Proceedings of International Conference on Mechatronics WM1-B-1Kumamoto Japan, 8-10 May 2007

Dental Patient Robotas a Mechanical Human Simulator

Hideaki Takanobul), Akito Omatal), Fumihiko Takahashi1), Keishi Yokota1), Kenji Suzuki1), HirofumiMiural), Mutsumi Madokoro2), Yoshikazu Miyazaki2), Koutarou Maki2)

1) Dept of Mechanical Systems EngineeringKogakuin University

1-24-2 Nishi-shinjuku, Shinjuku, Tokyo, Japantakanobu(4dieee. org

Abstract - The aim of this research is the development of apatient robot for use in actual clinical training. Electropneumatic regulators and electromagnetic valvesincorporated in the robot is operated by manipulating aircylinders. It is possible to conduct training assuming severalpatients enabling trainees to learn a flexible response under awide range of circumstances. A simple interface was used forease of operation. Further, a built-in sensor inside the oralcavity responds to the trainee's actions leading to a vomitingreflex and pain during drilling teeth. Attaching the painsensor to the body of test subjects, will also be useful fortraining social service workers during nursing careexaminations.

Keyword: Patient Robot, Dental, Phantom

I INTRODUCTION

Conventional robotics research in medicine is usuallyrelated to supporting surgical procedures and doctor'squestions to patients during interviews [1]. However, thereare not many examples on the development of patientrobots for supporting clinical training of medical staff suchas doctors and nurses. It is commonplace to use stationarymodels for therapeutic training in medicine. However,training based on the use of such models is inadequate dueto differences between the models and actual patients [2].Thus there are high expectations in the development ofanimated patient robots for use in medical training. Further,the development of simulators is being widely pursued inthe field of dental therapy training but there are noexamples of research on robots. We are developing patientrobots for dental therapy training. The robots are fitted withsensors that enable examination of the effects pain in theoral cavity resulting from drilling teeth and anestheticinjection.

II PRESENT STATUS OF DENTISTRY

A Dental school educationRecent dental school graduates of Japanese universities aresaid to lack clinical skills and experience in treating patients.The main reason is attributed to inadequate clinical training.Currently, so-called 'phantoms' (Fig. 1) consisting of asimple functional cephalic region and an arrangement of

2) Dept of OrthodonticsShowa University

2-1-1 Kitasennzoku, Otaku, Tokyo, Japan

teeth are used for clinical training but these models areconsiderably different than actual patients. Until recently,clinical training was carried out on consenting volunteerpatients. However, recent changes in ethical issues relatedto environmental studies, medicine and dentistry have madesuch clinical training difficult. Thus the potential danger ofdeclining clinical skills is a problem in dental therapytraining. Dental therapy skills often depend on thecompetence and ability of clinicians and it is necessary forthem to have extensive experience using methods andmodels that accurately reflect actual treatment proceduresand conditions. Further, it also important to have thecapability of being able to respond to a wide range ofcircumstances.

B Operating conditionsTo become a dentist, it is necessary to graduate from dentalschool by passing a national examination. This examinationis based on multiple choice (mark-sheet) questions. Thismethod is used to reduce the possibility of unfairexaminations that may result if tests were based oninterviews and monitoring clinical ability. However, asdescribed above, it can be said that in spite of the wellknown lack of skills of dental students, universities are stillproducing graduates based on knowledge instead of handson, clinical ability. It is known that there are manyaccidents in the first few years after graduating from dentalschool.

(a) FraUCLIC scenery (D) wrongFig. 1 Phantom for practical training

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(b) Head mechanism

(a) Whole viewFig. 2 Patient Robot

III SPECIFICATION OF ROBOT

A External structureThe patient robot has a height of 165cm. The skeleton ismade of metal and FRP is used for the skull (Fig. 2). Theteeth in the conventional model used for direct therapytraining, can be polished and can be easily replaced. Theartificial outer skin is made from a special vinyl chloridebased gum reproducing the form and sensation of actualskin. The robot has a total of 36 degrees of freedom (DOF),with patient movements being achieved by low pressurecompressed air from an air cylinder. The other joints arepassive components (Fig. 3). Further, by implementingalmost human-like joints, it is possible to install the robot inan actual dental therapy unit[3].

B Operation methodA double action air cylinder is used in the drive sections.The main pressure is set at 0.7[MPa] and differentialpressure to 0.35[MPa]. Further, blinking of the eyes andtongue movement are achieved by a diaphragm with asimple structure. Due to the high density of mechanicalparts housed in the cephalic region, a wire is attachedinternally to the tongue which has 3-DOF, and the tongue ismoved by pulling on the wire using a diaphragm attached tothe body of the robot.

supervisor can grade the trainee's response in real time. Arecord of the type and timing of sudden movements andtheir evaluation is stored as a table. This table can be usedin conjunction with video footage of training sessions bytrainees to check their performance.

E Image recoginitionThe patient's eye is simulated by a small camera embeddedinto the patient robot's right eye. The camera has beensuccessfully used to recognize and track trainees andinstruments used during treatment. Imaging recognition isachieved using the RGB colors of video images where thecolor of the trainee's hair is electronically recognized andthe robot's line of sight shown to the trainee (Fig. 6). Bythis procedure, it is possible to carry out therapy underconditions where the trainee is being watched by the patient.

Joint DOF3DOF ActiveIDOF Active

El:3DOF Passive

El]: IDOF Passive

Fig. 3 DOF of Patient Robot

C Control systemThe patient robot is controlled by electro pneumaticregulators and electromagnetic valves using an air cylinder.Since it is possible to control the electro pneumaticregulator by minute changes in pressure, feedback from aPC enables fine movement of the neck and mouth. Anelectromagnetic valve is used for simple ON-OFFmovements such as arms and eye lids. Feedback control isachieved by setting a trimmer potentiometer in parts whereelectro pneumatic regulators are used (Fig. 4).

D InterfaceThe patient robot is controlled using a PC (Fig. 5). Positioncontrol of the patient robot's mouth and neck is achievedusing voice recognition software that reacts to the trainee'sinstructions. Further, the supervising doctor can manipulatethe interface to produce movements due to coughing andreactions to pain to which trainees as expected to respond.After the robot exhibits sudden movements, a five levelpoint rating is displayed above the interface and the

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I I ~~~~ValveAmp)lifier e

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A/D _

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potentio meter

Fig. 4 System chart

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(7M) (0 for 7MPa)_ _mg~Electro-pneumatic

regulator

(3.5NPa)

Air cylinder

Enamel

DentineDental pulp

Voice operation part ion part of happening

Fig. 5 Interface

Strain gage

Fig.6 Image recognition

Also, the voice recognition software is useful for creatingmore realistic conditions to simulate actual conversationwith patients during training [4]. Further, we alsoreproduced the psychologically induced backwardmovement of the head when endodontic instruments appearin the patient's line of sight. This was made possible byattaching a vinyl tape of a color not found in the treatmentroom and electronically recognizing and storing the coloredtape.

IV SYSTEM INSIDE THE ORAL CAVITY

A Structure ofthe teethStarting from the outer surface, human teeth consist ofenamel, dentine and pulp (Fig. 7). Enamel is the hardestouter surface of teeth. It is colorless and semi-transparentwith a hardness equivalent to a Moha hardness of 6-7,which is comparable to that of quartz. Further, the thicknessof teeth depends on their type, with molar teeth beingtypically 1.1 1.3 [mm]. Dentine is covered with cement andproduces the shape of teeth with the pulp inside. Further,dental tubules are 2-3 [rtm] diameters pipes, and are slightlyharder than bones but have elasticity and are flexible. Thepulp fills the pulp cavity at the center of teeth and serves toproduce dentine and supply it nutrition; repair the dentine;protect it against bacterial infection; and transmit sensoryperception.

B Drilling teethDrilling enamel does not produce pain but pain does arisewhen the air turbine reaches the pulp. The body's tissuefluids circulate inside the dental tubule and intersect with

Fig. 8 Installation of tooth sensor (bottom view)

the tooth pulp. During drilling, fluctuations arise in thetissue fluid of the pulp tubule which stimulate nerve endsand ultimately leads to the sensation of pain. The pain dueto tooth decay is the same. The sensation of pain is feltwhen cold and hot substances are consumed, where tissuefluids in the tubules move and stimulate nerve ends due totemperature related expansion and contraction of fluids inthe tubules. That is, pain is felt when the dentine is drilledand the level of pain increases for prolonged drilling due toheat generated by friction. Further, acute pain is felt ifdrilling is continued into the pulp.

C Pain sensorfor drilling and grinding ofteethPain sensing is achieved by monitoring the load of drillingduring surgery by a sensor embedded in one of the 2ndmolar teeth on the left hand side. The sensor consists of astrain gauge sandwiched in gum, which is attached to theteeth arrangement model (Fig. 8). In this way, when thespring is compressed under the action of a load, a screw ispushed and the strain gauge sandwiched in the gum is bent(Fig.9). During this procedure, the voltage of the straingauge is recorded which is a measure of the load acting onthe tooth.

D Effusion ofbleedingFor dental students and trainees, the effusion of blood isone of several unexpected situations. Thus, in order to trainstudents to react calmly to unexpected bleeding duringsurgery, the patient robot is designed to reproduce theeffusion of blood. The main locations for bleeding in theoral cavity are regions inside of both cheeks and areasranging from the surface to below the tongue.

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between two silicone resin plates. This structure is only amere 0.4[mm] thick, and suitable for fitting into the oralcavity. Fig. 10 shows a structure that has been damaged byan air turbine.

E SalivaThe ease of performing dental surgery is affected by theamount of saliva. In particular, it is desirable that thesurface of teeth be dry when inserting fillings. If the volumeof saliva is large then the moist surface hinders adhesion ofthe fillings. Thus we have fitted a saliva mechanism to thepatient robot. Since 2/3 of saliva secretion is exuded fromthe parotid gland, the saliva is produced from the parotidgland of the patient robot. The tube from an externallyconnected air pump is placed into a water tank, an air pumpis used to push into the tube which flows out at the locationof the parotid gland inside the oral cavity. The saliva flowvolume for a patient at rest is 0.3 [ml/min]. Externalstimulation results in this volume increasing to between1.0-1.7[mllmin]. The patient robot is able to produce 7.7[ml/min], which reproduces the saliva flow patientsundergoing surgical procedures.

Strain gage_

Rubber Screw

Fig. 9 Mechanism of tooth sensor

V EXPERIMENTAL

A MethodThe performance of the patient robot was evaluated by 32members of Showa University (two clinical interns, 29students in the 5th year who had completed basic clinicaltraining using phantom heads; and one veteran doctor). Theexperiments were conducted using the functions availableat the present time and involved cavity preparation anddrilling of the 2nd molar on the left side of the jaw, that is,drilling of back molars. The experiments were conducted ingroups consisting of a trainee and two assistants. Thesupervisor evaluated the performance of the students bygiving instructions to the patient robot via the interface ofthe PC (Fig. 11). The view from the camera embedded inthe patient robot is shown in Fig. 12.

Fig. 10 Bleeding results

Fig. 11 Practice scenery that uses Patient RobotThe main reason for bleeding in these regions is due toaccidental contact of the air turbine with the cheeks ortongue during surgery of the 2nd molar, when patients areprone to move their tongue. For these reasons, the patientrobot is also designed so that bleeding results under theabove conditions from both cheeks and the tongue regionsas described. This is implemented as a three layeredstructure, consisting of red pigmentation sandwiched

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effusion ofbleedimg

useful

useless

0 20 40 60 80 100

[%]

B Experimental resultsFig. 13 shows a selection of the results of a questionnairefollowing the training.

Which components of the robot were well reproduced?-movement of the eyes, mouth and head and hardness ofthe lips.

-unexpected movements (neck, vomiting, sudden closureof the jaw)

-respiration, the act of swallowing, raising ofhand-the slow closure ofthe mouth during treatment

What components of the robot were not well reproduced?-The opening of the mouth was too small and the tonguemovement insufficient.

-the lips and buccal mucous membrane were too tight.The angle of the mouth too rigid.-It felt as though it would tear if pulled.-the pharynx was too deep inside the oral cavity-respiration movement was too large

What are the effective features ofthe patient robot?-Reproduction of the movement as found in actualpatients during surgery was instructive for learningabout the difficulties of treatment.

-Treatment was difficult due to hard lips. Unexpectedmovements were realistic.

-Different to conventional machines thus enablinginteractive learning.

-Voice recognition enabled students to respondindividually.

-The importance of talking became apparent.-A certain degree of tension was generated duringtraining.

What aspects were ineffective?-Cavity formation would become difficult to understand ifthe robot were to be used from the beginning.

-The lips and jaw angle were rigid.-I do not think that patients move in the same way as therobot.

-The timing of the mouth closing was a little differentfrom reality.

-There were occasions when there was not a response tothe actions of the trainee.

-I did not understand the reasons for certain reactionsduring treatments.

useful

useless

0 10 20 30 40 50 60 70 80

[%]

the performance ofthe patient robot

very effective

effective

same

ineffective

absolutelymeffective

0 10 20 30 40 50 60 70

[%]

Fig. 13 Results of a questionnaire

Regarding comments about the ineffectiveness of reactionsduring treatment, we think that improving the performanceof the sensors will resolve these problems. Also, we haveconsulted with dentists and been told that the rigidity of themouth is acceptable as designed and hence this issue is nota problem. The major differences of opinion between theclinical residents and students were the volume of themouth opening and stiffness of the lips. Clinical residentshave actual experience of treating patients and are familiarwith the rigidity of the lips and volume of the mouthopening and used the robot as in usual procedures.However, in the case of students who have not operated on

actual patients yet, there were many instances of commentsabout the rigidity of the lips, volume of the mouth openingand signs of forcibly opening the mouth.This is because the phantom usually used by dentalstudents for training, has a larger sized mouth opening thanactual patients and thus they find it difficult to carry outprocedures using actual sized models. Also, since students

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saliva

performed surgery by looking only into the oral cavity, theydid not notice the patient robot raising its hand in responseto pain. This cannot be reproduced using a training phantomand is another useful feature of the patient robot.

VI CONCLUSIONS AND FUTURE

A patient robot with an oral cavity mimicking unexpectedmovement due to vomiting and pain and functions to inducebleeding and saliva flow was developed and used forclinical training. Trainee students and clinical residentswere asked to complete a questionnaire about the patientrobot. The results showed the patient robot to be effectiveas a means of training students to respond to unexpectedmovements during surgical procedures. In the future, weintend to incorporate additional sensors such as those usedin the oral cavity, to enhance reactions to due pain so thatclinical students could train by themselves withoutsupervision.

REFERENCES

[1] Taro Gotoh etc: "Analogue robot for medical training" The8th Annual Conference The Virtual Reality Society of Japan, 2003

[2] Buchanan JAUse of simulation technology in dental education J Dent Educ. 2001Nov; 65(1 1) * 1225-3 1.

[3] Akihisa Okino, Hideaki Takanobu, Atsuo Takanishi"Development of ajaw robot for study and education" , The 15th

Annual Conference of The Robotics Society of Japan, pp.707-708,1997

[4] Hideyuki Yanagiya, Hideaki Takanobu, Kenji Suzuki, HirofumiMiura, Atsuo Takanishi, Mutumi Madokoro, Koutaro Maki:" Dental Patient Robot" , The 45th Annual Conference of

research reports of a student member, pp.191-192, 2006.[5] Structure of the teeth

http://www.yic.ac/kenkou/kouzou.html

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