The constrictor knot is the best ligature.

INTRODUCTION: An ideal ligature should tighten readily and remain tight. Ligature failure can be a critical complication of invasive procedures in human and veterinary surgical practice. Previous studies have tested various knots but not the constrictor knot. METHODS: A new test bench was employed to compare six ligatures using four suture materials. As tension in a ligature is not readily measured, the study employed a surrogate measurement: the force required to slide a ligature along a rod. Benchmark values tested each suture material wrapped around the rod to establish the ratio between this force and the ligature tension for each material. Each ligature was tested first during tightening and then again afterwards. The benchmark ratios were employed to calculate the tensions to evaluate which ligature and which suture material retained tension best. RESULTS: The model provided consistent linear relationships between the tension in the suture and the force required to pull the ligature along the rod. The constrictor knot retained tension in the ligature best (55-107% better than the next best ligature). Among the suture materials, polydioxanone had the greatest ability to retain the tension in a ligature and polyglactin the least. CONCLUSIONS: The constrictor knot showed superior characteristics for use as a ligature, and should be introduced into teaching and clinical practice for human and veterinary surgery. The new test bench is recommended for future testing of ligatures as well as objective comparison of suture materials.

Human PaCO2 and standard base excess compensation for acid-base imbalance.

OBJECTIVES: Renal and respiratory acid-base regulation systems interact with each other, one compensating (partially) for a primary defect of the other. Most investigators striving to typify compensations for abnormal acid-base balance have reported their findings in terms of arterial pH, PaCO2, and/or HCO3-. However, pH and HCO3- are both altered by both respiratory and metabolic changes. We sought to simplify these relations by expressing them in terms of standard base excess (SBE in mM), which quantifies the metabolic balance and is independent of PaCO2. DESIGN: Meta-analysis. SETTING: Historical synthesis developed via the Internet. PATIENTS: Arterial pH, PaCO2, and/or HCO3- data sets were obtained from 21 published reports of patients considered to have purely acute or chronic metabolic or respiratory acid-base problems. INTERVENTIONS: We used the same data to compute the typical compensatory responses to imbalances of SBE and PaCO2. Relations were expressed as difference (delta) from normal values for PaCO2 (40 torr [5.3 kPa]) and SBE (0 mM). MEASUREMENTS AND MAIN RESULTS: The data of patient compensatory changes conformed to the following equations, as well as to the traditional PaCO2 vs. HCO3- or H+ vs. PaCO2 equations: Metabolic change responding to change in PaCO2: Acute deltaSBE = 0 x deltaPaCO2, hence: SBE = 0, Chronic deltaSBE = 0.4 x deltaPaCO2. Respiratory change responding to change in SBE: Acidosis deltaPaCO2 = 1.0 x deltaSBE, Alkalosis deltaPaCO2 = 0.6 x deltaSBE. CONCLUSION: Data reported by many investigators over the past 35 yrs on typical, expected, or "normal" human compensation for acid-base imbalance may be expressed in terms of the independent variables: PaCO2 (respiratory) and SBE (metabolic).

Prevention of root caries with dentin adhesives.

This in vitro investigation determined the feasibility of using dentin adhesives to protect root surfaces against caries. The roots of 22 recently extracted human teeth were all painted with a protective lacquer leaving two unprotected small windows. On each specimen, one window (control) was left untreated and the other window (experimental) was treated using a dentin adhesive (Scotchbond Multi-Purpose). The roots were then immersed in an in vitro acetate/calcium/phosphate demineralization model at pH 4.3. After 70 days, the samples were removed and sectioned through the windows. The undecalcified ground sections were examined under transmitted and polarized light. Lesions characteristic of natural root caries were seen in the untreated control windows. No such lesions were apparent in the experimental windows. The results of this preliminary study suggest that dentin adhesives may provide protection against root caries.

Improved retention of acid-etched fixed partial dentures: a longitudinal study.

Debonding of acid-etched fixed partial dentures has been a problem since their introduction. A study was conducted to determine whether this problem could be resolved by modifying the mechanical retention of tooth preparations. Retentive grooves were prepared at the line angles to create mechanical locks for the resin bonded fixed partial denture. The 4-year retention of posterior resin-bonded fixed partial dentures improved from 60% to 95% by the placement of the proximal grooves. This study was conducted in a dental school clinic during a period of 10 to 52 months. The results demonstrated that design modifications were necessary to improve clinical longevity so that the restoration could be considered "permanent" in the traditional sense. The less-experienced dentist may be more confident of the treatment with the recommended modifications and projected longevity.

Posterior composite and glass ionomer/composite laminate restorations: 2-year clinical results.

The purpose of this investigation was to evaluate and compare the clinical performance of two posterior composite materials, and two placement techniques, unlaminated and laminated to glass ionomer base. Forty Class II carious lesions were randomly assigned for restoration with one of two composites: Status or Ful-Fil; and using one of two techniques: with and without a glass ionomer base. In the 20 restorations using the laminate technique, the glass ionomer base covered the dentin and extended to the cavosurface in the gingival third of the proximal box. The restorations were evaluated clinically at 24 hours, 6 months, 12 months and 24 months. The clinical parameters used for the examination were: anatomic form, marginal adaptation, color, secondary caries, marginal discoloration and contact. Bitewing radiographs were taken at 24 hours and at 24 months to evaluate gingival margin discrepancy. Impressions of the restorations were made for fabrication of stone dies. Of the 40 restorations, 38 (95%) were available for evaluation at 24 months. For both materials there was a deterioration in anatomic form, in marginal adaptation, and in marginal discoloration. Anatomic form was significantly worse with Status (P less than 0.05). Of the 20 restorations placed using the laminate technique, two had observable loss of the glass ionomer material. Radiographic radiolucencies were observed for both materials and with both techniques. For the laminate technique, all radiolucencies were between the glass ionomer and the composite. The radiographic observations did not change after the initial evaluation. All the restorations were functioning well at 24 months, but longer observation will be required to determine whether there is a clinically significant difference between the two placement techniques.

Informative imaging of multiple parameters for the practice of the anesthesiologist.

The development of informative design principles is necessary to permit logical, informative and understandable computer-aided imaging of the flood of measured parameters the practising anesthesiologist is currently confronted with. The computer-assisted workplace, furthermore, can use the computer to close the loop from sensor to therapy through software directed feed back control mechanisms. The general principles of information design should be based on the rule of three derived from the limited visual integration capacity of the human brain. Thus multiple parameters should be logically grouped in blocks of three strictly distinct from each other in the visual display output. Alarm signalisations have to include two senses: visual and audible and should use the large range of variability that is possible to make them distinct from each other. The operational keyboard should be logically designed with grouping in three parts: 1. a group of buttons for activation of operational screen information that appear with never more than three at the same time; 2. buttons for presetting of wanted parameter values, of alarm limits and for introduction of patient data with adjoint but strictly separated OK-mode necessity to alert that change is being made. 3. a row of buttons separated from the normal operational keyboard area for emergency changes and computer feed back mode bypass, for example. The most illogical, unoverseeable and confusing computeraided workplace can be organized to a fully assisting anesthesia workplace if proper design is applied. The use of a users' manual should be rendered unnecessary even to a computer-naive user. This can be achieved through adequate informative design and operational information flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Dental implants: a survey of patients' attitudes.

This study measured the psychologic attitudes of patients to implant prostheses and compared their status before and after therapy. Questionnaires were mailed to 95 patients with implants placed and restored at a university dental school. The implants had been in position for an average of 2.2 years. The patients had previously worn removable complete or partial dentures. Different questions addressed eating, speaking, relationships, employment, social life, esthetics, maintenance, and overall dental health. Sixty-one questionnaires were returned (64%). Satisfaction with the implant prosthesis was significantly greater than for the denture (p less than 0.0001). Responses to individual questions indicated that confidence was improved (88%), implants were worth the trouble (97%), the procedure would be worth repeating (89%), and overall dental health was improved (98%). This survey suggests that patients' attitudes toward their dental health improve significantly after treatment with implant prostheses.

Bonding glass-ionomer cements to chemomechanically-prepared dentin.

The aim of this investigation was to compare the shear bond strengths of two commercially available glass-ionomer cement base materials to remaining dentin: (1) after conventional caries removal and polyacrylic acid conditioning; (2) after chemomechanical caries removal (Caridex); and (3) after chemomechanical caries removal and polyacrylic acid conditioning. Ninety freshly extracted carious teeth were randomly assigned for caries removal with either the chemomechanical technique (N = 60), or with conventional mechanical drilling (N = 30). Caries removal was continued until the remaining dentin surfaces were judged sound. The remaining dentin in 30 of the teeth prepared with the chemomechanical technique, and in all of the teeth prepared with mechanical drilling, was treated with 10% aqueous polyacrylic acid for 10 seconds. Groups of 15 teeth were assigned for bonding with either Ketac-Bond or Shofu Glasionomer Base Cement. All bonded specimens were stored in a humidor at 37 degrees C for 24 hr. Shear bond strength was tested by means of a mechanical testing machine at a cross-head speed of 0.05 cm/min. Analysis of variance indicated no significant difference (p greater than 0.05) in the mean bond strength among the groups.