NOVUS™ Denture Liner
An Innovative Use of Polyphosphazene in Dentistry
By Lawrence Gettleman, DMD, MSD
Prior to the use of acrylic denture bases in the 1930s, complete dentures were made of vulcanized natural rubber and were somewhat resilient during chewing. Acrylics are much harder and inflexible, making dentures more difficult to wear, pinching the delicate tissues of the mouth between hard acrylic resin and the underlying residual bone. A number of resilient lining materials have been used against acrylic denture bases, but each has some drawbacks. Phthalate- or alcohol-plasticized acrylics bond well to the denture but harden in days or weeks because they lose plasticity. On the other hand, silicone rubbers remain resilient but do not bond as well, have a low mechanical storage modulus, and in many patients, grow fungus within pores in the bulk material, after antifungal agents have leached away. Polyurethane or vinyl polymers require more complex processing conditions, special equipment, have higher hardness, absorb environmental colorants, and also promote fungal growth.
The National Institute of Dental and Craniofacial Research listed the development of improved resilient lining materials as a goal for many years, and supported the creation of Novus at Gulf South Research Institute in New Orleans. It was determined that polyphosphazene (a semi-organic polymer) would be a good candidate as a resilient soft liner for dentures. Polyphosphazene was found to be nearly ideal due to its biocompatibility, energy absorption, acceptance of fillers and pigments, compatibility with an interpenetrating network of di- and tri-functional cross-linking acrylic monomers, and its ability to be compounded at various levels of hardness. The one-part material is designed to be cured without mixing at temperatures common to a dental laboratory, such as compression at 20.7 MPa (3000 psi) and heating up to boiling water temperature.
Unlike other resilient denture liners, Novus does not harden like plasticized acrylics and needs no periodic surface coating to restrict the migration of toxic plasticizers. It is passive to fungus overgrowth, requiring no periodic antimicrobial treatments, unlike silicone and urethane materials. Novus bonds well to acrylic denture bases without special adhesives, and it is surprisingly easy to grind, adjust, and polish with most rotary instruments.
The Novus laboratory-cured complete denture liner is shock-absorbent during chewing, offering more patient comfort with fewer adjustments and is resistant to surface and subsurface fungal growth so that there is no fouling, odor, or stain. The material is moldable around overdenture abutments or implant heads and bars to provide denture retention, stability, and support, and allows denture movement toward the abutments and tissues. Novus has low surface tension with excellent wetting and offers permanent softness, with a Shore A durometer between 35 and 45 and no plasticizers to leach out. It uses standard dental laboratory compression-molding processing steps, and the single-component paste has an unlimited shelf life, if refrigerated.
Lawrence Gettleman, DMD, MSD, is a professor of Prosthodontics and Biomaterial at the University of Louisville’s School of Dentistry in Louisville, Kentucky.
The preceding material was provided by the manufacturer. The statements and opin- ions contained therein are solely those of the manufacturer and not of the editors, publisher, or the Editorial Board of Inside Dental Technology.