Radiographs are very important diagnostic aids in all aspects of the field of dentistry, and especially in orthodontics.
There are two main types of radiographs:
Intraoral Radiographs – This includes periapicals, bitewings and occlusal films.
Extraoral Radiographs – includes orthopantomographs (OPG), hand-wrist radiographs, posteroanterior radiographs and lateral cephalometrics.
The following sections will cover the radiographs that are used mainly for Orthodontic purposes.
a) Occlusal Films:
It is required to visualize relatively large segments of the dental arch, including the palate, floor of the mouth, and a reasonable extent of lateral structures.
It is indicated to:
Locate roots, supernumerary, unerupted and impacted teeth especially cavities and third molars.
Localize foreign bodies and stones in the salivary glands duct.
Evaluate the integrity of the maxillary sinus outline.
Provide information relative to the fractures of the mandible and maxilla.
To determine to medial and lateral extent of pathosis (e.g. cysts).
b) Orthopantomographs (OPG):
Also termed panoramic radiography or rotational radiography. It is a radiographic procedure that produces a single image of the facial structures, including both the maxillary and mandibular arches and their supporting structures, such as the nasal cavity, maxillary sinuses and the temporomandibular joints.
The principles of the panoramic radiography where first described by Numata in 1933 and Paatero in 1948.
Originally the patient and the films rotated and the x-ray beam remained stationary. But this method was superceded by the development of apparatus which have the tube and the film rotating around the patient.
The x-ray source and film are simultaneously moved parallel to each other in opposite directions. While taking the radiographs, the Frankfort Horizontal Plane (FHP), should be parallel to the floor, and the occlusal plane should be lower anteriorly by 20-30 degrees, with the patient biting on a bite block.
Caution should be taken on the position of the chin: If the chin is tipped too high to the horizontal plane, the mandible will be distorted. If the chin is tipped too low the hard palate will superimpose the roots of the maxillary teeth.
To make sure of the distortion, we can check the width of the permanent mandibular teeth (molars) bilaterally. If one of them is wider than the other one by 20% the radiograph should be retaken.
Advantages of OPG’s
The film is extraoral, making it more comfortable for the patient.
A broad anatomic region is imaged, which includes the maxilla and the mandible.
It exposes the patient to less radiation. It is quick, convenient and easy for the assistant to take.
It can be performed on patients who cannot open their mouths and cannot tolerate intraoral radiographs, especially edentulous patients or patients with a suspected pathosis.
The time required for the procedure is short 3-4 min. including patient positioning and actual exposure.
Accepted by patients during presentations and education.
Gross lesions are visible.
Does not give the fine anatomic details such as the alveolar crest, margins of pathological lesions, bone pattern, caries, etc.
The image may be distorted if the patient is situated outside the focus.
Magnification, geometric distortion, overlapped images of teeth, especially premolar region, all can occur.
The projection can be taken only at one angle.
The view of the temporomandibular joint is distorted.
Expensive machine (3-4x more than the intraoral machine).
Indications for Usage
To assess the patient’s dental age based on the development and progress of mineralization of the teeth, eruption time and exfoliation of the primary teeth. So a comparison of the chronological and skeletal age can be done.
To evaluate present teeth, missing congenitally or impacted, ectopic eruption, malpositioned teeth, the presence or absence of third molars, supernumeraries, quality of restorations, resorption pattern of deciduous teeth, calcification of permanent teeth, asymmetric resorption of deciduous molars, integrity of root structures.
To determine the level of alveolar bone, the interdental crest, bone resorption (horizontal, vertical), infrabony pockets, trabecular pattern wide marrow space (esp. in young growing children), or narrow trabecular spaces (in older children and adults).
To note the presence of any pathological lesions, cysts, tumors, extensive or unique pathosis, ankylosis of deciduous teeth, susceptibility to caries, active carious lesions, root resorption.
c)Hand and Wrist Radiographs:
Predicting the pattern of growth; that is the amount, direction, duration, location and timing of the onset of pubertal growth, is important for the orthodontist when planning therapy and coordinating orthodontic treatment with the vital growth process. Hand and wrist radiographs can aid with this process of growth estimation.
This estimation of the skeletal age of bones or bone age, aids in determining the physical maturation status of the child. One of the indicators to verify the pubertal growth spurt is annual measurement of what has happened. Whereas our interest is to know what will happen in the future to judge the development stage of the child in relation to the child’s own growth curve, in order to decide whether the pubertal growth spurt has started or passed.
Advantages of the Hand and Wrist Radiographs
If differentiates the certain developmental stages towards full physical development. The sequence of such developmental or morphological changes is equal in all humans.
It is technically simple to make roentgenograms of the hand. An individual will pass through a regular series of changes in size and shape of the ossification centers of bone during their progress towards maturity.
Several systems have been developed to evaluate these series of growth changes. One which will be described in detail here, is a system produced by Leonard Fishman. Fishman’s analysis is based on skeletal maturation assessment (SMA). This system uses four stages of bone maturation located at six anatomic sites: the thumb, third finger, fifth finger and radius. In these six sites eleven maturational indicators (SMI’s) are found to cover the entire adolescent development period.
Sites of Skeletal Maturity Indicators
Which are related to: widening of the epiphyseal discs in one of the phalanges on the third or fifth finger, visibility of the ulnarmetacarpophalangeal sesamoid on the first finger (thumb), capping of selected epiphyses over their diaphyes, and the fusion of selected epiphyses and diaphyses. In addition to that ossification of the hook of the hamate and pisiform bone is also taken into consideration (figs. 20 a-d, & 21).
a. Width of Epiphysis
c. Capping of Epiphysis
Sites of Skeletal Maturity Indicators
The epiphyses and diaphyses in the proximal phalynx of the third finger are equally wide.
The epiphyses and diaphyses in the middle phalynx of the third finger are equally wide.
The epiphyses and diaphyses in the middle phalynx of the fifth finger are equally wide.
Ossification of the ulnarmetacarpophalangeal sesamoid on the first finger. This stage is found before maximal growth, but can also be found together with maximum growth.
The epiphyses form a cap around the diaphyses on the distal phalynx of the middle or third finger.
The epiphyses form a cap around the diaphyses on the middle phalynx of the third finger.
The epiphyses form a cap around the diaphyses on the middle phalynx of the fifth finger.
Ossification of the epiphysis in the distal phalynx on the third finger.
Ossification of the epiphysis in the proximal phalynx on the third finger.
Ossification of the epiphysis in the middle phalynx on the third finger. This stage: DP3U + PP3u +MP3u = all these stages are found after the stage of maximum growth is reached, most often from 1-4 years after
Complete union of epiphysis and diaphysis of the radius. The ossification of all the hand bones is complete and skeletal growth is finished.
Fig. 21 (D.S. = Developmental Stage, D = Description, F.A. = Females Age, M.A. = Males age)
Note: The best treatment time for orthodontic patients is 1-2 years before the growth spurt, after that time usually no growth will occur. Hence, the advantage of growth will be missed and treatment might be compromised
Radiographic identification of skeletal maturity indicators(fig. 22)
(For ease of interpretation, the first step is to determine the presence or absence of the abductor sesamoid of the thumb). d) Cephalometrics: Cephalometrics was first introduced to the world by Hofrath in Germany and Broadbent in the United States. Cephalometric radiography means measuring the head in the living individual through the use of radiographs. The original purpose of cephalometrics was to conduct research on growth patients in the craniofacial complex, but was soon used afterwards as a method to evaluate dentofacial proportions and clarify the anatomic basis for a malocclusion. Nowadays, lateral cephalometric radiographs are routinely used in orthodontic practices.
A cephalograph, which is a standardized radiograph of the head (cranium and face), is taken for the patient by the use of a machine termed the “Cephalostat” (cephalus meaning the skull or head, and stat meaning fixed or static position).
The basic equipment required to obtain a cephalometric view consists of an x-ray source, an adjustable cephalostat, a film cassette with radiographic intensifying screens, and a film cassette holder.
Components of the Cephalostat:
The cephalostat consists of the following:
Ear Rods: Two in number, one right and one left. These are tightened into the external auditory meatuses so that the patient is maintained in the mid-sagittal plane. Each ear rod has a metal ring of the same dimension, and in a correctly aligned cephalostat the radiograph shows a single ring. If two rings are seen it indicates an improperly aligned cephalostat.
Nasal Pointer: Which rest on the bridge of the nose (usually at the soft tissue nasion).
Orbital Pointer: This is optional, and if present it is fixed at the orbital region.
A Metal Millimeter Scale: This is fixed vertically to the nasal pointer to indicate the amount of magnification or distortion.
The patient is placed within the cephalostat using the adjustable bilateral ear rods placed within each auditory meatus, usually while the patient is in a standing position (fig. 24). The mid-sagittal plane of the patient is vertical and perpendicular to the x-ray beam. It is also parallel to the film plane, which in turn is also perpendicular to the x-ray beam. The patient's Frankfort plane (line connecting the superior border to the external auditory meatus and the infraorbital rim) is oriented parallel to the floor. The distance between the x-ray source and the mid-sagittal plane of the patient’s head is kept at a minimum of 5 feet (150cm), so reduce magnification.
Fig. 24 A fast Kodak blue brand 8” x 10” film is used. The film is exposed for 4/10 of 7/10 sec. at 90 KVP and 10MA, to penetrate the hard tissue and provide good details of both the hand and soft tissue.
Two views can be used with this type of radiographic method:
1. Posteroanterior View
It shows the vertical and transverse dimensions of the head. The primary indication for obtaining a posteroanterior cephalometric film is the presence of facial asymmetry. A tracing is made and vertical planes are used to illustrate transverse asymmetrics. Lines are drawn through the angles of the mandible and the outer borders of the maxillary tuberosity (fig. 25). Vertical asymmetry can be observed by drawing transverse occlusal planes (molar to molar) at various levels and observing their vertical orientation.
Fig. 25 2. Lateral Head or Profile View (lateral cephalometrics)
It shows the vertical and anteroposterior or sagittal dimensions. This type is most commonly used during orthodontic diagnosis.
Uses of Cephalometrics:
1. Classify the type of face.
Show the relationship between the basal parts of the maxilla and the mandible.
Evaluate the soft tissue profile.
Evaluate the position of the incisors in relation to the basal parts and the soft tissue profile.
To make a growth prediction when the orthodontic treatment is to be conducted during the growth period.
Research Purposes; Information about growth and development by longitudinal studies (serial cephalometric radiographs from birth to the late teens).
Detecting for any abnormalities or pathology e.g. a pituitary tumor of patency of the airway as enlarged adenoids.
Certain materials are used for this purpose, which are:
3-H drawing pencil
Transparent millimeter rule
Method of Tracing
Place the cephalograph on the table with the profile facing to your right hand.
Place the tracing paper over the film (the dull surface facing you), with the lower border of the paper extending about one inch below the chin point.
Tape the upper corners of the tracing paper to the radiograph.
The tracing should be carried out in a dark room on a light-viewing box.
Trace the soft tissue profile, then the hard tissue profile, and then the dentition according to the following tracing procedure.
If bilateral structures are present, draw both of them and take the average of the two.
Trace the reference points.
Tracing Procedures (fig. 26)
Trace the soft tissue profile starting with the forehead, then nose, then lips, then chin till the throat angle beyond the chin.
Trace hard tissue profile; start with the forehead and the frontal sinus.
Trace the nasal bone.
Trace the anterior nasal spine and the anterior contour of the maxilla up to the interdental alveolar crest between the central incisors.
Trace the floor of the nose and the roof of the palate. Trace the posterior nasal spine.
Trace the anterior contour of the mandible starting from the interdental crest between the lower incisors.
Trace the outline of the chin up to the symphysis.
Trace the lower border of the mandible from the symphysis to the angle of mandible.
Trace the posterior border of the ramus.
Trace the orbit from the supra orbital ridge to the most inferior portion on the lower border of the orbit known as orbitale.
Trace the zygomatic bone from the lateral contour of the orbit down to the triangular image. The lowest projection of the triangular image is called key ridge.
Trace the pterygomaxillary fissure which is seen as an inverted tear drop shape just above the posterior nasal spine. The anterior contour of the fissure represents the posterior surface of the maxilla and its posterior contour represents the pterygoid bone.
Trace the shadow of the external acoustic meatus. It appears as an oval radiolucency or opaque ring shadow due to ear rods and it lies behind the upper most surface of the condylar head.
Trace the sella turcica (saddle shaped pituitary fossa).
Trace the most prominent upper central incisor from crown to root.
Trace the most prominent lower central incisor.
Trace the upper and lower permanent first molars.
Trace the occipital bone.
Note: Use the template to trace the central incisors and first molar. Anatomic Points (Landmarks) of the Cephalometric Radiograph (fig. 27):
Nasion (N) – The most anterior point on the fronto-nasal suture.
Sella (S) – The mid-point of sella turcica.
Orbitale (or) – The most inferior anterior point on the bony margin of the orbit.
Porion (po) – The most superior point on the bone external auditory meatus.
Anterior Nasal Spine (ANS) – The most anterior point on the maxilla at the level floor of the nose.
Posterior Nasal Spine (PNS) – The most posterior point on the maxilla at the level floor of the nose.
Point A (A) – The deepest point on the anterior contour of the maxilla between ANS and alveolar crest usually it is approximately 2mm anterior to the apices of maxillary central incisor.
Point B (B) – The deepest point on the anterior contour of the mandible between the chin and alveolar crest.
Pogonion (pog) – The most anterior point on the curvature of bony chin.
Menton (Me) – The most inferior point on the mandibular symphysis.
Gonion (Go) – The most inferior posterior point on the angle of the mandible.
Upper Lip Point (UL) – The most anterior point of upper lip profile.
Lower Lip Point (LL) – The most anterior point of lower lip profile.
Soft Tissue Pogonion (pog) – The most anterior point on the profile of soft tissue chin.
Fig. 27 Cephalometric Horizontal Planes and Lines (fig. 28):
SN Line – This line, connecting the mid-point of sella turcica with nasion, is taken to represent the cranial base.
Frankfort Plane – This is the line joining porion and orbitale.
Maxillary Plane – The line joining anterior nasal spine with posterior nasal spine.
Mandibular Plane – the line joining gonion and menton.
Angular and Linear Measurements;
A series of angles in degree and a few linear distances in millimeters, are measured and compared with normal values. The differences from the normal are noted as plus or minus. When the differences are below or above the normal ranges, they are considered as abnormal.
The angles used in cephalometric analysis are formed at the junction of two planes, which could be horizontal or vertical planes.
The cephalometric analysis can be divided into three parts: Skeletal relationship, Dental relationship and Soft tissue relationship 1. Skeletal Analysis:
a) Antero-Posterior Relationship
SNA: Measured at the junction of SN line and NA line (fig. 29). It evaluates the antero-posterior position of the maxilla in relation to the anterior cranial base. The normal average is 81±3 (normal or orthognathic maxilla). When this angle is above the normal range it would be interpreted as protruded or prognathic maxilla, and when it is below the normal range, retruded or retrognathic maxilla.
SNB: Measured at the junction of SN line and NB line (fig. 30). It evaluates the antero-posterior position of the mandible in relation to the anterior cranial base. The normal average is 78±3 (normal or orthognathic mandible). When this angle is above the normal range, it would be interpreted as protruded or prognathic mandible, and when it is below the normal range, retruded or retrognathic mandible.
ANB: This angle is the difference between SNA and SNB angle and indicates the amount of skeletal discrepancy between maxilla and mandible in antero-posterior position (fig. 31). The normal average is 3±2 (skeletal class I). A larger than normal angle would indicate a skeletal class II, and smaller than 1 angle a skeletal class III.
b) Vertical Relationship
SN-Mxpl: Measured at the intersection of SN line to maxillary plane (fig. 32). It expresses the vertical inclination of the maxilla in relation to the anterior cranial base. The mean value is 8±3 (normal inclined maxilla), values greater than normal indicate a posterior inclination of the maxilla, and smaller values indicate an anterior inclination of maxilla.
FH-Mnpl: Measured at the intersection of Frankfort plane and mandibular plane and expresses the inclination of the mandible (fig. 33). The mean value is 28±4 (normal inclined mandible).
Angles greater than normal indicate the mandible is growing downward and backward or the mandible is steep (posterior inclination of the mandible).
Angles less than normal indicate an anterior inclination of the mandible, (mandible is growing forward and upward, mandible is horizontal).
MMpA: Measured at the intersection of the maxillary plane with the mandibular plane and relates the inclination of the mandible and the maxilla to each other (fig. 34). The mean value is 27±4 (normal interbasal angle). If the angle exceeds the normal there is skeletal open bite, whereas an angle less than the mean indicates skeletal deep bite.
Facial Proportion (FP): This is the ratio of the lower facial height to the total anterior facial height and it is calculated as a percentage according to this equation;
lower facial height
total facial height
Total facial height = lower facial height + upper facial height. Lower facial height: This is a linear measurement from menton perpendicular to maxillary plane.
Upper facial height: This is a linear distance is measured from Nasion perpendicular to maxillary plane (fig. 35).
In normal faces this index has a value of about 50% ± 2% (normal lower height). A larger than this ratio will indicate increased lower facial height, smaller than this value will indicate decreased lower facial height.
Fig. 35 Note: The MMpA reflects both posterior lower facial height and anterior lower facial height. Therefore in the case of patient who has an increased MnpA but average facial proportion it would appear that the posterior facial height is reduced (opposed to an increased lower facial height which result increased MMpA). This would be noticed when there is a discrepancy between the measurements of the facial proportion and the maxillary – mandibular plane angles (MMpA).
2. Dental Relationship
Uinc-Mxpl: Measured at the intersection of the long axis of the upper central incisor with the maxillary plane (fig. 36).
It evaluates the antero-posterior inclination of the most prominent maxillary central incisor. This angle averages 109 ± 6 (normal inclination of upper incisor).
A larger than normal angle would indicate proclination of the upper central incisor and smaller than normal angle would indicate retroclination of maxillary incisors.
Uinc-NA: This is a linear distance measured in millimeter from the most prominent incisal edge of the upper incisor perpendicular to NA line (fig. 37). It averages 4±2mm (normal position of upper incisor).
A larger than normal angle would indicate protrusion of upper central incisor and a smaller than normal angle would indicate retrusion of the central incisor.
Linc to MnPL: Measured at the intersection of the long axis of the lower central incisor with mandibular plane (fig. 38). It evaluates the antero-posterior inclination of the most prominent mandibular central incisor.
A larger than normal angle would indicate proclination of lower incisor and a smaller than normal angle would indicate retroclination of the mandibular incisor.
Linc-NB: This is a linear distance measured in millimeter from the most prominent incisal edge of the lower incisor perpendicular to NB line (fig. 39). It averages 4±2mm (normal position of lower incisor).
A larger than normal angle would indicate protrusion of lower central incisor and a smaller than normal angle would indicate retrusion of the mandibular incisor.
Linc to A-Pog: This is a linear distance measured in millimeter from the incisal edge of the lower incisor perpendicular to A-Pog line (fig. 40). This measurement averages +1±2mm (normal position of lower incisor). A larger than normal angle would indicate protrusion of lower central incisor and a smaller than normal angle would indicate retrusion of the mandibular incisor. To have a pleasing facial appearance, the tip of lower incisor lay on or just in front of this line.
Uinc-Linc: The interincisal angle measure at the junction of the long axis of upper central incisor with the lower central incisor (fig. 41) It averages 135±5 (normal proclination of upper and lower central incisors). The angle decreases with proclination of upper and lower incisors and increase with retroclination of incisors.
Fig. 41 3. Soft Tissue Relationship:
Upper Lip-EL: This is a linear distance measured from the most anterior point on the upper lip perpendicular to esthetic plane (tip of the nose to the soft tissue pogonion) (fig. 42). It averages -2 to -4 (normal position of upper lip which is inside the line). A larger angle indicates the protrusion of the upper lip and a smaller angle indicates the retrusion of the upper lip.
Lower Lip-EL: This is a linear measurement from the most anterior point on the lower lip perpendicular to esthetic plane (fig. 43). It averages from 0 to -2 inside the esthetic line (normal position of the lower lip). A larger angle indicates the protrusion of the lower lip and a smaller angle indicates the retrusion of the lower lip.
Cephalometrics Name : _________________________ Date : ____________