Effect of lateral cyclic loading on abutment screw loosening of an external hexagon implant system

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.

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.

Does Abutment Collar Length Affect Abutment Screw Loosening After Cyclic Loading?

A significant vertical space that is corrected with vertical ridge augmentation may necessitate selection of longer abutments, which would lead to an increased vertical cantilever. This study investigated the influence of different abutment collar heights on single-unit dental implant screw-loosening after cyclic loading. Fifteen implant-abutment assemblies each consisted of an internal hexagonal implant were randomly assigned to 3 groups: Group1, consisting of 5 abutments with 1.5 mm gingival height (GH); Group2, 5 abutments with 3.5 mm GH; and Group3, 5 abutments with 5.5 mm GH. Each specimen was mounted in transparent auto-polymerizing acrylic resin block, and the abutment screw was tightened to 35 Ncm with an electric torque wrench. After 5 minutes, initial torque loss (ITL) was recorded for all specimens. Metal crowns were fabricated with 45° occlusal surface and were placed on the abutments. A cyclic load of 75 N and frequency of 1 Hz were applied perpendicular to the long axis of each specimen. After 500 000 cycles, secondary torque loss (STL) was recorded. One-way ANOVA analysis was used to evaluate the effects of abutment collar height before and after cyclic loading. One-way ANOVA showed that ITL among the groups was not significantly different (P = .52), while STL was significantly different among the groups (P = .008). Post-hoc Tukey HSD tests showed that STL values were significantly different between the abutments with 1.5 mm GH (Group1) and with 5.5 mm GH (Group3) (P = .007). A paired comparison t-test showed that cyclic loading significantly influenced the STL in comparison with the ITL in each group. Within the limitations of this study, it can be concluded that increase in height of the abutment collar could adversely affect the torque loss of the abutment screw.

Influence of different maintenance times of torque application on the removal torque values to loosen the prosthetic abutment screws of external hexagon implants

PURPOSE

To analyze the torque application on prosthetic abutment screws using different maintenance times, to determine an influence on the removal torque values.

MATERIALS AND METHODS

A total of 40 external hexagon implants, 40 titanium screws, and 40 customized abutments were used. In group 1, the screws received a torque of 30 N·cm by instant torque application; in groups 2, 3, and 4, torque of 30 N·cm was applied and maintained for 10, 20, and 30 seconds, respectively. Removal torque was performed 10 minutes after torque application. Data were statistically analyzed using 1-way ANOVA and Tukey HSD test (α = 0.05).

RESULTS

The mean and standard deviation (±SD) of removal torque values found were 11.61 ± 1.43 N·cm for group 1; 18.64 ± 1.71 N·cm for group 2; 21.62 ± 0.97 N·cm for group 3; and 21.48 ± 1.55 N·cm for group 4. Groups 3 and 4 exhibited statistically higher values than group 2, which demonstrated significantly higher values than group 1 (P < 0.05).

CONCLUSIONS

A torque of 30 N·cm applied for 20 seconds seemed to be the best option when considering the removal torque values of external hexagon implants.

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.

Effect of cement washout on loosening of abutment screws and vice versa in screw- and cement- retained implant-supported dental prosthesis

PURPOSE

The purpose of this study was to examine the abutment screw stability of screw- and cement-retained implant-supported dental prosthesis (SCP) after simulated cement washout as well as the stability of SCP cements after complete loosening of abutment screws.

MATERIALS AND METHODS

Thirty-six titanium CAD/CAM-made implant prostheses were fabricated on two implants placed in the resin models. Each prosthesis is a two-unit SCP: one screw-retained and the other cemented. After evaluating the passive fit of each prosthesis, all implant prostheses were randomly divided into 3 groups: screwed and cemented SCP (Control), screwed and noncemented SCP (Group 1), unscrewed and cemented SCP (Group 2). Each prosthesis in Control and Group 1 was screwed and/or cemented, and the preloading reverse torque value (RTV) was evaluated. SCP in Group 2 was screwed and cemented, and then unscrewed (RTV=0) after the cement was set. After cyclic loading was applied, the postloading RTV was measured. RTV loss and decementation ratios were calculated for statistical analysis.

RESULTS

There was no significant difference in RTV loss ratio between Control and Group 1 (P=.16). No decemented prosthesis was found among Control and Group 2.

CONCLUSION

Within the limits of this in vitro study, the stabilities of SCP abutment screws and cement were not significantly changed after simulated cement washout or screw loosening.

Effect of intentional abutment disconnection on the micro-movements of the implant-abutment assembly: a 3D digital image correlation analysis

BACKGROUND

Implant-abutment assembly stability is critical for the success of implant-supported rehabilitation. The intentional removal of the prosthetic components may hamper the achievement of the essential stability due to preload reduction in the screw joint and implant-screw mating surface changes.

OBJECTIVE

To evaluate the effect of intentional abutment disconnection and reconnection in the stability of internal locking hex implants and corresponding abutments using the method of 3D digital image correlation.

MATERIAL AND METHODS

Ten conical shape and internal hexagon connection implants were embedded in acrylic resin and assembled to prosthetic abutments with 30 Ncm torque and assigned to two groups: group 1 - tested for static load-bearing capacity at 30° off-axis for two times and group 2 - underwent intentional disconnection and reconnection between tests. Micro-movements were captured with two high-speed photographic cameras and analyzed with video correlation system in three spacial axes U, V and W. Screw abutment and internal implant thread morphology was observed with a field-emission scanning electron microscopy.

RESULTS

After the intentional disconnection of the abutment, group 2 showed generally higher maximum displacements for U and V directions. Under 50N load, mean difference was 24.7 μm (P = 0.008) for U direction and -7.7 μm (P = 0.008) for V direction. No significant differences were found for maximum and minimum displacements in the W direction. Mean displacement of the speckle surface presented was statistically different in the two groups (P = 0.016). SEM revealed non-homogenous screw surfaces with scoring on group 2 plus striations and debris in the implant threads.

CONCLUSION

Micro-movements were higher for the group submitted to intentional disconnection and reconnection of the abutment, particularly under average bite forces.

The Effect of a Positioning Index on the Biomechanical Stability of Tapered Implant-Abutment Connections

The biomechanical stability of the implant-abutment connection is critical for the success of implant-supported restorations. This study investigated the effect of a positioning index on the abutment screw preload values of tapered connection implants. Twenty Morse taper implants presenting an internal locking hex received 10 solid and 10 straight screw retained abutments for cemented single-crown restorations. Ten abutments had a positioning index to fit the internal locking hex of the implant (straight), and 10 were locked only by the implant taper (solid). The preload values for each abutment screw after a tightening torque were registered by strain gauges. Prosthetic crowns were placed on each abutment and subjected to mechanical cycling. Detorque forces were applied to each abutment and compared with the initial torque values. Data were statistically analyzed using Kolmogorov-Smirnov and Student t tests. The nonindexed group presented higher initial preload (6.05 N ± 0.95 N) compared with the indexed group (4.88 N ± 0.92 N; P &lt; .05). After cycling, the nonindexed group exhibited less reduction of preload (13.84% ± 6.43%) compared with the indexed group (52.65% ± 14.81%; P &lt; .01). Indexed tapered abutments for single-crown restorations might represent greater biomechanical risk under function.

In vitro mechanical analysis of complete-arch mandibular implant-supported fixed prostheses abutment screws after cyclic loading

STATEMENT OF PROBLEM

Clinicians question when to evaluate for worn or loose implant-supported retainer screws to prevent possible clinical complications.

PURPOSE

The purpose of this study was to compare differences among initial and postdynamically loaded detorque values and identify physical structural changes of prosthetic retaining screws in a simulated implant-supported mandibular complete fixed prosthesis.

MATERIAL AND METHODS

Nine groups and nonloaded controls comprising a 5-implant-supported, milled titanium framework were fabricated and assembled (screw torque 35 Ncm). Dynamic loading (20 to 220 N) was applied to simulate 2 years of oral function. After testing, screw detorque values were measured (ΔT, initial-detorque value). A scanning electron microscopic analysis of screw threads was used to assess physical changes. Data were analyzed by 2-way ANOVA to determine the influence of loading and implant position on ΔT (α=.05).

RESULTS

ΔT values of loaded and nonloaded groups were compared separately at each implant position and showed a significant difference only for the implant in the central position (P=.002). All positions were compared in terms of ΔT values separately for loaded and nonloaded conditions. A significantly higher ΔT was found in 1 cantilever area of the loaded group, whereas a significantly lower ΔT value was found in the central position in the nonloaded group. No statistically significant differences were found in physical changes between loading and nonloading or among implant positions.

CONCLUSIONS

When delivering a multiimplant supported prosthesis, the application of dynamic loading and the sequence in which implant screws are tightened could influence the subsequent detorque value of a screw; they have no effect on the physical appearance of screws after extended function.

Torque loss under mechanical cycling of long-span zirconia and titanium-cemented and screw-retained implant-supported CAD/CAM frameworks

OBJECTIVES

This study evaluated the screw joint stability after cyclic loading of implant-supported titanium and zirconia CAD/CAM frameworks for fixed dental prostheses (FDPs) with different retention methods.

MATERIAL AND METHODS

Twenty four one-piece frameworks supported by six threaded implants placed in the maxilla were fabricated using a CAD/CAM technique (NeoShape). Dry-pressed porcelain crowns were luted to the frameworks to standardize the specimens. The specimens were then divided into four groups (n = 6) according to framework material (titanium or zirconia) and retention method for the prosthesis (cement- or screw-retained): G1, Ti-cemented; G2, Ti-screw-retained; G3, Zr-cemented; and G4, Zr-screw-retained. A digital torque ratchet was used to assess the initial preload removal torque. Torque was then reapplied and the specimens were submitted to a 200 N cyclic load, at a frequency of 2 Hz, underwater in controlled temperature of 37°, and for 1 × 106 cycles. An opposing lower dental arch was fabricated using bis-acrylic resin to simulate occlusal contacts in centric. After cyclic loading, postload removal torque was measured. Preload and postload torque loss was expressed as a percentage of the initial load. Data were submitted to a linear mixed-effects model for statistical significance (α = 0.05) to evaluate the effect of cyclic loading in the screw torque loss used with frameworks of different materials and retention methods.

RESULTS

Significant screw torque loss (%) was found for the tested groups (before/after cyclic loading, respectively): G1 (39.77/61.83), G2 (37.57/50.96), G3 (34.87/54.10), and G4 (47.56/73.50) (P < 0.05).

CONCLUSIONS

The screw removal torque was significantly reduced for all groups in this study after cyclic loading the specimens. Screw-retained zirconia specimens presented the highest torque loss before and after the cyclic loadings compared with the other specimens that were tested.

Bacterial Composition at the Implant-Abutment Connection under Loading in vivo

PURPOSE

Platform-switched implants have been demonstrated to prevent bone loss after loading. The present study evaluated bacterial composition of sites from implant-abutment connections of immediately loaded implants, which were placed in the anterior mandible. Ten patients participated in this study.

MATERIALS AND METHODS

A and B implant systems with two different prosthetic connections (Morse tapered vs internal polygonal butt-joint connections, respectively) were placed and loaded for 2 years. The abutments were removed (AB sample) after careful decontamination. Bacterial sampling of the abutments, inner part of the implants (before/visit 1 and after rinsing with chlorhexidine [CHX]/visit 2), and after new abutment connection and loading for 1 additional month, a new sampling (visit 3) was taken to compare the bacteria composition in association with the two connections. Bacterial profiles of samples were determined by using the human oral microbe identification microarray.

RESULTS

A total of 240 samples were analyzed taken at different time intervals. Nonparametric statistical analysis (Wilcoxon Rank sum) with uncorrected alpha (p < .05) and after corrections (Benjamini-Hochberg) found no statistical significance between the two connections. No significant changes in the overall microbial profiles were detected at the different time intervals. However, there were trends toward presence of periodontitis-associated species at the B implants in all samples (AB, visit 1, even after CHX irrigation) and after decontamination, abutment replacement, and 1-month loading period.

CONCLUSIONS

CHX irrigation does not seem to have any effect on decontamination of connections. As shown previously, there is significantly more bone loss around B implants compared with A implants. Although there was no statistical difference in the microbial profiles, there was indeed a trend for the presence of typical periodontal pathogens associated with the internal polygonal butt-joint connection. A possible scenario is that this connection tends to harbor the pathogens that may be involved in subsequent bone loss.

Carbon film coating of abutment surfaces: effect on the abutment screw removal torque

PURPOSE

To evaluate the effect of diamond-like carbon (DLC) coating of prefabricated implant abutment on screw removal torque (RT) before and after mechanical cycling (MC).

MATERIALS AND METHODS

Fifty-four abutments for external-hex implants were divided among 6 groups (n = 9): S, straight abutment (control); SC, straight coated abutment; SCy, straight abutment and MC; SCCy, straight coated abutment and MC; ACy, angled abutment and MC; and ACCy, angled coated abutment and MC. The abutments were attached to the implants by a titanium screw. RT values were measured and registered. Data (in Newton centimeter) were analyzed with analysis of variance and Dunnet test (α = 0.05).

RESULTS

RT values were significantly affected by MC (P = 0.001) and the interaction between DLC coating and MC (P = 0.038). SCy and ACy showed the lowest RT values, statistically different from the control. The abutment coated groups had no statistical difference compared with the control. Scanning electron microscopy analysis showed DLC film with a thickness of 3 μm uniformly coating the hexagonal abutment.

CONCLUSION

DLC film deposited on the abutment can be used as an alternative procedure to reduce abutment screw loosening.

Effects of different abutment material and surgical insertion torque on the marginal adaptation of an internal conical interface: an in vitro study

PURPOSE

To evaluate the marginal adaptation at implant-abutment connection of an implant featuring a conical (45° taper) internal hexagonal abutment with a connection depth of 2.5mm, comparing the performance of two identical abutments of different material (titanium grade-4 and Co-Cr-alloy).

METHODS

Twenty implants (3.75 mm×15 mm) were connected to non-matching abutments (5.5 mm×10 mm) of two different materials (titanium grade-4: n=10; Co-Cr-alloy: n=10). The specimens were separately embedded in epoxylite resin, inside copper cylinders, and submerged without covering the most coronal portion (5 mm) of the fixture. Five specimens per group were stressed simulating a surgical 100 Ncm insertion torque, while the others had no torque simulation. All specimens were subjected to a non-axial static load (100 N) in a universal testing machine, under an angle of 30° with respect to the implant axis. Once 100 N load was reached, low shrinkage self-curing resin was injected inside the cylinders, and load was maintained until complete resin polymerization. Specimens were cut and analyzed with optical and scanning-electron-microscope (SEM) to evaluate the marginal adaptation at the implant-abutment connection. Statistical analysis was performed using one-way ANOVA (p=0.02).

RESULTS

None of the 20 samples failed. The implant-abutment connection was able to guarantee a good optical seal; SEM analysis confirmed the absence of microgaps.

CONCLUSIONS

Within the limits of this study (small sample size, limited time) the marginal adaptation of the implant-abutment connection was not affected by the abutment material nor by the application of surgical insertion torque.

Stability of external and internal implant connections after a fatigue test

Objective:

The objective of this study was to compare the torque and detorque values of screw intermediates of external hexagon, internal hexagon, and Morse taper implants in single restorations before and after mechanical cycling.

Materials and Methods:

The study sample was divided into three groups (n = 10) as follows: group EH – external hexagon implant, group IH – internal hexagon implant, and group MT – Morse taper implant. Universal abutments were screwed on the implants, and metal crowns were cemented onto the abutment. The samples were submitted to a mechanical testing of 1 million cycles, with a frequency of 8 cycles per second under a 400 N load. The application and registration of the screw torque (T0) and detorque (T1) values of the intermediate were performed before and after the test. The results were statistically evaluated by analysis of variance (ANOVA) and Tukey's test (α = 0.05).

Results:

There was no difference between the values of T0 and T1 in the intra-group samples. However, the inter-group difference in T0 between the EH (12.8 N cm) and MT (18.6 N cm) groups and in T1 between the EH (10.4 N cm) and IH (13.8 N cm), EH and MT (19.4 N cm), and MT and IH (P = 0.001) groups were significant. The MT group showed a lower variation of T0 and T1.

Conclusion:

The internal implants, particularly MT, showed better stability in these cases when used for single restorations.

Correlation between microleakage and screw loosening at implant-abutment connection

PURPOSE

This study aimed to evaluate the correlation between microleakage and screw loosening at different types of implant-abutment connections and/or geometries measuring the torque values before and after the leakage tests.

MATERIALS AND METHODS

Three different abutment types (Intenal hex titanium, internal hex zirconium, morse tapered titaniuım) with different geometries were connected to its own implant fixture. All the abutments were tightened with a standard torque value then the composition was connected to the modified fluid filtration system. After the measurements of leakage removal torque values were re-measured. Kruskal-wallis test was performed for non-parametric and one-way ANOVA was performed for parametric data. The correlation was evaluated using Spearman Correlation Test (α=0.05).

RESULTS

Significantly higher microleakage was found at the connection of implant-internal hex zirconium abutment. Observed mean torque value loss was also significantly higher than other connection geometries. Spearman tests revealed a significant correlation between microleakage and screw loosening.

CONCLUSION

Microleakage may provoke screw loosening. Removing torque values rationally decrease with the increase of microleakage.

Determination of inner implant's volumes: a pilot study for microleakage quantification by stereomicroscopy and spectrophotometry

AIM

Microleakage quantification of fluids and microorganisms through the connections of different implant parts seems to be sparse. Moreover, no data exist regarding the determination of the volumes of inner parts of dental implant systems. This study aims to determine the volumes of inner parts of three dental implant systems with the same interface and to evaluate the microleakage phenomenon.

MATERIALS AND METHODS

Three implant system sets (Euro-teknika(®), Astra Tech(®) and Implantium(®)) were used in this study. Implants were inoculated with safranin, brain heart infusion and distilled water. After inoculation and assembly of the different parts, different inner volumes (V1, V2, V3, V4, V5 and V6) were measured and, the surfaces of the micro gaps were observed through a stereomicroscope. Implants containing safranin were immersed in vials containing distilled water. Samples then were taken to determine optical density using a spectrophotometer.

RESULTS

Regardless the used substance, volumes of the 3-implant systems are different. Although volumes V1, V 2, V 3 and V5 appeared to be constant within the same system regardless the used substance, volumes V4 and V6 were not.

CONCLUSION

The determination of the volumes and the evaluation of leaked substance using stereomicroscopic and spectrophotometric methods showed the accuracy of these methods and the importance of their use in the study of microleakage.

CLINICAL SIGNIFICANCE

Leakage is an important factor for chronic inflammatory infiltration and marginal bone resorption. Studies have shown fluid and bacterial leakage into abutment- implant (A-I) assemblies of certain implants with 'closely locked' abutments and the creation of a constant bacterial reservoir in the empty space found between the implant and the abutment.

Management of abutment screw loosening: review of literature and report of a case

Dental implant restoration has been widely accepted as one of the treatment modalities to replace missing teeth and to restore human masticatory function. The use of root form endosseous implant has increased considerably and this restorative option has become more refined with the introduction of newer designs and concepts. Long term post placement studies have reported prosthetic complications, including screw loosening, screw fracture, framework and implant fracture. Abutment screw loosening is the second most common cause of failure of implant supported restoration, next to loss of osseointegration. This is more seen in single implant supported restoration. Management of screw loosening is challenging and this clinical report describes the management of an implant abutment screw loosening of upper anterior teeth with minimal damage to the existing restoration making it possible to be reused and a literature review on the various factors associated with abutment screw loosening.

Influence of bone insertion level of the implant on the fracture strength of different connection designs: an in vitro study

OBJECTIVE

The aim of the present in vitro study was to assess resistance to static fatigue of implants with different connections at various insertion levels.

MATERIALS AND METHODS

Sixty implants and abutments were used with the smallest diameter of each model. Four groups (n = 15) were created on the basis of the implant design and connection: cylindrical external hexagon Ø3.30 mm (group 1), cylindrical internal hexagon Ø3.30 mm (group 2), conical internal hexagon Ø3.50 mm (group 3), and conical Morse taper Ø3.50 mm (group 4). Three insertion levels in resin were tested, 0 mm at the platform level (l1), 3 mm (l2), and 5 mm (l3) above the platform of the resin. All groups were subjected to quasi-static loading at 30° to the implant axis in a universal machine.

RESULTS

The mean fracture strengths for group 1 were 1,991 N (l1), 1,020 N (l2), and 767 N (l3); for group 2: 2,119 N (l1), 1,034 N (l2), and 903 N (l3); for group 3: 2,373 N (l1), 1,407 N (l2), and 929 N (l3); and for group 4: 1,710 N (l1), 1,680 N (l2), and 1,182 N (l3).

CONCLUSIONS

Resistance to loading decreases significantly with the loss of insertion, and the connection design between the implants and abutments can change the performance and resistance of the system.

CLINICAL RELEVANCE

When implants are used in areas where there is a possibility of bone loss, the selection of a connection type is an important consideration for the longevity of the system.

Effect of fatigue loading on the screw joint stability of zirconium abutment

PURPOSE

This study evaluated the effect of fatigue loading on the screw joint stability of a zirconium abutment connected to an external hexagon implant in vitro.

MATERIALS AND METHODS

Fifteen titanium and 15 zirconia abutments of 3 different heights (5, 8, and 11 mm) were connected to external titanium implants with titanium screws. A torque gauge was used to measure the reverse torque values before and after loading. An air cylindrical loading device was used to simulate mastication at a 45-degree angle to the longitudinal axis of the implant.

RESULTS

There were significant differences (P<0.05) before and after the loading of titanium (5mm) and zirconia (5, 8, and 11 mm) abutments.

CONCLUSION

Zirconia abutments for external hexagon implants had durability rates similar to those of titanium abutments after repeating load on the reverse torque of the abutment screw, indicating that the zirconia abutment could be reliably used instead of the titanium abutment.

Evaluation of microgap size and microbial leakage in the connection area of 4 abutments with Straumann (ITI) implant

A microgap between implant and abutment can lead to mechanical and biological problems such as abutment screw fracture and peri-implantitis. The aim of this study was to evaluate microgap size and microbial leakage in the connection area of 4 different abutments to ITI implants. In this experimental study, 36 abutments in 4 groups (including Cast On, Castable, Solid, and Synocta abutments) connected to Straumann fixtures (with their inner part inoculated with bacterial suspension) and microbial leakage were assessed at different times. The size of the microgap in 4 randomized locations was then measured by scanning electron microscope. The data were analyzed by SPSS software and by 1-way variance statistical test, Kruskal-Wallis, and their supplementary tests (Mann-Whitney HSD and Tukey's; α = .05) at the next step. The effect of using different types of abutments was significant on the mean microgap size (P < .001) and on the mean number of leaked colonies (CFU/mL) through the connection area of the implant and abutment within the first 5 hours of the experiment (P = .012); however, it did not significantly influence microleakage at 24 hours, 48 hours, and 14 days (P = .145). Using Synocta abutments compared with Solid abutments will not provide us with more accommodation, and vice versa. Using Solid and Synocta abutments can significantly decrease the microgap size; however, Cast On abutments do not show a significant difference in terms of microgap compared with Castable abutments. Microleakage in the connection area is comparable for these 4 abutments.

A rationale method for evaluating unscrewing torque values of prosthetic screws in dental implants

Objectives

Previous studies that evaluated the torque needed for removing dental implant screws have not considered the manner of transfer of the occlusal loads in clinical settings. Instead, the torque used for removal was applied directly to the screw, and most of them omitted the possibility that the hexagon could limit the action of the occlusal load in the loosening of the screws. The present study proposes a method for evaluating the screw removal torque in an anti-rotational device independent way, creating an unscrewing load transfer to the entire assembly, not only to the screw.

Material and methods

Twenty hexagonal abutments without the hexagon in their bases were fixed with a screw to 20 dental implants. They were divided into two groups: Group 1 used titanium screws and Group 2 used titanium screws covered with a solid lubricant. A torque of 32 Ncm was applied to the screw and then a custom-made wrench was used for rotating the abutment counterclockwise, to loosen the screw. A digital torque meter recorded the torque required to loosen the abutment.

Results

There was a significant difference between the means of Group 1 (38.62±6.43 Ncm) and Group 2 (48.47±5.04 Ncm), with p=0.001.

Conclusion

This methodology was effective in comparing unscrewing torque values of the implant-abutment junction even with a limited sample size. It confirmed a previously shown significant difference between two types of screws.

In vitro analysis of post-fatigue reverse-torque values at the dental abutment/implant interface for a unitarian abutment design

PURPOSE

This study analyzed baseline and post-fatigue reverse-torque values (RTVs) for a specific brand control abutment relative to a third party compatible abutment. The purpose of this study was to compare the abutments' fatigue resistance to simulated function, using RTVs as an indication of residual preload at the implant/abutment interface.

MATERIALS AND METHODS

Forty Straumann tissue-level implants were mounted in resin and divided into four groups (n = 10). Forty abutments were seated, 20 control and 20 third-party abutments, according to manufacturer guidelines. Ten abutments from each manufacturer were evaluated for RTV without fatigue loading, using a calibrated digital torque gauge to provide a baseline RTVs. Fatigue loading was carried out on the remaining ten specimens from each manufacturer according to ISO 14801 guidelines. A moving-magnet linear motor was used to load one specimen per sequence, alternating from 10 to 200 N at 15 Hz for 5×10(6) cycles. RTV was recorded post-fatigue loading. The results were subjected to two-sample t-testing and two-way ANOVA. Scanning electron microphotography was carried out on three specimens from both manufacturers at baseline and post-fatigue cycling to visualize thread geometry and the abutment/implant interface.

RESULTS

The data indicated that mean post-fatigue RTV observed for the control group was significantly higher than the third-party group (RTV 42.65 ± 6.70 N vs. 36.25 ± 2.63 N, p= 0.0161). Visual differences at the macro/microscopic level were also apparent for thread geometry, with third-party abutments demonstrating considerably greater variation in geometrical architecture than control specimens.

CONCLUSIONS

Within the limitations of this in vitro model, the effect of component manufacturer resulted in a significantly higher RTV in the control group (two-way ANOVA, p= 0.0032) indicating greater residual preload; however, there was no significant decrease in post-fatigue RTV for either manufacturer compared to baseline.

Sealing Capability and SEM Observation of the Implant-Abutment Interface

To evaluate the sealing capability of external hexagon implant systems and assess the marginal fit, two groups (n = 10 each) were employed: SIN (Sistema de Implantes Nacional, Brazil) and Osseotite, (Biomet 3i, USA). Sealing capability was determined by placing 0.7 μL of 1% acid-red solution in the implant wells before the torque of their respective abutments. Specimens were then placed into 2.5 mL vials filled with 1.3 mL of distilled water with the implant-abutment interface submerged. Three samples of 100 μL water were collected at previously determinate times. The absorbance was measured with a spectrophotometer, and the data were analyzed by Two-way ANOVA (P < .05) and Tukey's test. Marginal fit was determined using SEM. Leakage was observed for both groups at all times and was significantly higher at 144 hrs. SEM analysis depicted gaps in the implant-abutment interface of both groups. Gaps in the implant-abutment interface were observed along with leakage increased at the 144 hrs evaluation period.

Influence of the interface design on the yield force of the implant-abutment complex before and after cyclic mechanical loading

PURPOSE

The aim of this in vitro study was to evaluate the implant-abutment assembly of Astra Tech (AST), Bego (BEG), Camlog (CAM), Friadent (FRI), Nobel Biocare (NOB) and Straumann (STR) with respect to yield force before and after cyclic fatigue, using a static overload test with a test set-up according to ISO 14801.

METHODS

Ten specimens of each type were split into two homogenous groups: one half was tested for static yield force without any further treatment (control), whereas the other one underwent one million cycles of mechanical loading with 100N as the upper load limit. For load-to-failure testing, specimens were then placed in a stainless steel jig and loaded in a universal testing machine under an angle of 30° with respect to the implant axis until failure. Load-displacement curves were analyzed and the yield forces at which non-linear behaviour set in (Fp) were recorded. Statistical analysis was performed using one-way ANOVA and t-test, respectively, with the level of significance set at 0.05.

RESULTS

Statistical analysis revealed that the type of implant-abutment connection has a significant influence on Fp (p<0.001). Furthermore, dynamic loading proved to significantly influence Fp of BEG and CAM (p<0.001).

CONCLUSION

None of the implant-abutment types tested would be expected to fail under clinically relevant forces, but the type of implant-abutment connection significantly influences the yield force Fp.

Influence of lateral-oblique cyclic loading on abutment screw loosening of internal and external hexagon implants

To date, there is no evidence that internal anti-rotation configurations are better than external ones. The purpose of this study was to evaluate the effect of eccentric cyclic loading on abutment screw loosening in internal and external hexagon implants with either of these two screw materials, titanium (Ti) alloy versus gold alloy. The reverse torque value of the abutment screw was measured before (initial preload) and after loading (post-loading). The prepared assemblies were divided into four groups (A to D). Groups A and B used internal hex implants with gold alloy and Ti alloy abutment screws respectively. Groups C and D used external hex implants with gold alloy and Ti alloy abutment screws respectively. In all the groups, post-loading preload was significantly (p<0.05) higher than initial preload. Further, two-way ANOVA indicated that the implant-abutment connection did not have an effect, but the abutment screw material did. In particular, Ti abutment screws were less likely to come loose.

Theoretical Considerations: Implant Positional Index Design

Rotational freedom of implant positional indices in two-piece implants was investigated. The aim of the study was to determine, analytically, the rotational freedom of three different positional index designs, based on the hypothesis that it is not influenced by their geometric principle. Regular polygonal, polygon profile, and cam-groove patterns were analyzed. Schematic descriptions were made and idealized equations developed. Parameters influencing the extent of rotational freedom were identified for the different positional index designs. A general equation that describes the rotational freedom of differently designed indices was also formulated. The present analysis showed that the rotational freedom of positional indices can be analytically calculated and is influenced by different parameters. The rotational freedom of the positional index of commonly used implant-abutment connections depends on their geometric design and size.

Effect of repeated torque/mechanical loading cycles on two different abutment types in implants with internal tapered connections: an in vitro study

OBJECTIVES

Internal tapered connections were developed to improve biomechanical properties and to reduce mechanical problems found in other implant connection systems. The purpose of this study was to evaluate the effects of mechanical loading and repeated insertion/removal cycles on the torque loss of abutments with internal tapered connections.

MATERIAL AND METHODS

Sixty-eight conical implants and 68 abutments of two types were used. They were divided into four groups: groups 1 and 3 received solid abutments, and groups 2 and 4 received two-piece abutments. In groups 1 and 2, abutments were simply installed and uninstalled; torque-in and torque-out values were measured. In groups 3 and 4, abutments were installed, mechanically loaded and uninstalled; torque-in and torque-out values were measured. Under mechanical loading, two-piece abutments were frictionally locked into the implant; thus, data of group 4 were catalogued under two subgroups (4a: torque-out value necessary to loosen the fixation screw; 4b: torque-out value necessary to remove the abutment from the implant). Ten insertion/removal cycles were performed for every implant/abutment assembly. Data were analyzed with a mixed linear model (P< or =0.05).

RESULTS

Torque loss was higher in groups 4a and 2 (over 30% loss), followed by group 1 (10.5% loss), group 3 (5.4% loss) and group 4b (39% torque gain). All the results were significantly different. As the number of insertion/removal cycles increased, removal torques tended to be lower. It was concluded that mechanical loading increased removal torque of loaded abutments in comparison with unloaded abutments, and removal torque values tended to decrease as the number of insertion/removal cycles increased.

Preload and torque removal evaluation of three different abutment screws for single standing implant restorations

Several authors still consider the mechanical problems of fracture and component loosening as the main causes of failure of implant-supported restorations. The purpose of this in vitro study was to compare the preload of three types of screw for transmucosal abutment attachment used in single implant-supported prosthesis through strain gauge and removal torque measurements. Three external hex fixtures were used, and each received a transmucosal abutment (Cera One), which was fixed to the implant with its respective screw: Group A- gold screw, Group B- titanium screw and Group C- surface-treated titanium screw (Ti-Tite). Ten screws of each type were attached applying a 30.07+/-0.28 Ncm torque force and maintained in position for 5 minutes. After this, the preload values were measured using strain gauges and a measurement cell. Gold screws presented higher preload values (131.72+/-8.98 N), followed by surface-treated titanium screws (97.78+/-4.68 N) and titanium screws (37.03+/-5.69 N). ANOVA (p<0.05) and Tukey's test (p<0.05) were applied. Statistically significant differences were found among the groups for both preload and removal torque values. In conclusion, gold screws may be indicated to achieve superior longevity of the abutment-implant connection and, consequently, prosthetic restoration due to greater preload values yielded.

Cross-sectional analysis of the implant?abutment interface

The purpose of this study was to develop a technique to evaluate the implant-abutment gap of an external hexagon implant system as a function of radius. Six implants of 3.75 mm in diameter (Conexao Sistema de Protese Ltda, Sao Paulo, Brazil) and their respective abutments were screw connected and torqued to 20 N cm(-1). The implants were mounted in epoxy assuring an implant long-axis position perpendicular to the vertical axis. Each implant was grounded through its thickness parallel to implant long-axis at six different distance interval. Implant-abutment gap distances were recorded along the implant-abutment region for each section. Individual measurements were related to their radial position through trigonometric inferences. A sixth degree polynomial line fit approach determined radial adaptation patterns for each implant. Micrographs along implant sections showed a approximately 300 mum length implant-abutment engagement region. All implants presented communication between external and internal regions through connection gaps and inaccurate implant-abutment alignment. Average gap distances were not significantly different between implants (P > 0.086). Polynomial lines showed implant-abutment gap values below 10 mum from 0 mum to approximately 250 mum of the implant-abutment engagement region. Gap distances significantly increased from approximately 250 mum to the outer radius of the implant-abutment engagement region. The technique described provided a broader scenario of the implant-abutment gap adaptation compared with previous work concerning implant-abutment gap determination, and should be considered for better understanding mechanical aspects or biological effects of implant-abutment adaptation on peri-implant tissues.

Abutment rotational displacement of external hexagon implant system under lateral cyclic loading

PURPOSE

This in vitro study investigated the effect of lateral cyclic loading with different load positions and periods on abutment rotational displacement (RD) of external hexagon implant system.

MATERIALS AND METHODS

Four groups of five implant assemblies each were used. Each assembly consisted of Brånemark System Mk IV implant (Nobel Biocare AB, Göteborg, Sweden), CeraOne abutment (Nobel Biocare AB), and a cement-retained casting. A cyclic load of 50 N was applied centrally and perpendicular to the long axis of the implant for groups A and B for 0.25 and 0.50 x 10(6) cycles, respectively, while for groups C and D, the same load was applied at 4-mm distance eccentrically for 0.25 and 0.50 x 10(6) cycles, respectively. The displacement was evaluated by hand drawing a longitudinal line across the implant-abutment interface. Before and after loading, the lateral distance between two reference points on the abutment and implant was measured under high resolution (x200) and the difference formed the RD value. The data were analyzed with one-way analysis of variance and compared with Tukey test (alpha=0.05).

RESULTS

Group D had the highest mean of RD value (55.00 +/- 1.871 microm), while group A had the lowest (2.800 +/- 0.837 microm). Groups A and B had a high statistically significant difference in RD values, as compared to groups C or D (p < .001). Moreover, group C had statistically significant difference from group D (p=.011). Conversely, no statistical significance was obtained when group A was compared with group B.

CONCLUSION

Within the limits of this in vitro study, the RD of the external hexagon joint components occurred significantly under eccentric lateral loading when compared to centric loading. The displacement increased significantly with longer period of eccentric lateral loading.

Survival rate, fracture strength and failure mode of ceramic implant abutments after chewing simulation

The aim of this study was to compare titanium-reinforced ZrO(2) and pure Al(2)O(3) abutments regarding their outcome after chewing simulation and static loading. Forty-eight standard diameter implants with an external hexagon were divided into three groups of 16 implants each and restored with three different types of abutments (group A: ZrO(2) abutments with titanium inserts; group B: Al(2)O(3) abutments; group C: titanium abutments). All abutments were fixated on the implants with gold-alloy screws at 32 Ncm torque, and metal crowns were adhesively cemented onto the abutments. The specimens were exposed to 1.2 million cycles in a chewing simulator. Surviving specimens were subsequently loaded until fracture in a static testing device. Fracture loads (N) and fracture modes were recorded. A Wilcoxon Rank test to compare fracture loads among the three groups and a Fisher exact test to detect group differences in fracture modes were used for statistical evaluation (P < 0.05). All specimens but one of group B survived chewing simulation. No screw loosening occurred. The median fracture loads (+/-s.d.) were as follows: group A, 294 N (+/-53); group B, 239 N (+/-83), and group C, 324 N (+/-85). The smaller fracture loads in group B were statistically significant. The use of pure Al(2)O(3) abutments resulted in significantly more abutment fractures. It is proposed that titanium-reinforced ZrO(2) abutments perform similar to metal abutments, and can therefore be recommended as an aesthetic alternative for the restoration of single implants in the anterior region. All-ceramic abutments made of Al(2)O(3) possess less favourable properties.

Stability of Implant-Abutment Interface with a Hexagon-Mediated Butt Joint: Failure Mode and Bending Resistance

BACKGROUND

Clinical data showed that the external hexagon implant system with a gold abutment screw has reduced the problem of screw loosening or fracture. However, the behavior of the implant-abutment joint components with respect to unfavorable bending force is still unclear.

PURPOSE

This study investigated the joint instability and bending resistance of a single-tooth external hexagon implant system after lateral cyclic loading.

MATERIALS AND METHODS

Fifteen implant assemblies (Nobel Biocare, Göteborg, Sweden) were divided equally into three groups: A, B, and C. Each assembly consisted of a Brånemark System Mk IV implant (4 x 10 mm) mounted in a brass block, a CeraOne abutment (3 mm), and an experimental cement-retained superstructure. For group A, a centric lateral cyclic load of 50 N was applied for 1.0 x 10(6), whereas for group B, the same load was eccentrically applied for 1.0 x 10(6) cycles. Group C, the control, was not loaded. After cyclic loading, specimens were mounted in a universal testing machine, and the yield and bending strengths were measured (kg). The external hexagon surface texture was examined using a secondary electron microscope. The data were analyzed with one-way analysis of variance and compared by the Tukey test (alpha = .05).

RESULTS

For all test specimens, the abutment screw was plastically bent in the unthreaded portion. Group B had a significantly lower mean yield and bending strengths than group C (p = .005 and .010, respectively). Post-cyclic loading photographs showed that group B implants had marked burnishing around the hexagon corners. The bending force abraded both corner areas of the hexagon surface but left the middle area nearly intact for all tested groups. However, group B had the significantly lowest mean abraded area.

CONCLUSION

Within the limits of this study, eccentric rather than centric lateral cyclic loading negatively affected the resistance of the implant-abutment joint to static bending.

Influence of implant/abutment joint designs on abutment screw loosening in a dental implant system

The objective of this study was to investigate the influence of implant/abutment joint designs on abutment screw loosening in a dental implant system, using nonlinear dynamic analysis of the finite element method (FEM). This finite element simulation study used two dental implant systems: the Ankylos implant system (Degusa Dental, Hanau, German) with a taper joint (taper joint-type model), and the Bränemark implant system (Nobel Biocare, Gothenburg, Sweden) with an external hex joint (external hex joint-type model). The nonlinear dynamic analysis was performed using three-dimensional finite element analysis. In comparing the movement of the taper type-joint model and external hex type-joint model, it was found that the external hex type-joint model had greater movement than the taper type-joint model. The external hex joint-type model showed rotation movement, whereas the movement of the taper joint-type model showed no rotation. It was concluded that the nonlinear dynamic analysis used in this study clearly demonstrated the differences in rotation of components in dental implant systems with taper or external hex joints.