Nanoceramic CAD/CAM Restorations

INTRODUCTION
In keeping with the record pace of current technology, dental materials science has been improving, especially in the area of ceramics. The lines continue to blur as to what constitutes a ceramic, at least in the traditional sense. Ceramic, or porcelain, has traditionally been defined by the classification of its microstructure (amount and type of crystalline phase and glass composition) or by the processing technique (powder-liquid, pressed, or machined). However, advances in technology now offer materials whose majority constitutes ceramic particles, bound in a resin (polymer) matrix.^1,2 These materials have advanced to the point where they offer the durability of fired porcelain, with the flexural resiliency of composite resin.³ In addition, they are no longer layered and light cured but rather fabricated from a disc composed of ceramic nanoparticles and resin. It is from these discs that a restoration is manufactured via CAD/CAM. These monolithic discs are created with exacting specifications, including perfect ceramic-to-resin ratios, and evenly distributed ceramic particles. When fabricated at the nano level, these nanoceramics (also referred to as—and included in the category of—nanoceramic polymers) have unique properties previously unseen.

According to Professor Zhong L. Wang (Nano Research Group):⁴

Nanotechnology is the construction and use of functional structures designed from atomic or molecular scale with at least one characteristic dimension measured in nanometers. Their size allows them to exhibit novel properties and significantly improve physical, chemical, and biological properties, phenomena, and processes. When characteristic structural features are intermediate between isolated atoms and bulk materials in the range of about one to 100 nanometers, the objects often display physical attributes substantially different from those displayed by either atoms or bulk materials.⁴

A nanoparticle is defined as a particle between one and 100 nanometers in size.4 So that one can appreciate the size of a nanometer, the typical width of a human hair is 50 micrometers, and one nanometer is one 50,000th of a hair width. As can be imagined, these materials are truly in a league of their own.

Nanoceramic particles are milled to exacting standards. This is crucial, because when particles vary widely in size, uncontrolled agglomeration of powders due to attractive van der Waals forces can give rise to microstructural inhomogeneities. These uneven areas yield to stresses that can lead to crack propagation. Therefore, these precise materials avoid uneven areas of stress and are highly durable. In tests evaluating the fracture resistance of these materials, they showed a higher fracture resistance at thicknesses less than 0.5 mm versus all-ceramic restorations.⁵

Owing to these early research outcomes, nanoceramics have been indicated for use as a dental restoration including inlays, onlays, veneers, crowns, and bridges. In addition, nanoceramics show a remarkable ability to work with higher than normal occlusal forces regardless of abutment design. In a study by Joda et al,⁶ a laboratory investigation was conducted to analyze stiffness, strength, and failure modes of implant-supported, CAD/CAM-generated, resin nanoceramic crowns bonded to 3 different titanium abutments. Their conclusion was that monolithic implant crowns made of a resin nanoceramic material seemed to represent a feasible and stable prosthetic construction under laboratory testing conditions with strength higher than the average occlusal force, independent of the different abutment designs used in the investigation.⁶

Another beneficial feature of nanoceramic resin is the ability to bond to the resin matrix after milling.⁷ Therefore, composite resins can be used to characterize and adjust these restorations. Aesthetics and form can also be customized both intra- and extraorally, either before or after insertion. Thus, these restorations are dynamic and can be used throughout every stage of treatment, by adding to or removing the resin nanoceramic as needed.

In this article, the use of a recently introduced nanoceramic (NeaCera [Triple Crown Dental Laboratory]) will be demonstrated in the following case report. This product is composed of acrylic resins with organically modified ceramic nanotechnology materials that give a natural tooth appearance.8 It also assures high molecular weight, and high mechanical, chemical, and abrasion resistance. Owing to the high ceramic content, the material has a natural fluorescence, is highly biocompatible, and has excellent milling capacity.

CASE REPORT
Diagnosis and Treatment Planning
A 45-year-old male presented with a chief complaint of mobile teeth (Figures 1 and 2). Examination revealed a condition of severe aggressive generalized periodontitis9 and numerous carious lesions. The patient had a removable upper partial denture that he used solely for cosmetic appearances. He reported that having seen a previous dentist, he received an initial treatment plan that included full-mouth extractions and complete upper and lower dentures. However, due to a severe gag reflex, the patient was unable to tolerate complete dentures. Based on radiographs and a comprehensive exam, a 3-part phased treatment plan was created.

Treatment Plan Phase 1—The first step would be to extract any teeth that exhibited mobility greater than a Class 2. Extraction sites would receive ridge preservation for future implant placement. The remaining teeth would be restored and prepared for full-coverage nanoceramic restorations that would span the entire arch in the maxilla and mandible. In addition, scaling and root planing of these remaining teeth with a comprehensive home care regimen would be implemented.

Treatment Plan Phase 2—The second phase of treatment would include the placement of implants and enough time to allow for osseointegration. Upon completion of this healing phase, the remaining teeth would be extracted with bone preservation. The implants would be uncovered and used to retain the modified nanoceramic bridges.

Treatment Plan Phase 3—The final phase would consist of placing additional implants in bone grafted sites, allowing time for osseointegration and finally modify the nanoceramic bridges to become the final screw-retained restorations.

The following will now demonstrate the first phase of treatment (Treatment Plan Phase 1) using NeaCera nanoceramic restorations.

Figure 1. Preoperative photo of the maxillary arch.	Figure 2. Preoperative photo of the mandibular arch.
Figure 3. The maxillary arch at the time of extractions and preparations.	Figure 4. The mandibular arch at the time of extractions and preparations.

Figure 7. The final upper and lower nano­ceramic (NeaCera) restorations in place.	Figure 8. The smiling patient.

Preoperative Appointment
The patient was seen at a preoperative appointment for impressions of both arches and a bite registration that recorded his vertical dimension of occlusion. Stone models were sent to the laboratory team (Triple Crown Dental Laboratory, Baltimore, Md). On these models, teeth slated for extraction were carefully removed and the remaining teeth prepared for full-coverage restorations. The models were scanned using the NeaCera CAD software to create the superstructure. The data was sent to the CAM machine where the NeaCera nanoceramic discs were milled to exacting specifications of the final design. Upon completion, the laboratory team created the gingival aspects by adding layers using a gingival-shaded composite resin (GRADIA gum shades [GC America]) to the nanoceramic superstructure.

Operative Appointment
Under anxiolysis, both arches were anesthetized. Following complete removal of caries and gross crown preparations, core buildups were created for the upper and lower cuspids and molars. Clear matrix bands (ReelMatrix [Garrison Dental]) were placed around these teeth to contain the core restorations in a controlled manner. These clear matrices allow the curing light to reach the entire length and various depths of the restorations for a more rapid and complete cure. The sites were treated with a one-step, self-etching bonding system (Bistite II DC [Tokuyama Dental America]) and light cured (Sapphire Plasma Arc Curing Light [DenMat]). Next, the matrices were filled with a dual-cured radiopaque composite (Core Paste [DenMat]) and light cured. The matrices were removed and the crown preparations completed. The remaining teeth were extracted, the sockets filled with bone graft material, and sutured (Figures 3 and 4).

The ideal crown preparation design for nanoceramic restorations was created with an occlusal reduction of approximately 1.5 mm, an axial reduction of 1.0 mm, and a nonbeveled shoulder design. All line angles were rounded and the surfaces were also smoothed with a fine diamond. Following this, the nanoceramic restorations (Figures 5 and 6) were fitted to the prepared arches.

With the ability to add resin composites to the nanoceramic material, the roundhouse restorations were relined using silane and a methacrylate-based, light-cured restorative material. To avoid damaging the restorations, diamond burs were used with water spray and light pressure to create a passive fit, and they were also adjusted for optimal occlusion. Next, the intaglio areas to be bonded were air abraded with 50-µm aluminum oxide. The restorations were cleaned with normal detergent, then alcohol, and dried. Silane (Bistite II DC Ceramic Primer [Tokuyama Dental America]) was applied and allowed to dry followed by a light-cured resin bonding agent (Bistite II DC Ceramic Primer No. 1 A/B and Primer No. 2). A flowable composite resin (Estelite Flow Quick High Flow [Tokuyama Dental America]) was then injected into these areas and the restorations were seated back over the prepared teeth. The patient was instructed to close into the correct occlusion (Figure 7) and then the resin was light cured. The units were removed, shaped, and smoothed using a diamond impregnated rubber wheel (Dialite [Brasseler USA]). A final surface polish was imparted using a universal diamond polishing paste (5 to 10 µm and 2 to 5 µm) on a buffing wheel (Cotton Mop Universal polishing paste carrier [Komet USA]) (Figure 8).

CLOSING COMMENTS
As materials science continues to grow, dentistry continues to benefit. New items will continue to contribute to the health and well being of our patients. Nanoceramic restorations, when indicated, offer an excellent material choice for the clinician and patient.

References

1. Ruse ND, Sadoun MJ. Resin-composite blocks for dental CAD/CAM applications. J Dent Res. 2014;93:1232-1234.
2. Fasbinder DJ. Materials for chairside CAD/CAM restorations. Compend Contin Educ Dent. 2010;31:702-709.
3. Lauvahutanon S, Takahashi H, Shiozawa M, et al. Mechanical properties of composite resin blocks for CAD/CAM. Dent Mater J. 2014;33:705-710.
4. Wang ZL. What is Nanotechnology? nanoscience.gatech.edu/zlwang/research/nano.html. Accessed December 1, 2014.
5. Chen C, Trindade FZ, de Jager N, et al. The fracture resistance of a CAD/CAM Resin Nano Ceramic (RNC) and a CAD ceramic at different thicknesses. Dent Mater. 2014;30:954-962.
6. Joda T, Huber S, Bürki A, et al. Influence of abutment design on stiffness, strength, and failure of implant-supported monolithic Resin Nano Ceramic (RNC) crowns. Clin Implant Dent Relat Res. 2014 Mar 14. DOI: 10.1111/cid.12215. [Epub ahead of print]
7. Koller M, Arnetzl GV, Holly L, et al. Lava ultimate resin nano ceramic for CAD/CAM: customization case study. Int J Comput Dent. 2012;15:159-164.
8. Costa F, Rodrigues R, Filho HN, et al. Immediate high aesthetic performance oral rehabilitation with CAD/CAM system VIPI BLOCK TRILUX. Full Dent Sci. 2013;4:213-218.
9. Armitage GC. Development of a classification system for periodontal diseases and conditions. Ann Periodontol. 1999;4:1-6.

Dr. Shuman maintains a full-time general, reconstructive, and aesthetic dental practice in Pasadena, Md. He is a Master in the AGD, an Associate Fellow in the American Academy of Implant Dentistry, and a Fellow of the Pierre Fauchard Academy. An educator and author, he develops advanced, minimally invasive techniques. He is a dental education editorial board member for PennWell Publishing and for the past 20 years has personally authored a vast array of peer-reviewed published articles. Dentistry Today has named him a Leader in Continuing Education since 2005. He can be reached at (410) 766-5104 or via email at ian@ianshuman.com.

Disclosure: Dr. Shuman reports no disclosures.

Mr. Ben Zev is owner and operator of Triple Crown Dental Laboratory, a full service dental laboratory based in Baltimore. He can be reached at (888) 902-0011.

Disclosure: Mr. Ben Zev reports no disclosures.