The effects of in vitro fluoride mouth rinse on the antibacterial properties of orthodontic cements.

OBJECTIVES: To investigate the ability of orthodontic cements to regain their antibacterial effect after aging for 1 month, followed by 2 weeks of fluoride 'recharging' through daily fluoride rinse. MATERIALS AND METHODS: Four orthodontic cements were tested: composite resin-based materials (Transbond XT and Transbond Plus), a conventional glass ionomer cement (CX Plus) and dual-cured resin-reinforced glass ionomer cement (Fuji ORTHO LC) by direct contact test. After polymerization and a 30-day aging process, the samples were rinsed daily with 0.05% NaF solution for 14 days. Twenty-four hours after the last fluoride rinse, Streptococcus mutans cells (approximately 1 x 10(6) ) were placed on the surface of each sample for 1 h at 37°C to establish direct contact. Bacterial growth was monitored for 24 h by temperature-controlled spectrophotometry. Similar experiments were conducted after aging for 48 h and 72 h after the last fluoride rinse. One-way anova, two-way anova, and Tukey's multiple comparison test were applied to the data. RESULTS: Twenty-four hours after the last fluoride rinse, the resin-modified glass ionomer and the glass ionomer showed potent antibacterial properties, whereas the composite-based material Transbond XT encouraged bacterial growth. After 72 h, only Fuji Ortho LC maintained its bacteriostatic properties while all the other tested materials showed no antibacterial activity. CONCLUSIONS: Fourteen days daily fluoride rinse temporarily revives the antibacterial properties of the resin-modified glass ionomer cement and glass-ionomer-based cement.

Incorporation of chlorhexidine diacetate in provisional cements: antimicrobial activity against Streptococcus mutans and the effect on tensile strength in vitro.

AIM: To test the antibacterial capacities and tensile strengths of three commercially available provisional cements to which chlorhexidine diacetate was added and compare them to the same unmodified cements. METHODOLOGY: Sixty cylindrical samples were prepared from either three noneugenol provisional cements or the same cements modified by the addition of chlorhexidine diacetate at 7.5% w/w, with a total of 360 samples. The cements tested included Tempbond NE, Rely X Temp NE and Freegenol. Forty-eight samples from each cement were aged in saline that was replaced twice a week for up to 96 days. Twelve of these samples were removed at either 1, 15, 30 or 96 days and assessed for antibacterial properties against Streptococcus mutans with an agar diffusion test. Twelve samples of each cement, with and without chlorhexidine diacetate, were also tested 7 days after the initial setting for their tensile strength using a diametrical tensile strength test applied with an Instron machine. The results were analysed using either one-way or three-way anova. RESULTS: The addition of chlorhexidine diacetate resulted in provisional cements with antibacterial properties that persisted through ageing in saline for up to 96 days. The addition of chlorhexidine did not reduce the diametrical strength of the cements. CONCLUSIONS: The addition of chlorhexidine diacetate to provisional cements rendered all three cements antibacterial against S. mutans and this activity was maintained even after prolonged ageing of the cements, without compromising their tensile strength at 7 days.

A laboratory assessment of enamel hypoplasia of teeth with varying severities of dental fluorosis.

The effect of lifelong exposure to drinking-water containing fluoride on tooth enamel microhardness was investigated. Dental fluorosis of teeth from adult subjects, who lived continuously since birth in areas characterized by the hot climate of India, supplied by drinking-water containing between 0.5 and 8.7 parts/10 F, was estimated by the Dean score. Tooth enamel sections were examined from the enamel surface towards the dentino-enamel junction (DEJ) for microhardness. Separated enamel crowns were pulverized and analysed for fluoride. Regarding the distribution of the fluoride concentrations in the drinking-water, we selected a partition below and above 0.8 parts/10 F as a criterion for comparison between the results. Tooth enamel of humans from Israel living in a drinking-water area containing about 0.5 parts/10 F was also examined. Positive associations were evident between fluoride in drinking-water, fluoride concentrations in the bulk enamel and fluorosis selection. A significantly high inverse relationship was evident between the fluoride concentration of the drinking-water and the subsurface enamel microhardness. In similar fluoride-concentration drinking-water areas of India and Israel the microhardness of the subsurface enamel was less for the Indian teeth. The microhardness of the enamel near the DEJ for the three different water fluoride-concentration areas was not significantly different.

Effects of honey consumption on enamel microhardness in normal versus xerostomic patients.

The aim was to investigate the effect of honey on the microhardness of enamel in normal and xerostomic patients. Normal subjects and patients who were xerostomic after neck irradiation, wearing prosthetic appliances with slabs of human enamel inserted, were asked to consume a single teaspoonful of pure honey, pH 3.9. Measurements of the saliva pH were taken before, during and after a 5 min exposure to the honey. The pH of the honey-saliva mixtures decreased significantly from about 6 to 4 in both groups, returning to the baseline pH after the mixture was swallowed. The initial microhardness of the surface of the enamel slabs decreased significantly after consumption of a teaspoonful of the honey in the subjects with a regular saliva flow, whereas in the irradiated dry-mouth patients, no enamel microhardness decrease occurred. The supposed solubility-reducing factor present in honey which, according to the literature remains active in the absence of saliva, but will be inactivated by salivary enzymes, gives some support to the hypothesis that honey is less cariogenic in dry-mouth subjects. The absence of adequate controls in the present study prevents the investigation of how specific this effect is to honey.

Fluoride and hard cheese exposure on etched enamel in neck-irradiated patients in situ.

OBJECTIVES: The effect of a fluoride mouth rinse with hard cheese exposure was investigated on rehardening of an etched tooth enamel surface in subjects with radiation-induced hyposalivation in situ. METHODS: Ten patients, six males and four females of mean age 48 years, irradiated with 30 Gy per week for neck and head cancer, volunteered for the present intraoral study. The unstimulated saliva flow rate varied between 0.01 and 0.15 ml min-1. Enamel slabs, approximately 2 mm x 2 mm in size, cut from human molar teeth were embedded in self-curing acrylic resin to fit a microhardness tester. Hardness measurements were carried out on the polished and subsequently etched enamel surface, rinsed for 1 min in the mouth with 10 ml Meridol (GABA INT), containing 0.025% F as amine fluoride and stannous fluoride, and exposed alternatively to mastication of 20 g cheddar cheese for 5 min. RESULTS: Surface erosion of the enamel slabs decreased the mean hardness to a similar degree in all samples. The difference between the mean increased degrees of enamel microhardness following fluoride, fluoride and hard cheese, or repeated fluoride-cheese exposures was significant compared to the etched enamel values. The rate of rehardening derived from a second fluoride-cheese treatment was found to be improved significantly. It seems that the reduced saliva flow in xerostomic patients is sufficient to release bound calcium and phosphate from cheese products. CONCLUSIONS: It is suggested that for xerostomic patients frequent exposures to low-fluoride solutions combined with hard cheese consumption may prevent and remineralize initial demineralization.

Transverse bond strength of repaired acrylic resin strips and temperature rise of dentures relined with VLC reline resin.

This study measured the transverse strength of polymethyl methacrylate heat-cured resin samples repaired with Triad visible light-cured reline resin with and without bonding pretreatments and with autopolymerizing resin, and it measured the temperature rise of Triad resin during relining of complete dentures at various curing cycles. The results indicated that pretreatment with either monomer or Triad bonding agent improved the bond of the Triad visible light-cured reline resin to the heat-cured resin. However, the use of the monomer rather than bonding agent resulted in a stronger bond and obtained values similar to those of samples repaired with autopolymerizing resin. Polymerization of samples repaired with Triad resin in the curing unit for two cycles of 5 minutes with 1 minute between cycles resulted in bubble formation and severe distortion of the heat-cured resin in the samples. Curing of the relined dentures for 10 minutes as recommended by the manufacturer raised the average peak temperature to 120 degrees C. In addition, it was shown that interrupting the light curing cycle attenuated the temperature rise, but it also resulted in a relatively softer reline resin. A continuous light curing of at least 5 minutes with the adjunct temperature rise is required to reach 1-hour hardness of 21.8 Vickers hardness number of the Triad reline resin.

Interpositional bone grafting technique to widen narrow maxillary ridge.

A narrow edentulous alveolar ridge, less than 6 mm in the buccopalatal aspect, can prevent restoration by means of endosseous implants. A widening technique using alveolar ridge splitting and interpositional autogenous bone grafting is described. Accurate imaging of the alveolar bone shape and size was assessed with computerized tomography in a 1:1 scale. Following 6 months of healing, osseointegrated Brånemark implants were placed in the grafted sites.

Finite element analysis of a new system (IL) for supporting an implant-retained cantilever prosthesis.

A new system (the IL system) for supporting the distal extension of a cantilevered prosthesis is designed from a short implant and a special ball-type attachment. The finite element method was employed to analyze this system and the surrounding bone, as well as a conventional prosthesis, in two dimensions. Effective and maximum stresses in tension and compression were determined. A comparison of these quantities between the IL-supported prosthesis and a conventional prosthesis was carried out. It was observed that use of this system to support the distal extension of a cantilevered prosthesis dramatically lowers the stresses in the bone, cantilever, and implants. Therefore, this system may reduce failures within the implants, prostheses, and surrounding bone. Moreover, employment of a relatively long-span prosthetic extension in the posterior region of the jaw should be possible. This new system is recommended for completely and partially edentulous patients.

Microleakage of class 2 Superbond-lined composite restorations with and without a cervical amalgam base.

The purposes of the present study were: 1) to assess the microleakage at the cervical margin of Superbond-lined composite restorations with and without a cervical amalgam base and compare the results to cervical margins of composite restorations lined with Scotchbond 2, and 2) to compare the quality of the occlusal margins of Superbond-lined P-50 restorations with those bonded with Scotchbond 2. Forty-eight class 2 cavities were prepared in extracted or exfoliated primary molars. The teeth were randomly divided into three groups and restored as follows: Group A, amalgam + Superbond + P-50 (sandwich); Group B, Superbond + P-50; Group C, Scotchbond 2 + P-50 (control). Marginal leakage was assessed by the degree of dye penetration on sections of the restored teeth. The occlusal margins presented no or minimal leakage (degrees 0 and 1) in 53% of Group A restorations, 60% of Group B, and 44% of Group C. These differences were not statistically significant (P<0.05). The cervical margins showed moderate to severe dye penetration (degrees 2 and 3) in 94% of Group A, 47% of Group B, and 87% of Group C. These differences were statistically significant (P<0.05). The amalgam/Superbond/composite interface exhibited no leakage in 70% of the restorations. Although marginal leakage was not completely eliminated, Superbond exhibited significantly less leakage (P<0.05) at the cervical margins than Scotchbond 2 or amalgam with Superbond.

Enamel rehardening by bread consumption.

PURPOSE: To investigate the in situ rehardening effect by white or whole-meal bread on softened enamel. MATERIALS AND METHODS: Twelve volunteers wearing orthodontic removable appliances participated in this study. The intraoral test was chosen for measuring microhardness of enamel slabs inserted into the dental appliance. Average microhardness of enamel was calculated at three stages: At start (baseline), after exposing the enamel slabs to a citrus beverage (pH 3.4) for 30 minutes in vitro as a softening agent, followed by intraoral exposure for a duration of 5 minutes to stimulated secreted saliva by parafilm chewing (control), or to 15g white- and wholemeal-bread mastication respectively (experimental). RESULTS: A significant rehardening of the softened enamel surfaces took place following mastication of the two bread samples and salivary secretion. The differences in the rehardening potentials of the bread samples as compared to that of saliva were not significant. From the conditions chosen for the experiment, there was no sufficient evidence to support the hypothesis that bread eating with calcium and phosphate concentrations at the existent levels will afford a significant greater rehardening than saliva alone.

Diametral tensile strength and bonding to dentin of type I glass ionomer cements.

This study evaluated the diametral tensile strength of type I glass ionomer cements and measured their tensile and shear bond strengths to dentin with and without conditioning. Four brands of glass ionomer cement and one brand of zinc phosphate cement were tested. Disks of each cement type were prepared and the 7-day diametral compression test for tension was conducted. The shear and tensile tests, with and without 10% polyacrylic acid dentin conditioning, were performed with an Instron testing machine. Two additional groups, one for each bond test, were prepared and conditioned with 90% trichloracetic acid. No significant differences of the diametral strength were found among the various glass ionomer cements. The comparison of means suggests that, except for trichloracetic acid dentin pretreatment, the conditioning is an effective promoter of shear strength and has no significant effect (p < 0.01) on the tensile bond strength. However, trichloracetic acid was found to be a most effective dentin conditioner for both shear and tensile bond strengths (p < 0.01).

Enamel rehardening with cheese in irradiated patients.

Radiotherapy of head and neck malignancies results in severe xerostomia which induces radiation caries. Hard cheese has potent anti-cariogenic effects, even with minimal salivary gland function. Eight patients irradiated for neck cancer volunteered for this study. The saliva flow rate varied between 0.0-0.15 ml/minute. In vitro etched enamel slabs, prepared from human teeth, were exposed intraorally to parafilm stimulated salivary secretion for 5 minutes or, alternatively, to cheese compounds and saliva due to masticating 20 gm hard cheese for 5 minutes. Microhardness measurements were carried out on the enamel surface at start (baseline), after etching and after rehardening. Stimulated saliva or cheese compounds and saliva, due to mastication, induced rehardening of surface enamel in both, non-irradiated and irradiated subjects. The rehardening was significantly increased in the irradiated group consuming cheese as compared to rehardening by stimulated saliva only and not significantly less of that achieved in non-irradiated subjects. Rehardening achieved with stimulated saliva in irradiated patients was of a borderline-significant lower degree in comparison to non-irradiated subjects. The reduced rehardening capacity of a decreased saliva flow in irradiated patients may be complemented by cheese compounds. For xerostomic patients, hard cheese consumption may be regarded as effective to keep initial caries under control.

Effect of hydrogen peroxide and sodium perborate on the microhardness of human enamel and dentin.

The effect of 30% hydrogen peroxide and a paste of sodium perborate mixed with hydrogen peroxide at different temperatures and time intervals on the microhardness of human enamel and dentin was examined. Intact extracted human teeth were sectioned, embedded in acrylic resin, polished, and divided into four test groups related to surface treatment. The groups were 30% hydrogen peroxide at 37 degrees C, 30% hydrogen peroxide at 50 degrees C in an illuminated chamber, a paste of sodium perborate mixed with hydrogen peroxide at 37 degrees C, and a paste of sodium perborate mixed with hydrogen peroxide at 50 degrees C in an illuminated chamber. Teeth treated with distilled water at either 37 degrees C or 50 degrees C served as controls. The results indicated that treatment with 30% hydrogen peroxide reduced the microhardness of both enamel and dentin. This reduction was statistically significant after 5-min treatment for the dentin and after 15-min treatment for the enamel (p < 0.05). Treatment with sodium perborate mixed with hydrogen peroxide did not alter the microhardness of either the enamel or dentin at the tested temperatures and time intervals. It is therefore suggested that the use of high concentrations of hydrogen peroxide for bleaching purposes should be limited. Sodium perborate appears to be a less damaging bleaching agent.

Enamel rehardening by soft cheeses.

The in situ rehardening effect by soft cheeses: unsweetened, sucrose-sweetened and strawberry marmalade-flavored, pH 4.5, 4.25 and 4.0 as compared to secreted saliva, was investigated on softened enamel. Ten volunteers wearing orthodontic removal appliances participated in the study. The intraoral test was chosen for measuring microhardness of enamel slabs inserted into the dental appliance. Average microhardness was calculated at three stages: at start (baseline), after exposing the enamel slabs to a citrus beverage (pH 3.3) for 30 minutes in vitro as a softening factor and then intra-oral exposure during 5 minutes to 125 g soft cream cheese mastication, unsweetened and sweetened (experimental), or to saliva secretion, pH 6.8, only by mouth movements (control). Significant rehardening effects on the softened enamel surfaces took place following mastication of the various soft cheeses and salivary secretion. The differences in the rehardening potentials of the cheeses as compared to that of saliva were significant. The rehardening effect of the cheeses decreased (not significantly) in the following order: unsweetened cheese, sucrose-sweetened marmalade flavored cheese and sucrose-sweetened cheese. In spite of the acidic pH of the soft cheese substrates,--the buffering capacity of the protein compounds and the Ca,PO4 ions neutralize a softening effect--the rehardening effect is probably due to an uptake of Ca and PO4 ions by the softened surface enamel from the cheese bolus consumed over the entire 5-minute period.

The ratio between vertical and horizontal changes of impressions.

The purpose of this study was to analyze theoretically and experimentally the relations between the horizontal and the vertical changes of impressions taken with a mandibular stock tray. According to the theoretical analysis the ratio between the horizontal (delta X) and the vertical changes (delta Z) can be expressed as: [formula: see text] where mu is the Poisson's ratio and Lx and Lz are the horizontal and vertical dimensions of the die, respectively. With regard to the experimental findings the Poisson's ratio calculated by this expression was mu = 0.44 which fits the range of Poisson's ratio for rubber materials. In addition it was shown that the ratio between the vertical and horizontal strains is constant for a particular impression technique.

Effect of fluoride varnish on the retentive strength of provisional crowns luted with various temporary cements.

The retention of temporary crowns was studied with the use of a fluoride varnish (Duraphat) combined with various temporary cements. The mixture of Duraphat varnish and cement improved retention, with the exception of Opotow cement. Applying Duraphat varnish to the tooth surface before cementation enhanced the retentive strength of Tempbond, weakened the retention of Freegenol, but had no effect on Opotow cement. A "transfer effect" was observed, inasmuch as the Duraphat varnish encouraged adherence of the cement to the tooth structure rather than to the temporary crown.

Effect of cervical coating of ethyl cellulose polymer and metacrylic acid copolymer on the radicular penetration of hydrogen peroxide during bleaching.

Extraradicular leakage of oxidizing agents during bleaching is an undesirable event and thus need to be prevented. The effect of external cervical coating of ethyl cellulose (EC) and metacrylic acid copolymer (MAC) on the radicular penetration of hydrogen peroxide during intracoronal bleaching was examined. Single rooted human premolars extracted for orthodontic reasons were used. The cementum covering the cemento-enamel junction was mechanically removed and the teeth treated endodontically and bleached with 30% hydrogen peroxide. Radicular hydrogen peroxide penetration was measured before coating the teeth and after applications of 1-3 layers of EC or 3 layers of MAC external cervical coatings. It was found that the radicular penetration of 30% hydrogen peroxide was related to the number of layers of cervical EC coatings. Application of one layer of EC did not reduce the hydrogen peroxide penetration. Two and three layers of EC reduced the hydrogen peroxide penetration by 38% and 85% respectively. Three layers of MAC reduced the radicular hydrogen peroxide penetration in 83%. Statistically, a highly significant difference was found between the teeth coated with three layers of either EC or MAC and the noncoated teeth (p < 0.001). It was concluded that application of ethyl cellulose or metacrylic acid copolymer to exposed cervical root surfaces may effectively prevent extraradicular leakage of bleaching agents.

Microleakage of Class 2 glass-ionomer-silver restorations in primary molars.

The aims of this study were to assess microleakage at the cervical margins of class 2 "sandwich" restorations placed with two glass-ionomer-silver cements in primary molars, to compare the quality of the occlusal margins of these restorations to those prepared with Miracle Mix and Ketac Silver, and to assess by scanning electron microscopy (SEM) the marginal micromorphology of those restorations. Fifty-two class 2 restorations were prepared in extracted primary molars and were restored as follows: 1) Ketac Silver + Estilux Posterior (sandwich), 2) Miracle Mix + Estilux Posterior (sandwich), 3) Ketac Silver only, and 4) Miracle Mix only. No or minimal leakage was evident in most of the occlusal margins, whereas severe leakage was observed in almost 70% of the cervical margins of the Ketac Silver groups. Scanning electron microscopy evaluation demonstrated good adaptation at the buccal and lingual margins of all the restorations. Sixty-seven percent of the Miracle Mix restorations had no defects at the cervical margins, as opposed to only 17% of those with Ketac Silver.

Effect of trichloracetic acid on the microhardness and surface morphology of human dentin and enamel.

Trichloracetic acid is recommended for the treatment of external cervical root resorption. The present study examined the effect of 90% trichloracetic acid on the microhardness and surface morphology of human dentin and enamel. Intact extracted human teeth were sectioned and embedded in acrylic resin. Each tooth was grinded and highly polished exposing a flat surface of dentin and enamel. The teeth were treated with 90% trichloracetic acid for 30, 60 and 90 s. Vicker's microhardness of the dentin and enamel was assessed for each tooth before and after each treatment. In addition the surface morphology of a trichloracetic acid treated tooth was examined via SEM. The results showed that 90% trichloracetic acid caused a second order type reduction of the microhardness, as well as structural changes in both dentin and enamel.

Effect of hard cheese exposure, with and without fluoride prerinse, on the rehardening of softened human enamel.

The in situ rehardening effect was compared between Cheddar cheese consumption and saliva secretion with and without a fluoride pretreatment on softened human enamel. Ten volunteers wearing prostheses which held slices of human enamel participated in this study. Average microhardness of enamel was determined on the surface at baseline, after exposing to an acidic beverage, after exposing to saliva and mastication of cheese, with and without a mouth F prerinse (10 ml Meridol containing 0.025% F). The rehardening was increased in the groups consuming cheese compared to the saliva controls. The effect was increased by an F prerinse; the initial hardness of the intact enamel surface, however, was not reached.