Operative Dentistry: Cavity Preparation

Operative Dentistry

Principles of Cavity Preparation

• Gingival seat in Class II inlay cavities should clear adjacent teeth by 0.50 ± 0.20mm.
• Class II cavities begin in the proximal surfaces of bicuspids and molars.
• Incipient caries appears as opaque, chalky white areas when the tooth surface is dried. This is referred to as a white spot.
• Pit and fissure caries are seen in Class I cavities.
• Smear layer consists of enamel debris, microorganisms, and dentinal chips.
• A butt joint is a 90° joint.
• Enameloplasty eliminates shallow enamel fissures.
• Rubber dam is the best way to protect a prepared cavity from moisture.
• Retentive grooves in the proximal box of a Class II amalgam cavity should be round and elongated in the dentin.
• Primary prevention includes planning the patient's diet, prophylactic odontomy, and topical application of fluoride but not extending cavity preparation.
• Infected dentine shows both organic and inorganic components in irreversible form.
• Deepening the pulpal floor during cavity preparation provides retention form.
• Eburnation of dentine is seen in chronic caries.
• Incomplete debridement in deep carious lesions is done to allow secondary dentin formation first.
• Beveling of the pulpoaxial line angle of a Class II cavity prevents the fracture of amalgam.
• Restoration of a cusp using dental amalgam requires that at least 2 mm of cusp be removed to provide resistance form.
• Class I cavity preparation for amalgam and gold inlay both have mesiodistally divergent walls in common.
• In Class 2 inlay preparation, the pulpal floor should be at the same depth as in amalgam Class 2 preparation.
• Class IV cavity occurs on the proximal surface involving the incisal edge of anterior teeth.
• Retention for Class 5 restoration is placed in mesial and distal areas.
• Extension for prevention is directly related to the outline form of the cavity preparation.
• Mesiolingual and distobuccal pulp horns are likely to get exposed while preparing a Class II cavity on a maxillary first molar.
• In a Class 1 cavity prepared for silver amalgam, if extended to half the distance between the contact area and the fissures and the cusp tip, the direction of the buccal and lingual walls is converging.
• The reason for sealing caries during cavity preparation is to allow the formation of secondary dentin before excavation.
• In a cavity preparation in which the remaining thickness of dentin is more than 1.5mm, the ideal base is glass ionomer.
• The function of proximal grooves in a Class II cavity is retention form.
• An incipient carious lesion on an interproximal surface is usually located gingival to the contact area.
• In an ideal restoration, the gingival margin should be below the contact point but 1 mm occlusal to the gingival crest.
• Resistance form of cavity preparation includes a flat pulp floor, enough depth of the cavity, and restricted size of the external walls.
• During M.O.D. preparation, if one of the cusps is undermined, reduction of the cusp and inclusion in the preparation for onlay is indicated.
• Resistance form is that shape of cavity which allows the restoration to withstand occlusal forces and prevent displacement.
• A dental floss is applied to the distal bow of a clamp to prevent aspiration of the clamp.
• Air and water spray is commonly recommended procedure for debridement.
• The axiopulpal depth of the proximal box in Class II cavity is 0.2 to 0.8mm.
• The purpose of cavity preparation is to receive the restoring material.
• Intercuspal width ideally for Class II amalgam cavity should be 1/3.
• When removing a rubber dam, the first step is to cut the interseptal rubber with scissors.
• To avoid pulpal irritation below a resistant metallic restoration, the minimum dentin thickness which should remain is 1.5mm.
• According to Black's classification, caries on lingual pits of maxillary central incisors are Class I.
• In a Class II cavity in an incisor, the retentive points are placed in the dentin.
• Inappropriate margins in restorations are corrected primarily because they inhibit proper plaque removal.
• The most common cause of fracture at the isthmus of a Class II dental amalgam restoration is inadequate depth at the isthmus area.
• Saucering out of small pits to improve self-cleansing property is called enameloplasty.
• Mesial and distal wall of Class V cavity depends on the presence of carious lesion.
• The base of Class III preparation is the axial wall.
• While preparing the occlusal cavity for amalgam in the mandibular first premolar, the bur is tilted slightly lingually.
• Dovetail preparation of restoration to occlusal loading is not a consideration for obtaining a resistance form during cavity preparation.
• Gingivally, the depth of a Class V cavity is 0.75 - 1mm.
• For cast restorations the cavity wall should have a taper of 2-5 degrees.
• In a modified Class III cavity restoration, retention is obtained mainly by acid etching.
• During cavity preparation, more incidence of exposure is in Class II mesio-occlusal cavity.
• A transverse section of Class V through the axial wall is convex.
• The cavosurface angle for inlay cavity preparation is less than 90 degrees.
• Caries detection dye can stain granular necrotic tissue, dry, leathery dentin, and irreversibly denatured collagen.
• The modified Class III preparation uses a dovetail on the lingual side in the maxillary canine.
• Preparation of Class I cavities for dental amalgam, direct filling gold, or gold inlays all have occlusally converging mesial and distal walls in common.
• Beveling of axiopulpal line angle prevents fracture of M-O amalgam.
• Characteristics of a non-active carious lesion include brown or black discoloration and it is hard and leathery.
• In a Class III cavity in an incisor tooth, the retentive points are placed entirely in dentin.
• All enamel walls of a cavity preparation must consist of full-length enamel rods on sound enamel.
• In air-abrasive technology, the abrasive particles used are aluminum oxide.
• In an early carious lesion, the first structure to show evidence of destruction is the interprismatic substance.
• Extension for prevention in modern restorative dentistry is the least considered principle of cavity preparation.
• The wall absent in Class V lesion is a pulpal wall.
• Scrub gel is NOT a suitable lubricant when placing the rubber dam.
• When composites are placed exposed dentin should be covered with calcium hydroxide.
• A 2 mm thick dentin layer will best protect dental pulp under restoration.
• Composite resin provides the most conservative approach to restoring a tooth.
• A line angle is the junction of two plane surfaces of different orientation along a line.
• The tip diameter of a 245 bur used for conventional amalgam preparation is 0.8 mm.
• The total number of point angles present for Class II amalgam restorations is 6.
• A chamfer preparation is used for gold inlays as a gingival margin finish line.
• The base of the Class III preparation is the axial wall.

Amalgams

• Conventional amalgam alloy contains 65% silver, 30% tin, 5% copper and less than 1% zinc.
• Delayed expansion in zinc-containing amalgam alloys, when contaminated by moisture during trituration or condensation, can reach up to 400 µm/cm.
• Pin-retained amalgam restorations offer conservative tooth preparation, can be completed in one appointment, improve resistance and retention form, and are inexpensive compared to indirect restorations.
• Amalgam restorations are indicated for moderate to large Class I and Class II restorations, Class V restorations in non-esthetic areas, and foundations for badly broken-down teeth.
• During direct contact by opposing teeth, cusps and/or amalgam restorations are stretched laterally, producing tension and perhaps flexion.
• Amalgams without finishing and polishing will have a rough surface microscopically and results in concentration cell type of corrosion.
• The mercury content of finished restoration should be approximately 50wt%.
• High-copper amalgams are superior to low-copper amalgams in terms of corrosion, creep, and compressive strength.
• Gallium alloys are amalgam substitutes containing Ag-Sn particles in Ga-Indium liquid.
• Electrochemical corrosion occurs between dissimilar metals in contact.
• Stress corrosion occurs when metal at the site of maximum stress becomes more reactive than the unstressed metal.
• Crevice or concentration cell corrosion occurs in cracks or crevices due to the accumulation of plaque.
• The maximum safe level of occupational exposure to mercury is 50 micrograms/m3 of air.
• Amalgam is a brittle material with minimal edge strength.
• Minimum occlusal thickness of amalgam is 1.5 mm.
• The pulpal wall of Class I and Class II preparations should be flat with 1.5-2mm overall depth or 0.2mm into dentin.
• Use one pin per missing axial line angle in pin-retained amalgam restorations.
• The fewer pins possible should be used to achieve the desired retention for a given restoration.
• Self-threaded pins are the most retentive and most frequently used pins, retained by the resiliency of the dentin, and produce maximum crazing in dentin.
• Electrochemical corrosion produces extrusion at margins (creep), during which mercury from Sn-Hg(γ2) re-reacts with Ag-Sn (γ) particles and produces further Mercuroscopic expansion.
• An increased trituration time and increased condensation pressure would lead to a decreased creep rate.
• Amalgam has a 90 degree cavosurface angle.
• In amalgam fillings there is a wide buccolingual space, the double wedge technique should be used.
• Cavity with normal depth is closest to pulp in Class V Amalgams.
• The optimum depth for a pinhole in a tooth with a vital pulp is 2 mm.
• Axiopulpal line angle is beveled in amalgam preparation to facilitate bulk for amalgam in this critical zone.
• Conservative cavity for amalgam restoration is made using a Pear shaped bur.
• A major difference between a Class V cavity preparation for amalgam and one for composite resin by the acid-etch technique is the angulation of enamel cavosurface margins.
• The strength of amalgam decreases when pins are used in the cavity.
• Most modern precapsulated dental amalgam are formulated with 40-45% hg by wt.
• After amalgam polishing, the outermost surface has flattened crystals known as the Beilby layer.
• Low creep values of high copper amalgams increase its hardness.
• Indium is added to amalgam as it reduces gamma 2 phase.
• Burnishing of a dental amalgam restoration does NOT reduce creep.
• A well-packed, pre-measured capsule without leaks releases mercury during trituration.
• In self threaded pins, the pin hole is smaller than the pin channel by .004 inch in diameter.
• In a patient having a moderate carious lesion with heavy occlusal forces, amalgam is the restoration of choice.
• Discolored areas seen through the enamel in the teeth that have amalgam restorations are known as amalgam blues.
• Pinhole should never be prepared at different levels on the tooth regarding pin retained restoration.
• In pin retained amalgam restoration, failure is more likely to occur at the pin dentin interface.
• The color code for the "Regular" size pins in the TMS (Thread Mate System) pin system is gold.
• In mechanical trituration of amalgam, the working time is adversely affected.
• Cemented pins cause the minimum amount of stress in dentin.
• Amount of fluoride in amalgam is 1% SNf2.
• Least amount of mercury is required In Spherical alloy.
• Alfred stock was associated with the second amalgam war.
• The clinical condition shown depicts an amalgam tattoo.

Dental Instrumentation

• Ball burnishers should not be used to polish or finish amalgam.

Miscellaneous

• Use of tin oxide provides final polishing of dental amalgam to get a smooth surface .
• Chromium oxide polishing agent is referred to as a whitening agent.
• Aluminium oxide polishing powder is obtained from bauxite.
• Rouge is used for polishing gold restorations.
• The hardness of silicon carbide abrasives is the maximum.
• Electrolytic polishing is done polish chrome-cobalt castings.
• Acidophilic means can survive in acidic environment.
• Porcelain denture teeth have a higher abrasion resistance than gold.
• Titanium oxide achieves opacity in ceramics.
• To prevent porosity in dental porcelain it should be baked in vacuum.
• Porosity in porcelain at the condensation stage depends on shape and size of the particle.
• Condensation shrinkage of porcelain during firing depends on shape and size of particle.
• Metamerism is a phenomenon in which porcelain appears different under varying light condition.
• Machineable glass ceramic is dicor MGC.
• Calcium carbonate is not present in porcelain.
• Feldspar is the main constituent of porcelain.
• Highly glazed porcelain is the best tissue tolerated material for crown and bridge.
• Porcelain bonded to metal is strongest when it is fired under pressure.
• The glass infiltrated alumina core ceramic is inceram.
• Union of metal of porcelain fused restorations is by tin and indium oxides.
• HF is the chemical used for etching porcelain.
• Dual cure resin is the best cement for the cementation of porcelain laminates.
• Crack tooth syndrome is diagnosed by applying pressure on the tooth.
• When all diagnostic procedures fail to detect proximal caries, the last resort is mechanical separation.
• Bitewing radiographs can best detect with proximal caries.
• Cervical resorption is the most common complication of bleaching non vital tooth.
• Atropine is commonly used to control salivation in operative dentistry.
• Small occlusal cavities can most readily be diagnosed with an explorer and compressed air.
• Pain in cracked tooth syndrome is elicited mainly when pressure is applied.
• The distance between 2 holes in a rubber dam sheet is ideally is 6.3 mm.
• Digital Imaging fibre-optic trns-illumination(DIFOTI) can detect recurrent caries before it's visible on radiograph.
• Root caries has a slow progress and is secondary to gingival recession and remineralization is difficult, and it's not caused by actinomycosis viscosis.
• Vaseline is not true about lubricant for rubber dam placement as it does not have a water-miscble vehicle.
• The isolation done for root canal therapy of maxillary canine (Distal caries) from 2nd premolar to opposite lateral incisor.
• Dentin bonding agents do not alter dentin permeability as treatment of dentinal hypersensitivity.
• Apparent length size of the tooth can be increased by change (or alteration) in height of contour of tooth is not true about dental esthetic correction.
• Affected dentin is not been invaded by microorganisms .
• Feldspathic porcelain shows insignificant firing shrinkage.
• Digital imaging fiber - optic trnns-illumination (DIFOTI) is used to detect dental caries.
• Cone waxing technique is indicated for all purposes like preparing the single pattern in a badly broken down tooth,multiple pattern, and waxing the form of occlusal surfaces for accurate articulation of carving casting.
• Bases provide mechanical support for the restoration.
• Soft & cheesy is not true for a non active caries.
• Gallium containing alloys have silver, tin.
• Ceramic restorations are cemented using resin cement.
• Bisphenol A has the Similarity in the chemical structure of estrogen.
• A purpose of etching beveled enamel surface is to increase surface energy.
• Transformation toughening is found in ceramics containing tetragonal zirconia.
• Debonding is the most common cause of failure of tooth colored inlays/ onlays.