The effect of heat to remove cement on implant titanium abutment and screw / 대한치과보철학회지

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℃ 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 ± 1.07 Ncm in the control group and 26.55 ± 1.56 Ncm in the experimental group and showed statistically 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.

The effect of a titanium socket with a zirconia abutment on screw loosening after thermocycling in an internally connected implant: a preliminary study

PURPOSE: The aim of this study was to investigate the effects of a titanium component for the zirconia abutment in the internal connection implant system on screw loosening under thermocycling conditions. MATERIALS AND METHODS: Internal connection titanium abutments and external connection zirconia abutments with titanium sockets were connected respectively to screw-shaped internal connection type titanium implants with 30 Ncm tightening. These implant-screw-abutment assemblies were divided into two groups of five specimens each; titanium abutments as control and zirconia abutments with titanium sockets as experimental group. The specimens were subjected to 2,000 thermocycles in water baths at 5℃ and 55℃, with 60 seconds of immersion at each temperature. The removal torque values (RTVs) of the abutment screws of the specimen were measured before and after thermocycling. RTVs pre- and post-thermocycling were investigated in statistics. RESULTS: There was not screw loosening identified by tactile and visual inspection in any of the specimens during or after thermocycling. The mean RTV difference for the control group and the experimental group were -1.34 ± 2.53 Ncm and -1.26 ± 2.06 Ncm, respectively. Statistical analysis using an independent t-test revealed that no significant differences were found in the mean RTV difference of the groups (P > 0.05). CONCLUSION: Within the limitations of this in vitro study, the titanium socket for the zirconia abutment did not show a significant effect on screw loosening under thermal stress compared to the titanium abutment in the internal connection implant.

Evaluation of stability of interface between CCM (Co-Cr-Mo) UCLA abutment and external hex implant

PURPOSE: The purpose of this study is to evaluate the stability of interface between Co-Cr-Mo (CCM) UCLA abutment and external hex implant. MATERIALS AND METHODS: Sixteen external hex implant fixtures were assigned to two groups (CCM and Gold group) and were embedded in molds using clear acrylic resin. Screw-retained prostheses were constructed using CCM UCLA abutment and Gold UCLA abutment. The external implant fixture and screw-retained prostheses were connected using abutment screws. After the abutments were tightened to 30 Ncm torque, 5 kg thermocyclic functional loading was applied by chewing simulator. A target of 1.0 × 10⁶ cycles was applied. After cyclic loading, removal torque values were recorded using a driving torque tester, and the interface between implant fixture and abutment was evaluated by scanning electronic microscope (SEM). The means and standard deviations (SD) between the CCM and Gold groups were analyzed with independent t-test at the significance level of 0.05. RESULTS: Fractures of crowns, abutments, abutment screws, and fixtures and loosening of abutment screws were not observed after thermocyclic loading. There were no statistically significant differences at the recorded removal torque values between CCM and Gold groups (P>.05). SEM analysis revealed that remarkable wear patterns were observed at the abutment interface only for Gold UCLA abutments. Those patterns were not observed for other specimens. CONCLUSION: Within the limit of this study, CCM UCLA abutment has no statistically significant difference in the stability of interface with external hex implant, compared with Gold UCLA abutment.

Effect of abutment screw length and cyclic loading on removal torque in external and internal hex implants

PURPOSE: The purpose of this study was to evaluate the effects of abutment screw length and cyclic loading on the removal torque (RTV) in external hex (EH) and internal hex (IH) implants. MATERIALS AND METHODS: Forty screw-retained single crowns were connected to external and internal hex implants. The prepared titanium abutment screws were classified into 8 groups based on the number of threads (n = 5 per group): EH 12.5, 6.5, 3.5, 2.5 and IH 6.5, 5, 3.5, 2.5 threads. The abutment screws were tightened with 20 Ncm torque twice with 10-minute intervals. After 5 minutes, the initial RTVs of the abutment screws were measured with a digital torque gauge (MGT12). A customized jig was constructed to apply a load along the implant long axis at the central fossa of the maxillary first molar. The post-loading RTVs were measured after 16,000 cycles of mechanical loading with 50 N at a 1-Hz frequency. Statistical analysis included one-way analysis of variance and paired t-tests. RESULTS: The post-loading RTVs were significantly lower than the initial RTVs in the EH 2.5 thread and IH 2.5 thread groups (P<.05). The initial RTVs exhibited no significant differences among the 8 groups, whereas the post-loading RTVs of the EH 6.5 and EH 3.5 thread groups were higher than those of the IH 3.5 thread group (P<.05). CONCLUSION: Within the limitations of this study, the external hex implants with short screw lengths were more advantageous than internal hex implants with short screw lengths in torque maintenance after cyclic loading.

Influence of the implant-abutment connection design and diameter on the screw joint stability

PURPOSE: This study was conducted to evaluate the influence of the implant-abutment connection design and diameter on the screw joint stability. MATERIALS AND METHODS: Regular and wide-diameter implant systems with three different joint connection designs: an external butt joint, a one-stage internal cone, and a two-stage internal cone were divided into seven groups (n=5, in each group). The initial removal torque values of the abutment screw were measured with a digital torque gauge. The postload removal torque values were measured after 100,000 cycles of a 150 N and a 10 Hz cyclic load had been applied. Subsequently, the rates of the initial and postload removal torque losses were calculated to evaluate the effect of the joint connection design and diameter on the screw joint stability. Each group was compared using Kruskal-Wallis test and Mann-Whitney U test as post-hoc test (alpha=0.05). RESULTS: The postload removal torque value was high in the following order with regard to magnitude: two-stage internal cone, one-stage internal cone, and external butt joint systems. In the regular-diameter group, the external butt joint and one-stage internal cone systems showed lower postload removal torque loss rates than the two-stage internal cone system. In the wide-diameter group, the external butt joint system showed a lower loss rate than the one-stage internal cone and two-stage internal cone systems. In the two-stage internal cone system, the wide-diameter group showed a significantly lower loss rate than the regular-diameter group (P<.05). CONCLUSION: The results of this study showed that the external butt joint was more advantageous than the internal cone in terms of the postload removal torque loss. For the difference in the implant diameter, a wide diameter was more advantageous in terms of the torque loss rate.

The effect of various thread designs on the initial stability of taper implants

STATEMENT OF PROBLEM: Primary stability at the time of implant placement is related to the level of primary bone contact. The level of bone contact with implant is affected by thread design, surgical procedure and bone quality, etc. PURPOSE: The aim of this study was to compare the initial stability of the various taper implants according to the thread designs, half of which were engaged to inferior cortical wall of type IV bone (Group 1) and the rest of which were not engaged to inferior cortical wall (Group 2) by measuring the implant stability quotient (ISQ) and the removal torque value (RTV). MATERIAL AND METHODS: In this study, 6 different implant fixtures with 10 mm length were installed. In order to simulate the sinus inferior wall of type IV bone, one side cortical bone of swine rib was removed. 6 different implants were installed in the same bone block following manufacturer's recommended procedures. Total 10 bone blocks were made for each group. The height of Group 1 bone block was 10 mm for engagement and that of group 2 was 13 mm. The initial stability was measured with ISQ value using Osstell mentor(R) and with removal torque using MGT50 torque gauge. RESULTS: In this study, we found the following results. 1. In Group 1 with fixtures engaged to the inferior cortical wall, there was no significant difference in RTV and ISQ value among the 6 types of implants. 2. In Group 2 with fixtures not engaged to the inferior cortical wall, there was significant difference in RTV and ISQ value among the 6 types of implants (P < .05). 3. There was significant difference in RTV and ISQ value according to whether fixtures were engaged to the inferior cortical wall or not (P < .05). 4. Under-drilling made RTV and ISQ value increase significantly in the NT implants which had lower RTV and ISQ value in Group 2 (P < .05). CONCLUSIONS: Without being engaged to the inferior cortical wall fixtures had initial stability affected by implant types. Also in poor quality bone, under-drilling improved initial stability.

Screw Joint Stability under Cyclic Loading of Zirconia Implant Abutments / 대한치과보철학회지

PURPOSE: The purpose of this study was to evaluate the effect of abutment material on screw-loosening before and after cyclic loading. Among the different materials of abutments, zirconia and metal abutment were used. MATERIAL AND METHODS:: Two types of implant systems: external butt joint (US II, Osstem Implant, Korea) and internal conical joint (GS II, Osstem Implant, Korea) were used. In each type, specimens were divided into two different kinds of abutments: zirconia and metal (n = 5). The implant was rigidly held in a special holding to device ensure fixation. Abutment was connected to 30 Ncm with digital torque gauge, and was retightened in 30 Ncm after 10 minutes. The initial removal torque values were measured. The same specimens were tightened in 30 Ncm again and held in the cycling loading simulator (Instron, USA) according to ISO/FPIS 1480. Cycling loading tests were performed at loads 10 to 250 N, for 1 million cycles, at 14 Hz, (by subjecting sinusoidal wave from 10 to 250 N at a frequency of 14 Hz for 1 million cycles,) and then postload removal torque values were evaluated. RESULTS: 1. In all samples, the removal values of abutment screw were lower than tightening torque values (30 Ncm), but the phenomenon of the screw loosening was not observed. 2. In both of the implant systems, initial and postload removal torque of zirconia abutment were significantly higher than those of metal abutment (P .05). 4. In metal abutments, the removal torque ratio of GS II system (internal conical joint system) was lower than that of US II system (external butt joint system) (P .05). CONCLUSION: Zirconia abutment had a good screw joint stability in the condition of one million cycling loading.

The influence of abutment screw length and repeated tightening on screw loosening in dental implant / 대한치과보철학회지

Statement of problem: One of common problems associated with dental implant is the loosening of abutment screws that retain the implants. Purpose: This study was performed to investigate the influence of abutment screw length and repeated tightening on screw loosening in dental implant. Material and method: Forty nine Hexplants (13mm length, 4.3mm diameter, Ti grade IV, Warantec. Co. Ltd. Seongnam, Korea) and cementation type abutments(straight abutment) and abutment screws (0.4mm/pitch) were divided into 7 groups, depending on abutment screw length. Each implant and abutment was tightened to 30Ncm by torque controller(MGT50, MARK-10 Inc., USA) and the removal torque values were measured during 10 consecutive closure/opening trials Results and Conclusion: The results of comparing the removal torque value are as follows: 1. There is no significant difference in the removal torque value between groups in 10 consecutive closure/opening trials(p=0.97). 2. If the fractured abutment screw is engaged in longer than 2.425 thread length, there is no significant difference in the preload between the fractured abutment screw and the new abutment screw when both are equally tightened to 30 Ncm 3. The removal torque value in the 1st trial(24.510 Ncm) was lower than that in the 2nd,3rd,4th,5th,6th,7th trials and the removal torque value in the 2nd trials(25.551 Ncm) was maximum and was decreased in following trials. The removal torque value in the 1st trial was significantly lower than that in the 2nd,3rd,4th trials and was significantly higher than that in the 8th,9th,10th trials(p<0.05). 4. In the 2nd,3rd,4th,5th,6th,7th trials, the abutment screw was mainly influenced by settling effect and the higher preload was obtained. In the 8th,9th,10th trials, the abutment screw was mainly influenced by adhesive wear and the progressively lower preload was obtained.

Effects of electrical stimulation on healing of endo-osseous titanium implants in circumferential defect / 대한치주과학회지

Several experimental studies showed that the application of small amounts of electric current to bone stimulated osteogenesis at the site of the cathode and suggested that electrical currents promote osseointegration around dental implants. The purpose of this study was to determine the effect of direct microcurrent to endosseous titanium implants placed in bone defects. The right and left 2nd, 3rd and 4th mandibular premolars in ten mongrel dogs (15Kg of weight) were extracted. One monthe later, Ti-machined screw type implants(3.8 mm diameter x 8.5 mm length, AVANA(R), Ostem) were placed in surgically created circumferential defect area(width 5mm, depth 4mm). The implants were divided into three groups according to the treatment modalities: Control group- implants without electrical stimulation; Experimental group I- implants with allogenic demineralized freeze dried bone grafting; and Experimental group IIimplants allogenic demineralized freeze dried bone grafting and electric stimulation. The animals were sacrificed in the 4th and 8th week after implant placement and un-decalcified specimens were prepared for histological and histometrical evaluation of bone-implant contact ratio (BIC) and bone formation area ratio (BFA) in defect area. Some specimens at 8 weeks after implantation were used for removal torque testing. Histologically, there was connective tissue infiltration in the coronal part of defect area in control and the experimental group I, whereas direct bone contact was found in the experimental group II without connective tissue invasion. Average BIC ratios at 4 weeks of healing were 60.1% in the experimental group II, 47.4% in the experimental group I and 42.7% in the control. Average BIC ratios at 8 weeks after implantation were 67.6% in the experimental group II, 55.9% in the experimental group I and 54.6% in the control. The average BFA ratio was 84.0% in the experimental group II, 71.8% in the experimental group I and 58.8% in the control at 4 weeks, and the BFA ratios were 89.6% in the experimental group II, 81.4% in the experimental group I and 70.5% in the control at 8 weeks after implantation. The experimental group II showed also significantly greater BIC and BFA ratios compared to the control and the experimental group I (p<0.05). The removal torque values at 8 weeks after implantation were 56 Ncm in the experimental group II, 49 Ncm in the experimental group I and 43 Ncm in the control. There was a statistically significant difference among 3 groups (p<0.05). These results suggest that electrical stimulation improve and accelerate bone healing around endosseous titanium implants in bone defect.

Histomorphometric and Removal Torque Values Comparision of Rough Surface Titanium Implants