Influence of post material and length on endodontically treated incisors: An in vitro and finite element study

Clinical and laboratorial performance of rehabilitation of endodontically treated teeth: A systematic review

OBJECTIVE

This systematic review aimed to analyze the clinical (survival rate, failure risk, or fracture) and laboratory performance (fracture mode or failure) of rehabilitations of endodontically treated teeth, with and without posts.

MATERIALS AND METHODS

A systematic search was conducted in the Pubmed, Scopus, Web of Science, Embase, Cochrane Library, and OpenGrey databases up to March 2023, according to PRISMA guidelines. In vitro and clinical studies that compared the clinical and laboratory performance of endodontically treated teeth with and without intraradicular posts were included. Studies selection, data extraction, and risk of bias analysis were performed.

RESULTS

Thirty-one in vitro and 7 clinical studies were included. For in vitro studies, fiberglass post (n = 24) was the most mentioned. The follow-up time of the clinical studies ranged from 1 to 17 years, with the fiber-reinforced composite post (n = 3) being the most evaluated, and only failure risk proved to be more favorable for using intraradicular posts.

CONCLUSION

Rehabilitations of endodontically treated teeth with and without intraradicular retainers showed no difference in fracture resistance and failure mode, evaluated by in vitro studies. Clinical studies showed no difference in survival rate, but failure risk proved to be more favorable for the use of posts.

CLINICAL SIGNIFICANCE

This analysis revealed significant variability between results, however, most laboratory and clinical studies revealed no difference with using the post. Furthermore, it is important to emphasize the need to evaluate the coronary remnant and the general characteristics of the tooth in each situation.

Influence of size-anatomy of the maxillary central incisor on the biomechanical performance of post-and-core restoration with different ferrule heights

PURPOSE

The study aims to investigate the influence of the ferrule effect and types of posts on the stress distribution in three morphological types of the maxillary central incisor.

MATERIALS AND METHODS

Nine models were created for 3 maxillary central incisor morphology types: "Fat" type - crown 12.5 mm, root 13 mm, and buccolingual cervical diameter 7.5 mm, "Medium" type - crown 11 mm, root 14 mm, and buccolingual cervical diameter 6.5 mm, and "Slim" type - crown 9.5 mm, root 15 mm, and buccolingual cervical diameter 5.5 mm. Each model received an anatomical castable post-and-core or glass-fiber post with resin composite core and three ferrule heights (nonexistent, 1 mm, and 2 mm). Then, a load of 14 N was applied at the cingulum with a 45° slope to the long axis of the tooth. The Maximum Principal Stress and the Minimum Principal Stress were calculated in the root dentin, crown, and core.

RESULTS

Higher tensile and compression stress values were observed in root dentin using the metallic post compared to the fiber post, being higher in the slim type maxillary central incisor than in the medium and fat types. Concerning the three anatomical types of maxillary central incisors, the slim type without ferrule height in mm presented the highest tensile stress in the dentin, for both types of metal and fiber posts.

CONCLUSION

Post system and tooth morphology were able to modify the biomechanical response of restored endodontically-treated incisors, showing the importance of personalized dental treatment for each case.

Influence of post material and ferrule thickness on the fracture resistance of endodontically treated premolars: A laboratory study

STATEMENT OF PROBLEM

The influence of the ferrule thickness and post materials on the fracture resistance of endodontically treated teeth remains unclear.

PURPOSE

The purpose of this laboratory study was to evaluate the influence of post material and ferrule thickness on the fracture resistance of endodontically treated mandibular premolars.

MATERIAL AND METHODS

Sixty-four extracted and endodontically treated mandibular first premolars were used and divided into 4 test groups (n=16) depending on the ferrule thickness: F-0: without a ferrule, F-0.5: with a 0.5-mm ferrule thickness, F-1: with a 1-mm ferrule thickness, and F-1.5: with a 1.5-mm ferrule thickness. In groups with ferrules, the height ranged from 2 mm buccally/lingually to 1 mm proximally. Teeth in subgroups (n=8) were restored with either prefabricated glass fiber (FF) or titanium posts (FT) (ISO size 70 and length of 7.5 mm) and then adhesively restored with composite resin foundation materials. After foundation procedures, each specimen was restored with a cobalt chromium crown which was cemented with glass-ionomer cement. All specimens were subjected to dynamic loading in a masticatory simulator for 1 200 000 loading cycles with a nominal load of 5 Kg at 1.2 Hz and simultaneous thermocycling (5 to 55 °C). Specimens were then quasistatically loaded at 30 degrees in a universal testing machine until fracture. Fracture loads were analyzed by using 2-way ANOVA followed by the Tukey honestly significant difference test (α=.05).

RESULTS

Fracture loads ranged from 610 ±45 N (no ferrule - glass fiber post) to 1216 ±169 N (1.5 mm ferrule thickness - glass fiber post). A statistically significant increase in fracture resistance was observed with increasing ferrule thickness (P<.001). However, post materials did not show a statistically significant influence (P=.977).

CONCLUSIONS

Under the conditions of this laboratory study, increasing the ferrule thickness had a significant effect on the fracture resistance of endodontically treated teeth after thermomechanical fatigue, irrespective of post materials.

Comparative analysis of the biomechanical behavior of the maxillary central incisors restored with glass fiber post and cast metal post and core submitted to orthodontic forces: A study with finite elements

INTRODUCTION

Different types of intraradicular restorations and their insertion have an impact on teeth biomechanics. This study aimed to analyze the biomechanical behavior of maxillary central incisors restored with glass fiber post (GFP) and cast metal post and core (CMP) subjected to buccolingual and mesiodistal orthodontic forces using the finite element method.

METHODS

Two models of the maxillary central incisor with periodontal ligament, cortical bone, and trabecular bone were made. One of the models included intraradicular restoration with GFP, whereas, in the other, the incisor was restored with CMP. After creating the tridimensional mesh of finite elements, applying 2 orthodontic forces were simulated: 65 g of buccolingual force and 70 g of mesiodistal force. The forces were applied parallel to the palatal plane in the region of the bracket slot, located 4 mm to the incisal edge.

RESULTS

The maximum stresses generated in the GFP-restored root were 3.642 × 10-1 MPa and 4.755 × 10-1 MPa from the buccolingual and mesiodistal forces, respectively. Likewise, the stresses in the CMP restored root were 2.777 × 10-1MPa and 3.826 × 10-1MPa. The radicular area with higher stress on both models was located in the cervical third: on the buccal surface when the buccolingual force was applied and on the mesial surface when the mesiodistal force was applied. The highest stress levels were found on the CMP structure.

CONCLUSIONS

The incisor restored with cast metal post revealed lower stress values transferred to the root than the one restored with GFP. The stresses on the structure of the GFP were lower and more homogeneous than the ones found on the cast metal post. The difference among the stress values in the materials is within a safe margin for using both materials in relation to orthodontic forces.

Fracture resistance of endodontically treated teeth, restored with two post-core systems in different post space diameters (in vitro study)

BACKGROUND

Fracture resistance of post-core restoration depends on the design of the post, post diameter, post length, the type of adhesive cement used along with material of the core. Despite the different studies concerning the effect of post space diameter on the fracture resistance of endodontically treated teeth, more information regarding fracture resistance and the effect of different post space systems/materials and diameters is required.

AIM OF THE STUDY

This study aimed to evaluate fracture resistance of endodontically treated teeth, restored with two post-core systems in different post space diameters.

MATERIALS AND METHODS

Twenty freshly extracted maxillary central incisors were collected for this study. They were randomly divided into four groups according to intracanal post and its diameter. Group GN (glass-fiber post of 10-mm length and 1.3-mm diameter with composite core), group GW (glass-fiber post of 10-mm length and 1.75-mm diameter with composite core), group ZN (custom-made zirconia one-piece post-core of 10-mm length and 1.3-mm diameter) and group ZW(custom-made zirconia one-piece post-core of 10-mm length and 1.75-mm diameter). Fracture resistance for all samples was evaluated using the universal testing machine under a static load. The data was collected and statistically analyzed using One-Way ANOVA test. Modes of failure were assessed using stereomicroscope for each group.

RESULTS

The highest mean fracture resistance was recorded in group GW (638.7 ± 285.1 N), followed by group ZW (598.5 ± 127.6 N), then GN group (442.8 ± 65.38 N). The lowest mean fracture resistance was recorded in group ZN (435.3 ± 117.3 N). One-Way ANOVA test revealed that there was no statistically significant difference in fracture resistance values among the groups.

CONCLUSION

Post space diameter had an impact over the fracture resistance of endodontically treated teeth. Modulus of elasticity of post material had a major effect on the fracture resistance and mode of failure along with the restorability of the restored tooth. However, there was no statistically significant difference among the tested groups.

Evaluation of the Effects of Different Types of Resin Cement Systems on the Push-Out Bond Strength of the Fiber Post to Intracanal Dentin in Anterior Primary Teeth

Background

This study aimed to evaluate the effects of using three different resin cements on push-out bond strength (PBS) of fiber posts to root canal dentin of primary teeth.

Methods

Fifty primary canines were randomly divided into five experimental groups according to the type of the luting agent used for fiber post cementation after endodontic treatment and post space preparation as the following: Group 1: glass ionomer cement (GIC), Group 2: flowable resin composite, Group 3: etch and rinse (E&R) resin cement, Group 4: self-etch (SE) resin cement, Group 5: self-adhesive (SA) resin cement. The PBS values of the cemented fiber posts to root canals were measured. The data were statistically analyzed using a one-way analysis of variance, followed by Tukey's post hoc test.

Results

The highest mean PBS value was observed in Group 4 (SE resin cement), followed by Group 3 (E&R resin cement), and the lowest PBS value belonged to Group 1 (GIC), followed by Group 5 (p-values < 0.05). The mean PBS of Group 3 (E&R resin cement) was significantly higher than those of Groups 1 (GIC), 2 (flowable resin composite), and 5 (SA resin cement) (p-values < 0.05). However, no significant difference was found between the mean PBS of GIC and SA resin cement (p-value >0/05).

Conclusion

Using SE resin cement for fiber post cementation in primary anterior teeth showed the best results, followed by E&R resin cement. The lowest PBS was observed for GIC, followed by SA resin cement.

Current Insights on Fiber Posts: A Narrative Review of Laboratory and Clinical Studies

PURPOSE

The aim of this study was to review the literature related to the clinical performance and laboratory findings regarding fiber posts, as well as the cementation technique employed with their use.

MATERIALS AND METHODS

A literature search was performed using an electronic database, PubMed/Medline, between 2010 and 2023. The terms used were "intra coronal post, fiber post, post cementation, and post length". Titles and abstracts were initially screened, and a full-text assessment was conducted for those that fulfilled the inclusion criteria. The reference list of the collected papers was also screened for further relevant citations.

RESULTS

In this work, 135 potentially eligible studies were analyzed. Titles and abstracts of 90 studies followed the inclusion criteria and were selected for a full-text assessment, resulting in 50 studies selected. Moreover, additional studies from relevant citations were included, totaling 57 studies.

CONCLUSION

According to the laboratory and clinical studies revised, the survival rate between fiber and prefabricated and cast metal posts was similar, and failures were mainly related to the loss of retention. The intra-canal post length of less than two-thirds of the root length presented successful results when ferrule was present. Furthermore, the ferrule increased the longevity of teeth restored with fiber posts. Additionally, the use of a surface treatment protocol for fiber posts and the adhesive cementation technique both contributed to the clinical success and longevity of the intra-canal post.

The effect of different endodontic access cavity designs in combination with WaveOne Gold and TruNatomy on the fracture resistance of mandibular first molars: A nonlinear finite element analysis

INTRODUCTION

This study evaluated the effect of traditional and conservative endodontic access cavity designs in combination with WaveOne Gold and TruNatomy instrumentation systems on the fracture resistance of mandibular first molars by means of nonlinear finite element analysis (FEA).

METHODS

Micro-CT images of 4 human mandibular first molars were used to generate representative FEA models. The mandibular first molars samples were scanned before and after endodontic access cavity preparation and instrumentation of all 3 canals. Five nonlinear static loads were applied vertically and horizontally to specific contact points on the occlusal surface of the teeth. Maximum von Mises stress before failure and distribution of von Mises strains were recorded and compared between groups.

RESULTS

Molars with conservative endodontic access cavities required similar levels of loads to reach failure compared with their control samples, whereas molars with traditional endodontic access cavities required significantly reduced loads in order to fail. According to the numerical investigation, the type of instrumentation system was found to have an insignificant effect on the fracture resistance of the teeth under study. Von Mises stress was concentrated around the cervical region and in the larger distal roots for all numerical models.

CONCLUSIONS

The fracture resistance of mandibular first molars is influenced significantly by a reduction in dental hard tissue, which was found to control the level of the ultimate failure load for each tooth.

Customized Fiber Post Improves the Bond Strength and Dentinal Penetrability of Resin Cementation System to Root Dentin

OBJECTIVE

This study aimed to evaluate the effect of fiber post customization on the bond strength (24 hours and 6 months), resin cement thickness, and dentinal penetrability of Adper Scotchbond Multi-Purpose - RelyX ARC (AS-RA), RelyX U200 (R2), and Scotchbond Universal - RelyX Ultimate (SU-RU) cementation systems to root dentin from the cervical-, middle-, and apical-thirds of the post space.

METHODS

One hundred twenty bovine incisors were endodontically treated. After post space preparation, the roots were divided into six groups, according to the luting protocols (AS-RA, R2, SU- RU) and the type of fiber post [noncustomized post (NC) and customized post (C)]. Customization procedures were peformed using a resin composite (Z350 XT). 24 hours (n=60) or 6 months later (n=60), specimens from the cervical-, middle-, and apical-thirds of the post space were submitted to cementation system thickness measurement, bond strength evaluation, and dentinal penetrability analysis with Confocal Laser Scanning Microscopy (CLSM). Failure mode was classified as adhesive, cohesive, or mixed. Data were submitted to ANOVA and Tukey tests (α=0.05).

RESULTS

Cementation protocols with customized fiber posts presented the lowest cementation system thickness, regardless of the cementation system or post space-third (p<0.05), and the highest bond strength values (p<0.05), regardless of the third space (p>0.05), for both periods (24 hours or 6 months). The comparison of push-out bond strength values between 24 hours and 6 months showed a reduction in all groups for the cervical-third (p<0.05). For the middle-third, only noncustomized groups showed reduction (p<0.05). For the apical-third, no reduction was observed (p>0.05).

CONCLUSIONS

Anatomical customization favored both the bond strength of cements to dentin and the dentinal penetrability, but with lower cementation system thickness, regardless of cement composition and adhesive strategy.

Fatigue performance of endodontically treated premolars restored with direct and indirect cuspal coverage restorations utilizing fiber-reinforced cores

Objectives

The aim of this in vitro study was to investigate the fatigue survival and fracture behavior of endodontically treated (ET) premolars restored with different types of post-core and cuspal coverage restorations.

Materials and methods

MOD cavities were prepared on 108 extracted maxillary premolars. During the endodontic treatment, all teeth were instrumented with rotary files (ProTaper Universal) to the same apical enlargement (F2) and were obturated with a matched single cone obturation. After the endodontic procedure, the cavities were restored with different post-core and overlay restorations (n = 12/group). Three groups (A1–A3) were restored with either conventional composite core (PFC; control) or flowable short-fiber-reinforced composite (SFRC) core with/without custom-made fiber posts and without overlays. Six groups had similar post-core foundations as described above but with either direct PFC (B1–B3) or indirect CAD/CAM (C1–C3) overlays. Fatigue survival was tested for all restorations using a cyclic loading machine until fracture occurred or 50,000 cycles were completed. Kaplan-Meyer survival analysis was conducted, followed by pairwise post hoc comparisons.

Results

None of the restored teeth survived all 50,000. Application of flowable SFRC as luting-core material with fiber post and CAD/CAD overlays (Group C3) showed superior performance regarding fatigue survival (p < 0.05) to all the other groups. Flowable SFRC with fiber post and direct overlay (Group B3) showed superior survival compared to all other direct techniques (p < 0.05), except for the same post-core foundation but without cuspal coverage (Group A3).

Conclusions

Custom-made fiber post and SFRC as post luting core material with or without cuspal coverage performed well in terms of fatigue resistance and survival when used for the restoration of ET premolars.

Clinical relevance

The fatigue survival of direct and indirect cuspal coverage restorations in ET MOD premolars is highly dependent on whether the core build-up is fiber-reinforced or not. The combination of short and long fibers in the form of individualized post-cores seems to offer a favorable solution in this situation.

Comparison of the fracture strength of endodontically treated teeth restored with polyether ether ketone, zirconia and glass-fibre post-core systems

PURPOSE

This study aimed to compare the fracture resistance and fracture mode of maxillary central incisors restored with four different sizes and three different post-core systems.

MATERIALS AND METHODS

One hundred and twenty maxillary incisors were endodontically treated and randomly divided into three groups (12 subgroups). Post cavities for the narrow subgroups were prepared with 1.4-mm-diameter drills in lengths of 7.5 mm (SN) and 10 mm (LN). Post cavities for the wide subgroups were prepared with 1.6-mm-diameter drills in lengths of 7.5 mm (SW) and 10 mm (LW) (n = 10). Group F was restored with glass-fibre post and composite resin core, Group P was restored with custom PEEK post-core and Group Z was restored with custom zirconia post-core. All posts were cemented with a dual-cure resin cement. Zirconia copings were cemented. Specimens were loaded on the palatal surface with a universal testing machine, and the fracture strengths of the teeth were statistically analysed using ANOVA and post hoc Tukey tests.

RESULTS

Statistically significant differences existed between the fracture strengths of the post materials. The highest fracture strength was in Group F, and the lowest was in Group P. Evaluation of the fracture strengths of the post lengths and diameters demonstrated that the short-narrow group of Group Z had the lowest fracture strength (P < .05). The long-wide group of Group F showed the highest fracture resistance. In Group P, no statistically significant difference existed between the post-cores of different dimensions (P > .05). Irreparable fractures were observed mostly in Group Z, and decementation was more common in Group P.

CONCLUSIONS

PEEK post-cores showed sufficient fracture strength for the anterior region, similar to the other two post-core materials. PEEK post-cores showed more decementation and repairable fractures at lower forces, while restoration failure was mostly catastrophic for glass-fibre and zirconia posts.

Fatigue failure of anterior teeth without ferrule restored with individualized fiber-reinforced post-core foundations

OBJECTIVES

The aim was to explore the survival of extensively damaged anterior teeth without ferrule restored with different fiber-reinforced composite (FRC) post-core foundations and composite crowns.

MATERIALS AND METHODS

Sixty extracted upper central incisors were decoronated and randomly divided into four groups (n = 15). After endodontic treatment, the specimens were restored with different individualized fiber-reinforced post-core foundations as follows: control group (CTRL): multiple unidirectional FRC-post + dual-cure composite-core, PFC: multiple unidirectional FRC-post + packable short fiber-reinforced composite (SFRC), BPFC: Bioblock technique with only packable SFRC, BFFC: Bioblock technique with only flowable SFRC. After core build-up, the teeth were finalized with adhesively luted CAD/CAM composite crowns. Cyclic isometric loading (5 Hz) was applied at 100 N for 5000 cycles, and then 200 N and 300 N for 15,000 cycles each in a fluid chamber. The specimens were loaded until fracture occurred or when a total of 35,000 cycles were reached. Kaplan-Meyer survival analysis was conducted, followed by pairwise log-rank post hoc comparisons (Mantel-Cox).

RESULTS

The survival rates of the control (8279 cycles) and PFC (6161 cycles) were significantly higher compared to BPFC (3223 cycles) and BFFC (2271 cycles) (p < 0.05). Regarding fracture pattern, nearly all specimens fractured in a restorable manner.

CONCLUSIONS

For restoring extensively damaged anterior teeth, multiple unidirectional FRC posts are recommended.

CLINICAL RELEVANCE

Although different FRC post/core systems are available for the restoration of damaged root canal treated anterior teeth, multiple unidirectional FRC posts tend to be a good option when the ferrule is missing.

Effect of different restorative crown design and materials on stress distribution in endodontically treated molars: a finite element analysis study

Background

The purposes of this simulation study were to evaluate the stresses in the roots of endodontically treated molars with extensive coronal tissue loss which were restored by endocrowns (all-in-one core and crown) and traditional crowns with post-cores, during masticatory simulation using finite element analysis.

Methods

A mesio-distal cross-section of a lower right first molar was digitized and used to create 2-dimensional models of the teeth and supporting tissue; different crown designs, viz., endocrown with 2 mm occlusal clearance, endocrown with 4 mm occlusal clearance and post-core crown; different crown materials, viz., zirconia (Zr) and lithia-disilicate reinforced glass ceramic (LDRGC), and different post and core materials, viz., glass fiber (GF), stainless steel (SS) and metal cast (MC). An axial load of 600 N was applied to the central fossa of occlusal surface.

Results

The stress distributions were similar between Zr and LDRGC for periodontal ligament and alveolar bone. The root canal inner wall maximum principal stresses of SS post (70.8 MPa) and MC post (71.4 MPa) were higher than that of GF post (36.0 MPa) and endocrown (2.4 MPa).

Conclusion

The endocrowns reduced stress concentration for the root canal inner wall in comparison with the conventional post-core crown. Molars restored with endocrowns are less prone to root fracture than those with posts.

Fracture Resistance of Endodontically Treated Maxillary Premolars with a Longer Single Post and Shorter Double Posts of Different Sizes: An In Vitro Study

Aim:

The aim of this study was to determine if there is any difference in fracture resistance between different post sizes and lengths when more than one post is involved.

Materials and Methods:

Thirty extracted maxillary first premolars were endodontically treated and divided into three groups: In Group 1 (control group), no post space preparation was conducted and access cavities were restored with composite; in Group 2 (single post), post space preparation of 10 mm was carried out only in one of the canals; and in Group 3 (double post), post space preparation of 5 mm was conducted in both the canals. Appropriately sized glass fiber posts were cemented in Groups 2 and 3 followed by core buildup. The fracture resistance of the specimen was measured using a universal testing machine and the data analyzed. The mean fracture resistance values of the three groups were compared applying one-way analysis of variance (ANOVA) followed by post hoc Tukey’s test. The data were analyzed using Statistical Package for the Social Sciences software program, version 15.0. South Asia, Bangalore.

Results:

The control group had a significantly lower fracture resistance value as compared to Groups 2 and 3. No statistically significant difference was observed in the fracture resistance between Groups 2 and 3.

Conclusions:

No significant difference was observed between the fracture resistance of endodontically treated maxillary first premolars restored with size 3 single post of longer length and size 1 double posts of shorter lengths.

In vitro fracture resistance of zirconia, glass-fiber, and cast metal posts with different lengths

Aim:

Post-and-core restorations require sufficient length of the post for retention of the prosthesis and root strength. The effect of different lengths of prefabricated zirconia posts (ZPs) on the fracture strength of endodontically treated teeth needs evaluation. Hence, the aim of this study was to evaluate the in vitro fracture resistance of endodontically treated incisors restored with ZP, glass-fiber (GFP), and cast posts (CP) of different lengths.

Settings and Design:

Comparative in-vitro study.

Materials and Methods:

Sixty extracted incisors were endodontically treated, tooth preparations were carried out, and the impression of the coronal portion of each prepared tooth was made using polyvinyl siloxane impression material loaded in copper tubes. The coronal portion of each tooth was removed, maintaining a 2 mm ferrule. The teeth were restored with one of the three posts: CPs, GFP, or ZPs, with intraradicular lengths of either 6 or 8 mm (n = 10). The CP and core patterns were fabricated using post space impressions and core buildup and cast using Nickel–Chromium alloy. After composite resin core buildup of GFP and ZPs treated teeth using the previously made copper tube impressions, the teeth were loaded to fracture in an oblique direction in the universal testing machine.

Statistical Analysis Used:

Data were analyzed using two-way ANOVA and Tukey–Kramer tests (α = 0.05).

Results:

The highest and lowest values of fracture resistance were reported with ZP8 and GFP6 groups, respectively. There was no significant difference in fracture resistance between the posts of length 6 mm and 8 mm in CP, GFP, and ZP groups. There was no significant difference (P = 0.953) in fracture resistance between CP (284.8 N) and ZP (258.31 N) groups, while the GFP group (160.61 N) had a significantly lower value of fracture resistance than the CP and ZP groups. Two-way ANOVA test for fracture resistance of the post systems and post lengths showed that there was no significant correlation between the post systems and post length on the fracture resistance. There was a greater percentage of favorable fractures in GFP and ZP groups (65% each), than the CP group (20%).

Conclusion:

For the post systems tested, extending the post length does not significantly increase the fracture resistance of the restored teeth. The ZP represents a viable alternative to the cast metal post during the esthetic restoration of endodontically treated anterior teeth.

Bond strength of cemented fiber posts to teeth with simulated internal root resorption

Background

Teeth with internal root resorption (IRR) have guarded prognosis, considering that IRR defect could influence on the post bond strength. The aim of this study was to evaluate the bond strength and the bond interface between different glass fiber-reinforced posts (FRP) after cementation in teeth with simulated internal root resorption (IRR).

Material and Methods

Forty-five (45) human premolar roots with simulated IRR were embedded in acrylic resin blocks and cross-sectioned into two segments, enabling them to be re-approximated by screws. Intracanal medication was inserted for 15-days, removed by passive ultrasonic irrigation (PUI) and examined by stereomicroscopy. The push-out bond strength of two fiber reinforced composite posts (Rebilda Post - RP) and Rebilda Post GT – GT, (VOCO) were evaluated at the cervical and IRR regions (n = 20). And, the bonded interface between resin cement and root dentine was analysed by scanning electron microscopy (SEM).

Results

62.5% of IRR were not completely cleaned by PUI. Bond strength values at the cervical region (9.8 and 14.6 MPa) were higher than the IRR region (6.3 and 4.2 MPa). Micrographies showed bubbles in the cement and spaces in the bonded interface.

Conclusions

RP post showed better bond strength at the cervical region while GT had better bond strength at the IRR region.

Key words:Endodontics, root canal filling materials, root resorption, X-Ray microtomography.

Microtomographic Analysis of Resin Composite Core Material Porosity

PURPOSE

To nondestructively evaluate the porosity of ten contemporary resin composite core materials using microtomographic (microCT) analysis.

MATERIAL AND METHODS

Resin composite core material samples (n = 12) including dual-cure, visible light cure only, and a self-cure material were fabricated using a standardized mold following manufacturer's recommendations. After storage in phosphate buffered saline for one week, specimens were analyzed using a microCT unit at 5.3-µm resolution over a rotational range of 360°. Image 3D recombination and analysis was accomplished using microCT software. Evaluated parameters included material volume investigated, closed pore number and volume, as well as closed pore percentage. Parameter mean values were evaluated with Kruskal-Wallis/Dunn at a 95% confidence level (α = 0.05).

RESULTS

Mean percent total porosity with standard deviation identified significant differences in decreasing order as Ti-Core: 2.2 (0.4) > Ti-Core Auto E: 1.3 (0.3) = Ti-Core Flow Plus: 1.1 (0.02) > Clearfil Photo Core: 0.94 (0.5) = Clearfil DC Core Plus: 0.6 (0.18) = MultiCore Flow: 0.58 (0.1) > Fluorocore 2+: 0.14 (0.2) = Build-It FR: 0.068 (0.02) = Gradia Core: 0.03 (0.02) = Rebilda DC: 0.02 (0.01). A pilot microCT evaluation evaluating a mixing tip revealed incomplete mixture between the two resins with porosity introduced from turbulence as the materials are forced through the tip during preparation.

CONCLUSIONS

A wide range of porosity was identified between the ten materials evaluated. These preliminary results warrant more investigation evaluating additional resin composite core materials, the preparation capabilities of automix tips, and porosity presence in the unmixed materials.

A comparative evaluation of fracture resistance of endodontically treated premolar teeth reinforced with different prefabricated and custom-made fiber-reinforced post system with two different post lengths: An in vitro study

Aims

The aim of this study is to determine the mean failure load for each postsystem and the relationship between post lengths with the mean failure loads.

Materials and Methods

Ninety single-rooted decoronated mandibular premolar teeth were endodontically treated and randomly assigned to three groups with respect to their post length (2/3^rd and ½ of the root length). The first two groups were randomly divided into four subgroups, restored with the following postsystem: polyethylene-woven fiber posts, glass fiber tape, prefabricated carbon, and glass fiber posts. A composite core with no post served as control. All posts were cemented using dual-cure resin cement, and the same was used for core buildup. The standard cores were formed in each group. All the specimens were tested in a universal testing machine, and the load was calculated.

Results

One-way analysis of variance (ANOVA) showed that prefabricated glass fiber post had significantly highest fracture resistance when compared to other prefabricated and custom fiber-reinforced composite posts. Two-way ANOVA demonstrated no significant difference among the post lengths.

Conclusion

The results of this study showed that glass fiber posts showed higher fracture load, but post length did not significantly increase the fracture resistance of endodontically treated teeth.

Bonding of Core Build-Up Composites with Glass Fiber-Reinforced Posts

The purpose of this study was to investigate the bonding capacity of composite core build-up materials with prefabricated glass fiber-reinforced posts possessing different coronal morphologies. Five post types (Archimede Line (ARL), Fibrekleer (FBK), Glassix (GLX), Matrix Plus (MTP), and ParaPost White (PRW) and three core build-up materials (ClearfilPhoto Core (CPC), ClearfilDC Core (CDC), ClearfilNew Bond (CNB) of different curing modes (light-, self-, dual-cured respectively) were selected. The coronal part was embedded in the core build-up materials and the specimens were loaded under tensile force up to failure. The reliability (β) and characteristic life (σο, in Ν) of the debonding force were evaluated by Weibull statistics and the debonded specimens were subjected to failure mode analysis. The results showed that ARL, MPT posts were the most and GLX the least retentive, despite the core build-up material used. CPC provided the highest retention with four posts (FBK, GLX, MTP, and PRW), without statistically significant differences from CDC in two (FBK and MTP) and CNB in one (PRW). CPC and CDC were the most reliable core materials for two posts (ARL and PRW), with no statistically significant difference from CNB in three (FBK, GLX, and MTP). GLX and PRW demonstrated the highest (93%) incidence of post detachment from core, whereas FBK demonstrated the highest percentage of core material fracture, with most fractures occurring in CDC (57%). Post fractures were most prominent in MTP when combined with CNB. The presence of specific coronal retentive features did not essentially ensure increased strength with the core material, due to their delamination.

Development of a fiber-reinforced material for fiber posts: Evaluation of stress distribution, fracture load, and failure mode of restored roots

STATEMENT OF PROBLEM

The biomechanical behavior of post-restored roots with an experimental fiber-reinforced composite resin is unknown.

PURPOSE

The purpose of this in vitro study was to investigate the biomechanical behavior of an experimental composite resin (3-mm short glass fiber incorporated in methacrylate matrix with filler particles) used to produce the custom post itself or to reline fiber posts.

MATERIAL AND METHODS

Four testing groups (n=10) were created according to the root restoration method: FG, commercially available fiber post; FG+RC, fiber post relined with conventional composite resin; FG+EXP, fiber post relined with the experimental composite resin; and EXP, a custom post made of experimental composite resin. A three-dimensional finite element linear elastic analysis was performed by using geometric representations of groups, and the results were analyzed by von Mises (σ_vM) and maximum principal stress criteria. In sequence, 40 bovine incisors were assigned to these groups and subjected to a fracture load test (Instron 5965; 0.5 mm/min), and the failure mode was determined.

RESULTS

The EXP group showed more homogeneous stress distribution for σ_vM. ANOVA and the Tukey honestly significant difference (HSD) tests showed significant differences (P<.001) in fracture load (mean ±standard deviation; different superscript letters indicate statistical difference): FG+EXP (669.5 ±107.7)^A; FG (620.7 ±59.2)^A; EXP (506.5 ±27.0)^B; FG+RC (452.7 ±81.6)^B. No differences were found for failure mode (P=.595).

CONCLUSIONS

The experimental composite resin significantly increases fracture load when used to reline commercially available fiber posts and, irrespective of its use, presented lower stress concentration.

Direct Linear Measurement of Root Dentin Thickness and Dentin Volume Changes with Post Space Preparation: A Cone-Beam Computed Tomography Study

Aim:

The purpose of the present study was direct linear measurement of dentin thickness and dentin volume changes for post space preparation with cone-beam computed tomography (CBCT).

Materials and Methods:

Ten maxillary central incisors were scanned, before and after root canal and post space preparation, with Orthophos XG three-dimensional hybrid unit. Thirteen axial section scans of each tooth from orifice to apex and dentin thickness for buccal, lingual, mesial, and distal were measured using proprietary measuring tool and thereafter subjected to statistical analysis. Furthermore, dentin volume was evaluated using ITK-SNAP software.

Results:

There was statistically significant difference between the dentin thickness in pre- and postinstrumentation (paired t-test) and also between different groups (one-way ANOVA). In the shortest post length of 4.5mm the post space preparation resulted in 2.17% loss of hard tissue volume, where as 11mm longest post length post space preparation resulted in >40% loss of hard tissue volume.

Conclusion:

CBCT axial section scan for direct measurements of root dentin thickness can be guideline before and after post space preparation for selection of drill length and diameter.

Direct or indirect post crowns to restore compromised teeth: a review of the literature

Post crowns are restorations which utilise the root canal space to improve the retention and resistance form of teeth which lack coronal tooth structure. In recent years there have been significant developments in the materials, systems and evidence-base surrounding the provision of post crowns. This review aims to refresh the general dental practitioner's (GDPs) knowledge of the different factors that must be considered when placing a post crown, and how these factors can help guide the dentist in their decision to provide either a direct or indirect post and core.

Evaluation of Different Restoration Combinations Used in the Reattachment of Fractured Teeth: A Finite Element Analysis

Objective. The purpose of this study was to test different restoration combinations used for constructing fractured endodontically treated incisors by reattaching their fractured fragments. Methods. Seven types of 3-D FEM mathematical root canal-filled models were generated, simulating cases of (OB) reattaching fractured fragments; (CrPL) reattaching fractured fragments + ceramic palatinal laminate; (CmPL) reattaching fractured fragments + composite palatinal laminate; (CM) reattaching fractured fragments + coronal 1/3 of the root was filled using core material; (BP) reattaching fractured fragments + glass fiber post; (CP) composite resin restoration + glass fiber post; and (OC) composite resin restoration. A 100-N static oblique force was applied to the simulated teeth with 135° on the node at 2 mm above the cingulum to analyze the stress distribution at the tooth. Results. For enamel tissue, the highest stress values were observed in model BP, and the lowest stress values were observed in model CmPL. For dentine tissue, the highest stress concentrations were observed around the fracture line for all models. Conclusions. Reattachment of fractured fragments by bonding may be preferred as a restoration option for endodontically treated incisors; also, palatinal laminate decreases the stress values at tooth tissues, especially at the enamel and the fracture line.

Effect of fiber post length and abutment height on fracture resistance of endodontically treated premolars prepared for zirconia crowns

The purpose of this study was to compare the fracture resistance, mode of fracture, and stress distribution of endodontically treated teeth prepared with three different fiber post lengths and two different abutment heights, using both experimental and finite element (FE) approaches. Forty-eight human maxillary premolars with two roots were selected and endodontically treated. The teeth were randomly distributed into six equally sized groups (n = 8) with different combinations of post lengths (7.5, 11, and 15 mm) and abutment heights (3 and 5 mm). All the teeth restored with glass fiber post (Rely X Fiber Post, 3M ESPE, USA) and a full zirconia crown. All the specimens were thermocycled and then loaded to failure at an oblique angle of 135°. Statistical analysis was performed for the effects of post length and abutment height on failure loads using ANOVA and Tukey's honestly significant difference test. In addition, corresponding FE models of a premolar restored with a glass fiber post were developed to examine mechanical responses. The factor of post length (P < 0.01) had a significant effect on failure load. The abutment height (P > 0.05) did not have a significant effect on failure load. The highest mean fracture resistance was recorded for the 15 mm post length and 5 mm abutment height test group, which was significantly more resistant to fracture than the 7.5 mm post and 5 mm abutment height group (P < 0.05). The FE analysis showed the peak compression and tension stress values of 7.5 mm post length were higher than that of 11 and 15 mm post length. The stress value of remaining tooth decreased as the post length was increased. Within the limitations of this experimental and FE analysis study, increasing the post length inside the root of endodontically treated premolar teeth restored with glass-fiber posts increase the fracture resistance to non-axial forces. Failure mode is more favorable with reduced abutment heights.

Evaluation of Stress Distribution in Endodontically Weakened Teeth Restored with Different Crown Materials: 3D-FEA Analysis

This study evaluated the stress distribution in endodontically treated teeth, weakened (W) or not weakened (NW), restored with different materials of prosthetic crown using 3D-FEA. Models of a maxillary canine were constructed based on micro-CT images and divided into the groups: G1 (control) - sound tooth; G2 to G7 - endodontically treated teeth restored with glass fiber post (GFP); which G2 to G4 simulated NW root and G5 to G7 simulated W root. For crown material the teeth were restored with: G2 and G5: metallic coping and ceramic veneering, G3 and G6: zirconia coping and ceramic veneering, G4 and G7: alumina coping and ceramic veneering. Load of 180 N was applied at the incisal third of lingual surface at 45º. Models were supported by the periodontal ligament (x=y=z=0). The von Mises stress (VMS) values were calculated. The W teeth presented higher VMS at coping when compared to NW teeth and group G1 showed lower VMS value. For crown material, for both W or NW teeth, increasing VMS was found at metallic, zirconia and alumina coping, respectively. Metallic coping showed a better performance despite its unfavorable esthetics, suggesting as an appropriate material for prosthetic restoration of endodontically treated teeth.

Fracture Strength of Flared Root Canals Restored with Different Post Systems

Objective:

To evaluate the fracture resistance of different intra-radicular post systems in flared root canals.

Methods:

Sixty human canines were used. The coronal portion was removed and the root length was standardized at 17 mm. Canals were prepared and filled with gutta-percha/AH Plus sealer. Roots were embedded in self-polymerising acrylic resin blocks. According to the material used, the teeth were randomly divided into three groups (n=20): glass fibre post (GFP): GFP and Z350 resin composite core; pre-fabricated metal post (PMP): PMP and Z350 resin composite core; and cast metal core (CMC): CMC with silver-tin alloy. Coronal reconstruction involved fabrication of metal copings. Samples were submitted to mechanical compression testing at 45º in a universal test machine. Fracture pattern was evaluated under a stereoscope. The fracture strength values were submitted to one-way analysis of variance (ANOVA) and Tukey tests (α=0.05).

Results:

There was no statistically significant difference between the resistance values among groups (P=0.193). With regard to fracture pattern, GFP showed 55% and PMP 45% of Type I fractures, which considered repairable or favourable, whereas MCC presented 50% of Type V, which was considered irreparable or unfavourable.

Conclusion:

Glass fibre and pre-fabricated metal posts have good fracture resistance to compression and may be used for restoring flared root canals, since they presented fractures mainly involving the filling core, thus facilitating later repair.

The effect of glass fiber posts and ribbons on the fracture strength of teeth with flared root canals restored using composite resin post and cores

PURPOSE

This study evaluated the fracture strength and mode of failure of structurally compromised teeth with flared root canals restored using composite resin with four different systems.

METHODS

Sixty endodontically treated bovine teeth were uniformly shaped to simulate human mandibular premolars with flared root canals. The roots were divided into four groups of 15 specimens each based on the type of restoration: composite resin core only (control), glass fiber post, cylindroid glass fiber ribbons, and glass fiber post and ribbons. All specimens were loaded until fracture occurred using a universal testing machine. Average fracture loads were compared with a one-way ANOVA and Tukey HSD test (α=.05). The modes of failure were observed and the Fisher exact test and Bonferroni correction were used for statistical analysis.

RESULTS

The fiber post and ribbon group (1035.70N) and the fiber ribbon group (881.77N) showed significantly higher fracture strength than the controls (567.97N) (p<.05). The fiber post and ribbon group also showed significantly higher fracture strength than the fiber post group (769.40N). Almost all specimens showed unrestorable root fractures (p<.008). The control group had a significantly higher ratio of core sectional fractures (p<.017).

CONCLUSIONS

Cylindroid glass fiber ribbons significantly increased the fracture strength of the composite resin post and cores in the case of the dentin within the thin root canal wall. Based on the results, this study recommends the combined use of glass fiber post and ribbons.

Effect of fiber posts on the fracture resistance of maxillary central incisors with Class III restorations: An in vitro study

STATEMENT OF PROBLEM

Endodontically treated teeth with Class III restorations show reduced fracture resistance. The placement of glass fiber posts may affect fracture resistance and should be further evaluated.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of fiber posts on the fracture resistance of endodontically treated maxillary central incisors with Class III restorations.

MATERIAL AND METHODS

Forty extracted human maxillary central incisors were selected and divided into 4 test groups (n=10 each) according to the restoration strategy: control group; endodontically treated teeth without endodontic posts (GHT); endodontically treated teeth with 2 Class III restorations simulating coronal destruction (GCT); endodontically treated teeth with 2 Class III restorations and a carbon fiber post (GCF); and endodontically treated teeth with 2 Class III restorations and a glass-fiber post (GGF). The fiber posts were adhesively cemented with composite resin cement, and the cavities were restored with composite resin. After 3 months of water storage, all specimens were loaded at 45 degrees in a universal testing machine until fracture and evaluated for fracture mode. The data were analyzed using 1-way ANOVA, followed by the Tukey honest significant difference multiple comparisons test (α=.05).

RESULTS

Mean ±SD failure loads ranged from 687.5 ±84.0 N to 943.8 ±93.1 N. One-way ANOVA revealed a statistically significant difference among the groups (P≤.05). The control group (GHT) had significantly higher resistance to fracture than the other groups (P≤.05).

CONCLUSIONS

Within the limitations of this in vitro study, placement of a fiber post did not affect the fracture resistance of endodontically treated maxillary central incisors with 2 Class III restorations.

Fracture Strength of Weakened Anterior Teeth Associated to Different Reconstructive Techniques

Abstract This study evaluated the fracture strength of endodontically treated teeth submitted to reconstructive techniques through dynamic and static tests. Forty human anterior teeth were divided into 4 groups (n=10): GNW (non-weakened) - root restored with glass fiber post (GFP), GW - weakened root restored with GFP, GDA - weakened root restored with direct anatomic GFP, and GIA - weakened root restored with indirect anatomic GFP. The teeth were endodontically treated considering that experimental groups (GW, GDA and GIA) simulated weakened roots for restoration with GFP using different techniques. The GFP was luted with resin cement and the coronal portion was restored with composite resin and metallic crowns. All samples were submitted to chewing simulation at 60 cycles/min in a total of 300,000 cycles. The survival samples were further exposed to compressive loading at a crosshead speed of 1.0 mm/min in a universal testing machine. The load was applied at 135° to the long axis of the tooth until failure. Data were analyzed by ANOVA (a=0.05). After chewing simulation were observed: GNW: 100% of survival roots; GW: 70% of survival roots, and GDA and GIA: 80% of survival roots. The mean fracture strength values (N) were 280.6 (GNW), 239.0 (GW), 221.3 (GDA), and 234.1 (GIA) without significant difference among the groups (p=0.7476). The results suggested similar fracture strength in both weakened and non-weakened teeth regardless the reconstructive technique of root internal wall. Higher incidence of catastrophic fracture was observed in weakened teeth without restoration of the root internal wall.

Fracture resistance of teeth with oval canal morphology restored using oval and circular posts

The study aimed to evaluate the effects of different post morphologies and placement lengths on the fracture resistance of teeth with oval canal morphology that had been restored with crowns. Extracted mandibular premolars with similar dimensions were decoronated. After the root canal treatment, the teeth were mounted on acrylic blocks. Samples were randomly divided into four groups (n = 10 each). In groups C-10 and C-5, 10-mm- and 5-mm-long circular post spaces were created. In groups O-10 and O-5, 10-mm- and 5-mm-long oval post spaces were ultrasonically created. After post cementation, all specimens were restored with composite cores and prepared at height of 6 mm. Thereafter, all teeth were restored with crowns. After thermocycling, all specimens underwent fracture resistance testing. Oval posts and placement at 10-mm depth showed higher fracture resistance than circular posts and placement at 5-mm depth (P < 0.001). Increased post length and use of oval posts enhanced the fracture strength of teeth with oval canal morphology. Based on the results of this study, although the fracture resistance of teeth restored with crowns was enhanced by deep fiber post placement, the use of oval fiber post is recommended in cases where deep placement is impossible. (J Oral Sci 58, 339-345, 2016).

A novel anatomical short glass fiber reinforced post in an endodontically treated premolar mechanical resistance evaluation using acoustic emission under fatigue testing

This study evaluates the fracture resistance in an endodontically treated tooth using circular fiber-reinforced composite (FRC) and innovated anatomical short glass fiber reinforced (SGFR) posts under fatigue testing, monitored using the acoustic emission (AE) technique. An anatomical SGFR fiber post with an oval shape and slot/notch design was manufactured using an injection-molding machine. Crown/core maxillary second premolar restorations were executed using the anatomical SGFR and commercial cylindrical fiber posts under fatigue test to understand the mechanical resistances. The load versus AE signals in the fracture and fatigue tests were recorded to evaluate the restored tooth failure resistance. The static fracture resistance results showed that teeth restored using the anatomical SGFR post presented higher resistance than teeth restored using the commercial FRC post. The fatigue test endurance limitation (1.2×10⁶ cycles) was 207.1N for the anatomical SGFR fiber post, higher than the 185.3N found with the commercial FRC post. The average accumulated number of AE signals and corresponding micro cracks for the anatomical SGFR fiber post (153.0 hits and 2.44 cracks) were significantly lower than those for the commercial FRC post (194.7 hits and 4.78 cracks) under 40% of the static maximum resistance fatigue test load (pass 1.2×10⁶ cycles). This study concluded that the anatomical SGFR fiber post with surface slot/notch design made using precise injection molding presented superior static fracture resistance and fatigue endurance limitation than those for the commercial FRC post in an endodontically treated premolar.

Influence of diameter and intraradicular post in the stress distribution. Finite element analysis

Abstract Introduction The biomechanical behavior of endodontically treated teeth depending on the selected restorative material and tooth situation to be restored. Objective To analyze by the two-dimensional finite element method the biomechanical behavior of different diameters in intraradicular posts and teeth with coronal remaining of 2mm. Material and method Six models were made with three types of posts, as follows: Glass fiber post, carbon fiber post, and cast metal post, both with diameter # 1 (1.1 mm in diameter) and # 2 (1.3 mm of diameter). The modeling was performed using the Rhinoceros 4.0 program. The FEMAP 10.2 and NEiNastran 9.2 programs were used to develop finite element models. The loading used was 100N for axial and oblique forces. The results were visualized using the von Mises stress map. The statistical analysis was made using analysis of variance (ANOVA) and Tukey post-test, with a significance level of 5%. Result The oblique loading stress values were higher than the axial loading (p<0.001) for both situations. The glass fiber post showed the lowest concentrations of stress on both loads (p<0.001). The carbon fiber post presented significant difference compared to the cast metal post, only in the oblique load (p=0.007). The diameter did not increase the stress of the evaluated posts (p=0.302). Conclusion The fiber posts were more favorable for restoration of endodontically treated teeth; the increase of diameter did not influence the increase of tension; the oblique load was more harmful for both posts and tooth structure.

Stress Distribution in Roots Restored with Fiber Posts and An Experimental Dentin Post: 3D-FEA

Abstract The aim of this study was to compare the stress distribution in radicular dentin of a maxillary canine restored with either a glass fiber post, carbon fiber post or an experimental dentin post using finite element analysis (3D-FEA). Three 3D virtual models of a maxillary canine restored with a metal-ceramic crown and glass fiber post (GFP), carbon fiber post (CFP), and experimental dentin post (DP) were obtained based on micro-CT images. A total of 180 N was applied on the lingual surface of the incisal third of each tooth at 45 degrees. The models were supported by the periodontal ligament fixed in three axes (x=y=z=0). The von Mises stress (VMS) of radicular dentin and the intracanal posts was calculated. The structures of all groups showed similar values (MPa) and distribution of maximum von Mises stress. Higher stress was found in the apical third of dentin while the posts presented homogeneous stress distribution along the axis. The fiber and dentin posts exhibited similar stress values and distribution. Thus, the experimental dentin post is a promising restorative material.

Effect of fiber posts on the fracture resistance of endodontically treated anterior teeth with cervical cavities: An in vitro study

STATEMENT OF PROBLEM

How the placement of fiber posts affects the fracture resistance of endodontically treated maxillary central incisors with cervical cavities is not well documented.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of fiber posts on the fracture resistance of endodontically treated maxillary central incisors with cervical cavities.

MATERIAL AND METHODS

Fifty extracted human maxillary central incisors were selected and divided into 5 test groups (n=10) according to the restoration strategy: GHT, control group; endodontically treated teeth (ETT) without endodontic posts; GCV, ETT with cervical cavities simulating coronal destruction; GCF, ETT with cervical cavities and carbon fiber posts; GGF, ETT with cervical cavities and glass fiber posts; and GCP, ETT with cervical cavities and composite resin posts. After the fiber posts had been cemented with a resin cement and the foundations had been placed, all specimens were quasi statically loaded at 45 degrees in a universal testing machine until fracture. All specimens were evaluated for fracture modes. The data were then analyzed by 1-way ANOVA, followed by multiple comparisons with the Tukey HSD test (α=.05). The mode of failure was determined by visual inspection.

RESULTS

The mean ±SD failure loads for the groups ranged from 718.2 ±89.8 N to 943.8 ±93.1 N. In a 1-way ANOVA followed by post hoc testing, GGFs had a higher fracture strength than all other groups (P≤.05). However, GCPs had a lower fracture strength than all other groups. Statistically significant differences were observed among groups (P≤.05), except between the GHT group and the GCF and GGF groups (P=.075, P=.226). All groups except GHT showed complete favorable fracture mode within the cervical third of the roots.

CONCLUSIONS

Within the limitations of this in vitro study, placement of glass fiber posts significantly improved the fracture resistance of endodontically treated maxillary central incisors with cervical cavities.

Effects of metal- and fiber-reinforced composite root canal posts on flexural properties

The aim of this study was to observe the effects of different test conditions on the flexural properties of root canal post. Metal- and fiber-reinforced composite root canal posts of various diameters were measured to determine flexural properties using a threepoint bending test at different conditions. In this study, the span length/post diameter ratio of root canal posts varied from 3.0 to 10.0. Multiple regression models for maximum load as a dependent variable were statistically significant. The models for flexural properties as dependent variables were statistically significant, but linear regression models could not be fitted to data sets. At a low span length/post diameter ratio, the flexural properties were distorted by occurrence of shear stress in short samples. It was impossible to obtain high span length/post diameter ratio with root canal posts. The addition of parameters or coefficients is necessary to appropriately represent the flexural properties of root canal posts.

Evaluation of Temperature and Stress Distribution on 2 Different Post Systems Using 3-Dimensional Finite Element Analysis

BACKGROUND The mouth is exposed to thermal irritation from hot and cold food and drinks. Thermal changes in the oral cavity produce expansions and contractions in tooth structures and restorative materials. The aim of this study was to investigate the effect of temperature and stress distribution on 2 different post systems using the 3-dimensional (3D) finite element method. MATERIAL AND METHODS The 3D finite element model shows a labio-lingual cross-sectional view of the endodontically treated upper right central incisor and supporting periodontal ligament with bone structures. Stainless steel and glass fiber post systems with different physical and thermal properties were modelled in the tooth restored with composite core and ceramic crown. We placed 100 N static vertical occlusal loading onto the center of the incisal surface of the tooth. Thermal loads of 0°C and 65°C were applied on the model for 5 s. Temperature and thermal stresses were determined on the labio-lingual section of the model at 6 different points. RESULTS The distribution of stress, including thermal stress values, was calculated using 3D finite element analysis. The stainless steel post system produced more temperature and thermal stresses on the restorative materials, tooth structures, and posts than did the glass fiber reinforced composite posts. CONCLUSIONS Thermal changes generated stresses in the restorative materials, tooth, and supporting structures.

Micro push-out bond strength of resin cement in roots exhibiting the butterfly effect

The aim of this study was to determine the bond strength of resin cement in root sections with or without butterfly effect. Fifteen single-rooted human maxillary central incisors were decoronated and prepared up to size 40. After post space preparation, the resin cement was placed into the post space and the fiber posts were luted. 1 mm thickness slices were obtained and the presence of the butterfly effect was recorded. A push-out test was then used to measure the bond strength between the resin cement and root dentin. Data were analyzed using independent samples of t and χ(2) tests (p = 0.05). The sections exhibiting butterfly effect showed higher push-out bond strength values than those of without butterfly effect (p < 0.05). Butterfly effect can influence the push-out bond strength. Thus, this phenomena should be taken into account, when push-out bond strength test is performed. Root sections exhibiting butterfly effect resulted in higher push-out bond strength values to root sections without butterfly effect.

Stress distribution of endodontically treated teeth with titanium alloy post and carbon fiber post with different alveolar bone height: A three-dimensional finite element analysis

Objective:

A three-dimensional (3D) finite element analysis (FEA) on the stress distribution of endodontically treated teeth with titanium alloy post and carbon fiber post with different alveolar bone height.

Materials and Methods:

The 3D model was fabricated using software to represent an endodontically treated mandibular second premolar with post and restored with a full ceramic crown restoration, which was then analyzed using FEA using FEA ANSYS Workbench V13.0 (ANSYS Inc., Canonsburg, Pennsylvania, U.S.A) software.

Results:

The FEA showed the maximum stresses of 137.43 Mpa in dentin with alveolar bone height of 4 mm when the titanium post was used, 138.48 Mpa when carbon fiber post was used as compared to 105.91 Mpa in the model with alveolar bone height of 2 mm from the cement enamel junction (CEJ) when the titanium post was used and 107.37 Mpa when the carbon fiber post was used.

Conclusions:

Stress was observed more in alveolar bone height level of 4 mm from CEJ than 2 mm from CEJ. Stresses in the dentin were almost similar when the carbon fiber post was compared to titanium post. However, stresses in the post and the cement were much higher when titanium post was used as compared to carbon fiber post.

Effect of Photoactivation Timing on the Mechanical Properties of Resin Cements and Bond Strength of Fiberglass Post to Root Dentin

OBJECTIVES

This study tested the hypothesis that photoactivation timing and resin cement affect mechanical properties and bond strength of fiberglass posts to root dentin at different depths.

METHODS

Fiberglass posts (Exacto, Angelus) were luted with RelyX Unicem (3M ESPE), Panavia F 2.0 (Kuraray), or RelyX ARC (3M ESPE) using three photoactivation timings: light curing immediately, after three minutes, or after five minutes. Push-out bonding strength, PBS (n=10) was measured on each root region (coronal, middle, apical). The elastic modulus (E) and Vickers hardness (VHN) of the cement layer along the root canal were determined using dynamic indentation (n=5). A strain-gauge test was used to measure post-gel shrinkage of each cement (n=10). Residual shrinkage stress was assessed with finite element analysis. Data were analyzed with two-way analysis of variance in a split-plot arrangement and a Tukey test (α=0.05). Multiple linear regression analysis was used to determine the influence of study factors.

RESULTS

The five-minute delay photoactivation timing significantly increased the PBS for all resin cements evaluated. The PBS decreased significantly from coronal to apical root canal regions. The mean values for E and VHN increased significantly with the delayed photoactivation for RelyX Unicem and decreased from coronal to apical root regions for all resin cements with the immediate-curing timing.

CONCLUSIONS

The PBS of fiber posts to root dentin, E, and VHN values were affected by the root canal region, photoactivation timing, and resin cement type. Shrinkage stress values decreased gradually with delayed photoactivation for all the cements.

3D FEA of Hollow and Solid Design Zirconia Dental Dowels

PURPOSE

The aim of this study was to evaluate the stress distribution of hollow and solid design zirconia dowels.

MATERIALS AND METHODS

Finite element analysis (FEA) was used to investigate the influence of different dowel designs on the stress distribution of zirconia dowels. The coronal diameter of the dowel was 2.2 mm, the apical diameter was 1.8 mm, and the length was 15 mm. The diameter of the hollow space was 1.2 mm. Occlusal forces (both parallel and oblique) of 100 N were applied from the wider edge of the dowels simulating loads acting on the incisor during clenching and incising. The results were expressed in terms of von Mises criteria.

RESULTS

FEA revealed differences in stress distribution. During parallel load, the maximum tensile stress of the hollow design (89.40 MPa) was greater than the solid design (43.30 MPa). During oblique load, the maximum tensile stress of the hollow design (1437.90 MPa) was greater than the solid design (917.96 MPa). The maximum deformation was observed in the coronal part of the dowel in both designs under the two load directions.

CONCLUSIONS

FEA results showed that the hollow design zirconia dowels presented higher tensile stress.

Fracture resistance of endodontically treated roots with oval canals restored with oval and circular posts

INTRODUCTION

The aim of the present study was to evaluate the effects of post space preparations with circular and oval post drills and the placement of oval and circular posts on the fracture strength of roots with oval canals.

METHODS

Seventy mandibular premolars with oval root canals were decoronated. Fourteen teeth were used as a control group (group 1), and the root canals of the remaining teeth were prepared up to size #30. The root canals were filled, and the samples were randomly divided into 4 experimental groups as follows: post space preparation with circular-shaped drills (group 2), post space preparation with oval-shaped drills (group 3), circular post placement (group 4), and oval post placement (group 5). A fracture strength test was performed on each specimen, and the data were statistically evaluated using 1-way analysis of variance and Tukey post hoc tests.

RESULTS

The fracture strengths of the circular posts-placed group were higher than those of the oval post-placed group (P < .001). The post space preparation using oval-shaped drills significantly decreased the fracture strength of the roots compared with the control group (P < .001).

CONCLUSIONS

Within the limitations of the present study, oval posts did not provide a higher fracture resistance to endodontically treated roots with oval canals compared with circular posts. Therefore, clinicians should be aware that oval posts are similar to circular posts in terms of enhancing the fracture resistance of roots with oval canals.

Immediate and delayed photoactivation of self-adhesive resin cements and retention of glass-fiber posts

The aim of this study was to evaluate the effect of immediate and delayed photoactivation of self-adhesive resin cements (SARCs) on the retention of glass-fiber posts luted into root canals. Bovine incisors were endodontically treated, and post holes of 9 mm in depth were prepared. Fiber posts were luted using one of two SARCs, BisCem (Bisco Inc., Schaumburg, USA) or RelyX Unicem clicker (3M ESPE, Saint Paul, USA), or a regular (etch-and-rinse) resin cement (AllCem; FGM, Joinvile, Brazil). Photoactivation was performed immediately, or at 5 or 10 min after cementation. Root/post specimens were transversely sectioned 7 days after luting into 1-mm-thick slices, which were submitted to push-out testing in a mechanical testing machine. Bond strength data were analyzed by two-way ANOVA and Student-Newman-Keuls' method (α = 0.05). Immediate photoactivation resulted in the highest bond strength for Unicem. BisCem demonstrated higher bond strength values when photoactivated after a 10-min delay. Immediate photoactivation yielded the lowest bond strengths for AllCem, although no differences in bond strength were observed between photoactivation delayed by 5 and 10 min. In conclusion, the moment of resin cement photoactivation may affect the intraradicular retention of fiber posts, depending upon the resin cement used for luting.

A 3-dimensional finite element analysis of the restoration of the maxillary canine with a complex zirconia post system

STATEMENT OF PROBLEM

Zirconia posts exhibit high strength and toughness, but reliable bonding with the resin core is difficult to attain. The use of a ferrule has been found to improve stress distribution in the root of endodontically treated teeth.

PURPOSE

The purpose of this finite element analysis study was to measure the stress distribution in the post-core system and root structure of a maxillary canine.

MATERIAL AND METHODS

A right maxillary canine was embedded and subjected to a micro-computed tomography scan. Three-dimensional dynamic scan data were then transformed, and a finite element model of 4 dentin ferrule heights was designed with zirconia posts and heat-pressed glass ceramics for a complete crown restoration. Von Mises stresses were determined by applying a 300 N static load to the middle of the lingual surface of the crown.

RESULTS

When the ferrule height increased from 0 to 3 mm, the maximum von Mises stress of the zirconia post decreased from 196 to 149 MPa, and that on the zirconia post-dentin interface decreased from 174 to 132 MPa. The maximum von Mises stress decreased from 39.8 to 32.5 MPa in the apical root and from 59.5 to 49.9 MPa in the mid-root when the ferrule height increased from 0 to 3 mm.

CONCLUSIONS

Increased ferrule height is associated with reduced von Mises stress in the zirconia post and the post-dentin interface, with an apparent shift of von Mises stress to the root cervical area from the mid-root and the apex.

Influence of fiber post cementation length on coronal microleakage values in vitro and finite element analysis

AIM

This study aims to evaluate, the Influence of different fiber posts cementation lengths by finite element analysis (FEA) and coronal microleakage.

MATERIALS AND METHODS

Fifty anterior bovine teeth were sectioned to obtain roots with 16 mm length. The coronal length of the post was 6 mm for all groups, while the radicular length were varied 6, 8, 10 or 12 mm. The fiber posts surfaces were cleaned with alcohol and silanized. Then the posts were cemented using a two steps total etch-and-rinse adhesive system + conventional resin cement. Forty teeth were submitted to mechanical cycling (45°; 2.000.000 cycles; 90N; 4Hz; 37°C) and ten teeth with radicular length of 12 mm was not submitted, ser ving as c ontrol. So, the experimental design was composed by different ratios of post coronal length/post radicular length and mechanical cycling (MC): Gr1- 1/1 + MC; Gr2- 3/4 + MC; Gr3- 3/5 + MC; Gr4- 1/2 + MC. All groups were immersed in a 1% toluidine blue solution. After 24 hours, the teeth were longitudinally sectioned and the microleakage scores was given by a blind operator. Data were submitted to Kruskal-Wallis test (p = 0.05). The experimental variables were simulated in two-dimensional finite element analysis (2D-FEA). The maximum principal stress distributions were compared.

RESULTS

No difference was observed in microleakage values between the cycled groups, whilst the control groups showed the lowest values. FEA analysis showed similar maximum principal stress distribution between the groups.

CONCLUSION

Mechanical cycling affected the values of coronal microleakage and different cementation length generated similar values of coronal microleakage and stress distribution.

CLINICAL SIGNIFICANCE

These results showed that from the microleakage point of view, more conservative cementation lengths have the same effect as longer cementation lengths.

Fracture resistance of endodontically treated teeth restored with glass fiber reinforced posts and cast gold post and cores cemented with three cements

STATEMENT OF PROBLEM

Dental fractures can occur in endodontically treated teeth restored with glass fiber reinforced posts and cast gold posts.

PURPOSE

The objective of this study was to record the fracture strength of endodontically treated teeth restored with glass fiber reinforced or cast gold post and cores cemented with 3 cements.

MATERIAL AND METHODS

Forty-two single-rooted premolars with standardized weakened roots were endodontically treated and allocated to 6 experimental groups (n=7) defined by the 2 factors investigated: post system and cement. Three groups were restored with glass fiber posts and resin-modified glass ionomer cement, dual-polymerizing resin cement, or chemically active autopolymerizing resin cement. The other 3 groups were restored with cast gold post and cores and the same 3 cements. The cores of the glass fiber post groups were fabricated with composite resin core material. Metal crowns were cemented on the cores in the 6 groups. The entire system was subjected to continuous compression in a universal testing machine, and fracture limit and location (cervical third, middle third, or apical third) were noted. Two-way ANOVA and the Scheffé test were used to analyze the data and compare the groups (α=.05).

RESULTS

Two-way ANOVA showed significant differences in the post type (P<.001) and the cements (P<.001). The interaction between them (P<.001) was statistically significant in the fracture resistance of the endodontically treated teeth. The greatest interaction between post and cement was the glass fiber post with resin-modified glass ionomer cement, followed by the cast gold post and core with resin-modified glass ionomer cement.

CONCLUSIONS

The use of a glass fiber reinforced post and resin-modified glass ionomer cement increased the fracture resistance of endodontically treated teeth.