RESTO II:Chapter 17:

Class II Cast Metal Restorations

Cast Metal Restoration: -versatile -applicable to class II onlay preparation

▪Inlay: involves occlusal surface and one or more proximal surfaces of posterior tooth.

▪Onlay: involves cusp tips.

Introduction:

INLAY VS. ONLAY

Indications:Large RestorationsEndontically Treated TeethTeeth at Risk for FractureDental Rehabilitation with Cast Metals

AlloysDiastema Closure and Occlusal Plane

CorrectionRemovable Prosthodontic Abutment

High Carries rateYoung PatientsEstheticsSmall Restorations

Contraindications:

Advantages:

StrengthBiocompatibilityLow Wear Control of Contours

and Contacts

Disadvantages:

Number of Appointments and Higher Chair Time

Temporary Restorations

CostTechnique

SensitivitySplitting Forces

Class II Cast Metal Inlays

Initial Preparation:Carbide burs: 271-Tapered Fissure Bur 169L-Elongated Tapered Fissure Bur

Tooth Preparation for Class II Cast Metal Restoration

smooth vertical walls

Diamond bur: 8862-Flame-shaped marginal

bevels

Occlusal Step: No.271 burPunch cut: 1.5mm depth

Outline preparation extends mesially along the central groove or fissure to include the mesial fossa or pit.

Minimal facio-lingual cut.

Proximal box:No.271 burProximal ditching: mesiodistal width 0.8mm

approximately two thirds (0.5mm) of dentin and one third (0.3mm) of the expense of enamel.

•Final preparation:Removal of Infected Carious Dentin and Pulp

Protection:

No.2 or 4 bur-Round bur/Spoon Excavator-Used to excavate extensive carries

Glass Ionomer-BaseCalcium Hydroxide-Pulp protection

Preparation for Bevels and Flares

Flame-shaped, fine grit diamond bur is used to bevel the occlusal and gingival margins; it is also used to apply flares on distolingual and distofacial walls.

Flaring results to 30-40-degree marginal metal to inlay. The cavosurface design helps seal and protect the margins and results in strong enamel margins with an angle of 140-150 degrees.

Gingival Bevel purposes:

►Weak enamel is removed. If the gingival margins is in the enamel, it would be week if not beveled because of gingival declination of enamel rods.

►The bevel results in 30-degree metal that is burnishable because of its angular design. Bulky 110-degree metal along an unbeleved margin is not burnishable.

►A lap, sliding fit is produced at the gingival margin. This helps improve the fit of the casting in this region. With the prescribed gingival bevel, if the inlay fails to seat by 50μm, the void between the bevel on the tooth may be 20μm; however failure to apply such bevel would result in a void as great as failure to seat.

Partial onlay is used when a cast metal restoration covers and restores at least one but not all of the cusp tips of a posterior tooth.

Cusp-Capping Partially Onlay

Full Cast Metal OnlayFull Onlay restorations covers entire

occlusal surface.

Located completely in dentin

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

Grooves:

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

Minimal amount of taper on the vertical walls of preparation

Addition of proximal retention groovesPreparation of facial/lingual surface

groove extensions

Enhancement of Resistance and Retention Forms

Placed at expense of the gingival floor, creating an internal dentinal plane including gingivally-axially, locking the restoration & preventing proximal displacement

Reverse Bevel

Most efficient immobilizing retention, resistance means

Prepared in dentin with four vertical surrounding walls joining a floor at definite line & point angles

Can be located next

to marginal ridge with intact proximal wall

Should have a minimum size of 2mm in three dimensions, but should not have equal length, width & depth.

Internal Box

A preparation opening to the axial tooth surface with three, four or five surrounding walls & floors

They can be proximal, facial or lingual

External Box

Pins Can be cemented & threaded, parallel & non

parallel, vertical & horizontal, cast & wrought

Collar Is a surface extension completely surrounding

a cusp or a surface of a tooth

Skirt Is a specific extension involving a part of the

axial angle of a tooth

Skirts are thin extensions of the facial or lingual proximal margins of the cast metal onlay that extend from the flare to a termination just past the transitional line angle of the tooth.

A skirt extension is a conservative method of improving the retention and resistance forms of the preparation; usually prepared entirely in enamel.

Skirt

Slot is a internal cavity within a floor of preparation having a continuous surrounding walls & floors

Junction between the floor & surrounding walls is

rounded

Less locking than an internal box

Slot should have a 2 to 3 mm depth

Slot

Interocclusal Record:If the patient has sufficient canine guidance

to provide disocclusion of posterior teeth, the necessary registration of the opposing teeth can be obtained by:

(1) making a maximum intercuspation interocclusal record with commercially available bite registration paste

(2) making full-arch impressions and mounting the casts made from these impressions on a simple hinge articulator

Restorative Techniques for Cast Metal Restorations

Interocclusal record: one tooth

Full-arch casts: two or more prepared tooth are involved

Most commonly used bite registration pastes are composed of heavily filled PVS impression materials

Temporary Restoration:Requirements:

(1) should be non-irritating and protect the prepared tooth from injury

(2) should protect and maintain the health of the periodontium

(3) should maintain the position of the prepared, adjacent, and opposing teeth

(4) should provide for esthetic, phonetic, and masticatory function, as indicated

(5) should have adequate strength and retention to withstand the forces to which it will be subjected

Technique for Indirect Temporary Restoration Advantages:

(1) avoids the possibility of “locking on” the set temporary material into undercuts on the prepared tooth or adjacent teeth

(2) avoids placing polymerizing temporary material directly on freshly prepared dentin and investing soft tissue, reducing potential irritation to these tissues(3) post-operative cast made in the indirect technique affords an opportunity to evaluate the preparation (before the final impression) and serves as an excellent guide when trimming and contouring the temporary restoration

(4) fabrication of the temporary restoration can be delegated to a well-trained dental auxiliary

Making a post-operative plaster cast for indirectly forming a temporary restoration

Forming indirect temporary restorations

Trimming and adjusting the indirect temporary restorations

Advantages:(1) involves fewer steps and materials

because no post-operative impression and gypsum cast are required

(2) much faster than the indirect technique

Technique for Direct Temporary Restoration

Disadvantages: (1) chance of locking hardened temporary

materials into small undercuts on the prepared tooth and adjacent teeth

(2) marginal fit may be slightly inferior to the indirect technique

(3) more difficult to contour the temporary restoration without the guidelines offered by the post-operative cast

Forming the direct temporary restoration with pre-operative impression

Final ImpressionQualities:

(1) must became elastic after placement in the mouth

(2) must have adequate strength(3) must have adequate dimensional

accuracy, stability, and reproduction of detail

(4) must have handling and setting characteristics that meet clinical requirements

(5) must be free of toxic or irritating components

(6) must be possible to disinfect it without distorting it

Tissue Retraction

Polyvinyl Siloxane Impression

Tray Selection and PreparationMust be rigidTwo types: commercial stock and custom

madeStock plastic tray: convenient and saves

timeCustom resin tray made over a 2-3mm wax

spacer on the study cast is an excellent tray

Adequate bonding: special adhesive

Impression TechniqueAdvantages of automixing systems

(1) speed(2)consistent and complete mixing of

accelerator and base pastes(3) incorporation of very few air voids

during mixing and delivery to teeth