Dislodgment Effects of Different Cage Arrangements in Posterior Lumbar Interbody Fusion: A Finite Element Study.

The vertebral cage has been widely used in posterior lumbar interbody fusion. The risk of cage dislodgment is high for patients undergoing lumbar fusion surgery. Therefore, the main objective of this study was to use a lumbar fusion model to investigate the effects of cage dislodgment on different cage arrangements after PLIF. Finite element analysis was used to compare three PEEK cage placements, together with the fibula-type cage, with respect to the four kinds of lumbar movements. The results revealed that a horizontal cage arrangement could provide a better ability to resist cage dislodgment. Overall lumbar flexion movements were confirmed to produce a greater amount of cage slip than the other three lumbar movements. The lower part of the lumbar fusion segment could create a greater amount of cage dislodgment for all of the lumbar movements. Using an autograft with a fibula as a vertebral cage cannot effectively reduce cage dislodgment. Considering the maximum movement type in lumbar flexion, we suggest that a horizontal arrangement of the PEEK cage might be considered when a single PEEK cage is placed in the fusion segment, as doing so can effectively reduce the extent of cage dislodgment.

Incidence and risk factors of vertebral body collapse after posterior instrumented spinal fusion in elderly patients: An observational study.

This study investigates the incidence and risk factors of new vertebral body collapse (VC) after posterior instrumented spinal fusion in patients older than 70 years. This retrospective study analyzed the data of elderly patients who underwent posterior instrumented spinal fusion in the thoracolumbar spine between January 2013 and December 2017. The 2 subsamples comprised of patients who had experienced vertebral compression fracture (VCF) before the index spinal surgery (group 1, n = 324) and those who had not (group 2, n = 1040). We recorded and analyzed their baseline characteristics, their underlying comorbidities, and the details of their current instrumented spinal fusion. The incidences of new VC and screw loosening were recorded. In groups 1 and 2, the incidences of new VC were 31.8% and 22.7%, respectively, and those of new VC with screw loosening were 25.6% and 33%, respectively. The risk factor was upper screw level at the thoracolumbar junction (hazard ratio [HR] = 2.181, 95% confidence interval [CI]: 1.135-4.190) with previous VCF. The risk factors were age ≥ 80 years (HR = 1.782, 95% CI: 1.132-2.805), instrumented levels > 4 (HR = 1.774, 95% CI: 1.292-2.437), and peptic ulcer (HR = 20.219, 95% CI: 2.262-180.731) without previous VCF. Clinicians should closely monitor new VC after posterior instrumented spinal fusion in elderly patients with previous VCF with upper screw level at the thoracolumbar junction and in patients without previous VCF aged ≥ 80 years, with instrumented levels > 4 and peptic ulcer.

Combination of long- and short-axis alar sacroplasty techniques under fluoroscopic guidance for osteoporotic sacral insufficiency fracture.

BACKGROUND: Sacral insufficiency fracture (SIF) is rarer than osteoporotic vertebral compression fracture that occurs at other levels of the thoracolumbar spine. Percutaneous sacroplasty can effectively relieve pain and improve mobility. Several sacroplasty-based techniques have been reported to date. Sacroplasty is often performed with computed tomography-guided cannula placement, which is time intensive and results in greater radiation exposure than that resulting from fluoroscopy. Herein, we report our preliminary experience with a combination of long- and short-axis alar sacroplasty techniques under fluoroscopic guidance for osteoporotic SIFs. METHODS: We retrospectively reviewed 44 consecutive patients with symptomatic osteoporotic SIFs who underwent alar sacroplasty between January 2013 and February 2020. The study group comprised 19 patients who underwent a combination of long- and short-axis alar sacroplasty techniques under fluoroscopic guidance. The control group comprised the remaining 25 patients who underwent short-axis alar sacroplasty under fluoroscopic guidance. Visual analog scale (VAS) scores, operation times, injected cement volumes, and postoperative complications were recorded. RESULTS: The VAS score for pain decreased in both groups; however, no significant difference was noted between the study and control groups in injected cement volume (3.55 ± 0.96 vs 2.94 ± 0.89 mL). The operation time was longer in the study group than in the control group (32 ± 7.1 vs 28.04 ± 4.99 min; P = 0.046). No major complications were noted. CONCLUSION: A combination of long- and short-axis alar sacroplasty techniques can be effectively performed under fluoroscopic guidance for osteoporotic SIFs.

Effects of Injected Antiosteoporotic Medication Versus Oral Bisphosphonates on Rates of Repeated Vertebroplasty or Kyphoplasty.

PURPOSE: Vertebral compression fractures can recur within a few years after percutaneous vertebroplasty (PVP) or kyphoplasty. METHODS: We conducted a population-based study using data from the Taiwan National Health Insurance Research Database to investigate the efficacy of various antiosteoporotic treatments in reducing the prevalence rate of repeated PVP or kyphoplasty in patients hospitalized from January 1, 1997, to December 31, 2004. We included patients with vertebral compression fractures after PVP or kyphoplasty who received oral bisphosphonates (OB group; n = 6141) or injected drug therapies (injection group; n = 4308). FINDINGS: The incidence rate of repeated PVP or kyphoplasty was significantly lower in the I/Z/D (denosumab monotherapy or ibandronate or zoledronate with or without denosumab) group than in the OB group (crude subdistribution hazard ratio [sHR], 0.79; 95% CI, 0.70-0.90; P < 0.05; adjusted sHR, 0.77; 95% CI, 0.68-0.87; P < 0.0001). The analysis revealed a significantly lower incidence rate of repeated PVP or kyphoplasty in the I/Z group compared with that in the OB group (crude sHR, 0.82; 95% CI, 0.72-0.94; P = 0.0038; adjusted sHR, 0.80; 95% CI, 0.70-0.91; P = 0.0011). The denosumab group also exhibited a significantly lower incidence rate of repeated PVP or kyphoplasty than did the OB group (crude sHR, 0.61; 95% CI, 0.46-0.80; P = 0.0005; adjusted sHR, 0.58; 95% CI, 0.44-0.77; P = 0.0001). Although the teriparatide group had higher fracture frequency than did the OB group, the analysis revealed no significant difference between the OB and teriparatide groups with respect to the incidence rate of repeated PVP or kyphoplasty (adjusted sHR, 1.08; 95% CI, 0.92-1.26; P = 0. 3747). IMPLICATIONS: Injected antiosteoporotic medication was associated with lower rates of repeated vertebroplasty and kyphoplasty than was OB application.

Long-term total hip arthroplasty rates in patients with acetabular and pelvic fractures after surgery: A population-based cohort study.

BACKGROUND/OBJECTIVE: Osteoarthritis typically develops after surgery for traumatic fractures of the acetabulum and may result in total hip arthroplasty (THA). We conducted a population-based retrospective study to investigate the incidence of THA after treatment of acetabular, pelvic, and combined acetabular and pelvic fractures with open reduction-internal fixation surgery compared with that in the control group. DESIGN: A retrospective population-based cohort study. SETTING: Data were gathered from the Taiwan National Health Insurance Research Database. PARTICIPANTS: We enrolled 3041 patients with acetabular fractures, 5618 with pelvic fractures, and 733 with combined pelvic and acetabular fractures between January 1, 1997, and December 31, 2013, totaling 9392 individuals. The control group comprised 664,349 individuals. Study participants were followed up for the occurrence of THA until death or the end of the study period. RESULTS: The THA rates after surgical intervention were 17.82%, 7.28%, and 18.01% in patients with acetabular, pelvic, and combined acetabular and pelvic fractures, respectively. Moreover, they were significantly higher for the acetabular fracture, pelvic fracture, and combined-fracture groups (adjusted hazard ratios [aHRs] = 58.42, 21.68, and 62.04, respectively) than for the control group (p < 0.0001) and significantly higher for the acetabular fracture and combined-fracture groups than for the pelvic fracture group (aHRs = 2.59 and 2.68, respectively; p < 0.0001). CONCLUSION: The incidence rates of THA after surgical intervention in the pelvic fracture, acetabular fracture, and combined-fracture groups were significantly higher than that of the control group.

Comparison of Different Cervical Finish Lines of All-Ceramic Crowns on Primary Molars in Finite Element Analysis.

This study aimed to conduct a stress analysis of four types of cervical finish lines in posterior all-ceramic crowns on the primary roots of molar teeth. Four different types of finish lines (shoulder 0.5 mm, feather-edged, chamfer 0.6 mm, and mini chamfer 0.4 mm) and two all-ceramic crown materials (zirconia and lithium disilicate) were used to construct eight finite element primary tooth models with full-coverage crowns. A load of 200 N was applied at two different loading angles (0° and 15°) so as to mimic children's masticatory force and occlusal tendency. The maximum stress distribution from the three-dimensional finite element models was determined, and the main effect of each factor (loading type, material, and finish line types) was evaluated in terms of the stress values for all of the models. The results indicated that the loading type (90.25%) was the main factor influencing the maximum stress value of the primary root, and that the feather-edged margin showed the highest stress value (p = 0.002). In conclusion, shoulder and chamfer types of finish lines with a 0.4-0.6 mm thickness are recommended for deciduous tooth preparation, according to the biomechanical analysis.

Investigation of pullout strength in different designs of pedicle screws for osteoporotic bone quality using finite element analysis.

PURPOSE: The purpose of this study was to investigate pullout strength of three types of pedicle screws with and without cement augmentation in osteoporotic bone using finite element analysis. METHODS: Twelve 3D finite element models were created to investigate the effect of pullout strength when comparing between pedicle screw types and bone cement clouds. The bottom side of bone block model was constrained and U-shape head was applied 1 mm in direction of longitudinal axis of pedicle screw to perform pullout resistance. The material properties of the FEA was set as linear elastic, homogenous, isotropic condition. The element sensitivity of convergence testing has been performed and variation of the sequential analytical results was less than 3%. RESULTS: The results showed that the maximum total reaction force (133.8 N) was detected in the model of cannulated pedicle screw combined with a central pin with 4 ml cement augmentation, but, in contrast, the minimum total reaction force (106.8 N) was discovered in the model of cannulated pedicle screw without cement. A strong relationship (r = 0.9626) is found in comparison with the biomechanical results between pullout strength of sawbone testing and reaction forces of the FEA. CONCLUSIONS: The study concludes that the cannulated pedicle screw can not only provide an inner guider for cement flow and increase bending resistance (deflection effect) when a central pin is selected, but also can improve the pullout strength in the osteoporotic bone to add cement augmentation. The design of the cannulated pedicle screw is suggested for poor bone quality to change pullout failure.

High 2-year mortality and recurrent infection rates after surgical treatment for primary septic arthritis of the hip in adult patients: An observational study.

Primary septic arthritis of the hip is rare and potentially devastating in adults. Its optimal surgical treatment and clinical outcomes remain unclear.In this retrospective cohort study, we investigated mortality and reinfection rates after surgery of patients with septic hip arthritis. We reviewed patients treated for primary septic hip joints from October 2005 to December 2016. A total of 51 adult patients were identified, and 38 among them had destructive hip joints. A poor postoperative outcome was defined as mortality or recurrent infection within 2 years of surgery.After surgery, 7 (13.7%) patients died within 1 year and 5 (9.8%) patients developed a recurrent hip infection within 2 years. Therefore, poor outcomes occurred in 22% (n = 11) of the study cohort. Among the 38 patients with a destructive hip joint, 7 (18.4%) died within 1 year after surgery and 4 (10.5%) developed a recurrent hip infection within 2 years of surgery. Correlative infections other than infected hip joint and liver cirrhosis were identified as risk factors for poor outcomes.In conclusion, clinical physicians treating adult primary septic hip joints should be cognizant of the high failure rate of surgical treatment. In addition, the high mortality rate should be considered during the discussion of surgical treatment with these patients and their families.

Fracture Resistance of Monolithic Zirconia Crowns in Implant Prostheses in Patients with Bruxism.

The aim of this study is to determine the minimum required thickness of a monolithic zirconia crown in the mandibular posterior area for patients with bruxism. Forty-nine full zirconia crowns, with seven different occlusal thicknesses of 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 mm, were made by using a computer-aided design/computer-aided manufacturing system (CAD/CAM). Seven crowns in each group were subjected to cyclic loading at 800 N and 5 Hz in a servohydraulic testing machine until fracture or completion of 100,000 cycles. Seven finite element models comprising seven different occlusal thicknesses of 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 mm were simulated using three different loads of vertical 800 N, oblique 10 degrees 800 N, and vertical 800 N + x N torque (x = 10, 50, and 100). The results of cyclic loading tests showed that the fracture resistance of the crown was positively associated with thickness. Specimen breakage differed significantly according to the different thicknesses of the prostheses (p < 0.01). Lowest von Mises stress values were determined for prostheses with a minimal thickness of 1.0 mm in different loading directions and with different forces. Zirconia specimens of 1.0 mm thickness had the lowest stress values and high fracture resistance and under 800 N of loading.

Effects of cortical bone thickness and trabecular bone density on primary stability of orthodontic mini-implants.

BACKGROUND/PURPOSE: Mini-implant screws are now routinely used as anchorage devices in orthodontic treatments. This study used synthetic bone models to investigate how the primary stability of an orthodontic mini-implant (OMI) as measured by resonance frequency (RF) is affected by varying cortical bone thickness and trabecular bone density. MATERIALS AND METHODS: Three synthetic cortical shells (thicknesses of 1, 2, and 3 mm) and three polyurethane foam blocks (densities of 40, 20, and 10 pound/cubic foot) were used to represent jawbones of varying cortical bone thicknesses and varying trabecular bone densities. Twenty-five stainless steel OMIs (2 × 10 mm) were sequentially inserted into artificial bone blocks to depths of 2, 4, and 6 mm. Five experimental groups of bone blocks with OMIs were examined by Implomates® RF analyzer. Statistical and correlation analyses were performed by Kruskal-Wallis test, Wilcoxon rank-sum test, and simple linear regression. RESULTS: As trabecular bone density decreased, RF decreased; as cortical bone thickness decreased, RF also decreased. Simple linear regression analysis showed highly linear correlations between trabecular bone density and RF (R 2 > 0.99; P < 0.0001) and between cortical bone thickness and RF (R 2 > 0.98; P < 0.0001). CONCLUSION: The stability of an OMI at the time of placement is influenced by both cortical bone thickness and trabecular bone density. Both cortical bone thickness and trabecular bone density have strong linear correlations with RF.

Pullout evaluation of sawbone experiment in different types of pedicle screws combined with bone cement augmentation for severe osteoporotic spine.

PURPOSE: The conventional screw is unable to provide enough screw-bone interface strength for osteoporotic cencellous bone, and complications resulting from loosening or failure of the implants remain a significant clinical problem. Hence, the purpose of this study is to investigate pullout strength and energy in three types of the pedicle screws, including conventional solid pedicle screw, cannulated pedicle screw, and cannulated pedicle screw with a central pin, using osteoporotic sawbone test block with different bone cement volumes through pullout force testing. METHODS: The control group (n = 15) of the osteoporotic sawbone test block includes groups A, B, and C to reflect three types of the pedicle screws without bone cement augmentation. The cemented group (n = 45) of the osteoporotic sawbone test block includes groups D1, D2, D3, E1, E2, E3, F1, F2, and F3 to reflect three types of the pedicle screws with PMMA bone cement of 2, 3, and 4 mL augmentation. RESULTS: The results showed that the pullout strength and energy in the cemented group were significantly larger than that in the control group. Moreover, the best performances of the pullout strength and energy in the cemented group were evidenced obviously in the case of cannulated pedicle screw with a central pin with 4 mL bone cement augmentation. CONCLUSIONS: This study concludes that cement argumentation in the cannulated pedicle screw with a central pin can increase a pullout strength of pedicle screw for severe osteoporotic patients while bone cement of injective volume is limited.

Short-term and long-term revision rates after lumbar spine discectomy versus laminectomy: a population-based cohort study.

BACKGROUND/OBJECTIVE: Degenerative diseases of the lumbar spine were managed with discectomy or laminectomy. This study aimed to compare these two surgical treatments in the postoperative revision rates. DESIGN: A population-based cohort study from analysis of a healthcare database. SETTING: Data were gathered from the Taiwan National Health Insurance Research Database (NHIRD). PARTICIPANTS: We enrolled 16 048 patients (4450 women and 11 598 men) with a mean age of 40.34 years who underwent lumbar discectomy or laminectomy for the first time between 1 January 1997 and 31 December 2007. All patients were followed up for 5 years or until death. RESULTS: Revision rate within 3 months of the index surgery was significantly higher in patients who underwent discectomy (2.75%) than in those who underwent laminectomy (1.18%; p<0.0001). This difference persisted over the first year following the index surgery (3.38% vs 2.57%). One year afterwards, the revision rates were similar between the discectomy (9.75%) and laminectomy (9.69%) groups. The final spinal fusion surgery rates were also similar between the groups (11.25% vs 12.08%). CONCLUSION: The revision rate after lumbar discectomy was higher than that after laminectomy within 1 year of the index surgery. However, differences were not identified between patient groups for the two procedures with respect to long-term revision rates and the proportion of patients who required final spinal fusion surgery.

Resonance frequency analysis of miniscrew implant stability.

This study used resonance frequency (RF) analysis to assess miniscrew implant (MSI) stability during wound healing in a sample of 68 patients (41 women, 27 men; mean age, 27.7 years). The 104 MSIs included 66 placements in the buccal shelf (BS; 2.0 × 12 mm) and 38 placements in interradicular (IR; 1.5 × 8 mm) sites. Thirteen (12.5%) of the MSIs failed. A new RF detection device was used to measure RF at baseline (T0) and at 3 (T1), 6 (T2), 9 (T3), 12 (T4), and 15 (T5) weeks after placement. A linear mixed-effects model was fitted to change in RF values. As compared with the BS group, the IR group had significantly lower RF values on the right side from T0 through T4 and on the left side from T0 through T2. Insertion site and time of visit were significantly associated with RF value. The effects of time of visit significantly differed between the BS and IR sites. Starting from T0, the MSIs placed at both sites had significantly lower RF values at all intervals, except for T0-T1. Future studies should examine how the present clinical protocols can optimize timing of MSI loading to maximize the success rate.

Use of corticosteroids is not associated with repeated vertebroplasty or kyphoplasty within one year after the surgery in patient older than 50 years.

OBJECTIVE: The aim of this study was to investigate whether corticosteroid use increases the incidence of repeated PVP or kyphoplasty patients older than 50 years. METHODS: This study enrolled the data of 2,753 eligible patients from the Taiwan National Health Insurance Research Database who were exposed to systemic corticosteroids for at least 3 months during the first year preceding the first PVP or kyphoplasty. These steroid users were matched 1:1 in age, sex, and the index date of surgery with non-user controls during the enrollment period. All patients were followed for 1 year after the first PVP or kyphoplasty. The incidence of repeated PVP or kyphoplasty was compared between the steroid users and controls. A Cox proportional hazards model was developed to account for multiple confounding factors. RESULTS: The number of patients receiving repeated PVP or kyphoplasty was 233 (8.46%) and 205 (7.45%) in the corticosteroid and control groups, respectively. The Cox proportional hazards model revealed no association between corticosteroid use and repeated PVP or kyphoplasty. CONCLUSIONS: Systemic corticosteroid use for longer than 3 months is not associated with repeated PVP or kyphoplasty within one year of surgery in patient older than 50 years old. LEVEL OF EVIDENCE: Level III, Therapeutic study.

Osteoporotic sacral insufficiency fracture: An easily neglected disease in elderly patients.

Sacral insufficiency fractures (SIFs) are easily neglected by clinical physicians.The incidence of SIFs remains unclear in patients with symptomatic osteoporotic compression fractures of the lumbar-sacral area.This retrospective study was conducted by reviewing the medical records and radiological reports and by reading magnetic resonance (MR) images from August 2013 to July 2016. We identified 1233 cases with symptomatic vertebral compression fractures for which surgical interventions were performed. A total of 1144 cases were eligible for this study. Neglected diagnoses by radiologists and clinical physicians were calculated, respectively.The MR imaging (MRI) findings of SIFs were divided into the body (S1, S2, S3, and S4 levels) and alar areas (unilateral, bilateral, transverse, and none).A total of 34 (3.00%) cases with SIFs were identified through MRI. A significant difference was observed between 19 (6.53%) patients aged >80 years and 15 (1.76%) aged <80 years (P < .0001). Eight (23.53%) and 26 (76.47%) cases of SIFs were neglected by radiologists and clinical physicians, respectively. The S2 and S3 levels were the predominantly involved area (23/34; 67.65%). Furthermore, the bilateral alar area was the most commonly involved (19/34; 55.88%), as observed in coronal views of MRI.While treating other levels of osteoporotic compression fractures, radiologists and clinical physicians should be aware of SIFs, particularly when the patients are aged >80 years. The coronal oblique MR images of the thoracolumbar region should be carefully read to avoid neglecting SIFs.

Fracture resistance of monolithic zirconia crowns with different occlusal thicknesses in implant prostheses.

STATEMENT OF PROBLEM: The use of monolithic zirconia crowns in implant prostheses is increasing, especially when the interdental space is insufficient. However, fractures have been reported in clinical practice. PURPOSE: The purpose of this study was to determine the minimal thickness of a complete zirconia crown used for an implant prosthesis in the posterior dental region. MATERIAL AND METHODS: Fifty complete zirconia crowns were produced using a computer-aided design/computer-aided manufacturing technique. In each group, 5 crowns of varying thicknesses (0.4, 0.5, 0.6, 0.7, and 0.8 mm) were subjected to cycles of vertical and 10-degree oblique compressive loading at 5 Hz and 300 N in a servohydraulic testing machine. Five finite element models comprising 5 different occlusal thicknesses (0.4, 0.5, 0.6, 0.7, and 0.8 mm) were simulated at 2 loading angles (0 and 10 degrees) and 3 loading forces (300, 500, and 800 N). Data were statistically analyzed, and fracture patterns were observed with a scanning electron microscope. RESULTS: Cyclic loading tests revealed that the fracture resistance of the specimens was positively associated with prosthesis thickness (P<.01). Low von Mises stress values were obtained for prostheses with a minimal thickness of 0.7 mm under varying loading directions and forces. CONCLUSIONS: Zirconia prostheses with a minimal thickness of 0.7 mm had a high fracture resistance and the lowest stress values. Therefore, dentists and laboratory technicians should carefully choose the optimum thickness of zirconia prostheses.

Palatal bone thickness and associated factors in adult miniscrew placements: A cone-beam computed tomography study.

Palatal bone thickness measurements obtained by cone-beam computed tomography (CBCT) in 30 men and 28 women were evaluated for associated factors. Palatal bone thickness was measured at 20 locations unilateral to the midpalatal suture and posterior to the incisive foramen. Tongue position, presence of posterior crossbite, and palatal morphology were recorded. Lateral cephalograms acquired from CBCT data were used to calculate Frankfort-mandibular plane angles (FMA). At almost all sites, bone thickness was greater in males than in females, but the difference was statistically significant at only seven sites. Bone thickness showed no associations with tongue position, palatal morphology, or presence of posterior crossbite. In women, FMA significantly correlated with bone thickness at 12 locations. In conclusion, palatal bone thickness is unassociated with tongue position, posterior crossbite, or palatal morphology. In hyperdivergent women, however, available bone may be smaller than normal in the middle and posterior palatal areas; in such cases, a shorter than normal miniscrew may be needed to avoid penetrating the nasal cavity.

Morphometric analysis of the cranial base in Asians.

This study tested the hypothesis that developmental heterogeneity in cranial base morphology increases the prevalence of Class III malocclusion and mandibular prognathism in Asians. Thin-plate spline (TPS) graphical analysis of lateral cephalometric radiographs of the cranial base and the upper midface configuration were compared between a European-American group (24 females and 31 males) and four Asian ethnic groups (100 Chinese, 100 Japanese, 100 Korean and 100 Taiwanese; 50 females and 50 males per group) of young adults with clinically acceptable occlusion and facial profiles. Procrustes analysis was performed to identify statistically significant differences in each configuration of landmarks (P < 0.001). The TPS graphical analysis revealed that the greatest differences of Asians were the horizontal compression and vertical expansion in the anterior portion of the cranial base and upper midface region. The most posterior cranial base region also showed horizontal compression between the basion and Bolton point, with forward displacement of the articulare. Facial flatness and anterior displacement of the temporomandibular joint, resulting from a relative retrusion of the nasomaxillary complex and a relative forward position of the mandible were also noted. These features that tend to cause a prognathic mandible and/or retruded midface indicate a morphologic predisposition of Asian populations for Class III malocclusion.

Biomechanical effects of screw fixation in second mandibular reconstruction plate.

The purpose of this study was to investigate biomechanical effects of second reconstruction plate with different combinations of fixed screws in patient with mandibular tumor resection by three-dimensional finite element analysis (FEA). The FEA models were consisted of defected mandible, reconstruction plate with different screw holes, and bone screws. The results indicated that application of the second reconstruction plate appeared to increase stability and decrease stress magnitude on the plates and screws accompanying with increasing screw number. For clinical cost consideration in usage of the second reconstruction plate, the conclusion showed that the second reconstruction plate could offer a better mechanical efficacy accompanying with increase of screw quantity, but single screw applied for the second plate fixation to defected mandible of tumor resection was enough to stabilize without increase of screw quantities.

Influence of different implant materials on the primary stability of orthodontic mini-implants.

This study evaluates the influence of different implant materials on the primary stability of orthodontic mini-implants by measuring the resonance frequency. Twenty-five orthodontic mini-implants with a diameter of 2 mm were used. The first group contained stainless steel mini-implants with two different lengths (10 and 12 mm). The second group included titanium alloy mini-implants with two different lengths (10 and 12 mm) and stainless steel mini-implants 10 mm in length. The mini-implants were inserted into artificial bones with a 2-mm-thick cortical layer and 40 or 20 lb/ft(3) trabecular bone density at insertion depths of 2, 4, and 6 mm. The resonance frequency of the mini-implants in the artificial bone was detected with the Implomates(®) device. Data were analyzed by two-way analysis of variance followed by the Tukey honestly significant difference test (α = 0.05). Greater insertion depth resulted in higher resonance frequency, whereas longer mini-implants showed lower resonance frequency values. However, resonance frequency was not influenced by the implant materials titanium alloy or stainless steel. Therefore, the primary stability of a mini-implant is influenced by insertion depth and not by implant material. Insertion depth is extremely important for primary implant stability and is critical for treatment success.