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(continued)
Some of the latest innovations in the industry have reached the small world of the dental biomaterials
This technology is used when handling of some difficult materials, like titanium or some ceramics (alumina, zirconia), is not possible in a dental laboratory, chiefly because of the high cost of the required equipments. The traditional gypsum models from which the technician is creating his restaurations remain the 3D representation of the clinical situation. These models are scanned to create a virtual 3D model, and these data are sent to a distant milling center, where the actual frameworks are produced.
Principle
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| The command and data files, produced from the scanning data, are transmitted by Internet to a distant manufacturing center. www.cynovad.com |
Production and checking are done on an industrial basis, and the finished framework is then sent back to the dental laboratory by express mail. | The dental technician adds then the covering and esthetic layers of dental ceramics, according to the specific requirements of the clinical situation. |
Main applications in dentistry
- in house scanning of models: several types of scanners are available, either mechanical or optical (visible light or laser light). Many of the scanning systems can directly create the command files for the further milling at the production site: this limits however the choice of the milling center, which should match the scanning system.
- sending of files to distant milling centers: Internet has become the way of choice for these transfers of information
- milling of ceramics or metal framework: the milling centers can be either local (an other dental laboratory) or distant and serving several countries. Depending of the center, frameworks can be prepared in one single material, or in several, like titanium, alumina or zirconia.
As of now, telemanufacturing is limited to the production of the frameworks for metal-ceramic restorations. This is a direct consequence of the various levels of exigence for the esthetics of the restoration.
This is somewhat changing the role of the dental technician. He is active at two levels:
1st steps for telemanufacturing... for the scanning (and possibly for the designing of the virtual element and for the computing of the tool path for the milling machine)
...and after in the final control of the machined element before laying on the ceramics, and of course in the application of the cosmetic layers of ceramics
Principle
A system able to create 3D objects of any complexity by successive layers (slices). Each slice is produced by action of a laser light on a liquid material. This 2D shape of the solid slice is obtained by the movements of the laser, commanded by a computer
The precision is defined by the thickness of each slice
The process called stereophotolithography (SPL) has been developed in the 90's by Laser 3D (Nancy, France) , based on the French Patent No. 84 11 241 (CNRS- July 84.)
The principle of stereophotolithography applied to the rapid prototyping of 3D objects. |
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| Diagram of a typical stereophotolithograhy system, according to Kristi S. Anseth, Dept Chem. Eng. Univ. of Colorado at Boulder |  |
Main applications in dentistry
Orthodontics
How to replace brackets and braces in orthodontics treatments ?
By fabricating a series of clear removable aligners, used to induce successive teeth movements.
| A series of clear aligners is fabricated by SPL, starting from the initial positions of the teeth and progressively forcing the teeth to the various intermediary positions which have been calculated between the initial and the final positions. Usually, there is one aligner for each week. Each aligner picks from the situation created by the preceding one, and moves the teeth slowly to the next positions. http://www.invisalign.com |
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Maxillofacial surgery
How to evaluate and plan major cranio-facial reconstructions?
By fabricating 3D models of the skull from MRI and CT scans, and by cutting and reassembling the various elements
A commercial machine producing complex 3D objects in several colors is used to create the 3D models of skulls for the planning of difficult maxillofacial surgery |
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Technicity, however, is not only found in the realm of synthetic dental biomaterials. The age of biological solutions is coming...
One step beyond: tissue regeneration
Early successes in periodontal treatments call for more clinical applications
Guided Bone Regeneration (GBR)
also: Guided Tissue Regeneration (GTR)
Bone substitutes + Membranes ( Osseoconduction ) = Bone regeneration
| Guided tissue regeneration for periodental infra-bony defects (Cochrane review) Needleman IG, Giedrys-Leeper E, Tucker RJ, Worthington HV 1999 / Updated 2003 Objectives: To assess efficacy of GTR in treatment of periodontal infra-bony defects versus open flap debridement (= current standard of surgical periodontal treatment) Selection criteria: Randomised, controlled trials of at least 12 months duration comparing guided tissue regeneration (with or without graft materials) with open flap debridement for the treatment of periodontal infra-bony defects. Reviewers' conclusions: Overall, GTR was a little more effective in increasing attachment gain, reducing pocket depth and favouring gain in hard tissue probing at re-entry surgery, however there was marked variability between studies. (....) There is evidence that GTR can demonstrate a significant improvement over conventional open flap surgery but the factors responsible for success or failure are unclear from the literature. (....) http://www.cochrane.org/cochrane/revabstr/ab001724.htm |
Great expectations – getting rid of synthetics and letting the body reconstruct itself
Regaining tissues by osseoinduction
One application on the market for the treatment of periodontal defects uses a number of proteins, extracted from teeth, which self-assemble to create a matrix.
The dominant protein in this matrix is amelogenin
This treatment intended as an adjunct to periodontal surgery for topical application onto exposed root surfaces to treat periodontal intrabony defects
Concentrates of autologous platelets
Method developed by CHOUKROUN, ADDA, SCHOEFFLER and VERVELLE, January 2000
PRF = Platelet Rich Fibrin
The solid mass obtained from the patient's own blood contains the following growth factors in high concentration :
| PDGF = Platelet derived growth factor - Competency Factor - Chemotactic and mitogenic - Directly angiogenic |
TGF a and b = Transforming growth factor - Stimulates growth of fibroblasts - Stimulates DNA synthesis - Osseoinductor - Stabilizes extra cellular matrix - Favors cicatrisation |
Platelet rich fibrin
Preparation
The preparation includes three simple steps, which are taken directly in the practice:
- Collection of patient 's blood
- Centrifugation
- Separation in three fractions
Clinical use
Retrieval of blocks of PRF ready for grinding or spreading in plates. They are used on major bone defect, both as ground PRF and as PRF in plate to cover the site.
Degradables as matrices for tissue regeneration
Root shaped resorbable implants
RootReplica™ - This is a new therapy for prevention of atrophy of the alveolar crest after tooth extraction (see Company Profile in this issue for practical details)
- Original tooth and RootReplica™ : from the extracted tooth, an impression is immediately taken at chairside, and using that impression of the roots, an exact resorbable implant is instantly produced, within 5 minutes, from tiny beads of a resorbable material. A resorbable binder provides the conservation of the shape of that replica of the roots. The replica is then inserted in the alveola.
- Clinical situation : after insertion of the RootReplica™ , the volume of the extraction site is filled precisely and the bone of the alveolar crest can start to regenerate, due to the osseoconductor effect of the material. At 6 months, the bone has replaced enough of the replica to provide a sound bed for implantation.
Fabrication of an implant made of a calcium phosphate macroporous cement (brushite)
Brushite is easily bioresorbed. It can be transformed into a cement, which can be shaped by various techniques. One experimental procedure includes the fabrication of a macroporous implant from a wax model produced by SPL:
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| CAD drawing for wax model fabrication | Wax model of the pores obtained by stereophotolithography | Cement macroporous implant (brushite) |
This implant may be used as a scaffold for tissue regeneration
Documents kindly provided by Dr J. Lemaître, Oct. 2002 - Patent by ImplantOs, CalciphOs S.A. and EPFL, Switzerland
Rapid prototyping
TheriForm™ microfabrication technology
| Dispenses 800 microdrops/sec within 10 microns of the intended X-Y-Z positions Drops of binder hit a polymer powder, making it solidifiy, thus fabricating the sought object http://www.therics.com |
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| Series 2100 TheriForm™ http://www.therics.com |
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TheriRidge ™ Block / TheriForm™ microfabrication technology
| Using that technology, blocks of polymer can be shaped to missing parts of the cranio-facial area, thus leading to replacement of the missing bone, or possibly to its reconstruction by bone regeneration - Image acquired by MRI or CT scan, indicating the target area |
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The binder for the powder of special biodegradable polymer is dispensed by ink jet technology. The special “ comb polymer ” is designed to promote cell adhesion, thus stimulating bone regeneration. It can be made into 3D objects with the proper porosity to let the bony cells to grow easily within this shaped scaffold
Content
The faded (and fading) glories
The influence of public expectation
One step beyond: tissue regeneration