Laser effects on osteogenesis

Abstract

The traumatic or surgical cutting of a long bone is immediately followed by a sequence of repair processes in which the osteogenic cells of the periosteum start to proliferate and differentiate in osteoblast cells. In this work, we explored the influence of a He–Ne laser on osteogenesis after a controlled surgical fracture. We used young male adult Wistar rats (of mass between 250 and 300 g). The fracture was provoked by piercing a 2-mm-diameter hole in just one cortical tibia surface. Laser treatment was started 24 h after the surgery. The animals were separated into three groups, for different radiation doses, and after daily applications, they were sacrificed at 8 or 15 days. Light and electron microscopies revealed that the laser treatment of the lesion with doses of 31.5 and 94.7 J cm⁻² resulted in the formation of thicker bony trabeculae, which indicates a greater synthesis of collagen fibers and therefore that the osteoblastic activity was increased by the low-energy laser radiation.

Introduction

The effects of laser radiation on biological materials have been explored and successfully applied to new micro-surgery techniques. Some of these are already routine processes to treat human diseases such as myopia, diabetic retinopatia, glaucoma, retina displacement, cavernous angioma, face angioma and for tattoo removal, etc. In these procedures, a very high energy density is used and the laser action is to remove or to weld tissues or to destroy cells by purely thermal processes [1], [2], [3].

During the past decade, new methods which employ low-intensity laser irradiation have also been explored, seeking to establish purely photo-therapeutic processes. These methods have been classified as low-level laser therapy (LLLT) [4]. Previous studies in LLLT, suggest that osteogenesis can be stimulated by He–Ne laser radiation [5], [6], [7]. Trelles and Mayayo [5] performed experiments on manually induced fractured tibia in mice, verifying an increase in vascularization and a faster rate of bone formation in irradiated animals. They used an incident energy of 2.4 J (laser power=4 mW), applied every second day, but no information on the beam diameter or the energy density was given. Yaakobi et al. [6] used doses of 31 J cm⁻² (laser power=5.3 mW) on round holes made in the cortical tibia of male rats (Sprague–Dawley) and using radioactive ⁴⁵Ca²⁺ and alkaline phosphatase (ALP), measurements verified an increase in the rate and extent of the calcification of irradiated animals. Luger et al. [7] irradiated complete fractured rat tibias with three doses of 297 J cm⁻² each (laser power=35 mW) applied daily to the fractured area and the immediate areas above and below the fracture. Using biomechanical measurements, such as the maximal load at failure and structural stiffness of the tibia, they concluded that the laser irradiation enhanced bone healing.

In this work, we studied bone recovery in male rats (Wistar) subjected to doses of 3.15, 31.5 and 94.7 J cm⁻² through qualitative histological analysis by light microscopy and 3-D structural organization by scanning electron microscopy (SEM). A low laser power was used (1 mW) with the intention of minimizing any temperature-induced reactions. The irradiation enhancement on the rate of bone formation was clearly observed in the animals treated with the doses of 31.5 and 94.7 J cm⁻², being greater with the dose of 94.7 J cm⁻². However, the treatments with doses of 3.15 J cm⁻² did not present any apparent differences from the results of the controls.