Left Jaws Research Articles

Streptococci and actinomyces inhibit regrowth of Streptococcus mutans on gnotobiotic rat molar teeth after chlorhexidine varnish treatment.

Clinical studies suggest that the long-term suppression of mutans streptococci on tooth surfaces after intensive chlorhexidine therapy is mainly due to bacterial interference. Other streptococci and also Actinomyces naeslundii are proposed to inhibit regrowth of mutans streptococci after suppression by the agent. We have tested this hypothesis in gnotobiotic rats associated with Streptococcus mutans alone, or associated with S. mutans and strains of Streptococcus oralis, Streptococcus sanguis, Streptococcus gordonii, Streptococcus mitis biovar I, and A. naeslundii. Left lower jaws in these rats were treated with concentrated chlorhexidine varnish, and the return of S. mutans on the treated jaws monitored. In mono-associated rats, S. mutans regained the level of the untreated right lower jaw in approximately 1 week. In contrast, S. mutans remained suppressed for several weeks in rats multi-associated with other streptococci and actinomyces strains. The suppression was more pronounced in the rats fed on basal diet with little free sugars than in rats fed on a sucrose-containing diet. Counts of other streptococci recovered quickly from the intensive chlorhexidine treatment, but A. naeslundii remained suppressed for at least 1 week. The findings demonstrate the crucial importance of the oral microflora in controlling regrowth of mutans streptococci after chemotherapy.

Blood flow in healed and inflamed periodontal tissues of dogs.

The objectives of this study were to determine if increased blood flow associated with gingivitis would decrease following resolution of gingival inflammation in dogs with periodontitis; if increased blood flow in inflamed gingiva was associated with changes in the blood flow of alveolar bone, and if blood flow in gingiva and alveolar bone increased if periodontitis was reactivated by ligating teeth. Regional blood flow was measured in dogs with pre‐existing periodontitis, using radioisotope‐labelled, plastic microspheres. In the first experiment on 4 adult Beagle dogs, teeth in the left jaws were treated to resolve the periodontitis, while teeth in the right jaws were not treated. Gingival and bone blood flow were measured after 12 wk. Blood flow was significantly (p<0.05) lower in non‐inflamed healed gingiva (32.1±2.7 ml/min/100 g) than in inflamed gingiva (46.1±5.3 ml/min/100 g). No differences in the blood flow of alveolar bone underlying inflamed or non‐inflamed gingiva were present. In the second experiment, the right mandibular teeth of 5 dogs were treated to resolve periodontitis while teeth in the other quadrants were ligated for 4, 10 or 12 wk. The duration of ligation did not alter blood flow. Gingival blood flow around ligated maxillary and mandibular teeth was comparable and approximately 54% higher than around non‐ligated teeth (p±0.03). The difference in blood flow between gingiva with G.I. ± 1 and gingiva with G.I.±2 was significant (p±0.04). Blood flow in bone was not altered by changes in the inflammatory status of the overlying gingiva. The findings suggest that changes in blood flow associated with inflammation are reversible and that blood flow in alveolar bone is regulated independently of gingival blood flow.

Gingival health and frequency of tooth brushing in the beagle dog model. Clinical findings.

The aim of this experiment was to study clinical parameters when 3 different frequencies of plaque removal were applied to healthy gingivae in the beagle dog model. The maxillary first, second and third premolars of 12 beagle dogs, at the start of the experiment 2 years of age, were, after a thorough cleaning, submitted to daily plaque removal during a pre-experimental period of 8 weeks. At the start of the experiment, the dogs were distributed into 3 groups of 4 dogs each: one group was brushed 7 times a week, a second group was brushed 3 times a week and another group was brushed only once a week. Brushing was executed over a period of 24 weeks, on the right sides of the upper jaws. The left upper jaws served as controls. At regular intervals, the plaque index, the gingival index and probing depths were assessed. A "brushing effect" was calculated for each dog, to include information on all within-dog and between dog variations. Comparison of brushing effects revealed that in this experimental model, plaque removal with a frequency of 3 times a week was sufficient to preserve gingival health, whereas tooth brushing once a week resulted in gingival inflammation. Therefore it can be concluded that 3 times a week is the critical brushing frequency in the beagle dog model with healthy gingiva at baseline.

Repair of fractured lower jaws in the spotted salamander: Do amphibians form secondary cartilage?

AbstractSecondary cartilage forms on avian and mammalian dermal bones, both during normal ontogeny and during repair of fractures, but it has not been observed in any other vertebrate class. We fractured the left lower jaws of adult spotted salamanders, Ambystoma maculatum, to see whether secondary cartilage would form during fracture repair. It did not. Instead, periosteal hyperplasia produced a callus from which new dermal bone formed to bridge the fracture. Meckel's cartilage underwent superficial dissolution but showed a minimal chondrogenic response. A large callus cartilage did form, but it appeared to arise by metaplasia from connective tissue adjacent to the bone. Thus, the environment within the fracture is conducive to chondrogenesis but the periostea of the dermal bones either are not able to respond to that environment or are unable to synthesize cartilage‐specific products. Among recent vertebrates, the ability to form secondary cartilage is limited to birds and mammals and is not a primitive property of the periostea of dermal bones shared by “lower” vertebrate classes.

Vascular turnover of a continuously growing organ: The rat incisor

The vascular tissue supplying the pulp of the continuously growing and developing rat incisor was quantitatively analyzed in six female rats, weighing approximately 200 gm each. One hour after a single administration of 3H-TdR, 1 microCi/gm body weight, the rats were sacrificed and the lower left jaws excised and processed histologically. Every 20th section was evaluated for venular and arterial count, endothelial cell count, and percentage of labeled endothelial cells. It was found that the proliferative capacity of the vascular tissue of the rat incisor is confined to its most apical 3.0 mm-a zone defined as the vascular progenitor compartment. Daily production of endothelial vein cells and of veins within the progenitor compartment were calculated to be 7,392 cells/day and two veins/day, respectively. Generation time of these cells was found to be 3.56 days. Endothelial cell production within the progenitor compartment provides for the formation of new vessels and for the enlargement and elongation of existing ones. The vessels originating within the progenitor compartment move in an incisal and centripetal direction, while simultaneously undergoing a continuous process of aging, until their ultimate disintegration.

Effect of selective antimicrobial therapy on plaque and gingivitis in the dog

The present investigation was performed to assess the effect of selective antibiotic therapy on developing plaque and gingivitis in dogs, which at the start of the study had normal gingiva. Fifteen beagle dogs were used. Throughout the entire observation period the animals were fed a diet which favored plaque accumulation. A baseline examination involved assessments of plaque, gingivitis and gingival exudate. The subgingival bacterial flora was assessed by dark-field microscopy. Subsequently the teeth of the right jaws were allowed to accumulate plaque. A careful tooth-cleaning program was maintained in the left jaws. Plaque and gingivitis assessments were repeated and subgingival plaque sampled in the right jaws after 14 and 28 days. On experimental day 28 the second part of the study was initiated. The dogs were randomly distributed into three groups of five animals each. A new baseline examination was performed in the left jaws, after which all tooth cleanings were terminated. During the subsequent 28 days each group of dogs was treated with one of three antimicrobial compounds (vancomycin, metronidazole or clindamycin). Examinations were repeated after 14 and 28 days. The results demonstrated that systemic administration of antimicrobial substances can reduce the rate of plaque formation, change the composition of the developing subgingival microbiota and prevent (or retard) the onset of gingivitis. A comparison of the ability of the three compounds to prevent the formation of a "gingivitis-inducing" plaque revealed that metronidazole and clindamycin were markedly more effective than vancomycin. In fact, in dogs receiving metronidazole and clindamycin treatment, the initiation of gingivitis was almost entirely prevented during the 28 days of treatment.

Clearance rates of xenon-133 in non-inflamed and inflamed gingiva of dogs

Blood flow rates were compared in non-inflamed and inflamed gingiva in 4 dogs following a depot injection of 133Xe and external monitoring of the radioisotope. Only teeth in the left jaws were cleaned daily and gingival health maintained. Selection of sites for testing was dependent on Gingival Index scores of 0 (no inflammation) or 2 (overt gingivitis). Measurements were made of 133Xe clearance from the interdental and attached gingiva and alveolar mucosa of the 2nd, 3rd and 4th premolars. Data were analysed using the initial slope clearance rate determination of Sejrsen and Tonnesen (1968) and the stochastic method of Zierler (1965) to determine a blood-flow-to-volume ratio. There was a significantly ( p < 0.001) lower rate of clearance of 133Xe in alveolar mucosa compared to the other gingival sites, a difference not dependent on the presence of inflammation. There was no difference in 133Xe clearance rates in non-inflamed and inflamed gingiva. Thus the blood flow rate in the gingival nutritional capillary bed was maintained in chronically inflamed gingiva.

Orthodontic relapse in dentitions with reduced periodontal support: An experimental study in dogs

The purpose of the investigation was to assess whether supra-alveolar connective tissue formed following periodontal surgery carried out subsequent to orthodontic tooth movement is an effective barrier to relapse. The experiments were carried out on five beagle dogs. At the start of the study (Day 0) the mandibular third premolars (3P and P3) were extracted and experimental periodontal breakdown was initiated around the lower fourth premolars (4P and P4) by placing cotton floss ligatures around the neck of the teeth. After 180 days of plaque formation the cotton floss ligatures were removed. The diseased periodontal tissues around 4P were removed surgically and silver markers, serving as future reference points, were placed in the buccal bone plate close to the apex of the roots of 4P. At the same session amalgam fillings were placed in the buccal surface of the mesial and distal roots of 4P and P4. During the next 34 weeks (between Day 180 and Day 420), the dogs' teeth were brushed three times a week. On Day 225 orthodontic appliances were inserted bilaterally to tip 4P and P4. Active orthodontic forces were used between Day 225 and Day 300. Between Day 300 and Day 360 the orthodontic appliances served as retainers for the moved teeth. On Day 360 the periodontal tissues around P4 were removed surgically and silver reference points were placed into the bone as described earlier. On Day 360 the orthodontic appliances were removed. The dogs were sacrificed on Day 420. The difference in position of 4P and P4 was measured on radiographs taken on days 300, 360 and 420 and it was found that (1) during the 'period of retention' the difference in position of 4P and P4 was close to zero and (2) during the ‘period of relapse’ the movement of 4P and P4 was small and the difference between the right and left jaws not significant. The investigation demonstrated that no significant differences exist between supra-alveolar connective tissue formed prior to or after orthodontic tipping movements regarding the prevention of relapse.

The effect of metronidazole on the development of plaque and gingivitis in the beagle dog

The present investigation was performed in order to assess if the administration of metronidazole changed the composition of developing plaque in dogs, which at the start of the study were free from signs of gingivitis. Five beagle dogs were used. Throughout the observation period the animals were fed a diet which favored plaque accumulation. A baseline examination involved assessments of plaque, gingivitis and gingival exudate. Gingival biopsies were sampled and the tissue examined by a point counting procedure. The composition of the subgingival bacterial flora was assessed by dark-field microscopy. The bacteria were characterized into the following types: coccoid cells, straight rods, filaments, fusiforms, motile and curved rods and spirochetes. Following the baseline examination the teeth of the right jaws were allowed to accumulate plaque. A careful tooth cleaning program was maintained in the left jaw quadrants. Plaque and gingivitis assessments were repeated and biopsies sampled in the right jaws after 7, 14 and 28 days of no tooth cleaning. On experimental day 28 the second part of the study was initiated. A baseline examination was performed in the left jaws, after which the tooth cleaning program also in this part of the dentition was terminated. During the subsequent 28-day period each animal was given a dosage of 20 mg metronidazole/kilogram bodyweight/day. Clinical examinations and biopsies were repeated after 7, 14 and 28 days. The results demonstrated that metronidazole administered via the systemic route during a 28-day period can effectively decrease plaque and gingivitis development in dogs. The bacterial flora from subgingival sites of healthy gingiva was dominated by coccoid cells and straight rods. During the phase of developing gingivitis the percentage of coccoid cells and rods tended to decrease, while motile rods and spirochetes increased. During the 28 days of metronidazole treatment the subgingival plaque flora maintained its "healthy" composition, i.e. a gradual influx of motile rods and spirochetes was prevented.

Some effects of chlorhexidine on the plaque flora of the beagle dog.

Three series of experiments were performed during which Beagle dogs were given a plaque forming diet, in Series I 10 dogs were sprayed twice daily with 0.2 per cent chlorhexidine and 10 controls with saline for six months. In Series II the same treatment was used for 18 months in 16 dogs (8 treated. 8 controls). In Series III, comprising three dogs, the teeth of the left jaws, were subjected to two different concentrations of chlorhexidine for 5 + 5 weeks (2 resp. 0.1 %) while the teeth of the right jaws received saline treatment. During a subsequent period of 3 months all teeth were created with saline.Dental plaque was sampled at the end of the three experimental periods, in Series III also one, three, six and thirteen weeks later. The sensitivity to chlorhexidine of the plaque bacteria was tested using a modification of “the paper disc method”. In all series the plaque bacteria from chlorhexidine treated teeth displayed reduced sensitivity to the drug. After termination of the chlorhexidine treatment in the Series III‐experiments the reduced sensivity to chlorhexidine of plaque bacteria from chlorhexidine treated teeth slowly approached the corresponding values from saline treated teeth.Plaque samples taken after 18 months (Series II) were studied by means of a dilution‐plate method. The‐ dominating colonies from each plate were identified as gram‐negative aerobic rods. Most of the bacteria from chlorhexidine treated dogs grew on trypticase soy agar plates containing 320 μg/ml chlorhexidine. while bacteria from the saline treated animals only grew on plates containing 20 μg/ml.

Experimental periodontitis in the beagle dog.

The purpose of the present investigation was to study the sequential stages in the development of a periodontal lesion starting from a healthy periodontium. Twenty inbred Beagle dogs 10 months of age and weighing 10–12 kilos were used. The animals were equally divided into one experimental and one control group. Throughout the experiment all dogs were given a diet containing 400 gm pellets and 25 gm soya flower. From day zero the teeth (in the left jaws) of the control dogs were twice dally subjected to a careful but gentle brushing with tooth brush and dentifrice. The teeth of the experimental group animals were not cleaned. The dogs were examined at regular intervals during an 18 month period.The results show that it is possible in young dogs to induce gingivitis which gradually develops into periodontitis simply by allowing plaque to accumulate on teeth. The cleaned teeth did not show signs of gingivitis or periodontitis during the entire experiment. It is proposed that in the Beagle dog the progression of the lesion during an 18 month period may occur in three stages: I) subclinical gingivitis, II) clinical gingivitis and III) periodontal breakdown. Subclinical gingivitis was characterized by a rapidly increasing gingival exudation and migration of crevicular leukocytes, i. e. signs off acute inflammation. Clinical gingivitis was characterized by changes in gingival colour, texture and bleeding tendency but only minor alterations of the number of crevicular leukocytes. Periodontal breakdown, characterized by loss of subgingival fiber attachment, occurred only in areas of clinical gingivitis.

On the Premolar Teeth of Diprotodon , and on a New Species of that Genus

A short time since, I was requested by Dr. Cotton, F.G.S., to examine a series of Australian fossils in his collection, which were procured by Mr. Isaacs from Gowrie, in the district of the Darling Downs in Queensland, the same locality from which other specimens in the Hunterian and British Museums were obtained. These fossils consisted of numerous teeth and fragments of jaws of Macropus Atlas and M. Titan ; part of the upper jaw of a new species of Kangaroo, as large as these, but allied to Lagorchestes and Hypsiprymnus ; with three lumbar vertebrae, a sacrum, portions of two innominate bones, three ossa calcis, and a right metatarsal of the great toe, belonging to these Marsupials. The metatarsal is remarkable for its short and stout proportions. But the most interesting among these remains were fragments of Diprotodon , comprising sundry molar teeth, a small portion of the right ramus of a lower jaw, and parts of the right and left upper jaws of two distinct individuals. Of these upper jaws, the former, which I shall call No. 1 (P1. XXl. fig. 1), contained the premolar in place and the socket of the succeeding molar, with one fang in place. Fortunately, among the detached teeth, I found the crown and principal fang of this molar, and the premolar of the other side of the same skull. The other or left upper jaw, No. 2 (fig. 4), has a very different colour and texture, from the nature of the ferruginous matrix in which