 A thin shell crown or fixed partial denture can be made from any of the acrylic resins, and then that shell can be relined indirectly on a plaster cast or it can de directly relined in the mouth.  This technique saves chair-side time as the restoration is partially fabricated prior to preparation appointment.

Shell Fabrication Armamentarium  Items in over impression armamentarium  Items in cementation armamentarium  Liquid applicator  Powder blower

Shell fabrication Overimpression of diagnostic wax up is made before preparation appointment. Check it for completeness. Trim off thin flashes of impression material created by the gingival crevice to produce extra bulk of resin near the margins. One drop of monomer is deposited on the facial and lingual surface of imprint of each tooth to be restored

◄ Over impression made from diagnostic cast ► Thin edges of gingival margin trimmed off from over impression

◄ Monomer applied on over impression ► Polymer is applied

Keep monomer near the gingival portion of impression to prevent excess from accumulating in the incisal or occlusal area Extend covereage by the resin to one tooth imprint on either side of the teeth being restored. Gently spray enough polymer onto the surface of the impression to absorb the monomer Repeat process four times inverting the impression frequently to allow the material to run down the margins rather than puddling the incisal or occlusal areas of the tooth

Remove shall from impression after 4 minutes When teeth have been prepared, make a quadrant alginate impression and pour it thin mix of quick setting plaster. Trim off excess plaster on a model trimmer Remove areas on cast that duplicate soft tissues Try shell on the cast and make sure it fits properly. Relieve inner surface of the shell till it seats comfortably and without any resistance.

Coat tooth preparations on cast with separating medium. Monomer and polymer can be mixed directly in the shell or mixed in a dappen dish and transferred. Completely fill each tooth. Seat shell on prepared teeth on cast, wrap a rubber band around the shell and cast and place in a plaster bowl full of hot water for approximately 5 minutes.

Pressure pot can be used, this helps increase the strength of restoration. Once resin sets, remove rubber band and remove shell from cast. Trim and polish the restoration. If direct technique is used, seat shell on prepared tooth in mouth. When resin becomes rubbery elevate it 2mm and flush under it with water. Then remove restoration from mouth and place in warm water.

 Gingival flash removed and gingival embrasures opened up  Resin filled shell is seated on prepared tooth on cast

Resin shell is seated on prepared tooth in mouth

◄ Rubbery resin restoration dislodged from prepared tooth in mouth ► Partially polymerised provisional restoration removed from impression

► Also used to create provisional restoration on quick setting plaster ► Polymerisation produces very little heat and has minimal toxic effect on pulp and soft tissues, hence is best suited for direct technique

Method of Fabrication  Make an over impression using an aluminium sextant tray.  Trim excess from borders of impression and remove webs of material between imprints of teeth  To ensure adequate thickness o fresin along the margins of restoration, use a No.8 round bur and cut a trough in the gingival area o the tooth imprints in which restoration will be fabricated.

Border of over impression is trimmed. Material between imprints of teeth is removed

Gingival trough cut using No.8 Bur A midsagittal section of overimpression and provisional restoration shows a bulk of materall near the margins

► Complete tooth preparation and begin fabrication of the provisional restoration. ► Extrude required amount of base and catalyst pastes on a glass slab and mix well with a cement spatula for 30 seconds ► Place resin in overimpression with a syringe. Keep tip of syringe buried in the resin and fill cusp tips and incisal edges rom the bottom up to prevent voids ►Lubricate prepared teeth with petroleum jelly

► Place impression tray on teeth 2 minutes after start of mixing. Allow resin to set in mouth for 2 minutes. ► Check for excess material around margins for consistency ► Dislodge the restoration from the tooth or from impression. Remove as much exces as possible using scissors. ►Replace provisional restoration on tooth and ask patient to bite down on it several times

► Remove the restoration from mouth. Wipe off air inhibited resin using alcohol sponge. Repair any voids by mixing anther batch of resin ► Remove excess. Replace in mouth and check occlusion. Finish and polish restoration and seat with temporary cement.