Effect of fluoride and time intervals on bond strength and degree of conversion of an adhesive applied on bleached enamel

O objetivo desse estudo foi avaliar a influência do flúor e dos tempos de espera nos valores de resistência de união (RU) e no grau de conversão (GC) de um adesivo aplicado em esmalte clareado. Foram utilizados 60 espécimes de esmalte humano, embutidos em tubos de PVC e resina acrílica e submetidos ao tratamento clareador (n=18): Grupo HP: HP Maxx (peróxido de hidrogênio 35%); Grupo HPF: HP Maxx +aplicação tópica de flúor neutro 1,23%; Grupo PF: Opalescence Boost PF (peróxido de hidrogênio 38% contendo flúor 1,1%). Para o procedimento restaurador, os grupos foram subdivididos em 3 subgrupos (n=6), de acordo com o tempo de espera: imediatamente, 7 e 14 dias. Tubos tygon foram preenchidos por resina composta e posicionados na superfície de esmalte, para ser realizado o teste de microcisalhamento. O GC foi verificado em espectroscopia Raman. Os dados de RU (MPa) e GC (%) foram submetidos à análise de variância de 2 fatores e pós-teste de Tukey, e análise de variância de 1 fator e pós-teste de Dunnet (α=0,05). Os resultados de RU mostraram diferença entre o Grupo HP 14 dias (21,403,45), em relação aos grupos imediato (13,024,28) e 7 dias (13,672,92), da mesma forma que o Grupo HPF (14 dias: 18,082,74; imediato: 9,742,11 e 7 dias: 12,662,68). Para o GC, o Grupo HP e HPF imediato (57,027,61 e 66,898,57, respectivamente) diferiram estatisticamente dos tempos 7 e 14 dias (HP:78,156,80, HPF:78,628,67 e HP:77,274,60, HPF:88,095,83, respectivamente). Para o Grupo PF, não existiram diferenças entre os grupos experimentais e o grupo controle (p>0,05). Concluiu-se que a aplicação tópica de flúor não foi eficiente para reverter os baixos valores de RU e GC, sendo necessário aguardar 14 dias para se realizar o procedimento adesivo; quando da realização de restaurações imediatamente após o clareamento, o agente clareador fluoretado se mostrou eficiente na manutenção dos valores de RU e GC. Palavras-chave: Clareamento Dental. Peróxido de Hidrogênio. Adesivos Dentários.The objective of this study was to evaluate the influence of fluoride and time intervals on the bond strength (BS) and degree of conversion (DC) of an adhesive applied on bleached enamel. Sixty human enamel specimens were used, entrenched in PVC tubes and acrylic resin, and submitted to bleaching treatment (n=18): Group HP: HP Maxx (35% hydrogen peroxide); Group HPF: HP Maxx + 1,23% neutral fluoride application; Group PF: Opalescence Boost PF (38% hydrogen peroxide containing 1,1% fluoride). For the restorative procedure, the groups were subdivided into three subgroups (n=6), according to the time interval: immediately, after 7 and 14 days. Tygon tubes were filled with composite resin and positioned on the enamel surface, in order to perform the microshear bond test. DC was observed in Raman spectroscopy. BS (MPa) and DC (%) data were submitted to 2-way ANOVA and Tukeys post-test, and ANOVA and Dunnets post-test (α=0,05). The BS results showed differences between the Group HP in 14 days (21.403.45) compared to the groups immediate (13.024.28) and 7 days (13.672.92), the same as verified in Group HPF (14 days: 18.082.74, immediate: 9.742.11 and 7 days: 12.662.68). For DC, immediate Group HP and Group HPF (57.027,61 e 66.898,57, respectively) differed significantly from 7 and 14 days (HP: 78.156.80, HPF: 78.628.67 and HP: 77.274.60, HPF: 88.095.83, espectively). For Group PF, there were no differences between the experimental groups and the control group (p>0.05). It was concluded that fluoride topical application was not effective to reverse low BS and DC values, being necessary wait 14 days to perform the adhesive procedure; but when restorative procedures are required immediately after bleaching, the fluoridated bleaching agent was efficient to maintain BS and DC values

Evaluation of human enamel permeability exposed to bleaching agents

Aim: To evaluate the human enamel permeability after different external bleaching techniques. Methods: The coronal portions of 20 maxillary human incisors were covered with an acid resistant varnish, except the labial surface, to prevent dye penetration of silver nitrate. The specimens were divided randomly into four groups (n=5) according to the bleaching treatments: Group 1 (G1) - without bleaching agent (control group), Group 2 (G2) - 35% hydrogen peroxide (HP) – one session of three 10-min applications, Group 3 (G3) - 35% HP – 2 sessions of three 10-min applications, and Group 4 (G4) - 6% HP – 14 days (1h/day). G1 was exposed to artificial saliva only and in the other groups the bleaching agents were applied following the manufacturers’ recommendations. After bleaching, teeth were immersed in a 50% silver nitrate solution for 2 h and photodeveloped for 16 h. Then, three longitudinal slices of each tooth were photographed by an optical microscope (100x). The degree of dye penetration was analyzed in the middle third of the dental crowns using a 0 to 4 score system (0= no dye penetration, 1= less than half the enamel thickness, 2= half of the enamel thickness, 3= full extent of enamel without reaching the dentin, and 4= tracer agent reaching dentin). The data were analyzed statistically by the Kruskal- Wallis and Dunn tests (α=0.05). Results: The median (1st/3rd interquartiles) ranges were: G1: 0(0/0), G2: 2(2/3), G3: 3(3/3) and G4: 3(3/3). G2, G3 and G4 showed significantly higher dye penetration compared with G1 (p=0.0017). Conclusions: The use of bleaching agents increased dental enamel permeability, regardless of the bleaching technique

Evaluation of human enamel permeability exposed to bleaching agents

evaluate the human enamel permeability after different external bleaching techniques. Methods: The coronal portions of 20 maxillary human incisors were covered with an acid resistant varnish, except the labial surface, to prevent dye penetration of silver nitrate. The specimens were divided randomly into four groups (n=5) according to the bleaching treatments: Group 1 (G1) - without bleaching agent (control group), Group 2 (G2) - 35% hydrogen peroxide (HP) one session of three 10-min applications, Group 3 (G3) - 35% HP 2 sessions of three 10-min applications, and Group 4 (G4) - 6% HP 14 days (1h/day). G1 was exposed to artificial saliva only and in the other groups the bleaching agents were applied following the manufacturers recommendations. After bleaching, teeth were immersed in a 50% silver nitrate solution for 2 h and photodeveloped for 16 h. Then, three longitudinal slices of each tooth were photographed by an optical microscope (100x). The degree of dye penetration was analyzed in the middle third of the dental crowns using a 0 to 4 score system (0= no dye penetration, 1= less than half the enamel thickness, 2= half of the enamel thickness, 3= full extent of enamel without reaching the dentin, and 4= tracer agent reaching dentin). The data were analyzed statistically by the KruskalWallis and Dunn tests (α=0.05). Results: The median (1st/3rd interquartiles) ranges were: G1: 0(0/0), G2: 2(2/3), G3: 3(3/3) and G4: 3(3/3). G2, G3 and G4 showed significantly higher dye penetration compared with G1 (p=0.0017). Conclusions: The use of bleaching agents increased dental enamel permeability, regardless of the bleaching technique

Effect of light-curing units on gap formation and microleakage of class II composite restorations

Aim: This in vitro study evaluated gap width formation and marginal microleakage in Class II composite restorations light-cured with three different light-curing units. Methods: Standardized cavities in the proximal surfaces of 36 human third molars were made with margins located below the cementoenamel junction. Cavities were restored with Filtek P60 (3M ESPE), inserted with a photocondenser tip and light-cured with three different methods: GI - Optilux401 (halogen); GII - ColtoluxLED (LED) and GIII -UltraLumeLED5 (LED). After finishing the restorations, teeth were subjected to a thermal cycling regimen of 500 cycles (5°C ± 2°C and 55°C ± 2°C), totalizing 500 cycles. Thereafter, the teeth were sectioned in a buccolingual direction and in the center of the restorations. Half of the specimens (18) were used to evaluate marginal microleakage, by measuring of dye penetration in cross-sectioned specimens, and the other half was used to analyzed the gap formation width by SEM observations (1000X). Data were submitted to Kruskal-Wallis (α=0.05). Results: The mean values of gap width (µm) were: GI 3.28±3.34; GII 1.48±1.89 and GIII 3.11±3.45, and microleakage was not affected by the light-curing units. Conclusions: There were no differences between the light-curing methods in gap formation and marginal microleakage

Effect of bleaching agents containing fluoride or calcium on enamel microhardness, roughness and permeability

Abstract Aim: To evaluate the effect of different in-office bleaching agents on the permeability, roughness and surface microhardness of human enamel. Methods: For evaluation of roughness and microhardness, 40 hemi-faces of 20 premolars were subjected to initial roughness (Ra parameter) and microhardness (VHN) measurements. Thirty-two premolar's crowns were used for permeability test. Then, all specimens were randomly divided into four groups: C - without bleaching (control), HP35 - bleaching with 35% hydrogen peroxide (HP), HPF38 - 38% HP+fluoride, HPC35 - 35% HP+calcium. Final roughness (FR) and microhardness (FM) measurements were evaluated. For permeability, the 32 crowns were immersed in 1% sodium hypochlorite (20 min) and silver nitrate solutions (2 h) and subjected to developing solution under fluorescent light (16 h). Three sections from the crowns were analyzed in light microscope (100x) to evaluate the scores of permeability: Score 0 - no tracer agent penetration; Score 1 - less than half the thickness of enamel penetration; Score 2 - tracer agent reaching half the enamel thickness; Score 3 - entire enamel depth penetration, without reaching dentin and Score 4 - tracer agent reaching dentin. For roughness and microhardness evaluation were used one-way ANOVA and Dunnet post-test for independent samples, and t test for paired samples. For permeability, the data were analyzed by Kruskal Wallis and Dunn tests. Results: A significantly higher permeability and surface roughness were observed in groups HP35, HPF38 and HPC35 compared to the C group, as well as decreased microhardness (p<0.05). Conclusions: All bleaching agents increased permeability and surface roughness, and decreased microhardness of human enamel; thus, the addition of fluoride or calcium was not beneficial

Influence of different burs and acid ultrasonic agitation on the bonding of fiber posts to root dentin

e objective is to evaluate the influence of different burs used to prepare the root canal space and acid ultrasonic agitation on bond strength (BS) between glass fiber posts (GFP) and root dentin. Methods: After endodontic treatment, the root canal spaces of 36 extracted human canines were prepared, according to the rotary instrument used (n=18): carbide bur (CB), provided by the post manufacturer and a diamond bur (DB). In both groups, the fiber posts were cemented with the adhesive system Ambar and resin cement Allcem, following the manufacturer`s instructions. Previously to the cementation procedures, the groups were subdivided into 2 groups (n=9), according to the phosphoric acid application mode: conventional etching (CE) and active etching (AE), performed by ultrasonic tip, both for 15s. Before the cementation procedures and after the acid application, 1 root of each group was randomly selected for ultrastructural morphological evaluation by SEM. After 1 week of the cementation, 8 specimens per group were transversely sectioned into six 1-mm thick slices, the root canal regions (cervical, medium and apical) were identified and the push-out test was performed to evaluate BS. Data were analyzed by 3-way ANOVA and Tukey test (&#945;=0.05). Results: The results showed that the cross-product interaction of all factors was significant (P=0.035). Higher bond strength values were obtained when a DB with conventional etching, instead of CB, was used to prepare the root post space. Conclusion: It may be concluded that the use of diamond burs with conventional etching yields high BS values in all root canal thirds

Effect of bleaching agents containing fluoride or calcium on enamel microhardness, roughness and permeability

evaluate the effect of different in-office bleaching agents on the permeability, roughness and surface microhardness of human enamel. Methods: For evaluation of roughness and microhardness, 40 hemi-faces of 20 premolars were subjected to initial roughness (Ra parameter) and microhardness (VHN) measurements. Thirty-two premolars crowns were used for permeability test. Then, all specimens were randomly divided into four groups: C - without bleaching (control), HP35 - bleaching with 35% hydrogen peroxide (HP), HPF38 - 38% HP+fluoride, HPC35 - 35% HP+calcium. Final roughness (FR) and microhardness (FM) measurements were evaluated. For permeability, the 32 crowns were immersed in 1% sodium hypochlorite (20 min) and silver nitrate solutions (2 h) and subjected to developing solution under fluorescent light (16 h). Three sections from the crowns were analyzed in light microscope (100x) to evaluate the scores of permeability: Score 0 - no tracer agent penetration; Score 1 - less than half the thickness of enamel penetration; Score 2 - tracer agent reaching half the enamel thickness; Score 3 - entire enamel depth penetration, without reaching dentin and Score 4 - tracer agent reaching dentin. For roughness and microhardness evaluation were used one-way ANOVA and Dunnet post-test for independent samples, and t test for paired samples. For permeability, the data were analyzed by Kruskal Wallis and Dunn tests. Results: A significantly higher permeability and surface roughness were observed in groups HP35, HPF38 and HPC35 compared to the C group, as well as decreased microhardness (p<0.05). Conclusions: All bleaching agents increased permeability and surface roughness, and decreased microhardness of human enamel; thus, the addition of fluoride or calcium was not beneficial