78 model cast rpd. planning

planning

• Making the impression and cast

• Pouring the corrected cast

• Creating record bases and mounting casts – A working model is built with occlusal rims (wax structures) to help determine the correct bite and positioning.

• Modifying the master cast – Wax is added to non-pressure areas for relief, and certain undercuts are smoothed out (blockout) to help with the denture’s fit.

• Surveying and designing – The denture framework’s structure is planned carefully to ensure stability.

• Design transfer and additional wax adjustments – Parallel wax blockout, relief wax, and beading (small ridges) are added to prepare the mold for the framework.

• Duplicating the mold – The wax-relieved and blocked-out cast is duplicated to create a mold for the final framework.

• Making the refractory cast – This special cast includes all the relief and blockout details and will be used to make the actual denture framework.

three steps involved with making denture framework by using relief, block out ledges and ready made pattern forms?

• Prepare the base model – Start with a master cast (a detailed mold of the patient's mouth). Areas where the denture will sit are given extra space (relief), and certain undercut areas are smoothed out (block out) to prevent unwanted fitting issues. Small ledges are also shaped to help secure the clasps.

• Create the framework pattern – A major connector (usually a lingual bar) is formed to link both sides of the denture. Pre-made plastic clasp forms are positioned carefully to rest on supportive ledges. Additional wrought wire and a mesh structure are added to allow the denture base to attach properly.

• Finish the metal framework – The completed framework pattern is used to cast the final metal framework of the denture. Once done, it's placed back on the master cast to check the fit and prepare for final adjustments.

basic steps to making rpd

1. Impressions:- These are negative replica of patients hard and soft tissues of oral cavity, usually taken using alginate (Impression Material) in a special tray.

2. Model Preparation After Impression By Cast or Die materials.

3. Use a dental surveyor:- to determine heights of contour with a common path of insertion.

4. Framework:- Adaptating, and determining the positioning of clasps.

5. Waxing and Setup of artificial teeth.

6. Flasking:- The process of investing the cast and a waxed denture in a flask to make a sectional mould used to form the acrylic resin denture base:

• Mix the gypsum in proper water/powder ratio.

• The lower part of the flask is filled first. Put the model in it (max 1cm over the edge of the flask - without shaft).

• Soap water, isodent and other for isolation after hardening.

• Put the upper part and fill it with plaster.

• After hardening – put the flask in boiling water for 5 minutes.

• After that open it and remove the plasticized base plate and the wax. • Isolation.

7. Polymerization:

• Mix the acrylic resin (polymer + monomer).

• Stages of polymerization:

❖ Wet sand phase

❖ Sticky ("threads") phase

❖ Plastic ("working") phase

❖ Elastic ("gummy") phase

• Put the acrylic resin in the empty space, close the flask and press it.

• High temperature polymerization cycle:

❖ Long: put the flask in room temperature water, heat it for 30 minutes while the temperature rises till 60 degrees Celsius, on 60 degrees Celsius – for 1 hour, heat it for 30 minutes till 100 degrees Celsius, on 100 degrees Celsius – 30 minutes and slow cooling (2 and a half hours).

❖ Short: for 30 minutes after water starts to boil. (No more than 100 degrees Celsius, because the monomer evaporates on 100.3 degrees Celsius!)

8. After cooling:- remove the denture from gypsum.

9. Cleaning and polishing.

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