Technical Complete Denture Repair, Relining, and Rebasing PDF

Technical complete denture CHAPTER XI REPAIR, RELINING AND REBASING Repair Causes of denture fracture: A- Construction faults: 1- When posterior teeth, particularly upper, ar...

Technical complete denture CHAPTER XI REPAIR, RELINING AND REBASING Repair Causes of denture fracture: A- Construction faults: 1- When posterior teeth, particularly upper, are set outside the ridge. 2- Unbalanced articulation will result in abnormal stress being applied to the denture or the teeth. 3- Excessive relief sometimes accounts for a broken denture by reducing the midline denture thickness. 4- The use of incorrect dough consistency when packing, inadequate polymerization times and temperatures, and too rapid cooling after processing, will result in a denture base of reduced strength and dimensional inaccuracy. Causes of teeth off, but not broken 1- Insufficient packing of acrylic resin. 2- A film of grease, separating medium or wax on resin teeth. 3- Packing acrylic resin when the dough is at too advanced stage; there will be insufficient free monomer to unite with the acrylic resin teeth. B-Causes in the mouth: 1- Excessive force applied during mastication or by the patient clenching or grinding the teeth. 2- Alveolar absorption will cause the denture to be unevenly supported and is a common cause of fracture. 3- A labial frenum attached high on the ridge may necessitate a deep frenal notch in the denture. Such a notch may be the site of the commencement of a denture crack (fracture). 137  Technical complete denture 4- Inadequate relief of an upper denture in midline of the palate, Fatigue fracture may follow. C- Causes out of the mouth: Excessive pressure during cleaning or dropping the denture on the floor or onto a wash bowl. Repair of complete fracture: 1- The broken edges of the denture are cleaned of food and material debris, so the two parts will fit together well. 2- The parts of the broken denture must be reassembled accurately and fixed together by means of an old bur or matchsticks which are luted to teeth and the adjacent resin surfaces by means of sticky wax (Fig. 1-11). No wax is placed over the fracture, so that the tissue and palatal sides of the fracture can be examined to see that they are in correct apposition. Fig. (11-1): Left; fractured denture. Right; reassembling the fractured denture. 3- Plaster is vibrated onto the palatal surface of the denture to form the cast. 4- When the model has set the sticky wax is removed and the broken parts of the denture are removed from the model. 5- The resin on both sides of the break is cut away (2-3 mm) and beveled (Fig. 11-2). Then the cast is replaced, 138  Technical complete denture In the case of complete upper dentures, it is advisable to remove the entire palatal resin to minimize the warpage of the old acrylic resin during the polymerization of new material. A- Repairs using cold-curing resin The use of cold-cure acrylic resin is advised for all repairs in order to minimize the warpage of the old material. The possible weakness with cold cure material is the area of union of the old and new resin. Acrylic resin monomer is painted on the cut surfaces, and a cold-curing repair resin is placed in the break. Finishing and polishing of the denture are performed after curing of the repair resin. B- Repairs using heat-curing acrylic resin: The palatal or lingual area in the case of a lower denture is waxed up, together with the labial flange. The waxed-up denture is flasked. The denture on its model should be embedded completely in deeper section of the flask so that only the wax is exposed. Wax elimination, packing and curing of acrylic resin, Deflasking, finishing and polishing are carried out as for a new denture. Fig. (11-2): Left; the fracture line widened. Right; complete repair. 139  Technical complete denture Replacement of teeth 1- If an anterior tooth is loosened it should be stabilized with sticky wax at the incise edge and a plaster (index or matrix) overcast is poured to register the position (Fig. 11-3). Fig. (11-3): Left; tooth attached in position by sticky wax. Middle; Plaster index on denture. Right; Acrylic applied from palatal aspect. 2- When the plaster of the overcast has set, the tooth is removed. The wax is washed out. The resin on the lingual or palatal side is cut and a dovetail is prepared for the new resin. This gives adequate access and provides mechanical as well as chemical retention. 3-The index is coated with separating medium and placed in position. 4-The tooth is set in place by the help of the index. 5-The repair acrylic is made to fill the space around the teeth. It is then cured finished and polished If a tooth or teeth have been broken or are missing from a complete denture, a similar method is used for their replacement. New teeth must be waxed to the denture and it may be necessary to check the shade and position by reference to the mouth. In replacing posterior teeth, care must be taken to maintain correct occlusion by reference to the opposing denture. Repair of a fractured denture with missing part: Plaster or compound impression material is applied to the missing part, after setting of the impression material the denture is removed and a cast is 140  Technical complete denture poured. Self-curing resin is applied to restore the missing part (Fig. 11-4). Fig. (11-4): Left, compound impression for missing part. Right, repaired denture. Relining and rebasing Definitions: A Reline: is the resurfacing of the tissue side of a denture with new base material to provide more accurate fit. A Rebase is a process of refitting a denture by replacing the denture base material without changing the occlusal relation of the teeth. Objectives: 1- Improvement of complete denture retention and stability. 2- Restoring position of occlusal plane and improvement of appearance. 3- Restoration the vertical dimension of occlusion. 4- Restoration of evenness of occlusal pressure. 5- To alleviate pain due to rocking of the denture. Indications for relining and rebasing: 1- Adaptation of the denture bases to the ridges is poor due to resorption of the residual alveolar ridges. 2- For geriatric or chronically ill patients when the construction of new dentures can cause physical or mental stress. 3- Rebasing is additionally required in cases of: a- Porous denture base. b- Discolored or contaminated denture base. c- Repeated repair or relining of the denture. 141  Technical complete denture Contraindications: 1- Excessive ridge resorption- make new dentures. 2- When hyperplastic soft (Flabby) tissues are present 3- If the dentures have poor esthetics or unsatisfactory jaw relationships. Denture preparation for relining or rebasing: 1- Border extension is checked and corrected. 2- Undercuts are relieved. 3- Occlusal disharmony is corrected by selective grinding. 4- Pressure spots are adjusted. 5- Accurate posterior palatal seal is established. Clinical procedures: For either a rebase or a reline, an impression with the denture is made without incorporating errors in the occlusion, by having the patient bite in centric occlusion until the impression material sets. Laboratory procedures: The relining or rebasing impression is beaded, boxed and poured with dental stone. The cast is not separated from the impression. The difference between relining and rebasing is in the amount of old denture base removed and replaced. For rebasing (Fig. 11-5), the entire denture base is eliminated excepting the teeth and may be 2 mm of adjoining denture base. To facilitate removal of palatal section of maxillary dentures, holes are drilled in the palate before impression making. Fig. (11-5): Left: Perforation of denture. Holes drilled in palatal portion. Right: Trimming of the entire denture-bearing surface except for teeth for rebasing. 142  Technical complete denture One of the following methods can be used for conversion of the impression material to denture base material: I- Flask method II- Articulator or Jig or Hooper duplicator method. I- Flask method: 1- The cast with the denture is imbedded in a processing flask. 2- The flask is warmed to soften the impression compound before opening it to remove the impression material. 3- The border of the denture is roughened for relining or the base is trimmed for rebasing (Fig. 11-5). 4- Separating medium is applied on the plaster and stone molds, and heat-polymerized denture base resin is packed into the mold. The flask is closed and clamped to ensure maintenance of occlusal vertical dimension. 4- The acrylic is then processed. 5- After processing, the flask is cooled slowly and the denture is retrieved from the stone mold, finished and polished. II- Articulator or Jig or Hooper duplicator methods: 1- The cast and the denture are mounted on the upper member of the articulator (Fig. 11-6) or jig or Hooper duplicator (Fig. 11-7). 2- Plaster is mixed and applied on the l ower member of the instrument; the-upper member with its mounted upper denture is closed into the soft plaster mix to a depth of 1-2mm. 3- When the plaster occlusal index has completely set, the top and bottom member of the instrument are separated. The denture is removed from the cast, and all impression material is cleaned from the cast and the denture base. 4- For relining, the denture borders are squared to form a butt joint for the attachment of the new acrylic resin material. The palatal portion of the 143  Technical complete denture maxillary denture is removed close to the palatal surface of the teeth. For rebasing, the entire denture base and the palatal portion are removed. Fig. (11-6): Left: Completed mounting of relined impression with cast on the articulator with formation of index for the denture teeth. Right: Key or index of denture teeth. 5- The denture is positioned so that the teeth are placed in the occlusal index in the lower member of the instrument. 6- The post dam is prepared on the maxillary cast. 7- The denture is waxed-up. 8- The waxed-up denture is removed from the mounting, flasked, processed with heat-cure acrylic resin, finished and polished. Fig. (11-7): Left, diagram of a jig. A, upper member. B, denture with relining impression. C, plaster index. Middle, denture mounted to upper member of Hooper duplicator. Right, lower member of Hooper duplicator with plaster index. 144