The effect of dentin pre-treatment and heat-augmented cure on marginal gap formation of a dentin bonding agent

This study evaluated the effect of enhancing the cure of a DBA and the effect of dentin surface pre-treatment on marginal gap formation. Dentin cavities were prepared on extracted teeth and were pre-treated either with EDTA or phosphoric acid. Marginal leakage was expressed as percent length of margins with gaps. The mean percent length of margins with gaps for the chemically cured groups ranged from a maximum of 97% to a minimum of 85%. For the chemical/thermal-cured group, the mean percent length of margins with gaps was 95%, 95%, 73%, 35%, and 65%, corresponding to the following: pretreatment, no pre-treatment, EDTA, and phosphoric acid for 60, 15, or five s, respectively. SEM micrographs showed partial removal of one smear layer with EDTA and total removal of the smear layers with phosphoric acid. It is concluded that dentin pre-treatment methods have an effect on the percent length of margins with gaps when the DBA used had its cure supplemented with heat.

Resin-bonded fixed partial dentures: a recall study

A clinical recall program was initiated at the University of Minnesota to evaluate the longevity and factors affecting longevity of resin-bonded fixed partial dentures (FPDs). Of the 49 resin-bonded FPDs evaluated in the clinic, 43 were acid-etched metal, resin-bonded FPDs, four were combinations of resin-bonded and conventional FPDs, and two were composite resin pontics. None of the combination FPDs and one of the two composite resin pontics were judged as failed at the examination. Of the 43 acid-etched metal resin-bonded FPDs, 15 were found to be debonded (failure rate = 34.9%). The average length of service for the 43 FPDs was 47.3 months. The average time of placement to debondment was 33 months for the 15 debonded FPDs. The failure rate for maxillary FPDs and FPDs with two retainers were significantly lower than the failure rate for mandibular FPDs and FPDs with more than two retainers (p greater than 0.05). The clinical significance of the present study was discussed.

Alternating dissociated nystagmus with palatal myoclonus--a case report

An extraordinary eye movement was seen in a vegetative patient. His eyeballs were exotropic in the primary position and showed dissociated nystagmus which appeared alternately in each eye every few seconds. He also had palatal myoclonus quite asynchronous with the nystagmus. To our knowledge, there has been no such nystagmus documented in the literature. We report the new nystagmus with his EOG and brain MRI.

Effect of dental plaque age and bacterial composition on the pH of artificial fissures in human volunteers

Changes in sucrose-induced plaque pH profiles and the microbial composition of occlusal tooth surface fissures were analyzed using wire telemetry and bacterial culturing techniques. Four human volunteers wore appliances containing artificial fissures constructed with ion-sensitive field-effect transistor (ISFET) electrodes for 1, 2 and 4 days; 1 subject kept the electrode for 3 weeks. After monitoring the plaque pH response at the base of the fissure to a 10% (w/v) sucrose rinse the plaque was removed and analyzed for total viable bacteria, total and specific streptococci, lactobacilli and Actinomyces spp. One-day-old plaque showed a rapid drop in plaque pH to a minimum of 4.8 +/- 0.2, with 2-day-old plaque showing the most acidogenic pH profile (minimum pH 4.6 +/- 0.2). The 4-day-old plaque response was less acidogenic (minimum pH 5.0 +/- 0.3) than the results from days 1 and 2. Responses from 13- and 21-day-old fissure plaques showed greatly decreased acidogenic responses (day 21 minimum pH 5.7). Viable bacteria recovered from the fissure increased from approximately 4 x 10(6) colony-forming units on day 1 to 1.2 x 10(7) on days 2 and 4 and 1.7 x 10(7) on day 21. Streptococci (greater than 50%) and Actinomyces (greater than 10%) dominated in the fissure plaques and their levels were related to minimum pH. Since fissure plaque of all ages tested contained high concentrations of acidogenic bacteria, the decreased acidogenic response at the base of fissures with increasing plaque age suggests that maturing fissure plaques provide an increasingly greater diffusion barrier to fermentable carbohydrates.

Effect of the Coonrad elbow prosthesis on stresses in the humerus

The mechanical stresses that induce implant loosening or failure in the humerus are investigated in this study using the finite element technique. Using a specially developed casting and sectioning technique, the three-dimensional finite element meshes of an intact humerus and a humerus fitted with a Coonrad prosthesis were obtained from a human cadaver elbow. The most detrimental loads were the anteroposterior compression force and axial torque imposed at the joint surface during activities of daily living. The results also indicated that the cancellous bone and cement regions adjoining the hinge and stem-tip of the prosthesis exhibited higher stresses compared to the intact humerus.

Stress distribution in the ulna following a hinged elbow arthroplasty. A finite element analysis

The failure rates for total elbow arthroplasty, in comparison to those for hip arthroplasty, are quite high, and a precise understanding of the underlying causes still remains elusive. The presence of abnormal stresses is a known factor that accelerates loosening of hip and knee arthroplasties. Although a large number of biomechanical studies have led to a better understanding of elbow joint kinetics, very little is known about the stress distribution in this joint. The implantation of a Coonrad humeral component increases stresses in the bone and cement adjacent to the stem tip and hinge regions. An analysis of implanted ulnar stresses and a comparison of those stresses to implanted humeral stresses would improve our understanding of hinged elbow arthroplasty. For this reason, the distribution of mechanical stresses in the ulna are investigated in this study. Using a specially developed casting and sectioning technique, three-dimensional finite element meshes were obtained from an intact human cadaver ulna and an ulna fitted with a Coonrad prosthesis. The material properties were derived from values presented in the literature. Stress distributions in response to axial compression, axial torque, and anteroposterior (AP) force were computed. The cancellous bone and cement regions adjacent to the stem tip of the prosthesis exhibited higher stresses than those in the same regions of the intact case. The higher stresses in the ulna with an implanted prosthesis, as compared to the intact model, might initiate loosening or failure of the prosthesis. The stresses in the cortical bone region adjacent to the prosthesis head were decreased. This is consistent with the clinical observations of bone atrophy following total elbow arthroplasty.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of in vivo human dental plaque pH changes within artificial fissures and at interproximal sites

Ion-sensitive field-effect transistor (ISFET) pH electrodes were used to monitor changes in plaque pH at the base of artificial occlusal surface fissures and at interproximal sites. Bovine enamel was used to construct fissures (1.5 x 0.1 x 1.0 mm) containing a small ISFET electrode. The fissures were fixed to carrier appliances and worn by 4 human volunteers. After plaque accumulation for 4 days changes in pH were monitored by wire telemetry following 1-min rinses with 10% solutions of either sorbitol or sucrose. Results were compared to data obtained from interproximal sites in the same subjects. Responses to sorbitol in the fissure and on the proximal surfaces were minimal and showed no significant difference in minimum pH (5.9 +/- 0.4 and 6.1 +/- 0.3, respectively) and area under pH 7.0. The response to sucrose at the two sites was very different revealing unique pH profiles which were statistically significantly different with regard to minimum pH (5.0 +/- 0.3, fissure and 4.3 +/- 0.2, proximal) and area under pH 5.7. Thus, the acidogenic potential of fermentable carbohydrate at two caries-prone sites in the human dentition is significantly different and conclusions based on interproximal telemetry measurements may not be applicable to occlusal surface fissures.

Effect of chewing gum containing sodium bicarbonate on human interproximal plaque pH

The effect of chewing sorbitol gum containing sodium bicarbonate on interproximal plaque pH was determined by use of an ion-sensitive field-effect transistor (ISFET) electrode system with four human volunteers. Plaque pH was lowered by 2 min of chewing of a sucrose-containing toffee. After 20 min, either sodium bicarbonate or control gum was chewed for 10 min, and the pH was followed for an additional 20 min. The minimum pH after toffee chewing was elevated by both the control gum (4.5 +/- 0.3 to 5.2 +/- 0.5) and the sodium-bicarbonate-containing product (4.3 +/- 0.3 to 6.1 +/- 0.6) to levels which were significantly different (p less than 0.01). The rate of rise in pH was 2.6 times faster with the gum containing buffer compared with the control gum. In comparison with the control gum, the sodium bicarbonate gum caused the pH to remain at a higher level, approximately 0.5 pH units, for 20 min after gum chewing. The addition of sodium bicarbonate to gum containing sorbitol markedly enhanced its capacity to cause and maintain an elevation of interproximal plaque pH previously lowered by exposure to fermentable carbohydrate. Sodium bicarbonate may be useful in products designed to reduce the acidogenic challenge to the teeth following food ingestion.

Comparative study of encainide and quinidine in the treatment of ventricular arrhythmias

The antiarrhythmic efficacy and safety of oral encainide hydrochloride and quinidine sulfate were compared in a nine center double-blind crossover study in 187 outpatients with benign or potentially lethal ventricular arrhythmias. Patients with at least 30 premature ventricular complexes/h were randomized to receive either encainide, 25 mg four times/day, or quinidine, 200 mg four times/day, for 2 weeks. These doses were continued for another 2 weeks if a 75% or greater reduction in premature ventricular complexes was observed. If this reduction was not seen, encainide was increased to 50 mg four times/day or quinidine to 400 mg four times/day for an additional 2 weeks. Both drugs produced a statistically significant reduction in premature ventricular complex frequency compared with baseline values. Encainide produced a statistically significant greater mean reduction in total premature ventricular complexes than did quinidine during the initial dose phase and after dose adjustment. More patients required dose increases of quinidine (60%) than of encainide (51%). Early discontinuation of treatment resulting in advancement to the next study period occurred in 12 patients taking encainide and 38 patients taking quinidine (p less than 0.05). PR and QRS intervals increased significantly during encainide treatment, as did QTc and JT intervals during quinidine treatment. No adverse reactions resulted from these electrocardiographic changes. Adverse reactions were more common with quinidine than with encainide.(ABSTRACT TRUNCATED AT 250 WORDS)