Prosthodontics - Science topic

Thanks

TMD are multifactorial disorders. It is best to perform the management of TMD in a team approach and TMD specialist, facial pain specialist, orthodontist, prosthodontist (in older individuals), can work together in collaboration. For most cases, minimal intervention (less) is better.

Obrez et al., implemented a course for year two dental learners by providing significant clinical experience/exposure with real patients and the results display statistically significant improvement in the students’ achievements.

A Clinically Oriented Complete Denture Program for Second-Year Dental Students Ales Obrez,; J. Lee,; Anna Organ-Boshes,; Judy Chia-Chun Yuan, William Knight,

As far as I know, there isn´t a software like prepcheck to evaluate the RPD designs yet. You still need to work with models before you scan them and make the design. Last year I made the students to take pictures of their work: surveying the prosthetic ecuators and modifications if needed, and the clasp drawings with their phone camaras. They mounted the photographs in a powerpoint presentation and sent them to me for evaluation in a Moodle plataform. You need to take some time to evaluate all but I didn´t find other form. Maybe in the future (next year as we are seeing), I will take a few models and scan them to make simulations easer to grade. I hope you find a better solution.

Preclinical complete dentures curriculum survey.

Rashedi B, et al. J Prosthodont. 2003.

This is not exactly but may help you to get some answer.

About 45 years ago as I was starting out in dental school, a prosthodontist told me to always match the color of the teeth to the skin of the individual.  As I evolved as a clinician and then a clinical researcher, I looked back on those words to realized that the teeth come from a primordial cell, the same that lays down the skin, and as such the color of the teeth do match the shade and coloring of the skin of the individual.  According to the geographical nature of the skin, God gave us a builtin sun protection device called melanin.  So looking at the Vita guide and the extended Vita guide, it becomes obvious that the persons ethnic background determines the proper shade, so I developed a geographical shade format to follow, those people closest to the equator, having more melanin in their skin, a yellow/brown pigment get a yellow/brown Vita shade or A shade.  going north or south of the tropic of Cancer or Capricorn, get a gray/brown shade, or C shade.  Then looking at the longitudinal characteristics, people east of a line from the Ural mountains down through the middle east just east of the Mediterranean Sea, you simply add a red shade to the principal shade, or A shade becomes B shade and C shade becomes D shades.  Therefore, European extraction individuals have C shades, Africans have A shades, Chinese/Japanese and others above the tropic line has D shades and those between the tropic lines have B shades.  Hispanics have generally C shades from the European Hispanic/French backgrounds from invading groups mixed with native Indian populations that are D shades (red-gray-brown from migrations of populations across the Archipelago islands years past.  Watch out for invading groups and penal colonies evidenced by Australia  (predominately C shade), Brazil predominately C shade because of Portuguese settlement and South Africa predominately C shade because of Dutch settlement.  Always factor in the amount of indigenous population that may be in the ancestral history of the patient if the original shade does not match.  You will be about 95-98% correct if you just apply the basic rules and realized teeth generally darken with age as enamel is lost over time.  I know in this politically correct society that I have been profiling people but its better than making everything wrong by using A2 (the most popular shade to labs) and B1 the second most popular shade for "whiter teeth.  Ever wonder why you can pick out people especially those with single tooth anterior restorations?  The answer lies in the fact that the color of their teeth, shade, chroma, hue didn't match that of the surrounding skin color.  So much for fancy gadgets that cost a lot and often give you A2...

Ideally, the bruxism with parafunctional actions would be successfully treated  and the patient could wear a temporary crown in the interim. 

Alternatively most clinicians would place the most durable crown, (metal, Bruxir, porcelain fused to high noble gold, etc), with occlusion adjusted to minimize parafunctional damage combined with a functional orthotic as well as a night time sleep appliance. I do like the concept of an indirect composite crown as the composite will have more flexibility when struck by a parafunctional action. Those are my preference for implant crowns. 

I’m afraid you’ll not find any scientific evidence relating to this question, which can only be answered with clinical experience and statements like “this works for me”. With such limitations in mind, here is a rendition of my clinical experience – for what it’s worth:

My premise is that the impression for a complete denture should be taken with a minimum of tissue compression and displacement. Generally, because light body impression materials flow better than medium or heavy body ones, the former can be taken with lesser spacing than the latter without exposing the soft tissues to undue and unintended pressure and displacement. Also, a greater thickness of a light body impression material is considerably more difficult to manipulate clinically as it tends to flow all over the place.

I agree with Tugrui Sari that as a general rule spacing of 1.5 mm will suffice for a light body impression. However, sometimes greater and in fact also lesser spacing may be appropriate – depending on the case.

Greater spacing is indicated opposite areas with marked tissue resilience, such as a flabby ridge. These areas are easily localised clinically and should be marked on the cast over which the dental technician should be instructed to add one or more extra layer of wax. This may be all the more important because the primary impression, which is usually taken with a relatively heavy flowing alginate, will normally have displaced such soft tissues. A tight impression tray constructed on the resultant cast will perpetuate the displacement as it doesn’t allow the tissues to return to an unloaded position. Greater spacing is also indicated in areas with undercuts because otherwise it may be difficult to place the tray correctly in the mouth.

However, lesser spacing than 1.5 mm may be indicated, particularly for mandibular impressions, when the ridges are flat and even negative. With a normal spacing the correct placement of the tray in relation to the underlying tissues can then be extremely difficult because with a correspondingly wide tray one tends to lose sight of the anatomical landmarks, and a displaced tray will always result in a failed impression. The advantage of using a tray constructed directly on the cast in such cases, is that it is easier to localise correctly in the mouth – the disadvantage is the difficulty of manipulating the tray (and indeed the patient) in such a manner that it is seated without contacting the underlying tissues. This requires a lot of practice – like so many other aspects in removable prosthodontics. But what can one do… except try, try and try again. Who says removable prosthodontics should be easy?

Complete and interesting information provided by Dr. Abu-Hussein Muhamad.

There is something called as replica technique, i.e., light body in layered on the internal surface of the crown and placed over the tooth or die as we do with luting agent. After the light body sets, the crown is removed with the light body intact on the inner surface of the crown. Putty placed and allowed to set over the light body. After setting the putty is retrieved with the light body attached on it. This is then sectioned as per requirement or the area of study and observed under a Stereo microscope or SEM. Other method that I had thought of while doing my thesis study was, scan the die and scan the internal surface of the crown. The data acquired could be compared. the over all surface area of the die can be measured as well as the internal volume of the crown. Comparing both the values could give us an overall discrepancy. I understand your concern not to destroy the crown.

Diagnosis and treatment planning is the key. Informed patient coscent and thorough clinical examination must be done prior to the treatment.

Well if they are embedded and silent u can leave them as long as there are no symptoms. Go ahead with denture fabrication. However;  resorption rates are to be kept in mind and patient must be reviewed periodically. 

All the best 

Dear Dr. Eckert,

I totally agree with the all the factors that your stressed out. I would like to highlight also the fact that primary stability is still regarded as a crucial factor to achieve biologic stability. On the counterpart, it is interesting the number of recent reports showing that high insertion torque may have a detrimental effect of crestal bone stability as well as upon osseointegration. For instance, Cha et al. (JDR 2015) demonstrated in a multiscale analysis that high IT more than doubles this zone of dead and dying osteocytes. As a result, peri-implant bone develops micro-fractures, bone resorption is increased, and bone formation is decreased. Likewise, Simons (COIR 2014) showed that the thicker the cortical bone layer was at implant placement (and thus, higher IT), the greater the marginal bone resorption was. Therefore, I would consider further inadequate implant drilling protocol along with high bone density (and not quality since these from these reports might be extracted that poorer bone might be biologically better - richer vascularity compared with denser bone) might play important roles on implant failure. Interestingly, the recent reports by Derks (JDR 2015,2016) showed twice as much peri-implantitis and implant failure in areas of denser bone (mandible) compared to the maxilla.

Best,

Alberto

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.

Immediate, Delayed-Immediate, and Delayed implant placement: Which one is superior over the others? 

Is there any significant difference between them regarding primary stability, alveolar bone loss, and/or the success rate?

 ITI describes the immediate, early and traditional or conventional loading protocols. Are you talking about loading protocols or implant placement protocols relative to tooth removal?

Tooth extraction followed by implant placement (immediately or after a few months of healing) does not seem to result in any implant survival differences.  Most authors report a slightly improved been response if the implant is placed on the day of tooth extraction but this is often dependent upon the location in the dental arch.

Considering loading protocols there certainly is a difference in implant performance relative to loading protocol.  Of course there are factors that favor each protocol in different instances.  I suggest looking at the article by Gallucci et al that documents the consensus conference of ITI recommendations.  There is no straightforward simple answer.

Consensus statements and clinical recommendations for implant loading protocols. Gallucci GO, Benic GI, Eckert SE, Papaspyridakos P, Schimmel M, Schrott A, Weber HP. Int J Oral Maxillofac Implants. 2014;29 Suppl:287-90. doi: 10.11607/jomi.2013.g4. 

The article that Dr. Toffoli provided does a nice job of comparing different implant surfaces but from what I am seeing in the article all the surfaces were prepared by the same manufacturer. Does this matter? Well other manufacturers would certainly say that it does matter. I think that if you talk to one company that makes or uses an SLA surface they will claim that their SLA surface is different than someone else's SLA surface. In the Coelho article I think, if I'm reading this correctly,  that all the implants were 6-4 alloys. You cannot make a Ti Unite  surface on the 64 alloy, that's what the materials folks have told me at least. The largest producer of SLA surface implants uses a grade 4 titanium commercially pure. So the fact that all the implants in this cited study were made with an alloy, the fact that they were all made by one manufacturer and the fact that they did not test Ti Unite may make the information gathered from this article less valuable to you as a reader or you may look at it and have it not change your opinion at all. This is a question of interpretation.

If we were to say that machine  turned implants, the first generation of implants that were to undergo osseointegration, were the implants that would have the lowest early bone to implant contact this would probably be correct. After a year in function it may not make any difference. In fact micro roughened implants probably make the biggest difference within the first two weeks after the implant was placed and it may have little impact long-term. So when you ask the question of which surfaces better the reality is that there are two viable answers. The first answer might be that in the, let's be generous, first month of the implant being in the bone that micro roughened implants probably recruit more cellular activity and have more early bone to implant contact. The second answer might be that after three years of function it doesn't make any difference.

Why do we want early bone to implant contact? Perhaps this is the most important question. Remember that osseointegration occurs if you are able to limit micro motion, according to Brunski,  to less than 100 µm. Cameron and Pilliar  Compared 150 µm of micro motion to 29 µm of micro motion  and found out that 29 µm allowed osseointegration to occur but  150 interfered with it. So somewhere between 29 and 100 µm is the amount of micro motion that would still allow osseointegration to occur. The reason that we use micro-roughened surface is because it should induce more early bone to implant contact which then means that you have less need for patient compliance. If we ask a patient to avoid chewing on an implant or to avoid use of a removable prosthesis that is placed over the top of an implant we have to realize that most patients are relatively compliant but some patients are not compliant at all. If we figured that the majority are are relatively compliant and we can cut the time during which they need to be compliant in half or in one quarter of the original time requirement we probably will have a slight improvement in the osseointegration rate.

So which is better? Better if we are defining more rapid integration we would probably be able to say that there are slight differences and in many instances those differences are probably more related to study design rather than true superiority.   Long-term, it probably doesn't matter.

Specific to the two surfaces that were asked about, neither of these surfaces should corrode with time. 

Ethical decision making is not always easy.... but when you let you guide by the 4 principles, you are safe.

Respect for autonomy: respecting the decision-making capacities of autonomous persons; enabling individuals to make reasoned informed choices.

Beneficence: this considers the balancing of benefits of treatment against the risks and costs; the healthcare professional should act in a way that benefits the patient

Non maleficence: avoiding the causation of harm; the healthcare professional should not harm the patient. All treatment involves some harm, even if minimal, but the harm should not be disproportionate to the benefits of treatment.

Justice: distributing benefits, risks and costs fairly;  patients in similar positions should be treated in a similar manner.

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.

I always tell my students:' more dentistry more trouble'. Or another one: 'look on the panoramic radiograph which tooth in the mouth of the patient has the worst prognosis: it is often the most expensively treated tooth with a crown....'.

In other words: try to avoid overtreatment, think minimally invasive and base your decission on individual risk assessment. What do we know?

- Endodontically treated teeth have a higher risk for unfavourable fracture

- More tooth reduction leads to higher risk for tooth loss and restoration failure

- Bruxism, caries risk have a higher impact on restoration longevity then materials.

So if a first molar has an mod restoration and much tissue left buccaly and lingually, I would preferably make a minimal invasive restoration. If the tooth is heavily loaded (bruxism?) make a cusp capping restoration, If your good in direct techniques, make it direct, if you're good in indirect techniques, do it indirect (combined with Deep Margin elevation?). In a high caries risk situation, go for minimally invasive solutions, more direct restorations are probably more favourable. If the endodontic treatment is done on a crowned tooth, go for a new crown (when the old crown has failed, otherwise, go for a repair).

One cannot say which solution is the best, it's all dependant from risk assessment, the wishes of the patient, and trying to be as minimally invasive as possible. And of course which skills you have as a dentist.

 Good Morning,

Yes Dental Orthotics is an precise prosthetic adjutant prepared by TENSING the 5 and 7 th cranial nerves to rest the masticatory muscles so that you can record an perfect resting position of the mandible. This is accomplished by using EMG and ENG along with TENS gadgets. This Orthotic (Splint) is used invariably in TMD cases to resolve the symptoms as a first phase treatment which is reversible.

Hi Alexandros, thank you for your answer. There are plenty of studies measuring the precision of io-scanners, since that is as easy as it is important to measure. The exactness of any relevant system on the market is (no longer) of any conercen, IMHO. BUT there are huge differences in the handling and workflow. And these differences matter to me as a clinician.

Hi Mohammed. I use the closed tray technique in the following clinical situations:

1. Single implants. 2. two non splinted implants (eg lower overdenture). 3.Limited mouth opening or implants located at the back of the mouth where long screws will not fit. 4. relatively parallel implants (no more than 2 though) and implants with their long axis parallel to the path of removal of the custom tray.

I use the open tray technique in the following clinical situations:

1. two or more splinted implants.2. implants with 15 degrees of divergence or more. 3.  immediate loading protocol.

Hope i answered your question sufficiently.Best regards.

you may read the clinical study ( not a very recent one)

Int J Prosthodont. 2000 Mar-Apr;13(2):125-30.

Implant-supported mandibular overdentures retained with ball or bar attachments: a randomized prospective 5-year study.

Gotfredsen K1, Holm B.

This may be attributed to Costen's syndrome which is stated to be the result of prolonged over-closure and it consists of:

Mild catarrhal deafness and dizzy spells which can be relieved by inflation of the Eustachian tubes.

Tinnitus or snapping noise in the joint while chewing, and the affected joint may be painful, with limited or excessive movements.

Tenderness or dull pain while palpating over the affected TMJ.

Various neuralgic symptoms such as: burning or prickling sensation of the tongue, throat, or side of the nose.

Various forms of atypical head pain that refer to temporal region or base of the skull.

Dryness of mouth due to disturbed salivary gland function.

Regards,

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"

Please see my attachment. Thank you.

Zirconia post and cores aren't popular for a few reasons.  You can't bond them in unless you surface treat them and not many people have the materials to accomplish that.  That are very rigid which, in the event of a failure, is usually catastrophic.  They are also very difficult to adjust due to their high hardness value.

There are a variety of studies to support the feasibility of implant and tooth supported removable partial dentures

Clinical Outcome of Double Crown-Retained Mandibular Removable Dentures Supported by a Combination of Residual Teeth and Strategic Implants.

Rinke S, Ziebolz D, Ratka-Krüger P, Frisch E.

J Prosthodont. 2014 Sep 14. doi: 10.1111/jopr.12214. [Epub ahead of print

Unsplinted implants and teeth supporting maxillary removable partial dentures retained by telescopic crowns: a retrospective study with >6 years of follow-up.

Frisch E, Ratka-Krüger P, Wenz HJ.

Clin Oral Implants Res. 2014 Apr 16. doi: 10.1111/clr.12407. [Epub ahead of print]

Implant retention and support for distal extension partial removable dental prostheses: satisfaction outcomes.

Gonçalves TM, Campos CH, Garcia RC.

J Prosthet Dent. 2014 Aug;112(2):334-9

Implant Tooth-Supported Removable Partial Denture with at Least 15-Year Long-Term Follow-Up.

Mijiritsky E, Lorean A, Mazor Z, Levin L.

Clin Implant Dent Relat Res. 2013 Dec 27. doi: 10.1111/cid.12190. [Epub ahead of

Prognosis of implants and abutment teeth under combined tooth-implant-supported and solely implant-supported double-crown-retained removable dental prostheses.

Rammelsberg P, Bernhart G, Lorenzo Bermejo J, Schmitter M, Schwarz S.Clin Oral Implants Res. 2014 Jul;25(7):813-8.

Survival of double-crown-retained dentures either tooth-implant or solely implant-supported: an 8-year retrospective study.

Schwarz S, Bernhart G, Hassel AJ, Rammelsberg P.

Clin Implant Dent Relat Res. 2014 Aug;16(4):618-25.

Implant placement under existing removable dental prostheses and its effect on oral health-related quality of life.

Wolfart S, Moll D, Hilgers RD, Wolfart M, Kern M.

Clin Oral Implants Res. 2013 Dec;24(12):1354-9

Dental implants as strategic supplementary abutments for implant-tooth-supported telescopic crown-retained maxillary dentures: a retrospective follow-up study for up to 9 years.

Krennmair G, Krainhöfner M, Waldenberger O, Piehslinger E.

Int J Prosthodont. 2007 Nov-Dec;20(6):617-22.

Removable dentures with implant support in strategic positions followed for up to 8 years.

Kaufmann R, Friedli M, Hug S, Mericske-Stern R.

Int J Prosthodont. 2009 May-Jun;22(3):233-41; discussion 242

Use of dental implants to improve unfavorable removable partial denture design.

Mijiritsky E, Ormianer Z, Klinger A, Mardinger O.

Compend Contin Educ Dent. 2005 Oct;26(10):744-6, 748, 750 passim

Dear Giuseppo

thank you for your reply. the important thing is when can you decide if such inconsistent conditions will lead to resorption?. the response from one patient to another differ to clinically similar conditions. so again can you predict the response only from radiographs or you need other measures. 

But what with costs ? Why ? Allergy for Ni or Cr or acrylics? If Ni then try with Ni free alloy. If acrylics, the porcelain teeth will be needed. Alternatively, You can mill (CAM) the wax model and cast them in Ti in special lab.

Dear Alaa, The cuspal deflection is a reality and we have to take this parameter into account as much as the patient occlusion. Having said that i think that the dogma you cited in your statement is not reliable anymore. Each clinical situation is different and moreover this dogma and these old principles were right many years ago. A lot of progress have been made. At the moment, the bonding procedures and the less invasive dentistry permit to perform partial restorations instead of full coverage. Likewise, we try to avoid to place a post which can trigger more problems than advantages. Of course it doesn't concern the most of clinical cases but we have to keep in mind that the crown can be sometimes avoided.  In case of wide cavity and if the occlusion is favorable, you can sometimes indicated a bonded partial restoration with a cuspal coverage (ceramic or composite only or overlay). Sorry not to be in accordance with evidence based dentistry regarding this topic but i believe that we have to preserve the dental tissues and unfortunately the worst enemy of the tooth is often the dentist himself. Finally, the dogma you cited is a good point for the dentist business but not necessary for the patient...but it's an other topic...

The initial polymerization contraction is 1.5-3.5%, which causes problems with bulk fillings shrinking away from margins, but has little effect on layered build-ups. Wear resistance and flexibility are built into the composite, but do not necessarily directly relate to polymerization shrinkage.

Agreeing with the finding that bonding to enamel is more reliable as bonding to dentin, the question can be refraised as: is it contra-indicated to place a porcelain veneer with cervical part bonded to dentin? I would think that a certain risk for imperfections such as marginal staining would be higher for those situations and should be explained to the patient, but still the veneer can be placed. Alternatives like full crowns also have their risk profiles such as pulp necrosis, fracture etc. Comparing the techniques and possibilities I think the minimal invasive option still has the most advantages.

To make it more complicated: what has a better prognosis: a veneer bonded to enamel in a high caries risk patient or a veneer bonded to dentin in a low risk patient?

These aspects are very suitable to be investigated in practice based, (retrospective) pragmatic controlled trial designs.

The FGP technique is not always the panacea. We are practicing different approaches for the last 20 + years and I can assure you that:

1. You will need a very distinct indication.

2. One registration approach does not fit all indications.

3. You need a very detailled understanding of occlusion.

4. Translation into prosthodontic work does not work with all materials and techniques.

5. You need an excellent lab technician.

I think that everything the Peter just said is absolutely correct.

The key in removable partial denture treatment is not in the technique but is in the constant reassessment of the effect of the differential between compressible soft tissue and relatively un-compressible hard tissue. An altered cast impression is a way to capture the compressible soft tissue in a more compressed state than it would be if you simply made an impression with a free-flowing material initially. The key is to be able to assess the clinical situation when the differential differentially applies forces to one structure (let's say the teeth) rather than another (let's say the tissue).

From my standpoint I'm not exactly sure what I would teach if I were teaching at the undergraduate level. At the graduate level in a prosthodontic graduate training program I would probably be a lot more aggressive in my expectations. My graduate students, over the years, have routinely done altered cast impressions. I think this is a skill that they must understand. More importantly however is the ability to determine when a reline is important because that becomes the procedure that protects the patient from the differential in compressibility.

Fluid can not work so fast as chewing occurs. The deformed mucosal surface will not be ready for use in the next chewing cycle. Trauma and pain are the result of the slide and friction during denture destablization in the tilted position (with balancing contacts).

Please see:

https://www.researchgate.net/publication/233392646_The_influence_of_a_complete_lower_denture_destabilization_on_the_pressure_of_the_mucous_membrane_foundation?ev=prf_pub

Thanks to fluid, the area of tissue compression beneath a denture can be increased or pressure can be more evenly transfered . In the next cycle fluid must be ready for the next work. Only silicones are good in this case.

Moreover, the occlusal surface can vary during prolonged occlussion as the results of ongoing fluid flow ...

Film thickness, forces at the interphase , forces in the cement layer play an important role apart from the above sited reasons by others

Some probably very helpful papers:

J Prosthet Dent. 2003 Dec;90(6):556-62. Factors determining post selection: a literature review. Fernandes AS1, Shetty S, Coutinho I.

Effect of the crown, post, and remaining coronal dentin on the biomechanical behavior of endodontically treated maxillary central incisors.

Veríssimo C, Simamoto Júnior PC, Soares CJ, Noritomi PY, Santos-Filho PC.

Effect of ferrule height and glass fibre post length on fracture resistance and failure mode of endodontically treated teeth. Abdulrazzak SS, Sulaiman E, Atiya BK, Jamaludin M. Aust Endod J. 2013

In general, I agree. A crown with an insufficient margin should be remade completely. If you want to transfer the insufficiency to the dental technician for adaption, you can use the following approach:

1. Cut back the margin of the crown in the area of the gap 1.0 mm superior to the margin of the preparation. Make sure that there is a pronounced chamfer.

2. Take an impression (e.g. polyether) with the positioned crown.

3. The dental technician should cast the impression with a special resin.

Because of the shrinkage of the ceramics during the firing process, the marginal fit will be tolerable at best. Because of the limited strength of the veneering ceramic (approx. 80 MPa) it should be implemented only in case of small areas with margin insufficiencies, using a special margin ceramics (available e.g. by Vita Zahnfabrik, Bad Saeckingen, Germany).

Dear sir the prognosis depends on the case selection, how perfect your laboratory process the denture, the patient itself. It is a technique sensitive . The literature gives it as good prognosis, but i personally believe it is guarded

yes you can do this using virtual simulator with haptic device. Applied for Implantation, opertive dentistry and oral surgery.

BUT, the studies on fibre posts and cores are very low on evidence from a longevity point of view. Long term studies still show that the cast post and core survives long after prefabricated posts with composite cores and there simply aren't enough long term studies on fibre posts with composite or resin reinforced cores. Perhaps it's not the post that's the problem, but finding sufficient retention for the core. When that is compromised then case selection is vital. With comparatively new techniques, patients must be informed of the lack of long-term studies and if their occlusion is unfavourable they should be given the choice, one that is informed by the relative risks vs costs. We still advocate cast posts and cores, even if they are more expensive: they may not be in the long run!

in review done in 2011 byVasantha Kumar, he mention that "Cigrande in 1913 used the outline form of the fingernail to select the outline form of the upper central incisor

tooth", http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3095741/pdf/13191_2011_Article_58.pdf

prior to the preparation of tooth mark the occlusal contacts with articulating paper. During the occlusal preparation prepare the entire occlusal surface of the abutment except the marked occlusal contact. Complete the preparation leaving this occlusal ledge to be in contact with the opposing tooth. Impression is made and the bite registration is recoreded with the occlusal ledge still in place. Ask the laboratory technician to remove the ledge after articulation. We arbitarly trim the occlusal ledge and temperize the abutment. The only disadvantage is the arbitarary trimming of this occlusal ledge. However, the chances of inaccuracy are minimal.

Hi

If the main risk factor is bruxism and the teeth have undegone attrition, then even zirconia crowns can fail. The weak link is the ceramming layer on the zirconia as this can fracture.The occlusal scheme particularly anterior guidance should be flat so that the incisal edges are wide to reduce risk of fracture.

Snap On Smile is supported by natural teeth. It doesn't require any kind of preparation or cimentation, it just cover the teeth.