## 2 Materials and Methods
### Adhesive Interface Analysis  
For this analysis, forty-two caries-free human third molars (Ethics Committee Approval HUAP CAAE: 52273421.20000.5243) were disinfected in 0.5% chloramine-T solution at 4 \({}^{\circ}\)C for 7 days, stored in distilled water, and used within one month after extraction.  
The tooth's occlusal surfaces were flattened with the aid of a polisher (DPU 10, Struers, Copenhagen, Denmark) using 600-gri SiC papers, leading to a flat enamel surface. Occlusal cavities were prepared with a diamond bur (#4103, [PERSON], Sao Paulo, SP, Brazil) under water cooling (6 mm in mesio-distal width, 5 mm in bucco-lingual width, and 4 mm in depth) using a high-speed hand piece. Then, the teeth were randomly distributed into 6 experimental groups (n = 7), according to Table 2.  
The primer was actively applied on the tooth structure for 20 s, gently air dried for 5 s followed by the active application of the bond, and light-cured for 20 s. Afterward, the cavities were restored with each dental composite: the bulk-fill composite was inserted in a single increment and light-cured for 40 s (Radii Cal, SDI), and the conventional composite was inserted with the incremental technique using increments of up to 2 mm light-curing  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Experimental Adhesives** & **Composite** & **Experimental Groups** \\ \hline EA0 & Conventional (Z100, 3 MESPE, St. Paul, MN, USA) & EA0 CON \\ EA7.5 & Bulk-fill (Opus Bulk Fill, FGM, Brazil) & EA0 OBF \\ EA8.5 & Conventional (Z100, 3 MESPE, USA) & EA7.5 CON \\ EA9.5 & Bulk-fill (Opus Bulk Fill, FGM, Brazil) & EA7.50 BF \\ EA10.5 & Conventional (Z100, 3 MESPE, USA) & EA15 CON \\ EA10.5 & Bulk-fill (Opus Bulk Fill, FGM, Brazil) & EA15 OBF \\ \hline \hline \end{tabular}
\end{table}
Table 2: Experimental groups.  
for 20 s (Radii Cal, SDI). The occlusal surfaces were sequentially polished using SiC paper (#600, 800, 1200, 3000, and 4000) for 1 min each, in order to remove excesses and allow microscopic analysis. The teeth were placed in an ultrasonic bath (750 USC, Quimis, Rio de Janeiro, Brazil) for 10 min to remove any debris.  
Then, the analysis of the adhesive interface on the occlusal surface was performed, recording the perimeter of the tooth-restoration interface, and the sum of the gaps found along the entire length of the occlusal interface (Occlusal gaps-OG) with the aid of a confocal laser scanning microscope (CSLM-LEXT 3D OLS4100, Olympus, USA) at 5X magnification (Figure 1). Subsequently, a longitudinal cut in the bucco-lingual direction, close to the mesial surface of the cavity was performed using a slow-speed diamond saw (Isomet 1000 precision saw Buehler, Lake Bluff, IL, USA) so that the adhesive interface of the mesial adhesive interface was exposed for analysis (Figure 1). After sequential polishing using SiC paper and cleaning in an ultrasonic bath, as previously described, the perimeter of the mesial adhesive interface and the sum of the gaps found along the entire length of the mesial interface (mesial gaps-MG) were recorded. The presence of gaps was calculated in percentage, according to the following formulas:  
\[\%OG=\frac{OG}{BW+LW+MW+DW}, \tag{4}\]  
where \(OG\) is the sum of the length of the gaps found across the tooth-restoration interface from the occlusal surface, \(BW\) is the width of the buccal adhesive interface, \(LW\) is the width of the lingual adhesive interface, \(DW\) is the width of the distal adhesive interface.  
\[\%MG=\frac{MG}{BW+CW+LW}, \tag{5}\]  
where \(MG\) is the sum of the length of the gaps found across the tooth-restoration interface of the mesial surface, \(BW\) is the width of the buccal adhesive interface, \(CW\) is the width of the cervical adhesive interface, and \(LW\) is the width of the lingual adhesive interface.  
Figure 1: Schematic representation of specimen preparation for analysis under the confocal microscope and microctensile test.