Solid-state postpolymerization of l-lactide was studied by two different ways with 0.1 mol % of stannous 2-ethyl hexanoate as the catalyst. In a two-step method, the ordinary melt polymerization of l-lactide was first performed at temperatures higher than the crystallization temperature (T c) of poly(l-lactide) (PLLA), and then the postpolymerization was continued around the T c of PLLA. As PLLA crystallized in the second stage (e.g., when the temperature was changed from 140 to 120 °C), the monomer consumption was found to reach 100% because the monomer and catalyst could be concentrated in the amorphous part. Without the crystallization of PLLA occurring in the postpolymerization, a homogeneous supercooling state was formed to have a remaining monomer ratio exceeding 5 wt %. In the alternative one-step method where the polymerization was continued around the T c of PLLA, the polymer crystallization was induced during the polymerization to promote the monomer consumption to reach 100%. The kinetic analysis of this polymerization revealed that the rate of monomer consumption is inversely proportional to the square of the amorphous ratio of PLLA, which is opposite to the crystal ratio. However, the molecular weight did not increase with the monomer consumption. This should be because various oligomers are formed in the postpolymerization stage by the ester interchange reaction.

This study investigated the bonding effectiveness of newly designed self-etching adhesives to four types of adherends -enamel, dentin, zirconia, and gold (Au) alloy. Five experimental adhesives were prepared, which contained 3.0-5.0 wt% 6-methacryloyloxyhexyl phosphonoacetate (6-MHPA) or 6-methacryloyloxyhexyl 3-phosphonopropionate (6-MHPP), 3.0 wt% 4-acryloyloxyethoxycarbonylphthalic acid (4-AET) or 17.0 wt% 4-methacryloyloxyethoxycarbonylphthalic acid (4-MET), 0-0.5 wt% 6-methacryloyloxyhexyl 6,8-dithiooctanoate (6-MHDT) or 10-methacryloyloxydecyl 6,8-dithiooctanoate (10-MDDT), and varying contents of Bis-GMA, dimethacrylate monomers, water, acetone, and a photoinitiator system. After 2,000 times of thermal cycling, shear bond strengths (SBSs) between a resin composite (Beautifil II, Shofu Inc., Japan) and the four adherends, bonded using the experimental adhesives, were measured at 1.0 mm/min. No statistically significant differences in SBS for bonding to ground enamel, dentin, sandblasted zirconia and Au alloy (p>0.05) were found between experimental adhesives which contained 6-MHPA and/or 6-MHPP, 4-MET or 4-AET, 6-MHDT and/or 10-MDDT, Bis-GMA, and dimethacrylates. An adhesive layer of less than 5.0 µm thickness, by scanning electron microscopy observation, revealed strong adhesion to the four adherends. Therefore, the newly designed multi-purpose, self-etching adhesive strongly adhered to all the four adherend materials tested.

The bonding performance of a surface pre-reacted glass ionomer (S-PRG) filler-containing self-adhesive flowable resin composites to enamel and dentin were evaluated using a tensile bond test with thermal cycling. Also, the quantities of various ions released from the materials were measured using ICP atomic emission spectrometry and a fluoride ion electrode. The initial bond strengths of the materials were approximately 6 MPa, and decreased after thermal cycling. The S-PRG filler-containing self-adhesive flowable resin composites materials exhibited much higher ion release compared with the commercial self-adhesive flowable resin composite possibly due to different acidic monomers contained. It was suggested that the S-PRG filler containing self-adhesive flowable resin composites should be limited as a lining material or to restore small cavities in non-stress bearing areas.