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Biomedical subjects

L R Wilcox

Publications and source records attributed to L R Wilcox.

At least 19 recordsLinked to original sources
PubMed1999

Effectiveness of gutta-percha removal with and without the microscope.

The microscope may be useful in retreatment to enhance removal of gutta-percha (GP) and to identify deficiencies in the original treatment. This study compared the effectiveness of GP removal with and without a microscope. Forty-five extracted canines were stepback prepared and obturated with GP and Roth's sealer using lateral condensation. Teeth were stored for 17 months in a humidor, then divided into four groups: group 1 (n = 20)--GP removal without aid of the microscope (group 1 criteria for GP removal was lack of GP on final files and on paper points agitated within the chloroform-filled canal); group 2 (n = 20)--GP removal with the microscope. (In addition to group 1 criteria, canals were inspected with the microscope; additional GP was removed when identified. In both groups, GP was removed using a combination of mechanical instrumentation, chloroform solvent, and K-files); group 3 (n = 3)--positive control, canals remained obturated; and group 4 (n = 2)--negative control, canals were neither prepared nor obturated. Teeth were split longitudinally, photographed, then divided into thirds to compare the apical, middle, and cervical thirds. Remnants of GP and sealer on the canal wall were traced with a digitizer, and the remaining mean % GP was analyzed by t test. Group 1 had 8.3% remaining GP, and group 2 had 7.3% remaining GP. There was no significant difference demonstrated between the two experimental groups.

Device Removal↗
PubMed1997

The relationship of root canal enlargement to finger-spreader induced vertical root fracture.

The purpose of this study was to assess the effect of lateral condensation forces on the development of vertical root fracture (VRF) in teeth that have undergone controlled, measured internal root reduction (i.e. canal preparation). Thirty-four straight-rooted maxillary anterior teeth were used. For each tooth a simulated PDL was fabricated from a uniform 0.15 mm layer of silicone impression material. The teeth were mounted in resin to facilitate removal for observation. They were radiographed and measured at 2, 4, 6, and 8 mm from the apex. They were prepared with the step-back method so that the canal width was 20% of the total root width at 2, 4, 6, and 8 mm from the apex. They were obturated using a fine finger spreader attached to a jig that produced a static force of 3.3 kg for 15 s after placement of each gp point. Obturation was complete when the spreader did not penetrate apical to 8 mm from the apex. Twenty-four h after obturation the teeth were examined by transillumination for VRF. Teeth not exhibiting VRF were tested further after gp removal and canal enlargement of 30%, 40%, and 50% The teeth were sectioned at 2-mm increments with a diamond wafering saw and examined under stereomicroscope. No VRF occurred at 20% or 30%; 5 teeth fractured at 40% and 7 at 50%. These teeth had root surface craze lines that developed during testing. Craze lines had also developed in all 17 of the remaining unfractured samples. No VRF occurred after testing unless craze lines were previously present.

Humans↗
PubMed1996

Lateral condensation of small, curved root canals: comparison of two types of accessory cones.

This study compared the quality of the obturation of small, curved root canals laterally condensed with a medium-fine (MF) finger spreader and one of two types of accessory cones. Thirty small, curved canals of permanent molars were cleaned and shaped, then randomly separated into two groups. They were obturated with a standardized master cone and either MF conventional accessory cones of #25 standardized accessory cones. Cross-sectional outs were made at the 2-mm and the 4-mm apical levels. Digitized tracings were made from photomicrographic slides of the cross-sections to determine the percentage of gutta-percha within the canal areas of each cross-section. Statistical analysis revealed no significant difference between the two groups. Results of this study indicate there is no difference in the quality of obturation when using a MF finger spreader with either MF or #25 accessory cones.

Gutta-Percha↗
PubMed1996

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.

Dental Pulp↗
PubMed1996

Optical detection of hemoglobin in pulpal blood.

An in vitro, flow-through optical system was designed to measure hemoglobin (Hb) concentrations in the pulp space. The system included light-emitting diodes and a silicon photodetector positioned on opposing surfaces of human teeth. A syringe pump allowed a controlled flow of blood through the pulp chamber. The Hb concentration was computed as a nonlinear function of transmitted light intensity. Transmitted light intensities were also used as indicators of oxygenation level. Optical measurements correlated with Hb values measured by the conventional cyanmethemoglobin method (r=0.993). The mean percentage error was 5.8%, and the standard error of prediction was 0.77 g/dl for Hb concentrations ranging from 4 to 20 g/dl. Deoxygenated blood exhibited up to 31% lower transmitted intensity. Light transmission through teeth may be useful in the assessment of total Hb and blood oxygenation within the pulp chamber.

Animals↗
PubMed1996

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. Duncan's 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.

Chi-Square Distribution↗
PubMed1995

Effect of a final alcohol rinse on sealer coverage of obturated root canals.

An endodontic sealer is required to provide an apical and coronal seal in root canals. No previously reported methods of sealer placement completely coated canal walls. The purpose of this study was to dehydrate canal walls with alcohol and determine if this permitted better sealer coverage. Forty single-rooted teeth were prepared and divided into 4 groups of 10 teeth according to method of sealer placement and final irrigant: (a) by lentulo spiral and (b) file NaOCl, (c) lentulo and alcohol, and (d) file and alcohol. After canal preparation, groups 1 and 2 were irrigated with 1 ml of NaOCl and dried with paper points. Groups 3 and 4 were irrigated with 1 ml of alcohol and dried. AH26 (0.04 ml) dyed with charcoal black was applied to the apical end of the file or lentulo and placed in the canal to coat the walls. Gutta-percha without additional sealer was laterally condensed. Teeth were cleared and evaluated for location and amount of sealer visible. Data were evaluated by Kruskal-Wallis and analysis of variance. The results showed (a) no significant differences among the four groups, (b) all areas had sealer present, (c) the coronal third had > 50% sealer coverage in nearly all teeth, and (d) the middle and apical thirds showed the most variability in sealer coverage.

Analysis of Variance↗
PubMed1995

Endodontic retreatment with halothane versus chloroform solvent.

Chloroform has been the most widely used solvent in endodontics, but due to concerns about its safety, alternatives have been sought. The purpose of this study was to compare the effectiveness of gutta-percha removal and time of retreatment between halothane and chloroform used as solvents. Thirty mandibular premolars were prepared, obturated, and stored in a humidor for 14 months, after which they were randomly divided into two groups for retreatment. The teeth were retreated using either halothane or chloroform as the solvent. The time of retreatment was measured to the nearest minute. Retreatment was deemed complete when there was no evidence of gutta-percha or sealer on the files or paper points. Teeth were split longitudinally and photographed. The resulting slides were projected, the canals traced, and the areas of the canal, gutta-percha, and sealer were measured using a sonic digitizer. The results were analyzed statistically by t test. The results showed no significant difference in gutta-percha removal between the two groups. The chloroform group took significantly less time to retreat than halothane (7.7 min. versus 10.8 min, respectively).

Chloroform↗
PubMed1994

Endodontic retreatment of Thermafil versus laterally condensed gutta-percha.

The Thermafil device is becoming a popular obturating material. Because endodontic failures inevitably occur with all techniques, questions of retreatment of Thermafil-obturated teeth will also arise. The purpose of this study was to compare retreatment of Thermafil and laterally condensed gutta-percha. Thirty-five mandibular incisors were prepared with a stepback flare technique and divided into two groups. One group (n = 20) was obturated using Thermafil, the other group (n = 15) was obturated with laterally condensed gutta-percha. The teeth were stored in a humidor for 3 months to allow sealer to set. Retreatment of both groups was accomplished using a combination of heat and chloroform solvent. The time for retreatment was recorded. The teeth were split longitudinally and the amount of gutta-percha remaining in the root canal was measured and analyzed statistically. The results showed that in the coronal one-third of the canal, use of the Thermafil device resulted in significantly more remaining gutta-percha than use of laterally condensed gutta-percha. However, in the apical and middle one-third of the canal the difference in remaining gutta-percha between Thermafil and laterally condensed gutta-percha was not significant. The metal carrier was easily removed and the mean time for retreatment was 6.3 min for Thermafil compared with 5.7 min in the lateral condensation group.

Analysis of Variance↗
PubMed1994

Optical detection of pulpal blood.

An optical system to assess blood within the pulpal cavity was developed. The system included a light-emitting diode source, human incisor teeth, and a silicon photodiode detector. An automated syringe pump was used to flow bovine blood lengthwise through the teeth. Transmitted light intensities were recorded at a collection frequency of 20 reading/min and apparent absorbance units were calculated. The effects of blood concentration, blood flow rate, and pulp chamber size were investigated. It was found that changes in blood flow rate did not cause significant changes in transmitted light intensity. Increases in blood concentration and pulp chamber size resulted in larger absorbance values. These results suggest that photoplethysmography measurements may be sensitive to the amount of blood in the pulp chamber as it reflects the pulsatile-related expansion and contraction of capillaries within the pulp tissue.

Animals↗
PubMed1994

The effect of tooth preparation on retention and microleakage of cemented cast posts.

PURPOSE: Vibration from the high-speed handpiece may adversely affect the cement layer between a casting and a tooth, causing loss of retention or increased microleakage. This study assessed the effect of crown preparation on retention and microleakage of cemented cast post and cores. MATERIALS AND METHODS: Post and cores were fabricated for extracted teeth and cemented. Specimens were prepared for crown restorations, varying the preparation time and the rotary diamond instrument used. After thermocycling and immersion in a dye bath, tensile unseating force and linear dye penetration were measured. RESULTS: In general, retention decreased with increased severity of crown preparation; however, differences were not statistically significant (alpha = .05). Although the differing preparation conditions resulted in significant differences in microleakage, no consistent trends were evident. CONCLUSIONS: Crown preparation using high-speed rotary diamond abrasives of cast post and cores luted with zinc phosphate cement had no significant effect on their retention, but had varying effects on subsequent microleakage at the cement-tooth interface.

Analysis of Variance↗
PubMed1993

Thermafil retreatment with and without chloroform solvent.

A previous study reported that retreatment of Thermafil-obturated canals resulted in significantly more remaining gutta-percha than retreatment of those obturated with laterally condensed gutta-percha. The purpose of this study was to evaluate two retreatment methods in Thermafil-obturated canals. Thirty canals were cleaned and shaped. They were obturated with Thermafil and sealer. One-half were retreated using chloroform to aid in gutta-percha removal (group 1). The others were retreated without chloroform (group 2). The ease or difficulty of removing the metal carrier was assessed during each retreatment. The teeth were split longitudinally; the canal area and remaining gutta-percha area were measured in the coronal, middle, and apical thirds. The results were analyzed by analysis of variance. In each group, seven Thermafil devices were easy to remove and eight were difficult. No significant differences were found in comparing the two groups. However, when the factor of ease of removal was added there were significant differences. Group 2 had significantly less gutta-percha in the apical third (5.9%) when the device was easily removed than when it was hard to remove (54.2%). Group 2 canals were significantly cleaner in the apical third than group 1 canals whether the device was difficult (38.3%) or easy to remove (42.5%). Adequacy of Thermafil retreatment may be related more to the ability to easily remove the carrier than to the technique of gutta-percha removal.

Analysis of Variance↗
PubMed1991

Endodontic retreatment in small and large curved canals.

This study used a special jig system, photography, and a sonic digitizer to evaluate the change in canal size and location after retreatment in 20 teeth with small or large curved canals (greater than 23 degrees). During initial instrumentation, small canals enlarged twice as much as large canals in the coronal and middle areas. During retreatment, small and large canals showed 30 to 85% enlargement compared with that of the initial instrumentation. There was a trend, primarily during retreatment, for small canals to deviate more than large canals away from the original canal location.

Dental Pulp Cavity↗
PubMed1991

Endodontic retreatment in large and small straight canals.

The change in original canal size and location after canal preparation and after reinstrumentation using a step-back technique was studied in small and large canals with less than 20-degree curvature. Teeth were mounted in jigs and then sectioned. The jig permitted the sectioned teeth to be repositioned exactly. Slides were made of the canal in the coronal, middle, and apical at the following intervals: before instrumentation, after instrumentation, and after reinstrumentation. The increase in canal area and the direction of movement was measured. The data were analyzed by ANOVA and Duncan's multiple range test. The results showed: (a) All canal areas increased after retreatment. The retreated apical canal increased in area significantly more (25.4%) than middle (4.0%) or coronal (3.0%) regardless of whether the canal was large or small. (b) The retreated canals tended to move in the same direction they moved after first instrumentation.

Analysis of Variance↗
PubMed1991

In vitro evaluation of four methods of sealer placement.

Sealer is required during root canal obturation, although no studies have shown which method of sealer placement provides the best coverage. This study evaluated and compared four methods of sealer placement: file, lentulo spiral, ultrasonic files, and master gutta-percha cone. Forty mandibular incisors were prepared by a step-back technique. AH26 (0.04 ml) was applied to the placement device, the sealer was placed in the canal, and the canal was obturated with lateral condensation of gutta-percha. The specimens were cleared and evaluated for the presence of the sealer in the apical, middle, and coronal thirds of the canal. The results showed no statistically significant differences among the four groups. The greatest variation in sealer coverage was found in the apical level. Sealer coverage in the coronal and middle thirds was nearly identical regardless of sealer placement technique.

Bismuth↗
PubMed1990

Restoration of endodontically treated anterior teeth: an evaluation of coronal microleakage of glass ionomer and composite resin materials.

A glass ionomer material was evaluated for coronal microleakage in permanent lingual access restorations of endodontically treated anterior teeth. The material was tested as a restoration, placed over a zinc oxide-eugenol base, and as a base with an acid-etched composite resin veneer and a dentinal bonding agent. Restored teeth were thermocycled, immersed in silver nitrate, developed, and sectioned to assess microleakage. Significant coronal leakage was observed with all materials used.

Composite Resins↗
PubMed1989

Molar access: shape and outline according to orifice locations.

This study was designed to relate, in molars, the access outline on the occlusal surface to the canal orifices. The occlusal surfaces of maxillary and mandibular molars were photographed and prints made. The crowns were then sectioned at the level of the pulpal floor to expose the canal orifices. Transparent photographs of the orifices were taken and projected on the occlusal photograph; the orifice locations were marked directly on the print. Orifice location demonstrated a fairly regular pattern relative to the occlusal surface in all four molar groups. The resulting outline scribed from the orifices tended to be centered mesiodistally on the crown of each group and did not extend to the marginal ridges. The results indicate that classic access drawings are too far mesial.

Dental Pulp Cavity↗