Examination of the implant-abutment interface after fatigue testing

A Study on Screw Loosening in Dental Implant Abutment

Dental implants are integral in replacing missing teeth, providing durability and natural aesthetics through osseointegration-a process where the implant fuses with the jawbone to support a prosthesis. However, screw loosening presents significant challenges, potentially leading to implant failure, bone loss, and peri-implantitis. Contributing factors include micro-leakage, settling effects, loss of preload, abutment angulation, and inadequate torque application. Addressing these issues through proper torque management, anti-rotation features, and retightening protocols is crucial for implant longevity and success. This study outlines key causes and solutions for screw loosening in dental implants.

Evaluation of axial displacement and torque loss of Morse-type prosthetic abutments of different angular tapers to their respective implants

STATEMENT OF PROBLEM

The biomechanical stability of the implant-prosthesis assembly and its maintenance under function is a determining factor in the success of implant prosthesis rehabilitation, but studies of different angular tapers are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the axial displacement and torque loss of prosthetic abutments with Morse-type connections of different angular tapers after thermomechanical cycling by using microcomputed tomography (µCT) and a digital torque wrench.

MATERIAL AND METHODS

Eighteen Ø3.5×11.5-mm implants were embedded in polyvinyl chloride cylinders, and the 3 different types of abutments (n=6) with angular tapers of 11.5 degrees - Alvim Cone Morse (ACM-11.5), 16.0 degrees - Helix Gran Morse (HGM-16), and 24.0 degrees - Nobel Replace Conical Connection (NRC-24) were installed with the torque recommended by the manufacturers. To calculate the axial displacements of the abutments about the implants, zirconia maxillary canine crowns were fabricated using a computer-aided design and computer-aided manufacturing (CAD-CAM) system and cemented onto the abutments. Before and after thermomechanical cycling, the assemblies were scanned using microtomography (micro-CT) to assess axial displacement, and the torque losses were calculated after the abutments were finally unscrewed. A load of 100 N, frequency of 2 Hz, and 106 cycles with temperature variation of 5 °C to 55 °C were used for the thermomechanical cycling. Analysis of variance and the Tukey post hoc test (α=.05) were used for analysis.

RESULTS

A significant difference was observed between the abutments for axial displacement, measured after thermomechanical cycling (P=.002). The ACM-11.5 abutment showed the highest mean value (134.1 ±58.7 µm), different from HGM-16 (63.3 ±26.1 µm) (P=.013) and NRC-24 (42.7 ±8.7 µm) (P=.002); the 2 latter groups were similar to each other (P=.618). For the torque losses, no significant difference was found among the abutments (P=.928), but there were significant differences for the thermomechanical cycling (before and after) (P<.001) in that the loss of torque was greater after thermocycling.

CONCLUSIONS

The smaller the taper angle of the Morse-type prosthetic abutment, the greater its axial displacement, and the thermomechanical cycling significantly reduced pretorque, regardless of taper.

Mechanical stability of posterior implant-supported monolithic zirconia cantilever on titanium-base abutments. An in vitro study

PURPOSE

Investigate survival and technical complications of two-unit posterior implant-supported cantilever made of monolithic zirconia on titanium-base abutments (Zr-TiB) vs. porcelain-fused-to-metal on castable gold abutments (PFM-GA) using two different implant connections, internal butt-joint (IBJ) and internal conical (IC).

MATERIALS AND METHODS

Forty-eight implants (4.3 mm diameter) were divided into four groups (n = 12) to support 2-unit mandibular premolar cantilevers with two different materials (Zr-TiB vs. PFM-GA) and two connection types (IBJ vs. IC). Tested groups were as follows: (1) IBJ/Zr-TiB; (2) IBJ/PFM-GA; (3) IC/Zr-TiB; and (4) IC/PFM-GA. Specimens were thermomechanical aged (1,200,000 cycles, 98 N, 5-55°C) with occlusal axial load on the pontic. Catastrophic and non-catastrophic events were registered, and removal torque values measured before and after aging. Specimens surviving aging were subjected to loading until failure. Survival, total complication rates, torque loss (%), and bending moments were calculated.

RESULTS

From 48 specimens, 38 survived aging. Survival rates significantly varied from 16.7% (IC/PFM-GA) to 100% (IBJ/Zr-TiB; IBJ/PFM-GA; IC/Zr-TiB) (p < .01). Internal conical connection revealed significantly higher torque loss (IC/ZrTiB - 67%) compared to internal butt-joint (IBJ/Zr-TiB - 44%; IBJ/PFM-GA - 46%) (p < .01). Bending moments were higher in internal butt-joint connections than in internal conical (p < .05).

CONCLUSION AND CLINICAL IMPLICATIONS

Two-unit posterior implant-supported cantilever FDPs replacing mandibular premolars composed of monolithic zirconia on titanium-base abutments demonstrated higher mechanical stability compared to porcelain-fused-to-metal on castable gold abutments in this in vitro study. The internal conical connection combined with porcelain-fused-to-metal on gold abutments revealed a high number of failures; therefore, their clinical use may be considered cautiously for this indication.

In vitro study to analyze reverse torque values of attachment screws with multiple loosening/tightening preload cycles

PURPOSE

To determine the number of torque/reverse torque cycles attachment screws can withstand before fracture, and to record the magnitude of reverse torque values for each of the 10 cycles of screw tightening and loosening.

MATERIALS AND METHODS

The testing assemblies consisted of 30 temporary cylinder/multiunit abutment/internal connection implants (10 each from Dentsply Sirona Astra, Biohorizons, and Zimmer Biomet Dental). The assemblies were inserted into resin blocks, and temporary cylinders were connected to the multiunit abutments with new attachment screws and torqued to the recommended preload (15 Ncm Dentsply Sirona Astra; 15 Ncm Biohorizons; 10 Ncm Zimmer Biomet Dental) using a digital torque gauge instrument (Model 3, MARK-10 Corporation, New York, USA) at room temperature without lubrication. After 24 h, the attachment screws were reverse torqued with the same instrument and the values were recorded. The torque/reverse torque cycles were repeated every 24 h for 10 days. Data were analyzed using mixed model analysis. A second test included torquing the used screws (30) until fracture or stripping occurred. The reverse torque values were recorded and compared with new screws that were torqued until fracture or stripping. A sample of used and new attachment screws from each assembly were viewed under both laser microscope (LEXT OLS4000, 3D Measuring Laser Microscope, Olympus) and scanning electron microscope (JEOL-JSM6510, Tokyo, Japan). Data were analyzed using t-test.

RESULTS

Following 10 cycles of torquing and reverse torquing, the reverse torque values measured on day 10 were lesser compared with the reverse torque value measured on day 1 for 29/30 attachment screws (96.6%). According to the t-test used for the second test, the p-values among all three groups were ≥0.9 which were not statistically significant.

CONCLUSION

The results of this study indicated that after 10 cycles of torquing and reverse torquing attachment screws, the reverse torque values decreased. There were no statistical differences between the magnitude of torque necessary to fracture new and used attachment screws.

Evaluating the effect of the protector cap for castable implant abutments on reverse tightening values

STATEMENT OF PROBLEM

Screw loosening is the most common mechanical complication with implant prostheses. How the alteration of implant-to-abutment connection surfaces that occurs during laboratory procedures affects screw loosening is unclear.

PURPOSE

The purpose of this in vitro study was to compare the reverse tightening value (RTV) differences between custom castable abutments before casting, after casting in a conventional manner, and after casting with custom protector caps and pegs.

MATERIAL AND METHODS

Thirty implants with a standard-diameter conical connection (NobelReplace Conical Connection 4.3×13 mm; Nobel Biocare AG) and 30 premachined 4.3-mm GoldAdapt abutments (GoldAdapt; Nobel Biocare AG) were selected for this study. Specimens were divided into 3 groups (n=10): the uncast custom castable abutment group (UCCA) in which abutments were new and not cast; the unprotected custom castable abutment group (UPCCA) in which abutments were cast and devested with airborne-particle abrasion; and the protected custom castable abutment group (PCCA) in which abutments were cast by using protector caps and pegs made by milling zirconia and then devested with airborne-particle abrasion. All abutments in each group were tightened to 35 Ncm with a calibrated digital tightening device. After 10 minutes, all screws were retightened to 35 Ncm. At 3 hours, each screw was loosened, and the value at which the initial loosening occurred was documented as the RTV. The results were statistically analyzed with 1-way ANOVA to explore differences, and post hoc tests with Tukey adjustment were used for multiple comparisons.

RESULTS

Among the tested groups, the mean RTV ranged from 19.89 Ncm to 27.19 Ncm: UCCA 27.19 Ncm, UPCCA 19.89 Ncm, and PCCA 24.24 Ncm. A significant difference was found among the tested groups (P<.05).

CONCLUSIONS

Casting procedures, especially devestment with airborne-particle abrasion, affected implant-abutment connections and the seat site of the screw. Protecting the implant connection site and the seat site of the abutment screw with protector caps and pegs prevented a significant loss of the RTV.

Compressive Strength Evaluation of Three Distinct Implant Design Approaches

Objectives

The study was done to assess the implant-abutment interface static compressive. strength of three design types and implant-abutment connection failure style.

Materials and Methods

The implants at 306 with respect to the y-axis were aligned using a stainless steel holding device. Twenty specimens from each system totaled 60 total. A unidirectional vertical piston in a computer-controlled universal testing machine (MTS 810) generated static compression loading until failure. Specimens were macroscopically examined for fracture of the screw and implant, abutment looseness, and longitudinal displacement. Analysis of variance was used to analyze the data (ANOVA).

Result

The screw-vent system had a mean compressive strength of 335.6 22.7 psi for the Unipost system, 384.3 37.1 psi for the screw-vent system, and 245.3 25.4 psi for the ITI-1 piece abutment connection.

Conclusion

The connection between the Unipost implant and abutment showed a statistically significant variation.

Comparative analysis of the mechanical limits of resistance in implant/abutment set of a new implant design: An in vitro study

OBJECTIVE

The aim of the present in vitro study was to evaluate the resistance on quasi-static forces and in the fatigue mechanical cycling of a new implant design compared to two other conventional implant designs.

MATERIALS AND METHODS

Eighty-eight implants with their respective abutments were tested and distributed into four groups (n = 22 per group): Morse taper connection implant (MT group), conventional external hexagon implant (EH con group), new Collo implant of external hexagon with the smooth portion out of the bone insertion (EH out group), and new Collo implant of external hexagon with the implant platform inserted to the bone level (EH bl group). All the sets were subjected to quasi-static loading in a universal testing machine, and we measured the maximum resistance force supported by each sample. Another 12 samples from each group were submitted to the cyclic fatigue test at 4 intensities of forces (n = 3 per force): 80%, 60%, 40%, and 20%. The number of cycles supported by each sample at each force intensity was evaluated.

RESULTS

The three groups of implants with external hexagon connection had similar maximum strength values of the sets (p > 0.05). Meanwhile, samples from the MT group showed the highest resistance values in comparison to the other three groups (p < 0.05). In the fatigue test, the Collo out group supported a smaller number of cycles that led to the fracture than the other 3 groups proposed at loads of 80%, 60%, and 40%, and only at the load value of 20% all groups had the same performance.

CONCLUSIONS

Within the limitations of the present in vitro study, the results showed that the new Collo implant performs better when installed at bone level.

Bacterial infiltration and detorque at the implant abutment morse taper interface after masticatory simulation

This study evaluated the bacterial infiltration and the detorque of indexed and non-indexed abutments of Morse taper implants (MTI) after mechanical cycling (MC). 40 MTI were distributed into four groups: IIA (indexed implant abutments); NIIA (non-indexed implant abutments); IIAMC (indexed implant abutments submitted to MC); NIIAMC (non-indexed implant abutments submitted to MC), which were carried out under one million 5 Hz frequency and 3 Bar pressure. After mechanical cycling, all groups were immersed in a bacterial solution in Brain Heart Infusion Agar. After detorque, the bacteria infiltration was evaluated by counting the colony-forming units. For the bacterial infiltration, analysis was applied to the Kruskal-Wallis test (p = 0.0176) followed by Dunn's test. For the detorque analysis, the two-way repeated-measures ANOVA was applied, followed by the Tukey's test (p < 0.0001). Bacteria infiltration was highly observed in NIIA (p = 0.0027) and were absent in IIAMC and NIIAMC. The detorque values for IIA (19.96Ncm ± 0.19Ncm), NIIA (19.90Ncm ± 0.83Ncm), and NIIAMC (19.51Ncm ± 0,69Ncm) were similar and remained close to the initial value, while IIAMC (55.2Ncm ± 2.36Ncm) showed an extremely significant torque value increase (p < 0.0001). The mechanical cycling resulted in mechanical sealing of the implant-abutment interface, preventing bacterial infiltration in the indexed and non-indexed specimens, and increasing the detorque strength in the group of indexed abutments.

Evaluation of customized cobalt-chromium abutments fabricated with different manufacturing process versus titanium stock abutments on the marginal misfit -An in vitro study

Aim

Accurate fit of the abutment to the implant is required for the uniform load distribution throughout the assembly. The study aims to compare the marginal misfit of titanium stock abutments with the cobalt-chromium (CoCr) customized abutments fabricated with the different manufacturing processes in internal hex implant-abutment connection using an appropriate scanning technique.

Setting and Design

In vitro comparative study.

Materials and Methods

A total of 40 abutments were included in the study. Ten titanium stock abutments were used as control (Group CN) and 30 CoCr abutments were fabricated and taken as the test group. Stock abutments were scanned and from obtained images test group abutments were fabricated as follows: Ten cast abutments (Group CA), 10 sintered abutments (Group SA), and 10 milled abutments (Group MA). Endosseous implanst having internal hex connections were matched with 10 stock abutments and 30 customized CoCr abutments. Implants were mounted in a clear epoxy resin block and the abutments were then fitted onto the implants with a torque of 30Ncm. The marginal discrepancy at implant-abutment connections was measured with confocal laser scanning microscope.

Statistical Analysis Used

One-way ANOVA and Tukey's post hoc test was done for statistical analysis.

Results

One-way ANOVA revealed a significant difference in marginal misfit of abutments. The mean marginal misfit was lowest for stock abutments (0.35 ± 0.009 μm). Among the customized abutments, the mean marginal misfit was highest for cast abutments (2.44 ± 0.445 μm) followed by sintered abutments (1.67 ± 0.232 μm) and least for milled abutments (0.65 ± 0.041 μm). A significant difference was found in marginal misfit with cast abutments and sintered abutments when compared to stock abutments (P < 0.001). The difference in marginal misfit was insignificant between stock abutments and milled abutments (P = 0.052).

Conclusion

Difference in marginal misfit exists between the titanium stock abutments and customized CoCr abutments. Among the customized abutments, milled CoCr abutments have the least marginal discrepancy and cast CoCr abutments have a maximum marginal discrepancy. Milled CoCr abutments can be used as an alternative to titanium stock abutments.

Comparison of Mechanical Resistance to Maximal Torsion Stress in Original and Nonoriginal or Compatible Prosthetic Implant Screws: An In Vitro Study

Micromovements of the implant-abutment connection influence peri-implant bone preservation. The maximal torque after a cycle of implant prosthetic screw tightening using original components of different manufacturers and replicas produced by other companies is evaluated and quantified in this study. A total of 30 Mis Seven® standard platform implants and 30 interfaces were used, and 30 standard platform screws were tested, 10 Mis®, 10 Iconekt®, and 10 Exaktus®. The screws were tightened with an MIS® torquemeter until their respective fracture, and the fracture point was measured through the equipment's load cell, CS-Dental Testing Machine®. The screws were analyzed under an Olympus® SZ61 microscope. The fracture points were recorded and compared among all samples. To compare the mean values of the fracture torques, t-tests were performed using the reference values associated with each brand and the sample results. The variable “Place of Fracture” between the original Mis® brand and the Exaktus® replica compared to the Iconekt® replica presented a statistically significant difference (p < 0.001). When analyzing the variable “Fracture Torque,” although it was verified that the replica screws (Iconekt® and Exaktus®) had a lower maximum torque, 65.11 Nm and 62.89 Nm, respectively, compared to the original Mis® brand (70 Nm and 69 Nm), there were no statistically significant differences p > 0.05. Nonoriginal screws did not present different fracture resistances compared to the original Mis® brand screws. The fracture site of Iconekt® screws showed a different pattern compared to the other brands.

Effect of different tightening protocols on the probability of survival of screw-retained implant-supported crowns

PURPOSE

This study evaluated the effect of different tightening protocols on the probability of survival of screw-retained implant-supported anterior crowns.

MATERIALS AND METHODS

Seventy-two implants with internal conical connections (4.0 × 10mm, Ti-6Al-4V, Colosso, Emfils) were divided into four groups (n = 18 each): 1) Manufacturer's recommendations torque (25 N.cm for abutment's screw and 30 N.cm for crown's screw) (MaT); 2) Retightening after 10 min (ReT); 3) Torque 16% below recommended to simulate an uncalibrated wrench (AgT), and; 4) Temporary crown simulation (TeT), where crowns were torqued to 13 N.cm to simulate manual tightening, subjected to 11,200 cycles to simulate temporary crown treatment time (190 N), and then retightened to manufacturer torque (TeT). All specimens were subjected to cyclic fatigue in distilled water with a load of 190 N until 250,000 cycles or failure. The probability of survival (reliability) to complete a mission of 50,000 cycles was calculated and plotted using the Weibull 2-Parameter analysis. Weibull modulus and number of cycles at which 62.3% of the specimens would fail were also calculated and plotted. The failure mode was characterized in stereo and scanning electron microscopes (SEM).

RESULTS

The probability of survival was 69.3% for MaT, 70% for ReT, 54.8% for AgT, and 40.3% for TeT, all with no statistically significant difference. Weibull modulus was approximately 1.0 for all groups. The characteristic number of cycles for failure was 105,000 cycles for MaT, 123,000 for ReT, 82,000 cycles for AgT, and 54,900 cycles for TeT, with no significant difference between groups. The chief failure mode for MaT, ReT, AgT groups was crown screw fracture, whereas abutment screw fracture was the chief failure mode for the TeT group.

CONCLUSION

Tightening protocol did not influence the probability of survival of the screw-retained anterior crowns supported by internal conical implants (Ti-6Al-4V, Colosso, Emfils).

In vitro analysis of prosthetic abutment and angulable frictional implant interface adaptation: Mechanical and microbiological study

The aim of this study was to evaluate, in vitro, the microbiological sealing at the implant and different angles frictional prosthetic abutment interface, submitted or not to mechanical cycling, as well as the deactivation force and evaluation of the implant-abutment interface by scanning electron microscopy. For this study, the sealing capacity of eighty sets of abutments/implants of each angle, with and without mechanical cycling, with internal conical connection (locking tapper) (4.3 mm × 9.0 mm) constituted in Titanium alloy (Ti6Al4V), and stainless steel angled prosthetic abutment was evaluated (18Cr14Ni2.5Mo) according to ASTM F138-13a (Arcsys, FGM, Joinville, Brazil), 6 mm high and 4.2 mm in diameter at the coronary portion, and 3.5 mm high transmucosal, in 4 different angles (0, 5, 10 and 20°). After in vitro tests, 100% biological sealing was observed at the implant / prosthetic abutment interface within cycled and non-cycled conditions, for the straight, 5, 10 and 20° inclination groups. There was no statistically significant difference in the removal force of the prosthetic abutments at different angles, under non-cycled conditions; however, under mechanical loading, the deactivation force was significantly higher for straight prosthetic abutments than with 10 and 20° of angulation. Surface analysis revealed good adaptation between implants and abutments, and the presence of wear areas, independently of mechanical loading. It is concluded that the analysis of implant and prosthetic abutment interface revealed good adaptation between the parts, for all analyzed samples.

Correlation of Fracture Resistance of Dental Implants and Bite Force in Dogs described in the literature: An In Vitro Study

Dental implants are not routinely used for rehabilitation in veterinary dentistry. For some veterinarians, further studies are necessary to be considered for clinical use in animals. The objective of the present in vitro study was to evaluate static fatigue of dental implants and to correlate that with the bite strength of dogs described in the literature. Sixty implants and abutments were used with the smallest diameter of each brand of implant utilized in the study. Three groups (n  =  20) were created on the basis of the implant diameter, all with external hex connector: 3.30 mm (group 1), 4.0 mm (group 2) and 5.0 mm (group 3). All groups were subjected to quasi-static loading at 30° to the implant's long axis in a universal machine (model AME-5 kN). The mean fracture strength for group 1 was 964 ± 187 N, for group 2 was 1618 ± 149 N and for group 3 was 2595 ± 161 N. Significant differences between the groups with respect to resistance after the load applications were observed (P < .05). The diameter of implants affects the resistance to external forces during the application of non-axial strength (off-axis loading) and must be considered during the planning of rehabilitation to avoid problems.

Effect of Crown Height on the Screw Stability of Titanium Screw-Retained Crowns

PURPOSE

The aim of this in vitro study was to evaluate the effect of crown height on the screw stability of screw-retained titanium implant crowns subjected to cyclic loading conditions.

MATERIALS AND METHODS

Twenty-one implants with internal hex connections were placed in epoxy resin holders. Mandibular first molar screw-retained titanium implant crowns with UCLA type, crown-abutment connections were CAD/CAM fabricated. Seven crowns of 3 different heights (6 mm, 10 mm, and 14 mm) were made. The crowns were seated onto the implants and screws were tightened to 30 Ncm. The implants were clamped into holders and stepwise cyclic loads were applied to the occlusal surface at 30-degree angles to the long axes of the crowns. The detorque values were measured after each 5 million cycles. Before increasing the applied load, the crowns were secured with new screws and tightened to 30 Ncm. Failure times, survival estimates and detorque values were then analyzed. (alpha = 0.05).

RESULTS

Crown height did not significantly affect detorque values. However, five 14-mm crowns failed with varying fractures during the 475 N loading condition. Overall, a significantly lower survival for 14 mm crowns was found compared to 6 mm and 10 mm crowns (p = 0.004).

CONCLUSIONS

Crown heights of one-piece screw-retained titanium implant crowns did not significantly affect detorque values. Screw fracture, however, was greater for crown height of 14 mm than those of 6 mm and 10 mm.

Dental implant-abutment fracture resistance and wear induced by single-unit screw-retained CAD components fabricated by four CAM methods after mechanical cycling

STATEMENT OF PROBLEM

Computer-aided design and computer-aided manufacturing (CAD-CAM) methodologies allow the fabrication of custom dental implant abutments with a variety of materials and techniques. Studies on the mechanical strength of such components and the wear induced at their coupling interface during mechanical cycling are sparse.

PURPOSE

The purpose of this in vitro study was to measure the wear patterns at the hexagonal platform of dental implants induced by the installation and mechanical cycling of custom abutments fabricated by using 4 different CAD-CAM methods and to determine the compressive static resistance of the implant-abutment combinations.

MATERIAL AND METHODS

A CAD software program was used to design a custom abutment for a single-unit screw-retained external hexagon dental implant crown. The same design file was used to manufacture with 4 CAM methods (N=40): milling and sintering of zirconium dioxide (ZO), cobalt-chromium (Co-Cr) sintered by selective laser melting (SLM), fully sintered machined Co-Cr alloy (MM), and machined and sintered agglutinated Co-Cr alloy powder (AM). Prefabricated titanium abutments were used as a control (TI). Each abutment was installed onto a dental implant (4.1×11 mm), and the specimens were mechanically aged (1 million cycles, 2 Hz, 100N, 37 °C). After mechanical cycling, the hexagonal connection of the dental implants was examined with a scanning electron microscope (SEM), and unused dental implants (NI) were examined as a control (n=10). The images were analyzed with a software program to quantify the areas that showed wear. The implant-abutment combinations were reassembled and submitted to a compression test (1mm/min) with a universal testing machine. The data obtained were submitted to 1-way ANOVA (α=.05).

RESULTS

The mean ±standard deviation fracture load (N) of the specimens of each group were 1005 ±187 (ZO), 1074 ±123 (SLM), 1033 ±109 (MM), 1019 ±149 (AM), and 923 ±129 (TI). These values were statistically similar (P=.213). The mean ±standard deviation wear of the implants in squared-pixels were 1.1 ±0.38×10⁵ (ZO), 2.0 ±0.29×10⁵ (SLM), 1.0 ±0.38×10⁵ (MM), 1.1 ±0.27×10⁵ (AM), 1.1 ±0.33×10⁵ (TI), and 0.51 ±0.29×10⁵ (NI). The results indicated that, although significantly higher than those in in the control group (NI), the wear values found in the groups TI, ZO, MM, and AM were significantly lower than in the SLM group (P<.001).

CONCLUSIONS

The CAD-CAM abutments presented the same mechanical fracture load and wear measurements as the TI group, except for the SLM material, which showed increased wear. The failure mode from the load bearing test was the fracture of the abutments for the ZO group. The implants permanently deformed or fractured for the metal abutment groups.

Displacement and performance of abutments in narrow-diameter implants with different internal connections

STATEMENT OF PROBLEM

Displacement of abutments into conical connection implants during screw tightening may also occur during functional loading, creating unsettling forces that may cause loss of preload. A recent conical-hexagon connection with double friction fit (conical-hexagon connection) could prevent this axial displacement.

PURPOSE

The purpose of this in vitro study was to measure the 3D axial displacement of abutments with a conical-hexagon connection or conical connection in narrow-diameter implants. Removal torque values (RTVs), preload efficiency, and survival after cyclic loading were also compared.

MATERIAL AND METHODS

Narrow-diameter implants with a conical connection (Osseospeed EV, 3.0×13 mm-AST) and narrow-diameter implants with a conical-hexagon connection (Eztetic, 3.1×13 mm) were embedded in resin rods (G10) (n=6). Six titanium abutments per system were used, and their spatial relationship to the implant platforms after hand tightening was determined by using 3D digital image correlation. The abutments were tightened to the manufacturers' specified values, and the abutments' relative position was recorded again. The displacement of the abutment after tightening was calculated. The implants were subjected to cyclic loading (5×10⁶ cycles at 2 Hz) under 200-N loads at a 30-degree angle. After cyclic loading, the RTVs of screws were measured and compared with those specified by the manufacturers to calculate preload efficiency. ANOVA was used to compare the differences in displacements after tightening and to compare differences in RTVs after cyclic loading across the groups (α=.05).

RESULTS

The mean displacement in the U direction (X-axis) for the AST was -0.7 μm and -4.7 μm for ZIM, with no statistical difference (P=.73). The mean displacement in the V direction (Y-axis) for AST was -37.0 μm, and -150.0 μm for ZIM, with significant statistical difference (P<.001). The mean displacement in the W direction (Z-axis) for AST was -0.9 μm, and -23.0 μm for ZIM, with no statistical difference (P=.35). The survival of groups was similar (P=.058). During cyclic loading, 3 AST specimens fractured. After cyclic loading, mean RTV for AST was -8.77 Ncm, and -14.24 Ncm for ZIM, and these values were significantly different (P=.04). Preload efficiency was 28.1% for AST and 41.5% for ZIM.

CONCLUSIONS

Greater abutment displacements were observed with the conical-hexagon connection, which required a higher torque, as specified by its manufacturer. The abutments displaced more in the V-axis in both implants. Only the conical connection implant (Ti Grade 4, commercially pure) had failures during cyclic loading, but the survival of the implants was similar. After cyclic loading, the abutment screws in both systems lost some of their torque value. The abutment screws of the conical-hexagon connection implant maintained preload more efficiently during cyclic loading than those of the conical connection implant.

Implant Bio-mechanics for Successful Implant Therapy: A Systematic Review

Background:

Dental implants are considered the best treatment option for replacement of missing teeth due to high survival rates and diverse applications. However, not all dental implant therapies are successful and some fail due to various biological and or/mechanical factors. The objective of this study was to systematically review primary studies that focus on the biomechanical properties of dental implants in order to determine which biomechanical properties are most important for success of dental implant therapy.

Materials and Methods:

An electronic database search was performed using MEDLINE (PubMed), EMBASE, Google Scholar, and CAB Abstracts. Six principal biomechanical properties were considered to prepare the search strategy for each database using key words and Boolean operators. Human and animal studies (observational studies, trials, and in vitro studies) were included in this review. Human studies that were considered eligible needed to have subjects above 18 years who received permanent restorations after implant surgery and followed up for at least 6 months after receiving permanent restorations. Studies with subjects who had absolute contraindications at the time of dental implant surgery were excluded.

Results:

In total, 28 studies were included in the review after application of the eligibility criteria; 18 in vitro studies, 5 cohort clinical studies, 3 animal studies, and 2 nonrandomized trials. Six in vitro studies assessed loss of preload, five in vitro studies assessed fatigue strength, four assessed implant abutment connection design, and one assessed implant diameter. Two nonrandomized trials assessed torque and six observational studies assessed the effect of cantilevers. Gold alloy coating of abutment screws resulted in higher preload values followed by titanium alloy coating and gold coating; there was a difference in preload values between coated and uncoated screws when tightened repeatedly. Preload values decreased as a function of time with majority of preload loss occurred within 10s of tightening. The 8-degree internal conical implant performed better than the internal hex design. Higher rate of complications (porcelain chipping, de-cementation) was observed in the cantilever groups in studies.

Conclusion:

Biomechanical properties of implants like preload, torque, cantilever design, implant abutment design have profound effects on the survival rates of dental implants. With limiations, this review provides some important parameters to consider for successful implant therapy.

Influence of abutment angulation on loss of prosthetic abutment torque under mechanical cycling

STATEMENT OF PROBLEM

Internal conical connections provide mechanical stability for the prosthetic abutment and implant connection. However, some clinical situations require the use of angled prosthetic abutments that may increase stress on supportive implants by difference force vectors under cyclic loading.

PURPOSE

The purpose of this in vitro study was to measure the screw loosening values of prosthetic abutments with internal conical connections (indexed and nonindexed) having different angles under mechanical cycling.

MATERIAL AND METHODS

Thirty-six implants (4.0×13 mm, Titamax) with internal conical connections and their respective universal prosthetic abutments (n=36, 3.5×3.3 mm) were divided into indexed and nonindexed groups (n=18) with abutment inclinations of 0 (straight), 17, and 30 degrees. An insertion torque of 15 Ncm was applied according to the manufacturer's specifications. The specimens underwent fatigue testing of 500 000 cycles at a frequency of 2 Hz with a dynamic compressive load of 120 N at an angle of 30 degrees. The detorque values were measured by using a digital torque meter and tabulated for statistical analyses.

RESULTS

The specimens with indexed abutments had mean ±standard deviation detorque values of 6.72 ±2.29 Ncm under mechanical cycling, whereas those with nonindexed abutments had values of 8.98 ±1.84 Ncm. In the indexed group, the lowest detorque value was observed for abutments at 30 degrees compared with the straight group (P<.05). As for nonindexed abutments, similar detorque values were observed after increasing the abutment inclination (P>.05).

CONCLUSIONS

A decrease in detorque values in the indexed abutments related to their inclination was found under mechanical cycling, whereas the prosthetic abutments with 30 degrees of angulation had the lowest values. No decrease was found in the nonindexed abutments.

Comparison in Four Different Implant Systems of Mechanical Resistance to Maximal Stress in Prosthetic Screws-An In Vitro Study

Micromovements of the implant–abutment connection influence peri-implant bone preservation. This study evaluates and quantifies the maximal torque after a cycle of implant prosthetic screws tightening using original components. A total of 40 samples were tested: Megagen^®—Daegu, South Korea; Dentium^®—Gangnam-Gu, Seoul, Korea; BIOMET 3i^®—West Palm Beach, FL, USA and BTI^®—Álava, Spain. Screws from each manufacturer were subjected to maximal stress force until they fractured. The fracture points were recorded and compared among all samples. To compare the mean values of fracture torques, the reference values associated with each brand and the sample results were used in t-tests. ANOVA (analysis of variance) was used to compare the maximal resistance limit between brands, complemented with Tukey’s multiple-comparison test. The maximal considered level of significance was 5%. The average fracture force for the brands was 40.07 Ncm for Megagen^®, 53.39 Ncm for Dentium^®, 39.74 Ncm for Biomet 3i^®, and 68.84 Ncm for BTI^®. BTI^® screws showed the most resistance to fracture. According to the protocol that was applied, the implant–abutment connection demonstrated good resistance and a precise fit between these interfaces; therefore, in some cases, the presented values showed a lack of quality control and low fracture resistance.

Effect of dynamic cyclic loading on screw loosening of retightened versus new abutment screw in both narrow and standard implants (in-vitro study)

BACKGROUND

The purpose of this in-vitro study was to evaluate the effect of dynamic cyclic loading on screw loosening of retightened abutment screw versus new abutment screw in both narrow and standard implants.

METHODS

Separate acrylic resin blocks containing implant assembly (fixture, abutment, abutment screw, metal tube capping the abutment). Samples were divided into two main groups according to the diameter of implant: group 1 (GI 4.5-mm diameter) and group 2 (GII 3-mm diameter). Each group is subdivided into two subgroups according to the suggested option to manage screw loosening either by retightening (GIA, GIIA) or using new screws (GIB, GIIB). One hundred thousand cycles of eccentric dynamic cyclic loading (DCL) were applied before and after retightening or replacing the screw; then, removal torque loss (RTL) ratio was calculated, tabulated, and analyzed by t-student, ANOVA, pair wise Tukey's tests.

RESULTS

There were differences between GI and GII regarding the incidence of screw loosening process. Removal torque loss ratio was higher in GIB and GIIB where the old abutment screws were replaced by new screws for both standard implants (SIs) and narrow diameter implants (NDIs). There was significant effect of retightening and replacing the abutment screws after exposure to DCL.

CONCLUSIONS

Within the limitations of this in-vitro study, it can be conclude that screw loosening process occurred in both SIs and NDIs but with higher values in NDIs. It is better to retighten the screw of NDIs and SIs than replacing it with a new screw.

Influence of Implant Connection, Abutment Design and Screw Insertion Torque on Implant-Abutment Misfit

Background: An accurate fit at the implant-abutment interface is an important factor to avoid biological and mechanical complications. The aim of this study was to evaluate the marginal misfit at the implant-abutment interface on external and Morse taper connection, with straight and angulated abutments under different insertion torque loads. Materials and Methods: A total of 120 implants were used, 60 with external connection (EC) and 60 with Morse taper connection (IC). Straight (SA) (n = 60) and angulated abutments (AA) (n = 60) were randomly screwed to each connection at different torque levels (n = 10 each): 10, 20 and 30 Ncm. All specimens were subjected to thermal and cyclic loading and the misfit was measured by scanning electron microscopy. Data were analyzed with one-way ANOVA, t-test and Kruskal-Wallis test. Results: Significant differences (p < 0.001) were found between connections and abutments regardless of the torque applied. Morse taper connections with straight and angulated abutments showed the lowest misfit values (0.6 µm). Misfit values decreased as torque increased. Conclusions: The misfit was affected by the type of connection. The type of abutment did not influence the fit in the Morse taper connection. The higher the tightening torque applied the increase in the fit of the implant-abutment interface.

Effect of framework type on survival probability of implant-supported temporary crowns: An in vitro study

Background

This in vitro study evaluated the effect of framework type on the survival probability of temporary implant-supported crowns and on the implant platform structure after dynamic fatigue.

Material and Methods

Thirty (30) external hexagon implants (3.75 x 10 mm) were embedded in acrylic resin following the ISO-14801. Standardized temporary crowns (n=10, N=30) were manufactured in acrylic resin and divided according to the framework type: Total plastic, Plastic with CoCr base and Titanium. The crowns were installed onto the implants (20N.cm) and fatigued (100N, 2 Hz) to determine the crowns’ survival probability for missions of 300.000 and 600.000 cycles. Fatigue data were submitted to the Kaplan-Meier test followed by Wilcoxon and Log Rank, all with α = 5%. The implant platforms were parametrically inspected based on the scanning before and after the fatigue to evaluate the damage. The strain values were analyzed using One-way ANOVA and Tukey test, all with α = 5%.

Results

ANOVA revealed that the Total plastic showed less implant damage (-0.07 ± -0.03 mm) than the Plastic with CoCr base (-0.08 ± -0.04 mm) and the Titanium (-0.10 ± -0.01 mm) frameworks. Therefore, the framework type to manufacture implant-supported temporary crowns influences the fatigue survival of the restoration and the implant platform damage. The Plastic with CoCr base and Titanium frameworks showed superior reliability than the Total plastic framework which could not survive 600,000 cycles.

Conclusions

The Plastic with CoCr base and the Titanium framework are suitable for restorations over 3 months in use, without a difference in the implant platform damage.

Key words:Implant dentistry, axial loading, occlusion, methodo­logical study.

Accuracy of different electronic torque drivers: A comparative evaluation

PURPOSE

This study aims to evaluate the loosening torque on the implant fixture, and to assess the accuracy of difference electronic torque drivers.

MATERIALS AND METHODS

Three electronic torque drivers were used to measure the loosening torque on the implant system (AnyOne; MegaGen). The implant fixtures were divided among the 3 electronic torque driver types (W&H, SAESHIN, and NSK group) and 9 for each group. The screws were fastened at the implant fixture by three electronic torque drivers using the tightening torques recommended by the manufacturers of the drivers. After 10 minutes, the screws were again fastened at the implant fixture with equal torque. Then, the loosening torques were measured with an MGT12 torque gauge (MARK-10, Inc.). This measurement procedure was repeated 10 times under loosening torques of 15 Ncm, 25 Ncm, and 35 Ncm. In the statistical analysis, all values of loosening torque were analyzed with the one-way ANOVA and Kruskal-Wallis test (α=.05) for comparative evaluation.

RESULTS

There were significant inter-group differences at loosening torques of 15 Ncm and 25 Ncm (P<.05). The accuracy of the NSK driver was the highest, followed by SAESHIN and W&H. There was no significant difference between NSK and W&H at 35 Ncm (P>.05). The SAESHIN driver showed the closest loosening torque at 35 Ncm.

CONCLUSION

The most accurate loosening torques were SAESHIN at 35 Ncm, and NSK at 15 Ncm and 25 Ncm. Since the loosening torque may vary depending on the tightening torques and electronic torque drivers, periodic calibration of the electronic torque driver is recommended.

Effect of implant abutment connection designs, and implant diameters on screw loosening before and after cyclic loading: In-vitro study

AIMS

The purpose of this in-vitro study was to evaluate the screw loosening of two different forms of implant abutment connection designs, and two implant diameters by measuring removal torque value (RTV) before and after cyclic loading.

MATERIALS AND METHODS

Twenty implant fixtures were divided equally into 2 groups (N=10): group I fixture with conical hybrid connection (CH), and group II fixture with internal hex connection (IH). Each group was divided equally into two subgroups according to implant diameters: subgroup A (3.3mm), and subgroup B (4.2mm). Each fixture was vertically placed in the center of an acrylic resin block. The samples were fixed to the jig, and an implant abutment connected it with a 20 Ncm tightening torque. The samples were subjected to eccentric cyclic loading (at a distance of 5mm) away from center of abutment at 100,000 cycles. A digital torque gauge was used to evaluate screw loosening by measuring RTVs in (Ncm) before and after cyclic loading. The removal torque loss ratio before and after cyclic loading and the removal torque loss ratio between before and after cyclic loading were calculated and analyzed using the SPSS statistical analysis.

RESULTS

For GI the initial removal torque loss ratio measurement was (14.45±3.18) and decreased significantly after loading, it was (11.47±3.64). For GII the initial removal torque loss ratio measurement was (20.47±4.99) and increased significantly after loading, being (35.35±4.26). There is no significant effect upon screw loosening for two implant diameters.

CONCLUSION

Within the limitations of this study, the results suggested that conical hybrid connections showed a better screw stability than an internal hex connection. Therefore, the use of conical implants can be promoted as they have better screw stability compared to other systems.

Does the transversal screw design increase the risk of mechanical complications in dental implants? A finite elements analysis

The transversal screw was introduced in order to overcome some disadvantages of the transocclusal screw. However, its mechanical risk has not been studied sufficiently. The main purpose of this research was to assess and compare stress distribution in the screws and abutment of a single-crown implant with transversal and transocclusal screw models. Two 3D models were assembled to analyse a single-implant-supported prosthesis with transversal and transocclusal screws embedded in the jawbone. The crown was subjected to a static load of value 300 N with different levels of inclination. The transversal screw model, with an axial load of 15°, was the one with lowest stress values in all its components. However, the stress was greater with more inclined loads when compared with the transocclusal model. The prosthetic transversal screw showed much less stress than the rest of the components for any load inclination. The transversal screw design is the option with the lowest risk of mechanical complications, both in the prosthetic screw and in the abutment screw, when applying forces of lower inclination. The more oblique forces favoured a better biomechanical environment in the abutment and its screw in the transocclusal screw model.

Influence of contact configuration and lubricating conditions on the microtriboactivity of the zirconia-Ti6Al4V pair used in dental applications

Loosening and fracture of implanted dental crowns is a consequence of relative micromovements between the zirconia abutment and the titanium alloy of the implant, in a biochemical aggressive environment. Thus, it is important to establish the in vitro tribological testing conditions that better mimics such environment. The present work aims to evaluate the effect of ball-on-plate tests configuration on the tribological behavior of ZrO2/Ti6Al4V pair in dry and lubricated conditions, using different lubricants: water, artificial saliva solution and human saliva. Ceramic balls sliding on metallic plates (TiPlate) and metallic balls sliding on ceramic plates (TiBall) were tested and the coefficient of friction (CoF) and wear response was monitored trough nanotribological tests. Open circuit potential was also measured during the tests carried out in saline solution (artificial saliva) to access the tribochemical response. The wear mechanisms were evaluated by scanning electron microscopy and atomic force microscopy analysis. Relevant differences were found between the two configurations, with and without the presence of human saliva: TiPlate presented always a higher CoF than TiBall, which may have resulted from differences in the degradation and regeneration processes of the titanium passive film during sliding. TiBall demonstrated to be the best choice to reproduce the in vivo conditions, since the metallic surface contacts permanently with zirconia, impairing the titanium repassivation. Regarding the effect of the lubricants, it was observed that human saliva had a protective action of the surfaces, leading to the lowest CoF among the lubricants used (0.19 ± 0.05 for TiBall and 0.35 ± 0.08 for TiPlate) and neglectable wear.

Removal torque pattern of a combined cone and octalobule index implant-abutment connection at different cyclic loading: an in-vitro experimental study

Background

Despite the high survival rate of dental implants, screw loosening is frequently reported. Screw loosening can cause a misfit of the implant-abutment connection leading to peri-implantitis or abutment screw fracture. Therefore, studies about related factors and mechanism of screw loosening are needed. The aim of this study was to evaluate the decreasing pattern of removal torque values (RTVs) of a combined cone and octalobule index implant-abutment connection under different numbers of mechanical loading cycles.

Materials and methods

The study was performed in accordance with ISO 14801:2007. Eighty-four implants with the combined cone and octalobule index implant-abutment connection (PW Plus dental implant system, PW Plus Company) were used. All abutment screws were tightened 30 N cm twice with a 10-min interval. The control group was without cyclic loading and the experimental groups underwent different numbers of loading cycles until 2,000,000 cycles. Then, the abutment screws of all samples were untightened to measure the RTVs. The data were analyzed using ANOVA and Tukey’s HSD test.

Results

The RTVs of the control group decreased 7.78% compared to the insertion torque. All experimental groups from 50,000 to 2,000,000 cycles showed significant decreases in RTVs compared to the control group (P < 0.05). RTVs in the group of 50,000 cycles to 1,800,000 cycles did not change significantly, but there was a significant reduction of RTVs in the group of 2,000,000 cycles when compared to the group of 50,000 cycles (P < 0.05).

Conclusions

According to the setting condition for the fatigue test complied to ISO 14801:2007, the RTVs of the combined cone and octalobule index implant-abutment connection reduced significantly after 50,000 cycles and did not change significantly until 2,000,000 cycles.

Fatigue and microgap behaviour of a three-unit implant-fixed dental prosthesis combining conventional and dynamic abutments

This is an in vitro study composed by a fatigue test followed by an optical microscopy analysis. Dynamic abutments concept, recently introduced on screw-retained implant dental prosthesis, consists on the screw channel customisation according to the individual needs of each rehabilitation. Geometry and tightening torque differences advise the assessment of their mechanical performance. Clarify whether the combination of dynamic and conventional abutments in a three-unit implant-fixed prosthesis has detrimental effects either on the mechanical performance under cyclic loading or on the implant-abutment microgap dimensions. The fatigue test was performed in agreement with the ISO standard 14801. Then on the samples that resisted 5 million cycles, the implant-abutment microgap was measured on dynamic and conventional abutments using optical microscopy. Two unloaded samples were used as control group. The samples supported a load of 1050 N. The implant-abutment microgap measurement did not show statistically significant differences (p = .086) between loaded and unloaded groups, but the loaded conventional abutments showed a significant lower implant-abutment microgap (p = .05) than the loaded dynamic abutments. The combination of conventional and dynamic abutments do not seem to produce a decrease in fatigue resistance to a level below the mastication forces or an increase in the joint dimensions.

Influence of torsional strength on different types of dental implant platforms

AIM

The study assessed deformation of implant components submitted to torsion tests of 80 and 120 N · cm using an optical stereomicroscope.

MATERIAL AND METHODS

The following 3 types of Titaniumfix conical implant connections (n = 5) measuring Ø 4.0 × 11.5 mm were used: external, internal hexagon and Morse taper connections. The diagonal and lateral measurements of the hexagon implant platform were measured before and after the torsion test.

RESULTS

The torsion test using torque of 80 and 120 N · cm altered the implant dental platforms. All groups presented deformation of implant component after torque of 80 N · cm with no statistical difference among them. During torque of 120 N · cm, a difference in the Morse taper connection in relation to the internal and external hexagon connection was observed. The Morse taper connection implant, followed by the internal hex implant, underwent less deformation. Greater deformation occurred in the external hex implants.

CONCLUSION

For all the implants, high insertion torques deformed the implant platform preventing long-term maintenance and stability of implants.

Stability of the prosthetic screws of three types of craniofacial prostheses retention systems

Objectives

This study aimed to evaluate the stability of prosthetic screws from three types of craniofacial prostheses retention systems (bar-clip, ball/O-ring, and magnet) when submitted to mechanical cycling.

Materials and Methods

Twelve models of acrylic resin were used with implants placed 20 mm from each other and separated into three groups: (1) bar-clip (Sistema INP, São Paulo, Brazil), (2) ball/O-ring (Sistema INP), and (3) magnet (Metalmag, São Paulo, Brazil), with four samples in each group. Each sample underwent a mechanical cycling removal and insertion test (f=0.5 Hz) to determine the torque and the detorque values of the retention screws. A servo-hydraulic MTS machine (810-Flextest 40; MTS Systems, Eden Prairie, MN, USA) was used to perform the cycling with 2.5 mm and a displacement of 10 mm/s. The screws of the retention systems received an initial torque of 30 Ncm and the torque values required for loosening the screw values were obtained in three cycles (1,080, 2,160, and 3,240). The screws were retorqued to 30 Ncm before each new cycle.

Results

The sample was composed of 24 screws grouped as follows: bar-clip (n=8), ball/O-ring (n=8), and magnet (n=8). There were significant differences between the groups, with greater detorque values observed in the ball/O-ring group when compared to the bar-clip and magnet groups for the first cycle. However, the detorque value was greater in the bar-clip group for the second cycle.

Conclusion

The results of this study indicate that all prosthetic screws will loosen slightly after an initial tightening torque, also the bar-clip retention system demonstrated greater loosening of the screws when compared with ball/O-ring and magnet retention systems.

The influence of length of implant on primary stability: An in vitro study using resonance frequency analysis

Background

Primary stabilityis not sufficientin less contact area between the implant and bone, the healing process because will be disrupted due to micro-motions and fibrous tissue affects osseointegration.

Material and Methods

We implemented an in vitro experimental study of total 135 XiVE® implants were inserted in 22.5 bovine cow ribs with bone quality similar to a type IV human bone. Each rib end received a group of three different implant lengths, which were 8mm, 13mm and 15mm and had the same diameter 3.8mm. Immediately after the implant placement, its primary stability was measured using Osstell Mentor equipment. ANOVA Tukey’s honest to test the significant difference were performed for data analysis between the resonance measures of the different lengths of implants. Statistical significance was assessed at a level P< 0.05.

Results

A total of 45 implants were inserted for each length at cortical bone level. A significant difference between the three groups in favor of implant with 15mm length group (P = 0.000).

Conclusions

Increasing dental implant length is considered to play a fundamental role in increasing dental implant primary stability, even in poor bone quality, through controlling the bone preparation process.

Key words:Dental implants, primary stability, resonance frequency analysis.

Analysis of resistance to fatigue between straight solid and anatomic abutments of Morse taper system

Abstract Background The study of the phenomenon of fatigue is essential because implant failures usually are caused by this process. Purpose The objective of this study was to examine the fatigue resistance of straight and anatomical abutments joints that were submitted to cyclic loads. Material and method We used 37 Morse taper implants and 37 abutments, divided into two groups (n= 16: straight abutment, n= 21 anatomical abutment). The sets were submitted to cyclic loading (5 million) using servo-hydraulic equipment. Three sets from each group were subjected to bending tests to determine the maximum load resistance, which served as the parameter for comparison of the cyclic tests. We evaluated number of cycles, load and bending moment. Result Of the 31 abutments cyclically tested, 17 (54.8%) fractured in fewer than 5 million cycles; 8 (25.8%) of these were straight abutments, and 9 (29%) were anatomical. A total of 14 samples (45.2%) resisted the cyclic loading. According to Fisher's exact test, there was no difference between groups as the fracture. Conclusion Despite of the straight abutments have higher average load and bending moment on the anatomical, both types of abutments showed similar performance as the fracture strength in vitro.

Influence of sulfide concentration on the corrosion behavior of titanium in a simulated oral environment

This study assessed the corrosion behavior of titanium in response to sulfide by determining the effects of sulfide concentration and pH over immersion period. Corrosion was evaluated through changes in color, glossiness, surface characterization, and titanium release. Sulfide solutions were prepared in 3 different concentrations with Na2S, each in pH unadjusted (sulfide-alkaline) and pH adjusted to 7.5 (sulfide-neutral). Titanium discoloration increased and glossiness decreased as sulfide concentration and immersion period increased in sulfide-alkaline solutions. Coral-like complexes were observed on the surface of these specimens, which became more pronounced as concentration increased. Small amounts of titanium release were detected in sulfide-alkaline solutions; however, this was not affected by immersion periods. Corrosion was indicated through considerable surface oxidation suggesting the formation of a thick oxide layer. No significant changes in color and glossiness, or titanium release were indicated for titanium specimens immersed in sulfide-neutral solutions indicating that pH had a significant effect on corrosion. Our findings suggest that a thick oxide layer on the titanium surface was formed in sulfide-alkaline solutions due to excessive oxidation.

Effect of abutment screw length and cyclic loading on removal torque in external and internal hex implants

PURPOSE

The purpose of this study was to evaluate the effects of abutment screw length and cyclic loading on the removal torque (RTV) in external hex (EH) and internal hex (IH) implants.

MATERIALS AND METHODS

Forty screw-retained single crowns were connected to external and internal hex implants. The prepared titanium abutment screws were classified into 8 groups based on the number of threads (n = 5 per group): EH 12.5, 6.5, 3.5, 2.5 and IH 6.5, 5, 3.5, 2.5 threads. The abutment screws were tightened with 20 Ncm torque twice with 10-minute intervals. After 5 minutes, the initial RTVs of the abutment screws were measured with a digital torque gauge (MGT12). A customized jig was constructed to apply a load along the implant long axis at the central fossa of the maxillary first molar. The post-loading RTVs were measured after 16,000 cycles of mechanical loading with 50 N at a 1-Hz frequency. Statistical analysis included one-way analysis of variance and paired t-tests.

RESULTS

The post-loading RTVs were significantly lower than the initial RTVs in the EH 2.5 thread and IH 2.5 thread groups (P<.05). The initial RTVs exhibited no significant differences among the 8 groups, whereas the post-loading RTVs of the EH 6.5 and EH 3.5 thread groups were higher than those of the IH 3.5 thread group (P<.05).

CONCLUSION

Within the limitations of this study, the external hex implants with short screw lengths were more advantageous than internal hex implants with short screw lengths in torque maintenance after cyclic loading.

In vitro analysis of the microbiological sealing of tapered implants after mechanical cycling

OBJECTIVE

The aim of this in vitro study was to evaluate the mechanical behavior and bacterial microleakage at the implant/abutment-tapered interface following mechanical cycling.

MATERIALS AND METHODS

Two groups of screwless (Morse taper) implants (G1 and G2) and two groups of prosthetic screwed implants (G3 and G4) were tested. One group from each model (G2 and G4) were submitted to mechanical cycling, 500,000 cycles per sample, at a load of 120 N at 2 Hz prior to analysis. Microbiological analysis was performed via immersion of all samples in an Escherichia coli-containing suspension, incubated at 37 °C. After 14 days, the abutments were removed from their respective implants, registering the removal force (G1 and G2) or reverse torque (G3 and G4), and the presence of bacterial leakage was evaluated. Scanning electron microscopy (SEM) was performed to analyze the tapered surfaces of the selected samples. The Student t, binomial, and G tests were used for statistical analysis at a 5 % significance level.

RESULTS

The results showed no significant difference between removal force, reverse torque, and contamination values when comparing implants of the same type. However, when the four groups were compared, contamination differed significantly (p = 0.044), with G1 having the least number of contaminated samples (8.3 %). SEM analysis showed superficial defects and damage.

CONCLUSIONS

The abutment removal force or torque was not affected by mechanical cycling. Bacterial sealing of the implant/abutment tapered interface was not effective for any condition analyzed. Imprecise machining of implant parts does not allow a sufficient contact area between surfaces to provide effective sealing and prevent bacterial leakage.

CLINICAL RELEVANCE

The microscopic gap caused by unsatisfactory implant/abutment adaptation, surface irregularities, and plastic deformation of all parts enabled bacterial contamination of the oral implants.

The Effect of Tissue Entrapment on Screw Loosening at the Implant/Abutment Interface of External- and Internal-Connection Implants: An In Vitro Study

PURPOSE

To compare the removal of torque values of machined implant abutment connections (internal and external) with and without soft tissue entrapment using an in vitro model.

MATERIALS AND METHODS

Thirty external- and 30 internal-connection implants were embedded in urethane dimethacrylate. Porcine tissue was prepared and measured to thicknesses of 0.5 and 1.0 mm. Six groups (n = 10) were studied: External- and internal-connection implants with no tissue (control), 0.5, and 1.0 mm of tissue were entrapped at the implant/abutment interface. Abutments were inserted to 20 Ncm for all six groups. Insertion torque values were recorded using a digital torque gauge. All groups were then immersed in 1 M NaOH for 48 hours to dissolve tissue. Subsequent reverse torque measurements were recorded. Mean and standard deviation were determined for each group, and one-way ANOVA and Bonferroni test were used for statistical analysis.

RESULTS

All 60 specimens achieved a 20-Ncm insertion torque, despite tissue entrapment. Reverse torque measurements for external connection displayed a statistically significant difference (p < 0.05) between all groups with mean reverse torque values for the control (13.71 ± 1.4 Ncm), 0.5 mm (7.83 ± 2.4 Ncm), and 1.0 mm tissue entrapment (2.29 ± 1.4 Ncm) groups. Some statistically significant differences (p < 0.05) were found between internal-connection groups. In all specimens, tissue did not completely dissolve after 48 hours.

CONCLUSIONS

External-connection implants were significantly affected by tissue entrapment; the thicker the tissue, the lower the reverse torque values noted. Internal-connection implants were less affected by tissue entrapment.

Effect of mechanical cycling on screw torque in external hexagon implants with and without platform switching

This in vitro study evaluated the effect of mechanical cycling on the torque of retaining screw in external hexagon implants with platform switching (PS), regular platform (RP) and wide platform (WP). A total of 30 specimens were equally divided into 3 groups: PS, PR and WP. Each specimen was prepared with implants: 3.75 x 10 mm for RP group and 5.0x10 mm for PS and WP groups and its respective abutment with 32 Ncm torque. All groups were subjected to 106 cycles with 100 N (corresponding to about 40 months of chewing). The results were obtained with the reverse torque of each specimen and data were evaluated using ANOVA and Tukey test (p<0.05). The PS group showed statistically significant difference in screw removal torque (30.06±5.42) compared with RP (23.75±2.76) and WP (21.32±3.53) (p<0.05) groups; the RP and WP groups showed no statistically significant difference between them. It was concluded that the PS group showed higher reverse torque value, suggesting lower susceptibility of the abutment screw loosening.