# Universal Dental Adhesives: Cost-Effectiveness and Duration of Use
## 4 Discussion
The result of this study showed that three clicks with the TN in VivaPen packaging and one drop of the SB adhesive were associated with the highest amount of material utilized inside the cavity and were enough to completely wet the walls. The OB adhesive demonstrated moderate amounts of material applied close to the TN and SB groups, and a single drop was actually enough to wet the cavity; however, this adhesive lasted only for 20 days with 98 applications and was associated with the highest amount of waste in the applicator and the dosing plate, even though the capacity of the bottle was comparable to that of the other adhesives. The opening of the OB adhesive bottle has a wide lumen with no integrated features to control the amount of adhesive dispensed, which allowed two drops to come out of the bottle on six occasions. In addition, remnants from the adhesive material accumulated around the opening of the bottle. Although GP was associated with the least amount of waste, a single drop of this adhesive failed to completely wet the cavity walls on many occasions with the lowest median amount of material utilized. This might indicate the need for two drops of GP adhesive in order to completely wet the class II cavity for composite restoration. This is reflected on the low efficacy score for the GP adhesive. The TN group had the highest values for efficacy (0.337) and efficiency (3333.089) since it had the highest values for utilization of the adhesive compared to waste. This supports the claim that this method of delivery would decrease the amount of waste in relation to cost, providing high efficiency with 185 applications, close to what the manufacturer claims (190 for one VivaPen). Although the SB adhesive had the second highest value for efficacy, it was found to be the least efficient when correlated to cost (SB: USD 16.5/1 mL, TN: USD 106.8/1 mL). This is explained by the relatively high amount of waste associated with this adhesive. The main goal of CEA is to measure the trade-off between different resources and the outcome obtained [2]. ACER and ICER are some of the common methods used in CEA and play an important role in the assessment. However, both have different purposes and estimate different parameters. ACER for instance, measures the overall efficiency (cost to outcome) and provides an intuitive meaning about cost-effectiveness of one approach with a fixed budget independent of other options [2]. Nevertheless, sometimes it can be misleading and hide the high price of additional outcome gained per incremental cost. It basically distributes the cost over all subjects assuming all of them to have the same cost [1]. This can potentially lead clinicians to choose a less cost-effective approach. On the other hand, ICER reports on the incremental efficiency, which is the ratio of extra cost per  
Figure 2: Cumulative total waste per day for the four adhesives used in this study. extra effect compared to a common standard. Thus, it estimates whether the trade-off is cost-effective or not by looking into the true cost of additional gain in outcome [20, 21, 22]. In days of applications, the value of the ACER can estimate the potential increase in the price of the adhesive due to material waste. For example, the price of the SB and OB adhesives was USD 82 and USD 83.9, respectively. If we factor in the amount of waste associated with the bonding procedure, the actual cost of the adhesives will be USD 103 for the SB and USD 206 for the OB in order to utilize the wholeness of the material inside the bottle and not merely accepting that the material will be wasted. On the other hand, the ACER values for the TN and GP adhesives were the highest, costing USD 317 and USD 311, respectively. Utilizing the ICER data, buying an extra amount of material utilized per milliliter was USD 208 for the TN adhesive and USD 3.8 for the GP. The incremental cost of the OB adhesive was USD \(-\)38. In general, positive and negative ICER values indicate an increase and a decrease in benefit, respectively.