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 02/21/2019

Event Type  Injury  

Manufacturer Narrative

Nakanishi is scheduled to visit the dentist to obtain further information about the event and patient.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 [(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 (october 2015) since the device was shipped.According to the service record, after repairing the handpiece (replacement of cartridge and headcap), 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 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 after the start.Temperature measurements 21 seconds after the start are as follows: test point (1): 61.1 degrees c; test point (2): 85.6 degrees c; test point (3): 35.7 degrees c; test point (4): 24.8 degrees c.The rise in temperature was so sudden that the test was concluded 21 seconds into the planned 5-minute evaluation period.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 that the ball retaining part of the ball bearing in the cartridge was broken.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 ingress of foreign materials into the ball bearing that interfered with rotation, which led to the breakage of the ball bearing part.A lack of maintenance causes the above situation, which contributes 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 is scheduled to visit the dental office to 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 february 26, 2019, nakanishi received a phone call from a dealer about a handpiece overheating.Details are as follows.The event occurred on (b)(6) 2019.A dentist was performing a dental procedure using the z95l handpiece (serial no.: (b)(4)).During the procedure, the handpiece head overheated and burned a patient.

Manufacturer Narrative

The dentist refused to provide the patient id and weight.

Event Description

On may 22, 2019, nakanishi obtained the following detailed information on the event.The procedure the dentist was performing at the time of the event was cutting tooth #4 of the patient's upper right jaw.The patient was not under local anesthesia.During the procedure, the patient suddenly complained about pain on the right side of the patient's lower lip.The dentist observed a burn on the right side of the patient's lower lip.The dentist cooled the burned area and disinfected the area with iodine solution.The patient has had a follow up visit with the dentist, and the injury is healing normally.The dentist determined no further medical attention was required for treatment.

• 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: 8441502
• MDR Text Key: 139679214
• Report Number: 9611253-2019-00016
• 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: 06/17/2019

1 Device was Involved in the Event

1 Patient was Involved in the Event

• Date FDA Received: 03/21/2019
• 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: 03/01/2019
• Date Manufacturer Received: 05/22/2019
• Is This a Reprocessed and Reused Single-Use Device?: No
• Patient Sequence Number: 1
• Patient Outcome(s): Other
• Patient Age: 9 YR