US 3610227 A
Description (OCR text may contain errors)
United States Patent Clifford John Griffin 7 Sydney, New South Wales, Australia  Appl. No. 833,301
 Inventor  MEANS FOR RECORDING ORAL New  References Cited UNlTED STATES PATENTS 3,078,584 2/1963 Cohn 32/20 X 3,129,510 4/1964 Griffin..... 32/19 3,130,494 4/1964 MacKay 32/20 3,275,258 9/1966 PCICZ 242/190 3,495,789 2/1970 Gerfast 242/201 Primary Examiner-Richard A. Gaudet Assistant Examiner-Kyle L. Howell Attorney-Singer, Stem & Carlberg ABSTRACT: The invention is directed to an apparatus for recording oral proprioception (i.e. for recording the reflex ability and sensitivity of the mouth opening and closing muscles.) The apparatus comprises a frame which is pivotable from a frontal to a lateral position relative to a patient under test and a drive arrangement for feeding a strip of recording paper, which is disposed in a vertical plane, in a horizontal direction across and in contact with a guide frame which is fixed to the pivotable frame. A recording stylus is pivotably mounted to the pivotable frame, such stylus being adapted for connection with the patient's mandible and for marking the recording paper such that movement of the patient's mandible is represented graphically on the recording paper.
PATENTEDhcT SIB?! 3510.227
SHEET 2 UF 5 I nvcnlor j A norheys MEANS FOR RECORDING ORAL PROPRIOCEP'IION Research into the mandibular (lower jaw) position and into the performance of muscles responsible for the mandibular movements has been prompted due to the occurrence of physiological disturbances which have been tracedto a lack of harmony between the mandibular opening and closing muscles and to jaw misalignment and other mount deformities. It is suspected that such disharmony or deformities may be at least in part responsible for such complaints as locking of the jaws, limiting of the extent to which the mouth may be comfortably opened, and migraine headaches due to the nerve center controlling the mandibular muscles not being in equilibrium when the jaws are in the maximum position. The nerve controlling the mandibular muscles is centered high in the brain and continual impulses emitted therefrom due to disharmony of the mandibular muscles cause the surrounding nerves to react and produce the migraine type headache. Pure nervous agitation and disturbed muscular coordination may also occur, without migraine.
The inventor has observed that when a patient is asked to open and shut his jaws briskly (with his eyes shut) a reflex appears which lies on a graphical path traced by the mandible (lower jaw) between the teeth clenched position and a noncontact or nociceptive position. If the path traced is median or straight then the tooth position is good and the jaw muscles are working in harmony. If the path traced is not median or straight, the degree and direction of displacement of the graph line from an optimum position will indicate a defect which may be diagnosed and, by known methods, be corrected.
Thus, it is an object of the present invention to provide an apparatus of a comparatively simple nature for accurately recording oral proprioception by recording the reflex action of the mandible.
Heretofore, endeavors to record oral proprioception have involved the use of electromyographic devices. But such devices are of a complicated nature, they are inherently expensive and they are thus not generally employed in day-today dental surgery.
The present invention, however, provides an apparatus for recording oral proprioception comprising a mounting arm, a guide frame mounted to said mounting arm in a substantially vertical plane, means for continuously or intermittently feeding a strip of flexible sheet recording material, which is disposed in a substantially vertical plane, in a horizontal direction across and in contact with said guide frame, drive means adapted to selectively effect said feeding of sheet material in either direction, a recording stylus pivotably mounted to said mounting arm and adapted to mark a portion of said sheet material which is in contact with said guide frame, adjustable means carried by a support frame and adapted to position the skull of a patient relative to said mounting arm, means adapted to connect the mandible of said patient to said stylus whereby movement of the mandible is represented graphically on said sheet material.
The flexible sheet material may comprise a strip of paper or other material upon which a graph may be traced and the said means for transferring the sheet material preferably comprises a pair of spaced vertically disposed spools, one spool being located at each side of the paper guide frame.
One of said spools (i.e., a takeup spool) is connectable to a drive therefor at any given time. However the drive is preferably connectable to either one of said spools, as required, to permit selection (or reversal) of the transfer direction of the sheet material.
The apparatus above defined enables achievement of material feed rates at least as high as 0.220 meters. sec. or, in other words, a paper shift of 1 mm. per 4.5 msecs. This makes the performance and capabilities of the apparatus compatible with those of the more elaborate and expensive electromyographic devices.
The high material feed rate is desirable in order to achieve recordal of a positive and measurable indication of such phenomena as dental nociceptive reflex (D.N.R.) relative to a time base.
The invention will be more fully understood from the following description of a preferred embodiment thereof taken in conjunction with the accompanying drawings, wherein,
FIG. 1 is a perspective view of a recording apparatus which is shown pivoted to a lateral position in readiness to take a test on the seated patient,
FIG. 2 is an exploded partial view of a recording station section of the apparatus illustrated by FIG. 1,
FIG. 3 is a detailed, sectional, elevation view of the recording stylus shown in FIG. 1,
FIG. 4 is a detail view taken along section 4-4 of FIG. I, moulded cover portions of the apparatus being shown removed for clarity,
FIG. 5 is an end view, taken in the direction of arrow 5, of FIG. 4,
FIGS. 6 to 13 show graphical results of typical tests which may be carried out by the apparatus shown in FIGS. 1 to 5.
Refen'ing to FIG. 1, there is shown a recording apparatus (indicated generally as 20) which is pivotably mounted to a support member 21. The apparatus is pivotable through about axis 22 between a lateral position (wherein it is shown) and a frontal position (not shown) where the patient faces the recording paper.
The recording apparatus 20 is rigidly mounted to the support member 21, at point 23, through a fixed arm 24, and the support member is carried by a base portion 25 which is supported upon casters 26.
The support member 21 and the base portion 25 are shaped so as to be maneuverable into the position shown adjacent the side of a dental chair 27, and floor engaging friction stops 28 are mounted to the base portion 25 to hold the support member stationary when it is so positioned.
Referring now to the recording apparatus (20) per so. This is built on a cast aluminum mounting arm 29 (FIGS. 2, 4 and 5) which, in plan, is substantially T-shaped. The inner end of the arm comprises a boss portion 30 (FIG. 4) which carries ball races 31, the outer end of the mounting arm comprises a platform 32 and a downwardly projecting flange 33 to which a spool drive (hereinafter described) is mounted, and the intermediate arm portion has a structurally rigid I-section comprising a web 34 and end flanges 35.
The inner end of the arm 29 is pivotably mounted to the fixed arm 24 by a fixed shaft 36 which is joumaled in the bearings 31, and at the underside of the boss portion 30 there I are spring-loaded balls 37 which are adapted to engage in suitably positioned dimples for positively locating the arm 29 in either the lateral or the frontal position as required.
For the sake of appearance, three separate moulded plastic covers 38, 39 and 40 are mounted to the arm 29 and one cover 41 encloses the fixed arm 24. The covers 38 to 40 are not shown mounted to the arm 29 in FIGS. 4 and 5, and in FIG. 2 the cover 39 is removed. Cover 38 encloses all but the underside of the arm and the platform 32 (see FIG. 2), cover 39 encloses the platform 32 but for a window portion 42 (see FIG. 1), and cover 40 encloses the underside of the outer end of the arm-it being coextensive with the cover 41 on the fixed arm 24 when the recording apparatus is located in the frontal posi tion. All of the covers are attached by clips (not shown) and may; be readily removed from the respective arms.
Mounted to the platform 32 of the arm 29 is a paper guide frame 43 (FIGS. 1 and 2). Such guide frame is formed from sheet metal and it is concave about a horizontal axis which lies in the optimum plate of a marking pen (hereinafter referred to). The guide frame is bisected by the central axis of the arm 29 and it is disposed immediately behind the window 42.
To reduce friction between the guide frame 43 and recording paper 45 to be fed past same, the paper-contacting (concave) surface of the guide frame may vbe coated with polytetrafluoroethylene or some such suitable material.
End guides 44 form an integral portion of the guide frame 43 to hold the recording paper 45 in contact with the frame.
Rotatable spool shafts 46 are located one at each side of the recording paper guide frame 43. The spool shafts have a square upper end for engaging in a broached hole 47 in spools 48 and the shafts 46 are carried in bearing housings 49 which are screw mounted to the platfonn 32. Also, the spool shafts 46 pass through the platform to the underside thereof, as shown in FIG. 5.
The spools 48 have a cylindrical body portion 50, which surrounds but does not contact the bearing housings 49, and a lower flange portion 51. The periphery of the flange portion of each spool 48 is knurled or fluted and, as shown in FIG 1, it projects through a slot 52 in the respective side of the plastic cover 38. This permits manual feeding of the recording paper 45 from one spool to the other without removing the cover 39.
Spool drive pulleys 53 are mounted in driving engagement on the lower end of each of the drive shafts 46, such pulleys being hereinafter referred to as driven pulleys 53."
Drive belts 54 extend from a drive 55 to each of the driven pulleys 53.
The drive 55 comprises two double pole split-phase motors 56 and 56a mounted one above the other with a common vertical drive shaft 57 which interconnects and passes through the rotors of both said motors.
The two motors 56 and 56a are mounted below a reduction gearbox 58, and the two motors together with the gearbox comprise a single compact unit which is screw mounted to the arm flange 33 and to a cast projection 59 which extends downwardly from the underside of the platform 32. Mounted to a single output shaft 60 of the gearbox 58 are two adjacent drive pulleys 61 (FIG. 4), the drive pulleys each having fitted in their respective bores a one-way Torrington" type needle bearing which is press fitted on to the output shaft 60. One needle bearing is inverted relative to the other such that rotation of the output shaft 60 will drive one drive pulley 61 whilst the other may be kept stationary, and vice versa.
The stator windings of the respective motors 56 and 56a (or the connections to the windings) are arranged such that energization one of the motors will result in shaft rotation in one direction, whilst energization of the other motor will result in shaft rotation in the opposite direction. Thus, energization of, say, motor 56 will cause the gearbox output shaft 60 to rotate in a first direction, drive to be transmitted through lower drive pulley 61 to the right-hand driven pulley 53 (FIG. and consequent rotation of the right-hand spool 48. Similarly, energization of motor 560 will cause rotation of the gearbox output shaft 60 in a second (opposite) direction, drive to be transmitted through the upper drive pulley 61 to the left-hand driven pulley 53, and consequent rotation of the left-hand spool 48.
The drive pulley 61 which is not, at any one time, transmitting drive will idle on the shaft 60 and thus permit the reel 48 from which recording paper is being drawn to rotate. Such drive arrangement will tend to prevent over-running of the spool from which the recording paper is being drawn.
A suitable drive arrangement for use in the present invention is one wherein the motors 56 and 56a both have a shaft speed of 2,800 r.p.m. and the gearbox provides an output shaft speed of 63r.p.m. at 3.7 lb.ins. torque. Such a drive when used in conjunction with suitable size pulleys will provide an optimum recording paper transfer velocity of 0.125 meters sec.", but, if desired, stepped pulleys may be provided to achieve a selectable speed change system.
A gradual change in the transfer velocity of the recording paper due to a buildup of paper on the driven pulley will not significantly affect the results of graphs plotted on such paper because any one graph will be recorded over a very short time period.
A double-pole, double-throw switch 62 (FIG. I) is mounted to the recording apparatus for controlling energization of one or the other of the motors 56 or 56a (but not both simultaneously) and an indicator lamp 63 is provided to give indication of power-on". Two further indicator lamps 64 are also provided to give indication of direction of transfer of the recording paper 45 responsive to energization of the appropriate drive motor.
Mounted to the web 34 of the mounting arm 29 and projecting through an aperture 65 in the upper cover 38 is a recording stylus pivot bearing post 66. As shown in FIG. 3, the bearing post 66 is fitted at its upper end with a universal ball mounting 67 for the stylus 68. The ball mounting 67 allows for a large angular displacement of the stylus in any direction whilst maintaining maximum control over slackness in the support of the stylus.
The stylus 68 comprises a straight slender rod 69 which projects in one direction toward the paper guide frame 43 and in the other direction toward the patient. A retractable sleeve 70 is mounted to the inner end of the rod 69, said sleeve carrying at its free end a marking pen 71 and having at its other end a threaded bore for screw engagement with a threaded collar 72. A spring 73 acts to bias the marking into engagement with the recording paper 45.
Thus, the marking pen 71 is adapted to be manually locked in a retracted position when not required and to be manually released from that position, so to be urged by the spring 73 against the recording paper.
To connect the stylus to the patients's jaw, a tubular element 74 (FIG. 1) is telescopically fitted to the outer end of the stylus rod 69 and it is connected through a ball and socket joint 75 with a chin strap 76. The chin strap 76 is in turn securely fitted to the patient by connecting same through hellcal tension springs 77 with an adjustably fitted headband 78.
Then to locate the patient relative to the recording apparatus 20, there is a first adjustable support 79 for locating below the patient's nose and a second adjustable support 80 for locating against the patients forehead. One thumb screw 81 is arranged to permit adjustment of one support relative to the other and a further thumb screw 82 permits adjustment of both supports relative to the apparatus.
With the patient positioned as shown in FIG. I a headrest 83 of the chair 27 is adjusted to engage the back of the patient's head.
The nose and the forehead supports 79 and 80 remain fixed in the adjust position during turning of the recording apparatus from the lateral to the frontal position.
The patient is preferably positioned such that the ball joint 75 is located vertically above the pivot axis 22, but this is not critical as any relative movement between the patient and the stylus during turning of the apparatus will be accommodated in the telescopic coupling 74.
With the patient positioned as shown in FIG. I and with the stylus released, any movement of the patients jaw will be reflected in a graph traced on the recording paper.
Some standard tests which may be conducted utilizing the aforedescribed apparatus are hereinafter set forth by way of example.
The following nomenclature is however first given in order that a full understanding of the tests may be obtained. MANDIBULAR KINEMATOGRAM. A graphic record of mandibular movements obtained on the mandibular kinematograph (M.K.G.) when the patient opens and closes his mouth.
MANDIBULAR KINEMATOGRAPH (M.K.G.). A machine and accessories designed for recording mandibular movements.
INTERMITTENT FRONTAL MANDIBULAR KINEMATO- GRAM (I.F.M.K.G.). A record of intermittent mandibular movements from a frontal position.
CONTINUOUS FRONTAL MANDIBULAR KINEMATO- GRAM (C.F.M.K.G.). A record of rhythmic mandibular movements from a frontal position.
INTERMITTENT LATERAL MANDIBULAR KINEMATO- GRAM (I.L.M.K.G.). A record of intermittent mandibular movements from a lateral position. CONTINUOUS LATERAL MANDIBULAR KINEMATO- GRAM (C.L.M.K.G.). A record of rhythmic mandibular movements from a lateral position.
FRONTAL POSITION. The patient is placed in front of the mandibular kinematograph so that mandibular movements in a lateral and vertical direction are recorded. The head is orientated in the Frankfort plane.
CLENCI-I LINE. A line of the mandibular kinematogram depicting the position of the mandible relative to other positions when the teeth are clenched.
REST POSITION. The position of the mandible when the masticatory muscles are at physiological rest (resting tonus).
DENTAL NOCICEPTIVE REFLEX (D.N.R.). A reflex occurring when the upper and lower teeth are briskly brought into maximum tooth contact. It has two components an initial fast component indicating contraction and inhibition (latency) of the mandibular elevators and a slow component in which the mandible moves from the maximum tooth contact position to the noncontact or dental nociceptive position.
MANDIBULAR DISPLACEMENT. Displacement of the mandible relative to the skull in either a lateral, posterior, or anterior direction. The degree of displacement is assessed by the direction of the D.N.R.
VERTICAL DIMENSION. The distance between the base of the nose and the chin maintained by the dentition and alveclar bone.
LATERAL POSITION. The patient is placed side on to the mandibular kinematograph so that mandibular movements is an antero-posterior and vertical direction are recorded. MAXIMUM TOOTH POSITION. The position of the mandible when the maxillary (upper jaw) and mandibular teeth are maximally intercuspidated.
NOCICEPTIVE POSITION. The position of the mandible reflexly assumed by stimulation of nerve receptors in the periodontal membrane (just short of contact).
FRANKFORT PLANE. A line through the interior margin of the orbit directly under the pupil of the eye to the upper margin of the external auditory meatus.
As a test preliminary, a patient is seated in the dental chair 27 and the apparatus is located in the frontal position (i.e., such that the patient faces the recording paper). The height of the dental chair is adjusted such that the patients chin is located horizontally in approximate alignment with the recording pen pivot point 67 and vertically above the pivot axis 22 of the apparatus. The chin strap 76 and affixing head band 78 are then fitted to the patient, the chin is connected by the telescopic link 74 to the pivotable pencarrier 68, the pen is released to contact the recording paper 43, the forehead and nose supports 79 and 80 are adjusted to retain the patient in the selected position, and the patient is instructed to close his eyes.
The recording paper is then run at a constant velocity, first in one direction and then the other. A single line should be thus recorded on the paper. A gauge block of, say, mm thickness is then clamped by the patient between his teeth and the paper is again run at constant velocity in the two directions to produce a second single line on the paper, above the first recorded line. By measuring the distance between the two recorded lines, a ratio of actual teeth deflection (10 mm.) to recorded teeth deflection can be calculated.
The apparatus is then pivoted through 90to place the patient in the lateral position and the above described test preliminary is again conducted.
TESTS In the following tests, at the completion of each mouth-closing cycle the teeth of both both jaws are brought into maximum occlusal condition.
FIG. 6 represents the recordal of a patient's muscle reaction (as reflected through jaw movement) in the frontal position. With the recording paper stationary, the patient opens and shuts his jaws once, the recording paper is displaced manually and the exercise is repeated (twice, as shown in the subject FIG.). The record is called an intermittent frontal mandibular kinematogram (IFMKG) and it has been obtained from a patient who has almost perfect muscular coordination. The datum line 200 represents the mouth closed (teeth clenched) condition, the line 201 represents the jaw opening movement and the line 202, the jaw closing movement. The point 203 represents the dental nociceptive reflex (DNR), this reflex being a fast reopening tendency of the jaws which occurs after the maximum tooth closed position has been achieved and it represents a reflex repositioning to a noncontact position. The integrity of this reflex indicates the condition of oral proprioceptive mechanisms and, ideally, the opening and closing movement lines 201 and 202 should be superimposed.
FIGS. 7A and 78 represent the recordal of muscle reaction (as reflected through jaw movement, but hereinafter referred to only as muscle reaction) in the same patient as used to record FIG. 6. In this case however the patient opens and shuts his jaws rhythmically and the recording paper is run at a constant velocity (as hereinbefore described) first in direction A (FIG. 7A) and then in direction B (FIG. 7B). The line 204 represents a jaw opening movement and the line 205, a jaw closing movement. The line portion 206 represents the dental nociceptive reflex, the horizontal component representing a fast contraction and inhibition (latency) of the mandibular elevators, and the upward projection representing the opening of the mandible from a maximum tooth contact position to the nociceptive position. The graphical representation is termed the continuous frontal mandibular kinematogram (CFMKG) and, insofar as it has been obtained from a patient having almost perfect muscular coordination, FIG. 7A is an approximate mirror image of FIG. 7B.
FIG. 8 represents (on an exaggerated scale) the recordal of muscle reaction in the frontal position for a patient who has a left lateral displacement of the mandible. With the recording paper stationary (as in the case of FIG. 6), the patient opens and shuts his jaws once, the recording paper is displaced manually and the exercise is repeated. The datum line 207 represents the mouth closed condition, the line 208 represents the jaw opening movement and the line 209, the jaw-closing movement. Lateral displacement of the mandible is indicated by the deviation of the jaw closing line 209 over the section indicated by numeral 210 from point X.
FIGS. 9A and 98 represent the recordal of muscle reaction in the same patient as used to record FIG. 8. In this case the patient opens and shuts his jaws rhythmically and the recording paper is run at a constant velocity, first in direction A (FIG. 9A) and then in direction B (FIG. 9B). The line 2" represents a jaw-opening movement, the line 212, a jawclosing movement, and the line portion 213 represents the left lateral displacement. (In the direction A the displacement is closed-up due to the recording paper movement and, in the direction B, the displacement is opened-up by the carriage movement). The degree of mandible displacement is assessed by computing the average length of line portions 213 in FIGS. 9A and 93. Such length reflects the time duration for the jaws to achieve the maximum tooth position after a premature contact at point X (FIG. 8) has been made.
FIG. 10 represents the recordal of a patients muscle reaction in the lateral position. With the recording paper stationary, the patient opens and shuts his jaws once, the recording paper is displaced manually and the exercise is repeated. This record is termed an intermittent lateral mandibular kinematogram (ILMKG) and it is obtained from a patient who has near perfect muscular reaction. The datum line 214 represents the mouth closed (teeth clenched) position, the line 215 represents the jaw opening movement and the line 216, the jaw-closing movement. The point 217 represents the reflexopening movement (DNR). In this graph the nociceptive position and the clench position are virtually in the same horizontal plane. Also, the jaw closing movement reflects two basic mandibular movements, movement A-B reflects the mandibular condyle moving back into the glenoide fossa and the line B-C reflects mandibular closure along the hinge axis.
FIGS. 11A and 11B represent the recordal of muscle reaction in the same patient as used to record FIG. 10. In this case the patient opens and closes his jaws rhythmically and the recording paper is fed at a constant velocity in direction A (FIG. 11A) and then in direction B (FIG. 118). The lines 218 represents jaw-opening movements and the lines 219, jawclosing movements. The line portion 220 represents the dental nociceptive reflex, the horizontal component 221 representing a fast contraction and inhibition (latency) of the mandibular elevators and the vertical component 222 representing the opening of the mandible from a maximum tooth contact position to the nociceptive physiological rest position. This graphical representation is termed the continuous lateral mandibular kinematogram (CLMKG).
FIG. 12 represents the recordal of muscle reaction in the lateral position for a patient who has an anterior displacement of the mandible. With the recording paper stationary the patient opens and shuts his jaws once, the recording paper is displaced manually, and the exercise is repeated. The datum line 223 represents the mouth closed condition, the line 224 represents the jaw-opening movement and the line 225, the jaw-closing movement. At the point Y in the closing movement a premature contact is struck so that the mandible is displaced anteriorally from the maximum tooth position. The line Y-Z represents a slide of the mandible into the maximum tooth position.
FIGS. 13A and 13B represent the recordal of muscle reaction in the same patient as used in FIG. 12. In this case the patient opens and shuts his mouth rhythmically and the recording paper is moved, first in direction A and then in direction B, at a constant velocity. The lines 226 represent a jaw-opening movement, the lines 227 represent a jaw-closing movement, and the line portions 228 represent the mandible anterior displacement. The degree of anterior mandible displacement is assessed by computing the average length of the horizontal component of the line portions 228 in FIGS. 13A and 138. Such length also reflects the time duration for the jaws to achieve the maximum tooth position after a premature contact at point Y (FIG. 12) has been made.
I. In an apparatus for recording oral proprioception, a support frame, a substantially horizontal mounting arm connected to said support frame, a guide frame secured to said mounting arm and extending upwardly therefrom, feeding means mounted on said motFtirTg arm for moving a strip of flexible sheet recording material in a horizontal direction across and in sliding contact with said guide frame, reversible drive means for said feeding means, a recording stylus pivotally secured to said mounting arm and extending toward said recording strip on the guide frame for marking contact therewith, adjustable support means secured to said support frame and adapted for maintaining the skull of a patient in position adjacent said mounting arm, and means adapted to connect the mandible of the patient with said recording stylus whereby movements of said mandible are recorded graphically on said recording strip.
2. An apparatus according to claim 1 in which said feeding means comprises a pair of upright shafts rotatably mounted in said mounting arm one at each end of said guide frame, a spool nonrotatably secured to each of said shafts and adapted for windingly receiving and end portion of said recording strip, each of said shafts having a downwardly projecting extension, a pulley secured to each of said extensions, and belt means drivingly connecting said pulleys with said drive means.
3. An apparatus according to claim 2 in which said drive means comprises two electric motors mounted above each other in said mounting arm and each having a rotor, a common drive shaft interconnecting said rotors, a gearbox, said common drive shaft constituting the input shaft of said gearbox, an output shaft in said gear box, and a pair of drive pulleys mounted on said output shaft for cooperation with said belt means, one of said electric motors being adapted upon energization to efiect rotation of said common drive shaft in one direction and the other electric motor being adapted u n energization to effect rotation of said common drive sha t in the opposite direction, one of said drive pulleys being mounted on said output shaft by means of a first one-way necdle bearing which transmits drive to one of said drive pulleys upon energization one of said motors, and the other drive pulley being mounted on said output shaft by means of a second one-way needle bearing which transmits drive to the other drive pulley upon energization of the other motor.
4. An apparatus according to claim I including removable plastic covers enclosing said mounting arm, one of said covers being provided with a window in front of said guide frame, and each of said spools being provided with a circumferential flange a portion of which projects through a slot in the cover to permit manual rotation of the spool.