magnetic field at the same frequency and induce a minute current in the coil which when amplified can be displayed over a oscilloscope this energy is utilized in scanning procedure

Advantages of MRI1. MRI does not have hazards as it uses non

ionising electromagnetic radiation

2. Anatomical details are as good as in ct scan

3. Greater tissue characterisation is possible

4. Imaging of blood vessel, blood flow, visualisation of thrombus is possible

Disadvantages of MRI5. Time taken is more

6. Not used in patients with cardiac pacemaker

7. Non visualisation of bone makes it useless in bony lesions

tomography

Tomography can be used to visualize a section or a slice of the object and there by eliminate undesirable overlap.

Tomographic can be conventional or computed tomography.

Conventional tomography :

this is process by which a layer of a image with in the body is produced while the images of structure above and below that layer are made invisible by blurring.

Blurring of the image outside the plane of interest is accomplished by simultaneous movement of x ray tube and film during the exposure.

The tube and the film are connected so that movements occur around a point or fulcrum

As the distance from the point of rotation increases , amount of image blurring also increases

As the angle between the source/ film and tissue increases thickness of the image is reduced

Principles of tomography can be mechanically implemented in two ways ;

The x ray tube and film can move synchronously in opposite direction in parallel planes

The x ray tube and film can move synchronously and in opposite direction in parallel planes but with motions other than straight lines that is circular spiral etc

Computed tomography

this is also called CT or CAT (computed axial tomography)

Ct systems are mainly complex imaging systems which use thin beams of x ray that moves in asynchronous manner with an array of detectors which calculates and attenuate the x ray beam at different angles and in different planes

This data is spread in to computer which perform numerous calculations as per the program and constructs accurate image in the coronal axial plane

Advantages of ct scan Accurate visualization

Computer programming makes to view images in different shapes and densities.

Occlusograms

it is a tracing of photograph or a photocopy of a dental arch . Occlusograms are used for the following purposes:

to estimate occlusal relationships

To estimate arch length and width

To estimate the tooth movements required in all 3 planes of space

To estimate anchorage requirements

Occlusograms can be obtained in two ways

the occlusal surfaces of the upper and lower dental casts are photographed in a 1:1 ratio and a tracing of the photograph is made.

The cast are photocopied on a Xerox machine and the occlusal photocopy is used to obtain a tracing

Digital subtraction radiography

comparatively this decrease the amount of distracting background information and by allowing the eye to focus on the actual change that has occurred between two images.

technically this is a image enhancement method that remove the structured noise from the images.

Laser holography Holography is photographic technique for

recording and reconstructing images in such way that 3d aspect object can be obtain recorded image is called hologram

Laser is light amplification by stimulated emission of radiation

Holography is a wave front reconstruction process in which two coherent beams converge to produce a constructive and distractive interference pattern which is recorded on film

orthodontic applications of laser holography:

Storage of study model images

Measurement of incisor intrusion

To determine the centers of rotation produced by orthodontic process

Lower incisor space analysis

to access facial and dental arch symmetry

photocephalometry Thomas in 1978 developed

photocephalometry to better visualize soft tissues of patient

three radiopaque metallic markers with holes are placed on patients skin with adhesives and standard lateral and anterior posterior cephlograms are taken

Using the same position lateral and frontal photographs are taken

the photographs are printed to same size as the radiographs and are superimposed over the radiographic tracing taking the metallic markers as the guide

cineradiography

Basically radiographic motion picture

The subject is oriented properly and stabilized in modified cephalostat

an x ray motion picture is obtained using a cine camera which runs at 240 frames per sec

it is used to visualize swallowing pattern of patient

The x ray motion picture is studied using a movie projector

Thank you