Oral health professionals are at a high risk of developing work-related musculoskeletal disorders (WMSDs), with prevalence as high as 81% in dentists and 96% in dental hygienists.^1,2 WMSDs are characterized by discomfort, disability, or pain in joints or muscles aggravated by the performance of work tasks and activities that involve sustaining demanding and problematic postures.^3,4 The strenuous nature of clinical activities, repetitive movements of the hands, and prolonged static postures—particularly flexion and rotation of the neck and trunk—contribute to the high prevalence of work injuries and disorders.⁵ Persistent WMSD symptoms among dental professionals reduce working capacity, leading to workforce retention concerns, including career switching⁶ and premature retirement.^7,8

To mitigate the impact of posture-related WMSD symptoms in oral health professionals, further investigation is needed to develop effective preventive and maintenance strategies such as ergonomic education.^1,8-12 Preventative training and curriculum design in dental education settings are particularly crucial, as these are periods when dental professionals first develop their work habits.^13,14 In dental hygiene, it is estimated that students spend three times longer with a patient during their clinical rotations than a typical dental hygiene appointment.¹⁵ The extended amount of time spent on clinical practice, combined with long hours working on computers makes students vulnerable to prolonged poor postures, causing musculoskeletal concerns early in their careers.^13,16 Although ergonomics is frequently addressed during dental hygiene education,¹⁷ approximately three-fourths of participating dental hygiene students still develop musculoskeletal pain.⁵

The limited effect of dental education in mitigating WMSDs may be attributed to the complex interplay between individual and environmental factors in clinical settings⁷ that can lead to more frequent awkward, static postures and the development of WMSDs.^1,16,18 In this study, we use the term environmental factors to represent a range of ergonomic risk factors in dental clinical environments, including but not limited to practitioners’ working positions, patient positions, and dental tools and equipment (e.g., scaling instruments). Existing literature on risk factors contributing to WMSD development in dental hygienists and dental hygiene students has primarily focused on individual associations between musculoskeletal pain with tools and equipment use,^19,20 sitting versus standing protocols,^18,21 or operator positioning.^22,23 However, none of these aspects are performed in isolation, and there is a lack of literature investigating the combination of these risk factors in dental clinical or educational settings. To protect future and current entry-level dental professionals, a comprehensive assessment of these environmental factors can inform the design and development of effective environmental modifications, ergonomic training, and postural instructions in dental educational programs. As such, this study aimed to examine the relationship between environmental factors in dental training clinics and poor posture in emerging dental professionals.

This observational study was approved by the institutional review boards of the University of Southern California and Loma Linda University. All participants provided informed consent before data collection, and all patients signed photo release forms before the video data collection. A convenience sample of thirty-six right-handed female students from undergraduate dental hygiene programs at two universities was recruited and video-recorded during patient visits in the educational clinic.

Ten RULA evaluations were completed for each of 151 video observations, totaling 1510 individual RULA scores. Of these, we excluded 23 video clips with upright patient chair position (i.e., the angle between the floor and the patient chair greater than 55 degrees), resulting in 1487 RULA scores included in the final analysis. The 1487 video clips had an overall average RULA score of 4.8 and a median of 5, with scores ranging from 2 to 7. No video clips had an aggregate RULA score of 1, and only 5 videos scored 2; that is, less than 3% of videos demonstrated acceptable dental hygiene student postures. The most prominent RULA score was 4 (n=416), indicating moderate risk for poor posture. In looking at the subscales of the RULA, The arm and wrist scores (section A) were positively skewed with a median and mode of 3 (n=562), whereas neck, trunk, and leg scores (section B) were negatively skewed toward higher risks, with a median of 5 and a mode of 6 (n=312) (see Figure 1). Of the 1487 video clips, slighlty more than half of RULA scores fell into “high-risk” (54.5%) category.

Table 1 provides the frequencies of videos within the high-risk and low-risk categories for each environmental factor. Chi-square tests showed statistically significant differences in RULA scores when compared with clock position, scaling method, and sit/stand position variables, indicating a significant association between these variables and the RULA outcome. The low-risk group tended to be at clock positions 9, 10, 11, and 12, while the high-risk group clock positions were predominantly 1, 2, 7, and 8 . Across categorical variables that had a statistically significantly different distribution between risk groups, clock position 12 (mean = 4.1, SD = 1.1), sitting (mean = 4.7, SD = 1.2), and ultrasonic scaling (mean = 4.5, SD = 1.2) had the lowest average RULA scores. There were no significant associations between risk categories and chair position, head position, or mouth quadrant.

Univariate analyses comparing each environmental factor to the likelihood of high-risk RULA scores indicate that clock positions from 1 to 9 all were significantly associated with moderate to large odds ratios compared to the reference level of clock position 12. Positions 7 and 8 were the largest and were 9.1 times more likely to increase the odds of high-risk RULA scores. Clock positions 10 and 11 also increased odds by 1.9 times (Table 2). Hand scaling increased the risk of high-risk RULA scores by 2 times compared to ultrasonic scaling, and standing increased the odds by 1.9 compared to sitting.

All six environmental factors were considered in the predictive model based on the results of the univariate analyses. We ran a total of six multivariate predictive models. The final best-fit model with the smallest AIC value (AIC=1919.2; R² = 0.125) included clock position, sit/stand, and hand scaling method (Table 3). In the final model, standing during instrumentation versus sitting (OR 1.42, 95% CI 1.03-1.96, p=0.034) and hand scaling versus ultrasonic scaling (OR 1.67, 95% CI 1.28-2.18, p<0.001) were more likely to result in high-risk RULA scores. When compared to 12 o’clock, all other clock positions increased the odds of high-risk RULA outcome by at least two folds, with clock position 7-8 being the riskiest position, increasing odds of poor posture by more than 8 times (OR 8.4, 95% CI 5.02-14.50, p<0.001). Figure 2 depicts comparative examples from the three camera angles of these high-risk (i.e., sitting or standing at 7 or 8 using hand scaling) and low-risk postures (i.e., sitting at 12 using ultrasonic scaling).

The aim of this study was to explore the impact of environmental factors in dental educational settings on the risk of poor posture among emerging oral health professionals. Findings identified a combination of environmental factors involved in dental hygiene student clinical rotation sessions predictive of poor RULA scores, indicating a high risk of developing WMSDs. The final predictive model included three environmental factors—clock position, sit/stand position, and scaling method. The riskiest combination of environmental factors was manual dental scaling while students stood at clock positions 7 and 8. While clock positions 7 and 8 were the most hazardous, all clock positions between 7-10 and 1-4 have shown significant associations with high-risk RULA outcomes. In contrast, ultrasonic scaling tools and clock positions that offer more direct access to the patient’s mouth (e.g., clock position 12) were associated with lower RULA outcomes. Results from this study highlight the importance of orientation around the patient and the use of power-driven instruments to mitigate the risk of developing WMSDs due to poor postures among dental students.

RULA results indicate a moderate to high risk of developing WMSDs during dental hygiene clinical education sessions. Awkward postures associated with high-risk RULA outcomes in this study might be a contributing factor to the high prevalence of WMSD symptoms among dental hygiene students.^9,10 Although all students wore magnification loupes, which is known to help improve neck trunk postures,^41,42 the RULA subcomponent scores indicated that neck, trunk, and leg scores contribute more to the aggregate RULA outcomes than the upper arm and wrist scores. These subcomponent results align with the well-documented neck and back WMSD symptoms among dental professionals.^10,43 Growing evidence supports the need for more continuous and targeted ergonomic education in dental hygiene curricula since few programs emphasize body mechanics or self-analysis.^10,12,17 We suggest that ergonomics education during dental training should focus on reducing environmental hazards that could lead to awkward postures. The following paragraphs will dive into the influential environmental factors analyzed in this study.

Video observations of clinical patient visits in this study provided empirical evidence on the postural demands of different clock positions. Previous evidence on the relationship between working clock positions of dental professionals and WMSD development is either based on cross-sectional survey data or simulated laboratory studies. An early survey study suggested that working between clock positions 10 to 12 behind the patient was a significant predictor for carpal tunnel syndrome.⁴⁴ Several other studies found no significant differences in the prevalence of MSDs between sitting in front of (8 to 10 o’clock) and behind (10 to 12 o’clock) the patient.^45,46 A recent laboratory study quantifying the biomechanical demands of clock positions aligned with our study as they discovered clock position 8 was associated with the highest muscle activities due to difficulties maintaining a neutral spine in that position.²²

Similarly, we observed that students were more likely to bend or twist their trunks and necks while working in clock positions 7 and 8 due to the physical restrictions of the patient chair, resulting in higher RULA scores. Yet, it is worth noting that all clock positions between 7 and 10 should be used with great care. In particular, clock position 9 increased the odds of poor RULA outcomes by almost four times compared to clock position 12, even though participants could maintain a neutral spine and pelvic posture by placing their feet directly under the patient’s head position. Since clock position 9 is the most frequently adopted working position for right-handed dental professionals, dental schools should consider under what circumstances other positions might be adopted and train students to consider working in clock positions between 10 and 12 as much as possible during dental hygiene education programs.

Additionally, working clock positions must be considered together with students’ sit and standing positions, as we found that standing was a significant predictor of poor RULA outcomes. Our results were consistent with a recent study comparing seated and standing postures among dental hygiene professionals, which found higher RULA scores for standing than seated positions.¹⁸ The poor postural outcomes in standing position may be why alternating seated and standing protocol has not shown significant effects in improving ergonomic and pain scores in dental students.²⁰ While such intervention may help students break the routine of prolonged, static seating positions, our research suggested that the combined risk of standing and working in awkward clock positions 1 through 9 significantly increased the odds of poor ergonomic postural outcomes.

Besides clock positions, our study revealed the ergonomic benefits of introducing ultrasonic scaling instruments during dental clinical education. Despite evidence suggesting the benefits of ultrasonic scaling in reducing the physical workload of the upper extremities,⁴⁷ there is mixed evidence regarding whether ultrasonic scaling provides an ergonomic advantage over manual scaling. One study found no significant difference between manual and ultrasonic scaling,⁴⁸ whereas a more recent experimental study indicated postural and force-use advantages of power-driven scaling tools.⁴⁹ The results of this study indicated a statistically significant association between ultrasonic scaling and desirable postural outcomes based on video observations of dental hygiene students in naturalistic clinical environments. Our findings aligned with the experimental study where the authors found that power-driven instruments required less neck and head inclination as well as less wrist flexion, extension, and deviation.⁴⁹ Combined with the higher time efficiency when using ultrasonic scalers than manual instruments,^15,50 our study indicates the benefit of introducing ultrasonic scaling during dental hygiene education to prevent students from adopting awkward postures. The introduction of ultrasonic devices must be considered with regard to each patient’s oral health condition and diagnosis, and long-term clinical use in cases where manual technique may suffice could lead to increased risk in other ways. For example, it is worth noting that most existing studies on the use of ultrasonic scalers in dental hygiene practice point out that the vibration of ultrasonic instruments may contribute to damage in soft tissues and nerve receptors in the hands, which could damage tactile sensitivity⁵¹ and increase the risk of developing WMSD symptoms.¹

A practical insight of this study for clinical training is to consider multiple environmental factors when educating students on ergonomic techniques and how reducing one may help mitigate the effects of others. When students perform instrumentation activities using manual scalers instead of ultrasonic scalers, faculty may instruct the students to sit behind the patient in clock positions 10 to 12 and try to avoid prolonged standing between clock positions 7 to 10, especially 7 and 8. Similarly, when students have to work in front of the patient at clock positions 7 to 10, ultrasonic scalers and sitting positions may be preferable to mitigate the risk of developing WMSDs.

This study's findings should be interpreted cautiously relative to specific populations and factors examined. Firstly, the 1487 video observation clips only included right-handed female dental hygiene students. As such, the results are not intended to be generalized to all dental practitioners, and the results may not represent all dental hygiene students; it is unclear if clock position findings would be mirrored for left-handed individuals. Additional personal and patient factors that may have an important influence on posture were not explored in this analysis (e.g., age, skill level, patient disease level). Similarly, this study did not consider every potential environmental factor within dental hygiene education or oral health clinical settings (e.g., sharpness of manual instruments). Of particular note, the study could not explore the effect of magnification loupes on posture because all students wore loupes, and the videos did not allow for a valid determination as to whether the students were using their loupes appropriately (i.e., looking through versus over).

In addition to the population and selected factors, the interpretation of findings must be considered within the limits of the RULA assessment. Firstly, the binary coding for this analysis categorized a score of 3 and 4 as low risk, whereas only scores of 1-2 are acceptable according to the RULA instrument—this would have only accounted for five videos. The conservative grouping of scores 3-4 into the low-risk category with these videos does not allow for a nuanced understanding of absolute best practices. Second, although mitigation efforts were employed, observer effects could have changed the students’ postures; in such a case, our finding that more than half of students’ postures were high risk would also be conservative, raising even more concern about poor student postures. Finally, the RULA can only be interpreted as a proxy for the risk of developing upper-extremity MSDs. Future studies should further evaluate the development of WMSDs and related pain and symptoms.

Clock position, sit/stand position, and scaling method are predictors of risk for WSMDs for dental hygiene students during instrumentation tasks. Within these environmental factors, specific clock positions, standing, and hand scaling methods contribute the most to higher aggregate RULA scores, indicating a need for investigation and/or change in how these tasks are done. Conversely, clock positions behind the patient, sitting, and use of ultrasonic scaling tools have been indicated as safer choices. These findings have implications for dental hygiene education in terms of the importance of setting up the dental training clinical environment to reduce the risk of awkward postures associated with WMSD development, both among current dental hygiene students and future entry-level dental hygiene professionals.