Purpose
To review methods used to investigate marginal adaptation of crowns and fixed dental prostheses (FDPs), and to discuss testing variables employed and their influence on results.

Methods
Online libraries including PubMed, Scopus, and Ovid were searched for articles evaluating the marginal adaptation of crowns and FDPs using a combination of the keywords: “marginal accuracy,” “marginal fit,” “marginal gap,” “marginal discrepancy,” “fitting accuracy,” “crown,” and “FPD.” Peer-reviewed publications in English in the period 1970 to December 2011 were collected, evaluated by their abstract, and included if they met the inclusion criteria. The criteria involved studies evaluating marginal adaptation of crowns and FDPs through clear experimental protocols. Exclusion criteria involved longitudinal prospective and retrospective clinical evaluations, studies using subjective tactile sensation, and other predefined criteria.

Results
A total of 277 papers were identified; only 183 met the inclusion criteria. Direct view technique was used by 47.5% of the articles followed by cross-sectioning (23.5%), and impression replica (20.2%) techniques. The marginal gap values reported by these techniques varied among individual crown systems and across different systems because of variations in study type (in vivo vs. in vitro), sample size and measurements per specimen, finish line design, and stage at which the marginal gap was measured.

Conclusion
There was a substantial lack of consensus relating to marginal adaptation of various crown systems due to differences in testing methods and experimental protocols employed. Direct view technique was the most commonly used method of reproducible results. Also, conducting an experimental set-up of testing a minimum of 30 specimens at 50 measurements per specimen should produce reliable results. Additionally, using a combination of two measurement methods can be useful in verification of results.

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Accuracy and Reliability of Methods to Measure Marginal Adaptation of Crowns and FDPs: A Literature Review

Marginal and internal fit of metal-ceramic crowns fabricated with a new laser melting technology

Purpose: The purpose of this article is to review basic information about the alloys used for fabricating metal-ceramic restorations in dentistry. Their compositions, properties, advantages, and disadvantages are presented and compared. In addition to reviewing traditional noble-metal and base-metal metal-ceramic alloys, titanium and gold composite alloys are also discussed.

Materials and Methods: A broad search of the published literature was performed using Medline to identify pertinent current articles on metal-ceramic alloys as well as articles providing a historical background about the development of these alloys. Textbooks, the internet, and manufacturers' literature were also used to supplement this information.

Results: The review discusses traditional as well as more recently-developed alloys and technologies used in dentistry for fabricating metal-ceramic restorations. Clear advantages and disadvantages for these alloy types are provided and discussed as well as the role that compositional variations have on the alloys' performance. This information should enable clinicians and technicians to easily identify the important physical properties of each type and their primary clinical indications.

Conclusions: A number of alloys and metals are available for metal-ceramic use in dentistry. Each has its advantages and disadvantages, primarily based on its specific composition. Continuing research and development are resulting in the production of new technologies and products, giving clinicians even more choices in designing and fabricating metal-ceramic restorations.

Metal‐Ceramic Alloys in Dentistry: A Review

An evaluation of marginal fit of three-unit fixed dental prostheses fabricated by direct metal laser sintering system.

Statement of problem One of the most important factors in determining the clinical outcomes of fixed dental prostheses is the gap between the fixed dental prosthesis and the abutment. However, reports that investigated these gaps in the context of fixed dental prostheses fabricated with new technologies are few. Purpose The purpose of this study was to measure and analyze the fit of fixed dental prostheses. The fixed dental prostheses for the study were produced with the subtractive method (milling soft metal blocks), additive method (selective laser sintering), and traditional method (lost wax and casting). Material and methods Ten specimens were fabricated with the soft metal block, selective laser sintering, and lost wax and casting methods. The 3-dimensional measurement method was adopted to obtain the measure gap figures of the specimens. To fabricate a digital replica, computer-aided design reference casts were prepared by scanning the study casts, and silicone replicas were fabricated for each specimen. These silicone replicas were scanned and obtained 40 000 point cloud data. The study also defined the mean gap for each specimen by averaging approximately 40 000 gap points to evaluate the fit of the specimens. Data were analyzed with 1-way ANOVA and the Tukey honestly significant difference (α=.05). Results The mean gap was the smallest for fixed dental prostheses fabricated with the soft metal block, followed by the selective laser sintering, then the lost wax and casting. One-way ANOVA revealed statistically significant differences in the size of the gap among the 3 groups ( P P Conclusions The fit obtained with the new soft metal block and selective laser sintering techniques was better than that obtained with the traditional lost wax and casting method. Thus, fixed dental prostheses produced by using these new techniques can be considered clinically acceptable.

Three-dimensional evaluation of gaps associated with fixed dental prostheses fabricated with new technologies.

PURPOSE The aim of this study was to compare the marginal adaptation of metal-ceramic crowns made with 3 different metal substructures MATERIALS AND METHODS Seventy-five gypsum dies were fabricated from a master steel die They were randomly divided into 3 groups of 25 dies each A metal coping was prepared on each die using a different technique for each group: composite alloy, electroforming, and cast high-noble alloy Ceramic was baked on all of the samples following the same protocol and simulating the shape and size of a maxillary central incisor All specimens were evaluated under a stereomicroscope at 200x magnification The marginal gap was measured at 8 different points on each specimen before and after ceramic application and also on the master steel die A total of 3,600 measurements was evaluated The results were statistically elaborated by means of a t test and one-way analysis of variance (ANOVA) RESULTS The ANOVA revealed a significant difference in mean marginal gap before and after ceramic application within each group Electroforming (mean 32 microns) and high-noble alloy (mean 31 microns) showed better marginal fit after ceramic application and on the master steel die compared to composite alloy (mean 68 microns; P < 00001) CONCLUSION Marginal gaps are influenced by the application of ceramic and by the alloy used for the substructure, and the values obtained were within the limits of clinical acceptability (70 microns)

Comparison of marginal fit of 3 different metal-ceramic systems: an in vitro study.

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Comparison of marginal fit of 3 different metal-ceramic systems: an in vitro study.