PROVEN SCIENCE AND ARTISTRY LEAD TO QUALITY

Kuraray Noritake Dental enables the unique in-house production of raw materials. In contrast to our competitors, who source their raw materials externally (well known: Tosoh Cooperation), Kuraray Noritake Dental distinguishes itself by its unique in-house production of zirconia raw materials. Many years of expertise in manufacturing the company’s own powder have brought the material quality of KATANA™ to completely new dimensions, not only by controlling the degree of purity and particle sizes, but also by creating an optimal balance of binders, color pigments, stabilizers and other ingredients.

“WE CONTROL EVERY DETAIL.”

KATANA™ Zirconia STML NW with CERABIEN™ ZR FC Paste Stain
Sergio R. Arias DDS, MS Sung Bin Im, MDC, CDT

NEW SINTERING SCHEDULE

In addition to the new sintering programs, the traditional KATANA™ sintering programs can also be used, if desired.

Case by Dr. Daniele Rondoni, RDT

Check out how beautiful zirconia restorations are finalized using CERABIEN™ ZR FC Paste Stain, take a look at the color palette used by Dr. Daniele Rondoni to achieve outstanding aesthetic results.

“CERABIEN™ ZR Paste Stain is a material developed for micro-layering on the full-contour zirconia surface. With it, natural, true-to-life optical effects are created in an efficient way. I apply the pastes in the esthetic areas, while the functional parts of the restorations are only polished.”

Dentist:

DR. DANIELE RONDONI, RDT

Born in Savona in 1961 where he lives and has worked in his own laboratory since 1982 with his collaborators. Graduated from the dental technician school IPSIA “P. Gaslini” in Genoa in 1979. He continued his education by attending relevant workshops for the “Italian dental school“ and broadened his professional experience in Switzerland, Germany and Japan. Since 2011 Kuraray Noritake Dental International Instructor.

Case by Francesco Ferretti and Marco Nicastro

Aesthetic restoration of anterior teeth using KATANA™ UTML Full anatomical crowns, with vestibular stratification and BOPT*¹.

^{*1 Biologically Oriented Preparation Technique}

Initial situation

Final result

Shows excellent aesthetic properties of KATANA™ UTML and the perfect integration in harmony with pink tissues.

Figure 1. The patient requested a solution for an aesthetic problem due to unnatural look of old restorations and black triangles coming from past history of periodontitis. The resulting retraction of the tissues had left the margins of the prosthesis clearly visible, and the loss of the papilla peaks, together with the numerous black spaces between the crowns, required a complex therapeutic approach.

Figure 2. The treatment plan for the periodontal problems con-sisted of a non-surgical approach, with scaling and root planing, and the replacement of the previously fixed prostheses to recondition the marginal tissues and facilitate the restoration of a new, aesthetically pleasing gingival architecture.

Figure 3. From a functional point of view, we decided to reduce the deep frontal bite to restore a correct overjet-overbite ratio. This reduction was also important from an aesthetic point of view, as it allowed us to shape the various elements correctly.

Figure 4. We usually remove old prostheses before beginning a periodontal treatment, and make a first, provisional restoration to create an environment in which the soft tissues can heal. If we have to work beyond the cement enamel joint (CEJ), we prefer a vertical preparation for posts, and the purpose of the provisional restoration is to condition the marginal tissues using Dr. Loi’s BOPT.

Figure 5. For the BOPT, the vertical preparation of the post has a finish line that extends inside the gingival sulcus. The temporary conditioning of the tissues induced by the provisional prosthesis allows us to modify the level of the gingival parables to a certain extent.

Figure 6. The image on the left shows the clinical healing of the tissues one month after the initial periodontal treatment. The role of the provisional restoration, appropriately realigned, is clear. The conditioning of the tissue has been achieved by means of the provisional restoration, which has modified the level and shape of the marginal tissue. Once filled with correctly fitted crowns, the interproximal spaces will be further reduced after the definitive restoration.

Figure 7. The correct management of the provisional restoration is crucial for the healing of the tissues. The placement of a provisional restoration before the periodontal therapy has allowed us to create the right environment for complete healing. At the same time, the vertical preparation has allowed us to gradually condition the marginal gingival tissue by shortening or lengthening the provisional restoration as necessary.

Figure 8. One of the advantages of a vertical preparation is that taking the final impression is easy, because the absence of a horizontal finish line greatly simplifies the procedure. On the other hand, the BOPT also requires the taking of an impression of the sub-gingival portion of the preparation. The dental technician will have to decide marginal shape of restorations according to the position of the gingival line in consultation of the clinician, and based on the tests conducted with the provisional restoration.

Figure 9. After the casting of the model, we prepared the gingival area to accommodate an ideal configuration of gingival parables.

Figure 10. After making a wax model, we assessed whether the height of the gingival zenith level could be further corrected. This photo shows that gingival level of 21 was not yet ideal, so we stretched it distally.

Figure 11. Once the wax model was complete, we extracted the element from the model and evaluated its protrusion. It was only after joining the gingival protrusion to the arbitrary margin of the preparation that we proceeded to a scan and milled the crowns.

Figure 12. The restoration was carried out with Katana™ UTML zirconia based on the new formulation of cubic zirconium oxide. This ultra tralucent material was chosen because we were working with light and non-discolored posts.

Figure 13. We finished the crowns on a positional impression to help to improve the gingival adaptation; we had some dispersion of the tissues in the first precision impression due to the use of retractors. We finished the crowns with CZR FC Paste Stain colours and glaze.

Figure 14. The surface colours and the slight contrast created are highlighted in this black-and-white image taken with a blue filter.

Figure 15. In this translucent image, we can see the natural translucent effect of KATANA™ UTML and invisible fusion between abutments and crowns.

Figure 16. Clinical image one year after cementation made with PANAVIA V5; this shows the good clinical condition of the marginal tissue, with no signs of inflammation or bleeding. The BOPT allowed us to optimise the level of the gingiva without resorting to periodontal surgery, while the shape of the new crowns has made it possible to close all interproximal spaces for an optimally aesthetic result.

Figure 17. The brightness of the restorations (thanks to the use of a particularly translucent zirconia) combined with the shape of the incisors, has greatly im-proved the aesthetic of the restoration, even though the condition initially appeared to be particularly unfavourable.

Figure 18. Compared to the previous prostheses, the incisal reduction allowed not only for the optimisation of the functional phase by reducing the overbite, but also made it possible to achieve a more natural aesthetic, with the contour of the incisal margins following that of the lower lip.

Dentists:

FRANCESCO FERRETTI

Born in Rome on 15th March 1957, Francesco Ferretti gets his degree as dental technician at the Institute “Edmondo de Amicis”, in Rome. In 1980, he starts working and, from 1987 to 1994, he cooperates with IVOCLAR VIVADENT giving consulting as ceramist. In 1992 he starts working exclusively with Prof. Mario MARTIGNONI.

• After one year cooperation with Prof. Martignoni, he starts working with the ORAL DESIGN CENTER founded in Rome by Mr. Willi Geller, and becomes a partner, improving prosthesis esthetics.
• Is registered outside the course of dentistry at the University of Rome Tor Vergata.
• In 2001, he founds ESTECH DENTAL STUDIOS, in cooperation with Pentron for technical training and consulting.
• He has published articles and studies in Italian and American magazines. He is interested in Metal Free techniques.
• Winner of the 2004 Polcan Aiop.
• He is a member of: ANTLO LAZIO ( National Association of Lab Owners) with the president of the Lazio region 2013-2014.
• National cultural manager ANTLO 2017-2020.
• Teacher of prosthetics perfectioning at the University of Chieti for the year 2002, he has been re-confirmed for the year 2003, 2004, 2005 to deal with Metal Free.
• Teacher of prosthetics perfectioning at the University of Naples 2006.
• He has participated as a speaker at numerous conferences in Italy. ESCD member has participated as a speaker at ten in Florence 2009 and Turin 2013.

MARCO NICASTRO

Marco Nicastro takes a degree in “Odontoiatria e Protesi Dentaria (Dentistry and Dental Prosthesis) at the University of Rome “ La Sapienza in 1989. Since the beginning he is interested in prosthesis restoration dentistry and aesthetic problems.

• From 1990 to 1996 he attends Prof. Martignoni’s studio, where he develops his prosthesis knowledge.
• From 1993 to 1998 he cooperates as lecturer with the Oral Design Centre in Rome, directed by Mr. Ferretti and Mr. Felli, giving lectures and courses about aesthetic restoration either in Italy or in foreign countries. In the same period he enlarges his experience in aesthetics, attending training courses at the University of Geneva, in Switzerland.
• Since 1993 he has been cooperating with Mr. Francesco Ferretti in the organization of Courses and Conferences, paying particular attention to metal free methodology.
• Vice President of the European Society of Cosmetic Dentistry (ESCD).
• Founding member and active member of Gimnasium interdisciplinary CAD-CAM (GICC).
• Active member of the Italian Society of Conservative Dentistry (SIDOC).
• Partner of the Italian Academy of Prosthetic Dentistry (AIOP).
• President of Like Mine Dental Education in Rome since 2001.
• He won, with Francesco Ferretti, the Polcan award of the Italian Accademy of Prosthetic Dentistry in 2004.

Interview with Dr Imad Ghandour

In recent years, zirconia has emerged as the preferred choice for dentists who wish to perform restorative procedures with a reliable and metal-free material. With the recent development of multi-layered aesthetic high-translucency options, zirconia’s popularity has further increased. In comparison to the opaque whiteness of older generations of zirconia, these newer versions have an enhanced appearance and functionality that makes them suitable for natural-looking anterior restorations.

Kuraray Noritake Dental’s KATANA Zirconia disc range is made with a proprietary zirconia powder - processed in-house - that gives it its natural appearance. Suitable for zirconia prostheses, from single crown to full arch, it is an ideal option for restorations in both the anterior and posterior regions. We spoke with Dr Imad Ghandour, a prosthodontist with a strong scientific background and a private practice in Le Cannet in France, about his experiences with the KATANA Zirconia range in restorative procedures.

Dr Ghandour, when did you first start using zirconia as a material for your restorations?

In 1998, when I was still sintering manually, I began using zirconia alumina. It was nice to have an alternative to metal alloys that was much more aesthetic. From 2003, however, I started with VITA blocks, but only for frameworks - I would still build up with ceramics. Now, with so much of dentistry being digitally focused, there is a need for a material that can be milled without changing anything in the morphology of the teeth. Why? Because we need to be able to reproduce the treatment plan as accurately as possible. Simply put, the KATANA Zirconia range solves this need for me.

With respect to dentistry being digitally focused, how has this changed the role of the dentist regarding performing restorative procedures?

Well, it is clear that we have entered the age of digital dentistry. Around 80 per cent of restorations are conducted via CAD/CAM systems and without dentists even touching the materials themselves. There are great advances being made in the technologies that are available for everyday use in dental practices worldwide, and many of them can be used to assist dentists performing restorative procedures. It is important, though, to keep in mind that these technological advancements alone will not lead to better results - they should supplement the requisite hands-on skills and techniques that all dentists must first learn. With this base of fundamentals, we can then use digital dentistry to make restorative procedures more predictable and reproducible. Of course, to ensure the best results in restorative procedures, dentists also need to use the materials that have the best aesthetic and mechanical properties.

For how long have you been using Kuraray Noritake Dental’s KATANA Zirconia range, and what has your experience been?

I have been using KATANA Zirconia for a little bit more than one year. In that time, I have primarily used the KATANA Zirconia STML (Super Translucent Multi Layered) line and have been pleasantly surprised by how natural-looking the restorations I have made with the material are. For example, when I sinter a crown made of Katana Zirconia STML, I am amazed at how much the sintered material is reminiscent of a pearl - it truly brings to mind the idea of one’s teeth being one’s pearly whites.

When using KATANA, how do you ensure that you select the correct shade to achieve a natural look?

Firstly, no one - not a dentist nor a dental technician - can be absolutely certain that the shade and chroma of the restoration that is in one’s hand will be the same once it is in position in the oral cavity. This is due to the complexities of the oral environment - the pinkness of the gingivae, for one, can have a large impact on how the restoration appears, often making it seem far duller than it does in the light of a dental laboratory. This can cause dental practitioners to compensate and make prostheses that appear far brighter than they will when they are in place.

With a product like KATANA and its related glazing materials, however, I can create crowns and other restorations that have an optimal fluorescence and translucency and are able to maintain their shading better than any other ceramic material I have used. I am able to select a shade with the confidence that it will look exactly the same once placed inside the mouth, with its chroma remaining unabsorbed by the gingiva. Achieving a natural look, then, depends on choosing a shade that is as close to that of the surrounding dentition as possible. Since KATANA Zirconia UTML (Ultra Translucent Multi Layered) is available in 16 standard shades and a further four enamel shades, there is no shortage of options in this regard.

How does the multi-layered technology of KATANA Zirconia help you to achieve optimal and natural-looking aesthetic results?

Well, firstly, the layering of the material is designed to replicate the colour and translucency progression of natural teeth, which allows for restorations to blend in as much as possible. This multi-layered technology has also proved itself to be very handy when I am sintering crowns made of KATANA Zirconia. Simply put, if one sinters a crown quickly, it will be a little more opaque. If one sinters it at a higher temperature and quite slowly, it will be much more translucent. The multi-layered aspect of KATANA Zirconia is excellent in that it gives me the ability to make restorations more or less translucent depending on what is required.

Users of dental zirconia are really spoilt for choice these days. Countless manufacturers offer zirconia materials that differ in their mechanical and optical properties and indication range. What is not apparent at first sight is that the available products also differ with respect to the quality of the CAD/CAM blanks offered. Blank quality is highly dependent on the quality of the raw materials and is affected by different aspects during raw material processing, pressing and pre-sintering. This has a huge impact on the surface quality, edge stability, fit and processing requirements of milled restorations.

Raw material production

Pre-shaded dental zirconia typically consists of metal oxides, including zirconium oxide, yttrium oxide and aluminium oxide, as well as additives like binders and colour pigments or ions. Most manufacturers of dental zirconia obtain pre-fabricated powder from an external industry partner, the most popular option being Tosoh Corporation. In contrast, Kuraray Noritake Dental relies on an end-to-end in-house process. This includes the production and addition of the components forming the company’s innovative multilayered technology, which makes it possible to match the shades in the polychromatic blanks precisely to the colours of the VITA classical A1-D4 shade guide.

At Kuraray Noritake Dental, the powder is produced in-house.

Since more powder production steps are carried out in-house, this gives the company full control of the quality of the raw materials, their grain size and the purity of the formulation. It also allows for a precise alignment of the mechanical and optical product properties. Properties of zirconia restorations that are affected by the powder quality and composition include translucency and shade appearance, flexural strength, ageing behaviour and sintering performance.

Blank pressing

Zirconia discs and blocks used for CAD/CAM processing are usually produced by uniaxial and isostatic pressing. In the uniaxial compaction process, pressure is applied to the powder from one direction (uniaxial) or two directions (biaxial), whereas the isostatic compaction process involves virtually equal pressure applied from all sides. Hence, isostatic pressing typically results in a more uniform density distribution throughout the blank and a higher material homogeneity. These factors are prerequisites for a predictable processing and sintering behaviour and affect the fit of the final restoration. For optimal mechanical and optical properties of the zirconia material, it is essential to avoid large porosities, air pockets and impurities caused by airborne particles that are trapped during pressing.

At Kuraray Noritake Dental, a unique and extremely meticulous pressing process achieves a uniform pressure distribution and low risk of contamination by airborne particles. This specific procedure reduces gravitation forces and contributes to having as high as possible density of zirconia material. All the high-level preparation processes from raw material production to pressing are responsible for the high edge stability and surface quality of restorations milled from KATANA™ Zirconia.”

Pre-sintering

The pre-sintering procedure is necessary in that it gives the pressed blanks the required stability to be machinable with milling tools. The selected temperature profile and duration of the pre-sintering cycle determine the material’s strength and processing properties and have an impact on the final sintering process.

The unique pre-sintering procedure carried out in the production facilities of Kuraray Noritake Dental results in blanks that are stable in their pre-sintered state. Although more stable, pre-sintered KATANA™ Zirconia is machinable with common diamond-coated milling tools without any increased risk of breakage or higher tool wear.

A KATANA™ Zirconia blank ready for milling.

Fast sintering for the laboratory

The unique procedure has a positive impact on the surface smoothness after milling and can significantly shorten sintering times. In fact, the speed sintering program offered for all variants of KATANA™ Zirconia is the fastest one on the market. In the dental laboratory, the sintering times may be reduced to 90 minutes^*for single-tooth restorations and bridges of up to three units.

^*The material is removed from the furnace at 800°C.

Overview of the recommended sintering protocols.

Fast sintering for chairside

Using the KATANA™ Zirconia block with Dentsply Sirona’s CEREC system, it is possible to sinter single crowns up to three-unit bridges in 18-30 minutes without compromising the mechanical or optical properties.

The KATANA™ Zirconia block displays superior optical properties after 18 minutes of sintering compared with representatives of major competitors’ raw material after 30-minute and 60-minute sintering programs designed by Kuraray Noritake Dental based on the manufacturer's recommendations.

Unique KATANA™ Zirconia properties

Together, these efforts taken by Kuraray Noritake Dental to produce dental zirconia of exceptionally high quality make all the difference. The KATANA™ Zirconia series - KATANA™ Zirconia Ultra Translucent Multi Layered (UTML), Super Translucent Multi Layered (STML), High Translucent Multi Layered (HTML) and KATANA™ Zirconia High Translucent Mono Layered (HT) - have a homogeneous, high-density structure with low porosity and a high level of purity. This optimises the performance of the blanks during machining.

Surface roughness

SEM image, magnification 33X, of competitor material surface roughness. Image courtesy of Dr Kunkela, Kunkela Research Academy.

SEM image, magnification 33X, of KATANA Zirconia surface roughness. Image courtesy of Dr Kunkela, Kunkela Research Academy.

SEM images of non-polished KATANA™ Zirconia and a competitor’s material at 33x magnification. The four images of each material show the surface structure at different areas of a molar crown. In all areas, the surface of the restoration made of the competitor’s material is rougher and shows more porosity than the surface of the KATANA™ Zirconia crown directly after milling, according to Dr Josef Kunkela’s research results. One of the contributing factors to this result is the more densely pressed blanks with smaller grain sizes of KATANA™ Zirconia.

An optimised processing behaviour leads to regular restoration margins, smooth surfaces and a precise fit of the restorations. The latter is due to the fact that the milling behaviour and volumetric shrinkage during final sintering are highly predictable, so that a user designing a 20 µm cement gap will get what he or she desires. Owing to the great control over optical properties and precise match to the VITA classical A1-D4 shades, KATANA™ Zirconia is considered to be one of the most aesthetic dental zirconia options available on the market.

Excellent marginal fit

SEM images revealing the fit of restorations made of two different materials (lithium disilicate and KATANA™ Zirconia Block STML) on a tooth abutment. The KATANA™ Zirconia restoration shows a more regular margin and more precise fit (with a cement gap of 19-21 µm) than the lithium disilicate crown (cement gap 26-45 µm). Images courtesy of Dr Kunkela, Kunkela Research Academy.

Extremely regular margins of a KATANA™ Zirconia crown after milling, which is also a result of the favourable material structure.

In order to ensure all the desired material properties, including aesthetics and strength, one thing is essential: the machining carried out in the dental laboratory - milling and sintering - needs to adhere to the recommended protocols. This means that the milling machine and furnace should be cleaned and calibrated on a regular basis, which provides the conditions for optimised zirconia processing from the powder to the final, true-to-life dental restoration.

The use of highly translucent, gradient pre-shaded zirconia brings more efficiency into the dental laboratory. Due to the advanced properties of the materials, e.g. from the KATANA™ Zirconia Multi-Layered Series, true-to-life restorations may be created without any or with only a small vestibular layer of veneering porcelain. This saves a lot of time usually required for manual work around steps in the veneering of zirconia frameworks. At the same time, this also allows for a reduced wall thickness, beneficial in the context of minimally invasive dentistry.

In order to leverage the high aesthetic potential and balanced mechanical properties of these types of zirconia, however, it is essential that the restorations are processed under ideal conditions. The most advanced materials with the highest translucency are particularly sensitive to contamination during and after wet milling, contamination of the furnace chamber, and temperature variations during sintering. Possible undesirable effects include a grayish appearance of the restorations and low chroma, green, yellow, blue or gray traces in the restorations, white spots on the surface and variations in colour and translucency.

If carried out on a regular basis, the following measures will effectively eliminate these effects. Hence, they will support users in ensuring consistently beautiful results.

Optimizing the milling process

Blue or gray traces visible in the final restoration are usually the result of contamination of the cooling water with extrinsic particles in the context of wet milling, (which is usually conducted in chairside procedures). In most cases, silica particles left over from the processing of glass or silicate ceramics with the same milling unit are the root of the problem. The effect is easily avoided by thorough cleaning of the milling chamber, the water tank and the filter insert of the milling machine every time a different material needs to be processed. Another solution is dry instead of wet milling, which offers additional benefits such as shorter processing time and better quality edges and surfaces.

Decontamination of the furnace chamber

In general, the chamber of the sintering furnace should be cleaned before sintering. Important measures include the removal of dust inside the sintering chamber and cleaning of the heating elements, both done with a soft brush. The use of compressed air is contraindicated.

Unwanted optical effects that occur on restorations due to contamination of the sintering chamber include white spots on the restoration surface, a blue-grayish appearance and low chroma, and green or yellow traces in the material. White spots on a restoration surface are usually indicators of contaminated alumina sintering beads or the use of the wrong instruments for surface modification and sprue removal. The effect is avoidable through a monthly or even more frequent replacement of the sintering beads (as soon as they show any signs of discoloration) as well as the exclusive use of fine-grid diamond instruments for adjustments prior to sintering.

Alumina sintering beads may be the cause of white spots on a restoration surface if not replaced on a regular basis.

The blue-grayish appearance and low chroma may be attributed to mineral residues from dipping liquids in the chamber. They are effectively removed with the aid of a decontamination program to be selected in the furnace menu, which is run after inserting several residual pieces of a highly translucent, white zirconia blank. As soon as the decontamination cycle is completed, the chromatic intensity of the residual blank parts indicates whether a second cycle is required. In order to prevent the occurrence of a grayish appearance in new restorations, it is recommended to perform a decontamination program at least once per month.

Pieces of a white zirconia blank left over after milling.

MoSi₂ heating elements: Regeneration needed

If a restoration appears to be green or yellowish, it is most likely that the furnace is equipped with aging molybdenum disilicide (MoSi₂) heating elements in need of regeneration or replacement. The inner part of the elements is made of molybdenum (Mo), which is usually covered by a protective layer of silica (SiO₂). This layer is naturally built up during sintering at a temperature range between 1,000 and 1,600°C. As the thickness of the layer grows, its intrinsic residual compressive stress increases. This stress, as well as possible extrinsic influences, e.g. originating from acidic dipping liquids, may finally lead to cracks and a breakup of the protective layer. Once damaged, the molybdenum core is exposed. At a low temperature range of 400 to 600°C, the molybdenum reacts with oxygen in the sintering chamber, a process referred to as pest oxidation. The resulting molybdenum oxide (MoO₃), together with ions or metal oxides from colouring agents, is responsible for the green-yellowish discoloration on the surface of the restorations.

Restorations displaying greenish surface pigmentation.

Molybdenum disilicide heating element with a protective silica layer bursting off, leading to pest oxidation and the contamination of elements in the sintering chamber.

Regeneration firing, which involves a rapid heating rate and a long firing phase at approx. 1,450°C, aims at regenerating the layer of silica. This measure, however, works only a limited number of times, as a repeated process of pest oxidation and regeneration leads to aging of the heating element itself. Hence, it will ultimately lead to the need for replacement. The whole issue of pest oxidation may be effectively avoided by the use of a furnace with silicon carbide heating elements, which are highly aging-resistant and do not cause any discoloration. A positive side effect is that these types of heating elements deliver more constant temperatures.

Temperature control

Variations in translucency or chroma and pigmentation of restoration surfaces are often due to deviations of the actual sintering temperatures from the recommended temperature curve. The only way to solve this issue is temperature calibration. This measure is not only a prerequisite for aesthetic results, but also has a decisive impact on the mechanical properties of the restorations: if the maximum temperatures are too high, for example, the flexural strength of the zirconia materials may be expected to decrease¹.

Effect of temperature differences during sintering on restorations made of KATANA™ Zirconia UTML: The restorations were sintered at the same nominal temperatures in three different furnaces!

Temperature control is usually carried out with the aid of TempTABs or PTCRs (process temperature control rings). They are placed into the furnace on a sintering tray and typically processed by running a calibration cycle. After sintering, the tab or ring diameter is determined. As TempTABs and PCTRs exhibit controlled shrinkage, it is possible to calculate the actual sintering temperature based on the measured diameter. A conversion table supports the user in determining the deviation between the temperature actually reached and the temperature displayed on the furnace. Subsequently, the values displayed on the furnace are adjusted if necessary.

TempTAB on a sintering tray with restorations ready for sintering.

General recommendations

In order to set the stage for brilliant aesthetics and ideal properties of zirconia restorations, it is essential to ensure optimal processing conditions. Instead of troubleshooting carried out whenever discoloration appears after sintering, it is advisable to take the following actions on a regular basis as preventive measures:

• Cleaning of the milling machine’s water tank every time before starting to mill (wet milling only)
• Strict adherence to the sintering protocols recommended by the material manufacturer
• Removal of the dust from the sintering chamber and heating elements with a soft brush before each use
• Replacement of the alumina sintering beads whenever they show signs of discoloration (at least once per month)
• Exclusive use of fine-grid diamond instruments for sprue-removal and pre-sintering adjustments
• If possible: Use of furnace with silicon carbide heating elements
• Furnaces with molybdenum disilicide heating elements require constant visual control and regular regeneration cycles
• Running of a decontamination program with decontaminating powder or white zirconia residues (y-TZP) at least once per month
• Temperature control and calibration at least once per month

With these simple measures, it is possible to maximise the full potential of KATANA™ Zirconia Multi-Layered Series from Kuraray Noritake.

References
¹ Stawarczyk, B., Özcan, M., Hallmann, L. et al. The effect of zirconia sintering temperature on flexural strength, grain size, and contrast ratio. Clin Oral Invest 17, 269–274 (2013).

By Daniele Rondoni, RDT

Considering different criteria to select the ideal zirconia and frame design to meet the level of esthetics requested.

Step 1
Final Preparations.

Step 2
Zirconia Frame (KATANA Zirconia STML A2) cut-back designed to reproduce translucent incisal area.

Step 3
Application of 1st Internal Stain and firing.

Step 4
Application of 1st Luster, Clear Cervical and firing.

Step 5
Application of 2nd Internal Stain and firing.

Step 6
Application of 2nd Luster, and Opacious Body.

Step 7
Completion of firing.

Step 8
Completion of morphological correction.

Step 9
Post-operative view.

By D.T. Pier Francesco Golfarelli

Digital workflow and CAD/CAM shaping have now become a daily practice that helps to manage most cases, including the most extensive re-adaptations (rehabilitations).

KATANA™ HTML zirconia was selected, in consultation with the specialist, for the case presented here. It was principally chosen for its aesthetic and mechanical properties. One of our selection criteria was the advantageous lower abrasiveness level of zirconia. Because of its density, this material is less abrasive than the more traditional ceramics in combination with adequate mechanical polishing. Based on the initial situation, once the assembly in the articulator was completed, we designed a structure with anterior cutbacks for maximum aesthetics, while for the posterior teeth a monolithic solution was chosen for maximum strength and quality of the functional surfaces.

With the CORE & SHELL technique developed by the Noritake Italian Study Club, I can now fully exploit the optical properties of KATANA™ zirconia by integrating it, in the anterior area, with Noritake CERABIEN™ ZR ceramics. In the images here you can see the aesthetic results of the anterior and side areas, the mechanically polished monolithic surfaces and the special Noritake glaze.

Fig. 1 CAD Shaping - 3Shape Dental Designer

Fig. 2 Structure design with cutbacks

Fig. 3 KATANA™ HTML structure

Fig. 4 Occlusal surface – details

Fig. 5 Shade stain

Fig. 6 Shade Stain (SS)

Fig. 7 Core

Fig. 8 Internal Live Stain (ILS)

Fig. 9 Shell

Fig. 10 Shell Tissue

FINAL SITUATION

Fig. 11 Layering Details

Dentist:

D.T. Pier Francesco Golfarelli
Noritake Italian Study Club Teacher, Forlì

This case was conducted by Dr Davide Cortellini, owner of Studio Cortellini in Riccione in Italy, and dental technician Angelo Canale, owner of Canale dental laboratory in Rimini in Italy.

This patient came to the clinic to improve her chewing ability and aesthetic level. The physical examination revealed the presence of several endogenous erosive lesions that made chewing difficult, in addition to partly affecting the esthetics due to decrease in enamel thickness and the presence of dyschromic composite restorations. The possibility of using the new types of both tetragonal and cubic multilayer zirconia made it possible for us to plan the complete covering of all the elements with extremely conservative crowns with thicknesses between 0.5 and 1 mm in the axial and occlusal areas and up to 0.2 mm at the margin.

VERTICAL PREPARATIONS

Very conservative vertical preparations were carried out in the enamel without anesthesia. In the upper arch, the front group was prepared for full-veneer crowns, while the lower front group was treated with conventional lithium disilicate veneers without interproximal separation. In this case too, vertical preparations were carried out without finishing line. The impression was made using a 3Shape TRIOS intraoral scanner. The technician modeled the zirconia restorations that were then completed by the ceramist.

Knife Edge Preparation

SCANNING SEQUENCE

Digital DV models of temporary teeth

The three different materials were selected on the basis of the specific positions inside the mouth:

• UTML for the anterior teeth
• STML for the premolars
• HTML for the molars

The final result shows excellent integration between the 3 different types of zirconia and a good natural feeling.

MINIMAL PREP KATANA™ (KATANA™ MICRO LAYER)

HARMONIC OPTICAL INTEGRATION

The full-mouth rehabilitation procedure using three different types of zirconia led to a functional and beautiful treatment outcome. The optical integration between the materials is excellent and the high translucency especially in the anterior region creates a true-to-life appearance.

APPROACH WITH MINIMAL INVASIVE PREPARATIONS - REPORT ON THE SELECTION OF MULTI-LAYERED ZIRCONIA

Dental zirconia is no longer just the opaque framework material introduced two decades ago. Nowadays, it offers the high strength needed for long-span bridges, dentin-like translucency and strength perfect for thin-walled posterior crowns, or enamel-like optical properties for beautiful anterior restorations - depending on its composition and structure. Kuraray Noritake offers three types of dental zirconia - three with a multilayered structure created using patented powder coloring technology. They differ with regard to their optical and mechanical properties, which makes it possible to choose an ideal material for every clinical situation.

Dentists:

DR. DAVIDE CORTELLINI

Dr. Cortellini graduated with honours in Dentistry and Dental Prosthetics from the University of Siena in 1992. He won the scholarship of the Italian Society of Periodontology for the year 1994-95. He then received the opportunity to attend the Department of Periodontology and Fixed Prosthetics of Prof. NP. Lang at the University of Bern in Switzerland, carrying out clinical and research activities. He obtained the title of „Doctor Medicinae Dentium“ (D.M.D.) at the same university in 2000. Dr. Cortellini is the author of scientific publications in international journals of aesthetic dentistry. He is an active member and advisor to the Italian Academy of Prosthetic Dentistry, and a member of the International Academy for Digital Dental Medicine. He holds conferences in Italy and abroad and is dedicated to clinical activity in his own practice in Riccione, where he primarily focuses on aesthetic and digital prosthetics and complex prosthetic rehabilitation.

CDT. ANGELO CANALE

Mr. Canale is a dental technician graduated high school in 1981. He’s the owner of a dental laboratory in Rimini since 1986. He is specialized in fixed prosthesis on natural teeth and on implants with a metal free approach using different kind of materials. He is always interested about digital technique using CAD-CAM systems (in his laboratory the 80% of the work comes from digital impressions). He is co-author of international publications on PPAD, QDT, EJED and THE JOURNAL OF ADHESIVE DENTISTRY concerning the use of metal free in prosthesis. He is a speaker in national and international congress.

We are pleased to present the following short video series of MDT. Kazunobu Yamada using Katana Zirconia UTML for Stain & Glaze Wipeoff Technique.

Each step will be explained in the chapters below.