Role of Radiology in Orthodontics

Introduction

• Radiographs are an important diagnostic tool in assessing an orthodontic condition and in determining a suitable treatment plan.

History of orthodontic radiographs

• Hand-wrist radiograph

Classification of orthodontic radiograph

• Intra-oral radiograph.

• Extra-oral radiograph.

Intra-oral radiograph

• Periapical radiographs (I.O.P.A).

• Bitewing radiographs.

• Occlusal radiographs.

Periapical radiographs (I.O.P.A)₋ Paralleling technique.

₋ Bisecting angle technique

Advantages:

• Low radiation dose.

• Excellent clarity of teeth and their supporting structure.

• Possible to obtain localized view of area of interest.

Disadvantages:

• Assessment of entire dentition requires too many radiographs.

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

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. Uses:

1. 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 radiograph

• Panoramic radiograph

• Cephalometric radiograph

• Cone Beam Computed Tomography

• Application of 3D Imaging to Modern Orthodontics

• MRI (magnetic resonance imaging)

• Laser holography

• Cineradiography

Panoramic radiograph• Panoramic radiography has a role in support of orthodontic assessment both in pre-treatment

planning and also in post-treatment evaluation of success or failure.

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 over lapping of the

structures occur.

Cephalometric radiograph

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

It is of two types of projections:

• Lateral cephalogram.

• Postero-anterior cephalogram

Lateral cephalogramIndications:

• Initial diagnosis.

• Confirmation of the underlying skeletal and/or soft tissue abnormalities.

• Treatment planning.

• Monitoring treatment progress, e.g. to assess anchorage

requirements and incisor inclination.

• Appraisal of treatment results, e.g. 1 or 2 months before

the completion of active.

• Treatment to ensure that treatment targets have been met

and to allow planning of retention.

Posteroanterior (P-A) cephalogram

• A radiograph of the head taken with the x-ray beam perpendicular

to the patient’s coronal plane with the x-ray source behind the head

and the film cassette in front of the patient’s face. P-A cephalograms

are usually taken for evaluation and treatment planning of patients

with facial asymmetry.

Computerized Cephalometrics

• The process allows for automatic measurement of landmark

relationships. Depending on the software and hardware

available, the incorporation of data can be performed by

digitizing points on a tracing.

Photocephalometry

• Three radiopaque metallic markers with holes are placed on patient’s skin with adhesives and standard lateral and anterior posterior cephalograms are taken.

• Using the same position lateral and frontal photographs are taken.

Cone Beam Computed Tomography

Low-dose radiographic procedures (including maxillofacial CBCT) are those that result in doses below about 100000 µSv. The risk of cancer induction caused by low-dose radiographic procedures is difficult to assess.

Advantages:

• 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 which is 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.

Application of 3D Imaging to Modern Orthodontics

The 3-D technique goes beyond the limitations of 2-D analysis in many ways:

• Effective representation of true 3-D morphology of the cranial

structures without distortion, avoiding projection and

identification errors.

• Reduced operator bias because the measurements are performed

automatically.

• Ability to obtain CA using the three dimensions.

• The 3D imaging can be useful in evaluating treatment responses

to functional orthopedics, orthognathic surgery and growth of the face.

MRI (magnetic resonance imaging)

Advantages:

• MRI does not have hazards as it uses non ionizing electromagnetic radiation

• Anatomical details are as good as in CT scan

• Greater tissue characterization is possible

• Imaging of blood vessel, blood flow and visualization of thrombus is possible.

Disadvantages:

• Time taken is more.

• Not used in patients with cardiac pacemaker.

• Non visualization of bone makes it useless in bony lesions.

Laser holography

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.

Cineradiography

• Basically radiographic motion picture

• It is used to visualize swallowing pattern of patient.

• The x ray motion picture is studied using a movie projector.

Section 8Prepared by:

Mohamed Yakoub 244

Mahmoud Ahmed Abu Shama 245

Mahmoud Gamal 246

Mahmoud Salah 247

Mahmoud Ghareib 248