Cavity Preparation for Resin Composite Restoration PDF

Cavity Preparation for Resin Composite Restoration Conservative approach in operative dentistry Definition: Minimally invasive approach that focus on detecting, diagnosing & removing only damaged structure, preserving the remaining healthy tooth structure and emphasizin...

Cavity Preparation for Resin Composite Restoration Conservative approach in operative dentistry Definition: Minimally invasive approach that focus on detecting, diagnosing & removing only damaged structure, preserving the remaining healthy tooth structure and emphasizing the concepts of prevention and remineralization during restorative procedure § It refers to all procedures carried out to preserve the integrity of teeth and the masticatory system. § Prevention is the theme applied nowadays in operative dentistry rather than extension for prevention. § The concept of "Sealing for prevention"; e.g., using pit and fissure sealants, § Black's statement: "The day is surely coming when we will be engaged in practicing preventive, rather than reparative dentistry". The classic cavity preparation has been modified into what is known as "adhesive cavity design". Advantages of conservative/Adhesive cavity design: 1. Preservation of healthy tooth structure. 2. Decreased irritation of dentin-pulp complex and investing tissues. 3. Decreased fractured tooth and/or the restorations. 4. Decreased displayed area of the restorations. 5. Easier, quicker and standardized procedures. 1 Steps of Cavity Preparation: 1. Obtaining of the outline form 2. Obtaining of the resistance and retention forms 3. Obtaining of the required convenience form 4. Removal of the remaining carious dentin 5. Finishing of the cavity walls and margins 6. Performing the toilet of the cavity 1- Obtaining of the Outline form Cavity Outline is the shape of boundaries of the completed cavity. The external outline describes the external marginal boundaries & the internal outline describes the shape of the internal form of the preparation. The aim is to place the margins of cavities in sound enamel at areas not carious and less stress-bearing. The most important factors that govern the extension of the outline of the cavity are the carious lesion and the convenience of preparation to be easily seen, approached & restored. The cavity outline is limited only to defective enamel and dentin. Essentials of the outline form in Composite Cavity Preparation: 1. All carious enamel and dentin must be included in the outline. 2. All pits & fissures which are deeper than one third the enamel thickness should NOT be included in the outline (But rather sealed with pit & fissure sealant or treated with enameloplasty) 3. All weak or undermined enamel must be eliminated and included in the outline. (Undermined Enamel: Enamel not supported by Sound Dentin) 2 4. Adjacent cavities, approaching to each other, should ONLY be joined when the intervening tooth structures are: à Carious à Undermined à Weak (less than 1mm) à and if Crossed by a fissure (Sealed with pit & fissure sealant / Enameloplasty) This is specially considered with oblique and transverse ridges. 5. All severely weakened cusps and ridges that are subjected to occlusal forces must be reduced and included in the outline to be protected with appropriate restoration (cusp capping). 6. The outline form must be in the form of harmonious sweeping curves to avoid stress concentration and provide better esthetic. 7. The Cavo-surface angle given correct angulation according to the location of the margin. Composite CSA is 90◦ ( Butt Joint) in margins subjected to direct force + gingival margins & beveled in margins not subjected to direct force (ex. Labial) Pit & Fissure sealing: - Indicated in case of deep grooves liable to food stagnation and difficult to clean in recently erupted permanent molars. - Using pit & fissure sealing instead of preparing them to be included in the outline has preserved sound tooth structures 3 Preventive resin restorations (PRR) Definition: It's a preparation that eliminates the carious lesion only and restore it with a resin composite material with sealing of the remaining non-carious pits & fissures by pit & fissure sealant. Simple box preparation: Small proximal lesion without including occlusal fissures Outline forms: Rounded form for resin composite. With resin composite retention is based on the Micro- Mechanical Bonding. If there is sound occlusal fissure + proximal Caries ® Simple box preparation + fissure sealant to prevent any stagnation area. 2- Obtaining the Resistance & Retention forms Resistance form: design features in the cavity preparation which allows both tooth and restoration to resist the functional stresses of mastication without fracture. Preservation of tooth structure is mandatory. Walls à according to enamel rod direction, parallel to direction of enamel rods Floor à smooth & according to direction of the force, might not be even according to caries extension & removal. Proper depth & width to provide bulk of the restoration. 4 Sufficient bulk for composite (minimum 1- 1.5mm). Bonding to tooth structure reinforce the remaining weak tooth structure provided that it is not too weak, thin or undermined which need reduction and coverage with strong restorative material. Rounded line and point angles to increase the wettability and adaptation of the viscous resin composite by using suitable burs as round bur & burs with rounded end (330, 245, 246…. etc.) CSA is determined according to the site of the margin: - Non-stress bearing area (as labial surface) à beveled CSA. - Stress bearing area (as occlusal of posterior teeth)à butt joint CSA (90o). - Gingival margin à butt joint CSA (90o). Retention form: design features in the cavity which enables it to retain the restoration securely in function & prevent its displacement. It is provided with micromechanical means of retention (bondodontics) No macro-mechanical means of retention are needed. Co-relation between resistance & retention: Bonding to tooth structure reinforce the remaining weak tooth structure, provided that it is not too weak, by mono-block concept due to absence of wedging action by the restoration. 5  3- Obtaining of the required Convenience form Definition: features in the prepared cavity, making it more conveniently seen, approached and/or restored Just to improve the visibility & approach to the cavity during preparation & restoration. Micro-sized burs accompanied with magnifications (loupes & microscopes) improved the convenience. “CONSERVATIVE APPROACH” encouraged development of more precise tools & restorative materials to access & restore defects with Maximum Conservation to tooth structure and Minimum Cutting, for example: 1) Micro-Sized Burs: Help prepare smaller sized, more conservative cavities. 2) Magnification “Dental Loupes and Microscopes”: Improve vision for minute defects to allow for precise preparation for small defects without additional overcutting for vision. 3) Visibility “Fiber-Optic handpieces & Loupes with Auxiliary Light”: Increase visibility & illumination. 4) Restorative Material: New restorative materials that can treat defective lesions without the need of excessive cutting of tooth structure “Ex. Pit & Fissure Sealants. Magnification vLoupes: They are similar in appearance to eyeglasses % allow a magnification in the range of 2x-5x. They are sometimes associated with lighting by single spot halogen or fiberoptic lamps. Recently xenon lamps are used 6 v Microscopes: 1. They allow a magnification on in the range of 10x-25x. 2. The majority of procedures are undergone with range of 10x-12x. 3. Frequent adjustments wall mounted or ceiling mounted 4- Removal of remaining carious dentin Providing sound dentin is very critical to achieve successful and durable bonding to it. Many tools are used to discriminate between sound & carious dentin. The simplest way is using caries detection dyes (CDD). In posterior teeth, discolored sound dentin can be left as it doesn’t affect esthetic While in anterior teeth, discolored sound dentin must be removed or masked by opaquer to avoid esthetic impairment. Concepts of caries Removal and excavation I. Complete caries excavation Conventional strategy set by “G.V. Black” It involves removal of soft demineralized dentine (soft infected Dentin) and (firm affected dentin) before placing the restoration. This tissue is heavily infected with bacteria and is removed using a drill or sharp spoon like instruments (excavators), in order to stop the decay (carious)process. II. Stepwise excavation Involves the removal of carious tissue in stages. 7  Removal of peripheral demineralized dentin and the superficial parts of the necrotic and demineralized central dentine. Leaving the softened and wet tissue on the pulp wall. The base of the cavity is lined and then sealed with long temporary restoration for 2-12 months. Re-entry to put final restoration III. Partial caries removal Conservative approach strategy This technique is based on the concept that the carious process is guided by caries activity in the biofilm, therefore, this process could be stopped simply by sealing the cavity. After partial excavation, the base of the cavity may be lined with calcium hydroxide (although this is not essential) and the cavity is filled with a permanent restorative material, with no re-entry in the cavity. 5- Finishing of the cavity walls & margins Finishing of the enamel margin is a very crucial step to eliminate the microcracked enamel margin due to the cutting procedure. If the microcracks left unfinished à propagation of the cracks at the margin à leaky margin Beveled cavo-surface angle: to a 45° short bevel. This has the following advantages: Advantages of bevel: a) Increases the surface area & surface energy of enamel. b) Exposes the ends of enamel rods rather than the sides à more retentive etching pattern with micro- & macro-pores in enamel. 8  Etching pattern with beveled (A) and un-beveled (B) enamel margin c) Gradual color degradation between tooth and restoration à improve esthetics. - The width of the bevel is usually 1 -1,5 mm. - This width could be increased based on the retention requirements, e.g. in fractured class IV where the etched enamel will be the main retentive mode. The bevel is contraindicated in: à Stress-bearing areas, e.g. in occlusal surface of posterior teeth à to avoid chipping of composite in such areas. à Gingival wall to avoid chipping of thin enamel at the margin. 6- Toilet of the cavity It includes the removal of any debris, dentin chips, bacteria, providing a clean dry cavity and conditioning the cavity surface to receive and retain the restoration. Before application of resin composite the tooth structures (enamel & dentin) must be treated to provide strong bonding between them. Different adhesive approaches are now available to provide accepted and 9 durable bonding to tooth structures: Ø Etch & rinse approach Ø Self-etch approach Ø Glass ionomer approach Ø The most recommended protocol is Selective Etch Technique 10