Class I and Class V Preparation Fundamentals Flashcards
Dental Amalgam as a Restorative Material
Amalgam is an alloy of silver, copper, tin, and zinc, mixed with mercury to form an alloy that can be packed into a dental preparation, and which will set up to form a solid restoration
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properties of amalgam (5)
- High compressive strength and low tensile strength, which means it is brittle in small bulk.
- Sensitive to moisture contamination during placement. Water reacts with the zinc in the amalgam and causes an eventual expansion of the alloy out of the preparation.
- Amalgam is still a good choice in situations where moisture control is difficult. You can scrape off the top, contaminated layer and keep packing amalgam.
- Amalgam corrodes. Modern alloys
have a high copper content which
minimizes corrosion,but doesn’t
prevent it entirely. - Amalgam creates and regenerates a
seal between itself and the tooth,
because of the oxides formed—they
expand and fill tiny voids and prevent
microleakage. No other dental
restorative material does this.
disadvantages of amalgam (6)
- Poor esthetics.
- Need for good “mercury” hygiene.
- Remove more tooth structure for adequate bulk of material.
- Doesn’t bond to tooth structure.
- Thermal conductor, necessitating use of a liner or base to prevent post-
op sensitivity on deeper restorations. - Eventually may “ditch” at the margins, collecting plaque in that area.
advantages of amalgam (6)
- More forgiving in areas where moisture is hard to control.
- High wear resistance and compressive strength.
- Can be placed in less time than other options (lower cost.)
- Relatively long-lasting.
- Regenerates its seal.
- Is less prone to recurrent decay than bonded composite resin
restorations.
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indications for amalgam (8)
- Moderate to large Class I and Class II restorations.
- Heavy occlusal wear.
- High caries rate.
- Difficult isolation.
- Gingival margins on root.
- Class V restorations in non-esthetic zones.
- Temporary restorations on teeth with questionable prognosis.
- Buildups under crowns for extensively damaged teeth usually with supplemental retention (pins, posts, grooves)
principles of tooth preparation for amalgam restorations:
have a means for
isolation of the site
have a means for isolation of the site (3)
- visibility
- access
- moisture control (especially important when restoring)
isolation materials (4)
rubber dam (gold standard)
cotton rolls
retraction cord
ISOVAC
all — — must be removed from all margins
undermined enamel
undermined enamel
enamel that is not supported by dentin under it
Margins should be – degrees at the
cavosurface on all axial surfaces
90
On the occlusal surface, margins may be
SLIGHTLY — in some areas, but must
NEVER BE — anywhere on the tooth
obtuse
acute
dentin must support all
surface enamel
Ideal preps are — into the dentin
0.2mm to 0.5 mm
- Must prepare through the entire enamel layer.
- This is determined by caries in a live patient.
This will mean different — in different places on the tooth. It will depend on the — of the enamel in the
area
depths
thickness
The traditional teaching about the OUTLINE FORM of an amalgam preparation states that the preparation must not terminate in the bottom of a
FISSURED pit or groove
On class II amalgams, contact is broken (2)
facially and lingually
extension for prevention
Preparations should encompass all carious and badly demineralized areas
retention form
what holds a restoration in a tooth (RETAINS the restoration)
do amalgams bond to tooth structure?
no
Smaller amalgams are held in by (2)
converging walls and/or by retention grooves if no walls can converge
These are elements in the design of a tooth preparation that will help
both restoration and tooth resist
fracturing
Maintaining as much tooth structure as possible. This makes the TOOTH
less likely to
fracture
Having some areas on the floor of a multi-surface preparation that are
— to occlusal forces make the restoration less likely to
fracture
perpendicular
Rounding — on a preparation (at least a little bit) make
the TOOTH less likely to fracture.
internal line angles
Smoothly rounding — forms make the RESTORATION less likely to
fracture.
outline
Preparing to — — prevents weakness (resists fracture) in the restoration
proper depth
NEVER leave enamel on the
floor of a preparation
NEVER leave a partial-depth ledge on the
enamel wall of an occlusal preparation, like a class I amalgam
Avoid leaving — under an amalgam that is subject to occlusal stress. This could result in fracture of the restoration
sharp external line angles
• Ex. axial wall of Class II preparation
class 1 (3)
occurs in…
restores…
• Occurs in occlusal 2/3 of molar tooth • Restores a developmental pit • NOT a Class V (despite being on axial surface)
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Buccal Pit Preparation
Use the 330 bur to do the preparation. Its flutes are 1.5mm top-to-bottom,
so they are a gauge for the proper depth
- The 330 is an inverted cone form, so it will naturally converge walls.
- Tip it occlusally in the occlusal “apex” to avoid converging the wall there.
WALLS AT THE TERMINAL ENDS OF
THE BUCCAL AND LINGUAL GROOVES
— 3 DEGREES
DIVERGE
WALLS IN THE ISTHMUS AREAS --- 3 DEGREES ON EACH SIDE OF THE PREPARATION. ISTHMUS WIDTH IS --- MM MINIMUM.
CONVERGE
1 MM
WALLS ADJACENT TO MARGINAL
RIDGES — 3 DEGREES.
DIVERGE
— THE MESIAL OR DISTAL
WALL ADJACENT TO THE MARGINAL
RIDGE LEAVES — — FOR
THE RIDGE IN THIS AREA
DIVERGING
DENTIN SUPPORT
OCCLUSAL AMALGAM DEPTH :
.2mm inside dentino-enamel junction
MOLARS:
PREMOLARS:
2 MILLIMETERS
1.5 TO 2 MILLIMETERS
CONVERGING THE WALL ADJACENT TO THE
MARGINAL RIDGE RISKS
DESTRUCTION OF THE DENTIN SUPPORT FOR THE MARGINAL RIDGE
How to Avoid an Off-Axis Preparation:
ENTER TEETH PARALLEL TO THE LONG AXIS OF THE TOOTH CROWN
NOT THE PATIENT
BUR INCLINES MORE MESIALLY IN THE --- AND MORE DISTALLY IN THE --- THE FURTHER POSTERIORLY WE GO, DUE TO THE CURVE OF SPEE
MANDIBLE
MAXILLA
BUR INCLINES MORE LIGUALLY IN THE --- AND MORE BUCCALLY IN THE --- THE MORE POSTERIORLY WE GO, DUE TO THE CURVE OF WILSON
MANDIBLE
MAXILLA
prep too shallow
prep too weak
still in enamel
close to pulp, weakens tooth
Angular Outline Form Could Cause Areas of Stress Concentration In the Areas Marked Above in Red, —- Amalgam
Fracturing
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Analyze the Occlusion
Look for “Plunger Cusp” Situations (3)
Opposing cusps have
burrowed into old
restorations, creating
inclined plane contacts.
Shorten supporting cusps,
preserving correct cusp form.
Place new restorations,
elevating fossa bottoms
to restore contact in M.I.
(long axis forces restored).
Enter the tooth with a — Bur
Keep bur parallel to the
169
Long Axis of the tooth (both mesiodistally and faciolingually)
Insert your bur to a Depth of — mm. with the 169 bur.
1 ½
Hold the bur — to the long axis of the tooth while preparing
perpendicular
Keep the preparation as — as possible– just the width of the bur
Stop in the mesial and distal pits.
narrow
The 169 bur will give a slightly — prep. in all areas, since it is a
tapered fissure bur.
divergent
A 169 bur is a tapered — bur
fissure
A 169 bur is a tapered fissure bur
◦ It will prepare a preparation with — walls if held in a single plane.
◦ It has sharp edges on its tip, and will leave sharp — line angles in the prep.
◦ Its flutes measure 4mm. top to bottom.
◦ Half the depth of the bur head would cut a – mm. deep prep.
diverging
internal
2
At — mm. of depth on an
ordinary molar, the bur has
not penetrated into dentin
1.5
Using a 245 bur, insert to a depth of — (Molar) or — (Premolar)
2mm
1.5mm
A 245 bur is an inverted — bur, with
rounded edges on its flat end
cone
A 245 bur is an inverted cone bur, with
rounded edges on its flat end.
• If held in one plane, it will cut an — prep. with — internal line angles.
• Its flutes measure — top to bottom, so half the depth of its head will cut a — prep. and 2/3 of its head will cut to a depth of —
undercut, rounded
3mm
1 ½mm
2mm
Widen the isthmuses to 1mm, and converge their walls about
3◦ each
Tip the 245 bur enough mesially &
distally to — the mesial & distal walls 3-4⁰. Blend from these walls into the — walls of the isthmuses
diverge
converging
Diverge Walls at the Terminal Ends of Buccal and Lingual Grooves on Molars
Tip the 245 bur buccally or lingually to
— walls adjacent to the buccal
and lingual cusp ridges 3-4 ̊
diverge
class V buccal amalgam preparation restores
caries on the gingival third of the buccal and lingual surfaces of teeth
almost al caries starts —, but often spreads — onto the root surface
supragingivally
subgingivally
GINGIVAL RETENTION GROOVE
THERE IS A COMPARABLE OCCLUSAL RETENTION GROOVE AT THE
OCCLUSAL-AXIAL LINE ANGLE. THEY ARE IN DENTIN, JUST INSIDE THE
D.-E. JUNCTION EVEN WHEN THE AXIAL WALL IS DEEP DUE TO CARIES
Enamel in the cervical area is —
thinner
◦ preparation is not as deep as an occlusal amalgam
Since the preparation is in a smooth area, outline form is determined by
the
extent of caries.
◦ Rather than following anatomy
Since the prep. is in a convex surface and all amalgam margins must be
90◦,
all walls diverge
grooves are needed for
retention
The axial wall is — when caries is minimal
convex
a Bucco-lingual longitudinal section
shows
retention grooves and divergent walls
The entire thickness of the enamel is perpendicular to the — and is still supported internally by —
cavosurface
dentin
Class V Buccal Amalgam Preparation: Procedure
• Use the 169 bur to prepare the tooth to a uniform depth
of 1.5 mm.
• Keep the long axis of the bur perpendicular to the
surface of the tooth. In an ideal preparation, the axial
wall should be convex.
• In a live patient, the outline form is determined by extent
of caries
• Initial entry is made with a #2 round bur on SLOW
SPEED, excavating caries.
• Then use the 169 bur at high speed used to refine
internal line angles and cavosurface margins.
• Only extend deeper than 1.5 mm where caries must be
removed.
When caries extend on to root surface /subgingival the rules for depth may
change:
A. When there is minimum thickness of enamel: — depth.
B. When the margin is on the root: — depth.
1 mm
0.75 mm
A ¼ round bur is used to place an occlusal and a gingival retention groove
entirely in dentin, just inside the DEJ
On preps. with minimal axial depth, it will be necessary to bisect the (2)
occlusal axial and gingival axial line angles
on deep preps, the grooves still go
just inside the DEJ
when caries extends into the inter proximal embrasures
the problem:
the adjacent tooth blocks access for the side of a 169 bur
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when caries extends into the inter proximal embrasures
the solution: (3)
Excavate caries with #2 round bur
Use a gingival margin
trimmer to remove
undermined enamel
interproximally
Use the end of a
169 bur to define
internal line angles
interproximally
Caries may cause — in some areas.
Don’t…
unequal axial depth
dont remove healthy tooth structure deeper than 1.5 mm. just to get
even axial depth
Correct Way to Handle Deep Caries Situation:
Grooves Just Inside D.-E. Junction
