Indirect Restorations PDF

# Indirect Restorations ## Inlays - Indirect restorations which involve the occlusal and proximal surface(s) of posterior tooth ## Onlays - Indirect restorations which cap in addition one cusp (partial onlay) or all cusps (complete overlay). - Made of either metallic or non-metallic materials...

# Indirect Restorations ## Inlays - Indirect restorations which involve the occlusal and proximal surface(s) of posterior tooth ## Onlays - Indirect restorations which cap in addition one cusp (partial onlay) or all cusps (complete overlay). - Made of either metallic or non-metallic materials. ## Metallic Restorations - Could be fabricated from different alloys such as cast gold alloys (especially type III), low gold alloys, base metal alloys, nickel-chrome and titanium alloys. ## Non-Metallic Restorations - (tooth-colored restorations) are made of either ceramic materials or post cured resin composite restorative materials. ## Cast Gold Restorations - Cast gold inlay is a precise metallic duplicate for the prepared cavity which is fabricated outside the oral cavity and cemented in place in one piece in order to restore the lost tooth structure. ### Advantages of cast gold restoration: - Indestructibility in the oral fluids, i.e. insolubility and highly resistant to tarnish and corrosion - High strength properties - Dimensional stability - Biocompatibility - Allow achievement of optimum occlusion, contour and contact - Attain and maintain a high surface polish in view of its high abrasion resistance. However, it wears at the same rate as the tooth - Convenience of manipulation ### Disadvantages of cast gold restoration: - Inharmonious color - Lake of adaptability to cavity walls and margins due to the cement line - Less retention - High thermal conductivity - Number of appointments, time and cost - Part of the restoration quality is dependent on the lab work. ### Indications: - Extensive tooth involvement, including: - Badly broken-down teeth - Where the steepness of the cusps increases their tendency to split - Cracked or crazed teeth - Restoration of endodontically treated teeth - To restore cavities extending deep subgingivally - Correction of occlusion or when teeth suffer from wear, attrition or erosion or for diastema closure. - Adjunct to perio-therapy. - Fixed or removable prostheses abutments. - As a restoration for cases that requires saving of clinic chair-time, since most of the work can be completed in the lab. ### Contraindications: - High Plaque and Caries Indices - Where other permanent direct restorations are indicated for tooth conservation. - Developing or Deciduous Teeth. - Compromised Patient. - Esthetically sensitive areas. ## Design of cavity preparation: All the previously mentioned fundamentals of cavity preparations are required to be respected and applied throughout all steps of cavity preparations. However, the final cavity design has some different features compared with that used for direct metallic restorations (commonly amalgam). Differences will be listed with regards to each step of cavity preparation. ### Outline form: - Internal cavity walls must be uniformly tapered occlusally (slight occlusal divergence with a degree of taper 3-50 for each wall). This will result in a cavity that has wider external outline form than the internal outline form which is needed for the seating of any restoration fabricated outside patient mouth. - Cavo-surface margin should be beveled; This allows for burnishing of the metal alloy to bring the margins of the alloy in contact with enamel and prevent exposure of cement line. - Gingival seat Cavo-surface margin should be trimmed with GMT creating short bevel (30 degree and 0.5-1mm width). This enhances the seating ability of final restoration at this area. - All internal line angles must be well defined but not sharp. All axial walls and external walls should follow external tooth contour at the horizontal plan and converge occlusally toward each other with same degree of taper. - In case of occluso-proximal cavity preparation, primary flares that are regularly made with direct restoration to free the contact, are accompanied with secondary flares. Secondary flares must be uninterruptedly blended with the occlusal bevel and the gingival bevel. Secondary flares are thus created on proximal walls (facial and lingual walls). This means that in cast gold preparation the facial and lingual walls extend from the facio- or linguo-axial line angle into the facial or lingual embrasure in two planes. - Secondary flare is necessary for several reasons: - Extends the margins into the embrasures, making these margins more self-cleansable and more accessible to finishing procedures during the inlay insertion appointment. - Provides flexible arms of preparation to desired locations with minimal tooth involvement which add to restoration retention and to tooth reinforcement bodily and marginally. - Creates obtuse angled marginal tooth structure (140-150 degree). A more blunted and stronger enamel margin is produced because of the secondary flare. - Creates acute angled marginal metal alloy (30-40 degree). The direction of the flare results in 40-degree marginal metal. Metal with this angular design is burnishable; however, metal shaped at a larger angle is unsatisfactory for burnishing; while metal with an angle less than 30 degrees is too thin and weak, with a corresponding enamel margin that is too indefinite and ragged. - Reduces internal space errors marginally two to three fold and thus, establishes the most definite preparation termination with the least tooth structure sacrifice. - In case the outline form extended more than one third the intercuspal distance of the prepared tooth, onlay is recommended. - Cast gold restorations have high strength properties; thus giving the restoration bulk is not a prime request as for brittle direct restorative materials. However, care must be given not to subject thin sections to direct occlusal forces that causing plastic deformation of the materials which will lead to open margins. • Axio-pulpal line angle should be beveled to provide strong wax pattern at this area so that it does not warp at this are during handling. ### Resistance and retention form: - Tooth resistance could be attained by following all the early mentioned fundamentals, including that the walls should be parallel or perpendicular to force direction and should follow the enamel rods directions, having rounded but definite line angles and making the cavity outlines follow the sweeping curves. - Restoration resistance on the other side is not a crucial issue as compared to direct brittle restorative material due to the inherent strength property of this material. ### Axial retention: - Could be encountered mainly by friction of opposing walls. This governed by the degree of wall tapering, length, roughness, and cement type. Increasing the degree of tapering or occlusal divergence will decrease the frictional retention. - For proximal part, providing a dovetail whenever indicated, occlusal locks, proximal grooves, reverse gingival bevel and secondary flares are also means of retention. Proximal grooves should not interfere with the path of insertion and removal of the inlay. ## Ceramic Restorations - Increasing esthetic demands have led to more frequent use of tooth-colored restorative materials in posterior teeth. Many patients are no longer willing to accept extensive gold inlays and onlays. - The problems inherent with old types of porcelain such as material weakness and marginal integrity, combined with lack of an adequate cementing medium, initially made this an unsuccessful restoration. The recent development of reinforcing systems for porcelain, coupled with the ability to etch and bond the porcelain to the underlying etched tooth surface, has allowed these types of restorations to become more popular and successful. ### Advantages over metallic restorations: - Color blending with adjacent tooth structure could be well established enhancing aesthetic. In addition, this color match is durable. - A ceramic restoration will accumulate low plaque on its surface. - They offer lower thermal diffusivity which decreases the thermal irritation to the tooth. - Through bonding, they offer increase in the fracture resistance of the restored tooth. ### Disadvantages: - Technique sensitive, whereas much time and attention are required to be given when these restorations are fabricated and placed. - The probability of unbonded restoration to fracture during the try-in phase. - Number of appointments and laboratory fee is an added factor during treatment plan. - Potential of wearing of opposing tooth, however newer versions of ceramics are less abrasive. - In ceramics with surface stain, occlusal adjustment results in the loss of the surface colorants. - Marginal adaptation of machined ceramics still needs special attention. ### Indications: - Extensive tooth involvement with undermined or weak enamel. - Where metal allergy is a factor. - The restoration of teeth in an arch opposed by already present porcelain restorations. - Teeth where it is difficult to develop retention form. ### Contraindications: - Evidence of para-functional habits and aggressive wear of the dentition. • - Patients with gold restorations in opposing teeth. - The problems of maintaining a dry field. ## Preparation design requirements: - Same as indirect metallic restorations, all fundamentals should be followed. - Some differences in the cavity design should be encountered that are necessary to overcome the inherent weakness of these restorative materials. - Keeping a homogenous thickness of the material is of prime concern; the floor should have an even depth of 1.5-2.5mm. - The cavity walls should be slightly more divergent from the pulpal floor toward the enamel surface. - There is no need for frictional fit as required for metallic cast restorations. - The occlusal cavo-surface margin of the preparation should not be beveled. The cavo-surface margin should end into a well defined smooth butt joint or a Hollow-ground chamfer bevel. It was reported that the Hollow ground type of bevel offer some advantages over the butt joint such as exposing the enamel rods at right angle that aids in achieving more effective seal. Also it helps in color blending, making the demarcation line between tooth and restoration not perceptible. Despite these advantages, most dentists usually use the butt joint cavo-surface margin due to its preparation practicality and less chance for marginal defect during preparation. - All internal line angles must be rounded. This is achieved by performing the preparation with a specially designed tapered cylinder that has a flat end with a rounded radius. ## Indirect resin composite restorations Inlays and onlays made of resin composite are fabricated either intraorally (direct) or on a cast (indirect) or intra-orally and then adjusted on a cast (direct/indirect). After polymerization, the restoration is bonded in place with a resin luting cement. Resin composite inlays are aesthetic and have certain advantages over direct composite resin and bonded ceramic restoration. ### Advantages over direct resin composite restorations: - Less polymerization shrinkage; since compensation for shrinkage occurs through curing the material outside of the mouth. Uncontrolled polymerization shrinkage of direct composite could cause a marginal gap leading to pulpal irritation and tooth sensitivity. It can also cause cuspal flexure, which is sometimes associated with craze lines in the enamel and postoperative hypersensitivity. - Better control of contact area and contours. - Better marginal adaptation especially in the most critical areas such as proximal gingival seat. - Increased strength properties of the resin composite because of the postcuring process. Post-curing can be done by post-cure unit specially made for this purpose, under heat with and without curing light or curing box. Post-curing units for polymerization under pressure and vacuum are also available. - While the advantages over ceramics are: • Reduced or no lab fee if done in clinic. - Ready repairability of material intraorally. - Feasibility of occlusal surface adjustment. - Easy removal if replacement becomes necessary. - More user-friendly in clinic and lab. ### Disadvantages compared to direct resin composite are: - more tooth structure is required to be removed. - Reliable chemical bonding does not form between the restoration and the resin cement, as the inner surface has relatively few unreacted methacrylate groups. ### Disadvantages compared to ceramics are: - Adhesion of resin cement is more reliable to ceramic restoration than resin composite ones. - Although some onlay ceramics cause wear of opposing enamel, they also provide long-term occlusal stability, which resin composite may not provide. - Cavity design for indirect resin composite restoration: It is the same as that described for ceramic restorations. - Fabrication of the indirect resin composite restoration: Fabrication technique for the restoration depends on the specific system of materials being used. Three different fabrication techniques are available namely direct technique, indirect technique and combined direct-indirect (semi-direct). The indirect technique can be accomplished in one-visit or twovisit method.