3.6 Fixed partial dentures "Adapta system"

what is adapta system?

method for creating single crowns and FPDs with casted retainers. Suitable for all types of dental alloys used in FPDs.

what is key principle of adapta system?

• retainers and the pontic are made on a gypsum model with removable dies

• This allows the components to be disassembled and reassembled without changing their position or damaging the model

Step by step of adapta system

1. Casting a gypsum model with removable dies

2. wax modelling of the retainers

3. wax modelling of the pontic

4. placing the spruces, investing and casting

5. sand-blasting, cleaning, finishing and polishing

6. esthetic incrustation

1. Casting a two layered gypsum model

• parallel fixator used to ensure the two dies are parallel

  • Consists of: base, perforated plate, frame, guiding spokes

• Small brass pin with retentive tail is attached to the spoke and placed in centre of the stump, staying about 1 mm from the bottom of the impression. The number of pins corresponds to the number of the dies

2. Working cast model with removable dies

• flat saw used to make two converging notches at around 0.5-1mm medially and distally from the dies cervical area

• Modelling knife is sued to press on the pin and free it from the models socle

• This type of model is an essential part of the Adapta system

3. Adapting thermoplastic foil

Special thermoplastic materials, that burn without a trace are adapted over the die to form the cap

• Thick (base) foil - made of polyethylene or polypropylene. Diameter of 35 mm and thickness of 0.6 mm. Serves as a base for the wax up of the cap, which will be made on top of it

• Think (distance) foil - made of celluloid, has a diameter of 35 mm and thickness of 0.1 mm

Plasticized foils are pressed into a moulding material. Pressed until they sink above the gingival margin then held for 30 seconds (in material)

Two caps are separated, cut to size and positioned

• Two caps are placed back on the die

• Melted cervical wax is used to fill in the circular space between the carrier foil and preparation border

• Another test removal of the cap is made to check the quality of the wax’s application

How should the 2 newly formed caps be separated, cut to size and positioned in the 2nd step of adapta system?

• the spacer is cut to about 2mm above the gingival margin

• The carrier is cut to about 1 mm above the gingival margin

4. Crown (CAP) wax up

wax up is preformed on carrier foil with attention towards expressing the crown’s specific details such as the equator, occlusal surface and approximal contact. The wax layer should have a minimal thickness of at least 04mm

what are the requirements of the pontics in the 4th stage (crown(cap) wax up) stage of adapta system?

• Approximately connected to eax up of the retainers

• Vestibular contours are shaped like a window hich comes in slight contact with the alveolar ridge

• Lingual part is made oblique, convex and rounded like the true hygienic profile

• Pearl retentions (0.6mm) or “Il-shaped” wire retentions can be used for the vestibular window

5. Preparation for investing, casting, cleaning and polishing

• placing of spruce is done in accordance with the rules for diameter, length and positioning of the pins

• Alignment of spruce pin coincide with the longest diameter of the wax element

• Next step is forming the crucible with a diameter larger than that of the widest part of the wax object

• Process of casting is carefully executed in accordance with the rules for choosing a proper mold, investing, removal of the spruce, melting of wax and technological steps involved in working with specific metal alloy

6. Esthetic incrustation with acrylic resin

• vestibular surface is covered with a special coating of a colour neutralising varnish, such as Conalor (Spofa Dental), this material has variety of hues including pink and can successfully neutralise the metallic colour of the underlying alloy

• Colourless clear wax is used to model the profile and vestibular surface to the pontic and the retainers

What are advantages of Adapta system?

• Based on using cast with removable dies

• Good adaption and forming of the foils

• Easy to model and control even after removing the dies

• Can easily be removed and placed back without changing the position

• Dies imperfections can easily be corrected

• Parallelism or the guiding brass pins allow the simultaneous extraction and returning of the dies on the model

• Possibility of switching the thermoplastic forming stage to a wax dipping technique

what are disadvantages of Adapta system?

Adapta system runs risk of deforming wax-up when it is removed from the dies because of its thin wax walls; but this can easily be overcome by placing spruces which serve as a reinforcement tool

what is the difference between adapta system and wax dipping technique?

• Substantial difference is the replacment of thermoplastic foils with a wax heater tank set at a fixed temperature (89 - 91 degrees) which keeps the wax in a constant liquid state

what occurs during wax dipping technique?

1. Apply very thin layer of separating agent over the whole die

2. After isolation, dies are dipped in melted wax for about 1-2 seconds while carefully making sure the wax reaches 1-2mm above preparation junction

3. After dipping process is followed by two specific motions, done for about 1 sec

   3.1. Dipping then tilting the dies towards the tanks wall and extracting after rotating it to ensure that the last drop of wax flows towards one if the approximal walls

4. Wax excess is removed with a sharp instrument

5. This cap is an alternative of the polypropylene foil used in Adapta system