Indications, Treatment Plan, Diagnostic Approach
"This treatment outcome strongly depends on the therapeutic ap proach chosen, the driving force of which should be preservation of the thin remaining enamel. While a number of preparation techniques will lead to major dentin exposures, the principle of enamel preservation can be fulfilled by the use of a specific approach, ... a treatment rationale that incorporates a diagnostic template resulting from the interactive relationships between the clinician, the patient, and the dental laboratory. "
CAD/CAM vs. Composite: Which is better?
There has been quite the discussion on which of CAD/CAM or composites are better for a large restoration. If needing to fill a large MOD defect (5 mm depth by 5mm bucco-palatal width), the results and opinions have varied. However, it wasn't until a recent article by S Batalha-Silva et al, that really clarified the results for us. The in vitro study attempts to reduce variables while placing them in a controlled environment that can be easily reproduced. The research that was preformed was a fatigue resistance and crack propensity of large resin restorations. Paradigm MZ100 and Miris composites were used. After a series of fatigue testing, the survival rate of Paradigm MZ100 CAD/CAM group was 100% with minimal new crack propensity of 7%. The survival rate of Miris 2 composite direct restorations was 13% while their crack propensity was 47% with more severe cracks.
The longevity of a restoration is influenced greatly on things like, materials used, patient conduct, and dentist’s skills. One of the major problems, however, is the polymerization shrinkage stress of the the composite resins, especially with high C-factor defects. Strong adhesives can cause the composite material to exert cuspal stress which leads to movements and cracking. The best way to avoid polymerization shrinkage is to use post-polymerized restorations, composite resin inlay/onlays fabricated by CAD/CAM. It has been noted that some have found no clinical advantage of CAD/CAM milling over incremental direct restorations after a 5 year recall. Others have found a 85% survival rate of 3+ surface of direct composite restorations after 12 years. In spite of all of these recent reports, Indirect restorations are still considered the gold standard of restoring large defects. There are still the same polymerization shrinkage stresses but the forces are minimized in luting restorations because it is restricted to a thin cement layer, thus leading to superior marginal quality. It also needs to be noted that the luting procedure is the gold standard by reducing cracks in the cusp base. With cracks come possible microleakage and postoperative sensitivity. Other advantages that indirect restorations have is that they can provide anatomic contours, marginal adaptation, appropriate proximal contact, contour and occlusion because they are designed with the CAD/CAM program. The composite CAD/CAM blocks present acceptable wear properties. They are less brittle than porcelain and can be used in thinner layers, allowing more conservative preparation designs. The use of CAD/CAM, Paradigm MZ100 blocks, and immediate dentin sealing has proven to be a superior, conservative, and reliable biomimetic restoration.
With all of this information, it cannot be concluded that a large direct MOD defect is contraindicated for restoration with a direct composite, even with the higher crack propensity and failure at a higher load. These direct composite restorations can be beneficial to patient and practitioners who have limited access to newer CAD/CAM materials.
The article presents a myriad of information that can be further dissected down into other posts if time allowed. The research preformed is very thorough with lots of details. Please read the article which can be found here.
Which Material is best for CAD/CAM Milled Crowns?
There has been a great deal of research on metal-free tooth colored restorations along with developments in indirect prosthetic treatments which have lead to a bit of confusion as to which material if ideal. With so many options available to make a crown, its hard to know which one to trust and select for your patient. There are a variety of CAD/CAM materials, manufacturing systems, etc. So choosing the correct material is crucial for a higher prognosis and longevity of the crown.
Two main groups exist for metal-free, tooth colored, restorations. They are glass ceramic restorations and composite resins. Glass ceramics offer a variety of advantages such as: esthetic appearance, color stability, biocompatibility, and durability. However, some of the negatives that they have are, brittleness, susceptibility to fracture, along with abrasive wear of the opposing natural tooth. The composite resins have the advantages of: low abrasiveness to opposing teeth and low elastic modulus which allows for more absorption of functional stresses through deformation. The disadvantages of composite resin crowns are: wear, deterioration of surface finish, color instability and fracture. Some studies have shown that ceramic restorations tend to wear longer than composite resin crowns, while others have shown that the performance of composite resins have exceeded that of ceramics. Other reports have noted that they are similar. So where do we lie on this situation? So up to now, there is no clear cut consensus saying which restoration material is best. However, a new class of millable resin nanoceramic (RNC) blocks (LAVA Ultimate; 3M ESPE) has been made available to CAD/CAM systems. These blocks aren't true resin or ceramic. RNC combines the two existing groups into one material. However, it is mostly made of ceramic, of which it is 60% of its volume. While being mostly ceramic, it still maintains its flexibility and fracture resistance.
A fatigue resistance research project was preformed by Adriana Carvalho and team, to determine how these three groups would withstand these accelerated fatigue testing. It was noted that, with a simplified cementation process, resin nano ceramic and lithium dislocate crowns demonstrated improved fracture properties over feldspathic glass ceramic crowns. RNC also demonstrated significant practical advantages, such as less mill time, less milling bur usage, no need for firing, polishability, ease of occlusal adjustment, repairability, and friendly wear of antagonistic teeth. Resin nanoceramic should be the material of choice when preforming CAD/CAM milled crowns.
Information for this post was taken from the article mentioned above and is highly recommended to read. Please read to see how the research was preformed and to understand more of the details of the process.
How to be Biometically Responsible with Severe Dental Erosion
Making a suggestion for treatment for severe dental erosion, that allows for a good prognosis, can be a tough decision. There are many factors that come into play. The options normally include full coverage crowns with inlays being a good secondary choice. Ultra thin bonded posterior occlusal veneers represent a biomimetic alternative for these severe erosive lesions. Composite resins, Paradigm MZ100 or XR, are recommended as these had a 60% and 100% survival rate in a fatigue test. Empress Cad and e.max CAD initially failed at early stress levels. CAD/CAM composites may provide better fracture resistance for non retentive ultra thin occlusal veneers in posterior teeth with high load requirements. If porcelain is needed, e.max CAD for only normal occlusal conditions.
The progressive reduction of enamel thickness is a normal biological process. Accelerated conditions, due to GERD or GERD type related conditions, can lead to destructive consequences. Initial treatment should be to address the etiology of the condition to prevent further complications. Some potential treatment options are clinical follow ups, noninvasive dentin sealing with a filled dentin bonding agent, or even a conservative direct composite resin restorations. Some things to consider when restoring these types of cases are: maintaining occlusal vertical dimension, restoring proper shape and anatomy of the dentition, reducing sound dental tissues, as well as the patients desires and awareness of esthetics and tissue conservation. If the patient has already lost a great deal of tooth structure, treatments that require additional reduction may be contraindicated for a restoration. Only bonded ceramics and composite resins address the biomimetic principles of tissue conservation and esthetics. The developments of ceramics that are stronger (lithium disilicate glass ceramic), etchable, an machinable has extended the indications for bonded ceramic restorations.
Composite resins have also improved greatly, through a superior bond between the different phases. There is a greater amount of stress distribution due to the post-polymerization process. Some of the key characteristics are the low abrasiveness to antagonistic teeth (enamel preservation) and low elastic modulus that allows for more absorption of functional stresses through deformation. Thick CAD/CAM milled composite resin overlays have exceeded that of porcelain ones recently. Ultra thin composite restorations have also become indicated based on the same biomechanics of the composite. Enamel and dentin are unique tissues with highly specialized function. Using extremely thin “enamel-like” restorations, the bonding strategy becomes yet more important. When restoring a tooth, according to biomimetic principles, one should consider both the restorative materials that best emulates enamel and dentin, but also consider the simulation of the DEJ through the interfacial restoration-dentin bond, which can be considered a true composite structure. CAD/CAM composite resins can be recommended for fabricating ultra-thin occlusal veneers in posterior teeth even in patients with high load requirements. Composite should be the material of choice when restoring difficult dental erosion cases.
Luis Schlichting et al, wrote a beautiful article regarding these concepts and to which all material for this post was taken from. It is welt worth the read