Chapter 3 B: Class I And II Cavities For Amalgam Restorations Flashcards
Since when has amalgam been used in dentistry?
1826
The basic principles of tooth preparations are?
- Initial tooth preparation
- Final tooth preparation
Initial tooth preparation is:
- Outline form
- Primary resistance form
- Primary retention form
- Convenience form
Final tooth preparation is?
- Management of remaining caries
- Secondary resistance and retention forms
- Pulp protection if required
- Finishing of enamel margins
- Final inspection of the preparation
Extension for prevention is ?
All deep pits and fissures within 0.5mm of the cavity should be included
When would you join two cavities into one instead of making two separate preparations?
When the thickness of the wall between the two cavities is less than 0.5mm
Where should we avoid ending cavity margins?
In high stress areas such as cusp tips and crest of the ridges
The outline form means
Extending the preparation margins to the place that they will occupy in the final preparation
What should be kept in mind when making the outline form:
- Removal of all carious and defective pits and fissures
- Removal of all unsupported enamel
- Avoid ending cavity margins in high stress areas
- Placing margins on sound tooth structures
- Bur should be kept perpendicular to the long axis of the tooth and should be rotating when applied and removed
- Maintain the initial depth of 1.5mm, at least 0.2-0.5mm in dentin to provide strength
Regular, 125 µM refers to which color bur?
A: yellow
B: red
C: blue
D: green
E: black
C
X-fine, 28 µM refers to which color bur?
A: yellow
B: red
C: blue
D: green
E: black
A
Super coarse, 181 µM refers to which color bur?
A: yellow
B: red
C: blue
D: green
E: black
E
Fine, 60 µM refers to which color bur?
A: yellow
B: red
C: blue
D: green
E: black
B
Coarse, 151 µM refers to which color bur?
A: yellow
B: red
C: blue
D: green
E: black
D
Which burs are for finishing and polishing?
Yellow and red
Which burs are for preparations?
Blue, green, black
How should the bur be oriented for mesial and distal surfaces?
Orient it towards the respective marginal ridge that will result in a slight divergence which helps provide dentinal support for marginal ridges (95 degrees)
How should the external outline form be?
Smooth curves
Straight lines
Rounded angles
Resistance form is ?
The shape given to a preparation to enable it to withstand occlusal stresses
The primary resistance form should have the following features?
- shape of the preparation should be like a box, with a flat floor that follows the contour of the occlusal surface
- minimal occlusal depth of 1.5mm to provide adequate thickness of amalgam
- cavosurface angle of 90 degrees
- restrict the extension of the external walls to have strong marginal ridge areas with sufficient dentin support
- round off the internal line and point angles
Primary retention form is?
The form to prevent the restoration from being displaced
Retention can be increased by the following:
- occlusal convergence of 2-5% of the buccal and lingual walls
- slight undercut in dentin near the pulpal wall
- conserving the marginal ridges
The convenience form?
Facilitates and provides sufficient visibility, accessibility, and ease of operation in preparation and restoration of the tooth. For amalgam, it’s the form or shape that permits access of condensing and carving instruments
What else do we remove other than the caries in the final tooth preparation?
- remaining caries
- old restorative material
- adjacent deep pits and fissures
How are the soft caries in a large preparation removed?
Using a slow speed or spoon excavator
What is a two-step pulpal floor?
Only a portion of the tooth which is affected by caries is removed, leaving the remaining floor untouched
What does the use of pulp protectors depend on?
If the preparation is shallow or deep
In a shallow preparation?
Pulp protection is not need as it compromises thickness and thus compressive strength of the amalgam
In a deep preparation?
A base is placed on the deepest part in the thickness of 0.5 to 0.75 mm as to protect the pulp
At what stage of the final tooth preparation are all the unsupported enamel removed?
Finishing of the enamel walls and margins
Having a cavosurface margin of 90 degrees butt joint type provides?
Bulk to the restoration and provides maximum strength
What do we have to preserve in the maxillary first molar?
Oblique ridge
What do we have to preserve in the mandibular first premolar?
Transverse ridge
Buccal and lingual have to be?
Convergent
Mesial and distal have to be?
Divergent
What changes have to be made when making a preparation on the occlusal surface with buccal or lingual extension:
- extend the pulpal floor in the same plane to include the caries
- make a box type preparation with mesial and distal walls parallel
- place retention grooves in the mesial and distal walls
- remove all unsupported enamel by using a slow speed
Tilt, inclination
Clinical sequence of amalgam class I preparation:
Perpendicular to occlusal surface
Round bur to make the shape
Cylindric bur to make the floor flat
Can you have a class II that has buccal and lingual surfaces involved?
Yes
The different designs for class II cavities are?
Simple, compound, complex
How is a class II preparation initiated?
Same as the class I, through the occlusal surface
The outline form of a class II preparation is:
- Same as class I but extended proximally *mesial or distal depending on the caries
- Keep long axis of the bur parallel to the long axis of the tooth and maintain the initial depth of 1.5-2.0mm
- Extend the outline to include the central fissure
- Make isthmus width as narrow as possible but not wider than 1/4 the intercuspal tip distance
- Occlusal convergence
- Extend the preparation towards the contact area ending short by 0.8mm of cutting through the marginal ridge
- Proximal cutting is deep into the dentin (0.5-0.6mm) so that retentive locks are prepared
- Widen the preparation faciolingually to clear contact areas
- Proximal cut is occlusally convergent
- Clearance of facial and lingual margins of the proximal box are 0.2-0.5mm from the adjacent tooth
What provides favourable retention for amalgam
Occlusal convergence to facial, lingual walls
When do you make a reverse curve?
In teeth with broader contacts
Curve the walls inwards to the contact aras
What are the advantages of the reverse curve?
- conserves the sound tooth structure
- preserves the triangular ridge of the affected cusp
- 90 degree angle outer tooth surface —> increase resistance for tooth and material
How do you fracture the slide of enamel left in the contact area?
With a small chisel or enamel hatchet
Primary resistance form in class II preparation is achieved by ?
Box with flat pulpal and gingival floor
Primary retention form in class II cavities is achieved by?
Occlusal convergence of 2-5% of buccal and lingual walls
Bevelling of the enamel portion of gingival walls is done with ?
Gingival marginal trimmer
What are the modifications in class II preparations?
- Slot preparation
- Simple box preparation
- Conservative preparation for mandibular first PM and maxillary first molar
Indications for slot preparation:
- Proximal root caries in geriatric patients with gingival recession.
- When adjacent tooth is missing.
Design features of a slot preparation?
- preparation is normally approached from the facial aspect to a limited depth axially (0.75-1.25 mm).
- When margins are in enamel, go 0.5mm inside the dentin. Prepare 90 degree cavosurface margins, give retention grooves
Indications for a simple box preparation ?
- Small proximal caries, not involving the occlusal surface.
- Proximal surface caries with narrow proximal contact.
- Proximal caries in attrited teeth. (Bruxism patients).
Design feature of simple box preparation?
- prepare proximal box only with minimum facial and lingual extensions.
- For retention, converge facial and lingual extensions. Proximal retention locks are made for added retention in the proximal box. These have 0.5 mm depth gingivally and 0.3 mm occlusally.
What’s the difference between resistance and retention and one thing you can do to achieve them?
- resistance is: shape given to allow the restoration to withstand occlusal stresses. By: box with flat floor, rounded internal angles, cavosurface 90
- retention is: prevents the restoration from being displaced. By: occlusal convergence of 2-5% of buccal and lingual walls, undercut in dentin, conserving marginal ridges
