6 Photographic Documentation of the Oral Cavity
Since the genesis of photography in the early 19th century, the application of this technology was swiftly recognized and embraced by the medical community. This chapter will address the role of photography in the management of oral pathology and address pitfalls and potential limitations faced when documenting the oral cavity utilizing a photographic approach.
Since the mid-1940s, photography has been described, predominantly dental and dermatologic, for documentation of lesions within the oral cavity. 1 , 2 , 3 Photography provides clinicians with a tool that can aid in medical consultation, documentation, and education. 2 The clinical use of photographs may reduce the need for verbose and potentially time-consuming description of the oral cavity. A picture can also help reduce inter- and intraobserver variation in descriptions.
The oral cavity, however, poses a multitude of challenges for photographers, including restricted space, limited light, and variability of both depth and planes. Attempts have been made to address these technical challenges by using light-field digital (LFD) cameras (also known as plenoptic cameras). Unlike the standard digital modality, LFD cameras capture data in regard to color, intensity, and the direction of light vector entering the camera. Using these data, offline software can then reconstruct a two-dimensional picture with the ability for the viewer to focus on different areas of interest within the picture after the image has been captured. 4 The need, however, for specialized equipment, associated expense, and comparative low resolution have limited the use of this technology for oral photodocumentation. Therefore, the focus of this chapter will be the usage of conventional digital photography and how to optimize image quality of the oral cavity.
6.2 Camera and Equipment
When taking pictures of the oral cavity, there are two features that are essential for it to be useful: first, sufficient resolution to record both soft- and hard-tissue details and, second, true color representation. 5
The amount of detail seen on a picture is dependent on resolution, which is measured in pixels. A pixel refers to the smallest unit point within a digital picture that can be displayed and represented on a digital display. The pixels come together to make up the image. As such, the greater the number of pixels, the greater the amount of detail and the higher the resolution of the resulting picture. One megapixel (MP) corresponds to 1,216 × 912 pixels. There has been extensive discussion in the dermatology literature regarding the ideal photographic resolution required, with suggested values ranging from 0.4 to 1.3 MP. 6 This range falls well within the capacity of most new cameras currently available on the market, which typically have picture resolution starting at 3 MP. 6
Picture resolution is, however, not the only factor determining the quality of an image; the capacity of lens and camera are also of equal importance. Poor lens quality or incorrect camera shutter speed, despite high-resolution capacity, will result in decreased quality as color and tissue texture can be lost.
Given these considerations, the choice of camera should therefore be determined by the need of the clinician, practicality of use, and cost, while also considering basic camera features such as adequate lens quality, shutter speed, and optimizing resolution. When making this investment, it is also important to remember that the images produced not only will serve as baseline for follow-up but are also part of the permanent medical-legal record, and therefore needs to be documented with precision. 5
6.2.1 Digital Single-Lens Reflex Camera
Digital Single-Lens Reflex (DSLR) camera systems are considered the gold standard in dental photography. 7 A DSLR system is made up by the camera, lens, and flash system (see ▶ Fig. 6.1). There are two types of DSLR cameras available, with variable costs: semiprofessional and professional. The latter has additional features, the cost of which may not be justified for clinical use. 5 DSLR cameras tend to be modular, which allows the user to exchange the lens or flash system depending on the photographic needs.
Telephoto zoom lenses (TZL) are the most commonly used lenses for DSLR as they provide the user with an adjustable focal point. This allows the photographer to zoom in and provides closer framing of the object of interested without the shooter physically having to adjust where they are taking the photograph from.
Prime lens (PL) is a type of lens that has a fixed focal length. As a result, a user has to adjust the location from which he or she plans to take the picture (or use a prime lens with a different focal length) to ensure the object of interest is in focus and well framed. Traditionally, PL have been associated with increased picture quality and faster aperture. 8 The drawback, however, is the need to carry multiple lenses with different focal length, which is both cumbersome and expensive.
Macro Lenses (ML) are a fixed focal length lens designed to take pictures very up close and provides the photographer with images that are life size. The characteristics of ML are ideal for oral cavity photography, making ML popular among dentists. Review of the dental literature reveals a preference for an ML with a 100- or 105-mm focal length, which allows approximately 4- to 4.5-inch standoff. 7 An otolaryngologist—head and neck surgeon who uses a camera in both the clinic and the operating room, situations that require images to be taken from different distances, would therefore need multiple fixed focal length lenses.
Axial lighting (AL) is the most commonly used lighting by amateur photographers as most DSLR cameras have built-in flash units (▶ Fig. 6.1d). The built-in nature of this feature makes its use convenient and negates the need to carry additional equipment. AL, however, tends to create harsh shadows, uneven lighting, and possible asymmetric illumination. The built-in flash systems furthermore have a small range and most DSLR cameras do not permit flash intensity adjustment. 9
Ring flash (RF) is a circular flash that mounts on the lens, and provides 360 degrees of illumination around the lens. The benefit of this is that it minimizes shadowing, which is particularly important when using fixed focal lenses such as PL and ML. 7 , 10 RF provides good light for when taking a picture within a cavity such as the oral cavity. 9 The use of RF increases the cost of the equipment as this is not a standard accessory for a DSLR to be equipped with and requires the user to carry additional equipment.