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); Numbness (2415); Burn, Thermal (2530); Patient Problem/Medical Problem (2688); No Code Available (3191)

Event Date 06/27/2019

Event Type  Injury  

Manufacturer Narrative

According to the distributor, the dentist refused to provide the patient's weight.

Event Description

On july 23, 2019, nakanishi became aware of a handpiece overheating through a complaint input into the complaint database by a distributor ((b)(4)).Details are as follows: the event occurred on (b)(6) 2019.The dentist was performing a crown preparation for #19 of the patient's lower left jaw using the handpiece z95l (serial no.(b)(4)).During the procedure, the dentist observed tissue loosening from the patient cheek.After closer examination, the dentist found that the loose skin was the result of a burn approximately the size of a quarter.There was no blood from the injury.The dentist felt the head of the handpiece was extremely hot.The dentist followed up with the patient over the phone on the day when the event occurred, and the patient reported that they were feeling ok.A second follow-up call was made to the patient the week after the first call, and the patient reported that they were experiencing numbness around the burned area.On a third follow-up call made on (b)(6) 2019, the patient reported that they had removed a scab at the site of the burn, the injury was healing normally, and the numbness had subsided.

Manufacturer Narrative

Upon receiving the device involved in the mdr event from the distributor, nakanishi conducted a failure analysis of the returned device that included measuring the operating temperature of the device [(b)(6)].These activities are described in more detail below.Methodology used: a) nakanishi examined the device history record and the repair history for the subject z95l device [serial number (b)(6)].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.B) nakanishi conducted a visual inspection of the returned device and performed a simple movement test.There were no visible abnormalities, such as cracks or dents, on the outside of the handpiece.Nakanishi then set a test bur in the handpiece and rotated it by hand.Nakanishi observed that the bur did not rotate smoothly.C) nakanishi conducted temperature testing of the returned device in the following manner: c.1) 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.C.2) 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.C.3) 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 measurement 5 minutes after the start are as follows: - test point (1): 42.3 degrees c - test point (2): 48.8 degrees c - test point (3): 33.6 degrees c - test point (4): 28.5 degrees c identification of the specific failure mode(s) and/or mechanism(s) and the associated device components involved: a) nakanishi disassembled the handpiece and performed a visual inspection of the inside parts.Nakanishi observed abrasion of the rotation transmitting gear.B) 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: 1) nakanishi could not replicate the temperature rise at the time of the event; however, based on abnormality found in the inside parts observed in the visual inspection, as well as many years of experience, nakanishi identified that the cause of the overheating of the returned device was abnormal resistance during rotation caused by the abraded gear.2) a lack of maintenance causes abrasion of the inside parts, which contributes to the handpiece overheating.3) in order to prevent a recurrence of the handpiece overheating, nakanishi took the following actions: 3.1) nakanishi reviewed the operation manual and reconfirmed the clarity and understandability of the instructions.3.2) nakanishi reported the above evaluation results to nsk america and directed nsk america to remind the user of the importance of maintenance, as instructed in the operation manual.

Manufacturer Narrative

This supplemental report is sent as a correction because the initial report was inadvertently considered by fda to be a single mdr report.This supplement report clarifies that 1) the same event was initially reported separately by both the manufacturer and the initial importer and 2) the initial manufacturer report was therefore not intended as a single mdr report.The original report included on the front page both the manufacturer report number and the importer report number to cross-reference each report per "general instructions - for form fda 3500a medwatch (for mandatory reporting)" (form fda 3500a supplement (4/16) - form instructions).However, fda is in the process of updating the instructions to form 3500a to clarify that the cross-reference information should instead be placed in section h.10.This supplemental report now places the initial importer report number (1422375-2019-00014) in section h10 additional manufacturer narrative for cross-reference purposes, as requested by fda.

• 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: 8863421
• MDR Text Key: 153836249
• Report Number: 9611253-2019-00038
• 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: company representative
• Type of Report: Initial,Followup,Followup
• Report Date: 12/14/2020

1 Device was Involved in the Event

1 Patient was Involved in the Event

• Date FDA Received: 08/06/2019
• 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: 08/19/2019
• Date Manufacturer Received: 12/10/2020
• Is This a Reprocessed and Reused Single-Use Device?: No
• Patient Sequence Number: 1
• Patient Outcome(s): Other
• Patient Age: 57 YR