Effect of magnification factor by Galilean loupes on working posture of dental students in simulated clinical procedures: associations between direct and observational measurements

Introduction

Musculoskeletal disorders are one of the most common occupational issues faced by dentists and may begin as early as the professional training period (Garcia & Campos, 2013; Corrocher et al., 2014; Onety et al., 2014). Various risk factors may contribute to the development of these disorders (Onety et al., 2014; Presoto & Garcia, 2016; Presoto, Wajngarten & Garcia, 2016); however, one of the major causes of musculoskeletal disorders is poor working posture (Presoto & Garcia, 2016; Valachi & Valachi, 2003; Biswas et al., 2012; Garcia, Wajngarten & Campos, 2018). In dental training period the small operating field and the high-precision movements required are the main causes of poor working posture (Garcia et al., 2017).

The use of loupes in restorative dentistry is a strategy that may be used to minimize this issue, since loupes improve visualization of the operating field (Garcia et al., 2017; Wajngarten & Garcia, 2016; Carpentier et al., 2019). There seems to be a consensus in the literature that the improvement in operating field visualization provided by loupes increases diagnostic performance and dental procedure quality, (Congdon, Tolle & Darby, 2012; Wajngarten & Garcia, 2019; Resende et al., 2008; Maillet et al., 2008; Maggio, Vilegas & Blatz, 2011; Forgie et al., 1999; Farook et al., 2013; Eichenberger et al., 2015; Wajngarten & Garcia, 2018) as well as the ability to maintain a neutral working posture (Wajngarten & Garcia, 2016; Congdon, Tolle & Darby, 2012; Wajngarten & Garcia, 2019; Resende et al., 2008).

Though the use of magnification has been highly recommended in the field of dentistry, there are few evidence-based studies (Corbella et al., 2018) regarding the effects of magnification on working posture with a broad postural analysis combining direct and observational methods.

Surface electromyography (EMG) is a direct method that may be combined with observational methods. It consists of a non-invasive method that directly assesses muscle contraction (Pazos & Garcia, 2020). A study combining observational and direct methods may be able to suggest the possible magnification levels that could improve dental surgeons’ working posture. It may also start the discussions about the implementation of this tool during the professional training period, (Eichenberger et al., 2018; Hermens et al., 2000) during which students are more receptive to ergonomic training (Carpentier et al., 2019).

Although there are several magnification systems, it was observed in a previous study that the Galilean system showed a positive effect in working posture, (Pazos et al., 2020) and may therefore be a good choice for loupe implementation during the training phase of dental education programs (Resende et al., 2008).

Thus, the aim of this study was to determine the effects of different levels of Galilean loupe magnification on working posture during restoration procedures in simulated clinical conditions.

Materials and Methods

Results

Table 1 presents the mean, standard deviation, and summary of the two-factor ANOVA of the final score of CADEP during the cavity preparations and restorations on the first molars, according to magnification level used.

In the case of both the cavity preparations and the restorations, the CADEP-scores were significantly lower when working with the naked eye. No statistically significant differences were found between the different levels of loupe magnification. CADEP-scores did not differ significantly between the different teeth involved regardless the procedure. Although, at 2.5× and 3.5× magnification, CADEP-scores were higher in procedures performed in the 16, 26 (upper jaw). Only in cavity preparations, 3.0× magnification produced higher CADEP-scores in procedures in the 16, 26. During restoration procedures there were no significant differences in CADEP-scores regardless the teeth to which the procedure was applied to.

Table 2 presents the mean, standard deviation, and the summary of the two-factor ANOVA of the angular deviation of the neck during the cavity preparations and restorations on the first molars, according to magnification level used.

For both types of procedures performed, the angular deviation of the neck was greater when operators worked with the naked eye, regardless of the tooth involved. For the cavity preparations, the use of 3.0× and 3.5× magnification resulted in an angular deviation less than that seen in cases of 2.5× magnification. The angular deviation of the neck was also statistically significant higher in the preparations and restorations performed in the 16, 26 regardless of the magnification factor of the loupe used. During the restoration procedures, there were no statistically significant differences in operators’ neck angulation between the three different loupe magnifications evaluated.

Table 3 presents the mean, standard deviation, and the summary of the two-factor ANOVA of the EMG normalized values of the right and left sternocleidomastoid muscles during cavity preparations and restoration procedures performed on the first molars, according to the magnification level used.

The left sternocleidomastoid muscle contraction was found to be statistically significant only for the tooth factor during the cavity preparations. Figure 1 presents the 95% confidence interval of left sternocleidomastoid muscle activation organized by tooth being prepared.

Figure 1 shows that the left sternocleidomastoid muscle contraction was found to be lower in procedures performed on the right maxillary first molar and statistically different from the right mandibular first molar, regardless of the magnification level used.

Table 4 presents the mean, standard deviation, and summary of the two-factor ANOVA of the EMG normalized values of the right and left descending trapezius muscles during cavity preparations and restoration procedures performed on the first molars, according to the magnification level used.

Considering the cavity preparation, the right descending trapezius muscle showed statistical significance for the “magnification level” (p = 0.021) and “tooth” (p = 0.015) factors. For the “magnification level” the percentage of right descending trapezius muscle contraction was lower during the cavity preparations at 2.5× magnification. For the “tooth” factor this muscle also exhibited its lowest percentage of contraction when the right maxillary first molar was being prepared. Meanwhile, for the restoration, it was observed statistical significance just for the “tooth” factor, where it was observed greater activity on the right maxillary first molar and the left maxillary first molar than on the other teeth.

Considering the cavity preparation, the left descending trapezius muscle showed statistical significance only for the “tooth” factor (p < 0.01), where exhibited greater activity on the upper jaw. For the restoration, this muscle showed statistical significance for the “magnification level” (p < 0.01) and “tooth” (p < 0.01) factors. For the “magnification level” the activity of this muscle was highest when operators were working with the naked eye. For the “tooth” factor it was observed greater activity on the upper jaw.

Table 5 presents the mean, standard deviation, and two-factor ANOVA of the EMG normalized values of the right and left ascending trapezius muscles during cavity preparations and restoration procedures performed on the first molars, according to the magnification level used.

Considering the cavity preparation, the right ascending trapezius muscle showed statistical significance just for the “tooth” factor (p < 0.01), exhibiting greater activity on the lower jaw. During the restorations, this muscle showed statistical significance just for the “tooth” factor (p = 0.003) presenting lower activity on the left maxillary first molar and the right mandibular first molar.

Considering the cavity preparation, the left ascending trapezius muscle showed statistical significance only for the “tooth” factor (p < 0.01), presenting greatest activity on right mandibular first molar. During the restorations, this muscle showed statistical significance just for the “tooth” factor (p = 0.002) presenting lower activity on the left mandibular first molar.

Discussion

The objective of this study was to determine the effect of different levels of Galilean loupe magnification on working posture as measured by the modified CADEP, angular deviation from the neutral position of the neck, and muscle activation in the neck and upper back region during restoration procedures under simulated clinical conditions. The use of Galilean loupes at all magnification levels during the cavity preparations and restorations was found to positively influence working posture as measured by the compliance with ergonomic posture requirements and neck angulation.

The improvement in working posture result from the use of magnification systems may be explained by the improved visualization of the operating field (Carpentier et al., 2019; Branson et al., 2004; Branson et al., 2018; García-Vidal et al., 2019). Another issue to consider is the focal distance required by magnification systems, which controls the distance between the operator’s eyes and the patient’s mouth and thus prevent the operator from positioning themselves at an improper distance from the operating field, allowing them to adopt a more ergonomic posture.

In other studies, similar results have been reported. In a study that evaluated the effect of magnification on dental students’ working posture during the preclinical training phase, magnification was found to have a positive impact on posture and to reduce operators’ risk of developing musculoskeletal disorders (Kamal et al., 2020). Other studies have observed better posture scores among students who used loupes to perform periodontal procedures when compared to students who worked with the naked eye (Maillet et al., 2008; Branson et al., 2004). Another issue to consider is the combination of magnification loupes and an ergonomic stool that was found to have a positive influence on dental students’ working posture (Dable et al., 2014).

In studies that have considered the angular deviation of the neck, magnification was found to enable improved neck angulation during the preclinical training phase and during clinical procedures such as periodontal probing and diagnostics (Wajngarten & Garcia, 2019; Kamal et al., 2020; Branson et al., 2018). Although the magnification system has provided a reduction in the angular deviation of the neck, it still remains higher than what is considered neutral. This may be because, according to Rucker et al. (1999), the declination angle of the magnification loupes’ lenses must be finely adjusted for the operator to achieve a balance between eye stress and neck angulation. In this study, fully adjustable head-band loupes were used, which allowed the change of each of their characteristics, including the declination angle, each time the loupes were used. As this is a very delicate adjustment, the magnification loupe not specially adjusted for the operator in question may have caused greater neck angulations.

Another issue to be considered is the relationship between tooth location and angular deviation of the neck. It was observed that the angular deviation of the neck for both cavity preparations and restorations was greater during the work on the upper arch (Table 2). This could be due to the declination angle adjustment, which may differ on both arcs. It can be suggested that this angle has not been properly adjusted for the upper arch, resulting in a greater downward tilt of the head to be able to visualize the teeth in this arch (Rucker et al., 1999).

Regarding muscle activity in the neck and upper back, it was found in this study that the use of these loupes did not affect muscle activation. These results differed from those reported in prior research. Other authors reported less muscle contraction in the upper back muscles during the use of magnification loupes to perform preclinical activities (García-Vidal et al., 2019; López-Nicolás et al., 2019). One reason for this difference between this study and others may be the type of lenses selected. In this study, only headband loupes were used; other studies have used through-the-lens loupes. Headband loupes tend to be heavier, and the extra weight may cause greater muscle contraction, especially for inexperienced users. It is important to note that an increase in muscle activation during loupe use could support a contraindication for loupe use. The results presented in this study regarding muscle tension differ from what has been found in previous literature, therefor further studies about implementation of magnification in education environment should be conducted.

Tooth location was also found to influence the extent of muscle activation. The sternocleidomastoid muscle showed greater contraction for cavity preparation on right mandibular first molar, which may be related to one of the functions of this muscle, to allow the anterior flexion of the neck. The descending trapezius muscle presented greater contraction during the restorative procedures in the upper arch. This muscle acts in the elevation of the head, therefore, its greater activity can be justified by the need to keep the head forward.

Overall, it is possible that the greater muscle activity for cavity preparation in the lower arch is not related to the difficulty of visualization but to the access of the teeth, resulting in greater muscle load for movement control. On the other hand, it can be assumed that the greater muscle activity in the upper arch is related to the greater need to visualize restorative procedure details and not to movement control, as it is a reversible procedure. Other study in the literature has reported worse working posture during cavity preparations performed on the lower dental arch (Kamal et al., 2020). To our knowledge, however, no prior studies have considered the effect of tooth location on the operator’s muscle contraction.

The results presented here therefore support previous recommendations for the use of magnifying loupes that may help prevent the development of musculoskeletal disorders by improving practitioners’ work posture (Wajngarten & Garcia, 2019; Branson et al., 2004; Alhazzazi et al., 2016). However, the long-term effect of the magnification loupes on the working posture and the eye muscle fatigue should be considered before implementing these devices in the educational environment.

The study design proposed for this manuscript was laboratorial, conducted in a standardized condition by simulating the performance of clinical procedures in order to control possible interference caused by the difficulties faced when taking care of a real patient. Although it may be a limitation, due to the scarcity of studies with this approach, it is believed that it can contribute to the area of Occupational Health and to serve as a reference for other studies including the treatment of real patients.

Conclusions

It can be concluded that the use of Galilean magnification loupes while performing preclinical restorative dentistry procedures had a positive effect on compliance with ergonomic posture and the angulation of the neck; whilst, these loupes did not influence muscle activation in the neck or upper back region.

Supplemental Information