Before the advent of pressing technology ceramic restorations were most commonly produced using a process of combining liquid and powder into a slurry and then stacking this porcelain on the die. The ceramic is applied this way in layers and then fired. This process is still commonly used today and understanding the properties can allow us to use it to our advantage to achieve the clinical results we are after. Ceramics fabricated in this way are typically feldspathic or leucite reinforced glass, and used primarily for anterior restorations. The fabrication process is challenging and time consuming and requires a skilled ceramist to create both the esthetic results and a precisely fitting restoration. An advantage of this type of ceramic restoration is the ability the technician has to layer material of varying color and opacity.
Restorations can be made as thin as .3mm and therefore tooth preparation can be very conservative when utilizing this material. The material can be utilized for both full and partial coverage restorations. Due to the inherent physical properties of the ceramic and the creation process, restorations made this way have a relatively low flexural strength of 60-110mpa. With this is mind these restorations whether full or partial coverage must be bonded to the tooth for strength and durability using a etching/adhesive process. The intaglio surface of the ceramic is etched with hydrofluoric acid and then porcelain conditioner is applied prior to the resin cement.
Thank you very much for your blogs. I find your information very practical and helpful. I have recently read an article that stated that there is no consensus on how long to etch porcelain with hydrofluoric acid-that it really varies with the porcelain and varies with the brand of hydrofluoric acid. The article also stated that the frosty appearance actually indicates over etching of porcelain, and that this frostiness is a precipitate that should be removed by soaking the porcelain in ethanol preferably in an ultrasonic bath. Otherwise the bond strength will be diminished . I have never read this before. Can you please comment on this? Thanks very much.
There are a variety of different strength hydrofluoric acids on the market, and the etching time does vary based on the percentage. I am a big believer in following the manufacturers recommendations, and your lab should be able to tell you what porcelain they are using and the time based on what material you purchase. Your lab can also complete the etching process for you. If you are milling chairside, again the manufacturer will have a recommended protocol. As for the frost, cleaning the porcelain after etching is recommended. I do this with distilled water in an ultrasonic, I have not heard of using ethanol. One thing to make sure of is that you are not etching after your lab as the glass only needs this treatment once. if they are etching you simply need to clean the porcelain after try in.
Really good stuff! Ceramic restorations I feel is one of the better ways to improve the way your teeth look.
Hello there, v good articles with lots of practical and helpful info…..My qu was about feldspathic prep reduction guidelines for anterior crowns- i’ couldnt quite figure out why books and articles talk about allowing minimal reduction say 0.5-0.8mm margins for feldspathic minm prep crowns and yet for emax they recommend 1mm or + cervical margins despite emax being the stronger material….I’m amazed with feldspathic that it can allow such min’m preps (obviously in the anterior)….any thoughts?
Dentist from UK
The emax recommended thickness for bonded anterior veneers is minimum .3mm.