title: Improving clinical retention of one-step self-etching adhesive systems with an additional hydrophobic adhesive layer Paucity of Nanolayering in Resin-Dentin Interfaces of MDP-based Adhesives
abstract: BACKGROUND The durability of restorations bonded with one-step self-etching ( OSSE ) adhesive systems is inferior compared with that of restorations bonded with conventional adhesives . The authors conducted an 18-month r and omized clinical study to evaluate the clinical performance of two OSSE systems in noncarious cervical lesions applied as recommended or with an extra layer of hydrophobic adhesive layer after 18 months of clinical service . METHODS Thirty participants , each of whom had at least two pairs of similar-sized noncarious cervical lesions , took part in this study . The authors placed 120 restorations  , 30 in each of four groups : Clearfil S3 Bond ( Kuraray , Osaka , Japan ) ( CS ) and iBond Gluma inside ( Heraeus Kulzer , Hanau , Germany ) ( IB ) , and Clearfil S3 Bond ( CSB ) and iBond Gluma inside ( IBB ) with an extra layer of hydrophobic adhesive applied on top of them . They placed the restorations incrementally , using a resin-based composite . The authors evaluated the restorations at baseline and at 18 months following modified U.S. Public Health Service criteria . RESULTS At 18 months , the retention rate for the IB group was statistically lower than those for the CS , IBB and CSB groups . Marginal discoloration occurred in all groups and was statistically worse in the IB group . CONCLUSIONS The conversion of the iBond Gluma inside and Clearfil S3 Bond adhesive systems into two-step systems by means of applying an extra hydrophobic adhesive layer improved the clinical performance of these material s after 18 months of clinical service . CLINICAL IMPLICATION S The application of an extra hydrophobic adhesive layer over OSSE adhesive systems , layers improved the OSSE systems clinical performance , mainly in terms of retention rate Self-assembled nanolayering structures have been reported in resin-dentin interfaces created by adhesives that contain 10-methacryloyloxydecyl dihydrogen phosphate ( 10-MDP ) . These structures have been hypothesized to contribute to bond durability . The objective of the present study was to determine the extent of nanolayering in resin-dentin interfaces after application of commercialized  10-MDP-containing self-etch and universal adhesives to human dentin . Seven commercialized adhesives were examined :  Adhese Universal ( Ivoclar-Vivadent ) , All-Bond Universal ( Bisco , Inc. ) , Clearfil SE Bond 2 , Clearfil S3 Bond Plus , Clearfil Universal Bond ( all from Kuraray Noritake Dental Inc. ) , G-Premio Bond ( GC Corp. ) , and Scotchbond Universal ( 3 M ESPE ) . Each adhesive was applied in the self-etch mode on midcoronal dentin according to the respective manufacturer ’s instructions . Bonded specimens ( n = 6 ) were covered with flowable resin composite , processed for transmission electron microscopy , and examined at 30 r and om sites without staining . Thin-film glancing angle X-ray diffraction ( XRD ) was used to detect the characteristic peaks exhibited by nanolayering ( n = 4 ) . The control consisted of 15%wt , 10%wt , and 5%wt 10-MDP ( DM Healthcare Products , Inc. ) dissolved in a mixed solvent ( ethanol and water weight ratio 9:8 , with photoinitiators ) . Experimental primers were applied to dentin for 20 s , covered with hydrophobic resin layer , and examined in the same manner . Profuse nanolayering with highly ordered periodicity ( ~3.7 nm wide ) was observed adjacent to partially dissolved apatite crystallites in dentin treated with the 15 % 10-MDP primer . Three peaks in the 2θ range of 2.40 ° ( 3.68 nm ) , 4.78 ° ( 1.85 nm ) , and 7.18 ° ( 1.23 nm ) were identified from thin-film XRD . Reduction in the extent of nanolayering was observed in the 10 % and 5 % 10-MDP experimental primer-dentin interface along with lower intensity XRD peaks . Nanolayering and characteristic XRD peaks were rarely observed in specimens prepared from the commercialized adhesives . The sparsity of nanolayering in resin-dentin interfaces created by commercialized adhesives challenges its clinical effectiveness as a mechanism for improving bond longevity in dentin bonding
target: The 10-MDP monomer has the capacity to produce an acid-base resistant zone on the adhesive interface , which increases the response to acid-base challenges .
  The adhesion established by these systems is stable over time .
background: The incorporation of functional monomers in dental adhesive systems promotes chemical interaction with dental substrates , result ing in higher adhesion forces when compared to micromechanical adhesion only .
  The 10-MDP monomer , whose chemical structure allows for a polar behavior which is favorable to adhesion , also promotes the protection of collagen fibers through the formation of MDP-calcium salts .
  This systematic review aim ed to characterize the interface created by 10-MDP containing adhesive systems through an evaluation of the following parameters : Formation of nano-layered structures , capacity to produce an acid-base resistant zone , and adhesion stability .