Fracture Resistance of Premolars Restored with Partial Ceramic Restorations and Submitted to Two Different Loading Stresses

Crack Propagation and Fatigue Performance of Partial Posterior Indirect Restorations: An Extended Finite Element Method Study

Dental ceramics are susceptible to slow, progressive crack growth after cyclic loading. The purpose of this study was to investigate the progressive patterns of cracks in two different types of CAD/CAM ceramic materials used with three different partial posterior indirect restoration (PPIR) designs and to determine the materials' failure risk using a fatigue test. Standard initial cracks were formed in Standard Tessellation Language (STL) files prepared for three different PPIRs. The materials chosen were monolithic lithium disilicate (LS) and polymer-infiltrated ceramic networks (PICNs). The extended finite element method (XFEM) was applied, and the fatigue performance was examined by applying a 600 N axial load. The cracks propagated the most in onlay restorations, where the highest displacement was observed. In contrast, the most successful results were observed in overlay restorations. Overlay restorations also showed better fatigue performance. LS materials exhibited more successful results than PICN materials. LS materials, which can be used in PPIRs, yield better results compared to PICN materials. While inlay restorations demonstrated relatively successful results, overlay and onlay restorations can be specified as the most and the least successful PPIR types, respectively.

On the fracture behavior of molar teeth with MOD cavity preparation

Mesial-occlusal-distal (MOD) cavity preparations are commonly used to restore damaged teeth. While numerous in vitro cavity designs have been devised and tested, no analytical frameworks for assessing their resistance to fracture seem to exist. This concern is addressed here by resorting to a 2D slice specimen cut from restored molar teeth with rectangular-base MOD cavity. The evolution of damage due to axial cylindrical indentation is followed in situ. The failure begins with a rapid debonding along the tooth/filler interface and continues with unstable cracking from the cavity corner. The debonding load q_d is fairly fixed while the failure load q_f is insensitive to the presence of filler, increasing with cavity wall thickness h and reducing with cavity depth D. The growth of the corner crack is studied using a 2D fracture analysis in conjunction with the FEM technique. The ratio h = h/D emerges as a viable system parameter. A simple expression for q_f given in terms of h and dentin toughness K_C is developed that predicts well the test data. In vitro studies on full-fledged molar teeth with MOD cavity preparation show that the fracture resistance of filled cavities often exceeds by a large margin that of unfilled ones. Indications are that this may reflect load sharing with the filler. Thus, the fracture resistance of the unfilled cavity provides a lower bound to a compromised MOD filling after long-term aging in the mouth. This bound is well predicted by the slice model. Finally, it is recommended that MOD cavities be prepared, if applicable, such that h > D regardless of the tooth size.

Deep Margin Elevation: A Literature Review

A conservative approach for restoring deep proximal lesions is to apply an increment of composite resin over the preexisting cervical margin to relocate it coronally, the so-called “deep margin elevation” (DME). A literature search for research articles referring to DME published from January 1998 until November 2021 was conducted using MEDLINE (PubMed), Ovid, Scopus, Cochrane Library and Semantic Scholar databases applying preset inclusion and exclusion criteria. Elevation material and adhesive system employed for luting seem to be significant factors concerning the marginal adaptation of the restoration. This technique does not affect bond strength, fatigue behavior, fracture resistance, failure pattern or repairability. DME and subgingival restorations are compatible with periodontal health, given that they are well-polished and refined. The available literature is limited mainly to in vitro studies. Therefore, randomized clinical trials with extended follow-up periods are necessary to clarify all aspects of the technique and ascertain its validity in clinical practice. For the time being, DME should be applied with caution respecting three criteria: capability of field isolation, the perfect seal of the cervical margin provided by the matrix, and no invasion of the connective compartment of biological width.

Influence of Methodological Variables on Fracture Strength Tests Results of Premolars with Different Number of Residual Walls. A Systematic Review with Meta-Analysis

The aim of the current meta-analysis was to assess the impact of methodological variables in performing fracture strength tests of upper premolars. Medline (Pubmed), Embase and Google Scholar were screened for studies performing ex vivo fracture strength tests of intact upper premolars or premolars with 0, 1 or 2 walls lost. The outcome variable for each study was the maximum breaking load expressed in Newton (kg × m/s²). Methodological variables (i.e., simulation of the periodontal ligament, load inclination, tip position, tip diameter and thermocycling) were registered to perform subgroup analyses and meta-regression. Overall, 25 studies and 78 study groups were included in the meta-analysis. Intact premolars (17 study groups) were not significantly influenced by any of the methodological variables considered. Subgroup analysis for load inclination (30°/45° vs. 90°/150°) was significant for premolars with 0 (10 study groups), 1 (6 study groups) and 2 (45 study groups) walls lost; thermocycling was significant for premolars with 1 and 2 walls lost. A strong methodological heterogeneity across studies evaluating the fracture strength of upper premolars was highlighted, especially when 0, 1 or 2 walls were lost. Further studies are needed to standardize the methodology used in order to allow for across-studies comparisons.

Influence of Preparation Design and Restorative Material on Fatigue and Fracture Strength of Restored Maxillary Premolars

STATEMENT OF PROBLEM

Extensive carious lesions and/or large preexisting restorations possibly contribute to crack formation, ultimately resulting in a fracture that may lead to the loss of a tooth cusp. Hence, preparation design strategy in conjunction with the restorative material selected could be influential in the occurrence of a cuspal fracture.

PURPOSE

The purpose of this in vitro study was to evaluate the fatigue behavior and fracture strength of maxillary premolars restored with direct composite and indirect ceramic inlays and overlays, with different preparation depths in the presence or absence of cuspal coverage, and analyze their failure types.

METHODS AND MATERIALS

Sound maxillary premolars (N=90; n=10) were divided into nine groups: group C: control; group DCI3: direct composite inlay 3 mm; group DCI5: direct composite inlay 5 mm; group ICI3: indirect ceramic inlay 3 mm; group ICI5: indirect ceramic inlay 5 mm; group DCO3: direct composite overlay 3 mm; group DCO5: direct composite overlay 5 mm; group ICO3: indirect ceramic overlay 3 mm; group ICO5: indirect ceramic overlay 5 mm. In indirect ceramic, lithium disilicate restoration groups, immediate dentin sealing was applied. After restoration, all specimens were tested in fatigue (1,200,000 cycles, 50 N, 1.7 Hz). Samples were critically appraised, and the specimens without failure were subjected to a load to failure test. Failure types were classified and the data analyzed.

RESULTS

Zero failures were observed in the fatigue testing. The following mean load to failure strengths (N) were recorded: group ICO5: 858 N; group DCI3: 829 N; group ICO3: 816 N; group C: 804 N; group ICI3: 681 N; group DCO5: 635 N; group DCI5: 528 N; group DCO3: 507 N; group ICI5: 482 N. Zero interaction was found between design-depth-material (p=0.468). However, significant interactions were found for the design-depth (p=0.012) and design-material (p=0.006). Within restorations at preparation depth of 3 mm, direct composite overlays obtained a significantly lower fracture strength in comparison to indirect ceramic onlays (p=0.013) and direct composite inlays (p=0.028). In restorations at depth 5 mm, significantly higher fracture load values were observed in indirect ceramic overlays compared with the inlays (p=0.018). Indirect ceramic overlays on 3 mm were significantly stronger than the deep inlays in ceramic (p=0.002) and tended to be stronger than the deep direct composite inlays. Severe, nonreparable fractures were observed with preparation depth of 5 mm within ceramic groups.

CONCLUSIONS

The preparation depth significantly affected the fracture strength of tooth when restored with either composite or ceramic materials. Upon deep cavity preparations, cuspal coverage proved to be beneficial when a glass ceramic was used as the restorative material. Upon shallow cavity preparations, a minimally invasive approach regarding preparation design used in conjunction with a direct composite material was favorable.

Influence of material type, thickness and storage on fracture resistance of CAD/CAM occlusal veneers

OBJECTIVES

The present study aimed to evaluate the effect of restoration thickness, CAD/CAM material, and 6 months of artificial saliva storage on the fracture resistance of occlusal veneers.

MATERIALS AND METHODS

A total of 84 intact maxillary molars were sectioned 4.0 mm occlusal to the cementoenamel junction to expose the dentine. The teeth were assigned into 3 main groups according to the type of restorative material (e.max CAD, Vita Enamic, and Lava Ultimate). In each group, the teeth were allocated into 2 subgroups (n = 14) according to restoration thickness (1.0 and 1.5 mm). The veneers were adhesively bonded using dual-cure self-adhesive luting agent. A total of 42 specimens comprising half the tested subgroups were stored in distilled water for 24-h before the test. The remaining half was stored in artificial saliva at 37 ± 1 °C in an incubator for 6 months. All specimens (n = 84) were subjected to 5000 thermal cycles between 5 and 55 °C ± 2 before the fracture resistance test. The maximum force at fracture was recorded in Newton. Failure mode was analyzed using a stereomicroscope. The results were analyzed using a parametric Three-way ANOVA test.

RESULTS

The results of the Three-way ANOVA test revealed that material type and restoration thickness significantly affected fracture resistance values (p < 0.5), while 6 months of storage in artificial saliva had no significant effect on mean fracture resistance values (p˃0.5). The most common failure patterns in CAD/CAM resin composite and polymer-infiltrated ceramics were scores I and score II. For glass ceramic groups, score IV and III were more dominant.

CONCLUSIONS

All the tested CAD/CAM restorations in both thicknesses exhibited fracture resistance values exceeding normal and parafunctional bite forces. Polymer-infiltrated ceramics and CAD/CAM resin composite veneers showed more favorable fracture patterns.

Fracture strength of non-invasively reinforced MOD cavities on endodontically treated teeth

The purpose of this in-vitro study was to evaluate the fracture resistance and failure mode of non-invasively reinforced endodontically treated mandibular molars. Sixty freshly extracted defect-free mandibular molars were divided into four experimental groups with extensive MOD cavities on endodontically treated teeth with different restoration types and one control group with intact teeth (n  = 12). The groups were as follows: “Normal”: direct resin composite; “Ring”: glass fiber-reinforced strip (Dentapreg) wrapped around buccal and lingual walls followed by direct resin composite; “Inlay”: indirect CAD/CAM resin composite inlay; “Onlay”: indirect CAD/CAM resin composite onlay; “Intact”: Intact teeth (Control). Tetric EvoCeram and Adhese Universal (Ivoclar Vivadent) were used for direct restorations and Tetric CAD (Ivoclar Vivadent) adhesively luted with Adhese Universal and Variolink Esthetic LC (Ivoclar Vivadent) were used for indirect restorations. All teeth were submitted to thermo-mechanical cyclic loading. All samples were then submitted to a compressive load until fracture. Fracture load was noted and teeth were analyzed to classify the failure mode as either catastrophic (C) or non-catastrophic (NC). No statistically significant difference was found between fracture strength of the five groups when all specimens were considered (p = 0.1461). Intact group showed the lowest percentage of catastrophic failures (41.67%). Ring group presents less catastrophic failures (75%) than Normal group (83.34%), and failures of indirect restorations—Inlay and Onlay—were almost all catastrophic (91.67% and 100%, respectively).

Influence of Deep Margin Elevation and preparation design on the fracture strength of indirectly restored molars

The objectives of this in-vitro study were to investigate the influence of Deep Margin Elevation (DME) and the preparation design (cusp coverage) on the fracture strength and repairability of CAD/CAM manufactured lithium disilicate (LS₂) restorations on molars. Sound extracted human molars (n = 60) were randomly divided into 4 groups (n = 15) (inlay without DME (InoD); inlay with DME (IWD); onlay without DME (OnoD); onlay with DME (OnWD)). All samples were aged (1.2 × 10⁶ cycles of 50N, 8000 cycles of 5-55 °C) followed by oblique static loading until fracture. Fracture strength was measured in Newton and the fracture analysis was performed using a (scanning electron) microscope. Data was statistically analyzed using two-way ANOVA and contingency tables. DME did not affect the fracture strength of LS₂ restorations to a statistically significant level (p = .15). Onlays were stronger compared to inlays (p = .00). DME and preparation design did not interact (p = .97). However, onlays with DME were significantly stronger than inlays without DME (p = .00). More repairable fractures were observed among inlays (p = .00). Catastrophic, crown-root fractures were more prevalent in onlays (p = .00). DME did not influence repairability of fractures or fracture types to a statistically significant level (p > .05). Within the limitations of this in-vitro study, DME did not statistical significantly affect the fracture strength, nor the fracture type or repairability of LS₂ restorations in molars. Cusp coverage did increase the fracture strength. However, oblique forces necessary to fracture both inlays and onlays, either with or without DME, by far exceeded the bite forces that can be expected under physiological clinical conditions. Hence, both inlays and onlays are likely to be fracture resistant during clinical service.

Fracture behavior of Bi-structure fiber-reinforced composite restorations

OBJECTIVE

The aim of this study was to evaluate the fracture-behavior of direct composite restorations made with two different composite-core materials. In addition, fracture toughness (FT), flexural strength (FS) and flexural modulus (FM) of tested composites were evaluated.

METHODS

Twenty groups of posterior crown restorations were fabricated (n = 6/group). The groups were made of a 4-5 mm layer of composite-core materials (everX Flow and SDR Flow⁺) and covered by a 2 mm layer of conventional composite (G-aenial Anterior & Posterior, G-aenial Universal Injectable, Essentia, CeramX, Filtek Z500). Control groups were only made of conventional composites or composite-core materials. Crowns were statically loaded until fracture. Failure-modes were then visually examined. FT, FS and FM were determined for each tested composite (n = 6).

RESULTS

ANOVA revealed that crown restorations made only from everX Flow composite had significantly higher load-bearing capacities (3866 ± 263 N) (p < 0.05) among all the groups tested. No statistically significant differences were found in the load-bearing capacities between crowns made with different composite-core materials (p > 0.05). everX Flow exhibited the highest FT (2.8 MPa m^1/2) and Z500 presented the highest FS values (197 MPa) (p < 0.05) among tested composites. With regard to the failure-mode analysis, crowns that had a fiber-reinforced core material of everX Flow revealed delaminating of surface conventional composite from the substructure layer. While in crowns that had a core material of SDR Flow⁺ or having only conventional composites with no fiber reinforcement, showed a crushing fracture pattern.

CONCLUSION

Restorations combining a fiber-reinforced composite core and a surface layer of conventional composite, displayed promising performance related to fracture-behavior.

Can Fiber Application Affect the Fracture Strength of Endodontically Treated Teeth Restored with a Low Viscosity Bulk-Fill Composite?

Objective

The aim of this study is to evaluate the effects of different fiber insertion techniques and thermomechanical aging on the fracture resistance of endodontically treated mandibular premolar teeth restored using bulk-fill composites.

Materials and Methods

Eighty human mandibular premolar teeth were randomly divided into eight groups: Group IN, Group BF, Group PRF1, Group PRF2, Group IN-TMA, Group BF-TMA, Group PRF1-TMA ,and Group PRF2-TMA. Group IN (intact) and Group IN-TMA (intact but subjected to thermomechanical aging) served as control groups. In the other six groups, endodontic treatment was performed and standardized mesio-occluso-distal (MOD) cavities were prepared. In BF, PRF1, and PRF2, the cavities were restored with bulk-fill composite only, bulk-fill/Ribbond, and bulk-fill/additional Ribbond, respectively. In BF-TMA, PRF1-TMA, and PRF2-TMA, the teeth were subjected to thermomechanical aging after the restorations. All of the teeth were fractured on the universal testing machine. Fracture surfaces were analyzed with a stereomicroscope.

Results

Control groups showed significantly higher fracture strengths than tested groups (P<0.05). No statistically significant difference was observed among the tested groups (P>0.05). Most of the favorable fractures were seen in PRF1, PRF2, and PRF2-TMA. Most of the unfavorable fractures were seen in BF-TMA.

Conclusions

Although fiber insertion with different techniques did not increase the fracture strength of teeth restored with bulk-fill composites, it increased the favorable fracture modes. Thermomechanical aging did not change the fracture strength of the groups.

Fracture Resistance of Endodontically Treated Maxillary Premolars Restored With Different Methods

Purpose:

The purpose of this in vitro study was to evaluate the resistance and patterns of fracture of endodontically treated maxillary premolars (ETPs) restored with different methods.

Methods and Materials:

Mesio-occluso-distal cavities were prepared in 50 extracted caries-free human maxillary premolars after endodontic treatment. The teeth were divided into five groups (n=10), according to the restorative method. G1: intact teeth (control group); G2: conventional composite resin; G3: conventional composite resin with a horizontal glass fiber post inserted between buccal and palatal walls; G4: bulk-fill flowable and bulk-fill restorative composites; and G5: ceramic inlay. For direct restorations, Filtek Z350 XT, Filtek Bulk Fill Flowable Restorative, and Filtek Bulk Fill Posterior Restorative were used. Indirect restorations were fabricated from a pressable lithium disilicate glass-ceramic (IPS e-max Press) and adhesively cemented (RelyX Ultimate). All specimens were subjected to thermocycling (5°C to 55°C/5000 cycles) and additionally submitted to cyclic loading 50,000 times in an Electro-Mechanical Fatigue Machine. Next, the specimens were subjected to a compressive load at a crosshead speed of 1 mm/min until fracture. The fractured specimens were analyzed to determine the fracture pattern using a stereomicroscope, and then representative specimens were carbon coated to allow for the studying of the fracture surface under scanning electron microscopy. One-way analysis of variance (ANOVA) was used to compare fracture resistance of the groups. The results of fracture patterns were submitted to the Fisher exact test (α=0.05).

Results:

All specimens survived fatigue. Mean (standard deviation) failure loads (N) for groups were as follows: G1: 949.6 (331.5); G2: 999.6 (352.5); G3: 934.5 (233.6); G4: 771.0 (147.4); and G5: 856.7 (237.5). The lowest fracture resistance was recorded for G4, and the highest ones were recorded for G2, followed by that of G1 and G3. One-way ANOVA did not reveal significant differences between groups (p&gt;0.05). The highest repairable fracture rates were observed in G1 (100%) and G3 (80%).

Conclusions:

ETPs restored with conventional composite resin with or without horizontal fiber post, bulk-fill composite, and ceramic inlay showed fracture resistance similar to that of sound teeth. Conventional composite resin restorations exhibited the highest prevalence of unrepairable fractures, and the insertion of a horizontal fiber post decreased this prevalence. Intact teeth showed 100% of repairable fractures. It is difficult to extrapolate the results directly to a clinical situation due to the limitations of this study.

Mechanical properties and fracture behavior of flowable fiber reinforced composite restorations

OBJECTIVE

The aim was to evaluate the effect of short glass-fiber/filler particles proportion on fracture toughness (FT) and flexural strength (FS) of an experimental flowable fiber-reinforced composite (Exp-SFRC) with two methacrylate resin formulations. In addition, we wanted to investigate how the fracture-behavior of composite restorations affected by FT values of SFRC-substructure.

METHODS

Exp-SFRC was prepared by mixing 50wt% of dimethacrylate based resin matrix (bisGMA or UDMA based) to 50wt% of various weight fractions of glass-fiber/particulate filler (0:50, 10:40, 20:30, 30:20, 40:10, 50:0wt%, respectively). FT and FS were determined for each experimental material following standards. Specimens (n=8) were dry stored (37°C for 2 days) before they were tested. Four groups of posterior composite crowns (n=6) composed of different Exp-SFRCs as substructure and surface layer of commercial particulate filler composite were fabricated. Crowns were statically loaded until fracture. Failure modes were visually examined. The results were statistically analysed using ANOVA followed by post hoc Tukey's test.

RESULTS

ANOVA revealed that ratio of glass-fiber/particulate filler had significant effect (p<0.05) on tested mechanical properties of the Exp-SFRC with both monomer systems. Exp-SFRC (50wt%) had significantly higher FT (2.6MPam^1/2) and FS (175.5MPa) (p<0.05) compared to non-reinforced material (1.3MPam^1/2, 123MPa). Failure mode analysis of crown restorations revealed that FT value of the substructure directly influenced the failure mode.

SIGNIFICANCE

This study shows that short glass-fibers can significantly reinforce flowable composite resin and the FT value of SFRC-substructure has prior importance, as it influences the crack arresting mechanism.

Influence of Different Restoration Techniques on Fracture Resistance of Root-filled Teeth: In Vitro Investigation

OBJECTIVE

The purpose of this study was to determine the fracture strength of endodontically treated mandibular premolar teeth restored with composites and different reinforcement techniques.

METHODS AND MATERIALS

Forty-eight freshly extracted human mandibular premolar teeth were randomly divided into four groups: group IN, group CR, group FRC, and group PRF. Group IN consisted of teeth with intact crowns and served as the control group. In the other three groups, endodontic treatment was performed and standard mesio-occluso-distal (MOD) cavities were prepared. Then cavities were restored with hybrid resin composite only, flowable composite and hybrid resin composite, and Ribbond, flowable composite and hybrid resin composite in groups CR, FRC and PRF, respectively. All of the teeth were subjected to fracture by means of a universal testing machine, and compressive force was applied with a modified stainless-steel ball at a crosshead speed at 0.5 mm/min.

RESULTS

The highest values were observed in group IN, while the lowest values were determined in group CR. There was not any statistically significant difference between group CR and group FCR ( p>0.05). When groups CR, FCR, and PRF were compared, group PRF showed significantly better fracture strength than did groups CR and FCR ( p<0.05). It was determined that there was not any significant difference between group IN and group PRF ( p>0.05).

CONCLUSIONS

Polyethylene ribbon fiber considerably increases the fracture strength of mandibular premolar teeth with MOD cavities restored with composite.

In Vitro Fatigue Resistance of Teeth Restored With Bulk Fill versus Conventional Composite Resin

The aim of this study was to compare the fatigue resistance of restored teeth with bulk fill composite resin, conventional composite resin with incremental insertion and unprepared sound teeth. Twenty-eight extracted maxillary premolars were selected and divided into 4 groups based on composite resin and insertion technique: control (C), conventional composite resin with incremental insertion (I) and bulk fill composite resin with three (BF3) or single increment (BF1). The restored specimens were submitted to fatigue resistance test with a 5 Hz frequency. An initial application of 5,000 sinusoidal load cycles with a minimum force of 50 N and a maximum force of 200 N was used. Next, were applied stages of 30,000 load cycles with the maximum force increasing gradually: 400, 600, 800, 1000, 1200 and 1400 N. The test was concluded when 185,000 load cycles were achieved or the specimen failed. The fatigue resistance data were recorded for comparison, using the Kaplan-Meier survival curve and analyzed by log-rank test at 0.05 significance. Fractures were classified based on the position of the failure - above or below the cementoenamel junction (CEJ). Statistical analysis of the Kaplan-Meier survival curve and log-rank test showed a significant difference between groups (p=0.001). The fracture analysis demonstrated that only 28.58% of failures were below the CEJ in group C, while for groups I, BF1 and BF3 they were 42.85%, 85.71% and 85.71%, respectively. Teeth restored with composite bulk fill in both techniques present similar fatigue resistance values compared with those restored with a conventional incremental insertion of composite, while the fatigue strength values of unprepared sound teeth were higher. Furthermore, unprepared sound teeth showed a lower percentage of fractures below the CEJ.

Fracture resistance of endodontically treated teeth restored with indirect composite inlay and onlay restorations - An in vitro study

Objective

The purpose of this in vitro study was to evaluate and compare the fracture resistance and fracture mode of extensive indirect inlay and onlay composite resin restorations performed for endodontically treated premolars.

Materials and methods

A total of 55 extracted maxillary premolars were randomly divided into four groups. The first group (n = 15) remained untreated to serve as a positive control; the second group (n = 15) was endodontically treated with inlay cavities prepared and restored with indirect composite inlay restorations; the third group (n = 15) was also endodontically treated with onlay cavities prepared and restored with indirect composite onlay restorations; and the fourth group (n = 10) was endodontically treated with mesio-occlusodistal (MOD) cavities prepared and left unrestored to serve as negative controls. Dual cure indirect composite resin was used to fabricate the inlay and onlay restorations performed for the second and third groups, respectively. All teeth were subjected to compressive axial loading test using a metal ball (6 mm in diameter) in a universal testing machine (Instron 1195) with a cross-head speed of 0.5 mm/min until a fracture occurred. Statistical analysis of fracture resistance and fracture mode were performed with analysis of variance (ANOVA) (α = 0.05) and Kruskal–Wallis (α = 0.05) tests, respectively.

Results

For the four treatment groups, the mean fracture resistance values were 1326.9 N, 1500.1 N, 1006.1 N, and 702.7 N, respectively. Statistical analyses showed no significant differences between the mean fracture resistance of the intact tooth group and the inlay restoration group (p > 0.05), while significant differences were observed between the mean fracture resistance of all the other groups (p < 0.05). The Kruskal–Wallis test showed statistically significant differences between the fracture modes of the four groups.

Conclusion

Within the limitations of this study, endodontically treated teeth were successfully restored with indirect composite inlay and onlay restorations. However, the fractures that accompanied the inlay restorations were more severe and were unable to be restored.

Influence of crosshead speed on failure load and failure mode of restored maxillary premolars

We analyzed the effect of the crosshead speed of an applied load on failure load and failure mode of restored human premolars. Fifty intact, noncarious human premolars were selected. Class II mesio-occlusodistal preparations were made with a water-cooled high-speed preparation machine, and the teeth were restored with composite resin. The specimens were divided into five groups (n = 10 each) and tested individually in a mechanical testing machine, in which a 6.0-mm-diameter steel cylinder was mounted to vary the crosshead speed: v0.5: 0.5 mm/min; v1: 1.0 mm/min; v2.5: 2.5 mm/min; v5: 5.0 mm/min; and v10: 10.0 mm/min. The cylinder contacted the facial and lingual ridges beyond the margins of the restorations. Peak load to fracture was measured for each specimen (N). The means were calculated and analyzed with one-way analysis of variance followed by Tukey's test (a = 0.05). The mean load at failure values were (N) as follows: v0.5, 769.4 ± 174.8; v1, 645.2 ± 115.7; v5, 614.3 ± 126.0; v2.5, 609.2 ± 208.1; and v10, 432.5 ± 136.9. The fracture modes were recorded on the basis of the degree of the tooth structural and restorative damage: (I) fracture of the restoration involving a small portion of the tooth; (II) fractures involving the coronal portion of the tooth with cohesive failure of the composite resin; (III) oblique tooth and restoration fracture with periodontal involvement; and (IV) vertical root and coronal fracture. Varying crosshead speeds of 0.5-5.0 mm/min did not influence the failure load of restored maxillary premolars; however, increasing the crosshead speed to 10 mm/min decreased the failure load values and the degree of tooth structural damage.

Comparison of fracture resistance and failure pattern of endodontically treated premolars with different esthetic onlay systems: An in vitro study

Aim:

To compare the fracture resistance and modes of failures of three different aesthetic MOD onlays on endodontically treated premolars.

Materials and Methods:

Forty sound maxillary premolars were selected of which 10 untreated teeth were taken as control (Group I). The other thirty premolars were subjected to standardized MOD onlay preparations and root canal treatments and divided into 3 equal groups. Onlays were prepared in Group II- Indirect composite, Group III- Lithium Disilicate ceramic and Group IV- Full Zirconia. All onlays were cemented using Multilink Automix. All the 40 samples were subjected to fracture resistance testing on Universal testing machine. Also fractured specimens were observed under stereo-microscope for modes of failure.

Results:

Group IV presented the highest fracture resistance. Groups II and III presented no significant difference in fracture resistance from each other (P > 0.05). Group II and Group III showed significantly lower fracture resistance values than Group I. Coming to modes of failure, only Group IV had showed no cracks in any of the restorations.

Conclusion:

Full Zirconia MOD onlays increased the fracture resistance of endodontically treated premolars to a significantly higher level than the sound teeth.

Influence of preparation design and ceramic thicknesses on fracture resistance and failure modes of premolar partial coverage restorations

STATEMENT OF PROBLEM

Preparation designs and ceramic thicknesses are key factors for the long-term success of minimally invasive premolar partial coverage restorations. However, only limited information is presently available on this topic.

PURPOSE

The purpose of this in vitro study was to evaluate the fracture resistance and failure modes of ceramic premolar partial coverage restorations with different preparation designs and ceramic thicknesses.

MATERIAL AND METHODS

Caries-free human premolars (n=144) were divided into 9 groups. Palatal onlay preparation comprised reduction of the palatal cusp by 2 mm (Palatal Onlay Standard), 1 mm (Palatal-Onlay-Thin), or 0.5 mm (Palatal Onlay Ultrathin). Complete-coverage onlay preparation additionally included the buccal cusp (Occlusal Onlay Standard; Occlusal Onlay Thin; Occlusal Onlay Ultrathin). Labial surface preparations with chamfer reductions of 0.8 mm (Complete-Veneer-Standard), 0.6 mm (Complete-Veneer-Thin), and 0.4 mm (Complete Veneer Ultrathin) were implemented for complete veneer restorations. Restorations were fabricated from a pressable lithium disilicate ceramic (IPS-e.max-Press) and cemented adhesively (Syntac-Classic/Variolink-II). All specimens were subjected to cyclic mechanical loading (F=49 N, 1.2 million cycles) and simultaneous thermocycling (5°C to 55°C) in a mouth-motion simulator. After fatigue, restorations were exposed to single-load-to-failure. Two-way ANOVA was used to identify statistical differences. Pair-wise differences were calculated and P-values were adjusted by the Tukey-Kramer method (α=.05).

RESULTS

All specimens survived fatigue. Mean (SD) load to failure values (N) were as follows: 837 (320/Palatal-Onlay-Standard), 1055 (369/Palatal-Onlay-Thin), 1192 (342/Palatal-Onlay-Ultrathin), 963 (405/Occlusal-Onlay-Standard), 1108 (340/Occlusal-Onlay-Thin), 997 (331/Occlusal-Onlay-Ultrathin), 1361 (333/Complete-Veneer-Standard), 1087 (251/Complete-Veneer-Thin), 883 (311/Complete-Veneer-Ultrathin). Palatal-onlay restorations revealed a significantly higher fracture resistance with ultrathin thicknesses than with standard thicknesses (P=.015). Onlay restorations were not affected by thickness variations. Fracture loads of standard complete veneers were significantly higher than thin (P=.03) and ultrathin (P<.001) restorations.

CONCLUSIONS

In this in vitro study, the reduction of preparation depth to 1.00 and 0.5 mm did not impair fracture resistance of pressable lithium-disilicate ceramic onlay restorations but resulted in lower failure loads in complete veneer restorations on premolars.

Overlays or ceramic fragments for tooth restoration: an analysis of fracture resistance

PURPOSE

The aim of this study was to evaluate the mode of fracture and resistance of partial ceramic restorations of posterior teeth.

MATERIALS AND METHODS

Thirty healthy upper premolars were selected and divided into three groups (n = 10): Group 1- control, healthy unrestored teeth, group 2-teeth restored with ceramic fragments; and group 3-teeth restored with ceramic overlays. The restorations were manufactured with feldspathic ceramic and cemented with RelyX ARC resin cement. After being stored in distilled water for 7 days, the teeth were subjected to axial compression mechanical testing with a universal testing machine. Force was applied to the long axis of the tooth at a speed of 0.5 mm/min until fracture. The data were analyzed with one-way ANOVA and Tukey's test (5%). The mode of fracture was scored according to the degree of involvement of the tooth structure and the type of restoration.

RESULTS

A significant difference (p < 0.05) was showed between groups 2 (1155 N) and 3 (846.6 N), but there was no significant difference between group 1 and the other groups (1046 N), More extensive fractures were prevalent in the healthy teeth group (Group 1), which had no occlusal coverage; less severe fractures were found in groups 2 and 3.

CONCLUSION

We conclude that teeth restored with ceramic fragments may offer greater resistance to fractures compared to teeth that have overlay restorations.

Short fiber reinforced composite: a new alternative for direct onlay restorations

Objectives:

To determine the static load-bearing capacity of direct composite onlay restorations made of novel filling composite resin system which combines short fiber-reinforced composite resin (FC) and conventional particulate filler composite resin (PFC).

Methods:

Three groups of onlay restorations were fabricated (n = 8/group); Group A: made from conventional particulate filler composite resin (Z250, 3M-ESPE, USA, control), Group B: made from short fiber-reinforced composite resin (EverX posterior, StickTeck Ltd, member of GC group, Turku, Finland) as substructure with 1 mm surface layer of PFC, Group C: made from FC composite resin. The specimens were incrementally polymerized with a hand-light curing unit for 80 s before they were statically loaded with two different sizes (3 & 6 mm) of steel ball until fracture. Failure modes were visually examined. Data were analyzed using ANOVA (p = 0.05).

Results:

ANOVA revealed that onlay restorations made from FC composite resin had statistically significantly higher load-bearing capacity (1733 N) ( p < 0.05) than the control PFC composite resin (1081 N). Onlays made of FC composite resin with a surface layer of PFC gave force values of 1405 N which was statistically higher than control group ( p < 0.05). No statistically significant difference was found in the load-bearing capacity between groups loaded by different ball sizes

Significance:

Onlay restorations combining base of short fiber reinforced composite resin as substructure and surface layer of conventional composite resin displayed promising performance in high load bearing areas.

Fracture resistance of teeth restored with all-ceramic inlays and onlays: an in vitro study

Fracture resistance of inlays and onlays may be influenced by the quantity of the dental structure removed and the restorative materials used. The purpose of this in vitro study was to evaluate the effects of two different cavity preparation designs and all-ceramic restorative materials on the fracture resistance of the tooth-restoration complex. Fifty mandibular third molar teeth were randomly divided into the following five groups: group 1: intact teeth (control); group 2: inlay preparations, lithium-disilicate glass-ceramic (IPS e.max Press, Ivoclar Vivadent AG, Schaan, Liechtenstein); group 3: inlay preparations, zirconia ceramic (ICE Zirkon, Zirkonzahn SRL, Gais, Italy); group 4: onlay preparations, lithium-disilicate glass-ceramic (IPS e.max Press); and group 5: onlay preparations, zirconia ceramic (ICE Zirkon). The inlay and onlay restorations were adhesively cemented with dual polymerizing resin cement (Variolink II, Ivoclar Vivadent AG). After thermal cycling (5° to 55°C × 5000 cycles), specimens were subjected to a compressive load until fracture at a crosshead speed of 0.5 mm/min. Statistical analyses were performed using one-way analysis of variance and Tukey HSD tests. The fracture strength values were significantly higher in the inlay group (2646.7 ± 360.4) restored with lithium-disilicate glass-ceramic than those of the onlay group (1673.6 ± 677) restored with lithium-disilicate glass-ceramic. The fracture strength values of teeth restored with inlays using zirconia ceramic (2849 ± 328) and onlays with zirconia ceramic (2796.3 ± 337.3) were similar to those of the intact teeth (2905.3 ± 398.8). In the IPS e.max Press groups, as the preparation amount was increased (from inlay to onlay preparation), the fracture resistance was decreased. In the ICE Zirkon ceramic groups, the preparation type did not affect the fracture resistance results.

Influence of different load application devices on fracture resistance of restored premolars

This in vitro study analyzed the effect of different load application devices on fracture resistance and failure mode of maxillary premolars restored with composite resin. Sixty human maxillary premolars received standardized mesio-occluso-distal cavity preparations and were restored with composite resin. The specimens were randomly divided into 6 groups (n=10). Compressive loading was applied using 6 different metallic devices: S2: 2-mm sphere; S6: 6-mm sphere; C2: 2-mm cylinder; C6: 6-mm cylinder; WS: wedge shape device; and MAT: individualized metallic antagonist tooth. Data were analyzed statistically using one-way ANOVA and Tukey's test (α=0.05). The failure mode was recorded based on the 4 sequential levels. Statistical analysis revealed that WS presented significantly higher fracture resistance than S6 and C6. No significant difference was found among MAT, C2, S2 and S6. Sphere and cylinder with 6 mm were similar, with the lowest values of all groups. MAT presented the least number of catastrophic failures while C2, S2 and WS presented the highest. The type of load application device influences significantly the behavior of the teeth-restoration complex during mechanical fracture resistance test.

Fracture resistance of premolars restored with inlay and onlay ceramic restorations and luted with two different agents

PURPOSE

The purpose of this study was to evaluate the fracture resistance of human maxillary premolars restored with 2 ceramic systems (Vitadur Alpha and In Ceram) comparing 3 preparation designs and 2 luting agents.

METHODS

Seventy sound teeth were prepared to receive ceramic restorations (Vitadur Alpha; n=14) as follows: (1) control, sound premolars, with no preparation, (2) inlays, (3) partial onlays (palatal cuspid coverage), (4) total onlays (both cuspids coverage), and (5) total onlays with an In Ceram core. The ceramic restorations were cemented using Enforce or RelyX ARC (half restorations with each cement), placed into the cavity and held under pressure, except for the control group. The teeth were subjected to compressive axial loading at 0.5 mm min⁻¹ using a 9 mm steel ball until fracture. Data were analyzed by 3-way ANOVA and post hoc Tukey's test (α=.05).

RESULTS

There was a significant difference between cements and among preparation designs (P<.05). All restorations cemented with Enforce exhibited significantly higher fracture resistance (P<.05). Inlay restorations showed similar fracture resistance when compared to control group (P>.05). Partial and total onlays did not statistically differ and showed the weakest performance. The use of an In Ceram core did not produce higher fracture resistance.

CONCLUSIONS

Within the limitations of this study, the cements tested had different mechanical properties, while cuspid coverage did not result in improved fracture resistance of the restored teeth.

Ceramic inlays and partial ceramic crowns: influence of remaining cusp wall thickness on the marginal integrity and enamel crack formation in vitro

No information is currently available about what the critical cavity wall thickness is and its influence upon 1) the marginal integrity of ceramic inlays (CI) and partial ceramic crowns (PCC) and 2) the crack formation of dental tissues. This in vitro study of CI and PCC tested the effects of different remaining cusp wall thicknesses on marginal integrity and enamel crack formation. CI (n = 25) and PCC (n = 26) preparations were performed in extracted human molars. Functional cusps of CI and PCC were adjusted to a 2.5 mm thickness; for PCC, the functional cusps were reduced to a thickness of 2.0 mm. Non-functional cusps were adjusted to wall thicknesses of 1) 1.0 mm and 2) 2.0 mm. Ceramic restorations (Vita Mark II, Cerec3 System) were fabricated and adhesively luted to the cavities with Excite/Variolink II. The specimens were exposed to thermocycling and central mechanical loading (TCML: 5000 x 5 degrees C-55 degrees C; 30 seconds/cycle; 500000 x 72.5N, 1.6Hz). Marginal integrity was assessed by evaluating a) dye penetration (fuchsin) on multiple sections after TCML and by using b) quantitative margin analysis in the scanning electron microscope (SEM) before and after TCML. Ceramic- and tooth-luting agent interfaces (LA) were evaluated separately. Enamel cracks were documented under a reflective light microscope. The data were statistically analyzed with the Mann Whitney U-test (alpha = 0.05) and the Error Rates Method (ERM). Crack formation was analyzed with the Chi-Square-test (alpha = 0.05) and ERM. In general, the remaining cusp wall thickness, interface, cavity design and TCML had no statistically significant influence on marginal integrity for both CI and PCC (ERM). Single pairwise comparisons showed that the CI and PCC of Group 2 had a tendency towards less microleakage along the dentin/LA interface than Group 1. Cavity design and location had no statistically significant influence on crack formation, but the specimens with 1.0 mm of remaining wall thickness had statistically significantly more crack formation after TCML than the group with 2.0 mm of remaining cusp wall thickness for CI. The remaining cusp wall thickness of non-functional cusps of adhesively bonded restorations (especially for CI) should have a thickness of at least 2.0 mm to avoid cracks and marginal deficiency at the dentin/LA interface.

Fracture strength of teeth restored with ceramic inlays and overlays

This study evaluated the fracture strength of teeth restored with bonded ceramic inlays and overlays compared to sound teeth. Thirty sound human maxillary premolars were assigned to 3 groups: 1- sound/unprepared (control); 2- inlays and 3- overlays. The inlay cavity design was Class II MOD preparation with an occlusal width of 1/2 of the intercuspal distance. The overlay cavity design was similar to that of the inlay group, except for buccal and palatal cusp coverage The inlay and overlay groups were restored with feldspathic porcelain bonded with adhesive cement. The specimens were subjected to a compressive load until fracture. Data were analyzed statistically by the Kruskal-Wallis test at 5% significance level. The fracture strength means (KN) were: Sound/unprepared group = 1.17, Inlay group= 1.17, and Overlay group = 1.14. There were no statistically significant differences (p>0.05) among the groups. For inlays and overlays, the predominant fracture mode involved fragments of one cusp (70% of simple fractures). The fracture strength of teeth restored with inlay and overlay ceramics with cusp coverage was similar to that of intact teeth.

Fracture Resistance and Gap Formation of MOD Restorations: Influence of Restorative Technique, Bevel Preparation and Water Storage

Beveling of the cavosurface margin can improve resistance to fracture and the marginal adaptation of posterior composite restorations, reducing the deleterious effect of storage with thermal cycling on restoration quality. Generally, indirect restorations showed similar performance compared to direct restorations.

Tensile Bond Strength and Flexural Modulus of Resin Cements—Influence on the Fracture Resistance of Teeth Restored with Ceramic Inlays

The mechanical properties of resin cement can influence the fracture resistance of teeth restored with ceramic inlays. In general, cement with a higher elastic modulus resulted in a tooth/ceramic inlay that had a higher fracture resistance.

Fracture resistance of thermal cycled and endodontically treated premolars with adhesive restorations

STATEMENT OF PROBLEM

Cavity preparations have routinely been associated with decreased fracture strength of restored teeth.

PURPOSE

The purpose of this study was to evaluate the influence of endodontic treatment and thermal cycling on the fracture resistance of teeth restored with ceramic or composite resin inlay restorations.

MATERIAL AND METHODS

One hundred sound, maxillary premolars were selected. Twenty intact teeth served as a control group. Eighty teeth were prepared with MOD cavity preparations; half of them were also endodontically treated. Inlay restorations were prepared with composite resin (Filtek Z250) or feldspathic ceramic (Vitadur Alpha). Half of the specimens for each group were submitted to thermal cycling (500 cycles, between 5 and 55 degrees C, dwell time of 30 seconds). The specimens were subjected to compressive axial loading using a steel ball. Data were analyzed using 3-way ANOVA and post hoc Tukey's test (alpha=.05).

RESULTS

Except for those teeth restored with ceramic without endodontic treatment and thermal cycling, no other group achieved fracture strength similar to sound teeth. Ceramic and composite resin restorations provided similar resistance to fracture. There was a significant interaction between endodontic therapy and thermal cycling (P<.001). In the nonthermal cycled groups, endodontically treated teeth showed significantly lower fracture resistance (P<.001). All experimental groups had similar fracture strength when submitted to thermal cycling.

CONCLUSIONS

Both restorative techniques provided similar fracture resistance. Endodontic treatment decreased the fracture resistance of nonthermal cycled specimens, while thermal cycling decreased the fracture resistance of nonendodontically treated specimens.