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

Comparative Evaluation of Fracture Toughness and Flexural Strength of Four Different Core Build-up Materials: An In Vitro Study

AIM

To evaluate and compare the fracture toughness and flexural strength of four different core build-up materials.

MATERIALS AND METHODS

A total of 60 samples were divided into four groups (n = 15) group I: dual cure composite resin reinforced with zirconia particles (Luxacore Z), group II: light cure composite resin (Lumiglass DeepCure), group III: zirconia reinforced glass ionomer cement (GIC) (Zirconomer Improved), and group IV: chemically cure composite resin (Self Comp) respectively. All the core build-up materials were manipulated according to the manufacturer's instructions and poured into the mold. A universal testing machine applied a central load to the specimen in a 3-point bending mode. Fracture of the specimen was identified and the reading was recorded by the universal testing machine. The data were analyzed statistically using one-way analysis of variance (ANOVA) and then compared.

RESULTS

Group I showed the highest flexural strength (48.65 MPa) among all the groups while group IV showed the lowest flexural strength (17.90 MPa). Group I showed the highest fracture toughness (99.12 MPa) among all the groups while group IV showed the lowest fracture toughness (36.41 MPa.cm-0.5). When mean flexural strength and fracture toughness values of all four groups were compared by using one-way ANOVA, the compared data was highly significant.

CONCLUSION

Based on the findings of this study, dual cure composite resin was the material of choice in terms of flexural strength and fracture toughness for core build-up material followed by light cure composite resin.

CLINICAL SIGNIFICANCE

The core buildup material serves to strengthen the tooth structure, allowing it to withstand the forces of chewing and preventing the risk of tooth fractures. This material is essential in restoring damaged or decayed teeth, as it provides a stable foundation for further dental work. By reinforcing the tooth structure, the core buildup material ensures that the tooth can function properly and remain healthy for years to come. How to cite this article: Nakade P, Thaore S, Bangar B, et al. Comparative Evaluation of Fracture Toughness and Flexural Strength of Four Different Core Build-up Materials: An In Vitro Study. J Contemp Dent Pract 2024;25(2):191-195.

The effect of thermocycling on fracture toughness and hardness of different core build up materials

INTRODUCTION

Core build up materials are routinely used to restore grossly decayed teeth and in the oral environment they are subjected to changes in the temperature due to consumption of hot and cold food.

AIMS

The purpose of this study was to determine the effect of thermocycling on the fracture toughness and hardness of 5 core build up materials.

MATERIALS AND METHODS

Fifteen specimens were prepared for each of the following materials: DPI alloy, Miracle-mix, Vitremer, Fuji II LC and Photocore. American Standard for Testing Materials guidelines were used for the preparation of single-edge notch, bar-shaped specimens. Ten specimens of each material were thermocycled for 2000 cycles and the other 5 specimens were not thermocycled (non-thermocycled group). All specimens were subjected to 3-point bending in a universal testing machine. The load at fracture was recorded and the fracture toughness (K(IC)) was calculated. Vickers hardness test was conducted on the thermocycled and non-thermocycled group specimens.

RESULTS

Photocore had the highest mean K(IC) in both thermocycled and non-thermocycled groups. Miracle-mix demonstrated the lowest mean fracture toughness (K(IC)) for both thermocycled and non-thermocycled groups. By applying Mann Whitney 'U' test the Vickers hardness value in all materials used in the study is highly superior in non-thermocycled group as compared to thermocycled group (P < 0.01). Non-thermocycled Photocore showed highest hardness values of 87.93. Vitremer had lowest hardness of 40.48 in thermocycled group.

CONCLUSION

Thermocycling process negatively affected the fracture toughness and hardness of the core build-up materials.

The effect of thermocycling on the fracture toughness and hardness of core buildup materials

STATEMENT OF PROBLEM

Thermocycling has been shown to cause surface degradation of many dental materials, but its effect on the fracture toughness and hardness of direct core buildup materials is unknown.

PURPOSE

This study was designed to determine the effect of thermocycling on the fracture toughness and hardness of 5 core buildup materials.

MATERIAL AND METHODS

Fifteen specimens were prepared from each of the following materials: Fluorocore, VariGlass VLC, Valiant PhD, Vitremer, and Chelon-Silver. American Standard for Testing Materials guidelines for single-edge notch, bar-shaped specimens were used. Ten specimens of each material were thermocycled for 2000 cycles; the other 5 specimens were not thermocycled. All specimens were subjected to 3-point bending in a universal testing machine. The load at fracture was recorded, and the fracture toughness (K(IC)) was calculated. Barcol hardness values were also determined. Data were analyzed with 1-way analysis of variance and compared with the Tukey multiple range test (P<.05). Pearson's correlation coefficient was also calculated to measure the association between fracture toughness and hardness.

RESULTS

Fluorocore had the highest thermocycled mean K(IC) and Valiant PhD the highest non-thermocycled K(IC). Chelon-Silver demonstrated the lowest mean K(IC) both before and after thermocycling. One-way analysis of variance demonstrated significant differences between conditions, and the Tukey test showed significant differences (P<.05) between materials for both conditions. Most specimens also showed significant hardness differences between conditions. Pearson's correlation coefficient indicated only a mild-to-moderate correlation between hardness and fracture toughness.

CONCLUSION

Within the limitations of this study, the thermocycling process negatively affected the fracture toughness and hardness of the core buildup materials tested.

Dental resin composites containing ceramic whiskers and precured glass ionomer particles

OBJECTIVES

Glass ionomer, resin-modified glass ionomer, and compomer materials are susceptible to brittle fracture and are inadequate for use in large stress-bearing posterior restorations. The aim of this study was to use ceramic single crystal whiskers to reinforce composites formulated with precured glass ionomer, and to examine the effects of whisker-to-precured glass ionomer mass ratio on mechanical properties, fluoride release, and polishability of the composites.

METHODS

Silica particles were fused onto silicon nitride whiskers to facilitate silanization and to improve whisker retention in the matrix. Hardened glass ionomer was ground into a fine powder, mixed with whiskers, and used as fillers for a dental resin. Four control materials were also tested: a glass ionomer, a resin-modified glass ionomer, a compomer, and a hybrid composite. A three-point flexural test was used to measure flexural strength, modulus, and work-of-fracture. A fluoride ion-selective electrode was used to measure fluoride release. Composite surfaces polished simulating clinical procedures were examined by SEM and profilometry.

RESULTS

At whisker/(whisker + precured glass ionomer) mass fractions of 1.0 and 0.91, the whisker composite had a flexural strength in MPa (mean (SD); n = 6) of (196 (10)) and (150 (16)), respectively, compared to (15 (7)) for glass ionomer, (39 (8)) for resin-modified glass ionomer, (89 (18)) for compomer, and (120 (16)) for hybrid composite. The whisker composite had a cumulative fluoride release of nearly 20% of that of the glass ionomer after 90 days. The whisker composites had surface roughness comparable to the hybrid resin composite.

SIGNIFICANCE

Composites filled with precured glass ionomer particles and whiskers exhibit moderate fluoride release with improved mechanical properties; the whisker-to-glass ionomer ratio is a key microstructural parameter that controls fluoride release and mechanical properties.

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.

Evolution of post and core systems

Post and core systems have evolved dramatically over the past few years. Some procedures based on the use of resin-composite systems seem destined for failure in the long term. New glass ionomer based systems, employing resin hybrid materials should give rise to fewer complications and prove simpler to use. Nevertheless, intelligent case selection and the application of sound basic design principles are required to make the best use of any system.

Preparation of glass ionomer cement using N-acryloyl-substituted amino acid monomers--evaluation of physical properties

OBJECTIVES

The objectives of this study were (1) to develop polyacid formulations through the incorporation of amino acid-derived monomers with carboxylic acid groups at various distances away from the polymer backbone to allow for greater flexibility, less rigid ionic cluster formation and improved solubility, and (2) to test selected physical and handling properties of experimental ionomers with a conventional glass ionomer as a control.

METHODS

The polycarboxylic acids prepared and used in glass ionomer formulation in this study included N-acryloylglutamic acid (AGA) and N-acryloyl-6-aminocaproic acid (AACA)- modified acrylic acid- ++itaconic acid copolymers, where the acrylic acid:itaconic acid:amino acid monomers were combined in different proportions. The characterization and purity of the monomers were determined by FTIR and their melting points. The characterization of synthesized polymers included molecular weight and relative viscosity determinations. The compressive strengths, diametral tensile strengths, flexural strengths and fracture toughness of the experimental ionomers and a commercially available ionomer (control) were measured after storage in water, at 37 degrees C for 1 h or 7 d. The working times and setting times of the experimental ionomers were compared to the control specimens. Separate analysis of variance and Tukey's tests were used to study the statistical significance of the physical strength parameters as a function of materials and storage times.

RESULTS

Significant increases (p< 0.001) in diametral tensile, compressive, flexural strengths and fracture toughness were observed in the AGA co-polymers, while significant increases were observed in diametral and flexural strengths in the AACA co-polymers compared to the control Fuji II. The working and setting times of all except one experimental ionomer studied were comparable to the controls.

SIGNIFICANCE

The use of amino acid-modified acrylic monomers to produce water soluble copolymers of acrylic-itaconic acid offers a new route of discovery to produce chemical-cured glass ionomers with improved physical properties. The spacer chain length, the hydrophobicity of the chains, the molecular weight and viscosity of the polymer all played important roles in determining the physical properties of the material.

The fracture toughness of various core materials

PURPOSE

This study determined the fracture toughness of four core buildup materials.

MATERIALS AND METHODS

Single-edge notch, bar-shaped specimens conforming to the American Society for Testing Materials standard E-399 were fabricated for a high copper amalgam alloy, two composite resins, and a glass ionomer buildup material. The specimens were stored in air for 1 week and then tested in three-point bending mode with an Instron Universal Testing Machine (Instron Corporation, Canton, MA).

RESULTS

Fracture toughness values obtained were as follows: Fluorocore (composite resin; Caulk, Milford, DE), 1.54 MN.m-1.5; Ti-Core (composite resin and titanium; Essential Dental Systems, New York, NY), 1.34 MN.m-1.5; Valiant Ph.D. (amalgam; Caulk), 1.29 MN.m-1.5; and Coreshade Glass Ionomer Base Cement (Shofu Inc, Kyota, Japan), 0.55 MN.m-1.5.

CONCLUSIONS

Glass ionomer materials are probably unsuitable as core buildup materials because of their relatively low fracture toughness. Fluorocore, Ti-Core, and amalgam all had fracture toughness values significantly greater than the glass ionomer (P < .01).

A comparison of the diametral tensile strength, the flexural strength, and the compressive strength of two new core materials to a silver alloy-reinforced glass-ionomer material

This study compared three mechanical properties of two recently introduced core materials, a light-activated glass ionomer cement (VariGlass VLC) and a fluoride-release dual cure composite resin (FluoroCore), with those of a conventional silver-reinforced glass-ionomer cement (Miracle Mix). Seventy-two samples (eight per product for each property) were prepared for testing diametral tensile strength, flexural strength, and compressive strength. The specimens were cured, stored for 24 hours at 37 degrees C in 100% humidity, and tested with the use of an Instron universal testing machine. The results of this study indicate that the diametral tensile strength, flexural strength, and compressive strength of the FluoroCore and VariGlass VLC materials were significantly higher than those of the conventional Miracle Mix. The values obtained with FluoroCore material were consistently higher than those obtained with VariGlass VLC material.

Effect of design of prefabricated post heads on core materials

This study investigated post-core adaptation as it relates to core materials and post-head configuration. A total of 360 samples that consisted of three prefabricated post systems and three core materials of amalgam and composite resin of 1 and 3 mm post-head-covering thicknesses were made. Composite resin with a post-head covering of 3 mm was most resistant to compression, whereas amalgam was most resistant to retentive forces. The addition of titanium to composite resin as a reinforcement filler did not improve resistance to either compressive or tensile forces.

Failure characteristics of endodontically treated premolars restored with a post and direct restorative material

Ninety-one extracted maxillary premolar teeth were restored with a prefabricated post and amalgam, composite resin or glass-cermet core. Each group was again divided into three groups of 9-13 teeth to be subjected to an increasing load in one of three standardized directions (10, 45 and 90 degrees to the long axis of the tooth). Failure load and characteristics of failure were recorded. The glass-cermet-restored teeth had a lower strength than the other groups for every load direction (Student's t-test: P less than 0.01). Amalgam and composite resin groups showed a significant difference only for the 10 degrees loading condition (Student's t-test: P less than 0.02). Teeth restored with amalgam cores displayed a higher mean failure load, in combination with a 46% occurrence of root fracture.