2nd dental students

2. Principles of toothPrinciples of tooth
preparationpreparation
•Teeth are not regenerative tissue , once enamel or
dentine is lost as a result of caries , trauma or wear ,
restorative material must be used to restore form and
function
• They requires preparation to receive restoration
•These preparation must be based on fundamental
principles to achieve the success of prosthodontic
treatment
•A good preparation ensure that subsequent techniques
can be accomplished .

3. Biological considerationsBiological considerations
Affect thehealthof theoral tissuesAffect thehealthof theoral tissues
Mechanical considerationsMechanical considerations
Affect of theintegrityandAffect of theintegrityand
durabilityof therestorationdurabilityof therestoration
Esthetic considerationsEsthetic considerations
Affect theappearanceof thepatientAffect theappearanceof thepatient
The principles of tooth preparation may be
divided into three broad basic categories :

4. Principles of tooth preparationsPrinciples of tooth preparations
1- Biological principles1- Biological principles
• Prevention of damage during tooth preparationPrevention of damage during tooth preparation
– 1- Adjacent teeth1- Adjacent teeth
– 2- Soft tissue2- Soft tissue
– 3- Pulp3- Pulp
• Conservation of tooth structuresConservation of tooth structures
• Considerations affecting future dental healthConsiderations affecting future dental health
– 1- Axial reduction1- Axial reduction
– 2- Marginplacement2- Marginplacement
– 3- Marginadaptation3- Marginadaptation
– 4- Margingeometry4- Margingeometry
– 5- Occlusal considerations5- Occlusal considerations
– 6- Preventingtoothfracture6- Preventingtoothfracture
2- Mechanical principles2- Mechanical principles
3- esthetic principles3- esthetic principles

5. Principles of tooth preparationsPrinciples of tooth preparations
Biological principlesBiological principles
Prevention of damage during tooth preparationPrevention of damage during tooth preparation
1- Adjacent teeth1- Adjacent teeth
Techniqueof toothpreparationmust avoidandprevent damagetoTechniqueof toothpreparationmust avoidandprevent damageto
theadjacent toothsurfaces using:theadjacent toothsurfaces using:
a- Metal matrixbanda- Metal matrixband
b- enamel of thetoothbeingpreparedb- enamel of thetoothbeingprepared

7. 2- Soft tissue2- Soft tissue
Damageto soft tissueof theDamageto soft tissueof the
tongue, cheeks canbetongue, cheeks canbe
preventedbycarefulpreventedbycareful
retractionwithanaspiratorretractionwithanaspirator
tip, mouthmirrororflangedtip, mouthmirrororflanged
salivaejectorsalivaejector
Direct trauma, more likely withDirect trauma, more likely with
• sub gingival marginssub gingival margins
• Periodontal diseasePeriodontal disease
• Careless cuttingCareless cutting
• Aggressive use of retraction cordAggressive use of retraction cord
• Prevention of damage during tooth preparationPrevention of damage during tooth preparation
– 1- Adjacent teeth1- Adjacent teeth
– 2- Soft tissue2- Soft tissue
– 3- Pulp3- Pulp

8. 3- Pulp3- Pulp
Causes of pulp injuryCauses of pulp injury
a- Temperaturea- Temperature
b- Chemical actionb- Chemical action
c- Bacterialactionc- Bacterialaction
Tooth preparation must account for pulp chamber
and pulp size that decrease with age more
occlusocervically than faciolingually
• Prevention of damage during tooth preparationPrevention of damage during tooth preparation
– 1- Adjacent teeth1- Adjacent teeth
– 2- Soft tissue2- Soft tissue
– 3- Pulp3- Pulp

9. Causes of pulp injuryCauses of pulp injury
a- Temperaturea- Temperature b- Chemicalaction c- Bacterialactionb- Chemicalaction c- Bacterialaction
a- Temperaturea- Temperature
Thefollowingdiagrams show howThefollowingdiagrams show how
heat generationis affectedbyheat generationis affectedby
pressure, highrotationalpressure, highrotational
speed,watercolingandtype,speed,watercolingandtype,
shapeandconditionof cuttingshapeandconditionof cutting
instrumentinstrument
• Prevention of damagePrevention of damage
during tooth preparationduring tooth preparation
– 1- Adjacent teeth1- Adjacent teeth
– 2- Soft tissue2- Soft tissue
– 3- Pulp3- Pulp

10. Causes of pulp injuryCauses of pulp injury
a- Temperaturea- Temperature b- Chemicalactionb- Chemicalaction c- Bacterialactionc- Bacterialaction
b- Chemical actionb- Chemical action
Dentalmaterials suchas bases , restorativeresinsolvent andDentalmaterials suchas bases , restorativeresinsolvent and
lutingagent cancausepulpaldamagelutingagent cancausepulpaldamage
Cavityvarnishanddentinebondingagent formaneffectiveCavityvarnishanddentinebondingagent formaneffective
barrier but its effect oncrownretentionis controversial.barrier but its effect oncrownretentionis controversial.
Chemicalagent maybeusedforcleaningtoothpreparationtheyChemicalagent maybeusedforcleaningtoothpreparationthey
havebeenshownto bepulpal irritants .havebeenshownto bepulpal irritants .
• Prevention of damagePrevention of damage
during tooth preparationduring tooth preparation
– 1- Adjacent teeth1- Adjacent teeth
– 2- Soft tissue2- Soft tissue
– 3- Pulp3- Pulp

11. Causes of pulp injuryCauses of pulp injury
a- Temperature b- Chemicalactiona- Temperature b- Chemicalaction c- Bacterial actionc- Bacterial action
c- Bacterial actionc- Bacterial action
Pulpaldamageunderrestorations has beenattributed toPulpaldamageunderrestorations has beenattributed to
bacteriathat Eitherwereleft behindorgainedaccess to thebacteriathat Eitherwereleft behindorgainedaccess to the
dentinbecauseof microleakagedentinbecauseof microleakage
All carious dentinemust beremovedbeforeplacement ofAll carious dentinemust beremovedbeforeplacement of
restorationthat serveas foundationforFPDrestorationthat serveas foundationforFPD
• Prevention of damagePrevention of damage
during tooth preparationduring tooth preparation
– 1- Adjacent teeth1- Adjacent teeth
– 2- Soft tissue2- Soft tissue
– 3- Pulp3- Pulp

12. 1- Partial coverage rather than complete
coverage
2- Minimal practical convergence angle
3- Occlusal reduction follows anatomical
plane giving uniform restoration
thickness
onservation of tooth structures
Biological principle
1- prevention of damage
2- conservation of tooth
3- future dental health

13. 4- preparation of the axial wall as
uniform as possible even using
orthodontic repositioning .
5- Selection of margin
conservative and compatible with
other principles of tooth
preparation
6- Avoidance of unnecessary
apical extension of the
preparation
onservation of tooth structures

14. 1- Axial reduction
gingivitis is associated with FPD that have
excessive axial contour
Sufficient tooth reduction is required for
correct axial contour
Considerations
affecting future dental
health
Biological principle
1- prevention of damage
2- conservation of tooth
3- future dental health
1- Axial reduction
2- Margin
placement
3- Margin
adaptation
4- Margin geometry
5- Occlusal
considerations
6- Preventing tooth
fracture

15. Advantages of supragingival margins
1. They can be easily prepared
2. They can be easily finished.
3. They are more easily kept clean.
4. Impressions are more easily made, with less potential forsoft tissue
damage.
5.restorations can be easily evaluated at recall appointments
6. usually situated on hard enamel
.
2 -Margin placement
Wheneverpossible the margin of the
preparation should be supragingival
Consideration affecting
future dental health
1- Axial reduction
2- Margin placement
3- Margin adaptation
4- Margin geometry
5- Occlusal
considerations
6- Preventing tooth
fracture

16. Indication of subgingival margins
1. Dental caries, cervical erosion, or restorations extend
subgingivally,
2. The proximal contact area extends to the gingival crest.
3. Additional retention is needed.
4. The margin of a metal- ceramic crown is to be hidden behind the
labiogingival crest.
5. Root sensitivity cannot be controlled by more conservative
procedures
6. Modification of the axial contour is indicated.
2- Margin placement

17. 3- Margin adaptation
The more accurately the restoration Is
adapted , the lesser is the chance for
recurrent caries
A well designed margin has a smooth and
even margin not rough , irregular or stepped
Consideration affecting
future dental health
1- Axial reduction
2- Margin placement
3- Margin adaptation
4- Margin geometry
5- Occlusal
considerations
6- Preventing tooth
fracture

18. 4-Margin geometry
*Guidelines for margin design:
1-easy prepares ( not over extended(
2-easy identified in impression and on die
3-distinct boundary for wax pattern finish
4-sufficient bulk of material
5-conservation of tooth structure.
Consideration affecting
future dental health
1- Axial reduction
2- Margin placement
3- Margin adaptation
4- Margin geometry
5- Occlusal
considerations
6- Preventing tooth
fracture

19. 4- Margin geometry
1- Featheredge or shoulderless
Advantages
conservation of tooth structure,
Disadvantages
provide inadequate bulk at the margins
Indistinct
2- chisel edges
Advantages
conservation of tooth structure,
Disadvantages
Location of margin difficult to control

20. 3- Bevel edges
Advantages
Remove unsupported enamel
allow burnishing of metal
Disadvantages
extend preparation into sulcus if used
on
apical margin
Indication
Facial margin of maxillary partial
coverage
restorations and inlay and onlay
margin

21. 4- chamfer margin
Advantages
distinct and easily identified, provide
adequate bulk of material at the margins
Disadvantages
care is needed to avoid leaving a ledge of
unsupported enamel
Indication
Cast metal rest. , lingual margin of metal
ceramic restoration

22. 5- shoulder margin
Advantages
provide adequate bulk of material
Disadvantages
Less conservative to tooth structure
Indication
Facial margin of metal ceramic
restoration
All-ceramic crown
Preparation
Using tapered diamond with a flat tip
It should form 90 degree angle with
unprepared tooth surface

23. 6- Sloped shoulder
margin
Advantages
provide adequate bulk of material
Allow metal finishing to knife edge
Disadvantages
Less conservative to tooth structure
Indication
Facial margin of metal ceramic restoration
All-ceramic crown
7- Shoulder with bevel
Advantages
provide adequate bulk of material
In addition to advantage of bevel
Disadvantages
Less conservative to tooth structure
Extend preparation epically
Indication
Facial margin of posterior metal ceramic
restoration in which facial metal collar is used

24. 5- Occlusal considerations
Tooth preparation should allow sufficient space for
a functional occlusal scheme in the finished
restoration.
Consideration affecting future dental
health
1-Axial reduction
2-Margin placement
3-Margin adaptation
4-Margin geometry
5-Occlusal
consideration
6-Preventing tooth
fracture

25. • Disrupted occlusion ( tilting , supra-eruption ) need occlusalDisrupted occlusion ( tilting , supra-eruption ) need occlusal
analysis then considerable reduction to compensate for theanalysis then considerable reduction to compensate for the
supra-erupted tooth. )supra-erupted tooth. )

26. 6- Preventing tooth fracture
Consideration affecting
future dental health
1- Axial reduction
2- Margin placement
3- Margin adaptation
4- Margin geometry
5- Occlusal
considerations
6- Preventing tooth
fracture
Tooth preparation should be designed to prevent
fracture of restored teeth
Providing a cuspal coverage restoration (onlay)
rather than an inlay lessens the chance of such
fracture
However, although not conservative of tooth
structure, a complete crown is often a better solution