Search PubMed⌕ Search

Biomedical subjects

C M Russell

Publications and source records attributed to C M Russell.

At least 19 recordsLinked to original sources
PubMed2000

Water-enhanced crystallization of leucite in dental porcelain.

OBJECTIVE: The purpose of this study was to determine whether long-term exposure of dental porcelain to saliva during temporary cementation of a porcelain-fused-to-metal (PFM) restoration could enhance leucite crystallization if the restoration is refired. Such water-enhanced leucite crystallization in dental porcelains could lead to porcelain-metal thermal incompatibility problems. METHODS: Six commercial dental body porcelains and the Component No. 1 (leucite-containing) frit of the Weinstein et al. [13] patent were studied. For each porcelain, 30 coupon specimens were randomly assigned to a treatment group. Ten specimens were placed in artificial saliva, 10 in distilled water, and 10 in a desiccator and were stored for six months. At the end of the six months, an additional 10 coupons of each porcelain were prepared to serve as a control. All 40 specimens of each porcelain were randomized and subjected to one additional firing. Leucite weight fraction was determined by quantitative X-ray powder diffraction analysis via an internal standard technique. RESULTS: Comparisons among the treatments via the least-squares-means test-adjusting for porcelain showed that the saliva group mean leucite weight fraction was significantly higher than that of the other groups. The change in porcelain thermal expansion that would be associated with a leucite change in this range would be between 0.2 x 10(-6) K-1 and 0.3 x 10(-6) K-1. SIGNIFICANCE: The results of this work constitute the first demonstration that moisture absorbed by a porcelain can act as a glass modifier and enhance the crystallization of the glass during subsequent firing. The effect was sufficiently large to generate thermal expansion changes that would exceed the maximum safe mismatch between porcelain and metal.

Absorption↗
PubMed2000

Permeability of demineralized dentin to HEMA.

OBJECTIVES: The objectives of this study were to develop a macromodel of the demineralized layer of dentin that is formed after acid-etching, and to determine if the amount of HEMA uptake was responsive to air drying. The hypothesis that was tested was that HEMA uptake by demineralized dentin depends upon the degree of expansion of the collagen fibril network. METHODS: Dentin cubes (2 x 2 x 2 mm) were prepared in coronal dentin from extracted unerupted human third molars. They were incubated in 100% HEMA for up to 1000 min and then removed and blotted free of excess adherent HEMA. The HEMA taken up by each cube was extracted in 2 ml of water for 1 hr with shaking. This was repeated and the extracts combined. HEMA was quantitated spectrophometrically. The dentin cubes were then demineralized in 0.5 M EDTA for 10 days and the HEMA uptake remeasured at 1, 10, 100 and 1000 min. Then the cubes were air-dried and the HEMA uptake remeasured. After re-expanding the specimens in water, the cubes were stiffened in ascending concentrations of acetone of 100%, then allowed to air dry again in a more expanded state, and HEMA uptake was remeasured. Finally, after rehydration, the dentin cubes were "acid-etched" for 1 or 10 min with 37 wt% phosphoric acid and HEMA uptake remeasured. RESULTS: Before demineralization, the dentin took up little HEMA (ca. 4.8 x 10(-7) moles min-3) compared to after demineralization when the uptake for 10, 100 and 1000 min was 27.4, 43.8 and 51.4 x 10(-3) moles mm-3, respectively. Acid etching for 1 or 10 min had no effect on HEMA uptake. Air drying produced a 72% volumetric shrinkage but a 97% reduction in uptake. When the demineralized matrix was stiffened in acetone prior to air-drying, the volumetric shrinkage was only 27% and the HEMA uptake only fell 16% compared to the wet, fully expanded condition. SIGNIFICANCE: The results support the hypothesis that the uptake of HEMA by demineralized dentin depends on the degree of expansion of the dentin matrix.

Acid Etching, Dental↗
PubMed2000

Relapse in Angle Class II Division 1 Malocclusion treated by tandem mechanics without extraction of permanent teeth: A retrospective analysis.

Ideal orthodontic treatment should achieve long-term stability of the occlusion. The mandibular incisor segment has been described as the segment that is most likely to exhibit relapse after treatment and retention. Therefore, relapse of this is a challenge that clinicians need to address. The purpose of this study is to evaluate the amount of relapse that may occur in Angle Class II Division 1 patients, treated orthodontically with tandem mechanics. All cases in this study were treated without extraction of permanent teeth, and the patients were followed for at least 2 years after the end of the retention phase of treatment. Six predictors were investigated at pretreatment, posttreatment, and postretention periods. A synopsis of this study shows the correction of lower incisor crowding as measured by the irregularity index was stable over 5.2 years of postretention follow-up; but longer follow-up time revealed increased relapse of incisor irregularity. Intermolar width increased during treatment and remained stable in the follow-up period. Overjet and overbite corrections and changes in the lower incisor to mandibular plane angle were also stable in the follow-up period. In addition, the amounts of overjet correction and loss of expansion of intercanine distance after treatment were associated with increased irregularity index in the follow-up period. It appears the discrepancies between this and previously published works are sufficiently dramatic that the whole question of treatment philosophy and long-term stability may need to be reevaluated.

Cephalometry↗
PubMed2000

H+-induced tension development in demineralized dentin matrix.

Recent atomic force microscopy studies have shown that acid-etching dentin causes the surface to recede. The purpose of this work was to test the hypothesis that acidic solutions can cause contraction of demineralized dentin matrix. Small beams of dentin were cut from extracted human third molars. The central region of each specimen was completely demineralized in EDTA. Specimens held in a tester were immersed in acidic solutions, and the amount of tension was recorded. Test variables included gauge length, cross-sectional area, pre-strain, and pH. The results showed that immersion of demineralized dentin in acidic solutions caused tension that was directly related both to H+ concentration at pH < 2 and to pre-strain. The contractile stress development (ca. 0.2-0.4 MPa) was sufficient to cause a collapse of demineralized dentin matrix. The mechanism for this effect probably involves H+-induced conformation changes in the collagen matrix.

Acid Etching, Dental↗
PubMed1999

Elimination, via high-rate laser dilatometry, of structural relaxation during thermal expansion measurement of dental porcelains.

OBJECTIVES: Thermal expansion measurement of glassy materials is complicated by thermal history effects. Excess volume--trapped in quenched dental porcelains after firing--collapses via structural relaxation on first slow heating during conventional dilatometry, making the thermal expansion coefficient (alpha) obtained on first heating unreliable. The purpose of this study was to determine whether porcelain thermal expansion measurement at high thermal rates could minimize the influence of thermal history. METHODS: Eight thermal expansion specimens each of six body porcelains and the Component No. 1 (leucite-containing) frit prepared according to the patent by Weinstein et al. (US Patent No. 3,052,982) were subjected to three heat-cool conventional dilatometry runs at 3 degrees C/min, while eight thermal expansion specimens of each porcelain were reserved as untreated controls. Eight hollow, cylindrical specimens of the same brands were subjected to three heat-cool laser dilatometer thermal expansion runs at 600 degrees C/min, while eight cylindrical specimens of each porcelain were reserved as untreated controls. Thermal expansion data (25-500 degrees C) of all specimens were subjected to repeated measures analysis of variance. RESULTS: The alpha obtained on first slow heating was significantly lower than values for succeeding slow heat and cool runs in all porcelains (P < 0.001). High-rate alpha obtained on first heating was not significantly different from values of succeeding heat and cool runs in all porcelains (P > 0.05). SIGNIFICANCE: Conventional dilatometer measurements demonstrated occurrence of structural relaxation, as evidenced by the significant difference in the first heating and subsequent runs. High-rate laser dilatometry eliminated structural relaxation, thereby providing a thermal expansion measurement that is free of interference from thermal history effects.

Analysis of Variance↗
PubMed1999

A retrospective study of Angle Class I malocclusions treated orthodontically without extractions using two palatal expansion methods.

The correction and relapse of mandibular anterior crowding was evaluated in a population of 58 patients with Angle Class I malocclusion who were treated orthodontically without extraction of permanent teeth. The subjects were retrospectively evaluated from records taken before treatment, posttreatment, and postretention. The postretention period averaged 8 years (minimum of 4 and maximum of 20 years). All cases in Groups A and B were given orthopedic treatment to develop the maxillary apical base in the transverse and anteroposterior planes. Group A was treated with expansion of the inner bow of the face bow appliance (Kloehn), and Group B was treated with the Haas palatal expansion appliance. Both groups were then treated orthodontically with tandem mechanics. The response variables measured were: overbite, overjet, intercanine distance, intermolar distance, and irregularity index. Study groups A and B were not significantly different for subject age, retention, or postretention time. Moreover, the groups did not show significant difference for any of the response variables before treatment. However, there was a statistically significant difference in the treatment times (P =.0133). A statistically significant treatment effect was observed for most response variables in the groups. Overbite, overjet, and irregularity index were significantly reduced, intermolar distance was significantly increased, and intercanine distance showed no significant change in Groups A and B. In the postretention period, there was a tendency for variables to change slightly toward their before treatment values but no compromise of orthodontic correction was noted. The irregularity index in Group A was corrected from 4.8 to 1.1 mm and remained at 1.1 mm in the postretention period. The irregularity index in Group B was corrected from 5.1 to 1.2 mm (P =.0001) and changed slightly from 1. 2 to 1.7 mm (P =.0540) in the postretention period. We concluded that mandibular incisors tended to become more crowded postretention. However, in contrast to previous reports, we calculate this relapse to be small. Neither before treatment nor posttreatment variables were predictive of relapse.

Adolescent↗
PubMed1999

Width/length ratios of normal clinical crowns of the maxillary anterior dentition in man.

The purpose of this investigation was to analyze the clinical crown of the 3 tooth groups of the maxillary anterior sextant of the permanent dentition of normal subjects with respect to (i) width, length and the width/length ratios and (ii) determine if there is a correlation between tooth dimensions or tooth group ratios and subject height. Subjects (> or = 20 y.o.) were recruited for this study if (i) the free gingival margin on the facial surface of teeth in the maxillary sextant was positioned apical to the cervical bulge, (ii) there was no evidence of attachment loss; as determined by lack of a detectable CEJ and (iii) the marginal tissue was knife edged in form, firm in consistency and coral pink in color. Teeth were excluded if (i) there was evidence of gingival alteration, i.e., gingival overgrowth/hyperplasia, inflammation, altered passive eruption, attachment loss, gingival recession or history of periodontal surgery, or (ii) there was evidence or history of incisal edge/proximal tooth alteration as in, i.e., restorative intervention, traumatic injury or occlusal wear into dentin. At least 1 suitable tooth from each tooth group of the maxillary anterior dentition had to be present. A maxillary impression was taken and poured in yellow die stone. The widest mesial-distal portion and the longest apical-coronal portion of the test teeth were measured. Gender, ethnicity and subject height (SH) were recorded for each participant. Due to a limited ethnic diversity only data from the Caucasian group were analyzed. The mean coronal tooth width (mm) of males versus females was CI: 8.59 versus 8.06, LI: 6.59 versus 6.13 and CA: 7.64 versus 07.15. The mean coronal tooth length (mm) of males versus females was CI: 10.19 versus 9.39, LI: 8.70 versus 7.79 and CA: 10.06 versus 8.89. All width and length measures were significantly greater for males than for females. The mean coronal tooth width/length ratios for males versus females was CI: 0.85 versus 0.86, LI: 0.76 versus 0.79 and CA: 0.77 versus 0.81. A comparison between genders of the width/length ratios of the CI and LI were found not to differ, however the CA ratio for females was significantly greater than for males. A statistically significant difference was found to exist between the mean (cm) SH for males versus females: 181.2 versus 164.0. A positive correlation (p < or = 0.0001 to 0.0691) was found to exist between tooth group width/height ratios within genders. No significant correlation was found between any of the tooth dimensions or tooth group ratios and SH. The results of this study indicate that within male and female Caucasians, the mean width/length ratio of the maxillary 3 anterior tooth groups is 0.81. As well, within both genders there is a positive correlation between tooth group width/length ratios. The significance of these findings with respect to periodontal mucogingival plastic surgical procedures is discussed.

Adult↗
PubMed1999

Assessing dentin color changes from nightguard vital bleaching.

BACKGROUND: At-home bleaching with 10 percent carbamide peroxide in a custom-fitted tray has been reported to change the color of dentin. The purpose of this study was to validate the color change of dentin and to determine whether the color change was uniform or occurred from the outside (the dentinoenamel junction) to the inside (the pulpal wall). METHODS: The authors sectioned 10 extracted human teeth incisogingivally through the midfacial long axis, and sealed their cut surface against glass microscope slides. Identifying marks were placed on the glass over the tooth sections to serve as a color control and in the dentinal areas closest to the dentinoenamel junction and the pulpal wall. Teeth were bleached for 10 days with 10 percent carbamide peroxide. Photographs were taken from the glass-covered side of the teeth, digitized and converted to gray-scale levels (consisting of 256 shades of gray ranging from black to white). Marked areas were measured with a National Institutes of Health Image software program and analyzed statistically for changes in lightness between the control marks and the inner and outer dentinal marks over time. RESULTS: Paired t-tests and analysis of variance indicated a significant increase in lightness (P = .01) for the inner and outer dentinal areas during bleaching compared with the control areas. No significant differences were found in the rate of change for the inner and outer dentinal areas (P = .89). CONCLUSIONS: The increase in lightness confirms that a significant color change occurred in the dentin during bleaching with 10 percent carbamide peroxide. This change occurred throughout the dentin at a uniform rate, rather than from the outside inward. CLINICAL IMPLICATIONS: The results of this study show that at-home bleaching with 10 percent carbamide peroxide can change the color of dentin, which is important to treat intrinsic stains from tetracycline treatment, trauma and aging or inherited discolorations. The bleaching material easily penetrates the tooth to change the dentin color at the same rate throughout, indicating that the type of stain may be the important factor in determining bleaching success.

Absorptiometry, Photon↗
PubMed1999

A comparison of the efficacy of 2 powered toothbrushes in affecting plaque accumulation, gingivitis, and gingival bleeding.

BACKGROUND: The purpose of this 30-day blinded, parallel-design study was to compare the effect of 2 powered toothbrushes, the Rowenta MH700 and the Braun Plak Control Ultra, on reducing plaque accumulation, gingivitis, and gingival bleeding in a cohort of 60 healthy adults. METHODS: After baseline evaluation of plaque, gingivitis, and gingival bleeding, subjects were randomly assigned to one of the experimental groups, provided written and verbal toothbrushing instructions, and had their teeth polished. At 2 weeks (follow-up 1) and 4 weeks (follow-up 2), all clinical parameters were again evaluated. RESULTS: The Braun group demonstrated a nearly significant reduction in gingival index (GI) and a significant reduction in GI at follow-up 2. The Rowenta group demonstrated significant reductions in GI, plaque index (PI), and bleeding index (GBI) at both follow-up 1 and 2 examinations. At follow-up 1, the Braun group demonstrated a nearly significant reduction in GI, a significant reduction in PI, and a non-significant reduction in GBI. At follow-up 2, the Braun group demonstrated a significant reduction in GBI, but not a significant reduction in PI. The reduction in GI for the Rowenta group was significantly greater (P values of 0.0001 and 0.0001, respectively) than that demonstrated in the Braun group. However, the Rowenta group did not demonstrate a significantly greater reduction in PI (P values of 0.7135 and 0.3184 for follow-up 1 and follow-up 2, respectively) or GBI than the Braun group at either examination (P values of 0.0663 and 0.3397 for follow-up 1 and 2, respectively). CONCLUSIONS: The results of this study support the findings of numerous other studies that powered toothbrushes have great potential to remove plaque and improve gingival health and that the improvement can be demonstrated in a relatively short period of time.

Adolescent↗
PubMed1998

Evaluation: methods and strategy for evaluation--California.

In this report, the author documents the many successes in California's history of tobacco control efforts, and the primary role given to evaluation. She provides a comprehensive overview of California's multidimensional evaluation structure and concludes with key lessons gleaned from a decade of evaluation research.

California↗
PubMed1998

A relationship between proteinase activity and clinical parameters in the treatment of periodontal disease.

The objective of this research was to determine the effectiveness of a biochemical assay which measures proteolytic enzyme activity in gingival crevicular fluid (GCF) and to relate this enzyme activity to clinical parameters traditionally utilized for periodontitis detection. A clinical trial was conducted on 8 periodontitis subjects with > or =4 sites exhibiting a loss of attachment of > or =5 mm and probing depths of > or =5 mm with bleeding on probing. On each subject, a plaque index was performed, followed by GCF sampling at those sites which exhibited a loss of attachment and probing depths. GCF was analyzed for activity against benzoyl-L-arginine-p-nitroanilide in the presence (BAPNA w/gly-gly) and the absence (BAPNA w/o gly-gly) of glycyl-glycine and against MeOSuc-Ala-Ala-Pro-Val-pNA and Suc-Ala-Ala-Pro-Phe-pNA for neutrophil serine proteinases activity (elastase and cathepsin G, respectively). Subsequently, a gingival index was performed, attachment levels and probing depths were recorded using a constant force probe with bleeding on probing being noted. A split-mouth design was employed and half mouths were randomly assigned to the following treatment groups: group A, half of the mouth received scaling/root planing and polishing: group B, half of the mouth received no treatment (control). Subjects were treated, then instructed on toothbrushing and interdental cleaning. After 4 weeks, subjects returned to receive a plaque index; GCF sampling, gingival index, attachment levels, probing depths and bleeding on probing as described above. Using a paired Student t-test, the findings suggest that BAPNA w/gly-gly was significantly less in treatment sites than in non-treated control sites (p=0.05). No such correlation was found for other activities, including neutrophil serine proteinases which were shown to occur in GCF in free, proteolytically active forms. In addition, significant treatment effects were detected for probing depths (p= 0.03) which reduced by 1.3 mm and attachment levels (p=0.02) which gained 0.7 mm. The reduction of P. gingivalis from treated periodontitis sites as detected by a significant decrease in BAPNA w/ gly-gly may prove to be a valuable marker for periodontal disease activity.

Benzoylarginine Nitroanilide↗
PubMed1998

HLA-DR alleles are associated with IDDM, but not with impaired neutrophil chemotaxis in IDDM.

Insulin-dependent diabetes mellitus (IDDM) is a risk factor for periodontitis. Depressed neutrophil chemotaxis has been demonstrated in IDDM and in early-onset periodontitis (EOP). HLA-DR antigens are associated with both IDDM and periodontitis. This investigation sought to determine an association of HLA-DR3, -DR4, and -DR53 with impaired neutrophil chemotaxis in an IDDM sample. The neutrophil chemotaxis index of 41 diabetics and 27 controls was determined by a modified Boyden chamber method, and certain class II HLA genotypes were determined by polymerase chain-reaction amplification of genomic DNA by means of sequence-specific primers (PCR-SSP). The mean chemotaxis index of the diabetics was significantly less than that of the controls (p < or = 0.02). HLA-DR3 (p < or = 0.002), -DR4 (p < 0.003), and -DR53 (p < or = 0.001) were associated with IDDM. Neutrophil chemotaxis and glucose metabolism were not significantly correlated. None of the HLA-DR alleles was associated with impaired neutrophil chemotaxis. Therefore, the neutrophil chemotaxis defect of IDDM appears to be independent of these HLA-DR-associated genes.

Adolescent↗
PubMed1997

Effect of treatment concentration on lipopolysaccharide affinity for two alloys.

OBJECTIVE: This study compared gram-negative bacterial lipopolysaccharide (LPS) adherence to and elution from a Type III gold and a Ni-Cr-Be alloy using Escherichia coli LPS. METHOD: One-half of the specimens of each alloy were pre-treated with 500 micrograms non-radiolabeled E. coli LPS for 24 h at 37 degrees C. All disks were then incubated with 0.15, 15 or 150 micrograms radiolabeled E. coli LPS for 24 h at 37 degrees C. To evaluate radiolabeled LPS elution, specimens were transferred to LPS-free water and incubated for 24 h at 37 degrees C. The elution scheme, which consisted of 24 h incubations and subsequent transfer to new LPS-free water, continued for up to 96 h total elution. Radiolabeled LPS adherence and elution was determined through liquid scintillation spectrometry. Control disks not treated with LPS were evaluated throughout the study with an enzymatic assay to ensure that extraneous LPS contamination did not occur. A multifactor ANOVA (p = 0.05) was used to evaluate differences in adherence to alloy specimens based upon alloy type, pretreatment status and [3H]LPS concentration. A repeated measures analysis ANOVA (p = 0.05) was used to evaluate differences in elution patterns among groups over time. Least square means were compared in case of significant effects. RESULTS: Toxin uptake at each treatment concentration was significantly different from the other treatment concentrations. In addition, significantly greater amounts of [3H]LPS eluted from the non-pretreated Ni-Cr-Be alloy following the 0.15 and 15 micrograms radiolabeled [3H]LPS treatment, whereas no difference in elution was found among experimental groups following the 150 micrograms [3H]LPS treatment. SIGNIFICANCE: E. coli LPS, an LPS type representative of enteric bacteria common to the gingival sulcus, has differing affinities for the alloys. This affinity difference could influence periodontal inflammatory processes, thereby resulting in differing tissue responses adjacent to dental restorations fabricated from these materials. The interaction of other LPS types with these alloys could differ.

Adhesiveness↗
PubMed1997

Renal function in the noninsulin-dependent diabetic rat: effects of unilateral nephrectomy.

A new model of noninsulin-dependent diabetic (NIDD) is described which exhibits more prominent defects in renal function than does the standard neonatal NIDD model. To produce this model, 2-day-old neonatal male Wistar Kyoto (WKY) rats were injected intraperitoneally with streptozotocin (90 mg/kg; NIDD), while their corresponding nondiabetic controls were administered vehicle (citrate buffer, pH: 4.5; control). At 3 weeks of age, the animals were weaned, and 1 week later, under ether anesthesia, the animals underwent a right nephrectomy or a sham operation. Diabetes was confirmed by intraperitoneal administration of a glucose load (2g/kg), which resulted in significantly higher blood glucose concentration in the NIDD, compared to the nondiabetic rats. Surgical reduction of renal mass had no effect on the glycemic response to a glucose tolerance test in either group. Intravenous administration of an isotonic saline load resulted in a similar pattern of enhanced sodium and fluid excretion in the two-kidney sham-operated nondiabetic and NIDD rats. These responses were significantly higher than those observed in their counterparts with one remaining kidney. Yet, the natriuretic and diuretic responses to the saline load were significantly lower in the nephrectomized NIDD, compared to the nephrectomized nondiabetic rats. The glomerular filtration rate was similar in the sham-operated (two kidneys) NIDD and nondiabetic rats. In contrast, both the basal and saline-stimulated glomerular filtration rate were lower in the nephrectomized NIDD rats compared to the nephrectomized nondiabetic group. Mean arterial pressure was similar between the two nephrectomized groups, thereby ruling out a significant contribution from the pressure-diuresis-natriuresis mechanism to the reduction in sodium and fluid excretion in the nephrectomized NIDD rats. Thus, unilateral nephrectomy is an effective method of accelerating the manifestation of NIDD-related renal alterations. The mild, but progressive, nature of diabetes in this model should facilitate the investigation of temporal changes in renal function in NIDDM.

Animals↗
PubMed1997

Implant site assessment using panoramic cross-sectional tomographic imaging.

OBJECTIVES: The purpose of this study was to evaluate the ability of two different panoramic imaging systems to produce cross-sectional images with accurate vertical dimensions of the posterior mandible. STUDY DESIGN: Three partially edentulous human cadaver mandibles were used for this study. On each mandible, three potential implant sites were arbitrarily identified in an area between the mental foramen and the ascending ramus. Each site was imaged using two different panoramic machines. Using each image, the mandible's outline, cortical thickness, and position of the mandibular canal were traced on clear acetate film. The mandibles were then sectioned at each site to serve as a gold standard. The cadaver sections and tracings (corrected for magnification) were measured, recording the overall mandibular height, distance from the crest of the ridge to the superior aspect of the mandibular canal, and the thickness of the cortical bone at the most inferior aspect of the mandible. RESULTS: There were no significant differences between either of the system's image measures and the gold standard when considering the distance between the crest and the mandibular canal. Differences were noted between the systems measures and the gold standard in the assessment of the cortical bone thickness and the overall mandibular height. CONCLUSIONS: Both imaging systems can be useful for vertical measurements of a potential implant site in the posterior mandible.

Alveolar Process↗
PubMed1997

Tetracycline demineralization of dentin: the effects of concentration and application time.

The current investigation was initiated to study the effect concentration and application time has on the rate of tetracycline demineralization of dentin. Buccal and lingual surfaces of extracted bovine molars were ground to a smooth flat dentin surface using wetted silicon carbide discs. Standardized depressions were made in the dentin surface with a #909-055 diamond round wheel. Fresh tetracycline HCl (TTC-HCl) (Flavine Int. Inc.) solutions, i.e., 0, 25, 50, 75, 100, 125 and 150 mg/ml were prepared. A 30% citric acid solution was used as a positive control. The pH of each solution was recorded. 7 microl of each solution were pipetted into a depression and remained undisturbed for 1, 3, or 5 min. At the end of each application time period a fresh #3 cotton pellet was placed in the depression, once every 20 s for 1 min, to soak up the solution. The 3 pellets were placed in a 2.00 ml of 18 M omega H2O sample. As a measure of the rate of demineralization, the parts per million calcium (ppm Ca++) found in each sample were determined using atomic absorption spectrophotometry. Two-way analysis of variance was used to determine effects of TTC-HCI concentration and time on the rate of demineralization. No significant differences were found in the mean ppm Ca++ released at 1-, 3- and 5-min application times for 0, 25, or 50 mg/ml TTC. No significant differences were found in the mean ppm Ca++ released (i) between 3- and 5-min application times for 75, 100, 125 and 150 mg/ml TTC-HCl solutions and (ii) between 75, 100, 125 and 150 mg/ml TTC-HCl solutions within either the 3- or 5-min application times. The mean ppm Ca++ released at 3- and 5-min application times for 75, 100, 125 and 150 mg/ml TTC-HCI solutions were all significantly greater than the respective readings at the 1-min application time. The mean ppm Ca++ recorded for the 30% citric acid solution for all 3 application times were 3 to 5.5 x greater than the highest mean ppm Ca++ recording for TTC-HCl. The results of this study show that a 3-min application time of 75 mg/ml TTC-HCl solution is equally as effective at demineralizing dentin as is higher concentrations and/or longer application times, but was far less effective than a 30% citric acid solution.

Animals↗
PubMed1997

Expression of connexin 43 in rat mandibular bone and periodontal ligament (PDL) cells during experimental tooth movement.

Bone remodeling in response to force requires the coordinated action of osteoblasts, osteoclasts, osteocytes, and periodontal ligament cells. Coordination among these cells may be mediated, in part, by cell-to-cell communication via gap junctions. This study tests the hypothesis that the regulation of expression of connexin 43, a gap junction protein, is part of the transduction mechanism between force as applied to bone during orthodontic tooth movement and bone remodeling. To test this hypothesis, we examined connexin 433 expression in a rat model system of experimental tooth movement. To establish the model, we extracted maxillary first molars to initiate supra-eruption of opposing mandibular molars. The rats were killed at 0, 6, 12, 24, and 48 hrs post-extraction. The mandibles were removed, demineralized, and embedded in paraffin. To localize connexin 43 protein and mRNA, we used a specific antibody for immunohistochemistry and a specific cDNA probe for in situ hybridization. Western and Northern blot analyses were used to assess the specificity of the connexin 43 antibody and cDNA probe, respectively. We found connexin 43 protein expressed by osteoclasts (++ ++) and periodontal ligament cells (++ +) in compression zones, and by osteoblasts (++ ++) and osteocytes (++ ++) in tension zones of the periodontal ligament. In addition, connexin 43 mRNA was found in some bone and periodontal ligament cells. Connexin 43 protein was found, by densitometric analysis, to be higher in the periodontal ligament after exposure to force compared with controls (P < 0.001). The number of osteocytes expressing connexin 43 48 hrs after molar extraction was also significantly greater in bone subjected to tension when compared with controls (P < 0.001). The results of this study support the hypothesis that connexin 43 plays a role in the coordination of events during experimentally induced alveolar bone remodeling.

Animals↗