Inlays and Onlays

INLAYS AND ONLAYS

Contents

INTRODUCTION AND HISTORY

 CAST METAL RESTORATIONS

          - INDICATIONS AND CONTRAINDICATIONS

          - ADVANTAGES and DISADVANTAGES

          - FUNDAMENTALS OF CAVITY PREPARATIONS

Tooth preparations for Class II Inlays and modifications

Tooth preparations for cast metal Onlays and modifications  

ESTHETIC INLAYS AND ONLAYS

Recent advancements                   

DEFINITIONS

Class II inlay: involves the occlusal and proximal surfaces of a posterior tooth and may cap one or more, but not all, of the cusps.

Class II onlay: involves the proximal surfaces of a posterior tooth and caps all the cusps

CAST GOLD RESTORATIONS

Become less popular in recent years because of emphasis on esthetics but it remains an excellent restoration with a long history of clinical success

If used with care, gold alloy is considered to have the greatest longevity of any restorative material used in dentistry.

   Gold alloys can be used for

Intracoronal restorations(inlays)

Extracoronal restorations( full coverage crowns)

Combination of both(onlays or partial coverage crowns)

INDICATIONS

LARGE RESTORATIONS

ENDODONTICALLY TREATED TEETH

TEETH AT RISK FOR FRACTURE

DENTAL REHABILITATION WITH CAST METAL ALLOYS

DIASTEMA CLOSURE AND OCCLUSAL PLANE CORRECTION

REMOVABLE PROSTHODONTIC ABUTMENT

CONTRAINDICATIONS

HIGH CARIES RATE

YOUNG PATIENTS

ESTHETICS

SMALL RESTORATIONS

ADVANTAGES

Strength: gold alloy rarely fractures

Biocompatibility

Low wear : gold wears at a rate similar to enamel so does not cause accelerated wear of opposing tooth

Casts easily and accurately

Control of contours and contacts because of indirect technique for fabrication

DISADVANTAGES

Number of appointments and higher chair side time

Temporary restoration required

Higher Cost  than direct restorations

Technique sensitive

Splitting forces

Materials available

PURE GOLD

NOBLE METAL ALLOYS

BASE METAL ALLOYS

CERAMIC        ESTHETIC INLAYS & ONLAYS

COMPOSITE

INITIAL PROCEDURES

Occlusion : evaluation of contacts done before anesthesia or tooth preparation

Evaluation should include:

(1) Occlusal contacts in maximum intercuspation (MI) where teeth are brought into full interdigitation

(2) Occlusal contacts that occur during mandibular movements

Evaluate occlusal relationships in MI (A), and during mandibular movements (B and C).

Pattern of occlusal contacts influences

1)    Preparation design

2)    Selection of interocclusal records

3)    Type of articulator or cast development needed

ANESTHESIA

Local anesthesia of tooth to be operated

Adjacent soft tissues

Considerations for Temporary Restorations

Consideration must be given to method used to fabricate temporary restoration.

Preoperative impression required to reproduce occlusal, facial & lingual surfaces.

BASIC PRINCIPLES OF CAST RESTORATIONS

CONSERVATION OF TOOTH STRUCTURE:

Preparation should be made as CONSERVATIVELY  as possible

    -To maximize strength of remaining tooth

      structure

    -Lessen likelihood of post operative sensitivity &

      pulpal pathosis

    -Decrease likelihood of tooth fracture

RETENTION AND RESISTANCE FORM

Correctly incorporated, they resist unseating vertical, lateral and oblique forces acting on the restoration during function or parafunction

Retention form resists forces attempting to dislodge restoration parallel to the path of insertion

Resistance form resists forces attempting to dislodge a restoration obliquely to the path of insertion

Inlay taper

Basic requirement of all intracoronal cast restorations  is a DIVERGENCE of the cavity walls from floor of the preparation externally.

Similarly  for all extra coronal cast restoration walls must converge from cervical to occlusal surface

Line of draw

Describes the path of insertion and removal of the casting

It is the axis of taper( for a class I or II generally parallel to long axis of tooth)

It bisects the angle of convergence of tapered cavity walls to a point of their intersection

Factors affecting retention & resistance

1. Resulting stress

2. Final tooth preparation geometry

3. Luting material type & thickness

4. Tooth & crown surface texturing

Pulpal considerations

Prior to preparation, pulp should be tested for vitality & radiographs be taken.

Endodontic therapy should be done prior to restoration if required

Best pulpal protection: a thick layer of sound dentin(RDT>1mm)

If RDT<1mm, sealer or liner indicated, followed by an observation period to determine if tooth remains symptom-free.

FINISH LINES

Term “finish line” refers to the border of preparation where prepared tooth surface meets the unprepared surface

Type depends on clinical situation

A smooth, well defined finish line is beneficial regardless of the design

Common types for cast restorations: knife edged, chamfer and shoulder

Knife edged margin

Requires least amount of tooth reduction

Commonly used with a bell shaped tooth

Difficult to discern to a die & tends to result in over contoured restorations

Difficult to wax and cast accurately

Susceptible to distortion under occlusal forces

Commonly used on mesial aspect of a tipped molar, on lingual aspects of mandibular molars, on root surfaces of periodontally involved teeth

Chamfer configuration

Preferred finish line for cast gold extracoronal restorations

More conservative than shoulder & generates less stress at cement interface

Provides adequate room for its reproduction & adequate thickness of gold

Shoulder configuration

Used primarily where bulk is needed to strengthen restoration at the margins

Used in all porcelain or metal ceramic restorations

Least conservative for cast gold

Chamfer/shoulder with bevel

Bevelled margin-easier to detect in an impression

Makes margins of restorations more burnishable

Bevel :  a bevel is a finish line that follows the contour of the tooth and should be used only on finish lines that are more or less perpendicular to the path of insertion

Flare:  flare differs from a bevel in that a flare is a geometric plane inclined slightly to the path of insertion and cutting through the contour of the tooth .

A proper  flare will be narrower gingivally becoming wider occlusally

As the occlusogingival height increases, the occlusal divergence should increase

Lengthy preparations with minimal divergence (more parallel) may present difficulties during pattern withdrawal, trial seating, withdrawal of the casting, and cementing

Onlays

Indications:

1) Large restorations/caries

       Teeth that have been weakened by-

                                     -  caries or

                                     - large failing restorations,

(but where facial and lingual surfaces are relatively unaffected

—  Cuspal protection

Armamentarium

Enamel hatchet

Chisel

Gingival marginal trimmer

No.271 carbide bur

No.169L carbide bur

Flame shaped fine grit diamond

Round end fine grit diamond

Articulating paper

Finishing and polishing kit

Tooth preparation for MOD onlay

INITIAL PREPARATION

Occlusal reduction

No.271 tapered fissure carbide and round-end diamond bur used

•      Uniform depth cuts are placed-one on crest of each triangular ridge and one in each major developmental groove

•      1.5 mm clearance on functional cusps

•      1.0 mm clearance for nonfunctional cusp

Functional Cusp Bevel

—  No.271 carbide and Round end tapered diamond bur used

—  Make depth orientation cuts on the outward facing inclines of the functional cusp

—   Should be 1.5mm deep

Occlusal Shoulder

No.271 tapered carbide bur used

On buccal cusp of mandibular and palatal cusp of maxillary

Provides for greater bulk of metal on functional cusp

Increased resistance

Reinforced margin (more durable)

1 mm wide

preparation is gingivally below the functional outer aspect of the facial cusp to allow occlusion exclusively on restorative material and not on the interface.

Prepare pulpal floor along the central groove extend mesially and distally, facially and lingually

•      Should be 1.0mm shallower than the isthmus in an inlay because occlusal surface has been reduced already

  

 Proximal box preparation

—  No.271 tapered fissure carbide bur,169L bur used

—  Mesial and distal proximal boxes are prepared to the level of the gingival crest

—  Gingival floor should be 1mm wide

—  Proximal clearance = 0.5mm

—  FINAL PREPARATION

—  Removal of infected carious dentin and defective restorative materials and pulp protection

—  If  proximal box & occlusal step have been extended properly then any remaining caries or restorative material should be visible & be removed.

—  All horizontal surfaces i.e.pulpal floor, gingival floor and shoulder should be smoothened using an end cutting bur

Finishing bevels

Gingival bevel-

 flame diamond bur used

 0.5mm to 1mm wide

 Placed along the entire gingival floor of the box

 Should blend with the flares without forming an undercut.

Facial and lingual bevels-

Flame diamond used

0.5mm wide

Placed on buccal (maxillary)and lingual (mandibular)occlusal surfaces, should be blended into flares.

Bevel should result in 40 degrees marginal metal

—    Shallow (0.3mm) retention grooves

—    cut in facioaxial and linguoaxial line angles

—    with No. 169L carbide bur.

—    important for retention when the prepared tooth

     is short.

—    Grooves are in dentin near the DEJ and do not undermine the enamel.

Enhancement of resistance and retention forms

In the preparation of a tooth that has been grossly weakened by caries or previous filling materials and is prone to fracture under occlusal load the resistance form that cusp capping provides should be augmented by the use of skirts, collars or facial /lingual surface groove extensions.

Skirt preparation

Collar preparation

Slot preparation

Skirt preparation

Skirts are thin extensions of the facial or lingual proximal margins of the cast restoration that extends from the primary flare to terminate just past the transitional line angles of tooth

Advantages

conservative method of improving both resistance & retention forms

 relatively atraumatic -removes very little dentin usually entirely in the enamel

Disadvantage

Increases the display of metal on the facial and lingual surfaces –avoided on the mesiofacial margin of the maxillary molar and premolars. The other three line angles can be skirted

Indications

when the proximal portion of  a classII for an onlay is being prepared and the lingual wall is partially or totally absent the retention is  provided by skirt preparation of the facial margin and vice versa

recommended when proximal contours and contacts are to be extended more than the normal dimensions

when splinting posterior teeth  together with onlay. The additional retention and resistance is very useful  because of the  stress on each unit

Preparation:

Preparation done with slender flame shaped  fine grit instrument

Maintain the long axis of the instrument parallel to the long axis of the line of withdraw and translate the  instrument just beyond the line angle of the tooth

A 140^ocavosurface angle should be present

Use less than ½ of the tip of the instrument and translate it from the entrance cut  towards the proximal box to blend the skirt with the  primary flare and the  proximal gingival bevel

Do not over reduce the line angle as the bracing effect will be lost  .Slightly round any sharp angles

Collar Preparation

To increase the retention and resistance form when preparing a weakened tooth for a MOD onlay capping all the cusps , a facial or lingual collar or both may be provided

To reduce the display of metal the facial surfaces of the maxillary premolars and the first molars are usually not prepared for collar.

Preparation

use a no.271 carbide bur at high speed parallel to the line of withdraw

prepare a 0.8mm deep shoulder around the lingual surface to provide for a collar about 2-3mm high occlusogingivally

To provide for  a uniform thickness of metal, the occlusal 1mm of this  reduction should follow the original contour of the tooth

Bevel the gingival margin of the shoulder to result in a 30 degree metal angle at the margin

Slot preparation

After cusp reduction the vertical walls of the occlusal step portion of the preparation are reduced so they provide very little retention Form. In such cases necessary retention can be obtained by making a slot preparation

It is indicated in short clinical crowns and in  cusps that have been reduced

A slot removes more tooth structure than for a  pin but it is less likely to cause microfractures in dentin

Preparation

 Use a no.169L carbide bur

 Long axis should be parallel to the line of

    withdraw

 Is cut in the dentin it should be placed midway

    between pulp and DEJ

 Mesiodistally the width of the slot should be

    equal to diameter of the bur

 Faciolingually  2mm

 Depth 2mm gingival of normal position of pulpal floor

 It should be in dentin

Modifications in case of maxillary premolar and first molar

To decrease display of metal on facial cusp of maxillary premolar and mesiofacial cusp of 1^st  molar occlusal reduction on facial cusp ridge should be only 0.75 to 1mm

Cusps should not receive counter bevel but should be stubbed or blunted by sandpaper or disk or fine grit diamond to create a surface of 0.5mm width

To decrease display of metal the mesiofacial margin is minimally extended facially of contact so that it is barely visible hence secondary flare is omitted here.

Materials used

1) Alloys of gold –high gold alloys, low gold alloys

type II(medium)

Composition- Au-77%, Cu-7%, Ag-14%, Pd- 1%, balance- Sn, Zn, Fe.

2) palladium-silver alloys

3) Alloys of base metal

4) Porcelain

Preparation for porcelain( according to Vimal Sikri)

Functional cusp reduction=1.5mm for premolar, 2mm for molar

Nonfunctional cusp reduction= 1-1.5mm

Collar should be prepared-width=1-1.5mm

Occlusal step=1.5-2mm depth

Width of isthmus 1.5mm minimum

Axial reduction- 1.5mm

Cavosurface margin not to be beveled

For CAD/CAM Since the computer cannot accurately read bevels, convexities, steps or undefined angles, the preparation walls should be straight, uniform and flat

ESTHETIC INLAYS AND ONLAYS

James Summitt, third edition

General considerations

Preparations for ceramic and resin composite inlays and onlays same.

Divergent, relatively non-retentive preparation recommended due to ease of placement

Resistance form may be incorporated with rounded proximal boxes but grooves should not be used

Resistance & retention form mainly provided by adhesion to enamel & dentin.

Walls & floors of preparation should be smooth & even

Internal angles should be rounded to enhance adaptation of restorative material

Occlusal reduction should be anatomic & uniformly, a min of 2mm for strength

Bevels should be avoided because thin margins of resin composite & porcelain are susceptible to chipping.

When esthetic blend of material & tooth is important, as on facial surf of max. premolar, long chamfer may be placed

Adhesive cementation

Resin luting cement recommended as it bonds to enamel, dentin & restorative material

Luting resin cement limits microleakage, enhances strength of restoration & tooth

Dual cured luting resin and dual cure dentin bonding agents should be used to bond all indirect posterior bonded restorations

Resin composite inlays & onlays

Fabricated intraorally or on a cast

Advantages over direct restorations:

Better contacts & contours

Polymerization shrinkage not a problem

Types : Direct

                 Indirect

Direct resin inlays

Fabricated directly on tooth

After preparation, matrix placed on tooth

Preparation is bulk filled with resin composite & light cured from all directions

Matrix is removed & inlay is teased out of the preparation

Inlay is then postcured, tried in, adjusted & bonded

Direct/indirect resin inlays

An impression is made of prepared tooth & cast is poured

Master cast must be ready to use in a short time

Master die can be made from a silicone material or a master cast made from die stone

Restoration is fabricated on die & undergoes a primary(light cured) & secondary polymerization

Indirect resin inlays & onlays

Resin inlays & onlays are available t/h commercial labs

Newer gen of resin materials termed Ceromers(ceramic optimized polymers)  used

Four ceromer products:

Artglass(Heraeus Kulzer)

Belleglass(Kerr)

Targis(Ivoclar)

Skulptur  fibreKor( Jeneric/Pentron)

Have greater durability, fracture toughness, wear resistance, esthetics & repairability

Thank You..!!