Dentistry is a branch of medicine concerned with the prevention and treatment of tooth and gum disorders. Dentistry is divided into several highly specialized areas; endodontics is a branch of dentistry concerned with the treatment and diagnosis of diseases which affect the pulp and roots of the teeth, orthodontics is concerned with the prevention and correction of abnormally aligned teeth and periodontics is concerned with the treatment of abnormal conditions of the gingivae (gums).
Dental photography has emerged as a specialized field within medical photography. Clinical photographs of the oral cavity and teeth are useful to practitioners of all dental specialities as well as to oral and plastic surgeons. External facial views and intra-oral views can be used to document and monitor a number of conditions including malformations of the oral cavity, dental disease, reconstructive surgery and corrective procedures to the teeth. As with all aspects of medical photography standardization is essential to produce consistent, high quality, repeatable images.
Anatomy of the Oral Cavity
It is important that the medical photographer has a good working knowledge of the anatomy and physiology of the oral cavity and teeth. This knowledge enables them to produce accurate, repeatable records of a dental patient’s condition or treatment. The medical photographer should have a good understanding of teeth notation and be aware of common dental terminology. This allows them to accurately locate and document a variety of anatomical structures and pathological conditions within the oral cavity.
Most conditions of the face and mouth can be demonstrated by photographing anterior posterior (AP), oblique (45°) and lateral views. An AP and right and left lateral of the patient’s head and shoulders are generally all that are required for extra-oral views, although some consultants may also request oblique views. It is however important that both lateral views are taken to ensure any facial asymmetry shows clearly.
Extra-oral views can be taken with a standard camera and lens set-up using studio lighting. It is essential that the camera plane remains parallel to the anatomical plane and that the patient’s head remains straight when extra-oral views are photographed, otherwise distortion will occur. The photographer will also make sure that the orbito-helix line (outer canthus of the eye to the point on the junction of the helix of the ear to the head) is horizontal when photographing the AP and lateral views.
Intra-Oral Photography and ring flash/point source systems
Macro lenses are required when photographing intra-oral views as the teeth need to be photographed at high magnifications. Typical magnification ratios used for teeth are 1:1 and 1:2. Intra-oral views require maximum depth of field to ensure the entire dentition is sharply focused, therefore the highest aperture should be used.
The oral cavity cannot be lit sufficiently using standard studio lighting, for intra-oral views the source of illumination must be near to the lens axis and mounted at the front of the lens. There are two main methods of lighting the oral cavity, point source and ring flash. Point source is a short straight flash tube, it is called point source as its illumination is directional. The flash unit is mounted near the front of the lens on a flash bracket, this technique illuminates the oral cavity well but can cause shadowing.
Ring flashes have one or more curved flash tubes (the shape of a circle) built into the end of the lens. Ring flashes provide even, shadow-free illumination which is ideal for lighting the oral cavity. The only disadvantage to ring flashes is the distracting reflections which can occur on wet tooth enamel. These reflections can be reduced by asking the patient to swallow their excess saliva or by drying their teeth and gums on a piece of gauze before each photograph.
Dental retractors and mirrors
Views of the dentition can only be achieved using dental retractors as it is necessary to retract the cheeks and lips from the field of view in order to obtain clear intra-oral pictures. Dental retractors are available in metal, wire and plastic and come in paediatric and adult sizes. Dental retractors (if used properly) should provide both vertical clearance as well as horizontal retraction of the lips.
Dental mirrors can be used alongside retractors, the mirrors are available in glass and plastic and also in paediatric and adult sizes. There are two main types of dental mirrors, occlusal mirrors are designed to fit inside the patient’s mouth. The occlusal mirror can be tilted until the reflection of either the upper or lower dentition is visible, the photographer can then photograph the reflected image of the maxillary or mandibular arch.
Buccal mirrors are used when photographing the buccal surfaces of the posterior teeth. Buccal mirrors are often double ended and the smaller side can be used to photograph the lingual surfaces of the posterior and anterior teeth.
When dental mirrors are placed into the mouth misting can occur which can obscure the reflected image, this problem can be minimised by placing the mirror in a jar of warm water prior to use. It also helps if the patient breathes through their nose and not through their mouth during the procedure.
Medical photographers should be familiar with dental retractors and mirrors and have experience using them on themselves before they attempt to photograph any patients. This is important as retractors and mirrors can be uncomfortable or painful, particularly if the patient has limited jaw movement or mouth lesions. With experience the photographer can take intra-oral photographs quickly and with a minimum of discomfort to the patient. Where mirrors have been used the finished photographs will be a mirror image of the patient’s actual teeth so the photographer must manually reverse the image in photo editing software.
Health and safety issues
Medical photographers have a responsibility to their patients and other healthcare workers to ensure that their camera and dental equipment is sterile and safe to use. They must adhere to infection prevention policies rigorously when performing dental photography. Hands should be washed before and after patient contact and gloves should be worn to prevent the transfer of organisms from patient to photographer or vice versa.
Saliva and blood are both carriers of potentially infectious micro-organisms which can be transferred from the mouth onto dental mirrors and retractors. It is therefore essential that dental retractors and mirrors are sterilized after use to ensure no cross-contamination takes place. After the clinical photographs have been taken the used retractors and mirrors should be placed in a secure container and sent to a sterile services department to be cleaned. If this is not possible the equipment must be thoroughly sterilized in the medical illustration department before it can be reused.
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