Don't trust bitewings

Bitewings are a narrow view into a wider area. Generally, a size 2 film which the majority of dentists will use will show 4-5 teeth in view. This will usually miss the 8s, distal of the 7s and distal of the 3s depending on the anterior posterior positioning of your film. The posterior lateral surface of the tongue will tend to push the film superiorly and anteriorly and the curvature of the mandible will stop the film moving too far forwards.

Caries will only present on bitewings when a significant portion of the buccolingual width is involved. Therefore as it is well known, they are useful for diagnosing interproximal caries where the buccolingual width is narrow near the contact point. However, a few things can confuse the interpreter of the radiograph:

• Occlusal caries is unlikely to show up on a bite wing until large. If you see a radiolucency at the base of a fissure, it is very likely to be carious. Buccal and palatal pit caries show up better as they penetrate into the tooth in the same direction as the xray beam 
• I have been caught out a few times where there is caries evident intraorally with dark shadowing but it is sound radiographically. Always trust your clinical impression over the radiogaph. Bitewings should only be used to confirm a clinical diagnosis and determine the prognosis of the tooth.
• Radiolucent composite resins will catch you out like nothing else. I have cut into sound tooth structure thinking there was hidden caries sub surface when there was a radiolucent buccal or lingual composite near the contact point. If it doesn't feel right, it probably isn't. The majority of these are very old and so are discoloured and may require replacement anyway for aesthetic reasons but don't let them fool you. The difficulty is diagnosing caries under these restorations. the caries is likely to have a more jagged and less defined margin. If the radiolucent area is smooth and sharply defined, leave it alone.
• Not all teeth will be in the bite wing, pay extra attention to those that are outside. The 7s and 8s are high caries risk due to their inaccessibility to clean. Patients with sound 6-6 teeth can often show significant caries on the more posterior teeth. If you need an image of these teeth, take another bite wing or order an OPG. With your clinical interpretation, you need a clean tooth, use a probe to clean off the bulk of plaque and check for white spots/cavitation. The common areas for caries are the buccal and occlusal surfaces of upper 8s due to inaccessibility for cleaning and food trapping against the cheek.
• When interpreting your radiographs spend a good amount of time looking at them at the correct orientation with a good level of magnification/enlargement. If you just look at them in passing, and only look at the areas you're interesting in you will miss more subtle/incidental findings. I am beginning to make it a habit to spend a good 30 seconds scanning all over the radiograph looking at things systematically: bone levels, calculus, interproximal areas, fissure areas, restorations and pulp chambers. I have found that when I had only been scanning the radiographs briefly I was seeing obvious pathologies but misssing more subtle clues that I only saw once the patient had gone and I was managing the xray file.
• Once you have viewed your radiograph, go back to the mouth and clarify findings. clean and dry the teeth where there is a radiolucency visible and check for white spots/ cavitations. often a moderate sized interproximal lesion can be detected if you dry the teeth really well and look from the buccal and lingual. They will have often cavitated underneath the contact point before the marginal ridge collapses. Detect this visually or with a probe or by shredding floss.

It must be remembered that conventional dental radiography is a 2D image of 3 dimensional structures and are only representations of the relative radiographic qualities of the substrates in question. They are to be used as a guide to confirm and assess the prognosis of identified findings in the mouth. However, more often they can be utilised as a fail safe to allow us to detect pathologies that are poorly visible to direct visualisation. Interpretation must be done with care to avoid clinician neglect and we should all utilise strategies that aim to mimimise our margin for error.