Effects of an experimentally developed adhesive resin system and CO2 laser irradiation on direct pulp capping

This study examined the wound healing process of rat pulp directly capped with various experimentally developed adhesive resin systems and treated with CO2 laser irradiation. The experimental adhesive resins used in this study were made from Clearfil Mega Bond (MB). The adhesive resin groups were capped with a combination of the following primers and bonding agents: commercially available MB primer (MBP), experimental MB primer containing 2wt% N-methacryloyl 5-aminosalicylic acid (5-NMSA: MP3) and 5wt% 12-methacryloyloxydodecylpyridinium bromide (MDPB: ABP); and commercially available MB bonding agent (MBB), experimental MB bonding agent containing 5wt% and 10wt% hydroxyl-calcium phosphate (hydroxyapatite: MB1, MB2) and 5wt% dicalcium phosphate dihydrate (brushite: MB3) as a reparative dentin-promoter. The combination of the three primers and four bonding agents yielded the 12 adhesive resin groups used in this study. The CO2 laser group was irradiated with a laser and directly capped with MB. The CO2 laser used was an Opelaser 03S II SP, and irradiation conditions were as follows: a power output of 0.5 W, superpulse mode 1, repeat pulse mode (a cycle of 10 msec irradiation and 10 msec interval), defocused beam (approximately distance 20 mm from pulp exposure surface) and an irradiation time of three seconds, with air cooling. The control group was capped with Dycal (DY) and MB. After the direct pulp capping procedures were undertaken, all cavities were restored with Clearfil AP-X resin composite. The rats were sacrificed on the 14th post-operative day. The specimens were alternately stained with Mayer's H & E, Hucker-Conn bacterial stain and the ABC method on TGF-beta1. These stained sections were observed using light microscopy and the following parameters were evaluated: pulp tissue disorganization, inflammatory cell infiltration, reparative dentin formation and bacterial penetration. The results of this study include the following: all experimentally developed bonding agent groups showed reparative dentin formation; whereas, the MBB-capped groups showed very little reparative dentin formation. The descending order regarding the amount of reparative dentin formation was MB2 > MB3 > MB1 >>> MBB, which tended to be dependent on the concentration of the blended reparative dentin-promoter. In terms of the quality of the formed dentin, it was observed that MB1-capped teeth tended to form tubular dentin; whereas, MB2- and MB3-capped teeth formed irregular and osteodentin types of dentin. Among the primers used, the descending order regarding the amount of reparative dentin and tubular type dentin formation was MP3 > MBP > ABP. The descending order of migration of macrophages and leukocytes was ABP > MBP > MP3. The CO2 laser group showed a very irregular fibrous dentin matrix in the vicinity of the denatured and carbonized tissue but definite reparative dentin formation was not observed. The control group showed reparative dentin, which was very thick, compared with the other groups. In all the groups, pulp tissue showed almost normal morphology. Positive staining of TGF-beta1 was only observed slightly in some specimens of all groups. There was no difference in the staining of each group. Based on the results of this study, it was concluded that the combination of MP3 (containing 2wt% 5-NMSA) and MB1 (containing 5wt% hydroxyapatite) was effective in initiating an early repair process after direct pulp capping. CO2 laser irradiation is effective for field control, but a longer observation time will be required to determine findings concerning dentin bridge formation.