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Ceramo-Metal Bonded Restorations
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Question #1: What is kaolin, leucite, feldspar and quartz, and what role do they play in porcelain?
They are primarily used as ceramic fillers in a lower fusing glass.

Answer: Kaolinite: A mineral Al2Si2O5(OH)4 consisting of a hydrous silicate of aluminum that is polymorphous with dickite and nacrite and constitutes the principle mineral kaolin.
Leucite: a white or gray mineral KAlSiO2O6 consisting of potassium aluminum silicate occurring in igneous rocks (as recent lavas).
Feldspar: Feldspar is the commonest mineral on earth and is a group of usually, white, or nearly white, flesh-red, bluish or greenish minerals that are closely related in crystalline form. They are all aluminum silicates with potassium, sodium, calcium, or barium and occurs in crystals and crystalline masses that are vitreous in luster and break rather easily in two directions at approximate right angles to each other. They are essential constituents of nearly all crystalline rocks (as granite, gneiss, most types of basalt and trachyte) and on decomposition yield a large part of the clay of the soil and the mineral kaolinite.
Quartz: a mineral (SiO2) consisting of a silicon dioxide that usually occurs in colorless and transparent but sometimes yellow, brown, purple, or green hexagonal crystals. It is the second most common mineral on earth.


Question #2: Rather than metal inserts, can the porcelain just be made thicker?

Answer: Yes, but it will not stop crack propagation. It will take longer for failures to occur since cracks have to travel a greater distance and will do so more slowly due to the reduced flexure of the restoration.

Question #3: How thick can porcelain be before it is too thick?

Answer: Maximum thickness of 2 to 2.5 mm for conventional porcelain.


Question #4: How do you find a lab that knows how to make a metal insert or a porcelain inlay that fits?

Answer: Find one who has been trained in a study group program. A list is available from the Publisher.


Question #5: How well should I expect a CMBR inlay or onlay to fit at the margin?

Answer: As good as a typical casting.


Question #6: How long should a CMBR last clinically?

Answer: 8 to 16 years depending on design.


Question #7: Would you place a reinforced full porcelain crown (e.g. Inceram) in a stress bearing area, such as a first molar? How about premolars, anterior teeth?

Answer: I would only use it in anterior teeth at this time.


Question #8: With the newer high strength and reinforced porcelains that are now available and with the advancements in bonding, can we expect similar performance in all-ceramic restorations in posterior teeth?

Answer: Not right away. There is a learning curve for both the dentist and the laboratory technician. However, once the skills are acquired these restorations can be routine.


Question #9: Cad-Cam and Celay systems are capable of milling ceramic materials that are manufactured under industrial conditions and hence are much stronger than lab fabricated ceramics. Therefore, arenít these materials logical alternatives for ceramic onlays in stress bearing areas?

Answer: These materials have fewer flaws, which will reduce early failures, but it is unlikely they will prevent long term failures.


Question #10: Can materials, such as Inceram, be etched as conventional dental porcelains? If not, how can they be treated to facilitate resin bonding?

Answer: Earlier versions are not etchable. They should be internally sandblasted and cemented with conventional cements.

Question #11: Arenít conventional materials such as cast gold and amalgam still the most durable restorations in posterior teeth?
Answer: Cast gold is by far the superior dental material available. Amalgam is under heavy challenge from newer restoratives that are more conservative, esthetic and potentially longer lasting.


Question #12: What are your feelings on processed composite inlays and onlays?

Answer: They should be used as high quality provisional restorations.


Question #13: While longevity is the final test of a posterior ceramic, how do we interpret the claims made by new products and their use in all-porcelain posterior crowns and bridges?

Answer: Without long term clinical studies, they are likely to perform as poorly as similar materials in the past.


Question #14: What is the bottom line of these new porcelain systems? Should they be used for single anterior teeth only?

Answer: Yes, if the porcelain is enamel supported. In posterior teeth the ceramic must be metal supported.


Question #15: Do CMBRs last longer than indirect resin systems?

Answer: We know CMBRs work well, but no indirect resin system has yet undergone any long term clinical trials. It will be many years until we can compare them.


Question #16: Do CMBRs last as long as porcelain fused to metal crowns?

Answer: Functionally, no. However, many crowns need to be removed before they are worn out because of esthetics. In many patients, CMBR's have a longer esthetic life span.


Question #17: How long have CMBRs undergone clinical trials?

Answer: CMBRs have not undergone any formal clinical trials. They were first made in 1984, improved in 1986, and then improved again in 1994. They have only undergone clinical evaluation in the mouth by trained private practitioners. Many thousands have been placed, and a 5% breakage rate over 10 years is common with earlier designs. We have learned that the placement and extent of the metal insert is critical. Most units that have fractured have been found to have inadequate metal support in the proximal areas.


Question #18: What are the most critical steps in placing CMBRs?

Answer: There are two critical areas: 1) the unit must be fabricated in such a way that all porcelain surfaces under tension are supported by metal. 2) prior to cementation the unit must be carefully adjusted by the dentist so the fit is excellent. In this way the enamel will best support the remaining areas of porcelain.


Question #19: Why do some people have great success with these restorations and others do not?

Answer: Fit is critical. Poorly fitting units will fail prematurely. This is related to the quality of the preparation and impression taken by the dentist and the ability of the technician to fabricate a unit which will fit the impression with accuracy.


Question #20: Can any dentist make these units if they find the right lab?

Answer: No. From our experience there is no right lab. Most technicians can successfully make these units. However, from our experience, both the dentist and technician need to be trained in these technologies together. The dentist cannot train the lab and the lab cannot train the dentist. Both need individual and joint training by people experienced in this area.


Question #21: How does Empress compare to CMBR and composite Inlays?

Answer: Empress is a leucite reinforced porcelain system and should be compared to other porcelain reinforced systems as Inceram by Vita. Empress is heavily marketed and has thus gotten a lot of attention. Empress units are easier to make if the lab prefers waxing and casting the leucite core. We do not have clinical trials that compare these systems to each other.


Question #22: Where can a dentist and a technician learn how to do these procedures?

Answer: Presently CMBRs are only being taught in three dental schools on the west coast. However, private facilities have been built and will continue to be built to train dentist and technician teams in these procedures. Most brand name ceramic and indirect resin systems are taught by he manufacturer.


Question #23: What is Artglass from Kulzer? They say it is not a composite and not a porcelain. They say its a polymer. Could you explain this?

Answer: : Artglass is a laboratory processed composite resin similar to Charisma except it contains an extra filler made of smaller clusters of silica plates. By definition a polymer which contains a filler is called a composite. All light cured and autocured composites in dentistry contain polymers. All composites contain polymers. Artglass is a different composite, but it has not undergone clinical trials to determine if it is any better than the other indirect composites on the market.

Question #24: What is Belle glass from Belle de Saint Claire?

Answer: Belle glass is made my Kerr and it similar to the product Herculab. The major difference is that the material is pressure cured in nitrogen gas to reduce oxygen inhibition of the polymer.


Question #25: What is Concept by Ivoclar compared to all of these materials?

Answer: Concept is any indirect microfilled composite which contains larger amounts of filler than direct microfilled materials. It is heat and pressure cured to increase polymerization.


Question #26: Do indirect composites bond to the tooth as well as etched porcelain and etched metal?

Answer: No, this is the major weakness in these systems. Since the material is cured in the laboratory is not possible to get a chemical bond between the restoration and the luting cement. Different methods have been used to attach the indirect resin to the luting agent. However none have undergone clinical trials to compared them to bonded metal or bonded porcelain restorations.

Question #27: What is the best inlay and onlay material?

Answer: Gold, after over a dozen years of studying these systems that is what I chose to have placed in my mouth. I don't mind the small amount of metal that shows. However, my assistant, knowing as much as me in watching the clinical results of the materials prefers a tooth colored material. She has CMBRs in her mouth and likes them very much. Most of my patients, do not esthetics, prefer CMBRs over gold by about 5 to 1.


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