Restorations on upper and lower implants and the comfort of dynamic abutments

Dental prosthesis technician Damián Rodríguez Fernández illustrates the simple path to technical and esthetic success

One of the key factors for success in implantology is the correct placement of the implants. We come into contact with cases in the laboratory in which the implants are incorrectly angled, which causes esthetic problems. The dental technician is therefore obliged to employ his/her experience, and on occasion, a great deal of imagination to satisfactorily resolve each case, making everything more expensive. Sometimes external factors beyond our control mean the prostheses are a failure, and we are forced to repeat the work or to take a new approach to the initial design. In most cases, not overcomplicating and attempting to complete the work as simply and comfortably as possible guarantees a successful outcome.

When a casting process is the technique employed to obtain the metal structure, this article and wide-ranging literature clearly demonstrates the use of castable metal-based attachments is the best option to achieve a good fit in contrast to the use of attachments cast in their entirety.

There are currently available castable attachments with their mechanized base made of semi-noble alloys and Tilite® with titanium (biocompatible compound). The problem of using semi-noble or noble alloys is their high price and their specific weight, which increases the cost of the final prosthesis. That is why mechanized attachments made of Tilite® have been used in the case study described below, because they achieve materials savings of between 50% and 70% with no reduction in quality.

Case study

In order to provide quality prostheses, working protocols of the highest quality must be drawn up.
Two initial phases that must be looked at in detail when working with implants: production of the imprints and emptying the model in order to create an exact replica of the position of the implants. As already mentioned, the position of the implants in the working model must be exactly the same as in the mouth—to the millimeter—because in contrast to natural teeth, which can cope with imbalances in the prosthetic structures as a result of the tolerance of the periodontal ligament, the implants will not tolerate any kind of imbalance due to osseointegration. 

Most materials used to make imprints are not up to the job, and the failure of many prostheses derives from this. In this case study, in order to achieve a top-quality imprint, it has been undertaken with fast-setting and zero-expansion plaster material to thereby ensure the implants are perfectly positioned. This is the most exact type of imprint on par with the use of FRY dental guards, and it provides the patient and dental surgeon with more comfort. To make the master model, the individual emptying technique for implants is used in order to control the expansion of the plaster on the implant replicas.

Individual emptying technique description

Having cleaned the imprint received from the clinic, we screw the implant replicas to the transfers. The soft pink gums are placed, and the replicas are isolated with plastic sheaths. The plaster is poured into the imprint and left to set. In this way, we can monitor the expansion of the plaster to ensure that it does not affect the position of the replicas, which have been isolated. Subsequently, the sheaths are removed, and the small holes remaining are cleared.



It is no use creating a perfect imprint, if the next step, the printing, is not carried out accurately.
Once the model has been obtained, we place the screws of the imprint transfer in the replicas, which will provide a three-dimensional idea of the angle of the implants so the prosthetic work in the laboratory can be planned.

When the models have been assembled in the articulator and using the results of the preliminary exam of the angles of the implants, a decision is made to employ straight mechanized prosthetic attachments made of Tilite® in the lower jaw and mechanized dynamic abutments also made of Tilite® in the upper jaw in order to make two structures for hybrid prostheses all in Tilite® with titanium, the alternative to gold.

With the dynamic abutments screwed into the implant replicas, we then make the correction (by just pushing the chimney) of their incorrect angle and are able to make a structure screwed directly to the implant without anti-esthetic interferences resulting from outward screw. 


Silicon waxes are used to help cut the castable chimneys at the necessary height, and we then place the chimneys of the dynamic abutments in their final position.

Photopolymerizable resin is used to attach the chimneys of the dynamic abutments to their base so they do not move, and the abutments are joined together in both the upper and lower jaws by means of dental guards.

Once the photopolymerization is complete, the protocol is followed for the Sheffield passive fit by tightening the distal screw and the other loose screws, and checking that the passive fit is perfect. Subsequently, the distal screw is loosened, and the next screw is tightened while checking the structure sits passively on the implants. If the fit was not passive, the structure would have to be cut and joined once again with photopolymerizable resin, until the passive placement of the structure on the replicas was achieved.

It might seem like a waste of time, but our aim is to reduce errors to a minimum. If we do not get a perfect fit of the structure using the wax, we will never achieve the fit in the casting.

Once all the checks have been made, the structure is left to rest for 24 hours so the resin can become completely stable, and we can finish the waxing of the structures by adding the corresponding retention beads and placing the structure in the casting cylinder.



When casting, it is important to use the necessary quantity of metal. We recommend, therefore (when working with Tilite®), weighing the structure with the water baths and multiplying the value by 7.7 (specific weight) to provide the exact weight of the metal for the casting.

The casting is undertaken slowly in order to foster the burning and elimination of the wax and resins inside the cylinder.
The structures are cast with Tilite®, and we clean the coating structure. It must be noted that we are working with metal-based attachments so when the coating is removed, we cannot sand in this zone. In order to remove the coating when using mechanized abutments, we recommend the use of an acidic solution, such as Chelagess® (fluorhydric acid and chlorhydric acid); or the employment of a fiberglass pencil pressed against the base.


                             

After the structure has been cleaned, the Sheffield test is used once again to check the passive fit of the structure on the replicas.
We then go over the structure and paint it with opaquer to finish the resin.


Conclusion

As has been shown in the case study described above, the choice of the materials used in our prostheses on implants is very important. Tilite® is an alternative to gold alloys, which reduces the weight of the prostheses and their cost. In addition, dynamic abutments are an aid to solving esthetic problems caused by implants placed at an incorrect angle. When undertaking a quality piece of work, it is clearly essential to follow working protocols from start to finish, and to employ top-quality materials, to guarantee a technically and esthetically perfect job.

Bio

Damián Rodríguez Fernández is a dental prosthesis technician specializing in EDM (electrical discharge machining) and passive fits.



This article was provided by Damián Rodríguez Fernández, a partner of Talladium International Implantology.