Flow rate models in renal obstruction.

BACKGROUND: In acute unilateral renal obstruction, calculated divided renal uptake following injection of tracer may be normal. Divided renal function as measured by uptake may be insensitive to fall in renal plasma flow (RPF) to the obstructed kidney. This study analyses afferent flow rate parameters of optimised models of renogram time activity curves (TAC). Afferent flow rate parameters may have differing sensitivity to altered RPF from divided renal tracer uptake and may be more sensitive to changes in cortical function in renal obstruction. METHOD: Twenty-four background-corrected renogram TACs using 99mTc-labelled mercapto-acetyl-triglycine (MAG3) with a unilateral obstructive pattern and six normal control renograms TACs were studied. Optimised computed models of each curve were constructed using specialised software (ModelMaker, Cherwell Scientific) and using the Marquardt Least Squares method. Following optimisation to the TAC of each target renogram, the afferent flow rate parameters were calculated. RESULTS: Following optimisation of models, afferent flow rate parameters, expressed as arbitrary units, (mean 0.15, SD 0.06) in acutely obstructed kidneys, were typically reduced in comparison with those of normal kidneys (mean 0.44, SD 0.04). (Paired t test; P<0.005). By contrast, this reduction in afferent flow rate parameter was greater than the reduction in differential tracer uptake for the obstructed kidney (divided renal function of the obstructed group; mean 0.3, SD 0.14 compared with the control group; mean 0.45, SD 0.05 (P<0.05). CONCLUSION: Optimised modelling of TACs of obstructed renograms is feasible and may provide a more sensitive index of parenchymal dysfunction in early obstruction than comparing divided renal tracer uptake.

Breast sentinel node imaging with low-dose SPECT/CT.

OBJECTIVE: The critical factors in quality control for breast sentinel lymph node (SLN) biopsy are the SLN identification rate and the false-negative rate. Earlier reports have not formalized indications for use of single-photon emission computed tomography/computed tomography (SPECT/CT) lymphscintigraphy. In view of the potential advantages of the dual nature of structural and functional imaging of SPECT/CT, this study reports the false-negative rate resulting from nonvisualization of SLNs on SPECT/CT. METHODS: One hundred and eighty-seven consecutive female patients (age range: 30-87 years) with biopsy proved breast carcinoma (18 lobular, 159 ductal carcinomas, two mucinous carcinomas and eight ductal carcinoma in situ) were injected with 40 MBq of 99mTc sulphur colloid, and underwent SPECT/CT scanning 45 min later. RESULTS: Tracer uptake in the largest SLNs could be assessed in 158 patients. Two patients had SLNs close to the site of periareolar injection; the remaining SLNs were located in the ipsilateral axillae. Five patients had two or more SLNs identified on SPECT/CT. Twenty-nine patients (15.5%) had no SLNs identified on SPECT/CT; of these, 10 patients had metastatic infiltration confirmed peroperatively. This equates to an overall false-negative rate for SPECT/CT of 5.3% (expressed by convention, as percentage of total patient number). CONCLUSION: SPECT/CT lymphscintigraphy readily shows SLNs preoperatively and is practical in a clinical setting on patients without specific selection criteria. The false-negative rate may encourage more widespread use of this technique.

Gated single photon emission tomography MIBI stress perfusion imaging for assessing cardiac output and index in obese and non-obese patients.

OBJECTIVE: To compare cardiac index, (CI) [i.e. Cardiac output (CO) corrected for body surface area], stroke volume index (SVI) and left ventricular ejection fraction (LVEF) of obese and non obese patients using gated Gated Single Photon Emission Computed Tomography (SPECT) MIBI perfusion imaging. This was done in order to assess haemodynamic function, represented by CI and systolic function represented by LVEF and SVI. MATERIALS AND METHODS: Forty-one obese patients (BMI >30, mean 35.3) with 65 patients with BMI <30, (mean 25.8), referred for evaluation of chest pain, dyspnoea or inconclusive exercise ECG were studied in an outpatient setting following injection of 400MBq Tc99mMIBI. Gated SPECT imaging was performed after treadmill Bruce protocol. CO was calculated as product of SV and resting heart rate and CI determined. RESULTS: Mean CI was 2.26 l/min/m(2) for obese and 2.18 l/min/m(2) for non obese patients. T tests showed no significant difference in mean CI or in SV between the two groups although CO was significantly increased for the obese group. LVEF was elevated in the obese group, mean LVEF 62.5% compared with mean LVEF of 58% in the non obese group (P < 0.05). SVI was reduced for the obese group (P < 0.03). CONCLUSIONS: Haemodynamic function, as CI, was similar for obese and non-obese patients. Hypersystolic function, manifest as relatively increased LVEF, was noted in the obese group.

Analysis of compartmental models of type 4 nuclear renograms with calculation of flow rate parameters and instantaneous drainage rates.

OBJECTIVE: To estimate the dynamic rates of arterial delivery and renal drainage in renograms with the Homsy sign, using optimized computed compartmental modelling. METHODS: Eleven F-15 renograms and one F+15 renogram (using 99mTc-mercaptoacetyltriglycine) with the Homsy sign were studied, with 26 controls. Compartmental models were constructed for each renogram using components (blood, renal, bladder) linked by variables (arterial rate, drainage rate). Each model was optimized using the Marquadt least-squares method to numerical data from the time-activity curves (TACs). The model renal component at sample points along the TAC was minimized and the corresponding drainage rates calculated. RESULTS: The models were optimized, with a mean (range) r2 of 0.811 (0.68-0.88). There were continuous low drainage rates for all type 4 renograms, with no quadrupling of the flow rate, as predicted by the standard model. CONCLUSION: The standard model is unlikely to be correct and the Homsy sign is probably an artefact seen in patients with impeded urinary drainage. Computer modelling of individual renograms is feasible and can provide useful insights into the pathophysiology of renal uptake and drainage.

Fluoride release of glass ionomer-based luting cements in vitro.

STATEMENT OF PROBLEM: There is considerable variation in generic formulation and in reported fluoride release from resin-modified glass ionomer luting cements. PURPOSE: This study compared fluoride release from 2 generically similar resin-modified glass ionomer luting cements (Vitremer and Advance) with release from 2 conventional glass ionomer luting cements (Ketac-Cem and Fuji I). MATERIAL AND METHODS: Ten specimen disks of each of the 4 luting cements were fabricated and immersed in deionized water in individual polystyrene jars. The jars were stored in a humidor at 37 degrees C between test periods. At the same time each day, for 28 days, fluoride release from each specimen disk was measured in parts per million by testing the storage water. RESULTS: The 4 luting cements tested showed an initial high concentration of fluoride release during the first week, followed by a gradual decrease over the study period. Vitremer luting cement demonstrated the greatest mean cumulative fluoride release in parts per million over the study period (198), followed by Fuji I (140), Ketac-Cem (110), and Advance (99) luting cements. CONCLUSIONS: Resin-modified glass ionomer luting cements showed fluoride release comparable to the conventional glass ionomer luting cements. Vitremer luting cement released more fluoride over the 28-day period than the other cements.

The bond strength of an adhesive resin luting cement to a variety of surface treatments of a high-palladium copper alloy.

PURPOSE: This study evaluated the tensile bond strength of a bisphenol glycidyl methacrylate (Bis-GMA) resin luting cement with four different surface treatments of a high Pd-Cu alloy. MATERIALS AND METHODS: For each surface treatment type (tin-plated, porcelain furnace oxide, air-abraded, and finished-only), 15 opposing half-dumbbell-shaped samples were cast and prepared in new Pd-Cu alloy. Samples were luted with a Bis-GMA resin luting cement at a film thickness of 80 microns using a custom alignment apparatus. Samples were stored in distilled water at 37 degrees C for 24 hours, thermocycled for 1,000 cycles, and then stored for 30 days in distilled water at 37 degrees C. Samples were then subjected to fracture in tension at a loading rate of 0.5 cm/min with the bond strengths calculated in megapascals (MPa). The fractured surfaces were examined using stereomicroscopy and scanning electron microscopy at various magnifications ranging from 5.5x to 500x to determine the type of bond failure (adhesive, cohesive, or mixed). RESULTS: Tensile bond strengths (mean +/- SD MPa) were: tin-plated, 30 +/- 15.7; porcelain furnace oxide, 23 +/-n 8.6; air-abraded, 8 +/- 8.1; and finished-only, 4 +/- 4.5. Statistical analysis of the tensile bond values using an ANCOVA and Tukey's multiple comparison test at a significance level of 0.05 indicated that there was no difference between the tin-plated and the furnace oxide groups, as well as between the air-abraded and the furnace oxide groups. However, there was significant difference between the tin-plated, the air-abraded, and the finished-only groups. The observed bond failures were predominantly mixed and cohesive in nature with only one adhesive failure. CONCLUSIONS: There was no significant difference in the tensile bond strengths between the tin-plated group or the porcelain furnace oxide surface group. This suggests that the less-technique-sensitive porcelain furnace oxide surface treatment offers an alternative for achieving high metal-resin bonds to a high Pd-Cu alloy.

Elongation and preload stress in dental implant abutment screws.

A common problem associated with dental implant restorations is loosening of screws that retain the prosthesis to the implant. A method was developed to determine initial preload on UCLA-type abutment screws by measuring elongation after applying known tightening torques with a digital torque gauge. Loosening torque was also measured after tightening to 32 N-cm torque for gold alloy abutment screws and 20 N-cm for titanium abutment screws. Gold alloy and titanium abutment screws were each used to secure a gold UCLA hexed abutment to a titanium implant. Stresses and forces were calculated from the elongation measurements for three regions of each screw. Elongation of the screws after applying the manufacturer's recommended tightening torques were within the elastic range. Induced stresses were 57.5% and 56% of the yield strengths for gold alloy and titanium, respectively. Tightening of screws beyond recommended levels may be possible without producing plastic deformation. At manufacturer's recommended torques, mean preload was 468.2 (+/- 57.9) N using gold alloy screws and 381.5 (+/- 72.9) N with titanium screws.

Image processing of videofluoroscopy of patients with velopharyngeal insufficiency and hypernasal speech.

Eleven patients with hypernasal speech and velopharyngeal insufficiency (VPI), together with five normals, were evaluated by videofluoroscopy to assess velopharyngeal movement, velar lift and lateral pharyngeal wall movement. Computer processing of the images obtained was used to compensate for initial poor quality images by contrast and edge enhancement techniques and to provide objective measurement of the movements involved. It was demonstrated that objective computer aided analysis of videofluoroscopic images is feasible and may provide additional subtle diagnostic information when nasendoscopy is unavailable. In addition, results obtained showed an increased degree of velar lift and lateral pharyngeal wall movement for the more severely affected patients. These suggest a compensatory mechanism in operation for the more severe cases of VPI.

Infection control in a prosthodontic residency program.

Awareness of the need to incorporate an effective infection control program within a prosthodontic practice requires the faculty of a prosthodontic residency program to present a clear and workable model that will allow the flexibility necessary to accommodate the changes in infection control procedures and materials. The use of the barrier system to insulate the operatory, resident, faculty, and dental laboratory is discussed. Current disinfection and sterilization methods used to maintain the barriers are recommended.

Human bite force discrimination using specific maxillary and mandibular teeth.

The purpose of this study was to determine whether performance differences existed in subjects' self-generated bite force discrimination ability using maxillary and mandibular central incisors, canines, premolars and first molars. Two separate studies were conducted: (i) to assess whether performance differences existed in subjects' bite force discrimination ability using central incisors and premolars; (ii) to compare subjects' performance on bite force discrimination using central incisors, canines and first molars. Assessment of bite force was measured using a specially designed strain gauge scale allowing subjects to visually monitor when their biting force equalled a preset resistance. Resistance forces of 500, 1000 and 3000 g were selected as standards. Subjects were presented with a series of paired resistance settings, one at a time, the first of each pair being the standard and the second being the comparator setting of a predetermined amount. This paired-comparisons procedure was continued until the subjects' difference limen (DL) value (the threshold of discrimination between two forces) could be established. The first study revealed no significant (P greater than 0.05) overall difference in subjects' bite force discrimination ability relative to specific teeth. In contrast, in the second study a significant difference (P less than 0.05) was identified in subjects' performance relative to specific teeth; subjects' performed better using central incisors compared to first molars. In both studies, subjects' performance was significantly better (P less than 0.05) using the 500 g standard compared to the 3000 g standard in the first study, and compared to the 1000 g standard in the second study. No significant differences (P greater than 0.05) were observed between the performance of males and females in either study.

A preliminary study of the effects of tooth guidance on working-side condylar movement.

Clinical observations have indicated that lateral working-side tooth contacts can produce a posterior shift of the working-side condyle, resulting in pain in the temporomandibular joint. This study examined the influence of lateral retrusive and lateral protrusive tooth guidance on the movements of working condyles of the lateral pole. Four patients with lateral retrusive natural tooth contacts and four patients with lateral protrusive natural tooth contacts were studied. Movement of the lateral pole of the working condyle was recorded under the following conditions: (1) natural teeth in contact, (2) wearing of a mandibular acrylic resin splint that created lateral protrusive or lateral retrusive tooth guidance, and (3) a central bearing screw and bearing plate separating the teeth. The results indicated that the condition of the patient's temporomandibular joints was a crucial factor in consistency of condylar tracings. Condylar tracings from patients with temporomandibular joint condyle-disk lacking coordination were inconsistent and unreproducible. Consistent, reproducible tracings for patients without condyle-disk disorders indicated that lateral retrusive guidance can cause a more posterior pathway of the lateral pole of the working condyle than lateral protrusive guidance. Future studies are necessary to establish the relationship between lateral tooth guidance and temporomandibular disorders.

Influence of contraction mismatch and cooling rate on flexural failure of PFM systems.

The interactive influence of cooling rate and the sign and magnitude of thermal contraction difference between metals and ceramic veneers on bond strength have not been extensively analyzed, although numerous bond-test studies have been reported during the past two decades. A previous analytical study of residual incompatibility stress in bond-test specimens indicated that bond strength values may be of relatively little value if the residual stress state of the metal-ceramic specimens is not considered. The objective of this study was to determine the influence of cooling rate and contraction mismatch on the flexural failure resistance of metal opaque-porcelain strips. Specimens were subjected to four-point loading in an Instron testing machine until crack initiation occurred at the metal-ceramic interface. The residual stress states in the ceramic region were estimated from finite element stress analyses of the bond-test specimens by use of dilatometry data obtained at the cooling rate of 3 degrees C/min. The total stress induced from the residual stress and the applied flexural load was also determined for these specimens. Statistical analyses of the experimental data revealed that the slowly cooled specimens exhibited a significantly lower (p < 0.05) flexural strength compared with rapidly cooled specimens. Regardless of the cooling technique, metal-ceramic specimens with a negative thermal contraction difference (alpha m - alpha p < 0) failed at significantly lower (p < 0.05) flexural loads than did specimens with a positive thermal contraction difference.