• Structural Engineering and Mechanics
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• v.74 no.4
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• pp.567-576
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• 2020

Considerable controversy surrounds the choice of the best abutment type for implant prosthetics. The two most common structures are hex and non-hex abutments. The non-hex abutment typically furnishes a larger contact area between itself and the implant than that provided by a hex structure. However, when a hex abutment is loaded, the position of its contact area may be deeper than that of a non-hex abutment. Hence, the purpose of this study is to determine the different biomechanical behaviors of an internal bone-level implant based on the abutment type-hex or non-hex-and clinical crown length under static and cyclic loadings using finite element analysis (FEA). The hex structure was found to increase the implant and abutment stability more than the nonhex structure among several criteria. The use of the hex structure resulted in a smaller volume of bone tissues being at risk of hypertrophy and fatigue failure. It also reduced micromovement (separation) between the implant components, which is significantly related to the pumping effect and possible inflammation. Both static and fatigue analyses, used to examine short- and long-term stability, demonstrated the advantages of the hex abutment over the non-hex type for the stability of the implant components. Moreover, although its impact was not as significant as that of the abutment type, a large crown-implant ratio (CIR) increased bone strain and stress in the implant components, particularly under oblique loading.

• The Journal of Advanced Prosthodontics
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• v.13 no.1
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• pp.46-54
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• 2021

Purpose. The design of the implant-abutment complex is thought to be responsible for marginal bone loss (MBL) and might affect the condition of the peri-implant tissues. This the present study aimed to evaluate the influence of the implant-abutment complex on MBL and the peri-implant tissues in partially edentulous patients treated with dental implants and determine the most advantageous design. Materials and Methods. A total of ninety-one endosseous implants with different designs of implant-abutment complex [tissue level-TL (n = 30), platform switch-PS (n = 18), and platform match-PM (n = 43)] were reviewed for MBL, Probing Pocket Depth (PPD) and Bleeding on Probing (BoP). MBL was calculated for first year of the insertion and the following years. Results. The median MBL for the PM implants (2.66 ± 1.67 mm; n = 43) in the first year was significantly higher than those for the other types (P=.033). The lowest rate of MBL (0.61 ± 0.44 mm; n = 18) was observed with PS implants (P=.000). The position of the crown-abutment border showed a statistically significant influence (P=.019) and a negative correlation (r=-0.395) on MBL. BoP was found significantly higher in PM implants (P=.006). The lowest BoP scores were detected in PS implants, but the difference was not significant (P=.523). The relation between PPD and connection type revealed no statistically significant influence (P>.05). Conclusion. Within the limitations of the present study, it may be concluded that PS implants seem to show better peri-implant soft tissue conditions and cause less MBL.

• Journal of Periodontal and Implant Science
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• v.52 no.2
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• pp.170-180
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• 2022

Purpose: This study was conducted to assess the effect of hard and/or soft tissue grafting on immediate implants in a preclinical model. Methods: In 5 mongrel dogs, the distal roots of P2 and P3 were extracted from the maxilla (4 sites in each animal), and immediate implant placement was performed. Each site was randomly assigned to 1 of the following 4 groups: i) gap filling with guided bone regeneration (the GBR group), ii) subepithelial connective tissue grafting (the SCTG group), iii) GBR and SCTG (the GBR/SCTG group), and iv) no further treatment (control). Non-submerged healing was provided for 4 months. Histological and histomorphometric analyses were performed. Results: Peri-implant tissue height and thickness favored the SCTG group (height of periimplant mucosa: 1.14 mm; tissue thickness at the implant shoulder and ±1 mm from the shoulder: 1.14 mm, 0.78 mm, and 1.57 mm, respectively; median value) over the other groups. Bone grafting was not effective at the level of the implant shoulder and on the coronal level of the shoulder. In addition, simultaneous soft and hard tissue augmentation (the GBR/SCTG group) led to a less favorable tissue contour compared to GBR or SCTG alone (height of periimplant mucosa: 3.06 mm; thickness of peri-implant mucosa at the implant shoulder and ±1 mm from the shoulder: 0.72 mm, 0.3 mm, and 1.09 mm, respectively). Conclusion: SCTG tended to have positive effects on the thickness and height of the periimplant mucosa in immediate implant placement. However, simultaneous soft and hard tissue augmentation might not allow a satisfactory tissue contour in cases where the relationship between implant position and neighboring bone housing is unfavorable.

• Journal of Dental Rehabilitation and Applied Science
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• v.19 no.4
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• pp.257-268
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• 2003

The purpose of this study was to assess the loading distributing characteristics of implant prosthesis according to position and direction of load, under vertical and inclined loading using FEA analysis. The finite element model was designed according to standard fixture (4.1mm restorative component x 11.5mm length). The crown for mandibular first molar was made using UCLA abutment. Each three-dimensional finite element model was created with the physical properties of the implant and surrounding bone. This study simulated loads of 200N at the central fossa in a vertical direction (loading condition A), 200N at the outside point of the central fossa with resin filling into screw hole in a vertical direction (loading condition B), 200N at the centric usp in a $15^{\circ}$ inward oblique direction (loading condition C), 200N at the in a $30^{\circ}$ inward oblique direction (loading condition D) or 200N at the centric cusp in a $30^{\circ}$ outward oblique direction (loading condition E) individually. Von Mises stresses were recorded and compared in the supporting bone, fixture, and abutment screw. The following results have been made based on this study: 1. Stresses were concentrated mainly at the ridge crest around implant in both vertical and oblique loading but stresses in the cancellous bone were low in both vertical and oblique loading. 2. Bending moments resulting from non-axial loading of dental implants caused stress concentrations on cortical bone. The magnitude of the stress was greater with the oblique loading than with the vertical loading. 3. An offset of the vertical occlusal force in the buccolingual direction relative to the implant axis gave rise to increased bending of the implant. 4. The relative positions of the resultant line of force from occlusal contact and the center of rotation seems to be more important. 5. The magnitude of the stress in the supporting bone, fixture and abutment screw was greater with the outward oblique loading than with the inward oblique loading and was the greatest under loading at the centric cusp in a $30^{\circ}$ outward oblique direction. Conclusively, this study provides evidence that bending moments resulting from non-axial loading of dental implants caused stress concentrations on cortical bone. But it seems to be more important that how long is the distance from center of rotation of the implant itself to the resultant line of force from occlusal contact(leverage). The goal of improving implants should be to avoid bending of the implant.

• The Journal of Advanced Prosthodontics
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• v.7 no.1
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• pp.51-55
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• 2015

PURPOSE. Bone density at implant placement site is a key factor to obtain the primary stability of the fixture, which, in turn, is a prognostic factor for osseointegration and long-term success of an implant supported rehabilitation. Recently, an implant motor with a bone density measurement probe has been introduced. The aim of the present study was to test the objectiveness of the bone densities registered by the implant motor regardless of the operator performing them. MATERIALS AND METHODS. A total of 3704 bone density measurements, performed by means of the implant motor, were registered by 39 operators at different implant sites during routine activity. Bone density measurements were grouped according to their distribution across the jaws. Specifically, four different areas were distinguished: a pre-antral (between teeth from first right maxillary premolar to first left maxillary premolar) and a sub-antral (more distally) zone in the maxilla, and an interforaminal (between and including teeth from first left mandibular premolar to first right mandibular premolar) and a retroforaminal (more distally) zone in the lower one. A statistical comparison was performed to check the inter-operators variability of the collected data. RESULTS. The device produced consistent and operator-independent bone density values at each tooth position, showing a reliable bone-density measurement. CONCLUSION. The implant motor demonstrated to be a helpful tool to properly plan implant placement and loading irrespective of the operator using it.

• The Journal of Korean Academy of Prosthodontics
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• v.37 no.5
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• pp.607-619
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• 1999

Cortical support is an important factor, as the engagement of the fixture in strong compact bone offers an increased load-carrying capacity and initial stability. Because of the poor bone quality in the posterior mandible and other anatomic considerations, it has been suggested that implant fixtures be placed in these locations with apical engagement of the lingual cortical plate for so-called bicortication. The purpose of this investigation was to determine the effect of cortical engagements and in addition polyoxymethylene(POM) intramobile connector(IMC) of IMZ implant on implant load transfer in edentulous posterior segment of mandible, using three-dimensional (3D) finite element analysis models composed of cortical and trabecular bone involving single implant. Variables such as (1) the crestal peri-implant defect, (2) the apical engagement of lingual cortical plate, (3) the occlusal contact position (a vertical load at central fossa or buccal cusp tip), and (4) POM IMC were investigated. Stress patterns were compared and interfacial stresses along the bone-implant interface were monitored specially. Within the scope of this study, the following observations were made. 1) Offset load and angulation of fixture led to increase the local interfacial stresses. 2) Stresses were concentrated toward the cortical bones, but the crestal peri-implant defect increased the interfacial stresses in trabecular bone. 3) For the model with bicortication, it was noticed that the crestal cortical bone provided more resistance to the bending moment and the lingual cortical plate provided more support for the vertical load. But Angulation problem of the fixture from the lingual cortical engagement caused the local interfacial stress concentrations. 4) It was not clear that POM IMC had the effect on stress distribution under the present experimental conditions, especially for the cases of crestal peri-implant defect.

• The Journal of Advanced Prosthodontics
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• v.10 no.5
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• pp.388-394
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• 2018

PURPOSE. To measure axial displacement of different implant-abutment connection types and materials during screw tightening at the recommended torque by using a contact scanner for two-dimensional (2D) and three-dimensional (3D) analyses. MATERIALS AND METHODS. Twenty models of missing mandibular left second premolars were 3D-printed and implant fixtures were placed at the same position by using a surgical guide. External and internal fixtures were used. Three implant-abutment internal connection (INT) types and one implant-abutment external connection (EXT) type were prepared. Two of the INT types used titanium abutment and zirconia abutment; the other INT type was a customized abutment, fabricated by using a computer-controlled milling machine. The EXT type used titanium abutment. Screws were tightened at $10N{\cdot}cm$, simulating hand tightening, and then at the manufacturers' recommended torque ($30N{\cdot}cm$) 10 min later. Abutments and adjacent teeth were subsequently scanned with a contact scanner for 2D and 3D analyses using a 3D inspection software. RESULTS. Significant differences were observed in axial displacement according to the type of implant-abutment connection (P<.001). Vertical displacement of abutments was greater than overall displacement, and significant differences in vertical and overall displacement were observed among the four connection types (P<.05). CONCLUSION. Displacement according to connection type and material should be considered in choosing an implant abutment. When adjusting a prosthesis, tightening the screw at the manufacturers' recommended torque is advisable, rather than the level of hand tightening.

• Imaging Science in Dentistry
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• v.45 no.2
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• pp.73-80
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• 2015

Purpose: This study evaluated the effect of various head orientations during cone-beam computed tomography (CBCT) image acquisition on linear measurements of potential implant sites. Materials and Methods: Six dry human skulls with a total of 28 implant sites were evaluated for seven different head orientations. The scans were acquired using a Hitachi CB-MercuRay CBCT machine. The scanned volumes were reconstructed. Horizontal and vertical measurements were made and were compared to measurements made after simulating the head position to corrected head angulations. Data was analyzed using a two-way ANOVA test. Results: Statistical analysis revealed a significant interaction between the mean errors in vertical measurements with a marked difference observed at the extension head position (P<0.05). Statistical analysis failed to yield any significant interaction between the mean errors in horizontal measurements at various head positions. Conclusion: Head orientation could significantly affect the vertical measurements in CBCT scans. The main head position influencing the measurements is extension.

• The Journal of Korean Academy of Prosthodontics
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• v.51 no.4
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• pp.269-275
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• 2013

Purpose: The aim of this retrospective study was to evaluate the influence of implant diameter, length and placement to implant stability. Materials and methods: Total 90 implants (US II plus$^{TM}$, Osstem co, Busan, Korea) of 72 patients were determined as experimental samples. The factors of diameters(${\phi}$ 4 mm, ${\phi}$ 5 mm), lengths (10 mm, 11.5 mm, 13 mm), and implant placement (maxilla, mandible) were analyzed. The stability of the implants was measured by resonance frequency analysis (RFA) at the time of implant placement and impression taking. The difference of ISQ values according to patient's gender was evaluated by Independent t-test. ISQ values were compared between implant diameter, length and placement using one-way ANOVA and Tukey HSD test (${\alpha}=.05$). To compare ISQ values between at the time of surgery and impression taking, paired t-tests were used (${\alpha}=.05$). Results: The change of implant length did not show significant different on the ISQ value (P>.05). However, 5 mm diameter implants had higher ISQ values than 4 mm diameter implants (P<.05). Implants placed on the mandible showed significantly higher ISQ values than on the maxilla (P<.05). Conclusion: In order to increase implant stability, it is better to select the wider implant, and implants placed on mandible are possible to get higher stability than maxilla. ISQ values at impression taking showed higher implant stability than ISQ values at implant placement, it means that RFA is clinically effective method to evaluate the change of implant stability through the osseointegration. The consideration of the factors which may affect to the implant stability will help to determine the time of load applying and increase the implant success rate.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.34 no.6
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• pp.440-448
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• 2012

Purpose: The purpose of this study was to evaluate marginal bone loss of the alveolar crest on implants with or without guided bone regeneration and variables that have influenced. Methods: The clinical evaluation were performed for survival rate and marginal bone loss of 161 endosseous implants installed with guided bone regeneration (GBR) in 83 patients from September 2009 to October 2010 in relation to sex and age of patients, position of implant, implant system, length and diameter of implant. Study group (n=42) implant with GBR procedure, control group (n=41) implant without GBR technique. Simultaneous GBR approach using resorbable membranes combined with autogenous bone graft or freeze-dried bone allograft or combination. Radiographic examinations were conducted at healing abutment connection and latest visit. Marginal bone level was measured. Results: Mean marginal bone loss was 0.73 mm in study group, 0.63 mm in control group. Implants in maxillary anterior area (1.21 mm) were statistically significant in study group (P<0.05), maxillary posterior area (0.81 mm) in control group (P<0.05). Mean marginal bone loss 1.47 mm for implants with diameter 3.4 mm, 0.83 mm for implants of control group with diameter 4.0 mm (P<0.05). Some graft materials showed an increased marginal bone loss but no statistically significant influence of sex, implant type or length. Conclusion: According to these findings, this study demonstrated the amount of marginal bone loss around implant has maintained a relative stable during follow-up periods. We conclude that implants with GBR had similar survival rate and crestal bone level compared with implants in native bone.