The purpose of this study was to prove the effect of the soft laser (low level laser therapy) in the reconstruction and healing of hard and soft periodontal tissue after periodontal reconstructive surgery. In this experiment five Beagle dogs were used. The procedure was the following: 7 mm large periodontal defects were created in the mandibular vestibular face at the 4th premolar and the 1st. molar. The root surfaces were then instrumented to remove all cementum and the wounds immediately closed by replacing and suturing the flaps just coronal to the cementum-enamel junction. All the defects were filled up with collagen, and during a period of 4 weeks, 5 days a week, the teeth were treated with soft laser only on experimental side. The dogs were sacrificed 16 weeks postsurgery. Histometric recordings included height and area of alveolar bone regeneration, height of cement regeneration, connective tissue repair, and junctional epithelium. We evaluated the bone regeneration, the dental cement regeneration, the new PDL, the collagen sponges' persistence, root resorption and/or ankylosis histologically. Group means, standard deviations, and P values are shown (Student t test; n=5 y _X2; n=2). The size of regeneration with laser measured 1.8 ± 0.5 against 2.3 ± 0.8 on control (ns). Bone-values with laser were 2.1 ± 0.8 against 2.7 ± 1.0 on control (ns). The regenerated cement measured 1.7 ± 0.5 with laser against 2.8 ± 0.8 on control (p=0.006). The junctional epithelium measured 2.7 + 1.1 with laser against 2.8 ± 0.1 on control (ns). The connective tissue repair measured 2.2 ± 1.0 with laser against 1.6 ± 0.4 on control (p=0.04). Ankylosis was 0.0 ± 0.0 with laser against 0.0 ± 0.0 on control (ns). One found root resorption on 11/18 with laser against 7/18 on control. The irradiated bone presents architectural disorganization and an intense activity of bone remodeling. We could see some empty osteocytes lacunes and some osteocytes nucleus in picnosis or cariolisis. The PDL presents a few densities of functionally oriented periodontal fibers and was poorly irrigated. We couldn't find collagenous vehicles in both the experimental and the control groups. Our data suggest that laser helps with the soft tissue cicatrization but it stops the bone regeneration.