Written by Steve C. Futris, DDS Friday, 14 September 2012 16:05
The first prerequisite is adhesion, the focus of the article “Dread-Free Compound Impressions in Half the Time” published in Dentistry Today in September 2006 view the article at dentistrytoday.com). That article discussed how mucostatic impressions, if taken properly, would result in models that were almost clones of the patient’s ridges. This would give the molecular adhesion needed and desired in the resulting dentures, like the adhesion between 2 glass slabs.
The second prerequisite is to prove at the bite-rim stage (read the article “Semi-Processed Bite Rims for Dentures” published in Dentistry Today, August 2007, or visit dentistrytoday.com) that the models are accurate enough to produce bases with molecular adhesion. Semi-processed acrylic bases, as seen in Figures 1 and 2, are used to make the bite rims. If these bite rims with the semiprocessed bases prove to have the molecular adhesion that is desired in the mouth, then these bases and models are mounted on a semi-adjustable articulator, appropriate teeth are selected and set, and the new bases are fully processed.
MOUNTING THE BASES
The next 3 prerequisites describe how the author was taught to accurately mount bite rims and models using an interarch tracer (Simplex Intra Oral Gothic Arch Tracing Device [DENTSPLY Prosthetics]).
|Figure 1. Semiprocessed bite rim.||Figure 2. Bare ridges for added |
vertical and retention.
|Figure 3. Conventional mounting of models.||Figure 4. Interarch tracer for fully functional dentures.|
First, the models and rims are mounted with a centric bite (Figure 3) using a face-bow registration, etc. Then, the interarch tracer is applied (Figure 4).
The interarch tracer is used to accurately remount the lower model. This remounting of the lower model is an inexpensive 30-minute procedure that not only produces a corrected plane of occlusion, but it also provides the operator an assured (not assumed) centric relation mounting. Last, but not least, this interarch tracing provides the patient’s lateral and protrusive settings for the eminentia on the articulator. Without this patient’s eminentia settings, one cannot produce fully functional dentures. No 2 people have the same eminentia settings. (Read the article “Fabricating Fully Functional Dentures” published in Dentistry Today, November 2009, or visit dentistrytoday.com.).
ADDING TEETH TO THE BASES
Now, the wax rim measurements taken in the mouth, older photos of the patient, etc, are used to select the teeth. The author always uses 33° all-porcelain teeth (Trubyte Bioblend [anteriors] and Trubyte Bioform VF 33° [posteriors] [DENTSPLY Prosthetics]), and to avoid grinding away the retentive areas, the ridges are left bare (Figures 1 and 2). This not only allows more vertical room to set the teeth, but it also secures the wax additions to the acrylic bases. Note: The palate is also left void to facilitate the ruggae pattern insertion in the final wax-up (Figure 5). These ruggae not only aid in phonetics, they also give the tongue more traction in closures.
To begin setting the teeth, we must first lock the articulator in centric. The author’s sixth prerequisite is the use of the 20° posterior template (TruByte) for setting the upper teeth. This 20° plane alters the flat occlusal plane of the wax rim set by the Fox plane to be curved, the curve of Wilson mesiodistally, and the curve of Spee anteroposteriorly. Without this plane correction, a fully functional setup is not possible.
SETTING TEETH MADE EASY
Setting the upper anterior teeth, one tooth at a time, to the labial parameters of the wax rims, and the 20° plane and the crest of the ridges, one can see the resulting setup in Figure 6. We now set the first premolar on the 20° plane, making sure the lingual cusp tip hits dead-center on the lower midline upon closure (Figure 7). Finish setting the upper left in the same manner (Figure 8). One can now visualize how the curve of Spee sets the plane of occlusion in relation to the curve of the lower ridge (Figure 9). This curved occlusal relationship of the upper teeth to the curved lower ridges gives the dentures added stability while the dentures are functioning, and prevents the lower denture from rotating forward (distomesial), which can cause the elusive sore spots.
Having set the upper teeth in extra hard pink wax (Miltex), the occlusal anatomy of these 33° porcelain teeth will set themselves. Each lower tooth is placed in heated wax and locked into maximum intercuspation (MI) with its opposing upper tooth, while closing into the set vertical (Figure 10). This is the way nature sets the natural teeth during eruption when the infant swallows with the tongue, setting the vertical. Finish setting the lower posteriors in the same manner.
|Figure 5. Upper waxed-up denture, ready for processing.||Figure 6. Twenty-degree plane to set uppers.|
|Figure 7. Lingual cusps hitting dead center.||Figure 8. Twenty-degree plane for curve of Wilson and curve of Spee.|
|Figure 9. Curve of Wilson matches the lower ridge.||Figure 10. Occlusal anatomy sets lower teeth.|
|Figure 11. Setting lower anterior teeth in protrusive.||Figure 12. Lateral disclusion for shredding (chewing) efficiency.|
|Figure 13. Left cuspid disclusion in mouth.||Figure 14. Remount of the processed upper denture.|
Unlock the articulator so that the lower anteriors can be set by protruding the mandible one-half tooth to where the opposing cusp tips are apex to apex (Figure 11). While the posteriors are in this protruded position, the lower incisors are set edge-to-edge with corresponding upper incisors. This protrusive cuspid disclusion is created by having the distal marginal ridge of the upper cuspid ride up the mesial marginal ridge of the lower first premolar. In this protrusive move, the lower cuspid slides through the space left by the upper lateral not touching the 20° plane. This prevents the upper denture from being dislodged by the lower cuspid in protrusive. This added height of the lower cuspid provides for the lateral disclusion (Figures 12 and 13). By varying the height of the lower cuspid (Figure 12), we can control how close the opposing marginal ridges approximate each other without actually touching. In centric closure, the marginal ridges are like cookie cutters when closing into MI, and the shredding of the food is provided by the action of these marginal ridges in lateral excursions. Without the patient’s eminentia settings, any lateral and protrusive moves would not only result in the denture’s coming loose, but with porcelain teeth, there would be a clicking noise.
THE PROOF IS IN THE PUDDING
Now set the teeth on the right side in the same manner as was done on the left, and then the denture setups are ready for a wax try-in. The author always chills the setups in ice cold water before taking them into the mouth. This hardens the wax and prevents the individual teeth from moving with any prematurities. I want the dentures to lose adhesion if there are any prematurities in the occlusion. (Note: Never use adhesives during the wax try-in!)
|Table. The Author’s Vision of a Perfect Denture|
|A denture that seats passively on its ridges when the teeth are separated (molecular adhesion) |
A denture that is in centric relation prior to closure
A denture that will remain in centric relation on closure into maximum intercuspation (centric relation = centric occlusion)
A denture that will not dislodge while functioning
A denture that will enhance aesthetics and phonetics
A denture that is still seated passively on its ridges on opening after closure.
Having set the upper anteriors with the 20° plane and the lower anteriors set with the protrusive moves determined by the patient’s eminentia settings, the patient’s phonetics should be perfect. (Note: I mentioned this improvement in phonetics to a prospective denture patient, and she asked if she would be able to sing. I replied, “I’m sure you will be able to sing.” She was so pleased. She said, “That’s wonderful; I’ve never been able to sing before.”)
ALL CAN STILL BE LOST
Assuming the wax try-in went well, we are ready to replace the semi-processed acrylic bases with fully processed plastic bases. The author’s final prerequisite involves the use of remounting grooves. If you have never been to a commercial dental laboratory to see how dentures are processed, you should consider making it a priority to do so.
With remounting grooves on the bases of your models (Figure 2), you can be the quality control in the processing procedures. After the try-in, send the dentures on their articulator for finalizing the wax-up with specific instructions to have the final wax-up remounted for your approval. Check the occlusion of the remounted wax-up to see if you still have MI on every closure, etc. If all is well, remove the upper model from the articulator (Figure 5) and send it to the laboratory for processing. Again, issue specific instructions not to remove the denture from the model after processing—this is because it should be remounted on the articulator opposing the lower denture still in wax. After remounting the processed upper to the lower still in wax, make all corrections to the occlusion by moving the lower teeth still in wax (Figures 14 to 16). (Note: In these Figures, a case where there were severe changes to the occlusion in the processing of the upper denture is demonstrated. Usually, assuming one uses an excellent dental laboratory, these changes in the occlusion are less severe. You will find, however, that any changes will still require correcting the occlusion to MI by moving the opposing teeth while they are still in wax.)
|Figure 15. Corrections made to lower still in wax.||Figure 16. Lower denture is now ready for processing.|
|Figure 17. Final occlusal |
|Figure 18. Checking protrusive movements.|
|Figure 19. Final correction.||Figure 20. Pressure indicator paste corrections.|
|Figure 21. Maximum intercuspation is observed on every closure.|
There should be no grinding of the occlusion. Once MI is observed again on every closure, the lower model is sent into the laboratory for processing; with the same instructions not to remove the processed denture from its model, for it is to be remounted to the processed upper denture that is still on the articulator. Then, final adjustments to the occlusion are made (Figures 17 and 18). Once the occlusion is locked into MI on every closure, and the dentures can perform all the functioning moves as they did in the wax-up, they are ready to be removed from their models and finalized by the dental laboratory team.
NO SURPRISES ON DELIVERY DAY
On the day of delivery, do a bilateral cotton-roll check (Figure 19) for any discrepancies on the inner surfaces before checking for MI on every closure (Figure 20). In following these prerequisites, fabricating fully functional dentures was a gratifying experience for my patients and me. Holding the all-porcelain dentures in one hand while holding the camera in the other hand (Figure 21) would not have been possible unless the occlusion had been locked in MI; only one prematurity would make this impossible, and the dentures would have ended up on the floor (Table).
Based on many years of hands-on experience and teaching, this article summarizes all of the author’s prerequisites for fabricating trouble-free fully functional dentures. If you and your dental laboratory team follow the steps and principles outlined in this and the other articles by the author as published by Dentistry Today, you will be able to deliver trouble-free fully functional dentures.
Disclosure: Dr. Futris reports no disclosures.
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