CHAPTER 18: CLASS II CAST-METAL RESTORATIONS

Class II CAST METAL RESTORATION

• Versatile and especially applicable to Class II onlay preparations

• the process involves numerous dental materials, and requires meticulous attention to detail.

Class II inlay

involves occlusal surface + one or more proximal surfaces of posterior teeth

Class II Onlay

term used when cusp tips are included in the restoration.

INDIRECT PROCEDURE of class II CAST METAL RESTORATION

First appointment:

Tooth preparation

Impression taking

Second appointment:

Delivery and cementation of the cast-metal restoration

material qualities of class II CAST METAL RESTORATION

• can be made from a variety of casting alloys

• high compressive and tensile strengths.

• The American Dental Association (ADA) Specification No. 5 for Dental Casting Gold Alloys requires a minimum total gold-plus-platinum-metals content of 75 weight percent (wt%).

• unreactive in the oral environment and are some of the most biocompatible materials.

4 distinct groups of alloys are in use for cast restorations:

traditional high-gold alloys

low-gold alloys

palladium–silver alloys

base metal alloys.

INDICATIONS of cast-metal restoration

• large restoration

• Endodontically treated teeth

• Test at risk for fracture

• Dental rehabilitation with cast- metal alloys

• Diastema closure and occlusal plane correction

• Removable prosthodontic Abutment

CONTRAINDICATIONS of cast-metal restoration

• high caries rate

• Young patient

• Esthetic

• Small restoration

Advantage of cast-metal restoration

STRENGTH

BIOCOMPATIBILITY

LOW WEAR

CONTROL OF CONTOURS AND CONTACTS

disdvantage of cast-metal restoration

Number of appointments and extended Chair Time

TEMPORARY RESTORATIONS

COSTS

TECHNIQUE SENSITIVITY

SPLITTING FORCES

initial procedures

occlusion

anesthesia

ConSideration for Temporary ReStoration

Take pre-op impression for original contours

Materials: Alginate (cheap) or PVS (accurate, durable)

Modify impression if defects/missing cusps

Use sectional tray & check completeness

Store Alginate wet; PVS no wrapping needed

Tooth Preparation for Class II Cast-Metal Inlays

initial step: Occlusal Step / Proximal Box

final step: Removal of Soft Dentin and Pulp Protection / Preparation of Bevels and Flares

Occlusal step

• Bur and entry: No. 271 carbide bur, held parallel to long axis, enters pit/fossa near marginal ridge with a 1.5 mm punch cut.

• Depth: Maintain 1.5 mm depth regardless of dentin, caries, or restoration; do not exceed.

• Bur handling: High speed with air-water spray → reduces vibration, prevents bur breakage, and cools tooth.

• Orientation: Bur kept parallel to long axis; in mandibular molars/2nd premolars, tilt 5–10° lingually to protect lingual cusps.

• Extension: Extend along central groove to mesial pit; conserve marginal ridge dentin support.

• Enameloplasty: Used to conserve tooth structure if fissures are shallow; if fissure deeper than 1/3 enamel, include it in outline with bevel.

• Facial/lingual extension: Use No. 169L bur for final extensions and dovetail retention; avoid removing dentin under marginal ridge.

• Dovetail: Provides resistance against distal displacement of inlay.

• Distal extension: Extend into distal marginal ridge, widening faciolingually for box prep; walls should clear adjacent tooth by 0.2–0.5 mm.

• Final shape: Walls curve smoothly around cusps, isthmus just slightly wider than bur to conserve strength.

Initial step

• Carbide burs: Plane-cut, tapered fissure burs (No. 271 and No. 169L, Brasseler USA) for smooth vertical internal walls.

• Bur features: Straight sides and end surfaces help create uniform taper; No. 271 has slightly rounded corners to avoid stress-inducing sharp angles.

• Marginal bevels: Use a slender fine-grit flame-shaped diamond bur (No. 8862, Brasseler USA).

• Orientation / path of draw: Cutting instruments aligned to a single draw path (usually tooth’s long axis) to prevent undercuts.

• Wall divergence: Gingival-to-occlusal divergence 2–5° per wall.

• If walls are short → max 2° to improve retention.

• If occlusogingival height is greater → increase divergence for easier seating and removal.

Proximal box

• Initial ditch cut: With No. 271 carbide bur, cut a proximal ditch to isolate distal enamel. Slight pressure toward enamel guides bur; prevents cutting too deep into dentin.

• Dimensions: Ditch ~0.8 mm wide (bur tip), about 0.5 mm dentin + 0.3 mm enamel.

• Gingival depth check: Measure with bur or periodontal probe. Provide ~0.5 mm gingival clearance from adjacent tooth if caries is minimal.

• Extension: Extend ditch facially and lingually to cover caries or ideal limits; keep axial wall depth constant. Avoid overcutting facial, lingual, or gingival walls.

• Breaking enamel: After facial/lingual cuts toward enamel surface, thin enamel may break away; if not, remove with spoon excavator.

• Planing walls: Use hand instruments (straight or bin-angle chisel, enamel hatchet) to remove undermined enamel and smooth distofacial, distolingual, and gingival walls.

• Margins: Final facial/lingual margins should clear adjacent tooth by 0.2–0.5 mm.

• Finishing option: Fine-grit flame-shaped diamond can replace hand chisels for smoothing and beveling; postpone until after caries and old restorative material are removed.

• Retention grooves: Optional 0.3 mm grooves in facioaxial and linguoaxial line angles with No. 169L bur, especially if tooth is short. Bur held parallel to draw; grooves in sound dentin close to but not touching DEJ.

Final step: Removal of Soft Dentin and Pulp Protection

• Check for soft dentin: After initial prep, inspect with explorer.

• Isolation: Reduce saliva with anesthesia, cotton rolls, saliva ejector, and gingival retraction cord; cord also widens sulcus for beveling/flaring margins.

• Remove soft dentin: Use slow round bur (No. 2 or 4) or spoon excavator; light, intermittent cutting; avoid drying dentin.

• Shallow/moderate caries (<1 mm dentin over pulp): Place light-cured glass ionomer cement as base; shape with probe, light-cure, then trim excess with No. 271 bur.

• If pulp is nearly exposed: Apply rubber dam; if exposure occurs, consider root canal or direct pulp capping.

• Direct pulp capping criteria: small exposure (<0.5 mm), tooth asymptomatic, bleeding easily controlled, atraumatic exposure, clean rubber-dam field.

• Materials for pulp protection: First line calcium hydroxide liner (flow without pressure), then resin-modified glass ionomer base covering liner and peripheral dentin.

• Do not rely on base alone for pulpal wall resistance; at least two regions should have sound dentin.

• Consider extra retention (e.g., proximal grooves) if axial wall is mostly base.

• Old restorative material: Remove only if thin/nonretentive, caries beneath, symptomatic pulp, or defective margin; otherwise it may serve as base.

• Deep caries teeth: Future root canal possible—consider full metal occlusal coverage and skirts to improve resistance and prevent fracture.

Preparation of Bevels and Flares

Instrument: Use a slender, flame-shaped, fine-grit diamond bur (or No.169L carbide) at high speed to create bevels and secondary flares.

Without bevels: Metal too bulky or thin, weak enamel margin, risk of marginal leakage, fracture, or poor burnishing.

Purpose of bevels

• Remove weak enamel.

• Create a lap-fit seal at margins, improving casting fit and reducing cement line gaps.

• Produce a strong 140–150° enamel margin with 30–40° marginal metal that can be burnished.

Gingival bevel

• Usually 0.5–1 mm wide.

• Cord in gingival sulcus improves access and visibility; may be left or removed during beveling.

• Tilt instrument slightly mesially to achieve correct 30° metal angle.

Secondary flares

• Extend margins into embrasures for self-cleaning and easy finishing.

• Provide 40° marginal metal; too large (>40°) or too small (<30°) angles weaken metal or enamel.

• Occlusal bevels:

• About ¼ depth of wall; 40° marginal metal and 140° enamel.

• Strengthens enamel margins and prevents fracture, especially on marginal ridges.

• Axiopulpal line angle: Light bevel gives thicker, stronger wax p

Mesioocclusodistal prep

• Extend the preparation to include both proximal surfaces if the marginal ridge is too weak or if caries are on both sides.

• Ridge enamel is often stronger than it looks, so extension depends on clinical judgment.

Esthetic modification for Class II

• In maxillary premolars/first molars, minimize mesiofacial flare so the margin is barely visible.

• Omit secondary flare; instead use a chisel, enamel hatchet, or fine-grit disk.

Facial or lingual groove extension

• Extend the outline through faulty facial or lingual grooves to their termination for caries removal or retention.

• Maintain 1.5 mm depth; axial wall about 1 mm deep.

• Bevel the margins to create 30° metal at gingival and 40° at other margins.

Abutment teeth/gingival root-surface lesions:

• Extend margins to increase guiding planes or to include root-surface caries.

• Lengthen the gingival bevel instead of widening the gingival floor to avoid pulp encroachment.

Preserving maxillary first molar oblique ridge

• Keep a strong oblique ridge intact if only one proximal surface is carious.

• For distoocclusolingual lesions: reduce the distolingual cusp 1.5 mm, make a 2.5 mm axial wall in the lingual groove extension, and place mesioaxial/distoaxial retention grooves.

• Add a lingual counterbevel (30° metal) wide enough to clear occlusion.

Fissures in cusp or marginal ridges

Include fissures in outline; may need enameloplasty or beveling (40° metal on occlusal/mesial/distal, 30° on gingival) to remove weak enamel.

Cusp-capping partial onlay

• Cap a cusp when preparation extends more than half the distance from a primary groove to the cusp tip (or two-thirds = definite capping).

• Reduces risk of fracture and moves margin away from heavy stress areas.

• Reduce cusps with No. 271 bur to give 1.5 mm metal thickness (0.75–1 mm on facial cusp ridge for esthetics).

• Add a generous counterbevel (30° metal) beyond occlusal contacts.

• Because cusp reduction lowers wall height and retention, add proximal grooves or skirts for extra resistance.

Facial/lingual surface caries or injury

• For extensive lesions, choose between large inlay, onlay, or crown based on circumference of tooth damage.

• When only part of facial surface is involved, a conservative inlay/onlay with lingual groove extension is preferred to protect gingiva and conserve tooth.

• Defects may need a gingival shoulder and beveled margins (30° gingival, 40° facial) with added lingual groove or skirt for resistance.

Class II full Cast-Metal Onlays

• Builds on principles from inlays & partial onlays

• Covers all cusps of posterior teeth

• Acts as a middle option between:

Inlay → intracoronal restoration

Full crown → extracoronal restoration

Usually made before treatment

Sometimes discovered during inlay prep when cusp reduction is needed

Functions / Advantages of full Cast-Metal Onlays

Strengthens weakened teeth (caries/restorations)

Distributes occlusal forces → reduces fracture risk

More conservative than full crown (less tooth removal)

Supragingival margins → gentler on gingiva

Tooth Preparation for Class II full Cast-Metal Onlays

initial step: Occlusal Reduction / Occlusal Step / Proximal Box

final step: Removal of Infected Carious Dentin and Defective Restorative Material and Pulp Protection / Preparation of Bevel and Flare

Cusp reduction

• Improves access, visibility, cutting efficiency, and cooling

• Helps assess remaining crown height → determines divergence for retention

Preparation steps for Occlusal Reduction

• No. 271 bur, parallel to tooth’s long axis

• 2 mm pulpal floor along central groove

• Extend to sound tooth structure (not beyond ⅔ distance to cusp tips)

• 1.5 mm depth cuts on triangular ridges + groove regions → prevent thin spots

• Cusp reduction follows depth cuts → maintains original occlusal topography

• Infraoccluded cusp → reduce only for proper clearance

• Caries or deep old filling → not removed at this stage

• Avoid reducing marginal ridges fully until proximal boxes are prepared

Wall orientation & divergence

• Always oriented to single draw path (long axis) → no undercuts

• For mandibular molars/premolars → tilt bur 5–10° lingually to preserve lingual cusps

• Divergence:

2° for short walls (better retention)

Up to 5° for taller walls (allows seating/withdrawal of restoration)

Occlusal Step

Depth & Location

• 0.5 mm deep step in central groove (between reduced cusps & pulpal floor)

Extensions

• Facial/lingual → just past caries into sound tooth/restoration

• Mesial/distal → far enough to expose DEJ

• Along fissures → extend only if faulty

Design Features

• Facial & lingual walls → curved around cusps

• Isthmus → as narrow as possible, but on sound structure

• Step widens faciolingually near mesial/distal → for proximal box

Function

• Helps retention of restoration

• Provides bulk of wax/cast-metal → ensures rigidity

• Deeper caries or old fillings → not removed at this stage

Proximal Box in Onlay Preparation

• Prepared with No. 271 carbide bur

• Bur held parallel to long axis of tooth crown

• Technique is the same as for inlay preparation

Final Preparation for Class II full Cast-Metal Onlays

Removal of Caries & Pulp Protection

• After occlusal step + proximal boxes → caries/old restorations become visible

• Remove all infected dentin and defective restorative material

• Follow standard removal methods (as previously described)

• Provide pulp protection if needed

Preparation of Bevel and Flare for Class II full Cast-Metal Onlays

Instruments

• Fine-grit, flame-shaped diamond bur

• Gingival retraction cord placed first

Counterbevels

• On reduced cusps → wide enough, 30° marginal metal

• Margin should be below contact with opposing tooth

• If fissure near bevel → deepen bevel slightly

• No counterbevel on facial cusps of maxillary premolars & 1st molars → use stubbed margin (0.5 mm smooth surface for esthetics)

Beveling & Rounding

• Bevel gingival margins + flare proximal enamel walls

• Round junctions between bevels and flares

• Lightly bevel axiopulpal line angles → stronger wax pattern

• Round sharp corners → avoid casting/fit problems

• Metal angles: 40° (general), 30° (gingival margins)

Retention Grooves (if needed)

• Cut with No. 169L bur

• Depth: 0.3 mm, placed in facioaxial & linguoaxial line angles

• Indicated for short crowns after cusp reduction

• Must stay in dentin near DEJ (avoid undermining enamel)

• Bur held parallel to line of draw

Facial/Lingual Surface Groove Extension

Applied when:

• Facial fissure on mandibular molars

• Lingual fissure on maxillary molars

• Groove is included in outline (same as inlays)

Purpose:

• Remove defective fissure or

• Provide extra retention, even if groove is sound

• Example: mesio-occluso-disto-facial onlay (mandibular 1st molar)

Enhancement of Resistance and Retention Form

Needed when:

• Tooth crown is short (after cusp reduction)

• Tooth is weakened by caries or large restorations

Basic retention features (already used):

• Minimal taper (≈2° per wall)

• Proximal retention grooves

• Facial/lingual groove extensions

Extra reinforcement methods:

• Skirt extension (facial or lingual)

• Collar preparation (facial or lingual)

• Groove extensions on facial/lingual surfaces

Benefits:

• Protect weak cusps (facial or lingual, depending on molar)

• Distribute occlusal forces evenly

• Reduce risk of fracture

Skirt Preparation

Thin enamel extensions from facial/lingual proximal margins → past transitional line angle.

Improves retention & resistance with minimal dentin removal (mostly enamel).

Indications of Skirt Preparation

• Missing/inadequate proximal walls

• Split-tooth cases (strengthens tooth, braces against fracture)

• Extending proximal contact/contour

• Splinting posterior teeth with onlays (better stress handling, soldering, finishing)

• Improving occlusal plane in tilted molars

Advantages of Skirt Preparation

• Conservative

• Adds strength against fracture

• Useful in complex or weak teeth

disAdvantages of Skirt Preparation tooth.

• More visible metal on tooth surface (not esthetic)

• Avoid on mesiofacial margin of maxillary premolars & 1st molars

Preparation of Skirt Preparation tooth.

• Done with fine-grit, flame-shaped diamond

• Placed after gingival bevel & primary flare (or at same time)

• Maintain instrument parallel to line of draw

• Create vertical margin beyond line angle (140° enamel cavosurface, 40° metal angle)

• Skirt usually extends into gingival third of crown

• Avoid overreducing line angle → weakens bracing effect

• Blend skirt smoothly with flare and bevel; round sharp angles

Collar Preparation

Increases retention & resistance for weakened teeth in full onlays

• For mesio-occluso-distal onlays that cap all cusps.

• Avoid on facial surfaces of maxillary premolars & 1st molars (esthetic concern).

Preparation Steps of Collar Preparation

• Use No. 271 carbide bur at high speed, parallel to line of draw.

• Prepare 0.8 mm deep shoulder (same as bur tip diameter).

• Collar height: 2–3 mm occlusogingivally.

• Occlusal 1 mm reduction follows natural tooth contour.

• Round sharp line angles (avoid stress points).

• Bevel gingival margin with flame-shaped fine-grit diamond → 30° metal angle.

Advantage of Collar Preparation

Strong reinforcement for weakened teeth

disadvantage of Collar Preparation

More metal display (less esthetic).

Slot Preparation

Provides extra retention when vertical walls are too short (after cusp reduction).

Indications of Slot Preparation

• Mandibular 2nd molar with no tooth behind it (mesio-occlusal onlay).

• Maxillary 1st premolar needing disto-occlusal onlay, with intact mesial surface.

Advantages of slot vs box

• Conserves more tooth structure.

• Keeps tooth crown stronger.

• Shorter marginal outline (less risk).

Preparation of Slot Preparation

• Bur: No. 169L carbide parallel to line of draw.

• Cut slot in dentin, midway between pulp & DEJ.

• Dimensions:

Width: diameter of bur (mesiodistally).

Length: ~2 mm facio-lingually.

Depth: ~2 mm below pulpal wall.

• Mesial wall of slot must be in sound dentin for effective retention

Maxillary premolar case:

• Mesial slot, 1.5 mm wide FL.

• Helps reduce metal display and conserve tooth.

Modifications for Esthetics on Maxillary Premolars and First Molars

• Goal: Reduce metal visibility on facial surfaces.

• Facial cusp reduction:

• Only 0.75–1 mm at cusp ridge.

• Increases to 1.5 mm toward center for strength.

• No counterbevel:

• Cusps are stubbed/blunted with sandpaper disk or fine-grit diamond.

• Blunting width ≈ 0.5 mm.

• Mesiofacial margins:

• Extended just enough to hide metal from facial view.

• Secondary flare is omitted.

• Shaped with chisel/enamel hatchet → smoothed with disk.

• Cavosurface angle ≈ 40–50° gold angle.

• When more extension needed (caries, old restoration, patient esthetics):

• Use composite insert instead of porcelain-fused crown

• Temporary build-up with RMGI base, later reduced 1 mm for composite

• Small undercuts prepared in onlay wall (or during wax-up).

• Final step: bevel enamel margin + gingival groove (if enamel thin) → place composite veneer.

Endodontically Treated Teeth

Weakness:

• More prone to fracture, especially in posterior teeth.

Preferred restoration:

• Not full crown (to preserve gingiva).

• Fully occlusal coverage onlay with:

Skirt extensions

Collar preparations

Why:

• Provides extracoronal support → resists lateral forces and prevents fracture.

Foundation before onlay:

• Excavate pulp chamber to floor (+1–2 mm into canals)

• Place amalgam or composite foundation for a strong base.

When premolars are badly damaged:

• Prepare root canal for cast-metal or fiber-reinforced composite post.

• Post is cemented before onlay prep.

• Post depth: about ⅔ length of root, leaving at least 5 mm of apical filling intact.

Restoring the Occlusal Plane of a Tilted Molar

• Onlay is useful for tilted molars (especially mesially tilted).

• If occlusal surface is lower than desired plane → reduce occlusal surface less in that area.

• To raise tooth height while keeping proper width & contour:

. Extend counterbevels more gingivally on facial & lingual surfaces.

Mesiofacial & mesiolingual margins:

• Extended onto facial & lingual surfaces → helps recontour mesial surface and contact.

• Done best with skirt extensions → improves retention & resistance, conserves tooth.

• Less ideal: extending walls → does not improve strength, removes more tooth structure.

Cusp reduction check = same as for inlays.

Two Essential Procedures

• Interocclusal Record - Capturing occlusal relationships

• Temporary Restoration - Protecting prepared teeth

Before tooth preparation, the occlusal contacts should be carefully evaluated in:

• Maximum intercuspation

• All lateral movements

• Protrusive movements

Canine Guidance Consideration

If the patient has sufficient canine guidance to provide disocclusion of posterior teeth, registration can be obtained through two methods:

• One tooth preparation: Maximum intercuspation interocclusal record

• Two or more teeth: Full-arch impressions preferred

Method 1: Maximum Intercuspation Record

• Using commercially available bite registration pastes

• Best for preparing one tooth

Method 2: Full-arch Impressions

• Mounting casts on a simple hinge articulator

• Preferred when two or more prepared teeth are involved

Bite Registration Materials and Technique

• Dispense mixed material directly onto prepared teeth and opponents

• Patient closes completely

• Dentist observes uncovered teeth to verify maximum intercuspation

• Remove record when material has set

• Inspect for completeness - adjacent unprepared teeth should penetrate through material when held to light

• Set aside for laboratory use

Semiadjustable Articulator Method

Recommended when restoring large portion of posterior occlusion

Involves only little extra chair time

When information about pathways of cusps during mandibular movements is desired (such as group function):

Make full-arch impressions

Mount casts on properly adjusted semiadjustable articulator

Provides much more information about:

• General occlusal scheme

• Pathways of cusps

• Opposing cusp steepness

• Groove direction

• Anatomy of other teeth

Additional Requirements

• Full-arch tray for final impression

• More material required (especially with stock trays)

• Mandibular movement records

• Face-bow transfer records

Direct Technique

Fabricated intraorally directly on prepared teeth More popular

fewer steps

more popular

Risk of "locking on" with undercuts

Indirect Technique

Fabricated outside mouth using postoperative cast

more steps and complexity

less popular

Useful for preparations that might "lock on"

Advantages of Indirect Technique

• Avoids "locking on" - eliminates possibility of set temporary material locking into undercuts on prepared tooth or adjacent teeth

• Reduces tissue irritation - avoids placing polymerizing temporary material directly on freshly prepared dentin and investing soft tissue

• Preparation evaluation - postoperative cast affords opportunity to evaluate preparation before final impression and serves as excellent guide for trimming and contouring

• Delegation capability - fabrication can be delegated to well-trained dental auxiliary

Initial Steps of Indirect Technique

Make impression of prepared tooth with fast-setting impression material

• Use stock plastic impression tray painted with tray adhesive

• If using alginate:

4. Ensure teeth are slightly moistened by saliva

5. Apply alginate over and into preparation with fingertip to A avoid air trapping

6. Seat tray over region

7. After material becomes elastic, remove with quick pull in direction of draw

8. Inspect for completeness

9. Pour with fast-setting plaster or stone

Cast Inspection of indirect technique

• Inspect for negative or positive defects

• Small voids: Fill with utility wax

• Large voids: Repour impression

• Positives (blebs): Remove carefully with suitable instrument

Cast Preparation and Fitting of indirect retainer

• Seat postoperative cast into preoperative impression

• Cut away thin edges of postoperative impression material recording gingival sulcus for more thickness

• Trial-seat to verify complete seating

• Relieve soft tissue around perimeter if needed for full seating

• Mark margins of preparations on cast with red pencil

• Brush release agent on preparations and adjacent teeth

Temporary Formation of indirect retainer

• Mix tooth-colored temporary resin

• Insert into preoperative impression in area of prepared teeth

• For adjacent prepared teeth, material may be continuous

• Seat cast into preoperative impression

Trimming and Contouring of indirect retainer

• Use suitable burs to trim excess material along facial and lingual margins

• Red line previously placed helps in trimming (especially for auxiliaries)

• For multiple-unit temporaries: Use thin diamond instrument or No. 169L bur to refine interproximal embrasures

• Make cut through adjacent unprepared tooth 1 mm away from proximal contact

• Insert knife into cut and pry temporary off cast

• Improve contour of proximal surface for contact with adjacent unprepared tooth

• Do not disturb accurately formed contact area

Final Fitting of indirect retainer

• Trial-fit on patient's teeth

• Should make desirable contact with adjacent teeth

• Meet occlusal requirements with minimal adjustments

• Mark prematurities with articulating paper and reduce

• Smooth roughness with rubber point or wheel

• Set aside for cementation after final impression

Advantages OF Direct Technique

• Fewer steps and materials - no postoperative impression and gypsum cast required

• Much faster than indirect technique

disAdvantages OF Direct Technique

• Chance of locking hardened temporary materials into small undercuts

• Marginal fit may be slightly inferior to indirect technique

• More difficult contouring without postoperative cast guidelines

Requirements of Direct Technique

• Uses preoperative impression

• Trial-fit impression to verify complete seating

• Must eliminate undercuts in preparation and proximal areas

• "Block out" undercuts using resin-modified glass ionomer base

• Apply light film of water-based lubricant over exposed base

procedure of Direct Technique

Material Selection and Preparation:

For inlay and onlay preparations: Select temporary materials that become elastic before final set

Allows removal from undercuts without permanent distortion

Automixing tips are especially convenient

Mix material following manufacturer's instructions

Place material into preoperative impression in prepared tooth area

Take care not to entrap air

4. Place impression on teeth and ensure complete seating

5. Monitor setting time by rolling excess material into ball between fingers

6. Remove impression when material reaches firm stage

7. Remove temporary from tooth when sufficiently strong

8. Trim excess material

9. Use cavosurface margins visible inside temporary as trimming guide

Laboratory Procedures for Cast Metal Restorations

Fabrication of cast-metal restorations occurs in dental laboratories using replicas of prepared and adjacent unprepared teeth. Classic techniques involving impressions and gypsum casts are described.

Six Essential Qualities of Impression Material Requirements

• Must become elastic after placement to withdraw from undercut regions on prepared and adjacent teeth

• Must have adequate strength to resist breaking or tearing on removal

• Must have adequate dimensional accuracy, stability, and reproduction of detail for exact negative imprint

• Must have handling and setting characteristics that meet clinical requirements

• Must be free of toxic or irritating components

• Must be possible to disinfect without distorting.

• Cost

• Ease of use

• Working time

• Shelf life

• Pleasantness of odor, taste, and color

PVS (Polyvinyl Siloxane)

Most common material for indirect casting technique

have many advantages over other final impression materials:

• Excellent reproduction of detail

• Dimensional stability over time

• User friendly - easy to mix

• No unpleasant odor or taste

• Can withstand disinfection routines without distortion

• Two pastes: base and catalyst

• Disposable automix cartridge-dispensing systems

• Automatic mixing of accelerator and base pastes

• Provides excellent mixing of components

Tissue Retraction

Displace free gingiva temporarily away from tooth

Control flow of gingival hemorrhage and sulcular fluids

• Widen gingival sulcus to provide access for impression material

• Reach subgingival margins in adequate bulk to resist tearing during withdrawal

• Control hemorrhage and moisture using impregnated cords

Impregnation Agents

Styptics: aluminum chloride

Vasoconstrictors: epinephrine

Vasoconstrictor Contraindications:

Avoid in patients with: cardiac arrhythmias, severe cardiovascular disease, uncontrolled hyperthyroidism, diabetes, or those taking β-blockers, monoamine oxidase inhibitors, or tricyclic antidepressants

Retraction Cord Technique

• Anesthetize all sensory nerves to region

• Apply cotton rolls and insert saliva ejector

• Profound local anesthesia reduces salivation and allows painless retraction

• Select cord of suitable diameter

• Cut slightly longer than gingival margin length

• May extend from one margin to another on same or adjacent teeth

• Insert only in areas where cavosurface margin is subgingival

• Use edge of paddle-tipped instrument or side of explorer

• Start 2 mm facial to point where facial margin passes under free gingiva

• Insert progressively into remainder of sulcus

• Leave end exposed for grasping with tweezers

• Place to widen sulcus, not depress tissue gingivally

Special Retraction Considerations for Deep Margins:

Insert second cord of same or larger diameter over the first

Helpful when gingival margin is deep

Special Retraction Considerations for Thin Gingiva/Narrow Sulcus

• Use very small diameter cord to prevent trauma

• Example: facial surface of maxillary or mandibular canine

• May need second cord layered on top to keep sulcus from narrowing

Incorrect Placement of tissue retraction

Avoid placing cord too deeply in sulcus. This creates sulcus that is wide at bottom but narrow at top, causing impression material to tear during removal.

Hemorrhage Control

• Displaced cord: Assistant touches with dry cotton pellets or gentle air stream

• Excessive interproximal hemorrhage: Wedge cotton pellet moistened with aqueous aluminum chloride for several minutes

• Large tissue mass: Use cotton pack moistened with aluminum chloride

commercial stock trays

Convenient and time-saving

Custom resin tray:

Made over 2-3 mm wax spacer on study cast - excellent choice

Impression Material Thickness

• Greater than 3 mm: Increases shrinkage and chance of voids

• Less than 2 mm: May lead to distortion, tearing, or breakage during withdrawal

• Optimal range: 2-3 mm thickness

Automix System Advantages

• Speed

• Consistent and complete mixing of accelerator and base pastes

• Very few air voids during mixing and delivery

Two-Viscosity Technique

Light-bodied material: Inject around preparation

• Heavy-bodied material: Fill the tray

• Two dispensing guns needed

Impression Application Process

• Fill impression tray with heavy-bodied material - keep tip embedded to decrease air trapping

• Examine teeth - ensure field is clean and dry

• Remove moisture with compressed air if visible

• Gently remove retraction cord with operative pliers

• Ensure all preparation surfaces are clean, dry, and exposed

• Inject light-bodied material into opened gingival sulci and preparations

• Fill deliberately and progressively (distal to mesial) over and beyond margins

• Keep tip directly on gingival and pulpal walls

• Fill from gingival to occlusal aspect

• Regulate flow - not too fast ahead of tip

Final Steps of Impression Application Process

• Inject light-bodied material on occlusal surfaces of unprepared adjacent teeth

• Remove cotton rolls immediately

• Seat loaded tray over region

• Follow manufacturer's setting time instructions

• Test set by elastic recovery from indentation at tray periphery

working cast

an accurate replica of prepared and adjacent unprepared teeth that allows cast-metal restoration fabrication in the laboratory.

Dies

• Replicas of prepared teeth and adjacent unprepared teeth

• Should be individually removable for fabrication convenience

Split Cast Method

• Most used method for creating working cast with removable dies

• Requires two pours:

  • First pour: Produces removable dies

  • Second pour: Establishes intraarch relationships

Pindex System Advantages

• First pour becomes die segment - quick and easy

• Dowel pins positioned precisely where needed

• Dowel pins automatically parallel - facilitates die removal

Pouring the Final Impression

• Apply first increments in small amounts

• Allow material to flow into remote corners and angles

• Avoid trapping air

• Use surface tension-reducing agents if needed for better flow

• Fill impression so dies are 15-20 mm tall occlusogingivally after trimming

• May require boxing wax around impression before pouring

• Remove cast from impression

• Inspect for completeness

• First pour becomes removable dies