1 10 Restoration of teeth (complex restorations). Introduction 105 Cementation 124. Replacement of lost coronal tooth structure 105 Finishing 124. Choice of core material 106 Review and maintenance 125. Dental amalgam 107 Summary 125. Resin composite 107. Glass ionomer cements 107. Resin ionomers and compomers 108 INTRODUCTION. Preoperative assessment 108. Restorability of tooth 108 Traditionally, more extensive restorations on teeth were Pulpal/endodontic status 109 performed using non-adhesive techniques. The materials Periodontal/occlusal assessment 109 of choice were gold, porcelain and metallic Pin retention for core foundations 109 were placed either intra- or extracoronally and relied on Foundation restorations for endodontically treated the preparation having near-parallel walls, assisted by a teeth 110 luting cement to fill the marginal gap and help with the Crowns 112 retention process.
2 With the development of new materials Preoperative planning 112 and techniques for bonding to the tooth, there has been a Choice of material for indirect restorations 113 blurring of the methods used and often restorations rely on Gold 113 a multitude of factors for retention which incorporate Porcelain (ceramic) 114 both mechanical and adhesive principles. Indirect composite 114. Metal ceramic 115. Tooth preparation guidelines for indirect restorations 115 REPLACEMENT OF LOST CORONAL TOOTH. Features of preparations for indirect restorations 115 STRUCTURE. Types of finish margins 116. Preparation stages 116 Indirect restorations are frequently placed on teeth which Indirect adhesive restorations 116 have lost substantial amounts of tooth structure. Retention Tooth-coloured inlays 116 and resistance form are lost as the height of the tooth The dentine-bonded crown 118 preparation is reduced in relation to the intended occlusal Porcelain laminate veneers 119 surface position of the final restoration.
3 A foundation or Indications 120 core build-up restoration may be required to supplement Contraindications 120 retention and resistance form. The strength required of a Design considerations 121 foundation restoration will vary, depending on the location Tooth preparation 121 of the tooth in the dental arch, as well as on the design of Impression 123 the surrounding tooth preparation. Apart from acting as a Temporary cover 123 transitional restoration in the management of a damaged Laboratory aspects 123 tooth, a core build-up restoration must withstand crown Try-in 124 preparation and impression-taking and contribute to the 105. Restorative Dentistry form, it is impossible to separate these two features. Retention will prevent dislodgement of the restoration along a direction parallel to its path of insertion, whilst resistance prevents dislodgement in any other direction.
4 Minimal taper and maximum preparation height are criti- cal features for good retention. The fit of the restoration, any surface treatments which facilitate adhesion, and the nature of the cement lute are also important variables. If adequate retention and resistance form can be developed from natural tooth structure, the strength of any core or foundation restoration is less critical and minor depres- sions or undercuts in the tooth preparation can be restored with adhesive restorative materials. CHOICE OF CORE MATERIAL. Clinically, there are times when the remaining tooth struc- ture is so reduced that the margins of the crown must be placed at or just below the core. It is under these con- ditions that the choice of core material may be critical. Core build-up materials for direct placement include: Fig. Core build-up of lost coronal tooth structure. dental amalgam resin composite reinforced glass ionomer cements retention and support of a provisional crown before the resin-modified glass ionomers/compomers (polyacid- modified resin composites).
5 Definitive crown restoration is placed (Fig. ). Gold alloys and ceramics have been used as indirect When retention and resistance depend significantly on core build-up materials. Each candidate core material has the core build-up, the strength of the foundation restora- advantages and disadvantages. tion and its retention to the underlying tooth tissue can directly influence the survival of the restoration. Some core materials lack sufficient strength and/or adhesion to tooth tissues to serve this function. Posterior teeth are Box Desirable properties for a core material exposed to greater forces than are anterior teeth and the Compressive strength to resist intraoral forces direction of load differs. Teeth that have to serve as abut- Flexural strength to prevent core dislodgement during ments for fixed or removable prostheses are subject to function increased stress.
6 Biocompatibility with surrounding tissues Almost one-quarter of all posterior crowns were pro- Ease of manipulation vided with a pin or post retained core. The restoration of Ability to bond to tooth structure, pins and posts severely broken down teeth is an increasing problem for Capacity for bonding with luting cement or having the restorative dentist, as more patients retain their natural additions made to it teeth into older age. Clinical studies demonstrate an Coefficient of thermal expansion conductivity similar to increased incidence of tooth fractures in teeth with large dentine restorations compared with sound or minimally restored Dimensional stability teeth. Minimal water absorption Whilst advances in adhesive restorative materials and Short setting time to allow tooth preparation and core techniques may result in more predictable retention of placement to be carried out during the same visit restorations with compromised retention, the success of No adverse reaction with temporary crown materials or these techniques is still to be confirmed by clinical trials.
7 Luting cements Such techniques may be operator-sensitive as the success Cariostatic potential of an indirect restoration depends on the ability of the Low cost cement or resin lute to prevent dislodgement of the Contrasting colour to tooth tissue unless being used for restoration from the tooth preparation; the latter must anterior cores possess adequate retention and resistance form. Whilst resistance form is considered more critical than retention 106. 10 / Restoration of teeth (complex restorations). Fig. A composite core. Fig. An amalgam core. composite core materials possess similar compressive and Dental amalgam tensile strengths to amalgam cores. Only radio-opaque amalgam has adequate mechanical properties for many composites should be considered as core materials. The core build-up situations. It is radio-opaque and has been high coefficient of thermal expansion of composite cores shown to have superior cariostatic properties to com- and their greater potential for water uptake are negative posites.
8 It has high thermal conductivity and coefficient of aspects of these materials. In addition, eugenol-based thermal expansion. It is not adhesive to tooth structure, temporary cements may soften their surface or impede although methods of bonding amalgam using resin bonding of resin-based luting cements. Composite is best adhesives are available, and glass ionomer/resin ionomer as a direct core material when substantial coronal tooth cements show promise. Conventional dental amalgams set structure remains for bonding and where reliable moisture too slowly to allow tooth preparation during the same visit control may be obtained. Several composite core materials as core build-up. Modern fast-setting spherical alloys may contain fluoride which is released in trace amounts for up allow preparation 20 30 minutes after placement. Silver to 5 years but no clinically relevant cariostatic property has amalgam has been reported to be the most reliable direct yet to be established for these materials (Fig.)
9 Core build-up material under simulated clinical conditions because of its high compressive strength and rigidity Glass ionomer cements (Fig. ). Conventional glass ionomer restoratives are popular with many dentists as core materials because of their adhesive Resin composite properties and ease of handling. They are relatively slow- Composite core materials are becoming increasingly setting and their early resistance to moisture is poor. Many popular for core build-ups. Provided adequate moisture products are not radio-opaque. Although they may be control is obtained, these materials may be reliably bonded considered to have adequate compressive strength for use to tooth substance, and their command set nature allows as core build-up materials, their flexural strength and immediate tooth preparation. An incremental technique is fracture toughness are low. Conventional glass ionomer required to ensure complete polymerisation unless specific cements are therefore only suitable where there is sub- light-activated core composites are used.
10 Some of these stantial tooth substance remaining to support the material materials offer depth of cure of up to 8 mm (Cavex and where adequate resistance form may be obtained on Clearfil Photo-Core, Kuraray). Composite materials adapt natural tooth tissue. Cermet cements do not provide well to pins and pin-retained composite cores. Some resin advantages over conventional glass ionomers and often 107. Restorative Dentistry have poor adhesion to tooth structure. Recently intro- often amalgam remaining in proximal boxes, class V areas duced condensable glass ionomer cements may prove a and other regions. All previously placed materials should better alternative as these materials can be bonded more be removed (unless the operator has recently placed the reliably and are stronger. restoration and is sure it is reliably retained to sound tooth tissue), allowing teeth to be rebuilt without the risk of an insecure foundation or previous pulpal exposure remain- Resin ionomers and compomers ing undetected.