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Class I. cavity preparation for amalgam restoration.

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Presentation on theme: "Class I. cavity preparation for amalgam restoration."— Presentation transcript:

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 1-1.5 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  Removal:  -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!


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