**1.1 Classification of dental ceramics**

Classification of ceramics in dentistry is apparently an impossible task due to vast improvements made in the compositions. Nevertheless, the table provided here gives a general idea, say a bird's eye view of ceramics in dentistry.


In cements called glass ionomers, the glass forms the filler and acidic polymers form the matrix. The reaction that proceeds is usually an acid base reaction. Usually they are dispensed as powder containing glass powder, and liquid containing an acid, say, polyacrylic acid. When they are mixed, the acid in liquid etches the glass and reacts with calcium and other ions forming salts and the cement sets to a hard mass. Cements are direct restorative materials – i.e. manipulated and placed onto teeth directly, unlike other restorations that are made outside and fixed to teeth, called indirect restorations. They are highly advantageous as they are quick to set, release fluoride leading to anti-cariogenic

The use of ceramics are encouraged by their biocompatibility, aesthetics, durability and easier customization. The specialty of ceramic teeth is the ability to mimic the natural tooth in colour and translucency along with strength. Ceramics have excellent intraoral stability

Dental ceramics, since introduction have undergone numerous modifications in terms of chemistry. Ceramics have been able to give heed to the ever changing needs in dentistry. To delve deep into the relevance of ceramic in dentistry, one should understand the physics of forces acting in the oral cavity. The masticatory (chewing) force is the strongest force present here. Other minor forces include that of tongue and periodontal ligament, which do

The masticatory force is generated outside oral cavity by basically strong muscles, that move the jaw, open it or close it. Closure of jaw produces two kinds of forces. It is predominantly compressive in nature. Frequently impact kind of force is also experienced. Hence a ceramic has to undergo cycles of these forces indefinitely, without fracture, to result in a successful

In order to have a complete idea of what ceramic means to dentistry, we need to look at the

Classification of ceramics in dentistry is apparently an impossible task due to vast improvements made in the compositions. Nevertheless, the table provided here gives a

Category 1: Glass-based systems (mainly silica)

Category 2: Glass-based systems (mainly silica) with fillers usually crystalline (typically leucite or a different high-fusing

a) Low-to-moderate leucite-containing feldspathic glass b) High-leucite (approx. 50%)-containing glass, glass-ceramics

c) Lithium disilicate glass-ceramics (IPS e.max® pressable and

Category 3: Crystalline-based systems with glass fillers (mainly

Category 4: Polycrystalline solids (alumina and zirconia)

action, esthetic and chemically bond to tooth material.

and wear resistance adding to their durability.

not relate to the use of ceramics in dentistry.

complete range of ceramics used in this discipline.

general idea, say a bird's eye view of ceramics in dentistry.

glass)

alumina)

(Eg: IPS Empress)

machinable ceramics)

restoration of lost teeth structures.

**1.1 Classification of dental ceramics** 

**Microstructural Classification** 


Table 1. Classification of dental ceramics.


Table 2. Typical oxide composition of dental porcelain.

Ceramics in Dentistry 207

Similarly, ceramic teeth are manufactured in various shades, shapes and sizes to be used in complete dentures. Also, in case of gum recession, in fixed prosthesis, pink coloured

Chemical composition of these ceramics is based on silica network and potash feldspar (K2O.Al2O3.6SiO2) or soda feldspar (Na2O.Al2O3.6SiO2) or both. Potassium and sodium feldspar are naturally occurring minerals composed primarily of Potash and soda. The most important property of feldspar is its tendency to form crystalline mineral leucite when

Fig. 4. Scanning electron micrograph of amorphous glass (Russel Giordano et al, 2010).

ceramics are placed in the lost gum region to make it look natural.

**1.2.1 Category 1: Glass-based systems (mainly silica)** 

Fig. 3. All Ceramic Crown.

melted.

The classification based on microstructure will be dealt with in detail and an idea of classification by processing technique is added in this review. Other classifications are of academic interest.

Basically ceramics are used as indirect restorative materials such as crowns and bridges, Inlays/Onlays and dental implants. Recently ceramic braces are used in orthodontics.
