Class I Amalgam Restorations PDF

Class I Amalgam Restorations Sturdevant, South Asian Ed.,;20, Pg.361-368) AMALGAM  Dental amalgam is a metal-like restorative material composed of a mixture of silver-tin-copper alloy and mercury. properties:      Strength Longevity Ease of use and simplicity of the procedure Clinicall...

Class I Amalgam Restorations Sturdevant, South Asian Ed.,;20, Pg.361-368) AMALGAM  Dental amalgam is a metal-like restorative material composed of a mixture of silver-tin-copper alloy and mercury. properties:      Strength Longevity Ease of use and simplicity of the procedure Clinically proven success Self-sealing material over time Advantages: 1. Ease of use and simplicity of the procedure 2. Strength 3. Excellent wear resistance 4. Longevity and clinically proven success 5. Self-sealing material i.e. Corrosion 6. lower cost than other restorative materials Disadvantages 1. Non-insulating 2. Non-esthetic 3. Less conservative to sound tooth structure than bonded restorative materials 4. More complex tooth preparation compared to composite restoration 5. should be initially sealed 6. Mercury Content Indications: Amalgam is indicated for the restoration of a class I and II defects when the defect : 1. Moderate to large class I and II 2. Not aesthetically important 3. Cannot be well isolated 4. Extends onto the root surface 5. Foundation 6. Abutment for removable partial denture 7. Heavy occlusion  Contraindications:   Aesthetically important areas Small to moderate class I and II defects Clinical technique for Class I Amalgam Restorations:  Class I refers to restorations on the occlusal surfaces of posterior teeth, the occlusal two thirds of facial and lingual surfaces of posterior teeth and the lingual surfaces of anterior teeth Conservative Class I Amalgam Restoration  Initial tooth Preparation: is defined as establishing the outline form by extension of the external walls to sound tooth structure, while maintaining a specified, limited depth and providing resistance and retention forms. Outline form: Should include faulty, defective occlusal pits and fissures Resistance form 1. Extending around the cusps to conserve tooth structure 2. Keeping the facial and lingual margin extensions as minimal as possible 3. Minimally extending into the marginal ridges 4. Eliminating a weak wall of enamel by joining two outlines that come close together (i.e. less than 0.5 mm) 5. Extending the outline form to include enamel undermined by caries 6. Enameloplasty to conserve tooth structure 7. Specified limited depth for amalgam strength Primary Resistance Form     Flat pulpal floor to resist forces directed in the long axis of the tooth Minimal extension of external walls Strong, enamel margins (90 degree) Sufficient depth of 1.5 to 2 mm= 0.2 mm into dentin to result in adequate thickness of the restoration Primary Retention From  Occlusal convergence Technique:  The Recommended burs for conservative class I Preparations: Bur No. 245 or 330    Advantages of the Pear shaped carbide Burs: Occlusal convergence the slightly rounded corners of the end of the bur produce slightly rounded internal line angles   Bur Entry: Entering the most carious pit or the distal pit with the carbide bur rotating in a high speed handpiece with air-water coolant.  The bur should be oriented with the long axis of the tooth crown (perpendicular to the occlusal plane of the crown)   Depth: 1.5 to 2 mm depth should be established measured from the central fissure (The desired pulpal depth is usually 0.2 mm into dentin)  Carbide bur No. 245 has a 3mm blade depth. The specified depth for initial prep. Is half the length of the bur head  The 1.5 mm pulpal depth is measured at the central fissure. Depending on the cuspal incline, the depth of the prepared external walls is 1.5 to 2 mm   Mesial and distal walls should be in occlusal divergence to preserve the strength of the marginal ridges This requires a slight tilting of the bur distally and mesially.     For premolars: the distance from the cavity margin to the proximal surface usually should not be less than 1.6mm For molars , this minimal distance is 2 mm This will preserve dentinal support of the marginal ridges and prevent undermining. This will not affect the retention    Maintain the same depth and orientation and extend the preparation along the central fissure toward the mesial pit This may create flat pulpal floor Ideally, the width of the isthmus should be just wider than the diameter of the bur  The facio-lingual width should be minimal (about one forth the distance between the cusp tips) or 1 to 1.5 mm    Extension should ensure that all caries is removed from the peripheral DEJ For initial tooth prep., the pulpal floor should remain at the initial ideal depth, even if restorative material or caries remains The remaining caries is removed during final tooth preparation    The strongest and ideal enamel margin should be made up of full-length enamel rods resting on sound dentin Extend the margins into any radiating fissures with depth more than 1/3 thickness of enamel If the depth of the fissure is less than one third the thickness of enamel, enameloplasty is indicated Enameloplasty:  Eliminating the developmental fault by removing it with the side of a flameshaped diamond stone, leaving a smooth surface  The surface left by enameloplasty should be considered as external tooth surface and not as part of the cavity.    Amalgam should not be inserted in this area. Reduces the need for further extension into the fissures, conserving tooth structure. The surface left by enemeloplasty should meet the tooth preparation wall, with a cavo-surface angle no greater than approximately 100 degree If enemeloplasty is unsuccessful in eliminating any radiating fissure e.g. mesial or distal fissure that cross the marginal ridge or beyond, the operator has one of three alternatives: 1. Make no further change in the outline form except for patients at high risk for caries.  2. Extend through the marginal ridge when margins would be lingual to the contact 3. Include the fissure in a conservative Class II tooth preparation Final tooth Preparation I. Removal of any remaining infected dentin on the pulpal floor II. Pulp Protection III. Finishing external walls IV. Cleaning and inspecting the prepared tooth I. Removal of the remaining infected dentin (i.e. caries that extends pulpally from the established pulpal floor) is best accomplished using a discoid type spoon excavator or a slowly revolving, round carbide bur of appropriate size.   Stop the excavation when tooth structure feels hard of firm. This often occurs before all lightly stained or discolored dentin is removed Sclerotic dentin  Resistance form may be improved with flat floor peripheral to excavated area or areas II. Pulp Protection:  Shallow depths: dentin sealing is sufficient pulp protection  In deeper carious excavations where the remaining dentin thickness is judged to be about 1 mm, place a liner ( either calcium hydroxide or resin modified glass ionomer cement)     III. Finishing of the external walls Cavo-surface angle should be approximately 90 to 100 degree This results in 80 to 90 degree amalgam margins Amalgam is brittle material with low edge strength and tends to chip under occlusal stress it its angle at the margins is less than 80 degree. < 90 degree > 90 degree < 90 degree > 90 degree  IV. Every completed tooth preparation Should be inspected and cleaned before restoration. The tooth preparation should be free of debris after rinsing the cavity with air-water syringe. Other Conservative Class I Amalgam Preparations  The occlusal pits of the mandibular first premolar Bur tilt for entry. Cutting instrument is held so that its long axis is parallel with long axis of the tooth crown  The occlusal pits and fissures of the maxillary first molar