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M Larmas

Publications and source records attributed to M Larmas.

At least 55 records · Page 3Linked to original sources
PubMed1995

Mineral element analysis of carious and sound rat dentin by electron probe microanalyzer combined with back-scattered electron image.

We recently demonstrated the advantages of back-scattered electron images (COMPO) in the visualization of dentinal caries, and the relationship of the change in the dentin fluorescence pattern in caries lesions. However, the exact nature of these changes is not known. In this paper, the nature of the changes in the areas with reduced mineral content in COMPO images was investigated. We examined the relation of changes in mineral elements and the appearance of soft carious and sound dentin in COMPO images using a scanning electron microscope (SEM) equipped with an electron probe microanalyzer (EPMA). Rat molars with small dentinal caries lesions just under the DEJ were chosen for the study. The Ca, P, Na, Mg, Zn, F, and total contents were determined by EPMA from five different dentin sites, and the Ca/P and Mg/Ca ratios were calculated. Generally, the lowest contents were found in caries lesions and highest in mantle dentin, with the exceptions of Mg and Zn. The Ca/P ratio was lowest in mantle dentin and highest in carious dentin. The results confirm that the change in fluorescence in the dentinal caries lesion is correlated with the very initial changes in mineral content, and that EPMA used in combination with COMPO images is a useful tool for determining small changes in mineral elements in the carious and adjacent areas of dentin.

Animals↗
PubMed1995

Evidence that high-sucrose diet reduces dentin formation and disturbs mineralization in rat molars.

In addition to its caries-promoting effect, a high-sucrose diet reduces the apposition of mineralized dentin in young rats. This study was undertaken to test whether it has a similar effect on the width of the as-yet-uncalcified matrix, predentin. Female Wistar rats were weaned at the age of 3 weeks and fed for 7 weeks with either a high-sucrose diet, a non-cariogenic raw potato starch diet, or a non-cariogenic commercial powdered rat food (for reference). The sucrose diet induced the greatest number of caries lesions. Dentin formation was smaller and the predentin zone wider in rats fed a sucrose diet when compared with rats fed the reference diet. In rats fed a starch diet, dentin formation was smaller than in rats fed a reference diet, but no alterations in the areas of caries lesions or predentin width were observed. Widening of the predentin zone in rats fed a high-sucrose diet may reflect changes in odontoblast function, such as reduced matrix synthesis and possibly disturbed mineralization. Dentinal caries progression may thus be modulated by odontoblast function, not as much by matrix formation but rather by mineralization.

Analysis of Variance↗
PubMed1994

The effect of ovariectomy and high-sucrose diet on dentine formation and caries in growing rats.

Ovariectomized (Ovx) or sham-operated (Cnt) and tetracycline-labelled growing rats were fed either a commercial powdered standard rat diet (Ovx and Cnt) or a high-sucrose diet (Ovxsuc and Cntsuc). All animals were inoculated in the mouth with Streptococcus sobrinus. At 11 weeks of age the areas of caries lesions and dentinal apposition of the first and second molars and the areas of the pulpal cross-section of the incisors were determined. The area of dentinal apposition was largest in Cnt animals, the difference being statistically significant only in comparison with the Cntsuc animals. No such difference between the diets was found among the Ovx animals. The cross-section of the pulpal chamber was smallest in the Ovxsuc rats and largest in the Cnt animals, but no statistically significant differences were found between the groups. The caries lesions were significantly larger in Ovx, Ovxsuc and Cntsuc animals than in Cnt ones. Ovariectomy thus increased caries progression in growing rats, but the effect on dentine formation remained negligible. In this respect there is a difference between primary and secondary dentinogenesis.

Analysis of Variance↗
PubMed1994

Reduction in dentine apposition in rat molars by a high-sucrose diet.

The effects of high-sucrose and high-starch diets on dentine apposition were examined. One group of young Wistar rats (20 rats) received a high-sucrose (43%) diet; for the high-starch group (16 rats), sucrose was replaced with potato flour. The control group (18 rats) received standard laboratory rat food. The onset of dentine formation was marked with tetracycline. After 5 weeks lower molars were sectioned sagittally, and the areas of the dentine apposition and those of the dentinal caries were quantified. Dentine apposition was independent of sex. The high-sucrose diet reduced dentine apposition and induced caries progression. A negative correlation between dentine apposition and caries progression in the molars was found. This study suggests that a high-sucrose diet itself reduces primary dentine apposition.

Animals↗
PubMed1994

Effect of fluoride on the rate of dentin apposition and caries progression in young and old Wistar rats.

The effect of fluoride in drinking water on the progression of dentinal caries and dentin apposition was studied separately in young and old Wistar rats. The animals were inoculated with Streptococcus sobrinus and fed ad libitum on a 43% sucrose diet and distilled water supplemented with 0, 1, or 19 ppm fluoride. After a 7-wk (young) or 13-wk (adult) cariogenic challenge, the areas of dentinal caries and dentin apposition were quantified after tetracycline staining. Fluoride in the drinking water reduced the progression of dentinal caries and the speed of dentin formation in the young animals but only the progression of dental caries in the adult ones. Both the progression of carious lesions in the dentin and the rate of dentin apposition were 10 times faster during primary dentinogenesis.

Aging↗
PubMed1993

Evaluation of Gram's method of staining for the prognosis of root canal treatment in nonvital dental pulps.

An evaluation of Gram's method of staining of 601 nonvital dental pulps was performed. It gave positive results in 60.1% of the cases, the most frequent finding was gram-positive cocci. Preoperative x-ray status correlated significantly with the staining results but the size of the radiolucency did not. Previously treated teeth gave less positive staining results than other teeth. There was an obvious correlation between presence of bacteria and various complications (p < 0.001), but no differences were noted between the combinations of bacteria. The teeth that were the most resistant to complications seemed to be the lower canines. The staining results did not correlate with sex, systemic diseases, or preoperative symptoms. We believe that Gram's method of staining is a useful, rapid aid in root canal therapy, especially in complicated cases.

Adolescent↗
PubMed1993

Effect of fluoride on caries progression and dentin apposition in rats fed on a cariogenic or non-cariogenic diet.

The effect of fluoride in drinking water on the progression of dentinal caries and dentin apposition was studied in Wistar rats. The initiation of enamel caries lesions was first induced for 2 wk with S. sobrinus and a 43% sucrose diet after weaning. Thereafter the animals were fed on either a cariogenic or a non-cariogenic diet and distilled water supplemented with 0, 1, 7 or 19 ppm fluoride. The areas of dentinal caries and dentin apposition were quantified after tetracycline staining. Fluoride reduced dentinal caries progression after the initiation of lesions in the presence of a cariogenic diet at a concentration of 19 ppm F, and without sucrose at 1 ppm F. The effect of fluoride in reducing dentin apposition with a cariogenic diet was dose-dependent, whereas fluoride in non-cariogenic groups had practically no effect on dentin formation. These results suggest that fluoride together with a high concentration of sucrose in the diet might have an odontoblast-mediated effect on the regulation of the progression of dentinal caries.

Analysis of Variance↗
PubMed1993

Dentin caries recording with Schiff's reagent, fluorescence, and back-scattered electron image.

After being weaned, the Wistar rats (12) were fed on a sucrose diet for five weeks to induce dental caries. Tetracycline was injected intraperitoneally into 7 of them to label the mineralizing dentin front. Five rats without tetracycline injection were used to verify spontaneous fluorescence. The evidently carious area under one prominent fissure from each mandibular molar hemisected sagittally in the midline was photographed under ultraviolet light so that autofluorescence would be revealed. The jaws were then stained with Schiff's reagent and photographed under normal light and again under ultraviolet light. The areas of all the lesions were quantified planimetrically as they appeared on the photographs. The mineral contents of the areas were verified with the back-scattered electron images. The caries lesions revealed with Schiff's reagent also exhibited a change in the color of the dentin fluorescence regardless of the tetracycline labeling. The areas of these lesions followed the shapes of the lesions stained by Schiff's reagent but they were greater. Staining with Schiff's reagent was repeatable after the specimen was washed with ethanol for a few weeks. The loss of minerals was seen in the areas stained with Schiff's reaction but was also related to the change in dentin fluorescence, which seems to be a more sensitive indicator of the caries progression than Schiff's reagent, especially in the early phase of the carious process.

Animals↗
PubMed1992

The effect of ovariectomy on dentin formation and caries in adult rats.

Since acute osteoporosis is known to enhance bone remodeling and osteoid formation, it may also affect dentin apposition. We induced osteoporosis in 15-week-old Wistar rats by ovariectomy and dental caries by Streptococcus sobrinus infection in the presence of either a high sucrose (cariogenic) diet or a non-cariogenic diet. Intact animals with the same diets served as controls. After 99 days of cariogenic challenge the rats were killed, and the success of ovariectomy was confirmed by failure to detect ovarian tissue and observation of marked atrophy of the uterine horns. Areas of dentinal apposition during the experiment and carious lesions were quantified with a tetracycline method. Ovariectomy activated dentin formation significantly in rats fed either a high-sucrose or a non-cariogenic diet, indicating enhanced odontoblast function. The rate of dentinal apposition in adult rats was smaller than reported in young animals. The effect of ovariectomy on caries remained negligible.

Animals↗
PubMed1992

The effect of phenytoin medication on dentin apposition, root length, and caries progression in rat molars.

To determine the effect of phenytoin (PHT) on dentin apposition and the rate of caries progression in dentin, 40 Wistar rats were treated daily for 35 days with intraperitoneal injections of 5,5-diphenylhydantoin. Twenty-eight controls received saline with pH adjusted to that of PHT. One PHT and one control group were fed a 43% sucrose diet, and the others a non-cariogenic pellet diet. Streptococcus sobrinus was inoculated to induce caries. Schiff staining was used to determine caries. The areas of dentin apposition and dentinal caries lesions were quantified after tetracycline staining. The root lengths were measured. PHT reduced slightly the dentin apposition and activated significantly the progression of the dentinal carious lesions. No difference in caries initiation was found. The high-sucrose diet reduced dentin apposition and increased the rate of progression of existing caries greatly. Our study suggests that both the high-sucrose diet and PHT have an effect on secreting odontoblasts, which can be seen as an alteration in dentin apposition and caries progression rates in dentin.

Animals↗
PubMed1992

Saliva and dental caries: diagnostic tests for normal dental practice.

Salivary diagnostics is now entering the surgery of the modern dentist, although no test yet available is so specific and sensitive that caries can be diagnosed from saliva samples only. The present tests are useful for estimating the caries activity due to bad dietary habits (salivary lactobacilli), establishing the presence of infection (salivary mutans streptococci), and identification of salivary yeasts for the determination of the medical condition of the patient. Buffer capacity reveals the most important host response factor acting against caries, while measures of flow rate form the diagnostic basis for treatment planning. These tests, alone or in combination, are now so easy to perform that they should be used in every dental practice.

Dental Caries↗
PubMed1992

Odontoblast-mediated regulation of the progression of dentinal caries.

Osteoblasts and odontoblasts are both derived from the same mesenchymal cell line. Our aim was to investigate whether the processes of bone destruction and dentinal caries are biologically similar. The working hypothesis was that after the initiation of caries in the enamel, its rate of progression in the dentine is regulated by cell-mediated factors. Experimental caries was induced in the rat with a high sucrose diet combined with Streptococcus sobrinus infection. Both destruction of dentine and its apposition in the pulp under the carious lesions were measured after vital staining with tetracycline. Caries progression and dentine apposition were higher in developing teeth prior to apex "closure" than in adult, fully-formed teeth. Rats placed on a cariogenic diet during tooth development had an increased rate of caries progression. Fluoride administration via the drinking water was associated with decreased dentine apposition and little progression of dentine caries during the developmental stages. Dentine apposition was enhanced in adult rats placed on fluoride administration, while caries progression was reduced, whereas in animals subjected to metabolic acidosis dentine caries progression was enhanced, with reduced dentine apposition. In contrast, alkalotic animals had less dentinal lesions and smaller ones than the controls. Three theories are advanced to explain the observed changes: (i) They may be associated with changes in alkaline phosphatase activity in the pulpo-dentinal complex, (ii) they may be mediated by ionic changes in the dentinal fluid, or (iii) they may reflect the liberation of growth factors from dentinal matrix.

Acidosis↗
PubMed1990

Effects of low and high fluoride levels on rat dental caries and simultaneous dentine apposition.

The effects of various fluoride levels in drinking water on the development of enamel and dentinal caries and on dentine apposition were determined in Osborne-Mendel rats fed ad libitum either on a 43% sucrose diet and distilled water supplemented with 0, 1, 7 or 19 parts/10(6) fluoride, or on a non-cariogenic diet. The jaws were sectioned sagittally and fissure caries was assessed. The areas of the dentinal lesions and simultaneously formed dentine were quantified after tetracycline staining. There were fewer and smaller caries lesions in all fluoride groups than in the non-fluoride groups. The anti-caries effects of fluoride at 1 and 7 parts/10(6) were similar, but both had significantly less effect than 19 parts/10(6) fluoride. Much smaller dentinal lesions were seen with 19 parts/10(6) fluoride, which appears to have been accompanied by an even greater reduction in dentine apposition. Dentine formation in the third molars was significantly reduced in the rats fed a cariogenic diet. These observations suggest that a high-sucrose diet interferes with the formation of dentine in the developing tooth. Fluoride has a multiple effect; besides reducing the formation and progression of caries, it may also affect the dentinal response normally seen in the development of a caries lesion.

Animals↗
PubMed1990

Ossification of the antler in the Lapland reindeer (Rangifer tarandus tarandus).

A histological and histochemical study of biopsy specimens from the Lapland reindeer antler indicated that the intercellular matrix of the cartilage that forms the partitions of longitudinal channels becomes calcified at virtually the initial stage of formation. The lacunae at the peripheries of the cartilaginous partitions are invaded by osteoblasts in a process comparable to endochondral ossification. The very centres of the partitions evidently become directly converted into bone without the presence of e.g. osteoclasts. The osseous partitions are remodelled by osteoclasts. The antler increases in diameter by periosteal apposition.

Animals↗
PubMed1989

Salivary immunoglobulins, lysozyme, pH, and microbial counts in children receiving anti-neoplastic therapy.

Salivary immunoglobulins, lysozyme, pH, and microbial counts were determined in 55 children with cancer diseases (37 cured subjects and 18 acute ones) and 103 healthy subjects. 5-10 ml unstimulated whole saliva was collected and pH, immunoglobulins and lysozyme were measured. Chairside dip-slide cultivations were used for microbiologic cultures. Reduced salivary pH and an increased amount of lysozyme were found in the saliva of those children who had been cured of their cancer diseases, but ongoing cancer disease or the treatment provided for it reduced pH and increased the amounts of lysozyme, lactobacillus, Streptococcus mutans and some immunoglobulins. These findings suggest that children with childhood cancer may be more susceptible to dental diseases than healthy ones.

Adolescent↗