FOTOGRAFÍA DIGITAL EN ODONTOLOGÍA: TÉCNICAS Y LA IMPORTANCIA CLÍNICA

• Carlos Henrique Theodoro Batista
  Master's in the Dental Clinic, Federal University of Juiz de Fora, Juiz de Fora, MG, Brazil.
  
  
• Patrícia Rocha Coelho
  Master's in the Dental Clinic, Federal University of Juiz de Fora, Juiz de Fora, MG, Brazil.
  
  
• Karla Daniela Malta Ferreira
  Graduate Student in the Dental, Federal University of Juiz de Fora, Juiz de Fora, MG, Brazil.
  
  
• Maria das Graças Afonso Miranda Chaves ^III
  Doctor in Philosiphy (Oral Biopatology); Coordinator Program Postgraduate Master in Dental Clinic, Federal University of Juiz de Fora, Juiz de Fora, MG, Brazil.
  
  
  Corresponding Author
  Patrícia Rocha Coelho. Marechal Deodoro Street, number 1019, apt 203, Downtown, Juiz de Fora city, Minas Gerais, Brazil, CEP: 36015-460 Phone: (32) 9932-1100
  E-mail: [email protected]

INTRODUCTION

A digital camera is as important as any other equipment in a dental clinic up to date with technological advances. The utilization of photography is fundamental and images may be used for several purposes, including registration records, pre- and posttreatment evaluation, collection of clinical cases for didactic-pedagogic use, publication of scientific articles, legal protection, improvement of professional experience, a tool for professional advertising and marketing, besides others.(1, 2, 3, 4)

However, similar to any other dental equipment, the clinician must know the photographic resources and have technical and operational expertise to improve the performance and outcomes, also for the beginners.(4)

The digital technology has revolutionized and is well established in the clinical dental photography. Images from digital cameras are available in seconds and can be displayed on computer screens in minutes, which is advantageous compared to the long time and higher costs required for the processing of conventional photographs. Image editing softwares allow multiple actions such as rotation, enhancement, lighting, cropping, and even more sophisticated changes as desired.(5)

Though recent, the introduction of this feature in the dental clinic has been increasing.(6) Photographs are fundamental for record keeping in clinical dentistry and represent a valuable resource in Orthodontics (4). Thus, the aim of this paper is to provide information for obtaining photographs more effectively, as well as to contribute with some relevant questions for the selection and applicable settings of digital systems of semiprofessional and compact cameras, with a view to enhance the achievement of photographs with good quality and focus.


DIGITAL PHOTOGRAPHY

High-quality digital photographs are helpful in several dental specialties and their use may be highly beneficial (3). The need to capture patient images is fundamental for several reasons, especially for legal purposes, since the number of dentists involved in court cases has been increasing and is not expected to decrease. When photographic records are available, the professional has better conditions to prove the oral conditions of patient, (1, 5, 7) besides serving as expert evidence for reimbursement from health and dental insurance.(2)

Posttreatment photography is also important for a critical evaluation of treatment outcomes, encouraging the professionals to improve their own performance. Image magnification allows the observation of details that may had remained unnoticed, helping the professionals to detect their errors and decide how to solve them. They may also be used to demonstrate the correct procedure, thus being a valuable tool in the constant quest for excellence.(2, 8)

This technology has presented great evolution in the recent years, leading to the utilization of digital imaging in Orthodontics. The knowledge on digital photography aided the use of resources that enhanced the diagnostics, communication between professionals, laboratory technicians and patients, scientific illustrations, applications for didactic, counseling, research and publication purposes.(8, 9) Trevisan et al4 and Machado6 further mentioned the possibility of immediate visualization of the result of photographs, no costs with films and processing, and systematic management of images in the clinic as the main advantages of digital photography.

However, some disadvantages may be pointed out, as the need of knowledge on informatics (for camera settings and file transfer), higher cost compared to conventional equipments, the legal value of digital files and the obsolescence of equipments with the advances in technology.(10)


DIGITAL EQUIPMENT

The advent of digital technology allowed the popularization of digital cameras thanks to the technological developments that allowed the commercial availability of equipments of different brands, models, features and price.(11,12) Since the costs of these equipments have been reducing, a good cost-benefit relationship may be achieved.(3) Consequently, selection of the most suitable equipment for clinical photographs became more difficult and doubtful.(11,12) Selection among the hundreds of models available in the market requires knowledge on digital photography, which changes rapidly yet maintains similar characteristics with conventional photography.(2)

Machado et al (12) investigated the accuracy of orthodontists in differentiating conventional and digital photographs as well as checking their quality. For that purpose, ten digital and ten conventional photographs of excellent quality were printed on photographic paper with a resolution of 400 dots per inch (DPI) in a professional digital lab. The examiners indicated if the images had been obtained by conventional or digital cameras and judged the quality of each photograph. The authors concluded that the quality of digital photography is well acceptable for application in Orthodontics.

No specific photographic equipments are available for use in dentistry, yet the knowledge on the resources of either conventional or digital cameras is important for the achievement of high-quality photographs. It should be noted that the same equipment should allow the achievement of extraoral and intraoral photographs with the same standard.(9)

Compact semiprofessional and professional equipments are commercially available, yet the latter are the most suitable for application in clinical practice because they are equipped with single lens reflex (SLR) lenses, macro lenses of 50 mm or preferably 100 mm, and external ring flash for perfect illumination of the field.(4,15) These sophisticated equipments require training and knowledge on photographic techniques to ensure satisfactory results. Nevertheless, semiprofessional and compact equipments may also allow the achievement of photographs with acceptable quality, provided some prerequisites and knowledge on photography are available.(4)

In digital systems, image capture is performed by an electronic device called charge-coupled device (CCD), in which the thinner the dimensions of the CCD, the greater will be the amount of details in the image.(1) The CCD is used instead of conventional films and has the function to convert light into electrical energy. It consists of a grid of electrodes and a silicon layer comprising a chip, i.e. the sensors are in charge of capturing the image. It is related to the digital camera as the microprocessor is related to the computer, constituting the heart and mind of this system.(2)

Conversion of the image known as one pixel, which is the basic unit of image detail, is derived from the abbreviation of picture element.(1) Pixel is a single point that forms the image, corresponding also to the grain on the conventional paper images. The greater the number of pixels, the higher the image resolution or its fidelity, (2) as shown in Figure 1, in which all photographs are the same size (3.7 x 5.42 cm) but have different resolutions in pixels. If they were printed in this size, the quality of the first two (a and b) would be similar and progressively worsened in the other two (c and d). For further information on this aspect, observe the Table 1.

RESOLUTION

This characteristic is directly related to the final quality of images obtained6 and depends on the ability of the CCD in capturing the pixels, thus the higher the capacity of the CCD, the greater the number of pixels captured.(1,11) It is relevant to explain that selection of the resolution is directly related to the ultimate goal of images. The higher the captured file, the lower the number of images that can be stored in a computer hard drive or on the memory card of the camera because it will result in larger files.(5,13) The high resolution produces images with larger dimensions that occupy a higher number of bytes in the hard drive, typically leading the system to load them slowly, mainly on didactic presentations as those prepared on the Microsoft ® PowerPoint ® software.(6)

Machado et al (11) have emphasized that the resolution in megapixels (MP), which is often the main aspect advertised by manufacturers, is only one among several features that should be considered when choosing a digital photographic equipment. They concluded that the resolution in the MP per itself does not assure high-quality images, but rather only when associated with lenses with excellent optical quality and a proper lighting system.

Currently, there are digital cameras with 28MP resolution, allowing users to print images with high resolution of 300 DPI and sizes up to 52 x 39 cm.(6) The quality of images produced is the same when it refers to (1,2,3,4) or more MP, yet the final size of the image influences the file size.(13) Therefore, if these photographs are printed, the resolution of the camera will be related to the maximum size that the image can be enlarged on photographic paper.16 Thus, the resolution of photographs used for printing, scientific posters or publications will be directly related to the image size used, as shown in Table 1.

The actual resolution in which the image is captured may not be important if there is no need for photo-quality printing, thus setting the camera to record at lower resolutions can be helpful (1). Machado (6) has suggested the purchase of digital cameras compatible with the current market standard (10 to 15MP), yet the equipment should be set to work at lower resolutions (5MP, for example), meeting the routine needs with high quality. The camera may be set to the highest resolution possible when printing in larger sizes is necessary.

The images displayed on computer screens present average resolution of 72 DPI. Conversely, digital projectors have a resolution of 0,8 MP or 1024 x 768 pixels.(13) Therefore, when photographs are obtained to be displayed on the internet, sent by e-mail and viewed on a computer screen or in multimedia presentations, a resolution of up to 2 MP (1600 x 1200 pixels) (13) may be used. However, Hutchinson and Williams1 reported that these projected images do not lose details when they are created at resolutions greater than 1.3 MP. Accordingly, Machado6 in 2010 reported that images with resolution of 3 to 5MP meet those needs with good quality, while Morris8 suggested a minimum resolution of 6 MP.


FOCUSING AND FRAMING

Good composition and focus guide the story told by images and influence the emotional responses of patients. Images are tools that capture emotion, help the patients in making decisions and give rise to feelings of confidence, enhancing the treatment acceptance.(8)

Knowledge about the artistic arrangement and correct framing in intra- and extraoral photographs is fundamental, so that the image may actually reflect what the photographer aims to capture.(2)

The focus is reached moving the camera forward and backward to adjust the required distance, then the shutter button should be partially pressed to ensure the correct focusing by the camera.(2,14,15) The macro mode should be enabled in intraoral photographs. The correct framing is achieved with the aid of references according to the type of photograph desired.

Many errors can occur when taking photographs, including camera positioning, wrong focusing, under or overexposure of the field of view and positioning errors as the patient height in relation to the photographer, wrong Frankfurt plane, head positioning, hair covering the ears, eyes closed or soft tissues in incorrect position. Other possible errors include excess saliva, fogged mirror, dark buccal corridor, tongue not sufficiently retracted, non-observation of the distal margin of the first molar, or photographic retractors obscuring the field of view. (3)

Lip retractors provide a great contribution to the final outcome of intraoral photography. Two sizes are needed and the dental assistant should be trained for their utilization. Larger retractors are used for photographs in frontal view in 95% of patients, yet smaller retractors should be used in lateral view to provide greater horizontal than vertical retraction. Before taking the photograph, the retractor should be pulled as distally as possible to achieve an angle as perpendicular as possible to the molars and premolars. This will allow reproduction of the buccal segment of the sagittal discrepancy and also ensures observation of the distal aspect of first molars on the photograph.(16) In order to enhance the possibility of achieving good-quality and well-focused photographs, two or three shots should be achieved for each view and then the best image is selected.


LIGHTING

Lighting is one of the most important aspects for the achievement of high-quality photographs. Two basic flash systems are available for photography, namely the point flash and ring flash. In intraoral photography, the ring flash is usually the system of choice, (16) allowing uniform illumination, while the point flash has high intensity and provides pictures with excessive lighting, in which photographic details as texture and light and shade contrast are lost. These photographs invariably exhibit excess light, alter the natural color of teeth and soft tissues, producing low-quality photographs as a result of overexposed image (Figure 2). (2,4)

Most digital cameras have the flash connected laterally or above the objective (point flash), which produces an uneven distribution of light in the intraoral photography, creating unwanted shadows, which may be noticed as a shadow in the buccal corridor of the patient14, 15 on Figure 2.

The literature has reported several adjustments to eliminate these disadvantages. The light intensity emitted may be regulated by trial and error, adjusting layers of masking tape, coffee filter paper or tracing paper over the flash to get the necessary attenuation of light intensity (2,4,11) (Fig. 2 b), or alternatively by reducing the flash intensity on the camera settings. The correct lighting allows the observation of nuances and details of the teeth and periodontal tissue. Compare the photographs in Figure 2 (a) and (c).

Some authors (1) proposed turning on the dental unit light and turning off the flash, stating that the observation of teeth would be enhanced, yet this became unnecessary in cameras that allow adjustment of light intensity. Also, with a view to control the amount of light that will sensitize the camera CCD, some cameras allow adjustment of the exposure compensation, which varies from -2 to +2 in the average. Ideally, the intensity should be regulated as low as possible, compatible with the distance used in intraoral photographs. The equipment instructions should also be read to facilitate the adjustments in the equipament.(5) Thus, some trials may be performed for the achievement of more or less light according to the desired goal (11).

McKeown et al (14) suggested that, when achieving intraoral lateral photographs with cameras with a laterally connected flash, the camera may be rotated in horizontal direction to allow illumination of the area that would be shaded by the cheeks or retractors. Moving the camera further back from the patient may also allow light diffusion and better lighting of the area, yet a larger field would then be photographed. In that case, the image should be trimmed and rotated at 180° (Figure 3).

High-quality photographs in occlusal view are difficult to obtain with point flashes due to the proximity between patient and camera, which produces shadows. Besides the great distortion of the captured image, there is unwanted condensation of water vapor on the camera lenses because of patient breathing, causing loss of image quality.(4) McKeown et al (14) suggested focusing as distant from the mouth as possible, providing more light and reducing the shadows. In this situation, the area of interest represents only 20% of the area captured by the camera. Therefore, the picture must be trimmed saving only the area of interest, either lateral or occlusal. For that purpose, the camera resolution should be as large as possible to produce a good image after trimming, since 80% of the photograph will be discarded (Figure 4).

Finally, in most cases, the camera should be set in the "A" aperture priority mode, in which the desired aperture is selected and the equipment adjusts the shutter speed automatically. Thus, the amount of light is reduced and suitable for the short distance required in intraoral photographs, besides providing greater depth of field.(11)

Another possible option is setting the appropriate light intensity and the time required to achieve the image, which are represented by the exposure time and aperture. The aperture refers to the amount of light passing through the diaphragm to the CCD at a given moment, while the exposure time indicates the period during which that light is received. With different combinations of aperture and exposure time, a greater aperture may expose the CCD for less time and vice versa. Thus, the professional may select the photograph with better definition and balance between high and low light intensity, increasing and decreasing the depth of field.(2)


CONCLUSION

The high rate of innovations in the market often confounds dental professionals in the world of digital photography, which has been adopted by all dental specialties and became an important resource. Photographs can be easily obtained using the correct equipment, proper settings and the most effective techniques, thereby increasing the chances of obtaining high-quality images.