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‫ امير حمدي العميدي‬.‫د‬
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1. Cavosurface (margin): it's the junction between the wall of the cavity and the surface of the tooth .
2. Bevel: is the inclination that one line or surface makes with another when not at right angles .
3. Enamel wall: is that portion of the prepared cavity wall , consisting of enamel .
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4. Dentinal wall: is that portion of the prepared cavity wall , consisting of dentin and often it contains
retention grooves .
5. Embrasure: it's a V-shaped space that originate at the proximal contact area between adjacent teeth
and are named for the direction towards which they radiate .
6. Over-hang: any marginal restorative material excess usually referred to the gingival margin .
7. Contact area: It's the area of immediate proximity of one tooth with the another in the same arch .
Class VI (cl.VI): Cavities on the incisal edges and cusp tips of the teeth .
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1. Cl.I cavity preparation may include certain cases of exception, in this lecture we will discuss the lower 4
and the upper 6. The lower first premolar; the occlusal surface of this tooth shows the presence of the
transverse ridge joining the buccal and lingual cusps. This ridge separates between the mesial and distal
fossae that are joining by the coalesced central fissure; therefore, caries index in this ridge is very low and
and it must stay intact during cl.I cavity preparation of the lower 4 and two separate cavities should be
prepared around the cusps . Only when the caries is extended and include this ridge (it's width is less than
0.5 mm), it should be prepared with the fossae to obtain only one cavity . This cavity has an
anterioposteriorly tilted pulpal floor ; due to the fact that this tooth has high buccal cusp and lower lingual
cusp ; consequently , the pulp horns are also of variable height , flat pulpal floor preparation may expose the
pulp and cause pulp traumatic exposure , the tilt of the cavity is about (45°) and so the bur direction during
making the entry to the cavity .
The anatomical picture of this tooth shows us that it has a stout ridge crossing the occlusal surface
from the mesiolingual cusp to the distobuccal cusp, and therefore dividing the occlusal surface into mesial and
distal fossae.
This oblique ridge shows less degree of susceptibility to the caries, it is a coalesced part of the tooth,
and shouldn't included in our cavity preparation to preserve the tooth structure stronger and to maintain
efficient tooth function.
In case of extensive caries that the oblique ridge was involved either totally or partially (only 5 mm. is
remaining or less), it must be included in our cavity preparation; otherwise, two separated cavities should be
prepared on the distal and mesial fossae following the cusps and the grooves to obtain the dove-tail shape.
In some causes, the distal oblique groove is continued to the lingual surface, the caries may be extensive
to include all this groove and also the lingual groove that separates between the mesiolingual cusp and the
distolingual cusps , but restricted to the occlusal surface. Therefore our cavity preparation should be like this;
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Or the caries may involve even the lingual groove to appear again on the lingual surface, and in this case it
is called Cl.I with lingual extension (or there is Cl.I with buccal extension when the buccal surface of the tooth
is involved).
The preparation of such cases to amalgam restoration is somewhat different , if we continue our cavity
preparation from the occlusal surface to the lingual / buccal surfaces with the same bur but by deepening the
occlusal preparation to include these extensions , traumatic exposure of the pulp might takes place ; therefore
, we either :
1) We follow the general rule that that is saying " the bur should be perpendicular on the surface we
are working on " , so we incline the bur at the lingual surface and continue our preparation , or
2) At the termination of the lingual fissure on the occlusal surface, about the last 1.5-2 mm, we
continue our cavity preparation by deepening the cavity to the end of the caries on the lingual
surface.
Hand Instruments
The dental hand instrument consist of three essential parts :
1. Handle or shaft: it's the part that is grasped by the operator's hand while he's using the instrument.
2. Shank: it's the part that connects the shaft with the blade (nib).
3. Blade: it's the functional end of the instrument and it bears the cutting edge.
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Heat Treatment Hardening Treatment:
The steel is heated to 1500 to 16000 F (8150 C) and then quenched in oil to harden the working edge. Not
more than 1 - 2mm of the tip is heated for hardening purpose, otherwise the instrument will lose its balance
after sharpening. Hardens the alloy, but it also makes it brittle, especially when the carbon content is high.
TEMPERING TREATMENT. Cutting edges are usually tempered to produce additional hardness and to remove
some of the brittle properties. To accomplish this, the tip is reheated at a lower temperature. Quenched in
solutions of oil, acid or mercury at 200- 4500C for 10 min. This treatment relieves strains and increases
toughness.
Cutting Instruments :
1. Straight Chisel: used for planning or cleaving of the enamel or dentin , the blade terminates in a cutting
edge formed by one sided bevel the cutting edge of the blade is at right angle to the plane of the shaft .
The shank may be straight or angled , it's used with a push motion .
Hoe : is a form of a chisel in which the angle of the blade is greater than 12.5 , it's used with a pulling
motion .
2. Hatchet: it's a chisel blade instrument , the cutting edge is in the plane of the shaft . It's used for
planning or cleaving unsupported enamel or dentin during the cavity preparation and frequently , there
are proximal and gingival walls access position would dectate their use . Also , it may be useful in other
areas . The hatchet could be used to refine line and point angles in various forms of cavity preparation .
3. Gingival Margin Trimmer: the blade is curved , this curved blade is used to accentuate the lateral
scraping ability of the instrument . it's a double-ended instrument , used essentially for beveling gingival
cavosurface margins , also for roundening or beveling of axiopulpal line angles .
4. Spoon Excavator: the cutting edge is rounded and used for spooning carious material from the cavity .
The entire periphery is sharpened and the circular cutting edges are sharp .
5. Cleioid-Discoid: the claw-like end or cleioid end and the disk-like or discoid end , used mainly for
amalgam and wax carving .
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Condensing Instruments (condenser or plugger):
They are used to condense the amalgam in that cavity . The head of the instrument is of different sizes and
shapes , the surface of the head is either smooth or serrated and it could be either manual or mechanical
using ultrasonic waves .
Plastic Instruments :
These are used when the material is in the plastic stage .
They are used to manipulate the plastic restorative material
, including :
1. Ash no.6: it has (2) blades , each at one end , we use it
to adept the cement in the proximal box and to finish
carving of amalgam .
2. Ash no.49: it's double-ended instrument with ball and rounded ends .
Also it's used to adapt the cement in the cavity and to finish carving of amalgam , also to condense some
of the materials in the cavity .
Carving Instruments :
They are used to carve the proper shape of amalgam , also to carve the wax .
Burnishing Instruments :
They are with rounded edges , they are used to burnish , polish hardened metallic surfaces . Also to contour
matrices and to stretch margins of cast restorations (crown-inlay-onlay) .
Exploring Instruments :
They are used for exploring hard tissue defects and they could be either straight , sickle-shaped or angled .
They are used for caries detection . Angled type usually used for detection of interproximal caries , other are
used for other cases , they are named (Probes) .
Isolation Instruments :
Including rubber-dam , saliva ejector .
Other instruments :
Like dental mirror, amalgam carrier (by which we carry the amalgam from the container in tiny balls and
insert them into our cavity).
Rotary Instruments
This describes a group of instruments that turn on an axis to perform a work, the character of the work is
either cutting , abrasion , finishing or polishing tooth , tissue or various restoration materials . We call them
(BURS) , they made up of stainless-steel or tungsten carbide or diamond .
The cutting head of various shapes and sizes and various number of blades. They rotate at:
1. Conventional or low speed below 10000 rpm.
2. High speed between 10000 and 150,000 rpm.
3. Ultra speed above 150,000 rpm.
The types of burs are:
1. Round bur: the head is divided into blades; it could be either of steel or carbide.
It has different sizes, there are universal numbers to standardize them like
no.5 (no.1 – no.8) . The selection of bur depends on the purpose we are using
it for; it's used for establishing entrance to the cavity and for removal of caries.
For caries removal, we use large size round bur with slow speed. For penetration
into the cavity, we use small-size round bur . Very small-size round bur is used
for creating undercuts and retention grooves.
2. Fissure bur: it's used to obtain the out line form of the cavity and to increase
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it's size laterally for smoothening of the walls , floorsand margins . They are of different sizes and shapes
, could be either straight or tapered fissure bur , used for inlay and crown preparation .
3. Elliptical bur: or so called (Elongated round bur) . They have become popular as
a result of a trained toward a conservative cavity with rounded internal line angles .
4. Inverted-cone bur: it makes the floor of the cavity flat , but it cuts as well from
the walls and it makes them converge , it's suitable for providing undercuts .
Rotary Finishing and Polishing Instruments :
Burs used to polish the amalgam , composite or tooth surface . It could be either round or fissure burs , the
blades are more ; so it cuts finer . There is also the (Carborandum stone bur) , also we have brushes and
rubber-cup .
All rotary instruments are attached to a hand-piece (it's an instrument used to hold the rotary instruments ,
connected to a source of power such as motor or air)
Types of Hand-pieces :
1. Air-turbine hand-piece : a hand-piece with turbine powered by compressed air .
2. Contra-angle hand-piece .
3. Straight hand-piece .
Control of Operative Instruments :
In order to get a successful work , it's necessary to grasp the instrument as well as resting or balancing them
while they are in function .
Instruments grasps classified into :
1. Pen grasp: the control of the instrument
is gained be the grasp of the thumb and
the 1st finger on the handle with
additional thrusting power obtained from
the 2nd finger in firm contact with the
shank of the instrument . the cushion of
the 3rd finger provides a rest , this grasp
is most frequently used in operative
procedure and in the mandibular arch .
The action of the instrument is down
and away from the operator .
2. Inverted-pen grasp: the elements of this grasp
are the same as that of pen-grasp .
The action of the instrument is up and
toward the operator . It's usually applied
to the maxillary arch, the dentist usually stands behind and slightly to
the right of the patient . This grasp is usually carried out with the use
of the dental mirror . The palm and the fingers tips are directed
toward the operator by turning the wrist .
3. Palm and Thumb grasp: the handle is grasped between the
palm and the four fingers to provid firm control . The thumb
offers additional support , most frequently used in the
maxillary arch , but is adaptable to both arches .
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Sharpening of the Instruments by Hand:
Should be done always in order to get smooth surface during
cutting and without excessive force . The cutting edge is sharpened
by maintaining the original bevel . A special stone is used
called (Arkansas) stone, mechanical sharpeners are
also available .
Q- Notes :
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Cavity width should not exceed 1/4 intercuspal distance.
Removal of unsupported enamel (spread of caries in the D.E.J.) [ Enamel is brittle ].
Flat pulpal floor.
Rounded internal line angles.
Mesial and distal walls of cavity parallel or diverge occlusally .
In cl.II cavity, axiopulpal line angle beveled.
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Cavity width should not exceed 1/4 intercuspal distance.
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Flat pulpal floor.
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In cl.II axiopulpal line angle is beveled .
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Isthmus area isles slightly than 1/4 intercuspal distance .
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Depth of amalgam [brittle]; needs bulk more than 1mm.).
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Cavosurface line angle should be as near as possible to the right angle (90º-110º (
more than 90º will decrease thickness and cause fracture.
less than 90º will cause unsupported enamel fracture
 Over carving will cause decrease thickness of amalgam.
 Under carving will cause high spot stress concentration point.
Cavity margins must include full extent of caries or enamel decalcification; if not, lead to marginal breakdown.
Occlusal surface of posterior teeth contains on non-coalesced pits and fissures, these fissures or grooves
must be included in the cavity preparation. If not, possibility of recurrent caries at the junction of the
teeth with restoration.
 Using 1/6 intercuspal distance in the outline form of the cavity is more conservative for sound tooth
structure; but we will face the problem of relatively large head of the amalgam plugger (condenser);
therefore poor amalgam condensation may result in the failure of the restoration, otherwise, we must
fabricate smaller size hand instruments to be more conservative.
 Unsupported enamel on the labial surface of the anterior teeth is not removed; since it is required for
esthetic, also it withstands less forces of mastication.
 The optimum depth is (1.5-2 mm) in enamel and the proper extension into dentine is about (0.1-0.5
mm). The 2 mm measurement is usually the depth of the prepared external walls.
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