Getting incisal edges consistently correct

In ceramic technology development, we must recognize that pressing and milling is the newest in state-of-the-art technology, or maybe not art but science. So where did the art go?

Milling and pressing still leads us to hand modification using our artistic capabilities to achieve a tooth that looks like a tooth from a color point of view. Certainly it’s not enough to have a good material that will be strong, and not enough for this material to fit and function well, but it has to look right as well.

Some of the materials lose their strength advantages when a cut back technique is used. This refers to building up a restoration and then cutting back in critical areas to achieve desired color and characterization. The area that was cut back opens up the possibility of failures because the add-on materials aren’t as strong as the core restoration. In some cases, multicolored ingots are considered, and although they help establish dentin-enamel existence, they don’t achieve the fine details associated with natural teeth.

Along with these newer materials and techniques, the traditional hand-stacked porcelain technique is very dependent on the artistic abilities of the ceramist. The outcomes of these restorations are open to interpretation and vary greatly with each technician. These are unpredictable, uncontrollable art forms.

In addition, the variations in available thicknesses for fabrication vary from one restoration to another resulting in additional contributing factors. Without the proper room, achieving the desired color and the ability to build up internal structures are compromised.

Another issue to overcome is in communicating the objectives of both the dentist and patient. The dentist must be able to clearly communicate the options to patients and explain to patients what’s available to their unique situation. In turn, the laboratory must have a clear understanding of what is expected from them. This communication is critical to a successful case.

Hilla Technologies helps to address all of the previously mentioned issues. As a lab owner and ceramist, who had been confronting these issues daily and searching for answers, I developed the Hilla technology.

Hilla Technology

Shade selection is based on interpretation. Sending this information to the laboratory that’s using the selected shade as a guide is another level of interpretation. Figure A shows a typical drawing in the lab depicting what the doctor and patient chose for the final outcome.

Every ceramist will know how to read this information, but the results may differ based on their interpretation or artistic skill level. Hilla technology helps to provide not only a more direct way of communicating this information, but also provides a specific product that’s applied to the restoration that directly represents the selected information.

Hilla technology begins with a characterization guide that the dentist and the patient use to select the desired degree of characterization. The guide has four levels: I-00, I-20, I-30, I-40. The I-00 has no characterization and is used to explain what having no characterization or a monochromatic restoration will look like. The other levels show different intensities and how they affect a restoration’s overall appearance.

Case presentations

Two pressable veneers have been fabricated into a full contour. Our focus in the laboratory is to maintain the strength of pressable restorations and to avoid cutting back the restoration whenever possible. The cut back technique provides the ceramist with more room to build in the internal structures. However the materials that are being used to add on increase the chances of failure due to dissimilar add on materials. The strength of the add on material is significantly lower than the core material.

The ideal situation is to build the case to full contour and then stain the surface. Staining is contingent upon the individual ceramists and their ability to recreate a true realistic look of the tooth. It’s very challenging to paint in such a small environment and be predictable and consistent. The Hilla Digital Transfer (HDT), which is a pre-printed ceramic color pattern, solves this problem with ease and very little effort.

01 Two units are waxed up to establish a selected shape, function, general anatomy and surface details (Fig. B).

02 Using Pentron VP 6, the units are then sprued, invested and ready to be pressed in a pressing oven (Fig. C).

03 The material is pressed and divested (Fig. D).

04 The veneers are fitted on to the dies (Fig. E).

05 The shape, anatomy and surface texture are finalized.

06 The units are then glazed. If there is general overall colors to be introduced to the mix, add that color along with the glaze. For the Hilla Digital Transfer the glaze is the key to the process. During the glazing step the Hilla Digital Transfer is brought to the same glaze temperature and this causes the fusion of transfer to the tooth. Hilla Glaze can be fired at a wide range of temperatures and is able to be used on a wide spectrum of ceramic materials (Fig. F).

07 HDT I-30 intensity of the characterization is selected. Based on the size of the restorations, a digital transfer is selected from the medium-sized card and fit is verified by holding the tooth to be worked on next to it (Fig. G).

08 Using a pen such as a Sharpie, mark the tip of the lobes. The tips of the lobes can be placed at the edge of the tooth, or kept away from the edge to introduce more translucencies. Mesial and distal markings also will help with orientation as well as in consideration of the desired long axis of the tooth (Fig. H).

09 Use scissors to cut the HDT from the card. Then proceed to trim the excess (Fig. I).

10 Use tweezers to place the transfer in tap water and hold in the water for about 45 seconds (Figs. J and K).

11 Use fingers to gently apply a sliding pressure to release the HDT from the paper (Fig. L). Using the tools provided, place a small amount of rope wax on to the tool to help hold the veneer and aide in application process.

12 Place the HDT on the tooth surface (Fig. M) and align the dots in the proper locations. Use the adapting tool while applying slight pressure to remove any air or moisture from the surface and to aid in adapting the HDT to the surface of the tooth (Fig. N). Ensure that no air or water remains. Any excess material that may extend will be burnt off in the firing cycle (Fig. O).

13 To ensure there is no moisture remaining (because that would cause water to boil and cause a stain bubble) the tray with the veneers on it is placed on a hot plate at a warm temperature so the heat will dry the moisture rather than boil it (Fig. P).

14 The veneers are placed in the porcelain oven at a cycle specified for the HDT-Glaze is set for the firing of the HDT (Fig. Q).

15 The veneer is cooled (Fig. R). Then the veneers were placed on a model with a tooth-colored background to view the details (Fig. S). At this point if any additional colors need to be added on such as hyper calcification, or horizontal white lines, or any additional cervical colors, all can be added on. As a general rule to obtain and protect the colors, place on the surface and place another coat of glaze over to keep the “zip lock” effect on the colors. The Hilla Digital Transfer can be used internally as well with an enamel overlay placed over the HDT to provide for a different effect.

Hilla technology provides for a standardized tool to help communicate the incisal edge characterization first between the patient and the doctor and then between the doctor and the laboratory. This information then correlates to Hilla Digital Transfer, which when applied to the surface of a restoration provides the dentist and patient with a predictable result.

About the author

Uri Yarovesky, CDT, a ceramist, Owner and President of Opus One Laboratories Inc. and Owner and President of Hilla Technologies in Agoura Hills, Calif., is a graduate of LACC in Dental Technology. Yarovesky was the 2011 recipient of the NADL’s Inventor of The Year award and the 2010 recipient of the Outstanding Contributions to the Art and Science of Cosmetic Dentistry award from the American Academy of Cosmetic Dentistry. He has lectured extensively both in the United States and internationally. He is a current member of  the AACD, IADFE, ASDA, NADL, CDLA, and ACE.