The measurement you heard was more than likely a megapascal (MPa). It is named after the French mathematician (Pascal). Because the Pascal represents a very small quantity, the megapascal (MPa) is the preferred unit for these uses. It is a measurement of force, largely replacing the pounds per square inch unit (psi). It uses metric measurements, and is defined as 1 Newton per square meter. Well? What then is a Newton?? (Not a fig newton). A Newton is the force needed to accelerate 1 kilogram at the rate of 1 meter per second squared. Just remember: its the amount of FORCE per unit AREA.As a dentist you cannot just spit out a number to sound "cool", what are you measuring???? Compressive strength? Tensile strength? Fracture strength? Shear stress? (I can go on, and on). without considering other factors.... Just because the crown has a higher MPa doesn't mean its THE BEST, necessarily. Crowns are tooth replacements that cover the outer part of a natural tooth that is reshaped by the dentist. They are used to repair and strengthen the damaged teeth. Enamel is AWESOME... we cannot recreate it, but we make things that are SIMILAR to it. Enamel behaves differently under COMPRESSION vs. TENSION. Compressive strength is the stress state that causes a squeezing of the material. Enamel has a compressive strength of about 400 MPa. Tensile strength is the stress caused by pulling (elongating) the material. Enamel has a tensile strength of about 10 MPa (meaning it is brittle).In the traditional (old fashioned) way, there is a core made of metal alloy (usually gold) fused to layers of dental ceramic (known as a porcelain fused to metal crown, or PFM). The layered porcelain is the weakest point with a strength of approximately 100 MPa. We usually try to position this dark edge just underneath the tooth's gum line. However, if gum recession occurs, this grey dark line can show, thus spoiling the crown's appearance.With modern advances in dental materials, we have been able to eliminate the metal core and replace it with high strength materials. Due to their life-like translucency, All ceramic crowns can be the most cosmetically pleasing of all the different types of dental crowns, making them the go-to-choice for restoring front teeth There has been several "generations" of all ceramic crowns. I will review a few of the more commonly used ones: 1. Empress (Leucite reinforced): Some of the most beautiful restorations, because of the translucent nature of the material. These crowns are primarily made of leucite ceramic which scatters light similar to natural tooth enamel and blends in well with other teeth. Restorations fabricated with the Empress have a life like translucent quality to them. Because of their lower fracture strength (160 MPa), dentist recommends Empress crowns only for un-stressed anterior teeth, and on a person that does not grind their teeth. Limited use in today's world.Two of the most popular all-ceramic systems are zirconia-based or lithium disilicate-based. The question becomes, which system should be chosen and when? Strength and longevity become important parameters when making the choice. Lithium dislocate (Emax) crowns are monolithic (made of a single material). They can be very esthetic, as they allow light to be transmitted easily. Zirconia-based crowns in the front of the mouth are generally are veneered (because of the opaque nature of zirconia) with a relatively weak ceramic material. Because of this fundamental difference in composition, the behavior of these crowns could be quite different over time. Flexural strengths of zirconia and lithium disilicate are approximately 1000 MPa and 400 MPa, respectively. While zirconia, per se, is stronger, its weakness lies in the veneering ceramics, which has a flexural strength that is approximately 100 MPa. Monolithic versions of zirconia crowns (originally called Bruxzir crowns) are used frequently in back teeth, but tend to be very "white" or "opaque." Some companies have changed the polycrystalline structure in zirconia to make it more translucent for the front of the mouth, but subsequently, the strength has been reduced by about 1/2. 2. Emax (Lithium Disilicate): 400 MPa3. Zirconia (traditional): 1000-1200 MPa Zirconia (translucent): 500 MPaSummary: Anything can break, given enough force...All of the above mentioned options can look very esthetic (even the old fashioned versions), depending on the dentist and the laboratory technician...As with all information, ask your local dentist before choosing any treatment. Each case is unique!Hope that helps!
