Tensile bond strength of cast commercially pure titanium and cast gold-alloy posts and cores cemented with two luting agents

STATEMENT OF PROBLEM: In vitro studies on the retentive strengths of various cements used to retain posts have reported conflicting results. PURPOSE: The purpose of this study was to compare the tensile strength of commercially pure titanium and type III cast gold-alloy posts and cores cemented with zinc phosphate or resin cement. MATERIAL AND METHODS: Forty-two 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 posts and cores were made, and specimens were cast in commercially pure titanium and in type III gold alloy (n=7). Fourteen titanium cast posts and cores were submitted to surface treatment with Kroll acid solution and to scanning electron microscopy (SEM), before and after acid etching. The groups (n=7) were cemented with zinc phosphate cement or resin cement (Panavia F). Tensile strengths were measured in a universal testing machine at a crosshead speed of 0.5 mm/min. The results (Kgf) were statistically analyzed by 2-way ANOVA (alpha=.05). RESULTS: The 2-way ANOVA indicated that there were no significant differences among the groups tested. Retentive means for zinc phosphate and Panavia F cements were statistically similar. The bond strength was not influenced by the alloy, the luting material, or the etching treatment. SEM analysis indicated that the etched surfaces were smoother than those that did not receive surface treatment, but this fact did not influence the results. CONCLUSIONS: Commercially pure titanium cast posts and cores cemented with zinc phosphate and resin cements demonstrated similar mean tensile retentive values. Retentive values were also similar to mean values recorded for cast gold-alloy posts and cores cemented with zinc phosphate cement and resin cements.     

Seating and retention of complete crowns with a new adhesive resin cement.

The retentive property of cast gold complete crowns cemented with an adhesive resin cement (Panavia Ex) was compared with retention of crowns cemented with zinc phosphate cement (Flecks) and the conventional resin cement (Comspan). The effect of these agents on seating of crowns also was evaluated. Panavia cement exhibited the highest retentive strength, with values almost twice those obtained with zinc phosphate cement. However, the difference in mean retention values of crowns cemented with Comspan cement or with zinc phosphate cement was not statistically significant. Both resin cements used in this study provided better seating of crowns than did zinc phosphate 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.     

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.     

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.     

Effect of dowel space preparation and composite cement thickness on retention of a prefabricated dowel

PURPOSE: This investigation examined what effect cement thickness had on retention of prefabricated endodontic dowels luted with a composite resin cement (Panavia 21 OP; J Morita, Irvine, CA) into canals previously obturated with gutta percha and a eugenol-based sealer. MATERIALS AND METHODS: Sixty-four single-rooted teeth were decoronated, filed, cleaned, and sequentially shaped with sizes 2-5 Gates Glidden drills (Dentsply/Maillefer, Tulsa, OK) and 0.12 taper rotary instrumentation. Teeth were then divided into 4 groups of 16 specimens each. All specimens were obturated with gutta percha and a eugenol-based sealer. Dowel space preparation and dowel cementation were completed 1 week after obturation. Ten-millimeter-deep dowel spaces were prepared using dowel drills with 4 different diameters: size 5 Parapost drill (Group 1; Coltene/Whaledent, Mahwah, NJ); size 5.5 Parapost drill (Group 2; Coltene/Whaledent); size 6 Gates Glidden drill (Group 3; Dentsply/Maillefer); size 6 Parapost drill (Group 4; Coltene/Whaledent). Size 5 Paraposts were then cemented with Panavia 21 OP. After 48 hours of storage, specimens were mounted in polyvinyl chloride (PVC) pipe with acrylic, and the dowels were removed in tensile mode using a universal testing machine at 1 mm/min, with data recorded in kilograms. RESULTS: (all values in kilograms) Group 1 (Parapost 5) mean = 15.07, 95% confidence interval (CI) = +/-6.11; Group 2 (Parapost 5.5) mean = 25.60, 95% CI = +/-7.39; Group 3 (Gates-Glidden 6) mean = 43.15, 95% CI = +/-7.81; Group 4 (Parapost 6) mean = 37.75, 95% CI = +/-6.35. Analysis of variance and Bonferroni tests revealed that Group 3 had significantly greater mean retention strength values than Group 1 and Group 2 (p <.05), and that Group 4 had significantly greater mean retention strength values than Group 1 (p <.05). CONCLUSIONS: Paraposts cemented with Panavia 21 OP showed significantly greater retention in oversized dowel spaces compared with dowel spaces prepared with the manufacturers' matched dowel-drill set.     

Retention of endodontic dowels: effects of cement, dowel length, diameter, and design.

The retentive capacity of three preformed endodontic dowel designs was compared at two lengths and two diameters, with three different cements. The greatest single factor influencing retention of these devices was the design used. Of the types tested in this study, the most retentive were threaded, parallel-sided dowels screwed into tapped channels. Serrated, parallel-sided dowels cemented in matched cylindrical channels provided intermediate retention, and smooth-sided tapered posts were the least retentive. Another major factor in retention was the length of imbedment into dentin. An increase in dowel imbedment depth usually corresponded to increased retention. The effect of cement type was significant only with tapered dowels. Zinc phosphate cement was most retentive, carboxylate cement exhibited intermediate retention, and the epoxy cement was least retentive. For the other post designs, cement type had no significant effect on retentive capacity. Finally, variations in dowel diameter had no significant effect on retentive ability.     

Microleakage and marginal gap of adhesive cements for noble alloy full cast crowns

Very limited comparative information about the microleakage in noble alloy full cast crowns luted with different types of adhesive resin cements is available. The purpose of this study was to evaluate the microleakage and marginal gap of two self-adhesive resin cements with that of other types of adhesive luting cements for noble alloy full cast crowns. Fifty noncarious human premolars and molars were prepared in a standardized manner for full cast crown restorations. Crowns were made from a noble alloy using a standardized technique and randomly cemented with five cementing agents as follows: 1) GC Fuji Plus resin-modified glass ionomer cement, 2) Panavia F 2.0 resin cement, 3) Multilink Sprint self-adhesive resin cement, 4), Rely X Unicem self-adhesive resin cement with pretreatment, and 5) Rely X Unicem with no pretreatment. The specimens were stored in distilled water at 37°C for two weeks and then subjected to thermocycling. They were then placed in a silver nitrate solution, vertically cut in a mesiodistal direction and evaluated for microleakage and marginal gap using a stereomicroscope. Data were analyzed using a nonparametric Kruskal-Wallis test followed by Dunn multiple range test at a p<0.05 level of significance. The Rely X Unicem (with or with no pretreatment) exhibited the smallest degree of microleakage at both tooth-cement and cement-crown interfaces. The greatest amount of microleakage was found for Panavia F 2.0 resin cement followed by GC Fuji Plus at both interfaces. No statistically significant difference in the marginal gap values was found between the cementing agents evaluated (p>0.05). The self-adhesive resin cements provided a much better marginal seal for the noble alloy full cast crowns compared with the resin-modified glass ionomer or dual-cured resin-based cements.     

Comparison of the tensile bond strengths of cast metal crowns luted with resin cements

The limitation of photoactivation of dual-polymerized resin cements along the margins of metal restorations may adversely affect the mechanical properties of these cements, thus impairing the retention of restorations. The aim of this study was to assess the bond strength of cast metal crowns cemented with three dual-polymerized resin cements, using a chemically-activated resin cement and zinc phosphate as controls. Fifty nickel-chromium alloy crowns were cast and randomly assigned to five groups of equal size. Castings were cemented on their corresponding metal dies with one of the tested luting agents: Scotchbond Resin Cement, Enforce and Panavia F (dual-polymerized resin cements), Cement-It (chemically-activated resin cement) and Zinc Phosphate Cement (zinc phosphate cement). Specimens were stored in distilled water at 37 degrees C for 24 h and then loaded in tension until failure. Panavia F and Zinc Phosphate Cement provided the highest and lowest bond strength means, respectively. Scotchbond Resin Cement, Enforce and Cement-It cements exhibited similar intermediate values, but with statistically significant difference compared to the other materials (P < 0.05). Even with the restriction or absence of light activation, all tested dual-polymerized resin cements produced significantly higher bond strength than did the zinc phosphate cement and yielded similar or better results than the chemically activated cement. It should be pointed out that the findings of this study relate to a test scenario which does not mimic clinical circumstances and that further work is required to identify the clinical significance of the reported tensile bond strength differences between the different luting materials.     

Effect of surface roughness and cement space on crown retention.

The effects of varying luting agent space and internal surface roughness with different types of cores and cements were studied. One hundred eighty amalgam and 180 composite cores were cemented into standardized stainless steel retainers. Cores and retainers were divided into 12 groups according to core type, core diameter, and retainer roughness. Each group was further subdivided according to cement, A: zinc phosphate (ZOP); B: resin; and C: glass ionomer cement (GIC). Subgroups were divided into thermal-cycled and nonthermal-cycled groups. Thermal cycling was at 5 degrees to 55 degrees C, repeated 500 times. Cores were separated from their retainers with a compression rod in an Instron testing machine at a crosshead speed of 0.02 cm/minute. Results were as follows: Amalgam cores were most retentive. Resin and ZOP cements were equally retentive with amalgam cores, but GIC was less retentive. Resin cores cemented with resin cement were more than twice as retentive than those cemented with ZOP or GIC cements. Retainers with rough internal surfaces were most retentive. A reduced cement space between core and retainer was most retentive. Thermal cycling reduced retention.     

Comparative study of luting agents with composite resin cores

This study compared bond strengths of zinc phosphate and polycarboxylate cements in cementing cast gold crowns to composite resin cores. The study also compared the effect of thermocycling on the bond strengths in tension of the two cements under varied storage and thermocycling conditions. Sixty standard cores were made from composite resin material. Gold alloy crowns were cast for each core and cemented with zinc phosphate or polycarboxylate cement. The samples were stored for 1 day or 1 month and then cycled with 60-second dwell times between 5 degrees C and 55 degrees C distilled water baths for 5, 100, or 1000 cycles. The controls were stored for the same periods and were not cycled. Overall comparison of both storage periods and all cycled and noncycled groups revealed that zinc phosphate cement had significantly higher bond strengths than polycarboxylate cement. Increasing the storage time before cycling significantly increased the bond strengths for both cements. There was no difference between any of the cycle periods or the noncycled controls for either cement.     

Fatigue resistance of endodontically treated teeth restored with three dowel-and-core systems

STATEMENT OF PROBLEM: The successful restoration of endodontically treated teeth is enhanced by a crown design employing the ferrule effect. However, it is unclear which dowel-and-core system most effectively supports successful treatment. PURPOSE: The purpose of this study was to compare the load fatigue resistance of 3 dowel-and-core systems. MATERIAL AND METHODS: Fifteen endodontically treated maxillary central incisors were sectioned perpendicular to the long axis at a point 1.5 mm incisal to the cemento-enamel junction (CEJ). At the level of the CEJ, specimens were then prepared for crowns with 1-mm complete shoulder finish lines and 1.5 mm of axial wall height. The prepared teeth were divided into 3 groups (n=5) and restored with 1 of the following dowel-and-core combinations: Group CG, cast gold dowels and cores; Group TA, titanium alloy dowels (ParaPost XH) with composite cores; or Group FR, fiber-reinforced resin dowels (ParaPost FiberWhite) with composite cores. A dentin bonding agent (OptiBond Solo) was placed prior to the composite cores. Dowel-and-core castings and titanium alloy dowels were cemented with zinc phosphate cement. The fiber-reinforced dowels were cemented with a resin cement (ParaPost Cement). The crowns for all specimens were cast with an incisal notch for applying the fatigue load. The independent variable measured was the number of load fatigue cycles required to cause luting cement failure. The data were subjected to 1-way analysis of variance and the Student-Newman-Keuls test for 3 subsets (alpha=.05). RESULTS: The mean value+/-standard deviation for the cycles to failure for each group was: Group CG: 11,897+/-4080 load cycles, Group TA: 24,384+/-8231 load cycles, and Group FR: 50,696+/-7063 load cycles. Significant differences were found between all groups ( P<.05). CONCLUSIONS: Fiber-reinforced resin dowels and bonded composite cores under fatigue loading provided significantly stronger crown retention than cast gold dowels and cores and titanium alloy dowels with composite cores under fatigue loading.     

The use of reinforced composite resin cement as compensation for reduced post length

STATEMENT OF PROBLEM: Cements that yield high retentive values are believed to allow use of shorter posts. PURPOSE: This study investigated the use of reinforced composite resin cement as compensation for reduced dowel length. MATERIAL AND METHODS: The retention values of stainless steel posts (parallel-sided ParaPost and tapered Dentatus in 5-, 8-, and 10-mm lengths) luted with Flexi-Flow titanium-reinforced composite resin and zinc phosphate cements were evaluated. Single-rooted extracted human teeth with crowns (n = 120), removed at the cementoenamel junction, were randomly divided into 4 groups of 30 samples each. Different post lengths were luted with either Flexi-Flow or zinc phosphate. Each sample was placed into a specialized jig and on a tensile testing machine with a crosshead speed of 2 mm/min, applied until failure. The effect of different posts and cements on the force required to dislodge the dowels was evaluated with multiple analyses of variance (ANOVA). One-way ANOVA with Scheffé contrast was applied to determine the effect of different post lengths on the retentive failure of posts luted with the 2 agents. RESULTS: Flexi-Flow reinforced composite resin cement significantly increased retention of ParaPost and Dentatus dowels (P<.001) compared with zinc phosphate. One-way ANOVA revealed no statistically significant difference (P>.05) between mean retention of both dowels luted with Flexi-Flow for all posts length used (5 mm = 8 mm = 10 mm). Mean retention values of the groups luted with zinc phosphate showed a statistically significant difference (P<.001) for the different post lengths (10 > 8 > 5 mm). Parallel-sided ParaPost dowels demonstrated a higher mean retention than tapered Dentatus dowels (P<.001). CONCLUSION: In this study, Flexi-Flow reinforced composite resin cement compensated for the reduced length of shorter parallel-sided ParaPost and tapered Dentatus dowels.     

The Retention of Cast Metal Dowels Fabricated by Direct and Indirect Techniques

Purpose: To explore the effect of fabrication technique, cement type, and cementation procedure on retention of cast metal dowels.
Methods and Materials: Eighty intact single-rooted teeth were selected. The clinical crown was removed at the cementoenamel junction level. Each root was prepared to receive a cast metal dowel of 10-mm length and 1.45 mm in diameter. The 80 specimens were divided into two major groups of 40 based on fabrication technique (direct and indirect). Each group was further divided into four subgroups of ten based on the cement type (zinc phosphate and glass ionomer), and cementation procedure (with and without lentulo spiral). The dowels were subjected to a constantly increasing tensile force, in a universal Instron testing machine, at crosshead speed of 5 mm/min until failure.
Results: The most significant factor to affect retention was the cementation procedure, as cementation with lentulo spiral produced greater retention than cementation without the use of lentulo spiral ( p < 0.05); however, there seems to be a close interaction between fabrication technique, cement type, and cementation procedure ( p = 0.051). The least retentive group was the one fabricated by direct technique, cemented with zinc phosphate without the use of lentulo spiral.
Conclusion: Fabrication technique does not affect retention of cast dowels, except when zinc phosphate was the luting agent and placed in the canal space without using a lentulo spiral. The cementation procedure had a significant effect on retention; thus, it is recommended that cementation should be done using the lentulo spiral.     

EFFECT OF EUGENOL-BASED ENDODONTIC SEALER ON THE ADHESION OF INTRARADICULAR POSTS CEMENTED AFTER DIFFERENT PERIODS

Objective:

This study evaluated in vitro the influence of an eugenol-based sealer (EndoFill) on the retention of stainless steel prefabricated posts cemented with zinc phosphate and resin-based (Panavia F) cements after different periods of root canal obturation, using the pull-out test.

Material and methods:

Sixty upper canines were decoronated and the roots were embedded in resin blocks. The specimens were distributed into 3 groups, according to the period elapsed between canal obturation and post cementation: Group I - immediately; Group II - 72 h and Group III - 4 months. The groups were subdivided according to the type of cement used for post cementation: A - zinc phosphate and B - Panavia F. Following the experimental periods, specimens were subjected to pull- out test in an Instron machine with application of tensile force at a crosshead speed of 0.5 mm/min until post dislodgement. The maximum forces required for post removal were recorded (kN) and means were subjected to statistical analysis by 2-way ANOVA and Tukey-Kramer test (α=0.001)

Results:

There were statistically significant differences (p<0.01) between the posts cemented with zinc phosphate cement (0.2112 kN) and Panavia F (0.0501 kN). However, no statistically significant differences (p>0.05) were found between the three post cementation periods, regardless of the cement.

Conclusions:

It was concluded that the eugenol-based sealer influenced the tensile strength of the posts cemented with the resin cement, but had no influence on the time waited between root canal obturation and post space preparation/post cementation.     

Effect of Different Cements on the Biomechanical Behavior of Teeth Restored with Cast Dowel‐and‐Cores—In Vitro and FEA Analysis

Purpose: To test the hypothesis that the type of cement used for fixation of cast dowel‐and‐cores might influence fracture resistance, fracture mode, and stress distribution of single‐rooted teeth restored with this class of metallic dowels. Materials and Methods: The coronal portion was removed from 40 bovine incisors, leaving a 15 mm root. After endodontic treatment and standardized root canal relief at 10 mm, specimens were embedded in polystyrene resin, and the periodontal ligament was simulated with polyether impression material. The specimens were randomly divided into four groups (n = 10), and restored with Cu–Al cast dowel‐and‐cores cemented with one of four options: conventional glass ionomer cement (GI); resin‐modified glass ionomer cement (GR); dual‐cure resin cement (RC); or zinc‐phosphate cement (ZP). Sequentially, fracture resistance of the specimens was tested with a tangential load at a 135° angle with a 0.5 mm/min crosshead speed. Data were analyzed using one‐way analysis of variance (ANOVA) and the Fisher test. Two‐dimensional finite element analysis (2D‐FEA) was then performed with representative models of each group simulating a 100 μm cement layer. Results were analyzed based on von Mises stress distribution criteria. Results: The mean fracture resistance values were (in N): RC, 838.2 ± 135.9; GI, 772.4 ± 169.8; GR, 613.4 ± 157.5; ZP, 643.6 ± 106.7. FEA revealed that RC and GR presented lower stress values than ZP and GI. The higher stress concentration was coincident with more catastrophic failures, and consequently, with lower fracture resistance values. Conclusions: The type of cement influenced fracture resistance, failure mode, and stress distribution on teeth restored with cast dowel‐and‐cores.     

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.     

The retention of complete crowns prepared with three different tapers and luted with four different cements

STATEMENT OF PROBLEM: The role of adhesive properties of cements on the retentive strength of crowns with different degrees of taper is not clear. PURPOSE: This study evaluated the retention of full crowns prepared with 3 different tapers and cemented with 2 conventional and 2 adhesive resin cements. MATERIAL AND METHODS: One hundred twenty sound human molar teeth were assigned randomly to 1 of 12 groups, (n=10). The groups represented the 4 cements: zinc phosphate (Fleck's), a conventional glass ionomer (Ketac-Cem); 2 adhesive resin cements (C&B Metabond and Panavia); and 3 tapers of 6-degrees, 12-degrees, and 24-degrees within each cement. Crowns were cast with a high noble alloy. The 6-degree taper was considered the control within each cement group. Retention was measured (MPa) by separating the metal crowns from the prepared teeth under tension on a universal testing machine. Analysis of variance was used to test the main effects on the retentive strength of full crowns, namely cements, tapers, and failure modes. The Fisher's multiple comparison test was used to evaluate the source of the differences. The chi(2) analyses were used to examine the relationships between failure types, cements, and tapers. All statistical tests were conducted at alpha=.05. RESULTS: There was a significant difference in the main effect cement (P<.0001) and taper (P=.0002). The mean retentive strength values of both Fleck's and Ketac-Cem were significantly lower than the mean retentive strength values of both C&B Metabond and Panavia (P<.0001). The retention of crowns prepared with 6-degree taper was not significant from the 12-degree taper (P=.0666). The difference in retention was significant between the 6-degree taper and the 24-degree taper (P<.0001) and between 12-degree taper and 24-degree taper (P=.0178). The types of failure were adhesive in the cement (65%), cohesive in the tooth (31%), and assembly failure (fracture of embedding resin) (4%). The type of failure was dependent on the degree of taper (P<.0001) and on the type of cement (P<.0042). CONCLUSION: Within the limitations of this study, the retentive values of the adhesive resins at 24-degree taper were 20% higher than the retentive values of the conventional cements at 6-degree taper. The use of resin luting agents yielded retention values that were double the values of zinc phosphate or conventional glass ionomer cement.     

The retentive effects of pre-fabricated posts by luting cements

The purpose of this study was to compare the retention of two different pre-fabricated posts cemented to the root canal with four different adhesive luting cements and a zinc phosphate cement. The crowns of 100 freshly extracted human mandibular central and lateral incisors were removed at the cementoenamel junction and divided into two main groups (A = ParaPost and B = Flexi-Post) and further divided into five subgroups to evaluate the effects of five different cements (Rely-X ARC, Panavia F, ParaPost Cement, Flexi-Flow Natural and Adhesor) each with 10 samples. Post-holes were prepared on all of the roots following the manufacturer's instructions. Each sample was placed into a specialized jig and tensile strength tests performed by using testing machine with a crosshead speed of 0.638 cm min(-1) and force applied until failure. The data were analysed with one-way anova (Post Hoc a Scheffe's S test) and two-way anova (P < 0.001). The Flexi-Post dowels had a mean of 54.21 kg (s.d. = 9.37) and demonstrated statistically higher retention than ParaPost dowels with a mean of 33.93 kg (s.d. = 10.69) for all of the cement groups (P < 0.001). In Flexi-Post and ParaPost dowel groups; Rely-X ARC was statistically higher than the Panavia F, ParaPost Cement, Flexi-Flow Natural and Adhesor (P < 0.05). Adhesor was significantly lower than the other subgroups (P < 0.05). Resin luting cements have demonstrated very high tensile strength potential for a strong bond to dentin.     

Effects of various cementation methods on the retention of prefabricated posts

Para-Post dowels were cemented by using combinations of cement, cleansing agents, and dentinal treatments. The comparative retentive strengths were as follows: 1. Para-Post posts cemented with composite into mechanically corrugated post spaces recorded the greatest retention. 2. The retention of the posts cemented with composite into post spaces rinsed with 1 ml of 17% EDTA with a pH of 7.5 and followed immediately by 1 ml of 5.25% NaOCl was lowest. 3. The retention of the posts secured with zinc phosphate into mechanically corrugated post spaces was significantly higher than with untapped post spaces. 4. The retentive strength of the posts placed with glass-ionomer cement into post spaces, irrigated with 1 ml of 40% polyacrylic acid solution, and rinsed with distilled water was comparable to that of posts secured with zinc phosphate cement without roughened post spaces.