Soft lining materials and tissue conditioners are used in dentistry to improve the fit and comfort of dentures. They act as a cushion between the hard denture base and the underlying tissues, absorbing some of the impact during chewing and providing relief for patients who experience pain or discomfort.
Tissue conditioners are a type of soft denture liner that provides temporary relief for patients with ill-fitting dentures.
They are used for short-term purposes such as:
- Treatment, conditioning, provisional or diagnostic purposes
- Temporary relining of immediate dentures
- Speech aids for cleft palate patients.
- During implant healing to promote tissue health.
Why are Soft Lining Materials Used?
Some patients have specific conditions that make their oral tissues more sensitive. When the gum tissue is thin, it can’t absorb the impact of chewing properly, which puts more strain on the underlying tissue. This can be due to thin or sharp ridges, significant bone loss, or severe undercuts. The rigid materials used to make denture bases can cause chronic pain or soreness when in contact with these sensitive tissues.
Soft lining materials help alleviate this problem by providing a softer surface that reduces friction and absorbs shock. They create a cushioning layer between the denture and the gums, reducing the transmission of force during chewing. This makes wearing dentures more comfortable, especially for patients with ridge atrophy, bony irregularities, or other oral issues.
How Tissue Conditioners Work
The liquid component of tissue conditioner materials contains a mixture of ethyl alcohol (solvent) and an aromatic ester called dibutyl phthalate (plasticizer).
- The plasticizer lowers the glass transition temperature (Tg) of the polymer, making it soft and gel-like.
- When the material sets, it becomes a viscoelastic gel with elastic properties that act as a shock absorber.
However, the alcohol and plasticizer gradually leach out over time, causing the material to harden and lose its cushioning effect within a few days to a week or two. Hence the short-term use of tissue conditioners before switching to a longer-lasting soft denture lining.
Switching from tissue conditioners to temporary soft liners
Ideally, a tissue conditioner should be replaced with a fresh mix every 2 to 3 days to maintain its effectiveness. However, in cases where frequent replacement is not practical, temporary soft liners can be used instead.
These liners also improve the fit of ill-fitting dentures temporarily until a new denture can be made. Tissue conditioners can also be used as functional impression materials, allowing the dentist to obtain an accurate impression over a few days.
Potential problems for tissue conditioners
- Loss of softness:
Over time, both tissue conditioners and temporary soft lining materials harden or lose their elasticity, compromising their ability to provide cushioning and comfort. The resulting rough and irregular surfaces can cause trauma to the oral tissues.
- Prone to bacteria:
In addition, the hardened materials can be colonized by Candida, increasing the risk of denture-induced stomatitis. Fortunately, soaking the dentures overnight in a dilute solution of sodium hypochlorite (bleach), or using chlorhexidine can help reduce the risk of infection.
- Discoloration and unpleasant odor due to porosity
Porous materials can harbor bacteria and microorganisms, leading to oral health issues as discussed in the previous point. Additionally, porosity can cause the material to absorb fluids, which may result in discoloration and an unpleasant odor. Researchers are exploring methods to reduce the porosity of soft lining materials, thus improving their longevity and hygienic properties.
- Loss of aesthetic appeal
Color changes in soft lining materials can occur over time, leading to an undesirable appearance of the dentures. This can be particularly problematic for individuals who desire a natural-looking smile.
- Poor tear strength
This makes the soft lining materials susceptible to damage and premature wear. Researchers are focusing on enhancing the tear strength of these materials to improve their durability and lifespan.
- Debonding from the denture base
When the lining material detaches from the denture base, it can lead to instability, discomfort, and difficulty in chewing and speaking. Fortunately, there are new bonding techniques and adhesive agents that can help to improve the adhesion between the lining material and the denture base, ensuring a more secure and long-lasting bond. This is discussed below:
To manage most of these problems, denture wearers usually have to replace the tissue conditioner often, or switch to longer-term liners as soon as possible.
Methods to Improve the Adhesion of Denture Liners
One of the major challenges with soft denture liners is achieving a durable bond with the denture base. It is common for soft liners to detach from the denture base, which can lead to bacterial colonization and compromise the longevity of the liner.
Several factors can influence the strength of the bond, including the surface geometry, etching techniques, use of bonding agents, and the thickness of the lining material.
Fortunately, various techniques are employed to improve the bond strength and adhesion between the liner and denture base, including:
- Creating Surface Roughness
One method to enhance adhesion is by creating roughness on the acrylic surface that will come into contact with the liner. This roughening can be achieved using lasers or alumina abrasion techniques. By roughening the surface, the contact area between the liner and denture base increases, improving the bond strength.
- Chemical Etching
Chemical etching is another technique used to increase the bond strength between the acrylic denture base and the soft liner. Various chemical agents such as methyl methacrylate (MMA), acetone, or methylene chloride can be used to etch the surface of the denture base. This process creates micro-indentations and improves the surface area for bonding, leading to enhanced adhesion.
- Reinforcement with Woven Fibers
To reinforce the acrylic surface, net woven fibers of glass can be incorporated into the denture base. These fibers act as additional support, improving the bond strength between the liner and the denture base. The reinforcement helps prevent detachment and enhances the durability of the soft liner.
- Oxygen Plasma Treatment
An alternative method for surface roughening is oxygen plasma treatment. This technique involves exposing the denture base resin to a controlled plasma atmosphere. The plasma modifies the surface properties, increasing surface energy and creating micro-roughness. Oxygen plasma treatment has shown promising results in improving the tensile bond strength between the denture base resin and soft liner.
Soft lining materials for dentures, including tissue conditioners, help to improve the comfort of false teeth for denture wearers. And while they come with their own set of challenges, including porosity, loss of softness, debonding, rough surfaces, color changes, microbial colonization, and poor tear strength, ongoing research and development efforts are dedicated to overcoming these issues and enhancing the performance and durability of soft lining materials. With continued advancements, denture wearers can expect improved comfort, longevity, and oral health benefits from these materials.