## 4 Discussion
Only one tooth in the test group showed an increased sensitivity to temperature and occlusion immediately after capping. However, the complaints were of short duration, so no therapeutic intervention was indicated. At the time of the baseline examination (2 weeks after restoration), the patient reported an improvement and, at the first follow-up examinations, that tooth showed regular sensitivity without complaints. Postoperative sensitivity is, in principle, a possible complication after composite restorations and therefore often a secondary outcome measure in clinical trials while examining composite materials [16; 36]. Many authors focused on the impact of the used dentin adhesive system regarding the presence or absence of postoperative sensitivity [37; 38; 39; 40; 41]. Nevertheless, despite the significant improvements of adhesive systems, the bonded interface remains the weakest area of the composite restorations. The failure or degradation of this interface can result in poor marginal adaption, marginal discoloration, and the subsequent loss of retention or secondary caries of the restoration, as typical clinical findings. The interface between the tooth and restorative material is subjected to varying stresses during its lifetime. The volumetric shrinkage of the resin material during polymerization is dependent on the properties of the material used, the volume of resin material cured, filler type and amount, degree of polymerization, C-factor, monomer content, and application technique [42]. Laboratory and clinical studies have demonstrated excellent success rates for total-etch adhesives over the years [43; 44; 45; 46; 47]. Unfortunately, many clinical investigations have shown that postoperative hypersensitivity after a complete cavity etching is still a problem. To reduce technique sensitivity and the risk of postoperative sensitivity by dentin etching, self-etch adhesives that operate by acid etching with simultaneous monomer infiltration were developed. It is expected that self-etch adhesives prevent or reduce postoperative sensitivity due to their less aggressive and more superficial interaction with dentin [48; 49]. In the present investigation after 24 months, no postoperative hypersensitivity was detected (0%). Comparable results are difficult to evaluate in other studies, because the number of trials directly comparing the self-etch and etch and rinse system is small [36]. All fillings in this study were placed under absolute dryness using a rubber dam; the adhesive system was applied according to the manufacturer's instructions as a self-etch system. The recommended layer thickness and light-curing time of the placed composite materials was obeyed. The fact that one experienced dentist placed all the restorations might provide a further explanation. In addition, all the fillings were prepared under water cooling with the same grain size of the diamond burs. The present undesirable reactions of the pulp-dentin unit are therefore not due to gross processing errors of the materials investigated. Secondary caries was not detected after 24 months in any case. This is a comparable result to the research of [PERSON] et al. [18]. Trials exist that showed secondary caries after two years with the additional use of a flowable composite as a liner [31; 50]. However, the number of secondary caries is very low [31]. Furthermore, two fillings of the test group showed a discreet chipping of the superficial composite material of the distal margin after 12 months (Code Bravo). These fillings could remain in situ without the loss of proximal contact or other functions and showed satisfactory stability after 24 months. These findings are in accordance with the results of other studies [1; 18]. Regarding marginal discoloration, higher abnormalities were detected in comparable studies after 24 months [18; 31]. Recently published studies showed that polymerization time improved the mechanical properties of composite materials [51].