1. Class I. cavity preparation for amalgam restoration.

2. Advantages and disadvantages of amalgam
Has been used since the middle of the 19th century
Strong, easy to use, cheap
Durable
Not tooth-coloured
Does not bond to tooth structure
Inproper handling cause a safty hazard for the dental staff

3. Class I lesion (caries)
The occlusal fissure of premolars and molars
Vestibular or lingual/palatal pit caries in posterior teeth
Palatal surfaces of upper incisors
(secunder caries, inproper filling)

4. Types of class I cavity 1 surface: simple occlusal cavity
Compound, 2 surfaces :
-occluso buccal
-Occluso lingual or palatal
Complex class I (Occluso-bucco-lingual/palatal)
Buccal pit
Palatal pit in anterior teeth

5. Conventional class I. cavity
Usually prepared for amalgam restorations
Box-form: walls are parallel or slightly convergent
Occlusal fissure or at least those in the developmental grooves have been included (even when the caries has not extended throughout the fissures)
Prepare the whole fissure system

6. Cavity preparation: principles and steps
Founded by G.V. Black in the late 1800’s
Not only the carious tissue is removed, but also the proper retention and resistance form is maintained.
2 main phases: initial and final stages

7. Initial tooth preparation stages
1. Exploration of carious lesion
2. Outline form and initial depth
3. Primary resistance and retention form
4. Convenience form

8. Final tooth preparation stages
1. Removal of remaining infected dentin or old restorative material
2. Pulp protection (if indicated)
3. Secondary resistance and retention form
4. Procedures for finishing external walls (smooth surface)
5. Cleaning, inspecting

9. 1. Exploration of carious lesion
Small diameter round bur/ rounded fissure bur/ pear-shaped bur (diamond)/ inverted cone
Turbine (high speed, air-water)
Entering the deepest or most carious pit
The long axis of the bur is parallel to the axis of the tooth

10. 2. Outline form and initial depth
Margin should be placed on sound tooth structure
Undermined enamel prisms should be removed
Preparation should be performed
-to give access to all dentinal caries
-to obtain enamel margins supported by sound dentin
Should be smooth
No sharp angles

11. 3. Retention and resistance form
Retention form: prevents the dislocation of the restoration/filling in the cavity
Resistance form: the restoration:
- must be of adequate thickness- cavity must have adequate occluso-gingival depth
have a marginal design
To bear the forces of mastication without fracture or deformation
Remaining tooth structure must be left in the state that will resist the forces of mastication – as much sound tooth structure as possible must be maintained
Wider orovestibular width – tooth is more subject to fracture

12. 3. Retention and resistance form
Opposing walls should be parallel to each other (box form)
Opposing walls should converge occlusally (modified box form)
Pulpal floor should be flat and perpendicular to the long axis of the tooth
Mesial and distal walls should be parallel to the corresponding surface and diverge slightly from the pulpal wall to avoid undermining the marginal ridges
Enamel prism are directed roughly parallel to the long axis of the tooth (in most areas of the occlusal surface)
Enamel margins should be prepared at a 90-degree angle (less then 90 degree-more subject to fracture)

13. 3. Resistance and retention form
Bucco-lingual width: maximum one third of the intercuspal distance, preferable ¼ distance mm
Occluso-gingival thickness minimum1.5 mm, preferably 2 mm below DEJ (0.1 or 0.2 mm into the dentin)
Minimum extension into the marginal ridge mesial distal walls divergent occlusally (>10 degree)
Proximal surface should not be less than 1.6 mm. In case of molars 2 mm.
Join weekend ridge between two cavities (<0.5 mm apart)

14. Extended class I. Follow the main steps
Extended preparation (larger bucco- lingual and occluso-gingival extension)
Bucco-lingual width:
half of the intercuspal distance: cusp reduction and coverage with amalgam may be indicated
2/3 of the intercuspal distance: cusp reduction and coverage with amalgam should be indicated high risk for cusp fracture

15. 4. Convenience form Establishing resistance and retention form
Gives adequate convenience:
-to instrumentation
-removal of decay
-insertion of the restoration

16. Simple occlusal cavity
Varies in shape according to the numbers of cusps and orientation of pits and fissures

17. Simple occlusal cavity
Maxillary premolars: butterfly shape

18. Simple occlusal cavity
Mandibular first premolar

19. Simple occlusal cavity
Mandibular second premolar

20. Maxillary first molar Types of cavity forms
The oblique ridge should be cut, if it is crossed by deep fissure / is undermined by caries, or the distance between the mesial and distal cavitites is less than 0.5mm.

21. Two surface cavity class I
Occlusal surface
Buccal or lingual grooves of molars
Occlusal cavity preparation
Round ended fissure bur is held to the pulpal floor and parallel of the long axis of the tooth and moved towards the buccal/lingual direction along the fissure maintaining uniform depth until the bur reaches the buccal/lingual surface

22. Pit and fissure on facial or lingual surface only (buccal pit, palatal pit)
Shape: varies (oval, round , oblong) depending upon the extent caries
Walls continually joined and slightly convergent towards the cavosurface margin
Axial wall follows the contour of the buccal/lingual surface

23. Final tooth preparation
Removal of remaining defective enamel and infected dentin on the pulpal floor or old restorative material
Pulp protection
Procedures of finishing external walls
Final procedure of cleaning and inspecting the prepared tooth

24. Removal of remaining decay in the cavity
-excavator (spoon or discoid)
- (the biggest that fits the carious area/cavity) stainless steel round bur at slow speed
Until the tooth sructure feels hard and firm
Lesion is in lighter in color, sharp explorer for touching
Removal of decay should not affect resistance form
Caries detecting solution may be helpful

25. 2. Pulp protection Ideal or shallow depth: no liner or base indicated
Deep cavity:
Liner: CaOH2
Base: GIC, RMGI, carboxylate cement

26. 3. Procedures of finishing external walls

27. 4. Final procedure of cleaning and inspecting the prepared tooth
The prepared tooth cavity should be free of debris
Rinsing with air-water spray

28. Thank you for your attention!