Prefabricated teeth in individual implant prosthetics

implant technology ivoclarPatrick Zimmermann and Dominik Mäder present a field report on SR Ortholingual S DCL by Ivoclar Vivadent.

Figure 1: Graphic representation of the components in DCL acrylic, a strongly modified PMMA variant

Total prosthetics is one of the most challenging fields in dental technology. The authors have several years of experience in this ‘ultimate discipline’.

In this article, they will describe their experiences with the new prefabricated teeth, SR Ortholingual S DCL (Ivoclar Vivadent). They explain in particular detail about implant-supported dental restorations. These can be set-up with the lingualised posterior teeth, according to a proven occlusion concept.

At the same time, the article speaks for the recognition of individual total prosthetics.

In recent years, total prosthetics seems to have become the poor relation in dental restorations. Digital technology and full ceramics dominate the specialist media.

However, total prosthetics is still very much present in everyday dental laboratory life. To trivialise and/or neglect the subject in education and training would be irresponsible in the long term.

One look at the demographic trend shows that an increase in edentulous patients is to be expected in the coming years. In addition, the challenges are greater. Reasons are, for example, that the age at which patients receive initial treatment with full dentures is often when their adaptability is reduced and a strong resorption of the alveolar bone has occurred.

In addition, the number of younger dentists with experience in the art of producing removable dentures is diminishing (Grunert, 2008). For this reason, we will continue to work intensively with total prosthetics, in close collaboration with the dentists, in order to be able to offer patients state-of-the-art, safe treatment concepts.

Figure 2: The new SR Ortholingual S DCL, with a lingualised occlusal concept, is ideal for implant prosthetics

High expectations from the patients

In our opinion, it would be wrong to assume that the production of a full denture for an edentulous patient is economically unattractive. It is a question of perspective, because in terms of price, full dentures offer individual flexibility.

We are currently seeing a generational shift in older patients – from the post-war generation to the baby boomers (Schimmel et al, 2017).

These patients have become accustomed to the high level of dental care and dental technological possibilities available. They do not want to miss out on this in old age. Many elderly patients want aesthetic restorations that do not obviously look like dentures.

Thanks to the multitude of technologies and procedures available, it is possible to provide the patient with a restoration specifically suited to their requirements, from a wide range of processing techniques.

The end result can be a highly aesthetic, individually fabricated denture or the ‘simple’ digitally manufactured full denture. Function and statics are always highly important, irrespective of production technique.

Figure 3: Graphic representation of the occlusion concept (lingualised occlusion according to the mortar-pestle principle)

Total prosthetics in implant technology

Due to increased patient expectations, total prosthetics has also increased in relevance in the field of implantology.

We have to differentiate between the implant-supported fixed or partially removable bridge restoration and the removable hybrid restoration, i.e. with two retention elements. We will focus on the graduated implant concept from the Clinic for Reconstructive Dentistry and Gerodontology (Professor Dr M Schimmel) in Bern.

If possible, an implant restoration should last a lifetime. Manual strength and skill play an important role here. In many cases, due to the advantages, the removable option is selected (hygiene, patient comfort, and so on) (Schimmel and Zimmermann, 2017). Here, at least two implants are used in the edentulous lower jaw and at least four implants in the upper jaw as retention for the removable restorations.

Figure 4: Model of an edentulous lower jaw with an implant-supported bar. Ideally, a precise model analysis is always carried out before the implants are inserted, in order to prepare and achieve an optimal starting position for the functional set-up

Some examples of retention elements are bars, stud and anchor attachments (for example Novaloc, CM Loc, locators), ball head attachments or retention caps, depending on each individual patient situation. This is a relatively cost-effective concept, which has proven to be very successful amongst patients.

A higher-quality, fixed full-arch restoration option, which has proven its worth, is the Straumann Pro-Arch concept (Schimmel and Zimmermann, 2017).

With regard to setting the teeth up, the same principles apply for implant-supported total prosthetics as for mucosa-supported dentures. The fundamental specifications for the fabrication of full dentures and the correct model analysis must be mastered.

In order to ensure the long-lasting functionality of implant-supported restorations, the static aspects as well as the set-up and occlusal concepts must be taken into account. In addition, the materials (for example prefabricated teeth) must be carefully selected.

Prefabricated teeth made from DCL acrylic (double cross linked)

Figures 5 (above) and 6: A pair of articulated models with a bar and without dentures in the mandible and with both dentures set-up according to Gerber in lingualised occlusion (SR Ortholingual S DCL)
Figure 6

The number of implant-supported restorations is increasing, as is the demand for prefabricated teeth with increased abrasion resistance. Hardly any patient will accept that the prosthetic teeth have to be replaced or renewed shortly after their new dentures were finished. In our laboratory, we prefer to use prefabricated teeth, which guarantee a long service life from a material science point of view.

Demands on the prefabricated teeth are:

  • Biological tolerance
  • Abrasion resistance
  • Plaque resistance
  • Shade stability
  • High grinding strength
  • Good polishing qualities
  • A good bond with the denture base material.

One material that meets these requirements is the highly cross-linked DCL (double cross linked) acrylic used by Ivoclar Vivadent for various prefabricated tooth lines. In order to understand why the material is ideal for implant prosthetics, it is important to have an insight into the science behind the material. The DCL acrylic is a modified polymethyl methacrylate variant (PMMA), in which the polymer filler and matrix are evenly cross linked (Figure 1).

The DCL material displays a higher compressive strength but a similar flexibility to that of conventional PMMA. This is due to the double cross linking (matrix, polymer filler). It has eliminated the classic weakness of conventional PMMA teeth, for example exposure of non-cross-linked, soluble polymer beads during grinding.

The intelligently designed material structure of DCL acrylic ensures good stability and high abrasion resistance. As a result, the total prosthetic restoration can expect to have a longer service-life. In addition, the DCL acrylic is distinguished by a secure bond with the denture base material and is less susceptible to discolouration.

Figures 7 (above) and 8: Close-up view: the prefabricated teeth in the anterior region (SR Vivodent S DCL) have a strong, individual and natural appearance. The characteristic design of the pink aesthetics (SR Nexco Gingiva) gives a lifelike presence
Figure 8

Prefabricated teeth with lingualised occlusion

One of the basic requirements when setting the teeth up on a full denture is to set each individual tooth in such a way, that the denture will not tilt under masticatory pressure.

There are various set-up concepts, one of which is the classic Gerber method (according to Professor Albert Gerber). This method takes into account the forces generated during mastication and their transferral through the denture onto the supporting alveolar ridge. Important features in this concept are the lingualised, bilaterally balanced occlusion and the tooth-to-tooth occlusion. They are aspects that play a role in implant-supported total prosthetics.

The lingualised occlusion concept, in which the narrow supporting surfaces of the upper palatal cusps come into occlusal contact with the lower lingual fossae enables the autonomous masticatory stability of individual teeth, which is required in many situations. This means that horizontal shearing forces are reduced and the prosthesis and implants remain secure. We have been using the SR Ortholingual S DCL (Ivoclar Vivadent) for some time now, which are designed for lingualised occlusion (Figure 2).

The design of the SR Ortholingual S DCL takes into account the essential principles of lingualised occlusion (mortar-pestle principle).

Ideal partner for implant prosthetics: SR Ortholingual S DCL

We like to use the SR Ortholingual S DCL in implant prosthetics due to its special design.

The upper teeth have dominant palatal cusps and the lower teeth have a pronounced functional central fossa (Figure 3). The centric contacts are concentrated in the fossae of the lower teeth. The buccal cusps are set-up out of contact. This means the teeth are ideally suited for a lingualised set-up in tooth-to-tooth occlusal contact. If necessary, a tooth-to-two-tooth intercuspidation can be set up. The teeth also meet our expectations from a material science aspect. They are made of the DCL acrylic and have a high abrasion resistance and long service life.

Together with the SR Vivodent S DCL anterior tooth sets, the Ivobase system for pressing the denture base and the light-curing laboratory composite SR Nexco gingiva, we are able to produce restorations which are functionally and aesthetically pleasing and at the same time provide long-term stability.

Figures 9 and 10: Occlusal view of the upper and lower dentures. The teeth can be trimmed well, which means that facets can be cut into the teeth to give a more natural appearance and help with the functionality of the restoration
Figure 10

Experiences from everyday laboratory life

Here is a demonstration piece as an example: implant-supported bar in the edentulous lower jaw and full denture in the edentulous upper jaw (Figures 4 to 11). We produce many restorations of this type for patients and achieve good, stable results in function and aesthetics using SR Vivodent S DCL anterior teeth, SR Ortholingual S DCL posterior teeth, the Ivobase system and the SR Nexco Gingiva.

The prefabricated anterior teeth are distinguished by their characterised aesthetical appearance. The authentic surface texture and layered build-up of the teeth provides an age-appropriate, vibrant appearance resembling that of natural dentition. The exceptional shape design allows for a high level of individuality.

The natural, anatomical tooth shape with ‘real’ curvature allows a life-like set-up. The teeth can be individually adjusted by grinding lightly (for example age and gender). The layered build-up gives a natural appearance and has a good level of translucency.

Figure 11: Vital and real: in total prosthetics, there are many ways that lead to the final result – high-quality and individualised as shown here or using simple steps. However, there is no compromise on the static and function requirements

Set-up design

The posterior teeth have a multifunctional set-up design. This means they can be set-up according to the concept followed, either in a 1:1 or 1:2 teeth intercuspidation. The predefined cut facets simplify the set-up procedure. The teeth are easy to trim and polish. The design remains beautifully natural despite the lingualised shape. The anatomical shape of the teeth allows an individual set-up without making the interdental areas unnaturally large.

The length and width of the teeth are large enough to cover individual abutments – or, as in Switzerland, the popular root pin copings can be concealed. This, amongst other factors, means the teeth can be used well for implant-supported total prosthetics.

Sometimes the teeth are a little too short in the lingual and/or palatal region, but this can usually be compensated well. In our daily laboratory routine, we use the SR Ortholingual S DCL posterior teeth and the SR Vivodent S DCL anterior teeth for all our removable prosthetic requirements. The DCL acrylic is distinguished by its abrasion resistance and shade stability.

Conclusion

Total prosthetics continues to play an important role in dental laboratories and practices. The number of edentulous patients will continue to increase in future. In addition, the older generation is changing. The ‘new old people’ are accustomed to a high standard of dental medicine. They want their dental restorations to be inconspicuous – aesthetically as well as functionally.

In order to meet these high demands, it is essential to be well-skilled and competent in the field of total prosthetics. The dental technician is an important partner for the dentist, because total prosthetics is an ultimate discipline for them too.

References

Grunert I (2008) Neue Konzepte in der Totalprothetik, Zahnärztliche Mitteilungen 23:60-64

Schimmel M, Müller F, Suter V & Buser D (2017). Implants for elderly patients. Periodontol 2000.  Feb 73(1):228-240

Schimmel M, Zimmermann P (2017) Der betagte Patient, ZTM 8 (21) S. 536-547


This article first ran in Laboratory magazine. Read the latest issue of Laboratory magazine here.

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