Seminar on

Cavity designs for composite restorations

Submitted by:Aditi ChandraDepartment of conservative dentistry and endodontics MDS-12Cavity designs for composite restorationsIntroductionSkinner in 1959 wrote The esthetic quality of a restoration may be as important to the mental health of the patient as the biological & technological qualities of a restoration are to his physical or dental health.The search for an ideal esthetic material for restoring teeth has resulted in significant improvements in both esthetic materials and techniques for using them.Tooth-colored materials, such as composite, now enjoy universal clinical application and are used in almost all types and sizes of restorations. Such restorations are accomplished with minimal preparation since the bonding of composite to tooth structure is not mechanical, little or no discomfort, relatively short operating time, and modest expense to the patient when compared with esthetic porcelain crowns.Definition Dental composite is a highly cross-linked polymeric material reinforced by a dispersion of amorphous silica, glass, crystalline or organic resin filler particles and/or short fibers bonded to the matrix by a coupling agent. - Skinners Dental composite is traditionally indicated as a mixture of silicate glass particles within an acrylic monomer that is polymerized during the application. - Sturdevant Composite material is a compound of two or more distinctly different materials with properties that are superior to or intermediate to those of the individual constituent. - AnusaviceIndications Pit and fissure sealant Classes I, II, III, IV & V & VI restorations Foundations or core buildups Preventive resin restoration Esthetic enhancement procedure Partial veneers Full veneers Tooth color modification Diastema closure Cements (for Indirect restoration) Temporary restorations Periodontal splinting Replacement of large existing compromised restorations As root canal filling material Repair of ceramic or composite restorationsContraindications Large posterior restorations Poor isolation High caries index Poor oral hygiene Heavy occlusal forces e.g. bruxism and clenching habits Deep subgingival preparations extending onto root surfaceAdvantages Esthetics Conservation of tooth structure: Less extension Uniform depth is not necessary Mechanical retention usually is not necessary Adhesion to tooth structure resulting in : Good retention, Low microleakage, Minimal interfacial staining Increased strength of the remaining tooth structure Low thermal conductivity Alternative to amalgam Less complex tooth preparation Used almost universally RepairableDisadvantages Technique sensitivity Polymerization shrinkage : Marginal leakage Secondary caries Postoperative sensitivity Decreased wear resistance Gap formation Higher linear coefficient of thermal expansion marginal percolation. Difficult to place, time consuming & costly because: Requires multiple steps Insertion is more difficult Establishing proximal contacts, axial contours, embrasures, and occlusal contacts may be more difficult. Finishing and polishing procedures are more difficult.Definition of tooth Preparation Mechanical alteration of a tooth to receive a restorative material which will return the tooth and area to proper form, function, and esthetics. Preparation procedure includes all defective and friable tooth structureObjectives of tooth Preparation To remove all defects and give necessary protection to the pulp. To locate the margins of the restorations as conservatively as possible. To form the cavity so that under the masticatory forces the tooth and the restoration will not fracture and the restoration will not be displaced. To allow for the esthetic and functional placement of a restorative materialObjectives of Tooth Restorations To restore form/function and esthetics. To promote maintenance of integrity of hard and soft tissues of the oral cavity. To promote health and welfare of patients.

Initial clinical procedures1. Local anesthesia: - More pleasant & uninterrupted procedure. - marked reduction of salivation.2. Preparation of operative field: Removes plaque, calculus, pellicle and superficial stains. Avoids prophylactic pastes containing flavoring agents, glycerin or fluorides.3. Shade selection: Prior to drying of teeth. According to manufactures shade guide or VITA shade guide. Natural light is preferable. Shade tab is held near the teeth to be restored & is partially covered with lip or operator thumb Make the selection as rapidly as possible. To choose accurate color - small amt. of selected color shade material is placed on the tooth, in close proximity to the area to be restored & cured. If more time is needed, eyes are rested by looking at a blue or violet object.4. Isolation of operating field:Isolation is accomplished by-:A. Rubber damB. Cotton rolls with or without retraction cord. A. Rubber dam-: While restoring proximal surface, isolate several teeth. If lingual approach used isolate upto premolars. Class V restorations No. 212 clamp should be used.If proximal restoration will involve all contact area and /or extend subgingivally, insert wedge:1. Depress the interproximal soft tissue.2. Shields the dam & soft tissue from injury.3. Produces separation of teeth.B. Cotton rolls with or without retraction cord-: Alternative method. Placed in facial & lingual vestibule (mandible). If gingival extension extends subgingivally, cord is placed5. Other preoperative procedures: A. Preoperative wedging. B. Preoperative assessment of occlusal contacts Salient features for composite restorations Minimal extension Pulpal and /or axial wall of varying depth Enamel bevel - prepared enamel margins of 90 or greater. Butt joint on root surfaces - Creating 90 cavosurface margins on root surface. Roughening the prepared tooth structure with a diamond stone.

Cavity designs for composite Restoration Conventional Beveled conventional Modified Box shape Facial/lingual slot

Conventional Tooth PreparationTypical amalgam cavity preparation design.Outline form is the necessary extensions of external walls. Uniform dentinal depth, flat floor, butt joint and retention grooves in dentin.

Beveled conventionalBeveled conventional tooth preparations are similar to conventional preparations in that the outline forms have external boxlike walls, but with some beveled enamel margins.This design is most typical for class III, IV & V restorations. Modified tooth preparationPrimarily indicated for the initial restoration of smaller, cavitated, carious lesions usually surrounded by enamel & for correcting enamel defects.Have neither specified walls configurations, nor specified pulpal or axial depths.Have a scooped out appearance without definite internal line angles.

Box only preparationIndicated when only proximal surface is faulty with no extension present on the occlusal surface.Neither beveling nor secondary retention is usually indicated.

Facial / Lingual SlotIndicated in cases when a lesion is detected on the proximal surface but operator believes that the access to the lesion can be obtained from either facial or lingual direction, rather than through marginal ridge from an occlusal direction.

DIRECT POSTERIOR COMPOSITE CAVITY PREPARATION

CONVENTIONAL CLASS I TOOTH PREPARATIONFor moderate sized carious defects.Cavity preparation is similar to amalgam but with the following differences: Outline is kept conservative with minimal extension only as dictated by caries. Intercuspal width may be as less as 1/5th the intercuspal distance. No need for dovetail or secondary retentive features.Preparation is done using pear shaped or round / inverted cone diamond abrasive.Enter the tooth in the distal pit area of the faulty occlusal surface, with the diamond point positioned parallel to the long axis of the crown.Initial pulpal floor depth 1.5mm; 0.2mm inside the DEJAll the faults, caries, old restorative material are removed1.6mm and 2mm remaining tooth structure at marginal ridges for premolars and molars respectivelyMaintain uniform depth towards cusps or into facial and lingual grooves.Outline form should be extended to the sound tooth structureAny remaining caries or restorative material is removed with round burNo bevelling on occlusal marginFacial and lingual groove extensions are bevelled: 0.25-0.5mm width and at 45 degrees angle to the prepared wallAdjacent less involved areas --- more conservatively with sealants or minimally invasive preparations. MODIFIED CLASS I TOOTH PREPARATIONMinimally involved lesions or faults.Less specific in form, having a scooped out appearance.Preparation done using small round or inverted cone diamond point.

Pulpal depth is 1.5 mm or approximately 0.2 mm inside the DEJ --- not uniform.Shallow fissures radiating from pits are treated by enameloplasty and subsequently restored with composite.Mandibular premolars often have 2 separate faulty occlusal pits located in areas of minimal function.Outline form of each pit is similar to class VI modified preparation with small diamond points.Any shallow fissure that extends laterally from the pit is incorporated in the preparation by an extended cavosurface bevel or flare.Small radiating fissures also may be filled with sealant.

CLINICAL TECHNIQUE FOR DIRECT CLASS II COMPOSITE RESTORATIONSAssessment of the expected outline formAssessment of preoperative occlusal relationshipPreoperative wedging in the gingival embrasure of proximal surfaces to be restoredTOOTH PREPARATION: Conventional Modified Conventional design --- moderate to large restorations.Modified design --- smaller restorations. Preparation has 2 components CONVENTIONAL CLASS II TOOTH PREPARATION Used for moderate class II cavities. *Similar to class II amalgam cavity design: Box-like with uniform pulpal floor and axial wall. Pulpal floor and gingival seat are perpendicular to the long axis of the tooth. *In contrast to conventional amalgam preparation: Does not require secondary retentive features. Does not require 90 degree margins More conservative in preparation Have roughened preparation walls

Occlusal stepFacial, lingual proximal extensions --- visualized. DEJ serves as a guide for preparing the proximal box portion of the preparation. No. 330 or 245 diamond stone is used to enter the pit opposite the faulty proximal surface.Diamond stone is held parallel to the long axis of tooth Only faulty areas are included.Initial pulpal floor depth: 1.5 mm - 0.2mm inside the DEJOcclusal walls converge occlusally.Occlusal cavosurface angle is slightly obtuse.Proximal extensionThe preparation is now extended proximally on the affected side.Cavity is widened faciolingually to the extent of the proximal caries.The involved marginal ridge is thinned out to expose the proximal DEJ.0.5mm of marginal ridge is preserved to prevent damage to adjacent tooth.Proximal boxThe preparation is now extended in the gingival direction to place the proximal ditch cut.Extent of the ditch cut depends on the amount of caries.Remaining proximal enamel is broken using a thinner diamond point so as to develop the facial and lingual proximal walls.Gingival floor kept flat with a cavosurface margin of 90 degree.Gingival extension should be kept supragingivally.Axial depth should be minimal into the proximal DEJ 0.2mm into the DEJ.Final cavity preparation stageNo occlusal cavosurface bevels are required.No secendory retention features as composites bond micromechanically to tooth structure.When gingival seat is supragingival and well above the CEJ gingival cavosurface bevel can be placed.When the gingival seat is close to the CEJ no need to place bevel on gingival cavosurface margin.Bevels not indicated for facial and lingual walls of proximal box except where the proximal box is wide faciolingually.Bevels placed 45 degree to the facial and lingual cavosurface margins.If preparation extends on the root surface: 90 degree cavosurface margin. Axial depth of 0.75-1mm. No secondary retention form, usually. Any remaining infected dentin is removed with round bur.

MODIFIED CLASS II TOOTH PREPARATIONA. Saucer shaped / Scooped out preparation:For small, initial restorations.Objective-: Remove the fault as conservatively as possible. Create 90 cavosurface margins or greater. Remove friable tooth structure. Small round or inverted cone diamond is used to scoop out the faulty or carious material.Pulpal and axial depths are dictated by the depth of the lesionProximal facial and lingual margins >/= 90 degree.B. Box-only tooth preparation: Proximal surface is faulty, no lesion on occlusal surface Inverted cone or round diamond, parallel to long axis of tooth Axial depth 0.2mm inside the DEJ No bevelling / secondary retentionC. Facial or lingual slot preparation: Lesion is on proximal surface Access can be obtained from the facial or lingual direction Small round diamond is used Entry is made as close to the adjacent tooth as possible, preserving as much of the facial or lingual surface Axial depth: 0.2mm inside the DEJ Occlusal, gingival and facial cavosurface margins of 90 degrees or greater

CLINICAL TECHNIQUE FOR EXTENSIVE CLASS II COMPOSITE RESTORATIONS AND FOUNDATIONSMost of the occlusal contacts restored by the restorative material.The extensions will be on the root surface.The area will probably be difficult to isolate.Retention form --- micromechanical bonding of the composite to the enamel and dentin. Secondary retention features indicated because: The increased amount of missing tooth structure. Decreased amount of tooth structure available for bonding. Increased concern for retaining the composite into the tooth.Include grooves, coves, locks, slots or pins.Cusp capping indicated when occlusal extensions are more than 2/3 the distance from the primary groove to a cusp tip.Cusps reduced early to provide more access, visibility.Clearance --- 1.5 2 mm. Cusp reductions are blended with rest of the preparation.In endodontically treated teeth, extensions made several millimeters into each treated canal to increase surface area for bonding and mechanical retention.

CAVITY PREPARATION FOR ANTERIOR COMPOSITE RESIN RESTORATIONSCLASS III COMPOSITE RESTORATIONSLocated on the proximal surface of anterior teeth not involving the incisal angle.Because the bond of composite to enamel and dentin is so strong, most class III composite restorations are retained only by the micromechanical bond from acid etching and resin bonding.No additional preparation retention form is usually necessary.Lingual approach preferred: 1. The facial enamel is conserved for enhanced esthetics. 2. Some unsupported but not friable enamel may be left on the facial wall. 3. Color matching of the composite is not as critical. 4. Discoloration or deterioration of the restoration is not visible.Indications for facial approach include: 1. The carious lesion is located facially (to conserve tooth structure). 2. The teeth are irregularly aligned, making lingual access undesirable. 3. Extensive caries extend onto the facial surface. 4. A faulty restoration that was originally placed from the facial approach needs to be replaced.

CONVENTIONAL CLASS III TOOTH PREPARATIONThe primary indication is for the restoration of root surface.Cavosurface margins ---90 degree angle.External walls--entirely of dentin and cementum.Prepared to a sufficient depth pulpally to provide for: Adequate removal of caries, old restorative material or fault. The placement of retention grooves if deemed necessary.Grooves necessary in non-enamel, root surface preparations to increase retention of material and marginal seal. Continuous groove given in cases of large restorations.Grooves on the incisoaxial and gingivoaxial line angles--- moderately large restorations. Preparation ---beveled or flared only in the coronal part of the preparation.

BEVELED CONVENTIONAL CLASS III TOOTH PREPARATIONIndicated primarily for replacing an existing defective restoration in the crown portion of the tooth.Characterized by external walls that are perpendicular to the enamel surface, with the enamel margin beveled.Bevel width -- 0.25 0.5 mm sufficient using a flame shaped bur.All accessible enamel margins are beveled except gingival margin and lingual margins if the margins are located in heavy stress areas.The axial line angles may or may not be of uniform pulpal depth.Usually retention is obtained by bonding to enamel and dentin and no groove retention is necessary. If retention features are indicated---prepare them along the gingivoaxial line angle and sometimes the incisoaxial line angle with a No. round burs. Remaining old restorative material on the axial wall should be removed.Unless absolutely necessary, do not: Include the proximal contact area. Extend onto the facial surface. Extend subgingivally.The axial wall depth ---0.2 mm into dentin.Axial wall will be outwardly convex.If retention groove is to be placed, the axial wall depth ---0.5 mm into dentin at retention locations (prevent undermining enamel).If preparation outline extends gingivally onto the root surface, the depth of the axial wall at the gingivoaxial line angle should be 0.75 mmMODIFIED CLASS III TOOTH PREPARATIONMost used type of Class III tooth preparation.It is indicated for small and moderate lesions or faults and is designed to be as conservative as possible.The preparation design is dictated by the extent of the fault or defects and is prepared from a lingual approach when possible, with an appropriate size round bur or diamond instrument.No effort is made to produce preparation walls that have specific shapes or forms other than external angle of 90 degrees or greater.The extension axially --- not of uniform depth. Weakened, friable enamel is removed while preparing the cavosurface margins in a beveled or flared configuration with the round diamond.CLASS IV COMPOSITE RESTORATIONSClass IV caries are smooth surface caries found on the proximal surfaces of anterior teeth, involving the incisal edge of the tooth.Traumatic injuries also result in class IV defects.Class IV composite restorations are a conservative option for the above situations as compared to a ceramic crown.CLINICAL TECHNIQUEPreoperative assessment of the occlusion: It may influence the tooth preparation extention (placing margins in non-contact areas) Retention and resistance form features (heavy occlusion requires increased retention and resistance form).Occlusal factors may dictate a more conventional tooth preparation form, with more resistance form features: Boxlike, flat floors, and walls and floors parallel to the long axis and perpendicular to the occlusal forcesSecondary retention form features: Grooves and wider bevel.CONVENTIONAL CLASS IV TOOTH PREPARATIONRarely used for class IV restorations.Indicated --- cases in which any of the margins of the restoration extends onto the root surface.Cavosurface margins --- 90 degrees angles.Does not have bevels or flares.Retention features --- grooves or cove (increase the retention form).

BEVELED CONVENTIONAL CLASS IV TOOH PREPARATIONIndicated for restoring large proximal areas that also include the incisal surface of an anterior tooth.Retention of the composite restorative material in beveled conventional class IV tooth preparation may be obtained by groove or undercuts, dovetail extensions, threaded pin, or a combination of these.Arbitrary dovetail extension onto the lingual surface of the tooth may enhance both the restorations strength and retention, but it is less conservative and therefore not used often.Pin retention is sometimes necessary but, the use is discouraged for several reasons: Risk of perforation either into the pulp or through the external surface. Do not enhance the restorations strength. Pins may corrode because of microleakage of the restoration, resulting in significant discoloration of the tooth or the restoration. Despite of these disadvantages the pins are placed when a large amount of tooth structure is missing. MODIFIED CLASS IV TOOTH PREPARATIONIndicated for small or moderate lesions or traumatic defects.Objective --- remove as little tooth structure as possible, and providing for appropriate retention and resistance forms.No initial tooth preparation is indicated for fractured Incisal corners, other than roughening the fractured tooth structure.Cavosurface margins --- beveled or flared.Axial depth --- extent of the lesion, previous restoration or fracture.No groove or cove retention form is indicated.CLASS V COMPOSITE RESTORATIONSLocated in the gingival 1/3 of the facial or lingual surfaces of the tooth.During shade selection it should be remembered ---tooth is darker in the cervical third.Factors to be taken into consideration --- esthetics, caries activity, access to the lesion, moisture control and patients age.CONVENTIONAL CLASS V TOOTH PREPARATIONIndicated for lesion or defect entirely or partially on the facial or lingual root surface of a tooth.Features of the preparation: Axial depth --- 0.75 mm, provides adequate external wall width for: Strength of the preparation wall. Strength of the composite. Placement of the retention groove if necessary.Axial wall follows contour of the facial surface.Extensions --- extent of the caries, defect or old restorative material.All external preparation walls --- visible when viewed from a facial position.Retention grooves --- prepared along the entire length of the gingivoaxial and incisoaxial line angles. (0.25 mm deep)

BEVELED CONVENTIONAL CLASS V TOOTH PREPARATIONIndicated for replacement of existing defective restorations and for large new carious lesions.90 degree cavosurface margin that subsequently are beveled.Axial wall --- uniform in depth. Retention groove is not indicated when the periphery of the tooth preparation is located in enamel.Preparation on the root surface, depth of the axial wall --- 0.75 mm.Bevel --- 45 degree to the external tooth surface and width of 0.25 0.5 mm.Advantages are: I. Increased retention due to greater surface area of etched enamel offered by the bevel. II. Decreased microleakage due to increased bond strength between the enamel and the composite. III. Decreased need for groove retention form.MODIFIED CLASS V TOOTH PREPARATIONIndicated for the restoration of small to moderate carious lesions.Objective --- restore the lesion or the defect as conservatively as possible.No effort to make the walls as butt joint.No retention groove incorporated.Preparation is scooped out resulting in divergent wall Axial depth not uniform.

CLASS V TOOTH PREPARATION FOR ABRASION OR EROSION LESIONSOperators decision for restoration depends on: Presence of caries. If the notched area is causing gingival inflammation. In an esthetically critical position. Is very sensitive Is very large and deep pulpally. Is affecting the strength of the tooth. Requires only roughening of the internal walls with a diamond instrument. Beveling or flaring of all enamel margins. Placing a retention groove in non-enamel areas.Root surface cavosurface margin is 90 degrees.Placement of grooves results in increased Retention and decreased MicroleakageTOOTH PREPARATION FOR ABERRANT SMOOTH SURFACE PIT FAULT Most aberrant pit faults in enamel are restored best with use of a modified preparation. Outline form (includes extensions and depth) is dictated by the extent of the fault and/or caries lesion. Faults existing entirely in enamel are prepared with an appropriately sized round diamond instrument by merely eliminating the defect. Adequate retention is obtained by etching the enamel (the first step in applying restorative materials). When the defect includes carious dentin, the infected portion is removed also, leaving a flared enamel margin.

CLASS VI COMPOSITE RESTORATIONSClass VI fault is a small faulty developmental pit located on a cusp tip. Usually no anesthesia is required because the fault is entirely in enamel. The tooth is isolated with a cotton roll.Tooth preparation should be as small in diameter and as shallow in depth as possible. Enter the faulty pit with a small, round bur (No. '/4 or No. '/2) or diamond point oriented perpendicular to the surface and extend pulpally to eliminate the lesion.Visual examination and probing with an explorer often reveals that the fault is limited to enamel because the enamel in this area is quite thick. If the preparation is not already completed at this stage, complete the preparation using either a flame-shaped or round diamond instrument to roughen the prepared surfaces.If a faulty restoration or extensive caries is present on the cusp tip, a round bur of appropriate size is used for excavating remaining infected dentin. Stains that appear through the translucent enamel should be removed.Some undermined, but not friable, enamel may be left and bonded to the composite

CONCLUSIONComposites have unquestionably acquired a prominent place among the filling materials employed in direct techniques. Their considerable aesthetic possibilities give rise to a variety of indications.Also, these materials conserve the tooth structure better because they are retained by adhesive methods rather than depending on cavity design.Nonetheless, it should not be forgotten that they are highly technique-sensitive, hence the need to control certain aspects: correct indication, good isolation, choice of the right composite for each situation, use of a good procedure for bonding to the dental tissues and proper curing are essential if satisfactory clinical results are to be achieved.

REFERENCES Sturdevants Art of Science of Operative Dentistry: 5th edition - Theodore M. Roberson Restorative Dental Material-Robert G. Craig Phillips Science of Dental Materials- Kenneth J. Anusavice Operative Dentistry- Marzouk Terry D and Leinfelder K. Composite resin restoration: a simplified approach. Private dentistry, Apr 2008:24-38. Graham J Mount. Minimal intervention dentistry: cavity classification & preparation. International dentistry SA; 2009; 12(3): 54-63.