Advantages and disadvantages of Zirconia Crowns
The new era of dental materials is flourishing and much has to do with the advantages and disadvantages of Zirconia Crowns. Zirconia is an extremely strong and hard materiel, close to 1200 Mpa, compared to a traditional full porcelain crown at 250mpa. We measure in MPA’s or mega pascals. It is white and relatively opaque. So it is a great replacement for the previous metal that was used as a base underneath PFM’s, or porcelain fused to metal crowns. PFMs, were the standard of esthetic dentistry for the last 60 years or so.
Advantages and disadvantages of Zirconia Crowns
We are all familiar with the white crowns, that were relatively opaque, sometimes you saw a little metal sticking out at the gum line, causing a dark area at the neck of the tooth. These teeth were also often opaque and not terribly natural. This was because the metal had to be hidden by an opaque white color, so as not to see greyish in the crown.One problem was that the porcelain can chip off of the outside of the crown revealing an ugly grey color.
Zirconia crowns have overcome these problems. The zirconia comes either in small blocks that can be milled in a CEREC machine, or, as one of the few dentists in Israel with a Sirona Inlab system in my office, I can mill large restorations out of a puck of zirconia. Zirconia in its raw form is chalky. We mill it dry, and it needs to be put into an oven for 12 hours to sinter, or become hard. But once hard it is strong, tough and very exact in terms of its fit. One of advantages and disadvantages of Zirconia Crowns is that they are brittle. So we must be careful when adjusting the so as not to cause microscopic cracks which can lead to failure. All in all it is an amazing material and the advantages and disadvantages of Zirconia Crowns are far outweighed by the advantages.
Zirconia Crowns In A day
Zirconia Crowns In A day is one of the great breakthroughs in digital dentistry. The are only a handful of dentists in the country who employ CEREC technology, Dr. Ari Greenspan being the first. Let’s discuss Zirconia Crowns In A day.
Zirconia is a new form of dental material that allows us to mill it into a crown using CAD-Cam technology. We take a three dimensional image of the teeth, design that crown or bridge and then mill it on the spot. Zirconia oxide is a synthesized material that is exceptionally hard and has optical qualities similar to tooth. It has many advantages over standard porcelain fused to metal crowns, namely: esthetics, durability, strength and hardness as well as high biologic compatibility. Because it is milled and not cast in metal from a wax mold, there are virtually no discrepancies in fit. Until recently, the only way to get such a material for a crowns was through the traditionall’impression method. Another complication is that the zirconia is milled in an unfinished relatively soft states. It must then be finished and required hours and hours in an oven for a process known as sintering. The sintering requires special equipment that dentists don’t have.
Except in our office. We have recently started being one of just a handful of dentists in the entire country with the ability and equipment to produce Zirconia Crowns In A day using new and advanced technologies that reduce the sintering time.
The Inlab dental laboratory system is not really used by dentists because of the complexity. We wanted the ability to control every aspect of our lab work to ensure perfection. As a result, we now own a 5 axis sophisticated milling unit and the special ovens necessary to make Zirconia Crowns In A day.
If you have any questions please do not hesitate to contact us.
Emax cad porcelain
Emax cad porcelain is a new materiel being used to make dental crowns. It has numerous advantages over standard porcelain. The Cad in Emax cad porcelain stands for computer aided design , being used by the CEREC SYSTEM that allows for the manufacture of a CEREC crown in the dental office in an hour.
Emax cad porcelain is a material called lithium disilicate. It is exceptionally natural in its appearance and is hard to differentiate from natural teeth. But the greatness of this porcelain material is not in its beautiful esthetics, but rather in its strength.
In general, dental porcelain is a strong materiel. It has great strength under compression. Imagine putting a piece of glass on a perfectly flat surface with 1 drop of water under it. Drive a car over it and it won’t break but put one grain of sand under and it will. It has poor resistance to lateral forces or flexural strength. Porcelain strength is measured in MPaS or megapascals. Regular porcelain has something like 150 MPa’s but Emax cad porcelain is in the order of 400MPA’s. More than 2 times as strong as a regular porcelain crown with esthetic advantages.
When we make a CEREC Emax cad porcelain crown, it comes in a block that is not fully formed and once the crown is manufactured, it needs to be fired in a porcelain oven to be completed and brought to strength. It is quite fascinating as the materiel has a blue color until it is removed from the oven when it takes it’s final beautiful shape and hue.
Depending on the situation, we use this material for many of our crown solutions.The translucency,opalescence, and light diffusion properties of IPS e.max lithium disilicate were all designed to copy natural tooth for beauty and quality restorations.
The cerec technology allows us to take a monolithic block of porcelain and create an exact a perfectly fitting restoration. The entire thing takes only about an hour from start to finish. The Cerec Blocks of porcelain that we use and place into the machine to be ground down into crowns come in several types of materiel.
Types Of Cerec Blocks
Cerec Blocks fall into 3 main categories and each has it’s own uses. The original blocks were standard dental porcelain. These blocks have been around for many years. The are strong, very wear resistant and very esthetically pleasing. The advantage of this porcelain is that it has expansion and contraction characteristics similar to tooth making it comfortable with very few post op sensitivities. It can be stained and glazed to individualize each crown. The disadvantage is strength measure in mega pascals. These Cerec Blocks are among the weakest and can fracture if under extreme stress. Usually though they are fine and I have found them fracture only under very unusual circumstances and even then only on second molars.
Next is E-max or lithium disilicate blocks. These blocks are the strongest options around, they are very esthetic and have the smallest chance of fracturing. In fact it is quite rare that that ever happens. The only downside is that these Cerec Blocks must be fired in an oven in order to make them have their final strength. That means they need an extra 1/2 hour of time in order to finish the procedure.
Finally there are hybrid blocks which are made up of composite material with porcelain components. The advantages of these blocks is that have a certain microscopic flexibility making them useful in high stress situations.
No matter which if these Cerec Blocks we use, today we have a wide range of different options allowing us to give our patients one visit crowns in an hour that are esthetic, strong and comfortable