Fracture resistance of endodontically treated molars restored with horizontal fiberglass posts or indirect techniques

Fracture Resistance of Direct versus Indirect Restorations on Posterior Teeth: A Systematic Review and Meta-Analysis

The aim of this systematic review and meta-analysis was to compare static compression forces between direct composite resin restorations and indirect restorations for posterior teeth. All studies comparing mechanical properties of direct versus indirect restorations of posterior teeth were included from 2007 up to February 2024. A meta-analysis was conducted for static compression fracture resistance. Medline, Central, and Embase databases were screened. Twenty-four articles were included in the qualitative synthesis, and sixteen studies were finally included in the quantitative synthesis. There was no difference in terms of fracture resistance between direct and indirect restorations for posterior teeth (p = 0.16 for direct and indirect composite resin restorations and p = 0.87 for direct composite resin restorations and indirect ceramic restorations). Also, sub-group analysis with or without cusp coverage in each group revealed no discernable difference. Based on this study, it can be concluded that the choice between direct and indirect restoration approaches may not significantly impact fracture resistance outcomes. There was no statically significant difference between direct and indirect restorations for posterior teeth in all cases of restorations with or without cusp coverage and no matter the used materials. However, to better evaluate these materials, further studies are warranted.

Effect of fiber-reinforced direct restorative materials on the fracture resistance of endodontically treated mandibular molars restored with a conservative endodontic cavity design

OBJECTIVE

This study aimed to evaluate the fracture strength of teeth restored using fiber-reinforced direct restorative materials after endodontic treatment with a conservative mesio-occlusal access cavity design.

MATERIALS AND METHODS

A total of 100 extracted intact mandibular first molars were selected and distributed into a positive control group where teeth left intact and the following four test groups comprised of teeth with conservative mesio-occlusal access cavities that had undergone root canal treatment (n = 20/group): access cavity without restoration (negative control), bulk-fill resin composite with horizontal glass fiber post reinforcement, fiber-reinforced composite with bulk-fill resin and bulk-fill resin composite. Following thermocycling (10,000 cycles), fracture resistance was measured using a universal testing machine. Statistical analyses (one-way analysis of variance and the Tamhane test) were performed, and statistical significance was set at p < 0.05.

RESULTS

Groups with minimally invasive access cavities had lower fracture strength than intact teeth, regardless of the restoration material (p < 0.05). Fiber-reinforced composite groups demonstrated higher fracture strength than bulk-fill resin composite alone (p < 0.05). Fracture types varied among groups, with restorable fractures predominant in the fiber-reinforced composite groups.

CONCLUSION

This study suggests that using fiber-reinforced composite materials, especially in combination with bulk-fill resin composites, can effectively enhance the fracture strength of endodontically treated teeth with conservative access cavities. However, using only bulk-fill resin composite is not recommended based on the fracture strength results.

CLINICAL SIGNIFICANCE

When teeth that undergo endodontic treatment are restored using a conservative access cavity design and fiber-reinforced composite materials, especially in combination with bulk-fill resin composites, the fracture strength of the teeth can be effectively increased.

Fracture resistance and failure pattern of endodontically treated maxillary premolars restored with transfixed glass fiber post: an in vitro and finite element analysis

The aims of the study were to determine the effect of different types of endodontic sealers and the presence of a horizontal glass fiber post (HGFP) on the fracture resistance and fracture pattern of mesio-occluso-distal (MOD) restored upper premolars and to analyze the stress distribution. Sixty extracted upper premolars received root canal treatment (RCT) and a MOD cavity preparation. All MOD cavities were restored with the same composite resin (CR). The 60 teeth were divided randomly into 6 groups (n = 10); Group1= AH Plus sealer; Group 2= TotalFill BC sealer; Group 3= BioRoot RCS sealer; Group 4= AH plus sealer + HGFP; Group 5= TotalFill BC sealer + HGFP; and, Group 6= Bio Root RCS sealer + HGFP. All specimens were thermocycled and subjected to cyclic loading. Next, the specimens were subjected to a static load using a universal testing machine. Data were analyzed using two-way ANOVA. Two micro-CTs of the same upper premolar, one without the HGFP and later one with HGFP inserted were made and used to create two finite element (FE) models. For the fracture resistance, two-way ANOVA revealed significant differences for the effect of HGFP (p = 0.029), but no differences for the effect of root canal sealer type (p = 0.561). The HGFP groups showed higher restorable fracture compared to groups without HGFP (p = 0.013). Finite element analysis showed that the inclusion of HGFP reduces stress concentration at the occlusal interface and cervical region. Therefore, it can be concluded that HGFP significantly increased the fracture resistance of endodontically treated upper premolars with MOD cavities and reduced the risk for non-restorable fractures. The FE analysis supports the mechanical test results.

Fracture Resistance of Endodontically Treated Premolars Using Nanohybrid Composite, Fiber-Reinforced Composite, Horizontal Glass Fiber Posts, and Ceramic Inlays: An In Vitro Study

INTRODUCTION

This study evaluated the resistance to fracture of endodontically treated premolars (ETPs) with mesio-occluso-distal (MOD) cavities filled with nanohybrid composite (NHC), fiber-reinforced composite (FRC), horizontal glass fiber posts (HFP), and ceramic inlays (CI).

METHODS

Eighty-four intact maxillary premolars were taken, and endodontic treatment was performed followed by MOD cavity preparations (except in the control group). They were distributed into 7 groups based on type of restoration: intact teeth (control group), ETP + MOD (not restored), NHC, FRC + NHC, HFP + NHC, FRC + HFP + NHC, and CI groups. Samples were subjected to universal testing machine until the fracture occurred and failure mode was visually inspected.

RESULTS

Mean and standard deviation of fracture resistance of the 7 groups ranged from 265.6 ± 68.0 N to 1023.7 ± 76.5 N. The highest reading was noted for intact teeth followed by FRC + HFP + NHC group and then the CI group, with no significant difference among the 3 groups. The lowest reading was noted for the ETP + MOD group. Maximum unrepairable fractures were seen in the ETP + MOD and CI groups.

CONCLUSION

FRC + HFP + NHC combination and CIs increased the resistance to fracture of ETPs significantly.

Fatigue performance of endodontically treated molars reinforced with different fiber systems

OBJECTIVE

The aim was to investigate the fatigue performance of root canal-treated (RCT) molars restored with different direct restorations utilizing discontinuous and continuous fiber-reinforced composite (FRC) systems. The impact of direct cuspal coverage was also evaluated.

MATERIALS AND METHODS

One hundred and twenty intact third molars extracted for periodontal or orthodontic reasons were randomly divided into six groups (n=20). Standardized MOD, regular cavities for direct restorations were prepared in all specimens, and subsequently, root canal treatment and root canal obturation was carried out. After the endodontic treatment, the cavities were restored with different fiber-reinforced direct restorations as follows: SFC group (control), discontinuous short fiber-reinforced composite (SFC) without cuspal coverage (CC); SFC+CC group, SFC with cuspal coverage; PFRC group, transcoronal fixation with continuous polyethylene fibers without CC; PFRC+CC group, transcoronal fixation with continuous polyethylene fibers with CC; GFRC group, continuous glass FRC post without CC; and GFRC+CC, continuous glass FRC post with CC. All specimens underwent a fatigue survival test in a cyclic loading machine until fracture occurred or 40,000 cycles were completed. The Kaplan-Meier survival analysis was conducted, followed by pairwise log-rank post hoc comparisons between the individual groups (Mantel-Cox).

RESULTS

The PFRC+CC group was characterized by significantly higher survival compared to all the groups (p < 0.05), except for the control group (p = 0.317). In contrast, the GFRC group showed significantly lower survival compared to all the groups (p < 0.05), except for the SFC+CC group (p = 0.118). The control group (SFC) showed statistically higher survival than the SFRC+CC group (p < 0.05) and GFRC group (p < 0.05), but it did not differ significantly from the rest of the groups in terms of survival.

CONCLUSIONS

Direct restorations utilizing continuous FRC systems (in the form of polyethylene fibers or FRC post) to restore RCT molar MOD cavities performed better in terms of fatigue resistance when CC was performed compared to the same FRC restorations without CC. On the contrary, teeth restored with SFC restorations performed better without CC compared to the ones where SFC was covered.

CLINICAL RELEVANCE

In the case of fiber-reinforced direct restorations for MOD cavities in RCT molars, direct CC is recommended when utilizing long continuous fibers for reinforcement, however, should be avoided when only SFC is used for their reinforcement.

The influence of horizontal glass fiber posts on fracture strength and fracture pattern of endodontically treated teeth: A systematic review and meta-analysis of in vitro studies

PURPOSE

This systematic review and meta-analysis aimed to summarize available evidence regarding the effect of horizontal glass fiber posts (HGFPs) on fracture strength and fracture pattern of endodontically treated teeth (ETT) compared to controls without HGFP. The review protocol was registered on the OSF registries.

METHODS

Literature searches were conducted in MEDLINE/PubMed, Scopus, Web of Science, Embase, Google Scholar, and ProQuest for all relevant studies published up to February 2022. All in vitro studies that assessed the influence of HGFPs on fracture strength and fracture pattern of ETT whether mesio-occluso-distal or mesio-occlusal or DO cavities were considered eligible. Review Manager (RevMan) was used for the meta-analysis. Subgroup and funnel plot analyses were also performed. Quality assessment was conducted by two independent reviewers.

RESULTS

A total of 12 articles met the inclusion criteria, and 10 studies underwent quantitative evaluation. The pooled effect showed that fracture resistance of molar teeth restored with HGFP was significantly higher than teeth without HGFP (standardized mean difference [SMD]: 1.61, 95% confidence interval [CI]: 0.14, 3.09, p = 0.03), whereas marginally significant for premolars (SMD: 1.36, 95% CI: -0.00, 2.73, p = 0.05). Regarding fracture patterns, the presence of an HGFP significantly increased the occurrence of restorable fracture patterns for premolars (odds ratios [OR]: 4.15, 95% CI: 1.60, 10.82, p = 0.004) compared to controls, whereas the difference was not significant for molars (OR: 1.09, 95% CI: 0.43, 2.77, p = 0.85). Moderate risk of bias was identified in 9/12 studies; one study showed a high risk of bias and two studies showed a low risk of bias.

CONCLUSIONS

Within the limitations of this study, there is evidence from in vitro studies that the use of HGFP increases the fracture resistance of the ETT when compared to teeth without HGFP and also reduces the occurrence of non-restorable fractures for premolars. However, well-conducted in vitro and prospective clinical studies are warranted to validate this finding.

Biomechanical Performance of Mandibular Molars with Deep Mesio-Occlusal-Distal Cavities Rehabilitated with Horizontal Posts: A 3D Finite Element Analysis

Aim

To compare and contrast by three-dimensional finite element analysis the biomechanical performance of deep mesio-occlusal-distal cavities of mandibular molars reinforced by different sizes of horizontal fiber posts.

Materials and Methods

The finite element (FE) stress analysis was performed with the ANSYS, a commercial finite element method package. Based on the evidence-based scientific data and on the mechanical properties of materials, i.e., Young's modulus and Poisson ratio, the model of a mandible and mandibular first molar was replicated. The mandibular molar models replicating the clinical scenarios were simulated, designed, and built, assuming all materials to be homogenous, isotropic, and linearly elastic as follows: Model 1 control: the model of an intact first mandibular molar. Model 2: the prepared cavity mesio-occlusal-distal is replicated by the subtraction Boolean method. The remaining thickness of dentin is 1 mm. Model 3: these were rehabilitated by three different diameters of two horizontal fiber posts. Model 3A: fiber post diameter 1 mm, Model 3B: 1.5 mm and Model 3C: 2 mm. The dimensions of the cavity, the intercuspal distance between buccal walls and lingual walls, and the distance of placement of the post from occlusal reference points were all kept constant for all three subgroups of Model 3. The cavities of Model 3 were restored with Filtek bulk-fill posterior composite. After meshing the models, loads were defined on the buccal and lingual distal cusps with a constant value of 600 N and at an angle of 45°.

Results

The results of finite element analysis are expressed as stresses, i.e., tensile compressive, shear, or a combination known as von Mises stresses. The overall von Mises stresses were as follows: Model 1:154.83 Mpa; Model 2: 376.877 Mpa; Model 3A: 160.221 Mpa; Model 3B: 159.488 Mpa; Model 3C: 147.231 Mpa. Statistical analysis of the compiled data was carried out. It was seen that there was a significant difference in stress values from the intact tooth Model 1 and cavity Model 2 (p < 0.05) with means values of 53.1 and 139.22, respectively. The means of all subgroups were comparable but there was a statistically significant difference between Model 3, i.e., 3A (67.74), Model 3B (60.47), Model 3C (53.70), and Model 2. Model 1 and Model 3C had comparable mean values.

Conclusion

Rehabilitation of deep mesio-occlusal-distal cavities of molars with intact buccal and lingual walls with the aid of a horizontal post of any diameter has a similar stress distribution to an intact tooth. However, the biomechanical performance of a 2 mm horizontal post was exacting of the natural tooth. Horizontal posts can be included in expanding our restorative option for rehabilitating grossly mutilated teeth.

Effect of Successive In-office Bleaching Sessions on the Surface Properties, Substance Loss, Biaxial Flexural Strength, and Reliability of CAD-CAM Monolithic Materials

Little is known about the effects of in-office bleaching on the surface properties and on other aspects of CAD-CAM monolithic materials, especially when successive bleaching sessions are conducted. This study evaluated the effect of up to three successive in-office bleaching sessions on the microhardness, roughness, topography, substance loss, biaxial flexural strength (BFS), and reliability of CAD-CAM monolithic materials. Disks from Lava Ultimate (LU), Vita Enamic (VE), and IPS Empress CAD (EMP) were fabricated and submitted to one, two, and three bleaching sessions. In-office bleaching was performed with 40% hydrogen peroxide and each session consisted of three applications of 20 minutes each. The analyses regarding the aforementioned parameters were assessed before and after the first, second, and third bleaching sessions, except for BFS, which was evaluated at the baseline and after the third session. Weibull modulus was calculated from the BFS data. Bleaching decreased the microhardness of LU and VE from the third and second sessions, respectively, and affected neither the roughness nor the BFS of the three materials. However, in LU, it decreased the reliability and caused topographic changes, which were accentuated by the increase in the number of sessions. In general, LU and EMP showed, respectively, the highest and the lowest substance losses. Successive in-office bleaching sessions with the use of the protocol of the present study should be avoided in LU and VE.

Mechanical Performance of Direct Restorative Techniques Utilizing Long Fibers for “Horizontal Splinting” to Reinforce Deep MOD Cavities—An Updated Literature Review

Excessive cavity preparation and root canal treatment leads to a weakened tooth structure with a lower resistance to fracture. Fiber reinforcement is frequently used to reinforce such teeth, and multiple fiber types and possible applications exist. Various methods for utilizing long fibers to internally splint the remaining cavity walls in the case of large mesio-occluso-distal (MOD) cavities have been proposed; however, no summary of their performance has been written up to now. Our study aims to review the available literature to evaluate and compare the mechanical performance of the different materials and methods utilized for horizontal splinting in large MOD cavities. Three independent authors performed a thorough literature search using PubMed, ScienceDirect, and Google Scholar up until January 2022. The authors selected in vitro studies that used long fibers placed horizontally in posterior teeth with large MOD cavities to reinforce these teeth. From 1683 potentially relevant articles, 11 publications met our inclusion criteria. Seven out of eleven studies showed that horizontal splinting with long fibers improved the fracture resistance of the restored teeth. Three articles showed no significant difference between the fracture resistance of the restored groups. Only one article reported a lower fracture resistance to the horizontally splinted group, compared to conventional direct composite restoration. Within the limitations of this review, evidence suggests that long fiber reinforcement could be used to improve the fracture resistance of heavily restored teeth.

Evaluation of fracture strength of different restoration techniques applied to C-shaped 3D model teeth

The aim of this study is to investigate the effect of different restoration methods applied to model teeth with a C-shaped root canal configuration on fracture strength. A total of 76 artificial tooth models were made using images of a molar tooth with a C-shaped root canal anatomy. The teeth were randomly divided into seven groups and different restorations, such as resin composite (2), bundled fiber post and resin composite (3), vertical fiber post and resin composite (4), horizontal fiber post and resin composite (5), woven fiber post and resin composite (6) and composite endocrown (7) were applied to the different groups except control group (1). The artificial teeth were embedded in acrylic blocks and subjected to fracture tests. The data were analyzed using one-way analysis of variance, Monte Carlo Pearson Chi-square, Pearson Chi-square, and Fisher's exact test (P < 0.05). All groups differed in terms of fracture strength (P = 0.001). The highest fracture strength observed in group 6, and there was a significant difference between group 6 and group 4 based on a least significant difference pairwise comparison test. In terms of fracture type, the highest reparability percentage (100%) observed in group 7. The fracture strength values of endocrown restorations and woven fiber-reinforced resin composite restorations were found to be as high as those of the intact models. Considering also fracture restorability, endocrown restorations may be recommended for teeth with C-shaped root canal anatomy. The usage of the 3D tooth models in the studies offer a valuable opportunity in terms of the standardization of the samples, particularly in teeth with anatomical variations. This study shows that using of this technology, homogeneous groups can be created and experimental studies can be improved.

Functional Dental Pulp Regeneration: Basic Research and Clinical Translation

Pulpal and periapical diseases account for a large proportion of dental visits, the current treatments for which are root canal therapy (RCT) and pulp revascularisation. Despite the clinical signs of full recovery and histological reconstruction, true regeneration of pulp tissues is still far from being achieved. The goal of regenerative endodontics is to promote normal pulp function recovery in inflamed or necrotic teeth that would result in true regeneration of the pulpodentinal complex. Recently, rapid progress has been made related to tissue engineering-mediated pulp regeneration, which combines stem cells, biomaterials, and growth factors. Since the successful isolation and characterisation of dental pulp stem cells (DPSCs) and other applicable dental mesenchymal stem cells, basic research and preclinical exploration of stem cell-mediated functional pulp regeneration via cell transplantation and cell homing have received considerably more attention. Some of this effort has translated into clinical therapeutic applications, bringing a ground-breaking revolution and a new perspective to the endodontic field. In this article, we retrospectively examined the current treatment status and clinical goals of pulpal and periapical diseases and scrutinized biological studies of functional pulp regeneration with a focus on DPSCs, biomaterials, and growth factors. Then, we reviewed preclinical experiments based on various animal models and research strategies. Finally, we summarised the current challenges encountered in preclinical or clinical regenerative applications and suggested promising solutions to address these challenges to guide tissue engineering-mediated clinical translation in the future.

Stress Concentration of Endodontically Treated Molars Restored with Transfixed Glass Fiber Post: 3D-Finite Element Analysis

The loss of dental structure caused by endodontic treatment is responsible for a decrease in tooth resistance, which increases susceptibility to fracture. Therefore, it is important that minimally invasive treatments be performed to preserve the dental structure and increase the resistance to fracture of endodontically treated posterior teeth. To evaluate under axial loads, using the finite element method, the stress distribution in endodontically treated molars restored with both transfixed or vertical glass fiber posts (GFP) and resin composite. An endodontically treated molar 3D-model was analyzed using finite element analyses under four different conditions, class II resin composite (G1, control model), vertical glass fiber post (G2), transfixed glass fiber posts (G3) and vertical and transfixed glass fiber posts (G4). Ideal contacts were considered between restoration/resin composite and resin composite/tooth. An axial load (300 N) was applied to the occlusal surface. The resulting tensile stresses were calculated for the enamel and dentin tissue from five different viewports (occlusal, buccal, palatal, mesial and distal views). According to the stress maps, similar stress trends were observed, regardless of the glass fiber post treatment. In addition, for the G1 model (without GFP), a high-stress magnitude can be noticed in the proximal faces of enamel (7.7 to 14 MPa) and dentin (2.1 to 3.3 MPa) tissue. The use of transfixed glass fiber post is not indicated to reduce the stresses, under axial loads, in both enamel and dentin tissue in endodontically treated molar with a class II cavity.

Direct bilayered biomimetic composite restoration: The effect of a cusp-supporting short fiber-reinforced base design on the chewing fracture resistance and failure mode of molars with or without endodontic treatment

The aim of this study was to assess the chewing fracture resistance of compromised molars restored with direct composite resin (CR) restorations, with and without a short-fiber reinforcing (short-FRC) base. Wide extension of MOD cavities with removed palatal cusps preparations were simulated on 48 extracted maxillary molars. Five groups (n = 12) were designed: 1. control (intact teeth), 2. non-endodontically treated and 3. endodontically treated teeth with direct CR restorations (GC-Posterior), and 4. non-endodontically treated and 5. endodontically treated teeth with direct biomimetic bilayered restorations. Groups 4 and 5 included an anatomically shaped short-FRC base (everX Posterior), covered with a 2 mm CR layer (GC-Posterior). Restorations were subjected to chewing in water (1.5 Hz), with load of 85 N. Specimens were loaded until fracture or to a maximum of 120 000 cycles. Restorations that survived the chewing cycle were submitted to static load test (post-chewing test). The data were statistically analyzed using two-way ANOVA (p = 0.05) and fracture types with the chi-square test (p = 0.05). Fractures were classified into reparable, possibly reparable or non-reparable. All specimens survived the chewing cycle. The chewing fracture resistance of the direct biomimetic restorations prepared on non-endodontically treated teeth (2889 N) was statistically significantly higher than the direct CR counterparts (1966 N) (p = 0.00015), which was not the case for the groups with endodontically treated teeth (p = 0.257). Inclusion of a short-FRC base also influenced the fracture type resulting in most reparable fractures (67-75% versus 25% for biomimetic and CR groups respectively) (p = 0.054). Anatomically shaped i.e. a cusp-supporting design made of short-FRC base (everX Posterior) improved the chewing fracture resistance and fracture manner of compromised molars regardless of whether they were endodontically treated or not.

Structural Integrity Evaluation of Large MOD Restorations Fabricated With a Bulk-Fill and a CAD/CAM Resin Composite Material

AIMS

To evaluate the effect of two composite restorative techniques (direct bulk fill vs indirect CAD/CAM) on the fracture resistance and mode of fracture of extended mesio-occlusal-distal (MOD) cavity preparations.

METHODS

Fifty-one sound human mandibular third molars were divided into three groups (n=17). Extended bucco-lingual MOD cavities were prepared. Teeth in group 1 were restored with a bulk-fill resin composite (Filtek Bulk-Fill Posterior Restorative), teeth in group 2 were restored with composite computer-aided design/computer-aided manufacturing (CAD/CAM) inlays (Lava Ultimate), and teeth in group 3 served as control and remained intact. All specimens were submitted to thermocycling, and a fracture resistance test was performed using a Universal testing machine (0.5 mm/min). Mode of fracture was classified into five types. One-way analysis of variance and the Duncan test were used to analyze the fracture load data at a significance level of α = 0.05. A chi-square test was used for the analysis of fracture mode between the restorative groups.

RESULTS

Statistical analysis showed significant differences in fracture resistance among the experimental groups. The teeth restored with the bulk-fill composite exhibited lower fracture resistance (1285.3±655.0 N) when compared to the teeth restored with the composite CAD/CAM inlays (1869.8±529.4 N) (p<0.05). Mode of fracture showed the same distribution between the restorative groups.

CONCLUSIONS

Although both types of restorations failed at loads larger than those found in the oral cavity, the CAD/CAM composite inlays increased the fracture resistance of teeth with large MOD cavities when compared to direct bulk-fill composite restorations. The majority of fracture types were intraorally repairable for both restorative techniques.