In vitro fatigue resistance of glass ionomer cements used in post-and-core applications

Influence of Different Post Luting Cements on the Fracture Strength of Endodontically Treated Teeth: An In Vitro Study

Objective:

To evaluate the fracture resistance of endodontically treated mandibular premolars restored with glass fiber posts using different luting agents.

Methods:

Twenty-four extracted single-rooted mandibular premolars were endodontically treated, and post spaces were prepared to receive fiber posts. They were assigned to three test groups (n=8) according to the type of cement used for the cementation of glass fiber posts: RC group: adhesive resin cement group (etch and rinse), SC group: self-adhesive resin cement group, and GC group: glass ionomer cement group. Teeth in all groups were adhesively restored with a composite resin core material and crowned with Ni-Cr crowns. All specimens were subjected to tangential loading using a universal testing machine until fracture at 30°. Failure loads were recorded, and data were analyzed using one-way ANOVA followed by Tukey’s HSD test (α=0.05).

Results:

Specimens in the RC group were more resistant (258.3±12.7 N) to fracture than those in the SC (218.7±11.1 N) and GC (165.4±8.9 N) groups (P≤0.001). One-way ANOVA indicated that the type of cement had a significant effect on the fracture resistance of endodontically treated lower premolars (P≤0.001).

Conclusion:

The type of cement that was used to fix glass fiber posts was a determining factor of the fracture resistance of endodontically treated lower premolars.

Do Laboratory Results Concerning High-Viscosity Glass-Ionomers versus Amalgam for Tooth Restorations Indicate Similar Effect Direction and Magnitude than that of Controlled Clinical Trials? - A Meta-Epidemiological Study

Background

A large percentage of evidence concerning dental interventions is based on laboratory research. The apparent wealth of laboratory evidence is sometimes used as basis for clinical inference and recommendations for daily dental practice. In this study two null-hypotheses are tested: whether trial results from laboratory and controlled clinical trials concerning the comparison of high-viscosity glass-ionomer cements (HVGIC) to amalgam for restorations placed in permanent posterior teeth have: (i) similar effect direction and (ii) similar effect magnitude.

Methods

7 electronic databases were searched, as well as reference lists. Odds ratios (OR) and Standardised Mean Differences (SMD) with 95% Confidence intervals were computed for extracted dichotomous and continuous data, respectively. Pooled effect estimates for laboratory and clinical data were computed to test for effect direction. Odds ratios were converted into SMDs. SMDs from laboratory and clinical data were statistically compared to test for differences in effect magnitude. The analysed results were further investigated within the context of potential influencing or confounding factors using a Directed acyclic graph.

Results

Of the accepted eight laboratory and nine clinical trials, 13 and 21 datasets could be extracted, respectively. The pooled results of the laboratory datasets were highly statistically significant in favor of amalgam. No statistically significant differences, between HVGICs and amalgam, were identified for clinical data. For effect magnitude, statistically significant differences between clinical and laboratory trial results were found. Both null-hypotheses were rejected.

Conclusion

Laboratory results concerning high-viscosity glass-ionomers versus amalgam for tooth restorations do not indicate similar effect direction and magnitude than that of controlled clinical trials.

Comparative evaluation of compressive strength and flexural strength of conventional core materials with nanohybrid composite resin core material an in vitro study

Several dental materials have been used for core build-up procedures. Most of these materials were not specifically developed for this purpose, but as a consequence of their properties, have found application in core build-up procedures. Improvements in composites and the development of nanocomposites have led to their use as a core build up material due to their superior mechanical properties, optical properties and ease of handling. However it is not clear if they have better mechanical properties than the conventional core build up materials like amalgam, GIC and dual cure composite core build up material. The strength of the core material is very important and this study was undertaken to compare the mechanical properties of materials used for direct core foundations. The differences between the compressive strength and flexural strength of Filtek Z350 nanocomposite with conventional core build up materials like Amalgam, Vitremer GIC and Fluorocore were tested. Cylindrical plexi glass split molds of dimension 6 ± 1 mm [height] x4 ± 1 mm [diameter] were used to fabricate 15 samples of each core material for testing the compressive strength and rectangular plexi glass split molds of dimension 25 ± 1 mm [length] x 2 ± 1 mm[height] x2 ± 1 mm [width] used for fabricating samples for flexural strength. The samples were stored a water bath at 250 °C for 24 h before testing. The samples were tested using a Universal Instron testing machine. The results of the study showed that Fluorocore had the highest compressive strength and flexural strength followed by Filtek Z350 [nanocomposite] Amalgam had the least flexural strength and Vitremer GIC had the least compressive strength. Thus flurocore and nanocomposite are stronger than other core build up materials and hence should be preferred over other conventional core build up materials in extensively damaged teeth.

Scanning electron microscopy analysis of dental cements

The aim of this study was to compare in vitro the characteristics of different types of luting cements (zinc phosphate, glass-ionomer and resin based composite cement) using scanning electron microscopy (SEM) analysis and microleakage for the quality range of materials. Dental cements were mixed in accordance with the manufacturer's instructions and formed with posts in dental root canals of extracted teeth. The quality of cement was determined by SEM observation on horizontal sectioned roots with fixed posts according to specific pore and marginal gap diameter. The microleakage was measured on specimens immersed in Lofler (methylene blue) solution. The mean values of the maximal diameter of pores, marginal gaps and microleakage of conventional cements are remarkably larger in comparison with composite luting agents. In conclusion, the quality and efficiency of composite luting agents in comparison with conventional cements are more successful in protecting the interior of tooth from penetration of oral fluids, bacteria and bacterial toxins into unprotected dentine.

Treatment concepts for restoration of endodontically treated teeth: A nationwide survey of dentists in Germany

STATEMENT OF PROBLEM

Opinions concerning proper restoration of endodontically treated teeth (ETT) vary. A variety of techniques and materials for post-and-core restorations are available. The rationale for post placement performed by German dentists was unknown.

PURPOSE

The purpose of this study was to determine current opinions, applied techniques, and materials for the restoration of ETT in Germany.

MATERIAL AND METHODS

A nationwide questionnaire-based survey containing 18 multiple choice questions regarding treatment philosophies, favored post type, and materials for core foundations was mailed to 36,500 German general dentists. A total of 6029 questionnaires (16.5%) were returned. Data were evaluated in terms of the dentists' occupational experience and the frequency of post placement. Descriptive statistics were used to analyze the data.

RESULTS

Irrespective of their occupational experience, 52% of the surveyed dentists consider post placement for almost every postendodontic restoration of ETT. The majority of dentists (54%) believe that a post reinforces ETT. Cast posts and cores are used by 55% of all dentists, whereas 34% use prefabricated posts exclusively. Screw posts are the most popular prefabricated post type (47%). Composite resin (51%) is preferred for core foundation, followed by glass ionomer cements (GICs) (26%). Amalgam is seldom used (0.5%). Posts are placed primarily with zinc phosphate cement (51%), followed by GIC (38%).

CONCLUSION

The treatment philosophy of German dentists is not in complete agreement with recommendations found in the literature. The belief that a post would reinforce an ETT might explain the high frequency of post placements. Due to the partially inconsistent responses, it is difficult to derive a generalized treatment concept.

Effect of an adhesive resin luting agent on the dowel-head retention of three different core materials

STATEMENT OF PROBLEM

A dowel-and-core restoration may fail due to failure at either the dowel-tooth or dowel head-core material interface. Long-term clinical success of a dowel-and-core restoration depends on retention of both the dowel to the tooth and the dowel head to the core material. Thus, strengthening of the dowel head-core interface is important.

PURPOSE

This study evaluated the retention between a prefabricated dowel and 3 different core materials with or without a dual-polymerized adhesive resin luting agent.

MATERIAL AND METHODS

Sixty prefabricated dowels (Gold Plated Anchorage Post) were divided into 3 groups (n=20) consisting of 1 of 3 core materials, amalgam (Standalloy F), light-polymerized resin composite (Clearfil Ray), or glass ionomer (Chelon-Silver). Each core group was divided into 2 subgroups (n=10), and a dual-polymerized adhesive resin luting agent (Panavia F) was applied to the dowel heads of 1 of these subgroups before application of the core material. The manufacturing procedure was standardized by using a plastic index (4.5-mm internal diameter and 5-mm height) and a custom-made dowel holder, which held the dowel head. Prepared specimens were stored in water at room temperature for 3 months and then loaded to fracture in a universal testing machine with a crosshead speed of 0.05 mm/min until failure. Bond strengths were recorded (MPa). Data were analyzed with 2-way analysis of variance (ANOVA) in a 2 x 3 factorial randomized design (alpha=.05). Afterward, core material differences were computed with 1-way ANOVA for both of the bonded and nonbonded groups. Post hoc multiple comparisons were made with the Dunnett C multiple range test.

RESULTS

Dowel-head retention values (MPa) of the tested core materials (mean +/- SD) from the highest to the lowest were as follows: bonded amalgam core, 296.1 +/- 108; bonded composite core, 284.3 +/- 38.3; nonbonded composite core, 177.0 +/- 53.7; nonbonded amalgam core, 128.5 +/- 35.0; bonded glass-ionomer core (GIC), 128.0 +/- 24.5; nonbonded GIC, 61.8 +/- 13.3. Two-way ANOVA revealed significant differences between the core material groups and between the bonded and nonbonded groups (P <.001). The interaction between the core material and bond variables was also significant (P =.018). One-way ANOVA revealed statistically significant differences between the bonded (P <.001) and also between the nonbonded core material groups (P <.001). Post hoc multiple comparisons showed that the dowel-head retention of the GIC was significantly weaker than the post-head retention for amalgam and resin composite, whether bonded or not.

CONCLUSION

Within the limitations of this study, the adhesive resin luting agent tested appeared to have a significant strengthening effect on the dowel-head retention of the core materials.

Post placement and restoration of endodontically treated teeth: a literature review

The restoration of endodontically treated teeth is a topic that is extensively studied and yet remains controversial from many perspectives. This article reviews the major pertinent literature on this topic, with an emphasis on major decision-making elements in post placement and restoration of endodontically treated teeth. Recommendations are made for treatment planning, materials, and clinical practices from restorative and endodontic perspectives.