The secretory stage of amelogenesis in rat mandibular incisor teeth observed by scanning electron microscopy

In the scanning electron microscope (SEM), the structural organization of rat incisor enamel was divided into five regions: the initial prismless layer at the dentin-enamel junction; the decussating rods of inner enamel; intermediate enamel, where the structure changes from inner to outer enamel; outer enamel with parallel rods; and the surface prismless layer. There were alterations in the orientation of the ameloblasts and characteristic changes in the morphology of the Tomes’ processes during the secretion of each of these regions. Initially, the developing Tomes’ processes were seen within shallow pits which also contained fibrous material from dentin matrix. During the deposition of inner enamel, alternate rows of Tomes’ processes were held at right angles to each other by cytoplasmic projections which originated from the proximal regions of the Tomes’ processes. The cytoplasmic projections reorganized to perpendicular orientation relative to the enamel surface during the synthesis of outer enamel. Tomes’ processes of outer enamel appeared as elongated flaps extending parallel to the long axis of the tooth. In the late secretory stage, the microvillous projections disappeared and the Tomes’ processes were withdrawn into button-shaped structures which coalesced to form a smooth surface that rested on the enamel.     

Pharmacologic Interventions for Alcohol- and Cocaine-Abusing Individuals

Eighteen outpatients dependent on both cocaine and alcohol were randomly assigned to disulfiram or naltrexone in an open pilot study. Disulfiram treatment resulted in significantly fewer days of alcohol and cocaine use, with longer sustained periods of abstinence from both substances.     

Analysis of bone formation after sinus augmentation using β-tricalcium phosphate

Implant placement in the edentulous maxilla often represents a clinical challenge due to insufficient bone height after crestal bone resorption and maxillary sinus pneumatization. Several graft materials have been evaluated for augmenting the maxillary sinus to compensate for the lost vertical dimension. Allografts are readily available without the risk of disease transmission and the need for a second site surgery. The aim of this case series was to systematically evaluate the development and maturation of augmented bone in the maxillary sinus using beta-tricalcium phosphate. In 21 to 40 weeks post-sinus elevation, bone biopsies were taken and implants placed simultaneously. All specimens were demineralized and subjected to staining procedures (ie, Hematoxylin and Eosin [H&E], Goldner's staining, and tartrate-resistant acid phosphatase [TRAP]). Total bone increased over time, whereas the amount of graft material diminished. A lack of inflammatory reaction was noticed with the use of this graft material. In addition, TRAP staining revealed the presence of osteoclasts surrounding the remaining particles. During a 12-month follow-up, no implant failure or complications were observed.     

Buprenorphine for cocaine and opiate dependence.

Buprenorphine, a mixed opioid agonist/antagonist, has been examined not only for the treatment of opioid dependence, but also for concurrent dependence on both opioids and cocaine. Preliminary human studies have suggested that buprenorphine treatment may be associated with significantly less cocaine abuse than is treatment with methadone maintenance. Preclinical studies in both primates and rodents have also indicated that buprenorphine may reduce cocaine self-administration and attenuate place preference for cocaine. Two double-blind, randomized clinical trials comparing buprenorphine with methadone have failed to demonstrate that buprenorphine is superior to methadone in reducing cocaine abuse. However, the trial by Kosten and associates has suggested a larger reduction in cocaine abuse at 6 mg than at 2 mg daily of buprenorphine. This dose dependence is consistent with cocaine challenge studies in which buprenorphine attenuated cocaine effects at 4 mg, but not at 2 mg, daily.     

Alteration of fimbriation and cell hydrophobicity by sublethal concentrations of tetracycline

The effect of growth in the presence of sublethal concentrations of tetracycline on the extent of fimbriation and surface hydrophobicity of strains of Actinomyces viscosus and Bacteroides gingivalis , two species frequently isolated from patients with rapidly progressing periodontitis, was determined. Negatively-stained cells of A. viscosus strains LY7 and S2 and B. gingivalis strain 381 showed a dramatic reduction in the number of fimbriae on their surface when grown in the presence of 50% of the minimum inhibitory concentration of tetracycline as compared to untreated controls. Similar observations were made with fixed, lanthanum-stained thin sections. In addition to long fimbriae, the A. viscosus strains possessed stubby, densely staining tufts on their surface which were not affected by tetracycline. The hydrophobicity of antibiotic-grown A. viscosus and B. gingivalis cells was also found to be significantly reduced. The decrease in fimbriation and surface hydrophobicity of A. viscosus and B. gingivalis when grown in the presence of low concentrations of tetracycline may explain their reduced ability to attach to experimental pellicles. These observations suggest that part of the efficacy of tetracycline therapy for destructive forms of periodontal diseases may be mediated by an alteration of the adhesive properties of subgingival bacteria which affected their colonization.     

Bacteria of asymptomatic periradicular endodontic lesions identified by DNA-DNA hybridization

Abstract – Possible inclusion of contaminant bacteria during surgery has been problematic in studies of periradicular lesions of endodontic origin. Therefore, in this study, two different surgical techniques were compared. A second problem is that some difficult to cultivate species may not be detected using bacteriological methods. Molecular techniques may resolve this problem. DNA-DNA hybridization technology has the additional advantage that DNA is not amplified. The purpose of this investigation was to determine if bacteria from periradicular endodontic lesions could be identified using DNA-DNA hybridization. A full thickness intrasulcular mucoperiosteal (IS) flap ( n =20) or a submarginal (SM) flap ( n =16) was reflected in patients with asymptomatic apical periodontitis. DNA was extracted and incubated with 40 digoxigenin-labeled whole genomic probes. Bacterial DNA was detected in all 36 lesions. Seven probes were negative for all lesions. In patients with sinus tract communication, in teeth lacking intact full coverage crowns, and in patients with a history of trauma, 4–13 probes provided positive signals. Seven probes were positive in lesions obtained by the IS, but not the SM technique. Two probes were in samples obtained with the SM technique, but not the IS. Only Bacteroides forsythus and Actinomyces naeslundii genospecies 2 were present in large numbers using either the IS or the SM technique. The SM flap technique, in combination with DNA-DNA hybridization, appeared to provide excellent data pertaining to periradicular bacteria. These results supported other studies that provide evidence of a bacterial presence and persistence in periradicular lesions.     

Choroid plexus blood flow: evidence for dopaminergic influence

Choroid plexus blood flow was measured in adult female sheep using the radioactive microsphere technique. The response of choroid plexus, renal and cortical blood flow to the infusion of dopamine (11 sheep), haloperidol (7 sheep) and propranolol (6 sheep) were compared. Choroid plexus and renal blood flow significantly increased after dopamine infusion (55% and 49% respectively). Choroid plexus and renal blood flow decreased significantly following haloperidol infusion (−24% and 29% respectively). Cortical blood flow did not significantly change. Propranolol infusion did not significantly change blood flow in these regions. These observations suggest that dopaminergic mechanisms play a role in the regulation of choroid plexus as well as renal blood flow.     

Role of sucrose in colonization of Streptococcus mutans in conventional Sprague-Dawley rats.

The role of sucrose in the colonization of S mutans strain 6715 in conventional Sprague-Dawley rats was studied. A diet with 56% sucrose favored the oral colonization of the test strain compared to diets with 56% glucose or fructose or to laboratory chow as determined by recoveries from extracted teeth ground in tissue grinders. S mutans strain 6715 cells became well established in all rats fed a high sucrose diet with cell inoculums ranging from 10(8) to the lowest effective dose of 10(5) CFU once orally administered; in rats on nonsucrose diets, inoculation with even the highest dose only infrequently resulted in the establishment of S mutans strain 6715. Sucrose- and glucose- grown cells appeared to behave similarly. Colonization of S mutans strain 6715 occurred in all rats fed diets with a sucrose content ranging from 56 to as low as 1%. The establishment of S mutans strain 6715 on the teeth of rats fed diets with a sucrose concentration of 0.1 or 0.01% was impaired and comparable to the diet containing 56% glucose. In rats fed a high glucose diet, uniform establishment and persistence of the test strain occurred after frequent inoculations with about 5 X 10(8) CFU. The colonization under these conditions appeared to be independent of the intestinal canal as a bacterial cell source. These data suggest the possibility that S mutans can establish itself in the human mouth in the absence of dietary sucrose. In rats fed a high glucose diet and inoculated with 10(7) CFU or less, the cells gradually disappeared from the teeth; in contrast, the test strain implanted well in rats fed the sucrose favors firmer attachment of initially weakly attached cells via in situ new glucan synthesis. S mutans strain 6715 also appeared to have some affinity for teeth in the absence of dietary sucrose that may be of ecological significance. Once firmly established in rats fed a high sucrose diet, S mutans strain 6715 maintained itself in high numbers on the teeth after a switch to a high glucose diet during a 14-week period.     

Overexpression of transforming growth factor-β1 in teeth results in detachment of ameloblasts and enamel defects

Transforming growth factor- β 1 (TGF- β 1) is a key regulator of many cellular processes, including cell adhesion, the immune response and synthesis of extracellular matrix proteins. In the present study, we report the characterization of enamel defects in a transgenic mouse model overexpressing TGF- β 1 in odontoblasts and ameloblasts, its expression being driven by the promoter sequences of the dentin sialophosphoprotein gene. As reported earlier, these mice develop distinct dentin defects similar to those seen in human dentin dysplasia and dentinogenesis imperfecta. A further detailed examination of enamel in these mice revealed that from the early secretory stage, ameloblasts began to detach from dentin to form cyst-like structures. A soft X-ray analysis revealed that this cyst-like structure had a disorganized and partially mineralized matrix with an abnormal mineralization pattern and a globular appearance. In the molars, the enamel was not only pitted and hypoplastic, but enamel rods were completely lost. Thus, altered TGF- β 1 expression in the tooth seems to trigger detachment of ameloblasts and abnormal secretion and deposition of minerals in the cyst-like structures adjoining the dentin. We speculate that the altered expression of TGF- β 1 in teeth impacts the adhesion process of ameloblasts to dentin.