Increased Handpiece Speeds without Air Coolant: Aerosols and Thermal Impact

Abstract

This study assessed the impact of increased speed of high-speed contra-angle handpieces (HSCAHs) on the aerosolization of a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) surrogate virus and any concomitant thermal impact on dental pulp. A bacteriophage phantom-head model was used for bioaerosol detection. Crown preparations were performed with an NSK Z95L Contra-Angle 1:5 (HSCAH-A) and a Bien Air Contra-Angle 1:5 Nova Micro Series (HSCAH-B) at speeds of 60,000, 100,000, and 200,000 revolutions per minute (rpm), with no air coolant. Bioaerosol dispersal was measured with Φ6-bacteriophage settle plates, air sampling, and particle counters. Heating of the internal walls of the pulp chambers during crown preparation was assessed with an infrared camera with HSCAH-A and HSCAH-B at 200,000 rpm (water flows ≈15 mL min−1 and ≈30 mL min−1) and an air-turbine control (≈23.5 mL min−1) and correlated with remaining tissue thickness measurements. Minimal bacteriophage was detected on settle or air samples with no notable differences observed between handpieces or speeds ( P > 0.05). At all speeds, maximum settled aerosol and average air detection was 1.00 plaque-forming units (pfu) and 0.08 pfu/m3, respectively. Irrespective of water flow rate or handpiece, both maximum temperature (41.5°C) and temperature difference (5.5°C) thresholds for pulpal health were exceeded more frequently with reduced tissue thickness. Moderate and strong negative correlations were observed based on Pearson’s correlation coefficient, between remaining dentine thickness and either differential ( r = −0.588) or maximum temperature ( r = −0.629) measurements, respectively. Overall, HSCAH-B generated more thermal energy and exceeded more temperature thresholds compared to HSCAH-A. HSCAHs without air coolant operating at speeds of 200,000 rpm did not increase bioaerosolization in the dental surgery. Thermal risk is variable, dependent on handpiece design and remaining dentine thickness.

High-volume evacuation mitigates viral aerosol spread in dental procedures

“…We also conclude that the use of a high-speed dental handpiece is safer in terms of aerosol production and virus spread than the air turbine handpiece. Moreover, it can be used as a substitute for the air turbine handpiece during a pandemic or with infectious patients, as has been shown before 17 . This is especially important if a rubber dam or HVE cannot be used.…”

“…Previous studies examining the spread of virus-containing aerosols in dental procedures have focused on drill-type instruments 16 , 17 and ultrasonic scalers 18 , 19 . The present study provides data on virus-containing aerosol generation of additional common dental instruments and compares them in the same experimental setup.…”

Evaluation of aerosols in a simulated orthodontic debanding procedure

“…We assumed that the background concentration was the same across the face shield. Previous studies that have analyzed aerosolized virus from dental procedures has also successfully been completed in a clinic setting and not a laboratory setting 34,49 .…”

Safe use of PHI6 IN the experimental studies

“…Bacteriophages are commonly used as surrogates due to the detailed knowledge regarding their structure and host. Phi6, the bacteriophage used in this study, is an enveloped bacterial virus that is not infectious to humans, animals or plants and it has earlier been used as a surrogate to study coronaviruses, mainly in surface and disinfection testing [ [17] , [18] , [19] , [20] ], but recently also in aerosolized form [ 21 , 22 ]. Phi6 share a common virion architecture (two inner icosahedral shells and an outer lipid envelope with spikes) and a diameter of approximately 80 nm with SARS-CoV-2 [ 23 ].…”