A role for proteoglycans in mineralized tissue-titanium adhesion.

Biomechanical properties of the bone-titanium interface have rarely been studied, due to the technical limitations involved; whether biological bonding mechanisms exist has not been determined. We hypothesized that a selected set of proteoglycan/glycosaminoglycan complexes plays a role in establishing the adhesion between bone and titanium, and utilized the rat bone-marrow-derived osteoblastic culture model to gain an insight into the hypothesis. Gene expression of selected proteoglycan core proteins was up-regulated in the osteoblasts cultured on titanium compared with those on polystyrene. Various sulfated glycosaminoglycans were immunochemically localized at mineralized tissue-titanium interfaces. The administration of various glycosaminoglycan-degrading enzymes into the cultures resulted in a 25-45% reduction of the tissue-titanium interfacial strength, measured by a nanoscratch test; while the hardness and elastic modulus of the mineralized tissue, evaluated by nano-indentation, were not altered. In conclusion, glycosaminoglycan degradation resulted in a decreased interfacial strength between cultured mineralized tissue and titanium, but did not alter the intrinsic strength of the mineralized tissue, suggesting a role for proteoglycan/glycosaminoglycan complexes in the establishment of tissue-titanium adhesion.

Material characteristics of a novel shrinkage-free ZrSiO(4) ceramic for the fabrication of posterior crowns.

OBJECTIVE: To confirm the clinical applicability of a novel ZrSiO(4) (zircon) based shrinkage-free ceramic material, the flexural strength, fracture toughness and chemical solubility were tested. In addition, the fracture load of full crowns made from this material was tested after cyclic thermomechanical loading. METHODS: Flexural strength of 12 specimens was measured using a biaxial bending test. Fracture toughness was measured using 10 slotted box shaped specimens. The specimens were fractured using a universal testing machine; fracture loads were recorded. A chemical solubility test was performed in accordance with ISO norm 6872. Additionally, 32 ZrSiO(4) all-ceramic crowns were fabricated on extracted caries-free human molars. Sixteen Empress 2 and 16 PFM crowns served as a reference control. After artificial aging of 1.2 million cycles in the chewing simulator, the survival rate of the crowns was determined. The fracture load of all surviving specimens was obtained by loading the crowns until fracture in a universal testing machine. RESULTS: A flexural strength of 328MPa was found. The fracture toughness of the ZrSiO(4) ceramic was 5.16MPam(0.5). The chemical solubility amounted to 7.2microg/cm(2). All specimens survived the chewing simulation (survival rate: 100%); no crowns had to be re-cemented. A mean fracture strength of 1790N was found for Everest HPC for Empress 2 crowns, 1715N for Empress 2 crowns and 2416N for PFM crowns. Fracture loads of PFM crowns were significantly higher than for Empress 2 crowns (P=0.032) as well as ZrSiO(4)-crowns (P=0.007). There was no significant difference between ZrSiO(4)-crowns and Empress 2 crowns (P=0.743). SIGNIFICANCE: At the present stage, Everest HPC can be recommended for the fabrication of single crowns as an alternative to conventional PFM and other all-ceramic crowns, because its fracture strength exceeds average masticatory forces in the posterior region.

Fracture load and marginal fit of shrinkage-free ZrSiO4 all-ceramic crowns after chewing simulation.

The aim of this in vitro study was to evaluate the fracture load and marginal accuracy of crowns made from a shrinkage-free ZrSiO4 ceramic cemented with glass-ionomer or composite cement after chewing simulation. Thirty-two human mandibular molars were randomly divided into two groups. All teeth were prepared for and restored with shrinkage-free ZrSiO4 ceramic crowns (Everest HPC, KaVo). The crowns of group A (N = 16) were luted to the teeth using KetacCem and group B (N = 16) were adhesively cemented using Panavia21EX. Measurements of the marginal accuracy before and after cementation were made using replicas and an image analysis system. All specimens were exposed to 1.2 million cycles of thermo-mechanical fatigue in a chewing simulator. Surviving specimens were subsequently loaded until fracture in a static testing device. Fracture loads (N) were recorded. All specimens survived chewing simulation. The mean fracture loads (+/-s.d.) were Group A, 1622 N (+/-433); group B, 1957 N (+/-806). There was no significant difference between the two groups (P > 0.05). The marginal gap values before cementation were (mean +/- s.d.): Group A, 32.7 microm (+/-6.8); group B, 33.0 microm (+/-6.7). The mean marginal gap values after cementation were (+/-s.d.): Group A, 44.6 microm (+/-6.7); group B, 46.6 microm (+/-7.7). The marginal openings were significantly higher after cementation for both groups (P < 0.05). All test groups demonstrated fracture load and marginal accuracy values within the range of clinical acceptability.

Harder and stiffer bone osseointegrated to roughened titanium.

Mechanisms underlying the beneficial anchorage of roughened titanium implants have not been identified. We hypothesized that the implant surface roughness alters intrinsic biomechanical properties of bone integrated to titanium. Nano-indentation performed on two- and four-week post-implantation bone specimens of rats revealed that bone integrated to acid-etched titanium was approximately 3 times harder than that integrated to the machined titanium, both at the osseointegration interface and at the inner area of the peri-implant bone. The hardness of the acid-etched surface-associated bone was equivalent to that of untreated cortical bone at week 4, while the bone hardness around the machined surface was equivalent to that of the untreated trabecular bone. The elastic modulus of the integrated bone was 1.5 to 2.5 times greater around the acid-etched surface than around the machined surface. Analysis of the data suggests that the implant surface roughness affects the biomechanical quality of osseo-integrated bone, and that the bone integrated to the acid-etched surface is harder and stiffer than the bone integrated to the machined surface.

Survival rate, fracture strength and failure mode of ceramic implant abutments after chewing simulation.

The aim of this study was to compare titanium-reinforced ZrO(2) and pure Al(2)O(3) abutments regarding their outcome after chewing simulation and static loading. Forty-eight standard diameter implants with an external hexagon were divided into three groups of 16 implants each and restored with three different types of abutments (group A: ZrO(2) abutments with titanium inserts; group B: Al(2)O(3) abutments; group C: titanium abutments). All abutments were fixated on the implants with gold-alloy screws at 32 Ncm torque, and metal crowns were adhesively cemented onto the abutments. The specimens were exposed to 1.2 million cycles in a chewing simulator. Surviving specimens were subsequently loaded until fracture in a static testing device. Fracture loads (N) and fracture modes were recorded. A Wilcoxon Rank test to compare fracture loads among the three groups and a Fisher exact test to detect group differences in fracture modes were used for statistical evaluation (P < 0.05). All specimens but one of group B survived chewing simulation. No screw loosening occurred. The median fracture loads (+/-s.d.) were as follows: group A, 294 N (+/-53); group B, 239 N (+/-83), and group C, 324 N (+/-85). The smaller fracture loads in group B were statistically significant. The use of pure Al(2)O(3) abutments resulted in significantly more abutment fractures. It is proposed that titanium-reinforced ZrO(2) abutments perform similar to metal abutments, and can therefore be recommended as an aesthetic alternative for the restoration of single implants in the anterior region. All-ceramic abutments made of Al(2)O(3) possess less favourable properties.

Fracture strength and survival rate of endodontically treated maxillary incisors with approximal cavities after restoration with different post and core systems: an in-vitro study.

OBJECTIVES: This study compared the fracture strength and survival rate of endodontically treated crowned maxillary incisors with approximal class III cavities and different core build-ups. METHODS: Sixty-four caries free human maxillary central incisors were selected for standardized size and quality, endodontically treated and prepared with approximal cavities 3mm in diameter. Group 1 was restored with titanium posts, group 2 received zirconia posts, in group 3 the root canal was partially filled with a hybrid composite. In the control group, only the access opening was restored. All teeth were prepared for and restored with full cast metal alloy crowns and subsequently exposed to 1.2 million cycles in a computer-controlled chewing simulator with simultaneous thermocycling. In addition, the samples were loaded until fracture in a static testing device. RESULTS: One specimen with composite reinforced root canal did not survive the dynamic load test. The following median fracture strengths in Newtons for the different groups were: titanium post 1038, zirconia 1057, composite resin 750, control (no post) 1171. The fracture load in group 3 (composite resin) was significantly lower (P<0.05) than in the other groups. CONCLUSIONS: The reconstruction of endodontically treated single rooted teeth with approximal cavities can be successfully performed by closure of the endodontic and additional cavities with composite. Cementation of endodontic posts offers comparable but no advantageous fracture resistance. Enlargement of the root canal space after completion of endodontic treatment should be avoided and cannot be compensated for by injection of composite resin. Less catastrophic failures were observed without post reconstruction.

Survival rate and fracture strength of endodontically treated maxillary incisors with moderate defects restored with different post-and-core systems: an in vitro study.

PURPOSE: This study compares the survival rate and fracture strength of endodontically treated maxillary incisors with moderate coronal defects restored with different post-and-core systems after exposure to an artificial mouth. MATERIALS AND METHODS: Sixty-four caries-free human maxillary central incisors were selected for standardized size and quality, endodontically treated, and decoronated 2 mm coronal to the cementoenamel junction. Group 1 was restored with titanium posts and composite cores, group 2 received zirconia posts and a composite core, and in group 3 zirconia posts with a heat-pressed ceramic core were used. Teeth restored with cast posts and cores served as controls. All teeth were prepared and restored with complete cast crowns. All samples were exposed to 1.2 million cycles in a computer-controlled chewing simulator with simultaneous thermocycling. In addition, the samples were loaded until fracture in a static testing device. RESULTS: The survival rates of the different groups were: 94% for titanium/composite, 63% for zirconia/composite, 100% for the all-ceramic post and core, and 94% for the cast post and core. The following mean fracture strengths were obtained: titanium/composite = 425 +/- 155 N, zirconia/composite = 202 +/- 212 N, zirconia/ceramic = 378 +/- 64 N, cast post and core = 426 +/- 178 N. The lower fracture load in the group with zirconia posts and composite cores was statistically significant. The use of zirconia posts resulted in fewer oblique root fractures. CONCLUSION: Prefabricated titanium posts with composite cores, zirconia posts with heat-pressed ceramic cores, and cast posts and cores yield comparable survival rates and fracture strengths for the restoration of crowned maxillary incisors with moderate coronal defects. Survival rates and fracture strengths for zirconia posts with composite cores are significantly lower, so this combination cannot be recommended for clinical use.

Tricyclic antidepressants and cardiac conduction: changes in ventricular automaticity.

Ventricular dysrhythmias result from changes in the automaticity or the conduction properties of the specialized conduction system. Tricyclic antidepressants have been reported to cause ventricular dysrhythmias in humans and experimental animals. Consequently, it seemed to interest to determine whether these substances influence ventricular automaticity. Ventricular rhythm was produced in anesthetized dogs by blocking atrioventricular conduction. Low doses of imipramine, amitriptyline and nortriptyline resulted in small but significant increases in automaticity. Relatively high doses of these agents suppressed automaticity markedly. These changes could play a role in the development of dysrhythmias.

Suppression of ventricular automaticity by antidysrhythmic agents.

In view of the potentially important role of automaticity in the genesis of ventricular dysrhythmias, the effects of four widely used antidysrhythmic agents on ventricular automaticity were examined in anesthetized dogs at doses previously shown to antagonize experiments induced rhythm disturbances. Quinidine, and particularly procainamide, lidocaine and propranolol slowed ventricular rate in A-V blocked dogs. Quinidine and procainamide but particularly the last two agents also markedly prolonged overdrive suppression. Thus, all four substances depressed automaticity. However, propranolol was effective at doses substantially lower than those required to antagonize several experimental dysrhythmias.

A method for the placement of His bundle electrodes and production of atrioventricular block in dogs.

A multibarrell electrode designed for the location of the His bundle (HB) in open-chest dogs is described. The barrels may be used for the introduction of electrodes into the region of the HB for recording or pacing or for the injection of formaldehyde into the area to produce atrioventricular block.