The objective of this study was to determine the effectiveness of localized laser pulp surgery in the canine model. Effects of laser parameters on treatment outcome were also investigated. Pulpal exposure 3 mm in diameter were prepared in healthy teeth and left open to infection from the oral cavity for 72 hours. Pulpal tissue was then removed using high speed handpiece with sterile irrigation, or a CO2 laser. Teeth were monitored clinically, radiographically for 3 months. Results for each criterion were evaluated on a scale of 0-(-2). After sacrifice, histological assessment was made soft and hard tissue response. Results for each category were evaluated on a standard scale of 0-(-2). All evaluations were performed by 1 blinded, pre-standardized clinician. Statistical assessment using the chi-square test and Fisher's Exact Test associated laser treatment with a significantly better clinical, radiographic and histological treatment outcome. NIH RRO1192, seed grant funding form Loma Linda University, the Edna P. Jacobsen Charitable Trust for Animals, Inc. ©2004 Copyright SPIE - The International Society for Optical Engineering.

Plaque, calculus and altered cementum removal by scaling and root planing is a fundamental procedure in periodontal treatment. However, the residual smear layer contains cytotoxic and inflammatory mediators which adversely affect healing. Chemical smear layer removal is also problematic. In previous investigations effective smear layer removal was achieved using long pulsed irradiation at 1.06 μ. However, laser irradiation was not adequate as an alternative to scaling and root planing procedures and concurrent temperature rises exceeded thermal thresholds for pulpal and periodontal safety. It was the aim of this study to determine whether nanosecond pulsed irradiation at 1.06 μ could be used as an alternative or an adjunct to scaling and root planing. Sixty freshly extracted teeth were divided as follows: 5 control, 5 root planed only, 25 irradiated only, 25 root planed and irradiated. Irradiation was performed at fluences of 0.5 - 2.7 J/cm2, total energy densities of 12 - 300 J/cm2, frequencies of 2 - 10 Hz using the Medlite (Continuum) laser. Irradiation-induced thermal events were recorded using a thermocouple within the root canal and a thermal camera to monitor surface temperatures. SEM demonstrated effective smear layer removal with minimal microstructural effects. Surface temperatures increased minimally (< 3 C) at all parameters, intrapulpal temperature rises remained below 4 C at 2 and 5 Hz, F < 0.5 J/cm2. Without prior scaling and root planing, laser effects did not provide an adequately clean root surface.

Purpose

To assess noninvasive optical coherence tomography (OCT) and optical Doppler tomography (ODT) for early detection and evaluation of chemotherapy-induced oral mucositis.

Experimental design

Cheek pouches of 10 Syrian golden hamsters were imaged using OCT/ODT during development of chemotherapy-induced mucositis. I.p. injections of 5-fluorouracil and mechanical irritation induced oral lesions. At 2, 4, 7, and 11 days, one hamster was sacrificed and processed for histopathology. OCT images were visually examined; ODT results were semiquantified. Imaging data were compared with histologic findings.

Results

During the development of mucositis, OCT/ODT identified the following events: (a) change in epithelial thickness (beginning on day 2), (b) loss of surface keratinized layer continuity (beginning on day 4), (c) loss of epithelial (day 4 onwards) and submucosal integrity (day 7 onwards), (d) changes in axial blood flow velocity (increased on days 2 and 4; decreased on day 7), and (e) changes in blood vessel size (diameter doubled on day 2; quadrupled on day 4; unchanged on day 7). The semiquantitative imaging-based scoring system identified the severity of mucositis as defined by histopathology. The combination of imaging criteria used allowed for the detection of early, intermediate, and late mucositic changes. Imaging data gave higher scores compared with clinical scores early on, suggesting that the imaging-based diagnostic scoring was more sensitive to early mucositic change than the clinical scoring system. Once mucositis was established, imaging and clinical scores converged.

Conclusion

OCT/ODT identified chemotherapy-induced oral changes before their clinical manifestation, and the proposed scoring system for oral mucositis was validated for the semiquantification of mucositic change.

Thermal and histological events resulting from soft tissue incision using CO2 lasers at 9.3 μ or 10.6 μ, fitted with a hollow wave guide or an articulated arm delivery system respectively, were investigated. In 9 fresh pigs' mandibles, standardized incisions 3 cm in length were made in the oral mucosa. Incisions were performed in the cw mode at 1 W, 4 W, and 12 W. Thermal events were measured in adjacent soft tissues using thermocouples. Incisions were dissected out, fixed, embedded in paraffin wax, sectioned and stained with Serius Red. The Students' t-test for paired data was used to compare zones of necrosis, zones of collagen damage and thermal events. No significant temperature rise was measured during irradiation at any timepoints or power settings (p < 0.05). Results were very similar for the two lasers with significantly different results obtained only at the 12 W setting (p < 0.05). Vertical incision depths and horizontal incision widths did not differ significantly (p < 0.0001) at 12 W and 4 W. Horizontal and vertical zones of necrosis did not differ significantly (p < 0.0001) either between the two lasers at 12 W and 4 W. Thus the thermal and histological events occurring during soft tissue incision were similar using these two lasers, despite the difference in wavelength and delivery system.

We have proposed and experimentally demonstrated a new configuration of laser Doppler flowmetry for dental pulpal blood flow measurements. To date, the vitality of a tooth can be determined only by subjective thermal or electric tests, which are of questionable reliability and may induced pain in patient. Non-invasive techniques for determining pulpal vascular reactions to injury, treatment, and medication are in great demand. The laser Doppler flowmetry technique is non-invasive; however, clinical studies have shown that when used to measure pulpal blood flow the conventional back-scattering Doppler method suffers from low signal-to-noise ratio (SNR) and unreliable flux readings rendering it impossible to calibrate. A simplified theoretical model indicates that by using a forward scattered geometry the detected signal has a much higher SNR and can be calibrated. The forward scattered signal is readily detectable due to the fact that teeth are relatively thin organs with moderate optical loss. A preliminary experiment comparing forward scattered detection with conventional back- scattered detection was carried out using an extracted human molar. The results validated the findings of the simple theoretical model and clearly showed the utility of the forward scattering geometry. The back-scattering method had readings that fluctuated by as much as 187% in response to small changes in sensor position relative to the tooth. The forward scattered method had consistent readings (within 10%) that were independent of the sensor position, a signal-to-noise ratio that was at least 5.6 times higher than the back-scattering method, and a linear response to flow rate.

In this study, a fluorescence technique was developed for visualization of dentin using confocal laser scanning microscopy (CLSM). Eighteen extracted human teeth were used: 13 showing no clinical signs of caries and 5 with visually apparent decay. Preliminary study: All teeth were horizontally sectioned to approx. 200 μm thickness and pre-treated as follows: no pretreatment; vacuum only; ultrasonication only; sodium hypochlorite (NaOCl) only; vacuum and NaOCl; ultrasonication and NaOCl; or vacuum, ultrasonication and NaOCl. Samples were stained with Rhodamine 123 fluorescent dye at a concentration of 10-5 M in phosphate buffer saline for 1 to 24 hours. Caries study: Dentin surfaces, some with pre-existing caries, were visualized using CLSM. Most dentin tubules in sound dentin appeared open using CLSM, but most dentin tubules in carious dentin appeared closed or narrowed. Surface images obtained using CLSM were similar to those seen by SEM, but additional subsurface imaging was possible using CLSM at depth intervals of 1 μm to a depth of 30 - 50 μm. This technique shows good potential for non-invasive surface and subsurface imaging of dentin structures.

In spite of intensive research, lasers have not replaced conventional tools in many hard tissue applications. Low removal rates, loud operation noise, and mechanical and thermal damage are among the main obstacles to successful application of lasers. Ultrashort pulse lasers offer several advantages in their high per-pulse-efficiency, negligible thermal and mechanical damage and low noise operation. Practical applications of these devices, however, depends critically on sufficiently high volume removal which should match or even exceed the high speed drill. In our study, acoustical output of the USPL is compared to the low and high speed dental drill, Er:YAG, and Ho:YSGG lasers. Noise levels of the USPL are shown to be negligible in comparison with all other tested system. In addition, thermal characteristics of hard dental tissue ablation by ultrashort pulse laser of low and high pulse repetition rates are presented. Encouraging results showing temperatures increases smaller than 10°C even at the highest pulse repetition rates (1 KHz) are presented. A simple model for heat diffusion is discussed.

Previous studies have reported altered dentinal structure and properties after laser irradiation. It was the aim of this investigation to determine the thermal and ablative effects of XeCl irradiation in dentin and then to investigate microstructural and physicochemical changes in the residual dentin structure. Extracted human molar tooth roots were bisected and coated with acid-resistant varnish, leaving a window. After irradiation of one half at 1 Hz, 15 ns pulse durations, fluences of 0.5 - 2 J/cm2, both halves were subjected to acidified gelatin gel at pH 4.5. The carious lesions were bisected and used to perform SEM and microhardness measurements.

These investigations were performed to determine thermal, histological and incisional effects in soft tissue of laser irradiation at 9.3 um. Specifically, the consequences of varying pulse duration, interval and frequency, peak and average powers and energy densities were studied. In fresh pig's jaws, 6 standardized incisions, 3 cm in length, were made per parameter using a template and motorized jig. Incisions were made at various standardized anatomical sites, and surface thermal events monitored using an IR camera. Laser parameters investigated: power: 1 - 11 W, duty cycle: 10 - 90%, Pulse duration: 1 - 200 ms, at gated continuous wave. Superpulse and OptiPulse TM modes with 300 us pulses were also investigated. Incision width and depth as well as collateral tissue effects were assessed statistically. They were directly related to the parameters used. Ease of incision and effects on underlying bone were also parameter-related.