ABSTRACT
In recent years, interest in medical application of lasers especially as a surgical alternative is considerably increasing due to their distinct advantages such as non-contact intervention, bacteriostasis, less traumatization, minimal invasiveness, decreased bleeding and less heat damage. The present study aimed to evaluate the temperature changes and the consequent released thermal stress in cortical bone caused by an Erbium:yttrium aluminum garnet (Er:YAG) laser (Fideliss 320A, Fotona Inc., Deggingen, Germany) during osteotomy, using mathematical computation by means of Maple software, version 9.5 (Maplesoft, a division of Waterloo Maple Inc., Canada). The results obtained here were compared with the experimental measurements using Er:YAG laser in the osteotomy clinics. A bone slab with thickness of 1 mm was simulated in Maple software. Then, an Er:YAG laser emitting 100 µs pulses at a wavelength of 2940 nm were modeled. Two different clinical settings of the Er:YAG laser with 200 mJ and 400 mJ energies, both with 100 µs exposure and 500 µs silence were studied. To investigate the temperature distribution in the cortical bone, the time-dependent heat conduction equations were defined and solved in the Maple software. Finally, by defining the heat distribution function in the Maple, thermal stress in the bone was investigated. Results of the computations showed that, on the bone irradiated area (center of the bone surface) the maximum temperature rise was 0.8°C and 1.6°C, for 200 mJ and 400 mJ Er:YAG laser exposure, respectively. The temperature rise reached to its minimum at radial distances of 1.2 cm from the point of irradiated area for 200 mJ laser while it was 1.5 cm for 400 mJ laser. For 200 mJ laser the maximum derived radial (σ rr ), axial (σ zz ) and azimuthally (σ θθ ) stress components were 0.20, 0.16 and 0.08 MPa, respectively. While, for 400 mJ laser the maximum derived σ rr , σ zz and σ θθ stress components were 0.39, 0.31 and 0.16 MPa, respectively. These results confirm that use of 100 µs Er:YAG laser pulses with 500 µs silence at 200 and 400 mJ energies minimizes thermal tissue damage for the laser osteotomies, without continued water cooling (irrigation) on the exposed area.
ABSTRACT
BACKGROUND: A high rate of colorectal cancer occurrence is established in individuals with a positive family history of this type of cancer. OBJECTIVES: The aim of this study was to investigate the prevalence of colorectal cancer in first degree and second degree relatives of colorectal cancer patients. METHODS: Family medical histories of 489 first degree relatives of colorectal cancer patients were obtained by a questionnaire. 249 average risk patients with no family history of colorectal cancer were included as control patients. RESULTS: In our study from a total of 489 case patients, 153 (31.3%) had at least one close relative affected by colon cancer. Case-control analysis showed an odd ratio of 3.1 (95% CI, 2.07 to 6.27) for one and 5.7 (CI, 2.39 to 13.56) for two affected relatives. Cases with a positive family history had a 3.006 times greater risk in developing colorectal cancer if a first degree relative was affected comparing with a 4.9 times greater risk if a second degree family member was diagnosed with colorectal cancer. Our study indicated a higher risk for developing colorectal cancer in male family relatives 50 years and older. Rectal area was found the most tumor side affected in case and control patients. CONCLUSION: First-degree relatives of patients with colorectal cancer had an increased risk of developing this type of cancer. The risk was greater when diagnosis was in male, elderly patients and other first-degree relatives were affected.
