Biomedical subjects

M Larmas

Publications and source records attributed to M Larmas.

At least 37 records · Page 2Linked to original sources

PubMed1998

Effects of continuous glucocorticoid infusion on the progression of dentinal caries in growing rats.

This study was undertaken to test the effects of a low dose of continuous glucocorticoid infusion on the rate of progression of dentinal caries in molars of young rats. Forty-seven rats were inoculated in the mouth with Streptococcus sobrinus and fed ad libitum a cariogenic diet and 10% sweetened water. After 10 days of caries initiation ten animals were killed to serve as a reference group. In the rest of the animals the cortisone or placebo pellet was implanted subcutaneously in the back of the neck. The daily release of cortisone was 0.42 mg per rat. Sweetened water was changed to pure water, and the diet was the same cariogenic diet. After 6 weeks of medication the areas of dentinal caries were quantified planimetrically. Schiff's staining was used to classify caries. Although cortisone medication slightly increased the number of carious lesions, statistical significance was not reached. However, compared with the placebo group, the rats receiving cortisone medication showed significantly increased dentinal caries progression and severity of lesions. This study suggests that glucocorticoids with a cariogenic diet reduce the intrinsic modulation or response of the odontoblasts to caries attack.

Animals↗

PubMed1998

Comparison of dentin apposition and dentinal caries progression in the mandibular and maxillary molars of the rat.

To show that the rate and the rate of reduction of dentin apposition are about the same in mandibular and maxillary molars, 23 Sprague-Dawley rat pups were randomized into 2 groups on the day of birth. During lactation half of their dams received a standard rodent diet; the other half, a diet containing 41% sucrose. At the age of 3 weeks the pups were weaned, weighed, given an intraperitoneal injection of oxytetracycline hydrochloride, and inoculated with oral Streptococcus sobrinus. During the experiment the pups received the same diet as their dams during lactation. After 5 weeks the pups were decapitated, their jaws sectioned sagittally, the first and second molars photographed, and the areas of dentin apposition and dentinal caries measured planimetrically. The area of dentin formation was about the same in maxilla and mandible in the first molars, but slightly smaller in the mandibular second molars of the control group. The sucrose diet reduced dentin apposition significantly in both jaws, although the areas were significantly smaller in the mandibles than in the maxillae. Caries did not affect the rate of dentin apposition. The areas of caries lesions were smaller in the maxillary molars of both diet groups. The results show that the hypothesis of equal rate of dentin apposition in mandible and maxilla was not valid because the reduction, caused by sucrose, was more prominent in mandibular molars for unknown reasons. The reduction of dentin apposition was reflected as acceleration of caries progression among the diet groups and the jaws. It was concluded that the response of the pulpodentinal complex to sucrose and dentinal caries during the primary dentinogenesis cannot be seen as a formation of reactionary or reparative dentin, as with adult rats.

Animals↗

PubMed1998

Prolonged pacifier-sucking and use of a nursing bottle at night: possible risk factors for dental caries in children.

At the baseline of this cohort study we determined risk factors for colonization of oral lactobacilli and candida in a group of children (n = 166) whose mean age was 2.5 years. The results showed that pacifier-sucking and the use of a nursing bottle at night increase the occurrence of both salivary lactobacilli and candida. In the present study these children were followed for 2 years, and the progression of caries was recorded with particular reference to the etiologic factors measured before. The results of the logistic regression analysis showed prolonged pacifier-sucking (> or = 24 months) to be a significant risk factor for caries development in children, with a rather high relative risk (RR) of 3.5 (95% confidence interval (CI), 1.5-8.2; P= 0.003). Prolonged use of a nursing bottle at night (> or = 24 months) was also a risk factor, but less significant than pacifier-sucking (RR, 2.6; CI, 1.1-6.4; P= 0.03). On the grounds of this study we conclude that prolonged pacifier-sucking (> or = 2 years) and use of a nursing bottle at night are risk factors for dental caries in children.

Bottle Feeding↗

PubMed1998

A high sucrose diet decreases the mechanical strength of bones in growing rats.

High sucrose diets alter mineral metabolism in humans and animals. We examined the effect of a high sucrose diet on bone growth, composition and mechanical strength in growing rats. Weanling Wistar rats received a high sucrose (43 g/100 g) diet (9 males, 11 females). In the control diet (8 males, 8 females), sucrose was replaced with potato starch, providing an equal energy value. At the onset of the experiment, bones were marked by tetracycline. After 5 wk, the tibias and femurs were weighed, and maximum breaking strengths were determined. Tibias were cut at the tibia-fibular junction; the widths of the bone at the start of the experiment, the periosteal bone formation during the experiment, the widths of the medullary cavity and the final bone width were determined from tetracycline lines. Bone ash weight, Ca and P contents were determined. The breaking strengths of both bones were significantly lower in the sucrose-fed groups of both sexes. In females, the weight of both bones and the final width of the tibias were significantly lower in the sucrose-fed group. The Ca concentration in both bones and the P concentration in tibias were significantly lower in the sucrose-fed group. It was concluded that the metabolic interference induced by sucrose was the reason for the differences. The alterations were more pronounced in females, but independent of body weight.

Animals↗

PubMed1998

The effect of prosthesis disinfection on salivary microbial levels.

The aim of this study was to evaluate how the soaking of dentures in a disinfection solution affects salivary microbe counts and stomatitis of partially dentate patients. Patients soaked their dentures for 4 weeks randomly both in a disinfection solution and in a placebo solution. Mutans streptococci, lactobacilli and yeast counts were measured before and after each test period and also the flow rate, buffer capacity and pH of saliva were registered. Disinfection decreased all microbe levels investigated, but only lactobacilli counts decreased significantly. Placebo treatment had either no effect on salivary microbe counts or they increased slightly. Disinfection caused some reduction of the mucosal inflammation under the denture base, but could not completely remove stomatitis during the 4-week test period.

Adult↗

PubMed1998

Localization of estrogen-receptor-related antigen in human odontoblasts.

Estrogen receptors have been demonstrated in many osteogenic cell lines. Recently, we showed that estrogen deficiency induced by ovariectomy caused enhanced dentin formation in adult rats, suggesting that estrogen receptors may be present in dental tissues. Nothing is known about estrogen receptors in human teeth. We used immunohistochemical staining and immuno-blotting to demonstrate the presence of estrogen receptors in human pulp and/or the pulpo-dentinal border. Unerupted human wisdom teeth were surgically removed, frozen in liquid nitrogen, and prepared for immunological studies. Western blot analysis with monoclonal antibodies specific for human estrogen-receptor-related antigens demonstrated an approximately 29-kDa clear double band in the material scraped from the predentin-odontoblast border and in the fluid that emerged into the pulpal chamber, evidently from the odontoblasts. A weaker double band was also present in pulpal tissue samples. By immunohistochemical staining, estrogen-receptor-related antigens were visualized in the predentinal-odontoblast region and in the pulpal blood vessels. Our results suggest the presence of estrogen receptors in human teeth, and thus the previously reported enhancement of the dentin formation in rats after ovariectomy may be mediated via these receptors.

Adult↗

PubMed1998

A novel organ culture method to study the function of human odontoblasts in vitro: gelatinase expression by odontoblasts is differentially regulated by TGF-beta1.

Odontoblasts cannot be cultured by traditional cell culture methods, thus restricting in vitro studies. Here we present an organ culture method for human odonto-blasts that utilizes the pulp chamber as a culture crucible. Crowns of human third molars were dissected, pulp was gently removed, and the odontoblasts attached to and in the walls of the pulp chambers were cultured in serum-free OPTI-MEM medium, or DMEM/Ham's F12 medium containing 10% serum. Pulp tissues were cultured separately. Cell content and morphology were analyzed by SEM, and the removed pulps were examined by light microscopy. Proteins secreted into the medium with or without TGF-beta1 supplementation were metabolically labeled with [35S]methionine, and the total protein content was assessed by TCA precipitation and SDS-PAGE/fluorography. To assess the role of gelatinolytic enzymes on dentin matrix remodeling, we used enzymography to analyze the effect of TGF-beta1 on gelatinase A and B expression. SEM revealed odontoblasts in pulp chambers after 5 days of culture, with only few or no fibroblasts, and no alterations in the odontoblast cell morphology or differences between the cells cultured in serum-free and serum-containing media. Rarely were any odontoblasts present in pulp tissue. Radiolabeling revealed protein synthesis and secretion until day 6 in both the odontoblast and pulp cultures, with no marked differences between TGF-beta1-treated and control cultures. The level of gelatinase A remained constant up to 7 days, while gelatinase B expression was always low and decreased with time in culture. However, gelatinase B levels were markedly increased upon TGF-beta1 treatment of cells and remained high to day 7. The results suggest that this method provides a novel technique for the study of human odontoblasts in vitro and that odontoblasts can be cultured even in serum-free conditions.

Cells, Cultured↗

PubMed1998

The activation and function of host matrix metalloproteinases in dentin matrix breakdown in caries lesions.

Matrix metalloproteinases (MMPs) are a family of enzymes which, in concert, are capable of degrading collagen. We investigated whether human MMPs could participate in the degradation of dentin organic matrix after demineralization. We performed Western blot analyses using MMP-specific antibodies to identify MMPs in human dental caries lesions. Enzymography and functional activity assays, with 125I-labeled gelatin as substrate or quantitating the degradation of type I collagen, were used to determine the activity of purified and salivary gelatinolytic (MMP-2 and MMP-9) and collagenolytic (MMP-8) enzymes with and without acid-activation in pHs relevant to caries. Respective analyses were done with caries-related bacteria. We performed electron microscope analyses to assess the degradative activity of sterilized salivary host MMPs on demineralized human dentin. Human MMP-2, MMP-8, and MMP-9 were identified in demineralized dentinal lesions. The latent purified forms of these enzymes were activated at low pH (4.5), followed by neutralization, mimicking the conditions during caries progression. Incubation of human saliva at low pH followed by neutralization resulted in a four-fold increase in the gelatinolytic activity. No gelatinolytic or collagenolytic activity was observed in bacterial samples. The activated enzymes in saliva degraded demineralized dentin organic matrix in vitro. These results demonstrate the pH-dependent activation mechanism of MMPs, which may have a distinct role in different physiological and pathological conditions. They further demonstrate that host MMPs, activated by bacterial acids, have a crucial role in the destruction of dentin by caries.

Bacterial Proteins↗

PubMed1997

Effect of ovariectomy upon weaning on the morphometric parameters of femorae and tibiae of growing rats.

To assess the effects of early ovariectomy on whole bone density and several morphometric and serum markers of bone metabolism, female Wistar rats were ovariectomized or sham-operated upon weaning. The animals were fed ad libitum. After 8 weeks, the increase in the weight gains of ovariectomized rats was minute when compared with the control animals. The whole bone densities of the femorae of ovariectomized rats were slightly reduced when compared with the sham-operated animals. The proximal cross section of the femorae of the ovariectomized rats exhibited enhanced periosteal bone apposition and increased cortical area when compared with the sham-operated animals, but the differences were not statistically significant. The cancellous bone of the femora and the proportional areas of trabeculae of the proximal tibia were reduced in ovariectomized rats. It is concluded that ovariectomy upon weaning caused a clear tendency toward osteopenia. Cancellous bone was clearly affected after ovariectomy, indicating its relation to gonadal hormone regulation even during growth.

Animals↗

PubMed1997

Greater concentration of dietary sucrose decreases dentin formation and increases the area of dentinal caries in growing rats.

The effect of increasing dietary sucrose concentration on dentin formation and dentinal caries progression was studied. Weanling Wistar rats received 15, 30 or 43 g/100 g sucrose in a diet; for reference, another group was fed a nonpurified diet. At the onset, tetracycline was injected to mark the dentin formed during the experiment. After 6 wk, lower molars were sectioned sagittally; the areas and thicknesses of the dentin formation during the experiment and dentinal caries lesions were quantified separately in the first and second molars. Feeding the 43% sucrose diet resulted in a significantly lower dentin formation than in other diet groups (P < 0.05). The differences obtained from the area measurements were supported by thickness measurements. In the first molar, the 43% sucrose diet resulted in a significantly greater area of dentinal caries than in the other sucrose groups. The number and severity of caries lesions clearly increased as the concentration of sucrose in the diet increased (r = 0.5, P < 0.05 and r = 0.6, P < 0.05, respectively). This study suggests that the increase in the concentration of sucrose in the diet reduces dentin formation and increases the area of dentinal caries as well as the number and severity of caries lesions; the critical sucrose concentration appears to be between 30 and 43 g/100 g.

Analysis of Variance↗

PubMed1997

Risk factors for colonization of salivary lactobacilli and Candida in children.

We analyzed the occurrence of salivary lactobacilli and Candida in a sample of 166 children aged 1-4 years (mean, 2.5 years) in relation to possible risk factors for colonization of the microbes. The risk factors examined were sucking habits, feeding habits, symptoms of respiratory infections, and antibiotic therapy at the time of sampling. Lactobacilli occurred in 18% of the children's saliva, and Candida in 24%. In the logistic modeling the variables most strongly associated with the occurrence of lactobacilli were pacifier-sucking (relative risk (RR), 2.9; 95% confidence interval (CI), 1.1-7.0; P = 0.01) and antibiotic therapy (RR, 4.6; CI, 1.2-16.9; P = 0.01). The association between positive Candida test and use of a pacifier was also significant (RR, 4.8; CI, 2.1-10.7; P = 0.0001). The results of the study suggest that the use of a pacifier increases the occurrence of both salivary lactobacilli and Candida. It could therefore be a factor influencing caries susceptibility and activity in children.

Anti-Bacterial Agents↗

PubMed1997

The effect of two sucrose diets on formation of dentin and predentin in growing rats.

The effect of two high-sucrose diets on dentinal caries, dentin formation, and the predentin width was studied in Sprague-Dawley rats. Rats were weaned at the age of 3 weeks and for 4 weeks fed a non-cariogenic commercial rat food (R36) for control, a high-sucrose Stephan-Harris (S-H) diet, or a new high-sucrose (sR36) diet in which most of the barley and wheat flour of the control R36 diet were replaced by sucrose. The areas of dentinal caries, the areas of dentin formation, and the width of predentin and dentin were quantified. Both high-sucrose diets induced dentinal caries, and both reduced dentin formation and increased the width of predentin compared with the control diet. Moreover, rats fed the S-H high-sucrose diet showed significantly greater progression of caries and reduction of dentin formation relative to rats fed the new high-sucrose diet, sR36. The high-sucrose diet thus was a substrate for caries-inducing microbes and a significant, but possibly not the exclusive, substrate for host modulation of odontoblast function.

Animals↗

PubMed1997

The effect of early weaning on dentin formation and dentinal caries in rats.

The effect of early weaning on caries progression, dentin formation, and dentin mineralization was examined in four groups of rats. Two groups received a normal diet and were weaned on day 18 or 21, and another two received a sucrose-rich diet and were weaned on day 18 or 21. At age 35 days the lower molars were sectioned sagittally, and the areas of dentin formation and of the dentinal caries were quantified. The width of the predentin zone was measured from histologically stained sections of maxillary molars. Early weaning reduced dentin formation in the group on the high-sucrose diet only the first days; later this effect was partially caught up with. A high-sucrose diet significantly increased caries frequency and extension of caries lesions compared with a normal diet in both early weaned and normally weaned groups. The effect of early weaning on caries frequency and extension in the high-sucrose group was insignificant compared with the normally weaned group on a high-sucrose diet. The predentin zone was wider in the sucrose groups than in the control groups at the end of the experiment. These results indicate that the effect of sucrose on dentin formation was dependent on the stage of physiologic dentin formation, but early weaning as such did not affect this.

Analysis of Variance↗

PubMed1996

Effect of xylitol on dentin formation in molars of adult rats.

A xylitol-induced reduction in dentin formation has been observed in molars of post-weanling rats, but the effect in older animals with a slower rate of secondary dentinogenesis has not been investigated. We examined the effects of different concentrations of dietary xylitol on dentinogenesis in molars of young adult rats. The control group received a commercial basal diet, while for the other 3 groups, the same diet was supplemented with 5, 10 and 20% of xylitol. After 8 weeks, dentin thickness beneath the main fissures in the mandibular 1st and 2nd molars was measured. The final body weights did not differ between the groups. Dentin formation in the 1st molars of the 10 and 20% xylitol groups was significantly lower as compared to the controls, whereas no difference was found between these 2 groups. In conclusion, dietary xylitol reduces dentin formation in young adult rats in spite of the slow rate of dentinogenesis.

Animals↗

PubMed1996

Effect of low-dose glucocorticoid treatment on dentin formation and dentinal caries in rats.

The effect of a low dose of glucocorticoids on dentin formation and progression of dental caries was studied in young rats. The animals were inoculated in the mouth with Streptococcus sobrinus and fed ad libitum a high-sucrose, a high-starch, or a reference diet. The cortisone or placebo pellet was implanted subcutaneously in the back of the necks of the animals. After a 6-week experimental period the areas of dentin formation and dentinal caries were quantified planimetrically. Schiff's staining was used to classify caries. Cortisone reduced the dentin formation both in high-starch and reference diets, but it did not further affect the reducing effect of the high-sucrose diet on dentin formation. Cortisone did not affect the number or severity of dentinal carious lesions.

Analysis of Variance↗

PubMed1995

Morphological analysis of dentine formation in young rat molars during the recovery phase with calcium alone or combined with xylitol following a low-calcium dietary regimen.

The effects of dietary calcium deficiency and subsequent replenishment of the diet with calcium alone or with xylitol were studied. Thirty 3-week-old Wistar rats were labelled with an i.p. tetracycline injection. Twenty rats were fed a diet with 0.026% calcium (Ca-deficient); 10 received a 0.5% Ca diet (controls). After 3 weeks the tetracycline labelling was repeated. Replenishment of the diet was introduced for Ca-deficient rats, and 10 received additional 5% xylitol in the diet. After 4 weeks the labelling was repeated and the animals were decapitated. Dentine formation was measured by the tetracycline stripes in the lower first and second molars. Calcium deficiency during the first 3 weeks reduced dentine formation. In the control and xylitol groups, a much smaller amount of dentine was formed during the recovery period. With Ca alone, dentine formation was faster than in the controls or Ca-xylitol group and did not differ from the Ca-deficient period. These results indicate that in rat molars the odontoblasts can accelerate the rate of dentine formation when calcium is restored to the diet, at least during primary dentinogenesis. This effect was not seen when 5% xylitol was added to the replenishment diet.

Animals↗

PubMed1995

Effects of xylitol and carbohydrate diets on dental caries, dentine formation and mineralization in young rats.

Female Wistar rats were weaned at the age of 3 weeks and fed for 7 weeks either a high-sucrose diet, a non-cariogenic raw potato-starch diet, a high-sucrose diet with 5% xylitol supplement, a raw potato-starch diet with 5% xylitol supplement or a non-cariogenic, commercial, powdered rat food (Ewos R3) for reference. A low xylitol concentration reduced the progression and severity of carious lesions but did not affect dentine apposition or the width of predentine in rats fed high-carbohydrate diets. Widening of the predentine zone in rats fed a high-sucrose diet might reflect disturbed mineralization, which could not be explained by serum ionized calcium or phosphate ion levels and which could not be corrected by low xylitol concentrations. It is concluded that the reduced area of dentinal carious lesions after low xylitol supplementation is not dependent on dentine formation or mineralization, but rather on direct effects in the mouth.

Animals↗

PubMed1995

Effect of sucrose and xylitol diets on dentin formation and caries in rat molars.

To investigate the effects of a high sucrose diet and xylitol on secondary dentinogenesis and dentinal caries, a part of the sucrose in a high-cariogenic diet was replaced by xylitol. Fifty-four 3-wk-old Wistar rats were labeled with tetracycline and divided into groups. One group received a high sucrose diet (43% sucrose). In two other groups 5% and 20% of the sucrose was replaced by xylitol. A control group received non-cariogenic food. Six weeks later the mandibles were sectioned sagittally. Schiff staining was used to classify the caries, and the areas of dentin formed during the experiment and dentinal caries in first and second molars were measured planimetrically. The high sucrose diet reduced dentin formation of the molars, and this reduction was further increased by xylitol. Caries initiation and dentinal caries progression were significantly reduced by 20% xylitol, whereas only a slight reduction in caries progression was observed with 5% xylitol. Also, a negative correlation between the dentin formation and dentinal caries progression was observed in the high sucrose and 5% xylitol groups. In conclusion, xylitol together with high sucrose reduced dentin formation and dentinal caries progression, and the effect was dose-dependent.

Animals↗