A comparative study of the bond strengths of amalgam and alloy-glass ionomer cores

Comparative study of mechanical properties of direct core build-up materials

Background and Objectives:

The strength greatly influences the selection of core material because core must withstand forces due to mastication and para-function for many years. This study was conducted to evaluate certain mechanical properties of commonly used materials for direct core build-up, including visible light cured composite, polyacid modified composite, resin modified glass ionomer, high copper amalgam, and silver cermet cement.

Materials and Methods:

All the materials were manipulated according to the manufacturer's recommendations and standard test specimens were prepared. A universal testing machine at different cross-head speed was used to determine all the four mechanical properties. Mean compressive strength, diametral tensile strength, flexural strength, and elastic modulus with standard deviations were calculated. Multiple comparisons of the materials were also done.

Results:

Considerable differences in compressive strength, diametral tensile strength, and flexural strength were observed. Visible light cured composite showed relatively high compressive strength, diametral tensile strength, and flexural strength compared with the other tested materials. Amalgam showed the highest value for elastic modulus. Silver cermet showed less value for all the properties except for elastic modulus.

Conclusions:

Strength is one of the most important criteria for selection of a core material. Stronger materials better resist deformation and fracture provide more equitable stress distribution, greater stability, and greater probability of clinical success.

Comparative evaluation of bond strengths of different core materials with various luting agents used for cast crown restorations

The coronal cast restoration continues to be used commonly to restore mutilated, endodontically treated teeth. The tensile bond strength of luting cements is of critical importance as many of failures are at the core and the crown interface. An invitro study with aim to evaluate and compare bond strengths of luting cements between different core materials and cast crowns. A total of 45 extracted identical mandibular second premolars were endodontically treated and divided into 3 groups of 15 each. Specimens in first group were restored with cast post and core (Group C), and specimens in second group were restored with stainless steel parapost and composite core material (Group B) and specimens in third group were restored with stainless steel parapost and glass ionomer core build (Group G). Standardized crown preparation was done for all the specimens to receive cast crowns. Each group was further divided into 3 subgroups and were cemented using 3 different luting cements namely, resin cement, polycarboxylate cement, glass ionomer cement (Type I). The samples of each subgroup (n = 5) were subjected to tensile testing using Universal Testing Machine at a crosshead speed of 2 mm/min till the dislodgement of crown from the core surface was observed. The bond strengths were significantly different according one way ANOVA (F-150.76 and p < 0.0000). The results of the study showed that the specimens cemented with resin cement in cast core, composite core and glass ionomer core exhibited significantly higher bond strengths as compared to specimens cemented with glass ionomer and polycarboxylate cement. Composite resin core and resin cement combinations were superior to all other cement and core combinations tested.

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.

In vitro assessment of retention of four esthetic dowels to resin core foundation and teeth

STATEMENT OF PROBLEM

Several new esthetic dowel systems are currently available for the restoration of endodontically treated teeth. These dowel systems enhance the esthetic quality of all-ceramic restorations better than metallic dowel systems.

PURPOSE

The purpose of this study was to evaluate the retentive strength of composite and ceramic endodontic dowel systems to the tooth and to the core foundation.

MATERIAL AND METHODS

The following dowel systems were tested: resin dowels (Fibrekor [FR]; Luscent [LU]; Twin Luscent Anchor [TLU]); ceramic dowels (Cerapost [CR]; Cosmopost [CO]); and a titanium dowel (ParaPost XH [Ti]). In Part I of the study, core retention was tested by forming Bis-Core resin (n=12) cores around dowels followed by separation using a universal testing machine. In Part II, 60 (n=12) extracted human canines were endodontically treated, and dowel spaces were prepared using the corresponding drill for each dowel system. Nine-millimeter resin and ceramic dowels were cemented with C & B resin luting agent. Additionally, 2 groups (n=12) of Ti dowels cemented with C & B resin luting agent and zinc phosphate luting agent served as control groups. Retention was tested using a universal testing machine to separate the dowels from teeth. One-way analysis of variance and Student Newman-Keuls tests were conducted for statistical analysis (alpha=.05). Surface texture of all dowel systems tested was examined using SEM at original magnification x25 and x250.

RESULTS

Core retention of Ti was higher than all esthetic dowels tested (alpha<.05), but FR had higher core retention than the other esthetic dowels tested. Resin dowels had better retention to teeth than ceramic dowels (alpha<.05).

CONCLUSION

The esthetic dowel systems were less retentive for the resin core material than the titanium control. Resin dowel systems were more retentive in the root than the ceramic dowels but were similar to the titanium control.

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

STATEMENT OF PROBLEM

New glass ionomer cements exhibit better mechanical properties than their older counterparts. However, there is concern about their use as a core material in post-and-core applications.

PURPOSE

This in vitro study evaluated the fatigue resistance of 2 new glass ionomer cements, Shofu Hi-Dense and Fuji IX GP, and compared their mechanical behavior as a core material under masticatory load with a silver-reinforced glass ionomer (ESPE Ketac-Silver) and a silver amalgam (Cavex Avaloy LC).

MATERIAL AND METHODS

A total of 100 commercial plastic teeth were divided into 4 groups of 25 specimens each. Titanium posts were placed in the prepared root canals, and cores were built up in amalgam, silver-reinforced glass ionomer cement, and the 2 new glass ionomer cements. The post-and-core specimens were prepared for full cast metal crowns, which were fabricated and cemented with glass ionomer cement. Twenty specimens from each group were placed in a mastication simulator and cyclically loaded with a 400 N force for 1.5 million cycles. The 5 remaining specimens were used as controls. The specimens were sectioned and observed macroscopically and microscopically to determine the number of defects (alterations) in each material. Observed defects were verified with the Kruskal-Wallis test, and the 4 core materials were ranked with the Tukey multiple comparisons test.

RESULTS

The mean rank sum values of the defects were as follows: Cavex Avaloy LC Amalgam (16.75), Fuji IX GP (38.50), Shofu Hi-Dense (39.53), and ESPE Ketac-Silver (67.22). The amalgam alloy was significantly different (P< .05) from the others.

CONCLUSION

Under the conditions of this study, the 2 new glass ionomer cements used as core materials showed a higher number of defects than amalgam. These results suggest that their fatigue resistance may be inadequate for post-and-core applications.

Effect of prefabricated metal post-head design on the retention of various core materials

Retention of various post heads to core restorative materials is an important factor in the selection of prefabricated post systems and restorative materials for the restoration of endodontically treated teeth. This study examines the retention of a post-core prefabricated system in relation to core material and post-head design. A total of 60 samples were prepared using two different post systems (ParaPost Plus (PP) and ParaPost Unity (PU), with amalgam, composite or glass-ionomer as one of the core materials. The samples were tested using the Instron testing machine. The PP was superior to the PU prefabricated post with respect to the retention of various core materials. Retention values in descending order of magnitude were found to be: composite, amalgam and glass-ionomer (significantly lower). The rhomboid serrated design of PP was superior in retention to the rounded smooth UP system. Composite material proved to be superior in retention, closely followed by amalgam, with glass-ionomer significantly less retentive.

Diametral and compressive strength of dental core materials

STATEMENT OF PROBLEM

Strength greatly influences the selection of core materials. Many disparate material types are now recommended for use as cores. Cores must withstand forces due to mastication and parafunction for many years.

PURPOSE

This study compared the compressive and diametral tensile strengths of 8 core materials of various material classes and formulations (light-cured hybrid composite, autocured titanium containing composite, amalgam, glass ionomer, glass ionomer cermet, resin-modified glass ionomer, and polyurethane).

MATERIAL AND METHODS

Materials were manipulated according to manufacturers' instructions for use as cores. Mean compressive and diametral strengths with associated standard errors were calculated for each material (n = 10). Analyses of variance were computed (P <.0001) and multiple comparisons tests discerned many differences among materials.

RESULTS

Compressive strengths varied widely from 61.1 MPa for a polyurethane to 250 MPa for a resin composite. Diametral tensile strengths ranged widely from 18.3 MPa for a glass ionomer cermet to 55.1 MPa for a resin composite. Some resin composites had compressive and tensile strengths equal to those of amalgam.

CONCLUSION

Light-cured hybrid resin composites were stronger than autocured titanium containing composites. The strengths of glass ionomer-based materials and of a polyurethane material were considerably lower than for resin composites or amalgam.

Mechanical properties of direct core build-up materials

OBJECTIVE

This work was undertaken to measure mechanical properties of a diverse group of materials used for direct core build-ups, including a high copper amalgam, a silver cermet cement, a VLC resin composite and two composites specifically developed for this application.

METHODS

Compressive strength, elastic modulus, diametral tensile strength and flexural strength and modulus were measured for each material as a function of time up to 3 months, using standard specification tests designed for the materials.

RESULTS

All the materials were found to meet the minimum specification requirements except in terms of flexural strength for the amalgam after 1 h and the silver cermet at all time intervals.

SIGNIFICANCE

There proved to be no obvious superior material in all respects for core build-ups, and the need exists for a specification to be established specifically for this application.

Fracture strengths of three core restorative materials supported with or without a prefabricated split-shank post

PURPOSE

The aim of this study was to compare the fracture strengths of three restorative materials, a lanthanide reinforced composite (Ti-Core Natural), a silver amalgam (Tytin), and a hybrid glass ionomer (Advance), supported by either a multitiered, threaded split-shank post (Flexi-Flange) or with a dentin spur without a post.

MATERIAL AND METHODS

A total of 60 recently extracted single-rooted human teeth were divided into six groups of 10. All groups were stored at 100% humidity at room temperature for 1 week before testing. Each specimen was placed in a special jig at a 45-degree angle to the buccolingual axis and subjected to a load that was recorded in pounds and converted to Newtons on a universal testing machine, with a crosshead speed of 0.63 cm/minute until failure. Two-way analysis of variance followed by the Newman-Keuls pairwise multiple comparisons test were used to compare the results.

RESULTS

There was a statistically significant difference between core materials (p < 0.001), but not regarding post conditions. Ti-Core Natural material had a significantly larger mean failure threshold for fracture than either Tytin silver amalgam or Advance material and the letter two core materials (Tytin and Advance) do not differ from each other. There was no statistical difference between Ti-Core material supported by a post and Ti-Core material supported without a post.

Cyclic fatigue testing of five endodontic post designs supported by four core materials

PURPOSE

This pilot study examined the cyclic fatigue of five endodontic post systems (AccessPost, Flexi-Flange, Flexi-Post, ParaPost, and Vlock) with four core materials (Tytin silver amalgam, Ti-Core, Ketac-Silver and G-C Miracle Mix).

MATERIAL AND METHODS

In vitro cyclic fatigue was performed with a machine designed to simulate masticatory fatigue forces. An instantaneous force of 22.2 N (5 pounds) was applied to each post and core combination for a test configuration of 4,000,000 repetitions, or until failure occurred. The type of failure and number of repetitions at failure was recorded for each sample tested. Two-way analysis of variance (ANOVA) was used to compare groups.

RESULTS

All posts/core samples with Ti-Core composite and Tytin silver amalgam completed the test with no failures. All posts/core samples with Ketac-Silver material failed before the 4,000,000 test cycle configuration and all failures were core failures. All posts/core samples with G-C Miracle Mix material failed in a similar manner. Newman-Keuls multiple comparison test illustrated that, with this simulated fatigue test, Ti-Core material and Tytin silver amalgam were superior to both G-C Miracle Mix and Ketac-Silver materials.

Four different core materials measured for fracture strength in combination with five different designs of endodontic posts

The purpose of this in vitro study was to determine the fractural load of four core materials supported by five post designs. This study was divided into 20 groups with 10 samples per group. Specimens were placed in a special jig at a 45-degree angle, and the fracture load values, in pounds, were obtained with the use of a universal testing machine. A 5 x 4 factorial design was used to assess and compare the fractural strength, and a two-way analysis of variance was used to determine whether the buccolingual, mesiodistal, and height dimensions differed across groupings. Mean fracture load values were obtained. Flexi-Post dowel/Ti-Core material at 277.1 pounds and ParaPost dowel/ Tytin silver amalgam at 277.3 pounds recorded the greatest mean values. These values were not statistically different. ParaPost dowel/Ketac-Silver material had the lowest mean value (49.6 pounds). For all posts Tytin silver amalgam and Ti-Core material were significantly stronger than Ketac-Silver and G-C Miracle Mix material. Ketac-Silver and G-C Miracle Mix materials did not differ from each other. Results indicated that Ti-Core composite material is at least as strong as Tytin silver amalgam.

Reinforced glass-ionomer cements--a review of properties and clinical use

In recent years, two new metal-reinforced Glass-ionomers have been introduced. The aim has been to develop a cement which can be used successfully as a replacement for amalgam. This paper reviews the published literature on the mechanical properties and clinical use of both the cermet and so-called 'Miracle Mix' cements. The published results do not suggest an improvement in strength or adhesion to tooth material; wear resistance is improved, however. One problem encountered in reviewing this literature is the wide variation in test methodology and hence results. In clinical use, the metal-reinforced cement has been successful in Class I and II restorations, particularly using the tunnel technique, and has potential for use in a number of other applications.

Bending strength of Fuji and Ketac glass ionomers after sonication

Glass ionomer cements mixed by conventional methods contain voids that can decrease their overall strength. This study evaluated the effect of sonication on the reduction of air entrapment by measuring the bending strength in glass ionomer cements (Fujj-II and Ketac-fil). Glass ionomer cement was placed in identical-test vials and sonicated for 45s, 10s, or 0s. The bending strengths were measured (0.005 in min-1) after setting times of 1 or 2 weeks. Mean bending strengths (MPa +/- SD) for the 12 treatment both cements (P < 0.001) and sonication times (P < 0.001). The effect of setting time produced minimal increases in bending strength (P < 0.218). The sonication of freshly mixed glass ionomer cements is a possible solution for reducing voids to increase bending strength.

Effects of ultrasonic instrumentation on microleakage in composite restorations with glass ionomer liners

The aim of this study was to determine the effect of ultrasonic instrumentation on composite resin restorations lined with glass ionomer cement by measuring the extent of dye penetration at the restoration/tooth interface. Preparations, 2.0 mm in diameter and 2.5 mm in depth, were made with a 331 bur in 96 human molar teeth without a bevel. The teeth were restored with glass ionomer cement liners (Shofu) and one of two types of composite resin (Silux and P-30). Half of the samples were ultrasonically instrumented for 10 s. The teeth were immersed in 0.5% methylene blue dye solution and vertically sectioned. Microleakage was scored visually using a scale of 0 to 4. Statistical comparisons were made with chi 2 analysis and the Mann-Whitney U-test at the P less than 0.05 level. Microleakage was significantly different between both resin types (P less than 0.001), and between the lined and unlined resins (P less than 0.001) that were instrumented, particularly in the P-30 restorations. Although P-30 restorations exhibited much less microleakage than Silux, the use of a glass ionomer liner did not reliably reduce microleakage in either type of material after instrumentation with an ultrasonic device.

Retention of core composites, glass ionomers, and cermets by a self-threading dentin pin: the influence of fracture toughness upon failure

"Core composite" is available, and glass ionomer or materials based upon it (i.e., cermet, alloy/glass-ionomer mix) have potential for core-forming. Cores are retained routinely by pins, and the suitability of the retention of these materials by pins has been investigated. The maximum tensile force sustained by a particular self-threading dentin pin, selected for its retentive capability, was determined. Pins were embedded to a constant depth in cylindrical specimens. All specimens fractured at a force which correlated linearly with the fracture toughness of the embedding material. The glass-ionomer group of materials was inferior to the core composites, and doubts must surround the use of the former when retention of a core is dependent on dentin pins. The adhesive character of the glass-ionomer-based materials did not lead to failure forces higher than those predicted from their fracture toughnesses. When the data points for these materials were placed on a fracture force/fracture toughness plot together with data from earlier research, no point was displaced significantly from the straight line.

Microleakage in restorations with glass ionomer liners after thermocycling

The purpose of this study was to compare microleakage around two types of restorations lined with polyalkenoate (glass ionomer) cements after thermocycling. Preparations were made in 48 molars to a diameter and depth of 2.0 mm. Half of the preparations were lined with glass ionomer, and the remainder were not lined. Dental amalgam or glass ionomer restorative material was placed and the amalgams were left unburnished and unpolished. Selected restorations were thermocycled 625 times between 4 degrees C and 50 degrees C. Teeth were immersed in 0.5 per cent methylene blue solution, sectioned and visually scored for microleakage at X 100 magnification. Data analysis indicated significant differences in microleakage because of: thermocycling (chi 2 = 103.38, d.f. = 19,2P less than 0.0004); presence of glass ionomer liners (chi 2 = 53.28, d.f. = 19,2P less than 0.0001); and type of restorative material (chi 2 = 103.44,d.f. = 19,2P less than 0.0004). The use of a glass ionomer liner significantly reduced microleakage in both amalgam and glass ionomer restorations when subjected to thermocycling.

Silver-alloy powder and glass ionomer cement

This article examines some physical property improvements made when a spherical silver alloy powder is added to a hydrous, restorative (type II) glass ionomer cement. When this first metal-reinforced glass ionomer cement is handmixed thickly and quickly, physical properties and clinical handling are improved. These various improvements make this metal-reinforced cement similar in clinical applications to a biocompatible dental epoxy. Three clinical cases are illustrated to show how simply this metal-reinforced glass ionomer cement can be used in dental practices.