Chapter 6 B: General Principles In Cavity Preparations For Composite Resins

Question 1

Which restorative material requires a more conservative technique? (Amalgam/ CR)

Answer 1

CR

Question 2

What is the main principle of cavity preparation for CR?

Answer 2

Remove the least amount of healthy tooth

Question 3

The cavity design principles include?

Answer 3

• preventive extension
• retentive extension
• supportive extension
• tooth resistance extension
• material resistance extension
• pulp protection extension
• convenience extension
• aesthetic extension

Question 4

Which cavity design principle is practically not needed in CR?

Answer 4

Preventive extension

Question 5

Preventive extension:

Answer 5

1. Adjustment: enamel etching , CR has no expansion when polymerised
2. Can prepare isolated cavities in the occlusal surface, in pits and fissures with caries
3. If the cavosurface margin is interrupted by a deep groove (Especially if its discoloured) with the risk of recurrence, include the groove
4. Preventive extension is not even necessary in the proximal box, as far as good enamel etching is provided

Question 6

Isolated cavities can be prepared in the occlusal surface in pits and fissures if?

Answer 6

• areas with no cavities are respected
• especially important in lower molars

Question 7

For preventive extension, if the adjustment is good, then there is no need to follow?

Answer 7

All the occlusal fissure contours or eliminate contact with the adjacent teeth

Question 8

Which of the cavity design principles has the most changes with respect to amalgam? And why

Answer 8

Retentive extension , because resin adheres to the tooth and amalgam doesn’t

Question 9

Retention with enamel and dentin?

Answer 9

• very strong retention of the resin with enamel is achieved
• retention in dentin is reduced
• if good adhesion to dentin would be achieved, retention would be guaranteed

Question 10

Which tooth structure doesn’t need special preparation in retentive extension ?

Answer 10

Dentin

Question 11

What is the shape required to provide retention to the cavity?

Answer 11

No specific preparation

Question 12

The responsibility of the retention lies within the ?

Answer 12

Enamel, and has to be prepared so that the acid etching is as effective as possible

Question 13

How is retention achieved?

Answer 13

• by preforming a bevel on the enamel surface

Question 14

Do we talk about unsupported enamel when we’re working with CR?

Answer 14

No , just enamel

Question 15

Is the bevel divergent or convergent?

Answer 15

Divergent

Question 16

3 functions of the bevel?

Answer 16

1. Camouflages the line between tooth and filling; this has a great importance in class III and IV preparations
2. Increase the etching surface so that the retention will be greater
3. Achieve that the enamel surface etched are prisms heads and not the side

—> increases the efficacy of the adhesive system, inc the surface of enamel exposed to acid

Question 17

3 types of bevel:

Answer 17

• straight
• concave
• combined

Question 18

Straight bevel:

Answer 18

• better aesthetics, diffusing line between filling and enamel, eliminating the thickness of enamel
• inconvenient: leaves a very thin and fragile layer of resin, so we only use it when the margin compromises aesthetics and its not subjected to large occlusal loads

Question 19

Concave bevel:

Answer 19

• less aesthetic
• configures a better defined limit of the preparation and a greater thickness of composite

Question 20

Supportive extension:

Answer 20

• in composite the displacement is less important than in amalgam
• eliminate the caries considering their shape is round
• floor flat in proximal boxes to support the restoration and to prevent the material from moving around

Question 21

Tooth resistance extension:

Answer 21

• enamel rods without dentin support can be preserved although it has risk of fractures

Question 22

Material resistance extension:

Answer 22

• you can prepare shallow cavities without having to reach the dentinoenamel limit

Question 23

What should be avoided when preparing shallow cavities without having to reach the dentino enamel limit?

Answer 23

1. The cavosurface margin of the occlusal surface in the occlusion area with the opposing tooth , if it’s bevelled
2. The greater risk of fracture in the occlusal surface is produced by the bevels of the occlusion zones

Question 24

Pulp protection extension:

Answer 24

• keep it as far as possible from the pulp
• walls and floors are carved less defined following the form of the caries
• recommended to move away from the pulp horns
• follow the convexity of the pulp chamber

Question 25

Convenience extension:

Answer 25

• case specific
• goal is to facilitate the filling
• enlarging the cavity to ensure a good insertion
• preserving the enamel without dentin support can lead to carious dentin in the DEJ

Question 26

Aesthetic extension:

Answer 26

• making a bevel to dissimulate the union as a diffuse line
• class III and IV
• it’s also done when we open the cavity through the less visible area even if it’s uncomfortable
• or when we remove the dark dentin even though it’s healthy , it can be transparent through the enamel

Question 27

Simple rules for a class I preparation:

Answer 27

1. Remove caries
2. Remove deep grooves if colored
3. Remove the enamel that prevents the access of the instruments to the caries

Question 28

Class I preparation:

Answer 28

• cavity can be carved without penetrating dentin
• no preventive extension is necessary
• only remove areas with affected grooves or at great risk for caries
• floor can be rounded

Question 29

Swift, Jordan and Suzuki, Leinfelder, Wilson:

Answer 29

Avoid bevelling on the occlusal surface especially if the antagonist occludes near the cavosurface margin

Question 30

If the bevelling is made on the occlusal surface, it must be?

Answer 30

• short
• defined
• never in occlusion areas