A calcium phosphate cement (CPC) was examined for its ability to seal the root canal when used as... more A calcium phosphate cement (CPC) was examined for its ability to seal the root canal when used as a sealer-filler. Extracted human teeth were divided into three groups. Root canals were filled with either CPC paste containing dicalcium phosphate anhydrous (group 1), CPC containing dicalcium phosphate dihydrate (group 2), or gutta-percha points sealed with Grossman's cement (group 3). After filling, all specimens were kept in 100% humidity for 1 day, immersed in a CaPO4 solution or distilled water at 37 degrees C for 1 wk, and then immersed in 1% Poly-R dye solution at 37 degrees C for 1 wk, after which they were rinsed and sectioned longitudinally for microscopic examination. Specimens in groups 1 and 2, especially those aged in the CaPO4 solution showed considerably less dye penetration than those in group 3. The good sealing ability of the CPC against dye penetration in vitro suggests that it may provide an adequate seal of the canal without a separate sealer.
Effects of temperature (25 and 37°C), pH (4.9-10.5), and CaF2 on CaHPO4·2H2O (DCPD) hydrolysis we... more Effects of temperature (25 and 37°C), pH (4.9-10.5), and CaF2 on CaHPO4·2H2O (DCPD) hydrolysis were studied in a pH-stat. Octacalcium phosphate (OCP) was the product at pH 6.2-6.8 and 25-37°C; thermodynamically stable apatitic compounds were formed at higher pH and/or higher temperature. In the presence of CaF2, apatite was the product, its crystallinity improved, and the fluoride content increased as pH of the reaction decreased. The results demonstrate the remarkable ability of fluoride to promote the hydrolysis of an acidic calcium phosphate, DCPD, to apatite.
The effects of oral rinses on enamel fluoride uptake, caries, and plaque pH in rats were investig... more The effects of oral rinses on enamel fluoride uptake, caries, and plaque pH in rats were investigated by use of (1) an acidic calcium phosphate solution (CPS) saturated with dicalcium phosphate dihydrate (DCPD) and (2) a 1% fluoride solution. Osborne-Mendel rats, 19 days of age, were randomly assigned to one of four mouth-rinse treatment groups, with the two consecutively administered rinses being: H2O-H 2O; H2O-F; CPS-H20; and CPS-F. The treatments were administered on days 1 through 4, and the animals were provided with a cariogenic challenge throughout the study. The groups treated with F exhibited significantly higher mean levels of enamel-bound F than did the non-F groups. Furthermore, CPS significantly increased uptake of F by enamel when used as an adjunct to the F treatment. The caries scores of the CPS-F and H2O-F groups were not statistically different; however, a strong negative correlation was observed between enamel F content and caries scores, indicating that as more F...
A highly parallel incident x-ray beam combined with x-ray image magnification was used to obtain ... more A highly parallel incident x-ray beam combined with x-ray image magnification was used to obtain high-resolution microradiographs of dental specimens. Preliminary results obtained using a rotating anode x-ray generator show that limitations associated with conventional contact microradiography regarding (1) spatial resolution, (2) sample thickness, and (3) sample orientation, relative to the film, were significantly reduced.
Significant amounts of CaHPO4 · 2H2O (DCPD) were deposited in tooth enamel by pretreatment with a... more Significant amounts of CaHPO4 · 2H2O (DCPD) were deposited in tooth enamel by pretreatment with a solution saturated with respect to DCPD. When these enamel samples were treated with a given fluoride solution, the fluoride uptake increased with increasing amounts of DCPD produced by the pretreatment. The interactions between enamel and acidic solutions to yield DCPD can be understood as dissolution-precipitation reactions and analyzed through the use of solubility phase diagrams.
A constant-composition fluoride (F) titration method was used to measure the amount of leachable ... more A constant-composition fluoride (F) titration method was used to measure the amount of leachable F deposited on root surfaces in vitro by a 1-min rinse with a 12 mmol/l sodium fluoride (228 micrograms/g F) solution or a two-solution rinse that contained 2 mmol/l sodium fluorosilicate (228 micrograms/g total F ) and 10 mmol/l calcium chloride. The mean +/- standard deviations (n = 3) F uptake from the two rinse treatments were 0.70 +/- 0.24 micrograms/cm2 and 3.25 +/- 0.74 micrograms/cm2, respectively. In a separate experiment, the effects of sodium fluoride and the two-solution rinses on remineralization of root lesions were evaluated in an in vitro pH cycling model. The results showed that the average decrease in mineral loss (delta Z) in the two-solution rinse group (60%) was significantly greater than that obtained in the NaF rinse (41%) or the control (9%) group.
Application of monocalcium phosphate monohydrate (MCPM) gel, which produces small amounts of dica... more Application of monocalcium phosphate monohydrate (MCPM) gel, which produces small amounts of dicalcium phosphate dihydrate in enamel, was previously shown to increase the enamel reactivity with fluoride (F). This study was conducted to determine whether the MCPM gel treatment is also effective in enhancing F uptake by root surfaces of human teeth. The results show that samples receiving daily treatments with MCPM gel for 10 min followed by immersion in a 1-ppm F solution for 5 days acquired a significantly greater amount of F compared to the controls which had the same exposure to the F solution. Because the F solution was undersaturated with respect to calcium fluoride (CaF2), the F incorporated into the root is apparently apatitic and not CaF2. This experimental treatment should be feasible in the clinical situation since only a short treatment time was required and delivery of the MCPM gel to specific sites was relatively easy.
Previous studies demonstrated that a Ca pre-treatment greatly increases salivary F from a subsequ... more 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 μg/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.
Recent studies showed that salivary, plaque-fluid, and whole-plaque fluoride were significantly h... more Recent studies showed that salivary, plaque-fluid, and whole-plaque fluoride were significantly higher 120 min after subjects rinsed with a novel two-solution rinse than after they rinsed with a NaF rinse of the same fluoride concentration. In this study, the persistence of these increases was investigated overnight, a period of time that is more clinically relevant. Improved analytical techniques for the ultramicro determination of whole-plaque and plaque-fluid fluoride from the same sample are also described. Thirteen subjects abstained from toothbrushing for 48 hrs and rinsed for 1 min with a 12 mmol/L (228 ppm) NaF or the two-solution rinse before bedtime. Samples were then collected the following morning before breakfast: (1) Saliva samples were either clarified by centrifugation or acid-extracted with 1 mol/L HClO4; and (2) single-site molar plaque samples were centrifuged to obtain plaque fluid and/or extracted with 1 mol/L HC1O4. Results showed that, compared with NaF, the t...
A calcium phosphate cement (CPC) was examined for its ability to seal the root canal when used as... more A calcium phosphate cement (CPC) was examined for its ability to seal the root canal when used as a sealer-filler. Extracted human teeth were divided into three groups. Root canals were filled with either CPC paste containing dicalcium phosphate anhydrous (group 1), CPC containing dicalcium phosphate dihydrate (group 2), or gutta-percha points sealed with Grossman's cement (group 3). After filling, all specimens were kept in 100% humidity for 1 day, immersed in a CaPO4 solution or distilled water at 37 degrees C for 1 wk, and then immersed in 1% Poly-R dye solution at 37 degrees C for 1 wk, after which they were rinsed and sectioned longitudinally for microscopic examination. Specimens in groups 1 and 2, especially those aged in the CaPO4 solution showed considerably less dye penetration than those in group 3. The good sealing ability of the CPC against dye penetration in vitro suggests that it may provide an adequate seal of the canal without a separate sealer.
Effects of temperature (25 and 37°C), pH (4.9-10.5), and CaF2 on CaHPO4·2H2O (DCPD) hydrolysis we... more Effects of temperature (25 and 37°C), pH (4.9-10.5), and CaF2 on CaHPO4·2H2O (DCPD) hydrolysis were studied in a pH-stat. Octacalcium phosphate (OCP) was the product at pH 6.2-6.8 and 25-37°C; thermodynamically stable apatitic compounds were formed at higher pH and/or higher temperature. In the presence of CaF2, apatite was the product, its crystallinity improved, and the fluoride content increased as pH of the reaction decreased. The results demonstrate the remarkable ability of fluoride to promote the hydrolysis of an acidic calcium phosphate, DCPD, to apatite.
The effects of oral rinses on enamel fluoride uptake, caries, and plaque pH in rats were investig... more The effects of oral rinses on enamel fluoride uptake, caries, and plaque pH in rats were investigated by use of (1) an acidic calcium phosphate solution (CPS) saturated with dicalcium phosphate dihydrate (DCPD) and (2) a 1% fluoride solution. Osborne-Mendel rats, 19 days of age, were randomly assigned to one of four mouth-rinse treatment groups, with the two consecutively administered rinses being: H2O-H 2O; H2O-F; CPS-H20; and CPS-F. The treatments were administered on days 1 through 4, and the animals were provided with a cariogenic challenge throughout the study. The groups treated with F exhibited significantly higher mean levels of enamel-bound F than did the non-F groups. Furthermore, CPS significantly increased uptake of F by enamel when used as an adjunct to the F treatment. The caries scores of the CPS-F and H2O-F groups were not statistically different; however, a strong negative correlation was observed between enamel F content and caries scores, indicating that as more F...
A highly parallel incident x-ray beam combined with x-ray image magnification was used to obtain ... more A highly parallel incident x-ray beam combined with x-ray image magnification was used to obtain high-resolution microradiographs of dental specimens. Preliminary results obtained using a rotating anode x-ray generator show that limitations associated with conventional contact microradiography regarding (1) spatial resolution, (2) sample thickness, and (3) sample orientation, relative to the film, were significantly reduced.
Significant amounts of CaHPO4 · 2H2O (DCPD) were deposited in tooth enamel by pretreatment with a... more Significant amounts of CaHPO4 · 2H2O (DCPD) were deposited in tooth enamel by pretreatment with a solution saturated with respect to DCPD. When these enamel samples were treated with a given fluoride solution, the fluoride uptake increased with increasing amounts of DCPD produced by the pretreatment. The interactions between enamel and acidic solutions to yield DCPD can be understood as dissolution-precipitation reactions and analyzed through the use of solubility phase diagrams.
A constant-composition fluoride (F) titration method was used to measure the amount of leachable ... more A constant-composition fluoride (F) titration method was used to measure the amount of leachable F deposited on root surfaces in vitro by a 1-min rinse with a 12 mmol/l sodium fluoride (228 micrograms/g F) solution or a two-solution rinse that contained 2 mmol/l sodium fluorosilicate (228 micrograms/g total F ) and 10 mmol/l calcium chloride. The mean +/- standard deviations (n = 3) F uptake from the two rinse treatments were 0.70 +/- 0.24 micrograms/cm2 and 3.25 +/- 0.74 micrograms/cm2, respectively. In a separate experiment, the effects of sodium fluoride and the two-solution rinses on remineralization of root lesions were evaluated in an in vitro pH cycling model. The results showed that the average decrease in mineral loss (delta Z) in the two-solution rinse group (60%) was significantly greater than that obtained in the NaF rinse (41%) or the control (9%) group.
Application of monocalcium phosphate monohydrate (MCPM) gel, which produces small amounts of dica... more Application of monocalcium phosphate monohydrate (MCPM) gel, which produces small amounts of dicalcium phosphate dihydrate in enamel, was previously shown to increase the enamel reactivity with fluoride (F). This study was conducted to determine whether the MCPM gel treatment is also effective in enhancing F uptake by root surfaces of human teeth. The results show that samples receiving daily treatments with MCPM gel for 10 min followed by immersion in a 1-ppm F solution for 5 days acquired a significantly greater amount of F compared to the controls which had the same exposure to the F solution. Because the F solution was undersaturated with respect to calcium fluoride (CaF2), the F incorporated into the root is apparently apatitic and not CaF2. This experimental treatment should be feasible in the clinical situation since only a short treatment time was required and delivery of the MCPM gel to specific sites was relatively easy.
Previous studies demonstrated that a Ca pre-treatment greatly increases salivary F from a subsequ... more 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 μg/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.
Recent studies showed that salivary, plaque-fluid, and whole-plaque fluoride were significantly h... more Recent studies showed that salivary, plaque-fluid, and whole-plaque fluoride were significantly higher 120 min after subjects rinsed with a novel two-solution rinse than after they rinsed with a NaF rinse of the same fluoride concentration. In this study, the persistence of these increases was investigated overnight, a period of time that is more clinically relevant. Improved analytical techniques for the ultramicro determination of whole-plaque and plaque-fluid fluoride from the same sample are also described. Thirteen subjects abstained from toothbrushing for 48 hrs and rinsed for 1 min with a 12 mmol/L (228 ppm) NaF or the two-solution rinse before bedtime. Samples were then collected the following morning before breakfast: (1) Saliva samples were either clarified by centrifugation or acid-extracted with 1 mol/L HClO4; and (2) single-site molar plaque samples were centrifuged to obtain plaque fluid and/or extracted with 1 mol/L HC1O4. Results showed that, compared with NaF, the t...
Uploads
Papers by Laurence Chow