William T. Johnson

Coronal leakage of mixed anaerobic bacteria after obturation and post space preparation

OBJECTIVES The purpose of this study was to assess bacterial leakage of a mixed anaerobic community of organisms in obturated canals after post space preparation. STUDY DESIGN A mixed microbial community of strict anaerobic organisms (F. nucleatum, P. micros and C. rectus) was developed. With the use of an in vitro model system, coronal leakage was assessed in 40 anterior teeth after obturation and post space preparation. The specific leakage time in days for each organism to penetrate through the obturating material was determined. In addition, colonization of the apical canal space was assessed by scanning electron microscope after longitudinal splitting of randomly selected specimens. RESULTS Eighty percent of the teeth demonstrated coronal leakage of F. nucleatum and C. rectus by the 90 day interval. Bacterial penetration occurred from 48 days to 84 days. Scanning electron microscope examination showed a heterogeneous biofilm of coccal and bacillary species colonizing the apical portion of the canal wall. CONCLUSIONS This study demonstrated that coronal leakage phenomena do occur after loss of coronal seals. The model system developed using mixed, anaerobic bacterial cultures is more clinically relevant and may be used to assess bacterial penetration through gutta percha obturation.

Bacterial growth inhibition by amniotic fluid: VI. Evidence for a zinc-peptide antibacterial system

The zinc bacterial inhibitory activity of amniotic fluid is dependent on the presence of a second, organic component contained in amniotic fluid. The second component is heat stable, resists proteolytic digestion, and is present in amniotic fluid throughout pregnancy. Further, the component may be a peptide with a molecular weight of less than 5,000 daltons. Phosphate reversal of amniotic fluid inhibitory activity may result from interference with the organic component rather than zinc.

Examination of external apical root resorption with scanning electron microscopy

UNLABELLED External apical root resorption may be evident histologically but not visible radiographically until it is advanced. If working length is determined without considering this resorption, overinstrumentation or overfilling may occur. OBJECTIVE This study used scanning electron microscopy to examine the appearance and to compare the incidence of external apical root resorption in 40 teeth with differing pulpal and periapical diagnoses. STUDY DESIGN After extraction, 46 roots were sectioned horizontally 6 mm from the anatomic apex and prepared for scanning electron microscopy examination. Photomicrographs were scored by two blinded independent examiners. Apical resorption was categorized as: none, partial, or complete. Presence or absence of a funneling appearance of the resorption was also recorded. RESULTS Kruskal Wallis showed a significant difference in resorption between groups; teeth with irreversible pulpitis/normal periapex had the least resorption. Duncans multiple range test found radiographic apical lesions to have more resorption than those without lesions; teeth with necrotic pulps had more resorption than those with vital pulps. CONCLUSION Pulp necrosis with radiolucent apical pathosis is more likely to demonstrate resorption.

Bacterial growth inhibition by amniotic fluid: V. Phosphate-to-zinc ratio as a predictor of bacterial growth-inhibitory activity

Human amniotic fluid has been shown to contain an inorganic bacterial growth-inhibitory component, zinc. The average zinc concentration in amniotic fluid was 0.44 mug per milliliter. The phosphate concentration of amniotic fluid appears to determine the expression of zinc inhibitory activity. The average phosphate concentration was 92 mug per milliliter. For 22 fluid samples tested, a phosphate-to-zinc ratio of 100 or less predicted a bactericidal fluid. A ratio between 100 and 200 predicted a bacteriostatic fluid. A ratio of greater than 200 predicted a noninhibitory fluid. The possible clinical significance of the ratio is discussed.

Effect of ultrasonic vibration on post removal in extracted human premolar teeth

The purpose of this study was to determine the effectiveness of ultrasonic vibration in removing Paraposts from extracted teeth. Paraposts were cemented in mandibular premolars to a depth of 9 mm with zinc phosphate cement and the teeth placed in four groups. Group 1 received no vibration. Group 2 received vibration for 4 min, group 3 received vibration for 12 min, and group 4 received vibration for 16 min. Tensile forces were applied to the posts and mean dislodgment forces compared. The mean force (kg) required to dislodge the Parapost in group 1 was 24.92 +/- 1.64 SEM; in group 2, 25.01 +/- 1.80; in group 3, 24.08 +/- 2.29; and in group 4, 12.41 +/- 2.60. There was a significant difference between group 4 and groups 1 to 3 (p = 0.0003). Results of this study indicate that 16 min ultrasonic vibration is an effective method for removing Paraposts from human premolar teeth.

Storage-phosphor computed radiography versus film radiography in the detection of pathologic periradicular bone loss in cadavers

OBJECTIVES The purpose of this study was to compare D-speed film, E-speed film, and the Soredex Digora system with respect to the detection of periradicular pathosis. STUDY DESIGN Radiographic images of 100 cadaver jaws were made with E-speed film, D-speed film, and the Soredex Digora. Each set of 100 images was interpreted by four observers, with 30 days separating each of three viewing sessions from the next. The presence or absence of pathologic (inflammatory) periradicular bone resorption was determined by histologic examination of the samples. The observer performance was compared with the true histologic findings and evaluated with receiver operating characteristic and corrected receiver operating characteristic analysis. RESULTS No statistically significant differences were found in diagnostic performance among the three radiographic techniques. In addition, no imaging technique was a good indicator of pathosis as determined by histologic analysis. CONCLUSION Under the conditions of this study, it was determined that D-speed film, E-speed film, and the Soredex Digora were equivalent diagnostic imaging modalities with regard to the detection of pathologic periradicular bone resorption. No technique predictably indicated inflammatory resorption.

Detection of pulpal circulation in vitro by pulse oximetry.

Evaluation of pulse oximetry as a potential method of determining pulp vitality was the subject of this research. An in vitro model of pulpal circulation was fabricated to test the design for a dental pulse oximetry sensor. Blood samples equilibrated with hypoxic gas mixtures were circulated through the model by a peristaltic pump. A pulse was simulated by introduction of gas bubbles into the blood circulation. Pulse oximeter readings for saturation were recorded and compared with blood gas analysis results. Statistical analysis revealed no difference between pulse oximetry and blood gas analysis with a highly significant correlation coefficient. Clinical evaluation of this application is currently in progress.

Evaluation of Dental Pulp Sensibility Tests in a Clinical Setting

INTRODUCTION The goal of this project was to evaluate the performance of dental pulp sensibility testing with Endo Ice (1,1,1,2-tetrafluoroethane) and an electric pulp tester (EPT) and to determine the effect of several variables on the reliability of these tests. METHODS Data were collected from 656 patients seen in the University of Iowa College of Dentistry Endodontic graduate clinic. The results of pulpal sensibility tests, along with the tooth number, age, sex, number of restored surfaces, presence or absence of clinical or radiographic caries, and reported recent use of analgesic medications, were recorded. The presence of vital tissue within the pulp chamber was used to verify the diagnosis. RESULTS The Endo Ice results showed accuracy, 0.904; sensitivity, 0.916; specificity, 0.896; positive predictive value, 0.862; and negative predictive value, 0.937. The EPT results showed accuracy, 0.75; sensitivity, 0.84; specificity, 0.74; positive predictive value, 0.58; and negative predictive value, 0.90. Patients aged 21-50 years exhibited a more accurate response to cold testing (P = .0043). Vital teeth with caries responded more accurately to cold testing (P = .0077). There was no statistically significant difference noted with any other variable examined. CONCLUSION Pulpal sensibility testing with Endo Ice and EPT are accurate and reliable methods of determining pulpal vitality. Patients aged 21-50 exhibited a more accurate response to cold. Sex, tooth type, number of restored surfaces, presence of caries, and recent analgesic use did not significantly alter the results of pulpal sensibility testing in this study.

The application of molecular and immunologic techniques to study the epidemiology of Legionella pneumophila serogroup 1

We applied monoclonal antibody typing and restriction endonuclease analysis of plasmid DNA to study 28 clinical and 35 environmental (potable water) isolates of Legionella pneumophila serogroup 1 from three hospitals in Iowa between 1981 and 1986. Monoclonal antibody typing employed a panel of seven antibodies and delineated eight different subtypes. Plasmids were present in 57% of the isolates including 12 of 28 (43%) clinical and 25 of 35 (69%) potable water isolates. The plasmids ranged in size from 28 to 98 kilobase pairs and comprised eight distinct subtypes by restriction endonuclease analysis with Eco RI. Combination of monoclonal antibody and restriction endonuclease subtyping (composite subtyping) revealed 19 different composite subtypes of Legionella pneumophila serogroup 1. The most common composite subtype, 09:04, comprised 29% (18 of 63) of the isolates and was only found in clinical and potable water samples from a single pavilion in hospital A during an outbreak of Legionella pneumophila serogroup 1 pneumonia. Aside from this cluster the diversity of composite subtypes of Legionella pneumophila serogroup 1 observed in clinical and potable water sources over the 5-year period was striking. The combination of monoclonal antibody and restriction endonuclease typing resulted in improved strain delineation and a more useful use of epidemiologic markers for Legionella pneumophila serogroup 1.

Spectrophotometric analysis of microleakage in the fine curved canals found in the mesial roots of mandibular molars

Mesial roots from forty human mandibular first and second molar teeth were randomly assigned to two groups and obturated with laterally condensed gutta-percha or silver cones. Each group was divided into two subgroups. The first subgroup for each group consisted of specimens that had two canals with a common foramen. The second subgroup consisted of specimens with two canals and separate foramina. All specimens were obturated and exposed to 2 percent methylene blue dye at 37 degrees C. for a period of 30 days. A dye-recovery, spectrophotometric method was used to evaluate the apical microleakage. Results indicated no statistically significant difference in leakage between the groups or subgroups.