• Finish line extending in the lingual aspect increases the mechanical
retention and increases the surface area for bonding.
• The prepared tooth surface is smoothened and all sharp line angles
FIGURE 24-3 Completed laminate preparation using finishing
endodontically treated tooth and ideal
During endodontic treatment of the tooth, intracoronal and
intraradicular dentines are removed which leads to changes in actual
composition of the remaining tooth structure. Restoration of
endodontically treated tooth is dictated by the amount of coronal
tooth destruction and location of the tooth. The changes occurring in
endodontically treated tooth are:
• Considerable removal of coronal dentine makes the remaining tooth
susceptible to fracture to even normal functional forces.
• An endodontically treated tooth becomes more brittle due to loss of
moisture and loss of vital dentine.
• Usually, the tooth is prone to get discoloured after endodontic
• Therefore, it is important to restore an endodontically treated tooth.
• A post provides retention for core and coronal restoration.
• It protects remaining tooth structure by dissipating the functional
forces along the length of the post.
• It reinforces the remaining tooth structure.
• It should provide adequate retention within the root.
• It should provide adequate retention of the core and the crown.
• It should have rigidity in comparison to the dentine.
• It should be aesthetic, if indicated.
• It should be easily retrievable.
Classifications of post and core systems
On the Basis of the Technique of Fabrication
• Parallel-sided, serrated and vented post, e.g.
• Tapered self-threading systems, e.g. Dentatus
• Tapered smooth-sided systems, e.g. Kerr, Ash
• Parallel-sided, threaded post systems, e.g. Radix
Anchor, Kurer Anchor post systems
• Parallel-sided, threaded, split shank systems, e.g.
On the Basis of the Fit of the Posts
• Threaded parallel/tapered posts
On the Basis of the Material Used
Prefabricated posts are commercially available in different shapes and
sizes. They are very popular because of their simplicity.
Salient features of prefabricated posts
• These have less chairside time with no laboratory procedure.
• These need single appointment.
• These are easy to temporize.
• Comparatively less tooth structure is removed.
• As these posts are prefabricated, they cannot be designed according
to the anatomy of particular root.
• If coronal tooth structure is less, these should be used with caution.
These can be made of either metal or nonmetal. These can be of
different types, namely, tapered, parallel-sided, carbon fibre post or
Some of the commonly used prefabricated posts are described
Tapered smooth-sided post (fig. 24-4)
• This is most widely used and is the oldest one.
• This is a cemented post which is least retentive.
• This should not be used in the teeth that are subjected to high
FIGURE 24-4 Tapered post: (A) smooth sided; (B) serrated;
Tapered post with self-threading screws
• This is more retentive than smooth-sided cemented post.
• This produces greatest stress in dentine during placement.
• There is a high chance of fracture of the remaining tooth.
Parallel-sided posts (fig. 24-5)
• These provide much greater retention than tapered post.
• These produce less stress in dentine.
• These are cemented posts which can be used where high functional
FIGURE 24-5 Parallel-sided posts: (A) smooth sided; (B)
• Nonmetallic post introduced by P.B. Duret, M. Reynaiid and F.
• It is more flexible than metal post and its rigidity is similar to
• It is available as tapered, parallel-sided, smooth or serrated forms.
• There are less chances of tooth fracture.
• It is less aesthetic due to its dark colour.
• Adhesive system forms weaker bond with carbon fibre post than
• It has lower elastic modulus than the carbon fibres.
• It can be made of E-glass (electrical glass) or S-glass (high strength).
• Glass fibre post can be made of quartz fibre additionally.
• Quartz is pure silica in crystallized form with low coefficient of
• It is aesthetically compatible.
• It has greater fracture resistance.
• It is useful in curing by transmitting light through the post.
• It flexes with tooth structure.
• Translucent posts allow light transmission during polymerization of
• It facilitates the union of remaining dentine with light-cured resin
cement to restore the lost dentine.
• It effectively cures the light-cure resin deep into the canal.
• It provides strong foundation for the restorations.
• It can be effectively used in high aesthetic regions.
• It is a prefabricated split shank, parallel-sided threaded post.
• It provides maximum retention.
• It has greater flexure and fatigue strength than metal or zirconium
• Its modulus of elasticity is close to dentine.
• Sandblasting the posts prior to cementation enhances their
Steps involved in fabrication of custom-made
The principles of tooth preparation for endodontically treated tooth
are the same as that for any tooth.
Steps involved in preparing these teeth are (Fig. 24-6):
(i) To remove root canal filling material
(iii) Fabrication of dowel core
FIGURE 24-6 Ideal requirements for post space preparation.
To remove root canal filling material
• Obturation of the root canal is first completed with gutta-percha.
• Gutta-percha is then removed either by heated endodontic plugger
• The apical seal should not be disturbed by any of the methods used.
• Minimum 3–5 mm of the apical seal should be left intact.
• Peeso reamers or Gates Glidden drills are commonly used for post
space preparation (Fig. 24-7).
FIGURE 24-7 Post space preparation done with Peeso
• Peeso reamer or low-speed drills of different sizes are used to
• The aim is to remove any undercuts and to receive an appropriate
• The post space should not be prepared more than one-third of the
• Tooth structure should always be preserved as much as possible.
• A custom made post can be fabricated using two techniques,
• Pattern is fabricated directly in the patient’s mouth using pattern
• Canal is lubricated and plastic dowel is extended to the apical end of
• Resin is incrementally added onto the plastic dowel and placed and
removed several times into the canal.
• The resin should not be allowed to harden to the prepared canal.
• This step is repeated until properly fitting resin-coated dowel is
• Pattern post is rechecked for its fit and ease of removability.
• Pattern post is invested and casted.
• An orthodontic wire of appropriate length is tried into the apical
• The wire is coated with tray adhesive and the canal is lubricated.
• A light body elastomeric impression material is coated on the wire
and the canal is filled with the material using lentulo spiral.
• Wire is placed into the canal and elastomeric impression material is
injected around and over the prepared tooth.
• Impression tray is loaded with medium-body elastomeric
impression material or heavy-body elastomeric impression material.
• The impression tray is inserted and removed after the
• The impression is evaluated and poured with stone to get a working
• Wax pattern is fabricated in laboratory with inlay pattern wax.
• Core of the dowel is fabricated with wax.
• Fabricated dowel core is invested and casted.
Ferrule is defined as ‘a metal band or ring used to fit the root or crown of a
Ferrule is provided by extending the axial wall of the crown apical
to the missing tooth structure. The circumferential band of cast metal
reinforces the coronal portion of the tooth. Ferrule effect is enhanced
by giving a bevelled finish line and when the walls are very close to
parallel. It improves the structural durability of the endodontically
restored tooth by counteracting the lateral forces exerted during the
placement of the post (Fig. 24-8).
• It counteracts the lateral forces during post placement.
• It counteracts the functional leverage forces.
• It counteracts the wedging effect of tapered post.
FIGURE 24-8 Restoration with ferrule effect.
Inadequate ferrule may result in:
• Post loosening and cement failure
Resin-bonded prosthesis can be defined as ‘a fixed dental prosthesis
that is luted to tooth structures, primarily enamel, which has been etched to
provide mechanical retention for the resin cement’. (GPT 8th Ed)
Resin-bonded bridges were first described by A.L. Rochette in 1973.
The primary aim of these bridges was to replace missing tooth with
maximum conservation of the tooth structure. Earlier, mechanical
retention was employed to retain the prosthesis but with introduction
of electrolytic etching, micromechanical retention was used to bond
• To replace missing anterior tooth in children or young adults
• Grossly damaged or restored abutments
• Insufficient enamel for bonding
• Inadequate occlusal clearance
• Patient allergic to base metal alloys (nickel)
• It involves minimum reduction of the abutment tooth.
• Usually anaesthesia is not required.
• Supragingival finish line is usually given which aids in proper
• Temporary crown is not required.
• Preparation is in enamel only.
• It results in increased patient comfort.
• It results in reduced chances of pulpal damage.
• It involves less chairside time.
• Longevity is less than conventional FPDs.
• Space correction is difficult with resin-retained bridge.
• Small laboratory error is difficult to correct.
Resin-bonded bridges can be classified into the following types on the
basis of type of retention employed by the retainer.
(ii) Mechanical retention – Rochette bridge
(iii) Micromechanical retention – Maryland bridge
(iv) Macroscopic mechanical retention – Virginia bridge
• A natural tooth or acrylic tooth was bonded onto
the proximal and lingual surfaces of the abutment
• Usually a wire or steel mesh is used to support the
connector with composite resin.
• Limited durability, therefore, should be used for
replacement for shorter duration.
(ii) Rochette bridge (Fig. 24-9)
• Rochette (1973) employed the mode of mechanical
retention by perforating the metal casting and
bonding onto the tooth structure by silane coupling
• The wing-like retainers with funnel-like perforation
were heavily filled with composite resin to bond
• Livaditis used it on the posterior tooth by
extending the winged metal casting interproximally
and occlusally on the abutment tooth.
Limitations of cast perforation technique
• Due to metal perforation, strength is compromised.
• Wear of resin at the perforation can lead to
marginal leakage, increased stress and abrasion.
• Adhesion provided by perforations is limited.
(iii) Maryland bridge (Fig. 24-10)
• G.J. Livaditis and V.P. Thompson (1981)
developed an electrolytic pit corroding technique
for etching base metal alloys.
• Livaditis and Thompson used 3–5% nitric acid with
250 mA/cm2 of current for 5 min, followed by
placing in 18% hydrochloric acid in ultrasonic
cleaner for 10 min to achieve internal etching of the
metal casting. This type of etched metal prosthesis
Advantages of etched cast retainers
• Retention is improved three-fold as compared with
• The retainer can be made in thin section which can
• External surface of the metal retainer is highly
polished and resists plaque accumulation.
• Procedure is technique sensitive.
• Contamination of the surface decreases the bond
(iv) Virginia bridge (Fig. 24-11)
• It is based on lost salt crystal technique.
• P.C. Moon and J.L. Hudgins, F.J. Knap
incorporated salt crystals on the retainer pattern to
produce roughness on the internal surface of the
• Working cast is the first model sprayed and outline
of the framework is made on the abutment.
• Within these outline, cubic salt crystals of specific
size are sprinkled on the die leaving 0.5–1.0 mm
margin as crystal free around the outline.
• Retainer patterns are then fabricated with acrylic
• Patterns are removed after resin is polymerized
completely, cleaned, and placed in water to
• Cubic voids on the pattern are replicated in the cast
retainers which provide a mode of retention of
• Internal surface of the retainer is treated by air
abrasion with aluminium oxide.
• Nickel–chromium alloys required oxidation with
dilute solution of sulphuric acid and potassium
(v) Cast mesh FPD (Fig. 24-12)
• In this technique, net-like nylon mesh is placed on
the lingual surface of the abutment tooth on the
• This is then included in the retainer wax pattern.
• The wax pattern is casted in conventional manner.
• Meshed internal surface is seen on the cast retainer
which eliminates the need to etch the casting.
• This technique can be used in noble metal alloys.
• Its retentive ability is compromised, if mesh is
blocked during wax pattern fabrication.
FIGURE 24-9 Rochette resin-bonded fixed partial denture.
FIGURE 24-12 Cast mesh fixed partial denture.
In spring-retained FPD, the pontic is connected to the retainer with
flexible palatal bar (Fig. 24-13).
• A tooth and tissue-borne prosthesis where the masticatory forces
from the pontic are transmitted to the palatal mucosa before
FIGURE 24-13 Spring-retained FPD.
• Only one tooth, usually the posterior tooth, is prepared to be the
• It is the only design where diastema on either side of the pontic can
• Flexion of the palatal bar bears the forces and acts as a shock
• It is difficult to fabricate.
Resin cements used to lute FPDs
Resin cements have evolved rapidly in recent years.
• These are flowable composites of low viscosity.
• Initially, unfilled resin was used to lute perforated retainers.
• Then unfilled/filled composite resin with thin film thickness was
specifically used to bond resin-bonded bridges.
• Dentine bonding agents are incorporated into the cement as most of
the preparation is in dentine.
• HEMA (hydroxyethyl methacrylate), 4-META (4-methacryloxyethyl
trimelliate anhydride), and an organophosphate, such as 10-
methacryloxydecamethylene phosphoric acid, were incorporated
• The most commonly used resin cements are chemically-cure system
or light-cure system or dual-cure systems.
• Resin cements are insoluble in oral fluids.
• Chemically activated resin cements are supplied as two pastes; both
pastes are mixed on mixing pad for 20–30 s and used to lute crowns
• Light-cure resin systems are single component systems used to lute
resin-bonded prosthesis, veneers or orthodontic brackets.
• Dual-cure resin system again is supplied as two pastes. Chemical
activation is slow and it provides extended working time till the
time light is shown, thereafter it cures rapidly.
• Dual-cure cements should be used in prosthesis which has thickness
of up to 2.5 mm; beyond this, chemically activated resin should be
• Dual-cure cements have become the most commonly used luting
agents to bond FPDs in recent times.
• The excess cement should be removed before the cement fully
• Tin plating can improve bonding of noble metal alloys.
• Air abrading surface of base metal alloys with 50 microns alumina
particles improves its bonding.
• Silica bonding can again improve bonding to both noble metal and
CAD/CAM assistance in fixed prosthodontics
Duret developed the Duret system which is a CAD/CAM system
capable of generating single unit and multiple unit restorations.
• 1957: Dr Patrick J. Hanratty – father of CAD/CAM technology–
developed CAM software program called PRONTO
• 1971: Dr Francois Duret (France) – first dental CAD/CAM device
• 1979: P. Heitlinger and F. Rodder milled the equivalent of the stone
model used by a dental technician to make the crown, inlay or
• 1983: Dr Matts Anderson (Sweden) developed Procera.
• 1983: First CAD/CAM restoration by Dr F. Duret – introduced in the
Ganaciene Conference (France).
• 1985: Dr Werner Mormann and Dr Marco Brandestini
(Switzerland) – first commercial CAD/CAM system (CEREC).
• 1980s: Dr Dianne Rekow (USA) developed CAD/CAM system
using photographs and high resolution scanner – mill restorations
• A digitalization tool/scanner: It is an optical or mechanical scanner
(Fig. 24-14A). Optical scanner works on ‘triangulation procedure’,
e.g. Lava Scan ST and Everest scan. In mechanical scanner, master
cast is read mechanically line-by-line by a ruby ball to measure the
three-dimensional structure, e.g. Procera scan.
• Software that process data: Its basis is STL (standard
transformation language) data (Fig. 24-14B).
• Production technology: Subtractive manufacturing or additive
manufacturing (Fig. 24-14C). Subtractive manufacturing, e.g. CNC
(computerized numerical control) machining; additive
manufacturing, e.g. rapid prototyping.
FIGURE 24-14 Components of CAD/CAM system.
Processing devices distinguished by means of the number of milling
axis – 3-axis devices, 4-axis devices and 5-axis devices.
• Chairside production: Fabrication of restoration is done chairside in
one appointment, e.g. Cerec system (Sirona).
• Laboratory production: It is done on the master cast; 3D data are
formed in the laboratory with scanner. After this, CAD data
production restoration is fabricated by a milling machine.
• Centralized fabrication: It is done in a production centre.
Centralized production is done in a milling centre. Satellite scanners
in laboratory are connected with production centre via internet, e.g.
CAD/CAM manufacturing is done by two methods:
(ii) Subtractive manufacturing
Additive manufacturing or 3D printing
‘Additive manufacturing is a process of joining materials to make objects
from three-dimensional (3D) model data, usually layer upon layer, as
opposed to subtractive manufacturing methodologies’. [ASTM International
The process of additive manufacturing involves using images from
a digital file to create an object by laying down successive layers of a
Application of additive manufacturing in prosthodontics
• Fabrication of ceramic inlays, onlays, crowns and bridges
• Fabrication of maxillofacial prosthesis, drug delivery
• Used for making surgical guides for implant placement
• Used for fabrication of temporary crowns and bridges
• Used for fabricating customized implants
• Used for modelling scaffolds for tissue engineering and organ
• Used as ceramic paste for creating bone and bioresorbable polymers
• Used in direct metal laser sintering (DMLS) technique
• Laminated object manufacturing
• Laser powder forming techniques
• Selective electron beam melting
It involves removal of material from the raw block to obtain object of
desired shape and size through milling or unconventional machining
such as laser machining, electrical discharge machining.
• It uses images from a digital file to create an object by machining
(cutting or milling) to physically remove material and achieve the
• It is widely used in prosthodontics.
• It is the modern method of designing, developing and producing
restorations partially or completely.
• To design and mill metal, alumina and zirconia frameworks
• To scan and mill all ceramic crowns and bridges
• To fabricate inlays, onlays and ceramic laminates
• To fabricate stronger and better-fitting restorations
• Maxillary first molar has maximum root surface area of 433 mm²
and mandibular first molar has root surface area of 431 mm²; among
anterior maxillary teeth, canine has maximum root surface area of
273 mm² and mandibular central incisor has minimum 154 mm²;
among posterior mandibular teeth, first premolar has minimum
• Tooth preparation becomes difficult, if the long axis of the tooth
diverges or converges more than 25º from parallelism.
• Multirooted posterior teeth provide better periodontal support
• Bending or flexion of the fixed bridge varies directly to the cube of
the length and inversely with the cube of cervicoincisal thickness of
• More parallel the opposing walls of the preparation, more will be
• Optimum taper for prepared walls is 2–6º.
• For short clinical crown, additional retentive features such as
grooves, pins, slots and boxes are advocated.
• Self-threading pins are about five times more retentive than
• Ferrule helps in binding the remaining tooth structure together
preventing root fracture during function.
• Lost salt technique is used to fabricate Virginia bridge.
• Rochette bridge was the first used perforated retainer.
• Maryland bridge is the etched metal prosthesis.
• Single piece platinum reinforced porcelain bridge is called Swann
Preparation of Full Cast Crown, 368
Buccal Reduction and Lingual Reduction, 369
Finishing the Preparation, 369
Preparation for Partial Veneer Crown, 370
Preparation for PFM Crown, 372
Successful fixed prosthodontic treatment warrants successful crown
preparation. The crown preparation is essentially governed by the
Principles of Tooth Preparation
• Conservation of tooth structure
• Preservation of periodontium
(I) Conservation of tooth structure
Sound tooth structure should be conserved as far as
possible. Unnecessary reduction of the tooth should
be avoided. Even grossly damaged tooth should be
preserved with post and cores after endodontically
Simple guidelines to ensure preservation of tooth
structure during crown preparation:
• By giving minimal taper to the axial wall of the
• By following the anatomic planes during tooth
• By selecting a conservative finish line for the
• By avoiding unnecessary extension of the
• By preferring partial veneer restoration over full
veneer restoration when indicated.
Retention prevents the restoration from getting
dislodged by forces parallel to the path of
withdrawal. Retention is defined as ‘that quality
inherent in the dental prosthesis acting to resist the
forces of dislodgement along the path of placement’.
• Resistance is ‘the ability of the restoration to resist
its dislodgement by apically or obliquely directed
• Retention and resistance are often inter-related
properties in tooth preparation.
Some of their features are mentioned as follows:
More parallel the axial walls of preparation, more is
the retention. However, achieving parallel walls is
almost impossible and, therefore, 3–6° of taper is
recommended for optimum retention.
If the taper is increased by more than 20°
concentration increases sharply on the abutment
tooth. Therefore, during tooth preparation, taper
should be kept minimum for maximum retention.
Retention and resistance also depend on the surface
Greater the surface area of the prepared tooth, greater
is the retention. Preparations on the larger teeth are
more retentive than preparation on the smaller
teeth. Surface area can be enhanced to a limited
extent by providing features such as boxes and
• Retention is proportional to the paths of insertion
and removal. Maximum retention is achieved, if the
preparation has only single path of placement and
least when there are multiple paths.
• Resistance is also dependent on freedom of
displacement. More the freedom of displacement is
limited to twisting and torquing forces in a
horizontal plane, more will be the resistance of the
• Walls of the preparation should be made
perpendicular to the direction of force for adequate
• The occlusogingival height of the preparation is an
important factor for both retention and resistance.
• Longer preparation has more surface area and,
therefore, more retention. Longer preparation with
less inclination of the axial walls also enhances the
• Resistance to displacement for a short-walled
preparation on a large tooth is improved by adding
grooves or boxes on the axial walls.
(d) Substitution of internal features
• Resistance and retention can be improved by
incorporating internal features such as boxes, grooves
and pin holes on inclined axial walls.
• Substitution of internal features is done in cases
where it is difficult to achieve retention such as
overtapered short preparation, partial veneer
It is defined as ‘the specific direction in which a prosthesis
is placed on the abutment teeth or implant’. (GPT 8th
• It is important to survey the abutment teeth before
and during preparation visually to detect any
undercut or overtapering. Usually, one eye should
be closed to detect undercut in prepared tooth.
• Path of insertion should be considered
faciolingually and mesiodistally. The faciolingual
inclination of the path of insertion should be
avoided in porcelain fused to metal (PFM) or
partial veneer crown preparation, as it affects the
• Mesiodistal inclination of the path of insertion
should parallel the contact areas of the adjacent
Sufficient tooth structure should be removed in order
to create a space to accommodate adequate bulk of
restorative material which can withstand the
functional forces. The bulk of this material provides
adequate rigidity to the prosthesis and ensures its
Preparation Features that Ensure Durability
During preparation of the tooth structure, adequate
clearance is provided for the restorative material to
• The reduction should be done along the geometric
inclines of the natural tooth and the occlusal surface
should not be made flat, as it tends to shorten the
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