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Performance Evaluation of CEREC® MC XL Milling System

Utilizing Obsidian® Milling BlocksFebruary 25, 2016

A subsidiary of Glidewell Dental

RESEARCHERS

ABSTRACT

The CEREC® MC XL mill performance was evaluated on Obsidian® Milling

Blocks using identical IPS e.max® CAD/CAM milling parameters. The

results were benchmarked against IPS e.max CAD/CAM blocks in terms

of mill/bur performance and quality of the milled restoration. The CEREC

MC XL mill performance, handling, servicing and bur wear when milling

Obsidian MIlling Blocks were in line with and comparable to that of IPS

e.max blocks. Furthermore, both IPS e.max and Obsidian MIlling Blocks

gave acceptable final milled restorations.

Shreya Shah, BDS, MSPrismatik Dentalcraft, Inc.

Research Associate 18651 Von Karman Ave.

Irvine, CA 92612

AkashPrismatik Dentalcraft, Inc.

Vice President, Research & Development18651 Von Karman Ave.

Irvine, CA 92612

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ABSTRACTThe CEREC® MC XL mill performance was evaluated on Obsidian® Milling Blocks using identical IPS e.max® CAD/CAM milling parameters. The results were benchmarked against IPS e.max CAD/CAM blocks in terms of mill/bur performance and quality of the milled restoration. The CEREC MC XL mill performance, handling, servicing and bur wear when milling Obsidian Milling Blocks were in line with and comparable to that of IPS e.max blocks. Furthermore, both IPS e.max and Obsidian Milling Blocks gave acceptable final milled restorations.

STUDY OBJECTIVEIn February 2015, Sirona Dental Systems Inc. issued a statement expressing concern over certain materials from Glidewell Laboratories and the possible harm caused to CEREC milling machines or the possibility of excessive bur wear. The materials named included Obsidian lithium silicate ceramic. The statement expressed no factual basis for the concerns, stating only that Sirona had not “validated” the materials. Accordingly, the purpose of this study was to evaluate the performance impact on the CEREC inLab MC XL milling platform while milling Obsidian lithium silicate ceramic milling blocks. The study was performed by the Research and Development and Engineering Services departments at Prismatik Dentalcraft, Inc., a wholly owned subsidiary of Glidewell Laboratories.

STUDY DESIGNThe study was a controlled, randomized evaluation of the CEREC MC XL milling system’s ability to mill Obsidian lithium silicate crowns. A randomly selected maxillary crown design was milled 347 times over a period of two weeks (February 3–17, 2016). A tooth was prepared for the study and a vinyl polysiloxane impression taken. The stone model from that impression was scanned using the CEREC inEos Blue scanner (Model No. D3446, Serial No. 44427, Part No. 6284264, Manufactured in 2010), a crown was then designed with CEREC software (4.2.0), and milling facilitated by the CEREC MC XL milling machine (Model No. D3439, Serial No. 10664, Manufactured in 2008). The designed file was milled 347 times to simulate 26 months of average use by a dentist’s office and to evaluate the performance impact on the mill, while also evaluating the fit and overall anatomy of milled Obsidian restorations.

The CEREC MC XL mill performance evaluation was monitored by equipment service technicians at Prismatik Dentalcraft. Ten restorations were selected and evaluated by certified dental technicians in the Prismatik Research and Development Department for fit, margin, contacts and overall crown contours prior to and after crystallization.

Glidewell Laboratories has milled and processed over 10,000 IPS e.max blocks on CEREC MC XL milling platforms. Data on mill performance and bur usage for e.max blocks was aggregated and analyzed for benchmarking against Obsidian Milling Blocks (also know as “Obsidian CAD/CAM blocks”).

BACKGROUND INFORMATION REGARDING OBSIDIAN CERAMICObsidian lithium silicate glass ceramic from Glidewell Laboratories has FDA 510(k) clearances. The FDA 510(k) approval process is common for dental restorative materials and designates that the material is safe for human use. At the time of publication, 31,302 monolithic Obsidian restorations have been produced by Glidewell Laboratories and delivered to clinicians in the United States with statistical incidence rates similar to other similar materials used in dentistry.

Performance Evaluation of CEREC® MC XL Milling System Utilizing Obsidian® Milling Blocks

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OBJECTIVE OF CEREC MC XL PERFORMANCE TEST To evaluate the performance of the CEREC MC XL milling system for fabrication of Obsidian lithium silicate restorations for preparations requiring full-coverage crowns.

KEY METRICS EVALUTATED IN THIS STUDY

• Milling time

• Tool performance

• Mill performance

• Crystallization performance

• Material performance

MATERIAL AND METHODSTest Material: Obsidian Milling Blocks were milled with a CEREC MC XL system. 347 CAD/CAM blocks (size W14) were used in this evaluation. The MC XL mill used was Model No. D3439, Serial No. 10664, manufactured in 2008 and used software version 4.2.0. Of note, this CEREC MC XL unit was put into service in the laboratory in 2010 and had already milled 8,638 blocks prior to this study.

Test Method: One randomly selected vinyl polysiloxane impression from the All-Ceramic Fixed Crown Department at Glidewell Laboratories was studied by R&D. The impression was poured with dental stone and allowed to set for 20 minutes. The resulting stone model was then scanned; a crown designed and milled (Fig. 1). The scanned case followed the manufacturer’s protocol for designing and milling. Crown designs were generated utilizing CEREC software, version 4.2.0. At the time of this investigation, Obsidian Milling Blocks were not listed as a material choice in the CEREC software. As a result, the researchers used the closest material choice available (IPS e.max [Ivoclar Vivadent]), which set comparable parameters for designing and milling Obsidian restorations.

Single-unit Model was Scanned

Using inEos Blue

Designed Restoration Files

(Cerec software 4.2.0)

Same Designed File was Milled on Cerec MC XL

347 Times

Figure 1: Workflow used

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SCANNING AND DESIGNING OF CROWN USING CEREC INEOS BLUE SCANNER AND CEREC DESIGN SOFTWARE 4.2.0A case (stone model) was scanned using the CEREC inEos Blue scanner (Model No. D3446, Serial No. 44427, Part No. 6284264, Manufactured in 2010). A crown was designed and then milled using the MC XL milling machine. The scanned case followed the protocol of scanning the buccal and occlusal, then lingual and proximal surfaces (Figs. 2, 3). The crown was then designed using CEREC design software. The parameters used for designing were the same as those used for IPS e.max (Fig. 4).

Figure 2: Scanning the stone model

Figure 4: View of the designed crown for tooth #3Figure 3: View of the scanned file for tooth #3

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MILLING OF CROWN USING THE CEREC INLAB MC XL After employing the design software, an Obsidian lithium silicate block, which is in partially crystallized state, was placed in the CEREC MC XL unit for milling (Figs. 5–7).

Figure 5: Obsidian milling block seated in CEREC MC XL

Figure 6: Occlusal surface of Obsidian milling block with CEREC mandrel under 10x magnification

Figure 7: Intaglio surface of Obsidian milling block with CEREC mandrel under 10x magnification

CRYSTALLIZATIONObsidian Crowns were crystallized according to the manufacturer recommendations as outlined. The crystallization cycle was approximately 23 minutes long (Table 1).

RESULTSMilling time: Obsidian milling blocks performed well in the CEREC MC XL mill. Average milling time over the total 347

restorations was 15.46 minutes. A total of 89 hours, 26 seconds of active milling occurred during the performance

study. The per-crown milling time is well within acceptable range when compared to similar dental CAD/CAM milling

materials. For comparison purposes, the same crown design was subsequently milled out of IPS e.max, taking

approximately 15 minutes.

Ivoclar Programat® CS / CS2, EP 5000 / EP 5010, P Series

Stand-by Temperature 400°C

Vacuum Level 1 V11 (On) 400°C

Vacuum Level 1 V21 (Off) 780°C

Closing Time S 3 minutes

Holding Time H1 10 seconds

Heating Rate t1 90°C/min

Holding Temperature T1 780°C

Vacuum Level 2 V12 (On) 780°C

Vacuum Level 2 V22 (Off) 819°C

Holding Time H2 10 minutes

Heating Rate t2 40°C/min

Holding Temperature T2 820°C

Long-term Cooling L 680°C

Cooling Rate tL 50°C/min

TABLE 1: OBSIDIAN CRYSTALLIZATION CYCLE

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Tool performance: Milling tools used for this evaluation were standard CEREC MC XL tools (Step Bur 12S [Ref. 62 40 167], Cylindrical Pointed Bur 12S [Ref. 62 40 159]). Burs were changed upon receiving a prompt from the software. In total, the Step Bur 12S was changed 25 times and lasted for 14 crowns on average. The Cylindrical Pointed Bur 12S was changed 19 times and lasted for 19 crowns on average. When aggregated, there were 44 bur changes with sets requiring a change approximately every 16 crowns. As there are two burs, this is an average of eight crowns per bur used. As a reference, Glidewell Laboratories averages one bur used per eight IPS e.max milling blocks used on similar CEREC MX CL milling units.

The Sirona diamond tools used for this study (Step Bur 12S, Cylindrical Pointed Bur 12S) were of grit size ranging from 60–70 µm (Fig. 8), which is well within acceptable range and causes the least damage to tools and the glass-ceramic material being milled. Following CEREC software prompts for changing coolant, cleaning filters, and replacing burs was an adjunct for smooth functioning of the CEREC MC XL in the milling of Obsidian lithium silicate.

Figure 8: View of the Sirona 12s Step Bur at 100x magnification, displaying the grit size

CROWNS MILLED PER BUR

Obsidian Lithium Silicate 8

Sirona-approved Glass Ceramic 8

TABLE 2: CROWNS MILLED PER BUR

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Mill Performance: The CEREC MC XL was cleaned and the coolant was changed when prompted by the software or at a minimum of two times per day during the testing period. This is the same protocol used by Glidewell Laboratories when milling Sirona-approved glass ceramic blocks in similar mills. Coolant (CEREC Dentatec, SKU: 5809640) was prepared as per the manufacturer’s recommendations (25 ml per 1 liter of water used). Milling issues were categorized as disc loosening, decoupling and wrong bur placement, as shown in Table 3. The specific CEREC MC XL used as a milling platform performed well during the experiment and continues to mill multiple crowns daily at Glidewell Laboratories.

Crystallization Performance: The manufacturer-recommended Obsidian crystallization cycle runs for approximately 23 minutes and uses an Ivoclar Programat® CS2 furnace. The Sirona-approved glass ceramic material (IPS e.max) manufacturer-recommended cycle time runs 24 minutes 30 seconds (Fig. 9).

Figure 9: IPS e.max crystallization cycle on Ivoclar Programat CS2 oven as recommended in IPS e.max CAD Monolithic Solutions CHAIRSIDE Instructions for Use, page 50

MILLING ISSUES

Disc Loosening 1

Wrong Bur Placement 1

Disc Decoupled 1

Total Issues 3

TABLE 3: MILLING ISSUES EXHIBITED ACROSS 347 CROWNS

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Obsidian Performance: Minimal material issues were recorded through the duration of this study. Ten maxillary crowns were studied for fit, margin, contacts, and contour prior to and after crystallization (Figs. 10–17). All selected cases’ fit and contour were determined to be good. The margins were smooth and did not display any chipping or irregularities (Table 6). The contacts appeared to be tight, though this could be easily manipulated by changing the proximal contact parameters in the CEREC design software.

Figure 10: Pre-crystallized buccal

Figure 11: Crystallized buccal

Figure 15: Crystallized lingualFigure 14: Pre-crystallized lingual

Figure 12: Pre-crystallized proximal

Figure 13: Crystallized proximal

Figure 16: Pre-crystallized occlusal

Figure 17: Crystallized occlusal

OBSIDIAN PERFORMANCEAll images show 10x magnification

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SUMMARYObsidian milling blocks when milled in the CEREC MC XL mill resulted in clinically acceptable crowns that exhibited good marginal integrity. Milling times were as expected and acceptable when compared to milling times of similar materials in the MC XL. Bur performance mirrored similar results to comparable glass ceramics in wear and efficacy. Block performance matched similar milled glass ceramic blocks in the same mill. The CEREC MC XL as a milling platform performed well during the experiment. No mechanical or software issues were reported.

At the time of publication, Glidewell Laboratories has manufactured 31,302 Obsidian crowns that have been delivered to clinicians across the United States. Learn more about Obsidian lithium silicate by visiting www.obsidianceramic.com.

SUMMARY OF STUDY

Evaluation Parameter Obsidian lithium silicate on CEREC MC XL

IPS e.max on CEREC MC XL

Design Parameter Similar Similar

Milling Time Approx. 15 minutes Approx. 15 minutes

Bur Usage (Crowns Milled Per Bur) Approx. 8 crowns Approx. 8 crowns

Mill Performance, Handling and Servicing (e.g., cleaning, coolant changes)

Similar Similar

Crystallization Time Approx. 23 minutes Approx. 24 minutes

Restoration (Fit, Margin, Contour and Contacts) Excellent Excellent

TABLE 6: OBSIDIAN MILLING BLOCKS CRYSTALLIZATION FIT TEST

BEFORE CRYSTALLIZATION AFTER CRYSTALLIZATION

Sample Number Fit Margin Contacts Contour Fit Margin Contacts Contour

1 Good Good Tight Good Good Good Tight Good

2 Good Good Tight Good Good Good Tight Good

3 Good Good Tight Good Good Good Tight Good

4 Good Good Tight Good Good Good Tight Good

5 Good Good Tight Good Good Good Tight Good

6 Good Good Tight Good Good Good Tight Good

7 Good Good Tight Good Good Good Tight Good

8 Good Good Tight Good Good Good Tight Good

9 Good Good Tight Good Good Good Tight Good

10 Good Good Tight Good Good Good Tight Good

GL-4648-032316

Scan the QR code to view a 30-month Obsidian Clinical Study

Obsidian is a registered trademark of Prismatik Dentalcraft, Inc. Sirona and CEREC are registered trademarks of Sirona Dental Systems, GmbH. IPS e.max and Programat are registered trademarks of Ivoclar Vivadent.

A subsidiary of Glidewell Dental

REV ID 4571MKT 4371_2.0