August 27th, 2009 by admin
Endodontic materials are used to obturate the
root canal system of teeth when the pulp tissue
has been destroyed either as a consequence of
trauma or subsequent to tooth decay involving the
pulp and infection of the pulp tissue. The objectives
of endodontics are to:
• Clean and shape the root canal system to within Read the rest of this entry »
August 27th, 2009 by admin
These materials may be supplied as a powder and
liquid or as a powder which is mixed with water
(Fig. 30.1). For powder/liquid materials, the
powder is fi nely ground zinc oxide which sometimes
contains minor quantities of other oxides
such as magnesium oxide. The liquid is an aqueous
solution of polyacrylic acid of about 40% concentration.
In the powder/water materials the powder Read the rest of this entry »
August 27th, 2009 by admin
Glass ionomer restorative materials have been
available since the early 1970s and were derived
from the silicate cements (Section 20.8) and polycarboxylate
cements (Chapter 30). Polycarboxylates
were developed several years earlier and were
the fi rst dental cements for which an inherent
adhesion to tooth substance could be demonstrated.
They quickly gained popularity as luting
cements but could not be used as restoratives Read the rest of this entry »
August 27th, 2009 by admin
Having conditioned the dentine in order to remove
or modify the smear layer, the next stage is the
priming stage. This is a key stage in the procedure
as it is designed to change the chemical nature of the dentine surface and to overcome the normal
repulsion between the hydrophilic dentine and the
hydrophobic resin. The priming agents are similar
in nature to the di-functional chemical coupling
agents described in Section 23.4. Their nature is Read the rest of this entry »
August 27th, 2009 by admin
A composite material is a product which consists
of at least two distinct phases normally formed by
blending together components having different
structures and properties. The purpose of this is
to produce a material having properties which
could not be achieved from any of the individual Read the rest of this entry »
August 27th, 2009 by admin
These are supplied as a powder and liquid which
are mixed together. The composition is similar to
that given in Table 13.1 for denture base materials.
Briefl y, the materials consist of a powder and
liquid. The powder contains beads of polymethylmethacrylate
(<50 μm), chemical initiator (often a
peroxide) and pigment, whilst the liquid consists
of methylmethacrylate monomer and a chemical
activator (often a tertiary amine). The pigments Read the rest of this entry »
August 27th, 2009 by admin
The development of fi lling materials based on synthetic
polymers has been initiated by two major
driving forces, in addition to the obvious commercial
ones. Firstly, there was a requirement to
produce a material which could overcome the
major defi ciencies of the silicate materials, namely,
erosion, brittleness, acidity and a moisture sensitivity
which demanded very careful manipulation. Read the rest of this entry »
August 27th, 2009 by admin
Composition: These materials are supplied as two
pastes. Each paste contains a liquid silicone prepolymer
and fi ller and one of the pastes contains a catalyst. One paste contains a polydimethylsiloxane
prepolymer in which some of the methyl
groups are replaced by hydrogen (Fig. 19.6a). The
other paste contains a prepolymer in which some
methyl groups are replaced by vinyl groups (Fig.
19.6b). One of the pastes contains a catalyst which Read the rest of this entry »
August 27th, 2009 by admin
Composition: These materials may be supplied as
two pastes or as a paste and liquid. Whichever
method of dispensation is used the principle of the
setting reaction is similar and depends on the
cross-linking of hydroxyl-terminated polydimethylsiloxane
chains, brought about by an alkyl silicate
cross-linking agent and a tin compound as
catalyst. The ingredients required for this reaction Read the rest of this entry »
August 27th, 2009 by admin
Hydrocolloid impression materials used in dentistry
are based on colloidal suspensions of polysaccharides
in water. A colloidal suspension is
characterised by the fact that it behaves neither as
a solution, in which the solute is dissolved in the
solvent, nor as a true suspension, in which a heterogeneous Read the rest of this entry »
