m5l3

geometric configuration of tooth preparation

— must place the cement in compression to provide necessary retention

retention

Prevents removal of the restoration along the path of insertion or long axis of the tooth preparation

resistance

Prevents dislodgment of the restoration by apical or oblique forces and prevents movement under occlusal forces

two opposing vertical surfaces in the same prepaation

Essential element of retention

structural durability

Restoration must have adequate bulk to withstand occlusal forces. Bulk must be confined to prepared tooth space to maintain harmonious occlusion and normal axial contours, preventing periodontal problems.

occlusal reduction

Provides adequate bulk and strength for restoration.

1.5 mm

occlusal reduction for functional cusp clearance: GOLD

1.5-2 mm

occlusal reduction for functional cusp clearance: metal-ceramic

2 mm

occlusal reduction for functional cusp clearance: all ceramic

1 mm

occlusal reduction for non functional cusp clearance: GOLD

1-1.5 mm

occlusal reduction for non functional cusp clearance: metal-ceramic

lingually

direction of the functional cusp bevel of maxillary teeth

buccal/labial

direction of the functional cusp bevel of mandibular teeth

provides space for adequate bulk of material in heavy contact areas, reduces marginal discrepancy, resists fracture and chipping

what is the purpose of the functional cusp bevel

structural durability

axial reduction allows adequate thickness of restoration and is critical for —

cavosurface finish line

Margins must adapt to —

conserves tooth structure

advantages of feather edge margin

insufficient bulk

disadvantages of feather edge margin

not recommended

indications of feather edge margin

conserves tooth structure

advantages of chisel edge margin

difficult to control margin location

disadvantages of chisel edge margin

occasionally on tilted teeth

indications of chisel edge margin

removes unsupported enamel, allows finishing of metal

advantages of bevel margin

extends prep into sulcus if used on apical margin

disadvantages of bevel margin

facial margin of maxillary partial coverage restorations

indications of bevel margin

distinct margin, adequate bulk, easier to control

advantages of chamfer margin

risk of unsupported enamel lip

disadvantages of chamfer margin

cast metal restorations, lingual margin of metal-ceramic crowns

indications of chamfer margin

provides bulk for restoration

advantages of shoulder margin

less conservative for tooth structure

disadvantages of shoulder margin

facial margin of metal-ceramic crowns, complete ceramic crowns

indications of shoulder margin

bulk of material, combines advantages of bevel

advantages of sloped shoulder margin

less conservative of tooth structure

disadvantages of sloped shoulder margin

facial margins of metal-ceramic crowns

indications of sloped shoulder margin

bulk of material, combines advantages of bevel

advantages of shoulder with bevel

less conservative, extends apically

disadvantages of shoulder with bevel

facial margin of posterior metal-ceramic crown with supra-gingival margins

indications of shoulder with bevel

taper

Slight convergence of axial walls to permit restoration to seat.

converge

External walls —

diverge

internal surfaces — occlusally

inclination

wall’s relationship to long axis of tooth.