A New Perspective: From Ordinary to Extraordinary

Greg Campbell, DDS

KATANA^™ (Kuraray Noritake Dental, kuraraynoritake.com) is the original, multi-layered translucent zirconia that is now available in block form for CEREC^® (Dentsply Sirona, dentsplysirona.com) chairside CAD/CAM applications. The collaboration of these technologies from Kuraray Noritake Dental and Dentsply Sirona makes it possible to fabricate multi-layered zirconia restorations in a single visit. The innovative multi-layered zirconia provides a conservative, esthetic solution for patients' restorative needs. When performing these restorations, the author appreciates that there is less reduction and more strength and that bonding can be accomplished with a predictable clinical outcome.

Equipment Needed to Use KATANA^™ Zirconia Blocks

• CEREC^® software version 4.5.2 or newer
• Materials package update
• CEREC^® SpeedFire^™ oven
• Wet/dry milling unit or wet-milling unit with modified left step motor

Workflow With KATANA^™ Blocks

The KATANA^™ workflow is automated and more seamless than other chairside zirconia. The material may be "fast" milled, and restoration information transfers to the SpeedFire without any operator input.

Tooth Preparation Guidelines

Adequate reduction is more important in stress-bearing areas (occlusal) than in non-stress-bearing areas (proximal). Fractures are generally due to inadequate reduction in the fissure area or functioning cusp.

The author's preparations:

• 1.0 to 1.5-mm occlusal depth cut to achieve appropriate (desired) occlusal anatomy
• 1.0-mm functional cusp reduction
• 0.8- to 1.0-mm gingival chamfer reduction
• 6- to 8-degree taper to the axial walls

The occlusal milling offset parameter is turned off automatically in the CEREC^® software. The cursor detail reading in "analyzing tools" is the thickness that will be milled (ie, unlike with e.max^{^®} [Ivoclar Vivadent, ivoclarvivadent.com], the cursor detail requirement to obtain a thickness of 1.0 mm must read 1.2 to 1.3 mm).

Chamfer or shoulder margins are preferred, which allows a more accurate mill of the pre-sintered zirconia. If the clinician elects to do feather margins: to reduce the potential for chipping of the margins, milling should not be in fast mode.

Shade and KATANA^™ Block Selection

The CAD/CAM clinician may select from 15 shades. The shades include the 13 most common Vita Classical shades, plus NW (a bleaching shade) and a CL (clear) shade. The clear shade is the only block that is not multi-layered. The blocks are available in two sizes: 12Z and 14Z. It should be noted that 95% of restorations work best with the 12Z blocks, due to the multi-layering of KATANA^™ , which mimics the natural layers of the tooth. If the larger, 14Z block is selected for a molar, it will be difficult to position the restoration to mimic the natural layers because the block layers are much larger than the actual restoration. It is recommended to choose a block that fits the restoration well so that the natural layering in the block is used for proper esthetics.

KATANA^™ blocks sintered in the SpeedFire tend to be higher in shade value. When planning to polish only, without glazing, selecting one shade darker in value than the target shade is recommended. The same principle applies in cases requiring thicker wall restorations.

Getting Started With CEREC^®

The author, who has worked with KATANA^™ for the last 12 months, has recognized several key software points during that time that the user must navigate for success. The author suggests viewing the "Getting started with KATANA^™ blocks" webinar at KATANAblocks.us. The webinar illustrates how to fully navigate the process. As an example, below are a few key points that are discussed in detail in the webinar:

• In the Administration phase of the CEREC^® software, the user must decide to "mill" or "grind" the restoration and select ST for the CL (clear) block or STML for the remaining 14 shades. Most users will select the KATANA^™ Zirconia Block STML milling option (Table 1).

• In the Model phase, after the ideal model axis is set, the model steps can be expanded at the bottom of the screen, and the ideal insertion axis can be set to allow proper positioning of the restoration in the block. This step is not needed in CEREC^® software version 4.6X but is necessary in version 4.5.2.

• When bar codes are input, it should be remembered that the code is always a series of seven numbers, letters, and symbols. If the block only has six, one can simply hit the space bar at the end and hit enter.

Dry Milling vs Wet Milling

Kuraray Noritake Dental recommends dry milling using the Dry Milling Suction Unit (Dentsply Sirona); however, one can wet mill or grind this product. When dry milling, a 25 shaper carbide should be used on the left motor, and a 10 finisher carbide should be used on the right motor.

If wet milling is performed using a water reservoir con-tamin--ated with milling material other than zirconia (ie, silica-based glass ceramics, such as lithium-disilicate glass), the translucency and chroma of the restorations will be diminished. Before milling, it is necessary to clean the milling/grinding chamber, water reservoir tanks, and filters, as well as replace the distilled water and clean the inside of the pump. It is good practice to have two water reservoir tanks for more-efficient performance of the wet-milling operation.

Sintering

KATANA^™ requires the SpeedFire oven. SpeedFire is designed with a special induction technology that rapidly increases temperature and reduces traditional sintering times for KATANA^™ zirconia. In addition to increasing temperature rapidly, the SpeedFire oven achieves the higher temperature needed (1,560°C) for this unique zirconia and sinters in approximately 30 minutes.

When preparing restorations for milling, one should remove the sprue and smooth milling imperfections with a laboratory carbide at 4,000 rpm with light pressure. Restorations should always be placed in the center of the firing table (Figure 1), occlusal-surface down for posterior restorations and lingual-surface down for anteriors.

The manufacturer recommends sintering and then proceeding to post-sintering finishing, glazing, and staining. From the author's experience in working with Sean Han, CDT (Master's Arch) and Jean Chiha, CDT (North Star), pre-polishing KATANA^™ after milling and before sintering provides excellent esthetics and saves time. The author prefers a pre-sintering polishing technique using Twist polishers (Meisinger USA, meisinger.de). The 5 minutes of performing this technique saves several minutes of handling the zirconia on the back end and helps to eliminate the "pearl" effect that many clinicians encounter when polishing after sintering.

Finishing the Sintered Restoration

Polishing is a fast and easy procedure. It is very important to polish occlusal contact points or anywhere tissue contacts the restoration; tissue response will be better. Polishing is achieved using low rpm (4,000) and light pressure with constant movement. If the restoration becomes "pearly" during polishing, the clinician should simply micro-etch the surface and restart the polishing process, keeping in mind that low rpm, light pressure, and constant movement are required with zirconia.

Glazing Procedure

The clinician should sandblast (micro-etch) the crown surface with 30- to 50-μm aluminum oxide at 15 to 58 psi and clean the restoration ultrasonically with alcohol or acetone for 2 minutes or steam clean. Glaze should be applied around 30-μm thickness that has the same thermal coefficient of expansion as the restoration. The author uses the Cerabien^™ ZR FC Paste clear glaze made for KATANA^™ . If additional customization is needed, the clinician should characterize as necessary and then proceed to the oven to glaze. The restoration should be secured to a firing pin or stand (with firing paste). Firing time in the SpeedFire is just under 10 minutes, and the restoration may be glazed up to three times.

Delivering the Restoration

KATANA^™ may be bonded or cemented. The manufacturer recommends bonding, due to more than 20 years of research supporting bonding to zirconia with 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-based PANAVIA^™ (Kuraray Noritake Dental) resin cements.¹ The clinician is encouraged to separate opinions from research and select a preferred method of delivery.

Clinical Case

A patient presented with an old crown on tooth No. 19 with extensive caries. Caries were present on adjacent teeth as well (Figure 2 and Figure 3).

The old crown and caries were removed (caries detector was used to ensure optimal caries removal). To show the masking ability of KATANA^™ , the remaining stump was very dark and was not blocked out (opaqued) (Figure 4). Immediate dentin sealing was performed and buildup completed using Clearfil^™ AP-X (Kuraray Noritake Dental), a high-strength composite that mimics strong dentin properties (Figure 5).

The design was straightforward (Figure 6) and the restoration was ideally positioned in the block to obtain the desired outcome for the patient (Figure 7). The target shade was Vita A2, and due to the thickness of the desired restoration, one shade darker was chosen to mill. The KATANA^™ was dry milled in 15 minutes. The sprue was removed, and the crown was polished using Twist polishers at 4,000 rpm, with care taken not to touch margins.

All residual milling dust was removed with a brush, and the restoration was placed into the middle of the firing chamber of the SpeedFire oven and sintered for approximately 30 minutes.

The restoration was bonded using PANAVIA^™ V5 and the APC bonding to zirconia protocol from Markus B. Blatz, DMD, PhD.²

The case was completed with a pleasing esthetic outcome (Figure 8 through Figure 10). There was no show-through of the dark stump; the final restoration mimicked the natural tooth. There was a porcelain-fused-to-metal restoration on tooth No. 20 and a lithium-disilicate low-translucency restoration on tooth No. 18. The translucency of this restoration closely matched the patient's natural tooth, the first bicuspid.