Denture Soft Liners

Dr. Leslie Laing
Authored by:
Dr. Leslie Laing

Introduction

Denture soft lining materials provide a spongy, cushioned interface between the hard base of a denture and the oral mucosa. They are used “to resurface the tissue side of a removable dental prosthesis with new base material, thus producing an accurate adaptation to the denture foundation area”1. They are often prescribed for a patient who describes their denture(s) as being loose, slipping, or falling down, or causing pain, and sometimes are prescribed inappropriately. The denture must be clinically acceptable prior to having a reline procedure performed, since the procedure offers no advantage to an ill-fitting, malfunctioning, poorly made prosthesis. As Boucher explained, relining dentures “is one of the most difficult and trying procedures in prosthodontics, however, it can be effective if the denture was made correctly during the initial fabrication and if a precise technique is performed with meticulous attention to every detail 2”.

The liners are generally tear resistant, biocompatible, odourless and tasteless, resistant to abrasion, stable with respect to colour and dimension, easy to adjust and clean, insoluble and non-adsorbable in saliva, and have adhesive bond strength with little effect on the denture base material 3.

There are two categories of soft liners: those that are used in temporary or transitional situations, and those that are used on a more permanent basis. The latter ones will not be discussed further in this article.

Temporary Soft Liners

According to the International Organization for Standardization (ISO), short-term liners are those used intraorally for up to 30 days. These include the tissue conditioners and temporary soft lining materials. The materials are viscoelastic and able to flow under steady pressure and at the same time are resilient under such dynamic forces as chewing 3,4. As a result the energy is absorbed by the soft liner while undergoing deformation rather than by the underlying supporting tissues, allowing a “uniform distribution of stress at the mucosa/lining interface” 3,5. With proper care, the liners are generally tear resistant, biocompatible, odourless and tasteless, resistant to abrasion, stable with respect to colour and dimension, easy to adjust and clean, insoluble and non-adsorbable in saliva, and have adhesive bond strength with little effect on the denture base material4. They come in a powder and liquid form which are mixed to form slurry. The setting reaction is a physical, rather than chemical one in which the liquid, containing an aromatic ester and ethyl alcohol, penetrates the powder particles, typically composed of poly (ethyl methacrylate), to form a gel. Over time, as some of the components such as ethyl alcohol leach and evaporate, the gel hardens, which may necessitate frequent replacement of the lining.

Tissue Conditioners

These are soft materials (e.g., COE-Comfort) which are applied on a temporary basis to the impression/intaglio surface of a denture in situations where the oral mucosa has been traumatized4,5. By doing so, a more even distribution of load is achieved in the denture bearing area (DBA), which promotes healing of the traumatized tissues. It should be noted that prior to using tissue conditioners, the dentures should first be assessed and relieved of any areas of pressure, occlusal errors, or incorrect denture base extensions.

The use of a tissue conditioner and enforcement of improved oral hygiene may be indicated prior to the fabrication of a new prosthesis if there are indications of inflammation in the DBA. The tissue conditioning material should be replaced every 3-5 days for 2 or more weeks until the damaged oral mucosa returns to a healthy state.

Temporary Soft Reline Materials

These are soft materials (e.g., COE-Soft, Visco-Gel) which are applied on a temporary basis to the impression/intaglio surface of a denture. There are at least 3 situations where use of a soft reline is necessitated: 1) for an immediate denture until sufficient post-extraction resorption has occurred, which is usually a minimum of 6 months 3,4,6,7 2) following preprosthetic surgery such as removal of tori, exostosis, or reductions of tuberosities or the mylohyoid ridge to aid in post-extraction haemostasis and reduction of oedema by acting as a pressure bandage; and 3) following implant placement, whereby the denture is relieved in the area of the implant healing abutments and soft reline material is placed to prevent direct contact between the denture-base and the implant(s). In each of these cases, it is acceptable to leave the material in situ for a longer period of time than would be appropriate for a tissue conditioner, however, if left too long, it may itself cause tissue damage when it becomes rough and hard3,4. The material must still be changed frequently to maintain its resilience.

Method of Use

Prior to a tissue conditioner or soft reline material being applied, the intraoral tissues as well as the impression/intaglio surface of the denture must be clean and dry. Although the liquid monomer and powder may be mixed according to the manufacturer’s directions, this is one situation where the amounts may be varied according to the practitioner, depending upon the amount, flow, or viscosity of the material required. The liquid monomer is placed in a mixing bowl or cup. The powder is folded into the liquid in incremental amounts, taking care not to incorporate bubbles into the mixture. Powder is added to the liquid until the slurry resembles thick liquid honey. At this stage, the mixture is applied to the impression surface of the denture acrylic. The dentures are inserted and gently brought into maximum intercuspation or the appropriate interocclusal relation for approximately 2 minutes. To aid in patient comfort, patients may then be asked to bite down onto cotton rolls for a further 2 minutes. Muscle moulding is carried out concurrently. The material generally sets after approximately 6 minutes, after which time excess material is removed with a heated instrument, scalpel, or scissors, taking care to protect the moulded peripheries. The polished and occlusal surfaces of the dentures are then wiped clean with alcohol-moistened gauze.

Maintenance of temporary soft lining materials

When not in use, patients should be encouraged to keep the relined dentures in water rather than in a commercial denture cleanser which can cause bubbling and deterioration of the reline surface. The dentures should be rinsed in water after each meal, but brushing of the impression/intaglio surface should be avoided. Inappropriate cleaning techniques may have a damaging effect leading to a more rapid deterioration, discolouration, malodour, hardening of the reline material which may result in subsequent damage to the underlying intraoral supporting tissues4.

Limitations of Temporary Soft Reline Materials

Since the reline material is applied to the tissue side of the denture base, the addition will ergo cause a change in the vertical dimension. Excessive material may also cause the denture bases to shift during the reline procedure. It is imperative that the depth of the material applied not be excessive enough to cause the interocclusal space to be decreased causing a change not only in occlusion and aesthetics, but also in comfort.

Soft liners have also been shown to promote the growth of C. albicans3,8. Denture cleanliness is stressed to prevent fungal growth and subsequent staining and malodour.

 

References: 

The Glossary of Prosthodontic Terms. J Prosthet Dent 2005;94(1):10-92.

Hickey JC, Zarb GA, Bolender CL. Boucher’s prosthodontic treatment for edentulous patients. 9th edition. St. Louis (MO); CV Mosby Co.; 1985, p 99.

Garcia, L.T., Jones, J.D. Soft liners. Dent Clin N Am 2004;48:709-720.

Jagger, D.C., Harrison, A. Complete dentures – the soft option. An update for general dental practice. Br Dent J 1997;182(8):313-317.

Braden M, Wright PS, Parker S. Soft lining materials – a review. Eur J Prosthodont Restor Dent 1995;3(4):163-174.

Watt DM. Morphological changes in the denture bearing area following the extraction of maxilliary teeth. Edinburgh: University of Edinburgh, 1960. PhD Thesis.

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

Nikawa H, Yamamoto T, Hamada T. Effect of components of resilient denture-lining materials on the growth, acid production and colonization of Candida albicans. J Oral Rehabil 1995;22:817-824.