Estimates and relationships between aboveground and belowground resource exchange surface areas in a Sitka spruce managed forest.

Our knowledge of the nature of belowground competition for moisture and nutrients is limited. In this study, we used an earth impedance method to determine the root absorbing area of Sitka spruce (Picea sitchensis (Bong.) Carr.) trees, making measurements in stands of differing density (2-, 4- and 6-m inter-tree spacing). We compared absorbing root area index (RAI(absorbing); based on the impedance measure) with fine root area index (RAI(fine); based on estimates of total surface area of fine roots) and related these results to investment in conductive roots. Root absorbing area was a near-linear function of tree stem diameter at 1.3 m height. At the stand level, RAI(absorbing), which is analogous to and scaled with transpiring leaf area index (maximum stomatal pore area per unit ground area; LAI(transpiring)), increased proportionally with basal area across the three stands. In contrast, RAI(fine) was inversely propotional to basal area. The ratio of RAI(absorbing) to LAI(transpiring) ranged from 7.7 to 17.1, giving an estimate of the relative aboveground versus belowground resource exchange areas. RAI(absorbing) provides a way of characterizing ecosystem functioning as a physiologically meaningful index of belowground absorbing area.

Prevalence of dehiscences and fenestrations in modern American skulls.

BACKGROUND: The purpose of this study was to examine the prevalence, distribution, and features of alveolar dehiscences and fenestrations in modern American skulls and correlate their presence with occlusal attrition, root prominence, and alveolar bone thickness. METHODS: A representative sample of 146 dentate modern American skulls from a collection at the National Museum of Natural History were examined. RESULTS: The skulls were from subjects ranging in age from 17 to 87 years old (mean 49.1 years). The mean number of teeth per skull was 22.7 and the mean number of either dehiscence or fenestration defects per skull was 3.0. Of the 3,315 individual teeth examined, 4.1% (135) had dehiscences and 9.0% (298) had fenestrations. A dehiscence was present in 40.4% of the skulls, and a fenestration was present in 61.6% of skulls. Mandibular canines were most often affected by dehiscences (12.9%), while maxillary first molars were most often affected by fenestrations (37.0%). Sixty-seven percent of dehiscences were found in the mandible, and 58% of fenestrations were found in the maxilla. CONCLUSIONS: The presence of dehiscences and fenestrations were positively correlated with thin alveolar bone and negatively correlated with occlusal attrition. African-American males and Caucasian females were significantly more likely to have dehiscences, while African-American females were significantly more likely to have fenestrations.

Comparison of a controlled injection pressure system with a conventional technique.

OBJECTIVE: The purpose of this study was to compare a device that controls flow rate during injection through use of a foot pedal with a conventional atraumatic syringe injection technique. We determined the change from preinjection to postinjection anxiety, the pain perception, procedure tolerance, and anxiety about future injections. STUDY DESIGN: Dental injection anxiety questionnaires were completed by 80 endodontic patients immediately before and after administration of local anesthetic with the 2 experimental methods. Patients also completed visual analog scales to rate their pain perception during injection, their rating of the overall experience, and their anticipated anxiety about a future dental injection. RESULTS: Patients experienced significantly lower overall postinjection anxiety and pain of injection and had significantly more positive overall experience ratings with the conventional technique than with the controlled-rate procedure. CONCLUSIONS: A conventional atraumatic syringe injection technique was superior to a controlled injection pressure system in pain perception and procedure tolerance and in reducing postinjection dental anxiety.

Comparison of nickel-titanium and stainless-steel spreader penetration and accessory cone fit in curved canals.

The purpose of this study was to compare nickel-titanium and stainless-steel spreader penetration in curved canals. Twenty prepared plastic blocks with a 30 degrees curvature were used for each part of the study. In part 1, the force required to insert each spreader to within 1 mm of working length in an empty canal was measured. In part 2, the force required to insert each spreader to within 3 mm of working length was measured in a canal containing a master cone. In part 3, the depth of penetration of each spreader with a master cone in place using a 1.5 kg force was measured. Additionally, in part 3, the depth of penetration of the first accessory cone was measured. The results from part 1 showed that a nickel-titanium spreader required significantly less force than a stainless-steel spreader (0.30 kg vs. 0.59 kg). In part 2, a nickel-titanium spreader required significantly less force than a stainless-steel spreader (1.56 kg vs. 2.42 kg). In part 3, a nickel-titanium spreader penetrated significantly deeper than a stainless-steel spreader (15.0 mm vs. 14.0 mm). There was no significant difference in the depth of penetration of the first accessory cone used after either spreader (0.8 mm vs. 0.7 mm). Therefore, the potential for vertical root fracture in curved canals during lateral condensation may be minimized by using nickel-titanium spreaders.

Direct digital radiography versus conventional radiography for estimation of canal length in curved canals.

A recent development in direct digital radiography (DDR) has made it possible to make additive multiple point (click) measurements of onscreen images. Canal length was examined using four estimation methods: measurement of a conventional D-speed film radiograph, and onscreen DDR allowing two clicks, six clicks, and an unlimited number of clicks of the measuring device. Thirty extracted human teeth with root curvatures ranging from 7 degrees to 47 degrees (Schneider method) were examined. Actual canal length was measured using a millimeter rule and x 2 magnification. Teeth were mounted and prepared for conventional and DDR imaging. Estimated canal length was determined by three board-certified endodontists using each of the four techniques. A two-way analysis of variance indicated that all radiographic techniques resulted in canal lengths that were significantly different from the true canal length, and there was no significant difference between experimental groups, regardless of the canal curvature.

Comparison of the cleaning efficacy of passive sonic activation and passive ultrasonic activation after hand instrumentation in molar root canals.

The purpose of this study was to compare the cleaning efficacy of passive ultrasonic activation with that of passive sonic activation after hand instrumentation. Sixty curved molar canals were hand-instrumented to size 35 and divided into three groups. Group 1 received no further treatment. Group 2 received 3 min of passive sonic activation. Group 3 received 3 min of passive ultrasonic activation. The roots were split and photomicrographs (x20) were made of the apical 6 mm of canal. A transparent grid was placed over projected images, and the total number of squares covering the apical 6 mm of canal space and the number of squares containing debris were counted. A debris score was calculated for each specimen by dividing the number of squares with debris by the total number of squares. The mean debris scores were 31.6% for hand instrumentation only, 15.1% for the sonic group, and 16.7% for the ultrasonic group. The debris scores for the sonic and ultrasonic activation groups were significantly lower than that for the hand instrumentation only group (p < 0.01); however, there was no significant difference between the sonic and ultrasonic activation groups. Passive sonics after hand instrumentation produces a cleaner canal than hand instrumentation alone and is comparable with that of passive ultrasonics.

Wound healing and repair: a review of the art and science.

This chronological review of the major biological events that occur secondary to injury of mucoperiosteal tissue from either simple surgical wounding or trauma discusses the materials used to repair the compromised tissue surgically. Suturing techniques and post-surgical wound maintenance also are reviewed. The physiological stages of wound healing, factors affecting wound healing, and wound repair techniques are discussed.

Heat generation during ultrasonic instrumentation of dentin as affected by different irrigation methods.

Heat is produced by magnetostrictive ultrasonic scalers which may cause injury to pulpal and periodontal tissues. Water coolant flows around the instrument stack and is directed at the instrument tip to reduce the generation of heat. Sound surgical practice requires the use of a sterile coolant for ultrasonic scaling during surgery. Intermittent bulb irrigation is one way to deliver sterile coolant when using ultrasonic scalers not equipped with a dedicated sterile water reservoir. The purpose of this study was to compare the temperature rise in dentin during ultrasonic scaling using either ultrasonic handpiece irrigation or intermittent bulb irrigation. Twenty dentin/cementum root slabs were prepared for each thickness of 0.5, 1.5, and 2.5 mm. A 3.0 mm x 1.5 mm field was outlined on each slab to indicate the area of intended instrumentation. Each slab was mounted such that a thermocouple placed in contact with dentin opposite the area of instrumentation was shielded from irrigation. Twenty samples of each thickness were ultrasonically scaled during which dentin temperature was recorded every 5 seconds over a 30-second period. All 60 slabs were first treated with dental unit ultrasonic handpiece water irrigation, followed by no irrigation, and finally by bulb irrigation with sterile saline. Repeated measures analysis of variance indicated that there were differences among the three treatment groups for temperature change over the course of the study (P < 0.001). Dentin temperature increased with both decreasing slab thickness and with increasing duration of instrumentation. However, only scaling without irrigation produced a rise in dentin temperature from baseline to a level reported as deleterious to pulpal and periodontal tissues. Bulb syringe irrigation delivered as a continuous drip and ultrasonic unit water spray minimized heat generation to physiologically tolerable levels. Intermittent bulb irrigation appears to be a satisfactory alternative to use of ultrasonic scaler water spray for cooling during ultrasonic scaling at surgery.

Comparison of bioabsorbable laminar bone membrane and non-resorbable ePTFE membrane in mandibular furcations.

The purpose of the study was to compare clinical parameter changes and osseous regeneration in 12 pairs of comparable Class II mandibular molar furcation invasion defects using either a bioabsorbable demineralized laminar bone allograft membrane or a non-resorbable expanded polytetrafluoroethylene (ePTFE) membrane as a barrier in guided tissue regeneration. Measurements with calibrated periodontal probes were made to determine soft tissue recession, probing depth, and attachment levels. Defects within each pair were randomly selected for treatment with either bioabsorbable demineralized bone allograft membrane or ePTFE membrane. All defects were concurrently grafted with particulate demineralized freeze-dried bone allograft (DFDBA). Additional measurements were made at surgery to determine crestal resorption and the vertical and horizontal dimensions of the osseous defects. The temporal course and extent of membrane exposures were also recorded. The non-resorbable membrane was retrieved 6 weeks following placement. Six months following initial surgical treatment, each site was surgically re-entered and all soft and hard tissue measurements repeated. Descriptive statistical analysis revealed that both treatments resulted in significant within-group mean vertical and horizontal osseous fill, but no statistical difference emerged between the groups. As based on this pilot study, laminar bone membrane may be as effective as ePTFE when used in conjunction with DFDBA for treatment of Class II mandibular molar furcation bone defects. This pilot study of low power suggests that these two materials may be equivalent when used in conjunction with DFDBA. Further studies of much higher power and of the laminar bone alone as compared to positive and negative controls are required. Laminar bone does not require a secondary surgical procedure for removal and may undergo less frequent instances and degrees of exposure during healing.

Linear dye penetration of a calcium phosphate cement apical barrier.

Linear dye penetration was evaluated in teeth with open apices in which calcium phosphate cement was used as an apical barrier to facilitate obturation. The apical foramens of 42 extracted single-rooted human teeth were opened to a size 90 file. Half the teeth received apical barriers consisting of calcium phosphate cement (CPC) followed by obturation using a customized gutta-percha cone/ lateral condensation technique. The other half were obturated without benefit of apical barriers. Linear dye penetration was measured after 48 h exposure to India ink. The teeth receiving apical CPC barriers before obturation had significantly less dye penetration than teeth without apical barriers. Based on its proven biocompatibility and osteconductive potential, calcium phosphate cement may serve well as a replacement for calcium hydroxide in a single-visit immediate apical barrier apexification technique.

Comparison of triazolam, diazepam, and placebo as outpatient oral premedication for endodontic patients.

Triazolam and diazepam were compared as oral antianxiety agents in a randomized double-blind, placebo-controlled clinical study of 79 endodontic patients with elevated anxiety regarding endodontic treatment. Patients who scored > or = 10 on the Corah Dental Anxiety Survey received oral formulations of triazolam (0.25 mg), diazepam (5 mg), or placebo. Before, during, and after the endodontic procedure, patients completed psychomotor tests and anxiety scales, and were evaluated for 24-h postoperative recall. In comparison with diazepam and placebo, triazolam was significantly better for decreased anxiety (p < 0.05), impaired cognitive function (p < 0.05), patients' rating of drug effectiveness (p < 0.05), and amnesia to clinical events (p < 0.02) and pictures (p < 0.03). Diazepam showed similar trends compared with placebo, but to a lesser degree. Diazepam also had a much longer recovery period. No adverse effects were noted with either drug. These findings suggest that orally administered triazolam (0.25 mg) is a safe and more effective anxiolytic agent than diazepam (5.0 mg) for endodontic patients.

An in vitro study of furcation perforation repair using calcium phosphate cement.

Furcation perforations created in the pulpal floors of 30 extracted human molars were repaired with either light-cured glass ionomer cement (GI), calcium phosphate cement (CPC), or light-cured glass ionomer cement placed over a CPC matrix (M). After the cement was set, the teeth were immersed in India Ink for 48 h, dried, and sectioned longitudinally. Dye penetration into the furcation repair was independently evaluated by three board-certified endodontists. There was no significant difference in the mean extent of dye leakage among the three experimental groups. The use of CPC, with its enhanced biocompatibility, potential for osteoconduction, and sealing ability, may improve the prognosis of teeth with furcation perforations.

Studies of proliferative responses by long-term-cryopreserved peripheral blood mononuclear cells to bacterial components associated with periodontitis.

Freezing techniques provide a means for repeating and extending immunological assays with frozen aliquots of an individual's peripheral blood mononuclear cell fraction. Lymphocytes which are stored frozen for a limited time retain their ability to respond to polyclonal B-cell activators, mitogens, and antigens of dental interest. Our studies extend these previous findings by determining lymphocyte functional activity following frozen storage for up to 100 weeks. In addition, the autologous immune response was measured by spontaneous lymphocyte proliferation following 0, 1, 40, and 60 weeks of frozen storage. Peak responses for all individuals occurred at day 7 of incubation. The lymphocyte proliferative response to the superantigens toxic shock syndrome toxin-1 (TSST-1) and Staphylococcus enterotoxin A (SEA) were not changed after 100 weeks of frozen storage. Maximum responses varied among the individuals but occurred at equivalent stimulator concentrations. However, slopes generated from data obtained following 0, 4, 13, 20, 30, 50, 88, and 100 weeks of frozen storage showed no significant deviation from zero (P > 0.05) for all individuals tested. After 100 weeks of storage, the total changes in proliferative activity (counts per minute per week) were -2.1% +/- 16.8% and -5.5% +/- 17.0% for TSST-1 and SEA, respectively. The lymphocyte proliferative responses to pokeweed mitogen, concanavalin A, and sonicates of two periodontal pathogens (Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans) following frozen storage were similar to those with TSST-1 and SEA. These results indicate that peripheral blood mononuclear cells stored frozen may serve as appropriate controls to monitor changes in the disease state long-term periodontal treatment.

Gingiva thickness in guided tissue regeneration and associated recession at facial furcation defects.

Consistently successful regenerative therapy for furcation defects using membrane techniques remains a challenge for clinicians. The purpose of this study was to determine if the thickness of tissue used to cover the membrane influences postsurgery recession. Thirty-seven (37) moderate to advanced adult periodontitis patients presenting with at least one mandibular or maxillary molar class 1 or 2 facial furcation involvement participated in the study. Mid-facial presurgery recession was recorded from the cemento-enamel junction to the free gingival margin at a reproducible point. Mid-facial tissue thickness was measured using calipers at a point 5 mm apical to the gingival margin of the mucogingival flap reflected at the time of guided tissue regeneration surgery. Patients were divided into 2 groups based upon tissue thickness measurement. Patients were then re-evaluated for recession at 6 months postsurgery. Sixteen (16) patients with tissue thickness < or = 1 mm demonstrated a mean 2.1 mm increase in recession, while 21 patients with tissue thickness > 1 mm exhibited a mean 0.6 mm increase in recession. We conclude that there is less post-treatment recession (P < 0.01) for tissue thickness > 1 mm than tissue thickness < or = 1 mm. Hence, thickness of gingival tissue covering a membrane appears to be a factor to consider if post-treatment recession is to be minimized or avoided.

Orientation of the lateral roots of trees: II. Hydrotropic and gravitropic responses of lateral roots of Sitka spruce grown in air at different humidities.

Sitka spruce [Picea sitchensis (Bong.) Carr.] plants were grown under controlled conditions in specially designed boxes in which the plagiogravitropic lateral roots grew out from moist peat into an air space at one side. In one treatment the air was saturated with water vapour. In the other a linear horizontal gradient of water vapour pressure was maintained between the vertical peat surface and a porous membrane made from black cloth. Near the peat surface the vapour pressure gradient was equivalent to a soil water-potential gradient of about 0.48 MPa mm-1 . The angles of the roots before and after emergence from the peat were measured in different planes. In the saturated air treatment there was no significant change of angle after emergence but roots which emerged into the air with the humidity gradient grew more slowly and showed a marked change of direction. This deflection had two components; there was some tendency for the roots to be attracted to the moist peat surface (hydrotropism), and there was also a downward component (gravitropism). Mean deviation from the angle of emergence which would have resulted from a hydrotropic response alone was 58°, while deviation from the true gravitropic position was only 31°. Therefore under the conditions of the experiment the gravitropic response was considerably stronger than the hydrotropic one. The implications of these results are discussed for the growth of roots in soils, where water potential gradients generally do not seem to be sufficient to cause hydroptropic curvature. However, there was an enhanced gravitropic response of the tips of lateral roots subject to water stress and this may help control the orientation of roots near the soil surface.

Orientation of the lateral roots of trees: I. Upward growth of surface roots and deflection near the soil surface.

The main lateral roots of some tree species grow close beneath the soil surface, even on irregular or sloping ground. Experiments were carried out to explore the origin and behavior of such surface roots. Pinus contorta Douglas ex Loudon and Picea sitchensis (Bong.) Carr. plants were grown under growth room and glasshouse conditions. Lateral roots were excavated and vertical and horizontal co-ordinates measured. The liminal angles (0°= vertically downwards) of first-order lateral roots of seedlings of both species decreased linearly with depth of origin on the taproot, Some of the roots of highest origin had liminal angles > 90° (ie they grew upwards). However, these roots deflected downwards on approaching the soil surface. If additional soil was added soon after germination the upper lateral roots grew further in an upward direction and then deflected beneath the elevated surface. Two-year-old Picea sitckensis transplants were planted centrally in large containers of soil and an elevated ridge of soil was made 160 mm to one side of the plants. Vigorous upwardly growing roots developed from the damaged and bent root systems that had been produced in the forest nursery. The upwardly oriented roots deflected horizontally when their tips arrived below the flat peat surface, but when they extended beneath the ridge they turned upwards within it. As they approached the top of the ridge they again deflected downwards. It is concluded that the direction of growth of surface roots is the result of two opposing influences. Certain of the main lateral roots are plagiogravitropic and grow obliquely upwards but as these roots approach the soil surface they respond to some signal from the environment that causes downward deflection. The nature of the signal was not determined but it was shown that downward deflection occurred whether or not the soil was exposed to light. The biological importance of this form of surface root orientation is discussed. The growth behavior described enables the main lateral roots to explore the nutrient-rich surface layers of the soil while avoiding the injury to the root tip that would result from exposure.