Clinical review on liquid supported dentures

Transcription

1 Review Article Clinical review on liquid supported dentures Ashish R. Jain* ABSTRACT An ideal complete denture should be flexible and adapts well to the tissue surface and should provide proper retention. Conventional complete dentures lack flexibility and softness on the tissue surface and are more rigid. Due to the rigidity of the conventional dentures, the distribution of load is not even, especially in case of flabby, atrophic ridges with increased bone resorption. To overcome this disadvantage, the liquid dentures are fabricated in such a way that denture base is covered with a pre-fabricated flexible, foil which helps in proper adaptation to the mucosa in functional and non-functional states. Liquid-supported dentures provide good retention, stability, and support. The liquid supported denture allows continued adaptation and eliminates the disadvantages of denture designs based on the application of temporary tissue conditioners or soft liners. This article describes the uses of liquid supported dentures and its advantages. KEY WORDS: Denture base, Liquid supported denture, Masticatory forces, Ridge INTRODUCTION The edentulous residual ridge tends to change in dimensions due to changes that occur in mucosa and bone absorption. [1] The ideal properties of a denture are adequate rigidity on polished surface of the denture to bear masticatory forces and at the same time, flexibility and softness on the tissue surface for proper and even distribution of masticatory forces. Fibrous or flabby ridge is a superficial area of mobile soft tissue affecting the maxillary or mandibular alveolar ridges which his developed when hyperplastic soft tissue replaces the alveolar bone and is a common finding, particularly in long-term denture wearers. Such ridges are reported to be caused due to trauma from denture bases. Major problems encountered in these patients are loss of stability and inadequate retention of the dentures. These problems occur because of the easily distorted flabby tissue during impression making. An ideal denture base would continuously adapt to the mucosa and thus should be flexible. However, it also has to support the teeth during function and thus should be rigid. Obviously, these properties cannot be combined in one material, but in combinations of materials, Access this article online Website: jprsolutions.info ISSN: the base can be rigid where it needs to be strong and flexible when in contact with the soft tissues. [2] In 1961, Chas reported on the application of elastic impression materials on the mucosal side of the rigid base to relieve the traumatized soft tissue. Since then, a variety of tissue-conditioning materials has been introduced. [3] Another group of materials called soft liners has been used to relieve denture sore mouth problems. They essentially differ from the tissue conditioners because they are plastic and therefore flow continuously under masticatory pressures; until ultimately no material is left where it is required. Consequently, soft liners are also only temporary provisions because due to loss of plasticizer over period of time they lose their plastic properties. [4] CONVENTIONAL DENTURES Conventional dentures are removable denture which are fabricated for the replacement of teeth and the related structures. [5] The tissue surface of the denture is rigid leading to uneven distribution of load most commonly in case of flabby, atrophic, and unemployed ridges with excessive bone resorption. When conventional complete denture does not suit patient s needs, certain modifications are made to meet the Department of Prosthodontics, Saveetha Dental College and Hospitals, Saveetha University, Chennai, Tamil Nadu, India *Corresponding author: Dr. Ashish R Jain, Department of Prosthodontics, Saveetha Dental College and Hospitals, Saveetha University, Poonamallee High Road, Chennai , Tamil Nadu, India. Phone: dr.ashishjain_r@yahoo.com Received on: ; Revised on: ; Accepted on:

2 patient s requirements. Such dentures can be termed as special or unconventional complete dentures. Not every case of edentulism, either complete or partial, can be treated with conventional methods of denture fabrication. There is a need for slight modification in impression procedure or designing of the prosthesis to achieve best results in case of compromised conditions. VARIOUS TYPES OF NON- CONVENTIONAL DENTURES Characterized denture Cheek plumper Cu-Sil denture Duplicate denture Flexible denture Hallow denture Immediate denture Internally weighed denture Labeled denture Liquid supported complete denture Metal-based denture Dentures by neutral zone method Overdentures Saliva reservoir denture Sectional complete denture. LIQUID SUPPORTED COMPLETE DENTURE These dentures have a flexible base which is liquid filled to provide a cushioning effect to the ridged mucosa. They continuously keep on adjusting with the resorbing ridge to keep it well adapted. [6] LAYERS IN LIQUID SUPPORTED DENTURE Polythene sheet, Liquid (glycerine), Denture base, Denture teeth. [7] INDICATIONS Patients with flabby ridge Diabetic patients with rapid bone resorption Patients with xerostomia or atrophied ridges. [8] STEPS IN FABRICATION 1. Vacuum heat pressed polyethylene sheet (Biostar vacuum forming machine, Scheu-dental, Germany) of 1.5 mm thickness was adapted on the master cast. The sheet should be cut 2 mm short of the sulcus and should not extend in the posterior palatal seal area. 2. Now denture should be acrylized using heat resin along with sheet. 3. Finishing and polishing of the denture should be done and its checked in patients mouth for retention, stability, support, and border extension. The patient should be asked to wear the denture for at least 2 weeks so they can get adjusted to the new denture. 4. At recall appointment, the 1.5 mm thick sheet which was used as a spacer should be removed from the denture. Due to the removal of the sheet crevices were formed all along the denture orders. These crevices were helpful in final placement of 0.5 mm thick sheet. An addition silicone putty impression is to be made of the tissue surface of the denture and cast made of it. This helps to record the junction of the sheet to the denture. On this cast, a 1.5 mm thick sheet is used in place of 0.5 mm vacuum pressed thick polyethylene creating a 1 mm space. 5. The borders of the 0.5 mm thick sheet are placed in the crevice formed due to removal of 1.5 mm thick sheet. Cyanoacrylate adhesive and auto polymerizing acrylic resin are used to seal the borders and prevent the escape of liquid. 6. Glycerine is filled in this space by making two holes in the buccal flange area of the denture and injecting it through these holes and checking the vertical dimensions simultaneously. The holes are then sealed using self-cure acrylic resin. 7. Finally, the liquid supported denture is delivered to the patient. Denture care instructions must be given to the patient. The patient is also advised to clean the tissue surface using a soft brush and recalled for follow-up. [9] The principle of this design is that a liquid-supported denture provides the requirements postulated in the introduction. Thus, the denture base is covered with a pre-shaped, close-fitting, flexible foil to keep a thin film of liquid in its place. This design will act as a continuous reline for the denture and thus has advantages over existing denture design. An important function for retention is a close adaptation of the denture base to the soft tissue which is fulfilled by a fluid-supported, pre-shaped foil. When no forces are applied, the foil assumes the form in which it was preshaped during the processing phase. The liner acts as elastic tissue conditioner by which the original contours are preserved. [10,11] If masticatory loads are applied, the foil can adapt to the modified form of the mucosa because of the hydrodynamic plasticity of the supporting liquid beneath the foil. In this situation, the liner acts as a soft liner. After unloading, the foils recover its basic form. Apart from the combined benefits of tissues conditioners and soft liners, such a denture will 2277

3 have optimal stress distribution during masticatory functions. Load from biting forces and even bruxism will be distributed over a larger area. Thus, pressure spots and overloading of the supporting tissues may be reduced. Vertically directed loads will also be distributed in other directions by the liquid, which minimizes local stressing of the supporting tissues. The spreading of the pressure might also reduce problems at the mental foramen in a resorbed mandible, and a long-term advantage could be slower and more even resorption of the residual ridge. When loading of the base takes place, the liquid will be squeezed to the border where it contributes to a stabilizing pressure along the borderline. Although the fine detail of contour in the denture might be partially lost using acrylic resin, the overall close fitting of the liquid-supported denture will contribute positively to retention based on suction. The disadvantage of surface detail in a hard denture base is irritation of the soft tissue caused by lateral movements. [12] Moreover, retention that is also based on adhesion and wettability by saliva can be controlled using smooth hydrophilic materials. For retention of a denture, it is also essential that it has a proper form and a border seal that prevents the passage of saliva and air. [12,13] This seal is formed by the posterior palatal seal in the maxillary denture. The borders of the liquid-supported denture are formed of acrylic resin material covered by the foil. The surface of the foil will remain more dense than the worn surface of an acrylic resin denture which can be beneficial for patients with allergic reactions. Major problems associated with this case were the presence of combination syndrome due to unfavorable distributions of forces that can cause unfavorable tissue changes. These problems were solved by modifying the impression procedures and by fabrication upper liquid supported denture and lower cast partial denture. Liquid supported denture is based on the theory that when no forces are applied, the foil assumes the form in which it was pre-shaped during the processing phase. The liner acts as an elastic tissue conditioner by which the original contours, when the impression was made, are being preserved. If masticatory loads are applied, the foil can adapt to the modified mucosa because of the hydrodynamic plasticity of the supporting liquid beneath the foil. In this situation, the liner acts as a soft liner. Proper selection of the viscosity of the liquid ensures the desired inertia of the movements and thus stability. [2] PRECAUTIONS There should be a minimum of 3 mm thickness of the denture base. Proper seal should prevent microleakage. Denture care instructions should be given to the patient. Repair is possible. To prevent leakage, a dense foil which protects the denture from contamination of Candida albicans and other microorganisms, thus protecting the mucosa from bacterial irritation. [14,15] In this case, the polyethylene thermoplastic clear sheet was used because of its softness, flexibility, and biocompatibility. Glycerine was used because it is colorless, odorless, viscous, and biocompatible. [16] The adhesive used is n-butyle-2 cyanoacrylate, which is used in surgery as an alternative to suturing and as a protective covering over ulcers. ADVANTAGES Better retention, stability, support, and comfort due to continuous adaptation with the oral mucosa. Optimized atmospheric pressure, adhesion, cohesion, and mechanical interlocking in undercuts. Improved patient comfort due to smooth, flexible surfaces. Prevention of chronic soreness from rigid denture bases. Hydrodynamics of the liquid provides good adaptation of the base and as well as improves support, retention, and stability. Even distribution of masticatory forces which reduces overloading of tissue, preservation of residual ridge, and prevention of soreness. [7] INSTRUCTIONS TO THE PATIENT Denture care instructions were given to the patient. In case the liquid leaks out, the patient should inform the dentist, and the denture should be refilled. Repair was possible if the sheet gets ruptured and can be replaced over the preserved stone replica. Liquid supported denture is flexible and adapts well to the mucosa. [1] also it is rigid enough to support the teeth. The denture base is covered with a preshaped, close-fitting, flexible foil to maintain moisture between the denture base and the foil. This acts as a reline for the denture. [17] The close adaptation of the denture base to the soft tissues provides proper retention to the denture. [3] The polyethylene sheet was used due to its biocompatibility and excellent physical and mechanical properties. It is flexible, soft, and 2278

4 dense and protects the mucosa from bacterial and biomechanical irritation. [18] The adhesive used is n-butyl -2 cyanoacrylate which is used in surgery as an alternative suturing and as a protective covering over the ulcers, etc. For cushioning effect, glycerin was used which is a clear, colorless, and odorless liquid. It has proven safe in vivo studies. The thickness of denture base was at least 3 mm seal was perfect and was checked for microleakage. [19] SALIVA SUBSTITUTES In a study of management of xerostomia patient, artificial saliva was used in the fabrication of the denture to maintain salivary flow. A conventional maxillary complete denture was fabricated with a palatal portion being thinned out, and zinc oxide eugenol paste was used as a spacer over which a modeling wax sheet was adapted and processed in heat polymerized resin which was then attached to the maxillary complete denture after removing the spacer using auto-polymerizing resin. In acrylic plate, two small openings were made, and artificial saliva was filled using a syringe. [20] Two release holes of 0.2 mm are made, one in the rugae area and other one in the posterior part of the palate. For mandibular denture, the reservoir is fabricated in the lingual flange. The internal surface is cleaned with water every day and 7% sodium hypochlorite every 15 days. Different types of artificial saliva to overcome xerostomia for a longer period are available. In cases where saliva cannot be stimulated, the treatment involves the use of salivary substitutes. Salivary substitutes contain thickening agents such as carboxymethyl cellulose or mucin, Biotene, and mucopolysaccharides. Artificial saliva is used for xerostomia patients which humidifies the oral cavity, particularly protecting it from irritative mechanical or chemical factors and infections. Such preparations consist of aqueous solutions containing glycoproteins or mucins, and salivary enzymes peroxidase, glucose oxidase, or lysozyme. Polymers such as carboxymethyl cellulose have also been used with the aches to fabricate the reservoir dentures within the available space either in the maxillary denture or mandibular denture. The artificial saliva can be classified into three groups: a. Glycerine and lemon: They are the simplest but, if natural teeth are present, it may also cause erosion; glycerine is astringent and may sting the soft tissues. b. Based on carboxymethyl cellulose. c. Based on mucin; mucin-based artificial saliva has reservoirs. Milk can also be recommended as a salivary substitute. Few saliva substitutes are based on pig products (bovine/porcine) can also be used as a salivary substitute. A water-soluble extract of linseed oil has been found to have physical properties similar to glycoproteins of saliva. Salinum is based on this linseed oil. Few commercially available substitutes are lubricant containing lactose peroxidase, glandosane (fresenius), saliva orthona (nycomed) containing porcine mucin, Biotene containing polyglycerol methacrylate, lactoperoxidase and glucose oxidase, and salivix pastilles (tablets). CONCLUSION Flabby ridges are challenging to achieve stability and retention of the denture. Excision of the fibrous tissue and possibility implant-retained prostheses may not be possible in all cases. Considering conventional prosthodontics, the use of liquid supported denture has become more popular. Liquid supported denture is proved to have more advantages than the conventional complete dentures and thus fulfills the DeVan s dictum Preservation of what remains is of utmost important rather than meticulous replacement of what has been lost. It exhibits characteristics of plasticity and elastic recovery and provides good retention, stability, support, and patient comfort. REFERENCES 1. Atwood DA. 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