Participant recruitment

Purposive sampling was used for recruiting participants. We sought to increase the diversity of our study sample by including participants of both genders at various stages of training, and with various educational and specialty backgrounds. General dentistry residents undergoing training (novice dentists) in the dental department of Peking University Third Hospital in Beijing, China were invited to take part in the study. Recruitment continued until data saturation was reached (no new codes were generated), as determined by the principal investigator. In total, twenty-three general dentistry residents were recruited. Recruitment started on 14/01/2025 and ended on 15/02/2025. Four of the invited residents declined to participate in the study because of time constraints. Four participated in the pilot interviews, and nineteen participants were included in the final analysis. They were affiliated with four regional general hospitals located in different districts of Beijing. All participants had used ergonomic loupes (DFK surgical loupes, Zumax, China) and traditional loupes (SLE surgical loupes, Zumax, China) in the clinical setting for six months before the interviews. Both types of loupes were provided through the residency program and shared among residents. After the study, the residents could opt to buy their own loupes. The demographics of the nineteen participants are shown in Table 1.

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Table 1. Demographics of participants with respect to gender, age, dental education degree, specialty background, and year of residency.

https://doi.org/10.1371/journal.pone.0353061.t001

Data collection

Semi-structured face-to-face interviews regarding user experience of ergonomic loupes were conducted individually with participants in a quiet room without the presence of non-participants. One researcher (KXX), an experienced male general dentist (DDS) who had undergone substantial training in interview skills and qualitative analysis, conducted the interviews in Chinese. The interviewer was not involved as an instructor in the departments’ training program, so there was no hierarchical relationship between the interviewer and the participants, which may affect the openness of the interview. The interviews were conducted around a list of in-depth open-ended questions as an interview guide. The participants were encouraged to freely communicate their experience of ergonomic loupe usage and express their views on the topic. The draft interview questions were devised after studying themes of previous published qualitative research on dental loupes [18]. Each interview lasted around 30 minutes. Before the study, the interviewer (KXX) conducted pilot interviews with four participants to refine the question lists. The interview transcripts were reviewed by three clinician experts outside the research team. The participants’ and experts’ comments were collected and analyzed for face and content validity of the interview questions. The pilot interviews were excluded from the final study. The refined interview questions were centered around topics as follows:

1. Adaptation process and time required;
2. Symptoms associated with ergonomic loupe usage;
3. Effects on posture, visual acuity, and quality of treatment;
4. Advantages and disadvantages;
5. Usage scenario;
6. How are ergonomic loupes different from traditional loupes?

Data analysis

The interviews were recorded with the interviewer’s smartphone. The recordings were transcribed verbatim with the help of the Microsoft Voice Input system. The accuracy of the transcripts was verified by two researchers (YGL and NM). The verified transcripts were returned to participants for comments and correction. The thematic analysis method was used to analyze the interview transcripts. The analysis included six phases, as described by Braun and Clarke [27]: 1. familiarizing with the data; 2. generating initial codes; 3. searching for themes; 4. reviewing themes; 5. defining and naming themes; and 6. producing the report. Theanalysis was performed using NVivo 11 qualitative analysis software as a support. Initial line-by-line coding and candidate theme development were carried out individually by all four researchers. Following initial coding, researchers met to discuss and finalize coding and themes. All researchers checked the final codes and themes against the data. The findings of the analysis underwent member checking by 10 participants to ensure the trustworthiness of the analysis.

Advantages of using ergonomic loupes

Participants found working with ergonomic loupes tends to be minimally invasive.

“…and is more conservative…” (15). Some stated using ergonomic loupes could produce better treatment results. “…my treatment results are great owing to it…” (1), “…my scaling is better when I use ergonomic loupes…” (13). Many participants expressed that they had enhanced visual acuity when using ergonomic loupes. “…I can see my cavity preparation more clearly…” (10).

All participants mentioned that they had better posture when using ergonomic loupes, which reduced the onset of musculoskeletal disorders.

“…I sit straight and my neck is more comfortable…” (8), “…I used to have neck pain, now I don’t…” (12), “...It is definitely an ergonomic breakthrough, you don’t have to lower your head at all, you just look straight ahead, and you don’t have neck and back pain…” (1).

Participants found using ergonomic loupes offer better control of fine movements.

“…I have better control of fine movements…and my preparations are better when I use the ergonomic loupes…” (8)

Disadvantages of using ergonomic loupes

Some participants complained the ergonomic loupes had limited field of view.

“…the field of view is too small…” (11).

Some participants complained that she had to frequently switch between using peripheral vision to pick up instruments outside the operating field and looking through the loupes to see the tooth.

“…the switching was too often to get used to…” (11).

Some participants reported vibration of the loupes caused by sudden movement or physical tremors of the head.

“…you move slightly, because it is magnified, the field of view vibrates…” (12). Some participants mentioned fogging could be troublesome in cold weather. “…in winter, the glasses got foggy, because the water vapor got through the surgical mask and contacted the lens and caused fogging…” (1).

Some participants found splash protection a problem, while others found it less important.

“…it does not have protective glasses to shield your eyes. Even when you are wearing goggles, because you are looking straight ahead, the bottom of the mask is open, so particles and liquids can still get into your eyes. Once, my right eye got contaminated by a patient’s saliva. I didn’t rinse my eyes immediately. The patient had a little cough. The next day, my eyes got all red. I was diagnosed with viral conjunctivitis, which later developed into viral keratitis. My condition healed eventually after a month, leaving corneal scars. Luckily, my eyesight was not affected…” (2), “… splash contamination can be a problem” (14), “…if you are far enough from the patients, splash contamination (of the eyes) can be avoided…” (7). Some users with myopia had reduced working distance when they were using the loupes. “…because I have severe myopia, I had to lean very close to the patient…” (4).

Using ergonomic loupes for prolonged duration can cause discomfort. Commonly reported discomforts after prolonged use included eye strain, headache, and dizziness. Complaints about the heavy frame pinching the nose or ears were also reported.

“…my eyes were a little dry…” (10), “…when I got back from work, my eyes were red and dry, sometimes my extraocular muscles were painful, sometimes I couldn’t see clearly after taking off the loupe…” (1), “…it was a little heavy, my ears got painful…” (9), “…it was pinching my nose, you can see the imprint on my nose…” (3), “… I felt some dizziness…” (12), “…my head hurts after some time…” (5)

When using the ergonomic loupe, the viewpoint of the user is relatively fixed, it might be difficult for the user to change viewpoint during procedures.

“...It was not versatile enough, especially when you are doing surgery. When you are scaling, your posture is somewhat fixed, it is OK to use ergonomic loupes. But when you are doing surgery, you may want to change your viewpoint, and the ergonomic loupe may become troublesome...” (19)

Adaptation process

The ergonomic loupes may require some time for the users to adapt to them. Many participants reported hand-eye coordination problems when they started to use ergonomic loupes.

“…When I first put it on, it was strange, it was like my brain didn’t know where my hands were. It took me several minutes to get used to it…” (17), “…you were moving in the wrong direction, it was a little confusing at first…” (16), “…I had trouble controlling the depth of my preparation, the cavity I prepared (using an ergonomic loupe) was too shallow…”(9), “…the viewing angle was strange at first, but after some practice, I got used to it…” (16).

It was difficult for some participants to find the right working length and field of view.

“…it was hard to find the right working distance…” (8), “…I found it hard to use at first because it was difficult to find the field of view…” (10). However, the adaptation time was typically short. “…it was easy to use” (8), “…I got used to it after one or two cases” (10)

Why use ergonomic loupes

The users might choose specific clinical scenarios to use ergonomic loupes. Some participants reported using the ergonomic loupes only in procedures requiring fine motor control, while some reported using the loupes in every procedure.

“…I use it routinely, I even use it to find second mesio-buccal canals in maxillary molars…” (14), “...I use it for root canal treatment...” (18), “…I don’t use it for tooth extractions because of blood splash contamination…” (17), “…I use it for posterior teeth and when doing prosthetics…” (7).

Some mentioned that cost was the main factor to consider when choosing ergonomic loupes. “…I chose it not for any other reason, just because it was the cheapest, others were too expensive…” (13).

The users were weighing cost and benefit in deciding whether to use ergonomic loupes in clinical practice.

“…my neck was so painful, I had to use it, even though it causes eye strain, pinches my nose, or else I would have a cervical spine surgery in a few years if my neck condition worsened…” (1)

How are they different from traditional loupes

Compared with traditional loupes, ergonomic loupes had advantages in ergonomics.

“...compared to the traditional loupe, I don’t have to lower my head anymore, my waist is much better too. It is really an ergonomic breakthrough...” (18)

“...My posture is definitely better now than before, when I was using my Galilean type traditional loupes...” (19)

Compared with traditional loupes, the hand-eye coordination may be different for ergonomic loupes.

“...Because it is an ergonomic loupe, my hands may not be where I am looking at. It feels different. ” (19)