8-10, 14-24 have contributed to determine the degree of satisfaction with the surface, those that relate to questions 4, 7, 13-16, 19-24 have contributed to determine the degree of satisfaction with the weight and those relating to questions 1, 3-5, 7, 9-11, 14-17, 19-24 have contributed to determine the degree of satisfaction with the diameter.

The scores assigned to questions 1-8 have contributed to determine the degree of perceived safety, those that refer to questions 9-10 have contributed to determine the degree of safety, those that relate to questions 11-16 have contributed to determine the degree of comfort and those relating to questions 17-24 have contributed to determine the degree of overall acceptability.

The scores were then summed to obtain a value expressing the satisfaction of the physical characteristics and the perceived working on the investigated characteristic of the handle (Figure 1 satisfaction column; Table 2).

3. RESULTS

The mean age of the twenty-nine dental hygiene students enrolled (11 males, 18 females) was 25 ± 5 years; mean height 177 ± 15 cm; working hand was the right in 27 cases and the left in 2 case. In regard to the physical characteristics of the hand-piece (Figure 1), type A scored 0.9 for diameter, 1.1 for section 1.4 for weight and 1.9 for surface (knurled); hand-piece type B scored 1.6 for weight, 2.1 for surface (satin-finish in the central part, knurled at either end), 3.2 for section, and 3.7 for diameter; hand-piece type C obtained the most positive evaluation, scoring 2.6 for weight, and 3.8 for section (non-uniform cylindrical), 3.9 for surface (coating of anti-slip silicone) and diameter (variable, ends of greater diameter than central part). In regard to perceived working satisfaction, hand-piece A scored 1.2 for safety, 1.7 for perceived efficacy and comfort, and 1.5 for overall acceptability; hand-piece B scored 2.4 for perceived efficacy and safety, and 3.2 for comfort and 2.7 for overall acceptability; hand-piece C scored 3.1 for perceived efficacy, 3.6 for safety, 3.7 for comfort and 3.5 for overall acceptability (Table 2). The comments expressed freely by the hygienists were particularly emphatic in the case of actions that require greater force, for which a cylindrical hand-piece, of greater diameter and with knurled surface, was preferred.

4. DISCUSSION

To remove calculus, some students preferentially used the mechanical ablator, only using manual instruments to remove localized calculus deposits in sites of difficult access and for final polishing; others used the ultrasound ablator exclusively to remove extensive and heavy deposits of calculus, preferring to use manual instruments even to remove slight deposits of calculus as well as for the finishing phase of the session. In many cases, the posture of trunk and arms while working was inappropriate, although verbally correct statements were made. This is acceptable in some ways, since students vary their posture and working method depending on their

own and the patient’s needs. Conversely, though, it should be stressed that incorrect posture and working method increase the biomechanical load acting on arms and spine, increasing the risk of developing musculoskeletal disorders over time. The instrument hand-piece was in all cases held with a modified “pencil grip”, bringing the distal phalanges of the fingers into contact with the tool, including when repetitive forceful movements were made with bent wrist for prolonged times. Analysis of the students’ freely-expressed comments revealed preferences for a hand-piece of greater diameter for actions requiring particular force, such as the removal of abundant accumulations of calculus, whereas in all other cases no particular preference was expressed for any particular type of hand-piece. With regard to the evaluation of the physical characteristics of the instruments (Figure 1), the best scores were achieved by the hand-pieces of nonuniform cylindrical section, surface-coated with silicone, larger diameter, and lighter weight. With regard to perceived efficacy, safety and comfort, the highest scores were awarded to hand-piece C, followed by hand-piece B. These two hand-pieces were jointly awarded the highest score for overall acceptability (Table 2). These findings are in line with those reported by Simmer-Beck and Branson [24], who recommend the use of instruments for dental hygiene having diameter 10 mm, and with the study by Dong et al. [21,22] recommending instruments of approximately 15 g weight.

5. CONCLUSION

The literature is in agreement that hand-pieces of diameter between 6 and 8 mm require considerable muscular strength to control their function, such that prolonged use may lead to overloading the extrinsic and intrinsic muscles and tendons of the hand [10,14,15,21,22,26] and that those of greater diameter may restrict access to the posterior regions of the patient’s oral cavity [20] but they seem to be most effective in reducing fatigue [26]. It is also generally accepted that hand-pieces should preferably have knurled or grooved finish, or be coated with anti-slip material (as they require a lighter grip) and offer an adequate area of contact with the hand to avoid excessive localized pressure [21,22,24]. However, from a review of the literature, no indications emerge to correlate the size of the hygienist’s hand with the diameter of the instruments to be used except the study of Rossi et al. [27] even if an important risk factor for developing WRULDs is forceful pinching which occurs during dental scaling and root planning [22]. Since there is no universally valid instrument (“one size fits all”) for treating different teeth in different parts of the oral cavity [24], and dental hygienists are at greater risk for developing WRULDs due long hours of repetitive work (scaling and root planning) professional ergonomics should guide the selection toward instruments with hand-pieces of different diameters depending on their practical use [5,14,15, 18,21,22]; this would enable the activity of the muscles involved to be varied, reducing the risk of onset of MSDs due to repeated trauma. However, the importance of always assuming the best working position must not be forgotten (position of hygienist/position of patient/illumination) [8,17,18,20]. The strategies to be used to prevent MSD must include knowledge of this type of disorder, the identification of risk factors, and must also be based on the underlying principles of self-evaluation [10,17,23]. From our experience, educational programs in this connection are most effective when they are carried out directly at the work-place, recorded, and analyzed in periodic evaluation and correction sessions. It is also appropriate to teach moving and stretching exercises for the spine and arms, to be introduced into the daily routine [15,17,18]. It is to be hoped that intensive education to the prevention of MSDs be included in the initial training, then periodically repeated in post-graduation refresher courses [5,10,16,18]. Likewise, it is to be hoped that manufacturers of manual instruments understand the importance of a design that takes into account the individual variability among hygienists, rather than concentrating on “refined colors” and “attractive design”. It is important that design be based on specific characteristics that may be adapted to the individual hygienist, thus helping to reduce risk factors connected with an inappropriate grip.

ACKNOWLEDGEMENTS

The authors thank Mrs. Frances Cooper for linguistic revision of the article.

REFERENCES