The theory behind the technique is sound: the mucosa can displace many more times than the periodontal ligament and so cause more movement of the saddles than the rest of the denture which is against the teeth. This movement of the denture may make it harder to use. The theory that this movement produces a torquing effect on the abutment tooth remains just that: it is an in vitro observation only, with no clinical evidence. So if there is a way of reducing that differential movement between the distal extension base and the teeth, then this may make adaptation to the denture easier for the patient. That is what the altered cast technique tries to do.

However, there is no direct evidence that this technique contributes to the successful wearing of these dentures. Only one or two studies have looked at this, and could not draw a positive conclusion. On the basis of this, some Schools have stopped teaching this technique. However, there are two arguments that could be said to be in its favour: the first is purely anecdotal, and related to the experience of clinicians who make many of these dentures, whose overwhelming opinion is that patients find the dentures more easy to adapt to. This is not high level evidence of course, but is hard to ignore. The second, is that in a teaching institution, the technique for making an altered cast is the same as that needed when relining these dentures, and hence it is an excellent way of learning how to do that. There IS overwhelming evidence that RPDs need constant vigilance: from the patient to maintain oral hygiene and from the clinician to ensure that patient IS maintaining good oral hygiene and to to check on the necessity to reline the denture in order to reduce the displacement discrepancies between periodontal ligament and mucosa.

So my (mainly anecdotal) advice would be to always do an altered cast for mandibular Kennedy Class I and II cases and reline them regularly.

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.

I agree with what Peter and Owen said but I think we should differentiate an educational purpose for a training program from daily clinical practice. Regarding the use for an educational purpose, I agree with both. Regarding the daily clinical practice, I partially disagree. In our prosthodontic graduate training program we prefer to teach a variable approach. We use a metal framework with a provisional acrylic base combined with a wax try-in or preformed rims. During the session, we check the congruence of the base using a light body silicone applying maximum pressure on the anchor elements. In general, there is no need for a relining. This way the students learn how to check for the need of a relining without causing significant costs. Therefore, in my opinion, the dogmatic demand for relining a new denture causes costs without any need and adds a source for fabrication errors.

I think in the case of resorbed ridge in posterior regionwe should do alter cast to get accurate  impression and reduce post insertion problem because of displacement of base during chewing.

I agree with much of what Peter Owen says about the altered cast technique, especially the lack of evidence base for its use, but I disagree that the theory behind it is sound. The dissimilar compressibility of teeth and saddle supporting tissues in Kennedy Class I and II may possibly cause the denture to rotate and this rotation may torque the abutment teeth (mind you, not always in a distal direction as popularly believed).

Where we differ is the idea that the solution to this problem is to compress the viscoelastic tissues underlying the free-end saddles. As Steven E. Eckert states, the point of the altered cast technique is to take a compression impression of the underlying viscoelastic tissues.  At least in theory, this should reduce the denture movement because then the tissues are already compressed (or more accurately, displacement) to a degree. However, by doing so one may be in danger of exchanging one evil for a far greater one.

Provided the clasps retain actively, an RPD made this way will likely exhibit a constant pressure on the saddle supporting tissues as they try to regain their original shape. The physiologic reaction of bone to a constant pressure is resorption, which in my opinion is a cost too high to pay.

For the above reason a possible reduction of denture rotation will at best be transient.  Furthermore, the altered cast technique is not without risk because of the possibility of a displacement of the framework in relation to the abutments during saddle impression. This risk is particularly great in cases where there are only a few abutment teeth.

True, I have no more evidence to support my statement than Drs. Owen and Eckert. However, isn’t it reasonable to demand that the burden of proof of advantages should be furnished by those who recommend a more time consuming and complicated method? In my opinion, whatever technique you use, Kennedy Class I and II are inherently unstable, and there is nothing a dentist can do about that fact.

Nevertheless, in clinical practice a modified altered cast technique can be useful if the impressions of the saddle areas are less than perfect.  This is sometimes a problem – especially for inexperienced dental students. Then the impression of the saddle areas can be taken with a light bodied material on relieved saddle bases in order to reduce the risk of tissue displacement.

Otherwise I wholeheartedly agree with Dr. Owen in his emphasis on oral hygiene and regular monitoring of the patient. This is a sine qua non for long-term success.

To answer the original question: There is no reason why you should use the altered cast technique except for the above reason.

Many thanks to you, all of you.

I think that there are a number of topics that are being bandied about here. The question that I responded to, or at least my response, circled around where this skill needs to be taught. In teaching at Avenue a graduate-level prosthodontics training program I think that we are providing a skill in the knowledge to our graduate students that is very important.at the undergraduate level I think it would be very difficult to bring in the new wants his of this technique without over compressing the entire residual Ridge. The technique that I have utilized in that most people utilizes one of a selective pressure approach whereby the buckle shelf in the retromolar pad are fully engaged with the peripheral border material and then a free-flowing material is utilized to capture the residual Ridgeand the lingual contours although border molding of the lingual contours in the mylohyoid and retro mylohyoid area is accomplished.

I recently wrote an editorial in IJ OMI in which I described "a time to bid adieu to the removal dental prosthesis".  I know that my friends have told me that perhaps I'm pushing the envelope a little too much with this statement, if we truly are worried about bone resorption in the posterior aspects of the mandible I think we have to understand that any removable prosthesis will create compressive forces that will continue to cause an Exceller ration in bone resorption. Implants do not prevent bone from being resorb but they create a loading condition wherebyThe forces are transmitted along the axis of the implant and should be more favorable towards own retention. Indeed we are all losing bone as we sit here reading this note. None of us are growing taller, running faster or exceeding our previous athletic milestones as we age. We simply fall further and further behind, This is a sad but realistic truth that we must all face. If we want to reduce the progression of residual Ridge resorption we really should be avoiding transmucosal loading of underlying bone. There is real logic behind this.

The original question however was about the altered cast approach. My response relates to the educational benefits of understanding the technique and the skill-based benefits of being able to perform the technique consistently and predictably. This does not mean that it needs to be applied to every patient and I agree with the notion that at an undergraduate level you may do more harm than goodby teaching this technique because we simply don't have enough curriculum hours at the undergraduate level to ensure that this is taught in a comprehensive enough manner to ensure that the novice clinician can do it well.

Yes, it certainly improves tissue support for distal extension bases. However; may not be necessary for every case. Does not required in every patient but does make a lot of difference for selected cases.

http://www.jpda.com.pk/altered-cast-technique-improving-tissue-support-for-the-distal-extension-bases/

One could probably suggest that the answer to almost every clinical question is sometimes yes and sometimes no. The difficulty  is in identification of when yes is appropriate or when no is appropriate.

For an altered cast impression there are a couple of considerations that probably make logical sense. The longer the distal extension the greater the lever arm and the more likely for differential compressibility (between the vertical compression of a tooth versus the vertical compression of the soft-tissue). So one might suggest that the smaller the distal extension, the less anterior to posterior distance, the more likely it is that the altered cast would not be necessary. Of course a clinical assessment of soft-tissue compression is always going to be necessary. If the clinical assessment suggests that there is a short lever arm, a short distal extension, and if the clinical assessment is that the tissue is not very compressible then it is more likely that the altered cast impression will not be necessary.

One of the earlier proponents of the altered cast technique, Dr. Richard Frank, reassessed the need for an altered cast technique after having used this technique for decades. This reassessment came many years after he published articles that indicated that he was a proponent of this technique. When it was reassessed however the finding was that perhaps it is necessary far less frequently than originally thought.

The other realization is that if the tissue is compressible  and this compressibility was unappreciated until the prosthesis was inserted it would still be possible to perform a reline impression with border molding to accomplish the same thing that the altered cast impression would have accomplished. Perhaps the only difference between the altered cast which is identified before the final prosthesis is processed and the reline approach is that the former may have a greater potential to establish a satisfactory occlusion while the latter would be more likely to demonstrate less occlusal stability.

 As I stated in one of the earlier notes on this topic I still think that the altered cast impression demonstrates a clinical skill that is very important. The problem however is that teaching this to every student is probably fruitless because students have different technical skills. An altered cast technique and the laboratory procedures associated with its'  use  are technically demanding procedures.   Anticipation that every clinician is capable of performing the clinical and technical procedures required of this technique is, in my opinion, more than a bit naïve. This is something that educators need to be cognizant of. Dentistry is a profession that  demands a high level of manual dexterity among every clinician. This is completely different than medicine where technical skills are required for only a small percentage of medical doctors. Medicine is a cognitive practice and technical skills are generally limited to individuals who are involved in surgical disciplines. Dentistry, on the contrary, is quite technical and very demanding of manual skills. If an individual attends dental school it would be beneficial if clinical skills were identified quickly and those individuals who lacked clinical skills would either receive remediation or recommendation for another career. It seems harsh but failure to provide remediation or alternate recommendations may prevent a lifetime of frustration.

Thank you dear Dr. Rashid..

Thank you very very much dear Dr. Steven E Eckert .. your comments are always very interesting, valuable, and informative.