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Biomedical subjects

H Limeback

Publications and source records attributed to H Limeback.

At least 19 recordsLinked to original sources
PubMed2005

How does fluoride affect dentin microhardness and mineralization?

Fluoride (F) has been a useful instrument in caries prevention. However, only limited data exist on the effect of its long-term use on dentin mineralization patterns and microhardness. The objective of this study was to evaluate the influence of tooth F concentration ([F]) and dental fluorosis (DF) severity on dentin microhardness and mineralization. We collected 137 teeth in Montreal and Toronto, Canada, and Fortaleza, Brazil, where optimum or suboptimum levels of water F were 0.2 ppm, 1 ppm, and 0.7 ppm, respectively. Teeth were analyzed for DF severity, dentin [F], enamel [F], dentin microhardness, and dentin mineralization. Dentin [F] correlated with DF severity; enamel [F] correlated with dentin microhardness and dentin mineralization; DF severity correlated with dentin microhardness. Genetic factors (e.g., DF severity) and environmental factors (e.g., tooth [F]) influenced the mechanical properties (microhardness) of the teeth, while only the environmental factors influenced their material properties (e.g., mineralization). Fortaleza teeth were harder and less mineralized and presented higher dentin [F] values. Montreal teeth presented lower levels of DF when compared with both Toronto and Fortaleza teeth.

Adolescent↗
PubMed2004

Is fluoride concentration in dentin and enamel a good indicator of dental fluorosis?

Despite some studies correlating dental fluorosis (DF) and fluoride (F) concentration in dental enamel, no information is available about DF and dentin F concentration. Our objective was to determine the correlation between teeth F concentration and DF severity in unerupted human 3rd molars, and the correlation between dentin and enamel F concentrations in the same tooth. Ninety-nine 3rd molars were studied-53 from Fortaleza, Brazil (F water, 0.7 ppm), 22 from Toronto (1.0 ppm), and 24 from Montreal (0.2 ppm). DF severity was evaluated according to the Thylstrup-Fejerskov Index, while F concentration was analyzed by Instrumental Neutron Activation Analysis. DF severity varied between TF0 and TF4, while F concentration ranged between 39 and 550 ppm in enamel and 101 and 860 ppm in dentin. Our results showed correlation between dentin F concentration and DF (r(S) = 0.316, p = 0.001), but no correlation between enamel F concentration and DF (r(S) = 0.154, p = 0.133). No correlation was observed between dentin and enamel F concentrations in the same tooth (r(S) = 0.064, p = 0.536).

Adult↗
PubMed2003

Breastfeeding is protective against dental fluorosis in a nonfluoridated rural area of Ontario, Canada.

To determine the relationship between early infant feeding and dental fluorosis in a non-fluoridated area, 1367 children were examined for fluorosis and given a water sample vial and questionnaire. 752 families responded (55%). Breastfeeding was reported by 69% of respondents, with 53.6% breastfed < 6 months, 35.3% 6-12 months, and 11.1% > 1 year. Formula feeding was reported by 84% of respondents, with 60.3% and 39.7% formula fed for < 1 year and > 1 year, respectively. Fluorosis prevalence was 23.3% and was present in 27.2%, 19.6% and 13.8% of children breastfed for < 6 months, 6-12 months, and > 12 months, respectively (P < .05). About 87% of formula fed children had tap water added to the bottle. Breastfeeding for > 6 months may protect children from developing fluorosis in the permanent incisors. This study suggests that dental professionals should support efforts to increase the rate and duration of breastfeeding.

Bottle Feeding↗
PubMed2003

How does fluoride concentration in the tooth affect apatite crystal size?

Despite fluoride's (F) well-documented ability to prevent caries, the effects of F concentrations on enamel and dentin apatite crystals are unknown. The present study examined the hypothesis that tooth F concentration and tooth crystallite size correlate. One hundred human unerupted third molars were studied-53 from Fortaleza-Brazil (F water 0.7 ppm), 23 from Toronto (1.0 ppm), and 24 from Montreal (0.2 ppm). F concentration was analyzed by Neutron Activation Analysis and apatite crystal size by powder x-ray diffraction. A positive correlation between dentin F concentration and enamel crystallite length and width was found. Enamel crystallite length was significantly greater in teeth from Fortaleza than in teeth from Toronto (p = 0.011) and Montreal (p = 0.003). Enamel crystallite widths were significantly greater in Fortaleza teeth compared with those from Toronto (p = 0.020) and Montreal (p < 0.001). No difference in the dentin crystallite size was seen in the 3 regions. Thus, tooth F concentration and crystallite size correlate.

Analysis of Variance↗
PubMed1999

A re-examination of the pre-eruptive and post-eruptive mechanism of the anti-caries effects of fluoride: is there any anti-caries benefit from swallowing fluoride?

The belief that fluoridated water reduces caries incidence by half stems from years of fluoridation studies where the caries rates of people in various fluoridated and non-fluoridated communities were compared. By their nature, the water fluoridation trials were not able to distinguish between the topical effects of the fluoride in the water and the systemic effects of the fluoride that is inevitably swallowed and incorporated into developing teeth. Some attempts have been made to estimate the contribution of systemic fluoride to the control of dental caries but researchers are discovering that the topical effects of fluoride are likely to mask any benefits that ingesting fluoride might have. In this updated review of the pre-eruptive vs. post-eruptive benefits of fluoride in the prevention of dental caries, a re-examination of the literature, which is often cited to support the notion that swallowing fluoride, either in water or in pill form, was done in recognition of the mounting evidence for the topical mechanism as being the primary mechanism for the prevention of dental caries. Maximum benefits from exposing newly erupted teeth to topical fluoride in the oral cavity may have been seriously under-estimated. This has obvious implications for the use of systemic fluorides to prevent dental caries and forces everyone working in the field to examine more closely the risks and benefits of fluoride in all its delivery forms.

Administration, Oral↗
PubMed1999

Fluorosis risk in grade 2 students residing in a rural area with widely varying natural fluoride.

OBJECTIVES: This pilot study was performed to determine the prevalence of dental fluorosis and the association between fluorosis and a number of risk factors in a group of second grade students in a rural, non-fluoridated area of Ontario, Canada. METHODS: Of 1739 students screened during routine health surveillance, 1367 had erupted maxillary central incisors. Fluorosis was scored on these children using the Tooth Surface Index of Fluorosis (TSIF). A fluoride exposure questionnaire and water sample vial was sent home from school with each child. RESULTS: Valid responses were obtained for 752 children (55%). The prevalence of fluorosis in respondents was 23.3%, with 4.9% scoring TSIF of 2 or more. In bivariate analysis, several variables were significantly associated with the prevalence and/or severity of fluorosis. These included: water fluoride concentration, breast-feeding duration, professionally applied topical fluoride, fluoride supplement use, bottle-feeding, fluoridated mouthwash use, and early parental toothbrushing with toothpaste. In logistic regression analysis limited to children living at the current residence for 4 years or more, only four variables had significant independent effects. These were water fluoride concentration, breast-feeding duration, fluoride supplement use, and fluoridated mouthwash use. CONCLUSIONS: These findings indicate that fluorosis is an important concern in non-fluoridated areas. Fluoride supplements should not be recommended unless an independent home water test is performed. Breast-feeding for 6 months or more may protect children from developing dental fluorosis in the permanent incisors.

Analysis of Variance↗
PubMed1998

Implications of oral infections on systemic diseases in the institutionalized elderly with a special focus on pneumonia.

Systemic infection in the elderly patient living in a chronic care setting presents a significant burden to the health care system. The extent to which oral organisms cause systemic infections through hematogenous dissemination in the institutionalized elderly is still unknown. A more likely and common route of systemic infection by oral microorganisms is through aspiration of oropharyngeal fluids containing oral pathogenic microorganisms, which colonize the lower respiratory tract and cause pneumonia. Respiratory pathogens emerge in the dental plaque of elderly patients with very poor oral hygiene and severe periodontal disease. In the chronic care setting, aspiration of oropharyngeal fluids contaminated with these bacteria occurs in patients with diminished host defenses, resulting in bacterial pneumonia. This is also a problem in intensive care units in the hospital setting. In one study, pre-rinsing with a 0.12% chlorhexidine gluconate mouthwash significantly lowered the mortality rate from postsurgical pneumonia in patients undergoing open heart surgery. Selective digestive decontamination, a technique involving the topical application of antimicrobials to reduce the risk of colonization of the respiratory tract, has been used to reduce the incidence of nosocomial pneumonia in the acute care setting of hospitals. This technique has not been employed in the nursing home setting. Whether improving oral hygiene would also lower the risk in either of these settings has not been studied. A number of obstacles must be overcome in designing studies to investigate the relationship between oral infections and lung infections in the institutionalized elderly. Ethical issues must be addressed, and full collaboration of the medical team is required. Future studies should establish whether reducing the risk for pneumonia in the institutionalized elderly is possible through improved oral health.

Aged↗
PubMed1997

Oral health and history of respiratory tract infection in frail institutionalised elders.

OBJECTIVES: The purpose of this study was to look for a relationship between history of respiratory tract infection (RTI) and oral health in very old subjects. SETTING AND SUBJECTS: 302 frail elders (mean age: 85 years) living in a medical care facility were examined by one dentist. OUTCOME MEASURES: The incidence of RTI over 1 year had been recorded along with markers of nutritional status and degree of dependency. The oral examination comprised an evaluation of hygiene, quality of prostheses and the prevalence of caries, periodontal disease and mucosal disorders. RESULTS: One third (33%) of the subjects had experienced at least one episode of RTI, and a fifth (19%) had visited the dentist in emergency. The incidence of RTI had been greater among dentate subjects and those who came to the dentist in emergency. The dentate subjects with a history of RTI had higher plaque score (P = 0.02). Half (49%) of the subjects had oral disorders that could develop in a dental emergency and these subjects had had a higher risk of RTI (relative risk: 1.9, 95% confidence interval: 1.1-3.9). The presence of selected oral disorders associated with low serum albumin increased the relative risk of having had RTI to 3.2 (1.5-6.7). The association between presence of actual oral health problems and previous experience of RTI was more noticeable in those who had poor general health or were more debilitated. CONCLUSIONS: The present study suggests that poor oral hygiene and the presence of potential emergency could be major risk factors for RTI among the frail elderly.

Aged↗
PubMed1996

Comparison of recommended and actual mean intakes of fluoride by Canadians.

The findings of two separate 1993 reports, one of the actual intake of fluoride by Canadians and the other on their recommended fluoride intake, are summarized and compared. Recent increases in very mild and mild dental fluorosis suggest that the gap between current fluoride intake and recommended intake is narrowing. The daily swallowing of fluoride dentifrice makes a large contribution to the actual total daily fluoride intake, especially in children seven months to four years of age, the age group most susceptible to fluorosis in the anterior permanent teeth. Because of the available data and methods used in each study, the reported actual and recommended fluoride intakes vary greatly both within and between age groups. It is likely that individual variation in fluoride intake also varies greatly. Comparison of the data in the two reports revealed that, for breast-fed infants and nearly all other age groups without fluoridated water, the ranges of the estimates of actual intake are lower than the recommended ranges. However, for formula-fed infants and all other age groups using fluoridated water, the estimates of actual intake greatly exceed the recommended intake, especially for the seven months to four years age group. Ingestion of fluoride at these levels during tooth development will contribute to dental fluorosis. All of the age groups have fluoride intake estimates below levels at which skeletal signs of fluoride exposure are noticed. Nevertheless, exposure to fluoride should be closely monitored and inappropriate use of discretionary fluorides curtailed.

Adolescent↗
PubMed1995

Probing glucocorticoid-dependent osteogenesis in rat and chick cells in vitro by specific blockade of osteoblastic differentiation with progesterone and RU38486.

Glucocorticoids and sex-steroids can modulate osteogenesis in vivo and in vitro. Although the effects of glucocorticoids on bone cells in vitro have been described in detail, the role of sex-steroids is not as well defined. We examined whether sex-steroids influence bone metabolism indirectly by regulating glucocorticoid effects on bone. Interactions of the sex-steroid progesterone or its analog RU38486 with the glucocorticoid dexamethasone (dex) were studied in functional assays of osteogenesis. Three osteoblastic models were evaluated: (1) the rat bone marrow stromal cell (RBMC) nodule system; (2) the chick periosteal osteogenesis (CPO) model; and (3) ROS 17/2.8 cells. RU38486, progesterone, and unlabelled dex competitively inhibited 3H-dex uptake by ROS 17/2.8 cells as well as its (3H-dex) binding to cytosol preps. Both RU38486 and progesterone inhibited dex-induced increases in alkaline phosphatase in CPO cultures, in RBMC cultures, and in ROS 17/2.8 cells. Dex-induced decreases in cell proliferation in ROS 17/2.8 cells were reversed by RU38486 but dex-induced increases in proliferation in the CPO model were not affected. In CPO cultures, dex-induced increases in collagen synthesis were inhibited completely by RU38486 and progesterone. Dex-dependent nodule formation in the RBMC was blocked by RU38486. Both RU38486 and dex mediated reduction of calcium uptake in the CPO model but did not affect mineralized tissue area. The data indicate that RU38486 and progesterone competitively inhibit dex-mediated stimulation of osteogenesis in vitro; this inhibition is exerted on early but not late stage differentiation events of osteoprogenitor cells.

Animals↗
PubMed1994

Enamel formation and the effects of fluoride.

The exact biochemical events which result in enamel lesions from excess fluoride ingestion are still unknown. A number of effects of fluoride on enamel organs and on the enamel matrix components of developing teeth are, however, known. These are briefly reviewed, making reference to more recent studies. Two major influences of chronic, low-level fluoride exposure are proposed: fluoride interferes with the processes responsible for the efficient removal of organic matrix components, resulting in protein retention and disorganized enamel crystal formation, or fluoride disrupts the activities of the enamel organ cells which indirectly interferes with normal crystal formation.

Amelogenesis↗
PubMed1992

Dexamethasone recruitment of self-renewing osteoprogenitor cells in chick bone marrow stromal cell cultures.

Bone marrow stromal cells are a mixed population that contribute to the formation of the hematopoietic microenvironment. The osteogenic lineage includes populations of cells that, in culture, form discrete nodules of mineralized tissue when grown in the presence of ascorbic acid and sodium beta-glycerophosphate. We have used nodule formation to assay for the self-renewal capacity of osteoprogenitor cells in chick bone marrow cultures. To examine the regulatory influence of dexamethasone (Dx), first subcultures were grown continuously or split 1:1 at repeated subculture. Cells in continuous culture exhibited less than two population doublings, while cellular proliferation and alkaline phosphatase area were inhibited by 10(-8) mol/L Dx. Cells in split (redistributed) cultures exhibited up to 14 population doublings and cellular proliferation was also inhibited by Dx. In contrast with continuous cultures, redistributed cultures treated with Dx had increased alkaline phosphatase area and 15-fold larger amounts of mineralized tissue formation than controls. Osteogenesis was sustained for up to four subcultures and the ratio of mineralized tissue area to alkaline phosphotase positive cell area was at most 0.55. These data indicate that the osteogenic lineage of bone marrow stromal cells contains self-renewing progenitors that are recruited by Dx in culture and that at a maximum, only 55% of the alkaline phosphatase-positive cell population contributes to osteogenesis.

Alkaline Phosphatase↗