Martin Wehner

For the post-surgical treatment of oral wounds and mucosal defects beyond a certain size, the gold standard is still an autologous skin or mucosal graft in combination with complex suturing techniques. A variety of techniques and biomaterials has been developed for sutureless wound closure including different tissue glues or collagen patches. However, no wound covering that enables for sutureless fixation has yet been introduced. Thus, a new system was developed that allows for sutureless wound covering including a transparent collagen membrane, which can be attached to the mucosa using a specially modified 2λ laser beam with integrated temperature sensors and serum albumin as bio-adhesive. The sutureless wound closure system was tested for its applicability and its cytocompatibility by an established in vitro model in the present study. The feasibility of the laser system was tested ex vivo on a porcine palate. The in vitro cytocompatibility tests excluded the potential release of toxic substances from the laser-irradiated collagen membrane and the bio-adhesive. The results of the ex vivo feasibility study using a porcine palate revealed satisfactory mean tensile strength of 1.2–1.5 N for the bonding of the membrane to the tissue fixed with laser of 980 nm. The results suggest that our newly developed laser-assisted wound closure system is a feasible approach and could be a first step on the way towards a laser based sutureless clinical application in tissue repair and oral surgery.

In laser tissue soldering (LTS), a protein solution is thermally denatured and cross-linked to obtain a strong bond between tissues or tissue and a wound dressing. However, if the extension of the heat-affected zone is too large, wound healing is impaired by thermal tissue injuries. Therefore, heat input and coagulation depth have to be limited. We investigate the influence of wavelength and beam profile on coagulation depth using a soft tissue phantom in case of weakly (980 nm) and strong (1540 nm) absorbed laser radiation. The soft tissue phantom is doped with polystyrene (PS) beads to obtain similar scattering properties as natural tissue. The propagation of the laser radiation in the phantom is simulated by Monte–Carlo method and the optical penetration (OPD) depth calculated from isophotes. The simulation results are compared with the experimental determination of the coagulation volume. The results reveal that scattering effect of tissues on laser radiation increases the losses of a Gaussian beam profile laterally leading to a half-sphere coagulation volume. The depth profile of the coagulation follows approximately the intensity distribution of the laser beams as long as scattering effects are weak. As scattering effects become significant, as for 980-nm radiation, the intensity distribution of the laser beam in the tissue deviates from the original one, leading to different profile of the coagulation depth.

This study aimed to evaluate the possibility of introducing ultra-short pulsed lasers (USPL) in restorative dentistry by maintaining the well-known benefits of lasers for caries removal, but also overcoming disadvantages, such as thermal damage of irradiated substrate. USPL ablation of dental hard tissues was investigated in two phases. Phase 1—different wavelengths (355, 532, 1,045, and 1,064 nm), pulse durations (picoseconds and femtoseconds) and irradiation parameters (scanning speed, output power, and pulse repetition rate) were assessed for enamel and dentin. Ablation rate was determined, and the temperature increase measured in real time. Phase 2—the most favorable laser parameters were evaluated to correlate temperature increase to ablation rate and ablation efficiency. The influence of cooling methods (air, air–water spray) on ablation process was further analyzed. All parameters tested provided precise and selective tissue ablation. For all lasers, faster scanning speeds resulted in better interaction and reduced temperature increase. The most adequate results were observed for the 1064-nm ps-laser and the 1045-nm fs-laser. Forced cooling caused moderate changes in temperature increase, but reduced ablation, being considered unnecessary during irradiation with USPL. For dentin, the correlation between temperature increase and ablation efficiency was satisfactory for both pulse durations, while for enamel, the best correlation was observed for fs-laser, independently of the power used. USPL may be suitable for cavity preparation in dentin and enamel, since effective ablation and low temperature increase were observed. If adequate laser parameters are selected, this technique seems to be promising for promoting the laser-assisted, minimally invasive approach.