Principles of tooth preparation /certified fixed orthodontic courses by Indian dental academy

• PRINCIPLES OF TOOTH
PREPARATION

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INDIAN DENTAL ACADEMY
Leader in continuing dental education


• 1. CONSERVATION OF TOOTH
STRUCTURE


• A) Preparation of the canal:
• When creating post space remove only
minimal tooth structure form canal.
• Excessive enlargement can:
• Perforate
• Weaken the root tooth may split during
cementation of post or during subsequent
function.

• Pic of split root due to
post


• The thickness of the remaining dentin is the
prime variable in fracture resistance of the
root.


????
• Hunter et al (JPD 1989:62;166) did a invitro
study and concluded that teeth with a
thicker post (1.8mm) fractured more easily
than those with a thinner one( 1.3mm)


• Fig of root M-d thin,
concavitites.
• Can show a cross
section of tooth.


• B) Preparation of coronal tissue


• Every effort should be made to save as
much of the coronal tooth structure as
possible, because this helps reduce stress
concentrations at the gingival margin.1"


??
• Stein RS et al (JPD 1002;68:428) in their
study concluded that if greater than 2mm of
coronal tooth structure remains the post
design probably has a limited role in
fracture resistance of restored tooth.


Extending the preparation
apically
Creates a ferrule effect .

Extension of axial wall of the crown apical to
the missing tooth structure
Provides a ferrule.


• Purpose of ferrule ( JPD 1990)
 improve the structural integrity of pulpless
tooth by counteracting
• 1. the functional lever forces
• 2. the wedging effect of tapered dowels
• 3. the lateral forces exerted during insertion of
dowel
• Thus prevents root fracture.

Extensively damaged teeth
• Crown lengthening
• Orthodontic extrusion


• 2 Location where
ferrule can be given
• 1. Crown ferrule
ferrule created by the
overlying crown
engaging the tooth
structure


• 2. core ferrule: ferrule
is a part of cast metal
core


• Sorensen et al (JPD 1990:63;529) and Tjan
et al (JPD 1985;53:496)
• Ferrule formed as a part of core are less
effective than ferrule as a part of crown
• Ferrule effect at both the levels did not
increase fracture resistance as compared to
ferrule only at crown level.

• Ferrules that grasp
larger amount of tooth
structure are more
effective than those
that engage only a
small amount of tooth
structure.


• Libman et al (IJP 1995;8:155) found that 0.5-1
mm crown ferrule are ineffective , whereas 1.52mm crown ferrule is effective.
• Isidor et al (IJP 1999;12:78) increasing crown
ferrule length  increases fracture resistance
(1.25 & 1.55 mm)
• Concluded  ferrule length was more important
• Than post length in increasing tooth’s fracture
resistance.( ideal 2mm???)

• Sloping ferrule


• Sorensen at al
ferrules are more
effective when crown
encompasses
relatively parallel
prepared tooth
structure , than when it
engages sloping tooth
structure.

RETENTION FORM


ANTERIOR TEETH
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Post retention is affected by the
preparation geometry,
post length,
diameter,
surface texture,
and by the Luting agent

preparation geometry,
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canals with circular cross
section( Max CI) 
prepare post space with
parallel walls.

• Tapered canals if
parallel sided post given
canal has to be
considerably enlarged
weakening of root.
• Tepared post with
restricted amount of taper(
6-8 degrees)

FIG???
• Circular parallel posts are only effective in the
most apical portion of the post space because
majority of prepared post spaces demonstrate
considerable flare in the occlusal half.


Post Length


Standlee et al ( JPD 1978;39:401)

Increase in
dowel length



But relation is not linear


Increased
retention

Ideally post be as long as possible without
jeopardizing the apical seal
Or the strength or integrity
Of remaining tooth structure.

5mm of GP be left in apical area


If post too long
May damage apical seal
Risk of perforation if
apical third is curved or tapered


If post too short
increased chances of root fracture
(short post force applied near the incisal edge
Of the crown will generate a greater couple
increased possibility of root fracture
Decreased retention


Short root + tall clinical crown?
Post short compromised mechanics
Post long  compromised apical seal
3mm apical seal  acceptable


Post diameter
• Increase in post diameter to increase
retention not recommended. weaken
root.
• Prognosis good when post diameter < 1/3 rd
of cross sectional diameter of the root


Post surface texture


Serrated surface

> Smooth surface


Threaded dowel >

Smooth dowel


Luting agents


• Resin cements> GIC = zinc phosphate>poly
carboxylate.


• Choice of cement more important if post
has poor fit in canal.
• If rotation or post wobbles remake
• Resin cements  if post is dislodged and
has to be recemented.

• Resin cements affected by eugenol
containing RC sealers
• Eugenol contains 2-methoxy- 4-allyphenol
inhibits polymerization of composites.


Anthony H.L. Tjan et al (Q Int.
1992;23:839)
• Did a study to evaluate the effect of
eugenol- containing endodontic sealer
on retention of prefabricated pots luted
with adhesive composite resin cement.
They concluded that:
• Eugenol significantly reduced the
retention of parapost dowels luted with
panavia composite resin cement.

Irrigating the post space with alcohol
or etching with phosphoric acid gel
effectively restored the retention.
• The use of alcohol (ehtyl
alcohol/ethanol) as a canal irrigant
or etching with 37% phosphoric
acid gel was found to be effective
in restoring the resistance to
dislodgement of post. Irrigation
with alcohol produced a more
consistant and reliable result.

Posterior teeth
• Long post with circular cross section 
avoided curved, elliptical or ribbon
shaped roots perforation.
• .


Chances of perforation on distal surface of mesial root
And mesial surface of distal root


• Retention better by 2 or
more relatively short posts
in divergent canals
• Select canals that are
widest( palatal-max,
distal-mandibular) for
major post and then
prepare short auxiliary
post space in other canal
with same path of
withdrawl

Resistance form


• Rotational resistance


• Circular post should not
rotate during function.
• Sufficient tooth structure
present vertical coronal
wall prevents rotation
• Coronal dentine lost
small groove anti
rotational element

• Kurer et al (JPD
1977;38;515)
• Gave a method to prevent
rotation of threaded posts
by placing rotation lock.
• Sig: placement of post
without cement possible
facilitates removal of
dowel in needed.

Stress distribution
• Post and core improves resistance to
laterally directed forces by distributing
them over a large area.
• Post design should distribute stresses as
evenly as possible.


• Increase in post length decrease stresses.
• Parallel sided post more even stress distribution
than tapered post (wedging effect). But Parallel
sided post generate more stress at apex.
• Threaded post high stress conc during insertion
and loading.
• High stress during insertion of smooth parallel
sided posts as no place for escape for cement.
• Cement layer more even stress distribution.

Basic components used in
restoration of endodontically
treated tooth


• Restorations for endodontically treated
teeth are designed to :
• Protect remaining tooth from fracturing
• To replace missing tooth structure


• The final restoration will include a
combination of:
• 1. Dowel,
• 2. core
• 3. coronal restoration


Find a better pic
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Core: replaces lost coronal;
tooth structure and provides
retention for crown
Dowel: provides retention for
core and must be designed to
decrease the potential for root
fracture from functional forces.
Crown: restores the function
and esthetics and protects the
remaining root and coronal
structure from fracture.


• The selection of individual components will
depend on
• whether the tooth is anterior or posterior
• or whether significant coronal tooth
structure is missing.


• DOWEL


• dowel : a post, usually made of metal that is
fitted into a prepared root canal of a natural
tooth. When combined with an artificial
crown or core, it provides retention and
resistance for the .restoration (GPT-7)


• the dowel has both a retentive and protective
function:
• primarily to aid in the retention of the restoration
and
• to protect the tooth by dissipating or disbursing
forces along the length of the root.
• The dowel itself does not strengthen a tooth.
infact the tooth is weakened if dentin is sacrificed
to place a large diameter dowel.

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Ideal properties of the dowel.
Maximum protection of the root
Adequate retention within the root
Maximum retention of the core and crown
Pleasing esthetics, when indicated
High radiographic visibility
Retrievability
Biocompatibility

• CLASSIFICATION OF DOWELS


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By Stephen Cohen
Preformed dowels and custom cast dowels
Metallic and non metallic dowels
Rigid and flexible dowels
Aesthetic and nonesthetic dowels


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By Ricketts et al ( BDJ 2005;198: 533)
1 . Active Posts
A. Pre tapped posts
B. Self threading

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2.Passive Posts
A. Custom made or prefabricated
B. Parallel smooth or serrated
C.. Tapered smooth or serrated

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III
A.
B
C.
D.

Wein's Classification
Tapered smooth sided
Parallel, serrated and vented posts
Parallel threaded posts
Parallel threaded split shank posts.


give examples??
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Acc To Rosensteil
Prefabricated post
Tapered smooth sided posts
Tapered serrated posts
Tapered Threaded posts
Parallel smooth sided
Parallel serrated posts
Parallel Threaded posts

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Custom made post
Direct technique
Indirect technique

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Acc to material used
Wooden posts
Type III and Type IV gold alloy
Stainless steel
Gold Platinum alloy
Titanium/ Titanium alloy
Brass
Nickel chromium and Cobalt chromium
Cobalt chromium molybdenum alloy
Amalgam
Carbon fiber
Glass fiber
Ceramic Posts, Zirconium dioxide post

Retentive, Protective and
Esthetic qualities of
dowels


Retentive qualities:
• Dowel-to-root retention and
• Dowel-to-core retention.


Dowel retention varies with
• dowel design,
• dowel composition and
• cement type.


Dowel design and dowel retention


a) Dowel to root retention


Parallel sided

>


Tapered

Purton et al (IJP 1996;9:484)
Effect of serrations on carbon fiber
post retention within the root canal.


Increase in
dowel length




Increased
retention

• Variousdiameters for tooth ??? From
rosensteil


Dowel diameter
Increase in post diameter to increase
retention not recommended. weaken
root.


b) Dowel to core retention


One piece dowel
and core

>


Dowel with
locking feature

Large dowel head

>

Smaller dowel head


Dowel Composition and Dowel
Retention


• Dowel retention is a clinical quality that is
related to the underlying physical properties
of the dowel material. The inherent strength
of the dowel affects the dowel retention to
the root and to the core.


• Metal dowels are more fracture resistant 
more retentive than carbon fiber dowel


???
• Carbon fiber and glass fiberretained by
dentine bonding agents better retention


Core retention
• The composition of the dowel also affects
the ability to retain the core.


• Integrated dowel and
core systems in which
both the dowel and the
core are formed
simultaneously from
the same material
eliminate the dowel
and core interface.

• Dowel cementation and dowel retention.

• Retention for all types of dowels is
affected by the cement selection.


• zinc phosphate
• retention  mechanical means.
• no chemical bond to

dowel
or dentin
• lack of chemical bond  advantageous

• Glass ionomer cements
• bonds to dentin
• but not to dowel


• Resin cements examples?????
• bonds to dentin
• and most dowel materials


• Standlee et al (JPD 1992:68;913) did a study on
dowels retained by resin cements and concluded
these dowels achieved very high retention.
• Parallel dowels cemented with an adhesive cement
are equal in retention to screw type dowels,
without the inherent risk of screw threads in
dentine.
• This cement mediated maximum retention is not
risk free, as 80% of the roots fractured when
dowels were dislodged by force.

• Cement manipulation procedures and ease
of use  affect clinical retention of
cements to the dowel.

• Cement flow properties and consistency


• strength and retention of resin cements also
depends on complete setting.


• Protective qualities of dowels
• (resistance to root fracture )


• The dowel must furnish maximum
resistance to root fracture while providing
retention between the root and the core.


• Dowel design and resistance to root
fracture
• Dowel shape and resistance to root
fracture


• Parallel metal dowels distribute functional
loads to the root more passively than
tapered dowels.


• Isidor et al (IJP 1992;5:257)
• Martinez et al( JPD 1998;80;527)
• tapered dowels (including the customcast
dowel and core) that are closely adapted to
the internal shape of the root canal are more
likely to result in root fracture than are
parallelsided dowels.

• Self threading dowels high rates of root
fracture
• Standlee et al (JPD 1992:68;913)
• 40% of Self threading dowels failed by
angular and vertical root fracture.


??
• About fiber dowels>>>>> less fracture of
roos?????????????


• Dowel diameter and resistance to root fracture
•
• Sufficient to resist distortion and permanent
bending under functional forces
• Large risk of fracture
• Composition plays a role parallel metal
dowels narrower diameter than nonmetallic
dowelspreserve tooth structure.

• Dowel length’ and resistance to root fracture

• Long enough to reduce conc. Of force in areas embedded
in alveolar bone.
• Isidor F et al (IJP 1999;12:78)
 increasing dowel length from 5mm to 10 mm did not
increased the fracture resistance in teeth protected by
crowns designed with adequate ferrule.

• Dowel composition and resistance to root
fracture
• Metal and zirconia dowels stiffer than
dentinemore force conc. On root high chance
of root fracture
• Carbon fibre, glass fibre etcphysical properties
resemble those of dentineless force conc on root
(stress dissipated better) les chances of root
fracture.

ESTHETIC QUALITIES OF
DOWEL
• Metal and carbon fiber dowels non esthetic
not to be used in esthetically critical areas .
• Zirconia, fiberglas etc esthetic
• Zirconia stiffer than dentine esthetic
equivalent to preformed metal dowels.(fig??)


• ESTHETIC POST SYSTEMS


Carbon fiber post
(composipost(bisco)…), C
post(bisco) fig

• Introduced in 1990 by Duret .
• First non metallic post

• Consist of bundles of stretched carbon fibers
embedded in an epoxy resin matrix and aligned
along the long axis of post.
• Unidirectional fibers, 8 microns in diameter
• Carbon fiber by exerting uniform tension on the
filaments impart high strength to the posts.

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Advantage:
Clinical procedures are less time consuming
The modulus of elasticity of the metal post is ten times greater than
that of dentin. This incompatibility creates stress at the tooth cement
post interface occasionally causing post separation and failure.
Additionally the transmission of occlusal and lateral forces through the
metallic core can focus stresses at specific areas of the most anatomy
such as fulcrum resulting in fracture of remaining dentinal structure.
The carbon fibers have modulus of elasticity very similar to dentin,
this resemblance eliminates the stresses that are often formed at the
interface of different material.
Easy to remove for retreatment.


• Disadvantage
• Black colouunesthetic
• Radiolucencyvery difficult to detect
radiographically.
• Undergo degradation on repeated
mechanical loading and moisture
contamination reduced modulus of
elasticityrisk of debonding..

• Some studies??????


Ceramic posts
• have excellent esthetics and biological properties
• . Inherent weaknesses  low flexural strength and low
tensile strength prone to fracture.
• New ceramics like pressable ceramics, infiltrated
ceramics,and zirconia can be used.
• Zirconia posts high flexural strength and tensile
strength.
• Made from fined grained tetragonal Zirconium
polycrystals (TZP).

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Advantages
Good esthetics
Biocompatible
Other esthetic post systems lack strength,
Ceramic post are esthetic alternative to
metal posts.


• Disadvantages
• High chances of root fracture
• ?

• Trade names
• Cosmo post( Vivadent), Snow post (Danville?)??
• Biopost, TPZ post IPS Empress® Cosmo

• Glass fiber post
• Unidirectional glass fibers embedded in a
resin matrix


• Quartz fiber post(RTD post)


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Advantage:
Modulus of elasticity close to dentine
Esthetic
Made of resinbond strength of resin
cement enhanced.


• Disadvantage:
• Variable opacity
• Undergo degradation on repeated
mechanical loading and moisture
contamination reduced modulus of
elasticityrisk of debonding..


Polyethylene woven fiber
(Ribbond)
• Suggested for use with composite to
fabricate dowel and core.


• Intraradicular Rehabilitation
• Extensive decay or aggressive
instrumentation of the canal makes the
canal too wide for direct restoration. It is
difficult to position the post in an ideal
location for the subsequent restoration


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I. Luminex Light Transmitting
System( Dentatus)
The Light-Transmitting Technology
for restoring Structurally
Compromised Teeth
Fragile, thinwalled teeth
Extraction or cast post
Now luminex system
The clear light transmitting posts
polymerize lightcured composites
within the entire root canal. Luminex
light transmitting post (LTP) allows the
passage of light through its body but
does not bond to the composite resin..
After curing, the LUMINEX post is
removed, leaving a ready canal for a
corresponding metal post.


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Lucent Anchor system (Dentatus)
Fiber glass clear resin post

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designed to refract and transmit natural tooth
colors for esthetic post and core foundation.

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A benefit of the translucent anchor is that
it can be used with dual-cure resins and
bonding techniques, which allow sufficient
time for exact centering and seating of the
anchor, as well as a complete fill of the
composite inside the canal (

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radiolucent and is identified by surrounding
resin cement.

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luted to the post space by dual cure resin.
easy to remove for reaccess to the canals.


• Twin Luscent Anchors(Dentatus)


Anchor Design
Element

Benefit

Twin Luscent Anchor

Narrow radial
midsection

Mechanica
l
resistance

Provides double retention
against accidental debonding of
resins and other restorative
materials

Easy
release
Eliminates hydrostatic
of excess •Optimal choice for very
pressure
narrow and small canals,
resin
from 0.8 mm to 1.2mm

Original Luscent Anchor
•True taper

Longitudinal
vent-grove

Shape Matches
Root Form
•Twin Luscent and
Luscent Anchors
completely fit
within the confines
of natural teeth
•Anchor design is
Twin Luscent
tapered apically to
match root form,
minimizing

apical
seal

CEJ

Luscent

• II. Para Post Fiber White Post :
• The Para post fiber white post is a filled resin mono
directional fiber matrix with a flexural modulus
that very closely approximates that of the natural dentin.
The color of the post is white translucent, designed to
minimize shadowing under all ceramic restorations. The
parallel sided posts intended for passive seating in the
canal, and the antirotation I post head stabilizes the core
materials. The Parapost fibre which is available in four
diameters, color coded to match drills. The posts are
readily removed should endodontic retreatment be
necessary.

• III. FibreKor Post:
• The FibreKor post uses glass fibers bundled in a resin
matrix. The bundles are in turn impregnated with resin,
cured and precision milled. The white color of the post
blends in readily with dentin, eliminating the halo affect of
metal or
carbon fiber posts underneath allceramic restorations. The
modulus of elasticity of the FibreKor post is closely
matched to that of dentin, helping to distribute impact
forces more uniformly along the prepared canal interface.
The post is available in three diameters with sizematched
drills.

• IV. Aesthetic-Plus Post:
• The aestheticpost system is actually a series of
that can be used in a variety of situations. The
traditional posts are two stage fiber posts,
available in white or clear quartz fibers. There is
also a tapered white fiber post. The posts have
characteristics that are similar to their carbon fiber
ancestors, including high flexural strength and a
low modulus of elasticity. All the posts are
retrievable if required for endodontic retreatment.

D.T. LIGHT-POST (Bisco)
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constructed from unidirectional, pretensed, quartz
fibers bound in a resin matrix
produces a post with flexural strength exceeding that
of metal posts but with a modulus of elasticity very
close to that of dentin. dissipates stress rather than
transferring and concentrating stress in the residual
root structures
Because of its translucency, BISCO's D.T. Light
Posts will transmit light and can be used with light
cured or dualcured cements and adhesives.

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This post will intimately bond to the tooth structure
and core buildup composite

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This post is OPTICALLY TRANSLUCENT and
RADIOPAQUE, at the
same time.
Each of
the 3 sizes has an apical taper 0.02 (increase of
diameter/millimeter),
middle taper of 0.06, 0.08 and 0.10, and a parallel
coronal section for
maximum strength, surface area and core retention.

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ÆSTHETI-PLUSTM (2-Stage)
Aesthetic Fiber Post System
Bisco

• These posts can be
used with lightcured
or dualcured
adhesives.


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ParaPost fiber white (coltene
whaledent)
Glass Fiber 42%

White, translucent color minimizes the
possibility of shadowing in anterior
restorations.
Metalfree for esthetics and for patients with
metal allergies.
Flexural modulus measures closer to dentin
than other post materials.
Filled resin/unidirectional fiber matrix
strengthens the structure of the post without.
compromising flexibility.
Passive, parallelsided design mirrors the
qualities of metal ParaPostÆs.
Antirotational post head for excellent
adaptation of core material.
Specially fabricated to bond with most resin
cements and core materials.
Readily removed if endodontic retreatment
becomes necessary.
The posts are color coded for use with
existing ParaPostÆ drills.


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ÆSTHETIPOST® Carbon/Quartz

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FibreKor® Glass
Cosmopost™ Zirconium
Seventeen different FRC posts of various brands (Snowpost, Carbopost, Parapost, C
post, Glassix, Carbonite)

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CPOST (Bisco); G2: ÆSTHETIPOST (Bisco); G3: ÆSTHETIPLUS (Bisco); G4:
LIGHTPOST (Bisco); G5: D.T. LIGHTPOST (Bisco); G6: PARAPOST WHITE
(Coltene); G7: FIBERKOR (Pentron); G8: REFORPOST (Angelus).

• Snowpost (yellow) Unidirectional Silicazirconium fiber
(60 vol%) Carbotech, Ganges, France 1.2
• 2 Snowpost (red) Unidirectional Silicazirconium fiber (60
vol%

• In vitro comparison of the fracture resistance and
failure mode of fiber, ceramic, and conventional post
systems at various stages of restoration
• J Prosthodont. 2001 Mar;10(1):2636
• The fiber posts evaluated provided an advantage over a
conventional post that showed a higher number of
irretrievable post and unrestorable root fractures. At the
stage of final restoration insertion, there was no difference
in force to failure for all but the FibreKor material, which
continued to be weaker than all other tested materials. The
fiber posts were readily retrievable after failure, whereas
the remaining post systems tested were nonretrievable.

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AESTHETIPLUS
Quartz Fibers : 60 % volume
Epoxy Resin : 40 % volume

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AESTHETIPOSTCarbon Fiber Core: 10 % volume
Quartz Fiber Coating : 50 % volume

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COMPOSIPOST/CPOSTCarbon Fibers : 64 % volume

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D.T. LIGHTPOSTQuartz Fibers : 60 % volume

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RTD Fibre Posts

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Features of RTD Fibre posts
- Strongest of all the fibre posts in
existence (surviving where others fail)
- 4 times stronger than steel
- Post & Core formed in one office visit
- Integrates with & reinforces tooth
- Does not split roots
- Absorbs & Dissipates stress
- Widely researched & study supported
- Flexes with tooth
- Fatigue resistant
- Corrosion resistant, bonds with resin
cement
- Readily removable with re-access kit
Added advantages of Light Post
- Fibreoptic / light transmiting
- Translucent
- Aesthetic
- Ideal for an all ceramic restoration

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Double Tapered (DT) Light Post
The new double taper posts that
matches canal walls.
4 times stronger than steel
Tooth conservative
Reduces tooth stress
Tapers with canal walls
Resists dislodgment, is retentive and
has micromechanical attachement
Radiopaque
Light transmitting / fibreoptic
Flexes with dentine
Easily removed with Reaccess Kit
Translucent = invisible under
restorations
Aesthetic
Does not compromise colour of an all
ceramicc restoration


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The Original Light Post
The Light Post is the latest
evolution of the Composipost.
The Light Post's translucency
means it can be used with light
cured or dual cured cements
and adhesives. (Recommended
is Bisco's post cement HiX for
easy radiographic
identification.)
Parallel sided with step down
where the canal has already
been prepared.


Thank you
Leader in continuing dental education


Principles of tooth preparation /certified fixed orthodontic courses by Indian dental academy

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