Retna Apsari

Feasibility of fiber optic displacement sensor scanning system for imaging of dental cavity.

Abstract. The purpose of this study is to investigate the potential of intensity modulated fiber optic displacement sensor scanning system for the imaging of dental cavity. Here, we discuss our preliminary results in the imaging of cavities on various teeth surfaces, as well as measurement of the diameter of the cavities which are represented by drilled holes on the teeth surfaces. Based on the analysis of displacement measurement, the sensitivities and linear range for the molar, canine, hybrid composite resin, and acrylic surfaces are obtained at 0.09667  mV/mm and 0.45 mm; 0.775  mV/mm and 0.4 mm; 0.5109  mV/mm and 0.5 mm; and 0.25  mV/mm and 0.5 mm, respectively, with a good linearity of more than 99%. The results also show a clear distinction between the cavity and surrounding tooth region. The stability, simplicity of design, and low cost of fabrication make it suitable for restorative dentistry.

Effect of Q -switched pulses exposure on morphology, hydroxyapatite composition, and microhardness properties of human enamel

Ablation of healthy human enamel is demonstrated using a 8 ns pulses at wavelength of 1064 nm and 10Hz repetition rate from a Q-switched Nd:YAG laser. The ablation result shows that an enhanced structuring quality in comparison with non-Q-switched pulse exposure. The material removal remains localized in the area of the laser spot with no signs of collateral damage and cracks observed. As a comparison, exposure to longer pulses of 120 μs from non-Q-switched Nd:YAG laser increases the composition of hydroxyapatite as well as microhardness property of enamel, which produces a side effect of surface dehydration and crack. This study suggests that the application of Q-switched Nd:YAG laser as contactless drills in dentistry should be regarded as an alternative to the classical mechanical technique to improve the quality of the tooth treatment.

Dosimetry of laser radiation for in vitro cancer cells inactivation using exogenous chlorophyll and protoporphyrin IX (PpIX)

The aim of this research is to study dosimetry of red diode laser radiation for breast cancer cells MCF-7 inactivation with and without the addition of the photosensitizer. Chlorophyll and Protoporphyrin IX (PpIX) were used as exogenous photosensitizers in this research, each with a concentration of 0.25 mg/ml and 0.0006 mM based on the results of acytotoxicity assay. Energy doses of laser irradiation used in this research were between 0.68 to 6.80 J/cm2 with two different laser powers (10 mW and 20 mW). The results showed that the higher dose of laser energy, the greater the percentage of cancer cells death. At the same energy dose, the higher the laser power resulted in a higher percentage of deaths as well. The highest percentage of deaths produced by a laser with power 20 mW and irradiation time 10 minutes (energy dose of 6.80 J/cm2) was 68.75% for laser irradiation without photosensitizer, 83.15% for laser irradiation with the addition of chlorophyll, and 93.59% for the laser irradiation with the addition of PpIX. Based on these results, it could be concluded that the red laser irradiation with addition photosensitizer chlorophyll and PpIX can inactivate cancer cells and can be used as a candidate for photodynamic therapy.

The utilization of the displacement sensor system to estimate cavities in dentures based on optical imaging

The paper proposes an intensity modulation technique based on micro displacement sensor to image cavities in denture material. The cavity imaging for various types of denture materials, as well as the measurement of the diameter of the cavities are presented. The samples used in this study were Acrylic Denture, Nano Hybrid Composite, Varplast, Nano Filler, with a cavity diameter of 5mm per sample. Based on the analysis, the measurement of cavity diameter using the analog method resulted in 5.00 mm for Acrylic Denture, Nano Hybrid Composite, Varplast samples, and 5.50 mm for Nano Filler, with 97.65% of maximum accuracy. The feasibility of micro-displacement sensor system with fiber bundle 16 receivers using the optical imaging technique with a displacement order of 500 μm was able to measure the width of the sample cavity in denture materials with accuracy approximately between 89%–99.48%. High stability, the simplicity of design, and low cost of fabrication make the micro displacement sensor system feasible to be applied in dentistry, especially for measuring and imaging cavities on denture materials.

Tapered fiber optic sensor for potassium detection in distilled water

A simple sensor is proposed and demonstrated using a silica tapered fiber for sensing different concentration of potassium in de-ionized water. The tapered fiber is fabricated using a flame brushing technique to achieve a waist diameter and length of 10 μm and 80 mm, respectively. For a concentration change from 0 to 50 %, the ouput signal of the sensor decreases exponentially from -10.04 dBm to -11.11 dBm with linearity of more than 92%. The increment of potassium concentration increases the refractive index of the solution, which in turn reduces the index difference between core and cladding of the tapered fiber and thus allows more light to be leaked out from the fiber. This new potassium monitoring system provides numerous advantages such as simplicity of design and low cost of production.