Screw loosening and changes in removal torque relative to abutment screw length in a dental implant with external abutment connection after oblique cyclic loading

PURPOSE: This study investigated the effects of abutment screw lengths on screw loosening and removal torque in external connection implants after oblique cyclic loading. MATERIALS AND METHODS: External connection implants were secured with abutment screws to straight abutments. The abutment-implant assemblies were classified into seven groups based on the abutment screw length, with each group consisting of five assemblies. A cyclic load of 300 N was applied at a 30° angle to the loading axis until one million cycles were achieved. Removal torque values (RTVs) before and after loading, and RTV differences were evaluated. The measured values were analyzed using repeated measures of analysis of variance with the Student-Newman-Keuls multiple comparisons. RESULTS: All assemblies survived the oblique cyclic loading test without screw loosening. There was a significant decrease in the RTVs throughout the observed abutment screw lengths when the abutment-implant assemblies were loaded repeatedly (P < .001). However, the abutment screw length did not show significant difference on the RTVs before and after the experiment when the abutment screw length ranged from 1.4 to 3.8 mm (P=.647). CONCLUSION: Within the limit of this experiment, our results indicate that the abutment screw length did not significantly affect RTV differences after oblique cyclic loading when a minimum length of 1.4 mm (3.5 threads) was engaged. These findings suggest that short abutment screws may yield stable clinical outcomes comparable to long screws in terms of load resistance.

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.

A Surgical Method for Determining Proper Screw Length in ACDF

OBJECTIVE: We describe a surgical tool that uses the distractor pin as a reference for determining proper screw length in ACDF. It is critical that screw purchase depth be as deep as possible without violating or penetrating the posterior cortical wall, which ensures strong pull out strength. METHODS: We enrolled 81 adult patients who underwent ACDF using an anterior cervical plate from 2010 to 2012. Patients were categorized into Groups A (42 patients: retractor pin used as a reference for screw length) and B (39 patients: control group). Intraoperative lateral x-rays were taken after screwing the retractor pin to confirm the approaching vertebral level. The ratio of retractor pin length to body anteroposterior (A-P) diameter was measured as a reference. Proper screw length was determined by comparison to the reference. RESULTS: The average distance from screw tip to posterior wall was 3.0+/-1.4mm in Group A and 4.1+/-2.3mm in Group B. The ratio of screw length to body sagittal diameter was 86.2+/-5.7% in Group A and 80.8+/-9.0% in Group B. Screw length to body sagittal diameter ratios higher than 4/5 occurred in 33 patients (90%) in Group A and 23 patients (59%) in Group B. No cases violated the posterior cortical wall. CONCLUSION: We introduce a useful surgical method for determining proper screw length in ACDF using the ratio of retractor pin length to body A-P diameter as a reference. This method allows for deeper screw purchase depth without violation of the posterior cortical wall.

Relationship between the Length of Distal Locking Screws and Diaphyseal Screws in Volar Plate Fixation of Distal Radius Fractures

PURPOSE: To determine the relationship between the length of distal locking screws and diaphyseal screws in volar plate fixation of distal radius fractures. METHODS: A retrospective review was performed of 169 patients who underwent volar locking plate fixation for treatment of distal radius fractures. All patients received 2.4 mm LCP volar extra-articular distal radius plate (DePuySynthes). The length of the diaphyseal screw which was placed in the elongated hole was correlated with the length of a distal locking screw from radial most (D1) to ulnar most (D4). We also evaluated distal screw penetration of the dorsal cortex and plate removal rate. RESULTS: The length of the diaphyseal screw which was placed in the elongated hole strongly correlated with the length of a distal locking screw. Average D1 screw length was 2 mm longer than the diaphyseal screw, and average D2 screw length was 4 mm longer than the diaphyseal screw. D3 and D4 screw were 6 mm longer than the diaphyseal screw. Plate removal was necessary in 13 patients (8%) due to screw irritation. These patients had significantly longer screws than average. Flexor or extensor tendon ruptures did not occur in this cohort. CONCLUSION: The length of the distal locking screws can be estimated with the length of the diaphyseal screw. This information may help surgeons to select the adequate length of distal locking screws during volar plating of distal radius fractures.

A Study on Bone-Contact to Inter-Segmental Length Ratio of Rigid Fixation Screws used in Bssro for Mandibular Setback

OBJECTIVE: To evaluate the ratio between bone-contact length and inter-segmental length of the rigid fixation screw used in bilateral sagittal split ramus osteotomy (BSSRO) for mandibular setback. MATERIAL AND METHODS: Records of 40 patients with Class III malocclusion were selected. 20 of them had BSSRO, while the other 20 had BSSRO with maxillary LeFort I osteotomy. All of the patients had three noncompressive bicortical screws inserted at the gonial angle through transcutaneous approach. Two screws were inserted antero-posteriorly above inferior alveolar nerve and one screw was inserted below. The lengths of bone-contact and that of inter-segmental part were measured using cone-beam computed tomography. Ratio between these two measured lengths was calculated. RESULTS: Both bone-contact and inter-segmental lengths were longer in BSSRO group than in BSSRO with maxillary LeFort I osteotomy group. Ratio of bone-contact to inter-segmental length was lower in BSSRO group than in BSSRO with Lefort I group. Both bone-contact and inter-segmental lengths were longer at the antero-superior position than at the inferior position. However, their ratio showed little difference. CONCLUSION: This study suggest that stability of screws in BSSRO group was greater than in BSSRO with Lefort I group. Stability of screws at the antero-superior position was greater than at the inferior position. Ratio of bone-contact to inter- segmental lengths was 0.2 in average.

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.