Challenging complete denture construction
If planned and executed carefully, removable prosthodontics can be just as satisfying and predictable as fixed, says Kevin Lochhead.
Fabrication of complete dentures is often seen as one of the least favoured aspects of dental practice. But it doesn't have to be. There is certainly a significant amount of 'art' in the design and construction of dentures as well as the 'science'. Critical to success is not only your knowledge but that of your dental technologist – one of you (preferably both of you) needs to be interested in the art of achieving natural aesthetics.
Our position at Edinburgh Dental Specialists is that the clinician should take the lead in the artistic aspect of the design. Complete dentures are the perfect testing ground for smile design theories and concepts. Unlike placing veneers on teeth, if the patient is unhappy with the end result you can start again without any biological sacrifice and with much less financial loss. An hour or so setting teeth up directly in the patients mouth can teach you a vast amount about dental aesthetics.
Like every aspect of dental care, there are levels of service that you can offer. Four 15-minute appointments may be appropriate in undemanding, straightforward cases but will surely be wasted time for all parties in more complicated examples. The following case history describes the examination and treatment progression for the construction of new complete dentures in a long-term denture wearer. In this example, dental implants are used to aid retention. This, however, should not change the design and fabrication process.
65-year-old female, edentulous for 40yrs; last set of dentures fabricated two years ago.
Existing f/f –
The patient presented in some distress primarily due to her feeling that her problems were insurmountable. She had investigated dental implants previously but, due to the severe ridge resorbtion, was of the opinion that this was not possible. She had had many sets of dentures over the years with each becoming progressively less satisfactory.
In a complete denture case it is essential to try and assess what improvement can be achieved by fabrication of new dentures and whether these improvements will benefit the patient sufficiently to warrant starting the treatment in the first place. The worst case scenario being: fabrication of new prostheses and an unhappy patient, which will have wasted everyone's time and most likely result in a return of fees to the patient. Better not to have started at all.
In this case, the existing upper denture was well retained and the patient informed that, while we would expect to achieve a similar level of retention, improvement could not be guaranteed. The only improvement that could be anticipated in the upper would be aesthetically.
In the lower, the existing restoration had significant limitations being under-extended and aesthetically poor. It was the patient's wish to open her vertical dimension which would increase the height of the lower, potentially destabilising it further. It was necessary therefore to explain that in all reality the only improvement that she could confidently expect to achieve would be that of improved aesthetics. This would need to be the agreed reason for proceeding with new dentures.
No conversation on complete dentures i s medicolegally complete without a discussion on the possibility of dental implants. The McGillı consensus has stated that the minimum level of care for an edentulous patient should be a complete upper denture and an implant supported lower. This is a radical change from general practice as the understanding is that patients should be guided to an implant overdenture before even experiencing a complete denture. The reasons are sound:
In this particular case, while there was severe ridge resorbtion, palpation of the anterior mandible suggested about ı0mm of ridge height still being present below the thin residual ridge and similar width. This justified an OPG radiograph which confirmed sufficient bone for two implants to support an overdenture. (Figure 4)
Full discussion of implant therapy and what to expect ensued. In discussion it was explained to the patient that as well as the aesthetics it would also now be possible to confidently:
These were sufficient benefits for the patient to proceed with a full surgical consultation and treatment plan. The surgeon felt that it may also be possible to place four implants for a full arch fixed bridge but we did not think that this would offer any significant additional benefit to her and she elected to proceed with placement of two implants for an overdenture.
At the time of surgery, two ı3mm implants were placed with bicortical fixation for good primary stability. Nobel Biocare 'Branemark system' parallel walled external hex MkIII implants were used – these are the most scientifically documented implants, withover 40 years of publications on their safety, predictability, clinical success and longevity. It was decided that patient comfort during healing would be much improved if an immediate loading protocol was followed. The patient's denture was adjusted and relined to incorporate the special attachment housings. This process was made considerably easier by the minimal incision for implant placement. (Figures 5 and 6)
Immediate loading, while attractive for the patient, needs to be considered carefully, with the relevant literature being reviewed. The obvious main drawback is that, should an implant fail, not only is treatment delayed while another implant integrates, but there are the additional costs of the restorative components which have may have also been used and you may not be able to use again.
In this case, post operatively the patient had no bruising or swelling and immediately felt the benefit of implant retention.
After six weeks for tissue stabilisation, fabrication of the final prostheses were carried out.
Initially it was necessary to establish relaxation of the TMJs for accurate jaw registration and also to establish the correct OVD.
The only occlusal splint that can be used effectively with a denture patient is a pivot appliance. Here, pivots were added posteriorly to the lower denture and progressively adjusted until the desired OVD was achieved (this was established entirely through aesthetics and the patients feedback). (Figure 7)
Over 2-3/ı2 (?) the pivots had the desired effect of relaxing the muscles of mastication sufficiently to establish a reliable CR record.
Despite having the advantage of the implants for retention, there is really no excuse for taking shortcuts or compromising the design and fabrication of the final restorations. Optimum extension should be achieved to aid stability and smile design concepts used to establish the patient's wishes. With complete denture construction, the aesthetic guidelines of Earl Pound2 are especially useful.
If a patient is a class II skeletal relationship, you will be unlikely to achieve a good aesthetic outcome unless a class II incisal relationship is similarly followed, which is what was done in this case.
Denture fabrication proceeded as follows:
Material and component considerations
With all acrylic work we use a high impact acrylic which is made by Heraeus (Pala Express). This material is actually a cold cure formulation which also lends itself to processing of acrylic work on implant hybrid bars, much reducing the incidence of fracture.
One of the challenges using a cold cure material is incorporating natural staining to the surface. Heraeus do produce their own stains for the Pala system, these however are 'paint-on' to the final denture, which we find to be less natural than the 'sifting' technique. With the sifting technique, layers of acrylic powders are built up with monomer into the boiled out flask, before the base acrylic is processed. (Figure ı6)
With the PalaExpress material this can still be done despite the 'staining acrylic' being heat cured. The PalaExpress will still perform if taken to the required temperature to cure the stains. Staining built up in this way is extremely durable. As the stains are surface based it is essential that the finish surface is not adjusted or overly polished at finishing. This process is aided by the use of 'flexistone', a silicone rubber used to protect the flange of the denture during processing, which results in a clean, porosity-free surface being produced every time.
'Locator' attachments are available for most implant designs. They are our preferred overdenture attachment not only because of the ease with which the attachment caps be changed (and varying degrees of grip achieved) but our experience over the last ı5 years shows that the housing in this denture very rarely loosens, which was a regular problem with ball attachment housings (chair and lab processed).
On review, the patient was very pleased with the result achieved, feeling that they had exceeded her expectations and given her more confidence in all areas of life.
Aims and objectives:
To qualify for one hour's verifiable Continuing Professional Development, simply visit the Scottish Dental website and click on the CPD link to answer the questions www.scottishdentalmag.co.uk
Removable prosthodontics CPD questions
Q1. If implants are used for retention what shortcuts in denture construction can be expected?
a) Full denture extension is not required
Q2. What does the McGill consensus recommend as the minimum standard of care for an edentulous patient?
Q3. Increasing the vertical height of a lower complete denture will result in:
Q4. Benefits of implant retention of a lower denture include:
Q5. In a class skeletal class II case: