Effect of length of LOCATOR abutment and cement type on retention to intraradicular dentin in overdentures.

STATEMENT OF PROBLEM: Limited information is available on the effect of LOCATOR abutment length and luting cement type on retention to intraradicular dentin in overdentures. PURPOSE: The purpose of this in vitro study was to evaluate the effect of the length of a commercially available LOCATOR abutment and cement type on retention in the root canal. MATERIAL AND METHODS: Eighty LOCATOR abutments with a standard length of 6 mm were obtained. Half of them were shortened to 3 mm. Eighty recently extracted single-rooted teeth were divided into 2 groups. The post space was prepared to 6 mm in the first group and 3 mm in the second. After preparation, the LOCATOR abutments were luted with one of the following cements: dual-polymerized glass-reinforced resin cement (Parapost Paracore), dual-polymerized resin cement (Variolink II), self-adhesive resin cement (RelyX Unicem), and conventional cement (zinc phosphate). The tensile force required for the removal of the LOCATOR abutments from their corresponding roots was recorded. Data were statistically analyzed with 2-way ANOVA and the Tukey multiple comparison test. RESULTS: Both the cement type (P<.001) and the length of the LOCATOR abutment (P<.001) significantly affected the mean tensile forces. Dual-polymerized glass-reinforced resin cement (Parapost Paracore) presented significantly higher mean tensile forces for the LOCATOR abutment retention among all cements (P<.05). CONCLUSIONS: Regardless of the length, LOCATOR abutments luted with Parapost Paracore resin cement presented higher mean resistance to tensile forces compared with those luted with the other cements. LOCATOR abutments of 6 mm in length were more resistant to tensile forces than those of 3 mm in length in combination with all cements.

Heat Generation on Implant Surface During Abutment Preparation at Different Elapsed Time Intervals.

PURPOSE: The purpose of this study was to evaluate heat generation at the implant surface caused by abutment preparation using a diamond bur in a high-speed dental turbine in vitro at 2 different water-coolant temperatures. MATERIALS AND METHODS: Thirty-two titanium-alloy abutments were connected to a titanium-alloy implant embedded in an acrylic resin placed within a water bath at a controlled temperature of 37°C. The specimens were equally distributed into 2 groups (16 each). Group 1: the temperature was maintained at 20 ± 1°C; and group 2: the temperature was maintained at 32 ± 1°C. Each abutment was prepared in the axial plane for 1 minute and in the occlusal plane for 1 minute. The temperature of the heat generated from abutment preparation was recorded and measured at 3 distinct time intervals. RESULTS: Water-coolant temperature (20°C vs 32°C) had a statistically significant effect on the implant's temperature change during preparation of the abutment (P < 0.0001). CONCLUSION: The use of water-coolant temperature of 20 ± 1°C during preparation of the implant abutment decreased the temperature recorded at the implant surface to 34.46°C, whereas the coolant temperature of 32 ± 1°C increased the implant surface temperature to 40.94°C.

Pull-out retentive strength of fiber posts cemented at different times in canals obturated with a eugenol-based sealer.

STATEMENT OF PROBLEM: Currently, no standard luting protocol exists for fiber posts. In addition, no agreement has been reached on the time interval between canal obturation and post space preparation and cementation. PURPOSE: The purpose of this in vitro study was to evaluate the retention of fiber posts cemented with 3 different types of cement: Paracore, Variolink II, and RelyX Unicem cement after 24 hours or 2 weeks in root canals obturated with gutta percha and a eugenol-based sealer. MATERIAL AND METHODS: Seventy-two caries-free, freshly extracted, single-rooted human mandibular first premolar teeth with straight root canals were prepared and obturated with gutta percha and Endofil sealer. Specimens were divided into 2 groups (n=36): post spaces prepared 24 hours after obturation and post spaces prepared 2 weeks after obturation. Posts in both groups were luted with 1 of 3 different luting agents (n=12), ParaCore, Variolink II, or RelyX Unicem cement. Each tooth specimen was vertically secured in a universal testing machine, and a constant pull-out loading rate of 0.5 mm/min was applied until cement failure occurred. Data were statistically analyzed with 2-way and 1-way ANOVAs and t tests. RESULTS: Two-way ANOVA indicated statistically significant differences in mean post retention among the 3 cement types (P<.001) and among the means of the different time intervals investigated (P<.001). Significant differences were noted among all cement types tested between the 24-hour and 2-week time intervals (P<.05). CONCLUSIONS: Time elapsed between canal obturation and post cementation significantly influenced fiber post retention, regardless of the type of resin cement. Fiber posts showed significantly higher retention if cemented after 24 hours of obturation than if cementation occurred after 2 weeks.

Effect of surface treatment and type of cement on push-out bond strength of zirconium oxide posts.

STATEMENT OF PROBLEM: The effect of the surface treatment of zirconium oxide posts on their push-out bond strength is controversial. PURPOSE: The purpose of this study was to compare the effects of 2 surface treatments on the bond strength of zirconium oxide posts cemented with different cements and to assess the failure mode. MATERIAL AND METHODS: Seventy extracted human teeth were divided into 7 groups (n=10). Custom zirconium oxide posts (Cercon; Degudent) were fabricated for 6 groups. Posts in 3 groups were airborne-particle abraded (A). Posts in the other 3 groups were tribochemical silica coated (T). Three cements were used. Zinc phosphate cement was used to cement the zirconium oxide posts in groups AZ and TZ, RelyX ARC cement was used in groups ARA and TRA, and RelyX Unicem cement was used in groups ARU and TRU. Group C contained custom metal posts cemented with zinc phosphate cement. Specimens were horizontally sectioned into 3 sections and subjected to a push-out test. A mixed model analysis of variance, 1-way ANOVA, and the Tukey multiple comparison tests were used for statistical analysis. RESULTS: The highest push-out bond strength was recorded for Group ARU (21.03 MPa), and the lowest was recorded for Group ARA (7.57 MPa). No significant difference in push-out bond strength was found among the different surface treatments and root regions (P>.05). The type of cement had a significant effect on the push-out bond strength of zirconium oxide posts (P=.049). RelyX Unicem cement recorded (19.57 ±8.83 MPa) significantly higher push-out bond strength compared with zinc phosphate (9.95 ±6.31 MPa) and RelyX ARC cements (9.39 ±5.45 MPa). Adhesive failure at the post-cement interface was recorded for 75% of the posts cemented with zinc phosphate and RelyX ARC cements, while mixed failure was recorded for 75% of the posts cemented with RelyX Unicem cement. CONCLUSIONS: The type of cement used resulted in a statistically significant difference in the push-out bond strength of zirconium oxide posts, while both the surface treatment and root region resulted in no statistically significant effect after artificial aging. RelyX Unicem cement had significantly higher push-out bond strength than did zinc phosphate and RelyX ARC cements.

Effect of luting agents on the tensile bond strength of glass fiber posts: An in vitro study.

STATEMENT OF PROBLEM: Fiber posts can fail because of loss of retention; and it is unknown which luting agent provides the highest bond strength. PURPOSE: The purpose of this study was to investigate the tensile bond strength of glass fiber posts luted to premolar teeth with 6 resin composite luting agents. MATERIAL AND METHODS: Ninety-six single-rooted extracted human mandibular premolars were sectioned 2 mm coronal to the most incisal point of the cementoenamel junction. Root canals were instrumented and obturated with laterally condensed gutta percha and root canal sealer (AH26). Gutta percha was removed from the canals to a depth of 8 mm and diameter post spaces with a 1.5 mm were prepared. The specimens were divided into the following 6 groups according to the luting agent used (n=16): Group V, Variolink II; Group A, RelyX ARC; Group N, Multilink N; Group U, RelyX Unicem; Group P, ParaCore; Group F, MultiCore Flow. Each specimen was secured in a universal testing machine and a separating load was applied at a rate of 0.5 mm/min. The forces required to dislodge the posts were recorded. A 1-way analysis of variance (ANOVA) was applied to the mean retentive strengths of various cement materials (α=.05). RESULTS: Significant differences were recorded among the 6 cement types (P<.001). Three materials provided statistically equivalent mean bond strengths (RelyX Unicem, Paracore, and MultiCore Flow) that were significantly greater than for the other 3 materials. CONCLUSIONS: Fiber posts luted with RelyX Unicem, Paracore, and MultiCore Flow demonstrated significantly higher bond strengths.

Bond strength of overdenture locator posts cemented with seven luting agents.

STATEMENT OF THE PROBLEM: Post retention is crucial factor in restoration survival. Posts are commonly failed due to loss of retention. It is unknown which luting agents would provide the maximum bond strength for Locator overdenture posts. AIM: The aim of this study was to evaluate the bond retentive strengths of Locator overdenture posts cemented with 7 luting agents. MATERIALS AND METHODS: One hundred and five single rooted human teeth were decoronated and randomly assigned to 7 groups (n = 15). Post spaces were prepared with Locator post drills to the depth of 6 mm. The Locator posts were cemented with Variolink II, RelyX ARC, Multilink N, RelyX Unicem, ParaCore, or MultiCore Flow resin luting agents. Zinc phosphate cement was served as control group. Specimens were stored in water at 37°C for 24 hours. Each specimen was loaded in tension in an Instron universal testing machine. The maximum force required to dislodge each Locator post was recorded. Means and standard deviations were calculated and data were statistically analyzed with one-way analysis of variance (ANOVA). RESULTS: The highest mean bond strength value for Locator posts was recorded for MultiCore(®) Flow group (mean = 550.1 N), while the lowest mean value was for RelyX Unicem(™) resin cement group (mean = 216.8 N). A statistically significant difference in mean locator overdenture post bond strength was observed between the 7 cement types (p < 0.0001). ParaCore(™) and MultiCore(®) Flow groups had significantly higher bond strength than all other groups, but they were not differed from each other. CONCLUSION: Bond strength of Locator overdenture posts were influenced by the type of luting agents. MultiCore Flow and ParaCore resin cements offered the greatest retention. CLINICAL SIGNIFICANCE: The type of luting agents had a significant effect on the retention of Locator posts. The use of Core buildup resin cements as luting agent with Locator post demonstrated the greatest retention.

Effect of three endodontic sealers on the bond strength of prefabricated fiber posts luted with three resin cements.

STATEMENT OF PROBLEM: There is limited information in the literature regarding the effect of eugenol-based sealers on the bond strength of resin-bonded endodontic posts. PURPOSE: The purpose of this study was to evaluate the effect of 1 resin-based and 2 different eugenol-based endodontic sealers on the bond strength of prefabricated fiber posts luted with 3 different resin cements. MATERIAL AND METHODS: One hundred thirty-five prefabricated fiber posts were luted into extracted single-rooted teeth with 1 of 3 composite resin cements (Rely X Unicem, Paracore, and Variolink II). Specimens were divided into 3 groups with 45 teeth each. The first 2 groups were obturated with gutta percha and 1 of 2 eugenol-based endodontic sealers (Endofil, Tubli-Seal). The third group was obturated with a resin-based root canal sealer (AH26). The forces required for dislodgment of posts from their prepared post spaces were recorded by using a universal testing machine. Data were collected and a 2-way ANOVA was applied to the mean retentive strengths of various combinations of sealer and cement. A Tukey multiple comparison test was performed to determine which groups were significantly different (α=.05). RESULTS: Endofil and Tubli-Seal (eugenol-based sealers) groups had significantly lower bond strengths for the posts than the AH26 group (P<.001). There was no significant difference between the means of post bond strength for the Endofil and Tubli-Seal groups. There was significant difference among the means of post bond strength for all 3 cement groups (P<.05). CONCLUSIONS: Endofil and Tubli-Seal (eugenol-based) sealers demonstrated significantly reduced mean bond strength for prefabricated fiber posts luted with resin cement. Rely X Unicem resin cement exhibited higher mean bond strength than with Paracore and Variolink II resin cements when a eugenol sealer was used.

Effect of Luting Cement Film Thickness on the Pull-Out Bond Strength of Endodontic Post Systems.

Optimal bond strength between the prefabricated post/dowel to the surrounding dentin is essential. The present study aimed to analyze and compare the effect of three different cement film thicknesses on the pull-out bond strength of three different prefabricated post systems. Extracted natural teeth (N = 90) with similar root dimensions were acquired. Teeth were mounted in resin blocks, endodontically treated, sectioned at cemento-enamel junction, divided into three groups (A: Parapost Fiber Lux plus; B: 3M ESPE Relyx fiber post; and C: Parapost XP), and stored. Uniform post spaces were prepared for the groups (A and C: Length = 8 mm, Width = 1.5 mm; B: Length = 8 mm, Width = 1.6 mm). Each group (N = 30) was further subdivided into three subgroups (n = 10) based on the size (4, 5, and 6) of the post and cemented with resin cement (MultiLink-N, Ivoclar Vivadent). After thermocycling, the specimens were subjected to a pull-out test using a universal testing machine, and tensile force was recorded (MPa). Digital microscopic evaluations were performed for modes of failure. ANOVA and Tukey-HSD tests were used for statistics. Significant differences were observed for each tested material (p = 0.000). The lowest and highest bond strength values were recorded for Group C (Titanium post) and Group A (000), respectively. Multiple comparisons showed significance (p < 0.05) among all the groups, except for space 1 and space 2 (p = 0.316) for Group A. Most of the failures occurred within the cement-dentin and post-cement interface (Adhesive failures, 73.5%). An increase in the luting cement film thickness results in the decrease in pull-out bond strength of prefabricated posts luted with resin cement, irrespective of the type/material/shape of the post. The serrated fiber posts showed the highest pull-out bond strength compared to the smooth surfaced fiber posts or serrated metal posts. Increased pull-out bond strengths were observed when appropriate post space was created with the same sized drill as the post size.

Effect of endodontic sealers on push-out bond strength of cemented fiber posts.

OBJECTIVE: The purpose of this study was to compare the effect of eugenol-based and resin-based endodontic sealers on the push-out bond strengths of prefabricated fiber posts luted with different resin cements. METHOD AND MATERIALS: Ninety prefabricated fiber posts were luted into extracted singlerooted teeth with one of three resin cements (Variolink II, ParaCore, or Rely X Unicem). Each group was subdivided into three groups with 10 teeth each. The first two groups were obturated with gutta percha and one of two eugenol-based endodontic sealers (Endofil or TubliSeal) each. The third group was obturated with gutta percha and (AH26) resin-based root canal sealer. Push-out tests were performed in a universal testing machine by applying a load speed at 0.5 mm/min by using a 1-mm-diameter metallic plunger which induced a load in an apical to coronal direction. The maximum value for post dislodgement (in Newtons) was recorded. Data were collected and statistically analyzed using two-way ANOVA and Tukey multiple comparison tests (α = .05). RESULTS: The highest mean bond strength values were recorded for the AH26 sealer group (non-eugenol sealer) luted with Rely X Unicem resin cement (mean ± SD = 326.1 ± 66.1 N), while the lowest mean bond strength values were observed with posts luted with Variolink II resin cement into canals obturated with gutta-percha and Endofil (eugenol-based) sealer (90.3 ± 25.2 N). There was no significant difference between the means of push-out strengths for the Endofil and TubliSeal groups (P = .745). CONCLUSION: Eugenol-based sealers (Endofil and TubliSeal) significantly reduced the push-out bond strength of prefabricated fiber posts luted with resin cement.

Implant Fixture Heat Transfer During Abutment Preparation.

The purpose of the study was to evaluate the effect of water flow rate on the heat transmission in implants during abutment preparation using a diamond bur in a high-speed dental turbine. Titanium-alloy abutments (n = 32) were connected to a titanium-alloy implant embedded in an acrylic resin within a water bath at a controlled temperature of 37°C. The specimens were equally distributed into 2 groups (16 each) according to the water flow rate used during the preparation phase. Group 1 had a water flow rate of 24 mL/min, and group 2 had a water flow rate of 40 mL/min. Each abutment was prepared in the axial plane for 1 minute and in the occlusal plane for 1 minute with a coarse tapered diamond bur using a high-speed dental handpiece. Thermocouples embedded at the cervix of the implant surface were used to record the temperature of heat transmission from the abutment preparation. Heat generation was measured at 3 distinct times (immediately and 30 seconds and 60 seconds after the end of preparation). Statistical analyses were carried out using 2-way analysis of variance and the Student t test. Water flow rates (24 mL vs 40 mL) and time interval had no statistically significant effect on the implant's temperature change during the abutment preparation stage (P = .431 and P = .064, respectively). Increasing the water flow rate from 24 to 40 mL/min had no influence on the temperature of the implant fixture recorded during preparation of the abutment.

Effect of types of luting agent on push-out bond strength of zirconium oxide posts.

OBJECTIVE: The aim of this study was to investigate the effect of different luting agents on the bond strength of zirconium oxide posts in root canals after artificial ageing. MATERIAL AND METHODS: Thirty single-rooted extracted teeth were collected. Post spaces were prepared. Custom milled zirconium oxide posts (Cercon, Degudent) were fabricated. Specimens were divided into 3 groups (n=10), according to the luting agents used: group RA, conventional resin luting agent (RelyX ARC); group RU, self-adhesive resin luting agent (RelyX Unicem); and group Z, zinc phosphate luting agent (DeTrey). Specimens were subjected to thermocycling and water storage at 37°C. Specimens were horizontally sectioned into three sections and subjected to a push-out test with 0.5mm/min crosshead speed. The failure mode was assessed by scanning electron microscopy. Data were analysed by using 2-way ANOVA. RESULTS: The following bond strength values were obtained: group RA - 8.89 MPa, group RU - 10.30 MPa and group Z - 9.31 MPa. There was no significant difference in bond strength among the groups (P=0.500). Adhesive failure mode at the cement/post bonded interface was seen in 100%, 66.67% and 83.3% of examined sections in groups RA, RU and Z, respectively. There was no significant difference in bond strength among different root regions (P=0.367). CONCLUSION: The type of luting agent had no significant effect on the push-out bond strength of zirconium oxide posts after artificial ageing. CLINICAL SIGNIFICANCE: Conventional luting agents, such as zinc phosphate cement, seem to provide comparable retention to resin luting agents for cementing custom milled zirconium oxide posts.

Convergence angles of clinical tooth preparations achieved by dental students at King Saud University, Saudi Arabia.

The appropriate convergence angle (CA) for adequate retention and resistance of cast crowns has always been a matter of research and discussion. The purpose of this study was to measure the CA of tooth preparation for single crown (SC) or as abutments for fixed partial denture (FPD) carried out by final-year undergraduate dental students at the College of Dentistry, King Saud University and to compare them with the recommended CA. The convergence angles of 355 tooth preparations were evaluated and grouped into SC preparations and FPD abutment preparations. Dies were scanned using the computer-assisted design (CAD) system (Cercon, Degudent), and snapshots were then taken from buccal and mesial views. CA was calculated from a colored printout for each snapshot using a protractor. The overall mean CA was 18.56°. Only 32.7 percent of the preparations were within the recommended CA (<12°). The mean CA of SC (17.7°) was less than the mean CA for FPD abutment preparations (19.58°). The mean CA for anterior tooth preparations (15.8°) was significantly less than the mean CA for posterior tooth preparations (20.3°). The mean CA for mesio-distal axial wall preparations (16.66°) was less than the mean CA for the buccolingual axial wall preparations (20.45°). A wide range was found for the convergence of the axial walls among dental students. The recommended CA (<12°) was difficult to achieve clinically by these students.

Bond strengths of custom cast and prefabricated posts luted with two cements.

OBJECTIVE: This in vitro study evaluated the bond strength of custom cast and prefabricated posts luted with resin or zinc phosphate cements into unobturated canals of extracted teeth. METHOD AND MATERIALS: Forty-eight custom cast and prefabricated posts were placed into extracted single-rooted human teeth. Post-cavity preparation was 1.5 mm in diameter and 10 mm in depth. Specimens were randomly divided into 4 groups of 12 each. Two of the groups were then luted with resin cement, while the other two groups were luted with zinc phosphate cement. A pull-out bond strength evaluation was performed using a universal testing machine. The Kolmogorov-Smirnov test was used to prove normal distribution. Data were statistically analyzed using two-way ANOVA and the Student t test (alpha = .05). RESULTS: For both luting agents, the prefabricated posts group exhibited significantly less bond strength than the custom cast posts group (P = .0001). There were statistically significant differences in mean bond strength for the prefabricated posts group luted with resin cement vs the group cemented with zinc phosphate cement (P = .002). There was no significant difference between the mean bond strength values of custom cast posts luted with resin cement or zinc phosphate cement. CONCLUSION: Custom cast posts showed significantly greater bond strength than prefabricated posts when luted with either resin or zinc phosphate cements. The type of cement had less significance on the retention of custom cast posts.