To bitewing or not to bitewing?

To bitewing or not to bitewing? That is the question. Actually it’s just one of the many questions to be asked by a new graduate such as myself with regard to dental radiography!

While researching this rather confusing topic, I uncovered some disparity and conflicting information. One of the main documents I consulted was a report/study produced by the Victoria University of Manchester for the European Commission, the aim of which was to provide a practical guide to radiation protection for professional groups such as dentists. The study was based upon two relevant directives of the European Union: Directive 96/29/Euratom, which lays down basic safety standards to protect healthcare workers, their assistants and members of the general public with regard to ionising radiation, and Directive 97/43/Euaratom, which is to protect the health of individuals against ionising radiation in relation to medical exposure.

So why do we actually take radiographs in dentistry and when should we take them? The following is a whistle-stop tour of current regulations and recommendations and is most certainly not gospel. I have to admit that when Rinn instruments were unavailable in the past, there was many an occasion where I prayed while standing over the developer. And to be honest there was many an occasion where I managed to radiograph every anatomical feature of the human skull with no sign of a tooth!

Radiographs are essential for diagnosis, treatment planning and monitoring of lesion progression. A fundamental part of radiography is the exposure of both patients and clinical staff to X-rays. Only no exposure to X-rays can be deemed completely free of risk. When a patient undergoes radiographic examination millions of photons pass through their bodies, which can damage DNA within the chromosome. Most damage is repaired almost immediately, however, rarely, a portion of DNA can be permanently damaged – mutated – which may ultimately lead to tumour formation. Some studies have suggested an increased risk of tumour formation within salivary glands, the brain and the thyroid as a result of dental radiography. It all sounds very serious of all a sudden! Overall conventional radiography is associated with low dose and low risk for the individual patient, but risk is age dependent, being highest for the young and lowest for the elderly.

So can we justify recording a routine OPG for every new patient that comes through the door, charge them for it and send them on their merry way? Most certainly not. No radiograph should ever be recorded unless an appropriate history and clinical examination has first been undertaken. It is the responsibility of each dental practitioner to assess each patient at their initial visit as to which caries risk group they belong to – high, moderate or low – based upon clinical evidence of previous disease, dietary habits, social history, medical history, use of fluoride toothpaste, whether or not they live in a fluoridated area, their oral health practices, and saliva quality and quantity.

The report from the Victoria University of Manchester recommends the following:

1. If the adult or child is in the high caries risk category, posterior bitewings should be recorded at six-monthly intervals until they move into a lower risk category

2. If the adult or child is in the moderate caries risk category, posterior bitewings should be recorded at 12-monthly intervals until they move into the low risk category

3. If the adult or child (in the permanent dentition) is in the low caries risk category, posterior bitewings should be recorded every other year. For a child in the mixed dentition phase, 18-month intervals are recommended.

With regard to periodontal disease, radiographs can be used as an adjunct to FPC/BPE and are indicated where they may change patient management and prognosis. It recommends horizontal posterior bitewings for pockets less than 6mm and vertical bitewings for pockets greater than 6mm. Periapical radiographs can be recorded for symptomatic teeth.

In endodontics, the report recommends that radiographs are recorded in the following situations:

1. Pre-operative assessment 2. Working length estimation, where access to an electronic apex locator is not possible 3. Post-operatively – to assess the quality of the root filling

4. At a one-year review or if the tooth becomes symptomatic.

Conventional panoramic radiography has lower diagnostic accuracy than intra-oral techniques for caries detection and periapical pathology.

For the edentulous patient, in the absence of any clinical signs or symptoms, there is no justification for any radiographic examination, according to the report.

In implantology, the report recommends, having undertaken a systematic review of the literature, that imaging is essential in pre-op planning. Where this involves bone grafts and multiple potential implant sites, CT has been recommended. Post-op assessment is indicated to assess osseointegration or if the patient is symptomatic. If the patient is symptom-free, assessment can take place at 12 months to assess marginal bone levels, with subsequent reviews ranging from one to three years.

The study recommends pre-extraction radiography if:

1. There is a history of difficult extractions 2. There is clinical suspicion of unusual anatomy

3. Compromising MH

4. Teeth are impacted

5. Roots are buried

6. For lower 8s, to assess the anatomical relationship to IDN.

With regard to the recording of radiographs for pregnant patients the study states that given the low dose, the risk to the developing foetus is so slight there is no contraindication to radiography during pregnancy. Neither is there a need to use a lead apron, but its use continues to be advised, for no reason other than to allay patient anxiety. Lead aprons do not protect against scattered radiation internally and in the case of OPGs they physically interfere with the procedure and can degrade the final image. However, lead shielding of the thyroid gland should be used in cases where the thyroid is in the line of, or very close to, the beam. The Code of Practice for Radiological Protection in Dentistry, as prepared by the Radiological Protection Institute of Ireland (RPII) in 1996, states that special precautions should be taken during pregnancy and breastfeeding and that a dual leaded apron should be worn.

Consent should be informed, and should be obtained from the patient. Implied consent is not enough and relies solely on the patient not actively refusing to have the radiograph taken. Clinical records should have details of all radiographs recorded. The report also states that access to previously recorded radiographs should be first undertaken so as to avoid any unnecessary repeated exposure.

When investigating equipment factors in terms of the reduction of radiation dosage to patients, they recommend the following:

1. 65-70kV for intra-oral X-ray sets using AC equipment and 60kV for DC X-ray sets

2. Filtration of aluminium is a key method for reducing skin dose to patients

3. Rectangular collimation is a highly effective means of dose reduction in intra-oral dental radiography and should be utilised in combination with film holders incorporating beam aiming devices.

With regard to digital radiography the study states that it offers a potential dose reduction but a medical physics expert should be consulted to achieve dose reduction optimisation.

The purpose of Quality Assurance (QA) in dental radiology is to ensure consistently adequate diagnostic information while radiation doses are controlled to be as low as reasonably achievable (ALARA). QA should, according to the study, address image quality assessment, practical radiographic technique, patient dose, X-ray equipment and dark rooms, films, cassettes and processing, and should be implemented by the holder of the facility. The Health Service Executive (HSE) is currently intent on conducting a clinical audit in dental radiology through a clinical questionnaire and is required by law to do so in line with SI 478 (2002) and SI 303 (2007).

I reiterate that the above is only a brief fling in a vast and expansive topic. I always find it helpful to remember that what I’m looking for in dental radiology is the tooth, the whole tooth and nothing but the tooth! Finally, a huge thank you to Dr Donal McDonnell, senior lecturer and consultant in oral radiology, Cork University Dental School and Hospital, without whom the article would not have been brought to fruition.

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