192 lines
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Plaintext
192 lines
13 KiB
Plaintext
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T h e G R E E N Y w o r l d D o m i n a t i o n T a s k F o r c e ,
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I n c o r p o r a t e d
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Presents:
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\\___// \/\/ |____/ |_ __ _| 888 888 44
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888888888 4444
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"Medical Applications of Selective Laser Sintering (SLS)" by Otis
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----- GwD: The American Dream with a Twist -- of Lime ***** Issue #84 -----
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----- release date: 01-03-01 ***** ISSN 1523-1585 -----
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Fields of knowledge that were once completely diverse and unrelated have
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begun to come together. Among the most important of these for humanity as a
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whole are the multitude of (relatively) new links between medicine and other
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disciplines. Medicine is influencing the legal process: the advent of DNA
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evidence is a major step in the field of law enforcement. Computers are being
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used more frequently in the diagnosis of illness. Even materials engineering
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has contributed to some recent advances in medicine: the development of rapid
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prototyping technologies such as Selective Laser Sintering offer new hope to
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many due to their vast array of medical uses.
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The Selective Laser Sintering (SLS) process was developed at the University
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of Texas at Austin and is a patented process of DTM Corporation. It is like
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other sintering processes in that "materials are manufactured into useful
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shapes...by a high temperature treatment [a CO2 laser, in this case] that causes
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particles to join together and gradually reduces the volume of pore space
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between them" (Askeland 126). However, while many rapid prototyping processes
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"create parts within a vat of liquid resin," SLS "sinters - or fuses...[powdered
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materials] with a precisely guided laser to form solid, three-dimensional parts"
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(DTM).
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The process itself (see Figure 1) is similar to other rapid prototyping
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processes: "a laser sinters selected areas causing the particles to melt and
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then solidify" (Dolenc). The laser thus fuses the particles into whatever shape
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is desired, even allowing for excellent dimensional tolerances (depending on the
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size and complexity of the object formed, of course). The shape is specified in
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a "solid model 3-D CAD file, using the [international] industry standard STL
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format" (DTM). This allows intricate 3-D geometries to be formed from a large
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number of materials. In fact, "extremely complex geometries that could not
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otherwise be machined, cast or molded" can be produced through the use of SLS
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("Growing Parts"). The powdered material requirement of SLS also allows for
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the creation of a material or combination of materials "appropriate for
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virtually any manufacturing application" (DTM).
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Selective Laser Sintering is a quite useful technique. For the most part,
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SLS has been used in industrial rapid prototyping. It allows engineers to
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develop models of parts before mass production begins. These models can be
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analyzed and flaws can be determined before the actual manufacturing process has
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begun. Interestingly enough, the production of models was the impetus behind
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SLS's use in non-traditional manufacturing processes.
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Within the last few years, SLS (along with other rapid prototyping methods)
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has found a place in the medical field. According to Andy Christensen, general
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manager at Medical Modeling Corp., "'models are used for preoperative planning
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and surgical simulation, for communication with the patient and other surgeons,
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and for customization of off-the-shelf implants'" (Raplee 52). These models can
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be of either soft or hard tissue surgeries, showing the great flexibility of the
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SLS technology.
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Surgical planning is one of the main applications of SLS in medicine.
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Models built for this purpose allow surgeons to "rehearse incisions, measure
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grafts, and fit surgical resections before they operate," (Raplee 52) thus
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saving time during the actual procedure. The time saved reduces the patients'
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exposure to anesthesia and possibly decreases blood loss. Doctors often use
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these models to practice intricate surgeries. They are used for determination
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purposes, such as to find the least traumatic angle and position of entry for
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removal of tumors in the skull, near the eye (Ashley 53). Through use of these
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models, "doctors can literally practice removing a tumor on an accurate
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representation of the patient" (Crockett). The benefits to the patient of the
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doctor(s) practicing the surgery before operating are obvious but immeasurable.
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Also, the fact that SLS allows for composites of materials to be sintered
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permits the construction of "semitransparent and two-color models. Semitrans-
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parent models can illustrate...body and bone cavities. Two-color models can
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help a surgeon visualize radiopaque density differences...where a perceptible
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difference may be critical to the operation" (Raplee 52). There are indeed many
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effects of SLS and other rapid prototyping technologies on pre-surgical
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planning.
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The SLS technology has also been used to model and manufacture prosthetic
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limbs for amputees. The University of Texas "has developed a high-speed laser
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scanner for amputees called the UT Prosthetic Imager. This three-dimensional
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laser scanner and digitizer images a patient's residual limb in 10 seconds,
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acquiring a three-dimensional data file that describes the limb" (Ashley 51).
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The file is then adjusted by a prosthetist to improve fit, comfort, and
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stability. An SLS system then interprets the CAD files and manufactures a
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replacement prosthetic limb. Bill Rogers, a professor of Rehabilitation
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Medicine at the University of Texas Health Science Center in San Antonio, says
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that "'Rapid prototyping allows us to design in an integral fitting, which means
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you don't have to distort the end of the socket. It also means you can include
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the patient's specific alignment characteristics in the socket design'" (Ashley
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51). The rapid prototyping described by Dr. Rogers only refers to exterior
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prosthetics. There has also been work relating to surgical implants made by
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rapid prototyping, though not specifically by SLS. Stereolithography, another
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rapid prototyping technique that is similar to SLS in many ways (it is a
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sintering process that interprets CAD files directly) has been used extensively
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in the development of surgical implants (Ashley, Raplee). Another obvious use
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of SLS in medicine is the modeling and manufacture of artificial bones. The
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hard bone material is somewhat similar to other materials that are used in the
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SLS process. Researchers at the University of Leeds were some of the first to
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realize the medical applications of SLS. By 1995, the researchers had formed
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complete human adult and child skulls using the SLS technology. The skulls were
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scanned using computer tomography (CT). These scans were translated into the
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STL format, and the skulls were manufactured (Berry 91-96). These initial
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models were quite accurate. Use of SLS and other rapid prototyping techniques
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to model bones has continued in recent years.
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The Milwaukee School of Engineering and the Medical College of Wisconsin
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have been working on models of vertebrae for use in extremely human-like crash
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test dummies: "human vertebrae...consist of hard, dense cortical bone
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surrounding a soft, spongy trabecular bone. Creating a model of such a complex
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structure is now possible by linking CT imaging with RP [rapid prototyping]
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technology" (Crockett). Perhaps these artificial vertebrae (or further
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generations of artificial vertebrae developed in this manner) can one day be
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used to replace vertebrae in people. It is likely that work will continue in
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the area of rapid prototyping bones.
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While there are many benefits medical benefits of SLS and other rapid
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prototyping techniques, there are also many drawbacks. The problems the Leeds
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researchers encountered with translating CT data into STL format seem to have
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been lessened, but not completely overcome in the past few years. Raplee notes
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(quoting Christensen) that "Each year, thousands of surgeries are performed that
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could benefit from the use of models, yet 'models of the craniofacial skeleton,
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for instance, are sold for an average cost of $1,500 to $3,000,'...'Despite the
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benefits of its use, it can be a hard sell'" (53). These models are quite
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costly, and one can hardly blame a patient for not wanting to pay. Perhaps with
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the improvement of the technology (to incorporate CT data more easily) and the
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hardware required to build the models decreases in price (in general, technology
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tends to decrease in price over time), SLS-created models will be more
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commonplace in the hospitals of America.
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Possibly in the future, SLS and other rapid prototyping techniques can be
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used to manufacture models of soft tissues, as well as continuing to produce and
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improve prosthetics and artificial bones. The Leeds professors predicted the
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development of soft tissue models using SLS (Berry 95): "Possible future uses
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include building models of soft tissue organs such as the heart and vessels."
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However, the literature regarding such soft tissue models is rather scant. This
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is likely because research into these areas has not yet been published.
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SLS and other rapid prototyping techniques have a wide variety of medical
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applications. As time goes on, more applications will be available for rapid
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prototyped models in the hospitals and doctors' offices of America and the
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world. Millions of patients could benefit from this technology. Christensen
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states that, "'The future almost guarantees that growth will be seen in this
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area with better, faster, and cheaper machines and materials'...'One day we may
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see every patient who could benefit from this service get it'" (Raplee 53).
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Christensen's prediction for the future does not seem far-fetched at all.
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Mankind has already brought diverse fields such as materials engineering and
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medicine together; allowing everyone to benefit from this coupling cannot be far
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behind.
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Works Cited
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Ashley, Steven. "Rapid prototyping for artificial body parts." _Mechanical
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Engineering: The Journal of the American Society of Mechanical
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Engineers_ vol. 115, no. 5 (May 1993): 50-53.
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Askeland, Donald R. The Science and Engineering of Materials. Third edition.
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Boston, PWS Publishing Company, 1994.
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Berry, E., et al. "Preliminary experience with medical applications of rapid
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prototyping by selective laser sintering." _Medical Engineering &
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Physics_ vol.19, no. 1 (January 1997): 90-96.
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Crockett, Robert. "Building the Future, One Layer at a Time." The World & I.
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July 1999. http://www.worldandi.com/archive/nsjul99.htm. (15 April
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2000).
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Dolenc, Andre. "Selective laser sintering." 24 July 1994.
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http://www.cs.hut.fi/~ado/rp/subsection3_6_3.html. (2 May 2000)
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DTM Corporation. "A Process With Material Advantages." Austin, DTM
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Corporation, 1996.
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"Growing Parts." Los Alamos National Laboratory Daily Newsbulletin. 15 January
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1998. http://www.lanl.gov/orgs/pa/News/011598.html. (1 May 2000).
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Raplee, Jack. "Saving face: Rapid prototyping in the operating room ranges
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from the planning of bone cuts to the custom fit of implants."
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_Mechanical Engineering: The Journal of the American Society of
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Mechanical Engineers_ vol. 121, no. 6 (June 1999): 52-53.
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* GwD, Inc. - P.O. Box 16038 - Lubbock, Texas 79490 *
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"Payin' mental rent to corporate presidents." - Public Enemy, "He Got Game"
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--------------------------------------------------------------------------------
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-+- F Y M -+-
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GR33NY LIK3S mash3d p0tat03s
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MORE THAN FIVE YEARS of ABSOLUTE CRAP! /---------------\
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copyright (c) MM Otis/GwD Publications :PRIME THE PUMPS:
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copyright (c) MM GwD, Inc. : GwD :
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All rights reserved \---------------/
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