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• Orthopantomogram INTRODUCTION

Among the essential diagnostic aids, radiographs and photographs play an important role in the diagnosis of a particular case. In the previous chapter, we have already understood the importance and uses of cephalograms. The other important radiographs that are encountered for everyday use in a dental clinic include the or thopantornogram, the intraoral periapical views (IOPA's) and the bitewing radiographs.

In this chapter, we will discuss the orthopantomo- gram, the intraoral periapical radiographs, occlusal views, as well as the facial photographs.

WHY RADIOGRAPHS?

This question is very pertinent to answer. Radiographs give the true picture regarding the underlying struc- ture of the bone and associated structures. Radio- graphs are recommended for the following reasons: 1. Detection of pa thologies associated with the teeth

in particular and the jaws in general. These may include caries, periapical pathologies, odontomas, etc.

2. To determine the number, size and shape of the teeth.

3. To determine the exact eruption status, including placement and path of eruption, of the succedaneous teeth.

• Intraoral radiographs

o Intraoral periapical radiographs n Bitewing radiographs

o Occlusal radiographs • Facial photog raphs

4. For the calculation of total tooth material, Le. the mesiodistal dimensions of the permanent teeth. 5. For medicolegal purposes.

ORTHOPANTOMOGRAM

The orthopantomogram is considered an essential diagnostic aid and should be examined prior to undertaking any orthodontic treatment. Tt is not available routinely in dental clinics and the patient may require to be referred to special X-ray centers. The biggest advantage (Table 10.1) of this radiograph is that it provides visualization uf a large area uf interest to an orthodontist using a single radiograph. With its few drawbacks (Table 10.2),these are probably the most frequently preserved records of any orthodontic case in areas where this facility is available. The orthopantomogram has an inherent disadvan- tage that it requires extra space and the equipment, which by itself is expensive, but the radiograph covers the complete dentition and the underlying skeletal structure with amazing clarity at a fraction of the radia- tion dose of a full-mouth lOP A protocol.

For any student of orthodontics it is essential to be able to correctly read and interpret an orthopan- tomogram. It is advised that while reading an ortho- pantomogram a correct protocol must be followed so as not miss out any important diagnostic detail. The most convenient and simple method is presented.

1. A large anatomic area is visualized

2. The radiation exposure is low, less than that for four

JOPAs

3. Patientcooperation is rarely a problem

4. Lnter-operator variation isminimal

Table 10.2: Disadvantages of an orthopantomogram 1. Specializedequipment is required

2. Distortions, magnifications and overlapping of

structures are a problem

3. Definition of structures is not as good as in 10PAs

4. It is not standardized 5. lOPAsmay still be required Step 1

Orient the radiograph as when looking at the patient, i.e. with the patient's left side positioned on the clinician's right. The radiograph is then placed on a view box, which is uniformly lit (Fig. IQ.lA). Prefer to dim the remaining lights in the room.

Fig. 10.lA: OPG viewer Step 2

Start examining from the right condylar head and follow the outline along the neck and the posterior border of the ramus. Continue following the outline of the mandibular body to the symphyseal region anteriorlyalong the lower border of the mandible to the left condyle. Compare the outline for disconti- nu ties, radiopacities or radiolucencies and most importantly from an orthodontic perspective for symmetry. Asymmetry may result from faulty positioning of the patient or that of the cassette in its

bular cortex and the other structures including the mandibular canals, mental foramina, and the coronoid process (Fig. lQ.lB).

Condyle

Mandibular canal

Symphysis

Fig. 10.1B: Outline of the structures seen-including the condyles, coronoid processes, mandibularcortex, mandibular canals, menIal triangle, and the mental foramina

Step 3

Examine the medullary bone of the mandible for the usual anatomic landmarks and note anything sugges- tive of pathology, especially in the periapical regions of the teeth (Fig. lQ.lq. The third molar development and position should definitely be noted as it may play an important role in determining the type of retention planned and/or their enucleation if required.

Fig. 10.1C:Orthopantomogramwithall teeth clearly visible Step 4

Next, examine the cortical outline of the maxilla start- ing on the right side. Trace the pterygo-maxillary fissure, hard palate with the anterior nasal spine. Examine the nasal cavities and the nasal septum followed by the maxillary sinuses. It is advisable to

Ethmoid sinus Nasalcavlty "" / Orbital floor

••~.="'"~

Fig.10.10: Outlineof nasal cavities and the maxillarysinuses

Fig.10.1E: Radiopacities in the maxillaryanterior region compare the right and left sides especially of the nasal cavities and the maxillary sinuses (Fig. 10.10). Radiopacities in these regions could be suggestive of pathology (Fig. 1O.1E) or sometimes the presence of foreign body. These might reflect upon the breathing pattern of the patient.

Step 5

Margins of a number of soft tissue structures may be seen on the orthopantomogram. These include the--- tongue, soft palate, nose and earlobes (Figs 10.lF and G). Also, sometimes seen, though not as clearly, are the lip lines and the nasolabial folds.

Step 6

Radiopaque shadows, which superimpose on normal anatomic structures are called "ghosts" and are actually artifacts. These can sometimes pose a problem in radiographic interpretation. These are created when the X-ray beam projects through a dense object, e.g. the spinal cord and the opaque shadow of the object projects onto the opposite side of the radiograph.

Step 7

Finally evaluate the teeth for-presence, stage of development, state of eruption unerupted or impacted

Dorsum of tongue _{Soft palate}

Fig.10.1F: Outlineof soft tissue structures seen in an OPG

Fig.10.1G: Shadows of the soft tissues are more prominent is OPGs of edentulous patients

teeth, placement, root morphology and position, cavities, fractures, contacts, and/or any pathology (Fig. 10.lH). These findings have to be clinically cor- related and/or with TOPA's or bitewing radiographs. Teeth may appear to be magnified or minimized in the horizontal dimension depending on their position. The maxillary and mandibular cusp tips should be generally separate (unless there is a change in the cant of occlusion Fig. 1O.lI) and there should be gentle curve to the occlusal plane.

The orthopantomograrn may not be sufficient by itself. If any doubt arises it is recommended that an lOP A of the concerned region be taken (Fig. 10.1J).

Fig.10.1H(i):Outlineof an OPG highlightingmaxillaryand mandibularteeth

Fig. 10.1 H(ii):Orthopantomogramshowing mixed dentition

Fig. 10.11:Orthopantomogram showing decreased space between the maxillaryand the mandibularcusp tips due to the change in the cant of occlusion

Earlier, before the advent of the OPCs, the IOPAs along with the bitewing radiographs were the main stay for an orthodontist.