Extra-coronal Restorations Research Articles

Crowns and extra-coronal restorations: materials selection.

Materials selection is the second in the series on crowns and other extra-coronal restorations. Some of us are less than inspired by dental materials science. Nevertheless, many of the things that concern us clinically with crowns and their alternatives are based on material properties. We worry about the strength of the restoration, how well it fits and its aesthetics. We also worry about wear, occlusal control and biocompatibility. Not least of our concerns are dental laboratory charges, which inevitably have to be passed on to the patient.

Changing patterns and the need for quality

This series of articles is aimed at anybody who places crowns and other extra-coronal restorations (ie veneers and shims) on individual teeth. We hope that everyone from experienced practitioners to undergraduate students may find something of value. Whoever reads them, we would ask to do so with an open mind. We have tried not to be dogmatic, and the techniques and materials described are not the only ones available, but are the ones which accord with the principles we describe.

Conventional Endodontics And The Operating Microscope

Patients are increasingly wishing to undergo conventional endodontic treatment rather than to risk the loss of a tooth. Endodontic treatment in teeth that have been previously restored with extensive intracoronal or extracoronal restorations are often difficult to treat. The orientation of the root canals to the crown of the tooth may be lost, and this may often be compounded by the deposition of reparative dentin in the pulp chamber. The operating microscope allows better visualization of the working field, ensuring that the anatomy of the tooth is more readily inspected. This greatly enhances the clinician's ability to locate extra root canals and therefore increase the likelihood of a successful outcome. It should not be forgotten that the operating microscope also has a place in other fields of dentistry, especially restorative dentistry, and is an asset to both the specialist and the generalist.

CONVENTIONAL ENDODONTICS AND THE OPERATING MICROSCOPE

Patients are increasingly wishing to undergo conventional endodontic treatment rather than to risk the loss of a tooth. Endodontic treatment in teeth that have been previously restored with extensive intracoronal or extracoronal restorations are often difficult to treat. The orientation of the root canals to the crown of the tooth may be lost, and this may often be compounded by the deposition of reparative dentin in the pulp chamber. The operating microscope allows better visualization of the working field, ensuring that the anatomy of the tooth is more readily inspected. This greatly enhances the clinician's ability to locate extra root canals and therefore increase the likelihood of a successful outcome. It should not be forgotten that the operating microscope also has a place in other fields of dentistry, especially restorative dentistry, and is an asset to both the specialist and the generalist.

Assessment of shoulder dimensions and angles of procelain bonded to metal crown preparations

The metal ceramic crown is the most popular extracoronal restoration in the United Kingdom. These restorations may fail because of fracture or esthetics. A potential cause of failure is the quality and width of the facial shoulder preparation. In this study 24 extracted human teeth were prepared to receive metal ceramic crowns by one of three dentists. Preparations were replicated and scanned in the midfacial plane by a coordinates measuring machine with a noncontact probe. The x, y, and z surface coordinates were recorded. The results indicated a mean (±SD) shoulder width value of 0.752 mm (±0.174 mm) and a shoulder angle of 108.54 (±15.06) degrees. From these data it would appear that there are deficiencies in shoulder preparations, particularly in width. These inadequacies may have implications for longevity of the restoration and periodontal health in a clinical situation.

Durability of restorations in primary molars.

Techniques used to restore carious primary molars have changed over the past decade as new adhesive materials have been developed. The most meaningful way of assessing the efficacy of a technique is by clinical trials. This article reviews the information concerning amalgam, composite and glass polyalkenoate (ionomer) cement as well as extracoronal restorations. Stainless steel/nickel chrome crowns provide the most durable restoration, often surviving until the tooth exfoliates. Class II amalgam restorations, whilst being prone to fracture, have been shown to survive about 3 years, a figure that improves with increasing age of the child and the use of local anaesthesia. Over the shorter term resin-based composites appear to be at least as durable as amalgam, particularly with respect to the maintenance of a good anatomical form. In contrast, when assessed at 6 years the failure rate of composite restorations is high, 62%, whereas the failure rate of amalgam restorations at 5 years is as low as 20%. Glass ionomer cements and cermets are alternative materials for use in the primary dentition. The reported success rate of 33% over 5 years for conventional glass ionomer cements is encouraging, however cermets appear to be less successful but have not been evaluated over the longer term. Glass ionomer cements provide a means of restoring primary molars with minimal amount of destruction of sound tooth tissue and reduced treatment time for the young patient, whilst the local fluoride release is also a potential advantage.(ABSTRACT TRUNCATED AT 250 WORDS)

A preliminary investigation into the longevity and causes of failure of single unit extracoronal restorations

Four types of single unit restoration, including porcelain jacket, full and partial veneer, and metal ceramic crowns provided at the Prince Philip Dental Hospital in Hong Kong were investigated for evidence of failure. Of the 4658 units of restoration provided between 1981 and 1989, 100 restorations of each type were selected at random by computer. The relevant patients were identified and invited to return for a review appointment. A total of 132 patients attended and 152 crowns were examined. The average length of service was 34 months at the date of examination. Using strict criteria, 21(14 per cent) restorations were deemed to have failed. Technical failure was the most prevalent cause of failure, followed by aesthetic complaints and endodontic problems. The failure rates ranged from 2.4 to 7.8 per cent per year for the different crowns in order of. partial veneer < full veneer < metal ceramic < porcelain jacket crowns. Fracture of restoration, which affected metal ceramic and porcelain jacket crowns, was the single most frequent cause of failure observed in this study.

Clinical Technique for an In‐Office Porcelain Modification

All porcelain restorations, especially intra- and extracoronal restorations, have become an accepted treatment modality for the esthetic restoration of posterior teeth. One problem with these restorations is the limited ability to modify the porcelain when a proximal contact is not present or there is an open margin. Using a low-fusing porcelain in a glazing oven, practitioners can easily accomplish such modifications during the try-in and cementation appointment for porcelain inlays. This technique eliminates the need for returning the porcelain inlay to the laboratory for modification and a second patient visit to complete the restoration. This paper describes an in-office procedure for modifying porcelain restorations and a scanning electron micrographic evaluation of the etched porcelain surface after using this modification technique.

Retention and resistance in preparations for extracoronal restorations. Part II: Practical and clinical studies

I n 1956 Jorgensen’ first tested the relationship between retention and convergence angle in cemented complete veneer crowns. He used cones 8 mm in diameter at the base and 8 mm high. The convergence angle varied from 5 to 45 degrees in steps of 5 degrees. Instead of cast crowns, brass caps were used with the same base diameter, cemented with the same brand of zinc phosphate cement. To avoid errors in the cementation pressure, a vent was made in the cylindrical bore of the caps to provide an outlet for entrapped air. The maximum retentive value (81.3 gm/mm2) was obtained with the 5-degree convergence angle. The minimum value (57.4 gm/mm2) was with 45 degrees. At 10 degrees the retentive value was 41.4 gm, just about half that at 5 degrees. The relation between retentive force and convergence angle was found to be a hyperbola (Fig.

Retention and resistance in preparations for extracoronal restorations. Part I: Theoretic studies

Lewis and Owen’ sought a mathematic solution to find the best retentive configuration for complete crowns. They used the term “admissible” for a form that consists of three straight line segments AB, BC, and CD as in Fig. 1, where the sum of the angles a and b is not less than 180 degrees. This describes mathematically a preparation that is not undercut. The term “form” was used interchangeably for the exterior shape of the prepared tooth and the interior shape of the finished crown, which they assumed to be geometrically identical. A force is completely determined by specifying direction, magnitude, and point of application. All possible directions of this applied force (but not the magnitude and point of application) were considered, with respect to their effect on the crown’s retention. Lewis and Owen defined the “retentivity” of an acceptable preparation to be the range of directions of the applied force for which the crown does not move in relation to the tooth. For example, if for a given preparation the crown does not move under the influence of forces of directions, say between 75 and 100 degrees, but does move for forces having directions outside this range, that form shall be said to have a retentivity of 25 degrees. With the above definitions the problem can be reformulated for admissible forms. How can the angles a and b (Fig. 1) and the lengths AB and CD be selected so that the retentivity will be maximum? The authors divided the analysis into two parts, geometric and mechanical.

An evaluation of the marginal adaptation of extracoronal restorations during cementation

An evaluation of the marginal adaptation of extracoronal restorations during cementation

The Treatment of Carious Teeth: The Case for Extracoronal Restorations

The Treatment of Carious Teeth: The Case for Extracoronal Restorations