Transcript Objectives of cavity preparation - BMC

Principles of cavity
preparation
Tooth preparation
1. Definition.
2. Objectives.
3. Principles:
i. biological.
ii. Mechanical.
Definition
• Tooth preparation is the mechanical
alteration of a defective, injured, or
diseased tooth to receive a restorative
material that reestablishes a healthy state
for the tooth, including esthetic corrections
where indicated and normal form and
function.
Mechanical
alteration
Defective
Injured
Restorative
material
Diseased
tooth
Healthy state
Esthetic
Form
Function
Objectives of cavity preparation
•
1.
2.
3.
.
For tooth:
Remove the defect conservatively.
Provide necessary protection to the pulp.
Prevent further fracture of tooth.
Objectives of cavity preparation
• For the restoration:
1. Prevent further fracture of restoration
under masticatory forces
2. Prevent displacement of restoration
3. Allow for esthetic and functional
placement of restoration
.
Principles of cavity preparation:
• Biological principles.
i. Protection of the pulp(thermal, mech,
chem, bact.).
ii. Prevention of caries recurrence.
iii. Aseptic conditions.
• Mechanical principles.
I. Biological principles
Biological principles
• Health and integrity of remaining tooth tissues
1. Protection of the pulp
2. Prevention of caries recurrence
3. Aseptic procedures
1. Protection of the pulp.
i. Mechanical .
ii. Thermal.
iii. Chemical.
iv. Bacterial.
I. Mechanical irritation.
Protection of the pulp
AVOID!!!
1. Overcutting of enamel (width).
2.
Overcutting of dentin (depth)
Cutting of the OP
close to the cell body may result in irreversible injury
3.
Excessive pressure application during excavation or
use of rotary tools
4.
Injudicious use of small pointed instrument.
5.
Avoid use of eccentric rotary tools
phenomena.
6.
Cutting across recessional lines of pulp
“Shock-wave”
II. Thermal irritation.
Thermal irritation:
TTZ (thermal tolerance zone) of dentin which
ranges between 85-132 F
1. Minimizing the frictional heat resulting in
cavity preparation via, decreasing friction:
speed, pressure, area of cutting, mode and time
of cutting. Using tools with high cutting
efficiency (sharp, suitable, and proper sized).
2. the intentional use of coolants
• copious in amount
• Multi directed
Air-water spray jet is considered to be the most
appropriate (Why?)
 air drying stream
desiccate the dentin
 water stream
disturbs visibility during work.
The temperature of coolant should be that of the
mouth i.e.37 C (Why?)
• Lower temperatures
fogging, disturbs vision
and may irritate the pulp.
• Higher temperatures
not effective in cooling.
Thermal Injury:
“Blushing” of teeth during or after cavity prep is
attributed to frictional heat
• Pink or purple color due to vascular stasis
of sub-odontoblastic capillary plexus blood
flow which rupture and release RBC’s.
III. Chemical irritation.
Chemical irritation:
• Cavity cleansers, cavity sterilizers like
phenolic and alcoholic agents proved to
have an insignificant role in preventing or
decreasing secondary caries and thus their
use must be omitted.
• Chemical irritation to dentine-pulp organ
without pulpal bacterial contamination did
not produce harmful effects on the pulp in
spite the existence of a very thin protective
dentin bridge or even in cases of micro- or
macroscopic pulp exposures.
IV. Bacterial irritation.
Bacterial irritation:
• Sterilization of instruments is essential
since bacterial ingress to the pulp can pass
through minute undetected exposures in
case of thin dentine bridge barrier
• Use of rubber dam to isolate the field of
operation
:
2. Prevention of caries recurrence
Prevention of caries recurrence
1. Remove all carious enamel and dentin
2. Inclusion of all liable areas (pits &fissures)
Recurrent caries due to
improper extension
3. Removal of all undermind enamel
4-Correct CSA compatible with restorative material
3. Aseptic procedures.
Aseptic procedures
1. Use of sterile instruments
2. Isolation of operative field
3. Use of personal protective barriers
II. Mechanical principles
Mechanical principles
• Structural integrity of both tooth and
restoration demanding:
Provision of correct resistance
Provision of adequate retention
Correct cavity design decrease the magnitude
of
the
destructive
stresses
by:
• Inclination of walls
• Locating the margins
• Flat, smooth walls and floors
• Line and point angles
• The cavity design should decrease the deleterious and
damaging effect of tensile stresses created within the tooth
as a result of defect by:
1. Conservation
2. Removal of weakened tooth structure and undermined
enamel
3. Provision of bulk in the brittle restorations for stress
distribution so that the destructive forces could not
damage the brittle restoration.
4. Provision of adequate means of retention to prevent
displacement of restoration under functional forces.