Science topic

Dental Prosthesis - Science topic

An artificial replacement for one or more natural teeth or part of a tooth, or associated structures, ranging from a portion of a tooth to a complete denture. The dental prosthesis is used for cosmetic or functional reasons, or both. DENTURES and specific types of dentures are also available. (From Boucher's Clinical Dental Terminology, 4th ed, p244 & Jablonski, Dictionary of Dentistry, 1992, p643)
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If a 73 year old patient presents to your clinic with chief concern of inability to eat. You find that the patient has unstable occlusion as a result of erosive tooth surface loss. Moreover the patient has a forward head posture with a stooping back.
Where should the final occlusion be set? and how?
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It's a tough situation. The patient that you have described is one who has a physical disability that compounds their condition So you can really feel for this person. But we have to make sure that we listen to them with empathy while at the same time thinking about offering solutions that are physical rather than emotional. When you say that patient is impatient and does not comply with splints I would agree that this is probably true but to a great extent if they don't comply with the splint therapy they may well never achieve successful treatment.
Sadly, we can't treat everyone. Some people are refractory to treatment. For some patients, if they can't identify the problem we will never know if there is a solution for it.
A good friend of mine, when speaking to patients will tell the patient that they understand that the patient has a problem but the patient needs to understand that it is their problem and it doesn't get any better by making it the clinicians problem. It becomes an ownership of the problem situation. I can never own the patient's problem, the best I can do is try to help them treat it. So, once again, coming back to the statement that the patient grows impatient with splint therapy this makes sense to me but I can only help to solve a problem that has been developing for years and years (was this patient in their 70s) but any solution that I offer the patient is not going to have the immediacy that they would so desire. This patient will frequently become a dental shopper rather than becoming a dental patient.
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accuracy of 3D printer while printing 3D digital surgical guide for dental implant placement
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I am working in clinical environmental medicine. Heavy Metal often takes  part in chronic inflammation, thus supporting the evidence of cancer or other chronic diseases. Material comes from everywhere in our environment, dental prosthesis, drinkwater, food, coal-fired power plant. 
Language can be german, englisch, Italy, french.
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i need it for dental prosthesis research
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For the dental applications, you will not need a traditional fan beam 64 slice or multi slice system. You would need a cone beam CT for it. 
I'm sure, you will find a CBCT.
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How can you provide dental treatment to the patients with severe gag reflex. Specially recording the impressions become a serious problem for such patients .... how do we deal with this.
Please share your experience ?
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First start with the ABCs of dealing with this issue: The choice of trays that don't extend excessively; the choice of impression materials that don't easily flow backwards; and the choice of the right amount of this material so you dont end up with excess flowing backwards.
Then we move to the tricks that could be used, and I could mention a couple here: EITHER have the patient suck a candy made with the medical topical anesthetic tetracaine 1% until it begins to coat both the hard and soft palates, OR have the patient massage their hands with a chemical ice bag. The idea here is to keep the hypothalamus distracted and busy. As you know, the hypothalamus is the part of the brain that, besides other things, controls the gag reflex. So if you can keep this part busy with those "other things", then it will temporarily "forget" about the gag reflex.
Morning appointments are typically given for those anxious patients. To minimize the gag reflex, patients anxiety needs to be at a minimum. So anything that can be done to decrease the anxiety should be tried. Having a chair with heat and vibrating modes that the patient can control during the procedure also helps, since it provides a pleasing vibration meanwhile.
Nitrous oxide is a good way to calm the patient and their reactions to sensations during dental procedures.And finally, antianxiety elixir could be used.
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Profilometer
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Profilometers  can be used for roughness measurements of deantal material. However care must be taken  while using form removal.
In case of Dental implants it becomes all the more important beacuase these have tapper.
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Is it possible to achieve favorable maxillofacial re-construction from a natural and physiological standpoint, if implant placement is involved during treatment planning?
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It all depends upon how you look at the question of maxillofacial rehabilitation.
Are you looking at situations where you are doing primary reconstruction? If you're doing primary reconstruction without an ora-nasal (meaning that the communication was closed surgically), or any other, communication and if you have relatively thin mucosa, in contrast to thick skin, implant should proved to be a great benefit in the reconstruction of the patient as you are trying to replace dental units (Teeth).
The thing that we have to be careful of however is the notion that teeth are involved in trituration but not in manipulation of the food bolus.(see Curtis, D et al). So if there has been A fundamental change in the anatomy of the buccal mucosa, buccal musculature, Hard or soft palate, tongue, Floor the mouth, etc. The issues related to manipulation of the food bolus are probably more critical than the patient's ability to triturate food. Manipulation of the bolus puts that bolus of food either on the occlusal table or fails to put it in a position where trituration would occur. The functional deficit in this situation is the poor manipulation of the food bolus more so than the poor trituration of the bolus.
If you are not looking at reconstruction of the defect but instead are looking at a communication between the oral and nasal cavities and you are using an obturator to close that defect the immobility of the implants is a bit of a disservice because the obturator generally does move, hopefully just a little, in function. The patient generally does not chew on the side of the defect but that doesn't mean but nothing ever goes on to that side. If I have my preference I would prefer retention of teeth to support an obturator because there is physiologic mobility which is then magnified by the length of the lever arm before you get to supporting areas within the defect such as the pterygoid plate.
If you're talking about a mandibular defect, Whether reconstructed or not, there is almost always some discrepancy from the normal, Let's call that the pre-surgical, condition. This generally means that if you are using implants there is a horizontal discrepancy in many instances that must be accommodated. Of course if the lateral border of the tongue was also resected, which happens frequently when a mandibular discontinuity defect is created whether it is restored or not, the question of manipulation of the food bolus comes into play once again.
The short answer to your question is that dental implants usually serve the valuable purpose in the management of a maxillofacial defect. The long answer however is that there are a number of new and different considerations that must be made when implants are used in the management of maxillofacial defect. The thought processes that we may have used 30 years ago may need to be rethought as we introduce a new components into the treatment armamentarium. Implants are often an acceptable root substitute but they are not always going to function in the same way as the natural tooth root and we need to be cognizant of this and must modify our treatment appropriately.
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Cantilever FPDs, especially distal cantilevers, are discouraged in the texts and are prescribed with many precautions. What type of FAILURES are associated with them? Are the Forces and Biomechanics (and hence, the design considerations) similar for the lower and upper arches?
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When considering relatively classical dental literature the names of Laurell  and Lundgren  come to mind. These authors used long cantilevers in the natural dentition with  excellent long-term success which was most likely secondary to careful management of occlusion and the beneficial effect of tooth mobility as a "stress relief" mechanism. Not long after these authors we started to see more common descriptions of cantilever usage with implant retained dental prostheses were the implants, by necessity, were placed between the mental foramen and the cantilever was extended distally and bilaterally. Perhaps with the implant prosthetic approach the situation benefited from the fact that many of those early prostheses were opposed by complete dentures which then created the, thought to be, relief system. Over time however cantilever usage in the combination with implant supported bilateral prostheses has been quite efficacious  and eventually effective.
I mentioned previously, perhaps in response to another similar question, that there are number of critical factors and need to be considered when cantilevers are used in combination with implant retained prostheses. The situation must be curvilinear relative to the placement of the implants, there must be an appropriate relationship between the distance from the fulcrum to the anterior most abutment and its relationship to the length of the cantilever, there must be an appreciation of the type of material that is used for the framework that supports the cantilever, occlusion must be managed very carefully, the anticipated forces exerted by the patient must be considered, etc. it is not as simple situation where we can simply state that cantilevers work or that cantilevers don't work. When the myriad of considerations are managed appropriately cantilevers indeed do work but ignorance of or disregard to some of the critical factors will doom the treatment.
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1. CLAP- Cleft Lip And Palate
2. Any specific age in days/months/years
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 Infants born with a cleft of the palate (with or without cleft lip) are unable to breastfeed effectively and require special feeding equipment (such as squeezable bottles and teats) and many mothers need specialist feeding advice and support. While some maternity service providers and Maternal Child Health Nurses are able to provide general feeding support to new mothers, there remains significant confusion amongst both the lay and professional community about the effective feeding interventions for infants born with CL/P. As a result many families receive conflicting advice and experience significant and unnecessary emotional distress and fatigue during the first year of life if they are not able to access specialist cleft feeding support services. From the RCH cleft unit website 
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Kennedy Class IV.
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Thank you.
An interesting  question about  a historic  approach . However,in my view,cross arch stabilisation is very much  yesterday's game.
There can be very little ,if any, justification now  for removing 62-73% of sound tooth tissue (Edelhof and sorenson 2002) for multiple preparations to provide one path of insertion for such prostheses.
The concept was founded on the   now discredited  idea that distributing  occlusal load across multiple teeth to provide rigidity  stopped periodontal disease.
Most of  have  not believed that for over forty years (Axelsson and Lindhe). Double abutting as a concept  can contain the seeds of  later failure due to pulpal or structural problems .Splinting teeth  for cross arch stabilisation also makes it more difficult for the average person to keep things clean -hence later failure.
Just ask yourself-"would I have that  destruction done to your own remaining sound teeth if you were missing those teeth"
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Does anyone have an actual method for pull-of tests of zirconia crowns?
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Has anyone attempted on use of additive manufacture for dental ceramics?
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Hello Mam, 
Good to know the links were useful.
Objet uses PolyJet technology. In terms of materials, it's pretty similar to SLA. SLA can work on ceramic loaded resin suspension as well. Here, the matrix is the photocurable resins and ceramic nano/micro particles are dispersed in it. Please refer to this paper for a better understanding: 
My research work is on similar lines. I would be more than happy to share over a private conversation. 
As far as Z-Corp is concerned, it can work on ceramics but the intricacy levels will not match SLA/ PolyJet/ Milling (used in most CAD/CAM Dental Labs).
Looking forward to your reply 
Best Regards, 
Mohit 
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Does anyone have insight on how bone quality and debris around dental implants affect the coefficient of friction on the bone-implant interface?
Is there any literature available on the topic?
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Excluding the micro and macro structure of the implants , some concern regarding the bone-to-implant friction coefficient involves the trabecular fractures and the bone elastic modulus. Both are strictly related to stiffness of the bone that is dependent to the amount of mineral density and partially related to the bone collagen fibres orientation.
As consequence, no data exist to ensure a strong mean value for friction coefficient between bones and implant surface.
Nonetheless, significant correlation has been reported by K. Okuyama et al. (Spine 2000; 25(7):858–864) between bone mass and the insertion torque of the implants as well as between bone mass and pull-out strength. [T. C. Ryken, et al. (J Neurosurg, 1995; 83(2):325–329)--J. R. Chapman et al. (J Biomech Eng 1996; 118(3):391–398) ---C. A. Reitman, et al. (J Spinal Disord Tech, 2004; 17(4):306–311)] . However, the exact contribution of bone mass remained unclear as well as the role played by many additional parameters, such as insertion torque and implant screw design parameters.
The insertion techniques, especially for the case of undersize implant bed preparation, are intended to achieve compaction or "radial preload" of the peri-implant bone. Implants with radial preload presents a limited portion of the trabecular microstructure crushed [M. Windolf et al. Clin Biomech, 2009; 24(1):53– 58] as well as a limited portion of the trabecular bone microstructure permanently deformed elastically/plastically[S. Kold et al. Acta Orthop Scand, 2003; 74(5):591–595].
The elastic “spring-back effect” enhances the early implant fixation through frictional forces. During the onset of osseointegration, the spring-back effect is gradually lost thanks to the bone remodelling process [J. R. Green, et al. J Arthroplasty, 1999;14(1):91–97].
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I am writing a book about the intelligent design of the teeth, including the biofunctional mechanical forces of occlusion, and the method of construction of dental restorations, by copying the trilaminar pattern of the teeth. Any information about my question will be appreciated.
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One answer is  8-12 microns -Riis and Giddon
Other workers in this field that you should check were were Anderson and Picton
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I'm looking for a study that investigates short implants with removable prosthesis in the mandible. Can anyone give me a hint?
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Hi David, Steven and Lee,
Thank you for your hints - I spent the week-end searching PubMed and found some encouraging literature!