Biomedical subjects

Anupama V Sarma

Publications and source records attributed to Anupama V Sarma.

4 recordsLinked to original sources

PubMed2006

Adhesion of composite to enamel and dentin surfaces irradiated by IR laser pulses of 0.5-35 micros duration.

The characteristics of laser-treated tooth surfaces depend on the laser wavelength, pulse duration, spatial and temporal laser beam quality, incident fluence, surface roughness, and the presence of water during irradiation. Ablated surfaces are most commonly restored with adhesive dental materials and the characteristics of the ablated surfaces influence adhesion of restorative materials. Previous studies suggest that high bond strengths can be achieved using shorter laser pulses that minimize peripheral thermal damage. In this study, Er:YSGG, Er:YAG, and CO(2) lasers were used at irradiation intensities sufficient to simulate efficient clinical caries removal to uniformly irradiate bovine enamel and human dentin surfaces using a motion control system with a microprocessor-controlled water spray. The degree of spatial overlap of adjacent pulses was varied so as to investigate the influence of irradiation uniformity and surface roughness on the bond strength. Composite resin was bonded to the irradiated surfaces and shear bond tests were used to obtain bond strengths in MPa. The highest results were obtained using the Er:YAG pulses with pulse durations less than 35 mus without the necessity for postirradiation acid etching. Some of these groups were not significantly different from nonirradiated, acid-etch-only positive control groups.

Acrylic Resins↗

PubMed2004

Peripheral thermal and mechanical damage to dentin with microsecond and sub-microsecond 9.6 microm, 2.79 microm, and 0.355 microm laser pulses.

BACKGROUND AND OBJECTIVES: It is desirable to minimize peripheral thermal damage during laser irradiation, since thermal damage to collagen and mineral compromises the bond strength to restorative materials in dentin and inhibits healing and osteointegration in bone. There were two primary objectives of this study. The first objective was to measure the degree of thermal damage peripheral to incisions in dentin produced with lasers resonant to the specific absorption bands of water, collagen, and hydroxyapatite with varying pulse duration using polarized-light microscopy (PLM). The second objective was to use synchrotron radiation infrared spectromicroscopy (SR-FTIR) to identify the specific chemical nature of the optical changes observed under PLM in the respective zones of thermal damage peripheral to the laser incisions. STUDY DESIGN/MATERIALS AND METHODS: Precise incisions were produced in 3 x 3 mm2 blocks of human dentin using CO2 (9.6 microm), Er:YSGG (2.79 microm), and Nd:YAG (355 nm) lasers with and without a computer controlled water-spray. Optical coherence tomography (OCT) was used to obtain optical cross-sections of each incision to determine the rate of ablation. The peripheral thermal damage zone around each incision was analyzed using PLM and SR-FTIR. RESULTS: Thermally induced chemical changes to both mineral and the collagen matrix were observed with SR-FTIR with a 10 microm spatial resolution and those changes were correlated with optical changes observed with PLM. Minimal (<10 microm) thermal damage was observed for pulse durations less than the thermal relaxation time (Tr) of the deposited laser energy, with and without applied water at 9.6 microm and with only applied water at 2.79 microm. For pulse durations greater than Tr, greater peripheral thermal damage was observed for both IR laser wavelengths with and without the water-spray. There was minimal thermal damage for 355 nm laser pulses less than Tr with and without applied water; however, extensive mechanical damage (cracks) was observed. CONCLUSIONS: High resolution SR-FTIR is well suited for characterization of the chemical changes that occur due to thermal damage peripheral to laser incisions in proteinaceous hard tissues. Sub-microsecond pulsed IR lasers resonant with water and mineral absorption bands ablate dentin efficiently with minimal thermal damage. Similar laser parameters are expected to apply to the ablation of alveolar bone.

Collagen↗

PubMed2004

Selective targeting of protein, water, and mineral in dentin using UV and IR pulse lasers: the effect on the bond strength to composite restorative materials.

BACKGROUND AND OBJECTIVES: Previous studies have shown that during the laser irradiation of dentin and bone, thermal damage can be minimized by using a highly absorbed laser wavelength, laser pulses shorter than the thermal relaxation time of the deposited laser energy at that wavelength, and the addition of a layer of water to the tissue surface before ablation. The objective of this study was to investigate the influence of laser pulse duration and wavelength with and without the added water layer on the bond strength of composite to laser prepared dentin surfaces. The specific hypothesis that was tested was that thermal damage to the collagen matrix in dentin compromises the bond strength to composite restorative materials. STUDY DESIGN/MATERIALS AND METHODS: Three laser systems were employed that were tuned to water, collagen, and mineral absorption with pulse durations less than the thermal relaxation time of the deposited energy. The surfaces of human dentin were irradiated by laser irradiation from free-running and Q-switched Er:YSGG lasers, pulsed CO(2) lasers operating at 9.6-microm, and a Q-switched Nd:YAG laser operating at 355-nm. A motion control system and a pressurized spray system incorporating a microprocessor controlled pulsed nozzle for water delivery, were used to ensure uniform treatment of the entire surface. Shear bond testing was used to evaluate the adhesive strength in order to access the suitability of laser treated surfaces for bonding. Bonded interfaces were examined by SEM. RESULTS: All the laser groups had significantly lower bond strengths than the positive acid etch control group. The highest bond strengths were for the short pulse (< 5-microsecond) Er:YSGG and CO(2) laser groups with water. Laser groups without water had significantly reduced bond strengths and thicker layers of thermally damaged dentin. CONCLUSIONS: Thermal damage to the collagen matrix profoundly influences the bond strength to composite restorations.

Dental Bonding↗

PubMedDate not supplied

Selective removal of composite sealants with near-ultraviolet laser pulses of nanosecond duration.

It is often necessary to replace pit and fissure sealants and composite restorations. This task is complicated by the necessity for complete removal of the remaining composite to enable suitable adhesion of new composite. Previous studies have shown that 355-nm laser pulses from a frequency-tripled Nd:YAG laser can selectively remove residual composite after orthodontic bracket removal on enamel surfaces. Our objective is to determine if such laser pulses are suitable for selective removal of composite pit and fissure sealants and restorations. Optical coherence tomography is used to acquire optical cross sections of the occlusal topography nondestructively before sealant application, after sealant application, and after sealant removal. Thermocouples are used to monitor the temperature in the pulp chamber during composite removal under clinically relevant ablation rates, i.e., 30 Hz and 30 mJ/pulse. At an irradiation intensity of 1.3 J/cm2, pit and fissure sealants are completely removed without visible damage to the underlying enamel. At intensities above 1.5 J/cm2, incident laser pulses remove the resin layer while at the same time preferentially etching the surface of the enamel. Temperature excursions in the pulp chamber of extracted teeth are limited to less than 5 degrees C if air-cooling is used during the rapid removal (1 to 2 min) of sealants, water-cooling is not necessary. Selective removal of composite restorative materials is possible without damage to the underlying sound tooth structure.

Animals↗