Human factors applied to study of dentist and patient in dental environment: a static appraisal

the Journal of the American Dental Association

H um an factors applied to stu d y of dentist and patient in dental environment: a static app ra isa l

Sanford S. Golden,* D .D .S., L os Angeles

A study was made to determine (1) the influence of various sitting positions on human endurance during prolonged sit­ ting in dental chairs, and (2) the influ­ ence of standing as well as various sitting positions on the dentist’s operational efficiency and fatigue. The subject was able to sit for 12 continuous hours with­ out discomfort in an experimental dental chair. T h e supine seated position, with the chair back at an angle of 50 degrees from the vertical, is the most acceptable position for prolonged sitting. W hen the dentist stands for long periods, he ex­ periences strains which are absent when the work is performed in seated positions.

This paper constitutes a preliminary re­ port on studies designed to consider the operator, the patient and auxiliary per­ sonnel in the office surroundings and the dental experience. Factors in the dentist’s physiologic and physical well-being are

considered together with those related to com fort fo r the patient. Results o f such an endeavor conceivably will im prove the life o f the dentist and at the same time perm it him to “ provide better care with increased efficiency.” 1 In addition, such considerations may lead toward pleasanter doctor-patient relationship. This topic has been designated “ human factors in dentistry.” T h e term “ human factors” includes all physiological and physical elements con ­ cerned with the hum an being and the task he performs. W ood son 2 describes h u ­ man factors as follow s: Briefly, human engineering means engineer­ ing for human applications. More specifically human engineering is defined as follows: the design of human tasks, man-machine systems and specific items of man-operated equipment for the most effective accomplishment of the job, including displays for presenting informa­ tion to the human senses, controls for human operation and complex man-machine systems. In the design of equipment, human engineer­

18 • THE JO U R N A L O F THE A M E R IC A N DENTAL A SSO C IA T IO N

ing places major emphasis upon efficiency as measured by speed and accuracy o f human performance in the operation of the equip­ ment. Allied with efficiency are safety and comfort of the operator. By considering sensory capabilities, intellectual abilities, capacity for learning new skills, capacity for team or group effort and the understanding of body dimen­ sions, human engineering ultimately reduces the problem of training personnel, providing more effective utilization of personnel, pro­ ducing the amount of effort to perform the task involved.

In the days o f the N eolithic m an, hu­ m an factors relative to the perform ance o f tasks were o f ultimate im portance. T h e w eapon o f survival, the club, fo r example3 was probably fashioned by trial and error. A club not too fragile to perform the task, yet large enough to destroy an animal, was a necessary im plem ent for survival. This cou ld be called the first attempt in hum an engineering. M od ern m an has been busy systematiz­ ing established facts, some o f w hich have existed for hundreds o f years. His curi­ osity and constant search for systems have resulted in prolongation o f life. F or ex­ ample, g ood dietary habits were under­ stood by m any cultures lon g before p ro­ tein, carbohydrates and fats were known as such. T o d a y m an’s achievement in splitting the atom has resulted in new sources o f energy. H ow ever, a paper by Paul Friedlander,3 explained Plato’s “ corpuscular theory” which anticipated what is today the theory o f the splitting o f the atom. It is evident that the Greek culture realized the value o f com fort in the most basic position assumed b y present-day man. During prehistoric times m an first squatted or assumed the cross-legged p o ­ sition. It is logical that prehistoric man probably rested in the fold ed leg position on the ground and gradually fou n d co m ­ fort by using rock structures around him for seating. O n e o f the first discoveries o f pre-H ellenic life, a stone throne, was located about fou r miles o ff the coast o f Crete, in the palace o f M inos, the great­ est o f all M in oan palaces, in approxi­

mately 3500 B.C. This design is not unlike m any present-day vertical seats. As the culture o f m an progressed, so too did his desire fo r com fort. In 600 B.C. the Egyptian king reclined while his queen sat vertically in the typical so­ cial position o f her class. T h e Etruscan influence between 500 and 400 B.C. brought about the use o f the position o f greatest com fort— that is, reclining for both eating and sitting. From the social and functional view point, this period cou ld well be described as the m ost p rac­ tical in m an’ s history so far as sitting in ultimate com fort is concerned. Some 100 years later a great change in the design o f the chair took place in Athens, Greece, wherein a .semi-curve was evolved fo r a m ore reclining yet vertical seating posi­ tion. M o d e m day concepts o f chair d e­ sign have been evolved without consider­ ation for the hum an form and function. H UM AN FACTORS IN PRESENT-DAY PRACTICE

M an y contem porary dental groups have p ooled their ideas and have attempted to study m an-m achine relationships in the dental environment. T im e-m otion studies relative to various technics have been ex­ plored. T h e econ om ic aspects o f doctorpatient relations have been standardized through use o f m ore efficient accounting systems. Efficiency in instrumentation has been investigated in the dental school curriculum. M echanized technics have reached a zenith in dentistry. A ll o f these obviously bear some relation to human factors. W hat further m ethods o f m odern industry can be applied to human factors in today’s dental practice? Ideally, if the m odern theory o f human factors were related to a given field, “ a team ” w ou ld make a prolonged study o f the task to be perform ed by the subject in an ideal environm ent fo r a prescribed period o f time. It w ould seem logical that the first study o f hum an factors in den­ tistry by the “ team” should apply to both

G O LDEN . . . VOLUME 59, JULY 1959 • 19

the doctor, the patient and the dental assistant. In such a study o f the dental environm ent (o ffice ), it w ould b e neces­ sary to include the orthopedic surgeon, the hum an engineer, the anthropologist, the architect, the physiologist, the psy­ chologist, the business administration ex­ pert, and the industrial designer under the guidance o f the inform ed dentist. F or a successful ou tcom e to the study the cooperation o f the equipm ent m anu­ facturer w ould be required. O n e o f the prim ary considerations fo r ideal perform ­ ance is that the patient com es to the den­ tist in an adequate state o f preparation. Proper seating o f a patient is one area o f exploration o f human factors as applied to dentistry (Fig. 1 ). In enlarging on this idea, the question o f the ideal position fo r the operator arises. Statistics provided by various insurance groups reveal that sitting at any given task will prolong the operator’s life expectancy by some 17 per cent (Fig. 2 ) . Basic physiological and perform ance efficiency studies concerned with the den­ tal operator, the patient, and auxiliary personnel have not been reported in the literature. Studies on longevity o f the den­ tist are o f extreme im portance because o f the increase in population, the demands on the professional personnel, and a lack o f school facilities to increase the num ber o f dental graduates. T h e increase o f the population annually in the U nited States is approxim ately 2.5 m illion.4 A pp roxi­ mately 3,000 dental graduates are trained annually in the U nited States. T h e an­ nual death rate o f dentists in the U nited States is approxim ately 2,000. H en ce there is a net gain o f only 1,000 dentists per year to serve 2.5 million increased p op u ­ lation.1 Assuming that a seated position is pre­ ferred fo r the dentist, what then should be the location o f the patient to facilitate ease o f operation, to accom plish the greatest am ount o f accurate w ork in the shortest period o f time, and to provide the greatest degree o f com fort?

METHODOLOGY

T h e m ethod o f design that utilizes the human factor approach is used in the air­ craft industry as follow s: First the op er­ ator or pilot is placed in an ideal position, the controls are designed around him, then the fuselage and wings are built and finally a functionally efficient aircraft structure evolves. This m ethod was ap­ plied in evolving an experimental dental chair fo r the patient. T h e prime o b je c ­ tive was prolonged com fort for the pa­ tient as well as an efficient position fo r the dentist. T h e “ hum an factors team” involved in the design o f the experimental chair and positioning o f the operator consisted o f the follow in g: 1. T h e dental consultant. His p ro ­ fessional knowledge regarding necessary procedures and the needs o f the dental personnel were indispensable fo r such a project. 2. T h e human engineer. His under­ standing o f engineering principles co u ­ pled with a background in biology and physiological sciences qualified him to aid in the control systems. 3. T h e orthopedic surgeon. A knowl­ edge o f the basic skeletal patterns was keenly needed to avoid configurations in design w hich put the hum an subject in jeopardy. 4. T h e anthropologist. A id in the final design o f the equipm ent to obtain the greatest adaptation to hum an b od y sizes consistent with m odern anthropom etric data was given by the anthropologist. 5. T h e kinesthesiologist or muscle physiologist. Kinesthetic knowledge was utilized during the preliminary stages o f designing the equipment so as to inter­ pret muscle fatigue factors and determine the muscle areas involved. W hen the foregoing specialists were satisfied, the industrial designer was re­ lied on to com plete the styling and coordinate m axim um function with pleas­ ing esthetics. T h e architect was then con -

20 • THE JO U R N A L OF THE A M E R IC A N DENTAL A SSO C IA TIO N

Fig. I • Position of patient and dentist. Am ong dentists, 54.29 per cent die of circulatory disease; standing may be a factor. Patient is tense, grips armrests, puts pressure on footrest. Tension causes fatigue

suited with this new dimensional piece o f equipm ent so that he was able to plan a m ore efficient and pleasing dental en­ vironment. In order to understand fully the human factors approach to new design, the basic concepts o f the physiology (muscle, nerve, and b lood vessel function) o f the

human being were reviewed. T h e orth o­ pedist was consulted to learn the regions primarily involved in com fortable sitting (cervical, lumbar, and sacrococcygeal vertebrae) (Fig. 3 ) . T h e critical regions involved in prolonged sitting are the cer­ vical and sacral vertebrae. Clearly, ideal distribution o f force on the hum an spine

Fig. 2 • Optimum working position tor patient and dentist -for long periods of time. Complete relaxation for patient: all equipment is positioned out of patient's sight range when he is in reclined position

G O LDEN . .. VO LUM E 59, JULY 1959 • 21

would result in m axim um com fort. It is easy to understand how the sacral and a fused coccygeal vertebrae housing a g ood segment o f the spinal cord can b ecom e ir­ ritated by pressure in the vertical position o f sitting if com plete support is not given. This w ould result in pressure on the coccygeal vertebrae and subsequent ache in the small o f the back while sitting in the conventional vertical chair or straight-line design chair. Em pirical stud­ ies by the author revealed that in this position the subject experienced physio­ logical fatigue within seven to ten m in­ utes. Breaking o f the back section so that the trunk o f the body reclines fo r p ro­ longed periods o f time exerts a pulling o r stretching effect on the musculature in this “ small o f the back” and neck area. “ C onnective tissue” fatigue is evident from the complaints by the subject (p a ­ tient) . By putting the skeleton in a more ideal position— a semisupine position ( cradling the b o d y ) supporting the skeletal and muscular patterns throughout— the body weight is shifted to realize the aforem en­ tioned ideal, distribution o f force (Fig. 4 ) . A firm basis was established on which to start design o f a new seating m ethod for dental procedure.

Certain “ principles o f m otion econ ­ om y” were considered. T h e ease, speed, and accuracy o f manual operations may be increased by the application o f m otionecon om y principles, some o f which are listed as presented by Barnes, Hartson, and T ufts.2 1. T h e m otion sequence that employs the fewest basic divisions o f accom plish­ m ent is the best for perform ing a given task. 2. H ands should be relieved o f all work that can be perform ed m ore ad­ vantageously by the feet or other parts o f the body. 3. T ools, materials and controls should be located in an arc around the work place and as near the worker as possible. 4. T ools and materials should be pre­ positioned in order to eliminate searching and selecting. 5. T w o or m ore tools should be co m ­ bined wherever possible. 6. T h e height o f the w ork place and the chair should preferably be so ar­ ranged that alternate sitting and stand­ ing at work are easily possible. 7. Continuous, curved motions are preferable to straight-line motions involv­ ing sudden and sharp changes in direc­ tion.

Fig. 3 • Structure of human spine. (Atlas of O rth op ed ic Traction Procedures, C arlo ScL'dori C. V. M osby Co., 1954)

22 • THE JO U R N A L OF THE A M E R IC A N DENTAL A SSO C IA T IO N

Fig. 4 • S k e le to n in so m isu p in e p osition

8. R hythm is essential to the smooth and autom atic perform ance o f an opera­ tion and the w ork should be arranged to perm it easy and natural rhythm wherever possible. 9. Successive movements should be so interrelated that one m ovem ent passes easily into the next, each ending in a p o ­ sition favorable fo r the beginning o f the next movement. 10. Hesitation— or the tem porary and often minute cessation o f m otion— should be analyzed; its cause should be ac­ counted for and, if possible, eliminated.2 A design utilizing these principles per­ m itted: (1 ) equal distribution o f force, (2 ) m axim um com fort fo r the m ajority o f body sizes with (3 ) minimal adjust­ m ent and (4 ) allowed the target, the simulated m outh, rotated on a center axis activated by a fo o t pedal, to com e to the seated or standing dental operator with m inimum effort and final position­ ing consistent with m otion econ om y (Fig. 5 ). By providing an arc o f support in the pelvic region, adjusting only the head, this design is applicable to most

body sizes. W hen em ployed in the opti­ m um supine position, the patient is re­ clining at a definite physiological advan­ tage. (In 1949, M orehouse reported fatigue o f a pilot in the vertical seated position within 20 minutes while perform ­ ing his task. E lectrom yography was used.) M inim al points o f support are indicated by lower armrests, n o footrests, and gen­ erous headrests. T h e headrest also is used by the dentist as an armrest and body rest. MATERIAL

T h e author began a study fou r years ago, using a chair designed in this fashion, and tested some 5,000 sittings o f patients varying in age from 7 to 65 years, and ranging in height from 4 feet 1 inch to 6 feet 3 inches and in weight from 75 pounds to 191 pounds. T his is equal to a cross section o f 91 per cent o f the p op u ­ lation (T a b le 1). T h e physiological and anthropological discrepancies were checked under various clinical circum ­ stances, and the design was then sub­

G O LD EN . . . VO LUM E 59, JULY 1959 • 23

mitted to the kinesthesiologist fo r more exacting tests relative to stress and fa ­ tigue in various seated positions. A fter these preliminary steps, a controlled study was then devised with the follow ing o b ­ jectives : 1. D eterm ination o f the influence o f various sitting positions on hum an endur­ ance during prolonged sitting in dental chairs. 2. Determ ination o f the influence o f standing as well as various sitting posi­ tions on operational efficiency and fatigue in a simulated exhaustive dental opera­ tion. PROCEDURE

T h e subject reported to the laboratory and reclined on a cot until his heart rate and b lood pressure were lowered to a stable level. In most instances this pro­ cedure lasted 30 minutes. T he subject was then placed in position fo r the experi­ ment and tests to learn the follow ing were perform ed: (1 ) heart rate; (2 ) tapping rate; (3 ) oxygen consum ption; (4 ) tem ­ perature; (5 ) b lood pressure; (6 ) steadi­ ness. T h e experim ent was then begun and the tests were repeated in the order given each 20 minutes fo r the duration o f the experiment. T h e laboratory was maintained at a com fortable tem pera­ ture (6 8 -7 0 °F .) and the subject was free from distractions. T h e experiments usu­ ally started at 6 :0 0 p .m . and continued

Table 1 • Sample o f study o f experimental dental chair; fifty-five patients. (5,000 sittings over H /2 year sfudy)

Sex

Height

N o . of patients

A ve rage weight— lbs.

M M F F F F F F F M F F M M M M M M M

4' 4’- 6" S' S '- 1" S '- 2" 5 ' - 3" S '- 4" 5 ' - 5" 5 ' - 6" 5 ' - 7" 5 ' - 8" S '- 8" S '- 9" 5 '-1 0 " 5 '-1 1 " 6' 6 ' - 1" 6 '- 2" 6 '- 3"

1 1 2 2 2 4 8 4 7 3 1 1 3 6 2 2 2 2 2

89 76 125 102 108 128 109 124 149 155 115 153 167 168 160 180 185 190 191

A verage age— years 9Vi

9Vi 64 43 19 40 22 25 30 67 30 16 27 40 36 30 43 29 38

throughout the night until 6 :0 0 a .m . T h e investigators kept constant surveil­ lance over the subject and recorded all o f the subject’s remarks and behavior. D uplicate observations were m ade o f each experimental condition. PATIENT SEATING

Conventional Chair • T h e conventional dental chair em ployed in this study was adjusted so that the subject (simulating a patient) was tilted to a 40 degree angle. T h e headrest was adjusted so that the subject’ s head and neck were in normal alignment with his trunk. T h e fixed footrest provided a support fo r the subject’s feet and legs. Experimental Chair • T h e experimental

Fig. 5 • patient

Operative

positions of dentist and

dental chair provided three different sit­ ting positions. T h e contour o f this chair was such that the degree o f hip and knee flexion remained constant throughout the entire range o f adjustments. T he headrest was adjusted to suit the subject. T h e low er-leg rest on the experimental

24 • THE JO U R N A L OF THE A M E R IC A N DENTAL A SSO C IA TIO N

chair was designed to support the feet and lower legs from underneath. DENTIST SEATING

Stool • Pivoting from the base o f the

conventional dental chair, a free swing­ ing dentist’s stool perm itted the dentist to m ove in a revolving arc around the chair. D ou ble lever arms incorporated in the vertical shaft provided anterior and posterior shifting o f the dentist’ s seat tow ard and away from the chair. T h e ver­ tical shaft also offered a seat height ad­ justment. N o support to the dentist’s back was provided. Chair • A Fiberglas chair provided sup­ port to the back in an upright seated p o ­ sition. T h e chair allowed lateral rotation, but was otherwise fixed. OBSERVATIONS

A com parison was m ade o f backward in­ clination o f conventional and experi­ mental dental chairs and o f standing and sitting positions o f the dentist. T h e chairs (A , B) were adjusted to a m oderately supine position com m only em ployed in dentists’ offices. In this p o ­ sition the angle o f the trunk, measured by projection o f a line between the acrom ion and the greater trochanter, was 40 degrees backward from the vertical position. T h e chairs were adjusted so that the trunk and head positions o f the sub­ ject (simulating the patient) were the same in both chairs. T h e subject was per­ m itted to arrange his feet and legs in the most com fortable position, and was al­ low ed to make restless and random m ove­ ments during the course o f the experi­ ments. Backward Inclination • In order to study

the effects o f various degrees o f backward inclination o f the experimental chair, two additional positions were investigated. A n upright position with the trunk o f

the subject at 25 degrees (C ) and a supine position with the trunk at 50 de­ grees ( D ) . In b oth positions the headrest was adjusted to support the head and neck in norm al alignm ent with the trunk. T h e subject was perm itted to cross and uncross his legs and make other random motions. Standing • T h e dentist’s task was simu­

lated by positioning the standing subject at a point between the right position and the right-rear position alongside the den­ tal chair. W ith the left fo o t on the rheo­ stat and the m ajority o f the body weight supported by the right foot, the subject leaned forw ard at the waist about 5 de­ grees. T h e head was flexed about 50 d e­ grees from the vertical. T h e dentist leaned gently against the chair. T he height o f the chair was adjusted so the subject (simulating the dentist) was able to place the stylus at the m outh o f the dum m y (simulating a patient) while holding the elbow at right angles with the target m outh at a point between the elbow and the shoulder. T h e subject’s m iddle finger rested lightly against the dum m y’s dental arch. Sitting • T h e subject, simulating a seated dentist, sat so that the dum m y’s m outh was m idw ay betw een the subject’s elbow and shoulder, with the operator’s elbow held at a right angle. T h e subject’s body was inclined 5 degrees and his head 50 degrees. A n attempt was m ade to dupli­ cate the body position o f the dentist as m uch as possible in all o f the experi­ ments. PHYSIOLOGICAL MEASUREMENTS

Heart Rate and Blood Pressure • T h e

heart rate and b lood pressure o f both patient and dentist were used to indicate circulatory and em otional responses. Heart rate was ascertained by ausculta­ tion using a stethoscope and stop watch. B lood pressure was recorded at the

G O LDEN . . . VO LUM E 59, JULY 1959 • 25

brachial artery using a m ercury sphyg­ m om anom eter and a stethoscope.

consum ption, tidal volum e, inspiratory rate, m inute volum e and ventilation ef­ ficiency.

Body Temperature * B ody temperature

o f the dentist and patient was recorded in order to detect the effects o f effort and fatigue on tem perature-regulating m ech­ anisms. It was recorded at the right axilla by the use o f a thermistor ther­ mometer. Steadiness • A test o f finger grasp steadi­

ness o f the dentist was em ployed to in ­ vestigate neurom uscular coordination. T h e test consisted o f holding a 1 /1 6 inch diameter stylus that had been inserted into a Ys inch diameter cavity cylinder so as not to touch the sides o f the cavity with the stylus. T h e test was scored using a 1 /1 0 0 second electric chronom eter con ­ nected in series with the stylus and cavity cylinder so as to record cumulative time whenever the stylus rested against the floor o f the cavity. T h e noise from the operation o f the chronom eter warned the dentist that he was making an error, thus serving as a motivational factor in the system. Rate of Tapping • T h e level o f central

nervous system activity was recorded us­ ing the rate o f tapping test. A steel plate connected in series with a stylus and a telephone counter recorded the num ber o f taps perform ed by the dentist at m axi­ m um rate for one minute, timed by stop watch. In order to explore the speed o f m ovem ent in relation to other physiologi­ cal effects, the cumulative pause time was recorded during contact at each tap by connecting a 1/1000 second chronoscope in series with the plate, stylus, and cou n ­ ter. Respiratory Metabolism • Energy utili­ zation and respiratory efficiency o f both patient and dentist were investigated us­ ing a closed circuit 13.5 liter respirom­ eter. T his instrument furnished spiro­ grams w h ich yielded values for oxygen

• Studies o f muscle tension o f both subjects during the p ro­ longed w ork tasks were perform ed using an integrated electrom yograph. Surface electrodes were fastened over the m id ­ points o f the muscles w hich appeared to be brought under tension in the various work and seating conditions em ployed in this study. A ction current changes were recorded on a photokym ograph.

Electromyography

Trem or • T rem or is the oscillation co n ­

comitant with effort to maintain a fixed position or direction. It is m ost obvious in the tension type o f m ovem ent. T h e de­ gree o f trem or is measured by the distance o r num ber o f departures from the fixed path or position in a given time. Trem or decreases when work is against friction, m em ber is supported, and b od y is well supported while m em ber perform s activ­ ity. T rem or increases when effort is made not to tremble, and fatigue is present. It is greatest in vertical m otion, less in front-to-back and least in side-to-side motion. Steadiness is a generalized char­ acteristic, applicable to the same degree in a given individual over a wide variety o f tasks2 (Fig. 6 ) . DISCUSSION

Conventional vs. Experimental Chair • T h e subject (simulating a patient) was able to sit fo r 12 continuous hours with­ out discom fort in the experimental chair. In the first o f the tw o perform ances in the conventional chair, the subject was able to endure the position fo r only ten hours. In the second experiment, he remained in the chair fo r 12 hours. H e reported few er m inor complaints while seated in the experimental chair and remarked that he w ou ld prefer to use the experi­ mental chair if he was goin g to repeat the experience. His general reactions are

26 • THE JO U R N A L O F THE A M E R IC A N DENTAL A SSO C IA T IO N

C. Single point seat support D. Foot support =r pressure tension E. Ha n d grip “ pressure tension

E. Arm support

—

no pressure tens i o n

Fig. 6 • Positions of patient. Left: Patient fatigue results in seven minutes to maximum of a half hour when patient is upright. Right: M inor fatigue indications are present after three to four hours when patient is in semisupine position. Patient is completely relaxed and often sleeps during dental work

born e out by the physiological data. E lec­ tromyograms show that there was less strain on the muscle o f the back while sit­ ting in the experimental chair. Perform ­ ance, as evidenced by steadiness decre­ m ent scores, is maintained at a higher level w hen the experimental chair is used (Tables 2, 3 ). Influence of Chair Angle • T h e supine

seated position, with the chair back at an angle o f 50 degrees from the vertical, is the most acceptable position fo r p ro­ longed sitting. Contrary to com m on opinion, perform ance is not jeopardized w hen the patient is leaning back in co m ­ fort. Physiological processes are benefited by the supine position; energy is con ­ served, and b lood circulation is enhanced. T h e upright vertical position is the least econom ical o f hum an energy, and p ro ­ longed sitting in an upright position leads to early fatigue and an accom pany­ in g deterioration o f the patient’s per­ form ance. Figure 6 shows the patient in the upright and semisupine positions.

Standing vs. Sitting During Dental O per­ ations • A lthough the physiological data

obtained in this study d o not strongly sup­ port the reports o f the subject (simulatTable 2 • Results of electromyographic studies Electromyographic data Dehtlst (standing) Trapezius 1st test 2nd test Lattissimus dorsi 1st test 2nd test

Muscle potentials (microvolts) 50 65 95 85

Dentist (sitting) Trapezius 1st test 2nd test Lattissimus dorsi 1st test 2nd test

75 38 115

100

Patient (sitting) Lattisimus dorsi Conventional chair Experimental chair— aft Experimental chair— mid Experimental chair— forward

350

120 120 120

G O LDEN . . . VO LUM E 59, JULY 1959 • 27

ing the dentist) o f sensations during work in the various standing and seated posi­ tions, there evidently were strains in pro­ longed standing w hich were not present when the w ork was perform ed in seated positions. Since the site o f discom fort was reported to be near the origin and inser­ tion o f antigravity muscles, it is probable that connective tissue, not muscle, is re­ sponsible for fatigue in static work. Electrom yographic observations fail to show m uscular stress in quiet standing. Circulation is benefited w hen the dentist sits at his task. D iastolic b lood pressure, a sensitive index o f circulatory function, is noticeably increased during prolonged static w ork in the standing position. T h e chair used in this study did not appear to be superior to the stool as far as the data were concerned. H ow ever, subjects felt that the back rest afforded by the chair

m ade it more com fortable to use than the stool. FUTURE STUDIES

Further physiological studies on the den­ tal operator and assistant should be car­ ried out under dynam ic m ovem ent con ­ ditions to include electrom yography. This evaluation o f data m ay influence present dental procedures. T h e results o f these and other studies, in which the follow in g m en participated, L . E. M orehouse, Ph.D., Eugene M c C o n ­ nell, M .S ., Glen Egstrom, M .S ., and M r. N ick Stasinos, should be coordinated in the form o f a teaching m ethod utilizing m odern equipm ent and the sit-down den­ tal technic. T h e detailing o f all body movements o f the dental personnel re­ lated to the operatory procedure in all

Table 3 • Summary of physiological findings Patient

Conventional chair— mid­ position (40°)

Experimental chair Mid-position (40°)

Forward position (25°)

Supine position (50) M arkedly decreased Markedly decreased Unchanged

Minute volume

Decreased

Unchanged

Unchanged

O xygen consumption

Unchanged

Unchanged

Decreased

Steadiness

Decreased

Unchanged

Diastolic blood pressure

Unchanged

Unchanged

M arkedly decreased Unchanged

Heart rate

Decreased

Decreased

Decreased

Markedly decreased

Latissimus dorsi electromyogram

Increased

Unchanged

Unchanged

Unchanged

Unchanged *

Dentist Standing*

Sitting on s to o lf

Sitting on chairf

Minute volume O xygen consumption Steadiness Diastolic blood pressure Heart rate

Unchanged Unchanged Unchanged M arkedly increased Unchanged

Unchanged Unchanged Unchanged

Unchanged Unchanged Unchanged

Unchanged M arkedly decreased

Increased! Decreased

lattissimus dorsi electromyogram

Unchanged

Unchanged

Unchanged

*3-4 hours \S-bV2 hours $6 hours

28 • THE JO U R N A L OF THE A M E R IC A N DENTAL A SSO C IA T IO N

branches o f general dentistry w ould be a contribution to the dental profession. Data relative to the dentist standing and sit­ ting w ou ld apply to the dental assistant standing and sitting, assuming similar positions were used by both. Further stud­ ies o f tim e-m otion theories may prove that the first essential o f m otion econom y is the use o f a chairside dental assistant. 1001 Gayley Avenue

The physiologic study was done at the University of California at Los Angeles under a grant from the Ritter Corporation, Rochester, N.Y. ^Assistant professor, human factors research division, operative dentistry, School of Dentistry, University of Southern California. 1. Friedrich, R. H. Personal communication. 2. Woodson, Wesley E. Human engineering guide

for equipment designers. Berkeley, Calif., University of California Press, 1954. 3. Friedlander, Paul. Plato, vol. I. An introduction. New York, Pantheon Books, 1958. 4. A billion people in the United States? U. S. News and W orld Report Nov. 28, 1958. 5. Morehouse, L. E. Personal communication. 6. Kraus, Bertram. Personal communication. 7. Vandenberg, J. D. Human factors engineering I. Man and machine. Machine Design 30:108 April 17, 1958. 8. Roebuck, J. A., Jr. Anthropometry in aircraft engi­ neering design. J. Aviat. Med. 28:41 Feb. 1957. 9. Engineering staff, Ritter Corporation. Personal communication. 10. Marinacci, A. A . Clinical electromyography. Los Angeles, San Lucas Press, 1955. 11. Peters, G . E., and Drum, L. R. Human engineer­ ing— a new occupation. Personnel & Guidance J., Dec. 1957. 12. Wells, J. Gordon, and Morehouse, L. E. Electro­ myographic study of effects of various headward ac­ celerative forces upon pilot's ability to perform stand­ ardized pulls on aircraft control sticlc. J. Aviat. Med. 21:48 Feb. 1950. 13. American Dental Association, Bureau of Economic Research and Statistics. Mortality of dentists, 1951-1954. J.A.D.A. 52:618 Nov. 1956.

The interrelationship of periodontics and orthodontics

Edward A . L usterm an * D .D .S ., Rockville Centre, N .Y .

There is a large field in which the disci­ plines of orthodontics and periodontics m ay be employed to the benefit o f pa­ tients. Although some of the periodontal damage resulting from orthodontic treat­ ment is irreversible, much is transitory. T here should be more frequent consulta­ tion between orthodontist and periodon­ tist, and each should be familiar with the other’s literature.

It is incum bent on any practitioner o f the healing arts to have a wholesom e re­ spect for tissue. This encompasses a knowledge o f its histologic and path o­ logic characteristics and its capacity for alteration and repair. F or the orthodontist

as fo r all others in every field o f dentistry, this is sine qua non. T h e orthodontist’s m ajor function is to create harm ony out o f disharmony. Since, at best, perfection is elusive and ephemeral, the orthodontist’s objective is to achieve optim al im provem ent in every patient. Orthodontists share with all in dentistry the desire to restore m alocclu ded dentitions to proper function, to enhance the longevity o f the dentition, and to achieve these with due regard for tissue health, muscle balance and facial esthetics. O rthodon tic treatment may sometimes have undesirable side effects. These may include a greater or lesser degree o f root resorption, or perhaps the creation o f