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.

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.

Adjusting implant abutment for crown delivery is a common practice during implant installation. The purpose of this study was to compare the fracture resistance and stress distribution of zirconia specimens on four occlusal surface areas of implant abutment. Four implant abutment designs [occlusal surface area (SA) SA100, SA75, SA50, and SA25] with 15 zirconia prostheses over the molar area per group were prepared for cyclic loading with 5 Hz, 300 N in a servo-hydraulic testing machine until fracture or automatic stoppage after 30,000 counts. The minimum occlusal thickness of all specimens was 0.5 mm. Four finite element models were simulated under vertical or oblique 10-degree loading to analyze the stress distribution and peak value of zirconia specimens. Data were statistically analyzed, and fracture patterns were observed under a scanning electron microscope. Cyclic loading tests revealed that specimen breakage had moderately strong correlation with the abutment occlusal area (r = 0.475). Specimen breakage differed significantly among the four groups (P = 0.001). The lowest von Mises stress value was measured for prosthesis with a smallest abutment occlusal surface area (SA25) and the thickest zirconia crown. Thicker zirconia specimens (SA25) had higher fracture resistance and lowest stress values under 300 N loading.

Vertebral compression fractures can recur within a few years after percutaneous vertebroplasty (PVP) or kyphoplasty. 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). 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). Injected antiosteoporotic medication was associated with lower rates of repeated vertebroplasty and kyphoplasty than was OB application.

The aim of the present study is to use a 3D finite element analysis to investigate and compare the transverse displacement and stress distribution between stainless steel miniscrews and titanium alloy miniscrews used for monocortical and bicortical anchorage during miniscrew-assisted rapid maxillary expansions. Skull models were constructed to depict expansion after and before midpalatal suture opening at varying miniscrew insertion depths in four clinical scenarios: monocortical, monocortical deepening, bicortical, and bicortical deepening. Finite element analyses of miniscrew properties, including transverse displacement and von Mises stress distribution, were performed for each clinical scenario. Peri-implant stress was lesser in both bicortical anchorage models compared to both monocortical models. Transverse displacement in the coronal and axial planes was also greater and more parallel in both bicortical models compared to both monocortical models. Transverse displacement and peri-implant stress did not significantly differ between monocortical and monocortical deepening models or between bicortical and bicortical deepening models. From a biomechanical perspective, the bicortical deepening miniscrew anchorage is preferable to monocortical and monocortical deepening anchorage, because bicortical anchorage induces less stress on the peri-implant bone. Consequently, bicortical deepening anchorage should be considered the preferred option in challenging clinical scenarios in which strong anchorage is required for maxillary skeletal expansion.