Influence of contact configuration and lubricating conditions on the microtriboactivity of the zirconia-Ti6Al4V pair used in dental applications.

Loosening and fracture of implanted dental crowns is a consequence of relative micromovements between the zirconia abutment and the titanium alloy of the implant, in a biochemical aggressive environment. Thus, it is important to establish the in vitro tribological testing conditions that better mimics such environment. The present work aims to evaluate the effect of ball-on-plate tests configuration on the tribological behavior of ZrO2/Ti6Al4V pair in dry and lubricated conditions, using different lubricants: water, artificial saliva solution and human saliva. Ceramic balls sliding on metallic plates (TiPlate) and metallic balls sliding on ceramic plates (TiBall) were tested and the coefficient of friction (CoF) and wear response was monitored trough nanotribological tests. Open circuit potential was also measured during the tests carried out in saline solution (artificial saliva) to access the tribochemical response. The wear mechanisms were evaluated by scanning electron microscopy and atomic force microscopy analysis. Relevant differences were found between the two configurations, with and without the presence of human saliva: TiPlate presented always a higher CoF than TiBall, which may have resulted from differences in the degradation and regeneration processes of the titanium passive film during sliding. TiBall demonstrated to be the best choice to reproduce the in vivo conditions, since the metallic surface contacts permanently with zirconia, impairing the titanium repassivation. Regarding the effect of the lubricants, it was observed that human saliva had a protective action of the surfaces, leading to the lowest CoF among the lubricants used (0.19 ±â€¯0.05 for TiBall and 0.35 ±â€¯0.08 for TiPlate) and neglectable wear.

Semi-open hemorrhoidectomy.

The concept that hemorrhoidal disease is a consequence of disorders of the cephalic portion of the anal canal, i.e. weakness of the vascular cushions and the connective tissue, is the basis for modifying the usual surgical technique in many aspects. The two main differences of the method described are: (i) the internal plexus is treated by parceled ligature, avoiding resection of the mucosa, but providing a firm fixation of the submucosa and subsequent fixation of the anal epithelium to the underlying sphincter in the anal canal; (ii) the external plexus is removed preserving as much as possible the anal margin skin, and the resulting wound is partially closed, resulting in a small drainage area; and (iii) a firm fixation of the submucosa and subsequent fixation of the anal epithelium to the underlying sphincter are achieved without mucosa resection.

Laparoscopic total mesorectum excision.

The main controversy of colon-rectal laparoscopic surgery comes from its use as a cancer treatment. Two points deserve special attention: the incidence of port-site tumor implantation and the possibility of performing radical cancer surgery, such as total mesorectum excision. Once these points are addressed, the laparoscopic approach will be used routinely to treat rectal cancer. To clarify these points, 32 patients with cancer of the lower rectum participated in a special protocol that included preoperative radiotherapy and laparoscopic total mesorectum excision. All data were recorded. At the same time, all data recorded from the experience of a multicenter laparoscopic group (Brazilian Colorectal Laparoscopic Surgeons - 130 patients with tumor of the lower rectum) were analyzed and compared with the data provided by our patients. Analysis of the results suggests that a laparoscopic approach allows the same effective resection as that of conventional surgery and that preoperative irradiation does not influence the incidence of intraoperative complications. The extent of lymph nodal excision is similar to that obtained with open surgery, with an average of 12.3 lymph nodes dissected per specimen. The rate of local recurrence was 3.12%. No port site implantation of tumor was noted in this series of patients with cancer of the lower rectum.

Pre-operative radiotherapy in rectal cancer: evaluation of irradiation effects on cellular undifferentiation and its influence on prognosis.

BACKGROUND/AIMS: In spite of the new technology--stapler, antibiotics, anesthesia and new surgical and diagnostic procedures--the prognosis on treatment of cancer of the rectum has not changed in the last 50 years. Survival rates of 50-55% seems immutable in all published series. The main course for those results is the high incidence of recurrence, either local or widespread. Local recurrence is directly related to the number of undifferentiated cells and to the grade of wall invasion. So any kind of treatment that would diminish the number of undifferentiated cells and the size or the tumor wall penetration certainly would decrease the local recurrence rate, lengthening the interval free from cancer and, perhaps, modifying the long-term survival rate. Between 1978-1996, a total of 287 patients with rectal adenocarcinoma were treated by pre-operative RTD. METHODOLOGY: The same RDT protocol was used in all the patients: 400 cGy, 200 cGy/day, during 4 consecutive weeks (anterior and posterior pelvic fields). Surgery was performed 7-10 days after completion of RDT. RESULTS: Statistical analysis of the whole group showed that pre-operative RDT does decrease frequency of undifferentiated cells. Moreover, the incidence of local recurrence diminished after irradiation by 3.48%. Pre-operative RDT reduces tumor volume and wall invasion, as well as the mortality rate due to local recurrence (2.43%) and alters long-term survival rate (80.17%). CONCLUSIONS: Pre-operative radiotherapy is really effective in reducing the number of undifferentiated cells and in diminishing the carcinomatous infiltration of the rectal wall.

A comparison of nonoperative vs. preoperative radiotherapy in rectal carcinoma. A 10-year randomized trial.

From 1978 to 1980, 68 patients with rectal cancer were randomly allocated to either preoperative irradiation plus surgery or surgical treatment without any preoperative measures. The primary aim of the trial was to investigate the 5-year survival rate in both groups; a secondary aim was to analyze the local recurrence rate and finally the anatomopathologic tumoral classification after surgery. All patients were followed at least 8 years. The preoperative irradiation group (Group A) was submitted to 4000 cGy for 4 weeks and surgery was performed 1 week after irradiation. All tumors were classified anatomically and pathologically according to Broders' and Dukes' classifications. The results indicated that there is a significant difference in the five-year survival rates in both groups: group A had a corrected survival rate of 80 percent; group B (nonirradiated) had a corrected survival rate of 80 percent; group B (nonirradiated) had a corrected survival rate of 34.4 percent. The local recurrence rate was 2.9 percent in group A and 23.5 percent in group B. Regarding tumor regression, before radiotherapy 64.6 percent of the tumors were Broders' Grades 3 and 4; after radiotherapy these were reduced to 20.5 percent. As to Dukes' classification, 26.4 percent of the tumors were type C in group A and, in group B, 47 percent were considered as Dukes' C.