INTRODUCTION Orthodontic diagnosis deals withrecognition of the variouscharacteristics of the malocclusion. Orthodontic diagnosis should bebased on scientific knowledgecombined at times with clinicalexperience and common sense. diagnosis include case history,clinical examination and otherdiagnostic aids such as study casts,radiographs and photographs.
Comprehensive orthodontic diagnosis isestablished by clinical implementationcalled diagnostic aids. Orthodontic diagnostic aids are of twotypes namely’;1. Essential diagnostic aids2. Supplemental diagnostic aids
ESSENTIALDIAGNOSTIC AIDSThey are clinical aids that are considered veryimportant for all cases.The following are essential diagnostic aids;1. Case history2. Clinical examination3. Study models4. Certain radiographs; Periapical Bitewing Panoramic5. Facial photographs
Supplementaldiagnostic aids They are certain aids that are not essential inall cases. They may require specializedequipments that an average dentist may notpossess. The supplemental diagnostic aids include;1-Specialized radiographs ex;a-cephlometric radiographsb-occlusal intra-oral filmsc-selected lateral jaw viewsd-cone shift technique2.Electromyographic examination of muscleactivity
3.Hand wrist radiographs to assess boneage or maturation age4.Endocrine tests5.Estimation of basal metabolic rate6.Diagnostic set-up7.Occlusograms
CASE HISTORY Case history involves eliciting andrecording of relevant informationfrom the patient and parent to aidin overall diagnosis of the casePERSONAL DETAILS:NAME :the patient’s name shouldbe recorded for the purpose ofcommunication and identification.
AGE-the patients chronological age should berecorded. Age consideration helps in diagnosisas well as treatment planning. growth modification procedures usingfunctional and orthopaedic appliances arecarried out during growth period. SEX-patient’s sex should be recorded in casehistory. This is important in planing treatment,as thetiming of growth events such as growth spurtsis different in males and females.
ADDRESS AND OCCUPATION-recording ofaddress and occupation helps in evaluation ofsocio-economic status of the patient and theparents. CHIEF COMPLIANT -the patient’s chiefcompliant should be recorded in his/ her onwords. This help the clinician in identifying the prioritiesand the desires of the patient.
MEDICAL HISTORY- full medical history isrecorded before orthodontic treatment. Few medical conditions contraindicate theuse 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 informationon drug usage. The use of certain drugs like aspirin mayimpede orthodontic tooth movement. DENTAL HISTORY -it includes information on theage of eruption of the deciduous andpermanent teeth,decay,history of extraction,restoration and trauma to dentition. Past dental history helps in evaluation ofpatient and parent’s attitude towardstreatment.
PRENATAL HISTORY-it includeinformation on the condition of themother during pregnancy and the typeof delivery. Forceps delivery predispose to TMJinjuries that can result mandibulargrowth retardation Drugs like thalidomide or affectationwith some infection during pregnancylike german measles can results incongenital deformities of child.
POST NATAL HISTORY -it includesinformation on the type of feeding,presence of habits and on themilestones of normal development. FAMILY HISTORY- class 11,class111malocclusions and congenitalconditions such as clefts of lip & palateare inherited. Family history should record details ofmalocclusion existing in other membersof the family.
GENERAL EXAMIATION Height and weight-they provide clueto the physical growth and maturationof the patient. Gait-(way a person walks)abnormalities of gait are usuallyassociated with neuromusculardisorders that may have a dentalcorrelation. Posture-(way a personstands)abnormal postures canpredispose to malocclusion due toalteration in maxillo-mandibularrelationship.
Body build-(physique) A)aesthetic-thin physique and narrowdental arches. B)plethoric-obese with large squaredental arches C)athletic-normally built, neither thin norobese. normal sized dental arches.
SHELDEON CLASSIFICATIONOF BODY BUILD A)ECTOMORPHIC-tall and thinphysique B) MESOMORPHIC-averagephysique C)ENDOMORPHIC-short andobese physique
EXTRA ORAL EXAMINATIONSHAPE OF THE HEAD: A)MESOCEPHALIC-average shapeof the head. posses normal dentalarches B)DOLICOCEPHALIC-long andnarrow head . They have narrowdental arches C)BRACHYCEPHALIC-broad andshort head. broad dental arches
FACIAL FORMA)MESOPROSOPIC-average ornormal face formB)EURYPROSOPIC-face is broadand shortC)LEPTOPROSOPIC-long andnarrow face form
FACIAL SYMMETRY The patient’s facial symmetry isexamined to determinedisproportions of the face intransverse and vertical planes. Grossfacial asymmetry can occur as aresult of: A. congenital defects B.hemi-facial atrophy/hypertrophy C.unilateral condylar ankylosis andhyperplasia
FACIAL PROFILE The facial profile is examined by viewing thepatient from the side. the facial profile helps indiagnosing the gross deviation of maxillo-mandibular relationship. the profile is assessedby joining the following two reference lines.1. A line joining the forehead and the soft tissuepoint A(deepest point in curvature of upperlip)2. A line joining point A and the soft tissuepogonion(most anterior part of the chin)
STRAIGHT PROFILE-the two lines form nearlystraight line. CONVEX PROFILE-the two lines form an anglewith concavity facing the tissue. This kind of profile occurs as a result ofprognathic maxilla retrognathic mandible asseen in CLASS 11,DIVISON 1 MALOCCLUSION.STRAIGHT PROFILE CONVEXPROFILE
COCAVE PROFILE-the two reference lines forman angle with convexity towards tissue. This type of profile is associated with aprognathic mandible or retrognathic maxilla asin CLASS 11 MALOCCLUSION.
FACIAL DIVERGENCE Facial divergence is defined as anterior orposterior inclination of the lower face relative tothe forehead. ANTERIOR DIVERGENT-a line drawn between theforehead and the chin is inclined anteriorlytowards the chin..
POSTERIOR DIVERGENT A line drawn between the forehead and chin slantsposteriorly towards chin.
STRAIGHT/ORTHOGNATHIC The line between the forehead and the chin isstraight or perpendicular to the floor. The facial divergence is to a large extendinfluenced by patient’s ethnic and racialbackground.
ASSESSMENT OF ANTERO-POSTERIOR JAW RELATIONSHIP It can be assessed clinically. Ideally maxillary skeletal base is 2-3 mm ahead ofthe mandibular skeletal base when the teeth arein occlusion. Estimation is done by placement of index andmiddle fingers at the soft tissue point A and pointB respectively.
In skeletal CLASS11 PATIENTS, the index finger isanterior to middle finger or the hand pointsupwards.
In a skeletal CLASS 111 patient, the middlefinger is ahead of the forefinger or the handpoints downwards.
In a patient with CLASS 1 skeletal pattern thehand is at an even level.
ASSESSMENT OF VERTICAL SKELETALRELATIONSHIP The vertical skeletal relationship assessed bystudying the angle formed between the lowerborder of the mandible and the Frankforthorizontal plane(a line between the most superiorpoint of external auditory meatus and inferiorborder of orbit) Normally the two planes intersects at theoccipital region. In case the two planes meets beyond theoccipital region, it indicates a low angle case ora horizontal growing face. If two planes meet anterior to occipital region itindicates a high angle case or a vertical growingface.
EVALUATION OF FACIALPROPORTIONS A WELL PROPORTIONED FACE CAN BE DIVIDEDINTO THREE EQUAL VERTICAL THIRDS USINGFOUR HORIZONTAL PLANES AT THE LEVEL OF THEHAIRLINE,THE SUPRA ORBITAL RIDGE, THE BASEOF THE NOSE AND THE INFERIOR BORDER OFCHIN WITHIN THE LOWER FACE, THE UPPER LIPOCCUPIES A THIRD OF THE DISTANCE WHILECHIN OCCUPIES THE REST OF THE SPACE.
EXAMINATION OF LIPS The upper lip covers the entire labial surface ofupper anteriors except the incisal 2-3 mm The lower lip covers the entire labial surface oflower anteriors and 2-3 mm of incisal edge ofupper anteriors.
CLASSIFICATION OF LIPS COMPETENT LIP-THE LIPS ARE IN SLIGHT CONTACTWHEN MUSCULATURE IS RELAXED.
INCOMPETENT LIPS-they are morphologicallyshort lips which do not form a lip seal in arelaxed state. The lip seal can only be achieved by activecontraction of perioral and mentalis muscle.
POTENTIALLY INCOMPETENT LIP-they are normallips that fails to form a lip seal due toproclaimed upper incisor. EVERTED LIP-they are hypertrophied lips withweak muscular tonicity.
EXAMINATION OF THENOSE The nose to a large extend contributes to theesthetic appearance of a face. Nose size-normally the nose is one third of thetotal facial height. Nasal contour-the shape of the nose can bestraight, convex or crooked as a result of nasalin juries. Nostrils-they are oval and should be bilaterallysymmetrical. Stenosis of the nostrils mayindicate impaired nasal breathing
EXAMINATION OF CHIN MENTOLABIAL SULCUS-concavity seen below the lower lip.Deep mentolabial sulcus is seen in CLASS11,DIVISON 1malocclusion. MENTALIS ACTIVITY-NORMALY MENTALIS IS NOT ACTIVE ATREST. Hyperactive mentalis is seen in CLASS 11 DIVISON 1 CASES. CHIN POSITION AND PROMINENCE-prominent chin is usuallyassociated with class 111 malocclusion.DEEP MENTOLABIAL SULCUS ANDHYPERACTIVE MENTALIS SEEN IN CLASS 11DIVISON 1 MALOCCLUSION
NASOLABIAL ANGLE It is the angle formed between lower border ofthe nose and a line connecting theintersection of nose and the upper lip with thetip of the lip. This angle is normally 110 degree It reduces in patients with proclaimed upperincisors prognathic maxilla.
INTRA-ORAL EXAMINATIONEXAMINATION OF TONGUE ABNORMALITIES OF TONGUE CAN UPSET THEMUSCLE BALANCE AND EQUILIBRIUM LEADINGTO MALOCCLUSION. A PATIENT WHOSE TONGUE CAN REACH THE TIPOF THE NOSE IS SAID TO HAVE A LONG NOSE. THE LINGUAL FRENUM SHOULD BE EXAMINEDFOR TONGUE TIE
EXAMINATION OF THEPALATE Palate should be examined for the followingfindings;1. Dolicofacial patients have deep palate.2. Presence of swellings in the palate3. Mucosal ulcerations and indentations are afeature 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 maxillaryanterior proclination.
EXAMINATION OF GINGIVA GINGIVA SHOULD BE EXAMINED FOR1. INFLAMMATION2. RECESSION3. MUCOGINGIVAL LESIONS POOR ORAL HYGEINE IS ASSOSIATEDWITH ANTERIOR MARGINAL GINGIVITIS. ANTERIOR GINGIVITIS COMMON INMOUTH BREATHERS DUE TO DRYNESS OFMOUTH CAUSED BY OPEN LIP POSTURE.
EXAMINATION OF FRENALATTACHMENTS The maxillary labial frenum sometimes be thickfibrous and attached relatively low. This may lead to midline diastema. Abnormal frenal attachment are diagnosed byblench test.
EXAMINATION OF TONSILSAND ADENOIDS ABNORMALY INFLAMED TONSILS CAUSEALTERATIONS IN TONGUE AND JAW POSTURE THEREBY UPSETTING THE ORO-FACIAL BALANCE LEADINGTO MALOCCLUSION
ASSESSMENT OFDENTITION;Dental system is examined for ;1. Teeth present in the oral cavity2. Teeth unerupted3. Teeth missing4. Teeth erupted and not erupted5. Presence of caries,restorations,malocclusions,hypoplasia,wear anddislocation.6. Check for the occlusion based on ANGLES CLASS 1, 11, 1117. Record overbite overjet8. Check for crossbite9. Individual tooth irregularities such as rotation, displacement,intrusion and extrusion are noted.10. Check arch form
FUNCTIONALEXAMINATION It is now established that normal function ofstomatognathic system promotes normal growthand development of oro-facial complex. The functional examination should include thefollowing;1. Assessment of postural rest position and interocclusal space.2. Path of closure3. Assessment of respiration4. Assessment of TMJ5. Examination of swallowing6. Examination of speech
ASSESSMENT OF POSTURAL RESTPOSITION AND INTER-OCCLUSALCLEARANCE. The postural rest position of the mandible at which themuscles that closes the jaw and those that open them are, instate of minimal contraction to maintain the posture ofmandible. At postural rest position, a space exists between the upper andlower jaws. This space is known as FREEWAY SPACE. FREEWAY SPACE is 3mm in canine region.
Methods used to record the postural restpositionPHONETIC METHOD; the patient is asked to repeatsome consonants “m or c’’ or repeat a word likeMississippi. The mandible returns to postural rest position 1-2seconds after the exercise. The patient is told not to change the jaw, lip ortongue position after phonation, as the dentistparts the lips to study interocclusal space.
COMMAND METHOD THE PATIENT IS ASKED TO PERFOM CERTAINFUNCTIONS SUCH AS SWALLOWING. THE MANDIBLE TENDS TO RETURN TO REST POSITIONFOLLOWING THIS ACT.
Non command method The patient is observed as he speaks or swallows.The patient is no aware that he is beingexamined. This is usually being carried out by talking abouttopics unrelated to the patient while carefullyobserving him or not
Methods to measure inter-occlusalclearance VERNIER CALIPERS CAN BE USED DIRECTLY INTHE PATIENT’S MOUTH IN THE CANINE ORINCISAL REGION TO MEASURE FREEWAY SPACE. THIS IS DIRECT INTRA ORAL METHOD.
EVALUVATION OF PATH OF CLOSUREThe path of closure is the movement of mandible from the restposition to habitual occlusion . Forward path of closure: a forward path of closure occurs inpatients with mild skeletal and prenormalcy or edge to edgeincisor contact. In such patients ,the mandible is guided to amore forward position to allow the mandibular incisors to golabial to the upper incisors. Backward path of closure: class 11 ,division 2 exhibitpremature 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 orright side is associated with occlusal prematurities and anarrow maxillary arch
ASSESSMENT OF RESPIRATIONHumans may exhibit three types of breathing: nasal ,oral andoro-nasalTest to diagnose the mode of respiration: Mirror test : a double sided mirror is held between the noseand the mouth .fogging on the nasal side of the mirrorindicates nasal breathing while fogging towards oral sideindicates oral breathing Cotton test : a butterfly shaped cotton piece is placed overthe upper lip below the the nostrils . if the cotton flutters downindicates nasal breathing .this test is used to determine theunilateral nasal blockage Water test: the patient is asked to fill his mouth with water andretain it for a long period of time .while nasal breathersaccomplish this with ease , mouth breathers find it difficulttask.
Observation : in nasal breathers the external nares dilateduring inspiration .in mouth breathers ,there is either nochange in the external nares or they may constrict duringinspirationEXAMINATION OF T.M.J.The functional examination should routinely includeauscultation and palpation of temporomandibular jointand musculature associated with mandibular opening.The patient should be examined for the symptoms oftemperomandibular 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 measuringthe distance between the maxillary and mandibularincisal edges with mouth wide open.The normal inter incisal distance is 40- 45 mm
EVALUVATION OF SWALLOWINGIn a new born, tongue is relatively large and protrudesbetween the gumpads and takes part in establishingthe lip seal .this kind of swallow is called infantile swallowand is seen till one and half to two years of age .Infantile swallow is replaced by mature swallow as thebuccal teeth start erupting. The persistence of infantileswallowing can cause malocclusion .thus the swallowingpattern of the individual should be examined.The persistence of the infantile swallow is indicated bythe presence of the following features:a. Protrusion of the tip of tongueb. Contraction of perioral muscles during swallowingc. No contact at the molar region during swallowing
SPEECHCertain malocclusions may causedefects in speech due to interferencewith the movement of tongue and lips.this should be observed while talkingwith the patient .The patient can be asked to readout from a book or asked to countfrom 1-20 while observing the speech.Patients having tongue thrust habittend to lisp while cleft palate patientsmay have a nasal tone
ORTHODONTIC STUDY MODELSOrthodontic study models are accurate plaster reproductions ofteeth and their surrounding soft tissues .that are essentialdiagnostic aid that make it possible to study the arrangement ofteeth and the occlusion from all directions .Uses of study model include:a) They enable study of occlusion from all aspectb) Enable accurate measurements to be made in dentalarch.they help in the measurement of arch length, arch width,and tooth sizec) Help in assessment of treatment progress by dentist as well as bypatientd) Help in assessing the nature and severity of malocclusione) Helpful in motivation of patient and to explain the treatmentplan as weel as progress to patient and parentsf) Makes it possible to stimulate treatment procedures on castsuch as mock surgeryg) Useful to transfer records in case patient is treated by anotherclinician
GNATHOSTATIC MODELSThey are orthodontic study models where the base ofthe maxillary cast is trimmed to correspond to theFrankfort horizontal plane.DIAGNOSTIC SET UPIt was first propose by H.D. keslingDiagnostic set up is made from an extra set of trimmedand polished study models .the individual teeth andtheir associated alveolar processes are sectioned offand replaced on the model base in the desiredpositions .the diagnostic set up thus help in simulatingthe various tooth movement s that are planned forpatients
USES OF DIAGNOSTIC SET UP1. Useful in visualizing and testing the effect ofcomplex tooth movements and extractions on theocclusion2. Patient can be motivated by simulating the variouscorrective procedures in the cast3. Tooth size- arch length discrepancies can bevisualizedPROCEDURE The cast is cut using a fretsaw blade to separatethe individual teeth. A horizontal cut is made 3mm apical to gingivalmargin Vertical cuts are made to separate the individualteeth The individual teeth are set in desired positionusing a red wax
FACIAL PHOTOGRAPHS AS A DIAGNOSTIC AID Facial photographs offers a lot of information on the soft tissuemorphology and facial expression. Both extra-oral as well as intra- oral photographs are usefuldiagnostic aids. Three extra-oral views are routinely taken:a. Frontal viewb. Profile viewc. Oblique facial viewExtra-oral photograph are taken by positioning the patient insuch 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 PHOTOGRAPHS1. Useful in assessment of facial symmetry ,facialtype and profile2. Serve as a diagnostic records3. Help in assessing the progress of thetreatment
ELECTROMYOGRAPHYElectromyography is a procedure used forrecording the electrical activity of muscles theresting potential of a muscle fiber is 85-90mVElectromyograph is a machine used to receive ,amplify and record the action potential duringmuscle activity . Electromyogram is a recordobtained by such procedure . The action potentialpicked up by the electrodes are of two typesNeedle electrodes: used when muscles are placeddeep inside e.g. pterygoid muscleSurface electrodes :used when muscle is superficiallyplaced just below the skinHaving picked up the action potential with surface orneedle electrodes it is recorded either with thehelp of a moving pen in form of a graph orrecorded in form o f sound with help of a magnetictape recorder
Electromyography is used to detect abnormal muscle activityassociated with certain forms of malocclusiona. In severe classII ,division1 malocclusion the upper lip is hypo-funuctionl.Thus during swallowing ,the lower lip extendsupwards and forwards to place to force the maxilla labiallyand a strong mentalis activity is seen .E.M.G .can be used tostudy such a conditionb. Abnormal buccinator activity in classII ,division1c. Overclosure of jaw is associated with accentuatedtemporalis muscle activityd. Children with cerebral palsye. E.M.G . Can be carried out after orthodontic therapy to see ifmuscle balance is achieved
RADIOGRAPHS USED INORTHODONTIC DIAGNOSIS Radiograph routinely used for diagnosis inorthodontic s are classified into two groups1. Intra-oral radiograph2. Extra-oral radiograph
Intra –oral periapicalradiographs(I.O.P.A) They are radiographs that are used to view theteeth and their supporting structures. Two intra oral techniques are used forperiapical 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 toomany radiographs. They cannot be used in patients with high gagreflex and trismusAdvantages Low radiation dose Excellent clarity of teeth and their supportingstructure Possible to obtain localized view of area ofinterest.
BITEWINGRADIOGRAPHS It records the coronal part of upper and lowerdentition along with their supporting structure.1. Used to detect proximal caries2. Height and contour of inter alveolar bone3. To detect periodontal changes4. To detect secondary caries below restorations.5. To determine inter proximal calculus
OCCLUSAL RADIOGRAPHS Occlusal radiographs are used in patients whoare unable to open their mouth wide enough forperiapical radiographs.Uses1. To locate impacted or unerupted teeth2. To locate supernumerary teeth3. To locate foreign bodies in the jaw4. To diagnose the presence and extend of fractures
EXTRA-ORALRADIOGRAPHS THEY ARE USEFUL WHEN LARGE AREAS OF FACE ANDSKULL ARE TO BE VISUALIZED PANORAMIC RADIOGRAPH It enables viewing of both maxillary and mandibulararches with their supporting structures USES: Studying deciduous root resorption and rootdevelopment 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 andfractures of jaw
ADVANTAGES Broad anatomic area can be visualized Radiation exposure is low Can be used in patient who are unable totolerate intra oral films or unable to openthe mouth DISADVANTAGES Expensive equipment Inclination of anterior teeth cannot bevisualized Less clear images as in periapical films Distortion, magnification and overlappingof the structures occur
CEPHALOMETRICRADIOGRAPHS Specialized skull radiograph in which the head ispositioned in a specially designed head holdercephalostat. It is of two types1. Lateral cephalogram2. Postero-anterior cephalogram
OTHER RADIOGRAPHS HAND-WRIST RADIOGRAPHRadiograph of hand and wrist are useful in estimating theskeletal age of a person .the hand and wrist regionhave number of small bones whose appearance andprogress of ossification occur in a predictablesequence. This enables skeletal age of a person theyare useful in assessing growth for planning growthmodification procedures and surgical resectiveprocedures
RECENT ADVANCES indiagnostic 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 whichmakes use of electrostatic process as in Xeroxmachines Xerox radiography makes use of a aluminium platethat is coated with layer of vitreous selenium The selenium particles are given a uniformelectrostatic charge The charge plate is placed in a light tight, air tightcassette
When the film is exposed it causes a selectivedischarge of selenium depending up on the amountof radiation used and relative density of objects This pattern of electric discharge on the plate is calledlatent image The latent image is converted into visible image by aprocess called development in a unit called processor the plate is exposed to charged particle called toner This particles adhere to the charged areas in amountsproportional to the quantity of the charge present the image is now transferred on to a special kind ofpaper called Xerox opaque paper The unique feature of xero radiography is that itspossible to have both positive and negative image Once latent image is converted into real image on to apaper. The selenium plates can be dischargedcleaned and used again.
Difference of xero radiographic image fromconventional radiographic image.I. Exhibit high edge contrast due to aphenomenon called edge enhancementII. No special illumination is needed for viewingof Xerox radiographic imageIII. Choice of negative or positive image ispossibleAdvantages of Xerox radiographic are:I. Reduction in exposure timeII. Ease in manipulationIII. Ease of viewingIV. edge enhancement effectV. Cephalometric landmarks are easily identified
DIGI GRAPH It enables clinician to perform non invasiveand non radiographic cephalometricanalysis. Features of digi graph system includesI. A landmark can be identified as a point in3dII. A cephalometric analysis can be madeindependently of head positionIII. Parallelism of x ray in mid sagittal planeand symmetry of anatomic morphologybetween left and right side is notnecessary.digi graph allows all patients modelradiographs, photographs cephalogramsand tracing to be stored on one small disk-reducing storage requirements
MRI magnetic resonanceimaging MRI makes use of two fundamental properties of proton iespin and small magnetic movement The proton of hydrogen ion which is in water is utilized inMRI The proton behave like small spinning magnets and whenplaced in a magnetic field they tend to move parallel tothe field. Because of the spin the proton differently within their axisprogressing about the direction of the magnetic field. If a coil is now wound around a volume of protons ,theynow progress at 90 degree around the magnetic field atthe same frequency and induce a minute current in thecoil which when amplified can be displayed over aoscilloscope this energy is utilized in scanning procedure
Advantages of MRI1. MRI does not have hazards as it uses nonionising electromagnetic radiation2. Anatomical details are as good as in ct scan3. Greater tissue characterisation is possible4. Imaging of blood vessel, blood flow,visualisation of thrombus is possibleDisadvantages of MRI1. Time taken is more2. Not used in patients with cardiac pacemaker3. Non visualisation of bone makes it useless inbony lesions
tomography Tomography can be used to visualize a section or aslice of the object and there by eliminate undesirableoverlap. Tomographic can be conventional or computedtomography. Conventional tomography : this is process by which a layer of a image with in thebody is produced while the images of structure aboveand below that layer are made invisible by blurring. Blurring of the image outside the plane of interest isaccomplished by simultaneous movement of x raytube and film during the exposure. The tube and the film are connected so thatmovements 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 tissueincreases thickness of the image is reduced Principles of tomography can be mechanicallyimplemented in two ways ; The x ray tube and film can move synchronouslyin opposite direction in parallel planesThe x ray tube and film can move synchronouslyand in opposite direction in parallel planes butwith motions other than straight lines that iscircular spiral etcComputed tomography this is also called CT or CAT (computed axialtomography) Ct systems are mainly complex imaging systemswhich use thin beams of x ray that moves inasynchronous manner with an array of detectorswhich calculates and attenuate the x ray beamat different angles and in different planes This data is spread in to computer which performnumerous calculations as per the program andconstructs accurate image in the coronal axialplane
Advantages of ct scan Accurate visualization Computer programming makes to viewimages in different shapes and densities.Occlusogramsit is a tracing of photograph or a photocopy ofa dental arch . Occlusograms are used for thefollowing purposes:to estimate occlusal relationshipsTo estimate arch length and widthTo estimate the tooth movements required in all 3planes of spaceTo estimate anchorage requirements
Occlusograms can be obtained in two ways the occlusal surfaces of the upper and lowerdental casts are photographed in a 1:1 ratioand a tracing of the photograph is made. The cast are photocopied on a Xeroxmachine and the occlusal photocopy is usedto obtain a tracingDigital subtraction radiography comparatively this decrease the amount ofdistracting background information and byallowing the eye to focus on the actualchange that has occurred between twoimages. technically this is a image enhancementmethod that remove the structured noise fromthe images.
Laser holography Holography is photographic technique forrecording and reconstructing images in suchway that 3d aspect object can be obtainrecorded image is called hologram Laser is light amplification by stimulated emissionof radiation Holography is a wave front reconstructionprocess in which two coherent beams convergeto produce a constructive and distractiveinterference 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 producedby orthodontic process Lower incisor space analysis to access facial and dental arch symmetry
photocephalometry Thomas in 1978 developedphotocephalometry to better visualize softtissues of patient three radiopaque metallic markers with holesare placed on patients skin with adhesivesand standard lateral and anterior posteriorcephlograms are taken Using the same position lateral and frontalphotographs are taken the photographs are printed to same size asthe radiographs and are superimposed overthe radiographic tracing taking the metallicmarkers as the guide
cineradiography Basically radiographic motion picture The subject is oriented properly and stabilized inmodified cephalostat an x ray motion picture is obtained using a cinecamera 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 movieprojector