NSK
Report
- Report Number
- 9611253-2026-00003
- Event Type
- Injury
- Date Received
- January 15, 2026
- Date of Event
- December 12, 2025
- Report Date
- February 19, 2026
- Manufacturer
- NAKANISHI INC.
- Product Code
- EGS
- UDI-DI
- 04560264546769
- Adverse Event
- Yes
- Product Problem
- Yes
- Report Source
- Manufacturer report
- Reporter Location
- JA
- Reporter Occupation
- 003
Narratives
THIS EVENT OCCURRED IN JAPAN, BUT SIMILAR PRODUCTS ARE MARKETED IN THE US UNDER K182999. NAKANISHI IS STILL TRYING TO OBTAIN INFORMATION ABOUT THE EVENT, INCLUDING INFORMATION ABOUT THE PATIENT. UPON RECEIVING THE DEVICE INVOLVED IN THE MDR EVENT, NAKANISHI CONDUCTED A FAILURE ANALYSIS OF THE RETURNED DEVICE, WHICH INCLUDED MEASURING THE OPERATING TEMPERATURE OF THE DEVICE [REPORT NO. C251224-02]. THESE ACTIVITIES ARE DESCRIBED IN MORE DETAIL BELOW. METHODOLOGY USED: A) NAKANISHI EXAMINED THE DEVICE HISTORY RECORD AND THE REPAIR HISTORY FOR THE SUBJECT Z84L DEVICE [SERIAL NO. (B)(6)]. THERE WERE NO PROBLEMS OBSERVED DURING MANUFACTURING OR TESTING NOTED IN THE DHR. THE REPAIR HISTORY SHOWED ONE SERVICE RECORD SINCE THE DEVICE WAS SHIPPED. THE REPAIR DETAIL IS AS FOLLOWS: - (B)(6) 2023: THE CARTRIDGE, DRIVE SHAFT AND DOG CLUTCH WERE REPLACED. WITH RESPECT TO THE REPAIR ABOVE, THE SERVICE RECORD INDICATES THAT NAKANISHI PERFORMED ALL OF THE NECESSARY OPERATION CHECKS AND CONFIRMED THAT ALL OF THE CRITERIA WERE MET. B) NAKANISHI CONDUCTED TEMPERATURE TESTING OF THE RETURNED DEVICE IN THE FOLLOWING MANNER: B.1) 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. B.2) NAKANISHI ATTACHED A THERMOCOUPLE (SENSOR TO MEASURE TEMPERATURE) TO EACH OF THE TESTING POINTS. NAKANISHI ROTATED THE DEVICE'S MOTOR AT 40,000MIN-1, WHICH IS THE MAXIMUM RPM FOR THE MOTOR THAT DRIVES THE HANDPIECE (180,000MIN-1 FOR THE HANDPIECE), WITH WATER SPRAY, AND MEASURED THE EXOTHERMIC RESPONSE. B.3) NAKANISHI MEASURED THE TEMPERATURE RISE OF THE RETURNED HANDPIECE SET AT 180,000MIN-1 (MOTOR REVOLUTION 40,000MIN-1). NAKANISHI OBSERVED AN ABNORMAL TEMPERATURE RISE AT TEST POINTS (1) AND (2) 70 SECONDS INTO THE TEST. TEMPERATURE. MEASUREMENTS ABOUT 70 SECONDS AFTER THE START OF THE TEST WERE AS FOLLOWS: - TEST POINT (1): 53.0 DEGREES C. - TEST POINT (2): 83.7 DEGREES C. - TEST POINT (3): 35.6 DEGREES C. - TEST POINT (4): 29.2 DEGREES C. THE INCREASE IN TEMPERATURE WAS SO SUDDEN THAT THE TEST WAS CONCLUDED ABOUT 70 SECONDS INTO THE PLANNED 5-MIMUTE EVALUATION PERIOD. IDENTIFICATION OF THE SPECIFIC FAILURE MODE(S) AND/OR MECHANISM(S) OF THE ASSOCIATED DEVICE COMPONENTS WAS CONDUCTED AS FOLLOWS: A) NAKANISHI DISASSEMBLED THE HANDPIECE AND PERFORMED A VISUAL INSPECTION OF THE INTERNAL PARTS. NAKANISHI OBSERVED THE FOLLOWING: - THE BEARING RETAINER IN THE BALL BEARING ON THE REAR SIDE OF THE CARTRIDGE WAS BROKEN. - THE CARTRIDGE, GEARS AND INSIDE OF THE HEAD CAP WERE SOILED AND DISCOLORED. B) NAKANISHI TOOK PHOTOGRAPHS OF ALL THE DISASSEMBLED PARTS AND KEPT THEM IN THE INVESTIGATION REPORT NO. C251224-02. CONCLUSIONS REACHED BASED ON THE INVESTIGATION AND ANALYSIS RESULTS: A) NAKANISHI DETERMINED THAT THE CAUSE OF THE HANDPIECE OVERHEATING WAS FRICTIONAL RESISTANCE GENERATED BY CONTACT BETWEEN THE BALL BEARING RETAINER AND THE OUTER AND INNER RACES, AND BEARING BALLS, WHICH WAS CAUSED BY THE BROKEN BEARING RETAINER. B) NAKANISHI ALSO CONSIDERS THE POSSIBILITY FROM MANY YEARS OF EXPERIENCE, THAT THE CAUSE OF THE BROKEN BEARING RETAINER WAS THE INGRESS OF UNDESIRABLE MATERIALS INTO THE BEARING, WHICH INTERFERED WITH ROTATION. C) A LACK OF MAINTENANCE CAUSED THE ACCUMULATION OF DEBRIS ON THE INTERNAL PARTS, WHICH CONTRIBUTED TO THE HANDPIECE OVERHEATING. D) IN ORDER TO PREVENT A RECURRENCE OF THE HANDPIECE OVERHEATING, NAKANISHI TOOK THE FOLLOWING ACTIONS: D.1) NAKANISHI REVIEWED THE OPERATION MANUAL AND RECONFIRMED THE CLARITY AND UNDERSTANDABILITY OF THE INSTRUCTIONS. D.2) 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.
THE DENTIST REFUSED TO PROVIDE ANY INFORMATION ABOUT THE PATIENT'S WEIGHT.
ON DECEMBER 23, 2025, NAKANISHI RECEIVED A PHONE CALL FROM A DEALER ABOUT AN NSK HANDPIECE OVERHEATING. UPON RECEIPT OF THE INFORMATION, NAKANISHI MADE A PHONE CALL TO THE DENTAL OFFICE FOR FURTHER INFORMATION ABOUT THE EVENT. THE DETAILS ARE AS FOLLOWS: - THE EVENT OCCURRED ON DECEMBER 17, 2025. - THE DENTIST WAS PERFORMING A DENTAL PROCEDURE USING THE Z84L HANDPIECE (SERIAL NO. (B)(6)). - DURING THE PROCEDURE, THE HANDPIECE OVERHEATED, AND THE PATIENT RECEIVED A BURN INJURY.
ON FEBRUARY 3, 2026, NAKANISHI RECEIVED FURTHER INFORMATION ON THE EVENT FROM THE DENTIST. THE EVENT OCCURRED ON (B)(6) 2025, NOT (B)(6) 2025. AT THE TIME OF THE EVENT, THE DENTIST WAS PERFORMING TOOTH PREPARATION ON #5 TOOTH OF THE PATIENT'S UPPER LEFT JAW. THE PATIENT WAS UNDER LOCAL ANESTHESIA. DURING THE PROCEDURE, THE PATIENT COMPLAINED OF PAIN, AND THE DENTIST OBSERVED THAT THE PATIENT RECEIVED A THERMAL BURN ON THE INNER CHEEK, APPROXIMATELY THE SIZE OF A LITTLE FINGER. THE DENTIST WASHED THE PATIENT'S INJURY. THE PATIENT IS REPORTED TO BE HEALED NORMALLY WITHOUT NEED FOR ANY FURTHER MEDICAL TREATMENT. ACCORDING TO THE DENTIST, THERE WERE NO ABNORMALITIES OBSERVED IN THE DEVICE PRIOR TO USE.
Devices
| Seq | Brand | Generic | Product Code | Manufacturer | Model | Lot | UDI-DI |
|---|---|---|---|---|---|---|---|
| 99858 | NSK | HANDPIECE, CONTRA- AND RIGHT-ANGLE ATTACHMENT, DENTAL | EGS | NAKANISHI INC. | Z84L | 04560264546769 |
Patients
| Seq | Age | Sex | Outcome | Treatment |
|---|---|---|---|---|
| 1 | 50 YR | Female | Other |