1. Introduction

Dentists are highly exposed to the musculoskeletal disorders (MSD) because they usually take awkward postures, keep them in prolonged time and even use vibration tools. Prevalence of the MSD among dentists has been studied by using the standardized Nordic questionnaire of [5] in many studies. These studies surveyed the troubles of body segments and most of them reported that the low back trouble was most prevalent in dentists, followed by neck and shoulder troubles [1, 2, 6, 7, 8, 10]. However, Kerosu et al. [4] stated that troubles in the neck and shoulder were more dominant than in the low backs among dentists in Finland.

Since the troubles associated with the MSD can be varied by anthropometric, racial and cultural factors etc., a study is required to identify the characteristics of the troubles among Korean dentists. The previous studies of [3] and [11] investigate the prevalence of the MSD among Korean dentists and reported that Korean dentists experienced troubles more frequently in the neck and shoulder than low back. Because they used their own survey method, it is difficult to directly compare the characteristics of their troubles with those of previous studies which were mostly conducted in western countries.

It is necessary to identify the causes of physical workload in the aspects of dental operation to reduce the MSD of dentists in a direct manner. There have been attempts to find out the relations between the body troubles and personal characteristics such as age, gender, year of practice and hour of work [4, 6, 10]. In addition, the previous studies of [1] and [7] investigated the association between the troubles and physical/psychosocial workload such as working posture and stress. However, there were few studies to find the dental operation-related causes of the troubles, which can be used directly to solve the problems related to the MSD of dentists.

The present study surveyed the prevalence of the MSD in Korean dentists and attempted to find causes of the physical workloads in dental operation. A self-administered questionnaire including the standardized Nordic questionnaire was used to investigate body troubles, physical workload and causes of the physical workloads. In addition, the priority of improving dental instrument and environment was surveyed from Korean dentists.

2. Methods

2.1 Questionnaire

A questionnaire was prepared to survey 1) troubles of each body part, 2) physical workload, 3) causes of physical workload and 4) improvement priority of equipments in dental operating room. First, troubles related to MSD were examined using the standardized Nordic questionnaire. The questionnaire surveyed the occurrence of trouble for each body part during the last 12 months and last 7 days, and prevention of daily activity. More detailed questions such as change of job, prevention of work and leisure activity, and sought professional treatment due to the troubles were prepared for the neck, shoulder and low back. Moreover, the questionnaire had the basic questions regarding personal data such as age, height, weight, year of practice and hour of work per week.

The Physical workload of dental operations was assessed by using the method of [1] which assessed awkward posture, repetitive movements, strenuous exertion and use of vibration tools. The questionnaire about physical workload had the questions concerning the occurrence frequency of awkward posture in the neck, should, wrist/ hand and low back in routine dental operation. The questions on the frequencies of repetitive and strenuous movements of arms and hand, use of vibration tools and prolonged static posture were also included in the questionnaire. An ordinal four-point scale was used to answer the questions with ratings ‘seldom or never,’ ‘now and then,’ ‘often’ and ‘always.’

To identify the causes related to the physical workloads with respect to dental operation, potential candidates were collected from a group of dentists and the significance of them was evaluated. The potential candidates were collected from an interview of the focus group of five dentists (see <Table 1>). For example, ‘to keep direct view inside patient’s mouth’, ‘no support of hand with dental instruments’, ‘trouble in using dental instruments and operator stool’ and ‘delicacy and complexity of dental operation’ were selected as potential candidates related to the causes of awkward posture. The significance of the candidates on physical workload was evaluated with an ordinal four-point scale with ratings ‘not at al or little,’ ‘a little,’ ‘relative large’ and ‘large.’

Improvement priority of the equipments in dental operating room was assessed with an ordinal four-point scale with ratings ‘very appropriate,’ ‘appropriate,’ ‘better to be improved’ and ‘Need urgent improvement.’ Typical ten equipments were collected in dental operation room including operator stool, dental chair, operating light, dental units, cabinet of operating essentials and etc.

2.2 Participants

A total of 104 dentists (male : 76, female : 28) were participated in the survey; all of them had work experience of more than one year and lived in Seoul, capital of South Korea. Out of all the participants, survey data for 79 were used in the analysis, who answered the questionnaire in a complete manner. The rest respondents did not answer all of questions by mistake. The personal data of the available respondents was shown in <Table 2>.

2.3 Statistical Analysis

In the present study, the frequency of trouble occurrence for each body part was analyzed, and the dominant troubles were identified among Korean dentists. Next correlations between the troubles and personal data were conducted by using a contingency table and chi-square test. Then logistic regression analysis was performed to find the effect of physical workload on the trouble occurrence; odd ratios (OR) with 95% confidence intervals (CI) were calculated. In addition, causes in dental operation associated with the physical workloads were identified with the frequency analysis and the improvement priority of dental operating room equipments were also analyzed in the same way.

3. Results

3.1 Occurrence of Body Troubles

<Figure 1> shows the percentage of respondents reporting trouble in each body part in the last 12 months. Most Korean dentists had the body trouble in the neck and shoulder, and over 40% of respondents experienced the troubles in the low back, wrist/hand and upper back. Neck trouble (82%) was the most prevalent in Korean dentists, and shoulder (68%) and low back trouble (56%) followed. Especially, female dentists (69%) had wrist/hand trouble much more than males (37%).

<Table 3>~<Table 5> provide more detailed data of body troubles such as chronic troubles, work and leisure prevention and medical care for the neck, shoulder and low back, respectively. A quarter of the dentists who experienced the neck trouble suffered chronically over a month, and about 18% of them experienced the sick absence of work over eight days. Moreover, 26% of the dentists with the neck trouble had a medical treatment, and 43% reported recent neck trouble in the last week. The shoulder trouble of the dentists was similar to the neck trouble in the aspects of the detailed troubles. Over 50% of the dentists with the low back trouble suffered chronically, and 29% of them was absent in work on account of the low back trouble. In addition, the percentages of the respondents who had medical treatment and recent trouble in the last week were 24 and 29%, respectively.

3.2 Correlation between Body Troubles and Personal Characteristics

After the difference of body troubles between males and females was tested, the correlations between body troubles and age, height, weight, year of practice were analyzed for each gender by using the chi-square tests. This is because the age (male : 39.4yrs, female : 29.8yrs in average), height (m : 1.72xm, f : 1.64m), weight (m : 70.9kg, f : 50.9kg) and year of practice (m : 12.6yrs, f : 4.3yrs) were significantly different depending on gender (p < 0.05).

Although some significant correlations were found between body troubles and personal data, most of them were not significant. Female dentists reported body troubles more than males in the shoulder, wrist/hand, knee and ankle/foot, and the male dentists whose height was below 1.65 m reported neck troubles more than the others (p < 0.05). In addition, the male dentists with less than five years of practice had wrist/hand troubles more than the others (p < 0.05). However, significant correlations between body troubles and height, year of practice were not found in females, and age and weight were not associated with body troubles for both of male and female (p > 0.05). Moreover, there were no significant correlations between detailed data of body troubles and personal data in all of the shoulders, neck and low back (p > 0.05).

3.3 The Effect of Physical Workload on Body Troubles

The occurrence of body troubles in the shoulder, low back and wrist/hand were associated with the physical workload related to the corresponding body part, except for the neck. Logistic regression analysis between body troubles and physical workload elements (see <Table 6>) showed that the occurrence of low back trouble was related to the awkward posture of the low back (95% CI of OR = 1.1-6.9). The occurrence of shoulder trouble was associated with the strenuous exertion of the arm movement (95% CI of OR = 1.3 -10.5) as shown in <Table 7>. In addition, the occurrence of wrist/hand trouble was related to the awkward wrist posture (95% CI of OR = 1.8-13.4), the strenuous exertion of the arm movement (95% CI of OR = 1.0-6.6), and strenuous exertion of the wrist movement (95% CI of OR = 1.0-6.8).

3.4 Correlation between Body Troubles and Personal Characteristics

The occurrence of body troubles in the shoulder, low back and wrist/hand were associated with the physical workload related to the corresponding body part, except for the neck. Logistic regression analysis between body troubles and physical workload elements (see <Table 6>) showed that the occurrence of low back trouble was related to the awkward posture of the low back (95% CI of OR = 1.1-6.9). The occurrence of shoulder trouble was associated with the strenuous exertion of the arm movement (95% CI of OR = 1.3-10.5) as shown in <Table 7>. In addition, the occurrence of wrist/hand trouble was related to the awkward wrist posture (95% CI of OR = 1.8-13.4), the strenuous exertion of the arm movement (95% CI of OR = 1.0-6.6), and strenuous exertion of the wrist movement (95% CI of OR = 1.0-6.8).

Causes in dental operation related to physical workload were selected among the potential candidates for which the sum of the percentages of respondents’ ratings with ‘relatively large’ and ‘large’ was over 50%. As the causes associated with the awkward and strenuous neck posture, dentists dominantly selected ‘to keep direct view inside patient’s mouth’ (99%) and ‘delicacy and complexity of dental operation’ (80%) as shown in <Table 8>. The causes related to the other physical workload were summarized in <Table 9>. The causes selected by male and female dentists were slightly different. For example, male dentists selected ‘delicacy and complexity of dental operation’ (64%) as the causes of the awkward and strenuous arm posture, while females selected ‘trouble in using dental instruments’ (57%). In general ‘to keep direct view inside patients’ mouth’, ‘no support of the hand with dental instruments’, and ‘delicacy and complexity of dental operation’ were dominantly regarded as the causes of awkward and strenuous postures by dentists. In particular, female dentists frequently selected ‘troubles in using dental instruments’ as the causes of physical workload.

As results of analyzing improvement priority of the equipments in dental operating room, those of operating light, arrangement of workplace and conveniences were high showing the percentage sum of respondents ratings with ‘better to be improved’ and ‘urgent’ was over 75% (see <Table 10>). Additionally, the demand of urgent improvement for operator stool, cabinet of operating essentials and arrangement of workplace was fairly large showing more than 20%.

4. Discussion and conclusions

Neck trouble was most prevalent among Korean dentists, while the western dentist suffered from low back trouble mostly. Same as the studies of [3] and [11], the present study identified that the neck trouble was most prevalent in Korean dentists followed by the shoulder trouble. However, in most previous western studies, the low back trouble was reported to be more common than the shoulder and neck trouble. This seems to be caused by the difference of height between Korean and western dentists. For example, while the mean heights of Korean male and female dentists were smaller (1.71 and 1.64 m, respectively) than those (1.79 and 1.68 m, respectively) of the participants in [6]. It seems that the taller western dentists bent their low back more in routine dental operation than smaller Korean dentists who used neck more.

Moreover, there was a difference between Korean and western dentists in detailed body troubles. The response rates of all detailed body troubles for the neck and shoulder were larger than those of the low back in the present study (see <Table 11>). In contrast, in the previous study, the response rates of all detailed body troubles for the low back were larger than the other parts. Furthermore, the work prevention rates of Korean dentists were larger than those of western dentists for the three body parts.

Although the shoulder, low back and wrist/hand troubles were related with the physical workload of the corresponding body segments, there was no significant physical workload associated with the neck trouble in the present study. This is because while most dentists (82%) experienced the neck trouble, the physical workload was in large variation.

In particular, Korean female dentists had wrist/hand trouble more than the males, and most of them thought that its causes were related to dental instruments. The wrist/hand trouble of female dentists (70%) was as about twice large as that of males, and the females selected ‘trouble in use of dental instruments’ as the causes of related physical workload. They reported that the weight and grip size of dental instruments were not appropriate to them, therefore ergonomic design of the instruments will be necessary for preventing wrist/hand troubles in female dentists.

In addition, a new method to view the patient’s mouth should be considered in dental operation to reduce the neck and low back troubles. To keep direct view inside patient’s mouth was identified as the most dominant cause related to the awkward neck and low back postures by more than 90% of Korean dentists. In recent alternative methods to view the patient’s mouth indirectly were being developed using video camera or prism glasses. They were known to reduce muscle activity and discomfort by requiring less flexions in the neck and low back [9]. The new methods to view the mouth indirectly will be helpful to reduce the body troubles for dentists.

The dental equipment/environment needed to be improved was identified in the present study. Dentists experienced discomfort in using operating light because the light was frequently hided by his/her head and hand or dental instruments. Moreover, they thought that the back and arm rest of operator stool were not designed usefully and had difficulties in finding appropriate hand instrument in their cabinet of operating essentials.

Acknowledgement

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2012-0003457).