| Abstract|| |
This report presents an alternative method for the retention of partial dentures that relies on the engagement of tooth undercuts by a lining material. The lab procedures are also presented. A new maxillary and mandibular acrylic partial dentures were fabricated using elastomeric retention technique for a partially dentate patient. A partially dentate man reported difficulty in retaining his upper removable partial denture (RPD). The maxillary RPD was designed utilizing elastomeric retention technique. During follow-up, it was necessary to replace the retention rings due to wear. The replacement of the retention rings, in this case, was done through a chairside reline technique. Elastomeric retention technique provides exceptionally good retention can be indicated to stabilize, cushion, splint periodontally involved teeth, no enough undercut for clasps, eliminate extractions, single or isolated teeth.
Keywords: Cu-Sil overdenture, elastomer, elastomeric retention technique, retention rings, windowed partial denture
|How to cite this article:|
Revathi K, Reddy SS, Reddy KK. Enhancing retention of partial dentures using elastomeric retention rings. Indian J Dent Res 2015;26:328-32
Conventional partial denture designs tend to utilize clasping elements, guide planes in order to retain the appliance. The use of these techniques within the design of the appliance has been shown to be successful. Despite this, there are occasions when the pattern of tooth loss is such that the conventional techniques struggle to provide sufficient retention, especially, when there are few remaining teeth, and/or their position in the arch is unfavorable. Window partial denture using the relining material to engage tooth undercuts may be suitable in challenging cases to provide an alternative method to retain an appliance.,
|How to cite this URL:|
Revathi K, Reddy SS, Reddy KK. Enhancing retention of partial dentures using elastomeric retention rings. Indian J Dent Res [serial online] 2015 [cited 2019 Jan 21];26:328-32. Available from: http://www.ijdr.in/text.asp?2015/26/3/328/162889
A soft (resilient) lining material acts as a cushion between the hard denture base and the tissues to reduce the masticatory forces transmitted by the prosthesis to the underlying tissues. Elasticity ensures that the material will regain its original shape following deformation, while resilience is also important because it determines the rate of recovery.,
A review of the literature revealed two articles in peer-reviewed journals with regards to the retention technique described in the present paper. However, there were two references on the Internet that described a comparable technique with regard to the "Cu-Sil® overdenture."
| Case Reports|| |
In Case 1, the elastomeric material used was Molloplast-B® (Detax Cmbh and Co., KG, Germany). This is a heat-polymerized silicone rubber, and is supplied as a one-paste system activated by heat (immersion in boiling water for 2 h). An adhesive (y-methacryloxypropyltrimethoxysilane, a silicone polymer in a solvent) is supplied to aid bonding to the denture base. The adhesion of this material to polymethylmethacrylate is good, and it has been suggested that it is less prone to support the growth of Candida albicans, the lowest amount of microleakage than other comparable material.,
In Case 2, Super-Soft resilient denture liner (GC America Inc., USA) was used, it is a resilient, permanent heat processed liner that is suitable for old or new, maxillary, or mandibular dentures. This product contains zinc undecylenate, an antiseptic, astringent, and fungicidal agent that slows down the potential fungal growth and prevents odor. The controlled degree of softness, which is applied by adjusting the powder/liquid ratio, offers a range of softness to accommodate the patients.
The objective of the present paper was to present a report of two patients with very few remaining teeth, who were successfully rehabilitated using the windowed partial denture (WPD) concept. The technical stages of denture construction are also presented.
A 42-year-old man had reported to the dental department with missing teeth. On examination, he was partially dentate, with the remaining dentition consisting of 17 and 18 in the maxilla, and 47 in the mandible; where 17, 18, and 47 provided the occlusal stops [Figure 1]. A new maxillary and mandibular acrylic partial denture were fabricated with an improved retention from the elastomeric retention technique. The denture acrylic totally encircled the 17, 18, and 47 providing resistance to the tilting movements, and Molloplast-B® was used to line the windows in the denture base, thus, engaging the undercuts around these teeth. Even occlusal contact was achieved with freeway space of approximately 3 mm.
The patient was very happy with the esthetics, retention and function of his new denture follow-up was done for 1½ year.
A 63-year-old man had reported to the dental clinic with difficulty in retaining his upper removable partial denture (RPD). He was partially dentate with remaining dentition consisting of 21, 22 [Figure 2]. The patient had good oral hygiene and healthy periodontium around the two remaining teeth. The maxillary RPD was designed utilizing the two remaining teeth by using Super soft resilient denture liner for elastomeric retention technique. During 15 months follow-up, it was necessary to replace the retention rings on one occasion due to wear. The replacement of the retention rings, in this case, was done through a chairside reline technique using soft liner (soft denture reline material, GC Corporation, Tokyo, Japan), which is detailed in the discussion section of this article.
|Figure 2: Occlusal view showing remaining maxillary teeth (mirror-image)|
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The technical stages for the fabrication of an RPD utilize conventional denture processing techniques. A detailed account where will be given for the fabrication of the maxillary and mandibular RPD for the patient in Case 1; where Molloplast-B® was used, followed by a description of the special considerations, which were necessary for Case 2, where Super-Soft was used.
Following diagnosis and treatment planning, impressions were made. A working model was obtained. Casts were surveyed to highlight areas of undercut around the teeth to be included in the "window." After the occlusal registration stage, the models were articulated. Wax try-in of the dentures was done, and centric was reverified. The dentures were prepared for processing.
Both mandibular and maxillary dentures were sealed using wax. It is advisable to cover the occlusal surfaces of the teeth, where the elastomeric material is to be inserted to enable easy adjustment while trimming and to ensure that the elastomer has a tight fit against all surfaces except the occlusal surface.
The trial dentures were then flasked. The flasks were then inserted into boiling water for 10 min and then opened. All remaining wax within the flask was flushed out using a stream of boiling water. After the wax had been boiled off, the cast was left to dry. The undercut areas around the teeth (previously identified by surveying the cast) were then blocked out using soft putty material [Figure 3]. Heat cure acrylic (lucitone) was mixed as per the manufacturer's recommendations. All areas within the flask were coated with separating media (sodium alginate) to prevent monomer seepage into the plaster on curing. This ensures a clean denture when deflasked. When packing the acrylic into the mold, the trial pack technique was used because it allows the flask to be opened after compression of the acrylic.
|Figure 3: Usable tooth undercuts blocked with condensation silicone for trial packing|
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A polythene sheet was placed between the acrylic and the fitting surface of the mold. The flask was closed together with the plastic sheet in place and placed in the hydraulic press. The flask was left for 3 h in the hydraulic press for the acrylic to harden. The flask was opened, and the block-out putty material around the abutment teeth removed. The model was recoated with separating media. The silicone elastomeric material (Molloplast-B®) was placed around the abutment teeth in the area of undercut [Figure 4] without the polythene sheet, and the flask was closed and compressed in the hydraulic press. The flask was then placed in a clamp and cured overnight. The flask was opened, the flash trimmed off and the denture were rearticulated using the split cast technique. Occlusal errors were then identified and corrected by selective grinding. The occlusal surfaces of the abutment teeth were exposed by cutting away the acrylic over them [Figure 5] and [Figure 6]. The denture was then trimmed and polished [Figure 7].
|Figure 4: Soft lining material (Molloplast-B) around teeth prior to curing|
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|Figure 7: Fitting surface of denture demonstrating the elastomeric retention rings|
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In Case 2, the same above mentioned lab procedure was followed but Super-Soft was used. Since the retention ring was worn out in one of the occasions, the replacement of the retention ring was done through a chairside reline technique using a soft liner.
| Discussion|| |
A soft lining material may be defined as a soft elastic and resilient material forming all or part of the fit (impression) surface of a denture. Elasticity ensures that the material will regain its original shape following deformation while resilience is also important because it determines the rate of recovery. This has led some to label these materials as resilient, but soft lining material is more correct, as it is the softness or ease of deformation that particularly separates them from other denture base materials.,,
Permanent soft lining materials can be broadly classified as plasticized acrylic resins ("soft acrylics") or silicone elastomers ("silicone rubbers"). Both are subdivided into heat and auto-polymerized types.,,
Elastomeric retention technique involves the incorporation of "windows" in an acrylic partial denture, lined with a silicone reline material for effectively forming elastomeric retention rings, which fit snugly over the selected abutment teeth. Deformation of the soft lining material on seating the denture allows the retention rings to engage circumferentially undercuts on the abutment teeth, thereby increasing the retentive capabilities of the prosthesis.
WPD technique provides exceptionally good retention in otherwise very difficult circumstances. Can also be indicated when there is need to stabilize, cushion, and splint periodontally involved teeth need for a transitional denture, no enough undercut for clasps, eliminate extractions, single, or isolated teeth.,
However, these dentures have some disadvantages. Since, it covers the entire gingival margin of the abutment teeth, it is thought to increase plaque accumulation. In addition, the appliance may have a little tooth support, other than regions above the survey line on abutment teeth where the acrylic housing contacts tooth structure. Parafunctional activity such as bruxism should be considered (lingual reinforcement, or perhaps the use of a high-impact acrylic, to ensure adequate strength, and rigidity).,,,
Factors to be considered include the selection of abutment teeth, their number and location in the dental arch, the degree of undercut, and periodontal condition. Two or more abutments on opposite sides of the dental arch, which are adequately spaced will help to distribute functional forces, and provide a broader supporting base. However, single or adjacent abutments may also be used [Figure 2]. Canine, premolar, and molar teeth are the preferred abutments due to the greater support they can provide., The path of insertion and removal should be determined on the diagnostic cast. If the undercut on the selected tooth is too severe, an extra coronal restoration (e.g., crown) should be considered. If there is inadequate undercut, it can be created clinically by bonding composite resin onto the preferred abutment.
An effective home care regimen should be instituted. Patients should be reviewed at regular intervals to monitor their progress with the prosthesis and the condition of the abutments.
Deterioration of the retention rings will occur over a period of time, which include changes in the physical properties of the material (hardening, roughening, cracking, or tearing), loss of adhesion to the polymethylmethacrylate base or contamination by stains, calculus. They can be easily renewed using a conventional laboratory reline procedure or by chairside treatment. In laboratory technique, a pickup impression is made of the RPD, and the remaining natural teeth using a stock tray and irreversible hydrocolloid. Then, pour a model with the RPD in situ and replace the elastomeric retention rings in the denture.
Chairside treatment involves removal of the old retention rings, roughening of the adjacent acrylic, and application of two coats of adhesive (30 s apart), which is allowed to dry for 90 s. Soft lining material is then applied to the acrylic surface of the denture windows, and the denture inserted into the patient's mouth for approximately 3 min. The denture is then removed from the patient's mouth and immersed in water [Figure 8].
|Figure 8: Occlusal view showing denture relined with soft liner (mirror-image)|
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| Conclusion|| |
An alternative technique like WPD along with usage of resilient soft liners increases the longevity of remaining natural dentition in situations otherwise where patients or clinical circumstances complicate other prosthodontic treatment options.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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Department of Prosthodontics, A.C.P.M. Dental College, Dhule, Maharashtra
Source of Support: Nil., Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]