The Principle of Light Transmittance of Dental PMMA

The principle of light transmittance of dental PMMA is mainly based on its high transparency and excellent optical performance. Specifically, it can be analyzed from aspects such as molecular structure, light propagation mechanism, and material properties:

Molecular structure and light propagation

Linear and regular structure: The PMMA molecular chain is linear and relatively regular, with the molecules closely and orderly arranged. This structure ensures that light scatters less when propagating between molecules. Light can travel at the same speed without being dispersed in all four directions or interfering with each other, thus guaranteeing a high light transmittance.

Impurity influence: When there are impurities or defects in the molecular structure, the light propagation path will be disturbed, resulting in a decrease in light transmittance. For instance, during the production process, if the purity of the raw materials is not high and they contain unreacted monomers, catalyst residues or other impurities, these impurities will form scattering centers between molecules, causing light to scatter and reducing the light transmission effect.

Light propagation mechanism

Total reflection property: Due to the very low absorption rate of PMMA for light, it can be made into a total reflection material based on its critical Angle characteristic for total reflection. For instance, a PMMA sheet or rod-shaped object with an extremely smooth surface, when bent to a certain extent, can reflect all the light entering from one end within it and finally exit from the other end.

Reflection and absorption: When light enters PMMA from air, part of the light is reflected at the surface, part is absorbed by the material, and part passes through the material. The reflectivity of PMMA is relatively low, while its light transmittance is relatively high. For example, substituting the refractive index of PMMA, n=1.49, into the relevant formula, it is calculated that the theoretical transmittance of PMMA can reach 96%, and the remaining 4% is reflected away in the incident direction.

Material properties and light transmittance

Amorphous polymer: PMMA is an amorphous polymer with uniform texture. The arrangement of its internal molecules does not affect the speed at which light enters the interior and passes through each part, which helps maintain high light transmittance.

The range of light waves transmitted: PMMA can transmit most ultraviolet rays and some infrared rays, with a limit of 2600nm of light wave wavelength, which is unmatched by other plastics. This wide-range transmission characteristic makes PMMA have broad application prospects in the field of dentistry.