Which procedure takes place during the second appointment for the placement of a cast restoration?

Sequence

The post and core complex can be placed only after the endodontic treatment has been successfully completed. It must be securely in place before the crown preparation can start. If the endodontic procedure is not successful or not yet comfortable for the patient, it does not make sense to seal the endodontic access opening with a post and core that obstructs further endodontic intervention. Typically the practitioner should wait until all sensitivity has dissipated and the patient is comfortable enough to proceed with the post and core procedure without any need for local anesthesia. Should problems develop after the post has been placed, the bonded post is rather difficult to remove, and the tooth might require an apical endodontic procedure, or apicoectomy, directly through the buccal or lingual; this approach is certainly an option but a secondary one at best.

Cast Gold Post and Core

Cast gold post and core restorations can be fabricated with either direct or indirect techniques.

Passive posts

These are either custom-made cast posts or prefabricated posts. Custom-made cast posts and cores can be made from type III, type IV gold alloy or base metal alloys. The latter are harder and may predispose the tooth to root fracture. The impression technique produces a smooth-sided, tapered post that matches the original taper of the root canal preparation. This is an ideal choice for an irregular canal such as that seen in an upper second premolar tooth, which is wide and oval bucco-palatally at its entrance and much narrower apically (Figure 7.15). To take an impression of an irregular post hole the wash material is syringed around the entrance to the post hole and the plastic impression post is pushed through the unset wash, dragging it into the post hole. Before the wash sets the loaded impression tray is seated (see Chapter 13).

Although the use of cast tapered posts decreases the risk of root perforation apically, the retention of the post is compromised. Parallel-sided posts give better retention than tapered posts and can be used provided the rules set out under post space preparation are adhered to. Serrated posts have negative recesses in them and give more retention than smooth-sided posts. It is possible to custom-make a parallel-sided serrated post by using a system such as the ParaPost XP (Coltène Whaledent, UK; Figure 7.16). For each size post there is a smooth plastic impression post (the blue one can be seen in Figure 7.15). A retentive ‘mushroom’ shape can be created in the impression post at the end which is embedded into the impression by melting it with a hot metal instrument such as a flat plastic. The serrated burn out plastic post is then sent with the impression to the laboratory for the technician to wax a core around and cast using the lost wax technique (see Chapter 9). The final post type within the parapost XP kit is the metal temporary post which can be used in conjunction with temporary crown materials and techniques (see Chapter 14).

The use of custom-made cast posts and cores is more time consuming as additional clinical time and laboratory costs are incurred. It is preferable to fit the cast post and core and then take a further impression for the crown to reduce the chance of a compromised marginal fit (Figure 7.17). However, cast posts are preferred by many practitioners and so continue to have a use in operative dentistry.

7.24.2.1.1.1 Introduction

The production of cast metallic restorations, such as crowns, bridges, inlays, cast posts-and-cores in the dental laboratory is traditionally carried out by the lost-wax casting technique. The technique can be found back beyond 3000 BC, but it was not used in dentistry until Taggart in the early 1900s first developed the lost-wax casting technique by the use of gold alloys. Over the last century, for the manufacturing of removable partial dentures, the gold alloys were gradually replaced by cobalt–chromium (CoCr) alloys during the 1950s. At the end of the twentieth century, titanium made its entrée after its successful indication in implant dentistry. Owing to more esthetic demands of patients in the Western population, full metal crowns became the exception rather than the rule and are used only for indications were esthetics are of no concern (posterior area/cast post-and-cores) or when large occlusal forces are acting onto the teeth such as in patients suffering from bruxism, a disorder (during night) or bad habit (during daytime) characterized by grinding and clenching of the teeth leading to excessive wear or fracture of weakened teeth. Substructures/frameworks, that later on are porcelain veneered (see Section 7.24.2.3.1), are currently widely used, although also there ceramic-based substructures are rapidly gaining importance.

The basic principles of the lost-wax casting consists of a wax pattern that is molded of the desired shape, and this pattern is invested in a refractory investment. The wax is then removed by melting and burning, leaving behind a cavity of the desired tooth anatomy. This cavity can be filled with molten metal, so that the metal corresponds to the shape of the original wax pattern. The full clinical and technical events, used over decades in the production of cast dental restorations are as follows: tooth preparation, impression taking, model pouring, wax-up of the pattern, investing the wax pattern, wax burn-out and heating, melting and casting the alloy, finishing and polishing, heat treatments, and eventually luting of the restoration onto the teeth. Thus it can be seen that many different materials are involved in the production of a metal casting. These include impression materials, model and die materials, waxes, investment materials, casting alloys, and luting cements. Attention will be focused on the materials that are used and the requirements that are placed upon them for the restorations themselves and not on a detailed description of the various clinical and practical stages involved.

Teeth with Pulpal Involvement

When tooth fracture or caries involves the pulp and root development is complete, a routine pulpectomy and gutta-percha root canal filling should be completed. Because posts and cores do not strengthen endodontically treated teeth, their use is indicated only when the remaining coronal tooth structure does not provide adequate retention for definitive restoration. Restorations that do not use a post should be used whenever possible to replace missing tooth structure and serve as a retentive foundation. It is particularly important that the teeth in the mouths of accident-prone adolescents or in whom athletic trauma has previously occurred be restored without a post, if possible. This practice helps avoid irreparable damage in the form of root fracture in case the restored tooth is once again subjected to trauma. Even though trauma may result in restoration dislodgement or perhaps even fracture of the tooth, the tooth will have survived at least one more traumatic experience.

In the case of pulpal involvement when the root is incompletely formed, a pulpotomy followed by placement of an appropriate restoration is indicated. Subsequently, when root formation is completed, a pulpectomy is performed, followed by placement of the definitive restoration or crown, if needed.

Symptomatic Teeth With Previous Endodontic Treatment

The emergency management of teeth with previous endodontic treatment may be technically challenging and time-consuming. This is especially true in the presence of extensive restorations, including posts and cores, crowns, and bridgework. However, the goal remains the same as for the management of necrotic teeth: Remove contaminants from the root canal system and establish patency to achieve drainage.31,58 Gaining access to the periapical tissues through the root canals may require removal of posts and obturation, as well as negotiating blocked or ledged canals. Failure to complete root canal debridement and achieve periapical drainage may result in continued painful symptoms. The ability, practicality, and feasibility to adequately re-treat the root canal system must be carefully assessed before the initiation of treatment, as conventional retreatment might not be the optimal treatment plan. This is further discussed in Chapter 254.

3.2.2 Vertical Root Fracture

A fracture of the tooth that involves most of the root will induce pain on biting. Root fractures are more common in endodontically treated teeth that have been restored with a post and core. Pain on biting in such cases is therefore of periodontal origin. Initially there may be no clinical or radiographic signs. An isolated periodontal pocket in the area of the fracture is often found. Disease progression usually leads to a typical radiographic picture of a lengthwise rarefying osteitis. If left untreated infection and abscess formation may occur. Currently, the only treatment option for vertical root fractures is extraction.

Inadequate Retention

Extensively compromised teeth due to extensive fractures and/or caries lesions often need to be altered prior to final restoration. When there is a need to create a ferrule in a tooth that will receive a post-and-core restoration, crown lengthening may be needed to facilitate its placement without violation of the biologic width and adequate retention form. There is an overall consensus that 1.5 to 2 mm of ferrule is necessary for adequate retention of crowns and protection of the integrity of the remaining tooth structures. Crown lengthening may not be necessary if adequate ferrule can be achieved without violation of the biologic width. However, additional retention may be necessary; otherwise gingivectomy may be performed to temporarily remove gingival tissue.68

Gegauff highlighted that an attempt to gain adequate ferrule via crown lengthening procedure can negatively affect the tooth mechanical properties.69 The apical relocation of the crown margin after crown lengthening procedures leads to a thinner cross section in the ferrule area. Further, there is a reduction in the crown-to-root ratio that also may negatively affect the outcome of the treatment. Orthodontic extrusion may be another option to expose tooth structure in some clinical situations of inadequate retention. Yet crown-to-root ratio and apical location of the ferrule also will occur in orthodontic extrusion.

Patient Modifiers

The endodontic prognosis, final restoration plan, and anticipated fees must be presented to the patient before beginning endodontic treatment. For some patients, the added cost of the procedures required to restore the tooth to function such as crown lengthening, a post and core, and a crown may make the expense of the root canal treatment prohibitive. The patient may instead choose to have the tooth extracted. For medical-legal reasons, the dentist should document in the patient's record that all treatment options, including endodontic therapy, have been discussed before moving to extraction.

Some patients may choose to have root canal therapy to retain a tooth, but then delay the final restorative treatment because of cost considerations. Providing care in such a manner may worsen the prognosis for severely broken down teeth, leaving them more susceptible to fracture and endodontic treatment failure. Patients should be informed of this risk, and the conversation should be documented in the record.

Case study

A healthy 85-year-old woman presented to the dental office on an emergency basis with a coronal fracture of the maxillary right lateral incisor. The medical history was noncontributory. It was determined that the tooth required endodontic therapy, a post and core and a crown. The tooth was endodontically treated followed by the placement of a prefabricated post (RelyX fiber post, 3M ESPE) and a core build-up of composite resin (Filtek Z250, 3M ESPE) (Fig. 23-3A,B).

A shade was selected with Vita shade guide and a digital photograph (Canon D50 with macro lens, Canon Inc.) was made to aid the laboratory technician in fabricating proper tooth color and morphology. A digitally designed virtual wax-up of the tooth was constructed following margin marking (Fig. 23-3C).

After the sprue location was determined digitally, the data for the designed crown were sent to the computer-controlled milling machine. A provisional crown was made with bis-acrylic material (Tuff-Temp, Pulpdent Corp.) and delivered to the patient due to the lengthy procedure in the initial unscheduled emergency visit and scheduling requirements that precluded completing the restoration during the initial visit. The final restoration was completed using a D3-V1 Impulse mono-ceramic block (Ivoclar Vivadent). Following milling, the crown was customized using laboratory burs (Fig. 23-3D).

The crown was then stained and glazed using the IPS e.max ceram shade kit (Ivoclar Vivadent) on a white dental stone working model (Fig. 23-3E).

The crown was tried in and adjusted and, after the patient approved the esthetics, the restoration was cemented using a definitive composite resin luting cement (Multilink Automix, Ivoclar Vivadent) (Fig. 23-3F).