MAUDE Adverse Event Report: NAKANISHI INC. NSK; HANDPIECE, CONTRA- AND RIGHT-ANGLE ATTACHMENT, DENTAL

Model Number Z85L

Device Problem Overheating of Device (1437)

Patient Problems Burn(s) (1757); Burn, Thermal (2530)

Event Date 01/29/2021

Event Type  Injury  

Event Description

On (b)(6) 2021, 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.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 on (b)(6) 2021.The dentist was extracting tooth #6 of the patient's lower right jaw using the handpiece z85l (serial no.(b)(4)).The patient was under anesthesia.During the procedure, the dentist observed a whitish burn injury approximately 1cm in diameter on the patient's buccal mucous membrane.The dentist determined that the injury was too minor to require any treatment.According to the dentist, the handpiece rotated slower than usual prior to use.

Manufacturer Narrative

Upon receiving the device involved in the mdr event from the distributor, nakanishi conducted a failure analysis of the returned device [report no.C210204-05].These activities are described in more detail below.Methodology used: a) nakanishi examined the device history record and the repair history for the subject z85l device [serial no.Abl10029].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.B) nakanishi set a test bur in the handpiece, connected the handpiece to the motor, and tried to rotate the motor.However, the handpiece was locked and the motor did not rotate at all.Therefore, nakanishi was not able to conduct temperature testing of the device.Identification of the specific failure mode(s) and/or mechanism(s) and the associated device components involved: a) nakanishi disassembled the handpiece and performed a visual inspection of the internal parts.Nakanishi observed the following: - the bearing on the rear side of the cartridge was broken.- the gear was damaged.B) nakanishi measured the size of the burs returned with the subject handpiece and found that the total length of the burs was larger than the specifications in the operation manual.The values nakanishi obtained in the measurement are as follows. - total length: 27.96mm (specification in operation manual: 21mm) - diameter of the shank: ?1.596mm (specification in operation manual: ?1.590-1.600mm) - length of the area where the bur is held in the handpiece: 16.50mm (specification in operation manual: 10mm) - maximum working diameter: ?1.48mm (specification in operation manual: ?2.0mm) - total length: 22.91mm (specification in operation manual: 21mm) - diameter of the shank: ?1.594mm (specification in operation manual: ?1.590-1.600mm) - length of the area where the bur is held the handpiece: 11.88mm (specification in operation manual: 10mm) - maximum working diameter: ?1.47mm (specification in operation manual: ?2.0mm) nakanishi observed evidence of the bur slipping in the chuck and fracture/discoloration of the bur.C) nakanishi took photographs of all the disassembled parts and kept them in investigation report #c210204-05.Conclusions reached based on the investigation and analysis results: a) nakanishi could not replicate the temperature increase from the event, but based on the findings in the visual inspection, as well as many years of experience, nakanishi identified that the cause of the handpiece overheating was frictional resistance generated by contact between the ball bearing part and the outer race (bearing outer metal part), which was generated by centrifugal action due to the broken ball bearing part.B) a lack of maintenance caused the accumulation of debris on the inside parts, which caused debris ingress into the bearing leading to the broken ball bearing.This contributed to the handpiece overheating.C) use of the out-of-specification bur increased the probability of the ball bearing breaking, which could also be the cause of the broken bearing which led 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 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, checking of the handpiece prior to use, and using the device (bur) as instructed in the operation manual.

• Brand Name: NSK
• Type of Device: HANDPIECE, CONTRA- AND RIGHT-ANGLE ATTACHMENT, DENTAL
• Manufacturer (Section D): NAKANISHI INC.; 700 shimohinata; kanuma-shi, tochigi-ken 322-8 666; JA 322-8666
• MDR Report Key: 11382679
• MDR Text Key: 242758989
• Report Number: 9611253-2021-00011
• Device Sequence Number: 1
• Product Code: EGS
• Combination Product (y/n): N
• PMA/PMN Number: K182999
• Number of Events Reported: 1
• Summary Report (Y/N): N
• Report Source: Manufacturer
• Source Type: foreign,other
• Type of Report: Initial,Followup
• Report Date: 04/05/2021

1 Device was Involved in the Event

1 Patient was Involved in the Event

• Date FDA Received: 02/25/2021
• Is this an Adverse Event Report?: Yes
• Is this a Product Problem Report?: Yes
• Device Operator: Health Professional
• Device Model Number: Z85L
• Device Catalogue Number: C1062
• Was Device Available for Evaluation?: Device Returned to Manufacturer
• Date Returned to Manufacturer: 02/04/2021
• Date Manufacturer Received: 03/09/2021
• Is This a Reprocessed and Reused Single-Use Device?: No
• Patient Sequence Number: 1
• Patient Outcome(s): Other
• Patient Age: 59 YR
• Patient Weight: 50