CAD/CAM silicate ceramic blocks for the production of single-tooth restorations such as crowns and inlays have been available on the market for a long time. These are mainly targeted at dental practices, but dental technicians also benefit from the potential of modern CAD/CAM silicate ceramics in the form of blocks. GC Initial LiSi Block is a fully crystallised lithium disilicate ceramic for the production of single-tooth restorations that, from an aesthetic point of view, are uncompromising in many respects, even to the critical gaze of a dental technician.
For decades, we as dental technicians have dealt intensively with the imitation of natural teeth. It is one of our unique selling points and our personal merit to create ceramic restorations with artistry that imitate the tooth almost completely in shape and light optics. For some years now, monolithic production with its many advantages has been the focus of interest and often gives rise to a dichotomy. On one hand, we favour the manual layering of ceramics. With great attention to detail and the subtleties of layering technology, we can create highly aesthetic restorations that are difficult to beat in terms of individuality. On the other hand, monolithic production is economically attractive. Whether using pressing or CAD/CAM manufacturing, monolithic production is in competition with the layering technique, especially concerning posterior restorations. Silicate ceramics in particular have high aesthetic potential.
This is also of interest to dental practices, particularly because CAD/CAM blocks made of silicate ceramics promise the economical production of aesthetic crowns, inlays, etc. In order to be able to stake a claim on the production of single-tooth restorations in this changed environment, dental technicians should ascertain the potential of modern CAD/CAM materials in block form and, if useful, integrate them into their everyday work.
A charming alternative to layering
Owing to economical, time-saving production, the laboratory remains competitive in the field of single-tooth restorations. The icing on the cake is that dental technicians know how to achieve that bit extra from a restoration through their particular expertise, attention to detail and craftsmanship than is possible in the vast majority of dental practices; in any case, this should be our conciliatory claim as dental technicians because there are alternatives to the layering technique for the production of ceramic restorations. However, the high bar set by the layering technique still applies. The monolithic restoration should satisfy the critical eye of the dental technician in all respects. One material that meets this requirement is GC Initial LiSi Block. Especially in the posterior region, a fully crystallised lithium disilicate ceramic such as GC Initial LiSi Block (Fig. 1) represents a charming alternative to conventional production. Compared with zirconia, the uncompromised versatility (anterior or posterior region, monolithic or veneered), the high aesthetics and the possibility of adhesive luting are convincing in the field of single-tooth restorations. The ceramic, which is based on the proven high-density micronisation technology, has already conquered the hearts of many dental technicians as a pressing material (GC Initial LiSi Press). Now the success story is being continued with a CAD/CAM block.
A short excursion into materials science
Lithium disilicate ceramics belong to the group of reinforced silicate ceramics. The starting product is glass, in which corresponding crystals (reinforcing particles such as leucite or lithium silicate crystals) grow through controlled nucleation and crystallisation.1 Therefore, such ceramics are called reinforced silicate ceramics. GC Initial LiSi Block is an optimised or modified variant of the classic lithium disilicate ceramic. The fully crystallised lithium disilicate block possesses its final and optimal physical properties without the need for firing and is thus stable and fast to mill. GC Initial LiSi Block offers the same biaxial strength (of 408 MPa) with or without firing. The ceramic distinguishes itself from the other materials of its class by its significantly refined crystals. Owing to HDM technology, the crystals in the glass matrix are smaller and more evenly and more densely distributed. According to the manufacturer, this leads to a higher wear resistance, precisely fitting margins and highly aesthetic results, which we can confirm from our everyday laboratory work.
With regard to our targeted perfection, a monolithic crown made of GC Initial LiSi Block can be given an extra touch of naturalness with the GC Initial IQ ONE SQIN concept—a paintable colour and micro-layering ceramic system. It consists of three materials that are perfectly adapted for use together, ensuring an efficient and aesthetically convincing finalisation of monolithic and buccally micro-reduced restorations. Colour and fluorescence are added with GC Initial IQ Lustre Pastes ONE. These also serve as the connection firing for the SQIN ceramics, which enable optimal creation of the desired tooth shape with texture integration. Owing to their autoglaze effect, no additional glaze firing is needed. Both of these can be mixed with GC Initial Spectrum Stains, fine powder stains for infinite individualisation options. Depending on each case, you can use the elements of the system that you need.
Insight into the dental laboratory
As test users, we put GC Initial LiSi Block through its paces from a dental technician’s perspective. We wanted to know how well the ceramic works without any and with individualisation. Processing and accuracy of fit were also put to the test.
GC Initial LiSi Block in its pure version
For the first case, GC Initial LiSi Block was tested in its pure version: mill, polish, place. As usual, model preparation, construction and nesting took place (see the second case for a more detailed description). After separating the restoration from the sprue, we only slightly reworked the crown and polished it according to our protocol (Figs. 2–4). The accuracy of fit and the smooth edges were just as convincing as the beautiful colour effect. The surfaces after milling were homogeneous and had a semi-gloss sheen. The excellent polishability was also impressive; in just a few steps, a high gloss was achieved. The result was appealing (Fig. 5), and the procedure was an adequate alternative to other procedures but with a significantly reduced amount of work. For patient work, however, we always prefer some icing on the cake—the painting or micro-layering technique—to achieve the most from the crown. In that case, we would have characterised the crown a little darker.
Fig. 5: The crown milled from GC Initial LiSi Block and finished without additional firing.
Fig. 6: Preparing the model for crowns #25, 34 and 35.
Fig. 7: CAD construction of the fully anatomical individual crowns.
Fig. 8: The accuracy of fit and the warm colour effect in this pure state were convincing.
Fig. 9: The accuracy of fit and the warm colour effect in this pure state were convincing.
Fig. 10: Our polishing set for lithium disilicate crowns.
Fig. 11: The crowns on the model before individualisation by means of the painting technique.
GC Initial LiSi Block with an extra touch
In this case, three premolars were produced. The preparation of the virtual model as well as the CAD took place as usual in the software. In just a few simple steps, the fully anatomical crowns were created and ready for import into the CAM software (Figs. 6 & 7). High- and low-translucency blocks (in Shade A2) were tested. In addition, we had set different quality levels via the milling strategy (M1 CAD/CAM unit, Zirkonzahn; heavy wet, zirconia) to check the accuracy of fit. When calculating the milling paths, the quality levels can be adjusted dependingon the milling time. The software displays the required milling tools and informs about the required milling time.
The milling resulted in smooth and precisely fitting edges. The surfaces were also wonderfully silky. The first inspection of the model showed the extraordinarily good fit. There was no obvious difference between the milling quality levels. Only minor reworking—proximal fine adjustment, occlusal correction and homogenisation of the surfaces—was necessary after separation from the sprue (Figs. 8 & 9). Commercial abrasives can be used for this. We prefer the following combination: silicone polishers, polishing stones, buffs, bristles, ceramic fibre points and a good polishing paste (Fig. 10). An appealing result with natural opalescence and an inconspicuous beautiful colour effect was already apparent (Fig. 11). Because of the homogeneous, fine surface, the texture looked natural.
But we wanted that extra touch that distinguishes a crown created by a dental technician. With GC Initial IQ Lustre Pastes ONE, the crowns were individualised with a touch of 3D colours and glaze pastes (Fig. 12). GC Initial IQ Lustre Pastes ONE are a mixture of refined glass-ceramic particles and can therefore be easily applied and purposefully positioned. Depending on taste or need, subtle or intensive effects can be achieved. After the firing, we were inspired by the crowns’ natural fluorescence and their effect on the tooth-coloured stumps (Fig. 13).
This simple and economical approach produced a result that could match that of a conventionally manufactured crown. Owing to the inherent gloss of the GC Initial IQ Lustre Pastes ONE glaze pastes, a shiny surface was obtained (Figs. 14–16). This particular case did not require detailed surface texture. However, when more texture is necessary, like for a central incisor of a young patient, SQIN ceramics can be added on top. The GC Initial Spectrum Stains complete the range of possibilities.
Since no crystallisation firing had to be executed, the production time was significantly shorter. The fast milling process resulted in smooth and precisely fitting edges. Even after the characterisation or glaze firing, the accuracy of fit of the margins and the surface texture were retained. We were also convinced by the natural opalescence and the vividly warm colour effect without loss of value. An excellent gloss level could be achieved in just a few minutes by polishing. In addition, simple, effective individualisation was possible with the paintable colour and form ceramic concept GC Initial IQ ONE SQIN. If necessary, impressive characterisation can be achieved with a very thin layer of no more than 0.1–0.6 mm. GC Initial LiSi Block will complement the portfolio of materials in our laboratory. Especially when work needs to move quickly or if a high level of cost-efficiency is required, ceramics are not only an adequate alternative but also the material of choice in certain cases for single-tooth restorations. There is always our desire as dental technicians to achieve more for every restoration, and this is possible using GC Initial LiSi Block, offering natural beauty, simplicity and versatility.
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