م.د. محمد عبدالمنعم عبداللطيف

Tooth Preparation: General concepts for tooth preparation for composite restorations: 1. Conservation of tooth structure: Tooth preparation is limited to extent of the defect. For composite restorations, rule extension for prevention and proximal contact clearance, is not necessary unless it is required to facilitate proximal matrix placement. 2. Variable depth of pulpal and axial wall depth: Pulpal and axial walls need not to be flat. 3. Preparation of operating site: To facilitate bonding, tooth surface is made rough by using diamond abrasives. 4.

Alloy is a union of two or more metals. Amalgam: Amalgam is an alloy of mercury with any other metal. Dental Amalgam: Dental amalgam is an alloy of mercury with silver, tin, and varying amounts of copper, zinc and other minor constituents. Dental Amalgam Alloys: Dental amalgam alloys are silver tin alloys with varying amounts of copper, zinc and other metals.................

Esthetic dentistry has shown much advancement in materials and technology since the last century. Materials which have been used for esthetic restorations are silicate cement, glass ionomer, acrylic resins, composites and fused porcelain. R Bowen, in 1962 developed a polymeric dental restorative material reinforced with silica particles used as fillers. These materials were called ‘composites’. Nowadays, composite resins are considered as an economical and esthetic alternative to other direct and indirect restorative materials...........

Complex posterior restorations are indicated when tooth structure is missing due to cusp fracture, severe caries lesion development (two or more tooth surfaces are missing), and more retention and resistance forms are needed, or replacement of existing restorative material is necessary. To compensate the lost tooth structure, may be moderate, severe or total, one or more than one retentive device is utilized. The routinely used retentive devices are: i. Slots. ii. Locks. iii. Coves. iv. Cusp Coverage Complex Amalgams. v. Crown lengthening. vi. Pins. vii. Amalgam pin. viii.

A base is any substance placed under a restoration (1-2 mm in thickness) that blocks out undercuts in the preparation, acts as a thermal or chemical barrier to the pulp, and/or controls the thickness of the overlying restoration. Bases should have sufficient strength to withstand forces of mastication and condensation of permanent restorations (mechanical protection to the pulp). Zinc-phosphate, polycarboxylate, zinc oxide-eugenol (IRM), glass ionomer and resin cements have all been historically used as bases for direct and indirect restorations.........

Dental cements have been widely used in various clinical applications since the early twentieth century. They are used as filling materials, protective cavity liners, luting materials for crowns, bridges, inlays and orthodontic appliances, root canal fillings, and pulp capping. Various types of cements are available for different purposes. Dental cements are mainly used to provide protection to the pulp against irritants as the following: 1. Thermal protection against temperature changes. 2. Electrical protection against galvanic currents. 3.

Class V Tooth Cavity Preparations for Amalgam Restoration Class V lesion is present on the gingival third of facial and lingual surfaces of all teeth. Amalgam is not indicated for anterior teeth except when esthetics is of no concern, for example in very aged patients. Causes of Cl. V cavitation: 1. Dental caries. 2. Erosion: tooth loss caused by non-bacterial acids (Fig. 1). 3. Abrasion: tooth loss at gingival third due to mechanical action...............

It is a restoration in the proximal surface of the anterior teeth without involving incisal edge. Since amalgam is not esthetic restoration, it is not indicated for proximal surface of incisors and mesial surface of canines. It is indicated in the distal surface of maxillary and mandibular canines especially, if: 1. Caries do not undermine distal slopes of canines. 2. Labial axial angle is intact. 3. Even after removal of caries, sufficient tooth structure is present. 4. Restoration will not be directly loaded with occlusal forces.........

Class II restoration involves the proximal (mesial or distal) surfaces of premolars and molars. It termed MO; mesioocclusal, DO; disto-occlusal, or MOD; mesio-occluso-distally cavity. Outline of proximal preparations is controlled by the following factors: 1.Caries susceptibility of the patient 2.Age of the patient. 3.Position of gingiva 4.Extent of the caries on the proximal side 5.Dimensions of the contact area 6.Masticatory forces 7.Esthetic requirement of the patient................

Tooth cavity preparations for amalgam and composites have some differences. These differences varies from preparing good undercut to provide good retention for the amalgam filling to roughening the cavity walls to enhance composite filling’s adhesion to the dentine. All of these differences are listed in the following table......................