TIP 1: KNOW YOUR DENTAL TERMINOLOGY.
Dental terminology differs from medical terminology, because the jaw is curved. To indicate direction, the dental terms are:
- MESIAL – towards the midline
- DISTAL – away from the midline
- BUCCAL – towards the cheeks
- LABIAL – towards the lips
- PALATAL – towards the palate (maxilla)
- LINGUAL – towards the tongue (mandible)
The teeth have a crown, cervical region, root(s) and root apex (Fig 1).
Lesions may be described as PERICORONAL (around the crown) or PERIAPICAL (around the root apex). The surfaces of the teeth are:
- OCCLUSAL – the “biting” surfaces
- INTERPROXIMAL – the surfaces that touch other teeth
The spaces between teeth are DIASTEMAS.
TIP 2: KNOW YOUR DENTAL NUMBERING.
The dentition in numbered from mesial to distal in four quadrants. The central incisor is labelled “1” and the third molar is labelled “8”. Each quadrant also has a number (Fig 2), from 1 - 4 in a clockwise circle).
The deciduous (primary) dentition is numbered from 1 - 5 in the same way; the quadrants are labelled 5 - 8, to distinguish the teeth from the permanent dentition (Fig 3).
Alternatively, the primary dentition can be labelled A to E, with A being the central incisor and E the second molar.
TIP 3: KNOW THE DIFFERENCE BETWEEN THE PRIMARY AND PERMANENT DENTITION.
The normal child has 20 deciduous teeth: 2 incisors, 1 canine and 2 molars in each quadrant. The average adult develops 32 permanent teeth: 2 incisors, 1 canine, 2 premolars and 3 molars in each quadrant. The permanent teeth begin to erupt at ~7 years of age, and the deciduous teeth are typically lost by ~13 years. When a tooth erupts on one side of the jaw, the equivalent tooth on the other side should erupt within 6 months. If the tooth does not erupt within the expected time frame, it is described as IMPACTED (Fig 4).
The primary dentition is SMALLER than the permanent dentition, the ROOTS ARE SHORTER and the ENAMEL IS THINNER (Fig 5).
These features help distinguish between the deciduous and permanent dentition.
TIP 4: KNOW YOUR NORMAL VARIANTS.
It is common for certain teeth not to develop, and for extra teeth to develop. The teeth that are most often missing include the third molars, lateral maxillary incisors and second premolars. The developmental absence of 1 - 6 teeth (excluding the third molars) is known as HYPODONTIA. The developmental absence of more than 6 teeth (excluding the third molars) is known as OLIGODONTIA (Fig 6).
Extra teeth are known as supernumerary teeth (Fig 7).
They can occur anywhere in the tooth bearing regions of the jaws. An accessory tooth near the midline is known as a MESIODENS and an accessory tooth distal to the third molars is called a DISTODENS (Fig 8).
A tooth that is larger than normal is called a MACRODONT and a small tooth is a MICRODONT (Fig 9).
A tooth with roots that bifurcate low is called a TAURODONT (Fig 10).
Bone islands are common in the jaws, and are confusing for the dentist. They are areas of cortical bone in the medullary bone (Fig 11).
It is important for the radiologist to mention these in the report as our dental colleagues are not familiar with bone “lesions”.
Another variant is the Stafne bone defect or cyst. These are developmental salivary inclusion cysts in the mandible. These defects are always just anterior to the angle of the mandible, have a well-defined sclerotic rim and extend to the inferior mandibular cortex (Fig 12).
TIP 5: KNOW THE ARTEFACTS OF THE OPG TECHNIQUE, AND COMMENT ON THEM IF PRESENT.
GHOST IMAGES occur when an object or anatomic structure that is outside the focal plane, is dense enough to attenuate the x-ray beam and project an image. The images is projected on the opposite side to the real structure, and is blurred and magnified because it is not in the focal plane. As the x-ray tube is angulated up, the ghost image is also higher than the real image. The concept can be demonstrated by a patient wearing jewellery: The earring in the right ear has a sharply demarcated true image, the blurred ghost image is seen projected over the left maxillary sinus which is higher than the ear (Fig 13).
TIP 6: MENTION THE AREAS THAT A DENTIST WILL BE UNCERTAIN ABOUT.
Most dentists are very good at looking at the teeth on a radiograph. They are much less confident about the surrounding structures, such as the bones, sinuses, temporomandibular joints(TMJs) and soft tissues.
Osteoarthritis is very common in the TMJs. As with any other synovial joint, features include joint space narrowing, osteophyte formation, subchondral bone cysts, sclerosis and eventually flattening of the condyle (Fig 14).
The dentist will appreciate comments about the TMJs in the radiology report.
The maxillary sinuses are important in dentistry, as the roots of the molars frequently extend into the sinuses. Check the sinus for disease or fluid, especially if there is dental disease present (Fig 15).
About 10 % of maxillary sinusitis is due to dental disease
[2].
Soft tissue calcifications are also poorly understood by the dental community. The radiologist should comment on calcifications, assigning them as tonsillar, salivary, lymph node and vascular (Fig 16).
There is an association between carotid artery calcification on orthopantomogram and stroke risk
[3] (Fig 17).
TIP 7: KNOW THE COMMON LESIONS AND THEIR APPEARANCES – PERIAPICAL LUCENCIES, RADICULAR CYSTS, DENTIGEROUS CYSTS.
The large majority of jaw lesions are LUCENT, BENIGN and ASSOCIATED WITH A TOOTH.
PERIAPICAL LUCENCIES are common, and are lucent lesions that occur around the apex of a tooth. They show the expected features of a benign bone lesion: well-defined, short zone of transition, and little effect on adjacent structures (Fig 18).
It is not possible to distinguish the cause on imaging alone and clinical examination is important with regard to tooth vitality. It is best to simply describe these lesions as a periapical lucency, and mention which tooth is affected.
A RADICULAR CYST is a periapical lesion associated with a non-vital tooth. Often, the affected tooth has had root canal treatment (RCT), which is seen on imaging as dense material filling the pulp chambers of the treated tooth. The term radicular cyst is usually applied when the periapical lucency is at least 10 mm in size (Fig 18).
A DENTIGEROUS CYST is a cyst associated with the crown of an unerupted tooth. They are often seen in association with an unerupted third molar in a young adult (Fig 19).
They are unilocular, with a well-defined sclerotic margin, no internal septations and they insert in the cervical region of the tooth (the cemento-enamel junction).
TIP 8: MENTION THE RELATIONSHIP BETWEEN THE ROOTS OF THE THIRD MOLARS AND THE MANDIBULAR CANALS.
The relationship between the nerve and the roots of the third molar can be complex, with the nerve passing between or even winding around the roots in rare cases. While the nerve is not visible on imaging, the mandibular canal is well defined, and the relationship between the roots of the third molars and the canal is important.
The third molar may be completely above the mandibular canal, but often the roots are projected over or partly over the canal. It is these cases where the nerve is at risk during extraction, and needs to be highlighted in the report (Fig 20).
TIP 9: ANSWER THE CLINICAL QUESTION IF ONE IS RAISED.
Clinical information is often deficient on dental referrals, but if a specific clinical question is raised, it should be addressed in the report. For example, if the referral states “wisdom teeth”, the presence, position and relationship to adjacent structures should be described.
TIP 10: LOOK AT THE IMAGE – DON’T JUST USE A STANDARD REPORT SUCH AS “DENTITION AS SHOWN, NO NON-DENTAL ABNORMALITY”.
This is one of the most annoying phases in a dental report. It suggests to the dentist that the reporting radiologist has not looked carefully at the image and is not interested in their patient. There is also the question of “non-dental” – what does this mean?
Take the time to look properly at the film, just as you would any other x-ray. You might be surprised at what you will see! (Fig 21).