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INTRODUCTION: The available studies on extraction wound repair in humans are affected by significant limitations and have failed to evaluate tissue alterations occurring in all compartments of the hard tissue defect. AIM: To monitor during a 6-month period the healing of human extraction sockets and include a semi-quantitative analysis of tissues and cell populations involved in various stages of the processes of modeling/remodeling. MATERIAL AND METHODS: Twenty-seven biopsies, representative of the early (2-4 weeks, n=10), intermediate (6-8 weeks, n=6), and late phase (12-24 weeks, n=11) of healing, were collected and analysed. RESULTS: Granulation tissue that was present in comparatively large amounts in the early healing phase of socket healing, was in the interval between the early and intermediate observation phase replaced with provisional matrix and woven bone. The density of vascular structures and macrophages slowly decreased from 2 to 4 weeks over time. The presence of osteoblasts peaked at 6-8 weeks and remained almost stable thereafter; a small number of osteoclasts were present in a few specimens at each observation interval. CONCLUSIONS: The present findings demonstrated that great variability exists in man with respect to hard tissue formation within extraction sockets. Thus, whereas a provisional connective tissue consistently forms within the first weeks of healing, the interval during which mineralized bone is laid down is much less predictable. [ABSTRACT FROM AUTHOR]

The present investigation was performed in order to study the reaction of the gingiva in the deciduous and permanent dentition of dogs to 3 weeks of plaque accumulation. The study was carried out in 10 beagles, divided into 2 groups of 5 dogs each; group I and group II. When the dogs of group I were 10 weeks old, a meticulous plaque control regimen was initiated in order to establish clinically healthy gingiva. After 6 weeks of plaque control, the gingivae of the lower deciduous molars was exposed to a clinical examination, and biopsies as well as bacterial plaque samples were harvested from tooth 03P and 02P. A second plaque control regimen was initiated when the same dogs were 15 months old. After 6 weeks of plaque control, the gingiva of the permanent dentition was examined and biopsies sampled from tooth P3 and P4. In the dogs of group II, plaque control regimens of 3 weeks duration were initiated when the animals were 10 weeks and 15 months old. Clinical examinations were performed at the end of each 3-week period. Immediately after the clinical examinations. 3-week periods of plaque accumulation were initiated. Examinations and plaque sampling were performed after each of these 3-week periods and biopsies were sampled from the deciduous and permanent dentition as described for group I. The biopsies were processed for histometric and morphometric measurements. The findings from the experiment showed that careful plaque control resulted in the establishment of clinically healthy gingiva. In both the deciduous and permanent dentition, however, a clinically healthy gingiva was found to contain a small inflammatory cell infiltrate (ICT). 3 weeks of plaque accumulation resulted in both dentitions in the development of clinical signs of gingivitis and in the formation of comparatively large ICT. The large ICT of the permanent gingiva resided in the coronal portion of the free gingival unit, while in the deciduous dentition, the inflammatory lesion occupied a narrow tissue portion along the entire border of the dento-gingival epithelium. The ICT of the permanent gingiva harbored a larger portion of plasma cells than the inflammatory lesion studied in the deciduous dentition. [ABSTRACT FROM AUTHOR]

The aim of the present investigation was to study the validity of 2 different methods of sampling the subgingival microbiota. The composition of the flora was estimated using the dark-field microscope. Subgingival samples were obtained using either a curette or a Hamilton microsyringe for a subgingival washing. The method of determination of the composition of the subgingival microorganisms was found to be very reproducible when the same investigator performed the counting. Samples obtained by the washing technique had a slight but significantly higher proportion of coccoid cells when compared to samples obtained by curette. The calculation of the reproducibility of the washing technique as assessed in 6 immediately repeated samples from the same sites yielded a coefficient of variation of 40% for spirochetes and motile rods. When 9 repeated samples from each of 28 sites (14 with a curette, 14 with washing) were studied over a period of 32 days, no systemic alterations were observed in the % of spirochetes and motile rods. The variation within each individual site was high. For curette samples and washing samples, the coefficients of variation for spirochetes and motile rods were 85% and 63%, respectively. The present investigation clearly demonstrated that care should be taken in the interpretation of single samples of subgingival microbiota. A more relevant picture of the actual situation is achieved when trends of repeated samples over time are studied. [ABSTRACT FROM AUTHOR]

The present investigation was performed to study the effect of long-term, low dosage tetracycline Therapy on advanced periodontal disease in humans. 14 volunteers participated in the trial. Each of the participants had at least 4 pairs of diseased sites around contralateral premolars and incisors with deep pockets and advanced bone loss. The trial extended over a 50-week period and was designed as a double-blind split-mouth study. A Baseline examination included assessments of oral hygiene, gingival conditions, probing depth, attachment level and analysis of the composition of the subgingival microbiota in samples obtained from 8 selected diseased sites. All participants received oral hygiene instruction. In each patient 2 quadrants of the mouth, chosen at random, were treated by scaling and root planing. The 2 remaining quadrants were left unsealed. Following the Baseline examination the patients were randomly distributed into 2 groups of 7 members each. in one of the groups the patients received tetracycline on a daily basis during a 50-week period. The participants of the control group received placebo. Reexaminations were performed 2, 10, 20, 30 and 50 weeks after the Baseline examination. The findings demonstrated that in patients with advanced periodontal disease long-term tetracycline therapy in the absence of scaling resulted in the establishment of a subgingival microbiota almost devoid of motile bacteria and in markedly reduced signs of gingivitis, probing depth and attachment loss. ln fact, the alterations observed as a result of tetracycline administration to patients with excellent self-performed plaque control were similar to those obtained by conventional scaling and root planing in the control group. [ABSTRACT FROM AUTHOR]

The microflora of periodontal pockets and some histopathological characteristics of adjacent tissues from individuals with clinical signs of juvenile periodontitis were studied. Adult individuals with ordinary, rapidly advancing periodontitis served as controls. All of the patients had been referred for specialist treatment. Using criteria defined by Baer (1971), the patients were assigned to one juvenile periodontitis (eight patients), one post-juvenile periodontitis (seven patients) and one adult periodontitis group (seven patients). Only lesions around the first molars and central incisors were studied. Bacterial samples were obtained from each site and were examined by darkfield microscopy and different morphological forms identified. The soft tissue of the diseased sites was excised. The biopsies were placed in a fixative, cut in 1-mm-thick blocks and embedded in Epon. In semithin sections the infiltrated connective tissue (ICT) was identified and the ICT portion further processed for electron microscopy. The numeric and volumetric densities of different cells and structures of the ICT were determined using a morphometric point-counting procedure. The results showed that juvenile periodontitis lesions are associated with a subgingival microflora, the composition of which is different from that of adult periodontitis. Thus, in patients belonging to the adult periodontitis and post-juvenile periodontitis groups, motile microorganisms dominated the subgingival plaque samples, whereas deep pockets in juvenile periodontitis lesions contained a flora dominated by coccoid cells and straight non-motile rods. The most pronounced difference in the composition of ICT between the juvenile on one hand and the post-juvenile and adult periodontitis lesions on the other, was related to the amount of extracellular structures. Thus, in post-juvenile and adult periodontitis lesions, collagen and residual tissue made up around 50 % of the infiltrate. In the juvenile periodontitis lesions, however, extracellular structures occupied only around 20 % of the volume. In the ICT of the juvenile periodontitis sites, around 70 % of the volume was occupied by plasma cells and blast cells. The corresponding figures for the post-juvenile and adult periodontits sites were 50 and 30 %. [ABSTRACT FROM AUTHOR]

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The effects of 25 mg propiomazine were examined in ten healthy volunteers in a sleep laboratory setting. A significant decrease in sleep latency and a corresponding decrement in subjectively assessed sleep latency was found during drug treatment. The distribution of the different sleep stages was affected to a relatively small extent. Some evidence for a suppression of REM-sleep in the early part of the treatment period was found. Based on subjective assessment, the subjects rated their sleep quality as significantly improved during treatment. Ratings of 'drowsiness in the morning' were not different during baseline and drug treatment, but there was a significant decrease at withdrawal. [ABSTRACT FROM AUTHOR]

Objective: The aim was to examine the tissue composition of extraction sockets that had been grafted with deproteinized bovine bone mineral and allowed to heal for 6 months., Material and Methods: Twenty-five subjects with one tooth each scheduled for extraction and replacement with dental implants were recruited. The assigned teeth were carefully removed. The site/patient was thereafter allocated to a test or a control group. In the test group patients, Bio-Oss(®) Collagen was placed to fill the fresh extraction socket while in the controls no grafting was performed. After about 6 months of healing, a biopsy was sampled from the center of the extraction site. The specimens were decalcified, embedded in paraffin, sectioned, and stained in HTX. The proportions occupied by mineralized bone, osteoid, bone marrow, fibrous tissue, and Bio-Oss(®) particles were determined by morphometric point counting., Results: Mineralized bone made up 57.4 ± 12.4% of the control sites (C) and 48.9 ± 8.5% of the T1 sites (graft material not included). The amount of bone marrow (C: 7.1 ± 6.1%, T1: 2.1 ± 3.1%) and osteoid (C: 7.3 ± 4.9%, T1: 1.9 ± 2.1%) was about five times greater in the control than in the test sites. Fibrous tissue comprised 23.1 ± 16.3% (C) and 40.0 ± 11.9% (T1). I n the T2 sites (graft material included), the percentage mineralized bone was 39.9 ± 8.6 while the proportions of bone marrow and osteoid were 1.8 ± 2.5% and 1.6 ± 1.8%. Fibrous tissue occupied 32.4 ± 9.2% and Bio-Oss(®) particles 19.0 ± 6.5% of the T2 sites., Conclusion: Placement of the biomaterial in the fresh extraction socket retarded healing. The Bio-Oss(®) particles were not resorbed but became surrounded by new bone. This may explain why grafted extraction sites may fail to undergo dimensional change., (© 2013 John Wiley & Sons A/S. Published by Blackwell Publishing Ltd.)

Background: The composition of the fully healed edentulous ridge of the posterior maxilla was recently examined and was found to contain about 50% mineralized bone and 16% bone marrow., Aim: The objective was to examine the composition of the tissue of the fully healed ridge in different portions of the maxilla and the mandible in partially dentate subjects., Material and Methods: Eighty-seven healthy subjects were included. A trephine drill was used to harvest hard tissue specimens. The biopsies were decalcified, embedded in paraffin, sectioned, stained, and examined using a point-counting procedure., Results: The marginal portion of the jaws almost consistently contained a cortical cap that was significantly wider in the mandible than in the maxilla and twice as wide in the anterior as in the posterior segments of the mandible. Lamellar bone and bone marrow were the dominating tissue elements. Lamellar bone occupied about 63% of the tissue in the mandible and 46% in the maxilla. The maxilla contained about 23% bone marrow as compared to 16% in the mandible. In the mandible, 70% (anterior) and 57% (posterior) were made up of lamellar bone. In the maxilla, the proportion of lamellar bone in the anterior and posterior segments was similar (about 45%). Bone marrow occupied close to 40% of the anterior maxilla, while in the posterior maxilla and the anterior and posterior mandible marrow comprised between 13 and 18%., Conclusion: Marked differences existed with respect to tissue composition of the edentulous ridge between the maxilla and the mandible. The cortical crest was wider in the mandible than in the maxilla, and widest in the symphysis region of the mandible. The proportion of bone marrow was greater in the maxilla than in the mandible. The maxillary front tooth region was poor in lamellar bone but rich in bone marrow, while the anterior mandible contained large amounts of mineralized bone but small amounts of bone marrow., (© 2012 John Wiley & Sons A/S.)

Background: Early implant failures may document that the bone tissue or the wound-healing process following installation surgery was compromised. Subjects who have lost teeth for periodontal reasons exhibit more earlier implant failures than subjects who had experienced tooth loss for other reasons., Aim: To describe the tissue of the fully healed extraction sites in subjects who had lost teeth as a result of periodontitis or for other reasons., Material and Methods: Thirty-six otherwise healthy, partially dentate subjects with fully healed edentulous portions in the posterior maxilla were included. Nineteen of these subjects had lost teeth because of advanced periodontitis (group P) and 17 for other reasons (group NP). Using a trephine drill, a 4-6 mm long hard tissue specimen was harvested. The biopsies were decalcified, embedded in paraffin, sectioned, stained and examined., Results: The edentulous posterior maxilla was comprised of 47.1 ± 11% lamellar bone, 8.1 ± 7.1% woven bone, 4.3 ± 3.1% osteoid and 16.5 ± 10.4% bone marrow. There were no significant differences in the tissue composition of post-extraction sites of (i) P and NP subjects and (ii) premolar and molar sites., Conclusion: More than 50% of the edentulous maxilla was comprised of mineralized bone (lamellar and woven bone). The bone trabeculae frequently appeared to have a random orientation. The direction of the trabeculae rather than the lack of mineralized bone tissue may explain the clinical impression that the bone in the posterior maxilla provides limited resistance to mechanical instrumentation., (© 2011 John Wiley & Sons A/S.)

Objectives: The aim of the present study was to examine tissue integration of implants placed (i) in subjects who had lost teeth because of advanced periodontal disease or for other reasons, (ii) in the posterior maxilla exhibiting varying amounts of mineralized bone., Material and Methods: Thirty-six subjects were enrolled; 19 had lost teeth because of advanced periodontitis (group P) while the remaining 17 subjects had suffered tooth loss from other reasons (group NP). As part of site preparation for implant placement, a 3 mm trephine drill was used to remove one or more 2 mm wide and 5-6 mm long block of hard tissue [biopsy site; Lindhe et al. (2011). Clinical of Oral Implants Research, DOI: 10.1111/j.1600-0501.2011.02205.x]. Lateral to the biopsy site a twist drill (diameter 2 mm) was used to prepare the hard tissue in the posterior maxilla for the placement of a screw-shaped, self-tapping micro-implant (implant site). The implants used were 5 mm long, had a diameter of 2.2 mm. After 3 months of healing, the micro-implants with surrounding hard tissue cores were retrieved using a trephine drill. The tissue was processed for ground sectioning. The blocks were cut parallel to the long axis of the implant and reduced to a thickness of about 20 μm and stained in toluidine blue. The percentage of (i) implant surface that was in contact with mineralized bone as well as (ii) the amount of bone present within the threads of the micro-implants (percentage bone area) was determined., Results: Healing including hard tissue formation around implants placed in the posterior maxilla was similar in periodontitis susceptible and non-susceptible subjects. Thus, the degree of bone-to-implant contact (about 59%) as well as the amount of mineralized bone within threads of the micro-implant (about 45-50%) was similar in the two groups of subjects. Pearson's coefficient disclosed that there was a weak negative correlation (-0.49; P < 0.05) between volume of fibrous tissue (biopsy sites) and the length of bone to implant contact (BIC) while there was a weak positive correlation (0.51; P < 0.05) between the volume of bone marrow and BIC., (© 2011 John Wiley & Sons A/S.)

Objectives: The aim of this experiment was to analyze processes involved in the incorporation of beta-tricalcium phospate (TCP) particles in host tissue during healing following tooth extraction and grafting., Material and Methods: Five beagle dogs were used. Four premolars in the maxilla ((3)P(3), (2)P(2)) were hemi-sected, the distal roots were removed and the fresh extraction socket filled with TCP. The tooth extraction and grafting procedures were scheduled in such a way that biopsies representing 1 and 3 days, as well as 1, 2, and 4 weeks of healing could be obtained. Tissue elements such as cells, fibers, vessels, leukocytes and mineralized bone were determined. In deparaffinized sections structures and cells that expressed Tratarate resistant acid phosphate, alkaline phosphatase, and osteopontin were identified by the use of markers., Results: The porosities of the TCP particles were initially filled with erythrocytes that subsequently were replaced with mineralized bone. Some of the graft material was invaded by mesenchymal and inflammatory cells and disintegrated. Thus, small membrane bound granules appeared in the granulation tissue and the provisional matrix. In the process of hard tissue formation, partly mineralized (modified) TCP particles became surrounded by ridges of woven bone., Conclusions: It was demonstrated that the early healing of an extraction socket that had been grafted with beta-TCP involved (i) the formation of a coagulum that was (ii) replaced with granulation tissue and a provisional matrix in which (iii) woven bone could form. In this process the biomaterial was apparently involved.

Aim: The objective of this experiment was to analyze processes involved in the incorporation of Bio-Oss Collagen in host tissue during healing following tooth extraction and grafting., Methods: Five beagle dogs were used. Four premolars in the mandible ((3)P(3), (4)P(4)) were hemi-sected, the distal roots were removed and the fresh extraction socket filled with Bio-Oss Collagen. The mucosa was mobilized and the extraction site was closed with interrupted sutures. The tooth extraction and grafting procedures were scheduled in such a way that biopsies representing 1 and 3 days, as well as 1, 2 and 4 weeks of healing could be obtained. The dogs were euthanized and perfused with a fixative. Each experimental site, including the distal socket area, was dissected. The sites were decalcified in EDTA, and serial sections representing the central part of the socket were prepared in the mesio-distal plane and parallel with the long axis of the extraction socket. Sections were stained in hematoxylin and eosin and were used for the overall characteristics of the tissues in the extraction socket. In specimens representing 1, 2 and 4 weeks of healing the various tissue elements were assessed using a morphometric point counting procedure. Tissue elements such as cells, fibers, vessels, leukocytes and mineralized bone were determined. In deparaffinized sections structures and cells positive for tartrate-resistant acid phosphatase activity (TRAP), alkaline phosphatase and osteopontin were identified., Results: The biomaterial was first trapped in the fibrin network of the coagulum. Neutrophilic leukocytes [polymorphonuclear (PMN) cells] migrated to the surface of the foreign particles. In a second phase the PMN cells were replaced by multinuclear TRAP-positive cells (osteoclasts). The osteoclasts apparently removed material from the surface of the xenogeneic graft. When after 1-2 weeks the osteoclasts disappeared from the Bio-Oss granules they were followed by osteoblasts that laid down bone mineral in the collagen bundles of the provisional matrix. In this third phase the Bio-Oss particles became osseointegrated., Conclusions: It was demonstrated that the incorporation of Bio-Oss in the tissue that formed in an extraction wound involved a series of different processes.

Background: Although previous studies revealed the presence of autoreactive B cells (B-1a cells) in periodontitis lesions, no evidence was provided for an active role of such cells in the host response to microbial challenge. The aim of the present investigation was to study the reaction of B-1a cells to de novo plaque formation in subjects who were treated for severe chronic periodontitis., Methods: Fifteen white subjects with generalized, severe chronic periodontitis volunteered. Surgical periodontal therapy was performed in all quadrants of each subject after a period of infection control. After 6 months of healing (baseline), two gingival biopsies were harvested from each patient (probing depth <4 mm and no bleeding on probing; healed sites). The experimental gingivitis model was applied, and plaque accumulation was allowed for 3 weeks. Two additional biopsies were collected and prepared for immunohistochemical analysis on day 21., Results: The biopsies retrieved after 3 weeks of plaque accumulation contained larger proportions of CD19+ and CD5+ cells (B-1a cells) than biopsies representing baseline (healed sites) (7.38% +/- 2.80% versus 5.96% +/- 2.48%). The tissue fraction of cells carrying the markers for CD3 (T cells), CD19 (B cells), and Bcl2 (apoptosis-associated marker) were significantly larger in tissue samples collected after 3 weeks of plaque accumulation than in specimens from baseline (healed sites)., Conclusion: Autoreactive B cells (B-1a cells) are involved in the host response to microbial challenge in subjects with chronic periodontitis.

Background: Associations between different gene polymorphisms and severe chronic periodontitis have been demonstrated. However, the influence of such genetic variations on the production of related proteins needs to be clarified. The aim of the present investigation was to study the local expression of interleukin (IL)-10 and membrane-bound CD14 (mCD14) in relation to the -1087 IL-10 and -159 CD14 gene polymorphisms in subjects with chronic periodontitis., Methods: Fifty-three white subjects with generalized and severe chronic periodontitis volunteered. Twenty milliliters of blood was collected by venipuncture from each subject. DNA was isolated, and genotype analysis of the -1087 IL-10 and -159 CD14 gene polymorphisms was performed using polymerase chain reaction and restriction endonuclease mapping techniques. A gingival biopsy from one randomly selected diseased proximal site was also obtained from each subject. The biopsies were embedded, snap frozen, and prepared for immunohistochemical analysis. The inflammatory lesion was identified in the sections, and the proportions of IL-10+ and CD14+ cells were determined., Results: The proportion of IL-10+ cells in the peripheral area of the periodontitis lesions was significantly larger in subjects with the -1087 IL-10 GG genotype than in subjects with the AG or AA genotype. However, the local expression of the mCD14 receptor did not vary between subjects with different -159 CD14 genotypes., Conclusions: It is suggested that IL-10 expression in chronic periodontitis lesions is associated with a distinct genotype. The observation adds to our understanding of interactions between genetic and environmental factors in the development of human diseases.

Objective: The aim of the present study was to analyze some cytokine profiles of T-helper cells in periodontitis lesions., Material and Methods: 22 adult patients (7 females and 15 males, aged 24-66 years) with advanced and generalized chronic periodontitis were recruited. Clinical and radiographical characteristics of periodontal disease was assessed. From each patient a gingival biopsy was obtained from one randomly selected diseased interproximal site. The soft tissue sample was prepared for immunohistochemical analysis. Double staining was performed to detect cells positive for both the CD4 marker and different cytokines, i.e. interleukin (IL)-2, IL-4, IL-6 and interferon-gamma (IFN-gamma)., Results: The lesions in advanced periodontitis contained similar proportions of cells positive for the different cytokine markers examined. In addition, the number of cells expressing cytokine profiles for either T helper-1 (IFN-gamma + IL-2) or T helper-2 (IL-4 + IL-6) was similar., Conclusion: It is suggested that the lesions of periodontitis are regulated by a combined Th-1 and Th-2 function.

Aim: The aim of the present investigation was to study the local (gingival) and systemic occurrence of autoreactive B cells (CD5+CD19 positive) in subjects with a high or low susceptibility to periodontitis., Material and Methods: 2 groups of subjects (Group A and B) susceptible to periodontitis were included. Group A consisted of 22 adult patients (7 females and 15 males, aged 24-66 years) with advanced and generalized chronic periodontitis and group B comprised 7 children (4 girls and 3 boys aged 9-13 years) with localized aggressive periodontitis. 26 periodontally healthy subjects, Group C (aged 23-80 years, mean 49.6+/-16.3), were also recruited. Assessment of clinical and radiographical characteristics of periodontal disease was performed. Gingival biopsies and peripheral blood samples were obtained and prepared for immunohistochemical analysis. Blood samples only were obtained from the periodontally healthy subjects (group C)., Results: The proportion of autoreactive B cells (CD5+CD19 positive) of peripheral blood lymphocytes was about 6 times higher in group A and 4 times higher in group B than in the samples from the control subjects (group C). About 40-50% of the B cells in the peripheral blood of the periodontitis susceptible individuals expressed markers for autoreactive features while less than 15% of the circulating B cells in the subjects of group C exhibited such markers. The periodontitis lesion in the adult periodontitis patients contained a substantial number of B cells out of which about 30% demonstrated autoreactive features., Conclusion: It is suggested that both circulating and local B cells in periodontitis susceptible individuals have a higher propensity to autoreactive properties than B cells of patients with a low susceptibility to periodontitis.

Background: Most antidepressant and neuroleptic agents are metabolized by the polymorphic cytochrome P450 enzyme CYP2D6. This study evaluates the importance of the CYP2D6 genotype for the disposition of the neuroleptic agents perphenazine and zuclopenthixol., Methods: Patients treated with neuroleptic agents (n = 36) were studied prospectively with regard to CYP2D6 genotype and neuroleptic plasma concentration during oral treatment. Because no patient provided enough samples for individual kinetic modeling, a bayesian approach was used for determination of the clearance. Population kinetic parameters for this procedure were collected from retrospective therapeutic drug monitoring data (n = 113) by use of a nonparametric approach., Results: The CYP2D6 genotype significantly predicted the oral clearance of perphenazine and zuclopenthixol (p < 0.01 by multiple regression). The difference in clearance between homozygous extensive metabolizers and poor metabolizers was threefold for perphenazine and twofold for zuclopenthixol., Conclusion: The results show that the genotype for CYP2D6 is closely related to the oral clearances of perphenazine and zuclopenthixol. If this finding can be confirmed in a larger population, genotyping may become an important tool for the dosing of these two neuroleptic agents.

The present study in the beagle dog was performed to analyze whether micro-organisms from a subgingival microbiota could be translocated into or had the potential to invade the pocket epithelium and the gingival connective tissue during a phase of rapid breakdown of the attachment apparatus. An attempt was also made to assess whether tetracycline therapy suppressed the subgingival microbiota and changed the size and quality of the lesions in the gingival tissue. 5 inbred beagle dogs were used. Throughout the period of experimentation, the animals were fed a soft diet permitting gross accumulation of plaque and calculus. No mechanical plaque control measures were performed during the course of the study. On day 0, a 120-day period of periodontal tissue breakdown was initiated at the right mandibular 3rd and 4th premolars by tying cotton floss ligatures around the neck of these teeth. The process of tissue breakdown at the mandibular left 3rd and 4th premolars was started 30 days later. The ligatures were replaced once every 2 weeks during the subsequent 4-month period. On experimental day 120, the first biopsy was performed and gingival tissue sections prepared for light and electron microscopic assessment of a series of histometric characteristics. On day 120, a 30-day period of tetracycline (per os) administration was initiated. Each dog was given a dose of 500 mg tetracycline twice daily. On day 150, the biopsy procedure was repeated in the mandibular left premolar regions.(ABSTRACT TRUNCATED AT 250 WORDS)