In Vitro Comparison of Loss of Torque between Gold and Titanium Alloy Abutment Screws in Dental Implants without Any Cyclic Loads

A Biomechanical Comparative Analysis of Abutment Screw Head Designs on Preload Stability Under Oblique Compressive Forces: An In Vitro Pilot Study

The purpose of this study was to examine the impact of abutment screw head sizes on preload stability when secured to a standard external hex implant under oblique compressive forces. Fifteen metal crowns were divided into 3 equal groups. The first group had 5 angulated cemented crowns connected to a 3-mm-tall straight hexagonal abutment with an external hex abutment screw. The second and third groups each had 5 straight cemented crowns attached to a tapered abutment with flat-slotted and internal hex abutment screws, respectively. Samples were subjected to a static cyclic load until failure. Kruskal-Wallis H, Dunn, and one-way analysis of variance with Tukey honestly significant difference tests were performed. Cemented straight crowns supported by an angled abutment connected to implants with flat-slotted and internal hex abutment screw heads failed at an average of 4.24 × 106 cycles ± 3.31 SD and 12.67 × 106 cycles ± 5.47 SD, respectively. Cemented angled crowns supported by a straight abutment connected to identical implants with an external hex abutment screw survived 18.02 × 106 cycles ± 4.49 SD. The periotest value rate of change increased at a higher rate in crowns supported by angled abutments compared with straight abutments (p < .05). No cement failure was observed. Under the experimental conditions, larger abutment screw head sizes demonstrated greater stability of the abutment-abutment screw joint interface. Based on the in vitro findings, no cement failure was observed between the cemented crown and abutment connection. Future research with standardized comparative setups and larger sample sizes is needed.

Engaging vs. Non-Engaging Abutments: An In Vitro Study Evaluating Changes in Microgap and Screw Morphology

BACKGROUND

The purpose of this study was to compare the microgap size between engaging (E) and non-engaging (NE) abutments and screw morphology changes between E and NE abutments using scanning electron microscopy (SEM) before and after cyclic loading (CL).

METHODS

Thirty-six implants were arranged into four groups as follows: Group 1, single units with E abutments; Group 2, single units with NE abutments; Group 3, three-unit fixed partial dentures with a hemi-engaging design; and Group 4, three-unit FPDs with two NE abutments. The microgap was evaluated using a stereomicroscope. SEM was used to qualitatively evaluate screw morphology. The specimens were subjected to axial loading first and then lateral loading (30°) using the settings; one million cycles (1.0 × 106 cycles) for each loading axis.

RESULTS

There were no significant differences detected in the microgap sizes between the E and NE abutment groups. In addition, there were no significant changes in the microgap sizes after CL in the E or NE abutment specimens. More damage to the screws was noticed after CL compared to before, with no difference in the patterns of damage detected between the E and NE abutments.

CONCLUSIONS

No significant difference in microgap size was detected between the E and NE abutments. Furthermore, there was no significant difference in microgap size between the different prosthetic designs. From the SEM qualitative evaluation, there were similar screw morphology changes after CL between the E and NE abutments.

Silver coating on dental implant-abutment connection screws as potential strategy to prevent loosening and minimizing bacteria adhesion

Introduction: One of the main problems for the long-term behavior of dental implants are loosening of the implant-abutment connection screws and bacterial infiltration. The aim of this work is to increase the screw fixation by silver coating, providing superior mechanical retaining and antibacterial effect. Methods: Eighty dental implants with their abutments and screws have been studied. Twenty screws were not coated and were used as a control while the rest of screws were silver coated by sputtering, with three different thickness: 10, 20 and 40 μm and 20 screws per each thickness. Coating morphology and thickness were determined by scanning electron microscopy using image analysis systems. The screws were tightened for each of the thicknesses and the control with two torques 15 Ncm and 20 Ncm and tested under mechanical fatigue simulating oral stresses up to a maximum of 500,000 cycles. The remaining torques at different cycles were determined with a high-sensitivity torquemeter. Cell viability assays were performed with SaOs-2 osteoblasts and microbiological studies were performed against Streptococcus gordonii and Enterococcus faecalis bacteria strains, determining their metabolic activity and viability using live/dead staining. Results: It was observed a decrease in torque as cycles increase. For a preload of 15 Ncm at 100,000 cycles, the loosening was complete and, for 20 Ncm at 500,000 cycles, 85% of torque was lost. The silver coatings retained the torque, especially the one with a thickness of 40 μm, retaining 90% of the initial torque at 500,000 cycles. It was observed that osteoblastic viability values did not reach 70%, which could indicate a slight cytotoxic effect in contact with cells or tissues; however, the screw should not be in direct contact with tissue or living cells. Silver coating induced a significant reduction of the bacteria metabolic activity for Streptococcus gordonii and Enterococcus faecalis, around 90% and 85% respectively. Discussion: Therefore, this coating may be of interest to prevent loosening of implant systems with a worthy antibacterial response.