Fracture Resistance Of Teeth Research Articles

Comparative estimation of fracture resistance of teeth restored with new fiber impregnated composite, short fiber composite, and nanohybrid composite – An in-vitro study

INTRODUCTION. Composite resins, used in restorative dentistry, offer enhanced esthetic and mechanical qualities. Nevertheless, the significant issue of volumetric shrinkage during polymerization remains a concern. Shrinkage-induced stress has the potential to cause marginal defects and enamel and cuspal fractures, especially in high stress-bearing areas. The present study aimed at assessing and comparing the fracture resistance and fracture patterns of teeth restored with new impregnated cubical composite, short fiber reinforced composite, and nanohybrid composite in mesio-occlusal-distal (MOD) cavities.MATERIALS AND METHODS. This was an in-vitro study comprising 45 extracted premolars cleaned and mounted in resin blocks. The MOD cavities were prepared in all the samples and were divided into three groups; Group I samples restored using ESPE Filtek Z350 XT restorative composite syringeTM, Group II using GC EverX posterior compositeTM (4mm), and Group III using Fibrafill cube S. Restorations were finished and polished.RESULTS. The mean fracture resistance was 844.5±264.8, 1249.7±518.3, and 1240.8±453.3 in Group I, II, and III, respectively. Group II and III fracture resistance was comparable (p=1.00) but higher than Group I (p=0.03 with Group II, p = 0.04 with Group III). No significant difference was present in the favourable and nonfavourable fracture patterns between the three groups (p=0.108).CONCLUSIONS. Short fiber and cubic fiber integrated composites performed similarly in terms of fracture resistance resulting in favourable fracture, however better over conventional nanohybrid composites.

Influence of Endodontic Cavity Design on Interfacial Voids, Class II Resin Composites Sealing Ability and Tooth Fracture Resistance: An In Vitro Study.

Objective: The aim of this in vitro investigation is to study the effect of endodontic cavity design on interfacial voids, class II resin composite sealing ability, and fracture resistance in mandibular premolars. Methods: A total of 48 single-rooted mandibular premolars received compound class II preparations with either traditional flare access cavities (group A) or contracted endodontic cavity preparations (group B). Each study group was subdivided according to the coronal restoration into two sub-groups as α and β. In the α group, a microhybrid composite was used after etch-and-rinse bonding technique using an MDP-containing universal adhesive. In the β group, a self-adhesive composite was used as coronal restoration after endodontic treatment (n = 12) for each subgroup. A micro-CT analysis was performed to assess the obturation interfacial voids and tracing of class II cervical interfacial adaptation. The tooth fracture resistance testing was then performed adding an extra group of 12 sound non-prepared teeth, which were tested as the control for fracture strength testing. A one-way ANOVA and post-hoc testing were used together with descriptive statistics for an analysis of the mean values of obturation interfacial voids. A two-way ANOVA was used to assess the fracture resistance test results, and to find the influence of endodontic access design and the type of composite material on the fracture resistance testing. Chi-square testing was employed to analyze the cervical interfacial seal of the class II restorations. Results: A one-way ANOVA revealed that there were no statistically significant differences between test groups in the amount of obturation interfacial voids (p > 0.05). There were no statistically significant differences between test groups in terms of cervical interfacial sealing ability (p > 0.05). A two-way ANOVA revealed that no statistically significant differences between test groups including the control group existed in terms of the fracture resistance testing (p > 0.05). Conclusions: Although it does not improve tooth fracture resistance, the contracted endodontic access cavity does not deteriorate the quality of obturation in terms of the interfacial porosity. The self-adhesive composite does not improve the efficiency of cervical interfacial adaptation or tooth fracture resistance regardless of the endodontic access cavity shape, yet it revealed a substantial load-bearing capacity.

Fracture resistance of teeth restored with different bioactive restoratives

Fracture resistance of teeth restored with different bioactive restoratives

Endodontic Access Cavity Design and Fracture Resistance: A Systematic Review and Meta-Analysis of Conventional vs. Newer Access Cavity.

The era of minimally invasive dentistry has led to the development of new access cavity designs. The impact of various access cavity designs on the fracture resistance of teeth has been extensively studied. The primary aim of this systematic review and meta-analysis is to evaluate and compare the effects of recent modifications in endodontic access cavity design- specifically, conventional, conservative, and truss designs on tooth fracture resistance. Three independent reviewers searched studies across six different databases (PubMed, Scopus, EBSCOhost, BVS, Wiley, and Google Scholar) from January 2000 to July 2024, following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The articles were then screened using strict inclusion and exclusion criteria. A quality assessment was performed using a modified version of the quality assessment of in-vitro studies according to the QUIN (Quality Assessment Tool For In Vitro Studies) tool, categorizing the selected articles into low, moderate, and high risk of bias. Quantitative data synthesis was conducted to combine equivalent results using STATA. Forest plots were created with the level of significance set at 0.05 (p = 0.05). Out of 243 articles, 14 met the strict inclusion criteria. Among the selected articles, 11 showed a low risk of bias and three showed a moderate risk. The meta-analysis revealed that fracture resistance of conservative and truss access designs is significantly higher than that of conventional endodontic access, with a standardized mean difference (SMD) of 2.61 (95% 1.47 to 3.74; p-values <0.001) and SMD = -1.26 (95% confidence interval (CI): -1.81 to 0-0.71; p<0.001). The heterogeneity (I²) values for these comparisons were 92% and 65.6%, respectively. The extent of the access cavity has a substantial impact on tooth fracture resistance. Newer conservative and truss endodontic access designs offer better fracture resistance compared to conventional endodontic access.

Effect of Pulp Chamber Access, Instrumentation, Obturation, and Restoration on the Fracture Resistance of Endodontically Treated Canine Teeth in Dogs.

Veterinary studies documenting the effect of endodontic treatment on tooth fracture resistance are scarce. The objective of this ex vivo study was to evaluate the effects of mesial access preparation and restoration, as well as pulp chamber access, instrumentation, obturation, and restoration, on the fracture resistance and characteristics of canine teeth in dogs. Sixty-five dog canine teeth were divided into 4 groups: 1. Standard endodontic treatment through a mesial access only; 2. Treatment as per group 1, adding an incisal access, instrumentation and obturation of the pulp chamber, and restoration of the access; 3. Treatment as per group 2, without pulp chamber obturation or restoration of the incisal access; and 4. Untreated teeth. The fracture resistance and characteristics of each group were documented using axial compression testing, angled 45° disto-occlusal to the long axis of the crown. The maximum force prior to fracture in groups 1, 3, and 4 were not statistically different, demonstrating that restored mesial and incisal accesses with pulp chamber instrumentation did not statistically affect fracture resistance. However, obturated and restored group 2 teeth demonstrated decreased fracture resistance compared to all other groups (P < .001). Additionally, 26.7% of group 1 teeth sustained complicated crown fractures, while 100% of group 2 teeth fractured within the obturation or restorative materials, preventing pulp exposure in these cases. Although the cause and clinical importance of decreased tooth fracture resistance following pulp chamber obturation and restoration remains unknown, it may provide protective value for maintaining a coronal seal in the event of tooth fracture.

Effect of Two Techniques of Separated File Removal Systems on Dentin Loss and Fracture Resistance of Teeth (In Vitro Study)

Effect of Two Techniques of Separated File Removal Systems on Dentin Loss and Fracture Resistance of Teeth (In Vitro Study)

In-vitro evaluation of fracture resistance of teeth restored with different high-viscosity glass ionomer restorative materials and bulk-fill composite resins

ObjectivesThis study aimed to evaluate the effect of restorations made with a glass-hybrid restorative system (GHRS), a high-viscosity glass ionomer restorative material (HVGIC), a high-viscosity bulk-fill composite resin (HVB), a flowable bulk-fill composite resin (FB), and a nanohybrid composite resin (NH), which are commonly preferred in clinical applications on the fracture resistance of teeth in-vitro.Materials and methodsOne hundred intact human premolar teeth were included in the study. The teeth were randomly divided into ten groups (n = 10). No treatment was applied to the teeth in Control group. Class II cavities were prepared on the mesial surfaces of the remaining ninety teeth in other groups. For restoration of the teeth, a GHRS, a HVGIC, a HVB, a FB, and a NH were used. Additionally, in four groups, teeth were restored using NH, GHRS, and HVGIC with open and closed-sandwich techniques. After 24 h, fracture resistance testing was performed. One-way ANOVA and Tukey HDS tests were used for statistical analysis of the data.ResultsThe fracture resistance values of Control group were statistically significantly higher than those of GHRS, HVGIC, FB, NH, HVGIC-CS, GHRS-OS, and HVGIC-OS groups(p < 0.05). There was no statistically significant difference observed between the fracture resistance values of Control, HVB, and GHRS-CS groups (p > 0.05).ConclusionIt can be concluded that the use of HVB and the application of GHRS with a closed-sandwich technique may have a positive effect on the fracture resistance of teeth in the restoration of wide Class II cavities.Clinical relevanceThe use of high-viscosity bulk-fill composite resin and the application of glass-hybrid restorative system with the closed-sandwich technique in the restoration of teeth with wide Class II cavities could increase the fracture resistance of the teeth.

An Evaluation of the Fracture Resistance of Teeth with Simulated External Cervical Resorption Cavities Categorized Using Three-Dimensional Classification.

(1) Background: External cervical resorption causes dental hard tissue destruction that may reduce the fracture resistance of affected teeth. By using a compressive strength test, this study aimed to evaluate the fracture resistance of teeth with simulated external cervical resorption cavities that have different three-dimensional classifications. (2) Methods: In total, 170 teeth with simulated external cervical resorptions were divided into 16 experimental groups (n = 10) and 1 control group (n = 10) based on the three-dimensional classification: 1Ap, 1Bp, 1Cp, 1Dp, 2Ap, 2Bp, 2Cp, 2Dp, 3Ap, 3Bp, 3Cp, 3Dp, 4Ap, 4Bp, 4Cp, 4Dp and a control group. Defects were restored with mineral trioxide aggregate. The fracture resistances of the samples were statistically analyzed using two-way repeated ANOVA and the Bonferroni correction for multiple comparisons at a significance level of p < 0.05. (3) Results: The lowest resistance to fracture was observed in samples with vertical height level "4" and circumferential spread of "D" (p < 0.001). In the groups with circumferential spreads "B", "C" and "D", there were significant differences between the samples with vertical height levels "1", "2", "3" and "4" regarding fracture resistance (p < 0.001). (4) Conclusions: The circumferential spread and vertical height of the external cervical resorption influenced the fracture resistance of the affected teeth.

Universal Adhesive Application Modes Differentially Affect the Fracture Resistance of Resin Composite Restored Teeth.

This study evaluated the fracture resistance of teeth with mesio-occluso-distal (MOD) resin composite restorations using universal adhesive (Single Bond Universal; SBU) in three different manipulation modes compared with those using two-step self-etch (Clearfil SE bond; CSE) and 3-step etch-and-rinse (Scotchbond Multi-Purpose; SBMP) adhesives at 24 hours and after thermocycling. One hundred and sixty maxillary premolars were assigned into eight groups of 20 each. Intact teeth and nonrestored cavity-prepared teeth served as controls. For the remaining specimens, cavities were restored with resin composite using different adhesives-SBU in self-etch, etch-and-rinse, or selective enamel etching modes; CSE in self-etch or selective enamel etching; and SBMP. Specimens from each group were either stored in 37°C water for 24 hours or further submitted to thermocycling for 30,000 cycles (n=10), then subjected to axial compression stress until fracture. Fracture patterns were observed microscopically. Data were statistically analyzed at a 95% confidence level. Among the restored teeth, mean failure load of the group using SBMP was the highest at both short-term and long-term evaluation periods (p<0.05). Fracture strengths of the SBU groups where enamel was etched with phosphoric acid prior to the adhesive application were similar and were greater than in those specimens without pre-etching (p<0.05). After thermal aging, a significant decrease in fracture resistance value was detected only for the group using SBU in etch-and-rinse application mode (p<0.05). For the self-etch strategy, SBU demonstrated lower load to fracture than CSE following thermocycling; all specimens failed at and beneath the crestal level (p<0.05). Application of SBU universal adhesive in selective enamel etching mode provided higher and more stable fracture resistance of teeth with MOD resin composite restorations than in self-etch mode.

Evaluation of fracture resistance of teeth with Class II Mesio-Occluso- Distal cavities restored by three different esthetic restorative materials: An In-vitro study

Aim - The aim of present investigation was to assess fracture resistance of teeth with Class II Mesio-Occluso-Distal (MOD) cavities filled with Microhybrid composite, Nanohybrid composite and Cention-N. Materials and Methods - 40 extracted maxillary premolars were kept in 0.1% thymol solution for 7 days, then subsequently in normal saline until use. All specimens were embedded 2mm below Cemento-enamel junction (CEJ) in self cure acrylic resin molds. They were then arbitrarily divided in 4 groups, each with 10 specimens (n=10). Group 1 consisted of intact teeth (Control group), whereas Group 2,3 and 4 contained prepared teeth with standardized class II MOD cavities filled with Microhybrid composite, Nanohybrid composite and Cention-N respectively. All the specimens were finished using composite finishing &amp; polishing kit and were stored in 100% humidity at 37℃ for 24 hours. Each specimen was subjected to Fracture resistance (N) under Universal Testing Machine. Data collected was subjected to One-way analysis of variance and then subsequently to Tukey’s post-hoc test. Differences in groups were considered significant at p ≤ 0.05. Results - The results showed that Cention-N exhibited highest fracture resistance whereas Microhybrid composite had least fracture resistance when compared to other restorative groups. Conclusion - It can be inferred that Cention-N can be preferred for restoration of Class II MOD cavities in maxillary premolars over Nanohybrid composite or Microhybrid composite. Keywords - Cention-N, fracture resistance, Mesio-Occluso-Distal cavities, Microhybrid composite, Nanohybrid composite, Universal testing machine

Comparison of Different Endodontic Access Cavity Designs on the Fracture Resistance of Tooth in WaveOne Gold and TruNatomy Instrumentation.

An important aspect of the preparation of the access cavity and biomechanical preparation of the root canal is to safeguard as much of the tooth's framework as possible without affecting access and visibility. To compare the impact of the conservative design of access preparation and traditional design of access preparation in association with TruNatomy endodontic instrumentation and WaveOne Gold endodontic instrumentation on resistance to fracture by the design of a cavity for endodontic access using finite element analysis. Micro-CT radiographic images of 16 human first permanent molars of the mandible were included in the study to create representative finite element analysis computational models. A significant reduction in load for failure after endodontic preparation was observed in TDAP subcategories as compared to specimens with CDAP. However, the reduction in load for failure was comparable in both endodontic instrument systems within the CDAP and TDAP. A significant reduction in load for failure after endodontic preparation was observed in the traditional design of access preparation subcategories as compared to specimens with the conventional design of access preparation.

Comparison of fracture resistance of posterior tooth restored with cention-n, zirconomer and universal composite restorative material: An in-vitro study

The aim of this study was to access and compare fracture resistance of tooth restored with Cention-N, Zirconomer and Filtek Z350 XT. Seventy five extracted maxillary premolar were divided into five groups; (Group I) Unprepared intact teeth, (Group II) Teeth with class II mesio-occluso-distal (MOD) cavity prepared and unrestored, (Group III) Teeth with class II MOD cavity prepared and restored with Zirconomer (Shofu Inc), (Group IV) Teeth with class II MOD cavity prepared and restored with Cention N, (Group V) Teeth with class II MOD cavity prepared and restored with Universal Composite Restorative Material (Filtek Z350 XT). Specimen was individually tested in a universal testing machine for facture resistance. Filtek Z350 XT showed statistically significant fracture resistance as compared to Group II, Group III and Group IV (P&amp;#60;0.001). Cention-N showed better fracture resistance than Zirconomer but didn’t vary statistically. All the test restorative material showed acceptable fracture resistance under load. Long term clinical evaluation is required to access their behavior intraorally.

Comparison of conventional preparation with modified access preparation on fracture resistance of primary molars - A finite element analysis

ObjectiveTo investigate the influence of Conventional Straight (CS) line and Modified Straight (MS) line access preparations with various restorative materials on the fracture resistance of primary molars using Finite Element Analysis (FEA). MethodologyThree FEA models for each of the primary molars were divided into Group I- Intact tooth model; Group II- Model with CS outline and Group III- Model with MS outline. Based on the restorative material used, Group II and III were further subdivided into subgroup 1- GIC restoration, subgroup 2 – composite resin with GIC base and subgroup 3- Stainless Steel Crown (SSC). Each model was subjected to 5 different force loads directed at the occlusal surface. Maximal von Mises (VM) stresses calculated from stress distribution patterns. ResultThe maximum displacement, in all the models of primary molars were seen in GIC restored models in molars with both CS and MS access whereas the minimal displacement was seen in the SSC restored molars of MS group. ConclusionIn primary maxillary second molar and mandibular first and second molar with intact marginal ridges, the fracture resistance of tooth with MS outline restored with GIC base followed by Composite resin was comparable with the tooth restored with SSC and CS outline. Clinical outcomeBased on the results of this FEA analysis, composite restorations with MS outline would be appropriate for endodontically treated primary molars that have intact margins.

Systematic review fracture resistance of endodontically treated posterior teeth restored with fiber reinforced composites- a systematic review

BackgroundLarge cavity designs and access cavities impair endodontically treated tooth fracture resistance. As the tooth’s strength is known to reduce significantly after the root canal treatment, occlusal loading as a result of functions such as chewing, biting and certain parafunctional tendencies makes the endodontically treated tooth vulnerable to fracture. Hence, after endodontic treatment, it is vital to give adequate and appropriate restorative material to avoid tooth fractures. Accordingly, the choice of such restorative material should be dictated by the property of fracture resistance.ObjectiveThe goal of this study was to conduct a systematic review and critical analysis of available data from in vitro studies examining the fracture resistance of endodontically treated posterior teeth restored with fiber-reinforced composites.MethodologyThe Preferred Reporting Items for Systematic Review and Meta-Analysis (PRIS-MA) Statement was used to guide the reporting of this systematic review A comprehensive literature search was performed using MEDLINE (via PubMed), Scopus, ScienceDirect, Google Scholar, and LILACS. A manual search of the reference lists of the articles was also performed. The databases provided a total of 796 studies from the electronic systematic search. The databases provided a total of 796 studies from the electronic systematic search. Two reviewers scrutinized the papers for eligibility based on inclusion/exclusion criteria and extracted data. The studies were assessed for their potential risk of bias. Based on modified JBI & CRIS (checklist for reporting in vitro studies) guidelines, along with the methodology and treatment objective, we have formulated 13 parameters specifically to assess the risk of bias. A total of 18 studies met the inclusion criteria and were included for qualitative analysis. Considering the high heterogeneity of the studies included, a meta-analysis could not be performed.ResultsThe majority of the included studies had a moderate or high risk of bias. When compared to traditional hybrid composites, fiber-reinforced composites showed increased fracture resistance of endodontically treated teeth in the majority of investigations. On the other hand, limited evidence was found for the bulk fill composites. Moreover, moderate evidence was found for the fracture resistance of inlays and fiber posts with fiber-reinforced composites for core build-up in endodontically treated teeth. No evidence could be found comparing the fracture resistance of endo crowns and fiber-reinforced composites in endodontically treated teeth.ConclusionAccording to the research, using fiber-reinforced composites instead of conventional hybrid composites improves the fracture resistance of endodontically treated teeth. However, there was a high risk of bias in the research considered. No judgments could be reached about the superiority of one material over another based-on comparisons between other core restorations.

Effect of two thermally-treated rotary nickel-titanium files with and without root canal filling on fracture resistance of teeth, an ex-vivo study.

Effect of two thermally-treated rotary nickel-titanium files with and without root canal filling on fracture resistance of teeth, an ex-vivo study.

An In vitro Comparative Evaluation of the Fracture Resistance of Teeth with Mesio-Occluso-Distal Preparations Restored with Different Esthetic Materials by Bulk-Fill and Incremental Methods

Introduction: One of the most popular restorative materials today is resin-based composite. Volumetric shrinkage is brought on by polymerization, which can cause contraction stress, microleakage, and adhesion failure. Adhesive restorations have several benefits, including the ability to preserve more healthy tissue and “reinforce” the remaining tooth structure. These benefits go beyond just being attractive. Materials and Methods: Eighty extracted human maxillary premolars were entrenched in a self-cured acrylic resin in a rubber mold cylinder (2.5 cm width-3 cm height). These were arbitrarily divided into 5 groups: 2 control groups (positive control group and negative control group) (n = 10) and 3 experimental (n = 20) groups (microhybrid composite, nanocomposite, and Giomer). The mesio-occluso-distal (MOD) cavities were prepared in 70 samples. After MOD cavities preparation, groups were further subdivided into two subgroups for bulk-fill and incremental methods. Universal Tofflemire Retainer and band were placed on the prepared cavities. The self-etch adhesive was applied on all aspects of the preparations and then it was light-cured using a light-curing unit for 15 s. Now, cavities were restored with different esthetic materials and methods. In the bulk-fill method, the MOD cavity was restored with a solitary increase of restorative material and light cured from all directions of tooth for 20 s each. In the incremental technique, the proximal box on both sides was reconstructed first in a gradual manner, in which two oblique increments and one horizontal increment were restored and treated for 20 s. Then, two oblique increments of material were used to reestablish the occlusal component, and it was once more light-cured for 20 s. Fracture resistance was checked using a steel bar with a diameter of 4.5 mm that was positioned in the middle of the occlusal surface and a crosshead speed of 3 mm/min, all of the samples were compressed axially loaded. Results: The fracture resistance of microhybrid composite resins in bulk technique was significantly higher than that of nanocomposites and Giomer. However, the fracture resistance of nanocomposite in the incremental method was significantly higher than the other two restorative materials. Conclusion: The quality of restoration depends both on the material and method used during the restoration procedure. Both factors are dependent on each other. Superior fracture resistance was shown by microhybrid composites when restored with the bulk-fill technique and nanohybrid composites when restored with the incremental technique.

Evaluating the Effect of Different Intra-Orifice Barriers and Various Bleaching Agents on the Fracture Resistance of Teeth After the Walking Bleach Procedure: An In Vitro Study.

Objective This study aimedto evaluate the effect of three different commercially available intra-orifice barriers and bleaching agents on root canal-treated teeth. Materials and methods Forty-five freshly extracted single-rooted incisors, canine, and premolars were collected and stored in 10% formalin. Root canal procedures were performed on the extracted teeth and these were classified into three groups and three subgroups (n=5). Group 1: resin-modified glass ionomer cement (RMGIC); placed at the level of cemento-enamel junction (CEJ) and cured for 20 seconds. Group 2: BiodentinTM (Septodont Ltd., Saint Maur des Fausse´s, France); powder and liquid were mixed according to the manufacturer's instructions and placed at the level of CEJ, and waited for 15 minutes to set. Group 3: bulk-fill composite; placed at the level of CEJ. Group A was treated with 35% carbamide peroxide (Ultradent Opalescence 35% PF regular). Group B was bleached with 35% hydrogen peroxide (Pola Office). Group C,which was the control group, was treated with distilled water. The bleaching procedure was repeated once every seven days for a period of three weeks. After bleaching, every sample was sectioned 2 mm above the level of CEJ to remove the crown.Auniversaltesting machine (UTM) was used for the evaluation of the fracture resistance of teeth.Data were analyzed for significance by using analysis of variance (ANOVA) and further pair-wise comparison was performed by pos-hoc analysis. The level of significance was set at p<0.05 Results There was a significant difference between the fracture resistance of the three materials when bleached using distilled water (p<0.05). The fracture resistance of Group 3 was significantly greater than that of Group 2 and Group 1 (p<0.05). The difference in the fracture resistance between Group 1 and Group 2 was nonsignificant (p>0.05). Conclusion Walking bleach performed via bleaching agents 35% carbamide peroxide and 35% hydrogen peroxide leads to a reduction in the fracture resistance of endodontically treated teeth; 35% hydrogen peroxide causes more fracture resistance reduction than carbamide peroxide of the same concentration. The presence of intra-orifice barriers leads to greater fracture resistance and reinforcement of endodontically treated teeth that undergo the walking bleach procedure. Bulk-fill composite can be used as an intra-orifice barrier with good fracture resistance.

The Effect of Ferrule/Crown Ratio and Post Length on the Applied Stress and Strain Distribution to the Endodontically Treated Maxillary Central Teeth: A Finite Element Analysis.

Objectives: One of the most common methods used for the reconstruction of endodontically treated teeth is post and core and crown. Various factors such as the remaining tissue above the cutting margin (ferrule) affect the fracture resistance of teeth restored with post and core and crown. This study aimed to investigate the effect of ferrule/crown ratio (FCR) on the strength of maxillary anterior central teeth using finite element analysis. Materials and Methods: A 3D scan of a central incisor was obtained, and the data were transferred to Mimics software. Then, a 3D model of the tooth was designed. Next, 300N load was applied at a 135° angle to the tooth model. Force was applied to the model both horizontally and vertically. Ferrule height was considered to be 5%, 10%, 15%, 20%, and 25% in the palatal surface and 50% in the buccal surface. The length of post in the model was 11, 13, and 15mm. Results: By increasing the FCR, stress and strain distribution increased in the dental model and decreased in the post itself. As the horizontal angle of load application increased, the level of stress and strain created in the dental model increased as well. The closer the force application site to the incisal area, the higher the stress and strain would be. Conclusion: Maximum stress was inversely correlated with FCR and post length. In ratios of 20% and higher, insignificant changes occurred in stress and strain patterns in the dental model.

Comparison of fracture resistance of teeth with prepared protaper next, protaper gold, and hyflex CM rotary files

Preparation of the root canal system is a crucial step in root canal treatment. Endodontically treated teeth differ structurally from healthy, untreated teeth. This can lead to root cracking by creating pressure on the canal wall, reducing the fracture resistance of the tooth. Different designs, including cross-sectional shape, tip, taper, flute, radial land, helix angle, rake angle, and pitch, can influence the outcome of the root canal preparation and the risk of root fracture. The purpose of this study was to evaluate the fracture resistance of teeth after root canal preparation using three different NiTi rotary files: ProTaper Next (PN), ProTaper Gold (PG), and HyFlex CM (HC). Thirty premolars with a single and straight root canal were decoronated at the cementoenamel junction, leaving 14 mm of the root. The subjects were divided into 3 groups. Group 1 (n = 10) was prepared using PN, group 2 (n = 10) was prepared using PG, and group 3 (n = 10) was prepared using HC. After instrumentation and irrigation, the specimens were subjected to a continuous vertical compressive force (crosshead-speed of 2.28 mm/sec) in order to record the force (in newtons) until root fracture. To describe the surface characteristic of the dentinal root after the preparation, a section fragment from the apical third of the specimens was observed using a scanning electron microscope (SEM) at 2500x magnification. The micrographs were analyzed according to the Hulsman’s method. The results demonstrated that there was a statistically significant difference in root fracture resistance among the three groups. (p = 0.043). The LSD post hoc test indicated that HC showed a higher root fracture resistance (p &lt; 0.05) compared to both PN and PG. In conclusion, the different file systems of PN, PG, and HC instruments generate different root fracture resistance of teeth. In comparison to PN and PG, HC instruments tend to result in increased fracture resistance.

Different Designs of Deep Marginal Elevation and Its Influence on Fracture Resistance of Teeth with Monolith Zirconia Full-Contour Crowns.

Background and objectives: Even with the demand for high esthetics, the strength of the material for esthetic applications continues to be important. In this study, monolith zirconia (MZi) crowns fabricated using CAD/CAM were tested for fracture resistance (FR) in teeth with class II cavity designs with varying proximal depths, restored through a deep marginal elevation technique (DME). Materials and Methods: Forty premolars were randomly divided into four groups of ten teeth. In Group A, tooth preparation was conducted and MZi crowns were fabricated. In Group B, mesio-occluso-distal (MOD) cavities were prepared and restored with microhybrid composites before tooth preparation and the fabrication of MZi crowns. In Groups C and D, MOD cavities were prepared, differentiated by the depth of the gingival seat, 2 mm and 4 mm below the cemento-enamel junction (CEJ). Microhybrid composite resin was used for DME on the CEJ and for the restoration of the MOD cavities; beforehand, tooth preparations were conducted and MZi crowns were and cemented using resin cement. The maximum load to fracture (in newtons (N)) and FR (in megapascals (MPa)) were measured using the universal testing machine. Results: The average scores indicate a gradual decrease in the load required to fracture the samples from Groups A to D, with mean values of 3415.61 N, 2494.11 N, 2108.25 N and 1891.95 N, respectively. ANOVA revealed highly significant differences between the groups. Multiple group comparisons using the Tukey HSD post hoc test revealed that Group D had greater DME depths and showed significant differences compared with Group B. Conclusions: FR in teeth decreased when more tooth structure was involved, even with MZi crowns. However, DME up to 2 mm below the CEJ did not negatively influence the FR. Strengthening the DME-treated teeth with MZi crowns could be a reasonable clinical option, as the force required to fracture the samples far exceeded the maximum recorded biting force for posterior teeth.