A calcium prerinse required to form calcium fluoride in plaque from a sodium fluoride rinse.

The purpose of this study is to determine whether a calcium (Ca) prerinse used before a 228 µg/g (ppm) fluoride (F) rinse would induce the formation of 'calcium fluoride-like' (CaF2-like) deposits in human dental plaque. Sixty minutes after the use of the Ca prerinse/F rinse, plaque samples were collected from 10 volunteers, homogenized, and split into 2 aliquots. The plaque mass from one aliquot was then extracted with a 'plaque-like' solution that extracted all the CaF2-like deposits. The total F in both aliquots was then determined and compared. The results demonstrated that, as in previous studies, the Ca prerinse induced large increases in plaque fluid and total plaque F. However, unlike previous results without the Ca prerinse, 30% of the plaque F deposits were CaF2 or CaF2-like. Given that maintaining an elevated F concentration in the vicinity of a developing lesion may play an important role in the cariostatic effect of this ion, and the potential advantages of CaF2-like deposits as an F source, these results suggest that a Ca prerinse may increase the cariostatic effect of topical agents.

No calcium-fluoride-like deposits detected in plaque shortly after a sodium fluoride mouthrinse.

Plaque 'calcium-fluoride-like' (CaF(2)-like) and fluoride deposits held by biological/bacterial calcium fluoride (Ca-F) bonds appear to be the source of cariostatic concentrations of fluoride in plaque fluid. The aim of this study was to quantify the amounts of plaque fluoride held in these reservoirs after a sodium fluoride rinse. 30 and 60 min after a 228 microg/g fluoride rinse, plaque samples were collected from 11 volunteers. Each sample was homogenized, split into 2 aliquots (aliquots 1 and 2), centrifuged, and the recovered plaque fluid combined and analyzed using microelectrodes. The plaque mass from aliquot 1 was retained. The plaque mass from aliquot 2 was extracted several times with a solution having the same fluoride, calcium and pH as the plaque fluid in order to extract the plaque CaF(2)-like deposits. The total fluoride in both aliquots was then determined. In a second experiment, the extraction completeness was examined by applying the above procedure to in vitro precipitates containing known amounts of CaF(2)-like deposits. Nearly identical fluoride concentrations were found in both plaque aliquots. The extraction of the CaF(2)-like precipitates formed in vitro removed more than 80% of these deposits. The results suggest that either CaF(2)-like deposits were not formed in plaque or, if these deposits had been formed, they were rapidly lost. The inability to form persistent amounts of CaF(2)-like deposits in plaque may account for the relatively rapid loss of plaque fluid fluoride after the use of conventional fluoride dentifrices or rinses.

AMORPHOUS CALCIUM PHOSPHATE COMPOSITES AND THEIR EFFECT ON COMPOSITE-ADHESIVE-DENTIN BONDING.

This study evaluates the bond strength and related properties of photo-polymerizable, remineralizing amorphous calcium phosphate (ACP) polymeric composite-adhesive systems to dentin after various periods of aqueous aging at 37 °C. An experimental ACP base and lining composite was made from a photo-activated resin comprising 2,2-bis[p-(2'-hydroxy-3'-methacryloxypropoxy)phenyl]propane (Bis-GMA), triethylene glycol dimethacrylate (TEGDMA), 2-hydroxyethyl methacrylate (HEMA) and zirconyl dimethacrylate (ZrDMA); designated BTHZ. An experimental orthodontic composite was formulated from a photo-activated resin comprising ethoxylated bisphenol A dimethacrylate (EBPADMA), TEGDMA, HEMA and methacryloxyethyl phthalate (MEP); designated ETHM. In both composite series three fillers were compared: 1) freshly precipitated zirconium-modified ACP freshly precipitated (as-prepared Zr-ACP), 2) milled Zr-ACP and 3) an ion-leachable fluoride glass. In addition to the shear bond strength (SBS), work to fracture and failure modes of the orthodontic composites were determined. The SBS of the base and lining ACP composites appeared unaffected by filler type or immersion time. In the orthodontic ACP composite series, milled ACP composites showed initial mechanical advantages over as-prepared ACP composites, and produced higher incidence of a failure mode consistent with stronger adhesion. After six months of aqueous exposure, 80 % of specimens failed at the dentin-primer interface, with a 42 % overall reduction in bond strength. BTHZ and ETHM based ACP composites are potentially effective anti-demineralizing-remineralizing agents with possible clinical utility as protective base-liners and orthodontic cements, respectively. The analysis of the bond strength and failure modalities suggests that milled ACP composites may offer greater potential in clinical applications.

Ca pre-rinse greatly increases plaque and plaque fluid F.

Previous studies demonstrated that a Ca pre-treatment greatly increases salivary F from a subsequent NaF rinse. This study examines if these increases are found in plaque and plaque fluid F. Thirteen individuals accumulated plaque before rinsing with: (1) 12 mmol/L NaF (228 microg/g F), (2) 150 mmol/L Ca rinse, or (3) the Ca rinse followed by the F rinse. One hr later, plaque samples were collected, the plaque fluid was recovered, and the plaque residues were extracted 5 times with pH 6.8 or pH 4.8 buffers, and then by acid. The F in each extract after the Ca rinse/F rinse greatly exceeded the corresponding F from the NaF rinse. Consequently, the Ca rinse/F rinse increased the total plaque F and the plaque fluid F by 12x and 5x, compared with the NaF rinse alone. These and the previous salivary results suggest that a Ca pre-treatment may increase the cariostatic effects of topical F agents.

Salivary fluoride from fluoride dentifrices or rinses after use of a calcium pre-rinse or calcium dentifrice.

The low concentration of available calcium (Ca) in oral fluids limits the formation of Ca-mediated fluoride deposits that maintain oral fluoride (F) after a topical F treatment. The purpose of this study was to examine if a high concentration of Ca would increase salivary F when used before a F rinse or dentifrice. We found that a Ca pre-rinse (150 mmol/l Ca lactate) or Ca dentifrice (0.084 g Ca glycerolphosphate per gram dentifrice) used immediately before a 60 s 228-ppm F rinse (12 mmol/l NaF) produced a 4.6x or 3.6x increase (p < 0.05) respectively in the 1 h salivary F concentrations over the F rinse alone. Reducing the post-Ca F rinse to 10 s still produced a significant 2.2x increase in salivary F compared to the 60 s F rinse alone. Used with a conventional 1,100 ppm F (i.e. 1,100 microg F per gram) NaF dentifrice (Crest), the above Ca pre-rinse increased 1 h salivary F levels by 2.3x over the F dentifrice alone. However, a F rinse given before a Ca rinse produced no increase in 1 h salivary F concentrations. Although the persistence of these increases requires further study, these results suggest that a moderately high concentration of Ca given shortly before a F rinse or F dentifrice may increase the cariostatic effect of the F product.

Effect of a calcium prerinse on salivary fluoride after a 228-ppm fluoride rinse.

The objective of this study was to determine if a concentrated calcium prerinse given before a fluoride rinse would cause an increase in the post rinse sali vary fluoride (F). A panel of 5 subjects used a 30, 150 or 300 mmol/l calcium lactate prerinse followed by a 1-min NaF rinse. All calcium prerinses significantly increased the 1-hour saliva F relative to the NaF control without a prerinse. The maximum increase was produced by the 150 mmol/l calcium lactate prerinse and was about ninefold higher than the NaF control.

Continuous-fiber preform reinforcement of dental resin composite restorations.

OBJECTIVES: Direct-filling resin composites are used in relatively small restorations and are not recommended for large restorations with severe occlusal-stresses. The aim of this study was to reinforce composites with fiber preforms, and to investigate the effects of layer thickness and configurations on composite properties. It was hypothesized that fiber preforms would significantly increase the composite's flexural strength, work-of-fracture (toughness) and elastic modulus. METHODS: Glass fibers were silanized, impregnated with a resin, cured, and cut to form inserts for tooth cavity restorations. Also fabricated were three groups of specimens of 2mm x 2mm x 25 mm: a fiber preform rod in the center of a hybrid composite; a thin fiber layer on the tensile side of the specimens; and a thin fiber layer sandwiched in between layers of a hybrid composite. These specimens were tested in three-point flexure to measure strength, work-of-fracture and modulus. Optical and scanning electron microscopy were used to examine the restorations and the fiber distributions. RESULTS: Microscopic examinations of insert-filled tooth cavities showed that the fibers were relatively uniform in distribution within the preform, and the inserts were well bonded with the surrounding hybrid composite. Specimens consisting of a fiber preform rod in the center of a hybrid composite had a flexural strength (mean (SD); n=6) of 313 (19)MPa, significantly higher than 120 (16)MPa of the hybrid composite without fibers (Tukey's at family confidence of 0.95). The work-of-fracture was increased by nearly seven times, and the modulus was doubled, due to fiber preform reinforcement. Similar improvements were obtained for the other two groups of specimens. SIGNIFICANCE: Substantial improvements in flexural strength, toughness and stiffness were achieved for dental resin composites reinforced with fiber preforms. The method of embedding a fiber preform insert imparts superior reinforcement to restorations and should improve the performance of direct-filling resin composites in large restorations with high occlusal-loads.

Remineralization effect of a low-concentration fluoride rinse in an intraoral model.

A previous study showed that a sodium hexafluorosilicate-calcium chloride-based two-solution fluoride (F) rinse containing 6 mmol/l of F was more effective than a 12 mmol/l F sodium fluoride rinse in depositing F on tooth surfaces and increasing oral F levels. The present study compared the remineralization effects of these two rinses in an intraoral de- and remineralization model. The results showed that the 6 mmol/l F two-solution rinse produced greater remineralization in increasing lesion mineral contents and reducing lesion depths. The results demonstrated that the effectiveness of an F regimen depends less on the F dose and more on the ability of the treatment to utilize F efficiently for remineralization.

Changes in lactate and other ions in plaque and saliva after a fluoride rinse and subsequent sucrose administration.

The purpose of this study was to examine plaque and saliva composition after a fluoride rinse and subsequent sucrose application. Fifteen subjects accumulated plaque for 48 h, and then rinsed with a fluoride rinse based on 228 microg/g (ppm) Na2SiF6 and some received no rinse. After 60 min, upper and lower buccal molar plaque samples and 1-min saliva samples were collected. The subjects then rinsed with 10% g/g sucrose solution, and 7 and 15 min later, a second and a third set of samples were collected. Plaque fluid and clarified saliva were then recovered from these samples by centrifugation, and the remaining plaque acid extracted. The plaque fluid, centrifuged saliva, and plaque extract samples were then analyzed using micro techniques for pH, free calcium, phosphate, organic acids (plaque fluid and saliva only) and fluoride. Considering both the fluoride rinse and no-rinse groups, the most notable compositional changes in saliva 7 min after the sucrose rinse were pH -0.40 unit, free calcium 0.42 mM, lactate 5.2 mM, phosphate -1.3 mM, and fluoride 2.8 microM; while in plaque fluid, the corresponding changes were pH -1.59 unit, free calcium 1.5 mM, lactate 35 mM, phosphate -1.6 mM and fluoride -26 microM. After sucrose rinsing, undersaturation was found with respect to dicalcium phosphate dihydrate in saliva and plaque fluid and with respect to tooth enamel in some plaque fluid samples. Plaque fluid composition appeared to be strongly influenced by salivary clearance, diffusive loss of ions into the water phase of the rinse, and lower jaw pooling of the sucrose and fluoride components of the rinses. After the experimental rinse, the fluoride concentration in plaque fluid [86 +/- 22 mM (upper molar site), 162 +/- 150 mM (lower molar site)], saliva (26 +/- 18 mM), and whole plaque [99 +/- 97 microg/g (upper molar site), 197 +/- 412 microg/g (lower molar site)] was comparable to the values in previous studies using this rinse. These very high plaque fluid fluoride concentrations, compared with the 'no-rinse' samples, induced an approximately 0.3-unit increase in the plaque fluid pH 7 min after the sucrose rinse, a small decrease (approximately 20%) in lactate production and a modest increase in enamel saturation. Although these changes were all statistically significant, no correlation was found between the decrease in lactate concentration and plaque fluid fluoride, pH or whole plaque fluoride.

Therapeutic drug monitoring: do the improved outcomes justify the costs?

In the 30 years that therapeutic drug monitoring (TDM) has moved from an abstract consideration to a routine intervention, issues remain over justifying the benefits in the light of the ever-increasing competition for budgetary resources. Resolving the issues is constrained by various methodological concerns. These include considerations such as: (i) the changed environment of knowledge and practice during the generation in which TDM has been used and evaluated; (ii) the predominance of studies using system-related rather than patient-centred outcomes; (iii) using a timeframe for analysis that is too short; (iv) a lack of rigour in many of the pharmacoeconomic analyses; and (v) excessive use of a site-specific rather than a societal perspective. Current observation suggests that the greatest benefit of TDM accrues from targeted or specialty populations: those with severely decompensated renal function, those at the extremes of age, and those using immunosuppressive, some antineoplastic, some psychotherapeutic and some anticonvulsant drugs. In these situations, safe and humane practice considers TDM a necessity without respect to cost. But for many routine situations with drugs for which TDM has commonly been used in the past, present reliance on the intervention may have become excessive in the light of today's knowledge base of practitioners.

Effect of a water rinse on 'labile' fluoride and other ions in plaque and saliva before and after conventional and experimental fluoride rinses.

Labile reservoirs are important in maintaining ion concentrations in oral fluids, especially after a fluoride dentifrice application, where a persistent increase in fluid fluoride can mitigate or reverse caries progression. In this study, the effect of experimental and conventional fluoride rinses on the in vitro and in vivo water-induced release of fluoride, calcium, phosphate, acetate and hydrogen ions from oral reservoirs was examined. At the start of each experiment, 13 subjects rinsed either with a conventional 228-ppm fluoride NaF rinse, a 228-ppm fluoride controlled-release rinse (CR rinse) or received no rinse. Sixty minutes later upper and lower molar plaque samples and 1-min saliva samples were collected. The subjects then rinsed with deionized water for 1 min, and 7 min later, a second set of samples was collected (in vivo study). Plaque fluid and clarified saliva were then recovered from samples by centrifugation, and the remaining plaque mass was sequentially extracted with water and acid to measure the water-extracted and total whole-plaque fluoride (in vitro study). All the samples were analyzed using microtechniques for pH, free calcium, phosphate, organic acids (plaque fluid) and fluoride (plaque fluid, centrifuged saliva and plaque extracts). Results showed that in vivo water rinsing decreased acetate and phosphate in plaque fluid, and fluoride in plaque fluid and saliva, but had no effect on plaque fluid pH. In vivo water rinsing, however, increased plaque fluid free calcium, apparently due to water-induced loss of calcium-binding ions. Water- or fluoride-rinse-induced changes in plaque fluid concentration were greater at the lower molar site, suggesting that rinse pooling may influence ion distribution. Before the water rinse, plaque fluid, saliva and whole-plaque total fluoride values were 1.7, 2 and 4 times higher after the CR rinse compared to the NaF rinse. Furthermore, the CR rinse deposited approximately 11 times more water-extracted fluoride compared to the NaF rinse, suggesting a 'more efficient' precipitation of 'labile' or 'loosely bound fluoride'. The results presented here, and in previous studies, suggest the possibility of formulating effective fluoride dentifrices with a lower fluoride content than is currently in use.

[The studies on microtensile bond strength measurements of two dentin adhesives].

OBJECTIVE: The purpose of this study was to investigate the feasibility of a modified microtensile method used to test bond strengths of two current one-bottle dentin bond systems (Prime & Bond NT, PBNT; Prime one Mirage, P-One) with a parallel match design. METHODS: 15 extracted, caries-free human molars were cut to expose occlusal dentin. A 5 mm deep slot was prepared in each crown to divide the crown into nearly equal halves for accepting treatment of the two dentin bond systems, respectively. After 24 h storage in distilled water at 37 degrees C, the bonded teeth were subjected to two treatments: 5 teeth were tested without further treatment and 10 teeth were thermocycled (2400 cycles, between 5 degrees C and 55 degrees C) prior to bond strength testing. Hour-glass shaped specimens with a distance of approximately 1.0 mm at the narrowest portion were cut from each tooth and tested in tensile mode. RESULTS: Bond strengths (mean MPa) were: for PBNT: 42 & 31, and for P-One 64 & 38 without and with thermocycling, respectively. Two-way ANOVA revealed a significant difference in bond strengths(P < 0.001) between the two systems and when thermocycled. However, a pairwise multiple comparison (Tukey test) showed that after thermocycling the difference between the two systems was not significant (P > 0.05). Regression analysis showed that a correlation existed between the two systems' tensile bond strength values grouped by tooth (correlation coefficient r = 0.575, P < 0.05). CONCLUSION: The modified microtensile method with a parallel match design is feasible and suitable for evaluating two different bonding systems or dentin treatments.

Whisker-reinforced dental core buildup composites: effect of filler level on mechanical properties.

The strength and toughness of dental core buildup composites in large stress-bearing restorations need to be improved to reduce the incidence of fracture due to stresses from chewing and clenching. The aims of the present study were to develop novel core buildup composites reinforced with ceramic whiskers, to examine the effect of filler level, and to investigate the reinforcement mechanisms. Silica particles were fused onto the whiskers to facilitate silanization and to roughen the whisker surface for improved retention in the matrix. Filler level was varied from 0 to 70%. Flexural strength, compressive strength, and fracture toughness of the composites were measured. A nano-indentation system was used to measure elastic modulus and hardness. Scanning electron microscopy (SEM) was used to examine the fracture surfaces of specimens. Whisker filler level had significant effects on composite properties. The flexural strength in MPa (mean +/- SD; n = 6) increased from (95+/-15) for the unfilled resin to (193+/- 8) for the composite with 50% filler level, then slightly decreased to (176+/-12) at 70% filler level. The compressive strength increased from (149+/-33) for the unfilled resin to (282+/-48) at 10% filler level, and remained equivalent from 10 to 70% filler level. Both the modulus and hardness increased monotonically with filler level. In conclusion, silica particle-fused ceramic single-crystalline whiskers significantly reinforced dental core buildup composites. The reinforcement mechanisms appeared to be crack deflection and bridging by the whiskers. Whisker filler level had significant effects on the flexural strength, compressive strength, elastic modulus, and hardness of composites.

American translation, modification, and validation of the St. George's Respiratory Questionnaire.

BACKGROUND: The St. George's Respiratory Questionnaire (SGRQ) is a 50-item health status survey specific for chronic obstructive pulmonary disease (COPD) and other respiratory diseases that is available in British English but not American English. The SGRQ's symptom-reporting component requires a 1-year reporting period, which may be too long for reliable and accurate patient recall. OBJECTIVES: The objectives of the present study were to translate the SGRQ from British to American English, modify the reporting period of the symptom-reporting component from 1 year to 1 month, and assess the reliability, validity, and sensitivity to change of this translated modified version in a sample of patients with COPD. METHODS: Based on input from American patients with COPD and health professionals, the SGRQ was translated into American English (SGRQ-A) and then translated back to British English. For SGRQ-A reliability and validity studies, patients were asked to report symptoms experienced over 1 year (reporting period in the original SGRQ) and 1 month (modification made to SGRQ-A). We evaluated 102 patients with COPD (50% female; mean age, 68 years; mean forced expiratory volume in 1 second [FEV1], 1.01 L) at an administrative session before and after completion of a pulmonary rehabilitation program. The SGRQ-A, Chronic Respiratory Disease Questionnaire (CRQ), 36-Item Short Form Health Survey (SF-36), 6-minute walk (6MW), Medical Research Council (MRC) Dyspnea scale, and pulmonary function tests (FEV1 and % predicted FEV1) were used in the assessment battery. RESULTS: The SGRQ-A showed good agreement with the original SGRQ when translated back to British English. Internal reliability (Cronbach alpha) was > 0.70 for all SGRQ-A components except the 1-year symptom-reporting component. Test-retest intraclass correlations were 0.795 to 0.900. Construct validity was strengthened when all SGRQ-A components (except 1-year symptoms and most 1-month symptoms) correlated (P < or = 0.01) with the MRC Dyspnea scale, 6MW, all SF-36 concept scores, and 80% of CRQ domains (r = 0.30-0.72). Discriminate validity was demonstrated when all components of the SGRQ-A with the modified 1-month symptom-reporting period were shown to discriminate better between disease-severity groups (based on patient self-reports of disease severity) than did pulmonary function tests and the 6MW. Responsiveness of the SGRQ-A to change in health status was demonstrated when scores on the Symptoms-1 month and Total-1 month components detected significant improvements in patients' health status (P = 0.02 and P = 0.04, respectively). CONCLUSION: The SGRQ-A with a modified 1-month symptom-reporting period demonstrated reliability and validity in this sample of patients with COPD. Key words: chronic obstructive pulmonary disease, St. George's Respiratory Questionnaire, American translation, reliability, validity, symptom recall.

Dental resin composites containing ceramic whiskers and precured glass ionomer particles.

OBJECTIVES: Glass ionomer, resin-modified glass ionomer, and compomer materials are susceptible to brittle fracture and are inadequate for use in large stress-bearing posterior restorations. The aim of this study was to use ceramic single crystal whiskers to reinforce composites formulated with precured glass ionomer, and to examine the effects of whisker-to-precured glass ionomer mass ratio on mechanical properties, fluoride release, and polishability of the composites. METHODS: Silica particles were fused onto silicon nitride whiskers to facilitate silanization and to improve whisker retention in the matrix. Hardened glass ionomer was ground into a fine powder, mixed with whiskers, and used as fillers for a dental resin. Four control materials were also tested: a glass ionomer, a resin-modified glass ionomer, a compomer, and a hybrid composite. A three-point flexural test was used to measure flexural strength, modulus, and work-of-fracture. A fluoride ion-selective electrode was used to measure fluoride release. Composite surfaces polished simulating clinical procedures were examined by SEM and profilometry. RESULTS: At whisker/(whisker + precured glass ionomer) mass fractions of 1.0 and 0.91, the whisker composite had a flexural strength in MPa (mean (SD); n = 6) of (196 (10)) and (150 (16)), respectively, compared to (15 (7)) for glass ionomer, (39 (8)) for resin-modified glass ionomer, (89 (18)) for compomer, and (120 (16)) for hybrid composite. The whisker composite had a cumulative fluoride release of nearly 20% of that of the glass ionomer after 90 days. The whisker composites had surface roughness comparable to the hybrid resin composite. SIGNIFICANCE: Composites filled with precured glass ionomer particles and whiskers exhibit moderate fluoride release with improved mechanical properties; the whisker-to-glass ionomer ratio is a key microstructural parameter that controls fluoride release and mechanical properties.

Physicochemical evaluation of bioactive polymeric composites based on hybrid amorphous calcium phosphates.

Amorphous calcium phosphate (ACP)-filled methacrylate composites were recently found to effectively remineralize in vitro caries-like enamel lesions. Their inferior mechanical properties compared to glass-filled composites, however, limit their use as a dental restorative material. In this study, the feasibility of introducing glass-forming elements (tetraethoxysilane or zirconyl chloride) during the low-temperature synthesis of ACP was investigated. Composites based on such hybrid fillers (mass fraction, 40%) were evaluated to establish whether hybridization strengthened the composites via improved interfacial interactions with the polymer phase without compromising the release of the mineral ions. Two types of visible-light cured resins were prepared: BTHZ resin from 2, 2-bis[p-(2'-hydroxy-3'-methacryloxypropoxy)phenyl]propane (BisGMA), triethylene glycol dimethacrylate (TEGDMA), 2-hydroxyethyl methacrylate (HEMA) and zirconyl methacrylate (ZrM), and TP resin from TEGDMA and pyromellitic glycerol dimethacrylate (PMGDM). Hybridized fillers and BTHZ- and TP-based composites were characterized by the IR spectroscopy, X-ray diffraction, dissolution/transformation kinetic studies, and biaxial flexure strength (BFS) testing before and after immersion in buffered saline solutions. The feasibility of improving the BFS via hybridization, while retaining, if not enhancing the remineralizing potential was demonstrated for BTHZ-based composites. Both BFS and remineralizing ability of the TP-composites, however, deteriorated upon their exposure to an aqueous environment. Therefore, hybridized ACP-filled BTHZ composites have a potential for utilization in more demanding restorative, sealant, and adhesive applications.

Effect in vitro acidification on plaque fluid composition with and without a NaF or a controlled-release fluoride rinse.

Plaque fluid ion concentration changes, especially fluoride, in response to the pH decrease associated with a cariogenic episode are important components of the caries process. A "controlled-release" (CR) fluoride rinse, based on the controlled release of fluoride in the presence of calcium, has been shown to form large fluoride reservoirs in resting plaque. In this study, the in vitro acid-induced release of fluoride, and other ions, was examined in 48-hour-fasted plaque fluid from subjects (n = 11) who received no rinse, or who used a 228-ppm CR or NaF fluoride rinse 1 hr before being sampled. After collection, the plaque was centrifuged to yield plaque fluid, acidified (0.1 microL of 0.5 mol/L HCl per milligram plaque), and then re-centrifuged before a second sample was obtained. Although previous studies indicated a higher plaque fluid fluoride after the new rinse relative to NaF, no statistically significant difference was observed here. Average fluoride release after acidification (average pH, 5.2) was statistically greater following the use of the CR rinse (153 micromol/L) compared with the NaF rinse (17 micromol/L). No fluoride release was seen in the no-rinse samples. The pH, free calcium, phosphate, acetate, propionate, and buffer capacity were not affected by the different amounts of fluoride deposited in the plaque. However, following acid addition, an increase in free calcium and phosphate was observed, which was also independent of the rinse. The large release of fluoride following acidification suggests that the new rinse may provide an improved cariostatic effect.

Indentation modulus and hardness of whisker-reinforced heat-cured dental resin composites.

OBJECTIVES: Recent studies showed that ceramic whisker reinforcement imparted a two-fold increase in the strength of dental composites. The aim of this study was to investigate the indentation response and measure the elastic modulus, hardness, and brittleness of whisker-reinforced heat-cured resin composites as a function of filler level, heat-cure temperature, and heat-cure duration. METHODS: Silica particles were fused onto silicon nitride whiskers to facilitate silanization and to roughen the whiskers for improved retention in matrix. Whisker filler mass fractions of 0, 20, 40, 60, 70, 74 and 79% were tested. Heat-cure temperature ranged from 100 to 180 degrees C, and duration from 10 min to 24 h. A nano-indentation system enabled the measurement of elastic modulus. Fracture toughness was measured and composite brittleness index was calculated. An inlay/onlay composite and a prosthetic composite were tested as controls. RESULTS: Whisker filler level and heat-cure duration had significant effects on composite properties, while heat-cure temperature had non-significant effects. The whisker composite with 79% filler level had a modulus in GPa (mean (SD); n = 6) of 26.9 (1.0), significantly higher than 15.1 (0.2) of an inlay/onlay control, and 16.1 (0.3) of a prosthetic control (Tukey's multiple comparison test; family confidence coefficient = 0.95). The fracture toughness in MPa.m1/2 was 2.22 (0.26) for the whisker composite, higher than 0.95 (0.11) for inlay/onlay control, and (1.13 +/- 0.19) for prosthetic control. The brittleness index was (0.49 +/- 0.07) for whisker composite, lower than (1.02 +/- 0.12) for inlay/onlay control and (0.63 +/- 0.13) for prosthetic control. SIGNIFICANCE: Whisker filler level had a profound influence, heat-cure duration had significant effects, while temperature did not have significant effects, on the properties of whisker composite. The whisker composite had significantly higher elastic modulus and fracture toughness, and lower brittleness than the inlay/onlay and prosthetic controls.

Strengthening composite resin restorations with ceramic whisker reinforcement.

Due to their tendency to fracture, current composite formulations are unsuitable for use in large stress-bearing direct posterior restorations that involve cusps. This study investigated the use of single-crystalline ceramic whiskers for the reinforcement of composite resins. The whisker-reinforced composite materials exhibited physical characteristics (i.e., flexural strength, work-of-fracture, and elastic modulus) that were significantly greater (P < 0.05; Student's t test) than those of traditional composite formulations. The experimental materials also had a surface smoothness that was essentially comparable to hybrid composite control specimens.