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

Model Number Z95L

Device Problem Overheating of Device (1437)

Patient Problem Burn(s) (1757)

Event Date 03/16/2024

Event Type  Injury  

Event Description

On march 19, 2024, a nsk z95l handpiece was returned from a distributor 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 dental office for further information about the event including information about the patient.The details are as follows: the event occurred on march 16, 2024.The dentist was performing a caries removal for #4, #5 and #6 teeth of the patient's upper jaw using the z95l handpiece (serial no.(b)(6)).The patient was under anesthesia.During the procedure, the dentist found a whitish burn injury in the patient's oral cavity.The dentist applied an oral ointment to the burn injury.The dentist has had a follow up with the patient and applied an ointment to the injury.The patient is reported to be healing normally with no additional medical treatment necessary.

Manufacturer Narrative

The dentist refused to provide information about the patient's age, gender, and weight.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 (b)(6).There were no problems observed during manufacturing or testing noted in the dhr.Were also no repair history records since the device was shipped.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 (200,000min-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 200,000min-1 (motor revolution 40,000min-1).Nakanishi observed an abnormal temperature rise at test points (1) and (2) a few seconds into the test.Temperature measurements about 17 seconds after the start of the test were as follows: test point (1): 88.5 degrees c.Test point (2): 110.0 degrees c.Test point (3): 32.4 degrees c.Test point (4): 30.1 degrees c.The increase in temperature was so sudden that the test was concluded about 17 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 drive shaft, dog clutch, and headcap were soiled and discolored.B) nakanishi took photographs of all the disassembled parts and kept them in the investigation report no.(b)(4).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 ball bearings.B) nakanishi also considers the possibility from many years of experience, that the cause of the broken bearing retainers 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.

• 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
• Manufacturer (Section G): NAKANISHI INC.; 700 shimohinata; kanuma-shi, tochigi-ken 322-8 666; JA 322-8666
• Manufacturer Contact: sean kaufman ; 1800 global parkway; hoffman estates, IL 60192 ; 2245128921
• MDR Report Key: 19068385
• MDR Text Key: 339672649
• Report Number: 9611253-2024-00020
• Device Sequence Number: 1
• Product Code: EGS
• Combination Product (y/n): N
• Reporter Country Code: JA
• PMA/PMN Number: K972569
• Number of Events Reported: 1
• Summary Report (Y/N): N
• Report Source: Manufacturer
• Source Type: Foreign,Distributor
• Reporter Occupation: Non-Healthcare Professional
• Type of Report: Initial
• Report Date: 04/09/2024

1 Device was Involved in the Event

1 Patient was Involved in the Event

• Date FDA Received: 04/08/2024
• 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: 03/22/2024
• Date Manufacturer Received: 03/19/2024
• Was Device Evaluated by Manufacturer?: Yes
• Date Device Manufactured: 06/08/2018
• Is the Device Single Use?: No
• Is This a Reprocessed and Reused Single-Use Device?: No
• Type of Device Usage: Reuse
• Patient Sequence Number: 1
• Patient Outcome(s): Other
• Patient Sex: Female
• Patient Ethnicity: Non Hispanic
• Patient Race: Asian