Effect of Duplication Techniques on the Fitting Accuracy of CAD-CAM Milled, 3D-Printed, and Injection-Molded Mandibular Complete Denture Bases

BACKGROUND

Digital technology has been introduced in prosthodontics, and it has been widely used in denture duplication instead of a conventional denture duplication technique. However, research comparing different denture duplication techniques and how they affect the fitting accuracy of the denture base is scarce.

OBJECTIVES

The aim was to assess the impact of duplication techniques on the accuracy of the fitting surface of computer-aided design and manufacturing (CAD-CAM) milled, 3D-printed, and injection-molded complete denture bases (CDBs).

METHODOLOGY

This study involved fabricating a mandibular complete denture base with three marked dimples as reference marks (A, B, and C at the incisive papilla, right molar, and left molar areas) using a conventional compression molded technique. This denture was then scanned to generate a standard tessellation language (STL) file; after that, it was duplicated using three different techniques (milling, 3D printing, and injection molding) and five denture base resin materials-two milled CAD-CAM materials (AvaDent and IvoBase), two 3D-printed materials (NextDent and HARZ Labs), and one injection-molded material (iFlextm). Based on the denture base type, the study divided them into five groups (each with n = 10). An evaluation of duplication accuracy was conducted on the fitting surface of each complete denture base (CDB) using two assessment methods. The first method was a two-dimensional evaluation, which entailed linear measurements of the distances (A-B, A-C, and B-C) between reference points on both the scanned reference mandibular denture and the duplicated dentures. Additionally, a three-dimensional superimposition technique was employed, involving the overlay of the STL files of the dentures onto the reference denture's STL file. The collected data underwent statistical analysis using a one-way analysis of variance and Tukey's pairwise post hoc tests.

RESULTS

Both evaluation techniques showed significant differences in fitting surface accuracy between the tested CDBs (p ˂ 0.001), as indicated by one-way ANOVA. In addition, the milled CDBs (AvaDent and IvoBase) had significantly higher fitting surface accuracy than the other groups (p ˂ 0.001) and were followed by 3D-printed CDBs (NextDent and HARZ Labs), while the injection-molded (iFlextm) CDBs had the lowest accuracy (p ˂ 0.001).

CONCLUSIONS

The duplication technique of complete dentures using a CAD-CAM milling system produced superior fitting surface accuracy compared to the 3D-printing and injection-molded techniques.

Impact of different chemical denture cleansers on the properties of digitally fabricated denture base resin materials

PURPOSE

To compare the impact of three different chemical denture cleansers (CDCs) (Corega, chlorhexidine, and hydrogen peroxide) on the surface roughness, microhardness, and color stability of 3D-printed, computer-aided design and computer-aided manufacturing (CAD-CAM) milled, and heat-polymerized denture base material (DBM).

MATERIALS AND METHODS

A total of 420 disc-shaped specimens (10 ± 0.1 × 2 ±0.1 mm) were fabricated using three different construction techniques: three-dimensional (3D) printing (n = 140), CAD-CAM milling (n = 140), and heat-polymerization (n = 140). Sixty specimens (20 of each DBM) were used for baseline (pre-immersion) measurements (T1 ) for the tested surface properties (hardness [n = 10/material] and roughness [n = 10/material]). The remaining 360 specimens (n = 120/material) were investigated for surface roughness, microhardness, and color change after immersion for 1 year (T2 ) in distilled water or CDCs (n = 30/solution and n = 10/test). The data were analyzed using two-way ANOVA, one-way ANOVA followed by post-hoc Tukey's test at a significance level of less than 0.05.

RESULTS

Significant differences were observed in the effects of the tested CDCs on the surface roughness, micro-hardness, and color stability of varying DBM specimens (p < 0.05). Corega showed the highest surface roughness and color change in all DBMs while H2 O2 resulted in the lowest microhardness for all DBMs. The lowest changes in all tested properties were seen with distilled water followed by chlorhexidine. A significant effect of type of cleanser, denture base material, and the interaction between the two was seen on all measured properties (p < 0.05).

CONCLUSIONS

The tested CDCs significantly affected the surface properties of all DBMs but at varying degrees. Corega produced the highest negative effect on roughness and color change while H2 O2 dramatically affected the microhardness. Prolonged use of CDCs should be cautiously followed.

Effect of Different Occlusal Tooth Forms of Mandibular Overdenture Retained by an Immediate Loaded Single Implant on the Masticatory Efficiency and Oral Health-Related Quality of Life

Aim

To study the masticatory efficacy and oral health-related quality of life (OHRQoL) of participants wearing a mandibular overdenture retained by an immediate loading single implant with different occlusal tooth forms.

Materials and Methods

For this nonrandomized controlled trial study, 27 edentulous participants were selected and randomly divided into three groups (n = 9) based on occlusal tooth forms of the mandibular implant overdenture (MIOD). Group I: participants received an MIOD with an anatomical tooth form; Group II: participants received an MIOD with a semianatomical tooth form; and Group III: participants received an MIOD with a nonanatomical tooth form. For each participant, a single implant (screw root form) was inserted into the midline of the mandibular ridge to support the MIOD. For each group, the masticatory efficiency was evaluated after 3 months, and the OHRQoL of the participants was evaluated after 3 and 6 months. One-way ANOVA and post hoc Tukey's test were used for data analysis (P < 0.05).

Results

The masticatory efficiency of the anatomic and semianatomic tooth forms was higher than that of the nonanatomic (P < 0.05). Moreover, the improvement in the participants' OHRQoL in the anatomic group was more significant than that of other groups (P < 0.05).

Conclusion

There was a greater improvement in masticatory efficiency and participants' OHRQoL when fitted with an anatomic tooth form mandibular overdenture retained by an immediate loading single implant than with a semianatomic or nonanatomic tooth form.

Elastic, optoelectronic and photocatalytic properties of semiconducting CsNbO3: first principles insights

The cubic phase of CsNbO₃ (CNO) perovskite has been hypothesized to investigate the elastic, electronic, photocatalytic, and optical properties for various technological applications using first-principles method. The pressure dependent structural stability has been confirmed from computed elastic constants. Relatively high value of elastic moduli, large hardness and toughness suggested that CNO would be applicable to design industrial machineries. The ductile to brittle transition is noticed at 20 GPa. The indirect bandgap of CNO proclaims its suitability for photovoltaic and IR photodetector applications. The total and partial density of states are calculated to show in evidence the contribution of individual atomic orbitals in the formation of bands. The pressure changes orbitals hybridization which can be substantiated by the change in the bandgap. Strong covalency of the Nb-O bond and antibonding character of Cs-O have been anticipated by the Mulliken population analysis and by the contour maps of electron charge density. The low carrier effective mass and high mobility carriers predict the good electrical conductivity of the material. The calculated values of conduction and valance band edge potential illustrate the excellent water-splitting and environmental pollutants degradation properties of CNO.

Efficacy of Occlusal Splints and Low-Level Laser Therapy on the Mandibular Range of Motion in Subjects with Temporomandibular Joint Disc Displacement with Reduction

Aims and Objectives

The study was carried out to evaluate the efficacy of four conservative therapeutic modalities on the mandibular range of motion (MRM) in subjects with anterior disc displacement with reduction (ADDwR) of the temporomandibular joint (TMJ).

Materials and Methods

One hundred patients (64 women and 36 men) were selected, and randomly distributed into four groups. Group I: Subjects receiving behavioral therapy (BT). Group II: Subjects receiving low-level laser therapy (LLLT). Group III: Subjects receiving maxillary anterior repositioning splint (MARS). Group IV: Subjects receiving stabilization splint (SS). The MRM was evaluated for each patient before treatment and after 6 months. Paired t test and one-way analysis of variance (ANOVA) tests were used for statistical analysis followed by a post hoc Tukey test (P ≤ 0.05).

Results

All groups showed significant improvement in MRM after 6 months of treatment (P ≤ 0.05) except for BT. There was a significant improvement for SS and MARS on the different movements of MRM, more than for LLLT and BT (P ≤ 0.05).

Conclusion

The MARS and the SS are effective in increasing the MRM for patients with ADDwR.

Evaluation of Surface Properties and Elastic Modulus of CAD-CAM Milled, 3D Printed, and Compression Moulded Denture Base Resins: An In Vitro Study

Objectives

This study evaluated the surface roughness, surface hardness, and elastic modulus of CAD-CAM (Computer-aided design/computer-aided manufacturing) milled, three-dimensional printed and conventional compression-moulded denture base resins.

Materials and Methods

Thirty specimens (65*10*3 mm) were fabricated and divided into 3 groups (10 for each group) according to the type of denture base resin, Group I contained specimens of milled denture base resin, Group II contained specimens of 3-dimensional printed denture base resin, Group III contained specimens of polymethyl methacrylate heat cured denture base resin. The surface roughness of all specimens was evaluated using an atomic force microscope. Then by using the three-point bending test, the elastic modulus of the 30 specimens was evaluated. Finally, after fracturing the specimens from the bending test, the fractured specimens of the 3 groups were used to evaluate hardness using the Vickers hardness test. Data were analyzed using one-way ANOVA and Tukey's pair-wise post hoc tests.

Results

There were significant differences between the tested groups (P< 0.05). The milled denture base resins showed the lowest surface roughness (27.46 ± 5.45 nm) when compared with printed (47 ± 7.01 nm) and conventional (39.72 ± 4.72 nm) denture base resins (P< 0.05); however, there was a significant increase in elastic modulus and hardness of milled (3240.06 ± 61.23 MPa and 29.18 ± 3.44 Vickers hardness number) and conventional (3017.16 ± 215.32 MPa and 22.44 ± 0.98 Vickers hardness number) denture base resins when compared with printed denture (576.65 ± 37.73 MPa and 2.64 ± 0.37 Vickers hardness number) base resins (P< 0.05).

Conclusions

Milled denture base resins showed the lowest surface roughness, and highest hardness and elastic modulus among the three groups.

Comparison of Dimensional Changes Between CAD-CAM Milled Complete Denture Bases and 3D Printed Complete Denture Bases: An In Vitro Study

PURPOSE

This study compared the dimensional changes between the computer-aided design and computer-aided manufacturing (CAD-CAM) milled complete denture bases (CDBs) and three-dimensional (3D) printed CDBs.

MATERIALS AND METHODS

One maxillary completely edentulous stone model was fabricated with three reference points at the incisive papilla, right molar, and left molar areas marked as X, Y, and Z, respectively. It was scanned to produce a standard tessellation language (STL) file, which was imported to a metal milling machine software to produce the metal model. This metal model was used to fabricate 30 CDBs for analysis in this study. The CDBs were divided into three groups (n = 10 each) according to the fabrication method used as follows: Group 1, CAD-CAM milled CDBs; Group 2, 3D printed CDBs; and Group 3, conventional compression molded CDBs. The CDBs of all groups were scanned after fabrication, and the dimensional changes in each were evaluated by two methods. The first was the two-dimensional evaluation method that involved linear measurement of the distances between the reference points (X-Y, X-Z, and Y-Z) of the scanned reference cast and dentures. The second method was the 3D evaluation method that involved the superimposition of the STL files of the dentures on the STL file of the reference cast. Data were calculated and were statistically analyzed using one-way analysis of variance and Tukey's pairwise post hoc tests.

RESULTS

There was a significant difference in the dimensional accuracy between the CAD-CAM milled, 3D printed, and conventional compression molded CDBs (P<0.05).

CONCLUSION

The dimensional accuracy of the CAD-CAM milling system in complete denture fabrication is superior to that of the compression molding and 3D printing systems. This article is protected by copyright. All rights reserved.

Influence of Different Beverages on the Color Stability of Nanocomposite Denture Base Materials

BACKGROUND

The effect of beverages on nanocomposite denture base materials is neglected. Therefore, this study aimed to investigate the influence of different beverages (coffee, tea, cola, and mineral water) on the color stability of nanoparticles-modified denture base materials (DBMs).

MATERIALS AND METHODS

A total of 280 specimens (n = 10/group) were prepared from heat-polymerized acrylic resin modified with different concentrations (3% and 7%) of zirconium dioxide (nano-ZrO2), titanium dioxide (nano-TiO2), and silicon dioxide (nano-SiO2) nanoparticles, while 0% was taken as a control. Color change (∆E) of the specimens was evaluated after simulating 6-month immersion time in four commonly used beverages, coffee, tea, cola, and mineral water, as experimental groups. Color stability was measured using a spectrophotometer, and then values were converted to National Bureau of Standards units (NBS units). The one-way ANOVA test was applied to compare color change (ΔE) results followed by Bonferroni's post hoc test (α = 0.05).

RESULTS

The results showed that the heat-polymerized acrylic resin modified with different types of nanoparticles showed lower color changes after being immersed in beverage solutions compared to the unmodified group (P < 0.001), so the color stability of heat-polymerized acrylic resin was significantly enhanced by the addition of several nanoparticles; nano-ZrO2 showed the lowest ΔE followed by nano-TiO2 and then nano-SiO2. Regardless of the filler type, 3% concentration showed lower mean ΔE than 7% concentration. Regarding the beverage solutions, the greatest color change was found in the coffee group followed by tea and cola, while water showed the least changes.

CONCLUSION

Modification of heat-polymerized acrylic resin with certain amounts of nano-ZrO2, nano-TiO2, and nano-SiO2 may be useful in improving color stability.

Management of Internal Derangement of Temporomandibular Joint Disc Displacement with Reduction Using Two Different Lines of Treatment

Objetive: This study was to compare the effectiveness of arthrocentesis versus the insertion of anterior repositioning splint (ARS) in improving the mandibular range of motion (MRM) for patients with the temporomandibular joint (TMJ) anterior disc displacement with reduction (ADDwR). Methods: 36 patients diagnosed as ADDwR were recruited and divided randomly into two groups. The first group (G1) was treated by arthrocentesis, and the second (G2) was treated using ARS. All patients were reexamined after six months. Results: Except that for protrusive movement, there were significant differences between the two groups for the percentage changes of the MRM as measured by the amount of pain free opening, unassisted opening, maximum assisted opening, right lateral and left lateral movements (p < 0.05). Conclusion: Within the context of the current study, the non-invasive, lower cost ARS, provided better results in improving the MRM when managing ADDwR cases.   Keywords Arthrocentesis; Anterior repositioning splint; TMD; Internal derangement; Anterior disc displacement; Mandibular range of motion.

Comparative study of some mechanical properties of cobalt chromium and polyether ether ketone thermoplastic removable partial denture clasps: an In-vitro Study

Objective: was to evaluate the retentive force, fatigue resistance and deformity of clasps made from two materials cobalt chromium and poly ether et her ketone (PEEK). Material and Methods: sixteen models were fabricated, each one having lower 1st molar. Models were divided into two groups according to materials, group I (GI) for cobalt chromium (Co-Cr) and group II (GII) for PEEK. Each testing models and its clasps were mounted inside universal testing machine, the retention was measured by applying withdrawal force to it by this machine at 5 mm/min. The Fatigue resistance is measured by the reduction in retention through repeated insertion and removal cycles using robot a chewing simulator. Removal and insertion cycling of clasps was carried out for 360, 730, 1080, 1,440,2,116 and 2,880 cycles (corresponding to 3,6,9,12, 18 and 24 months of simulated clinical use of a RPD) to simulate the fatigue resistance test. Deformity was measured before and after each cycling using a digital micrometer. Statistical analysis was done by 2-way-ANOVA test to detect significance effects of each variable. Results: Retention and fatigue resistance, after 360,730, 1080, 1,440,2,116 and 2,880 cycles totally the difference between Co-Cr and PEEK groups was statistically non-significant (P = 0.0980>0.05) where (Co-Cr > PEEK). Deformation results, regardless to evaluation time, Co-Cr group recorded statistically significant higher deformation mean value than PEEK group (P = 0.008<0.05). Regardless to material group, deformation mean value changed non significantly by time (P = 0.2882> 0.05). Conclusion: PEEK clasps (1.0 mm in cross section diameter) engage 0.50 mm undercut provide sufficient retention nearly similar that of Co-Cr clasps.KeywordsFlexible clasps; Polyether ether ketone, PEEK; Thermoplastic resin; Partial denture.

Electric field and aging effects of uniaxial ferroelectrics Sr x Ba1-x Nb2O6 probed by Brillouin scattering

Static and dynamic heterogeneity of disordered system is one of the current topics in materials science. In disordered ferroelectric materials with random fields, dynamic polar nanoregions (PNRs) appear at Burns temperature and freeze into nanodomain state below Curie temperature (T _C). This state is very sensitive to external electric field and aging by which it gradually switches into macrodomain state. However, the role of PNRs in such states below T _C is still a puzzling issue of materials science. Electric field and aging effects of uniaxial ferroelectric Sr _x Ba_1-x Nb₂O₆ (x = 0.40, SBN40) single crystals were studied using Brillouin scattering to clarify the critical nature of PNRs in domain states below T _C. On field heating, a broad anomaly in longitudinal acoustic (LA) velocity at low temperature region was due to an incomplete alignment of nanodomains caused by the interaction between PNRs. A sharp anomaly near T _C was attributed to the complete switching of nanodomain to macrodomain state owing to the lack of interaction among PNRs. After isothermal aging below T _C, the noticeable increase of LA velocity was observed. It was unaffected by cyclic temperature measurements up to T _C, and recovered to initial state outside of a narrow temperature range above and below aging temperature.

Goldenhar syndrome - a case report

Goldenhar syndrome is a developmental abnormality of 1st & 2nd branchial arch involving the craniofacial microsomia with ocular & vertebral abnormality. Though most of the cases are sporadic, some familial association is also found in autosomal dominant or recessive manner. Teratogenic effect of some toxic substances may lead to the condition. Ocular abnormalities are epibulbar dermoid, lipodermoid & coloboma. Otic defects are preauricular tags, microtia, anotia & conductive hearing loss. Cardio-pulmonary & genitourinary abnormalities are common associations. Here we have described the case of a 10 years old girl had ocular, auricular & vertebral changes consistent with Goldenhar syndrome, she was managed with multidisciplinary approach and she was symptomatically improved but corrective surgery was planned as schedule of respective department.

Multifocal skeletal tuberculosis in children

Multifocal bone involvement is though rare but is reported from some countries where tuberculosis is endemic. Here we report a case of three years old boy was admitted in Bangabandhu Sheikh Mujib Medical University, Dhaka with the complaints of difficulty in walking ,low grade fever for six months, swelling over the back, elbow joint, knee joint and upper part of forearm and legs for two months. Family history of tuberculosis was positive. Mantoux test was 18 mm, ESR 85 mm in first hour, chest X-ray reveals right hilar lymphadenopathy, X-ray dorsolumber spine shows wedge shaped deformity in T11, L4 and with paravertebral collection from L2-L4. X-ray of legs, knee joint and forearms show multiple lytic lesions in shaft with periosteal reaction and cortical thickening. Ultrasonograph of whole abdomen shows psoas abscess. Culture of bone marrow aspirate reveals Mycobacterium tuberculosis. Patient was given an anti tubercular regimen with Rifampicin, Isoniazid, Pyrazinamide and Streptomycin for initial two months which to be followed by Rifampicin and Isoniazid for another 10 months.

Ontogeny of human fetal testicular apoptosis during first, second, and third trimesters of pregnancy

During spermatogenesis in human adults, testicular germ cells proliferate, differentiate, and die by apoptosis. However, little is known about the temporal or spatial nature of this programmed cell death. Such information may be useful for understanding prenatal developmental biology as well as spermatogenesis during adulthood, particularly in the context of germ cell disorders. We undertook this study to determine 1) whether apoptosis occurred in a cell-specific fashion in the germ cell population and the supporting somatic cells; and 2) whether apoptosis varied with gestational age. We examined human fetal testicular tissues obtained from 17 karyotypically and structurally normal fetuses of mothers who underwent spontaneous or induced abortions. Three gestational ages were defined as follows: group A, 12-13 wk gestation (n = 5); group B, 20-22 wk gestation (n = 7); and group C, 37-40 wk gestation (n = 5). Morphology in conjunction with in situ end labeling was used to identify and quantify apoptotic nuclei in fetal gonadal tissues. The results of this study suggest that gonadal apoptosis occurred in germ cells, Sertoli cells, and Leydig cells at all gestational ages. Apoptotic death was highest in the Leydig cells, followed by germ cells and Sertoli cells. There was a significant positive correlation between the apoptosis of germ cells and Sertoli cells (P < 0.01) and a negative correlation between healthy germ cells and Sertoli cells (P < 0.001). There was also a negative correlation between the intratubular cell number and the gestational age. Specifically, the proportion of Sertoli cells decreased with gestational age, although there was no significant change in the germ cell in relation to gestational age. No such relationship was found in the Leydig cell population, all of which reside outside the seminiferous tubules. These results are the first to suggest that fetal testicular apoptosis begins in the first trimester, occurs in the three major cell types, and continues throughout pregnancy. Our data also suggest that in the fetal gonad, germ and Sertoli cell proliferation and death may be controlled by a genetic program distinct from that of the Leydig cells. This information is relevant to the understanding of abnormal spermatogenesis associated with infertility and to germ cell tumors in adult life.

Adenocarcinoma in a continent colonic urinary reservoir

We report the first case of an adenocarcinoma developing in a continent ileocolonic urinary reservoir. The tumor presented 7 years after the urinary diversion and more than 6 years after the resection of a Dukes' B lesion of the left colon. This report demonstrates that the colonic segment used for urinary diversion retains its malignant potential and that surveillance pouchoscopy should be performed in these patients.

Tunica vaginalis flap for the management of disabling Peyronie's disease: surgical technique, results, and complications

OBJECTIVES

To discuss the surgical technique for tunica vaginalis flap (TVF) in the management of disabling Peyronie's disease and to evaluate the results and complications.

METHODS

Twelve patients underwent the TVF technique. Through a scrotal incision, the most dependent part of the tunica was dissected from the testicle and epididymis. The flap measured at least 4 cm in width and its upper extremity was left attached to the cremasteric muscle. Subsequently, the flap was brought underneath a groin skin bridge to cover the dorsal penile defect.

RESULTS

All patients were pain free. Seven patients (58.3%) were able to achieve a satisfactory erection with good vaginal penetration. Five patients (41.7%) were unable to perform sexually secondary to disabling chordee in 3 patients, glanular hypoesthesia in 1 patient, and venous leakage in 1 patient.

CONCLUSIONS

TVF is an adequate alternative for correction of distortions of Peyronie's plaque in patients with disabling disease. TVF is at present our first choice in the management of this disease. If penetration is still impaired following recurrent curvature, a Nesbit ventral plication can be used as a secondary procedure.

A trans-reservoir technique for correction of ureterointestinal obstruction in continent urinary diversion

Following construction of a continent colonic urinary reservoir, 5 uretero-colonic reimplantations became obstructed at the anastomotic site. In these obstructed units previous percutaneous balloon dilation and stent placement had failed and they were subsequently treated by a new reimplantation procedure. Preoperatively, in all ureteral units a percutaneous ureteral stent was inserted to facilitate intraoperative recognition of the ureteral meatus. The technique included a trans-reservoir approach, which allowed easy localization of the stent and anastomotic site. The ureter was dissected free from the intestinal wall and then was mobilized into the lumen of the reservoir. After excision of the scarred distal ureteral segment and spatulation of the proximal healthy ureter, a new direct mucosa-to-mucosa reimplantation was performed leaving the ureter stented. This trans-reservoir approach (occasionally done through an abdominal transverse muscle splitting incision) allows for shortening of the operation, and avoids the time-consuming and more complicated transabdominal lysis of adhesions. All newly reimplanted ureters (100%) showed evidence of adequate ureteral drainage without residual obstruction on followup excretory urography or furosemide renography up to 45 months postoperatively. The trans-reservoir approach for refractory ureteral reimplantation obstruction in continent colonic reservoirs has been associated with no morbidity or mortality, and facilitates the solution to a difficult clinical problem.

Derivation of closed-form expression for the cerebral circulation models

Loops which occur due to anastomosing vascular networks, such as the circle of Willis, cannot be analyzed analytically using any of the published mathematical models. This paper presents the theoretical basis of a new model of the cerebral circulation loops which occur due to the circle of Willis. Equations of the model are presented and justified. The transmission line equations obtained from the linearized Navier-Stokes equations and the linearized dynamic deformation equations of the arterial wall are solved analytically to compute the hemodynamic parameters. A comparison of simulation result with experimental data shows that the agreement between experimental and theoretical results is satisfactory and more accurate than the numerical solution.

Hydrodynamic simulation of arterial networks which include compliant and rigid bypass grafts

The conditions required to produce an ideal bypass graft have not yet been determined. In order to understand the hemodynamic impact of bypass grafts on cardiovascular function, a hydrodynamic model for the part of the human arterial network below the renal arteries has been constructed. The results from this physical model were used to validate a digital computer model of the arterial network developed by the authors, that incorporated loops which occur due to bypass grafts. The hydrodynamic model was designed to study the interaction between an arterial stenosis and bypass graft and, in particular, the effect of the compliance of the graft on their function. In the model, similarity laws have been maintained with regard to geometry, viscosity, peripheral resistance, wall elastic properties, pulse shape, and blood flow rate. Measured and predicted pressure and flow wave-forms showed an increase in their mean and peak values for the healthy leg when the bypass graft was closed. There was also a severe pressure drop across the stenosis and a marked decrease in mean and pulsatile flow in the stenotic leg. The stenosis in the hydrodynamic model produced similar behaviour to published results obtained on animals. When the graft was open, the agreement between our experimental and theoretical model was within 5% and both the pressure and flow waves were almost similar at the maxima and minima in both legs. Although the arterial system is non-linear, the non-linearities are shown to be of insignificant magnitude and therefore, we have concluded that the pressure flow relationship is essentially linear. The effect of the degree of compliance of the graft and the 'steal' phenomenon due to the graft have been investigated. It was found that there were no significant differences in the flow delivery between the compliant graft and stiff graft. Also, there was no 'steal'. Thus the compliance of the graft is not a significant factor in promoting its patency.

Urological aspects of hemicorporectomy

The indications for hemicorporectomy are few. However, with improvements in surgical techniques, anaesthesia and post-operative surgical care, hemicorporectomy may again become a reasonable treatment for certain patients with malignancies of the pelvis. A 2-stage procedure is described which consists of an initial staging celiotomy with urinary and faecal diversions. A non-refluxing colon conduit is the preferred form of urinary diversion. The hemicorporectomy is performed approximately 2 weeks later. No complications were encountered in the post-operative period. Our experience and a review of the literature suggest that hemicorporectomy is a reasonable salvage procedure for certain patients with pelvic malignancies.

Haemodynamic model of a unilateral iliac stenosis with an aortoiliac bypass

A hydrodynamic model for the part of the human arterial network below the renal arteries has been constructed using specially fabricated distensible tubes and a pulsatile pump to simulate an aortoiliac bypass. The experiments and the computer model indicated that no 'steal' occurred due to the insertion of the bypass graft. Also, the results showed that the length of the stenosis had a non-systematic apparent effect on the physiological significance of the obstruction and that the kinetic power represented only a small percentage of the total power. The total power efficiency of the bypass graft was unaffected by its elastic properties. The experimental investigation also indicated that the pressure drop across the stenosis was considerably larger than the drop calculated using the Poiseuille flow relationship when the stenosis was severe. Therefore, a critical arterial stenosis value cannot be defined as an obstruction of a constant percentage reduction of luminal area. It varies directly with the effective cross-sectional area and inversely with the flow rate. The value of angiography in assessing the functional significance of any arterial stenosis is therefore limited. A better method for evaluation requires quantitative measurements of local blood pressure and blood flow, not only at rest, but also under conditions creating augmented flows due to exercise.

[Continent urinary diversion with the Florida pouch]

Continent urinary diversion (Florida Pouch) has been performed on 151 patients. The surgical technique utilizes a detubularized extended right colon segment, a doubly-plicated segment of ileum and a non-tunneled uretero-intestinal anastomosis. Mortality rate was 1.3%. Early and late complication rates have been minimal. 2.8% were incontinent. No radiographic renal damage has been noted and electrolyte abnormalities have not been a problem. The procedure is highly recommended to those surgeons performing continent urinary diversions.

Theoretical model for assessing haemodynamics in arterial networks which include bypass grafts

The paper presents a theoretical model which can be used to simulate a vascular network which includes loops and bypass grafts, a feature not possible with previous models. Using the linearised Navier-Stokes equations, the linearised equation of a uniform thick-walled viscoelastic tube, and the equation of continuity, the model is applied to a vascular network which includes a bypass graft. This method represents each segment of an artery or graft by a four-terminal-network whose A, B, C, D parameters are functions of the frequency and physical characteristics of the segment. The model predicts the flow and pressure waveforms at any point in the human arterial network very accurately when compared with data obtained from normal patients, patients with arterial stenoses and for hypertensive patients. The model also gives results which are in close agreement with hydraulic experimental data for the input impedance of systems with bypass loops.