Fracture of fiber-reinforced composites analyzed via acoustic emission

Optimizing fracture resistance of endodontically treated maxillary premolars restored with preheated thermos-viscous composite post-thermocycling, a comparative study. Part I

PURPOSE

This research aimed to investigate fracture resistance of endodontically treated maxillary premolars restored using preheated thermo-viscous and fiber-reinforced bulk fill resin composite, in vitro.

METHODOLOGY

Sixty sound human maxillary premolars were selected and divided randomly into 6 groups of ten teeth each (n = 10). Group 1; is the positive control with sound unprepared teeth (P), Group 2; is the negative control in which Mesio-occluso-distal (MOD) cavities were left unrestored (N), Group 3; includes the teeth restored by incremental packing with conventional nanohybrid composite (ChP), Group 4; includes teeth restored with short fiber reinforced bulk fill composite (EF), Group 5; includes teeth restored with preheated thermo-viscous bulk fill composite (VB), and Group 6; includes teeth restored using packable bulk fill composite (XF) Tested restorative materials were bonded with a universal adhesive in self-etch mode. Teeth were kept in distilled water for 24 h at 37 °C proceeded by thermocycling (5- 55 °C, 1200×). Teeth were then exposed to compressive load till fracture at a crosshead speed of 1 mm/min. One-way ANOVA followed by Tukey post-hoc test was implemented to compare between more than two groups in non-related samples. The significance level was established at α = 0.05 for both tests.

RESULTS

Intact teeth significantly recorded the highest fracture resistance values among all groups. A significant difference was recorded among all the tested groups, with the EF recording the highest values, followed by the VB group then the XF group and ChP that recorded the lowest data. Negative control premolars significantly recorded the lowest fracture.

CONCLUSIONS

After thermocycling, endodontically treated maxillary premolars restored with pre-heated thermos-viscous composite did not exhibit an increase in fracture resistance. Notably, our findings indicate that short fiber-reinforced composite demonstrated significantly higher fracture resistance compared to other types of composites assessed in this study. This suggests the potential superiority of short fiber-reinforced composite in enhancing the overall structural integrity of endodontically treated teeth subjected to occlusal forces.

Current treatment approaches of newly graduated, intern dentists and dentists in doctoral and specialty training to teeth with excessive substance loss (cross-sectional study)

Aim: New treatment options have been developed as alternative post-retaining restorations and crowns that preserve remaining tooth tissue in endodontically treated teeth with excessive substance loss. This study, current treatment approaches newly graduated, intern and doctoral or specialist dentists in teeth excessive coronal destruction were evaluated. Material and Method: This cross-sectional study, online questionnaire consisting of 22 questions, 3 parts was applied. First part consists of demographic information participants, second part consists of questions measuring awareness about preferred indirect restorations, last part consists of current treatment approaches newly graduated, intern and doctoral or specialist dentists. Total 234 voluntary participants questionnaires were evaluated. Obtained data were analyzed with IBM SPSS V23. Results: In restoration of endodontically treated buccal mesial walls (least 2 mm thick) molars, participants all 3 groups preferred posterior adhesive indirect restorations according to their titles. Considering level of awareness, participants high group preferred posterior adhesive indirect restorations more in restorations endodontically treated buccal lingual walled molar teeth. Participants all 3 groups preferred use fiber under composite strengthen teeth in the restoration of teeth with excessive substance loss. Conclusion: According to the results, it was determined that awareness and knowledge level of dentists who received specialty or doctoral training about new current treatments was higher than other newly graduated and intern dentists. It was observed that participants group with high level awareness mostly preferred posterior region indirect adhesive restorations such as endocrown and onlay.

Effect of Inlays, Onlays and Endocrown Cavity Design Preparation on Fracture Resistance and Fracture Mode of Endodontically Treated Teeth: An In Vitro Study

PURPOSE

To evaluate the fracture resistance and failure modes of endodontically treated mandibular molars restored with different designs of inlays, onlays and endocrowns.

MATERIALS AND METHODS

Extracted mandibular third molars (n = 180) were used. An access cavity was prepared on the occlusal surface of each tooth and the roots were obturated with gutta percha. All specimens were randomly divided into 6 groups (n = 30/group) according to the cavity design and the restoration material used. C: control group without access cavity preparation. IE: MOD inlay preparation with EverX Posterior (GC Europe) in the pulp chamber. IG: MOD inlay preparation with G-aenial Universal Flo (GC America) in the pulp chamber. OE: onlay preparation with EverX Posterior (GC Europe) in the pulp chamber. OG: onlay preparation with G-aenial Universal Flo (GC America) in the pulp chamber. EC: endocrown with an empty pulp chamber. All restorations were fabricated with CAD/CAM system using CERASMART^® (GC Dental products Europe, Belgium) CAD/CAM blocks. Specimens were thermal-cycled and were subjected to a compressive load applied at 30° angle relative to the long axis of the tooth with a universal testing machine. Results were statistically analyzed by ANOVA followed by Tukey post hoc tests. Chi-square test and Fisher Exact tests were used for the comparisons among groups.

RESULTS

The mean fracture strength was significantly different between the groups (p < 0.001); it was significantly highest for intact teeth, followed by endocrowns (p = 0.021). The strength was significantly lower for inlays (with G-aenial Universal Flo and EverX Posterior), intermediate for onlays with EverX Posterior followed by onlays with G-aenial Universal Flo.

CONCLUSIONS

Endocrowns exhibited higher fracture resistance than other tested composite resin groups. Endocrowns and onlays showed a more favorable failure mode than inlay restorations.

Bonding Interaction and Shrinkage Stress of Low-viscosity Bulk Fill Resin Composites With High-viscosity Bulk Fill or Conventional Resin Composites

OBJECTIVE

To analyze the shrinkage stress, bonding interaction, and failure modes between different low-viscosity bulk fill resin composites and conventional resin composites produced by the same manufacturer or a high-viscosity bulk fill resin composite used to restore the occlusal layer in posterior teeth.

METHODS & MATERIALS

Three low-viscosity bulk fill resin composites were associated with the conventional resin composites made by the same manufacturers or with a high-viscosity bulk fill resin composite, resulting in six groups (n=10). The bonding interaction between resin composites was tested by assessing the microshear bond strength (μSBS). The samples were thermocycled and were tested with 1-mm/min crosshead speed, and the failure mode was evaluated. The post-gel shrinkage (Shr) of all the resin composites was measured using a strain gauge (n=10). The modulus of elasticity (E) and the hardness (KHN) were measured using the Knoop hardness test. Two-dimensional finite element models were created for analyzing the stress caused by shrinkage and contact loading. The μSBS, Shr, E, and KHN data were analyzed using the Student t-test and one-way analysis of variance. The failure mode data were subjected to chi-square analysis (α=0.05). The stress distribution was analyzed qualitatively.

RESULTS

No significant difference was verified for μSBS between low-viscosity bulk fill resin composites and conventional or high-viscosity bulk fill composites in terms of restoring the occlusal layer (p=0.349). Cohesive failure of the low-viscosity bulk fill resin composites was the most frequent failure mode. The Shr, E, and KHN varied between low-viscosity and high-viscosity resin composites. The use of high-viscosity bulk fill resin composites on the occlusal layer reduced the stress at the enamel interface on the occlusal surface.

CONCLUSIONS

The use of high-viscosity bulk fill resin composites as an occlusal layer for low-viscosity bulk fill resin composites to restore the posterior teeth can be a viable alternative, as it shows a similar bonding interaction to conventional resin composites as well as lower shrinkage stress at the enamel margin.

Microtensile bond strength between a UDMA fiber post and different resin cements: Effect of pre-surface treatment

During a fiber post cementation, bonding failure often occurs at the junction between the fiber-post and resin-cement. Because this failure requires better characterization, we evaluated if different post surface treatment can affect the bond strength of urethane dimethacrylate (UDMA) fiber-posts with resin-cements. Three groups were created: G1: no treatment/silane; G2: ethyl alcohol (96° GL)/silane; G3: 24% H₂O₂/silane and further divided into four subgroups: I-Unicem/3MESPE; II-BisCem/Bisco; III-Panavia SA/Kuraray and IV-DuoLink/Bisco. Blocks of cured resin cements and posts placed in the center were serially cut into bar-shaped specimens and loaded into a micro tensile testing machine. ANOVA indicated no significant differences among post surface treatments (p>0.05), however, significant within the resin cements (p<0.05) and the interaction of both (p<0.05). The G3/IV showed the highest bond strength values. SEM showed that surface treatments on UDMA fiber posts presented no benefits in terms of surface roughness, thus, should not be performed.

Fracture Resistance of Endodontically Treated Teeth Restored With Bulk Fill, Bulk Fill Flowable, Fiber-reinforced, and Conventional Resin Composite

The aim of this in vitro study was to evaluate the fracture resistance of endodontically treated teeth restored with different types of restorative resins.

METHODS AND MATERIALS

Seventy-two sound maxillary premolar teeth were randomly divided into six groups (n=12). The teeth in the first group were left intact and tested as unprepared negative control (group I) specimens. The teeth in the remaining five groups were prepared with MOD cavities and endodontically treated. The teeth in one of the five groups (positive control group II) were unrestored. The rest of the prepared cavities were restored as follows: group III: bulk fill resin composite/Filtek Bulk Fill (3M ESPE); group IV: bulk fill flowable resin composite + nanohybrid/SureFil SDR Flow + Ceram.X Mono (Dentsply); group V: fiber-reinforced composite + posterior resin composite/GC everX posterior + G-aenial posterior (GC Corp.); and group VI: nanohybrid resin composite/Tetric N-Ceram (Ivoclar/Vivadent). Each restorative material was used with its respective adhesive system. The restored teeth were stored in distilled water for 24 hours at 37°C and were then thermocycled (5-55°C, 1000×). Specimens were subjected to a compressive load until fracture at a crosshead speed of 0.5 mm/min. The data were analyzed using one-way analysis of variance followed by the post hoc Tukey honestly significantly different test (p<0.05).

RESULTS

Sound premolar teeth (group I negative control) showed significantly higher fracture resistance than did the other tested groups (p<0.05). No statistically significant differences were found in the fracture resistance values of the restored groups (groups III, IV, V, and VI) (p>0.05). The lowest values were obtained in the positive control group (group II); these values were significantly lower than those of the other groups (p<0.05).

CONCLUSION

The fracture resistance values of endodontically treated teeth restored with either bulk fill/bulk fill flowable or fiber-reinforced composite were not different from those restored with conventional nanohybrid resin composite.