Application of a Long-Term Resilient Lining Material

INTRODUCTION
Edentulous patients may experience chronic pain and discomfort with denture wear, as they may have advanced residual resorbed ridges, severe undercuts, thin or sensitive mucosa, and/or areas of congenital or postoperative maxillofacial defect.^1-5 Avitaminosis,^6,7 debilitating disease, poor oral hygiene,^8-10 smoking,¹¹ or microbial involvement^6,12,13 may aggravate soreness and inflammation in the denture-bearing soft tissues. These adverse conditions make it difficult for patients to tolerate dentures, resulting in short-duration of wear and discontinuation of use.

Implants may improve the denture-bearing foundation’s capacity for denture retention, stability, and support of the prostheses, ultimately leading to improved patient comfort and compliance.^14-16 However, implant placement is not indicated in all patients due, at least in part, to limiting medical conditions, financial constraints, inadequate bone quantity and quality, and any unwillingness of the patient to undergo dental surgical procedures.

Advantages of Long-Term Resilient Denture Liners
Long-term resilient denture liners (LRDLs) improve comfort and retention of the prostheses through functional shock absorption, via maintenance of intimate contact with the underlying tissues.¹⁷ LRDLs may lower—and more evenly distribute—functional and parafunctional occlusal forces to the denture-bearing soft tissues.¹⁸ In turn, they may significantly improve masticatory efficiency¹⁹ and functional mandibular movement, decrease chewing time, and maximize occlusal force generation.^20,21 Use of LRDLs may also improve speech, increase retention and stability of the prostheses, reduce pain and soreness, and facilitate the positive psychological impact of comfort and long-term denture wear.^22-24

Figure 1. The patient’s vertical dimension of occlusion is recorded with a divider.	Figure 2. An interocclusal record is made with a vinyl polysiloxane (VPS) registration material.

Figure 3. Applying the dye solution (left) helps to ensure even and uniform reduction (right).

LRDL Categories and Indications
The 2 major categories of available LRDLs are the acrylic-based LRDL (AB-LRDL) and silicone-based LRDL (SB-LRDL); each may be a chemically activated or heat-activated material.⁵ AB-LRDLs chemically bond to polymethyl methacrylate resin, permitting incremental application and allowing control of material viscosity to facilitate the needs of varying clinical conditions. However, the high sorption and solubility rate of AB-LRDLs decrease clinical longevity and color stability^25-27 while increasing the potential for bacterial biofilm formation.⁵ Therefore, most AB-LRDLs are applied as interim liners for a maximum of 2 to 4 weeks. Despite their superior elasticity, AB-LRDLs harden more readily compared to SB-LRDLs.

SB-LRDLs are more desirable for long-term usage due to their increased clinical longevity, increased color stability, decreased sorption and solubility rate, and decreased biofilm formation compared to AB-LRDLs.⁵ However, if used for more than 6 to 12 months, they appear to be susceptible to fungal colonization,²⁸ leading to increased hardness and solubility, decreased stress relaxation, and eventual failure.²⁹ Their adhesive properties also decrease with time, leading to bond failure between the liner and denture base acrylic resin.^29-32

Figure 4. A previously formed interocclusal record positioned against the occlusal surface of the denture (top left). A rigid viscosity VPS impression material is injected in 4 locations (top right). The denture is then placed in the patient’s mouth to form “stops” (bottom).	Figure 5. Evaluation of stops (top left). Areas of excessive tissue contact are marked with an indelible marker (top right). The stops are then trimmed with an acrylic resin bur to reduce areas of excessive tissue contact (bottom).

Figure 7. Denture borders are relieved by 1.0 to 2.0 mm prior to making the definitive impressions.	Figure 8. Extra-light viscosity VPS impression material is loaded on the intaglio surface of the denture.

Phosphazene-Based Lining Material Reintroduced
A phosphazene-based lining material (Novus resilient liner [White Square Chemical]) was recently reintroduced to the market. This material was successfully introduced as a dental lining material in 1989; however, its production was discontinued in 1995.³³ Data from clinical studies comparing patient preferences³⁴ and resistance to fungal overgrowth^35,36 between the Novus and SB-LRDLs has confirmed the advantages of the Novus material. Clinical trials report that Novus-lined dentures resist the growth of Candida albicans in almost all patients, while more than one-half of the silicone-lined dentures became contaminated with the fungus.^35,36 Reported benefits of this material include radiopacity, the ability to engage bony undercuts and implant abutments, excellent durability (due to the lack of plasticizers), resistance to fungal biofilm formation, decreased porosity, ease of adjustment, excellent shock absorption, and increased patient comfort. This material also bonds well to acrylic resins without the need for adhesives and has an unlimited shelf life, if refrigerated.³⁷

This article describes the clinical steps for lining a maxillary denture opposing mandibular natural dentition using the Novus lining material.

Figure 9. The completed definitive impression.

CLINICAL TECHNIQUE
Step 1. Record the vertical dimension of occlusion (VDO) with a Boley gauge (Figure 1) and maintain it for the entire procedure.

Step 2. Place the existing denture in the patient’s mouth and guide the patient to centric relation (CR) mandibular closure. Make an interocclusal record (in CR position) with a vinyl polysiloxane (VPS) registration material (Futar Fast [Kettenbach LP]) (Figure 2).

Step 3. Relieve the intaglio surface uniformly and adequately with standard laboratory rotary instruments (Universal Acrylic Kit [Komet]) to provide adequate bulk for impression material. Application of a dye solution helps to ensure even and uniform reduction (Figure 3).

Step 4. Apply a suitable VPS adhesive (Caulk VPS Tray Adhesive [Dentsply Sirona Restorative]) on the intaglio surface of the denture.

Step 5. Accurately reposition the previously formed interocclusal record against the occlusal surface of the denture. Inject nickel-sized circles of a rigid viscosity VPS impression material (Aquasil Rigid [Dentsply Sirona Restorative]) on the intaglio surface of the maxillary denture in 4 locations (the incisor, both molars, and mid-palate). These locations may be changed to avoid mucosa that is compressible or mobile. Place the denture (with the interocclusal record) in the patient’s mouth, ensuring that it is centered over the edentulous ridge. Ask the patient to occlude on the interocclusal record to maintain CR posture and the existing VDO throughout the procedure (Figure 4). Upon complete polymerization of the impression material, remove the denture and evaluate the “stops.” Indicate areas of excessive tissue contact with an indelible marker. Trim marked areas with a sharp blade or slow-speed laboratory rotary instruments (Figure 5). These formed stops provide a constant pathway and position for denture reinsertion and maintain appropriate space for subsequent impression material.

Step 6. Apply the VPS adhesive along the denture’s peripheral borders.

Step 7. Dispense the rigid viscosity VPS material (Aquasil Rigid) along the denture’s peripheral borders (Figure 6, left). Carefully place the denture in the patient’s mouth and ensure that it is centered over the edentulous ridge using the tray stops (Figure 6, right). Accomplish border molding movements to generate physiologically extended borders. Following complete polymerization of the impression material, remove the denture from the mouth and evaluate the borders to ensure adequate anatomic and functional detail. Adjust areas of denture base “show through” with laboratory rotary instruments or a sharp blade. Relieve all the border extensions by 1.0 to 2.0 mm prior to making the definitive impression (Figure 7).

Step 8. For the definitive impression, load the denture with a light (or an extra-light) viscosity VPS impression material (Aquasil XLV [Dentsply Sirona Restorative]) (Figure 8). Carefully place the denture in the patient’s mouth and ensure that it is centered over the ridge using the tray stops. Accomplish border molding movements to physiologically record all borders. Following complete polymerization of the VPS material, remove the impression from the mouth and evaluate its anatomic, functional, and surface detail. Trim away excess material with sharp scissors or a blade (Figure 9).

Figure 12. Novus lining material (White Square Chemical) was introduced into the denture. Note: Denture borders are not covered with the lining material.

Figure 14. A reticulated foam polishing wheel was used for adjustment.	Figure 15. The denture lined with Novus—finished, polished, and in place.

Step 9. Bead and box the impression, and then pour the impression twice in a Type IV dental stone (FlowStone [Whip Mix]) to procure 2 casts (Figure 10). The Novus lining material cannot be applied chair side, as it must be processed in the lab. The thickness and extent of the Novus lining material can be controlled using a pressure formed spacer (Duran 1.5 mm [Great Lakes Orthodontics]).³⁷ The spacer is pressure formed on one of the casts. The margin of the soft-lining material should be placed below the denture border for a maxillary denture and above the denture border for a mandibular denture.³⁷ To accomplish this, the spacer should be trimmed 2.0 to 3.0 mm short of the intended denture border extension (Figure 11). The spacer, the master cast, the maxillary denture, and detailed written instructions are then sent to the laboratory team for rebasing the denture, and for indirectly introducing and processing the lining material in the denture (Figure 12). Detailed instructions for the laboratory steps can be obtained from the manufacturer (wsqchem.com). If extension of the lining materials over the denture border is desired, the spacer should be extended up to the intended denture border extension.

Step 10. Evaluate and adjust the intaglio surface (Figures 13 and 14), denture borders, and cameo surface; evaluate and refine the occlusion; and then deliver the maxillary denture to the patient (Figure 15).

CLOSING COMMENTS
In the authors’ experience, dentures lined with the Novus material have remained in clinical use for up to 4 or 5 years with no need for replacement. Novus offers excellent durability, consistent long-term softness, and a unique chemistry that makes it suitable for complete denture patients with xerostomia as well as those with a history of persistent candidiasis. Well-controlled clinical investigation is required to validate the use of Novus as a definitive denture lining material.

References

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Dr. Massad is an associate professor in the department of graduate prosthodontics at University of Tennessee Health Science Center (UTHSC) in Memphis; an associate faculty at Tufts University School of Dental Medicine in Boston; an adjunct associate faculty of the department of comprehensive dentistry at UTHSC Dental School in San Antonio; and an adjunct professor in the department of restorative dentistry at Loma Linda University in Loma Linda, Calif. He maintains a private practice in Tulsa, Okla. A textbook was published and released in 2017 by Dr. Massad with co-authors Drs. David Cagna, Charles Goodacre, Russell Wicks, and Swati Ahuja titled Applications of the Neutral Zone in Prosthodontics. He can be reached at joe@joemassad.com.

Disclosure: Dr. Massad reports a paid consulting relationship with White Square Chemical.

Dr. Ahuja graduated with a BDS degree from Nair Hospital Dental College (India) in 2002. She migrated to the United States and earned her MDS degree and certificate in prosthodontics from UTHSC in Memphis (2009). There, she was an assistant professor in the department of prosthodontics. During that time, she was appointed as the coordinator of the TMD clinic and the T-scan expert (bite correction) for the advanced prosthodontic program due to her diverse training and skills. Dr. Ahuja has migrated back to India and is currently an adjunct assistant professor in the department of prosthodontics at UTHSC. She is a consultant for several private dental clinics in Mumbai, India, as well as for the Lutheran Medical Center in New York City. She has lectured internationally on various prosthodontic topics at various dental conferences. She has multiple publications in peer-reviewed, international journals and is co-author of the textbook Applications of the Neutral Zone in Prosthodontics. She is a reviewer for many journals and is an editorial board member for International Journal of Experimental Dental Sciences. She can be reached via email at sahuja@uthsc.edu.

Disclosure: Dr. Ahuja reports no disclosures.

Dr. Cagna is associate dean of postgraduate affairs and professor and director of the advanced prosthodontics program in the department of prosthodontics at the UTHSC College of Dentistry in Memphis. He received his dental degree from the Medical University of South Carolina (1990) and completed his residency training and master of science degree at the UTHSC at San Antonio (1994). He is a Diplomate and director of the American Board of Prosthodontics and a Fellow of the American College of Prosthodontists. He maintains a private practice in the UT Dental Faculty Practice (Memphis) He is co-author of the textbook Stewart’s Clinical Removable Partial Prosthodontics and has authored numerous professional articles. He can be reached via email at dcagna@uthsc.edu.

Disclosure: Dr. Cagna reports no disclosures.

Dr. Wicks is professor and chairman of the department of prosthodontics at the UTHSC College of Dentistry in Memphis. He received his dental degree from the University of Tennessee and was in private general practice until 1990. In 1993, he received a master’s degree and certificate in the specialty of prosthodontics from the University of Texas at San Antonio. Since then, he has conducted prosthodontic research and directed the undergraduate curriculum in removable prosthodontics and dental implants at the UTHSC College of Dentistry. In 1995, the American College of Prosthodontists recognized Dr. Wicks as the “Outstanding Young Prosthodontist” in America. He was appointed to the “Academy of Distinguished Teaching Professors” at UTHSC and has received the annual “Distinguished Dental Faculty Award” from the College of Dentistry. He can be reached at rwicks@uthsc.edu.

Disclosure: Dr. Wicks reports no disclosures.

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