Retention strengths of five luting cements on prefabricated dowels after root canal obturation with a zinc oxide/eugenol sealer: 1. Dowel space preparation/cementation at one week after obturation

PURPOSE: This investigation examined the effect of 5 different cements on the retention strength of prefabricated endodontic dowels placed into root canals previously obturated with gutta percha and a zinc oxide/eugenol (ZOE) sealer. MATERIALS AND METHODS: Ninety-six single-rooted teeth were decoronated, filed, cleaned, sequentially shaped, and divided into 6 groups of 16 specimens each. Five of the groups were then obturated with gutta percha and a ZOE sealer. One group was not obturated and served as the control group. Dowel space preparation and dowel cementation for all groups were completed 1 week later. Ten-mm deep dowel spaces were prepared using size 6 Gates Glidden drills. Size 5 Paraposts were then cemented with 5 different cements: Panavia 21 for group 1 (unobturated controls) and group 2; Ketac-Cem glass ionomer for group 3; Fleck's zinc phosphate for group 4; Parapost (composite) Cement for group 5; and C&B Metabond 4-META for group 6. After 48 hours, the dowels were removed using a universal testing machine in tensile mode at 1 mm min(-1). RESULTS: The following results were found (all values in kg): group 1 (controls; Panavia 21) mean = 61.81, 95% CI = +/-8.65; group 2 (Panavia 21), mean=43.15, 95% CI = +/-7.81; group 3 (Ketac-Cem), mean =34.45, 95% CI = +/-4.93; group 4 (zinc phosphate), mean = 25.07, 95% CI = +/-5.03; group 5 (Parapost Cement), mean = 24.99, 95% CI = +/-5.35. None of the group 6 (C&B Metabond) specimens developed measurable bond strengths, so this group was excluded from parametric statistical analyses. An analysis of variance (ANOVA) showed a significant effect of group; pairwise multiple comparison procedures (Tukey test) showed that group 1 (controls) had significantly greater retention than all other groups (p <0.001); group 2 (Panavia 21) had significantly greater retention than groups 4 (zinc phosphate) and 5 (Parapost cement) (p <0.001). None of the other pairwise comparisons were statistically different. CONCLUSION: Paraposts cemented with Panavia 21 in unobturated root canals exhibited significantly higher retention than Paraposts luted with Panavia 21 and 4 different cements into dowel spaces prepared 1 week after obturation with gutta percha/ZOE sealer (p <0.001). Among the obturated groups, Panavia 21 cement (group 2) demonstrated significantly greater retention of Paraposts than zinc phosphate (group 4) and Parapost composite (group 5) cements (p <0.001). Ketac-Cem glass ionomer cement (group 3) had intermediate retention values that were not statistically different than those of groups 2, 4, and 5 (p >0.05). The 4-META cement, C&B Metabond, failed to polymerize.     

Effect of endodontic sealers on dowels luted with resin cement

PURPOSE: This study evaluated the retention of prefabricated parallel-sided dowels luted with resin cement in extracted teeth that were obturated with gutta percha using a eugenol sealer or a calcium hydroxide sealer. MATERIALS AND METHODS: Extracted maxillary incisor roots (N = 51) were instrumented to simulate conventional root canal therapy and divided into 3 groups (n = 17). One group was not obturated. Second and third groups were obturated with gutta percha using a eugenol-containing or calcium hydroxide-containing sealer. Gutta percha was removed using a heated plugger, and dowel spaces were prepared to a 7 mm depth. Dowel space walls were acid etched and primed, and prefabricated stainless steel dowels were luted using resin cement. After 24 hours, the load required to dislodge each dowel along a path parallel to its long axis was measured and recorded. A one-way analysis of variance (alpha = 0.05) was performed to identify differences in the means among groups. The incidence of failure within the cement or at the dentin-cement interface was also recorded. RESULTS: No statistically significant difference was found among the control (159.9 +/- 96.3 N), eugenol sealer (153.1 +/- 77.3 N), and calcium hydroxide sealer (192.0 +/- 89.3 N) groups. Nearly all specimens displayed adhesive failure at the dentin-resin cement interface. CONCLUSIONS: Conventional endodontic obturation using a eugenol-containing or a calcium hydroxide-containing endodontic sealer did not affect retention of prefabricated stainless steel dowels luted with resin cement.     

Effect of three root canal sealers on the retentive strength of endodontic posts luted with a resin cement

AIM: This investigation examined what effect three different sealers had on retention of endodontic posts (Parapost) luted with a resin cement (Panavia 21 OP). METHODOLOGY: Sixty-four single-rooted teeth were decoronated, filed, cleaned, and shaped with a size 5 Gates-Glidden drill and 0.12 taper G.T. rotary instrumentation (Dentsply/Tulsa Dental). Teeth were then divided into four groups of 16 each. Group 1 was not obturated, and served as a control. The other three groups were obturated with gutta-percha using a different sealer for each group. Group 2 used a eugenol containing sealer (Kerr Pulp Canal Sealer), group 3 a resin sealer (AH-26), and group 4 a calcium hydroxide sealer (Sealapex). After 1 week's storage at 100% humidity, 10-mm deep post spaces were prepared with a size 6 Gates-Glidden drill, and size 5 Paraposts were cemented. Following 48 h of storage, samples were mounted in a PVC pipe with acrylic, and the posts were removed vertically using a universal testing machine at 1 mm min-, with data recorded in kilograms. RESULTS: The mean values of force required to remove the posts were: group 1 = 61.80, SD = 16.21; group 2 = 43.14, SD = 14.66; group 3 = 48.54, SD = 17.84; group 4 = 53.52, SD = 18.77. Using anova and Bonferroni tests, group 1 demonstrated significantly greater mean retention strength values than group 2, but no other significant differences existed between groups. CONCLUSION: The chemical formulation of root canal sealers did not significantly affect the retention of endodontic posts luted with resin cement.     

Comparison of Two Luting Agents Used for the Retention of Cast Dowel and Cores

PURPOSE: The first purpose of this study was to compare the retentive values of zinc phosphate and Panavia F resin cements when used for luting cast dowel and cores. The second purpose was to determine whether the use of a lubricant when making the resin pattern for a custom dowel and core would have an effect on the final retention of dowels cemented with either zinc phosphate or Panavia F cements. METHODS AND MATERIALS: Sixty-three caries-free extracted single-rooted human teeth were randomly divided into three groups of 21. Root canal preparations were standardized for all 63 teeth. Clinical protocols for fabricating and cementing dowel and core restorations were examined, comparing zinc phosphate and Panavia F resin cements. Direct dowel patterns were fabricated using the Para Post system and cast in a noble metal alloy. Group I dowel spaces were lubricated with GC lubricant prior to dowel pattern fabrication and cleaned with Cavidry solvent before cementing the cast dowel and core with zinc phosphate cement. Group II dowel spaces were rinsed with water only prior to dowel pattern fabrication. The dowels and cores in this group were cemented with Panavia F resin cement. Group III dowel spaces were lubricated with GC lubricant prior to dowel pattern fabrication; the dowel spaces were cleaned with Cavidry solvent before the cast dowel and cores were cemented with Panavia F cement. The tensile force necessary to remove the cast dowel and cores was determined using a universal testing machine. Results were statistically analyzed using one-way ANOVA and Tukey's HSD test. RESULTS: The dowels and cores in Group I had significantly higher retentive values than either of the two Panavia F groups (p< or = 0.001). No difference in retentive values (p > 0.05) was found between dowels luted with either of the lubricating agents in the Panavia F groups. CONCLUSIONS: Zinc phosphate cement had higher retentive values when cementing cast dowel and cores than Panavia F. The type of lubricant used for the resin dowel fabrication (water or GC lubricant that was removed with a solvent) had no effect on the retention of cast dowels cemented with Panavia F.     

Effectiveness of hand and rotary instrumentation for removing a new synthetic polymer-based root canal obturation material (Epiphany) during retreatment

Aim To evaluate the effectiveness of hand and rotary instrumentation for removal of vertically compacted Epiphany and gutta‐percha during retreatment. Methodology Sixty extracted single‐rooted maxillary central incisors were enlarged to size 40 using FlexMaster instruments. The teeth were randomly divided into four groups of 15 specimens each. The canals of two groups were obturated using vertically compacted Epiphany. The others were filled with vertically compacted gutta‐percha and AH Plus sealer. One Epiphany group and one gutta‐percha group was reinstrumented with Gates Glidden burs and Hedström files. In the other two groups, obturation material was removed using Gates Glidden burs and RaCe rotary instruments. After clearing the roots, the area of remaining obturation material on the root canal wall was measured using a computer image analysis program. Statistical analysis was performed using Repeated Measures Analysis of Variance and anova . Results Retreatment of specimens obturated with gutta‐percha showed significantly more remaining obturation material than specimens filled with Epiphany (P < 0.05). No difference was found between the removal with Hedström files and with RaCe instruments (P > 0.05). Regarding the mean time of retreatment and time required for reaching the working length, Hedström files were significantly faster than RaCe instruments (P < 0.05). The times did not depend on the kind of obturation material (P > 0.05). Conclusions Vertically compacted Epiphany in combination with Epiphany Root Canal Sealant was removed more effectively than gutta‐percha and AH Plus sealer. Hedström files were more rapid than RaCe rotary instruments.     

An in vitro comparison of cast metal dowel retention using various luting agents and tensile loading

STATEMENT OF PROBLEM: No clear consensus exists regarding the choice of luting agents for the retention of cast metal dowels used as a treatment alternative for endodontically treated teeth with excessive loss of coronal tooth structure. PURPOSE: The purpose of this in vitro study was to investigate the retention of the dowel/luting agent/tooth complex while applying different luting agents to cast metal dowels under vertical tensile loading. MATERIAL AND METHODS: Sixty extracted, noncarious mandibular premolars with roots of approximately 15-mm length were selected. For each tooth, a tapered root canal preparation was completed to a maximum diameter of 1.60 mm and a length of 11 mm, a common clinical configuration to accommodate cast metal dowels. Sixty cast metal dowels were fabricated for the tooth specimens and cemented with 1 of 3 luting agents (n = 20): zinc-phosphate cement (ZPC) as a control, phosphate-methacrylate resin luting agent (PMRL, Panavia F), and phosphate-methacrylate resin luting agent with metal dowel surfaces modified with a silane coating technique (PMRLS, Panavia F + Siloc). Tensile bond strength (TBS) of the specimens was measured with a universal testing machine at a crosshead speed of 0.5 mm/min. Data (kg) were statistically analyzed using a 1-way analysis of variance and a Scheffe multiple range test (alpha=.05). The homogeneity of variances was analyzed using the Levene test. RESULTS: The TBS values of ZPC (34.2 +/- 10.54 kg) were significantly higher than PMRL (22 +/- 9.57 kg) and PMRLS (21.7 +/- 7.64 kg). There was no significant difference between the PMRL and PMRLS groups. CONCLUSION: Within the limitations of this study, the use of zinc-phosphate cement provided greater TBS for cast metal dowels than the resin luting agent with and without the silane coating technique. The TBS values with and without the silane coating technique were not statistically different.     

Effect of different root canal obturating materials on push-out bond strength of a fiber dowel

Purpose: During dowel space preparation, the instrumentation forms a thick smear layer along with sealer‐occluded dentinal tubules. The purpose of this study was to evaluate the effect of different obturating materials on push‐out bond strength of a fiber dowel. Materials and Methods: Fifty human uniradicular teeth were decoronated and prepared using the step‐back technique. The specimens were divided into five groups on the basis of obturating materials: group I received no obturation; group II (ZOE) gutta‐percha and zinc oxide eugenol sealer; group III (ZOAH) gutta‐percha and AH plus sealer; group IV (GF) GuttaFlow; and group V (RE) with Resilon Epiphany system. Dowel spaces were made with manufacturer's provided drills, and a fiber dowel was luted. Horizontal slices were obtained from the middle third, and push‐out bond strength (S) was evaluated. Statistical analysis was carried out using one‐way ANOVA and post hoc Tukey's test. Results: The push‐out bond strength values in the control group, ZOE, ZOAH, GF, and RE were 9.303 ± 0.565 MPa, 8.859 ± 0.539 MPa, 8.356 ± 0.618 MPa, 9.635 ± 0.435 MPa, and 8.572 ± 0.256 MPa, respectively. There was no statistically significant difference between the S values of all the groups (p > 0.05). Conclusion: There was no effect of different tested obturating materials on the push‐out bond strength of fiber dowels; however, further studies should be conducted.     

Effect of Obturating Systems,Dowel Materials,and Adhesive Luting Techniques on the Resistance to Fracture of Endodontically Treated Teeth

Purpose: The aim of this study was to assess the role of obturating systems, dowel materials, and adhesive techniques on the resistance to fracture of endodontically treated teeth. Material and Methods: Eighty maxillary central incisors were selected and randomly divided into two groups according to the obturating system (n = 40); group I: gutta‐percha and Roeko sealer; group II: RealSeal. Both groups were further subdivided into two subgroups; subgroup A: using ceramic dowels (Cosmopost); subgroup B using fiber dowels (Easy Post). Each subgroup was assigned to two divisions according to the adhesive luting technique; division V (total‐etch) Variolink II resin cement; division U (self‐adhesive) RelyX Unicem. Composite core build‐up was made using a core former. Each specimen was loaded 2 mm from its incisal edge on the palatal side at a 135° angle with the long axis of the tooth using a universal testing machine with a load cell of 5 KN at a crosshead speed of 0.5 mm/min until fracture. Failure loads were recorded in N. Scanning electron microscopic examination at the dentin/resin interface (1000x) was performed. Three‐way ANOVA was used to test the effect of obturating system, dowel material, adhesive technique, and their interactions (obturating system * dowel material, obturating system * adhesive, dowel material * adhesive, obturating system * dowel material * adhesive). Duncan's test was used for pairwise comparison. The significance level was set at p≤ 0.05. Statistical analysis was performed with SPSS 16.0. Results : The mean resistance to fracture (617.4 N) was statistically significantly higher in the ceramic dowel with gutta‐percha and Variolink (GP/C/V) group than in the other groups. The RealSeal and RelyX fiber dowel group's mean resistance was the lowest and was significantly lower than the other groups. Conclusions : In this study, three factors played a part in enhancing the resistance to fracture of endodontically treated teeth. High resistance to fracture was achieved when ceramic dowels were luted with total‐etch technique in gutta‐percha‐obturated teeth.     

Retention of fiber posts to the optimally and over-prepared dowel spaces

PURPOSE

To assess the retention of glass fiber post cemented with self-adhesive resin cement into optimum and over-prepared root canals following obturation in the presence of either eugenol (EB) or calcium hydroxide (CB)-based sealers.

MATERIALS AND METHODS

Roots of extracted premolars were endodontically-treated in 5 groups (n = 10). Roots of Group 1 (control) were left with no obturation and then optimally prepared to receive endodontic dowels. Other root canals were obturated with gutta-percha in the presence of either eugenol-based (Groups 2 and 4) or calcium hydroxide-based (Groups 3 and 5) sealer. Dowel spaces were prepared with optimal diameter in Groups 2 and 3, one size larger in Groups 4 and 5. Standardized fiber posts were luted to the prepared spaces using self-adhesive resin cement and itsretention was then tested on an universal testing machine. Both one-way ANOVA and Tukey''s HSD comparisons (α=0.05) were used to identifythe significance of inter-group retention differences. Scanning electron microscopy (SEM) of both optimally and over-prepared dowel spaces was also considered to figure the nature of their interior out.

RESULTS

The post retention was significantly higher to the non-obturated, optimally-prepared dowel spaces of Group 1 compared to the obturated, optimally-prepared ones of Groups 2 and 3. For each dowel space diameter, root canals obturated using CB of Groups 3 and 5 showed significantly higher dowel retention compared to those obturated using EB of Groups 2 and 4. Post retention to the over-prepared dowel spaces of Groups 4 and 5 was significantly higher than that recorded for the optimally-prepared ones of Groups 1-3. SEM images revealed traces of endodontic sealer and gutta-percha on the walls of the optimally-prepared dowel spaces.

CONCLUSION

Despite the adverse effect of endodontic sealers on the retention of fiber posts, the over-preparation of dowel spaces helps to improve the retention.     

The effect of two root canal sealers on the retentive strength of glass fibre endodontic posts

This study was undertaken to examine the effect of eugenol-containing and non-eugenol-containing root canal sealers on the retention strength of glass fibre endodontic posts (ParaPost Fibre White) luted with a resin cement (ParaPost cement). We also examined the mode of failure that occurred visually by using scanning electron microscopy. Seventy-two single rooted, recently extracted, premolar teeth were root canal treated and randomly divided into two groups. Group 1 was obturated with gutta percha and a calcium hydroxide-based sealer (Sealapex, Kerr). Group 2 was obturated with gutta percha and a eugenol-based sealer (Tubli-Seal Kerr). The teeth were stored for 1 week in distilled water at 37 degrees C and then prepared for 9 mm posts with a 1.40-mm drill. The matching glass fibre post was luted with a resin cement following the manufacturer's instructions. The samples were stored for 1 week and thermocycled. The posts were removed from the root canals using a calibrated testing machine in tensile mode. The mean dislodging force for group 1 was 190.46 N and for group 2 was 183.8 N, with standard deviations of 54.9 and 56.0 N respectively. The t-test indicated no significant difference between the two groups. Failure of the posts occurred mainly within the resin layer. This study showed that under experimental conditions there was no statistically significant difference between Sealapex sealer and Tubli-Seal sealer on the retention of glass fibre posts using a resin cement.     

Tensile bond strength of cast commercially pure titanium dowel and cores cemented with three luting agents

PurposeThe purpose of this study was to compare the tensile strength of commercially pure titanium dowels and cores cemented with zinc phosphate or resin cements.MethodsTwenty-one extracted human canines were endodontically treated. The root preparations were accomplished using Largo reamers (10 mm in depth and 1.7 mm in diameter). Acrylic resin patterns for the dowel and cores were made, and specimens were cast in commercially pure titanium (n = 7) and divided in three groups: TZ–CP Ti dowels luted with zinc phosphate luting agent, TP–CP Ti dowels luted with Panavia F and TR–CP Ti dowels luted with RelyX U100. Tensile strengths were measured in a universal testing machine at a crosshead speed of 0.5 mm/min. The results (N) were statistically analyzed by ANOVA and Tukey tests (α = 0.01).ResultsThe ANOVA indicated that there were significant differences among the groups tested. A Tukey multiple comparison procedure was performed and revealed statistically significant higher retention values for the dowel luted with RelyX U100 when compared with zinc phosphate or Panavia F.ConclusionCast commercially pure titanium dowels and cores fixed with RelyX U100 cement presented superior bond strength retention when compared to zinc phosphate and Panavia F.     

Comparison of titanium dowel retention using four different luting agents

STATEMENT OF PROBLEM: Luting material, surface properties, and loading conditions affect the retention of prefabricated dowels to varying degrees. PURPOSE: The purpose of this study was to evaluate the effect of roughening of the dentinal walls and artificial aging on the retention of prefabricated tapered titanium dowels, using 4 different luting materials. MATERIAL AND METHODS: One-hundred twenty-eight single-rooted teeth were selected, the coronal aspect of each tooth was removed, and the remaining root received endodontic therapy. All specimens were divided into 4 groups (n=32). Dowel spaces were prepared to a depth of 10 mm using ISO 90 rotary cutting instruments. Tapered titanium dowels were luted with the following luting materials: zinc-phosphate cement (Harvard cement), glass-ionomer cement (Ketac Cem EasyMix), resin composite luting agent (Panavia 21) with autopolymerizing dentin primer (ED-Primer), or a self-adhesive composite luting agent (RelyX Unicem). Both composite luting agents were used without acid etching of the canal dentin. Each luting agent was used under 2 conditions: in 1 subgroup (n=16) the dentinal walls were not roughened, and in the other subgroup (n=16), walls were roughened with a diamond rotary cutting instrument. Eight specimens from each subgroup were stored in water at 37 degrees C for 3 days; the other 8 specimens were stored for 150 days and subjected to simulated aging conditions using 37,500 thermal cycles (5 degrees C/55 degrees C) and 300,000 mechanical loading cycles with 30 N. Dowel retention (N) was measured using a universal testing machine with a crosshead speed of 2 mm/min. Data were analyzed using 2- and 3-way ANOVAs and the Tukey HSD test (alpha=.05). RESULTS: The dislodged dowels were examined microscopically to evaluate mode of failure. The nonroughened dentinal walls showed no significant differences between the different luting agents. Roughening the dentinal walls increased the retention significantly for all groups. This increase was significantly higher for the resin composite groups (P=.0001). Storage for 150 days with thermal cycling and mechanical loading caused a significant decrease in dowel retention (P=.001). The failure mode was purely adhesive at the luting material-dentin interface for all dowels cemented in nonroughened root canals. A mixed failure mode, adhesive at the luting material-dentin interface and cohesive in the luting material, was observed for dowels cemented in roughened root canals. CONCLUSION: Roughening the dentinal walls and the use of resin luting cements provided statistically significant increases in dowel retention values.     

In vitro assessment of retention of four esthetic dowels to resin core foundation and teeth

STATEMENT OF PROBLEM: Several new esthetic dowel systems are currently available for the restoration of endodontically treated teeth. These dowel systems enhance the esthetic quality of all-ceramic restorations better than metallic dowel systems. PURPOSE: The purpose of this study was to evaluate the retentive strength of composite and ceramic endodontic dowel systems to the tooth and to the core foundation. MATERIAL AND METHODS: The following dowel systems were tested: resin dowels (Fibrekor [FR]; Luscent [LU]; Twin Luscent Anchor [TLU]); ceramic dowels (Cerapost [CR]; Cosmopost [CO]); and a titanium dowel (ParaPost XH [Ti]). In Part I of the study, core retention was tested by forming Bis-Core resin (n=12) cores around dowels followed by separation using a universal testing machine. In Part II, 60 (n=12) extracted human canines were endodontically treated, and dowel spaces were prepared using the corresponding drill for each dowel system. Nine-millimeter resin and ceramic dowels were cemented with C & B resin luting agent. Additionally, 2 groups (n=12) of Ti dowels cemented with C & B resin luting agent and zinc phosphate luting agent served as control groups. Retention was tested using a universal testing machine to separate the dowels from teeth. One-way analysis of variance and Student Newman-Keuls tests were conducted for statistical analysis (alpha=.05). Surface texture of all dowel systems tested was examined using SEM at original magnification x25 and x250. RESULTS: Core retention of Ti was higher than all esthetic dowels tested (alpha<.05), but FR had higher core retention than the other esthetic dowels tested. Resin dowels had better retention to teeth than ceramic dowels (alpha<.05). CONCLUSION: The esthetic dowel systems were less retentive for the resin core material than the titanium control. Resin dowel systems were more retentive in the root than the ceramic dowels but were similar to the titanium control.     

A Comparison of the Retention of Three Endodontic Dowel Systems Following Different Surface Treatments

Purpose: Practitioners have several options during the selection of a dowel for core restoration, including metal and glass fiber materials. Retention of the cemented dowel is critical for the success of this type of restoration. The purpose of this in vitro study was to evaluate the effect of two surface treatments on the retention of three types of dowels placed into prepared canals with a resin cement.
Materials and Methods: Following the removal of the clinical crown, gutta percha was used to restore canals prepared to size 40 in 90 extracted human anterior teeth. The access openings were then sealed, and the teeth stored in water for 3 weeks at 37°C. Post preparations were made to a depth of 9 mm, and parallel ParaPost, FibreKleer, and FibreKor dowels were each used to restore 30 teeth. Ten dowels in each group received no surface roughening treatment, 10 were air abraded with 50 μ aluminum oxide, and 10 were air abraded with CoJet. The specimens were stored in water for 24 hours at 37°C following dowel placement and prior to debonding with an Instron Testing Machine.
Results: The forces (N) required in tensile load to dislodge the dowels for each group were: ParaPost/CoJet 214.04 ± 91.72, FibreKleer/AlOxide 196.07 ± 57.69, ParaPost/AlOxide 184.46 ± 35.05, FibreKleer/CoJet 176.36 ± 42.43, FibreKor/AlOxide 174.32 ± 53.64, ParaPost/Unroughened 174.14 ± 40.74, FibreKor/CoJet 167.16 ± 35.94, FibreKor/Unroughened 116.69 ± 37.01, and FibreKleer/Unroughened 96.88 ± 33.45. Post hoc analysis demonstrated that the unroughened FibreKor and FibreKleer dowels had significantly less retention than all other test groups ( p ≤ 0.05).
Conclusion: Surface roughening with air abrasion increases retention in dowels cemented with a resin cement. Both the aluminum oxide and CoJet systems were equally effective in this regard.     

Effect of eugenol-containing and resin endodontic sealers on retention of prefabricated metal posts cemented with zinc phosphate and resin cements

PurposeThe aim of this study was to compare the effects of two endodontic sealers on the retention of posts cemented with zinc phosphate or resin cement.Materials and methodsCrowns of 72 mandibular premolars were removed at the cementoenamel junction. Root canals were prepared and specimens were randomly divided into two groups of 36. In each group, 12 specimens were obturated with gutta percha only; 12 specimens with gutta percha/ZOE sealer and 12 specimens with gutta percha/AH26. In the first group, 10 mm Post spaces were prepared with Peeso reamers size 4 and, size 5 stainless steel Paraposts were cemented in with zinc phosphate. In the second group, 10 mm Post spaces were prepared with Fiber Lux size 5.5 drills and size 5 Paraposts were cemented with Panavia F_2.0. After mounting in resin blocks, posts were pulled out by universal testing machine at 1 mm/min and results were analyzed by two-way ANOVA and Dunnett test.ResultsMean forces (in Newtons) required to remove posts cemented with zinc phosphate in canals obturated without sealer, with ZOE, and with AH26 sealers were 270 ± 83, 281 ± 128 and 266 ± 67, respectively; and for posts cemented with Panavia F_2.0 were 520 ± 290, 464 ± 212 and 229 ± 108, respectively. Statistical analysis showed that AH26 significantly reduced retention of posts cemented with Panavia F_2.0 (p < 0.05).ConclusionDifferent sealers had no significant effect on retention of posts cemented with zinc phosphate. However posts cemented with Panavia F_2.0 showed reduced retention in canals obturated with AH26.     

Computed tomography assessment of three techniques for removal of filling material

In this study, computed tomography (CT) was used to assess three techniques for root canal filling removal. Seventy‐five roots of extracted human lower incisors were filled with zinc oxide‐eugenol sealer and gutta‐percha and separated into three groups before gutta‐percha removal (group 1, Gates Glidden burs + K‐type hand instrumentation; group 2, K‐type reciprocating instrumentation + NSK TEP E16R; group 3, ProTaper rotary instrumentation + NSK NAC E16R). Specimens were CT‐scanned before and after filling removal. The mean rate of filling removal was 94.88%. Reciprocating instrumentation was the most effective and manual instrumentation associated with Gates Glidden burs was the least effective technique. Removal rate was significantly different for the three groups according to one‐way anova (P = 0.049). The Tukey test showed a significant difference between groups 1 and 2 (P = 0.039) only. CT proved to be a reliable method for assessing root filling removal techniques.     

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 (alpha=.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.     

Residual dentin thickness in bifurcated maxillary premolars after root canal and dowel space preparation

Residual dentin thickness in 25 extracted bifurcated maxillary premolars after canal and Parapost preparation was assessed using acrylic muffle, after embedding in polyester resin and sectioned horizontally. After each procedure, the residual dentin thickness was compared to the original dentin thickness at eight aspects in three root levels. Residual dentin thickness measurements were calculated using photographs and a Digitizer. In the lingual aspect, the original dentin thickness averaged 0.99 mm (coronal slice) and 0.78 mm (middle slice). Dentin removal after dowel preparation was 31%. Three-way ANOVA with repeated measures was used. The difference in residual dentin thickness was highly significant regarding procedure (canal and dowel preparation, p < 0.0001), slice (middle, coronal, p < 0.0001), and the eight aspects (p < 0.0001). This in vitro study emphasizes the minimal dentin width of the buccal root, especially towards the bifurcation. Thus, dowels should be avoided in this root.     

Effect of an adhesive resin luting agent on the dowel-head retention of three different core materials

STATEMENT OF PROBLEM: A dowel-and-core restoration may fail due to failure at either the dowel-tooth or dowel head-core material interface. Long-term clinical success of a dowel-and-core restoration depends on retention of both the dowel to the tooth and the dowel head to the core material. Thus, strengthening of the dowel head-core interface is important. PURPOSE: This study evaluated the retention between a prefabricated dowel and 3 different core materials with or without a dual-polymerized adhesive resin luting agent. MATERIAL AND METHODS: Sixty prefabricated dowels (Gold Plated Anchorage Post) were divided into 3 groups (n=20) consisting of 1 of 3 core materials, amalgam (Standalloy F), light-polymerized resin composite (Clearfil Ray), or glass ionomer (Chelon-Silver). Each core group was divided into 2 subgroups (n=10), and a dual-polymerized adhesive resin luting agent (Panavia F) was applied to the dowel heads of 1 of these subgroups before application of the core material. The manufacturing procedure was standardized by using a plastic index (4.5-mm internal diameter and 5-mm height) and a custom-made dowel holder, which held the dowel head. Prepared specimens were stored in water at room temperature for 3 months and then loaded to fracture in a universal testing machine with a crosshead speed of 0.05 mm/min until failure. Bond strengths were recorded (MPa). Data were analyzed with 2-way analysis of variance (ANOVA) in a 2 x 3 factorial randomized design (alpha=.05). Afterward, core material differences were computed with 1-way ANOVA for both of the bonded and nonbonded groups. Post hoc multiple comparisons were made with the Dunnett C multiple range test. RESULTS: Dowel-head retention values (MPa) of the tested core materials (mean +/- SD) from the highest to the lowest were as follows: bonded amalgam core, 296.1 +/- 108; bonded composite core, 284.3 +/- 38.3; nonbonded composite core, 177.0 +/- 53.7; nonbonded amalgam core, 128.5 +/- 35.0; bonded glass-ionomer core (GIC), 128.0 +/- 24.5; nonbonded GIC, 61.8 +/- 13.3. Two-way ANOVA revealed significant differences between the core material groups and between the bonded and nonbonded groups (P <.001). The interaction between the core material and bond variables was also significant (P =.018). One-way ANOVA revealed statistically significant differences between the bonded (P <.001) and also between the nonbonded core material groups (P <.001). Post hoc multiple comparisons showed that the dowel-head retention of the GIC was significantly weaker than the post-head retention for amalgam and resin composite, whether bonded or not. CONCLUSION: Within the limitations of this study, the adhesive resin luting agent tested appeared to have a significant strengthening effect on the dowel-head retention of the core materials.     

Comparative evaluation of fracture resistance of structurally compromised canals restored with different dowel methods

Purpose: The objective of this in vitro study was to evaluate and compare the fracture resistance and fracture mode of endodontically treated teeth with wide root canals restored with various dowel methods. Materials and Methods: Fifty human uniradicular mandibular premolar teeth were decoronated and endodontically treated. The canals were widened with diamond points. The specimens were divided into five groups on the basis of type of dowel method used: conventional custom‐made cast metal dowel; single glass fiber‐reinforced resin dowel; glass fiber‐reinforced resin dowel with accessory fiber dowels; relined glass fiber‐reinforced resin dowel; and dowels formed with the help of polyethylene fiber ribbon‐reinforced resin composite. Specimens were restored with indirect composite crowns, and 150,000 cycles of cyclic loading were applied. The specimens were loaded to test the fracture resistance and fracture mode (repairable and nonrepairable). Results: The cast metal dowel groups had the highest fracture resistance but showed nonrepairable fracture in 90% of specimens. Conclusions: Cast metal dowels had the highest fracture resistance but led to nonrepairable fracture while restoring the wide root canals under cyclic loading. Specimens restored with fiber dowels, accessory dowels, relined dowels, and ribbon‐reinforced resin provided adequate fracture resistance with increased incidence of repairable fractures.