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); Burn, Thermal (2530); Patient Problem/Medical Problem (2688)

Event Date 07/27/2018

Event Type  Injury  

Manufacturer Narrative

The dentist refused to provide information about the patient's id.

Event Description

On august 7, 2018, an nsk handpiece z95l 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 dentist for further information about the event.The details nakanishi obtained from the communication are as follows.The event occurred on (b)(6) 2018.The dentist was removing a dental crown from the patient's upper right tooth #6 using the handpiece z95l (serial no.(b)(4)).The patient was not under anesthesia.During the procedure, the dentist became aware of a one-centimeter white burn injury on the patient's upper right lip.According to the dentist, there were no abnormalities in the handpiece observed prior to use.When the patient returned for a follow-up visit on (b)(6) 2018, the patient reported to the dentist that she had applied ointment to the burned area at her discretion.In the follow-up visit, the dentist confirmed the patient was healing normally.

Manufacturer Narrative

Upon receiving the device involved in the mdr event from a distributor, nakanishi conducted a failure analysis of the returned device that included measuring the operating temperature of the device [(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 number (b)(4)].There were no problems observed during the manufacturing or testing noted in the dhr.The repair history showed 1 service record (august 2015) since the device was shipped.According to the service record, after repairing the handpiece (replacement of cartridge, drive shaft and dog clutch), nakanishi performed all of the necessary operation checks and confirmed that all of the criteria were met.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 a 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 point (1) and (2) a few seconds after the start.The following are the maximum temperatures the test points reached in the 5 minutes evaluation period.Test point (1): 53.0 degrees c.Test point (2): 68.0 degrees c.Test point (3): 37.8 degrees c.Test point (4): 31.7 degrees c.Identification of the specific failure mode(s) and/or mechanism(s) and the associated device components involved: nakanishi disassembled the handpiece and performed a visual inspection of the inside parts.Nakanishi observed the following phenomena: the bearing retainer (ball retaining plastic part) on the cartridge's rear side was partially broken.There was debris (abrasive powders/foreign materials) on the other parts.Nakanishi took photographs of all of the disassembled parts and kept them in the investigation report # (b)(4).Conclusions reached based on the investigation and analysis results: nakanishi identified that the cause of overheating of the returned device was due to frictional resistance generated by contact between the ball bearing part and the outer race (bearing outer metal part), which was generated by centrifugal action during rotation due to the broken ball bearing part.Nakanishi considers the possibility from many years of experience that the cause of the ball bearing part being broken was the ingress of debris (abrasive powders/foreign materials) into the ball bearing that interfered with rotation, which lead to the breakage of the ball bearing part.A lack of maintenance causes the above situation, which will contribute 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.

• 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 75081 ; 9724809554
• MDR Report Key: 7813489
• MDR Text Key: 118153548
• Report Number: 9611253-2018-00036
• 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: distributor,foreign
• Reporter Occupation: Non-Healthcare Professional
• Type of Report: Initial,Followup
• Report Date: 09/25/2018

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: 08/07/2018
• Initial Date Manufacturer Received: 08/07/2018
• Initial Date FDA Received: 08/24/2018
• Supplement Dates Manufacturer Received: 09/03/2018
• Supplement Dates FDA Received: 09/25/2018
• Was Device Evaluated by Manufacturer?: Yes
• Date Device Manufactured: 12/18/2012
• 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
• Patient Age: 36 YR
• Patient Weight: 48