RESILIENT LINERS

INTRODUCTION

During normal function in dentulous subjects, the vertical and lateral forces are directed or transmitted mainly to the periodontium, whereas in edentulous condition with complete dentures, the mucous membrane in denture bearing area is forced to accept these loads. These forces tend to compress or distort the mucosa to varying degree according to location, thickness and histology of mucosa. These forces vary in magnitude before being transmitted to bone. Thus denture bearing mucosa is forced to serve the same purpose as the periodontal ligament that provides support for natural teeth.

Accordingly it would be desirable to have a denture base that is compressive on the tissue side but rigid or hard on the occlusal side and shock absorbing as well as selectively resilient compatible with resiliency of the tissues, able to recover to its original shape when deforming forces are removed.

This quest led to the development and use of resilient liners in complete denture treatment that would efficiently increase the thickness of the oral tissues by serving as an analogue of the mucosa and periosteum with its relatively low elastic modulus.

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TERMINOLOGY

1. Plasticity : The quality that does not allow a structure or material to return to its original form on removal of an external force.

2. Elasticity : The quality that allows a structure or material to return to its original form on removal of an external force.

3. Elastic limit : The greatest stress to which a material may be subjected and still be capable of returning to its original dimensions when such forces are released.

4. Modulus of Elasticity (E) : The term modulus of elasticity describes the relative stiffness or rigidity of a material which is measured by the slope of the elastic region of the stress-strain diagram.

5. Resilience : Can be defined as the amount of energy absorbed by a structure when it is stressed to its proportional limit.

6. Viscoelasticity : After removal of an applied load if the recovery takes place slowly or if a degree of permanent deformation remains, the material is said to be viscoelastic.

7. Flexibility : The quality of a material being flexible.

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Resilient Denture Liner*

A soft (resilient) lining material may be defined as a soft elastic and resilient material forming all or part of the fit (impression) surface of a denture.

(ANSI/ADA Specification No. 75)

* Qudah S., et al : Soft lining materials in prosthetic dentistry : A review. Int. J. Prosthodont., 1990, 3 : 477-483.

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Tissue Conditioner

Wilson and Associates (1966)+ defined a tissue conditioner as a soft material which is applied temporarily to the fitting (basal) surface of a denture to distribute the load equally, thus permitting mucosal tissues to return to their normal contours.

Starcke and Associates (1972)+ defined the tissue conditioner as a soft, resilient, temporary reliner which acts by reducing and evenly distributing stress on the mucosa of the basal seat.

+ Razek, MKA: Assessment of tissue conditioning materials for functional impressions. J. Prosthet. Dent., 1979; 42 : 376-380.

HISTORICAL BACKGROUND

The earliest soft lining material recorded (soft rubber) was used by Twitchell in 1869.

“Velum” a soft natural rubber was used in 1940 with vulcanite in conjunction with obturators and as a soft lining for mandibular complete dentures. This material had high water absorption, and it became foul and ill fitting over a period of time.

In 1945, Matthews used poly(vinyl chloride) powder with a liquid di-n-butyl phthalate plasticizer in the form of a

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paste as a facial prosthetic material and as a soft liner for patients with chronic mucosal tenderness.

Lammie and Storer described the use of poly(vinyl chloride) plasticized with di-butyl-phthalate and found it to be an unsatisfactory material because it hardened in a short period of time (6-12 months) due to the plasticizer leaching out. Dioctyl phthalate was a better choice for a plasticizer to keep the liner soft.

In the late 1940’s Nelson used butyl phthalate butyl glycollate as a plasticizer for vinyl chloracetate to improve adhesion between the lining and the poly(methyl methacrylate) denture base. Lammie and Storer reported this material to have high water absorption, hardening and cracking. They also described a German product, plastupalate, which was a polymer of 35 parts of methyl methacrylate to 65 parts of butylester acrylic acid. However, it has drawbacks like low bond strength and low resistance to abrasion.

Softdent soft lining material, a hydrophilic gel based on glycol methacrylate ester chemistry, was developed by Whichterle and Lim in 1961. Due to its high solubility it was not used much.

Silicone rubber materials based on poly (dimethyl siloxane) have been used as soft liners since 1958. Later

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materials that could be processed with poly(methyl methacrylate) at room temperature became available.

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REVIEW OF LITERATURE

Denture soft lining materials act as a cushion between the hard denture base and the tissues to reduce the masticatory forces transmitted by prosthesis to the underlying tissues.

For the first time Tylman, S.D. (1943) reported the clinical use of soft or resilient lining for dentures.

Mathews (1945) reported the use of plasticized poly-vinyl-chloride as a soft liner for a specific clinical situation.

According to Lammie and Storer (1958), resilient liner could be useful in the complete lower denture where the patients shows a senile atrophy, in developing maximal retention where the ridges have bilateral undercuts in the mouth, where a hard median palatal raphe is associated with a poor retentive potentiality and in obturators for acquired and congenital defects of palate. This soft material according to them will be tolerated even by the traumatized tissue particularly where radiotherapy has been done. They attributed the loss of resiliency of denture soft liners to leaching of plasticizers when in contact with water.

Gonzalez, J.B., and Laney, W.R. (1966) studied some of the properties of the resilient material which can be used in denture prosthesis to prevent chronic soreness and found that the temporary resilient plastics can be used for a

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relatively short time which can prevent chronic soreness from dentures and permanent resilient plastics could be used for longer periods of time for patients with ridge atrophy and they also found that the other properties of the permanent flexible plastics were found to be important in their selection such as colour stability, ease of finishing and polishing high abrasive resistance and strength.

Laney W.R. (1970) stated that a variable thickness of resilient liner would help to equalize the pressure over the edentulous ridge especially over the prominent bony spicules subjected to a greater amount of applied force.

Parker S. and Braden M (1982) stated that soft lining materials were classified broadly into two types, namely silicone elastomers and soft acrylics, while the soft acrylics had excellent adhesion to poly (methyl methacrylate), they had poor elastic properties and hardened due to the leaching out of plasticizer whereas the silicone soft liners had excellent elastic properties but adhesion to poly(methyl methacrylate) was poor and they deteriorated in the oral environment and also supported the growth of Candida albicans. They also described two techniques to formulate soft acrylics without easily leachable plasticizers.

Brown D. (1988) stated that if a resilient soft lining was present, a considerable amount of energy could be absorbed in its deformation, thus less had to be absorbed by the tissues of the patient. He also described the glass transition

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temperature, a property related to the resilience of polymers. Also a number of different types of resilient liners and their properties were described and concluded that the desirable properties of the materials were far from perfect.

Mack P.J. (1989) described the indications and applications as well as the disadvantages and contraindications of soft lining materials. He concluded that the success or failure of a soft lining material is dependent not only upon the physical properties of the material but also the function of the material as well as the tissues which come in contact with the material.

Mack P.J. (1989) described five group of materials that had been made available in detail viz. the natural rubbers, vinyl co-polymers, hydrophilic polymers and the silicone and acrylic based soft lining materials. He concluded that an ideal soft liner was still not available.

Qudah S., Harrison A. and Huggett R., (1990) reviewed the soft lining materials including their historical development, clinical indications, desirable properties and limitatons of those currently available. They concluded that further research and development was necessary to achieve a material with optimum properties.

Braden M., Wright P.S. and Parker S. (1995) reviewed soft lining materials and also the laboratory testing and clinical studies of these materials. They concluded that some

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success can be achieved by using heat polymerized silicone rubber materials. Though no complete satisfactory soft lining material was available.

Jagger D.C. and Harrison A (1997) have updated on the use of permanent soft lining materials with their indications, limitations and maintenance. They have criticized on the view that soft liners are frequently used in conjunction with chronic pain under a lower denture. Whereas it would be more appropriate to find the cause and eliminate it.

MATERIALS AVAILABLE AND THEIR COMPOSITION

On the basis of their chemical structure soft lining materials can be broadly divided into the following groups:

1. Natural rubbers.2. Vinyl co-polymers.3. Hydrophilic polymers.4. Silicone based compounds.5. Acrylic based compounds.

1. Natural rubbers :

Soft natural rubber was used as a soft denture liner as early as 1869. Unfortunately, all natural or ‘velum’ rubbers rapidly take up saliva and hence become unaesthetic and foul after a short time in the mouth. There is not at present any commercially available soft lining material based on a natural rubber product.

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2. Vinyl co-polymers:

Vinyl co-polymers (e.g., Corvic, Imperial Chemical Industries, Australia) were the first synthetic materials that could be considered to show any degree of clinical success. In the oral cavity poly vinyl chloride (PVC) proved to be a relatively brittle substance and polyvinyl acetate (PVA) over-pliable. Although these materials were unsatisfactory, a copolymer of the two was developed with dioctyl phthalate as the plasticizer and zinc oxide (0.5%) and calcium sterate (5%) were added to improve the flow characteristics of the unset material. Gelation could only occur in heated dry moulds.

Gradual loss of plasticizer resulted in hardening of the material. This material though was not popular amongst dental profession.

Appearing slightly later than these first synthetic materials was a resilient soft denture material based upon the urethane molecule. This product consisted of a triple chemical grouping: A polyfunctional hydroxy compound, a poly functional isocyanate and a catalyst. The resultant material had good initial flexibility and edge strength, but unfortunately had high water absorption, thus deteriorating. This material also did not gain any acceptance either.

3. Hydrophilic polymers:

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Hydrophilic polymeric materials would seem at first to provide the ideal soft denture lining material - hard enough to trim and adjust at room temperature yet demonstrating a clinical compliance at 37°C that could render the material suitable for the purposes of tissue conditioning or as a longer term soft lining product. The perceived young’s modulus for one such commercially available substance (Hydrocryl, Hydron Dental Products Inc., New York, USA) varies from 2000 MPa when dry to 2.0 MPa when wet.

The main disadvantage was their water absorption by as much as 20%. The base polymer is hydroxy-ethyl-methacrylate with ethylene glycol dimethacrylate as a cross linking agent. Due to their high water absorption, these materials are not in use now a days.

4. Silicone based compounds:

These materials could be either heat cured or autopolymerized.

The silicone rubber materials are basically composed of polymers of dimethyl siloxane – a viscous liquid that can be cross linked to give good elastic properties. The cross linking agent is normally an alkyl-silane, and the reaction is usually catalyzed by an organometal salt or benzoyl peroxide.

Molloplast-B, a heat-polymerized silicone rubber is supplied as a one-paste system activated by heat (boiling

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water for 2 hours), an adhesive (Y-methacryloxy propyl trimethoxysilane, a silicone polymer in a solvent) is supplied to aid bonding to the denture base. The silicone autopolymer Flexibase is supplied as a paste and a liquid system. The liquid or the catalyst is a mixture of dibutyl tin dilaurate and ethyl polysilicate. Wright states that because silicone rubbers have no natural adhesion to poly (methyl methacrylate), an adhesive compound of a silicone polymer in a volatile solvent must be used.

Gettleman et al have recently based an interesting soft lining material on a bulk elastomeric polymer poly (fluoroalkoxy) phosphazine. By milling in a suitable monomer, and both methyl and n-butyl methacrylate have been reported, together with a suitable initiator, a promising material has been achieved. The incorporation of the methacrylate of course confers good adhesion to the denture and most physical properties fall within the middle range of established acrylic and silicone rubber soft lining materials. The material is marketed under the trade name “Novus”. This material has a drawback of having high water absorption.

“Flexor” a poly dimethyl siloxane perfluoralkanol dimetacrylate is a fluoro silicone material recently developed. It has low water absorption.

5. Acrylic based compounds:

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Both the heat-processed and autopolymerizing acrylic resin soft lining materials consists of powder and liquid components. The powder is believed to contain acrylic polymers and copolymers and the liquid is methyl methacrylate monomer and a plasticizer. The purpose of the plasticizer, usually di-n-butyl phthalate, is to reduce the transition of the polymer from liquid to solid below mouth temperature. Thus at mouth temperature, the material is semi liquid and therefore soft, this reduces the modulus of elasticity of the soft material to a satisfactory level. The chemical composition of the acrylic resin soft linings is similar to that of the acrylic resin denture base material, thus no adhesive is required to form a bond.

EXPERIMENTAL SYSTEMS

i. Natural Rubber/ PMMA Graft Copolymer System:

A material was evaluated comprising a natural rubber/poly(methyl methacrylate), graft copolymer, cured at 100°C by a sulphur/zinc dimethyl dithiocarbamate system. Adhesion was achieved with a toluene solution of the graft polymer, applied to the PMMA denture.

This gave excellent results mechanically and showed greatest promise clinically. Unfortunately, it had to be abandoned because of the potential dangers of mucosal reaction to the dithiocarbamate.

ii. Powdered Elastomer Soft Acrylic Systems:

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The concept that initiated this work was to retain the advantages of soft acrylic systems, but to avoid the need for plasticizers.

Elastomers in powder form are manufactured by cryogenic grinding, or from Latex; many use talc or other silicates as a separating agent and are to be avoided because they result in very high water uptake.

Powdered elastomers will form easily handleable doughs, with the right choice of monomer and the cured products have acceptable strength and adhesion to PMMA.

iii. Fluoropolymers:

Recent work reported from Japan suggests the use of visible light cured soft resins prepared by combining fluoroalkyl methacrylate monomers with a vinylidene fluoride/hexafluoropropylene co-polymer, or a vinylidene fluoride/tetrafkuoroethylene / hexafluoropropylene copolymer. They are reported to be more wettable than silicones to have low solubility and low residual monomer. Softer resins could be prepared by using lower molecule weight fluoropolymers. Such materials have been reported before, but they have not become widely available. There is one heat cured material of similar chemistry currently on the market (Kurepeet).

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DESIRABLE PROPERTIES OF A RESILIENT LINER

For maximum efficacy, soft lining materials should display the following properties:

1. They should be easily processed using conventional laboratory equipment.

2. They should exhibit minimal dimensional change during processing and such change should be the same as that of the denture base materials.

3. Water absorption should be minimal. Bates and Smith comment that a large water absorption may lead to swelling and stresses at the denture base interface, tending to increase distortion and reduce bonding. Ideally, the total water absorption should be close that of the acrylic resin denture base polymers, reported at 2.2%. The effects of prolonged immersion in water have been discussed by Braden and Causton. If swelling occurs, the bacteria and nutrient material in the mouth will find their way between the lining and the denture base, and the area becomes unhygienic.

4. The materials should have minimal solubility in saliva. Ideally the plasticizer (used in some materials) should not leach out with time, however, if leaching does occur, it should be minimal.

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5. They should retain their resilience. The degree of resilience will depend on the chemical composition of the material and the thickness of the soft lining. Several authors suggest that a thickness of 2 to 3 mm is most appropriate.

6. They should bond sufficiently well to poly (methyl methacrylate) to avoid separation during use. If the strength of the bond between the two materials is weak, separation takes place during use and such localized areas of separation rapidly become unhygienic because of the difficulty of cleaning.

7. Adequate tear resistance is of practical importance to resist rupture during normal use. This is because the propagation of a crack or small tear at the periphery of the soft lining could lead to failure and detachment of the material.

8. They should be easily cleaned and not affected by food, drink or tobacco. It is also important that the resilience and surface texture of the lining be unaffected by freely available denture cleaners of all types.

9. They should be non toxic, odourless and tasteless to encourage long term wear of the denture by the patient.

10. They should be aesthetically acceptable and their colour should match that of the denture base material.

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11. They should be easy to finish and polish. Adequate finishing and polishing of most of the resilient materials is quite difficult. The use of high speed sand paper disks, freezing the material, or the use of heated instruments has been suggested. The molding of the resilient plastic in the laboratory procedures is critical so that when cured it will need the least amount of finishing.

LIMITATIONS IN USE OF RESILIENT LINERS

The use of soft lining material on the fit (impression) surface of the denture is limited by a number of factors. These include:

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1. Reduction of the denture base strength:

The replacement of part of the denture base with a soft and easily deformable material will have an obvious effect on the flexibility and strength of the denture as a composite structure. When inter-ridge distance is limited and the denture base thickness is minimal, the placement of a soft lining will further reduce the overall strength of the denture and inevitable increase the tendency of the denture base to fracture.

2. Loss of softness and resilience:

Some of the soft linings are not stable in an aqueous environment such as the oral cavity. This is true of those materials using a plasticizer to increase softness and resilience, since the plasticizer will leach out and cause the lining to harden, limiting its usefulness. Thermal effects from the ingestion of hot and cold food and drinks may also have a deleterious effects.

3. Colonization by Candida albicans:

It has been suggested that the porosity of soft linings allows water absorption and the diffusion of nutrient material, which can easily become colonized by Candidal organisms.

4. Difficulty in keeping soft linings clean using normal denture cleaning methods:

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The use of conventional denture cleansers may cause bleaching, and the surface may become bubbled if an oxygenating cleaner is used. Ingested materials also present a problem. Bell has reported discolouration from various drinks, and tobacco staining has been reported by Makila and Honka and Bascom. The poor oral hygiene of most dentures with soft linings has generally been blamed on the difficulty in cleaning.

5. Dimensional instability:

Some soft linings lose their plasticizer with time, and most of them absorb water, these factors may cause dimensional chagnes.

6. Failure of adhesion:

A common finding is failure of adhesion between the silicone soft linings and the denture base resulting in ‘peeling off’ of the soft lining. A poor laboratory procedure may be the cause, although rough handling at an unsupported junction is a common culprit.

7. Difficulties in finishing and polishing:

Soft lining materials are difficult to trim, finish and polish. If excessive force is used, they may overheat or tear, leading to poor surface finish.

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The longevity of the soft liner though depends on correct processing procedures and proper home care.

INDICATIONS FOR USE FOR RESILIENT LINERS

1. Thin, non-resilient mucosal coverage

The provision of a resilient liner beneath a rigid denture base can improve both masticatory efficiency and oral comfort for patients presenting with a reduced thickness or lessened resilience of the oral mucoperiosteum.

2. Poor ridge morphology where the mental nerve is at the crest of the ridge

In some individuals, the gradual resorption of bone can lead to the mental nerve lying on the surface of the alveolar ridge. The nerve can be trapped between the denture and the tissue causing pain. Inclusion of appropriate relief on the master cast together with a soft lining may help to reduce the pressure on the nerve.

3. Persistent denture sore mouth

It may be due to occlusal problems, underlying bony irregularities, reduced keratinization of the epithelium with increasing age, and atrophic changes in postmenopausal women. If these have been eliminated but discomfort persists, soft lining materials may be used to line the fit (impression) surface of the denture. To be effective, a

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permanent soft lining should be about 2 to 3mm thick. The lining acts to absorb part of the force of occlusion, releasing the stored energy as elastic recoil. It therefore increases a patients ability to use a denture comfortably and may lead to relief of the symptoms of chronic soreness.

4. Acquired or congenital oral defects

Lammie and Storer suggested that soft lining material could be used for the cleft palate patient, or an acquired oral defect related to trauma, to improve retention of the denture by engaging undercuts. Soft lining materials are also used for obturators after maxillofacial surgery.

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5. Xerostomia

A soft lining may be indicated in those with a reduced saliva flow, possibly as a result of degenerative changes in the salivary glands, radiotherapy or drug therapy. Adequate saliva is benefit to the denture wearer both for lubrication and to aid retention and its absence can result in loose denture since the forces of adhesion, cohesion and negative atmospheric pressure are lacking.

However, the use of silicone resilient liners which lack wettability may result in trauma to the mucosa due to friction if the denture is loose and is dragged across the tissues. Candidal colonization of permanent resilient linings is a common feature in the edentulous patient with a dry mouth.

6. The need to promote mucosal healing

After implant surgery or with immediate dentures the dentures can be lined with resilient liners. The soft lining material assists in producing an even distribution of functonal load over the entire denture bearing area, avoiding local concentration of stress and to a limited degree reducing the overall load falling onto the denture bearing area.

7. In cases of bilateral undercuts

Lammie and Storer suggested that soft lining material may be indicated in the treatment of areas of bilateral undercuts, where placing a rigid acrylic resin denture is

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difficult and there is a problem of retention. Its use in this situation allows the denture to be placed over the prominence and since the soft material is elastic, it will spring back into close contact with the undercut area. Not only does this prevent air entrapment under the denture from reducing the retention, but the retention will be increased as the material will need to be deformed to remove the denture.

8. Irregular foundation

In the presence of a maxillary torus, mandibular tori, prominent mylohyoid ridges or in irregular bony foundations, soft lining may be indicated because there is usually an associated very thin mucosa covering these bony projections. However, the use of soft lining material in the maxillary arch is limited by the subsequent increase in thickness of the denture.

9. Single denture opposing natural teeth

In patients who have single denture either maxillary or mandibular opposing natural teeth or patients who are bruxers, the soft lining material acts to absorb part of the force of occlusion, releasing the stored energy as elastic recoil.

10. Mandibular distal extension base partial dentures

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Whitsitt et al state that soft lining material may be useful for improving retention in mandibular distal extension base partial dentures where there is retromylohyoid undercut and the presence of teeth limits the available paths of placement, resulting in an absence of valuable retentive and stabilizing areas of the denture extensions. To overcome this problem, acrylic resin material in undercut region of the retromylohyoid fossa is replaced with soft lining material.

MAINTENANCE OF PERMANENT SOFT LINING MATERIALS

Denture cleanliness is essential to prevent malodour, poor esthetics and the accumulation of plaque and calculus with its deleterious effects on the oral mucosa. Permanent soft linings can be colonized by Candida albicans and if not cleaned thoroughly can become stained and harbour odours.

Care must be taken in choosing an appropriate method of denture hygiene as inappropriate cleaning regimes can have deleterious effects causing hardening or bleaching of the soft lining.

For both silicone and acrylic resin soft lining materials, similar cleaning procedures are recommended. In brief, the denture should be rinsed after every meal and debris removed by brushing with a soft brush, liquid soap and cold water. The denture should be soaked in an alkaline hypochlorite solution for 20 minutes in the evening. The

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denture should be rinsed thoroughly with cold water overnight. The other main types of denture cleanser available for purchase over the counter can have mild effects on soft linings such as loss color from immersion in acidic cleansers.

Heavy smoking, fruit juices, tea, coffee, and wine cause discolouration and staining of the denture. Adjustment of the soft lining to ease pressure points caused by errors in the fit surface is best achieved by using the bur/trimmer provided with the resilient liner.

HOME RELINERS

Over the counter reliners or home reliners though not available in India, but available in the west cause more harm than good. This is because the customer believes the material can be used indefinitely, understanding only that new applications or changes must be made periodically. Because the customer has had no professional training and very likely, inadequate professional instruction in regard to his dentures and their maintenance, he is not expected to know of the changes occurring in his oral tissues.

Home reliner materials either induce or, certainly, perpetuate pathologic changes in the oral tissues. The affected tissues are the mucosa of the denture bearing areas and the supporting alveolar bone. Each additional application of the home reliner requires more material. This indicates

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bone resorption which creates more space between the tissue surface of the denture and the residual alveolar ridge.

When the home reliner material is applied to the denture and the denture is placed in the mouth, there is noticeable immediately an increase in the vertical dimension of occlusion with a concomitant decrease in the interocclusal distance. With insufficient interocclusal distance, the soft tissues are traumatized and resorption and deformation of the underlying bone occurs.

For these reasons the dental profession must be more emphatic in its instructions to denture patients. Patients must be instructed to return to the dentist for adjustments or corrections instead of using home reliner materials applied by an untrained individual.

Some specific controls regarding the sale of home reliner materials to the general public should be instituted by the appropriate federal agency.

CONCLUSION

The search for the ideal soft lining material for use beneath a removable dental prosthesis has resulted in the experimental and commercial exploitation of many different substances. Of the multitude of preparations advocated, none to date perfectly meets the exacting requirements for the ideal soft denture lining material, although careful use of

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heat polymerized silicone rubber materials have achieved some success.

Despite the considerable concern over the physical behaviour of this group of dental materials, their dimensional instability and their poor longevity, they hold an important place in the treatment of edentulous or partially edentulous patient.

It is hoped that the present resurgence of interest in the soft denture lining materials will lead to the early formulation of a material that is simple to form, stable in function and closely similar in visco elastic properties to the load-bearing mucoperiosteal tissue of the mouth.

Also it is hoped that more dentists use this invaluable material in their day-to-day practice, for the comfort of the patient.

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BIBLIOGRAPHY

1. Braden M., Wright P.S. and Parker S. : Soft lining materials – A review. Eur. J. Prostodont. Rest. Dent., 1995; 3 : 163-174.

2. Brown D. : Resilient soft liners and tissue conditioners. Br. Dent. J., 1988; 164: 357-360.

3. Gonzalez J.B. and Laney W.R. : Resilient materials for denture prosthesis. J. Prosthet. Dent., 1966; 16 : 438-444.

4. Jagger D.C. and Harrison A. : Complete dentures – The soft option. Br. Dent. J., 1997; 182 : 313-317.

5. Lammie G.A. Storer R. : A preliminary report on resilient denture plastics. J. Prosthet. Dent., 1958; 8 : 411-424.

6. Laney W.R. : Processed resilient denture liners. Dent. Clin. North. Amer., 1970; 14; 531-551.

7. Lekha K. : Comparative evaluation of physical properties and effect of water sorption of three different resilient liners currently available in India – An in vitro study, 1996 : Dissertation submitted to Karnatak University in partial fulfillment of the requirements for the degree of Master of Dental Surgery in Prosthodontics (Not published).

8. Mack P.J. : Denture soft lining materials : Clinical indications. Aust. Dent. J., 1989; 34: 454-458.

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9. Mack P.J. :Denture soft linings : Materials available. Aust. Dent. J., 1989; 34 : 517-521.

10. Means C.R. : The home reliner materials : The significance of the problem. J. Prosthet. Dent., 1964; 14 : 1086-1090.

11. Parker S. and Braden M. : New soft lining materials. J. Dent., 1982; 10 : 149-153.

12. Qudah S., Harrison A. and Huggett R.: Soft lining materials in prosthetic dentistry : A review. Int. J. Prosthodont., 1990; 3 : 477-483.

13. Razek MKA : Assessment of tissue conditioning materials for functional impressions. J. Prosthet. Dent., 1979; 42 : 376-380.

14. Von Fraunhofer J.A. and Sichina W.J.: Characterization of the physical properties of resilient denture liners. Int. J. Prosthodont., 1994; 7 : 120-128.

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CONTENTS

Introduction

Terminology

Historical Background

Review of Literature

Materials and Composition

Desirable Properties

Limitations

Indications

Maintenance

Homeliners

Conclusion

Bibliography

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