A well-fitting record base is critical for the evaluation of the vertical dimension of occlusion, the centric relation position of the mandible relative to the maxilla and the trial set-up of the denture teeth. A retentive record base with contours similar to the definitive complete denture provides the opportunity for the clinician and the patient to appropriately evaluate the prosthesis prior to processing the denture base.
A vacuum formed thermoplastic trial denture base provides the opportunity to evaluate extensions, the posterior palatal seal, lip support and articulation of speech sounds while maintaining the master cast intact.
The MiniSTAR S (Great Lakes Orthodontics) has the ability to apply positive pressure onto the master cast while simultaneously creating a vacuum beneath the master cast in order for a thermoplastic material with adequate and predictable thickness to be fully adapted to the supporting structures.
- Construct a working model, modify to add posterior palatal seal and apply separating medium.
- Position cast within the vacuum-forming machine using lead pellets to expose the area of the denture base.
- Heat the 1.5mm thick Clear Splint Biocryl material for 70 seconds, apply air pressure, vacuum and cool.
- Cut material to land area, remove trial base and trim.
- Roughen the residual ridge portion of the denture base with an acrylic bur.
- Add "sticky-wax" to the record base; add wax rims, complete inter-occlusal records and mount working models.
- Complete denture tooth set-up contour wax by adding thickness to the border areas and to the denture base providing adequate tissue support.
- Complete denture trial appointment, evaluate as appropriate for denture tooth esthetics, tissue support, occlusal contacts and phonetics.
- Have patient sign esthetic approval for complete denture trial appointment.
- Proceed to final processing and finishing of the definitive denture.
The limited flexibility and smooth intaglio surface created by the Biocryl material allows for the record base to be removed from the working model without abrasion while providing for a comfortable and retentive fit for the patient during construction of a removable denture prosthesis. The thermoplastic material is easily removed during the boil-out of the wax within the flasks and does not interfere with the final processing of the denture base. In addition evaluating speech sounds, border extension and tissue support, the depth of the posterior palatal seal created on the working model can be verified in order to avoid addition of cold cured acrylic, a reline or a rebase procedure after the denture is finished.
The Clear Splint Biocryl material provides the opportunity to visualize the landmarks present on the working model in order to aid in positioning the denture teeth in wax prior to an intra-oral evaluation, however other colors are available. The thermoplastic material can be made to fit over dental implant supported abutments as a record base to aid in the construction of the definitive prosthesis.
A minimum of 1.5mm thickness of the Splint Biocryl material is recommended to construct a stable and retentive record base and is primarily used for an immediate denture that will eventually be relined and works best with a traditional compression processing technique. Adding a layer of copyplast to the master model creates uniform thickness for a definitive complete upper denture and facilitates the injection molding process.
The thermoplastic materials, pressed over the working model, create a stylized duplication of the anatomic features particularly in the palate. This detail helps the patient to adapt to a palatal coverage prosthesis and addresses a common error of creating thin areas of acrylic over the palatal rugae.
Douglas G. Benting, DDS, MS, FACP, Spear Visiting Faculty [ www.drbenting.com ]