4.3. Practical work (task) that are fulfilled in class:
- Preparation of the all plastic RPD to the repaire.
- Select materials for repaire.
- Method of the flaskingby the reverse method
- Method of the flasking by the combined method
- Technology of polymerization
- Technology of prosthesis grinding
- Technology of prosthesis polishing
Content of the theme:
The repair of dentures can be a puzzling and difficult part of prosthesis construction. This problem can be handled as a laboratory procedure, but knowledge of the preparation and of the technical phase is essential whether it is handled in the office or sent outside the office. Often this service is required by patients on an emergency basis because tooth and denture fractures seem to occur at most inopportune times.
It is well for the dentist to be aware of the hazards in repairing a denture. Many repairs are difficult to assemble correctly so that they will cause the dentures to be ill-fitting. If a second process of curing by heat is necessary, changes will occur because the old resin resoftens during processing. These changes may cause a change in occlusion and in the fit of the denture over the basal seat. For this reason, it may be advisable to make a new centric relation record, mount the denture, and regrind it after the repair has been completed. It is well to mount and regrind dentures after a period of time, even though repair has not been made; therefore these two services might as well be combined.
The availability of autopolymerizing or cold-curing resins for repairs simplifies the repair procedure. The technique avoids the potential warpage of the dentures that results from reprocessing, and the entire operation can be carried out in much less time than by the heat-curing method. It is not necessary to flask the denture to cure the new resin.
Breakage of individual teeth, as well as breakage of the entire denture, is often caused by a change in occlusal relations, and remounting and regrinding would then be essential to prevent breakage from occurring again. It is impossible in laboratory procedures to return a perfectly adjusted occlusion. It is also well to advise the patient that the tissues will change during the elapsed time that the denture is not worn, but that they will readjust in a short time. The patient must not think that the denture is entirely to blame when the denture does not feel the same immediately on insertion.
Repairs on complete and removable partial dentures may include fractured dentures, or replacing fractured, missing or loose teeth. These repairs may be caused by changes in the oral tissues, careless handling, etc. Figure 1 shows a simple denture base fracture.
Fig.1
The repair procedures will include aligning the fractured parts, pouring a plaster cast (matrix), widening the fracture line and making retentive grooves, applying self-curing acrylic resin, adjusting, and polishing. When the pieces of the denture base cannot fit against one another in a precise relationship, or one or more fragments have been lost, this type of a fracture is classified as complex. Since complex fractures should be repaired by prosthetic technicians, they will not be covered in this chapter. To repair a simple denture base fracture, perform the following steps (A-H) shown in figure 2:
1. Align the fractured denture parts and apply sticky wax over the fracture line on the external surfaces of the denture.
2. Stabilize the parts by positioning denture burs with sticky wax as shown in step A.
3. Block out all undercuts on the internal surface that will be exposed to the plaster with a wet pumice mix or block out wax (step B). Do not block out undercuts along the fracture line. Blocking out the undercuts enable you to remove the plaster cast after it sets.
4. Prepare a plaster mix.
5. Slowly pour the plaster into the internal surface of the denture. The plaster cast should cover the fracture line, but not the entire denture. This procedure is accomplished by holding the denture in you hand and gently resting it against the vibrator.
6. Place the denture in an upright position (step C) and allow the plaster to cure.
7. Once the plaster is set, gently remove it from the cast.
8. Remove the denture burs and all traces of the sticky wax and pumice.
9. With a new denture bur, widen the fracture lines (step D) on the denture and place retentive grooves along the fracture line.
10. Paint two thin, even coats of tinfoil substitute on the cast (step E).
11. Align the denture parts on the cast and hold them in place with sticky wax at the posterior edges (step F).
12. Prepare the self-curing acrylic resin.
13. Moisten the brush with monomer and dip it into the polymer (powder), and apply it to the fractured area. Repeat this procedure until the fracture is covered and slightly overfilled. 14. Allow the denture to stand for a few minutes until the sheen of the resin disappears from the surface.
15. Place the denture and the cast in a pneumatic curing unit (step G).
16. Cover the denture with lukewarm water (115°F) and secure the lid.
17. Attach the rubber tubing to the air valve on the lid and till with compressed air to 20 psi. 18. The curing process will take 30 minutes. Note: If a pneumatic curing unit is not available, place denture and cast in a bowl of lukewarm water for 30 minutes or until the resin hardens. This is not the recommended procedure but may be used in emergencies.
19. Gradually turn the air release valve on the lid to relieve the inside pressure. When the pressure gauge reads zero, carefully remove the lid. 20. Remove the repaired denture base from the pressure pot.
21. Using a denture bur, trim all excess acrylic from the denture (step H).
22. Polish the external surfaces with pumice and a muslin or brush wheel that is mounted on a bench lathe. If a lathe is not available, you may use a mandrel- mounted wheel on a straight handpiece.
23. Disinfect and place denture in a prosthetic bag with water for delivery.
Figure 2.—Denture base fracture repair steps
DENTURE TOOTH REPAIRS The original tooth can be reattached if it is still intact, but some repairs will require a new denture tooth. The following procedures describe simple denture tooth repairs that do not involve the facial denture base plastic (complex fracture). The example given is of an anterior tooth that fell out. If the facial denture base plastic needs repair, a prosthetic technician or a dental officer will perform the repair. To accomplish a denture tooth repair, perform the following steps (A-F) as shown in figure 2:
1. Roughen the lingual aspect of the acrylic teeth to guarantee good chemical bonding with the repair material. Use an inverted bur to undercut a hollow opening in the lingual aspect of the acrylic tooth.
2. Make a box preparation (step A) in the denture base, lingual to the tooth to be repaired. 3. Position the tooth (step B) in its seat and sticky wax it in place from the lingual. 4. Construct a plaster cast facial matrix to hold the tooth in position during repair. It should include the tooth that is being repaired and the tooth on each side (step C).
5. Clean all wax from the box preparation (step D). After the plaster has set, remove the matrix and
6. Paint the matrix with a tinfoil substitute (step E).
7. Reassemble the denture, the tooth, and the matrix in correct aligment. Sticky wax the tooth to the matrix, and the matrix to the denture (step F).
8. Place self-curing resin to the repair area in the same manner as described in the denture base repair section. Build up the repair resin slightly higher than the surrounding denture base.
9. Place the tooth repair in a pneumatic curing unit and follow the same steps as described in the denture base repair section for curing, finishing, and polishing. 10. Disinfect and place the repaired denture in a prosthetic bag with water.
Figure 2.—anterior denture tooth repair steps
Materials for self-control:
Tests for self-control (tables, diagrams, drawings, graphs)
The courses of denture base fracture.
Differences between simple and complex fractures.
Steps of denture base repair.
Steps of denture tooth repair.
Materials for denture base repair.