Is CAD-CAM future or present?
Partial bonded restorations are proving more and more to be one of the best solutions available for endo treated and weakened posterior teeth, adhesive cuspal coverage is not only a valid alternative for a crown, but in many cases means the salvation of axial tissue in order to retain a restoration, that with the preparation of a crown it would have been lost.
The dream of having these kind of restorations in a single appointment is getting near, CAD-CAM (Computer Assisted Desing – Computer Assisted Manufacture) restorations are getting more and more precise, faster and user friendly, and the materials to do so are dropping its prices or are already very convenient, an alternative not only for the clinician, but for the technician.
Is CAD-CAM future or present?
An Article by Anna Salat and Jordi Manauta, from a clinical case by Anna Salat
August 25th 2013
Tooth 15 after a root canal treatment and a provisional restoration Fermit®. In the single CAD-CAM appointment the composite build-up is done; the whole dentin and subgingival margin are systematically covered, leaving the enamel margin free from composite during preparation, covering only subgingival dentin for convenience reasons.
Tooth preparation with full occlual coverage and mesial and distal boxes. There were 3 remaining walls but thinner than 1.5mm so a total coverage was indicated.
Teeth covered with powder (Cerec Optispray) needed to create contrast for the digital impression which was carried out under rubber dam in a very comfortable way.
Image of Cerec Optispray.
Screen shot of Cerec Sirona software. A three dimensional model is created from which some parameters have to be introduced by the user as the margin location and type of restoration. In this step we were delimiting the margins of the restoration.
After all parameters have been introduced the software creates the tooth virtually. The shape given by the software can be modified (for example sharpening grooves, tighten contact areas, create more space for cement or give more volume to any cuspid) before sending the information to the milling unit
We can appreciate how almost half of the restoration is created. After 3 minutes of milling, part of the restoration is appearing from the composite block.
Milling procedure of composite block (Lava Ultimate, 3M Espe, A3 HT) by burs which take as an average 12 minutes to create one overlay.
A simplified morfology created by the digital unit and milling machine. The scarce anatomy is still one of the CAD-CAM inconvenient.
Important: This is the main trick to learn from this article. A sharp and deep primary sulcus is the ONLY guaranty for composite tints and characterizations to be strong, natural and durable, acting as a container for them.
In order to refine the anatomy, a tungsten bur modified with a diamond disc in order to create a fine tip is used to create sharp grooves in the composite to redefine the anatomy. As described by Dario Adolfi in the Non edge technique (3) and its variation for composite described in the book Layers (4).
A rounded No. 1/2 diamond bur is used to develop the slopes that characterize each ridge from each cusp, widening from the bottom to the surface.
Once the anatomy is defined we proceed to sandblasting in order to remove debris and condition the surface for the correct bonding of the stains.
After sandblasting we obtain a surface ready to receive the bonding agents and characterizations.
Adhesive was applied in order to fix correctly the stains. Note that in the polishing stage all the adhesive will disappear.
View of the restoration after applying brown tint (Tokuyama Brown Stain) into the sharp central groove created for this effect. Is useless to apply stains in areas where they cannot be contained, the effect will disappear in matter of weeks.
To give the restorations a lustrous polish a diamond paste (Diamond Twist SCL, Premier, USA) is used with the goat brush (Shiny S, Micerium, Italy) and then the same paste with the felt wheel (Shiny F, Micerium) for high luster.
The polishing appliances, goat brush and felt wheel (Micerium) and a Diamond Perioset bur for finishing (Finishing Style Kit, Styleitaliano by Komet).
Overlay try-in .The marginal adaptation and the contact points are checked and adjusted if necessary. No further corrections were necessary in this case.
For adhesive cementation. The composite build-up is Sandblasted (even though is chemically fresh) with 50 microns Al3O2 particles at a distance of 2-3 cm. Also the inner part of the restoration is sandblasted, otherwise bonding will be defective.
Materials used for the cementation steps; orthophosphoric acid (Total Etch, Ivoclar Vivadent), silane (Ultradent) and two step adhesive (Optibond Fl, Kerr).
Orthophosphoric acid etching of enamel margins and exposed dentin. The sandbalsted composite was not etched. There is the trend of etching the sandblasted composite for cleaning as well.
Applying silano to the inner part of the restoration and letting it dry.
Applying primer (Primer bottle from Optibond Fl) to the inner part of the resotration.
Bonding application to the inner part of the restoration.
Applying primer and bonding to the tooth (Optibond Fl, Kerr) after having applied silane coupling agent to the composite resin.
Regular composite was preheated when already placed in the restoration (CALSET Try-Tray composite heater). Preheated composite for cementation has to be carefully chosen, not every composite has the ideal consistency and generally are too stiff to use even when heated. The composite used in this case was Filtek A3 body from a carpule, which has an ideal consistency, unlike to this same composite brand from a syringe (thanks to Dr. Giuseppe Marchetti for the Tip)
Microvibes (Smile Line, Switzerland) a vibrating instrument with a ceramic tip, was used to settle in place the overlay with the pre-heated cement and displace tixotropicaly the excess.
After few secconds of pressure and vibration, excess flow through the margins.
The main advantage of cementing with regular composite is the extended time of this stage, where we can settle the restoration in a very precise way. Excess removal with fissura instrument (LM instruments, powered by Style Italiano). This is only posible when a preparation is projected to have accesible margins 360°. This is not only useful for the cementation phase, but in the future for secondary caries assessment, margin maintenance or re-intervention.
Extended polimerization to guaranty the best posible convertion of an exclusively photocuring material. Semi translucency of the ingot chosen allows us not only to have better aesthetics of the restoration, but it allows light to penetrate better than in a conventional enamel-dentin stratified restoration.