Dr S Mukhtarun Nisar Andrabi Assistant Professor Conservative Dentistry amp Endodontics Contents Introduction Historical Perspective Indications amp Contraindications Advantages amp Disadvantages ID: 911740
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Slide1
Cast Metal Restorations
Dr. S. Mukhtar-un- Nisar Andrabi
Assistant Professor
Conservative
Dentistry & Endodontics
Slide2Contents
Introduction
Historical Perspective
Indications & Contraindications
Advantages & Disadvantages
Tooth preparation for Cast Restorations
General Principles Bevels, Margins & Flares
Preparation for Metal Inlays & Onlays
Partial & Full Cast Crown
Step By Step Procedure For Cast Restorations
Conclusion
Slide3Introduction
TOOTH PREPARATION
:“Tooth preparation is defined as the mechanical alteration of a defective, injured, or diseased tooth to best receive a restorative material that will reestablish a healthy state for the tooth, including esthetic corrections where indicated along with normal form and function”
Slide4Introduction contd.
RESTORATION :
“Restoration is defined as any material or prosthesis that restores or replaces lost tooth structure, teeth or oral tissue.
CAST
: “Life size likeness of some desired form” “To produce a shape by thrusting a molten liquid or plastic material into a mold possessing the desired shape” Casting: “Something that has been cast in a mold; an object formed by the solidification of a fluid that has been poured or injected in a mold”
(Glossary of
Prosthodontic
Terms - 8)
Slide5Historical Background
1835 –
John Murphy First Inlay Fabricated Porcelain inlays
1880 –
Ames & Swasery Used burnished foil technique for fabricating Inlays
1897
- D. Philbrook First CAST INLAY is attributed to him Introduced the concept of forming an investment around a wax pattern Eliminating the wax and filling the mold with a “Gold alloy”
1907
– W.M. Taggart “Lost wax technique” Reported the development of “Pneumatic Pressure Casting” Introduced the technique for Cast Gold Dental restorations Popularized the Gold Inlay as a Dental restoration
Slide6Indications
Replace lost tooth structure (In extensively involved teeth)
Restoration of
endodontically
treated teeth
correction of Occlusion & Diastema closure
support for partial or complete dentures
Retainers for fixed prosthesis
partially sub-gingival restorations
Cracked teeth (Vertically, horizontally or diagonally)
As an adjunct to successful PDL therapy by correction of tooth anomalies which predispose to PDL problem
Slide7Contraindications
Developing or deciduous teeth
High Plaque or Caries indices
Occlusal disharmony
Dissimilar metals
Small restorations
Esthetics
Slide8Advantages
Higher strength (Compressive, Tensile, Shear & Yield)
Ability to reproduce precise form and minute details
Control of contours and contacts
Biocompatibility of materials (Noble or passivated alloys)
Not affected by tarnish & corrosion
Increased longevity
Fewer voids, less internal stresses, no layering effect when compared to amalgam
Cast restorations can be better finished, polished or glazed, thus better tissue tolerance & no harm to PDL organ
Slide9Disadvantages
Technique sensitive
No. of appointments
Higher chair time
High Cost
Splitting forces
Slide10Mouth preparation prior to Cast Restorations
Every measure is to be taken to ensure longevity & success of a cast restoration
Control of Plaque
Control of Caries
Control of periodontal problems
Control of pulpal health of tooth
Slide11Initial Procedures
1.Occlusion
2.Anesthesia
3.Consideration for temporary restorations
Slide12Occlusion.
Before an anesthetic is administered and before preparation of any tooth, evaluate the occlusal contacts of the teeth.
An evaluation should include:
(1) the occlusal contacts in maximum intercuspation
(2) the occlusal contacts that occur during mandibular movements
The pattern of occlusal contacts influences
the preparation design,
the selection of interocclusal records, and
type of articulator or cast development needed.
Slide13Anesthesia.Local anesthesia of the tooth to be operated on, as well as the adjacent soft tissues, usually is advocated.
Anesthetizing these tissues eliminates pain and reduces salivation, resulting in a more pleasant operation for both the patient and the operator.
Slide14Temporization
Before preparation of the tooth, consideration must be given to fabricate the temporary restoration.
Most temporary restoration techniques require the use of a preoperative impression to reproduce the occlusal, facial, and lingual surfaces of the temporary restoration to the preoperative contours
Slide15Principles of preparation for indirect restorations
(1) Preservation of tooth structure
(2) Retention and resistance
(3) Marginal integrity
(4) Strength and structural durability
(5) Occlusal stability
Slide16Preservation of Tooth Structure
• Protection from fracture and wear
e.g. Providing cuspal coverage
• Pattern of tooth substance removal
e.g. Anatomical reduction.
• Type of restoration
The mechanical characteristics of the material chosen will dictate the amount of tooth substance removed
Slide17Retention & Resistance
Retention prevents removal of the restoration along the path of insertion or long axis of the tooth preparation
Resistance prevents the dislodgement of the restoration by forces directed in an apical or oblique direction and prevents any movement of the restoration under occlusal forces
Slide18Retention & Resistance
General features of tooth preparation:
A). Preparation Path:
Prep should have a “Single Insertion path”
Path is parallel to long axis of tooth crown
Helps in retention & decreases the micro movements of restoration during function
All reductions in tooth structure should be oriented towards ONE path (Withdrawal & Insertion path of future wax pattern)
B). Apico-Occlusal Taper:
For max retention, opposing walls & axial surfaces should be perfectly parallel to each other
C).
Circumferential Tie:
The peripheral marginal anatomy of the preparation is called as the “Circumferential Tie”
Slide19Retention Features
1) Principal/Primary Retention forms:
Box preparation and flat floor
Parallelism: internal walls must be almost parallel
Dovetails : occlusal dovetails aid in retention
Surface area- frictional retention
Masticatory loads directed to seat the restoration
2) Secondary/Auxiliary Retention forms :
Grooves , pins , slots, skirts etc.
Luting Cements: Their action is primarily mechanical, locking the cast to tooth structure by filling the space between them. Luting cements used: Type I GIC, Zinc Polycarboxylate
Slide20Grooves
Located completely in
dentin and extend
upto
the entire wall.
Can be located at the mesial & distal wall/the gingival floor of the facial or lingual portion of a cavity preparation
Should be located as internally as possible, adjacent to the axial wall
Prevent lateral displacement of the mesial, distal, facial & lingual parts of restoration
Can also be located externally in extra coronal preparation, they can be placed anywhere where there is sufficient dentin bulk without impinging on the pulp chamber, root canal system or other anatomy
Slide21Internal proximal grooves for added retention
Inclusion of external facial grooves
Slide22Resistance to lingual & rotational forces may be provided by proximal grooves
Internal grooves can be prepared in walls of inlays for added retention
Slide23Slots
Slot is a internal cavity within a floor of preparation having a continuous surrounding walls & floors
Junction between the floor & surrounding walls is round
Slot should have a 2 to 3 mm depth
The slot is cut in dentin so that if it were to be extended gingivally, it would pass midway between the pulp and the DEJ
Slide24A and B, Cutting distal slot for retention for MO onlay to treat terminal molar having large cement base (x) resulting from extensive occlusal and mesial caries. C, Section of A
D and E Preparing mesial slot for retention for DO onlay to treat maxillary first premolar
F, Section of D.
Slide25Skirts
Skirts are thin extensions of the facial or lingual proximal margins of the cast metal onlay that extend from the primary flare to a termination just past the transitional line angle of the tooth.
A skirt extension is a conservative method of improving both the retention form and the resistance form of the preparation.
Usually the skirt extensions are prepared entirely in enamel.
The addition of properly prepared skirts to three of four line angles of the tooth virtually eliminates the chance of post restorative fracture of the tooth because the skirting encompasses and braces the tooth against forces that might otherwise split the tooth.
Slide26Depth cut for skirt
Blending of the skirt with primary flare
Slide27Indications For Skirting
The addition of skirt extensions is recommended:
For teeth that exhibit the split-tooth syndrome.
when the proximal surface contour and contact are to be extended more than the normal dimension to develop a proximal contact.
when improving the occlusal plane of a mesially tilted molar by a cusp capping onlay
when splinting posterior teeth together with onlays.
Slide28Contraindications
skirts are not placed on the
mesiofacial
margin of maxillary premolars and first molars because of esthetic reasons.
A disadvantage of skirting is that it increases the display of metal on the facial and lingual surfaces of the tooth.
Slide29Collar PreparationTo increase the retention and resistance forms when preparing a weakened tooth for a MOD onlay capping all cusps, a facial or lingual "collar," or both, may be provided
facial surfaces of maxillary premolars and first molars are not usually prepared for a collar.
Slide30A, First position of bur in preparing for lingual collar on weakened maxillary premolar. Section drawings of first position of bur and
second and third positions (C). D, Beveling lingual margin. E, Completed preparation. F, Completed onlay
Slide31Structural DurabilityStructural durability of a cast restoration depends upon the following:
Occlusal reduction
Functional Cusp Bevel
Axial Reduction
Slide32Marginal Integrity
The margin of the restoration (or finishing line) is the area at which the restoration ends and presents a junction of restorative material and tooth substance at the tooth surface.
In determining the shape of tooth reduction at the margin, the aim must be to produce as small a marginal gap or discrepancy as possible.
Slide33Marginal Integrity
Marginal integrity is an important aspect of a restoration.
The peripheral marginal anatomy of the preparation should exhibit the “Circumferential Tie”& Should fulfill the requirements advocated by Noy:
If the prep ends on enamel, the enamel must be supported by sound dentin
Enamel rods forming the cavosurface margin should be continuous with sound dentin-
FLARES
Enamel rods forming the cavosurface margin should be covered with a restorative material-
BEVELS
Angular cavosurface angles should be trimmed
Slide34Sub-gingival MarginsA sub-gingival margin may be inevitable when:
Caries or a crack extends subgingivally.
A restoration extends subgingivally.
Extra axial length is required for retention.
Aesthetics are essential
Slide35Margin configurations
Slide36Bevels
Cast metal restorations require beveled margins
Bevels
are defined as “flexible extensions” of a cavity preparation, allowing the inclusion of surface defects, supplementary grooves and other areas on the tooth surface.
Bevels create an obtuse angled marginal tooth structure (Strong tooth anatomy)
Produce an acute angled marginal cast alloy (most amenable to finishing & burnishing)
Slide37Types Of Bevels
Partial Bevel:
Involves part of the enamel only.
Not used in cast restorations
Short Bevel
:
Includes entire enamel wall but no dentin
Long Bevel
: Includes all of the enamel wall and up to one half of the dentinal wall Most frequently used bevel for cast materials
Full Bevel:
Includes all of the dentinal and enamel wall Well reproduced by all 4 classes of cast alloys
Deprives prep of internal resistance & retention
Counterbevel
:
When capping cusps this protects & supports them. Given opposite to an axial wall on the facial and lingual surfaces .
Slide38Functions Of The Bevels
Beveling can serve four useful purposes in the tooth preparation for a casting:
it produces a stronger enamel margin,
it permits a marginal seal in slightly undersized castings
it provides marginal metal that is more easily burnished and adapted, and
it assists in adaptation of gingival margins of castings that fail to seat by a very slight amount.
The bevel of the margin in a preparation for castings should produce a cavosurface angle that results in
30- to 40-degree marginal metal
Slide39Facial and Lingual Flares
Primary Flare:
Conventional & basic part of circumferential tie facially & lingually for an Intra-coronal prepn.
Similar to a Long bevel (enamel & part of dentin)
Specific angulation - 45° to the Inner Dentinal wall proper
Brings the facial and lingual margins of the cavity prepn to cleansable – finishable areas
Indicated for the facial and lingual proximal walls of an intra-coronal prepn
Slide40Secondary FlareIs always a flat plane superimposed peripherally to a primary flare
Prepared solely in Enamel (may contain dentin)
Has various angulations depending on the involvement, extent and function
Importance :
Extends the margins into the embrasures, making these margins more self-cleansing and more accessible to finishing procedures during the inlay insertion appointment
Results in 40-degree marginal metal
A more blunted and stronger enamel margin is produced because of the secondary flare.
Slide41Tooth Preparation for Inlays
An Inlay is an intra-coronal cast restoration which involves the occlusal and proximal surfaces of a posterior tooth
The preparation should be as conservative as possible
Occlusal width of the preparation should not exceed 1/3
rd
of the Intercuspal distance
The occlusal contacts should be entirely on gold or enamel & not on the margins of the restoration
First occlusal preparation is done & then proximal box is prepared
Maintain the long axis of the bur parallel to the long axis of the tooth crown at all times
Slide42Proposed outline form for DO preparation. B, Dimensions and configuration of No. 271, No. 169L, and No. 8862 instruments.
C, Conventional 4-degree divergence from line of draw (line xy).
Slide43Punch cut to a depth of 1.5 mm to establish the depth of
the pulpal wall
Dovetail retention form is created by extension
Dovetail portion of inlay fits into dovetail portion of preparation only in
an occlusal-to-gingival direction
Slide44Slide45Occlusal Preparation Of Inlay
Slide46Proximal Preparation For Inlay
Slide47Slide48Slide49Slide50Slide51Tooth Preparation For Onlayscast metal onlay by definition caps all of the cusps of a posterior tooth and can be designed to help strengthen a tooth that has been weakened by caries or previous restorative experiences
.
The cast metal onlay restoration spans the gap between the inlay, which is primarily an intracoronal restoration, and the full crown, which is a totally extracoronal restoration.
Slide52Tooth Preparation For Onlays
Slide53Tooth Preparation For Onlays
Slide54Partial Coverage restorations
Covers only a portion of the outer circumference of the tooth but completely covers the occlusal surface.
Advantages of partial-coverage restorations include:
Preservation of tooth structure due to part of the clinical crown not being reduced
Natural landmarks more likely to be preserved
Better seating on cementation
Access for pulp testing is maintained.
Slide55Disadvantages of partial-coverage restorations include:
Limited retention and resistance form.
Aesthetic limitations.
Technically demanding
Partial-coverage Restorations Include:
Three quarter crown:
indicated when buccal cusp is intact & needs to be protected for esthetics
Seven eight crown :
indicated when a tooth needs cuspal coverage but a sound mesiobuccal cusp is present
Slide56¾ Crown On A Maxillary Premolar
7/8 Crown On A Maxillary Molar
Occlusal View Buccal View
Slide57Full Cast Crown
It includes the coverage of the entire coronal portion of the tooth
Indication :
extensive loss of tooth structure is the most common indication
Correction of malposition occasionally
It is the most retentive of the casting designs
Retention is provided primarily by extracoronal walls
Slide58Full Crown tooth preparationProximal reduction
Occlusal reduction
Facial & lingual (axial) reduction
Refinement
Slide59Step By Step Procedure For Cast Metal Restorations
Mouth preparation
Tooth preparation
Interocclusal records
Temporization
Final impression
Working casts and dies
Wax patterns
Spruing, investing, and casting,
Seating, adjusting, and polishing the casting
Trying-in the casting,
Cementation
Slide60Interocclusal Records
Before preparation of the tooth, the occlusal contacts in MI and in all lateral and protrusive movements should be carefully evaluated.
The necessary registration of the opposing teeth can be obtained by
(1)making a MI
interocclusal record with commercially
available bite registration pastes or
(2) making full-arch impressions and mounting the casts made from these impressions on a simple hinge articulat
or
Slide61Temporization
Between the time the tooth is prepared and the cast metal restoration is delivered, it is important that the patient be comfortable and the tooth be protected and stabilized with an adequate temporary restoration.
Temporaries can be fabricated:
Intraorally directly on the prepared teeth
(direct technique)
Outside of the mouth using a postoperative cast of the prepared teeth
(indirect technique).
Slide62Fabrication Of Direct Temporary Restoration
Slide63Final Impression
The most common impression materials used for the indirect casting technique are the
polyvinyl siloxanes (addition reaction
silicones).
Impression Technique:
Tissue retraction:
Mechanical- Copper Band, Rotary Curettage
Chemomechanical- Retraction Cords
Electrosurgery
Tray Selection and Preparation
Inject light-bodied material around the preparation
Make the full impression with light body
Removing and Inspecting the Impression
Slide64Working Casts And Dies
The working cast is an accurate replica of the prepared and adjacent unprepared teeth
A working cast with removable dies of the prepared teeth is desirable
Individual die preparation is done by two pours –
PINDEX SYSTEM
Slide65PINDEX SYSTEM
Base of die segment is trimmed flat and approximately parallel to the occlusal surfaces with a model trimmer. Dies should be approximately 15 mm tall occlusogingivally
.
Die segment on Pindex machine, ready to drill hole, & holes drilled on die
Dowels inserted into the holes with cynoacrylate
Slide66Painting of separator
Boxing of the cast
Final cast
Separation of base
Cutting of individual dies & trimming of removable dies
PINDEX SYSTEM
Slide67Wax Patterns
Direct Technique:
a pattern directly intra-orally from the tooth itself.
Indirect Technique:
a wax pattern formed on the prepared die
Slide68Spruing, Investing, And Casting
A sprue must be attached to the bulkiest portion of the wax pattern & it must be at an obtuse angle to the pattern & should be directed away from thin or delicate parts of the pattern
Wax patterns must be invested without any delay to avoid distortion, if delay is unavoidable the pattern must be stored as seated on the die.
Investments:
Gypsum Bonded- Gold Alloys
Phosphate Bonded- Base Metal Alloys
Casting
Centrifugal
Induction based
Slide69Types Of Casting Alloys
CLASS –I
These are gold based alloys and includes all four types of gold alloys
CLASS-II
low gold alloys with gold content as little as 5%
CLASS-III
Non-gold platinum based alloys
CLASS-IV
nickel chromium based alloys
CLASS-V
Castable moldable ceramics
Slide70Seating, Adjusting, and Polishing the Casting
The internal margins are inspected under magnification and adjusted as necessary with small diamond stones and carbide burs. Adjustments are restricted to areas where binding contact occurs.
The sprue is removed by abrasive (carborandum) discs. Discs and stones are used for gross recontouring at the attachment area.
A fine grit sand paper disc is applied for removing pits and irregularities from the axial walls.
Rubber points and small carbides are used for selective finishing of occlusal morphology.
Final polishing of the surface are done using rouge on a brush.
The polished restoration is then cleaned using an ultrasonic cleaner.
Slide71Adjusting, and Polishing the Casting
Slide72Try In Of Casting
Initially seat casting on tooth by applying ball burnisher in pit anatomy
Ensure complete seating using masticatory pressure by having patient close on Burlew wheel interposed between casting and opponent tooth
Inspect marginal fit within 0.2 mm of seating
If the discrepancy is greater than 0.2mm the casting should be discarded
Slide73Cementation
Cement Selection
.
Cementation Technique
Isolate the tooth from saliva with the aid of cotton rolls (and saliva ejector if necessary) dry the preparation walls, but do not desiccate them
Mix the cement following the manufacturer's instructions
Apply the cement mix generously to the preparation side of the casting
Place the casting with the fingers or with operative pliers
Place a Burlew disc over the casting, and request the patient to close and exert biting force
After the cement has hardened, excess is cleaned off with an explorer and air-water spray
A cement line should not be visible at the margins
Slide74Conclusion
Cast metal inlays and onlays offer excellent restorations that may be underutilized in dentistry. The technique requires multiple patient visits and excellent laboratory support, but the resulting restorations are durable and long lasting.
Cast metal onlays in particular, can be designed to strengthen the restored tooth while conserving more tooth structure than a full crown.
Disadvantages such as high cost and esthetics limit their use, but when indicated they provide a restorative option that is less damaging to pulpal and periodontal tissues than a full crown
.
Slide75