Biochemical Changes in Bone Grafts Stabilized with Rigid Plates: II. Cortical Grafts

The effect of rigid plate fixation on the chemical composition of cortical interposition grafts was studied in rabbit tibio-fibular bones.

The concentration of hexosamines increased both in the graft and in the host bone during the first 6 weeks, but thereafter decreased. The concentrations of hydroxyproline and nitrogen increased throughout the experiment. The ratio of hexosamines to hydroxyproline increased in the graft for the first 6 weeks, indicating formation of immature osteoid and bone during this period, but thereafter decreased.

The calcium concentration of the graft decreased significantly during the first 12 weeks and remained below normal (-10 to -19 per cent). The mineralization of the graft, assessed by the ratio of calcium to hydroxyproline, decreased continually. The results suggest that cortical bone grafts stabilized with rigid plates heal with only slight chemical signs of callus formation. The demineralization of the graft reflects the porotic changes that take place under the plate.     

Bonding polycarbonate brackets to ceramic: effects of substrate treatment on bond strength.

This study evaluated the effects of 5 different surface conditioning methods on the bond strength of polycarbonate brackets bonded to ceramic surfaces with resin based cement. Six disc-shaped ceramic specimens (feldspathic porcelain) with glazed surfaces were used for each group. The specimens were randomly assigned to 1 of the following treatment conditions of the ceramic surface: (1) orthophosphoric acid + primer + bonding agent, (2) hydrofluoric acid gel + primer + bonding agent, (3) tribochemical silica coating (silicon dioxide, 30microm) + silane, (4) airborne particle abrasion (aluminum trioxide, 30microm) + silane, and (5) airborne particle abrasion (aluminum trioxide, 30microm) + silane + bonding agent. Brackets were bonded to the conditioned ceramic specimens with a light-polymerized resin composite. All specimens were stored in water for 1 week at 37 degrees C and then thermocycled (1000 cycles, 5 degrees C to 55 degrees C, 30 seconds). The shear bond strength values were measured on a universal testing machine at a crosshead speed of 1 mm/min. Brackets treated with silica coating with silanization had significantly greater bond strength values (13.6 MPa, P =.01) than brackets treated with orthophosphoric acid (8.5 MPa). There was no significant difference (P =.97) between the bond strengths obtained after airborne abrasion with aluminium trioxide particles followed by silanization (12 MPa) and hydrofluoric acid application (11.2 MPa) (ANOVA and Tukey test). Although brackets conditioned with orthophosphoric acid exhibited only adhesive failures of the luting cement from the ceramic surface, other conditioning methods showed mixed types of failures. Airborne particle abrasion with aluminium trioxide or silica coating followed by silanization gave the most favorable bond strengths. The types of failures observed after debonding indicated that the critical parameter was the strength of the adhesive joint of the luting cement to both the bracket and the ceramic.     

Incidence and Prognosis of Ischemic Heart Disease with Respect to Geographical Area

ABSTRACT. Ischemic heart disease is more common in East Finland than in West Finland, but systematic comparison and follow-up of incidence figures have not been possible. In 1972 the personal identification number became included in the hospital discharge records, which made it possible to link death certificate data with hospital records from the whole country. The results of this study suggest that high mortality from IHD in some regions is more closely associated with high incidence than a high fatality rate. The proportion of deaths outside hospitals showed large variation by province but this had rather little effect on the total one-year survival rates.     

The effect of a 3-methacryloxypropyltrimethoxysilane and vinyltriisopropoxysilane blend and tris(3-trimethoxysilylpropyl)isocyanurate on the shear bond strength of composite resin to titanium metal.

OBJECTIVES: The aim of this study was to evaluate the reactions of silanes prior to attaching the composite to titanium and evaluate these silanes as coupling agents. Veneered titanium may be used as a prosthetic material. METHODS: Two silane solutions, a mixture of both gamma-methacryloxypropyltrimethoxysilane and vinyltriisopropoxysilane, and tris(3-trimethoxysilylpropyl)isocyanurate were prepared as 2 wt% in two different (95% 2-propanol and 90% acetone) solutions. A control, 2 wt% gamma-methacryloxypropyltrimethoxysilane was prepared in both solutions. These six silane solutions were applied onto flat titanium surfaces. The samples (N = 250) were divided into two main groups: air-dried (room temperature) and heat cured for 1 h at 110 degrees C. Sinfony veneering composite was applied and light-cured on the titanium. The control group was non-silanized. The specimens were assigned to two subgroups: not thermocycled, and thermocycled (5000 cycles, 5-55 degrees C). Shear bond strength of the composite was tested at a crosshead speed of 1.0 mm min(-1). Fresh silane solution hydrolysis, and condensation reaction on titanium surface were monitored by FTIR spectrometry. RESULTS: Dry samples could be successfully tested, while thermocycling after 3700 cycles had gradually de-bonded the composite from the silanized titanium substrate. For dry samples, statistical analysis (ANOVA) showed that solvent and silane significantly affected the shear bond strength. The silane mixture in 2-propanol reacted at room temperature yielded 11.3 MPa (Standard deviation, SD, 3.6 MPa) and on the other hand, tris(3-trimethoxysilylpropyl)isocyanurate in 2-propanol yielded 10.7 MPa (SD 8.0 MPa) and gamma-methacryloxypropyltrimethoxysilane 20.4 MPa (SD 12.2 MPa). Non-silanized samples yielded 4.8 MPa (SD 2.1 MPa). SIGNIFICANCE: In all solvents used, silanes reacted chemically with the titanium surface and covalent Si-O-Ti- and -Si-O-Si- bonds were evident.     

Assessment of material- and technique-related complications following sagittal split osteotomies stabilized by biodegradable polylactide screws

OBJECTIVE: The aim of this retrospective clinical study was to determine whether there are any material-related problems and increased occurrence of postoperative mandibular nerve and temporomandibular joint dysfunctions in connection with the use of biodegradable self-reinforced poly-L-lactide (SR-PLLA) screws for bone fixation after bilateral sagittal split osteotomies (BSSO). STUDY DESIGN: Forty consecutive patients who underwent BSSO and mandibular advancement that included fragment fixation using SR-PLLA screws were monitored for an average of 2.2 years postoperatively. RESULTS: The osteotomy sites healed uneventfully with no adverse reactions. The incidence of postoperative sensory disturbances of the inferior alveolar nerve was 27%. Symptoms of temporomandibular joint disorders (TMJD) observed preoperatively in 73% of patients were reduced to 48% after surgery. CONCLUSION: The occurrence of postoperative sensory disturbances and TMJD symptoms in this study did not deviate strikingly from that of other studies using conventional osteosynthesis. No specific complications related to the screw material were observed.     

Effect of water and artificial saliva on the low cycle fatigue resistance of cobalt-chromium dental alloy

Statement of problem. Fatigue of denture clasp alloys causes clasp failures and decreases the retention of removable partial dentures. Little information is available on how the environment (dry, water, artificial saliva) effects the fatigue behavior of cast cobalt-chromium alloy clasps. Purpose. This study determined the effect of water and the artificial saliva on the resistance of cast cobalt-chromium alloy to the deflection fatigue. Material and methods. Test bars (n = 10) were tested either dry, in water, or in artificial saliva (Fusayama type) with a constant deflection fatigue test. The number of loading cycles before fracture was registered as resistance to fatigue. To establish whether there were indications of alloy corrosion occurring during the fatigue test, the testing liquid was analyzed retrospectively with an atomic absorbance spectroscopy. To determine elemental composition of the fracture surface, fracture surfaces of the test bars were analyzed with a scanning electron microscope and energy dispersive spectroscopy. Results. The bars that were tested dry had a mean fatigue resistance of 78,000 loading cycles, whereas test specimens tested in artificial saliva had a resistance of 59,000 loading cycles and 36,000 for those tested in water. Atomic absorbance spectroscopy revealed small amounts of cobalt (Co) in testing water and in artificial saliva. Energy dispersive spectroscopy analysis revealed differences in elemental composition of a fatigue fracture surface compared with that of a 1-bend fracture. Conclusions. The results suggest that both water and artificial saliva reduce the fatigue strength of cobalt-chromium alloy, explained by corrosion of the alloy in the wet environment. (J Prosthet Dent 1998;80:708-13.)     

Depth of light-initiated polymerization of glass fiber-reinforced composite in a simulated root canal

PURPOSE: The possibility of polymerizing glass fiber-reinforced composite (FRC) material into the root canal was preliminarily evaluated by determining the depth of light-initiated polymerization of FRC. MATERIALS AND METHODS: The material used was polymer-preimpregnated E-glass fiber reinforcement, which was further impregnated with light-polymerizable dimethacrylate monomer resin. The same resin without fiber reinforcement was used as a control. Six different lengths (range 4 to 24 mm) of light-protected cylinders filled with the test materials were light polymerized from one end. The degree of monomer conversion was determined from the other end by FT-IR spectrometry. Infrared spectra were recorded at six time points from the beginning of polymerization. The microhardness of the test materials was measured from the light-exposure surface toward the other end of the cylinder. RESULTS: Both groups showed a reduction in the degree of conversion with increased lengths of the cylinder. The FRC group showed a higher degree of conversion in the longest sample group compared to the resin group. Microhardness measurement confirmed the constant reduction of the degree of conversion by the reduced Vickers hardness values with increased cylinder length of the FRC. CONCLUSION: Generally, the glass FRC showed an almost equal degree of conversion after light curing as monomer resin without fibers. However, in the longest cylinders, FRC showed a slightly higher degree of conversion compared to resin only; this might be due to the fibers' ability to conduct light.     

Myotonic dystrophy type 2 found in two of sixty-three persons diagnosed as having fibromyalgia

Because of its high prevalence, fibromyalgia (FM) is a major general health issue. Myotonic dystrophy type 2 (DM2) is a recently described autosomal-dominant multisystem disorder. Besides variable proximal muscle weakness, myotonia, and precocious cataracts, muscle pain and stiffness are prominent presenting features of DM2. After noting that several of our mutation-positive DM2 patients had a previous diagnosis of FM, suggesting that DM2 may be misdiagnosed as FM, we invited 90 randomly selected patients diagnosed as having FM to undergo genetic testing for DM2. Of the 63 patients who agreed to participate, 2 (3.2%) tested positive for the DM2 mutation. Their cases are described herein. DM2 was not found in any of 200 asymptomatic controls. We therefore suggest that the presence of DM2 should be investigated in a large sample of subjects diagnosed as having FM, and clinicians should be aware of overlap in the clinical presentation of these 2 distinct disorders.