1. Denture Lining materials

2. Rationale for use - Contours of soft tissues change continuously.
Underlying bone resorb. These result in inferior retention. (Especially for immediate dentures)
If occlusal relationship and vertical dimension of occlusion are acceptable, relining or rebasing might be the options.
Also indicated sometimes for geriatric patients, for lower costs, for porous dentures,

3. Relining
Relining is a process in which a film of plastic is added to the inside of the denture to obtain an improved fit with the denture-bearing mucosa, and restoring stability and retention. This is accomplished by:
1- making an impression of the denture bearing mucosa using the denture as a tray, reflasking the denture, removing the impression material, and packing and curing the new liner.
2- making a chairside reline where the reline material is used to make the impression.

4. - Two different types of reline materials may be used: permanent or temporary.
- Permanent relining material may be either a heat-accelerated, chemically accelerated, or light-activated acrylic. The relining process is carried out either by a flasking procedure or curing in a light chamber, depending on the type of material. Permanent reline materials may be identical to those from which permanent denture bases are made.

5. Concerns about relining procedures:
1- A good chemical bond is desired between the reline plastic and the denture plastic.
2- Satisfactory strength of the relined denture is necessary.
3- No warpage or dimensional change should result in the denture because of the relining procedure.
4- Relining should take as short a time as possible for patient convenience.

6. Classifications of relines
Laboratory vs chairside.
Impression vs functional impression techniques.
Hard acrylic vs resilient.
Permanent vs temporary.
Complete vs partial dentures.

7. Laboratory-based relining technique:
- Impression material is removed from the denture.
- Resin is added using the compression molding technique.
- Low-polymerization temperature (74°C-77°C) is desirable to minimize distortion of the original denture base.
- Chemically activated resin is more appropriate.
- The resin is mixed, added to tissue surface of existing denture, compressed and permitted to polymerize.
- Denture is then recovered, finished and polished.

10. Chairside (temporary) relining
- Some materials are intended to be used intraorally. This entails the making of the impression with the relining material.
- Clinically approved materials should not produce excessive heat to injure the tissues.
- Cause minimal worpage of existing dentures, hardening time of 6-15 min.

11. The chair-side reline denture materials.
- They are supplied in the market as liquid and powder.
- They have properties of cold-cured acrylic resin.
- The material could be used as an impression , and as soon as the material become rubbery it should be removed from the patient mouth and allow to cure out of the patient mouth to avoid the exothermic effect

12. Porosity of some materials may lead to bad odors.
- Heat from polymerization of some materials can burn mucosa, in addition to irritation from monomer.
Porosity of some materials may lead to bad odors.
- Material may become distorted if the relined denture is removed from the patient’s mouth before complete polymerization
- Some materials exhibit greater dimensional change during polymerization than is the case for processed materials
- Some materials exhibit weaker or variable bond strength to denture base
- Patient may experience discomfort and unpleasant taste
- Some materials may exhibit cytotoxicity
- Colour stability may be poor
• Some materials have a limited lifespan (temporary relines)

13. Other types of relining resins
- Source of heat can be: water bath, light or microwave energy.
- Significant heat may be generated, leading to denture base distortion.
- The light-activated material is used directly in the denture to record the tissue surface. A bonding agent is used before placing the material in the denture. Polymerization is achieved in a light chamber. The light-activated acrylic allows the entire reline procedure to be completed in 30 to 45 minutes.

14. Rebasing denture bases
- Rebasing refers to a technique in which the dimensional relations of the teeth are maintained and the entire denture base is replaced. A cast is prepared from an impression made in the denture. After flasking, all of the old plastic is removed except around the teeth. The denture is then processed according to standard procedures with new acrylic. The end result is a new denture base retaining the original teeth in the same position as in the original denture.

15. Tissue Conditioners
Soft elastomers used to treat irritated mucosa supporting a denture, or after surgery. They are mixed at chairside, placed in the denture, and seated in the patient's mouth. These materials will conform to the anatomy of the residual ridge, gel in that position, and continue to flow slowly after application. They are used only for short-term applications and should be replaced every few days (max 2 weeks). Inhibition of the growth of oral bacterial flora is associated with some materials, and this should promote healing of inflamed tissues.

16. -
Composed of a powder containing poly(ethyl methacrylate) and a liquid containing an aromatic ester-ethyl alcohol (up to 30%) mixture. The plasticizer (dibutyl phthalate) is a large molecule.
- Liquid does not contain acrylic monomers, no polymerization occurs.
- Large molecular weight plasticizer minimizes entanglement of polymer chains. Chains slip past each other. This movement allows for rapid change in shape of the soft liner and gives the material soft consistency.
- Very soft elastomers with very low hardness values. They will show a weight loss of from 4.9% to 9.3% after 24 hours as a result of the loss of alcohol. These materials deform easily, Within a few days, tissue conditioners become stiffer as a result of the loss of alcohol.

17. The properties that make tissue conditioners effective are:
1- The viscous behavior, which allows adaptation to the irritated denture-bearing mucosa over a period of several days.
2- The viscoelastic and elastic behavior, which cushions the cyclic forces of mastication and bruxism. The viscoelastic properties are influenced by the molecular weight of the polymer powders and the power/liquid ratio.
However, the soft consistency of the material makes it less durable, and it is considered as a short-term denture liner.

18. the mineral oil lubricant being applied to the teeth and palatal surfaces.

19. 19

20. The upper pictures show the tissue conditioner components being mixed together. The consistency of the material is very viscous 20

22. 22

23. Trimming off excess flash from the denture borders23

25. Soft Denture Lining Materials
- Short-term Soft Liners
Long-term Soft Liners
Requirements:
1- High bond strength to the denture base.
2- Dimensional stability of the liner during and after processing.
3- Permanent softness or resilience,
4- Low water sorption.
5- Color stability,
6- Ease of processing.
7- Biocompatibility.

26. Soft Lining materials
- Functions and rationale for use:
Absorb some of the energy produced by masticatory impact (shock absorber).
Soft fragile oral mucosa.
Irregular alveolar ridge or severe undercuts.
Acquired or congenital defects of the palate

27. Soft Lining materials
Heat-activated.
Chemically-activated.

28. Chemically activated soft lining materials
- Conventional mouth-cured soft liners are used for periods to improve the comfort and fit of an old denture until it can be remade or permanently relined. After several weeks they may begin to foul and debond from the denture. They are mixed chairside, placed in the denture, and seated in the patient's mouth until polymerized, which generally takes a few minutes. Three types of materials are generally used:

29. 1. Powder-poly(ethyl methacrylate) and peroxide initiator; liquid-aromatic esters, ethanol, and tertiary amines 2. Powder-poly(ethyl methacrylate), plasticizers such as ethyl glycolate, and a peroxide initiator; liquid-methyl methacrylate and tertiary amines 3. Addition silicone elastomers - Biocompatibility of these materials is of interest because it has been demonstrated both in vitro and in vivo that both tissue conditioners and chairside soft liners leach out significant amounts of alcohol and phthalate esters

31. Heat-activated soft liners
- Acrylic resin based, vinyl resin based or silicones. - More durable. - Long-term but not permanent (1 year). Tend to pull away from the denture base or become porous and foul smelling. - Used with denture patients who experience chronic soreness with their dentures because of heavy bruxism or poor health. - Their finishing is difficult because of their softness. - Many tend to increase in hardness with time and their physical and mechanical properties are affected by storage in water or in the oral environment.

32. - When placed in water, plasticizers and other components may leach out over extended periods while water is absorbed until equilibrium is reached. Absorbed water can have a detrimental effect on the adhesion of soft liners to acrylic denture bases. An ideal processed soft liner would have no soluble components and low water sorption. - Processed soft liners are intended to be used for extended periods. Candida albicans, and other microorganisms may grow on and within the liner, resulting in a rough and hardened surface. Antimicrobial agents have been proposed to eliminate this problem, but they do leach too. Color changes have also been demonstrated for some liners subjected to accelerated aging.

33. - Regarding bonding with denture bases, the polyphosphazine material demonstrated higher bond strength. Most manufacturers recommend processing the soft liner and the denture base acrylic at the same time to improve the bond strength. Recently, bonding agents have been introduced that significantly increase the bond strength of several addition-silicone elastomers to denture base resin. - Regarding viscoelasticity, the silicones were more stable over time than the other materials. - Growth of Candida albicans and other microorganisms continues to challenge the use of short- and long-term soft denture liners. Excellent oral and denture hygiene and the use of antimicrobial agents are effective in minimizing this problem.

34. - Unfortunately, many of the short- and longterm resilient denture liners contain significant amounts of plasticizers, many of which have questionable biocompatibility. Phthalate esters can cause epithelial changes . The potentially premalignant changes are a cause for concern because the amount of this plasticizer leached from a typical soft liner may be between 10 and 40 times greater than environmental and food uptake. Although this amount of plasticizer is low, demonstrated biocompatibility of soft denture liners should be considered.

35. Acrylic resin based heat activated soft liners
- Powder: Acrylic resin polymers and copolymers. - Liquid: Appropriate acrylic monomers and plasticizers. - When mixed the resin is pliable with glass transition temperature below mouth temperature. - Platicizers provide flexibility but can leach out producing rigid liners. - Higher methacrylates produce lower Tg, so less plasticizer is required.

36. Glass transition temperature
The glass transition temperature, Tg, is the temperature at which a glass becomes brittle on cooling, or soft on heating. More specifically, it defines a pseudo second order phase transition in which a supercooled melt yields, on cooling, a glassy structure and properties similar to those of crystalline materials e.g. of an isotropic solid material. Tg is usually applicable to wholly or partially amorphous solids such as common glasses and plastics (organic polymers).

37. Below the glass transition temperature (Tg) amorphous solids are in a glassy state and most of their joining bonds are intact. In inorganic glasses, with increased temperature more and more joining bonds are broken by thermal fluctuations so that broken bonds (termed configurons) begin to form clusters. Above Tg these clusters become macroscopic large facilitating the flow of material. In organic polymers, secondary, non-covalent bonds between the polymer chains become weak above Tg. Above Tg glasses and organic polymers become soft and capable of plastic deformation without fracture. This behavior is one of the things which make most plastics useful.

38. Vinyl resin based heat activated soft liners
- Poly (vinyl cholride) and poly (vinyl acetate).
Both chairside self-cured and laboratory heat-cured are available.
Examples: Easy-fit and Dinabase soft liners
Plasticizers do leach too.
Mechanical, micromechanical and chemical bonding (through adhesives).

39. Silicone rubber soft liners
Very successful
Have better durability than acrylics, but inferior bonding, and grow fungal infections easily
- Can be chemically activated or heat-activated.
- Chemically activated materials are supplied as two component systems that polymerize via condensation reaction. Similar to condensation silicone impression materials.

40. Sofreliner Tough® is an addition-cured silicone material for relining dentures.

41. Silicone rubbers soft liners
Technique for the heat-activated material: - Denture is relieved. - Adhesive is applied. - Material is mixed and applied via compression molding and allowed to polymerize. - Denture is recovered, finished and polished. - Heat activated material is one component systems supplied as pastes or gels. Also are applied by compression molding.

42. - Heat activated soft liners are either applied to polymerized denture bases or they may be polymerized in conjunction with the denture base. - Adhesives can be: rubber-poly (methyl methacrylate). - When cured in conjunction with denture bases, the materials do not require an adhesive.

43. Other soft liner polymers
- Poly urethane (light-cured).
Poly phosphazine, e.g: Novus.
Polyurethane or vinyl polymers require more complex processing conditions, special equipment, have higher hardness, absorb environmental colorants, and also promote fungal growth
Polyphosphazene was found to have good biocompatibility, energy absorption, acceptance of fillers and pigments, bonds to acrylic base, does not leach plastizers, resist candida and easy to grind. The heat-cured is processed with compression at 20.7 MPa (3000 psi) and heating up to boiling water temperature

45. Soft liners
Concerns:
- Silicone liners adhere poorly to denture bases. They also undergo significant volume changes with the gain or loss of water.
- Leach of plasticizers produce more rigid material. If the plasticizer content is high, then the probability for leaching is increased.
- If the thickness of the liner is high, then the denture base will be weakened.
- Adhesives may partially dissolve the denture bases.
- Difficult to clean, producing bad taste and odors.
- Mechanical cleaning or denture cleansers can damage soft liners especially silicones.
- Mycotic activity, mainly candida albicans is prominent problem.

46. Thank you