Evaluation of Dental Hand Instruments

HUMAN F A C T O R S , 1973, 15(4), 401-406 Evaluation of Dental Hand Instruments T. EDWIN EVANS, JR.,’ LUIGI F. LUCACCINI, JOSEPH WILLIAM HAZELL, and...
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HUMAN F A C T O R S , 1973, 15(4), 401-406

Evaluation of Dental Hand Instruments T. EDWIN EVANS, JR.,’ LUIGI F. LUCACCINI, JOSEPH WILLIAM HAZELL, and ROBERT J. LUCAS, Division of Dental Health, P.H.S., D.H.E.W., Dental Health Center, Sun Francisco, California

A newly-develqped, multiple-function dental syringe, designed to improve the efficiency of the dental team in performing restorative operations, was evaluated in mechanical tests, mock clinical trials, and field tests with live patients. Field tests indicated the new device to be superior to the conventional equipment configuration of separate instruments generally used by dental assistants in terms of the number of hand movements required, total cutting time, and operator preference. Suggestions for redesign are presented together with a revised evaluation procedure for future studies.

INTRODUCTION Emphasis upon “four-handed, sit-down dentistry,” in which the dentist and his assistant work together as a chairside team, coupled with the advent of the high-speed air turbine dental drill, has resulted in a style of dental operation in which it is necessary to remove large amounts of coolant water and tooth sludge from the mouth during the operation. The “washed field” technique, as it is sometimes called, has led to a growing interest on the part of dental equipment manufacturers in the instruments used by the dental assistant. In the cavity preparation phase of a restorative operation, the dentist cuts away decayed tooth structure to form a cavity or receptacle for restorative material (e.g., amalgam filling material). To assist him, the dental assistant performs several services including (in addition to evacuation of coolant and tooth debris) the provision of air, water, and air-water spray. A number of multiple-function instruments or

’ Currently

syringes has been developed which combine some or all of the above functions in the same syringe. Reducing the number of instruments handled by the dental assistant through a multiple-function syringe has the potential advantage of freeing a second hand more often to provide such assistance to the dentist as passing and retrieving instruments. Unfortunately, dental instrumentation is often designed on the basis of individual requests or feedback from the dental practitioner and not from an established research base. New products reaching the market rarely undergo the field testing and evaluation needed to demonstrate their utility. Dentists have learned through personal experiences (or those of colleagues) that manufacturers’ claims regarding new equipment cannot be accepted without question. At present, however, no ,viable alternative to the “hard way” exists in determining the value of a new piece of dental equipment.

METHOD 0bject ives

Regional Dental Program Director, H.E.W., Region I, John F. Kennedy Federal Building, Boston, Massachusetts 02203.

The pilot study reported here represents an attempt to evaluate a multiple-function dental

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HUMAN FACTORS

syringe designed to improve the efficiency of the dental team in performing restorative operations. Other objectives were to stimulate interest in the area of dental equipment evaluation, to clarify some of the steps involved in dental equipment evaluation, and to generate specific suggestions for redesign of the syringe if factors were uncovered which limited the usefulness of the device. Dental Syringe

The device evaluated was a recently-developed 4-way dental syringe. It is shown in Figure 1. The device has two control levers and a set of yoked control knobs, all operable by thumb motion. Air and water streams are activated by depressing, respectively, the left and right levers shown in Figure 2. Although some gradation in air and water pressure are possible, the control levers function basically in an “on-ofl” fashion. Spray is achieved by activating both control levers simultaneously. The control levers spring back when released, Figure 2. Controls for 4-way s v r iwe .

Figure 1 . Four-way syringe (male hand).

thus requiring positive thumb pressure to maintain air, water, or spray. Aspiration is controlled by rotating the yoked control knobs (thumbwheels) located to the sides of the levers. The control knobs can be adjusted to a desired level of vacuum and left alone, thereby freeing the thumb to operate the two control levers as needed. The control knobs, joined by a common shaft, provide duplicate control functions to the operator, thus accommodating left-handed, as well as right-handed, operators. The 4-way syringe is constructed primarily of anodized aluminum. The stainless steel syringe tip has a 45” bend, a beveled end, and rotates to provide access to difficult-to-reach areas in the mouth. It can be removed for sterilization. Supply lines for air, water, and vacuum are contained within a single hose which exits through t h e bottom of the handle.

T. E D W I N E V A N S , J R . A N D O T H E R S

The device weighs about 3.5 oz. (without hose). I t measures approximately 6 in. along the axis of the handle and 4.75 in. along the axis of the syringe tip; the diameter of the handle is 0.75 in. Approximately 16 oz. of thumb pressure are required to activate the air-control lever, and 12 oz. for the water-control lever. A smaller, companion 3-way syringe, which does not include suction, is shown in Figure 3, together with a separate suction device. Air, water, and spray are provided by the operation of two levers in the same fashion as with the 4-way syringe. The 3-way syringe and the separate, handheld suction device are representative of the conventional equipment configuration used by dental assistants. Procedure Three series of tests were performed on the 4-way syringe. (1) Mechanical performance tests were conducted to ascertain whether the device satisfied basic requirements for air and water pressure and for evacuation capacity. (2) Mock clinical trials consisted of simulated restorative dental operations conducted in the normal manner with t h e exception that the operations were carried o u t o n a manikin instead of a live patient; these were included (a) to determine whether the device functioned satisfactorily and safely before proceeding to the live clinical

Figure 3. Three-way syringe.

August, 1973-403 setting, and (b) to test the reliability of operation under conditions of sustained use. (3) Field tests, which comprised the bulk of the study, compared the 4-way syringe with the conventional 3-way syringe and separate suction device configuration under a variety of clinical settings in which routine restorative dental operations were performed on dental patients. Four areas of comparison were of particular interest. These were: motion economy, time economy, operator energy costs, and operator preference. The 4-way syringe and the conventional equipment (3-way syringe and separate suction device) were installed for 1-week periods in five locations in the San Francisco area, chosen to represent a cross-section of the various modes of dental care available. Two private dental offices were used, as well as clinic settings at a community health center, a U. S. Public Health Service Hospital, and a U. S. Coast Guard base. A t each site, a team of a dentist and one dental assistant was chosen to use the devices installed. During the first 4 days of the 1-week installation period at each site, the dental assistant used the 4-way syringe exclusively in order to become familiar with the operation of the device. On the fifth day, the team performed two restorative operations of comparable difficulty o n a patient. In one operation the dental assistant used the 4-way syringe while in the other the conventional equipment was used. The order of operations was counterbalanced across operating teams. Data collected during the field tests follows. (1) Motion economy of the dental assistant, measured in terms of the number of hand movements recorded in videotape and motion picture records taken during each operation. Hand movements were measured for the initial 8-min. operating period during which cavity preparation normally occurs and the assistant uses the syringe most frequently. Hand movements were counted as any movement, loaded or unloaded, of either hand into or o u t of an area defined as the operating field. To define

404-August, 1973 the operating field, a circle was drawn on a projection screen and the projector was adjusted so that when films of each operation were projected on the screen, the patient’s mouth was a t the center of the circle and all normal dentist-assistant transfer points and assistant-patient delivery points fell within the circle. Films of each operation were viewed by two observers to determine the number of hand movements made by the assistant during the initial 8-min. period. (2) Time economy, determined for the cutting phase of the operation from the same records. Cutting time (the duration of that part of the cavity preparation phase during which the dentist employs highand low-speed drills and tlie assistant washes the operative site and removes water and debris) was calculated as seconds per tooth surface involved in order to correct for varying difficulty of treatment across patients. (3) Energy costs for the dental assistant, calculated from 20-min. samples of expired air collected with a respirometer. (4) Operator preferences and other comments obtained in tape-recorded interviews with team members after the operations. The number of comparison trials (locations) was chosen (a) on the basis of the minimum reduction in number of hand movements of the dental assistant expected with the 4-way syringe, and (b) from an estimate of the standard deviation of the number of hand motions during an operation. These values were determined by reviewing a theoretical task analysis of a standard team dental operation provided by MacIntyre (1968). Assuming a minimum reduction in hand movements of 30 and a standard deviation of 20, a sample size of five was determined to be sufficient to show significance with the two-tailed t-test, with a = .05 and p = .10 (Owens, 1962).

RESULTS

As a result of mechanical testing, a modification was made to the air and water outlets at

HUMAN F A C T O R S the syringe tip to increase delivery pressure; however, air and water pressure, though adequate for dental purposes, were.not at the levels preferred by experienced operators even after modification. Otherwise the device was found to function satisfactorily in terms of the services delivered. Mock clinical trids revealed a number of minor operational problems (eg., leaks) which were corrected before proceeding to field tests. This second stage of tests indicated that the device did not appear to impede restorative procedures or pose safety problems €or the patient. The mock clinical trials also provided an opportunity to check the assumption regarding the reduction in number of hand movements expected in the clinical setting. The results of field tests generally favored the 4-way syringe in comparison with the conventional equipment configuration. The average number of hand movements made by the dental assistant was found to be 65 with conventional equipment and 42.4 with the 4-way syringe. This reduction of about 35% with the 4-way syringe was significant with t = 4.29, p < .02. Similarly, about 91 sec. per surface were required in the cutting phase with the conventional configuration in contrast to 84 sec. with the 4-way syringe. The reduction in cutting time of about 8%was significant with t = 2 . 7 2 , ~< .lo. Energy expenditure failed to differentiate between performance with the 4-way syringe and conventional equipment. In both cases, dental assistants expended an average of about 23 cal./min./kg. Interviews with dentists and dental assistants revealed a highly favorable attitude towards the 4-way syringe. Nine of the ten team members indicated that they would prefer to have the device in their personal dental armamentarium even if i t were to cost more than the conventional equipmen t. Although users of the 4-way syringe were highly favorable in their opinions of the device, several suggestions for redesign were proposed which agreed with and supplemented those obtained independently from a biomechanical

T. EDWIN E V A N S , J R . A N D OTHERS

engineering consultant (Tichauer, 1970). Their comments include the following proposed modifications: 1. Syringe tip a. Add plastic cover to tip end to protect against chipping tooth enamel. b.Develop a smaller diameter tip for use in surgical procedures. c.Permit rotation of the syringe tip to reach all areas of the mouth easily. 2. Handle a. Reduce size and length (particularly for female users) to increase ease of handling. b. Change handle shape from circular to oval to increase stability of grip when used for retraction of the cheek. 3. Controls a. Widen control knobs and enlarge depth and width of grooves to increase traction of control surface. b. Replace “on-off” action control levers with variable control range to permit gradations in air and water pressure. c. Reverse direction of rotation of levers from downward to upward to conform to thumb motion. d. Separate and shape-code control levers to minimize inadvertent actuation. 4. Hose a. Reduce stiffness to lower the pull on user and to increase ease of changing syringe position with respect to the mouth.

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phase, benefits are obtained by dentists in other stages of operation when hand-cutting instruments are being used since the 4-way syringe frees one of the assistant’s hands for instrument transfer. Other advantages which accrue from the reduction in the number of instruments in the operating field are increased visibility, greater accessibility to areas in the oral cavity, and reduction in patient discomfort. It should be pointed out that there are certain disadvantages to combining several functions in the same instrument, although they did not pose problems in the restorative procedures employed in this study. In some cases two functions must be provided simultaneously a t separate locations. “Hosing down” an area within the mouth, for instance, requires separate placement of the water source and of the aspirator which is not possible with this device. Furthermore, in specialized surgery, such as endodontia or oral surgery, not all the functions of the 4-way syringe are required and accidental activation of unwanted functions could be detrimental to the operation. Finally, this syringe’s enlarged tip diameter (which is needed to accommodate aspiration) makes the pin-point delivery of services required in some specialized operations difficult. With respect to the evaluation of dental hand instruments, experiences gained during this pilot study suggest that revisions to the procedures employed would be desirable. Inappropriate operator work habits observed on the videotape recordings indicate that specific attention should be paid to training the operator thoroughly in the use of the prototype. Even with the relatively simple device tested DISCUSSION here, a 32-hr. familiarization period was not The evidence from this pilot investigation sufficient for these experienced operators to indicates that the 4-way syringe is mechanically develop fully-efficient work patterns with the satisfactory and, when used properly, will cut 4-way syringe. Videotaped performance records down on movements by the dental assistant provided evidence that both unwanted activity into and out of the working area. It provides a and improper use of the conventional equipwashed field of operation properly evacuated so ment may have been responsible for the failure as to reduce the time required for cutting cavity to show differences between devices in operator preparations. In addition to the advantages energy cost, again suggesting a need for obtained during the cavity cutting or drilling training.

HUMAN FACTORS

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A second important modification would be to conduct more performance testing during the mock clinical triaI stage. Standardizing dentists' operating speeds and styles, and equating restorative problems (clinical cases) for difficulty, proved to be problems. Control of these sources of variation could be achieved more easily in the mock clinical trial setting with dentists and assistants trained to a particular operating technique and using a patient manikin with a standardized clinical problem. It is unrealistic to expect this degree of standardization of the dental team whose concerns are the patient being treated and the other demands of the live practice environment; however, a testing situation removed from the pressures and distractions that accompany treating live patients would allow adoption of a standard technique. The realism of dental patient simulation devices now under development (Lucaccini, Podshadley, - . and Kreit, 1970) spges& that the of studies with such manikins would have increased validity for the live patient situation.

ACKNOWLEDGMENTS The authors wish to thank the dentists and dental assistants who served as subjects in this study, and the staff members of the Biomechanics Laboratory, University of California, San Francisco Medical Center, for assistance in data collection. A prototype of the 4-way syringe tested was made available through the cooperation of Mr. Wolfgang Laskowsky.

REFERENCES Lucaccini, L. F., Podshadley, D. W., and Kreit, L. H. The role of human factors in dental education. Human Factors, 1970,12,39-46. MacIntyre, M. L. Design for a preclinicd course in chairside dental assisting. Unpublished paper, Dental Health Center, 14th Avenue and Lake Street, San Francisco, calif.94118,1968. Owens, D'. B. Handbook of statistical.tables. Reading: Addison-Wesley,1962. Tichauer, E. R. personal communication. D~~~~~~~ 10, 1970. ~

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