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DENTURE BASE REPAIRS Midline fracture of the maxillary denture most common fracture. ridges resorb and remodel. palatal bone does not resorb. “high-centering” of the denture. rocking effect accelerates bone loss. leads to a stress fracture. #1 rule when repairing fractures of a complete or partial denture Always fit the pieces of the denture together with sticky wax and place it against the opposing denture or a cast of the opposing teeth to ensure that the denture is correct for the patient. Some patients have been known to supply someone else’s denture. Repairing a Fractured Complete Denture When a midline fracture of a maxillary complete denture occurs, the cause must be determined. As with any fracture, this must be corrected if the repair is to be successful. First, assemble the pieces and try them against a cast of the opposing dentition. 1. Align the parts of the fractured denture and splint them into position using long shank dental burs, coat hanger wires, plastic sticks, or large paper clips. “Tack” these to the teeth with sticky wax. Avoid wooden sticks as these can absorb water and warp. 2. Block out all undesirable undercuts that are more than 10mm from the fracture site with wet tissue paper, putty, or wet pumice. Leave about 2mm of the denture flange borders uncovered and pour a base of quick-set plaster or stone. 3. After the stone has set, remove the bracing rods and sticky wax. Remove the denture pieces from the stone matrix, clean them and the matrix, reassemble them to ensure that they can be accurately positioned. 4. Bevel the approximating surfaces so that there is a 3mm gap on the outside and a 2mm gap on the cast side. This will allow you to see that the acrylic is filling the entire area. Replace the pieces in position on the cast and check for accuracy. 5. “Rabbet” the polished side of the approximating pieces about 3mm wide and half way through so that there is a gap totaling about 8mm in the surface area between the pieces. Leave out any small pieces, and replace them entirely with repair acrylic. 6. Paint separating medium on the cast at least 10 mm to either side of the fracture line. “Tack” the parts in position to the cast base with sticky wax. Use the “brush-bead” method to overfill the repair area with repair acrylic. Place the entire assembly in warm water in a pressure pot and allow it to cure. 7. After the acrylic has set for ten minutes, remove the denture repair from the stone matrix and finish the denture with successively finer abrasives until a high shine is achieved. Check the tissue side for irregularities and repair and/or smooth them. 8. Inspection of the denture shows a smooth line at the junction of the denture base acrylic and the repair acrylic. Note the repair acrylic has permeated the crack in the denture tooth. This tooth can now be replaced in a subsequent procedure. The following pictures will demonstrate how you will successfully repair a fracture of a mandibular compete denture. This is the procedure you will complete in the lab exercise. Red DuralayR resin will be used so that the juncture can be easily seen. If this were done on a patient’s denture, a repair acrylic matching the denture’s original acrylic would be chosen. First approximate the broken pieces and fix them in position with a non-absorbing splinting material (Wire, plastic,etc.) Use sticky wax to lute these braces to the denture base. Check the tissue surface to make sure that the pieces are in close contact and there is no wax or other debris on that surface. Use polyvinylsiloxane putty (Reprosil®) to block out the area away from the fracture site. Leave about 10 mm. of the surface on the tissue side bare of any putty. Press pieces of paper clip into the putty before it sets to provide retention of the putty to the plaster base of the repair cast. Pour a mounting plaster base to complete the repair cast. Remove the splinting material and all the sticky wax from the denture surface and the repair cast. Remove the denture pieces from the cast and inspect the area under the fracture site for any defects. Replace the denture pieces on the cast and examine them to ensure that they fit precisely back into place. Remove approximately 1.5 mm. acrylic from the proximal surfaces of the fracture line on the polished surface and 1 mm on the tissue side, forming a gap of 2 mm. on the tissue surface and 3 mm. on the polished surface. Place the pieces back on the cast and verify these dimensions. It is necessary that this amount of gap be present to allow enough visual and working access so the repair acrylic can be placed and fill the entire repair site. Remove enough acrylic from the polished surface side of the denture to allow a gap of 8-10 mm. This process is called “rabbeting”and provides an increased surface area that affords a stronger joint between the old and new acrylic. BEVEL CAST RABBET CAST Paint the area under the site to be repaired with ALCOTE, a tin-foil substitute. Replace the denture parts and lute them in place with sticky wax. Note the amount of visual and working access provided by the rabbeting and beveling. The method to be used to apply repair acrylic to the denture in this exercise is called the “brush-bead” method. Dappen dishes containing monomer and polymer are arranged close to the denture. The brush is first “wetted” in the liquid monomer. Then it is dipped in the polymer powder. This will cause a small bead to form on the wetted end of the brush. These beads are placed in the repair site to make the repair. Wet the fragment edges with monomer. Moisten brush in monomer and dip it in polymer. Brush bead the wet polymer on the repair site. Add additional acrylic until the entire site is slightly over-filled. Place the repair cast and denture in a water bath to cure. Dip the brush in monomer and dry it thoroughly on a paper towel to remove any residual acrylic to prevent ruining the brush. If this step is forgotten, the acrylic will harden and the brush will be ruined. Extra acrylic is added to overbuild the repair site area to assure that there is sufficient thickness of high quality acrylic. Moisture from the water bath can cause a rough surface to form. Remove the repaired denture from the repair cast and verify that the tissue side has been repaired. Remove the denture from the cast and check to make sure that the acrylic is of good quality and covering all the desired areas. Place the dentures together and ensure that they occlude properly. If the occlusion is off, then the repair is not accurate. This is a very good reason to make sure you fit the dentures together before making the repair cast. The patient may be giving you a mismatched set. After ensuring that the dentures fit together properly, remove the excess acrylic with a denture bur and use abrasives and polishing agents to polish the repaired area, taking care to not over-polish the area or the teeth. Also be sure to change the polishing wheel for each abrasive. Can you tell where this denture has been repaired? You have to look closely to discern the repair site because the repair acrylic blends together so precisely with the original acrylic. This is how a repair should look! A reline of the denture will likely be necessary to correct the conditions that led to the fracture in the first place. Often what the patient really needs is a new denture. If the patient balks at these suggestions, have them sign the record stating that they understand the potential for future fractures and are willing to take the risk and assume the responsibility. This fracture is not completely across the entire denture. Cover the break with sticky wax. If there is a gap between the teeth, then squeeze them back together and splint them. Pour a modified working cast after blocking out non-essential areas. Since the pieces are together, polyvinylsiloxane putty can be used to make this repair cast. Clean off all the sticky wax and open the crack with a fissure bur to 2 mm. On the polished side, use a round-nosed acrylic bur to reduce the acrylic and increase the surface area to be bonded. Overfill the fracture site with autopolymerizing resin. This will assure that a high quality of acrylic will be left after finishing. The acrylic that contacts the water will be porous and look “grainy”. Cut back the excess acrylic, finish, and polish the repaired denture. Correct any irregularities found on the tissue surface. Repairing a Complete Denture that has Multiple Breaks A A. Assemble the broken pieces of the denture to determine if the denture can be repaired successfully. If there is any part missing, sticky wax the denture back together and place it in the mouth. Make an alginate impression of the denture in the mouth and pour it up with the denture left in the impression, and pour it with a fast-set plaster. B B. If all the parts are available and will fit back together with a reasonable assurance of accuracy, fix them together with sticky wax. Splint them with metal or plastic sticks & block out any nonessential undercuts. Pour a cast in quick set plaster or stone. C C. Rabbit and bevel the breaks as usual, but leave out the broken piece. Paint the cast with tinfoil substitute and reposition only the large pieces back on the cast.
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