The implementation of a radial-basis function network to approximate spectra of the signal reflected by a fibre Bragg grating sensor is reported. This algorithm helps the interpretation of the data acquired with equipment as an optical spectrum analyser. Results using a double-peaked spectrum from a uniform fibre Bragg grating sensor show that the common practice of fitting the spectrum with different interpolation methods and finding its peak, or directly finding the maximum intensity position of the raw spectrum, would cause a larger error when compared to searching for the peak of an approximated spectrum using the proposed neural network. An example is demonstrated through two experiments measuring the volumetric shrinkage of polymeric resin using a uniform FBG and a HiBi FBG embedded in the material. The obtained accuracy is higher than that obtained with the simple non-processed peak detection.

The use of fibre Bragg grating sensors to study dental materials like resin-based composite and gypsum products is reported. Two commercially available composite resins and three types of gypsum products were tested in order to determine polymerization contraction and setting expansion. Temperature and strain evolution during the hardening phase of the material were also obtained. The presented technique can be a good tool for dentists in order to better manipulate a material and predict how it will behave in vivo.

The use of Fibre Bragg Grating sensors to study the setting expansion of dental materials like resin based composites and gypsum is reported. Temperature and strain evolution during the hardening phase of the material are obtained.

Abstract-This study describes a localized method -using optical fiber Bragg gratings (FBGs) -to determine the human bite force at the very moment of occlusion, in maximum intercuspidation. The FBG was encapsulated in a silicone splint between uppers and lowers first molars and avoiding pre-contact with the other teeth in a dentition model. Gypsum dental castings of two volunteers are performed in a semi-adjustable articulator in the occluded situation to maintain angulations of the occlusal plane within normal occlusion. The sensor was characterized in vitro for both volunteers and the human bite force is measured in vivo. The orthodontic forces on the sensor are acquired at four moments: before of occlusion (free situation), occlusion, biting and maximum bite. The measured maximum bite forces are 85 N for female (brachyfacial) volunteer and 76 N for male (mesofacial) volunteer, between right uppers and lowers first molars. The difference can be associated to the facial pattern. The results obtained show the possibility to employ the optical encapsulated sensor to perform measurements of orthodontic forces in order to analysis different types of facial patterns with minimum of interference at occlusion.Index Terms-fiber Bragg gratings, human bite force, in vivo measurements, optical fiber sensors.

Fibre Bragg grating is used to determine resin-based composite shrinkage. Two composite resins (Freedom from SDI and Z100 from 3M) were tested to determine the polymerization contraction behaviour. Each sample of resin was prepared with an embedded fibre Bragg grating. A LED activation unit with wavelength from 430 nm to 470 nm (Dabi Atlante) was used for resin polymerization. The wavelength position of the peak in the optical reflection spectra of the sensor was measured. The wavelength shift was related to the shrinkage deformation of the samples. Temperature and strain evolution during the curing phase of the material was monitored. The shrinkage in the longitudinal direction was 0.15 +/- 0.02% for resin Z100 (3M) and 0.06+/-0.01% for Freedom (SDI); two-thirds of shrinkage occurred after the first 50 s of illumination.