Class III Cavity Preparation

Alaa Sabrah, BDS, MSD, PhD 11 Dec, 2014

Goals and Objectives

1.

2.

3.

4.

5.

What is the definition of class III cavity?

Identify the different types of class III cavity Preparation?

Compare and contrast different approaches to caries for class III ?

Compare the design and retention form for the different types of class III cavity Preparation?

Describe the clinical technique for treating class III carious lesion?

Definition

 Class III- Smooth surface, involves

proximal surface

of

anterior tooth

H. Devlin Operative Dentistry, Springer-Verlag Berlin Heidelberg 2006

Type of Approach

Facial Approach Lingual Approach Depends or

caries location

,

extent of caries

,

access to carious lesion

• Facial approach: caries location, alignment of teeth, replacement restoration  Lingual approach

preferred:

more esthetic, conserves facial enamel  use unless it would remove excessive amount of tooth structure  staining less visible if it occurs

Clinical Technique

5.

6.

7.

1.

2.

3.

4.

Anesthesia (Pt comfort, decrease salivary flow).

Occlusal assessment (determine design, adjust the restoration function).

Shade selection (before dehydration).

Isolation (visibility, effective bonding).

Tooth preparation.

Pulp Protection.

Restoration.

Tooth Preparation

Class III Conventional Beveled Conventional Modified Conventional

Tooth Preparation

       Indication: restoration of root surface.

Why? No enamel margin Design: Butt Joint margins. Walls = walls for amalgam Cavosurface margin=90˚ External walls ┴ root surface.

Uniform depth.

External wall 0.75 mm

Tooth Preparation steps

1.

2.

Outline form: No. ½, 1, or 2 round carbide bur or diamond bur. Initial depth 0.75 mm.

Remove caries: pulpal depth dictated by carious lesion or existing restoration.

External wall 0.75 mm

Tooth Preparation steps

3.

 Retention: Retention grooves can a) b) c) increase retention, decrease effect of polymerization shrinkage, increase marginal seal by resisting tooth flexural forces.

Tooth Preparation steps

3.

Retention:  o Retention grooves placement: No. ¼ round bur o Internal portion or the external wall.

o 0.25mm from root surface.

o 0.25mm depth.

0.25mm from root surface 0.25mm depth

Tooth Preparation steps

3.

Retention:  Retention grooves location: o The bisector of the angle formed by the junction between axial wall and external wall.

Tooth Preparation

Class III Conventional Beveled Conventional Modified Conventional

Tooth Preparation steps

 Indication: restoration of

large carious lesion

or replacing

defective restoration

in the

crown

.

 Why? More retention/resistance are needed  Design: some beveled enamel margins with conventional wall design.  Cavosurface margin=45˚ on beveled, 90˚ on non beveled margins.  External walls ┴ enamel surface

Tooth Preparation steps

1.

Outline form: No. ½, 1, or 2 round carbide bur or diamond bur.  Point of entry: a) b) c) Within

inciso-gingival dimension

of carious lesion or defective restoration.

Instrument ┴ enamel surface.

Neck of the bur as far into the embrasure as possible.

Tooth Preparation steps

1.

Outline form: No. ½, 1, or 2 round carbide bur or diamond bur.

 Point of entry:

d) Incorrect entry

: overextend the lingual outline into potential stress areas (marginal ridges) and unnecessarily weakens the tooth.

Tooth Preparation steps

1.

Outline form: No. ½, 1, or 2 round carbide bur or diamond bur.  Axial wall: a) b) Initial depth 0.2 mm into dentin.

Outwardly convex: following normal external tooth contour and DEJ inciso-ginigivally and facio-lingual.

Tooth Preparation steps

2.

Remove caries: undermined enamel can be left in

non-stress area

. 3.

Retention:  Enamel bevel or flare  Retention groves

Tooth Preparation steps

3.

Retention:  a) Bevel Increase surface area.

b)

c) d)

Flame shaped or round diamond bur.

45˚

to the external tooth surface.

0.25-0.5 mm

width.

e)

f)

All accessible enamel margin

except gingival margin

.

Avoid

on

lingual margin

if the margin is

subjected to occlusion

.

45˚

Tooth Preparation steps

3.

Retention:  Retention grooves a) b) c) Not necessary unless the cavity is too large.

Along incio-axial and gingivo-axial line angle.

No. ¼ round bur.

Tooth Preparation steps

3.

Retention:  Retention grooves a) b) c) 0.2mm inside DEJ.

0.25 mm depth.

Bisect the angle formed by the junction of axial wall and external wall.

Tooth Preparation

Class III Conventional Beveled Conventional Modified Conventional

Tooth Preparation

      Indications:

small and moderate

lesions or faults designed to be as conservative as possible in the

crown

.

Why? All enamel margins Design: scooped or concaved Cavosurface margin ≥ 90˚ External walls = no shape.

Only include caries or defective restoration.

Tooth Preparation steps

1.

Outline form: No. ½, 1, or 2 round carbide bur or diamond bur.  Point of entry: a) b) Within inciso-gingival dimension of carious lesion or defective restoration.

Instrument ┴ enamel surface.

c) Neck of the bur as far into the embrasure as possible.



Axial wall not uniform in depth.

Tooth Preparation steps

2.

Remove caries: undermined enamel can be left in

non-stress area

. 3.

Retention:  Enamel bevel or flare

Combined cavity preparation design

 What if the caries extends on both crown and root surface?

Pulp Protection

 Place calcium hydroxide in deep caries on the axial wall.  Add RMGIC linear to protect the calcium hydroxide from being dissolved by Acid etch application.

Restorative Procedure.

 Anterior teeth: Aesthetic restoration (composite) is almost always indicated.

 Composite contraindicated for restoration extended on root surfaces.

Restorative Procedure.

 Add RMGIC linear to .

1.

Decrease microleakage on root surface 2.

Decrease gap formation.

3.

Decrease recurrent caries formation.

Class III Resin Restoration

Class III Resin Restoration  Use clear Mylar strip to provide “proximal wall” to restore against  Place wedge between the teeth gingivally to seal the cervical margin, and protect the adjacent teeth.

Class III Resin Restoration  Etching:  Manufacture instruction.

 Placed 0.5mm beyond the prepared margins.

 15-30 s.

 Wash and dry.

 Dentin should remain moist (NO over drying or polling of excess water I allowed).

Class III Resin Restoration  Place bonding agent according to manufacturer instructions.

 Air dry to remove any solvent.

 Light cure for 10-20 s.

Class III Resin Restoration  Restoration  Restore with resin composite.

 Contour with resin placement instrument  Adapt and hold mylar strip and cure

Class III Resin Restoration  Finish and Polish Restoration  Finishing burs, strips for interproximal, discs to contour and polish, #12 scalpel blade for gingival flash

Class III Resin Restoration  Maintain Proximal Contact  Wedge slightly separates teeth, aids in creating proximal contact with resin  Use finishing burs, stones or scalpel for contouring

Class III Resin Restoration Finishing discs Finishing Strips

Class III Resin Restoration  Proximal finishing strips and discs  Finishing and polishing  Use strips in “S” motion, do not remove proximal contact

Class III Resin Restoration  #12 scalpel works well to finish flash at cervical margin, use with care  Polish surface with Soflex discs

Class III Resin Restoration