• The Journal of Korean Academy of Prosthodontics
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• v.40 no.2
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• pp.193-200
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• 2002

For the purpose of decreasing the chair time in implant cases, the time needed to loosening and fastening the screw must be shortened. Nowadays, the two typical designs of screw head are slot and hexa form. This study aimed at the shortening of loosening and fastening time by modifying the slot and hexa form. Total of twelve dentists participate in these experiments, four of them were experienced and eight of them were novice dentists. 1. There were many differences in the speeds of screw loosening and fastening between personal experiences. Experienced dentists are faster than novice dentists. 2. There were many differences in the speeds by angulation of the implant, by the conditions of the muscle tonicity. 3. Revised slot and hexa Heads show the slightly shortened time for acrew looseing and fastening.

• The Journal of Korean Academy of Prosthodontics
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• v.40 no.3
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• pp.275-286
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• 2002

Statement of problem. Surface alteration of the implant screws after function may be associated with mechanical failure. Theses metal fatigue appears to be the most common cause of structural failure. Purpose. The purpose of this study was to evaluate surface alteration of the implant screws after function through the examination of used and unused implant screws in SEM(scanning electron microscope). Materials and methods. In this study, abutment screws(Steri-oss, 3i), gold retaining screw(3i) and titanium retaining screw(3i) were retrieved from patients. New, unused abutment and retaining screws were prepared for control group. Each of the old, used screws was retrieved with a screwdriver. And retrieved implant complex of Steri-oss system was prepared for this study. Then, SEM investigation and EDS analysis of abutment and retaining screws were performed. And SEM investigation of cross-sectioned sample of retrieved implant complex was performed. Results. In the case of new, unused implant screws, as maunfactured circumferential grooves are regularly examined and screw thread are sharply remained. Before ultrasonic cleansing of old, used implant screw, a lot of accumulation and corrosion products were existed. After ultrasonic cleansing of old, used implant screws, circumferential grooves as examined before function were randomly deepened and scratches increased. Also, dull screw thread was examined. More surface alterations after function were examined in titanium screw than gold screw. And more surface alteration was examined when retrieved with driver than retrieved without driver. Conclusions. These surface alteration after function may result in the screw instability. Regularly cleansing and exchange of screws was recommended. We recommend the use of gold screw rather than titanium screw, and careful manipulation of the driver.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.46 no.2
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• pp.133-142
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• 2020

Objectives: In this study, we determined the incidence and pattern of screw loosening in patients who received dental implants. Materials and Methods: Patients who received implants between January 2008 and October 2013 and completed their prosthetic rehabilitation were evaluated for the incidence, frequency, and onset of screw loosening using dental charts and radiographs. The association between each factor and screw loosening was analyzed using the chi-square test and a multivariate analysis with binary logistic regression models (P<0.05). Results: Total 1,928 implants were placed in 837 patients (448 males, 389 females), whose follow-up period after loading varied from 0.25 to 70 months (mean period, 31.5 months). Screw loosening occurred in 7.2% of implants. Most cases occurred less than six months after loading. Among those, 22.3% experienced recurrent screw loosening. Screw loosening was most common in the molar region (8.5%) and frequently associated with an implant diameter of ≥5 mm (14.2%). External implant-abutment connections (8.9%) and screw-retained implant prostheses (10.1%) showed higher incidence of problems than internal implant-abutment connections and cement-retained implants, respectively. Screw loosening was most common in implant prostheses with single crowns (14.0%). Conclusion: Within the limits of the current study, we conclude that the incidence of screw loosening differs significantly according to the position of implant placement, the type of implant and manufacturer, implant diameter, the type of implant-abutment connection, the type of retention in the implant prosthesis, and the type of implant prosthesis.

• The Journal of Advanced Prosthodontics
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• v.13 no.1
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• pp.65-70
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• 2021

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.

• Journal of Korean Dental Science
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• v.6 no.1
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• pp.27-33
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• 2013

The introduction of osseointegrated dental implants in dentistry brought about a new era in everyday dental practice. For the past 50 years, prosthetic restoration with implant-supported prosthesis has developed into a viable and predictable treatment option. Alongside the increasing use of dental implants is the occurrence of many complications during implant placement (surgery), in the mechanical or prosthetic problem, and in the biological aspect. In particular, abutment or screw fracture as one of the mechanical complications can put the dentist in a tight spot in a clinical situation. It is hard to remove the fractured abutment and screw to restore it properly. Therefore, it is very important that clinicians consider possible complications in advance and make an appropriate treatment plan. We discuss cases of abutment fracture and mechanical/prosthetic complications together with the causes and solutions.

• The Journal of Korean Academy of Prosthodontics
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• v.36 no.5
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• pp.721-737
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• 1998

Abutment screw loosening of implant restorations is a common problem in the treatment of dental implant. The purpose of this study was to calculate stress and preload from the elongation measurements and to determine maximum tightening torque without plastic deformation of the screw. The length of each gold alloy UCLA screw was measured after tightening to the manufacturer's recommended torque of 32 N-cm. Similarity, titanium UCLA screws were measured after tightening to the manufacturer's recommended torque of 20 N-cm. Loosening torque was also measured after tightening to 32 N-cm torque for gold alloy abutment screws and 20 N-cm for titanium abutment screws. The results were as follows ; 1. There was a regressive relationship between screw elongation and tightening torque (gold alloy : $r^2=0.987$, titanium : $r^2=0.978$), and the mean preload calculated from elongation measurements was $501.11{\pm}26.85\;N$ (gold alloy) and $399.43{\pm}7.61\;N$ (titanium). 2. Stress calculated for the gold alloy and titanium screws at maximum recommended tightening torque was less than 60% of their respective yield strengths and with-in the elastic range. Maximum tightening torque without plastic deformation was 61 N-cm (gold alloy) and 39 N-cm (titanium). 3. For titanium screws, there was a significant difference between loosening after trial 1 and loosening after trials 2 to 5 (p<0.05). No statistically significant difference was seen in mean loosening torques between the first and subsequent trials for gold alloy screws.

• The Journal of Korean Academy of Prosthodontics
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• v.42 no.1
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• pp.94-109
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• 2004

Statement of problem : Several domestic dental implants have been developed since dental treatment being implants are increasing and popularized. However, they have not been used in domestic market like imported goods. Material and methods : This study was carried out to compare domestic and imported implants in aspect of fitness, dental implant fixture and abutment screw using scanning electron microscope. All experiments were performed under dry condition. Results : 1. Only in aspect of relation of dental implant fkxture and abutment screw, except only one group with point contact, good fitness was existed. 2. Home products must presevere in their efforts, so as excellent to fit.

• The Journal of Korean Academy of Prosthodontics
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• v.56 no.3
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• pp.179-187
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• 2018

Purpose: The purpose of this study was to investigate the effect of heat applied to disintegrate cement on the removal torque value and fracture strength of titanium abutment and abutment screw. Materials and methods: Implants, titanium abutments and abutment screws were prepared for each 20 piece. Implant abutments and screws were classified as the control group in which no heat was applied and the experimental group was heated in a vacuum furnace to $450^{\circ}C$ for 8 minutes and cooled in air. The abutments and screws were connected to the implants with 30 Ncm tightening torque at interval 10 minutes and the removal torque value was measured 15 minutes later. And the fracture strength of abutment screw was measured using universal testing machine. Results: The mean removal torque value was $27.84{\pm}1.07Ncm$ in the control group and $26.55{\pm}1.56Ncm$ in the experimental group and showed statistically significant difference (P < .05). The mean fracture strength was $731.47{\pm}39.46N$ in the control group and $768.58{\pm}46.73N$ in the experimental group and showed statistically no significant difference (P > .05). Conclusion: The heat applied for cement disintegration significantly reduced the removal torque value of the abutment screw and did not significantly affect fracture strength of the abutment screw. Therefore, in the case of applying heat to disintegrate cement it is necessary to separate the abutment screw or pay attention to the reuse of the heated screw. However further studies are needed to evaluate the clinical reuse of the heated screw.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.486-491
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• 2004

A comparative study on the implant screw loosening under the initial clamping force and cyclic loads was conducted. The experiments were performed to evaluate the screw loosening behavior of the internal and external implant systems. It was found that the screw loosening torques of implant systems were significantly affected by the way how the abutment and fixture were connected due to the difference in the load transfer mechanism between abutment and fixture.

• The Journal of Korean Academy of Prosthodontics
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• v.51 no.4
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• pp.276-283
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• 2013

Purpose: The purpose of this study was to investigate the fit and screw joint stability between Ready-made abutment and CAD-CAM custom-made abutment. Materials and methods: Osstem implant system was used. Ready-made abutment (Transfer abutment, Osstem Implant Co. Ltd, Busan, Korea), CAD-CAM custom-made abutment (CustomFit abutment, Osstem Implant Co. Ltd, Busan, Korea) and domestically manufactured CAD-CAM custom-made abutment (Myplant, Raphabio Co., Seoul, Korea) were fabricated five each and screws were provided by each company. Fixture and abutments were tightening with 30Ncm according to the manufacturer's instruction and then preloding reverse torque values were measured 3 times repeatedly. Kruskal-Wallis test was used for statistical analysis of the preloading reverse torque values (${\alpha}=.05$). After specimens were embedded into epoxy resin, wet cutting and polishing was performed and FE-SEM imaging was performed, on the contact interface. Results: The pre-loading reverse torque values were $26.0{\pm}0.30Ncm$ (ready-made abutment; Transfer abutment) and $26.3{\pm}0.32Ncm$ (CAD-CAM custom-made abutment; CustomFit abutment) and $24.7{\pm}0.67Ncm$ (CAD-CAM custom-made abutment; Myplant). The domestically manufactured CAD-CAM custom-made abutment (Myplant abutment) presented lower pre-loading reverse torque value with statistically significant difference than that of the ready-made abutment (Transfer abutment) and CAD-CAM custom-made abutment (CustomFit abutment) manufactured from the same company (P=.027) and showed marginal gap in the fixture-abutment interface. Conclusion: Within the limitation of the present in-vitro study, in domestically manufactured CAD-CAM custom-made abutment (Myplant abutment) showed lower screw joint stability and fitness between fixture and abutment.