TERMINOLOGY OF DENTAL MATERIALS

The science of dental materials has got certain terminologies which are being
frequently used and the students should be acquainted with them as because
these may seem to be peculiar or Greek to them. This chapter will be devoted
entirely to the nomenclature that are being used in the various fields of
dentistry. particularly in connection with the dental materials that are
extensively used in the practice of the art and science of dentistry.

The main objective of the conservative (restorative) dentistry is to restore the
lost esthetic and function of the diseased or lost tooth structure (by caries or
trauma). On the other hand, the main aim and objective of the prosthetic
dentistry is to replace the lost tooth or teeth by artificial1 means thereby
maintaining the lost esthetic and function of the mouth of an individual.

Restoration

It is a conservation work which restores the lost esthetic, shape (anatomy)
and function (physiology) of a tooth. This work can be performed inside the
patient’s mouth e.g. a filling with restorative materials (Figs. 1-1 & 1-2), or it
can be made outside the patienť’s mouth and then cemented in place e.g. an
inlay, a crown, an onlay or a fixed bridge (Figs. 1-3, 1-5, 1-6, 1-7 and 1-8).
Restoration is fixed in nature and the patient cannot remove it. In
nonmetallic or metallic restoration, the cavity is to be lined by cements (Fig. 1-4).

Appliance

It is an artificial technique by which replacement of missing teeth are carried
out for proper speech, esthetic and masticatory function of an individual (e.g.
Complete and partial dentures and removable bridge) or by which malaligned
teeth are treated (c.g. Removable orthodontic appliance).

An appliance is usually removable in nature, 1.e. the patient carn wear it or
take it out (Figs. 1-9, 1-10, 1-11, 1-12. 1-13 and 1-14). But there are sorne
appliances which are fixed in nature and are taken out after the treatmerit te-g
Fixed orthodontic appliance and splint).

Crown

It is a fixed restoration for the entire or major part of coronal (crown) portion
of a natural tooth. A full veneer cast gold crown is shown in Fig. 1-5. This sort
of crowm is made for the posterior tooth which is to bear strong masticatory
forces
For the anterior teeth, for esthetic reason, a crown with porcelain (porcelain
jacket crown, Fig. 1-6) or a porcelain faced jacket crown (porcelain-fused-to-
metal crown, Fig. 1-7) can be used.

Bridge

It is a replacement for a missing tooth or teeth tFi1g. 1-8). The two teeth
adjacent to the space are called abutments and they are to be prepared for
restorations (crowns) to support the artificial tooth which 1s called pontiC. The
restorations are cemented on the abutments.

Partial denture

It is a prosthetic appliance which is used to replace one or a number of tooth
or teeth but not all. Clasps are used here to attach the partial denture to the
remaining abutment teeth. The artificial teeth are fixed on a saddle made of
metal rame works (igs. 1-9 & 1-10) or of acrylic resin. It also contains
occlusal rest to resist the tissue-ward movement of denture and lingual bar or
palatal Dar or plate to connect two components of the denture when needed.

Complete denture

It is a prosthe tic appliance which is used to replace all ot the missing natural
teeth. It has two component partS: (aj complete upper and (bj complete lower. It
consists of a base (denture base) on which the artificial teeth are attached and
the base may be: (a) metallic or [b) nonmetallic. The base has got periphery and
post-dam area (tor upper denture). For Complete denture, see Figs 1-1l and
1-12.

Impression and model

An impression is the negative likeness or imprint of the standing teeth and
oral tissues. A model is the positve likeness or replica of the standing teeth and
oral tissues.
For appliances and restorations that are to be made outside the mouth of
the patient, an impression is taken and from thisS impression a model or cast 1s
made with model material. On this model a patterm is made in dental wax
which after processing is fitted in the mouth of the patient.

A model may be of two types

1. Study model.
2. Working model.

Study model is that model on which the scheme of the future appliance is
made by surveying it, eliminating the undercuts with plasticine and drawing
with an indelible pencil the shape of the saddle, clasps, lingual or palatal bars
etc.

Working model on the other hand is that model on which the pattern of the
restoration or appliance is made with dental waxes to transform it into a
permanent dental material, nonmetallic or metallic. For details of these, see
chapters 2, 3, and 25.

Viscosity

It is the property of a fluid that resists the force tending to cause the fluid to
flow. It is due to internal frictional forces within the liquid. In some dental
materials, we do want viscosity and in some we do not. Students will have an
idea regarding viscosity when they will go through different chapters (A viscous
substance means a sticky, thick or adhesive material).
dental

Adhesion

It is the molecular force of attraction in the area of contact between unlike
materials that acts to hold them together. So, it is the force of attraction
between unlike molecules. Adhesive means sticky or tenacious. In dental
materials we want adhesion in restorative materials (e.g. glass ionomers), but
not in impression materials.

Cohesion

It is the molecular force of attraction between particles of a substance that
acts to unite or bind them. So, it is the force of attraction between molecules of
the same kind. Cohesive means characterized by or causing cohesion. In
impression materials, restorative materials and denture base materials (e.g
acrylic resins), this property of the material is essential.
causing cohesion.

Plasticity

It is the quality or capability of being moulded, receiving any shape to be given or being made to assume a desired form. Plastic substances are capable of being moulded or of receiving any form.Plastic substances are capable of being moulded or of receiving any form. At rest, these substances are dimensionally stable i.e. they do not undergo expansion or contraction. But when they are subjected to any external force they deform or change their shape. So, plastic substances have got flow. In impression materials, cements and amalgams plasticity is needed for manipulation. But in cases of denture base materials, plasticity should not be present else they will be dimensionally unstable. Many of the plastics especially acrylic resins show flow on static loads (cold flow) which is an undesirable
property of a denture base material, artificial teeth and jacket crowns.

Flow

When an amorphous material (shapeless or not crystalline) changes its
shape under extermal pressure, it is said to have flow. In other words, flow 1s
the deformation of an amorphous material due to external force.
In dental materials, flow is seen in waxes and amalgam (during
Condensation before its setting). Flow is desirable in impression materials but
not in restorative materials or denture base materials.

Creep

It is the deformation of a mass of material which has completely set or
hardened subjected to a constant stress. In other words, we can define it to be
any deformation of the clinical restoration (filling), that might take place after it
has set hard under constant masticatory stress. For more details, see chapter 11.

Linear coefficient of thermal expansion

It is defined as the change in length per unit length of a material when its temperature is raised or lowered one degree. For its implication in dentistry, see
chapter 11.

Tarnish and corrosion

Tarnish means loss of brightness of the metal surface. Corrosion means
attacking of the metal surface by some medium in close contact with it and in
course of time, the structure of the metal may be completely disintegrated
resulting weakening of the material. For greater detail, see chapter 11. (Dental Materials 1-5 )