prosthetic polymers and resins Flashcards
what is a complete denture?
An artificial, removable dental prosthesis consisting of artificial teeth embedded in a denture base.
Substitutes the entire dentition and associated structures of the maxilla / mandible
Denture base is supported by oral tissues, teeth, or implants, and is generally made of polymers
what is the general technique of creating a complete denture?
Take an impression of arch of interest
Generate a dental cast using the impression
A resin record base is fabricated on the cast
Wax is added to the record base
Teeth are positioned in the wax
Choose a denture flask
Encase the complete tooth arrangement in a suitable investing medium
Open the denture flask and eliminate the wax
Introduce a resin denture base material into the clean mold cavity
Polymerize the denture base resin
Recover the denture
Prepare the denture for insertion
How are denture bases mainly fabricated?
Denture bases are mainly fabricated using poly methyl methacrylate resins which are advantageous for their relative ease of fabrication
Fabrication pursued via a polymerization process (this is an exothermic reaction)
Tinted to provide any shade and degree of translucency
Color and optical properties remain stable
Physical properties adequate for dental applications
What are heat activated denture base resins?
Heat-activation is the main process used in fabricating denture bases
Thermal energy provided by water bath or microwave oven
Composition:
1) Powder PMMA prepolymerized spheres plus benzoil peroxide (initiator)
2) Liquid component that includes hydroquinone (inhibitor) and glycole dimethacrylate (cross-linking agent)
Stored under specific temperatures, with a limited shelf-life
You can’t put the metal flask into the microwave because you can’t put metal in the microwave! Duhhh. It would have to be a different material like glass or something. Benzoil peroxide (initiator) is from year 1!!!!. 100% polymerization is never achieved.
what is the compression molding technique?
Heat-activated denture base resins are shaped via compression molding
what are the intial requirements in mold preparation for compression techniques?
Absolute accuracy in impression making, cast generation, record base fabrication, articulator mounting, tooth arrangement, and wax contouring
What happens after the master cast and completed tooth arrangement are removed from the dental articulator?
The master cast and completed tooth arrangement are removed from the dental articulator
The lower portion of dental flask is filled with freshly mixed dental stone
The upper portion of the selected denture flask is positioned over the lower portion of the flask, and dental stone is mixed and poured into the denture flask and allowed to set
The denture flask is immersed in boiling water.
Metal is a good conductor of heat so it is put in boiling water.
The segments are separated to reveal the record base
The record base and softened wax are carefully removed
What is the purpose of a selection and application of a separating medium, what about examples of them and what about how you apply it?
Purpose: To prevent direct contact between the denture base resin and the mold surface
Examples of separating agents: cellulose lacquers and solutions containing alginate compounds, soaps, and starches
Application: A fine brush is used to spread the separating medium onto the exposed surfaces of the stone mold. The liquid is guided through interdental regions without contacting the exposed portions of acrylic resin teeth
Why is the polymer-to-monomer ratio important?
Crucial because of polymerization shrinkage (21%)
To avoid it, manufacturers pre-polymerize a significant portion of the denture base material. This can be thought of as pre-shrinking.
Powder and liquid components mixed using a 3:1 ratio, respectively which yields a volumetric shrinkage of 6% (linear shrinkage 0.5%)
There are little balls of pre-polymerized material.
What does the polymer-monomer do when they interact?
Upon mixing in the proper proportions, the polymer/monomer mix produces a workable mass. Upon standing, the mass undergoes five distinct stages with time: Sandy Stringy Doughlike Rubbery or elastic Stiff
what is the dough forming time?
Time required for the resin mixture to reach a doughlike stage
ANSI/ADA Specification No. 12: < 40 min
In clinical use, most resins reach doughlike consistency in < 10 min
what is the working time?
Duration of doughlike stage of the denture base material
ANSI/ADA Specification No. 12: at least 5 min
what is packing for the mold part?
Placement and adaptation of a denture base resin within the mold cavity
Over-packing leads to a denture base that exhibits excessive thickness and resultant malpostioning of prosthetic teeth
Under-packing leads to porosity
To avoid over-packing and under-packing, pack the mold cavity in several steps
what is the injection molding technique?
Uses a specially designed flask
One half of the flask is filled with freshly mixed dental stone, and the master cast is settled into the stone
Sprues are attached to the wax denture base
The resin is introduced into the cavity
As the material polymerizes, additional resin can be introduced into the mold cavity
what is the polymerization procedure?
Above 60oC, molecules of benzoil peroxide decompose to provide free radicals with unpaired electrons
Each free radical reacts with an available monomer to initiate chain-growth polymerization
Reaction is terminated by either: coupling of two growing chains or through the transfer of a single hydrogen ion from one chain to another
