Dental News - E4D chairside CAD/CAM restorations: Case presentations and lessons learned

Dr. Wally Renne, USA

Mon. 24. February 2014

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Despite the increasing popularity of the current CAD/CAM laboratory systems and continuing technical advances, some clinicians have remained reluctant to incorporate the very same CAD/CAM techniques into their clinical chairside practices. Two often-repeated misconceptions relate to the perceived lack of strength and lack of aesthetics of the ceramics available for use with these systems. A wide variety of materials are available to use with the E4D Dentist System (D4D Technologies), and each has a separate set of aesthetic and mechanical properties that must be considered. This article will review current materials and show clinical examples of restorations made using the E4D Dentist System.

One distinct advantage of chairside CAD/CAM is having the ability to make restorations in a single visit from a solid pre-manufactured block that is essentially flawless in construction. A pre-manufactured block is made in ideal conditions, and as a result, has an ideal density with none of the residual porosity found in many layered or pressed porcelains.

Porosities may act as a weak point and lead to the build-up of internal tensile stress in the ceramic and eventually cause a catastrophic failure. Monolithic restorations have several distinct advantages over layered restorations when it comes to mechanical properties. Layered restorations are often veneered with weak feldspathic glasses that can chip or break, especially if not supported properly by the framework.

Furthermore, one does not need to worry about delamination and micro-chipping of the veneering porcelain, which has been reported to be as high as 25 per cent for porcelain-fused-to-zirconium restorations.(1)

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IPS Empress (Ivoclar Vivdent) is a feldspathic glass with approximately 45 % leucite crystals for dispersion strengthening. The 5 μm leucite crystals improve strength and fracture toughness by acting as “roadblocks” to prevent crack propagation. IPS Empress is an aesthetic material and is available in polychromatic blended shades that give the restoration a layered appearance. Empress Multiblock has a flexural strength around 160 MPa and requires isolation and attention to detail when bonding to ensure long-term success.

IPS Empress has been on the market for approximately 24 years, and as a result, good clinical research on the longevity of these restorations exists in the literature. A literature review conducted by Brochu and El-Mowafy evaluated and summarized six clinical studies that met their inclusion criteria. They concluded the survival rates for IPS Empress inlays and onlays ranged from 96 per cent at 4.5 years to 91 per cent at seven years. IPS Empress crowns had a survival rate ranging from 92 per cent to 99 per cent at three to 3.5 years.

For both crowns and onlays, most failures were due to bulk fracture.2 In general, IPS Empress has higher failure rates in the posterior than the anterior and higher fracture rates on molars compared with premolars. (3–6) Therefore, IPS Empress is an excellent material choice in the anterior for aesthetically demanding patients. However, alternative materials exist for posterior use.

Case presentation
A new patient called the office and said his crown “exploded.” He presented to the clinic with the crown missing on tooth #9 (Fig. 1). The E4D Dentist System was used to make a digital impression of the preparation and the bite registration. Using the intuitive design features in the E4D software, a restoration was designed (Fig. 2). An IPS Empress CAD Multi A1 restoration was milled and characterized using IPS Empress Universal Stains. For delivery, the crown was prepared by etching with 4.9 % hydrofluoric acid for 60 seconds and silanated for 60 seconds with Monobond-Plus (Ivoclar Vivadent). The tooth was pumiced; Optibond XTR (Kerr) was applied and cured for 20 seconds; and Nexus 3 resin cement (Kerr) was used to bond the crown (Fig. 3).

The use of IPS Empress has been selective partly because of the popularity of IPS e.max CAD (lithium disilicate). IPS e.max CAD comes in a lithium metasilicate state (blue colour) that is not fully crystallized but can be easily machined. The milled restoration is then placed in the oven for 19 to 26 minutes to crystallize the glass. During crystallization, the lithium metasilicate crystals are replaced with lithium disilicate crystals, increasing flexural strength from around 160 MPa to 360 MPa.

IPS e.max was introduced to the market in 2006. Gehrt and colleagues followed 104 IPS e.max crowns in 44 patients and found the corresponding survival rate for all restorations was 97.4 per cent after five years and 94.8 per cent after eight years of clinical service with location not significantly impacting survival rate.7 These results were for IPS e.max press restorations that were cut back and veneered. It can be hypothesized that monolithic chairside milled IPS e.max may perform better.

In a 10-year study, Kern et. al. found three-unit fixed partial dentures (FPDs) made from monolithic lithium disilicate ceramic showed five- and 10-year survival and success rates that were similar to those of conventional metal-ceramic FPDs.(8) They concluded that for the monolithic lithium disilicate FPDs, the calculated survival rate was 100 per cent after five years and dropped to 90.8 per cent (when considering only catastrophic ceramic fractures) and 87.9 per cent (when considering catastrophic ceramic fractures and biological failures) after 10 years.(8)

It is interesting to note that all catastrophic failures occurred in molars.8 Single-unit monolithic IPS e.max can be expected to perform better than FPDs in this study.

Interestingly for both clinical studies mentioned, the restorations that were conventionally cemented performed just as well as those that were bonded.(7,8) Therefore, assuming proper retention and resistance form has been achieved, it is acceptable to conventionally cement monolithic IPS e.max restorations.

Because of the incredible flexural strength of IPS e.max, some clinicians were concerned that
IPS e.max may be aggressive on the opposing dentition. In a clinical study, Silva et. al. found IPS e.max to be more gentle on the opposing enamel than feldspathic ceramics with a wear rate on enamel similar to natural definition.(9) Chairside CAD/CAM allows the clinician to predictably provide more conservative restorations, such as IPS e.max inlays and onlays, that have a longevity similar to full coverage crowns.(10) The advantage to onlays over crowns is the conservation of healthy tooth structure and subsequent prolonging of the tooth’s life cycle.

Chairside milled onlays are an ideal restoration compared with direct resins. Despite their popularity, large posterior resin-based composite (RBC) restorations last only six to seven years.(11,12) RBC restorations have poor clinical longevity, higher recurrent caries and greater need for replacement compared with the alternative, high-copper amalgam.(13–17)

Amalgam and cast gold are not a popular option for many patients because of aesthetic concerns, and an E4D onlay restoration is the ideal treatment for many patients who refuse these alternative treatments. Milled inlays and onlays have been shown to be very successful.

One study found a success rate of 90.4 per cent after 10 years with older feldspathic ceramics as well as older milling and design technology.(18)

In this case, the patient was not happy with the aesthetics of the amalgam restorations, and she had recurrent caries on the mesial of tooth #13. The E4D Dentist System was used to make a digital model, and the design software proposed well-contoured, anatomical restorations that were milled out of e.max CAD HT A2 blocks. For delivery, the restorations were prepared by etching with 4.9 % hydrofluoric acid for 20 seconds and silanating for 60 seconds with Monobond-Plus (Ivoclar Vivadent). The tooth was pumiced clean; Optibond XTR (Kerr) was applied and cured for 20 seconds; and Nexus 3 resin cement (Kerr) was used (Figs. 4–6).

Despite the benefits of onlays, single-unit crowns are still the preferred restoration for the general dentist, and the E4D Dentist System fabricates excellent restorations with a short learning curve. With the strength of IPS e.max, predictable restoration of second molars using the E4D Dentist System is possible (Figs. 7–9).

Once the learning curve of single-unit restorations is mastered, it will not be long before the benefits of the E4D Dentist System become apparent for more complicated cases. A 37-year-old male presented for a consult for dentures. He had been to several dentists and an immediate denture was the treatment plan he had selected. He presented with severe acid erosion and abrasion from a combination of gastroesophageal reflux disease (GERD) and bruxism (Figs.10 & 11).

Occlusal examination revealed a lack of anterior guidance and posterior support. The lateral pterygoids were sensitive to palpation, and upon visual examination it was noted that he had hypertrophic masseters. Lip commissures were folded and he appeared to have a collapsed vertical dimension of occlusion (VDO). He did not close in a repeatable po sition and had a severe anterior deviation from centric relation.

When evaluating the location of the gingival margins it was determined that compensatory eruption had taken place. However, based on the closest speaking space during the production of sibilant sounds, the patient had excess freeway space.

It was determined that the patient lost vertical dimension of occlusion, and therefore compensatory eruption did not keep up with the rate of erosion. Two centric-relation (CR) records were made using bimanual manipulation, a custom triad jig and a rigid bite material. The case was mounted on a semi-adjustable articular in centric relation and the mounting was verified with the second CR record.

It was decided (based on freeway space, aesthetics and phonetics) that to recapture the lost VDO the patient needed to be opened 2.5 mm in the anterior; this correlated to around 1 mm in the posterior. A diagnostic wax-up was made. The teeth were prepared and temporized based on the diagnostic wax-up (Figs. 12 & 13). The patient was kept in temporaries for six weeks to verify tolerance of the new vertical dimension, phonetics (particularly “F” and “S” sounds) and CR.

In the provisionals, anterior guidance was established with no balancing interferences during lateral excursive movements. CR was stable and at the end of the six-week trial period the patient was painfree upon palpation of his lateral pterygoid muscles, and the provisionals did not show signs of malocclusion, such as fracture or accelerated wear. His central incisors were hitting just inside the wet-dry line of the lower lip during “F” sounds. During “S” sounds, the closest speaking space, the patient’s maxillary and mandibular anterior teeth did not touch.

Once verified, a vinyl polysiloxane (VPS) impression of the temporaries was made along with a bite registration. At this point, centric relation was equal to maximum intercuspal position (MIP). The E4D Dentist System system’s clone feature copied the occlusion of the provisionals exactly (Fig. 14).

The software, DentalLogic, allows the clinician to superimpose the provisional “clone” model over the re storation design to determine accuracy (Fig. 15). One of the most powerful features of the software is the ability to turn the clone model clear and analyze how accurately the software has copied the anatomy and occlusion. The accuracy of this is within microns and an intuitive colour map displays the discrepancy that exists between the temporaries and the final crown design (Fig. 15).

The restorations were milled and prepared by etching with 4.9 % hydroflouric acid for 20 seconds and silanating for 60 seconds. The tooth was then pumiced, curing solution applied and cured for 20 seconds. The restoration was then ready for cementation.

The occlusion was identical to the provisional and thus no adjustments were needed on the day of delivery. With the option now to use IPS e.max HT, this case had a better aesthetic result because the LT block appears slightly monochromatic and opaque.

Summary
Dental patients typically want tooth-coloured indirect restorations; and with the newer ceramics that are available for chairside milling, the same highquality ceramic restorations that labs are producing can be fabricated in a single appointment.

With a chairside CAD/CAM system, large, technique-sensitive and inferior direct resins require less treatment planning because milled IPS e.max onlays can take their place. Chairside CAD/CAM dentistry is not the only way to provide patients with high-quality restorations, but it certainly is the most exciting from both a clinician’s and patient’s viewpoint.

Multiple-visit, single-unit restorations; singleunit temporaries; difficult resins; expensive monthly fabrication fees; and bonding restorations after weeks of contamination with temporary cement and saliva is routine for most dentists who have not invested in CAD/CAM technology. The old adage “what you don’t know you don’t miss” holds true.

Editorial note: A complete list of references is available from the publisher.

This article was published in CAD/CAM international magazine of digital dentistry No. 3/2013.

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