BEUDAMED
    FDA Adverse Event Injury Summary report: N

    NSK

    MDR report key: 8904999 · Received August 19, 2019

    Report

    Report Number
    9611253-2019-00040
    Event Type
    Injury
    Date Received
    August 19, 2019
    Date of Event
    July 20, 2019
    Report Date
    August 19, 2019
    Manufacturer
    NAKANISHI INC.
    Product Code
    EGS
    PMA / PMN Number
    K972569
    Adverse Event
    Yes
    Product Problem
    Yes
    Report Source
    Manufacturer report
    Reporter Location
    JA
    Reporter Occupation
    003

    Narratives

    Additional Manufacturer Narrative · 1

    UPON RECEIVING THE DEVICE INVOLVED IN THE MDR EVENT FROM THE DEALER, NAKANISHI CONDUCTED A FAILURE ANALYSIS OF THE RETURNED DEVICE THAT INCLUDED MEASURING THE OPERATING TEMPERATURE OF THE DEVICE [C190729-05]. THESE ACTIVITIES ARE DESCRIBED IN MORE DETAIL BELOW. METHODOLOGY USED: NAKANISHI EXAMINED THE DEVICE HISTORY RECORD AND THE REPAIR HISTORY FOR THE SUBJECT Z85L DEVICE [SERIAL NUMBER (B)(4)]. THERE WERE NO PROBLEMS OBSERVED DURING MANUFACTURING OR TESTING NOTED IN THE DHR. THERE WERE ALSO NO REPAIR HISTORY RECORDS SINCE THE DEVICE WAS SHIPPED. NAKANISHI CONDUCTED TEMPERATURE TESTING OF THE RETURNED DEVICE IN THE FOLLOWING MANNER: TEMPERATURE SENSORS WERE ATTACHED TO THE EXTERIOR OF THE DEVICE AT VARIOUS TEST POINTS. THIS INCLUDED THE POINT MOST PROXIMAL TO THE PATIENT (TESTING POINT (1)) AND POINTS FURTHER TOWARD THE DISTAL END OF THE DEVICE (TESTING POINTS (2) THROUGH (4)). THE TEST SETUP WAS PREPARED TO TAKE TEMPERATURE MEASUREMENTS AT ALL POINTS SIMULTANEOUSLY, INCLUDING A REFERENCE MEASUREMENT AT AMBIENT ROOM TEMPERATURE. NAKANISHI ATTACHED A THERMOCOUPLE (SENSOR TO MEASURE TEMPERATURE) TO EACH OF THE TESTING POINTS. NAKANISHI ROTATED THE DEVICE'S MOTOR AT 40,000 MIN-1, WHICH IS THE MAXIMUM RPM FOR THE MOTOR THAT DRIVES THE HANDPIECE (200,000 MIN-1 FOR THE HANDPIECE), WITH WATER SPRAY, AND MEASURED THE EXOTHERMIC RESPONSE. NAKANISHI MEASURED THE TEMPERATURE RISE OF THE RETURNED HANDPIECE SET AT 200,000 MIN-1 (MOTOR REVOLUTION 40,000 MIN-1). NAKANISHI OBSERVED AN ABNORMAL TEMPERATURE RISE AT TEST POINTS (1) AND (2) A FEW SECONDS AFTER THE START. TEMPERATURE MEASUREMENTS 21 SECONDS AFTER THE START ARE AS FOLLOWS: TEST POINT (1): 66.4 DEGREES C. TEST POINT (2): 98.9 DEGREES C. TEST POINT (3): 48.2 DEGREES C. TEST POINT (4): 30.1 DEGREES C. THE RISE IN TEMPERATURE WAS SO SUDDEN THAT THE TEST WAS CONCLUDED 21 SECONDS INTO THE PLANNED 5-MINUTE EVALUATION PERIOD. IDENTIFICATION OF THE SPECIFIC FAILURE MODE(S) AND/OR MECHANISM(S) AND THE ASSOCIATED DEVICE COMPONENTS INVOLVED: NAKANISHI DISASSEMBLED THE HANDPIECE AND PERFORMED A VISUAL INSPECTION OF THE INSIDE PARTS. NAKANISHI OBSERVED THE FOLLOWING PHENOMENA: THE BEARING RETAINER (BALL RETAINING PART) ON THE REAR SIDE OF THE CARTRIDGE WAS BROKEN. THE ROTATION TRANSMITTING GEAR WAS ABRADED AND DEFORMED. NAKANISHI TOOK PHOTOGRAPHS OF ALL OF THE DISASSEMBLED PARTS AND KEPT THEM IN INVESTIGATION REPORT #(B)(4). CONCLUSIONS REACHED BASED ON THE INVESTIGATION AND ANALYSIS RESULTS: NAKANISHI IDENTIFIED THAT THE CAUSE OF THE OVERHEATING OF THE RETURNED DEVICE WAS ABNORMAL RESISTANCE DURING ROTATION CAUSED BY THE BROKEN BEARING RETAINER. NAKANISHI CONSIDERS THE POSSIBILITY FROM MANY YEARS OF EXPERIENCE THAT THE CAUSE OF THE BEARING RETAINER BEING BROKEN WAS THE INGRESS OF UNDESIRABLE MATERIALS INTO THE BEARING. A LACK OF MAINTENANCE CAUSES THE ACCUMULATION OF DEBRIS ON THE INSIDE PARTS, WHICH CAUSES DEBRIS INGRESS INTO THE BEARING DURING ROTATION. THIS CONTRIBUTES TO THE HANDPIECE OVERHEATING. IN ORDER TO PREVENT A RECURRENCE OF THE HANDPIECE OVERHEATING, NAKANISHI TOOK THE FOLLOWING ACTIONS: NAKANISHI REVIEWED THE OPERATION MANUAL AND RECONFIRMED THE CLARITY AND UNDERSTANDABILITY OF THE INSTRUCTIONS. NAKANISHI REPORTED THE ABOVE EVALUATION RESULTS TO THE DENTIST AND REMINDED THE DENTIST OF THE IMPORTANCE OF MAINTENANCE AND CHECKING OF THE HANDPIECE PRIOR TO USE TO PREVENT OVERHEATING, AS INSTRUCTED IN THE OPERATION MANUAL.

    Description of Event or Problem · 1

    ON JULY 29, 2019, AN NSK Z85L HANDPIECE WAS RETURNED FROM A DEALER TO NAKANISHI FOR REPAIR. THERE WAS A NOTE WITH THE DEVICE STATING THAT THE DEVICE HAD OVERHEATED AND BURNED A PATIENT. UPON RECEIPT OF THE INFORMATION, NAKANISHI MADE A PHONE CALL TO THE DENTIST FOR FURTHER INFORMATION ABOUT THE EVENT. THE DETAILS NAKANISHI OBTAINED FROM THE COMMUNICATION ARE AS FOLLOWS. THE EVENT OCCURRED AROUND (B)(6) 2019 (EXACT DATE IS UNKNOWN). THE DENTIST WAS PERFORMING A DENTAL PROCEDURE ON A TOOTH OF THE PATIENT'S UPPER RIGHT JAW USING THE Z85L HANDPIECE (SERIAL NO. (B)(4)). THE PATIENT WAS NOT UNDER ANESTHESIA. DURING THE PROCEDURE, THE PATIENT COMPLAINED ABOUT THE HANDPIECE FEELING TOO WARM. THE DENTIST FOUND A TWO OR THREE-MILLIMETER BROWNISH BURN INJURY ON THE PATIENT'S BUCCAL MUCOSA. THE DENTIST DID NOT PROVIDE THE PATIENT WITH ANY MEDICAL TREATMENT FOR THE BURN BECAUSE THE PATIENT SAID THAT IT WAS NOT NECESSARY.

    Devices

    Seq Brand Generic Product Code Manufacturer Model Lot UDI-DI
    700543 NSK HANDPIECE, CONTRA- AND RIGHT-ANGLE ATTACHMENT, DENTAL EGS NAKANISHI INC. Z85L

    Patients

    Seq Age Sex Outcome Treatment
    1 55 YR Other