Does Maintaining a Bottle of Adhesive Without the Lid Signif icantly Reduce the So lvent Content ?

on the solvent loss of the etch-and-rinse adhesive systems. Three 2-step etch-and-rinse adhesives with different solvents (acetone, ethanol or butanol) were used in this study. Drops of each adhesive were placed on an analytical balance and the adhesive mass was recorded until equilibrium was achieved (no significant mass alteration within time). The solvent content of each adhesive and evaporation rate of solvents were measured (n=3). Two bottles of each adhesive were weighted. The bottles were maintained without their lids for 8 h in a stove at 37 oC, after which the mass loss was measured. Based on mass alteration of drops, acetone-based adhesive showed the highest solvent content (46.5%, CI 95%: 35.8-54.7) and evaporation rate (1.11 %/s, CI95%: 0.63-1.60), whereas ethanol-based adhesive had the lowest values (10.1%, CI95%: 4.3-16.0; 0.03 %/s CI95%: 0.01-0.05). However, none of the adhesives bottles exhibited significant mass loss after sitting for 8 h without their lids (% from initial content; acetone 96.5, CI 95%: 91.8101.5; ethanol 99.4, CI 95%: 98.4-100.4; and butanol 99.3, CI 95%: 98.1-100.5). In conclusion, maintaining the adhesive bottle without lid did not induce significant solvent loss, irrespective the concentration and evaporation rate of solvent. Does Maintaining a Bottle of Adhesive Without the Lid Signif icantly Reduce the So lvent Content?


Introduction
Even with the evolution of adhesive systems in last decades, the establishments of a predictable bonding interface in dentin tissue remains a challenge for the clinicians (1-3).Self-etching adhesive systems has gained popularity; however, etch-and-rinse adhesives are still a suitable option to adhesive procedures on clinical practice.For etch-and-rinse adhesives, a phosphoric acid is applied previously to adhesive system and removes partially the mineral content of dentin tissue to expose the collagen mesh (4,5).Interfibrillar spaces in the collagen mesh are maintained by water, while organic solvents in the adhesive displace this water from the demineralized dentin to allow the infiltration of resin monomers (5,6).Furthermore, these solvents also help the water evaporation from dentin allowing a proper adhesive polymerization (7)(8)(9).Thus, a reduction in the solvent content can compromise the infiltration of adhesive resin and the effectiveness of the dentin bond (10).
Acetone and alcohols are the main organic solvents used in adhesive systems due to high volatility and low cost.These solvents present different volatilities and are added to adhesives in concentrations ranging from 30 to 80% (10,11).This variation is due to fact that more volatile solvents are commonly added in higher concentrations (10,11).However, it has been reported that the repeated opening of the adhesive bottle during the clinical procedure can permit the spontaneous evaporation of solvents (10)(11)(12)(13).However, few information is actually available about a possible the solvent loss over time when the adhesive bottle is maintained in an open state.Thus, the aim of this study was to investigate the effect of maintaining an adhesive bottle without its lid in terms of the solvent content.The hypothesis was that significant loss of solvent would occur when the bottle was left open over time under simulated warm environment to accelerate the solvent evaporation.

Material and Methods
Three 2-step etch-and-rinse adhesives with different solvent types were used in this study.The composition and manufacturers of each adhesive are described at Table 1.To determine the solvent content of the adhesive and the evaporation rate of each solvent, one drop of each adhesive was dispensed in an analytical balance (JEX-200, YMC Co. Ltd, Kyoto, Japan) and mass alteration of drop was evaluated.The adhesive mass was recorded at 5-s intervals until it reached equilibrium at room temperature.The equilibrium was determined when no alteration of mass occurred within time.The solvent content was determined as the ratio between the final and initial weights (Solvent content in % = (final weight/ initial weight)*100).The average evaporation rate was calculated as the weight loss at the moment of equilibrium, divided by the time (in s) to reach this point.The solvent content and evaporation rate were measured in triplicate.
To determine the solvent loss when the bottle was maintained without its lid, two full bottles of each adhesive were placed individually over the analytical balance to measure the initial weight.The lids were removed, and the bottles were placed in a stove at 37 °C for 8 h.After this storage period, the bottles were weighted again with the lids.The full adhesive content was removed from the bottle, and the empty bottles were weighted.The adhesive/solvent content of the bottles was determined by subtracting the weight of the empty bottle from the weight of the full bottle before and after the storage in stove.The ratio between the final and initial weights of adhesive/solvent was used to determine the solvent loss.Data of solvent content, rate of evaporation, and solvent loss were submitted to one-way analysis of variance (ANOVA) and Tukey's test (α=0.05).Data analysis was performed using the SigmaStat v.3.5 statistical software package (Systat Software Inc., Chicago, IL, USA).

Results
ANOVA showed significant effect for adhesive (p<0.001)regarding the solvent content.Stae showed the highest and Ambar the lowest solvent concentration, while XP bond presented intermediate values.For evaporation rate, ANOVA also showed significant effect for adhesive (p<0.001).Stae (acetone) demonstrated the highest evaporation rate among the adhesives evaluated followed by XP Bond (butanol) and Ambar (ethanol), which showed the lowest evaporation rate values.ANOVA did not show significant effect for adhesive (p=0.191)regarding the solvent loss after 8 h.The superior limit of the confidence interval (95%) calculated was higher than 100% for all adhesives, demonstrated absence of significant difference from the initial content.The results are presented in Table 2. Figure 1 illustrates the solvent loss of adhesive drop within the time.

Discussion
The adhesives evaluated in this study showed significant differences in solvent concentration.The acetone-based adhesive showed the highest solvent content, whereas the ethanol-based solvent presented the lowest content.These findings confirm previous reports that acetone-based adhesives present higher solvent content because of the relatively high vapor pressure of acetone (184.3 mmHg at 20 ºC), which results in elevated volatility (14).Interestingly, the ethanol in Ambar presented a lower evaporation Confidence Interval is an interval that estimates of the population parameter.
Figure 1.Solvent loss from adhesive drops.rate than the butanol in XP Bond.The vapor pressure of ethanol (43.7 mmHg at 20 ºC) is almost 10-fold higher than that of butanol (4.9 mmHg) (14-15).However, it has been demonstrated that the addition of water to ethanol as co-solvent increases the retention of both solvents (16).This occurs because the water evaporation increases the monomer/water ratio and reduces the vapor pressure of water, reducing the ability of water and ethanol to evaporate from adhesive (17).
Considering the solvent volatility, it was expected that maintaining the adhesive bottle without a lid would result in a significant loss of solvent, especially for the acetonebased adhesive.However, no significant solvent loss was observed over the 8-h experiment.Thus, the hypothesis of the study was rejected.Despite the high volatility of organic solvents used in these adhesive systems, bottles are designed to reduce solvent lost.The "smart" designs of bottles have been developed seeking to reduce the solvent loss from the adhesive bottles during the clinical procedures.Clinically, the bottle was not maintained open for long periods of time as in the simulation of present study.However, the maintenance of bottle without lid for shorter periods during for several times results long time to volatilization of solvents.Despite the possibility to maintain the bottle open for long time, the results demonstrate the efficacy of these "smart" designs to not allow a significant solvent content loss.A previous study also demonstrated reduced solvent loss from the adhesive bottle (11).
Significant loss of solvent content from 2-step etchand-rinse adhesives has a detrimental effect on the bond strength to dentin tissue (10).Thus, it has been advocated that the lid of the bottle be replaced immediately after dispensing the adhesive, to avoid solvent loss (13).The outcomes of the present study indicate that maintaining the adhesive bottle without a lid does not result in significant solvent loss.However, these findings must be viewed with caution because there may be other factors (i.e.agitation of bottle before to remove lid, storage of adhesive without refrigeration, etc.) that were not evaluated which may also affect the solvent loss.