Preparation of extensively damaged vital teeth.

it is important to remember that the strength of a tooth is directly proportional to the quantity of remaining enamel and dentine. Loss of tooth structure is attributed to caries, repeated replacement of failed restorations, fractures, endodontic access cavities and tooth preparation for extra-coronal restorations.

The essential difference between cores onvital and non-vital teeth is that, in the former,retention is solely from coronal dentine, whilefor the latter, additional support is gained fromintra-radicular posts. A variety of methods isavailable for gaining retention on vital teethincluding pins, cavity modifications, dentinebonding agents (DBAs) and luting cements.

PinsPins have been advocated for generations as ameans of retaining cores on vital teethHowever, pins have numerous disadvantages, and their use should be questioned in many clinical situations.Many studies have shown that pins cause dentine crazing and tooth fracture, and are potentially perilous to the pulp and periodontium. Furthermore, no difference in retention is observed with pins or other methods of supporting a core

Pins are one of the oldest methods for buildinga foundation on structurally compromised vital

teeth.

Porcelain onlay case study: pre-operative viewshowing failing composite filling with secondary caries inmandibular first molar.

Cavity modificationInstead of using pins, another method for retentionis modifying the remaining tooth structure.This includes creating undercuts, boxes, slots or grooves for obtaining retention for the restorative material, particularly in conjunction with DBAsIf teeth are excessively broken down, crown lengthening or orthodontic extrusion should be considered for ‘gaining’ extra tooth structure. Cuspal coverage also helps retention of the final restoration, and when thecusp width is less than 1mm, it should be reduced sufficiently to accommodate an appropriate thickness of the overlying restorative material.

Porcelain onlay case study: preparation for indirect ceramic onlay, necessitating a minimum of 2mm occlusal clearance to accommodate a sufficient bulk of porcelain.

Porcelain onlay case study: post-operative viewshowing cemented porcelain onlay.

Dentine bonding agentsUsing DBAs with resin or amalgam cores increases retention by enhancing bond strength and reducing microleakage. The disadvantage is the highly technique-sensitive and protracted clinical protocol.

Luting cements

Core materialsThe choice of core material will profoundly affect survival of the ultimate restoration, and is dependent on whether a fill-in or build-up is necessary.A fill-in assumes that sufficient dentine architecture is present, and that the restorative material is used purely to fill voids, without acting as a supporting platform. When minimal dentine is available, a build-up acts as the platform for supporting the extra-coronal restoration.Therefore, a build-up requires greater mechanical resilience than a fill-in material. The popular materials include amalgam, GIs, resinmodified glass ionomers (RGIs) and resin composites with DBA.

Amalgam core build-up.

For vital teeth, the direct technique is the method of choice, using amalgam, resin composites, GI or RGI filling materials. DBAs in conjunction with resin composites and amalgam increase retention while preserving the maximum amount of remaining tooth substrate. Amalgam has long clinical success, and using amalgam adhesives further enhances its mechanical properties

GIs offer direct adhesion to dentine and are cariostatic, but due to low tensile strength and resistance to fracture, are not recommended for areas of high occlusal stresses. Composite filling materials are a better alternative, but are plagued with disadvantages of microleakage. Essentially, the linear thermal expansion of resin compositesis different from natural teeth, which causes post-operative sensitivity, pulpal pathosis and microleakage.

To circumvent microleakage, flowable composites used as liners below composites offer superior accessibility and adaptability for difficult cavity recesses

Radiographic evaluationA radiograph will reveal the amount of residualtooth, decay, quality and extent of any existing

filling, periodontal and endodontic status.

Intra-oral evaluationA careful examination, with transillumination,

will reveal tooth and/or existing filling(s) fractures.Minor fractures may be salvageable, but

extensive or deep vertical root fractures usuallyrequire extraction.

VITAL TEETH – CLINICAL PRACTICE

Pre-assessment for cores on vital teethBefore proceeding to build-up or fill-in structurally

compromised vital teeth, the followingitems should be considered.

Clinical sequelae for cores on vital teethIf, following the above evaluation, a core is practical, the clinical protocol is as follows:(1) Isolate tooth with rubber dam(2) Remove exiting filling(s), decay and reduce cusps that are either fractured (or display

fractures lines), or less than 1 mm in cross section(3) Assess remaining tooth substrate for either fill-in, or build-up with retention by strategicplacement of retentive boxes, grooves and pins(4) If necessary, place suitable matrix band and wedges for supporting the core material(5) Select fill-in or build-up material (6) Follow manufacturer’s instructions for the chosen restorative material(7) Remove rubber dam(8) Carry out immediate or delayed tooth preparation (depending on the material) for the coronal restoration9)Fabricate a chairside therapeutic temporary restoration, before making an impressionfor the definitive restoration