DESIGN PRINCIPLES FOR A GOOD ACRYLIC PARTIAL DENTURE
In a similar manner to an RPD design for a cobalt-chromium denture, the casts should be surveyed and, where appropriate, articulated to assist in the design. The design of acrylic dentures will follow the same principles involved with a cobalt chrome denture3 and should consider the following:
- Bracing and reciprocation
- Indirect retention
- Review of completed design.
Saddles are designed to fill the edentulous space to be replaced. However, the saddle must be fully extended in the distal extension edentulous area. When designing the denture the clinician should look to increase the tooth borne support of the denture and not rely exclusively on mucosal support. This may be obtained by finishing the denture above the survey line in those places where the acrylic components contact the tooth.
The acrylic has been finished above the survey line in order to obtain support from the remaining teeth
It is possible to avoid contact with the gingiva and obtain relief by blocking out the dentogingival junction, although this is controversial. It has been found that deterioration in gingival health will occur whether relief is present or not.
Retention will generally be a wrought clasp, which will be attached to the acrylic and will require reciprocation. Connection will usually be acrylic or, where strength and reduction in bulk is indicated, then a cast cobalt chrome framework is designed. In order to obtain indirect retention, the clasp must always be placed between the saddle and the indirect retainer. Finally, the completed design is reviewed against a checklist of the design principles.
Wherever possible, any coverage of gingival margins should be avoided or reduced to an absolute minimum and this is combined with a high level of oral hygiene.
Any uncovering of the gingival tissues is beneficial as shown by the old denture design
(a) compared to the newer design (b).
The patient should be instructed in the correct oral hygiene measures and advised on correct denture care, both at the insertion stage and review. This should include disclosing of the denture on review appointments and indicating where the denture is not being cleaned properly. The use of a suitable denture cleanser is advocated.
If there are metallic components associated with the denture, such as clasps, then these should not be placed in the cleanser. Avoidance of candida albicans growth within the denture will prevent denture stomatitis. The subsequent inflammation and swelling of the tissues will lead to an ill-fitting denture.
(a) The oral mucosa exhibits inflammation owing to candidal infection and there is plaque retained around the teeth. (b) Disclosing of the denture shows that compliance with denture hygiene instruction is required to remove the plaque.
Processing of RPDs
A simple, but often overlooked, technique to provide well-fitting acrylic dentures is to ask the technician to block out undercuts, including any interdental spaces prior to processing. First, the cast is surveyed to the path of insertion (which is generally vertical to the occlusal plane). The undercuts on the master cast are blocked out with wax or plaster and a duplicate cast is obtained.
The undercuts are blocked out with wax prior to obtaining a duplicate cast.
The denture is then processed on this duplicate cast. If such a simple but effective technique is not done, then the acrylic denture will only fit once the undercuts are removed. This process takes place by the chairside and may often turn out to be a lengthy procedure. As the clinician attempts to fit the denture, excessive acrylic is often removed, leading to the denture not contacting the hard and soft tissues.
The six design features required for a successful Every denture