Class I. cavity preparation for amalgam restoration.

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

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)

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

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

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

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

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

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

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

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

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)

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)

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

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

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

Simple occlusal cavity Maxillary premolars: butterfly shape

Simple occlusal cavity Mandibular first premolar

Simple occlusal cavity Mandibular second premolar

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.

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

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

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

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

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

3. Procedures of finishing external walls

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

Thank you for your attention!