Above: Dr. Anil Kishen holds a representation of the digital readout from the laser measurement system
Photo: Jeff Comber
An unusual visual effect that prevents television news anchors from wearing striped ties and checked shirts – known as the moiré effect - is the driving force behind a novel laser measurement technique that could be leveraged to develop non-invasive methods for studying tooth structure before and after certain dental treatments, says Dr. Anil Kishen, Discipline Head of Endodontics at the Faculty of Dentistry.
A project first conceived during Kishen’s doctoral work in biomedical engineering at Singapore’s Nanyang Technological University (NTU), this two-laser beam technique offers researchers the ability to study hard tissues under clinically realistic loads on teeth, and to track the resulting stiffness and breakage within the microstructures of the dentin and enamel (the hard outer shell and inner shell covering the roots of the tooth) - even at the hard-to-measure junction between these two structures - with pinpoint accuracy.
“Traditionally, to study the effects of force on dental structures you just mount a sample in a machine and apply loads markedly higher than physiological loads,” describes Kishen. “But what you end up with is material properties such as stiffness averaged over the entire test specimen. This is not accurate, since stiffness differs at every point in the dentin,” he argues.
Kishen’s imaging technique, on the other hand, relies upon something called optical interferometry – essentially, a wave-based investigative technique more common to engineering – that results in a whole-field analysis of the tooth and its microstructure with extremely high resolution and under conditions of force natural and realistic to the human mouth.
During experiments, a laser beam splits across the surface of a tooth sample in two parallel lines, which interacts with the hard tissue and creates a virtual grid of the tooth structures at a resolution of 2400 lines per millimetre.
The measurements are transferred to a digital output in dark and light lines known as a moiré pattern. On television, such an effect makes superimposed lines or dots seem to jump and blur. With this technique, on the other hand, the lasers capture a complex map representing different levels of strain placed on the microstructure of the tooth. When the lines or “fringes” in the digital output are clumped close together, the strain on the tooth microstructure is significant. When the fringes appear further apart, the strain on the tooth is diminished.