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

Model Number Z95L

Device Problem Overheating of Device (1437)

Patient Problems Burn(s) (1757); Pain (1994); Superficial (First Degree) Burn (2685)

Event Date 02/10/2021

Event Type  Injury  

Manufacturer Narrative

The dentist refused to provide any information about the patient.

Event Description

On (b)(6), 2021, nakanishi received a phone call from a dental office about an nsk handpiece overheating.Upon receipt of the information, nakanishi visited the dental office for further information about the event.The details nakanishi obtained from the visit are as follows: the event occurred around (b)(6), 2021.(the exact date is unknown.) the dentist was removing a crown for root separation during the tooth extraction procedure using the z95l (serial no.(b)(4) or z85l handpiece (serial no.(b)(4).The patient was under anesthesia.During the procedure, the device overheated and burned the patient, however neither the dentist nor the patient noticed the injury.A few days later, when a follow-up was conducted with the patient, the patient reported pain in the buccal mucous membrane.The dentist was made aware of the burn injury.The dentist could not identify which one of the two devices caused the above event.Therefore, nakanishi is submitting two separate mdrs for this event based on the information from the dentist.This mdr is regarding the z95l handpiece with the serial number (b)(4).

Manufacturer Narrative

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.(b)(4)].These activities are described in more detail below.Methodology used: a) nakanishi examined the device history record and the repair history for the subject z95l device [serial number (b)(6)].There were no problems observed during the manufacturing or testing noted in the dhr.The repair history showed 2 service records (may 2018 and december 2018) since the device was shipped.According to the service records, after repairing the handpiece (replacement of cartridge, drive shaft, and dog clutch for both of the repairs), 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 40,000 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.B.3) 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 into the test.Temperature measurements about 10 seconds after the start of the test were as follows: - test point (1): 68.2 degrees c; - test point (2): 99.7 degrees c; - test point (3): 32.0 degrees c; - test point (4): 32.7 degrees c.The increase in temperature was so sudden that the test was concluded about 10 seconds into the planned 5-minute 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 ball bearing on the rear side of the cartridge was broken.- the gear was damaged, discolored, and soiled.B) nakanishi took photographs of all the disassembled parts and kept them in investigation report #(b)(4).Conclusions reached based on the investigation and analysis results: a) nakanishi identified that the cause of the overheating of the returned device was frictional resistance generated by contact between the ball bearing part and the outer race (bearing outer metal part), which was caused by the broken ball bearing.B) nakanishi considers the possibility from many years of experience that the cause of the broken ball bearing was the ingress of undesirable materials into the bearing.C) a lack of maintenance caused the accumulation of debris on the internal parts, which caused debris ingress into the ball bearing during rotation.This contributed to the handpiece overheating.D) nakanishi took the following actions in order to prevent a recurrence of the handpiece overheating.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.

• 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: 11449368
• MDR Text Key: 241785326
• Report Number: 9611253-2021-00016
• Device Sequence Number: 1
• Product Code: EGS
• Combination Product (y/n): N
• PMA/PMN Number: K972569
• Number of Events Reported: 1
• Summary Report (Y/N): N
• Report Source: Manufacturer
• Source Type: foreign,other
• Type of Report: Initial,Followup
• Report Date: 04/07/2021

1 Device was Involved in the Event

1 Patient was Involved in the Event

• Date FDA Received: 03/09/2021
• Is this an Adverse Event Report?: Yes
• Is this a Product Problem Report?: Yes
• Device Operator: Health Professional
• Device Model Number: Z95L
• Device Catalogue Number: C1034
• Was Device Available for Evaluation?: Device Returned to Manufacturer
• Date Returned to Manufacturer: 02/19/2021
• Date Manufacturer Received: 03/12/2021
• Is This a Reprocessed and Reused Single-Use Device?: No
• Patient Sequence Number: 1
• Patient Outcome(s): Other