Restorations with CAD/CAM technology

Transcription

1 Clin Dent Rev (2018)2:8 TECHNIQUES Restorations with CAD/CAM technology Geraldine Weinstein 1 W. Stephen Howard 2 Richard Fox 3 Received: 28 November 2017 / Accepted: 4 January 2018 Ó Springer International Publishing AG, part of Springer Nature 2018 Abstract Predictable all ceramic restorations utilizing computer-aided design/computer-aided milling have been made possible by following carefully outlined directions. A combined understanding of the capabilities of software, the milling unit, ceramic properties and the bonding process allows a dentist to create indirect restorations that exhibit desirable qualities. Keywords CAD/CAM restorations Inlay Onlays Crowns e.max Ceramic restorations Quick reference/description Computer-aided design/computer-aided milling (CAD/CAM) technology is a part of modern dentistry that helps to fabricate predictable restorations. While various materials exist for CAD/CAM, proper selection should be done on the basis of the indications. Considerations would include occlusal wear, ability to bond to tooth structure, full coverage versus partial coverage restorations, and retentiveness of the restoration. Lithium disilicate (e.max) has shown significant fracture resistance in all types of restorations when compared to feldspathic porcelain. In long-term studies, e.max has exhibited the strongest bond to enamel tooth structure. More recently, zirconia blocks have become available for CAD/CAM restorations. Zirconia has & Geraldine Weinstein gweinstein@uchc.edu W. Stephen Howard WSHoward@dental.ufl.edu University of Connecticut School of Dental Medicine, Farmington, CT, USA University of Florida College of Dentistry, Gainesville, FL, USA Detroit, MI, USA

2 8 Page 2 of 9 Clin Dent Rev (2018)2:8 shown the greatest fracture resistance when compared to all ceramic materials; however, its bond strength to tooth structure is minimal compared to that of e.max. Indications All ceramic restorations Crownlays Endocrowns Replacing missing laterals Implant crowns Inlays/onlays/partial coverage crowns Materials/instruments IPS e.max blocks or feldspathic blocks Set of burs Retraction cord for gingiva Hand instruments CEREC Optispray CAD/CAM acquisition unit and milling unit (DENTSPLY-Sirona CEREC or Planmecca E4D or other similar brand) Procedure Owing to the advancements of ceramic materials and resin cements, minimal tooth preparation is possible with CAD/CAM restorations. The goal in preparation is to ensure the occlusal and axial clearance to support the thickness of the ceramic of choice. Retentive preparation of the tooth is not always necessary if ideal bonding of the ceramic restoration to the tooth can be achieved. Careful consideration and design of the tooth preparation can preserve tooth structure and insure longevity of a vital pulp. Vital teeth with large restorations that are bonded have been shown to have greater resistance to fracture than non-vital teeth. CAD/CAM technique involves tooth preparation, scanning, restoration design and milling. This is followed by glazing the porcelain and sintering, and finally bonding of CAD/CAM restoration to the tooth. Tooth preparation Select the tooth shade prior to anesthetizing the patient and preparation of the tooth. The teeth are less likely to be desiccated at this point. If the tooth to be treated has an intact occlusal surface (an existing crown or caries limited to the interproximal surfaces), consider scanning the occlusal and utilizing the copy feature of your

3 Clin Dent Rev (2018)2:8 Page 3 of 98 software of choice to simplify your design process later on and preserve the existing occlusal scheme. Decide on your material of choice for restoring the tooth and follow the manufacturer s recommendations for preparing the tooth appropriately (Figs. 1, 2). Anesthetize the patient and start tooth preparation beginning with the occlusal reduction. Depth cuts should be placed on the occlusal surface with proper burs. Ensure that the occlusal clearance is appropriate to the material of choice (Fig. 3). Use of depth cuts on the preparation along the facial (mandibular functional cusps) or palatal (maxillary functional cusps) will ensure the thickness of porcelain in the area. An understanding of your milling unit is essential when preparing teeth for CAD/ CAM restorations. Familiarity with the milling burs and the software capabilities is essential for successful outcomes (Figs. 4, 5). Smooth chamfers or shoulders along the margins are preferred finishes. Edges and transitions from floors to walls should be rounded. In the interproximal area, ramps are preferable compared to traditional box preparations. Margins should be smooth and continuous. Preparation shoulders, incisal edges, or cusp tips should be at least mm in diameter to allow for proper milling. Sharp edges along the preparation may result in improper milling causing the restoration not to seat completely. Undercuts in the preparation walls are not milled by the software. This creates a larger gap between the restoration and the tooth surface that will be filled with cement. The software s mill preview displays these undesirable areas (Fig. 6a, b). To create a good contact, adjacent contact areas should be smooth prior to scanning (Fig. 7). CAD/CAM workflow CAD/CAM technique includes four steps: Fig. 1 Inlay and onlay preparation guidelines for e.max (printed with permission from Ivoclar)

4 8 Page 4 of 9 Clin Dent Rev (2018)2:8 Fig. 2 Anterior and posterior crown preparation guidelines for e.max when using traditional cementation. For crowns that are to be bonded to the tooth with resin cement, occlusal clearance for crowns can be as minimal as 1 mm (printed with permission from Ivoclar) Fig. 3 Depth cut burs are a good way to mark proper reduction of the occlusal surface Fig. 4 CEREC milling unit details

5 Clin Dent Rev (2018)2:8 Page 5 of 98 Fig. 5 Depth of the preparation should never exceed the length of the bur Fig. 6 a Undercuts should be blocked or removed from the preparation. b Cross-sectional view with the restoration shows gaps between the tooth and the milled restoration Scanning Before scanning, properly isolate the tooth and check for Visibility of preparation margin Occlusal clearance Undercuts Sharp edges Check if the preparation exhibits a path of draw

6 8 Page 6 of 9 Clin Dent Rev (2018)2:8 Fig. 7 Irregularities in the adjacent tooth cause problems with cementation and ultimately the contact Since scanning is the final impression of the preparation, visualization must be achieved. Gingival retraction cord, hemostatic agents, or laser/electro surgery should be used to facilitate visualization of the margins. Design and milling Special features of the CAD/CAM system should be learned as this will enhance the abilities to design and mill the restoration (Figs. 8, 9). Glazing the porcelain and crystallizing A glaze spray can be used prior to a combined crystallization and glaze firing cycle (Fig. 10). Follow the manufacturer s directions as per system chosen. Fig. 8 Specific views in the chosen system allow improved visualization of preparation margin

7 Clin Dent Rev (2018)2:8 Page 7 of 98 Fig. 9 a The Planmeca-designed crown can be virtually placed to improve esthetics and occlusion. b Virtual placement of CEREC crown, with tools available for editing of proposed crown and occlusal scheme Fig. 10 One-step crystallization and glaze spray for e.max Bonding of CAD/CAM restoration Prepare both the crown surface and the tooth surface prior to bonding. It is best to complete preparation of the e.max crown prior to preparing the prepared tooth in order to avoid contamination of the tooth (Table 1). Following the manufacturer s directions is essential to the success of the bonding process. Pitfalls and complications Under-reduced areas on occluding surfaces can lead to thin spots in the porcelain and ultimately fracture of the restoration. Roughness around the margins can result in open margins. If undercuts are present in the interproximal area, the restoration does not seat properly (Fig. 11).

8 8 Page 8 of 9 Clin Dent Rev (2018)2:8 Table 1 Workflow in preparing e.max CAD restoration and the prepared tooth Prepared tooth surface Milled e.max crown Clean Pumice, rinse with water and isolate Clean crown with Ivoclean or steamer to remove debris from milling and firing paste Etch Prime and bond Cement Phosphoric acid etch (follow manufacturer s directions) Rehydrating the tooth after etching can be done in one of two ways: 1. Apply Consepsis (2% chlorhexidine) as it improves stability of the bonding to dentin and is antibacterial. Blow off excess to avoid pooling 2. Alternatively, in patients with sensitivity, after etching, use GLUMA (desensitizer from Heraeus Kulzer) to seal the dentinal tubules Wet tooth with one-step primer and bonding agent. Scotchbond Universal (3M) is a popular one, which is applied in a thin coat, gently thinned with an air syringe, and light cured IPS e.max CAD crowns are traditionally bonded to the tooth with resin cement for increased fracture resistance. In addition to following directions of the luting cement, the tooth should be kept isolated from any saliva or blood contaminants. Care should be taken to quickly floss and remove excess cement prior to light curing. A post-cementation radiograph is recommended to insure the crown is seated completely and all excess cement is removed Hydrofluoric acid etch (for e.max, recommendation is 20 s, rinse and dry) Apply silane to the crown and blow off excess (follow manufacturer s directions) Fig. 11 Undercuts in the interproximal boxes prevent a path of draw. Line shows where the preparation should end in order to have a path of draw

9 Clin Dent Rev (2018)2:8 Page 9 of 98 Further reading 1. Perdigao J, Swift EJ, Walter R (2014) Fundamental concepts of enamel and dentin adhesion. In: Heymann H, Swift E, Ritter A (eds) Art and science of operative dentistry, 6th edn. Mosby, St. Louis, p Fasbinder D, Dennison J et al (2010) A clinical evaluation of chairside lithium disilicate CAD/CAM crowns a two-year report. JADA 141: Biacchi GR, Basting RT (2012) Comparison of fracture strength of endocrowns and glass fiber post retained conventional crowns. Oper Dent 37(2): Carvalho AO, Bruzi G, Anderson RE, Maia HP, Giannini M, Magne P (2016) Influence of adhesive core buildup designs on the resistance of endodontically treated molars restored with lithium. Oper Dent 41(1): Weinstein G, Howard WS, Fox R (2017) Indirect restorations wit CAD/CAM technology. In: Weinstein G, Zientz M (eds) The dental reference manual: a daily guide for students and practitioners, 1st edn. Springer, Cham 6. Ferencz J, Silva N, Navarro J (eds) (2014) High-strength ceramics: interdisciplinary perspectives. Quintessence, Illinois 7. Gehrt M, Wolfart S, Rafai N, Reich S, Edelhoff D (2013) Clinical results of lithium-disilicate crowns after up to 9 years of service. Clin Oral Invest 17(1):