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 05/26/2020

Event Type  Injury  

Manufacturer Narrative

The dentist refused to provide information about the patient's id, age, 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 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 an abnormal temperature rise at test points (1) and (2) a few seconds into the test.Temperature measurements 22 seconds after the start of the test were as follows: test point (1): 92.1 degrees c, test point (2): 120.3 degrees c, test point (3): 32.8 degrees c, test point (4): 32.8 degrees c.The rise in temperature was so sudden that the test was concluded 22 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: nakanishi disassembled the handpiece and performed a visual inspection of the internal parts.Nakanishi observed the following phenomena: the ball bearing on the rear side of the cartridge was broken.There was debris on the other parts.Nakanishi took photographs of all of the disassembled parts and kept them in investigation report # (b)(4).Conclusions reached based on the investigation and analysis results: nakanishi identified that the cause of the overheating of the returned device was abnormal resistance during rotation due to the broken bearing.Nakanishi considers the possibility from many years of experience that the cause of the broken bearing was the ingress of undesirable materials into the bearing.A lack of maintenance caused the accumulation of debris on the internal parts, which caused debris ingress into the bearing during rotation.This 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 the clarity and understandability of the instructions.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.

Event Description

On (b)(6) 2020, nakanishi received a phone call from a dealer that an nsk dental handpiece had overheated and burned a patient.Upon receipt of the information, nakanishi contacted the dental office to obtain detailed information and learned that the device had burned another patient on the same day.Nakanishi is submitting two separate mdrs for these two patients.The information nakanishi received from the dental office about the second patient is as follows.The event occurred on (b)(6) 2020.A dentist was performing a dental procedure on a patient using the z95l handpiece (serial no.(b)(4)).During the procedure, the handpiece head overheated and burned the patient.

• 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: 10160846
• MDR Text Key: 199987092
• Report Number: 9611253-2020-00025
• 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,other
• Reporter Occupation: Non-Healthcare Professional
• Type of Report: Initial
• Report Date: 06/17/2020

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: 06/03/2020
• Initial Date Manufacturer Received: 05/27/2020
• Initial Date FDA Received: 06/16/2020
• Was Device Evaluated by Manufacturer?: Yes
• Date Device Manufactured: 09/24/2012
• 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