Glass Fiber Dowels Research Articles

Fatigue and failure analysis of restored endodontically treated maxillary incisors without a dowel or ferrule

Statement of problemInformation on the survival and mode of failure of endodontically treated incisors without a ferrule and restored without dowels is lacking. PurposeThe purpose of this in vitro study was to compare the survival and failure mode of endodontically treated incisors without a ferrule and restored with bonded ceramic crowns and various composite resin foundation restorations without dowels with a control group with fiber dowels. Material and methodsForty-five decoronated endodontically treated bovine incisors without ferrule were divided into 3 experimental groups and restored with different adhesive foundation restorations without dowel: nanohybrid composite resin (Nd), bulk-fill composite resin foundation restoration (NdB), and fiber-reinforced bulk-fill composite resin (NdFR). A control group with conventional foundation restorations (glass-fiber dowel with nanohybrid composite resin foundation restoration without ferrule) (D) was included for comparison. All teeth were prepared to receive bonded lithium disilicate ceramic crowns luted with dual-polymerizing composite resin cement and were subjected to accelerated fatigue testing. Cyclic isometric loading was applied to the incisal edge at an angle of 30 degrees and a frequency of 5 Hz, beginning with a load of 100 N (5000 cycles). A 100-N load increase was applied each 15 000 cycles. Specimens were loaded until failure or to a maximum for cycles endured of 1000 N (140 000 cycles). Groups were compared by using the Kaplan-Meier survival analysis (log rank test at α=.05 and pairwise post hoc comparisons) and life table analysis for load-at-failure (followed by Wilcoxon pairwise comparison α=.05). ResultsAll the specimens failed before 140 000 load cycles. Even though no statistically significant differences were found between the experimental groups without dowel (P>.127), the fiber-reinforced foundation restoration yielded the highest mean ±standard deviation cycles to failure (46 023 ±4326) compared with Nd (38 899 ±2975) and NdB (39 751 ±2998). NdFR, however, outperformed the foundation restoration with glass-fiber dowel (35 026 ±2687) (P<.05). Most failure in groups without dowel were restorable, while 100% of catastrophic failure (unrestorable) were found in the group with dowels. ConclusionsBased on the present in vitro study, dowels did not improve the performance of the adhesive restoration of endodontically treated incisors without a ferrule. The use of a short fiber-reinforced composite resin foundation restoration without a dowel was able to not only improve the resistance of the restorations compared with adhesive foundation restorations with dowels but also minimize catastrophic failures.

Effect of Apical Root Canal Perforation Size on Push-out Bond Strength of Glass Fiber Dowels

To evaluate in vitro effect of apical root canal perforation size on push-out bond strength of glass fiber dowels cemented to sound or perforated root canals using two different adhesive systems. A total of 120 human-extracted intact upper central incisors were selected. Teeth were sectioned 3 mm coronal to cement enamel junction, and the remaining root received endodontic root canal therapy. The roots were divided into two experimental groups according to the root condition: either sound (n = 40) or apically perforated (n = 80). Dowel spaces were prepared for all specimens to a depth of 10 mm. Roots were restored with glass fiber dowels. The experimental group was further subdivided into four subgroups (n = 20) according to the adhesive system used and apical perforation size: group I, perforated root 2 mm apically, dowel cemented using total-etch adhesive cement; group II, perforated root 2 mm apically, dowel cemented using self-etch adhesive cement; group III, perforated root 4 mm apically, dowel cemented using total-etch adhesive cement; and group IV, perforated root 4 mm apically, dowel cemented using self-etch adhesive cement. The control group, sound root, was divided into two subgroups: group I, sound root, dowel cemented using total-etch adhesive cement, and group II, sound root, dowel cemented using self-etch or total-etch adhesive cement. Each root was then cut horizontally, and root segments were prepared to be tested. The bond strength between dowel and dentin was measured with universal testing machine using a push-out test. The two-way analysis of variance (ANOVA) was used to analyze the data and post hoc Tukey's test (α = 0.05). Root canal perforation and the type of adhesive system used resulted in significant differences in push-out bond strength (p < 0.05). Regardless of root canal perforation size, glass fiber dowels in normal root canals had significantly higher mean bond strength values (9.2 ± 1.4 MPa) compared with perforated root canals (6.1 ± 1.4 MPa). Also, self-etch protocol had significantly higher mean bond strength values (9.1 ± 1.3 MPa) compared with total-etch protocol (6.2 ± 2.1 MPa). The apical root perforation size caused a direct effect on the bond strength of the glass fiber dowels cemented to dentin by reducing the bond strength values to the root dentin regardless of the adhesive system used. Prior to perforation repair, dentist or endodontist should evaluate the perforation size to predict the treatment outcome.

Evaluation of Fracture Resistance and Sites of Failure of Different Dowel Core Restorations: An In-Vitro Study

Background: Dowel Cores are often required in endodontically treated tooth to aid retention and resistance for a final prosthetic crown. Studies concerning the role of post-core systems on the fracture resistance with different dowel material remain controversial. Aim: This experimental study aimed to investigate the fracture resistance strength and failure mode of 3 dowel systems (glass fiber, indirect resin, and prefabricated metal with resin core). Methods: Twenty-one extracted human maxillary central incisors were first endodontically treated and then separated into 3 equal groups randomly;1st group consisted of glass fiber dowel, 2nd group consisted of indirect resin dowel, and 3rd group consisted of the prefabricated metal dowel. All specimens were restored with resin core and indirect resin crown. A testing force was applied with a universal testing machine (at 135 o angle) at 3 mm from the incisal edge of crown and forces were measured. Statistical tests were done using One-way ANOVA and Chi-square Test. Results: There was no significant difference (P-value &gt;0.05) of the fracture resistance among glass fiber dowel, indirect resin dowel and pre-fabricated dowel with indirect resin crown. The prefabricated metal dowel had maximum fracture resistance (566 ±157.771 N) followed by Glass fiber dowel (541.047 ±199.571 N) and indirect resin dowel and post (444.550 ±139.788 N). Conclusion: Glass fiber dowel, indirect resin dowel and prefabricated metal dowel with resin core and indirect resin crown systems showed statistically insignificant fracture strength values and mode of failure.

Detection of root fractures in glass fiber and metal cast dowel-restored teeth: Accuracy of Computed Tomography vs Digital Radiography

Objective: Detection of root fractures in dowel-restored teeth is challenging. Even though cone-beam computed tomography (CBCT) has shown higher sensitivity than intraoral radiography, artifacts may be generated in the presence of intraradicular posts. This study assessed the accuracy and reproducibility of CBCT and digital radiography (DR) in detecting root fractures in teeth restored with metal cast dowel and core (MCDC) or glass fiber dowel and resin composite core (GFDRCC). An additional aim was to evaluate the presence of beam hardening artifacts in CBCTs, especially in teeth restored with glass fiber dowel.Methods: Roots of bovine incisors were endodontically prepared, filled, sealed and randomly divided into two groups to receive MCCDC or GFDRCC (n=15). CBCTs and DRs were obtained prior to and after fracture induction.Results: CBCT were more accurate than DR in detecting root fractures in dowel-restored teeth. Beam hardening was observed in 100% of CBCT obtained from teeth restored with MCDC and in 93% of those in which GFDRCC had been used. Inter-observer agreement was moderate for both CBCT and DR images.Conclusion: Regardless of the dowel type, even though beam hardening had been observed in virtually all dowel-restored teeth, CBCT was the most accurate diagnostic tool in detecting root fractures.

Detection of root fractures in glass fiber and metal cast dowel-restored teeth: Accuracy of Computed Tomography vs Digital Radiography

Objective: Detection of root fractures in dowel-restored teeth is challenging. Even though cone-beam computed tomography (CBCT) has shown higher sensitivity than intraoral radiography, artifacts may be generated in the presence of intraradicular posts. This study assessed the accuracy and reproducibility of CBCT and digital radiography (DR) in detecting root fractures in teeth restored with metal cast dowel and core (MCDC) or glass fiber dowel and resin composite core (GFDRCC). An additional aim was to evaluate the presence of beam hardening artifacts in CBCTs, especially in teeth restored with glass fiber dowel.Methods: Roots of bovine incisors were endodontically prepared, filled, sealed and randomly divided into two groups to receive MCCDC or GFDRCC (n=15). CBCTs and DRs were obtained prior to and after fracture induction.Results: CBCT were more accurate than DR in detecting root fractures in dowel-restored teeth. Beam hardening was observed in 100% of CBCT obtained from teeth restored with MCDC and in 93% of those in which GFDRCC had been used. Inter-observer agreement was moderate for both CBCT and DR images.Conclusion: Regardless of the dowel type, even though beam hardening had been observed in virtually all dowel-restored teeth, CBCT was the most accurate diagnostic tool in detecting root fractures.

Push-out bonding strengths of four different dowel systems luted with two different adhesive systems

This in vitro study investigates the bonding capacity of resin cements to dowels, using the push-out bonding strength of four different dowel systems, namely, stainless steel dowels (SSD), resin-supported polyethylene fiber dowels (RSPFD), zirconia dowels (ZD), and superpost glass fiber dowels (GFD), luted in root canals, using two different resin cements, namely, Multilink Automix Cement and Clearfil Esthetic Cement. Ninety-six maxillary central incisor teeth were sectioned below the cementoenamel junction, and the roots were treated endodontically. Then the roots were placed into four groups, based on the dowel systems used. The roots were further placed into two subgroups, based on the cement type used as subgroup A and subgroup B. Push-out bonding tests were performed on the bonded specimens, which were cut into 1 mm thick sections. A two-way ANOVA test and Tukey’s HSD tests were performed. The push-out bonding strength values for SSD, ZD, and RSPFD were not significantly different (p > 0.05). The means for GFD were significantly higher than the means for ZD (p < 0.05) when Multilink Automix Cement was used. However, when Clearfil Esthetic Cement was used, the means for RSPFD were significantly higher (p < 0.001) than the means for the other systems. When Clearfil Esthetic Cement was used, the RSPF dowel system provided significantly higher bonding strength values than the other systems.

Microleakage of different dowel systems luted with resin cements

Aims: The purpose of this study was to compare microleakage of dowel systems: Stainless steel dowel system (SSD), resin-supported polyethylene fiber dowels (RSPFD), Zirconia dowels (ZD) and glass fiber dowels (GFD) luted with two different resin cements. Materials and Methods: The root canals of 96 teeth were restored and two resin cements (Multilink Automix and Clearfil Esthetic cement) were used in cementation procedure. Using the computerized fluid filtration method, microleakage of the specimens was measured at 1 week, and 6 months. Results: The data indicated that the microleakage values varied according to the luting cement used ( P P P > 0.05). Conclusion: Esthetic dowels tested exhibited less microleakage compared to stainless steel dowel system. Statistically, Multilink Automix cement showed higher microleakage than Clearfil Esthetic cement.

In vitro fracture resistance of glass-fiber and cast metal posts with different designs

PURPOSE: To evaluate the in vitro fracture resistance of roots with glass-fiber and metal dowels with different designs. METHODS: Fifty-endodontically treated maxillary central incisors were embedded in acrylic resin. Ten of them received only the coronary preparation, and the remaining forty were embedded (except for 4mm of the cervical area) after removing the clinical crowns. Specimens were divided into five groups (n=10): control (teeth with only coronary preparation), cylindrical cast dowel, conical cast dowel, cylindrical glass-fiber dowel and conical glass-fiber dowel. Specimens were subjected to an increasing compressive load (N) until fracture. RESULTS: ANOVA indicated significant difference (P<.05) among the groups, and the Tukey-Kramer´s test identified these differences. The control group (867±243 N) presented the highest values and was statistically similar to cylindrical glass-fiber dowel group (711±180 N). There is no significant difference among the metal dowel cylindrical (435±245 N) or conical (585±164 N) group and conical glass-fiber dowel (453±112 N). Cylindrical glass-fiber dowel (711±180 N) and conical cast dowel and core (585±164 N) groups had intermediate values and did not differ from each other. CONCLUSIONS: Cylindrical glass fiber dowels represent a viable alternative to the cast-metal dowel cylindrical or conical. Cylindrical glass fiber dowels also increase endodontically treated incisors' resistance to fracture.

Three-dimensional FEA of Effects of Two Dowel-and-Core Approaches and Effects of Canal Flaring on Stress Distribution in Endodontically Treated Teeth

The aim of this 3D finite element analysis (FEA) was to assess stress distribution and levels in endodontically treated teeth restored with two dowel-and-core systems with differing root canal configurations. Four 3D finite element models of a laser-digitalized maxillary central incisor embedded in alveolar bone were created. Internal morphology data and mechanical properties of the materials were obtained from the literature. Models included a (1) sound tooth (control) versus an endodontically treated maxillary central incisor with a crown ferrule preparation with two restorative approaches of a ceramic crown over a (2) gold alloy dowel-and-core or (3) glass-fiber dowels with composite cores (4) the latter with a flared root canal. A 100 N static load was applied in the center of the palatal surface at a 45° angle, and the stress distribution pattern was analyzed using ANSYS(®) software. In Model 1 (control), maximum stresses occurred at the coronal third of the buccal (2.32 × 10(7) Pa) and palatal aspects of dentin. The stress peak value of the model (2.45 × 10(7) Pa) occurred on the palatal aspect of the enamel at the level of the cementoenamel junction. With the insertion of dowels with thin cement layers (Models 2 and 3), stress concentrations in radicular dentin decreased, while they increased in the dowel/cement/dentin interface. These models exhibited the greatest stress peak values in the incisal margin of the gold alloy core (18.9 × 10(7) Pa) and in the cement layer (4.7 × 10(7) Pa). In Model 4, stress peak value was observed in the porcelain crown (4.62 × 10(7) Pa), and there was no stress concentration inside the cement layer. Within the limits of this study, the results suggest that the use of dowels and cements with mechanical properties similar to those of dentin, and an increased cement layer thickness, results in mechanical behavior similar to the physiological behavior of a sound tooth.

Sealing Ability of Three Fiber Dowel Systems

To study the sealing ability of two new fiber dowel systems. Thirty-six extracted single-rooted teeth were endodontically treated and randomly assigned to two new fiber dowel systems and a control group: (1) an E-glass-based dowel, everStick-POST, cemented with ParaCem Universal DC resin cement (EV); (2) a glass-fiber dowel, RelyX Fiber Post, cemented with RelyX Unicem self-adhesive resin cement (RX). The control group was restored with a glass-fiber dowel, ParaPost Fiber Lux, cemented with ParaCem Universal DC resin cement (PP). The roots were isolated and immersed in a 50 wt% ammoniacal silver nitrate solution for 24 hours followed by 8 hours in a photo-developing solution. The roots were sectioned in 1-mm-thick disks perpendicular to the long axis of the root. The specimens were processed for backscattered FESEM observation. For each tooth, the depth of silver infiltration into the root canal was measured by ranks from 0 to 8. For each disk, silver infiltration was measured as the percentage of leakage around the adhesive interface. Data were analyzed with Kruskal-Wallis nonparametric tests at a significance level of 95%. When the silver infiltration was computed from the coronal to the apical aspects of the root, RX resulted in the lowest degree of silver infiltration, but not statistically different from that of EV (p < 0.148). RX, however, resulted in a lower depth of silver infiltration than the control group PP at p < 0.023. EV resulted in a statistically similar depth of penetration to PP (p= 0.492). Although the total mean percentage of silver infiltration at the dentin-resin cement interface was statistically similar for all groups (p= 0.632), EV resulted in the greater number of disks with silver infiltration (23 out of 96), followed by PP (21 out of 96) and RX (14 out of 96). None of the specimens showed leakage around the dowel-resin cement interface. The use of the E-glass dowels in EV did not improve the root-wall sealing ability compared with the control group PP. The system RX, which uses a new simplified self-adhesive protocol, resulted in a lower depth of silver infiltration than the control group PP.

A Systematic Review of Dowel (Post) and Core Materials and Systems

The aim of this systematic review was to determine which dowel (post) and core system is the most successful when used in vivo to restore endodontically treated teeth. A MEDLINE, a Cochrane, and an EMBASE search (three specified searches) were conducted to identify randomized (RCT) and nonrandomized controlled clinical trials (CCT), cohort (CS), and case control studies (CCS) until January 2008, conducted on humans, and published in English, German, and French, relating to dowel and core systems for restoring endodontically treated teeth. Also, a hand search was conducted, along with contact with the authors when needed. The MEDLINE, Cochrane, and EMBASE searches identified 997, 141, and 25 published articles, respectively. Ten articles from the MEDLINE and seven articles from the Cochrane search (that were also identified in the MEDLINE search) met the inclusion and validity assessment criteria. Six out of the ten studies were RCTs, two were CCTs, and two CSs. The RCT studies suggest that carbon fiber in resin matrix dowels are significantly better than precious alloy cast dowels (number needed to treat, NNT = 8.30). Tapered gold alloy cast dowels are better than ParaPost gold alloy cast dowels (NNT = 13.15). ParaPost prefabricated dowels are slightly better than ParaPost cast dowels (NNT = 175.4). Glass fiber dowels are significantly better than metal screw dowels (NNT = 5.46), but worse than titanium (NNT =-21.73) (moderately). Carbon fiber dowels are worse than gold alloy cast dowels (significantly) (NNT =-5.81) and than amalgam dowels (NNT =-125) (slightly). The CCT studies suggest that metal dowels are better (NNT = 21.73) but also worse than cast dowels (NNT =-33.33) depending on the remaining amount of coronal hard tissue. Quartz fiber dowels show success rates similar to and worse than glass fiber-reinforced dowels (NNT =-37.03). The results from the CS studies suggest that carbon fiber in resin matrix dowels are better (moderately) than carbon fiber + quartz and quartz fiber dowels. Titanium dowels with a composite build-up are better (moderately) than gold alloy cast dowels. According to the studies of the highest levels of evidence, carbon fiber in resin matrix dowels are significantly better than precious alloy cast dowels (RCT). Glass fiber dowels are significantly better than metal screw dowels (RCT) and moderately better than quartz fiber dowels (CCT). Carbon fiber dowels are significantly worse than metal dowels (of precious alloy) (RCT). Prefabricated metal dowels are slightly better than cast dowels (RCT), but moderately worse when no collar of the dentin above the gingiva could be achieved (CCT).

Microtensile Bond Strength of Nonmetallic Dowels Bonded to Radicular Dentin with Self‐Etch Adhesives

The bonding potential of nonmetallic dowels to root dentin, particularly with new self-etch adhesives, has not been fully investigated. The aim of this study was to determine microtensile bond strength (microTBS) of nonmetallic dowels, including a novel glass fiber dowel, when bonded to radicular dentin with self-etch adhesives. Crowns of extracted anterior teeth were severed, and endodontic treatment was performed. Teeth were divided into six groups according to dowel/adhesive. Teeth received dowels as follows: group I: Light Post + Clearfil-SE Bond/Panavia-F (SE/PF), group II: Light Post + Xeno III/Panavia-F (XN/PF), group III: ParaPost Fiber White + SE/PF, group IV: ParaPost Fiber White + XN/PF, group V: everStick Post + SE/PF, and group VI: everStick Post + XN/PF. Teeth were sectioned to produce 1 mm specimens from both cervical and middle thirds with the dowel at the center. Specimens were tested in a special machine, and microTBS values were determined. Mean microTBS values and SDs in MPa for the cervical region were as follows: group I: 10.36 (1.88), group II: 8.51 (1.41), group III: 11.61 (1.06), group IV: 9.37 (1.61), group V: 14.22 (1.16), and group VI: 12.97 (1.69). Group V had the highest mean value-significantly higher than the means of groups I, II, III, and IV (p < 0.0001 to p < 0.02). For the middle region: group I, 9.72 (1.61); group II, 7.62 (1.42); group III, 10.28 (0.75); group IV, 8.48 (1.51); group V, 13.23 (1.06); group VI, 11.07 (1.49). Group V also had highest mean value-significantly higher than the means of groups I, II, III, and IV (p < 0.0001 to p < 0.004). everStick glass fiber dowel, bonded with either adhesive, showed the highest microTBS. Microtensile bond strengths were not significantly different with cervical root dentin than with middle root dentin.

Microleakage of endodontically treated teeth with different dowel systems

Statement of problem Several new esthetic dowel systems are available for the restoration of endodontically treated teeth, but little is known about how effectively these dowels seal the restored teeth. Purpose The purpose of this in vitro study was to compare microleakage of 3 esthetic, adhesively luted dowel systems with a conventional dowel system. Material and methods The root canals of 41 human intact single-rooted extracted teeth were prepared using a step-back technique. The teeth were randomly divided into 4 experimental groups (n=10), and 1 tooth served as a positive control. The decoronated roots were obturated with gutta-percha using lateral condensation. Roots were restored with 1 of the following dowel systems according to the manufacturer's instructions: (1) stainless steel dowels (ParaPost), (2) glass fiber dowels (Snowpost), (3) resin-supported polyethylene fiber (Ribbond) dowels, or (4) zirconia dowels (Cosmopost). Using a fluid filtration method, coronal leakage of the specimens along the dowel space and root canal restorative material was measured. Fluid movement measurements were made at 2-minute intervals for 8 minutes to measure the presence of voids existing in the obturated canals, at 1 week, 3 months, and 6 months following dowel insertion. A repeated-measures analysis of variance (ANOVA) was used to analyze logarithmic transformations of data (time and dowel material) for significant differences. The Tukey HSD test and paired 2-tailed tests were used to perform multiple comparisons (α=.05). Results The data indicated that the leakage values varied according to the dowel system used ( P<.01). There was significant interaction between dowel systems and time of testing ( P<.01). The sealing ability of zirconia dowels decreased over time ( P<.01), but sealing abilities of stainless steel and resin-supported polyethylene fiber dowels remained constant ( P>.05). The sealing ability of glass fiber dowels increased at 3 months ( P=.032) and remained constant over the next 3 months ( P=.758). Statistically, resin-supported polyethylene fiber and glass fiber dowels showed the lowest coronal leakage when compared with stainless steel and zirconia dowels at all time periods ( P<.01). There were no significant differences between resin-supported polyethylene fiber and glass fiber dowels at any time period. The initial leakage measurement in zirconia dowel and stainless steel dowels were similar ( P=.914), but became significantly different at 3 and 6 months ( P<.01). Conclusion Resin-supported polyethylene fiber dowels and glass fiber dowels tested exhibited less microleakage compared to zirconia dowel systems. The latter system should be further evaluated because of its unacceptable level of leakage.

An in vitro study evaluating the effect of ferrule length on fracture resistance of endodontically treated teeth restored with fiber-reinforced and zirconia dowel systems

Statement of problem There are few published studies analyzing the effects of different ferrule lengths of endodontically treated teeth in relationship to newly developed fiber-reinforced and zirconia dowel systems. Purpose This in vitro study compared the effect of 3 different ferrule lengths on the fracture resistance and fracture patterns of crowned endodontically treated teeth restored with 4 different esthetic dowel systems. Material and methods The crowns of 123 human maxillary canines were removed at the cementoenamel junction and the roots were endodontically treated. Three master tooth models were prepared to ferrule lengths of 1.0 mm, 1.5 mm, and 2.0 mm to produce 3 master analogs. Each root was embedded in autopolymerizing resin with a 0.2-mm layer of silicone impression material to simulate the periodontal ligament. Forty analogs of each master tooth, with ferrule lengths of 1.0 mm, 1.5 mm, and 2.0 mm were produced with copy-milling (Celay system). Each group was further subdivided into 4 groups of 10 specimens each and restored with 4 different esthetic dowel systems (quartz fiber, glass fiber, glass fiber plus zirconia, and zirconia). All dowels were luted with adhesive resin cement (RelyX ARC), restored with composite cores (Valux Plus), and Ni-Cr alloy (Wiron 99) complete crowns. All specimens were loaded at 130 degrees to the long axes in a universal testing machine at a crosshead speed of 1 mm/min until fracture. Fracture patterns were classified as failures above or below the incisal third of the roots. The data were analyzed with 2-way ANOVA and Tukey HSD tests (α=.05). A Fisher exact test was conducted for evaluation of the mode of failure (α=.05). Results Mean failure loads (kg) for quartz fiber, glass fiber, glass fiber plus zirconia, and zirconia groups, respectively, with the 3 ferrule lengths were: 1.0-mm ferrule specimens: 98.09 ± 2.90, 85.36 ± 2.82, 80.24 ± 1.88, 70.11 ± 2.48; 1.5-mm ferrule specimens: 101.0 ± 2.88, 87.58 ± 2.83, 89.8 ± 2.09, 82.71 ± 2.14; 2.0-mm ferrule specimens: 119.5±1.78, 99.84±1.23, 98.6 ± 1.64, 95.42 ± 1.02. Teeth prepared with 2.0-mm ferrules demonstrated significantly higher fracture thresholds ( P<.001). There were no significant differences in fracture patterns. Conclusion Increasing the ferrule length of the endodontically treated teeth from 1 mm to 1.5 mm in specimens restored with quartz-fiber and glass-fiber dowels did not produce significant increases in the failure loads ( P=.084, P=.119, respectively). No significant difference was detected between glass-fiber and glass-fiber plus zirconia dowels with 1.5-mm and 2.0-mm ferrules ( P=.218, P=.244, respectively). However, fracture thresholds were higher for all 4 dowel systems when the specimens were prepared with a 2.0-mm ferrule length ( P<.001).

Malleable cast iron—Its history in the United States

There are few published studies analyzing the effects of different ferrule lengths of endodontically treated teeth in relationship to newly developed fiber-reinforced and zirconia dowel systems.This in vitro study compared the effect of 3 different ferrule lengths on the fracture resistance and fracture patterns of crowned endodontically treated teeth restored with 4 different esthetic dowel systems.The crowns of 123 human maxillary canines were removed at the cementoenamel junction and the roots were endodontically treated. Three master tooth models were prepared to ferrule lengths of 1.0 mm, 1.5 mm, and 2.0 mm to produce 3 master analogs. Each root was embedded in autopolymerizing resin with a 0.2-mm layer of silicone impression material to simulate the periodontal ligament. Forty analogs of each master tooth, with ferrule lengths of 1.0 mm, 1.5 mm, and 2.0 mm were produced with copy-milling (Celay system). Each group was further subdivided into 4 groups of 10 specimens each and restored with 4 different esthetic dowel systems (quartz fiber, glass fiber, glass fiber plus zirconia, and zirconia). All dowels were luted with adhesive resin cement (RelyX ARC), restored with composite cores (Valux Plus), and Ni-Cr alloy (Wiron 99) complete crowns. All specimens were loaded at 130 degrees to the long axes in a universal testing machine at a crosshead speed of 1 mm/min until fracture. Fracture patterns were classified as failures above or below the incisal third of the roots. The data were analyzed with 2-way ANOVA and Tukey HSD tests (α=.05). A Fisher exact test was conducted for evaluation of the mode of failure (α=.05).Mean failure loads (kg) for quartz fiber, glass fiber, glass fiber plus zirconia, and zirconia groups, respectively, with the 3 ferrule lengths were: 1.0-mm ferrule specimens: 98.09 ± 2.90, 85.36 ± 2.82, 80.24 ± 1.88, 70.11 ± 2.48; 1.5-mm ferrule specimens: 101.0 ± 2.88, 87.58 ± 2.83, 89.8 ± 2.09, 82.71 ± 2.14; 2.0-mm ferrule specimens: 119.5±1.78, 99.84±1.23, 98.6 ± 1.64, 95.42 ± 1.02. Teeth prepared with 2.0-mm ferrules demonstrated significantly higher fracture thresholds (P<.001). There were no significant differences in fracture patterns.Increasing the ferrule length of the endodontically treated teeth from 1 mm to 1.5 mm in specimens restored with quartz-fiber and glass-fiber dowels did not produce significant increases in the failure loads (P=.084, P=.119, respectively). No significant difference was detected between glass-fiber and glass-fiber plus zirconia dowels with 1.5-mm and 2.0-mm ferrules (P=.218, P=.244, respectively). However, fracture thresholds were higher for all 4 dowel systems when the specimens were prepared with a 2.0-mm ferrule length (P<.001).