MAUDE Adverse Event Report: NAKANISHI INC. NSK; HANDPIECE, CONTRA- AND RIGHT-ANGLE ATTACHMENT, DENTAL

Model Number Z95L

Device Problem Overheating of Device (1437)

Patient Problems Burn(s) (1757); Pain (1994); Burn, Thermal (2530)

Event Date 01/04/2021

Event Type  Injury  

Manufacturer Narrative

The same adverse event in this report has been reported to the fda separately by the initial importer, nsk america corporation, under report number 1422375-2021-00005.

Event Description

On january 23, 2021, nakanishi became aware of a handpiece overheating through a complaint input into the complaint database by a distributor (nsk america).Details are as follows: - the event occurred on (b)(6) 2020.- a dentist was performing a crown preparation for #7 of the patient's teeth using the z95l handpiece (serial no.(b)(4)).- the patient was under local anesthesia.- during the procedure, the patient reported a sharp pain on their cheek.- the dentist observed a superficial burn injury to the left cheek, approximately 1cm in diameter.- the burn was immediately treated with a topical application of vitamin e oil, and the dentist determined that further medical attention was not necessary.

Manufacturer Narrative

Upon receiving the device involved in the mdr event from the distributor, nakanishi conducted a failure analysis of the returned device, which included measuring the operating temperature of the device [report no.C210123-02].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 no.(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 temperature testing of the returned device in the following manner: b.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.B.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.B.3) 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 68 seconds after the start of the test were as follows: - test point (1): 60.8 degrees c; - test point (2): 84.8 degrees c; - test point (3): 33.5 degrees c; - test point (4): 32.7 degrees c.The increase in temperature was so sudden that the test was concluded 68 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: a) nakanishi disassembled the handpiece and performed a visual inspection of the internal parts.Nakanishi observed the following: - the bearing retainer on the rear side of the cartridge was broken.- the internal parts were discolored and soiled.B) nakanishi took photographs of all the disassembled parts and kept them in investigation report #(b)(4).Conclusions reached based on the investigation and analysis results: a) nakanishi determined that the cause of the overheating of the returned device was abnormal resistance during rotation due to the broken bearing retainer.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.B) 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.C) in order to prevent a recurrence of the handpiece overheating, nakanishi took the following actions: c.1) nakanishi reviewed the operation manual and reconfirmed the clarity and understandability of the instructions.C.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.

• 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: 11326219
• MDR Text Key: 232329191
• Report Number: 9611253-2021-00008
• 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
• Report Date: 03/26/2021

1 Device was Involved in the Event

1 Patient was Involved in the Event

• Date FDA Received: 02/14/2021
• 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: 02/18/2021
• Date Manufacturer Received: 03/01/2021
• Is This a Reprocessed and Reused Single-Use Device?: No
• Patient Sequence Number: 1
• Patient Outcome(s): Other
• Patient Age: 61 YR
• Patient Weight: 79