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

Model Number Z95L

Device Problems Overheating of Device (1437); Temperature Problem (3022)

Patient Problems Burn(s) (1757); Injury (2348); Patient Problem/Medical Problem (2688)

Event Date 07/01/2020

Event Type  Injury  

Manufacturer Narrative

The dentist refused to provide information about the patient's id and weight.Upon receiving the device involved in the mdr event, nakanishi conducted a failure analysis of the returned device that included measuring the operating temperature of the device [report no.(b)(4)].These activities are described in more detail below.Methodology used: nakanishi examined the device history record and the repair history for the subject z95l device [serial no.(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 a visual inspection of the returned device and observed oil oozing out of the handpiece head.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 rises in temperature at the testing points as shown below; however, the temperatures were not high enough to cause a burn injury.Temperature measurements 5 minutes into the test were as follows: test point (1): 41.5 degrees c.Test point (2): 45.8 degrees c.Test point (3): 32.3 degrees c.Test point (4): 32.6 degrees c.Identification of the specific failure mode(s) and/or mechanism(s) of the associated device components was conducted as follows: nakanishi disassembled the handpiece and performed a visual inspection of the internal parts.Nakanishi observed that the underdrive gear was slightly abraded.Nakanishi took photographs of all the disassembled parts and kept them in investigation report # (b)(4).Nakanishi then cleaned the inside of the handpiece using nakanishi pana spray plus and measured the exothermic situation yet again.There was no abnormal rise in temperature during the 300-second test period (see below).Nakanishi observed that the returned handpiece was operating within temperature specifications without showing abnormal temperatures in any of the 2 temperature measurements.Test point (1): 34.7 degrees c.Test point (2): 35.3 degrees c.Test point (3): 30.3 degrees c.Test point (4): 30.3 degrees c.Conclusions reached based on the investigation and analysis results: nakanishi could not identify the exact cause of overheating of the returned device because nakanishi was not able to replicate the temperature rise at the time of the event.The only abnormality nakanishi observed during the evaluation was abrasion of the underdrive gear during the visual inspection.Nakanishi did not identify the cause, but based on the findings in the visual inspection, as well as many years of experience, nakanishi considers the possibility that the cause of the handpiece overheating was abnormal resistance during rotation due to the abraded internal part caused by temporary ingress of foreign materials or residual lubricant into the handpiece.A lack of maintenance caused debris ingress into the underdrive gear, leading to the abrasion which contributed 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 clarity and understandability of the instructions.Nakanishi will report the above evaluation results to the dentist and remind the dentist of the importance of maintenance and checking of the handpiece prior to use to prevent overheating as instructed in the operation manual.

Event Description

On july 3, 2020, nakanishi received a phone call from a dealer about an nsk handpiece overheating.The information nakanishi obtained from the communication is as follows: the event occurred on (b)(6) 2020.The dentist was carrying out an abutment preparation for #4, #5, #6 and #7 of the patient's upper right jaw using the z95l handpiece (serial no.(b)(4)).When the procedure was completed, the dentist found a blister on the inside of the patient's cheek.The dentist broke the blister as a treatment for the burn injury.A follow-up with the patient is scheduled.

• 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: kenneth block ; 800 e campbell rd.; suite 202; richardson, tx ; 4809554
• MDR Report Key: 10337023
• MDR Text Key: 207911494
• Report Number: 9611253-2020-00032
• Device Sequence Number: 1
• Product Code: EGS
• Combination Product (y/n): N
• Reporter Country Code: JA
• PMA/PMN Number: K182999
• Number of Events Reported: 1
• Summary Report (Y/N): N
• Report Source: Manufacturer
• Source Type: foreign,other
• Reporter Occupation: Non-Healthcare Professional
• Type of Report: Initial
• Report Date: 07/29/2020

1 Device was Involved in the Event

1 Patient was Involved in the Event

• 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: 07/09/2020
• Initial Date Manufacturer Received: 07/03/2020
• Initial Date FDA Received: 07/29/2020
• Was Device Evaluated by Manufacturer?: Yes
• Date Device Manufactured: 12/03/2019
• 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 Age: 24 YR