• Journal of Dental Rehabilitation and Applied Science
• /
• v.36 no.4
• /
• pp.222-231
• /
• 2020

To use the external connection implant (EXT) appropriately, the inter-implant distance should be carefully considered during placement, and the bones raised above the implants should be trimmed during the second surgery. The hex abutment is more useful than the non-hex abutment. EXT is particularly useful when the inter-arch space is limited. The tissue level (TL, internal butt connection) implant has a biomechanical advantage of coronal wall thickness and a biological advantage of an inherent transmucosal smooth surface. During TL implant restoration, an abutment can be selected using the abutment and fixture margins with considerations for the inter-arch space. Since no single type of implant can satisfy all the cases, it is necessary to select the appropriate type, considering the occlusal force and the bone condition.

• The Journal of Korean Academy of Prosthodontics
• /
• v.42 no.6
• /
• pp.664-670
• /
• 2004

Statement of problem. One of the common problems of dental implant prosthesis is the loosening of the screw that connects each component, and this problem is more common in single implant-supported prostheses with external connection. Purpose. The purpose of this study was to examine the changes of detorque values of abutment screws with external connection in different abutment heights. Materials and methods. After cyclic loading on three different abutment heights, detorque values were measured. Abutments were retained with titanium abutment screws tightened to 30 Ncm (30.5 kgmm) with digital torque gauge as recommended by the manufacturer. Replacing abutments, implants and titanium abutment screws with new ones at every measurement, initial detorque values were measured six times. In measuring de torque values after cyclic loading, Avana Cemented Abutments of 4.0 mm collar, 7.0 mm height (Osstem Co., Ltd., Seoul, Korea) were used with three different lengths of 5.0, 8.0, 11.0 mm. Shorter abutments were made by milling of 11.0 mm abutment to have the same force-exercised area of 4.5 mm diameter. Sine curve force (20N-320N, 14Hz) was applied, and detorque values were measured after cyclic loading of 2 million times by loading machine. Detorque values of initial and after-loading were measured by digital torque gauge. One-way ANOVA was employed to see if there was any influence from different abutment heights. Results. The results were as follows: 1. The initial detorque value was 27.8$\pm$0.93 kgmm, and the ratio of the initial detorque value to the tightening torque was 0.91(27.8/30.5). 2. Measured detorque values after cyclic loading were declined as the height of the abutment increased, that was, 5.0 mm; 22.3$\pm$0.82 kgmm, 8.0 mm; 21.8$\pm$0.93 kgmm, and 11.0 mm; 21.3$\pm$0.94 kgmm. 3. One-way ANOVA showed no statistically significant differences among these (p>0.05). 4. Noticeable mobility at the implant-abutment interface was not observed in any case after cyclic loading at all.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.22 no.1
• /
• pp.55-74
• /
• 2006

The external contour of an implant can have significant effects on the load transfer characteristics and may result in different bone failure rates for different implant system. The purpose of this study was to investigate the effects of crest module shape and occlusal load direction on bone failure modes of five commercially available dental implant systems. Five different implant systems with internal connection; ITI (Model 1), Astra (Model 2), Bicon (Model 3), Friadent (Model 4), and Paragon (Model 5), comparable in size, but different in thread profile and cest module shapes, were compared using the finite element method. Conclusively, in the internal connection system of the implant-abutment connection methods, the stress-induced pattern at the supporting bone according to the abutment connection form had differenence among them, and implants with narrowing crestal module cross-sections at the top of the cortical bone created more favorable load transfer characteristics in this region. But it is considered that the future study is necessary about how this difference in the magnitude of the stress have an effect on the practical clinic.

• Journal of Technologic Dentistry
• /
• v.42 no.2
• /
• pp.99-105
• /
• 2020

Purpose: A study analysed the stress distribution of abutment screw and supporting bone of fixture by the tightening torque force of the abutment screw within clinical treatment situation for the stability of the dental implant prosthesis. Methods: The finite element analysis was targeted to the mandibular molar crown model, and the implant was internal type 4.0 mm diameter, 10.0 mm length fixture and abutment screw and supporting bone. The occlusal surface was modeled in 4 cusps and loaded 100 N to the buccal cusps. The connection between the abutment and the fixture was achieved by combining three abutment tightening torque forces of 20, 25, and 30 Ncm. Results: The results showed that the maximum stress value of the supporting bone was found in the buccal cortical bone region of the fixture in all models. The von Mises stress value of each model showed 184.5 MPa at the 20 Ncm model, 195.3 MPa in the 25 Ncm model, and 216.5 MPa in the 30 Ncm model. The contact stress between the abutment and the abutment screw showed the stress value in the 20 Ncm model was 201.2 MPa, and the 245.5 MPa in the 25 Ncm model and 314.0 MPa in the 30 Ncm model. Conclusion: The increase of tightening force within the clinical range of the abutment screw of the implant dental prosthesis was found to have no problem with the stability of the supporting bone and the abutment screw.

• The Journal of Korean Academy of Prosthodontics
• /
• v.51 no.4
• /
• pp.315-322
• /
• 2013

Purpose: To evaluate the axial displacement of implant-abutment assembly after cyclic loading in internal tapered connection system. Materials and methods: External butt-joint connection implant and internal tapered connection implant were connected with three types of abutment for cement-retained prostheses, i.e. external type abutment (Ext group), internal tapered 1-piece abutment (Int-1 group), and internal tapered 2-piece abutment (Int-2 group). For each group, 7 implants and abutments were used. The implantabutments assemblies were clamped into the implant holder for vertical loads. A dynamic cyclic loading was applied for $150{\pm}10N$ at a frequency of 4 Hz. The amount of axial displacement of the abutment into the implant was calculated at each cycle of 0, 5, 10, 50, 100, 1,000, 5,000, and 10,000. A repeated measures analysis of variance (ANOVA) for the overall effect of cyclic loading and the pattern analysis by linear mixed model were used for statistical analysis. Differences at P<.05 were considered statistically significant. Results: The mean axial displacement after 10,000 cycles were $0.714{\pm}0.488{\mu}m$ in Ext group, $5.286{\pm}1.604{\mu}m$ in Int-1 group, and $11.429{\pm}1.902{\mu}m$ in Int-2 group. In the pattern analysis, Int-1 and Int-2 group showed continuous axial displacement at 10,000 cycles. There was no declining pattern of axial displacement in the Ext group. Conclusion: The pattern of linear mixed model in Ext group showed no axial displacement. There were continuous axial displacements in abutment-implant assemblies in the Int-1 and Int-2 group at 10,000 cycles. More axial displacement was found in Int-2 group than in Int-1 group.

• The Journal of Korean Academy of Prosthodontics
• /
• v.46 no.6
• /
• pp.561-568
• /
• 2008

STATEMENT OF PROBLEM: Currently, many implant systems are developed and divided into two types according to their joint connection: external or internal connection. Regardless of the connection type, screw loosening is the biggest problem in implant-supported restoration. PURPOSE: The purpose of this study is to assess the difference in stability of abutment screws between the external and internal hexagonal connection types under cyclic loading. MATERIAL AND METHODS: Each of the 15 samples of external implants and internal abutments were tightened to 30 N/cm with a digital torque gauge, and cemented with a hemispherical metal cap. Each unit was then mounted in a $30^{\circ}$ inclined jig. Then each group was divided into 2 sub-groups based on different periods of cyclic loading with the loading machine (30 N/ cm - 300 N/cm,14 Hz: first group $1{\times}10^6$, $5{\times}10^6$ cyclic loading; second group $3{\times}10^6$, $3{\times}10^6$ for a total cyclic loading of $6{\times}10^6$) The removal torque value of the screw before and after cyclic loading was checked. SPSS statistical software for Windows was used for statistical analysis. Group means were calculated and compared by ANOVA, independent t-test, and paired t-test with ${\alpha}$=0.05. RESULTS: In the external hexagonal connection, the difference between the removal torque value of the abutment screw before loading, the value after $1{\tims}10^6$ cyclic loading, and the value after $1{\times}10^6$, and additional $5{\times}10^6$ cyclic loading was not significant. The difference between the removal torque value after $3{\times}10^6$ cyclic loading and after $3{\times}10^6$, and additional $3{\times}10^6$ cyclic loading was not significant. In the internal hexagonal connection, the difference between the removal torque value before loading and the value after $1{\times}10^6$ cyclic loading was not significant, but the value after $1{\times}10^6$, and additional $5{\times}10^6$ cyclic loading was reduced and the difference was significant (P < .05). In addition, in the internal hexagonal connection, the difference between the removal torque value after $3{\times}10^6$ cyclic loading and the value after $3{\times}10^6$, and additional $3{\times}10^6$ cyclic loading was not significant. CONCLUSION: The external hexagonal connection was more stable than the internal hexagonal connection after $1{\times}10^6$, and additional $5{\times}10^6$ cyclic loading (t = 10.834, P < .001). There was no significant difference between the two systems after $3{\times}10^6$, and additional $3{\times}10^6$ cycles.

• The Journal of the Korean dental association
• /
• v.53 no.11
• /
• pp.804-816
• /
• 2015

PURPOSE: The aim of this study was to evaluate the influence of the oxide layer removal process in the Co-Cr-Mo (CCM) abutment after casting procedure on the prosthesis settlement and screw stability. MATERIALS AND METHODS: CCM abutments of four different interface conditions (CCM-M; machined, CCM-O; oxide layer formed, CCM-B; blasted, CCM-P; polished after blasted) and gold abutment (Gold-C; Cast with type III Gold alloy) were used. The initial settling values of abutments were evaluated according to the difference of implant-abutment length when the tightening torques were applied at 5 Ncm and 30 Ncm, and the settling values of abutments caused by loading were evaluated according to the difference of implant-abutment length before and after loading with 250 N, 100000 cycle. The loss ratios of removal torque for abutment screws were evaluated according to the difference in value of removal torques under 30 Ncm tightening torque applied before and after cyclic loading. RESULTS: The CCM-P and CCM-B group showed a higher initial settling value compared with the Gold-C group (P<.05), while the Gold-C group showed the highest settling values caused by loading (P<.05) and no significant differences were observed for between CCM groups (P>.05). The loss ratio of removal torque values for the CCM-B, CCM-P groups did not differ significantly from that of the Gold-C group (P>.05). CONCLUSION: Even though the oxide layer was removed by different methods, CCM abutment with internal conical connection structure showed lower abutment settling and similar screw loosening after cyclic loading compared with gold abutment.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.29 no.2
• /
• pp.111-118
• /
• 2013

Purpose of present study is to investigate the effects of thread pitch in coronal portion in scalloped implant with 2 different connections on loading stress using 3 dimensional finite element analysis. Scalloped implant with 4 different thread pitches (0.4mm, 0.5mm, 0.6, and 0.7mm) in the coronal part was modeled with 2 different implant-abutment connections. Platform matching connection had the same implant and abutment diameter so that they were in flush contact at the periphery while platform mismatching connection had smaller abutment diameter than implant so that their connection was made away from periphery of implant-bone interface. Occlusal loading of 100N force was applied vertically and 30 degree obliquely to all 8 models and the maximum von Mises bone stress was identified. Loading stress as highly concentrated in cortical bone. Platform mismatching scalloped implant with small thread pitch (0.4mm) model had consistently lowest maximum von Mises bone stress in vertical and oblique loads. Platform matching model had lowest maximum von Mises bone stress with 0.6mm thread pitch in vertical load and with 0.4mm thread pitch in oblique load. Platform mismatching connection had important roles in reducing maximum von Mises bone stress. Scalloped implant with smaller coronal thread pitch showed trend of reducing maximum von Mises bone stress under load.

• Structural Engineering and Mechanics
• /
• v.6 no.3
• /
• pp.259-274
• /
• 1998

The test results from non-destructive and destructive field testing of a three-span deteriorated reinforced concrete slab bridge are used as a vehicle to examine the reliability of available tools for finite-element analysis of in-situ structures. Issues related to geometric modeling of members and connections, material models, and failure criteria are discussed. The results indicate that current material models and failure criteria are adequate, although lack of inelastic out-of-plane shear response in most nonlinear shell elements is a major shortcoming that needs to be resolved. With proper geometric modeling, it is possible to adequately correlate the measured global, regional, and local responses at all limit states. However, modeling of less understood mechanisms, such as slab-abutment connections, may need to be finalized through a system identification technique. In absence of the experimental data necessary for this purpose, upper and lower bounds of only global responses can be computed reliably. The studies reaffirm that success of finite-element models has to be assessed collectively with reference to all responses and not just a few global measurements.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.33 no.3
• /
• pp.189-198
• /
• 2017

Purpose: This study aims to analyze the stress distribution of mandibular molar restoration supported by the implants with external hex and internal taper abutment connection design. Materials and Methods: Models of external connection (EXHEX) and internal connection (INCON) implants, corresponding abutment/crowns, and screws were developed. Supporting edentulous mandibular bony structures were designed. All the components were assembled and a finite element analysis was performed to predict the magnitude and pattern of stresses generated by occlusal loading. A total of 120 N static force was applied both by axial (L1) and oblique (L2) direction. Results: Peak von Mises stresses produced in the implants by L2 load produced 6 - 15 times greater than those by L1 load. The INCON model showed 2.2 times greater total amount of crown cusp deflection than the EXHEX model. Fastening screw in EXHEX model and upside margin of implant fixture in INCON model generated the peak von Mises stresses by oblique occlusal force. EXHEX model and INCON model showed the similar opening gap between abutment and fixture, but intimate sealing inside the contact interface was maintained in INCON model. Conclusion: Oblique force produced grater magnitudes of deflection and stress than those by axial force. The maximum stress area at the implant was different between the INCON and EXHEX models.