Correlation between microleakage and screw loosening at implant-abutment connection

Microbial Leakage through Three Different Implant-Abutment Interfaces on Morse Taper Implants In Vitro

The objective of this study was to evaluate microbial leakage by means of genome counts, through the implant-abutment interface in dental implants with different Morse taper abutments. Fifty-six samples were prepared and divided in four groups: CMC TB (14 Cylindrical Implants-14 TiBase Abutments), CMX TB (14 Conical Implants-14 TiBase Abutments), CMX PU (14 Conical Implants-14 Universal Abutment) and CMX U (14 Tapered Implants-14 UCLA Abutments). Assemblies had their interface submerged in saliva as the contaminant. Samples were subjected either to thermomechanical cycling (2 × 106 mechanical cycles with frequency of 5 Hz and load of 120 N simultaneously with thermal cycles of 5-55 °C) or thermal cycling (5-55 °C). After cycling, the contents from the inner parts of assemblies were collected and analyzed using the Checkerboard DNA-DNA hybridization technique. Significant differences in the total genome counts were found after both thermomechanical or thermal cycling: CMX U > CMX PU > CMX TB > CMC TB. There were also significant differences in individual bacterial counts in each of the groups (p < 0.05). Irrespective of mechanical cycling, the type of abutment seems to influence not only the total microbial leakage through the interface, but also seems to significantly reflect differences considering individual target species.

The effect of contaminating media on the static and dynamic mechanical resilience of dental implant abutments' screws: In vitro study

INTRODUCTION

This in vitro study aims to biomechanically evaluate the influence of medium contamination for example, saliva, blood, chlorhexidine (liquid and gel), and fluoride mouthwash on the biomechanical behavior of implant abutments' screws under static and dynamic loading.

METHODS

Forty five Ti6Al4V commercial dental implants and abutments were tested in this study. Two main mechanical tests were carried out in the selected media. The first, static, aimed to evaluate the torque loss after the first tightening. The second, dynamic, involved a random cyclic load range between 0 and 200 N to evaluate torque loss due to mastication. In addition, metallographic longitudinal and cross-sections of the abutment-implant apparatus were examined to evaluate the abutment screw-abutment-implant interface.

RESULTS

The static torque test showed that irrespective of the media, no statistical difference in static torque loss was found prior to dynamic loading. For the dynamic tests, torque-angle evolution analysis during tightening to 30 Ncm and after the spectrum loading, showed the same global mechanical behavior for all media, but the statistical analysis indicated a difference between the groups in reverse torque values (RTV) and in the torque loss due to dynamic loading. The medium groups CHX, CHX-gel, and Fluoride mouthwash, showed a meaningful torque loss due to loading, but the medium groups, control (no medium), blood and saliva showed an opposite trend and required a higher torque to open the abutment screws. The microstructural analysis revealed clear signs of cold-welding/galling, post-dynamic loading in these latter groups.

CONCLUSIONS

The presence of lubrication/contamination media (CHX mouthwash/CHX-gel/Fluoride mouthwash) reduces the preload generated due to tightening but prevents damage due to galling. The observed reduction of RTV clearly emphasizes the need for frequent abutment screw retightening for implant-supported prosthetic long-term stability.

Effects of the internal contact surfaces of dental implants on screw loosening: A 3-dimensional finite element analysis

STATEMENT OF PROBLEM

The effects of the internal contact surfaces of dental implants on screw loosening have yet to be investigated.

PURPOSE

The purpose of this 3-dimensional finite element analysis (FEA) study was to evaluate and compare the mechanical effects of the abutment implant angle (θ), the abutment screw head diameter (D), and the abutment screw length (L) on screw loosening.

MATERIAL AND METHODS

A total of 27 models presenting various mechanical scenarios were built by using combinations of 3 different θ (30 degrees, 45 degrees, and 60 degrees), D (2.65 mm, 2.75 mm, and 2.85 mm), and L (4 mm, 5 mm, and 6 mm). In FEA, a static test with a 200-N force inclined 30 degrees in the implant axial direction was applied to the upper surface of the abutment to evaluate and compare the maximum von Mises stresses of the implant components and the maximum total deformation in all models. In addition, modal analysis was applied to identify the natural frequencies in all models under free (unforced) vibration, and a Kruskal-Wallis statistical test (α=.05) was performed, followed by multiple pairwise comparisons by using the Dunn test.

RESULTS

The Kruskal-Wallis test found a significant influence of the θ on implant stress, total deformation, and natural frequency (P<.001). For example, increasing the θ from 30 degrees to 45 degrees and 60 degrees can considerably reduce the model's natural frequencies to 18% and 26%, respectively. Similarly, the test underscored the significant impact of the D on both abutment screw stress and abutment stress (P=.010 and P=.002, respectively). However, the L appeared to have no significant effect on any of the dependent variables (P>.05).

CONCLUSIONS

The θ and the D significantly influenced the stresses of dental implant components, total deformation, and natural frequency of the model, which may impact the mechanical stability of the screw joint. However, the L does not appear to affect these values significantly.

Escherichia coli Cellular Activity and Frontal Trizonal Evaluation of Microspace Between Implants and Abutments Under Calibrated Cyclic Stress

AIM

To evaluate microspace and microleakage between implant and abutments subjected to pre- and post-calibrated cyclic stress.

MATERIALS AND METHODS

Twelve screw-retained implant prostheses with BioHPP polyetheretherketone (PEEK) abutment (Noris Dental Implant System Ltd., Nesher, Israel) (Group I) and 12 screw-retained implant prostheses with computer-assisted design/computer-assisted manufacturing (CAD/CAM) milled zirconia abutment (DentGallop, Houston, TX, USA) (Group II) were connected to their respective implant, and the prosthetic screw was torqued to 30N/cm (Noris). The microspace was evaluated using scanning electron microscopy (SEM; TeScan, Brno, Czech Republic). Twenty-four samples were then induced to cyclic stress (Lokesh Industries, Pune, India) simulating 180 days duration of oral stress. The microspaces (Group IA and Group IIB) were measured post-cyclic stress. Group I and II were again renamed into Group Ia and Group IIb for microbial study. Both implant assemblies were immersed in fresh soybean casein digest broth (SCDB) (Himedia, Mumbai, India) and subsequently inoculated with 1.0µL E. coli suspension (Himedia) at the open end and incubated at 37ºC for seven days. After the incubation period, cellular activity was determined by the spread plate method, and total colony-forming units (CFU) were calculated. The results were evaluated using independent T and Mann-Whitney tests.

RESULT

Average and microspace at the implant-abutment junction of Group I samples in the front right was 12.98µm, center 13.76µm, front left 13.22µm, and in Group II samples, the front right was 18.52µm, center 17.84µm, front left 18.58µm.After being subjected to cyclic loading, the mean levels of the vertical microgap for Group IA samples were: in the front right region 10.37µm, in the center 9.34µm, in the front left 10.51µm and in Group IIB samples front right was 14.59µm, center 13.39µm, front left 13.8µm. Independent t-tests showed insignificant differences between the two groups. The median value of microbial leakage of Group Ia samples after cyclic loading was 30 x 103 CFU/ml, and Group IIb samples were 42 x 103 CFU/ml and were significant.

CONCLUSION

There was minimal variation in the mean microspace between the BioHPP PEEK abutment and CAD/CAM milled zirconia abutment, and it was insignificant before and after cyclic stress. BioHPP PEEK abutment-titanium implant interfaces showed significantly decreased microbial leakage than CAD/CAM milled zirconia abutment-titanium implant interfaces after cyclic stress.

Effects of Blood Contamination and Decontamination Protocol on Reverse Torque Value of Abutment Screws in Dental Implants: An In Vitro Study

Background and Objective: Loosening of abutment screws in dental implants is a mechanical complication that affects prosthetic treatments and hence, patient satisfaction. Blood contamination of abutment screws may play a role in this phenomenon. However, only limited research attention has been given to this issue. In the present study, we determined the effect of blood contamination and decontamination protocol on the reverse torque value (RTV) of abutment screws. Materials and Methods: A questionnaire-based survey was sent to 210 implantologists requesting feedback on their attitude to the blood contamination issue and the decontamination protocols used. The survey responses were used in a selection of the decontamination solutions that were used in the subsequent in vitro study on the effects of blood decontamination protocol on the RTV of abutment screws. Thus, three study groups were used (n = 20 abutment screws in each group): Group 1 (control group; blood-contaminated screws); Group 2 (screws decontaminated with 5.25% sodium hypochlorite (NaOCl) solution); and Group 3 (screws decontaminated with normal saline solution (0.9%)). Then, each of the connections were subjected to thermocycling, and RTVs of the screw were measured using a digital torque meter. Intragroup and intergroup RTVs were analyzed for significance using analysis of variance (ANOVA) and Tukey's honestly significant difference (HSD) tests. Results: 48% of the implantologists responded to the survey; 80% of them were concerned with blood contamination in the implant connection, especially before abutment loading and 85% of them used either chlorhexidine solution or normal saline solution as the decontamination agent. The mean RTV for Group 2 screws (30.27 ± 2.8 N.cm) was significantly greater than that for Group 3 screws (26.02 ± 1.99 N.cm) which, in turn, was significantly greater than that for Group 1 screws (23.64 ± 1.84 N.cm). Conclusion: Decontamination of blood-covered connections using 5.25% NaOCl solution or normal saline solution restores the RTV of abutment screws. This finding may have clinical relevance in that the decontaminated screws may contribute to the low incidence of screw loosening and, ultimately, improved patient satisfaction.

Comparison of reverse torque values of abutment screws with the application of oil-based and water-based antibacterial agents

Background

Using antibacterial agents to remove the foul odor of the implant cavity and prevent peri-implantitis can affect the detorque values and lead to the loosening of the abutment screw. This study investigated the effects of tetracycline and chlorhexidine gel on detorque values.

Methods

This in vitro study was carried out on three groups of five implants. Group G1 was the control group, and no material was applied to the implant cavity. In group G2, the implant cavity was first filled with artificial saliva and then with chlorhexidine gel. In group G3, the implant cavity was first filled with artificial saliva and then with tetracycline. The abutments were tightened with 25 N/cm2 and then loosened. Finally, the detorque values were calculated.

Results

The highest detorque values were recorded in group G1. Group G3 showed the lowest detorque values. ANOVA showed significant differences in mean detorque values (P<0.05) between the three groups.

Conclusion

According to this study, applying antibacterial agents decreased the detorque values and increased the risk of screw loosening. The reduction of detorque values was more pronounced with the oil-based antibacterial agent (tetracycline).

Stability of implant-abutment connection in three different systems after fatigue test

Aim

Abutment screw loosening of implant-supported prosthesis causes a mismatch between the abutment and the implant. This screw loosening is influenced by the implant-abutment connection type, however, with contradictory results reported in different studies. The present study evaluates the stability of abutment-implant connections in three different systems before and after the fatigue test.

Settings and Design

Thirty implants (4.3 mm in diameter and 12 mm in length) were divided into three groups of 10: Implantium, Zimmer, and straight internal hexagonal connection (SIC) implants.

Materials and Methods

Two torques of 35 Ncm with an interval of 10 min were applied, followed by measuring removal torque value (RTV). The samples were re-torqued and then underwent a simulation of 1-year chewing clinical performance of dental implant under axial force of 400 N, with a frequency of 8 Hz (one million cycles). After fatigue test, the RTV was calculated and recorded.

Statistical Analysis

The mean RTVs obtained before and after cyclic load were analyzed by SPSS version 22 software using multivariate analysis.

Results

Significant differences in RTV and role of cyclic loading were found between SIC and Implantium groups (P = 0.006 and 0.021, respectively), as well as between Zimmer and SIC groups (P = 0.032 and 0.006, respectively), but not between Zimmer and Implantium groups (P = 0.771 and 0.248, respectively).

Conclusion

The type of connection could affect the screw loosening, the preload loss, and the implant component stability. SIC group revealed the highest RTVs before and after cyclic loading.

Evaluation of sealing efficacy and removal convenience of sealing materials for implant abutment screw access holes

Background

Sealing materials are used to fill abutment screw access holes (SAH) to prevent microleakage and protect the central screws in oral implant restoration. However, thus far, no consensus has been reached on sealing material selection. In this study, a comparison of the sealing efficacy and removal convenience of different sealing materials for cement-retained implant restoration was conducted.

Methods

Various sealing materials were classified into five groups, namely, gutta-percha (GP), temporary restorative paste (TRP), vinyl polysiloxane (VPS), polytetrafluoroethylene (PTFE) tape, and onlay resin (OR), and 35 sets of analog-abutments were allocated into five groups of seven specimens. A sealing efficacy test was conducted using a modified dye-penetration method, in which a lower absorbance indicated better sealing efficacy. For the removal-convenience test, the materials were removed from each SAH after solidification, and the retrieval time was recorded.

Results

On days 1 and 10, PTFE exhibited the highest absorbance value with significant differences compared to the other groups. On day 30, TRP and PTFE showed significantly higher absorbance values than GP, VPS, and OR, but no significant difference was detected between TRP and PTFE (p = 0.424). The absorbance values of TRP and PTFE from days 1, 10, and 30 showed significant intragroup differences, while those of the other groups did not. In terms of the removal convenience on days 1, 10, and 30, VPS achieved the best performance, followed by PTFE, OR, TRP, and GP.

Conclusion

Within the limitations of this experiment, VPS and OR showed better sealing efficacy against microleakage and a more convenient removal than the other materials; thus, VPS and OR are recommended for clinical use.

Current complications and issues of implant superstructure

The purpose of this review is to search for complications of dental implant superstructures and consider the issues involved. This narrative review was performed by searching through PubMed databases and review articles that were published after 1990. Misfitting of the superstructure can result in loosening of screws, reduced preload, and in some cases, significant stress around the implant. External connection modalities and single implant prostheses have been reported to have more loose or broken abutment screws. In addition, when zirconia abutment was used for platform shifting, the rate of fracture of the abutment was considered to be high. Additionally, it was reported that men were significantly at an increased risk of abutment fracture. As for the retention mechanism of implant overdenture, stud attachment (Locator type) should receive more attention to wear and damage of retention parts than other attachments. The causes of the complications of implant superstructures have not been clarified in some cases, and further verification is required. Verification of complications is considered important to obtain a long-term prognosis for superstructures of implants. It will be necessary to further verify complications of implants in the future.

Evaluation the loosening of abutment screws in fluid contamination: an in vitro study

Screw loosening is one of the most common clinical problems of dental implants. Research on the influencing factors of screw loosening is very important to prevent screw loosening. The purpose of this in vitro study was to evaluate the influence of liquid contamination on the screw loosening. According to the contamination condition, forty-five abutment screws were divided into three groups (n = 15): no contamination, artificial saliva contamination, and mouthwash contamination. The preload and friction coefficient of the abutment screws were recorded. Then, the reverse torque values (RTVs) and settlement were measured after 3.0 × 10⁵ and 6.0 × 10⁵ cycles. The surface wear of the screws was analyzed. Finally, the stress distribution of the abutment screws was calculated by finite element analysis (FEA). The results showed that fluid contamination reduced the friction coefficient, increased the preload, decrease the settlement, improved resistance to screw loosening, and reduced wear on the thread surface. Appropriate antimicrobial lubrication may improve the anti-loosening performance of abutment screws and prevent excessive wear on the threaded surface.

Three interfaces of the dental implant system and their clinical effects on hard and soft tissues

Anatomically, the human tooth has structures both embedded within and forming part of the exterior surface of the human body. When a tooth is lost, it is often replaced by a dental implant, to facilitate the chewing of food and for esthetic purposes. For successful substitution of the lost tooth, hard tissue should be integrated into the implant surface. The microtopography and chemistry of the implant surface have been explored with the aim of enhancing osseointegration. Additionally, clinical implant success is dependent on ensuring that a barrier, comprising strong gingival attachment to an abutment, does not allow the infiltration of oral bacteria into the bone-integrated surface. Epithelial and connective tissue cells respond to the abutment surface, depending on its surface characteristics and the materials from which it is made. In particular, the biomechanics of the implant-abutment connection structure (i.e., the biomechanics of the interface between implant and abutment surfaces, and the screw mechanics of the implant-abutment assembly) are critical for both the soft tissue seal and hard tissue integration. Herein, we discuss the clinical importance of these three interfaces: bone-implant, gingiva-abutment, and implant-abutment.

Influence of Anodizing Stages on the Preload Force of Implant–Abutment Screws and Their Benefits Regarding the Concept of Immediate Implant Placement—An In Vitro Study

The tightening torque applied to a screw in a provisional restoration immediately after implant placement in a fresh extraction socket is often too low to gain sufficient preload force. Therefore, abutment screw loosening is a common complication. The aim of this study was to investigate whether it is possible to increase the preload force of a given tightening torque by anodizing parts of the implant–abutment complex. In test group 1 (TG1), only the abutment screw was anodized, in four different stages, whereas in test group 2 (TG2), the abutment and the threaded sleeve were anodized in four anodizing stages (TG2a–TG2d). The control group (CG) consisted of non-anodized components. The results were tested for normal distribution, and the components were subsequently parametrically analyzed using a linear model. Both test groups showed higher preload forces compared to the non-anodized control group. The CG obtained an average preload force of 390 N at a tightening torque of 35 Ncm. Comparable values were already obtained at a tightening torque of 20 to 30 Ncm in TG1c/D and TG2b/d. It can be concluded that anodization of abutment screws and components is an effective measure to increase the preload force of the abutment screws by a given tightening torque.

Analysis of Torque Maintenance and Fracture Resistance after Fatigue in Retention Screws Made of Different Metals for Screw-Retained Implant-Borne Prosthesis Joints

Purpose

The aim was to evaluate the effect of different metallic alloys used in the manufacture of retention screws for universal cast to long abutment (UCLA) abutments for external hexagon (HE) and Morse taper (MT) connection implants, as well as of mechanical cycling on torque maintenance and fracture resistance through electromechanical fatigue testing by mastication followed by compression testing.

Methods

Sixty implants were used, 30 MT and 30 HE, with their respective titanium UCLA abutments and retention screws of 5 different materials (n = 6): Ti cp grade 2, Ti cp grade 4, Ti cp grade 4 hard, Ti grade 5—Ti6Al4V and surgical steel (DSP® Biomedical). The assemblies were positioned in an electromechanical masticatory fatigue testing machine. The fracture strength test was performed by compression testing in a universal testing machine EMICDL-200.

Results

The cycled screws and new screws of each alloy group for each connection type were evaluated, obtaining the maximum force (FM), in order to verify the effect of mechanical cycling. The data were tabulated and submitted to appropriate statistical analysis (α = 0.05).

Conclusion

It was concluded that for the MT, the alloy with the best performance was steel, both in the maintenance of torque and in the compression test, and cycling negatively influenced the maintenance of preload for this connection. The alloy material did not influence torque maintenance for HE. The new screws that were subjected to EMIC showed higher strength. The alloy with the lowest strength was Ti grade 2.

Effect of Application of a Bio-Adhesive on the Removal Torque Value and Rotational Misfit at the Implant-Abutment Junction: An In Vitro Study

The aim of this study was to assess the effect of application of a recently developed bio-adhesive (Impladhesive) to abutment screw threads on the removal torque value and rotational misfit at the implant–abutment junction. This in vitro study evaluated 20 implant fixtures and 20 straight abutments. Specimens were randomly divided into two groups (n = 10) with/without adhesive application. In the adhesive group, the abutment was dipped in Impladhesive before torquing. In the control group, the abutment was torqued conventionally without adhesive application. The removal torque value was recorded after completion of the cyclic loading of 500,000 cycles with 2 Hz frequency and 75 N load. Rotational misfit was recorded using a video measuring machine. After applying the torque, the change in the bisector angle on the abutment hex was recorded for each implant. The biocompatibility of Impladhesive was evaluated using a MTT cell vitality assay. Normal distribution of data was assessed using the Kolmogorov–Smirnov test. Data were analyzed using a t-test and Pearson’s correlation coefficient The application of Impladhesive at the implant–abutment interface resulted in significantly greater mean removal torque value compared to the control group (p = 0.008). In addition, the mean rotational misfit at the implant–abutment interface was significantly lower in the use of Impladhesive compared to the control group (p = 0.001). In addition, the cell vitality was found to be greater than 80% at all evaluated time points. It can be concluded that the application of Impladhesive on the abutment screw significantly decreased rotational misfit and increased the removal torque value. Future studies are needed to evaluate the efficacy of this bio-adhesive an in vivo setting.

Microgap and bacterial microleakage during the osseointegration period: An in vitro assessment of the cover screw and healing abutment in a platform-switched implant system

STATEMENT OF PROBLEM

Microgap and bacterial microleakage at the implant-prosthetic abutment interface are recognized concerns for implant-supported restorations, leading to inflammation of the peri-implant tissues, with deleterious consequences for crestal bone levels. However, little is known regarding the interface established between the implant and the healing abutment or cover screw placed for the osseointegration phase.

PURPOSE

The purpose of this in vitro study was to characterize the implant-cover screw and implant-healing abutment interfaces of a platform-switched implant system to determine the microgap and bacterial microleakage of the system and evaluate the biological response and functionality of an interface sealing agent.

MATERIAL AND METHODS

The interfacial microgaps of the implant-healing abutment and implant-cover screw interfaces were characterized by scanning electron microscopy (n=10), and bacterial microleakage was evaluated after colonization with Enterococcus faecalis in a 30-day follow-up (n=10). The sealing efficacy and irritation potential of a silicone-based sealer were determined by using the hen's egg test on chorioallantoic membrane assay. The 2-sample t test was performed to compare means between groups, and data presented with the Kaplan-Meier method were compared statistically by using the log-rank test (α=.05).

RESULTS

The interfacial microgap was less than 2.5 μm for both systems. Bacterial microleakage was noted in approximately 50% of the specimens, particularly at early time points, at both the healing abutment and cover screw interfaces. The silicone-based sealer prevented bacterial leakage in the experimental setting.

CONCLUSIONS

The implant-healing abutment and implant-cover screw interfaces of the tested system, despite the low microgap, allowed for bacterial microleakage after internal colonization. The use of a nonirritating silicone-based sealing agent effectively sealed the system.

Performance of different abutment/implant joints as a result of a sealing agent

Purpose This in vitro study aimed to evaluate the effectiveness of a sealing agent in sealing the abutment/implant interface and the preload maintenance of retaining screws after mechanical cycling.Methods Six groups (n = 12) were evaluated according to the abutment/implant system (external-hexagon implant and UCLA abutments, EHU; Morse taper implant and UCLA abutments, MTU; and Morse taper implant and flexcone abutments, MTF) and the presence of an anaerobic gel sealing agent (control group, no sealing agent; experimental group, sealing agent). Toluidine blue (0.7 μL) was inserted into each implant and the abutments were attached to the implants using a digital torque wrench to evaluate the sealing of the abutment/implant interface. The specimens were tested through mechanical cycling (1 × 10⁶ cycles, 2 Hz, and 130 N). Dye release from the abutment/implant interface was analyzed using a spectrophotometer, and the reverse torque values were obtained using a digital wrench. Reverse torque and dye release data were measured after mechanical cycling and analyzed using ANOVA and Tukey's test (α =.05).Results All experimental groups showed higher reverse torque values than the control groups (P <.05). In general, the MTU and MTF experimental groups, as well as the MTF control group, showed no significant dye release at different periods (P >.05).Conclusions The use of a sealing agent improved the preload maintenance of screw-retained implant-supported prostheses. The sealing agent was effective in sealing the Morse taper connection.

Comparison of the Morse Cone Connection with the Internal Hexagon and External Hexagon Connections Based on Microleakage - Review

The gap formed at the abutment-implant interface brings about a bacterial colonization. In addition, a bacterial reservoir can be established within the implant. The build-up of microorganisms around the implant can cause soft tissue infections and bone loss around the implant, which can lead to implant failure. Our literature review aimed to evaluate the infiltration at the implant-abutment interface, comparing the Morse cone connection with the external hexagon and internal hexagon connections. A literature search using the PubMed database was performed on March 24, 2021. The search terms were combinations of "Morse cone" or "Morse taper" with each of the following terms (individually): "microleakage", "leakage", "infiltration", and "penetration". The inclusion criterion was in vitro studies comparing the Morse cone with the external hexagon and/or internal hexagon, based on infiltration at the implant-abutment interface. The exclusion criterion was the evaluation of microleakage at the implant-abutment interface after applying a sealant over this region. The search was expanded as needed. There was no limit on the year of publication, and only articles written in English were included. In addition, references cited in included articles were also included in this review when they were appropriate. This literature review concluded that, in most cases, the microleakage in the Morse cone connection was lower when compared with the external hexagon and internal hexagon connections.

Comparison of the Effect of Four Different Abutment Screw Torques on Screw Loosening in Single Implant-Supported Prosthesis after the Application of Mechanical Loading

Background

The complications of implant-supported prostheses can be classified into mechanical and biological ones, one part of which is associated with screw loosening. This study was aimed to compare the effect of four different abutment screw torque techniques on screw loosening in single implant-supported prostheses following the application of mechanical loading.

Materials and Methods

In this experimental study, a total of 40 implants in acrylic blocks (6 × 10 × 20 mm) were mounted perpendicular to the surface. They were then randomly divided into four groups: (1) torquing once with 30 Ncm, (2) torquing three times with 30 Ncm and 5-minute intervals, (3) torquing once with 30 Ncm, opening the screw, and retorquing with 30 Ncm, and (4) torquing once with 35 Ncm. The torque values were confirmed by using a digital torque meter. Then, the samples underwent a force (2 cps, 0.453-11.793 kg) for three hours before the measurement of detorque values. The screw loosening force (torque) was then measured and recorded. The obtained data were analyzed by SPSS (version 22) software using one-way ANOVA and Tukey post hoc test at a 5% error level.

Results

The maximum mean detorque values of the abutment screws in single implant-supported prostheses were reported for groups 4 (27.8 ± 1.3), 1 (26.8 ± 1.3), and 3 (25.1 ± 1.3), and the minimum mean detorque value was found in group 2 (24.9 ± 1.2). Moreover, no significant difference was observed between groups 2 and 3 (p > 0.05), but a significant difference was found between groups 1 and 3 and other groups (p < 0.05).

Conclusion

The increase in the torque value increased the torque loss. However, the detorque value in group 4 showed the least difference with the value recommended by the manufacturer (30 Ncm).

Screw stability of CAD-CAM titanium and zirconia abutments on different implants: An in vitro study

BACKGROUND

Limited information is available regarding the removal torque values (RTVs) of screws of different abutment materials when used with different implants.

PURPOSE

To evaluate the effect of implant type and abutment material (zirconia; Zir and titanium; Ti) on the RTVs of abutment screws after cyclic loading.

MATERIALS AND METHODS

Internal conical connection implants (CC, OsseoSpeed TX) and modified internal conical connection implants (MCC, OsseoSpeed EV) (n = 10) were clamped in resin dies. Zir and Ti (N = 20) custom abutments were tightened to implants (20 Ncm for CC and 25 Ncm for MCC) as specified by their manufacturers. The abutments were cyclically loaded by using a sequentially increased loading protocol; 2-million cycles under 100 N, 3-million cycles under 200 N, and 2-million cycles under 300 N loads with 2 Hz. After 7 million cycles, RTVs (Ncm) were measured by using a torque gauge. The data were analyzed with ANOVA by using the restricted maximum likelihood estimation method. Tukey-Kramer adjustment was used for any significant interaction of implant-abutment pairs (α = 0.05).

RESULTS

Two CC implants, 1 with Ti and 1 with Zir abutment, fractured during cyclic loading (under 300 N loads within the 6th and 7th million cycles) and discarded for statistical analysis. Only implant type had a significant effect on RTVs (p <0.001). Screws of Ti abutments on MCC implants had significantly higher RTVs than the screws of Ti (p = 0.003) and Zir (p = 0.005) abutments on CC implants.

CONCLUSIONS

Implant type affected the RTVs, however, the RTVs were higher than the initial torque values for all groups. Screws of Ti abutments on implant, which required greater initial torque values had higher RTVs than the screws of Ti and Zir abutments on the implant that required smaller initial torque values. RTVs were similar for Zir and Ti abutment screws within each implant type.

Effect of fluid contamination on reverse torque values in implant-abutment connections under oral conditions

PURPOSE

Implant mechanical complications, including screw loosening, can influence dental implant success. It has been shown that torque values are affected by contamination occurred in implant-abutment (I/A) interface. This study aimed to examine the effects of blood, saliva, fluoride and chlorhexidine contamination on reverse torque values (RTVs) of abutment screws in oral conditions.

MATERIALS AND METHODS

50 fixtures were mounted into the stainless-steel holders and divided into five groups (n = 10). Except control group (NC), fixture screw holes in other groups were contaminated with chlorhexidine (CG), saliva (SG), blood (BG), or fluoride (FG). Abutment screws were tightened with a digital torque meter. I/A assemblies were subjected to thermocycling and cyclic loading. The mean RTVs were recorded and data were analyzed with one-way ANOVA and Tukey test.

RESULTS

Except for specimens in SG (20.56 ± 1.33), other specimens in BG (21.11 ± 1.54), CG (22.89 ± 1.1) and FG (24.00 ± 1.12) displayed significantly higher RTVs compared to NC (19.00 ± 1.87). The highest RTVs were detected in CG and FG.

CONCLUSION

The obtained data robustly suggest that RTVs were significantly affected by fluid contaminations. Specimens in FG and CG displayed the highest RTVs. Therefore, clinicians should have enough knowledge about probable contaminations in I/A interface in order to manage them during clinical procedure and to inform patients about using oral care products.

Abutment screw loosening in implants: A literature review

This review was intended on major factors contributing to abutment screw loosening. A search of Pubmed and Google Scholar, as well as a manual search, was conducted. Publications and articles accepted for publication up to February 2020 were included. Out of 150 studies retrieved, a total of 57 were selected for this review. Dental implants are associated with a complexity of abutment screw loosening. Implantologists and prosthodontists should be aware of factors that contribute to this problem. In this review previously identified factors were collected, the consideration of which can help to reduce the frequency of abutment screw loosening.

A Comparative 3D Finite Element Computational Study of Three Connections

Masticatory overload on dental implants is one of the causes of marginal bone resorption. The implant–abutment connection (IAC) design plays a critical role in the quality of the stress distribution, and, over the years, different designs were proposed. This study aimed to assess the mechanical behavior of three different types of IAC using a finite element model (FEM) analysis. Three types of two-piece implants were designed: two internal conical connection designs (models A and B) and one internal flat-to-flat connection design (model C). This three-dimensional analysis evaluated the response to static forces on the three models. The strain map, stress analysis, and safety factor were assessed by means of the FEM examination. The FEM analysis indicated that forces are transmitted on the abutment and implant’s neck in model B. In models A and C, forces were distributed along the internal screw, abutment areas, and implant’s neck. The stress distribution in model B showed a more homogeneous pattern, such that the peak forces were reduced. The conical shape of the head of the internal screw in model B seems to have a keystone role in transferring the forces at the surrounding structures. Further experiments should be carried out in order to confirm the present suppositions.

Incidence of abutment screw failure of single or splinted implant prostheses: A review and update on current clinical status

Osseointegrated implants have been widely used for decades with high survival and success rates. However, mechanical complications continue to be reported in the literature, and their clinical management can be often very challenging for the clinician while there is no consensus on the ideal management. The aim of this manuscript was to review the risk factors of abutment screw complications, to identify the most recent incidence of screw failure in the clinical setting and report on the methodology used and the outcome of intervention. Clinical studies and reports were reviewed that reported on abutment screw looseness and/or fracture. A search of the electronic database PUBMED was conducted in November 2018, including manuscripts published in English from 2004 to 2018. Study selection: animal studies, narrative reviews, expert opinions and communications/letters were excluded. Further exclusion criteria included reports on occlusal prosthetic screws and fracture of abutments, and reports that did not provide adequate data. A total of 12 manuscripts were finally included that reported on single implant crowns or 2-unit implant fixed dental prosthesis. To conclude, the most current abutment screw loosening incidence ranges between 7% and 11%, while the abutment screw fracture incidence was found to be 0.6%. The majority reported on fracture of the screw body. Screw loosening or fracture was often located at the first molar restored area, while the maxillary central incisor area was also reported as an area that presented screw fracture. No single abutment screw failure management can be identified as the ideal treatment approach.

In vitro assessment of connection strength and stability of internal implant-abutment connections

BACKGROUND

Various connections have been machined to improve the fit between the dental abutment and implant. In vivo, the instability created by imprecisely fitting components can cause soft tissue irritation and bacterial colonization of the implant system. The aim of this study was to quantify abutment stability under in vitro force applications.

METHODS

Abutment stability and fit were quantitatively measured after application of rotational, vertical, and horizontal forces.

FINDINGS

The abutment connection held by friction (Friction-Fit) was the only group to have 0° angular rotation. A significantly greater vertical force was required to pull the abutment from the implant for the Friction-Fit connection as compared to all other experimental groups. The abutment connection held by a mechanically locking friction-fit with four grooves (CrossFit) and Friction-Fit demonstrated significantly lower lateral movement as compared to all other connections. The remaining connections evaluated included two hexagon connections that rely on screw placement for abutment fit (Conical + Hex #1 and Conical + Hex #2), one connection with protruding slots to align with recessed channels inside the implant (Conical + 6 Indexing Slots), and an internal connection that allows for abutment indexing every 120° (Internal Tri-Channel).

INTERPRETATION

Internal connection geometry influenced the degree of abutment movement. Friction-Fit and CrossFit connections exhibited the lowest rotational and horizontal motions. Significant differences were found between Friction-Fit and CrossFit following the application of a vertical force, with the Friction-Fit requiring a significantly greater pull force to separate the abutment from the implant.

Production of a Piece of Custom-Made Abutment Screwdriver: Technique and Case Report

Crown fractures, framework fractures, and abutment screw loosening or screw fracture are examples of mechanical implant failures. Abutment screw loosening is a serious problem that can result in abutment screw fractures. This clinical report describes the production method of a custom-made abutment screwdriver piece for a patient with abutment screw loosening.

Influence of Abutment Surface Treatments on Screw Loosening of Morse Taper Implants

PURPOSE

To evaluate the effect of blasting and bonding on abutment surface to prevent screw loosening in Morse taper connections.

MATERIAL AND METHODS

Twenty-eight Morse taper connection implants were divided into 4 groups: no treatment (G1), blasting (G2), bonding (G3), and blasting + bonding (G4). In groups G2 and G4, the abutments were blasted with aluminum oxide granules; in groups G3 and G4, the conical abutment region was covered with a thin layer of bond thread lock agent. In all implants, the abutment-implant joint was tightened at a torque of 35 Ncm. The specimens were submitted to the mechanical cycling, under an oblique load for 1.0 × 10 cycles. The torque was measured with a digital torque meter. Data were analyzed by the t test, one-way analysis of variance, and Tukey tests (95%).

RESULTS

The loosening strength was significantly higher in group G4 (35.83 ± 3.02 Ncm). There was no significant difference among groups G1 (25.86 ± 1.96 Ncm), G2 (25.86 ± 3.29 Ncm), and G3 (26.14 ± 2.12 Ncm).

CONCLUSION

The association of blasting and bonding on abutment surface can be used to prevent screw loosening in Morse taper implants.

Influences of microgap and micromotion of implant-abutment interface on marginal bone loss around implant neck

OBJECTIVE

To review the influences and clinical implications of micro-gap and micro-motion of implant-abutment interface on marginal bone loss around the neck of implant.

DESIGN

Literatures were searched based on the following Keywords: implant-abutment interface/implant-abutment connection/implant-abutment conjunction, microgap, micromotion/micromovement, microleakage, and current control methods available. The papers were then screened through titles, abstracts, and full texts.

RESULTS

A total of 83 studies were included in the literature review. Two-piece implant systems are widely used in clinics. However, the production error and masticatory load result in the presence of microgap and micromotion between the implant and the abutment, which directly or indirectly causes microleakage and mechanical damage. Consequently, the degrees of microgap and micromotion further increase, and marginal bone absorption finally occurs. We summarize the influences of microgap and micromotion at the implant-abutment interface on marginal bone loss around the neck of the implant. We also recommend some feasible methods to reduce their effect.

CONCLUSIONS

Clinicians and patients should pay more attention to the mechanisms as well as the control methods of microgap and micromotion. To reduce the corresponding detriment to the implant marginal bone, suitable Morse taper or hybrid connection implants and platform switching abutments should be selected, as well as other potential methods.

Microleakage at the Different Implant Abutment Interface: A Systematic Review

INTRODUCTION

Presence of gap at the implant-abutment interface, leads to microleakage and accumulation of bacteria which can affect the success of dental implants.

AIM

To evaluate the sealing capability of different implant connections against microleakage.

MATERIALS AND METHODS

In January 2017 an electronic search of literature was performed, in Medline, EBSCO host and Pubmed data base. The search was focused on ability of different implant connections in preventing microleakage. The related titles and abstracts available in English were screened, and the articles that fulfilled the inclusion criteria were selected for full text reading.

RESULTS

In this systematic review, literature search initially resulted in 78 articles among which 30 articles only fulfilled the criteria for inclusion and were finally included in the review. Almost all the studies showed that there was some amount of microleakage at abutment implant interface. Microleakage was very less in Morse taper implants in comparison to other implant connections. Majority of studies showed less microleakage in static loading conditions and microleakage increases in dynamic loading conditions.

CONCLUSION

In this systematic review maximum studies showed that there was some amount of microleakage at abutment implant interface. External hexagon implants failed completely to prevent microleakage in both static and dynamic loading conditions of implants. Internal hexagon implants mainly internal conical (Morse taper) implants are very promising in case of static loading and also showed less microleakage in dynamic loading conditions. Torque recommended by manufacturer should be followed strictly to get a better seal at abutment implant interface. Zirconia abutments are more to microleakage than Titanium abutments and there use should be discouraged. Zirconia abutments should be only restricted to cases where there was very high demand of aesthetics.

Comparative study of abutment screw loosening with or without adhesive material

PURPOSE

The purpose of this study was to achieve more retention and stability and to delay or prevent screw loosening.

MATERIALS AND METHODS

Twenty implants (Implantium 3.4 mm, Dentium, Seoul, Korea) were divided into 2 groups (n = 20). In the first group, an adhesive material was applied around the screw of the abutments (test group). In the second group, the screws are soaked in saliva (control group). All the screws were torqued under 30 N/cm, Then, the samples were gone through a cyclic fatigue loading process. After cyclic loading, we detorqued screws and calculated detorque value.

RESULTS

In comparison with the control group, all the implant screws in the test group were smeared with the adhesive material, showing significant higher detorque value.

CONCLUSION

There are significantly higher detorque values in the group with adhesive. It is recommended to make biocompatible adhesive to reduce screw loosening.

Removal torque evaluation of three different abutment screws for single implant restorations after mechanical cyclic loading

PURPOSE

The aim of this study was to evaluate the removal torque of three different abutment screws and pull out strength of implant-abutment connection for single implant restorations after mechanical cyclic loading.

METHODS

The study was performed in accordance with ISO 14801:2007. Three implant groups (n=15) were used: group A, PW Plus® with flat head screw; group B, PW Plus® with tapered screw; and group C, Conelog® with flat head screw. All groups had the same implant-abutment connection feature: cone with mandatory index. All screws were tightened with manufacturer's recommended torque. Ten specimens in each group underwent cyclic loading (1×106 cycles, 10 Hz, and 250 N). Then, all specimens were un-tightened, measured for the removal torque, and underwent a tensile test. The force that dislodged abutment from implant fixture was recorded. The data were analysed using independent sample t-test, ANOVA and Tukey HSD test.

RESULTS

Before cyclic loading, removal torque in groups A, B and C were significantly different (B> A> C, P<.05). After cyclic loading, removal torque in all groups decreased significantly (P<.05). Group C revealed significantly less removal torque than groups A and B (P<.005). Tensile force in all groups significantly increased after cyclic loading (P<.05), group A had significantly less tensile force than groups B and C (P<.005).

CONCLUSIONS

Removal torque reduced significantly after cyclic loading. Before cyclic loading, tapered screws maintained more preload than did flat head screws. After cyclic loading, tapered and flat head screws maintained even amounts of preload. The tensile force that dislodged abutment from implant fixture increased immensely after cyclic loading.