Survival of Four Conical Implant Abutment Connections After Removal of the Abutment Screw and Simulated Cyclic Loading: An In Vitro Comparative Study.

This in vitro study evaluated the mechanical behavior of different conical connection implant systems after abutment screw withdrawal. Four conical connection systems were selected based on different conical half-angles: Ankylos (5.7°), Cowell (7.0°), Straumann (7.5°), and Astra (11.0°). In each system, 5 implants and abutments were used (n = 5). According to the recommended value, each abutment screw was torqued to settle the abutment and then withdrawn through a predesigned hole of the cemented crown. The retentiveness of the abutment was evaluated by the following mechanical testing. All specimens were subjected to cyclic loading of 20-200 N, 30°, and 4-mm off-axis to the implant axis, for 106 cycles. The pullout forces and axial displacements of the abutments were measured. The data of the Cowell system was obtained from our previous work. All groups other than Astra group, in which abutment loosened after abutment screw withdrawal, passed the cyclic loading test. Straumann group demonstrated a significantly lower pullout force (27.4 ± 21.1 N) than Ankylos (160.1 ± 41.4 N) and Cowell (183.7 ± 30.5 N) groups. All groups showed abutment rebound after screw withdrawal except Straumann group. In addition, Ankylos, Cowell, and Straumann groups demonstrated axial displacement after cyclic loading. In terms of the retentiveness of the abutment after abutment screw withdrawal examined in this study, Ankylos and Cowell groups had much higher retentiveness than Straumann group, while Astra group had none. Conical angle could be a key design parameter to make abutment screw withdrawal after conical abutment settlement feasible, but more studies must be conducted for clinical application.

Abutment screw withdrawal after conical abutment settlement: A pilot study.

OBJECTIVE: This study investigated the effects of abutment screw withdrawal after conical abutment settlement on the stability of the implant-abutment connection. MATERIALS AND METHODS: Twenty implants of a conical connection system were used. Two two-piece abutment designs were used: cone only (n = 10; NI) and cone plus octagonal index design (n = 10; I); for each design, five samples were used with (S) and without (NS) abutment screw withdrawal before a cyclic test. Finally, four groups, namely Gr S(NI), Gr S(I), Gr NS(NI), and Gr NS(I), were included. The cyclic test included cyclic loading of 20-200 N, 30°, and 4-mm off-axis to implant axis at 10 Hz for 106 cycles, simulating a clinical time interval of 40 months. The fatigue cycles were recorded. The axial displacement of the conical abutments during abutment settlement, screw withdrawal, and cyclic loading were measured. Abutment morphology was examined through scanning electron microscopy (SEM). RESULTS: Only Gr NS(NI) failed the test, indicating that without the index design and abutment screw withdrawal, and connection stability seriously deteriorated. Gr NS(I) exhibited significantly higher axial displacement into the implant after abutment settlement than did Gr NS(NI). It also exhibited continuous axial displacement into the implant after cyclic loading. SEM after cyclic testing in Gr NS(I) revealed marked burnishing on lateral edges of the index, indicating that the index design provides an antitorsional ability. CONCLUSION: Although this study has few limitations, abutment screw withdrawal is feasible in this conical implant-abutment connection system with index design.

Mechanical performance of conical implant-abutment connections under different cyclic loading conditions.

OBJECTIVES: Conical implant-abutment connections are popular for its anti-bending performance; on the other hand, the torsional and axial forces also play important roles in occlusion. However, so far there were scarce studies on their effects on connection stability. Therefore, this study seeks to investigate the mechanical performance of conical connections under different cyclic loading conditions. METHODS: 15 conical implant-abutment assembles (Cowell Medi, Busan, South Korea) were divided into 3 groups according to different cyclic loadings. In group BTA, the loading condition of the posterior occlusion was simulated (20-200 N, 30° off-axis and 4 mm eccentric to implant axis), generating a bending moment, a torsional moment, and an axial loading. In group BT, a bending moment and a torsional moment of the posterior occlusion were applied (10-100 N, 90° off-axis and 4 mm eccentric to implant axis). In group B, only a bending moment was applied (10-100 N, 90° off-axis and through implant axis). The fatigue testing machine ran at 10 Hz until failure, or to the upper limit of 106 cycles. The fatigue cycles and failure modes were recorded. Besides, the value of the torque loss of the abutment screw, the difference between initial torque and post-load reverse torque, was calculated. The data were statistically analyzed. Morphologies of the abutment conical surface were examined by scanning electron microscopy. RESULTS: In group B and BTA, all samples passed the test (106 cycles). While, in group BT, all abutments generated rotation within 140 cycles, showing significant differences compared to the other two groups (p < 0.001). However, from SEM observations, both group B and BT showed marked fretting wear, indicating obvious micromotion in the connection. Whereas group BTA showed indentation of tight contact, attributed to the axial loading. In terms of the torque loss of the abutment screw, the torque loss in group BT was much more than the other two groups with statistically significant differences (p < 0.05). CONCLUSION: Owing to the effect of the bending moment, marked fretting wear was generated in the conical connections and further led to loss of the anti-torsional ability. However, adding an axial loading could improve their anti-torsional ability significantly.

Effects of Axial Loading on the Pull-out Force of Conical Connection Abutments in Ankylos Implant.

PURPOSE: The aim of this study was to assess the effects of simulated axial loadings on the pull-out force required to disengage a two-piece conical connection abutment from an implant. MATERIALS AND METHODS: Ten conical connection abutments (Ankylos Regular/X Abutment, Dentsply-Friadent) and 10 implants (Ankylos C/X Implant) were used. The implant-abutment assemblies were divided randomly into two groups: control group (C) and experimental group (E). For group E (n = 5), a cyclic load of 18 to 180 N at a frequency of 10 Hz to 106 cycles was applied centrally and along the long axis of the implant, whereas for group C (n = 5), each sample was put on a workbench without cyclic loading at the same time during the testing period. Before mechanical loading, the initial torque values and the total lengths of tested samples of groups C and E were recorded. After cyclic loading, the postloading reverse torque value, the total length, and the pull-out force of tested samples of groups C and E were recorded. The difference between the initial torque value and the postloading reverse torque value was defined as the total torque loss. The difference between the initial total length and the postloading total length was defined as the axial displacement. The data were analyzed by independent t test. RESULTS: The mean pull-out force of the experimental group was 77.60 N (SD = 6.16 N), which was significantly larger than that of the control group (mean = 55.28 N; SD = 9.41 N) (P < .05). The mean total torque loss and the mean axial displacement of the experimental group were both significantly higher than those of the control group (P < .05). CONCLUSION: Simulated axial loading increased the pull-out force of loaded abutments in comparison with unloaded abutments. Under simulated axial loading, the pull-out force of abutments tended to increase as the axial displacement of abutments and the total torque loss of abutment screws were both increased.

Optimization of the Conical Angle Design in Conical Implant-Abutment Connections: A Pilot Study Based on the Finite Element Method.

Conical implant-abutment connections are popular for their excellent connection stability, which is attributable to frictional resistance in the connection. However, conical angles, the inherent design parameter of conical connections, exert opposing effects on 2 influencing factors of the connection stability: frictional resistance and abutment rigidity. This pilot study employed an optimization approach through the finite element method to obtain an optimal conical angle for the highest connection stability in an Ankylos-based conical connection system. A nonlinear 3-dimensional finite element parametric model was developed according to the geometry of the Ankylos system (conical half angle = 5.7°) by using the ANSYS 11.0 software. Optimization algorithms were conducted to obtain the optimal conical half angle and achieve the minimal value of maximum von Mises stress in the abutment, which represents the highest connection stability. The optimal conical half angle obtained was 10.1°. Compared with the original design (5.7°), the optimal design demonstrated an increased rigidity of abutment (36.4%) and implant (25.5%), a decreased microgap at the implant-abutment interface (62.3%), a decreased contact pressure (37.9%) with a more uniform stress distribution in the connection, and a decreased stress in the cortical bone (4.5%). In conclusion, the methodology of design optimization to determine the optimal conical angle of the Ankylos-based system is feasible. Because of the heterogeneity of different systems, more studies should be conducted to define the optimal conical angle in various conical connection designs.

Injectable adipose tissue combined with stem cells for soft-tissue augmentation: A pilot study for dental applications.

BACKGROUND/PURPOSE: Bone resorption and soft-tissue defects are the typical physiologic responses after tooth extraction. Various dental ridge augmentation techniques have been applied and lack of the soft tissue is the major factor causing the failure. We propose that the adipose-derived stem cell can be useful in soft-tissue augmentation in dental applications. The objective of this study was to optimize the operation procedures for the isolation of adipose stem cells and tissues. Accelerated clinical protocols for effective transplantation of adipose tissue with high amount of adipose stem cells shall be developed. MATERIALS AND METHODS: Operation parameters were designed and optimized for the extraction of adipose tissue-derived stromal vascular cells. The optimized accelerated procedure was washing the lipoaspirate samples one time. Collagenase was then added and samples were incubated in a water bath for 30 minutes at 37°C and centrifuged at 1200g for 3 minutes. A mouse animal model was applied to evaluate the soft-tissue-filling effects using the optimized procedure. RESULTS: The animal model tests demonstrated the filling and regeneration of the soft tissues with significant angiogenesis. CONCLUSION: This pilot study demonstrated the feasibility of soft-tissue augmentation applications.

The Potential Risk of Conical Implant-Abutment Connections: The Antirotational Ability of Cowell Implant System.

BACKGROUND: Conical implant-abutment connections are popular because of good antibending performance. However, the cross section is round, and the antirotational ability is questionable because restorations in the oral cavity also have to bear torsional moments resulting from chewing patterns. PURPOSE: The purpose of this study was to investigate the antirotational ability of conical implant-abutment connections with and without an index. MATERIALS AND METHODS: Conical connection implant system (Cowell Medi, Busan, South Korea) was selected. Two kinds of cyclic loading, a bending moment with (C) and without (L) a torsional moment, were respectively applied to two kinds of abutments, pure cone (N-Octa) and cone with an octagonal index (Octa). The number of cycles to fatigue and the failure modes was recorded. Morphologies of the abutments were examined with scanning electron microscopy. RESULTS: Only group C(N-Octa) passed the fatigue test, whereas the other three groups failed because of different failure modes. In group L(N-Octa), all abutments generated rotation within 150 cycles. In groups C(Octa) and L(Octa), all abutments fractured but in different areas. CONCLUSIONS: In Cowell implant system (taper angle = 7°), there was no antirotational ability in purely conical connections. Adding an octagonal index could provide an antirotational function but could compromise the antibending strength of the abutment.

The effect of clockwise and counterclockwise twisting moments on abutment screw loosening.

OBJECTIVES: Abutment screw loosening is one of the most common complications of dental implants. When occlusal loading is applied, bending and twisting moments are counteracted by the implant-abutment connection held with the abutment screw. Restorations in different quarters of the oral cavity might bear clockwise or counterclockwise twisting moments that result from a regular chewing pattern. The aim of this study was to investigate the effect of different directional twisting moments on abutment screws. METHODS: Twenty 3i implants were divided into four groups of C, R, L, and O. Each assembly consisted of an implant, abutment, and superstructure. For group C, a cyclic load of 10-100 N for 10(6) cycles was applied centrally and perpendicular to the long axis of the implant, whereas for groups R and L, the same load conditions were applied eccentrically in clockwise and counterclockwise directions, respectively. Group O was left unloaded. The difference between the initial torque and post-load reverse torque was defined as the total torque loss. The data were analyzed by Kruskal-Wallis test. The surface of the abutment hexagon corners were examined with SEM after loading. RESULTS: No abutment screw loosening was found after loading. Total torque loss of groups C, R, L, and O were 10.50 ± 0.58, 9.56 ± 1.01, 9.98 ± 1.81, and 9.58 ± 0.94 Ncm, respectively. There were no statistical differences among the four groups. SEM observations showed marked burnishing at the hexagonal corners on the compression sides of the R and L groups. CONCLUSIONS: Within the limitations of this study, there was little effect of twisting moment direction on the total torque loss of an internal hexagon connection implant system. This could be attributed to the anti-twisting mechanism of the internal hexagon connection.