Clinical Advantages of Coaxial Illumination

The physical stress of clinical dental practice is an occupational risk factor for developing musculoskeletal disorders. Coaxial illumination, combined with magnification, can improve visual acuity and ergonomics, and enhance clinicians’ diagnostic capabilities.^1–3 A quality light source and magnification will reduce strain on the eyes and the need to lean in closer to the oral cavity, improving clinical posture.

Oral health professionals work in the small, dark area of the oral cavity, limiting visual acuity. A good lighting system can help improve practitioners’ ergonomics, reduce fatigue, and is essential for optimizing visual performance and comfort. A study related to nursing and medication dispensing errors found that adequate lighting was one of the top environmental solutions for avoiding mistakes.⁴ Dental providers need to detect slight tissue changes and pathology that are even smaller and more intricate than medication labels. 

The purpose of clinical illumination is to help operators see the oral cavity and anatomical features clearly, while maintaining a comfortable working posture. Good clinical illumination should provide the following:⁵

• Prevent the clinician from being forced into poor working postures
• Help see the detail and color of the point of interest
• Enable control of light intensity and reduce eyestrain

LIMITATIONS TO OVERHEAD LIGHTING

Traditionally, the light used to illuminate the oral cavity during treatment has been an overhead light on a track or a chair-mounted light — neither of which provides significant benefits to visual acuity. Studies have found that overhead lighting is often out of reach, causing the clinician to use awkward postures to reach it, and it frequently cannot be adjusted with one hand.^6,7 Study results also show that overhead lighting provided inadequate luminance levels for the operating field.^6,7 Iacomussi et al⁸ analyzed the effects of overhead lighting on clinical practice. They found this type of lighting creates overhead glare, illuminance (brightness) and luminance (distribution) levels that were too high or too low, and luminance uniformities that were too high or too low.⁸ While overhead lights are typically adequate for illuminating flat objects, they are less effective at illuminating deeper body cavities, such as the mouth.⁵ 

Clinical interest in enhancing visual acuity and reducing the risk of musculoskeletal disorders has increased the popularity of coaxial illumination. This type of lighting provides a parallel source of light, reducing the incidence of shadows in the field of vision.³ During dental treatment, clinicians easily block their source lighting, compromising neck and back ergonomics (Figure 1). Coaxial illumination eliminates this problem by providing a separate target source of light.

With coaxial illumination, lights are usually directly mounted to custom-fitted loupes. A variety of styles, weights and types of lights are available, including cordless versions. No matter the type, the purpose of coaxial illumination is to enhance visual acuity during delicate procedures. A properly designed illumination system should provide a uniform beam (without glare), constant beam pattern within the clinician’s working range, and high detectability of anatomical features.⁵

LIGHT EMITTING DIODE TECHNOLOGY

Use of  light emitting diode (LED) technology   provides an excellent source of illumination in the dental field. These lights are extremely small, lightweight, and provide a high-quality light source with greater output than traditional light sources and better color rendering.⁹ These are desirable qualities in a mounted light, as correct brightness and true color allow for clearer vision and may make tissue and anatomic changes more discernable during diagnosis and treatment. However, the greatest output is not necessarily the safest.¹⁰ Compared with fluorescent lighting, Hawes et al¹¹ demonstrated that LED lighting provides the best visual acuity as measured by symbol identification and color recognition. 

CLINICAL CONSIDERATIONS

Finding the light that best supports ergonomic practice is important. Classified into four types according to how the light beam is generated, LED headlights include single lens optic, reflective optic, single lens/reflective optic, and achromatic multi-lens optic.⁵ Single lens optics are not uniform, contain blue light around the main beam, and their beam patterns and color uniformity fluctuate with changes in working distance. By comparison, achromatic multi-lens optics offer uniformity in beam patterns and color.⁵ 

Clinical LED lights come in varying colors: neutral white, cool white, and extreme cool white. It is important to evaluate the beam uniformity and color rendering before choosing a light. Shine the light on a white piece of paper to check for uniformity. The edges of the beam should not appear ragged or fading. Check the color rendering by illuminating anatomical objects to make sure they are true to color. In order to see accurate colors, consider an LED light with a neutral white color, or a color that accurately portrays the anatomical structure.⁵ The intensity of the beam should also be considered, as too high an intensity could cause glare, which is potentially harmful to the clinician and patient. Intensity levels that are too low may lead the clinician to hunch or lean forward, or even strain the eyes in an attempt to see more clearly. A light with an adjustable beam intensity may eliminate many of these issues. The light’s weight and size should be considered, as a light that is too heavy or cumbersome may force the clinician into unhealthy postures.

Another consideration is that in response to the COVID-19 pandemic, many operators are practicing with face shields. In these cases, it is important to ensure the face shield is compatible with loupes and coaxial illumination systems. Ideally, the face shield should not press against the loupes or light. Clinicians should also check uniformity and distribution of the coaxial light with the face shield to ensure the face shield does not produce glare that could affect visual acuity or ergonomics.  

CONCLUSION

Due to the nature of practice, oral health professionals have an increased risk for musculoskeletal disorders. Proper lighting can reduce these risks and help clinicians maintain ergonomic positioning. Coaxial illumination using LED lights can offer proper distribution and color rendering. Operators should carefully consider the beam, color, weight and size before introducing a light into clinical practice. Future research is needed into different types of lights, the beams and colors produced, and how they affect vision and the visual inspection of the oral cavity during dental diagnosis and treatment. When properly worn and carefully chosen, coaxial illumination may enhance not only visual acuity, but also proper clinical posture. 

Key Takeaways

• Combined with magnification, the use of coaxial illumination can enhance visual acuity and ergonomics, and improve oral health professionals’ diagnostic capabilities. 
• While overhead lights are typically adequate for illuminating flat objects, they are less effective at illuminating deeper body cavities, such as the mouth.⁵
• In concert with operatory lighting, coaxial illumination provides a parallel source of light, reducing the incidence of shadows in the field of vision.
• Coaxial illumination systems are usually directly mounted to custom-fitted loupes. A variety of styles, weights and types of lights are available, including cordless versions.
• A properly designed illumination system should provide a uniform beam (without glare), constant beam pattern within the clinician’s working range, and high detectability of anatomical features.⁵
• Operators should carefully consider the beam, color, weight and size before introducing a light into clinical practice.

References

1. Holt ER, Hoebeke R. Shine a light. Dimensions of Dental Hygiene. 2012;10(9):25–27.
2. Bly J, Jordre BD. Improve visability. Dimensions of Dental Hygiene. 2015;13(1):21–33.
3. Branson B, Simmer-Beck M. Visual acuity without injury. Dimensions of Dental Hygiene. 2009;7(9):48–49.
4. Mahmood H, Chaudhury H, Gaumont A, Rust T. Long-term physical environments effect on medication errors. Int J Health Care Qual Assur. 2012;25:431–441.
5. Chang BJ. Ergonomic benefits of surgical telescope systems: selection guidelines. J Calif Dent Assoc. 2002;30:161–169.
6. Knulst AJ, Mooijweer R, Jansen FW, Stassen LP, Dankelman J. Indicating shortcomings in surgical lighting systems. Minim Invasive Ther Allied Technol. 2011;20:267–275.
7. Matern U, Koneczny S. Safety, hazards and ergonomics in the operating room. Surg Endosc. 2007;21:1965–1969.
8. Iacomussi P, Carcieri P, Rossi G, Migliario M. The factors affecting visual discomfort of dental hygienist. Measurement. 2017;98:92–102.
9. Kralikova R, Wessely E. Lighting quality, productivity and human health. Available at:  https:/​/​www.researchgate.net/​publication/​312326077_​Lighting_​Quality_​Productivity_​and_​Human_​Health. Accessed April 7, 2021.
10. Assessing the Photobiological Safety of LEDs. Available at: library.ul.com/​wp-content/​uploads/​sites/​40/​2015/​02/​UL_​WP_​Final_​Assessing-the-Photobiological-Safety-of-LEDs_​v3_​HR.pdf. Accessed April 7, 2021.
11. Hawes BK, Brunye TT, Mahoney CR, Sullivan JM, Aall CD. Effects of four workplace lighting technologies on perception, cognition and affective state. Int J Ind Ergon. 2012;42:122–128.

From Decisions in Dentistry. September 2021;7(9):22-23.