Fracture resistance of three different all-ceramic crowns: In vitro study

PURPOSE

To evaluate the fracture resistance and failure mode of three different all-ceramic crowns; CEREC Bloc, IPS e.Max Press and Cercon in a simulated clinical situation.

METHODS

30 extracted maxillary premolars were prepared and randomly assigned to three groups equally according to the type of crown used. The first was the CEREC group: monolithic feldspathic crowns (CEREC Blocs). The second was the E.Max group: monolithic lithium disilicate crowns (IPS e.Max Press). The third group was the Cercon group: bilayered partially stabilized zirconia crowns (Cercon). All crowns were cemented using dual-cured resin cement (ParaCore). The specimens were then subjected to thermocycling (5-55°C/500 cycles) and loaded to failure at an angle of 45° to the occlusal surface of the crown. Failure data was statistically analyzed using one-way ANOVA and Tukey's HSD post hoc test at α= 0.05. Fractographic analysis was performed to determine the fracture modes of the failed specimens.

RESULTS

The mean fracture values for CEREC, E.Max and Cercon groups were 387± 60 N, 452 ± 86 N, and 540 ± 171 N, respectively. Significant differences were found between CEREC and Cercon groups (P< 0.05). Catastrophic fracture within the ceramic crown was the major failure mode of the CEREC group. For E.Max and Cercon groups, the major failure mode was exhibiting severe tooth fracture while the ceramic crown remained intact.

CLINICAL SIGNIFICANCE

CEREC, IPS e.Max Press and Cercon crowns are clinically applicable as they exceeded the normal masticatory forces. However, the CEREC crown is preferred as it maintains the integrity of the natural abutment.

Influence of dentin and enamel on the fracture resistance of restorations at several thicknesses

PURPOSE

To investigate the effect of substrate and thickness on the fracture resistance of bonded dental restorative materials.

METHODS

Cylindrical restorations (d = 4.0 mm) of resin composites Filtek Supreme XTE, Clearfil AP-X, Lava Ultimate and glass-ceramic IPS e.max CAD were fabricated at thicknesses of 0.5 mm, 1.0 mm and 2.0 mm respectively (n = 10 per group) and adhesively bonded to bovine enamel or dentin. The load to failure (LtF in N) of all specimens was determined in a universal testing machine and two one-way ANOVAs with a post hoc LSD tests and separate independent samples t-tests, performed at a significance level of 5%.

RESULTS

At 0.5 and 1.0 mm, direct resin composites bonded to dentin showed a higher LtF than when bonded to enamel, while the indirect materials showed reversed results (P< 0.05). At 2.0 mm there was no difference except for LU. A direct relationship between LtF and increasing thicknesses on enamel was found, while on dentin the LtF of direct resin composite restorations was less dependent on the thickness.

CLINICAL SIGNIFICANCE

For restorations up to 1 mm thickness, a substrate with a matching elastic modulus has a positive effect on the fracture resistance of glass-ceramics and resin composite restorations. When bonded to enamel, restoration thickness plays an important role in the fracture resistance. When bonded to dentin, thickness only affects the fracture resistance of indirect restoratives.

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

OBJECTIVE

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

METHODS AND MATERIALS

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

RESULTS

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

CONCLUSIONS

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

Effect of synthetic and natural-derived novel endodontic irrigant solutions on mechanical properties of human dentin

This study aimed to evaluate the effects of different synthetic and natural-derived root canal irrigants (6% sodium hypochlorite [NaOCl], 6% calcium hypochlorite [Ca(OCl)₂] and 6.5% grape seed extract [GSE]) on dentin mechanical properties (flexural strength, ultimate tensile strength [UTS] and fracture resistance). Rectangular-shaped beams and hourglass-shaped sections obtained from mid-coronal and root dentin were treated with 6% NaOCl, 6% Ca(OCl)₂ or 6.5% GSE for 30 min. The irrigant solutions were replaced every 5 min. Then, the dentin specimens were rinsed with distilled water (DW) followed by incubation with 17% EDTA for 1 min, and thoroughly rinsed with DW again. Specimens from the control group were tested without prior irrigation. After treatment with the irrigants, dentin beams were used to assess the flexural strength (n = 10) while UTS was evaluated using the root dentin hourglass-shaped sections (n = 10). Similarly, roots with 1 mm of dentinal wall thickness were obtained from human teeth and treated with the same irrigant solutions (n = 10). A compressive loading was applied to the coronal surfaces of roots until fracture. The values of each mechanical test were statistically analyzed individually by one-way ANOVA followed by Tukey HSD test (P < 0.05). NaOCl significantly reduced the mechanical properties of dentin in all mechanical tests (P < 0.05) and no statistical difference was found among Ca(OCl)₂, GSE and control group (P > 0.05). It can be concluded that Ca(OCl)₂ and GSE may be alternative irrigant solutions, since they do not negatively affect the dentin mechanical properties.

Fracture resistance of endodontically-treated mandibular molars restored with different intra-radicular techniques

PURPOSE

To evaluate fracture resistance and failure mode of endodontically-treated mandibular molars restored with different intra-radicular techniques.

METHODS

75 human mandibular molars were randomly divided into five equal groups. Teeth were standardized, endodontically-treated and restored according the assigned group as follows: amalgam core only, prefabricated titanium post in the distal canal and amalgam core, composite core only; fiber post in the distal canal and composite core. One group of untreated sound teeth was used as a control. Non-precious metal crowns were fabricated and cemented on the prepared specimens with Rely X U200 resin cement. All specimens were subjected to a compressive load at crosshead speed 0.5 mm/minute, 25° to the long axis of the tooth. Failure loads and modes were recorded.

RESULTS

Mean failure loads among the groups were significantly different (P= 0.035). Post-hoc multiple pair-wise comparisons revealed the amalgam core and composite core groups produced significantly lower fracture resistance than the control group (P= 0.041 and P= 0.025, respectively) and no significant differences among the different intra-radicular techniques (P> 0.05). The composite core with fiber post and amalgam core with titanium posts showed the highest percentage of favorable failures (67%) and non-favorable failures (87%) respectively.

CLINICAL SIGNIFICANCE

The composite core with fiber post is the most appropriate intraradicular restoration in cases of severely compromised molars.

Comparison of Different Post Systems for Fracture Resistance: An in vitro Study

INTRODUCTION

Endodontic restoration becomes a challenging task for the clinician because of severe loss of coronal tooth structure owing to trauma, caries, restorative, and endodontic procedures. The restoration of these teeth requires the use of a post and core as individual units or as abutment supports for fixed or removable restorations in a predictable long-term manner.

AIM

To compare and assess the compressive bond strength of glass, quartz, and carbon fiber posts restored with porcelain-fused-to-metal (PFM) crown.

MATERIALS AND METHODS

A total of 45 upper central incisor teeth having straight root canals, similar anatomically root segments, and fully developed apices were selected. Teeth were divided into three groups of 15 teeth after endodontic treatment. Group I: Teeth inserted with the prefabricated glass fiber post. Group II: Teeth inserted with the quartz fiber post. Group III: Teeth inserted with carbon fiber post. The posts were placed and core was fabricated using composite restoration followed by PFM crown cementation using adhesive resin. Compressive load required to fracture the tooth was measured using a universal loading machine. The difference between the variables was assessed by one-way analysis of variance, followed by Tukey's post hoc test.

RESULTS

The compressive strength exhibited by carbon fiber posts was highest with a mean of 668.33 ± 26.397, followed by quartz fiber post (635.80 ± 30.390). Least compressive strength was exhibited by glass fiber post (567.53 ± 26.632). An analysis of variance shows statistically highly significant difference (p < 0.005) among the posts used.

CONCLUSION

This study concluded that the carbon fiber posts had higher compressive strength than other quartz, glass fiber posts.

CLINICAL SIGNIFICANCE

Endodontic treatment results in loss of a significant part of the tooth structure. Posts restore these teeth and provide retention.

Effect of CAD/CAM glass fiber post-core on cement micromorphology and fracture resistance of endodontically treated roots

PURPOSE

To investigate the fracture resistance of weakened roots restored with prefabricated or CAD/CAM-customized posts and cores as well as the thickness of the cement film and the presence of voids in the cement.

METHODS

The roots of 40 human premolars were weakened by removing internal dentin with a diamond bur (2.5 mm in the coronal third and 1.5 mm in the apical third) and restored with prefabricated posts (PPs) or customized posts (CPs) with or without a zirconia crown (n= 10). Posts and crowns were cemented with resin cement. Microtomography was used to determine the thickness of the cement film and whether voids were present. After fatigue testing (1 million cycles, 50 N, 5 Hz, 36.5°C), the specimens underwent compression testing with an oblique load (30°, 1 mm/minute) and fracture strengths were recorded (N). Fracture strength and film thickness were analyzed with ANOVA and the Games-Howell test; the variable presence of voids was analyzed with the Mann-Whitney test (α= 5%).

RESULTS

Mean fracture strengths varied between 640.4 and 792.9 N and did not differ significantly between groups. The CP group had a thinner cement film and fewer voids than the PP group. There was a positive, statistically significant correlation (Spearman, R=0.488, P= 0.029) between these variables.

CLINICAL SIGNIFICANCE

CAD/CAM-manufactured glass-fiber posts and cores do not affect the fracture strength of flared root canals or cause catastrophic failure of the root when used with zirconia crowns.

Fracture resistance of single-rooted pulpless teeth using hybrid CAD/CAM blocks for post and core restoration

PURPOSE

The purpose of this study was to determine whether there is a significant difference in the fracture strengths of hybrid computer-aided design/computer-aided manufacturing (CAD/CAM) blocks and fiber posts for post and core restorations in both ferrule and nonferrule pulpless mandibular canines.

MATERIALS AND METHOD

Forty extracted human mandibular canines were divided into ferrule and nonferrule groups and restored with hybrid CAD/CAM blocks using either the CAD/CAM system or fiber posts (control). Thus, there were four subgroups of ten specimens each. A 45-degree oblique load was applied with a crosshead of 0.5 mm/min, and the fracture loads were recorded. The mode of fracture was evaluated using an optical microscope at 3× magnification, and the data were tabulated and statistically analyzed using the Mann-Whitney U test and the t test, respectively, for the existence of significant difference at a 0.05 significance level.

RESULTS

No statistically significant difference was found between the fracture strength under oblique loading when using hybrid CAD/CAM blocks and fiber posts in both ferrule and nonferrule groups. The failure mode distribution of the nonferrule group presented no unfavorable failures, whereas failures in the ferrule groups were spread out between the Favorable and Unfavorable groups.

CONCLUSIONS

The results show that hybrid CAD/CAM blocks can be considered as an alternative restorative system in post and core restorations. Further basic and clinical research should be conducted to support the improvement of this system.

Impact of Various Irrigating Agents on Root Fracture: An in vitro Study

INTRODUCTION

Irrigating solutions are used for cleaning and removing dentinal debris, and the other remains from pulpal space during biomechanical preparation. Therefore, we evaluated the impact of various irrigating agents on root fracture at 5-minute time exposure.

MATERIALS AND METHODS

We sectioned 60 permanent maxillary premolars with fully formed root structures transversely maintaining the root length of approximately 14 mm. Five study groups were made comprising ethylenediaminetetraacetic acid (EDTA), cetrimide, citric acid, and so on as various irrigating agents. A universal force test machine was used to calculate the force which was enough to fracture each root. Analysis of variance (ANOVA) test was used to access the level of significance.

RESULTS

About 10% citric acid solution as an irrigating agent showed minimal fracture opposing results, whereas 10% EDTA solution showed the maximum fracture resistance of root portion.

CLINICAL SIGNIFICANCE

Selection of suitable EDTA concentration that has minimal adverse effect on the mechanical properties of the tooth is very important for the successful management of tooth fracture.

CONCLUSION

About 10% EDTA provided the highest fracture resistance, necessitating the use of irrigating solution in root canal therapy (RCT). Further research with higher and different study groups is required to search for more efficient irrigating solution to improve the outcome of RCT.

An in vitro Evaluation of Fracture Resistance of endodontically treated Teeth with Different Restorative Materials

AIMS

The aim of the present study is to compare and assess the fracture resistance of root canal treated teeth with different restorative materials.

MATERIALS AND METHODS

The present in vitro study was carried out on seventy-five freshly extracted, noncarious, single-canal human lower-first premolars with similar anatomic characteristics. Teeth were randomly assigned to five groups with 15 teeth being present in each group. Group I is control group (no alteration done), group II is restored with silver amalgam after endodontic therapy, group III is restored with posterior composite after end-odontic therapy, group IV is restored with posterior glass ionomer cement (GIC) after endodontic therapy, and group V is restored with miracle mix after endodontic therapy. Universal testing machine was used to assess the fracture strength. Analysis of variance (ANOVA) test followed by Tukey's post hoc test were used to determine the significant difference between each group. A p-value of < 0.05 was considered as statistically significant.

RESULTS

The mean fracture resistance of control group showed highest fracture resistance with a mean Newton of 1083.33 ± 136.78. Among the restorative material, the highest fracture resistance was shown by teeth restored by composite (845.46 ± 47.36), followed by silver amalgam (845.46 ± 47.36). There was statistically significant difference among all the restorative materials compared with the control group (p < 0.05). However, among the teeth restored with silver amalgam and miracle mix, there was no statistical significance (p > 0.05).

CONCLUSION

The present study concludes that composites are found to be having more fracture resistance followed by silver amalgam on endodontically treated premolar teeth.

CLINICAL SIGNIFICANCE

Restoring nonvital teeth represents a major challenge for clinicians as they are extensively damaged due to caries and endodontic access preparations. With various restorative materials in the market, it becomes difficult for the clinician to choose the better restorative material for postendodontic restoration.

Fracture strength of the remaining dental structure after different cavity preparation designs

The aim of this in vitro study was to evaluate the loss of tooth structure after cavity preparation for direct (retentive) and indirect (nonretentive) restorations and its relationship to the fracture strength of the prepared tooth. Sound human third molars (60 maxillary and 60 mandibular) were randomly assigned into 12 groups (n = 10) according to the type of cavity preparation and the respective buccolingual width. Class II mesio-occlusodistal cavity preparations, for both indirect inlay and direct resin restorations, were prepared with standardized dimensions of one-half, one-third, or one-quarter of the occlusal intercuspal distance. Fracture resistance was lower and weight loss was greater for all nonretentive preparations. Greater losses in weight and fracture resistance occurred when the buccolingual width for both types of cavities increased, except for the weight loss of the one-quarter and one-third indirect cavity preparations in the mandibular molars, and the fracture resistance of the one-half and one-third direct cavity preparations in maxillary molars. Higher tooth structure loss and lower fracture strength were recorded after preparation of the inlay cavities.

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.

[The resistance of teeth to vertical root fractures after mechanical preparation and irrigation of root canal (pilot study)]

The aim of the study was to assess the influence of external root anatomy, time of irrigation and the rate of mechanical enlargement of root canals on root fracture resistance. Thirty six bovine teeth were decoronated and divided into 2 groups: with round and oval forms of axial root slices. The root canals were mechanically enlarged according to standard protocol and prepared for post placement. Individual cast posts were made for each tooth, the diameter of posts comprised 1/2 or 1/3 of the root diameter in different subgroups. After mechanical enlargement, the canals were irrigated with 3% sodium hypochlorite for 10 or 60 minutes in different subgroups. The teeth with posts were subjected to static vertical load by universal testing machine with the speed of 1 mm per minute. The load that had led to fracture initiation was noted. Analysis of variances was used to assess the statistical significance of the

RESULTS

No statistically significant differences were found between the groups with different protocols of mechanical preparation and irrigation. Teeth with round axial root slice were significantly less susceptible to fractures than ones with oval shape of axial root slice taking into consideration the protocols of mechanical preparation and irrigation.

The effect of temporary restorative materials on fracture resistance of endodontically treated teeth

This study was designed to investigate the fracture strength of endodontically treated teeth temporarily restored with some commonly used interim materials. Of 90 extracted maxillary premolars used in this study, 15 were left intact as the positive control. Endodontic treatment was performed on the remaining 75 teeth. The endodontically treated teeth were then randomly assigned to 5 groups (n = 15). One group was not restored and served as the negative control. In the remaining 4 experimental groups, the teeth were restored with a temporary cement: Zonalin, IRM, Coltosol, or Fuji II LC resin-modified glass ionomer (RMGI). The fracture strengths of all teeth were measured with a universal testing machine. The fracture strength of teeth restored with RMGI was significantly greater than that of other groups (P < 0.001), including intact teeth (P = 0.025). The fracture strength of teeth restored with other temporary materials was significantly lower than that of intact teeth (P < 0.05) but not significantly different from that of the negative control. From a structural resistance standpoint, RMGI may be the best choice for short-term temporary restoration of endodontically treated teeth. Other types of temporary restorative material had no reinforcing effect on tooth structure.

[Fracture strength of elastic and conventional fibre-reinforced composite intraradicular posts--an in vitro pilot study]

OBJECTIVES

The purpose of this in vitro investigation was to evaluate the reinforcing effect of different fibre-reinforced composite (FRC) posts and insertion techniques in premolar teeth when using minimal invasive post space preparation.

MATERIALS AND METHODS

Thirty two extracted and endodontically treated premolar teeth were used and divided into four groups (n = 8) depending on the post used (Group 1-4). 1: one single conventional post, 2: one main conventional and one collateral post, 3: one flexible post, 4: one main flexible and one collateral post. After cementation and core build-up the specimens were submitted to static fracture toughness test. Fracture thresholds and fracture patterns were recorded and evaluated.

RESULTS

The multi-post techniques (group 2 and 4) showed statistically higher fracture resistance compared to group one. Regarding fracture patterns there was no statistically significant difference between the tested groups.

CONCLUSION

The application of multiple posts seems to be beneficial regarding fracture resistance independent from the used FRC post. Fracture pattern was not influenced by the elasticity of the post.

Comparison of the Resistance of Teeth Instrumented with Different Nickel-Titanium Systems to Vertical Root Fracture: An In Vitro Study

INTRODUCTION

This study compared the fracture resistance of teeth instrumented with ProTaper Universal (Dentsply Maillefer, Ballaigues, Switzerland), ProTaper Next (PTN, Dentsply Maillefer), WaveOne (Dentsply Maillefer), Twisted File (SybronEndo, Orange, CA), Mtwo (MT; VDW, München, Germany), and Revo-S (MicroMega, Besançon, France) nickel-titanium systems and obturated with compatible gutta-percha cones of finishing files using the single-cone technique and a resin sealer.

METHODS

The study included 72 mandibular premolar teeth. The roots were covered with additive silicone and placed in Eppendorf tubes, which were filled with a self-curing acrylic. The tubes were separated into 6 groups: prepared with the ProTaper Universal (F4 40/.06) (group 1), prepared with the PTN (X4 40/.06) (group 2), prepared with the WaveOne reciprocating file (40/.08) (group 3), prepared with the Twisted File (40/.04) (group 4), prepared with the MT (40/.06) (group 5), and prepared with the Revo-S (AS 40/.06) (group 6). After the preparations were completed, all the teeth were filled with the appropriate gutta-percha systems. The force (N) was applied at a 1-mm/min crosshead speed until the roots fractured. Differences among the groups were analyzed by Tukey and analysis of variance tests.

RESULTS

Group 2 was the most resistant to fracture, and group 5 was the least resistant. The difference in the fracture resistance between the 2 groups was statistically significant (P = .019). The resistance of group 3 and group 6 to vertical root fracture was similar, and the resistance of group 4 was slightly lower than that of the other groups (P = .058).

CONCLUSIONS

The roots instrumented with the MT were the least resistant, and the roots instrumented with the PTN were the most resistant to VRF.

Fracture resistance of weakened roots restored with different intracanal retainers

The purposes of the study were to evaluate the effect of mechanical cycling (MC) on the fracture resistance of endodontically treated weakened roots restored with different intraradicular retainers and to analyze the failure mode. Eighty bovine roots were prepared and restored: 20 roots were reconstructed with cast post-and-cores (CPCs); 20 with fiber posts (FPs); 20 with fiber posts with larger coronal diameter (FPLs); and 20 with anatomic posts (APs). Metal crowns were cemented in all the roots. Half of specimens from each restoration strategy (n = 10) were submitted to MC: CPC-MC, FP-MC, FPL-MC, and AP-MC. The specimens were subjected to a fracture resistance test. The results showed that the type of retainer used was statistically significant (P < 0.0004). The CPC specimens demonstrated a fracture resistance similar to that of the APs, but greater than that of the FPs and FPLs. MC was statistically significant (P < 0.003) and affected AP-MC fracture resistance, which was lower than that of CPC-MC and similar to those of FP-MC and FPL-MC.

Fracture strength of endodontically treated maxillary premolars supported by a horizontal glass fiber post: an in vitro study

INTRODUCTION

The purpose of this study was to evaluate the effect of a horizontal glass fiber post on the fracture strength of endodontically treated maxillary premolars with mesioocclusaldistal (MOD) cavities.

METHODS

Sixty extracted intact upper premolars were collected, treated endodontically (except for the control group), and divided into 5 test groups (n = 12) depending on the restoration type: G1 (control group, untreated teeth), G2 (MOD preparation without restoration), G3 (MOD preparation with resin composite restoration), G4 (MOD preparation with resin composite restoration and a horizontal fiber post inserted between buccal and palatal walls), and G5 (MOD preparation with a horizontal fiber post only). The specimens were stored in normal saline at 37°C for 2 months. Then specimens were quasi-statically loaded in a universal testing machine until fracture occurred. Failure loads were then analyzed with one-way analysis of variance, followed by multiple comparisons by using Tukey honestly significant difference test (α = .05). The mode of failure was determined by visual inspection.

RESULTS

Mean (standard deviation) failure loads for groups ranged from 411.8 N (±103.9) to 994.5 N (±147.3). One-way analysis of variance showed significant differences between fracture resistances of groups (P < .001). Tukey honestly significant difference test showed significant differences in fracture resistance within groups (P ≤ .05) except between the G1 (control group) and group G4 (P ≥ .05). All groups (except G4) had almost favorable fracture mode within the cervical third of the roots.

CONCLUSIONS

Under the conditions of this in vitro study, a horizontal glass fiber post in a MOD cavity increased significantly the fracture resistance of the endodontically treated upper premolars.

Fracture Resistance of Roots Restored with Four Different Fiber-Reinforced Composite Posts

OBJECTIVE

The aim of this study was to compare the resistance to vertical root fracture of root-filled teeth restored with four different fiber-reinforced composite (FRC) post systems and two types of dual-cured resin luting agents.

MATERIALS AND METHODS

Ninety extracted human maxillary central incisors were selected and decoronated to obtain a standardized root length of 14 mm. After root canal obturation, post spaces were prepared to a depth of 10 mm with a No. 3 post drill. The specimens (n = 80) were divided into two groups (n = 40) according to the resin luting agents used: group 1, Variolink II + ExciTE DSC; group 2, RelyX Unicem. These groups were subdivided into four subgroups (n = 10) and restored with one of the following post systems: (a) DT Light, (b) DT Light SL, (c) FRC Postec and (d) Everstick, while the remaining 10 teeth served as controls. The roots were subjected to axial compressive loading using a 2.2-mm-diameter metal sphere in a universal testing machine (0.5 mm/min). A factorial experiment with a single control group (analysis of variance) was used to test the resistance of the specimens.

RESULTS

Groups 2a (DT Light + RelyX Unicem; 398.5 N) and 1b (DT Light SL + Variolink II + ExciTE DSC; 431.1 N) had significantly higher resistance to fracture than the control group (334.1 N; p < 0.05). DT Light SL and FRC Postec Plus were more resistant to fracture when Variolink II was used as the luting cement. DT Light and Everstick had higher fracture resistance when they were luted with RelyX Unicem (p < 0.05).

CONCLUSION

The results of this study indicate that the use of quartz fiber posts (DT Light and DT Light SL) with an adhesive luting cement in root-filled teeth may reinforce the root to some extent.

Resin bonding to root dentin: influence of the alveolar bone level and thickness of the cement layer

AIM

Aim of the present study was to evaluate the influence of the alveolar bone level and thickness of the cement layer on the push-out bond strength of fiber posts luted to root dentin.

METHODS

We prepared post spaces in 60 bovine roots (16 mm), embedded in acrylic resin to simulate different scenarios of alveolar bone resorption. They were divided into six groups (N.=10), according to the factors "alveolar bone level" (14, 10, and 7 mm) and "cement thickness" (post no. 3/control and post no. 1/ thicker cement layer): G14P3 - 14-mm root + post n. 3; G10P3 - 10-mm root + post n. 3; G7P3 - 7-mm root + post n. 3; G14P1 - 14-mm root + post n. 1; G10P1 - 10-mm root + post n. 1; and G7P1 - 7-mm root + post n. 1. The fiber posts (White Post DC, FGM) were luted, and composite cores were made. Each specimen was subjected to mechanical cycling, and four slices were obtained from each root specimen and subjected to push-out testing in a universal testing machine. The data (MPa) were analyzed by ANOVA (two way) and Tukey's test (5%).

RESULTS

The factor "cement thickness" (P=0.0057) significantly influenced bond strength, but the factor "alveolar bone level" (P=0.0605) did not. The thicker cement layer/post n. 3 presented bond strength values higher than those with cement layer/post n. 1.

CONCLUSION

Bond strength was not influenced by different scenarios of alveolar bone resorption, although higher bond strength values were found for thinner cement layers.

Fracture resistance of permanent anterior incisors using fiber-reinforced composite posts

This in vitro study investigated whether permanent anterior incisors that are endodontically treated with cemented fiber-reinforced composite (FRC) posts without additional canal preparation can potentially increase the resistance to fracture and thus reduce the rate of clinical failure in root canals. Extracted human permanent maxillary central incisors (n = 120) were randomly assigned to 2 experimental groups (n = 60): thermocycled (Group 1) and non-thermocycled (Group 2). These 2 groups were then further divided into 3 subgroups (n = 20). Subgroup 1.1 specimens had root canals prepared and obturated with FRC posts placed. Subgroup 1.2 specimens were prepared and obturated, but did not receive posts. Subgroup 1.3 specimens did not receive root canal preparation, and served as a control. The same processes were repeated for Subgroups 2.1, 2.2, and 2.3, respectively. Significant differences were found between the thermocycled and the non-thermocycled subgroups. Subgroup comparison within the thermocycled group (Group 1) showed significantly higher fracture resistance values for the teeth with post cementation (P < .0001).

The fracture resistance of teeth restored with different adhesive dowels

OBJECTIVE

Fiber-reinforced composite dowels are suggested to be a better alternative to metal dowels. This in vitro study evaluated the fracture resistance and fracture modes of teeth restored with nine different dowel systems.

MATERIALS AND METHODS

Ninety mandibular pre-molar teeth were decoronated and nine homogenous groups were composed. Root canal and dowel canal preparations were made and nine different dowel systems were used to fabricate restorations. Core build-ups were made with a composite resin core material. Specimens were mounted in acrylic resin blocks and continuous compressive force was applied until fracture occurred. Fracture resistance and fracture mode data were collected. One-sample Kolmogorov-Smirnov and one-way ANOVA tests were performed for the fracture resistance data of the groups.

RESULTS

There were no significant differences among the fracture resistances of the groups. All specimens of the pre-fabricated stainless steel dowel group fractured catastrophically. However, even in the worst-case, five specimens of the fiber-reinforced composite groups had favorable fracture modes.

CONCLUSIONS

The teeth restored with fiber reinforced composite dowels were as resistant to fracture as teeth restored with stainless steel dowels. Fracture modes of teeth restored with fiber reinforced composite dowels were more advantageous than teeth restored with pre-fabricated stainless steel dowels.

Influence of immediate dentin sealing techniques on cuspal deflection and fracture resistance of teeth restored with composite resin inlays

SUMMARY This research evaluated the influence of immediate dentin sealing (IDS) techniques on cuspal deflection and fracture resistance of teeth restored with composite resin inlays. Forty-eight maxillary premolars were divided into four groups: G1, sound teeth (control); G2, without IDS; G3, IDS with Clearfil SE Bond (CSE); and G4, IDS with CSE and Protect Liner F. The teeth from groups 2, 3, and 4 received mesio-distal-occlusal preparations. The impressions were made with vinyl polysiloxane, followed by provisional restoration and storage in water for seven days. The impressions were poured using type IV die stone, and inlays with Filtek Z250 composite resin were built over each cast. The inlays were luted with Panavia F. After storage in water for 72 hours, a 200-N load was applied on the occlusal surface using a metal sphere connected to a universal testing machine, and the cuspal deflection was measured with a micrometer. The specimens were then submitted to an axial load until failure. The following mean cuspal deflection (μm) and mean fracture resistance (N) followed by the same lowercase letter represent no statistical difference by analysis of variance and Tukey (p<0.05): cuspal deflection: G1, 3.1 ± 1.5(a); G2, 10.3 ± 4.6(b); G3, 5.5 ± 1.8(ac); and G4, 7.7 ± 5.1(bc); fracture resistance: G1, 1974 ± 708(a); G2, 1162 ± 474(b); G3, 700 ± 280(b); and G4, 810 ± 343(b). IDS with CSE allowed cuspal deflection comparable with that associated with sound teeth. The application of Protect Liner F did not contribute to a decrease in cuspal deflection. The IDS techniques did not influence the fracture resistance of teeth.