Day 3 lecture 1 Flashcards
Axial wall
Concave/convex according to shape of original tooth.
Depth
1- Total depth of the cavity preparation 2- Maintain uniform depth in dentin 3- 0.5mm into dentin
Enamel rods anatomy
Head, tail, interrod enamel
Amalgam margin
Amalgam carved too deep results in acute angles a and b and stress concentrations within the amalgam, potential for fracture.
Amalgam carved with appropriate anatomy, results in an amalgam margin close to 90, although the enamel cavosurface margin is obtuse.
oblique ridge
maxillary molars
Mandibular first premolar
DO NOT extend into transverse ridge of mandibular 1st premolar unless it is undermined by caries (class 1)
Conservation of tooth structure
Cavity outline should extend around the cusps (conservative approach)
• Shape: Flowing curves around triangular ridges
• Isthmus Width: should not exceed 1/3 intercuspal distance
-preferable 1/4 intercupal distance.
Long axis
midline axis of tooth
Central pit
Bottom of cusp valley
Peripheral 1/3
enamel rods pointed away from long axis
Middle 1/3
enamel rods pointed parallel to long axis
Central 1/3
Enamel rods pointed toward long axis.
Outline form
- Include all major pits and fissures
- Placing the margins (cavosurface margin) on sound strong tooth structure
- Extend around the cusp for conservation of tooth structure
- Minimal extension of the buccal and lingual walls….minimal extension into triangular ridges (from the central groove to the cusp tip)
- Minimal extension into the marginal ridges (include the mesial and distal pits and partially include the fossa groove)
- Depth of the cavity preparation should be 0.2- 0.5 mm into dentin/1.5- 2.0mm on ivorine teeth
Class 1 buccal and occlusal wall
The 2 opposing walls converge occlusally
• This occlusal convergence of the 2 opposing
walls provide the primary retention form
• The walls take the shape of the 330 bur
• Keep the bur angulation with the long axis of the tooth
• Don’t overconverge by tilting the bur … undermined enamel.
Class 1 other walls
Walls diverge around the remaining developmental (primary) grooves if any:
•
To follow the direction of the enamel prisms. Enamel prisms tend to diverge further from central groove
Buccolingual extension
Minimal extension of the buccal and lingual walls … minimal extension
from the central groove to the cusp tip (conservation of triagular ridges)
• Isthmus B-L dimension should not exceed 1/3 intercuspal distance
• Isthmus area is usually narrower than at the dovetail
Class 1 mesial and distal walls
Diverge the mesial and distal walls slightly toward the occlusal to follow the direction of the enamel rods without involving the marginal ridge (Conserve the marginal ridge)
Class 1 Mesiodistal extension
1.6 mm of tooth structure should be left between cavosurface margin and the proximal contact area (conservation of marginal ridge)
• If cavosurface margin is past the crest of the marginal ridge then you are too far extended
Class 1 pulpal floor
• Flat and Smooth
• Perpendicular to the long axis of the tooth
Smooth: no irregularities, minimizes stress concentrations
Flat: don’t slope pulpal floor except for man 1st premolar
You want forces to be perpendicular
Pulpal Depth
Adequate depth: resistance form
• Clinical depth is 0.2-0.5 mm beyond dentinoenamel junction (DEJ) • Typodont
From cavosurface margin to the pulpal floor = 1.5mm at the fossa 1.75-2.0mm at the ridges
Class 1 cavosurface margin
Flowing smooth curves. 90/100 degrees
Not sharp …no irregularities
Axial walls class V
Convex - follows external surface of tooth, uniform dentinal depth (0.5mm). This depth protects the pulp chamber sufficiently. If you are not convex, you increase axial depth, getting too close to the pulp.
Base material
Replaces dentin- used to protect pulp following depper preps.
Why class Vs are only 1 mm deep
not an occlusal surface - not a constant, direct force. 1 mm amalgam prep is sufficient due to this.
