Finishing and polishing of cast metal framework/prosthodontic courses

FINISHING AND POLISHING OF
CAST METAL
FRAMEWORK
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
www.indiandentalacademy.com

Introduction

Contents :-
Definition
Purpose of finishing and polishing
Classification of finishing and polishing devices
Design of abrasive instrument
Types of the abrasives
Finishing and polishing of the cast metal framework
Fitting the framework
Biological hazards of finishing and polishing
Review of literature
Summary and conclusion
References

Definition :-
 Finishing – Process of removing surface defects or scratches
created during the contouring process through the use of cutting
or grinding instruments or both.
 Cutting – process of removing material from the substrate
by use of a bladed bur or a abrasive embedded in a binding
matrix on a bur or disk.
 Grinding – Process of removing material from a substrate by
abrasion with relatively coarse particles.
 Polishing – Process of providing luster or gloss on a material
surface.

Abrasion
“A process of wear whereby a hard rough surface
( like a sand paper disk ) or hard irregular shaped particles ( like
those in a slurry ) plough grooves in a softer material and cause
materials from these grooves to be removed from the surface”.

Purpose of finishing and polishing
Provides 3 benefits of dental care-
Oral health
Oral function
Esthetics

Classification
Finishing and polishing devices
Abrasive and polishing devicesCutting instruments
Bonded abrasives Coated abrasives Loose abrasives

Design of abrasive instrument
Abrasive grits – Abrasive grits are derived from materials that
have been crushed and passed through a series of mesh
screens to obtain different particle size ranges.
Dental abrasive grits are classified as –
Coarse
medium coarse
medium
fine
super fine

Colour coding of burs

Bonded abrasives
These consists of abrasive particles incorporated through a
binder to form grinding tools such as points,wheels,separating
discs and abrasive strips.
The abrasives are bonded by four methods:
1. Sintering.
2. Vitreous bonding.
3. Resinous bonding.
4. Rubber bonding

Bonded instrument should be trued.

Coated abrasives
Coated abrasives are fabricated by securing abrasive particles to
a flexible backing materials with a adhesive material.
Non bonded abrasives
They are applied with synthetic foam,rubber felt or chamois cloth.

Types of abrasives
Natural abrasives :
Arkansas stone Sand
Chalk Tripoli
Diamond Cuttle
Emery Quartz
Garnet Kieselguhr
Pumice
Zirconium silicate
Corundom

Manufactured abrasives : Silicon carbide
Aluminum oxide
Synthetic diamond
Rouge
Tin oxide

1. Arkansas Stone :
Semi-translucent , light grey , siliceous sedimentary rock
emended in Arkansas
Contains mico-crystalline quartz .
Small pieces are attached to metal shanks and trued to various
shapes for fine grinding of tooth enamel and metal alloys.

2. Chalk :
mineral form of calcite
contains calcium carbonate
used as a mild abrasive paste to polish enamel, gold fillings
3.Corundum :
Largely replaced by alpha aluminium oxide due to its superior
physical properties .
Available as bonded abrasive and is used primarily to grind
metals.

4.Diamond :
Transparent colorless mineral composed of carbon
Called SUPER-ABRASIVE because of its ability to abrade any
known substance .
Hardest substance known .
Used on ceramic and resin based composite materials.
Supplied as – bonded abrasive , diamond abrasive pastes ,
abrasive strips .

5. Emery :
Consists primarily of a natural oxide of aluminium called
corundum.There are various impurities present , such as iron
oxide which also act as abrasives .Usually bound to paper discs
and can be used on gold or porcelain.
6. Garnet :
Includes several minerals , which posses similar physical
properties and crystalline form like silicates of Al,Co,Mg, Mn.
Usually coated on paper or cloth with a binder. Cuts both metal
and porcelain.

7. Pumice :
Highly siliceous material of volcanic origin .
Suitable for use as an abrasive or a polishing agent according to its
particle size .Can be used for many operations from smoothening
of denture bases to the polishing of teeth in the mouth.
8. Quartz :
The particles are pulverized to form sharp angular particles , which
are useful in making coated discs . Used to finish metal alloys.

9. Sand :
-It’s a mixture of small mineral particles predominantly
composed of silica.
-Sand blasting
-Coated abrasives

10. Tripoli :
It’s a siliceous rock
Mild abrasive and polishing agent
Used for polishing metal alloys.
11. Zirconium silicate :
Occurs in nature as Zircon .
Is ground to various particle sizes and used as a polishing agent
It is used as a constituent of dental prophylactic pastes and in
abrasive impregnated polishing strips and discs .

13.Kieselguhr :
It is composed of siliceous remains of minute aquatic plants know
as diatoms .
It is an excellent mild abrasive and polishing agent .
12. Cuttle :
A fine , relatively soft polishing agent made from calcified internal
shell of cuttle fish .
It is used on paper discs for polishing of metal margins .

Manufactured abrasives
Silicon carbide :
First of the synthetic abrasives to be developed .
It is the basic material of carborundum
Supplied as an abrasive in coated discs, vitreous bonded and
rubber bonded instrument.

Rouge:
It is a fine red powder composed of iron oxide.
Its blended in cake form.
Excellent polishing agent for gold and noble metal alloys.
Aluminium oxide:
Its widely used in dentistry to make bonded abrasives,coated
abrasives and air propelled grit abrasives.
Sintered aluminium oxide is used to make white stones which are
used for finishing metal alloys.

Mohr’s Knoop Vickers

Finishing and polishing of cast metal framework
It should be completed in a systematic sequence.
Principles in finishing the casting –
• High speed
• Excessive pressure should be avoided
• Definite sequence of finishing
• Clean polishing wheel should be used

 Quenching
 Sandblasting
- Its used to clean the alloy surface
- To achieve both microretentive topography and increased surface
area
- Pickling

Finishing can be done with a handpiece or a bench lathe.

Fitting the cast metal framework
Fit the framework to the teeth
Adjust the framework to opposite occlusion

Fitting the framework to teeth
Use of disclosing media
-Jeweler’s rouge dissolved in chloroform
-Disclosing waxes

Electropolishing
Electrolytes –
1. Ethylene glycol – 80%
Conc Sulphuric acid – 15%
Water – 5%
2. 3parts of Phosphoric acid
1 part of glycerine
1 part of water

Rimatitan

Biological hazards -
Silicosis –
Berylliosis –
Aerosols produced during finishing and polishing can be
controlled by –
Personal protection
Adequate ventilation

Review of literature
A.Kevser Aydin (1991) evaluated the finishing and polishing
techniques on surface roughness of chromium-cobalt castings
and concluded that the best surface finish was obtained when
sand blasting,
hard stone,
medium abrasive disk,
second sand blasting,
electro polishing,
hard rubber point,
hard felt disk,with pumice slurry,
and soft brush with polishing paste were used progressively.

Dr. Ponnanna A.A. (1999) under the able guidance of Dr. N.P.Patil
sir evaluated the polished surface characteristics of Co-Cr
castings subsequent to finishing and polishing techniques.
A total no. of 30 disc shaped test specimens of cast Co-Cr alloy
were fabricated for the evaluation of surface characteristics
Conclusion
1. Various finishing and polishing techniques employed for the
surface Rx of cast Co-Cr alloys revealed improved surface
characteristics using the sequence of sandblasting, coarse grit
abrasive, medium grit and the fine grit abrasive.

2. Perthometric evaluation of the surface characteristics seems to
be a better method of evaluation of finished and polished
surface.
3. Loss of weight of metal affecting the physical quality of the alloy
can be carefully avoided by judicious sandblasting and
application of proper grit of abrasive agents.

Dr Srinivas reddy (2002) under the able guidance of Dr. N.P.Patil sir
conducted a study to evaluate the effects of different finishing and
polishing agents on the surface roughness of the cast pure titanium.
A total of 60 specimens were cast in commercially pure titanium.They
were divided into three groups of 20 specimens each.

Group A was finished with tungsten carbide and polished with
black, brown and green rubber points.
Group Bwith gold finishing and polishing kit.
Group C with specific titanium kit.
Surface roughness was measured with a pertherometer
instrument.
It was concluded that surface roughness was less on a cast
titanium specimens which were finished and polished from
cutters designed specifically for titanium

Conclusion

References -
Anusavice K.J. “Phillips Science Of Dental Materials” 11th
edition,
Philadelphia,W.B. Saunders
Aydin A.K. “Evaluation of finishing and polishing techniques on
surface roughness of chromium-cobalt castings.”J.P.D.,1991;65:763-
767
Craig R.G. “Dental Materials, properties and manipulation”. 8th
edition
Jeffries S.R. “The art and science of abrasive and finishing and
polisjhing in restorative dentistry”. DCNA,1998;42(4): 613-628.
Kern M.,Thompson V.P. “Effect of sandblasting and silicoating
procedures on pure titanium”. J.Dent.,1994;22:300-306.
Laboratory procedures for inlays, crowns and bridges ;Dereck
stanonougth www.indiandentalacademy.com

Morris F., Brudvik J.S. “Influence of polishing on cast clasp
properties”. J.P.D.,1986;55:75-77.
Morrow R.M.,Rhoads J.E., Rudd K.D., “Dental laboratory procedure,
removable partial dentures”. 2nd
edition
Mc Cracken’s Removable partial denture prosthodontics. 11th edition,
2004.
Richard .Troxell “The polishing of Gold casting”J.P.D:1959:9:668-675.
Stewart, Rudd and Kuebker: Clinical Removable denture
prosthodontics. 2nd
edition, 2001.

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