Prosthodontics Sheet #13 PDF

13 Asma’a Abu-Qtaish Lajneh Teejan Rasha Alomoush 1|Page  Processing errors, laboratory remount and occlusal adjustments Topics to be covered in this lecture: - Laboratory remount - Selective grinding - Finishing the denture After we finish flasking, packing...

13 Asma’a Abu-Qtaish Lajneh Teejan Rasha Alomoush 1|Page  Processing errors, laboratory remount and occlusal adjustments Topics to be covered in this lecture: - Laboratory remount - Selective grinding - Finishing the denture After we finish flasking, packing and curing we have to check the denture before we send them for insertion appointment , the occlusal vertical dimension is correct and there’s no occlusal errors happened during processing. ❖ Sources of occlusal errors - changes in the states of TMJs - Inaccurate interocclusal records by the dentist - Errors in transferring relations to the articulator - Ill-fitting record bases - Change of vertical dimension at articulator - Incorrect arrangement of post teeth - Dimensional Changes in the wax after setting up of the teeth (since the wax isn’t dimensional stable ). This should be very slight if the occlusion of the wax-up carefully examined before flasking. - Failure to close flasks completely during processing or use to much pressure. ❖ Processing errors - The expansion of the investing material during the processing. - The expansion after denture processing may increase vertical dimension of occlusion (VDO). - Polymerization shrinkage of resin and may release some internal stress at deflasking. - Heat generation at Finishing and polishing. Poor laboratory technique can result in the movement of individual teeth or in an increase in occlusal vertical dimension of the denture. 1) Excessive packing pressures resulting in the artificial teeth being forced into the investing plaster. 2|Page 2) Normal packing pressures breaking the investing plaster ( if we have a pour mix or a thin layer plaster between the teeth and the flask border ) and causing movement of the teeth when the layer of investing plaster is weakened as a result of : porosity in the mix ; the use of incorrect powderwater ratio ; an inadequate thickness of plaster between the walls of the flask and the denture. 3) If pressure on the flask is released during The curing cycle, the two halves are likely to Separate, thus increasing the VDO of the complete Denture. 4) Separation of the two halves of the flask by An excess layer of resin during processing, which Can be avoided If we did a proper trial closure of the flask before we start curing. ❖ Remounting: ✓ Laboratory: Performed after deflasking before the dentures are handed to the patient for insertion ✓ Clinical: Done on new recordings from the patient and new mounting In this lecture we will talk about laboratory remount: o Before seeing the patient for the insertion appointment, the processed dentures must be retrieved from the lab and the maxillary cast must be remounted on the articulator, using the original plaster mount. o The goal of the laboratory remount and occlusal re-equilibration is to bring back the pre-processing VDO, and the incisal pin contacts the incisal table again on the articulator. → Advantages - Errors in the processed denture are easily spotted on the articulator rather than in patient’s mouth. - Correcting occlusal errors before denture insertion provides the patient with comfort and psychological confidence. Which done by: - Selective grinding is performed to remove only premature occlusal contacts, thus restoring occlusal vertical dimension and centric occlusion. In order to correct these errors, the dentures are returned to the articulator after deflasking. The casts are repositioned on the original plaster mountings (that we did after we do the jaw relation in the patient mouth) using the key (index) in the base of the cast. The casts are attached to the plaster mountings by sticky wax. 3|Page - Split-cast mounting technique. The trial dentures had been mounted on an average movement articulator. - Before the master casts were plastered to the articulator, location grooves were cut into each cast. - A film of petroleum jelly was applied to the location grooves and to the peripheral areas of each cast; as a result, the master casts were readily detached from the topping plaster before processing. - Remember what you have done when you finished the occlusal relationship between the two wax rims, you did the mounting, then the indices on the master cast so we can easily separate it when we do flasking procedure, - We kept the mounting and the articulator with the same relationship,as it is after we take or separate the master cast with the trial denture. - After we finish processing of the denture, we get the denture attached to the master cast and the indices are there, and we can back it to the original mounting and fix it by sticky wax. - Then we start to do Selective grinding and checking the relationship between the upper and lower teeth. - In order to do the correction and get our incisal pin contacting against incisal guiding table and we get our original vertical dimension of occlusion the condylar elements of the articulator are locked in the centric relation and the articulator is closed. - If the incisal pin does not touch the incisal guide table the occlusal vertical dimension has been changed and must be re-established. → The sequence of steps should be as follows: 1. Restore the vertical dimension. 2. Refine centric occlusion. 3. Perfect working and balancing occlusion. 4. Correct protrusive occlusion. ❖ Selective grinding Modifying the occlusal surfaces of the teeth by selective grinding will eliminate most of the errors caused by processing changes. 4|Page → But selective grinding will not correct these errors: o Errors produced by the impressions or jaw relation records. o Errors during mounting. o Errors developed when the dentures are removed from the casts or are polished. - To avoid dimensional and occlusal changes, patients should be advised to store dentures in water. Once the preprocessed VDO is regained by adjusting all initial occlusal contacts at centric position, then special care is required to keep it. - Avoid further adjustment on functional cusps during the excursive movements. - Selective grinding is carried out using articulating paper to mark the area of premature contacts. - Adjust the articulator to the proper setting. - Use red articulating paper for making centric occlusion and blue articulating paper for eccentric movements. - Grind the teeth with small green or diamond stones. This is the articulating paper used to And here, we put the marks on mark the premature contact the Upper and lower teeth Use A bur to deepen the marks in the fossae of the teeth, avoid reducing any cusp tips. ❖ Restore the vertical dimension - If we notice a lateral shift of the tooth or the tooth shifted to produce a high cusp, this will increase the vertical dimension. - Don’t grind or reduce the cusp tips, unless it’s very high in the centric and eccentric occlusion, but rather we reduce the fossae or inclined plane of the cusp. 5|Page - If the error is due to high cusp we grind/deepen the fossae - If the error is due to lateral shift, buccal or lingual shift we grind the cusp inclined. ❖ Obtain even contact in centric occlusion 1) Lock the upper arm of the articulator in centric relation. Check the occlusion by opening and closing the articulator, and lightly tapping the teeth together on red articulating paper. That’s to find out any premature Contact and centric occlusion 2) Then after that we Loosen the locks on the condylar elements and move the denture in besides eccentric movements. Using blue articulating paper between the teeth. - If the cusp is high in centric occlusion only, deepen the opposing fossa. - If the cusp is high in both centric and eccentric position, reduce the cusp tip. - Reduce the teeth until the incisal pin touches the incisal guide table and we get uniform contact exists on all posterior teeth. Anterior teeth should not touch in centric occlusion. (a) Balanced occlusion with contact on the working side (left) and on the balancing side (right). The arrows indicate the direction of movement of the mandible as it returns to the intercuspal position. (b) A premature contact on the balancing side causes separation on the working side. (c) A premature contact on the working side causes separation on the balancing side. (d) Balancing contact on posterior teeth in protrusion ❖ Adjust the working relation After finishing the vertical dimension and centric relation, now we check the working sides by: - Loosen the centric locks and use blue articulating paper as we said before - As a rule what we do in selective grinding procedure here the centric holding are not ground. These are the maxillary palatal cusps and the mandibular buccal cusps. Why? Because these cusps are essential to maintain the recorded vertical dimension. - If interferences exists in the working side reduce either the upper buccal cusps or the lower lingual cusps. B.U.L.L. Rule. - In the BULL rule reduce the lingual inclines of the upper buccal cusp and the buccal inclines of the lower lingual cusps. 6|Page - On the balancing side If interference exists on the balancing side reduce the lingual slope of the lower buccal cusp, the lower buccal cusp is a centric holding (functional) cusp so grind carefully and do not reduce the cusp tip. ❖ Adjust protrusive relations - If the anterior teeth have heavy contact with no contact / separation on the posterior teeth, grind the labial surface of the lower anterior and the palatal surface of the upper anteriors. - If heavy posterior contact exists with no anterior contact reduce the distal inclines of the maxillary cusps and the mesial inclines of the mandibular cusps. Premature contact 7|Page Sometimes we may use some kind of abrasive paste added to the teeth and to all movement to refine our occlusal relationship, but if we use it excessively this will lead to reducing the vertical dimension and reducing the sharpness of the teeth. ❖ Carborundum paste milling - The articulator is moved through all the excursive movements using carborundum paste to smooth the various gliding surface of the teeth. - Milling must be done lightly to prevent losing balancing contacts which might decrease the vertical dimension. a. Move the articulator into right lateral, left lateral and protrusive movements. b. Move the articulator in a circular movement. - Use light strokes do not force or press. - When milling is completed remove all traces of carborundum. The ground surfaces of the teeth must be polished when grinding has been completed. - Carborundum paste should not be indiscriminately used to eliminate errors in the occlusion of cusped teeth. Aggressive use of the paste could decrease vertical dimension and the sharpness of the cusps. - If carborundum paste is used, smoothing of minute irregularities must be limited to only a few gliding movements of the articulator. ❖ Fabrication of facebow transfer jig Now we’re done with the laboratory remount, and we will do a step that helps us later while doing the clinical remount and save the relationship of the: - The upper cast is attached to the upper mounting, and a record of its relationship to the articulator is made in plaster on the lower mounting ring. - Fast-setting plaster is added on the lower mounting ring, and the teeth of the upper denture are pressed into the plaster while the cast is in its keyed position on the articulator. - This facebow transfer jig also can be made after the final wax-up, just before investing the maxillary denture. Only the incisal and occlusal surfaces of the denture teeth engage the plaster. Fabrication of remount index of upper denture 8|Page Once we done all adjustments, now it’s time to Separate the denture from the cast, and the master cast destroyed, then we refine the denture, we do finishing to remove any sharpness using carbide burs (with different Shapes). Then, we remove blebs carefully with discoid carver or mounted rubber points. (Polishing) Use wet rag wheels mounted on a lathe to polish the external surfaces up to the peripheral fold Maneuver the denture so that depressed or concave areas are polished Use a felt wheel revolving at slow speed and Hi-Shine polishing agent to impart a high gloss on concave external surfaces of the denture Finish gingival embrasures and other hard- to-reach areas at low speed with Hi-Shine and soft bristle brush wheels 9|Page Scrub hard-to-clean areas very well under running water with a denture brush and soap ❖ References: 1. Chapter 12, Prosthesis Insertion and Follow-up Appointments, Zarb, Hobkirk, Eckert and Jacob, Prosthodontic Treatment for Edentulous Patients, 2013, 13th ed, Elsevier. 2. Chapter 25, Completing a Laboratory Remount, Golden, Treating the Complete Denture Patient, 2020, 1st ed, Wiley. 3. Chapter 27, Remove Complete Denture from the Cast and Finish, Golden, Treating the Complete Denture Patient, 2020, 1st ed, Wiley. THE END OF SHEET #13 ‫ فيحمد‬،‫ فينجح‬...‫وتطيب الحياة لمن يسعى‬ ُ ‫ فيحمد‬،‫ثم يسعى… فيفشل‬ ‫ فيحمد‬،‫ثم يُبتلى… فيصبر‬ ‫ فيحمد‬،‫ثم ينازعه القدر… فيفهم‬ ‫ فيحمد‬،‫ثم يستسلم لمن بيده ما ٓالت االٔمور … فيطمئن‬ ‫فالحمدهلل دائ ًما وأبدًا حمدًا طيبًا مباركًا فيه‬ 10 | P a g e