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On september 27, 2017, nakanishi received an e-mail from a distributor ((b)(4)) about a handpiece overheating.The details are as follows.The event occurred on (b)(6) 2018.The surgeon was extracting the patient's teeth using the sga-e2s handpiece (serial no.: (b)(4)).At the completion of the procedure, the surgeon removed the drapes and identified that the patient had sustained burn injuries to the patient's mouth.The surgeon identified that after several seconds, the end of the handpiece (the section which touches the patient's mouth) became incredibly hot when in use-to the point that it couldn't be touched even with a double-gloved hand.There were multiple injuries.Multiple small burns were present inside the mouth, and one burn located at the top left corner of the mouth was identified as a full thickness burn, which may result in long-term damage.The surgeon applied otocomb ointment to the affected area and followed up with the patient to explain what happened.
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On september 27, 2018 and october 25, 2018, nakanishi sent emails to the distributor for additional information about the patient.However, nakanishi received no reply from the distributor.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)(4)].These activities are described in more detail below.Methodology used: nakanishi examined the device history record and the repair history for the subject sga-e2s device [serial number (b)(4)].There were no problems observed during the manufacturing or testing noted in the dhr.There were also no repair history records since the device was shipped.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.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 (80,000 min-1 for the handpiece), with water spray, and measured the exothermic response.Nakanishi measured the temperature rise of the returned handpiece set at 80,000 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.Temperature measurements 36 seconds after the start are as follows: test point (1): 73.9 degrees c; test point (2): 82.3 degrees c ; test point (3): 26.2 degrees c; test point (4): 27.9 degrees c.The rise in temperature was so sudden that the test was concluded 36 seconds into the planned 5 minute evaluation period.Nakanishi cleaned the inside of the handpiece using nakanishi pana spray plus.Nakanishi observed debris being expelled from the head of the handpiece by using a white filter to catch anything that was expelled.After cleaning and lubricating the handpiece as defined in the operation manual, nakanishi measured the temperature of the handpiece.Even after cleaning, nakanishi observed a quick rise in temperature.Temperature measurements 51 seconds after the start are as follows: test point (1): 75.7 degrees c; test point (2): 70.9 degrees c; test point (3): 30.8 degrees c; test point (4): 29.8 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: there was a great amount of debris on the bearing incorporated in the test point (1).The bearing incorporated in the test point (2) was broken.There was debris and corrosion on the other parts.Nakanishi took photographs of all of the disassembled parts and kept them in the investigation report # (b)(4).Nakanishi then replaced the broken bearings with new bearings and measured the exothermic situation yet again.There was no abnormal rise in temperature during the 300-second-test period (see below).Nakanishi confirmed that the returned handpiece was operating as expected and within temperature specifications once the broken bearings had been replaced.Test point (1): 43.7 degrees c; test point (2): 36.3 degrees c; test point (3): 33.2 degrees c; test point (4): 32.2 degrees c.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 caused by the corroded/broken bearings due to the ingress of undesirable materials into the bearings.A lack of maintenance causes the accumulation of debris on the inside parts, which causes debris ingress into the bearing during rotation.This 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 confirmed the cautionary statements about overheating of the device in the manual.In spite of the fact that the cautionary statements were included in the operation manual, nakanishi updated the operation manual to provide detailed reprocessing methods.Nakanishi reported the above evaluation results to (b)(6) and directed (b)(6) to remind the user of the importance of maintenance, as instructed in the operation manual.
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