Prosthodontics, Special Patient Care, Maxillofacial Prosthetics, and Weintraub Center, UCLA School of Dentistry

Silicone Mask Frames

Our goal is to provide our healthcare colleagues with N95-like performance with readily available ASTM Level 3 surgical masks (L3SM).  Despite efforts to ramp up manufacturing, supply of N95 respirators remains severely limited. As COVID infection and hospitalization rates spike, N95 supply among LA county hospitals are on “yellow” alert, with enough N95 respirators for only 9-29 days of operation.   Although N95 respirators are the preferred respiratory protective device (RPD) for dental aerosol generating procedures, the supply chain for N95 is severely limited during global COVID-19 pandemic.  Compared to N95’s, L3SM’s are more readily available, and offer similar filtration (L3SM filter 98% of particles>0.1 micron vs N95 filter 95% of particles>0.3 microns).  L3SM also resist against pressurized splashes (160 mmHg), and offer more comfort for wearing and breathing.  However, L3SM lack adequate seal against the face, rendering their 98% filtration meaningless due to leakage from the peripheries.  Solutions involving rubber bands and pre-tied ear loops have been suggested, but these do not provide adequate seal according to NIOSH approved tests. Custom 3D printed mask frames created from 3D scanning human faces is a promising method for improving mask seals, but frames are relatively uncomfortable, bulky, and non-scalable due to slow print-speed.  Also, rigid frames lose their seals during speech and other common mouth motions.

To overcome these limitations, we created medical grade silicone mask frames that fit over L3SM to create tight seals.  As universal solutions, they can be manufactured in a high throughput manner to lower the cost to well below 10% of printed frames, and can be stock-piled to avoid wait time between scanning and printing.  Besides improving comfort, their high stretchability accommodate speech and face movements.  Level 3 surgical masks have been dismissed as N95 alternative despite providing good protection against viral pathogens (Seto et al 2003; Loeb et al 2009) and pressurized splashes, because surgical masks lack reliable seal on human faces against aerosol transport.  Indeed, the number of particles leaking through the face seal is often much higher than particles passing through the filter material (Grinshpun et al 2009).  Despite the face-seal leakage, surgical masks were found to be as effective as N95’s in reducing the risk of SARS infection among hospital frontline workers (Seto et al 2003).   The immediate objective of this project is to quantify the effectiveness of silicone mask frames by measuring fit factor, which measures total inward leakage at rest and during facial motions.  A minimum fit factor of 100 is considered passing for half face N95 respirators.

References

ASTM F2100-11 Standard, American Society for Testing and Materials

Coffey et al 1998, Am. Ind. Hyg. Assoc. J. 59:862–870

Grinshpun et al  2009;  J Occup Environ Hyg, 6:593–603

Food and Drug Administration (FDA): “Guidance for Industry and FDA Staff. Surgical Masks - Premarket Notification [510(k)] Submissions: Guidance for Industry and FDA.” Washington, D.C.

Loeb et al 2009;  J. Am. Med. Assoc. 302:1865–1871

OSHA 3352-02 2009: Assigned Protection Factors for the Revised Respiratory Protection Standard

Rengasamy et al. 2009,  J. Int. Soc. Res. Prot. 26:54–70

Rengasamy et al 2014a, J Occup Env Hyg, 11: 388–396

Rengasamy et al 2014b, Ann. Occup. Hyg., 58 (2): 206–216

Rengasamy et al 2018, J Occup Env Hyg, 15(8): 616–627  

Seto et al 2003; Lancet 361:1519–1520,

Zhuang et al 2003, AIHA Journal 64:730–738

Silicone mask frames team