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

Nakanishi did not receive any information about the patient.Nakanishi is scheduled to visit the dentist to obtain further information.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 43 seconds after the start of the test were as follows: test point (1): 63.9 degrees c.Test point (2): 90.4 degrees c.Test point (3): 31.0 degrees c.Test point (4): 30.2 degrees c.The rise in temperature was so sudden that the test was concluded 43 seconds into the planned 5-minutes 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 that the bearing on the rear side of the cartridge was broken.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 retainer 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 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 (b)(6) 2020, nakanishi received a phone call from a dealer that an nsk dental handpiece had overheated and burned two patients.Therefore, nakanishi is submitting two separate mdrs for the two patients.The information nakanishi received from the dealer about the first patient is as follows.The event occurred around (b)(6) 2020 (exact date is unknown).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.

Event Description

On july 1, 2020, nakanishi received detailed information on the event from the dentist.The event occurred on (b)(6) 2020.At the time of the event, the dentist was performing an infected root canal treatment after removal of the crown.The patient was not under anesthesia.When the procedure was completed, the patient reported that they had felt heat in the mouth during the procedure but hesitated to tell the dentist about it.The dentist found that a thumb-size mucous membrane was exfoliated from the patient's cheek.The dentist provided terramycin ointment and azunol gargle liquid to the patient.On june 19, 2020, a follow-up was conducted with the patient and the injury has healed normally.According to the dentist, there were no abnormalities observed in the device prior to use.

Manufacturer Narrative

The dentist refused to provide the patient id, weight, ethnicity, and race.

• 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: 10146880
• MDR Text Key: 202513014
• Report Number: 9611253-2020-00026
• 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: 07/22/2020

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: 06/01/2020
• Initial Date Manufacturer Received: 05/26/2020
• Initial Date FDA Received: 06/12/2020
• Supplement Dates Manufacturer Received: 07/01/2020
• Supplement Dates FDA Received: 07/21/2020
• Is This a Reprocessed and Reused Single-Use Device?: No
• Patient Sequence Number: 1
• Patient Outcome(s): Other
• Patient Age: 68 YR