Development of novel laser processes for ophthalmology and dentistry

Abstract

This thesis is focused on the development of novel laser processes for ophthalmology and dentistry. Firstly an in-depth investigation into the possibility of using 10.6 μm CO2 laser radiation for removal of hard dental tissue is presented. Different processing regimes are investigated to find optimal processing parameters that allow precise tissue removal without introducing any unwanted damage. Moreover the temperature increase during laser processing is measured to ensure process safety at the early stage research. When using a water spray the maximum recorded temperature increase in the pulpal chamber was ~3 oC (for a repetition rate of 250 Hz) which is below the critical level of 5.5 oC which would cause tissue necrosis. The application of picosecond plasma mediated ablation of porcine sclera to create cavities which could form portals of entry to enhance drug delivery to the posterior eye is also investigated. To ensure that the process would not present a risk of unwanted damage to the eye both the temperature rise in the tissue and power transmission through the tissue is investigated during laser processing. The feasibility of this tissue modification as a means to improve drug permeation through the sclera is investigated with a Franz cell setup. It was found that if a drug (fluorescein dextran was used to simulate drug diffusion) is placed in a 5 mm by 5 mm by 100 μm cavity its permeation through the tissue increases by 11 – 12 times in first 5 hours compared to unmodified tissue. To support experimental work and provide insight to the physical mechanism of the tissue removal process two theoretical computational models are developed. First an ALE moving boundary model is applied to investigate single pulse removal of hard dental tissue. For single line plasma mediated scanning ablation of porcine sclera a 2D finite element blow-off model is which confirms the presence of a heat accumulation phenomenon that can influence the depth of the cavity formed. Consequently in this thesis the viability of two laser processes for application to modification of hard dental and soft scleral tissue has been demonstrated which opens up the possibility for developing novel procedures for surgery and dieses treatment.