Histological, histochemical and immunohistochemical studies on the regeneration of pulp tissue of male rats after exposure to low intensity laser therapy

The purpose of this study was to investigate the biomodulation effect of low intensity laser therapy (LILT) on regeneration process of exposed rat dental pulp after direct capping by Ca(OH)2. Forty healthy male albino rats ranged from 220-250 grams were used in this investigation. Animals were divided into 2 groups. Group (I): Animals of this group served as control group and were subjected to moderate cervical cavity preparations in middle thirds of lingual surfaces of upper incisors. This is followed by Ca(OH)2 as pulp capping agent and modified glass ionomer as permanent restorations. Group (II): Animals were subjected for similar procedure of group (I). This is followed by laser application using aluminum gallium arsenide (AlGaAs) diode laser source (660 nm, 3 mW, 18 J/cm2; Pocket Lase, Orotig. Med, S.r.I, Italy) at 0.5-1 cm distance from tooth surface. LILT was standardized at 4-second exposure per point; buccal, palatal, mesial and perpendicular to the tooth axis. (Godoy et al, 2007). After 5, and 30 days, the rats were sacrified and maxillae including prepared central incisors were removed. Then sections were prepared for histological, histochemical and immunohistochemical analysis. Results obtained after 5 days of pulp exposure revealed that lased dental pulp was less damaged and degenerated figures were decreased when compared with non-lased dental pulp. Pulpal responses were significantly more accentuated and seemed to be restricted to the areas underneath the region submitted to cavity preparation and laser application when compared to other control group. One main difference between lased and non-lased group was the presence of intense vascularization at exposure sites, coronal and pulp cores with no evidence of large hemorrhagic areas as were found in control groups. After 30 days, LILT exposure sites showed marked increase of active tertiary dentinogenesis. Matrix deposition by newly differentiated odontoblast-like cells and calcification areas were increased when compared with control group. In most of lased dental pulp specimens, tubular calcified tissues were observed more than those of non-lased group which exhibited osteodentin formation at exposure sites. In other words, formation of dentin-like cells after LILT rather than bonelike tissue secreted by osteoblast-like cells observed in control group. Immunohistochemical demonstration of caspase-3, revealed marked increase of immunoreactivity of pulp tissue than that of non-lased control group.