Revision of the failed pedicle screw in osteoporotic lumbar spine: biomechanical comparison of kyphoplasty versus transpedicular polymethylmethacrylate augmentation.

OBJECTIVES: In this study, we aimed to compare of kyphoplasty versus transpedicular polymethylmethacrylate (PMMA) augmentation biomechanically in the revision of the failed pedicle screw in osteoporotic lumbar spine. MATERIALS AND METHODS: Bone mineral density (BMD) of lumbar vertebrae collected from four bovines were measured. Each vertebra was decalcified with hydrochloric acid solution to obtain osteoporotic specimens. Primary polyaxial pedicle screws were inserted into the pedicles and pulled out until they failed. The pullout strength results of all specimens were recorded. Revision pedicle screws were randomly inserted into the same pedicles by either pedicle hole PMMA augmented (group 1) or kyphoplasty (Xvoid™) PMMA augmented pedicle screws (group 2). The pullout strength results of all specimens were re-recorded. RESULTS: The mean BMD significantly decreased from 1.686 ± 227.9 g/cm(2) to 1.432 ± 157.1 g/cm(2) following decalcification (p<0.001). In group 1, the mean pullout strength of primary screws significantly decreased from 3443 ± 1086 N/m(2) to 2088 ± 924 N/m(2) following pedicle screw augmentation (p=0.006). In group 2, the mean pullout strength of primary screws decreased from 3702 ± 1063 N/m(2) to 3664 ± 1057 N/m(2) following kyphoplasty augmentation (p=0.934). Pedicle screw augmentation group achieved significantly lower pullout strength values than kyphoplasty pedicle hole augmentation group (p=0.002). CONCLUSION: Although pedicle hole PMMA augmentation is the gold standard for the failed screws in an osteoporotic bone, kyphoplasty augmented pedicle screw seems to be more effective method increasing the pullout strength.

Clamp fixation to prevent unfolding of a suture knot decreases tensile strength of polypropylene sutures.

PURPOSE: Although sutures evolved in last decade and the product spectrum broadened largely, they can be still classified into two: monofilament and multifilament. Sutures are the mainstay of orthopedic procedures like fascial closures, tendon repairs or tenodesis. In every repair, a suture loop is created. This suture loop is prone to failure due to suture elongation, knot slip and suture breakage. As the knot is the stress riser in a suture loop, the majority of acute loop failure occurs just adjacent to the knot. Monofilament sutures have higher bending stiffness and tendency to untie than multifilament sutures. The first throw of monofilament sutures have tendency to untie, which decrease loop tension and result in loss of achieved tissue approximation. METHODS: Although a common practice is to fix the first throw via a clamp before the locking one is tied, it can be hypothesized that a potential deforming effect can lead to a decrease in ultimate failure load of a monofilament suture loop. RESULTS: Fixing the first throw significantly reduced the ultimate failure load of monofilament nonabsorbable polypropylene sutures (Prolene) (62.2 ± 8 N vs. 72.7 ± 9 N, p = 0.019). The ultimate failure load achieved by monofilament sutures Polyglyconate (Maxon) and Nylon (Ethilon) and braided absorbable Polyglactin (Vicryl) were not affected by fixing the first throw. CONCLUSION: Under microscopic examination, polypropylene sutures were found to be deformed by clamp fixation, while the others were not. Polypropylene sutures can be easily damaged when it is fixed by a clamp during knot tying. Presented data demonstrated that in real surgical situations clamp fixation of polypropylene knots can damage the suture loop and carry the risk of acute failure of repair site during early rehabilitation.

The effects of three different desensitizing agents on the shear bond strength of composite resin bonding agents.

The aim of this study was to evaluate the effects of three desensitizing agents on the shear bond strengths of four different bonding agents used to bond composite resin to dentin. A total of 160 extracted human molars were sectioned parallel to the occlusal plane under water cooling, polished and randomly divided into 4 groups of 40. Each group was treated with a different desensitizing agent (Tooth Mousse, Ultra-EZ, Cervitec Plus), except for an untreated control group. Each group was then randomly subdivided into 4 groups of 10, and a different dentin bonding agent (XP Bond, AdheSE, Adper Prompt L-pop, GBond) was applied to each group in order to bond the specimens to a resin composite (Gradia Direct) built up using a plastic apparatus. A Universal Testing Machine was used to measure the shear bond strength of each specimen. Statistical analysis was performed using one-way ANOVA and Tukey's tests. With the exception of the Control/AdheSE and Ultra-EZ/XP Bond groups, no statistically significant differences were found in the shear bond strength values of the groups tested. These findings suggest that the use of different desensitizing agents does not affect the shear bond strength of various adhesive systems used to bond resin composite to dentin.

Effect of different cavity disinfectants on shear bond strength of composite resin to dentin.

PURPOSE: The aim of this study was to evaluate the effect of different cavity disinfectants on dentin bond strengths of composite resin applied with two different adhesive systems. MATERIALS AND METHODS: One hundred mandibular third molars were sectioned parallel to the occlusal surface to expose midcoronal dentin. The dentin surfaces were polished with waterproof-polishing papers. The specimens were randomly divided into 5 groups of 20 each. In group 1, the specimens were not treated with any cavity disinfectants and served as control. From groups 2 to 5, dentin surfaces were treated with the following cavity disinfectants, respectively; 2% chlorhexidine solution, 2.5% NaOCl, 1% chlorhexidine gel, 3% H2O2. The specimens were then randomly divided into 2 subgroups including ten teeth each to evaluate the effect of different bonding systems. Dentin bonding systems were applied to the dentin surfaces and the composite buildups were created. After the specimens were stored in an incubator for 24 h, the shear bond strength was measured at a crosshead speed of 1 mm/min. The bond strength data were analyzed with one way analysis of variance and Tukey-HSD tests. RESULTS: There was no significant difference between chlorhexidine gel and control groups regardless of the type of the bonding agent (p > 0.05). On the other hand, pretreatment with NaOCl, H2O2 or chlorhexidine solutions had a negative effect on the shear bond strength of self-etching bonding systems. CONCLUSION: The findings of this study suggest that when NaOCl, H2O2 or chlorhexidine solution are used as a cavity disinfectant, an etch-and-rinse bonding system should be preferred.