Magnification for the Dental Hygienist

Magnification lenses used in dentistry have improved significantly in the past decade. During the mid-1980s, veteran dentists were still wearing the single-lens, flip-down loupes, featuring tiny opera like glasses protruding at an angle from a fixed metal bar. The loupes were held securely to the operator’s forehead by a narrow band. When chairside, the dentist could flip the metal bar down, lean in toward the patient until the magnified image was properly focused, and begin treatment.

Improvements in magnification lenses have made them an asset to many dental professionals, including those without natural visual impairment. In the academic setting, many dental and dental hygiene students purchase loupes as they begin their preclinical exercises.¹

CLINICAL SKILL

Does the use of optical magnification improve clinical skill? The natural assumption is the bigger the object, the better we see, thus, the better we work. Dental studies using magnification technologies available in the mid-1990s provide conflicting evidence. A study conducted by Donaldson et al evaluated 52 third-year dental students’ performance on amalgam preparations in a pediatric setting.¹ Students were randomly assigned to wear or not wear loupes. Students using loupes were allowed to choose from 1.75 magnification clip-on loupes or 2.0 magnification frame-mounted loupes. Tooth preparations performed at baseline were compared to tooth preparations done after 8 weeks of clinical practice. Outcomes at both intervals were based on student self-evaluations. The authors reported no significant differences in clinical outcomes between groups at baseline or final evaluation.

A study of simulated patient care produced contrasting results. According to Leknius et al, student performance was enhanced by using loupes.² In this study, 155 students in a preclinical prosthodontics lab practiced restorative preparations by trimming prepared dies. A cross-over study design was implemented, allowing both groups the use of visual magnification. All final products were evaluated by the same technician for errors. Results indicated that student performance was significantly enhanced with the use of loupes.

ERGONOMICS

Musculoskeletal injury induced by improper ergonomics and compromised postures is also of concern to dental professionals. Does the use of optical magnification improve posture, thereby reducing the risk of musculoskeletal injury?

A study by Branson et al shows promising results.³ This randomized crossover design study evaluated the posture of 22 senior dental hygiene students during a periodontal probing exercise. Student performance was videotaped with an overhead camera then evaluated using Branson’s Posture Assessment Instrument (PAI). PAI ratings of acceptable, compromised, or harmful are based on 10 components of posture. Dental hygiene faculty who previously calibrated on the PAI system served as evaluators. Though posture was deemed acceptable with or without loupes, the authors reported significantly less deviation from the ideal neutral posture when students wore magnification lenses. In addition, the study surveyed student opinion concluding that most participants found the loupes comfortable and perceived an improvement in the quality of their work and posture.

PURCHASE POINTS

Understanding the importance of magnification power, image quality, weight, depth of field, and declination angle enables the clinician to make a wellinformed, educated purchase.

Magnification power and image quality are optical performance factors. For optimal clinical performance, loupes must provide the amount of magnification needed for each task and the resultant image should be crisp and clear. Magnification size defines the visual increase of the object of focus and is influenced by the working distance of the operator to the patient. To maintain a clear image, longer working distances require higher magnification. Most companies offer a range of 2.0 x to 5.5 x with 2.5 x to 3.0 x being the most popular for dentistry.⁴ As magnification power increases, the viewing area or field width decreases, resulting in reduction of peripheral vision and greater disorientation when the operator shifts vision from the work site to the surrounding area.

Image quality or resolution depends on the convergence of the telescopes on the loupes and the quality of lens design. If the telescopes are properly aligned, image quality is improved, resulting in a clear, precise focal point. Misalignment can result in poor image quality and double vision. Convergence capability can be preset or adjustable depending on the type of loupes used. Through-the-lens loupes have a fixed convergence, whereas front lens-mounted loupes provide an adjustable setting.

Weight, depth of field, and declination angle are ergonomic factors to consider when purchasing loupes. Weight depends on the materials used in the frame, lenses, and scopes. Loupes should rest comfortably on the operator’s head and nose. Lightweight frames, often made of titanium, that are carefully balanced and provide snug nose pads tend to be most comfortable. Though light weight is important, achieving it by the use of inferior materials, screws, or mounting fixtures is counterproductive.

Also important is depth of field or the working distance from the clinician’s eyes to the work site. The operator’s physical size and accommodation ability of the eyes should be taken into consideration. The operator should be allowed some movement during procedures. Loupes with an appropriate depth of field allow the operator to adjust for physical comfort while maintaining focus on a specific object. Hence, a longer depth of field allows the operator a broader range of movement. To determine proper working distance, custom fitting can be provided by product sales representatives.

Finally, and perhaps the most critical consideration in the purchase of loupes, is the declination angle. The declination angle is formed by the line of sight in neutral eye position and the actual line of sight made by the declined eye as the operator focuses on the work area. There is a direct relationship between the working angle of the head and neck muscle fatigue.⁵ The proper declination angle allows the operator’s head and neck to stay in a neutral position. A neutral position ranges between 20° to 25°.⁶ As head tilt increases, neck fatigue is more rapid. A declination angle that is too small forces the clinician to tip the head toward the chest. A declination angle that is too large requires that the clinician adjust by severely declining the eyes or flexing the neck backward.

Before deciding on a final purchase, clinicians should also discuss with the product manufacturer illumination features, optical filters, lens covers and infection control recommendations (Table 1). Table 2 provides a list of loupes manufacturers serving the dental field.

REFERENCES

1. Donaldson ME, Knight GW, Guenzel PJ. The effects of magnification on student performance in pediatric operative dentistry. J Dent Educ. 1998;62:905-910.
2. Leknius C, Guenther JE, Quiring D. The effect of magnification on the quality of die trimming. J Dent Educ. 1996;60:219.
3. Branson BG, Bray KK, Gadbury-Amyot C, et al. Effect of magnification lenses on student operator posture. J Dent Educ. 2004;68:384-389.
4. Chang BJ. Guidelines for selecting ergonomically correct surgical telescope systems. The Academy of Dental Therapeutics and Stomatology. Nov 2003; CE5.
5. Chaffin DB. Localized muscle fatigue—definition and measurement. J Occup Med. 1973;15:346-354.
6. Nield-Gehrig JS. Goucher J. Fundamentals of Periodontal Instrumentation. 5th ed. Philadelphia: Lippincott Williams & Wilkins; 2004:11-15.

From Dimensions of Dental Hygiene. November 2006;4(11): 28, 30-31.