There are 4 different types of full dentures.  They are "standard dentures", "immediate dentures", "implant retained dentures", and "Cu-Sil dentures".

The standard denture

As you can see from the picture below, the back of a standard denture ends just behind the hard bone in the roof of the mouth.  They do this because they require as much surface area as possible to maximize retention and stability .  In the case of people who gag, the back of the denture can be cut forward making the denture base look more and more like an arch.  However, the more it is cut back, the less stable and retentive it will be!

Standard dentures are made for people who are already missing all their teeth. The top denture relies on "suction" to retain it, and the hardness of the underlying tissues for its stability.  It generally takes 4 or sometimes more appointments to make a set of standard dentures.   

The first appointment consists of an oral examination, sometimes X-Rays, and a set of impressions of the upper and lower edentulous (toothless) ridges (gums). These impressions are poured with plaster to form accurate models of the shape of the edentulous ridges.  Other parameters are determined such as the shade, size and shape of the teeth that will be placed on the new dentures. 

Upon occasion, the dentist will recommend surgical alteration of the ridges to remove flabby tissue which will interfere with the stability of the denture, and sometimes to alter the shape of the underlying bone allowing for a better fit.  In most cases, such surgery is not essential, but can create the conditions for a MUCH more satisfactory final denture.  Alterations like this are generally money well spent!  

In some offices, the first set of impressions are used to make custom fitting impression trays for a second, more accurate impression.  In this case, there will be one extra appointment in addition to the standard 4 mentioned above.

The second appointment consists of deciding how "long" to make the teeth, determining the plane of the tooth setup (when you smile, the teeth should be parallel to a line between the pupils of your eyes), and the correct relationship of the upper and lower teeth so that when you bite together, the upper and lower teeth line up correctly.  This is done using a lose fitting denture base and a rim of wax to approximate the position of the teeth. 

Both upper and lower wax rims are adjusted to fit correctly in the patient's mouth so he can speak correctly without the wax rims "clicking" together, and so that the upper and lower rims fit together evenly.  Ideally, the wax rim should be visible slightly below the patient's lip when the lip is at rest.  When the patient smiles, the position of the lip is marked in the wax to help the lab decide which set of teeth are appropriate for this patient.  Once these relationships are correct, the rims  are sent to the lab where they are used to fabricate the wax-try-in. 

The third appointment is called the "wax try-in".  The lab returns the loosely fitting tray from the second appointment with the actual final plastic teeth lined up along the outer edge of the wax rim.  The wax try-in looks just like a real denture, except that the base fits loosely on the gums, and the teeth are embedded in wax instead of plastic.

This gives us the opportunity to see how the denture looks and works before we are committed to the setup.  At this point, if something is wrong, it can be changed.  If the teeth look too long, or the patient clicks when talking, or the midline is wrong, we can send the denture back to the lab where a technician can melt the wax and reset the teeth to specification.  Here, the patient is smiling, and the upper lip falls at the top of the teeth, which is the ideal result.

We try the denture in as many times as necessary until the teeth look and function like we want them to. What you see is what you get!  When everything is perfect, the denture is sent back to the lab to be processed and finished.  The old lose fitting base and all the wax are discarded, and replaced by a tightly fitting plastic denture base.

The fourth appointment is the insertion date when the patient walks out of the office with new dentures.  The plastic tends to shrink while being processed, so some adjustment is usually necessary before they will get the suction that you might associate with a new denture.

Immediate dentures

Immediate dentures (sometimes called temporary dentures ) are actually made BEFORE the natural teeth are extracted.  The patient walks into the office with natural teeth, and walks out with false teeth.  The teeth are extracted, and a prefabricated denture is inserted directly over the bleeding sockets.  The patient is still numb from the extractions, and nothing hurts until he gets home.  Generally, most patients do not complain of much pain after their teeth are extracted and the immediate denture is inserted.  The denture acts like a band aid and reduces pain.  

The construction of an immediate denture requires only one or two preliminary appointments before the insertion date, depending on how many natural teeth the patient has left.  They usually work out reasonably well.  When the patient leaves, he looks much better than when he walked into the office.  The bone that supported the original teeth is still intact, and the gum tissue is firm.  For the first week or so, the denture remains stable and reasonably retained. 

But there are a number of problems associated with immediate dentures.  These problems account for the alternate name; "temporary dentures":

1. If the patient has more than one or two remaining front top teeth, it is usually impossible to do a wax try in .  The denture teeth are placed in about the same position as the natural teeth before extraction.  Even though the denture teeth will be straight, and clean, their position may not be ideal because there is no way to preview them as we do with a standard denture.  For this reason, not everyone will be happy with the final appearance of their immediate denture, and may wish to invest in a new one at the end of about a year when most of the healing has taken place.

2. After the natural teeth are extracted and the immediate denture is inserted, there is a relatively fast loss of the bone that used to hold the natural teeth in place.  By the end of three weeks, enough bone has been lost that there is a LOT of space between parts of the denture and the healing gums.  This leads to rapidly increasing looseness and sore spots which must be removed frequently.  In some offices, the dentist will include a free temporary "soft" reline at about one month after the extraction/insertion date.  This is a simple way to tighten the denture against the gums, and since the material is a bit rubbery, and frequently medicated, it makes the denture much more comfortable until enough healing has taken place to do a permanent "hard" reline (at additional charge).  

3. At the end of 4 to 6 months, the immediate denture must be relined with the same acrylic that the denture base was made from originally.  The longer you wait, (no more than 6 months), the longer you can expect the denture to remain tight before another reline is needed.  The hard reline is a separate procedure and the cost is NOT generally included in the original price of the immediate denture.  Thus the immediate denture ends up costing a bit more than the standard denture when the cost of the reline is taken into account. The hard reline marks the official transition of the immediate denture into a standard denture.

Cu-Sil dentures

There are a number of  drawbacks associated with full dentures,  and not everyone can successfully wear them.  In many instances, false teeth are not especially useful because of retention or stability problems.  For this reason,  even a single healthy tooth left in place can stabilize an otherwise unstable full denture.   

Only recently has it become possible to build a denture leaving a hole here and there to allow a few remaining teeth to poke through without ruining the suction which generally holds the denture in the mouth.  The Cu-Sil denture has holes for natural teeth.  These holes are surrounded by a gasket of stable silicone rubber which hugs the natural teeth and allows the rest of the denture to rest against the gums giving the benefit of suction in addition to the mechanical stability offered by the immobility of the natural teeth. These are especially useful in situations in which the remaining teeth are on the same side or area of the arch as in the example below.  Even a single remaining tooth in the arch can increase the stability of the entire denture several hundred percent over a completely edentulous (no teeth) arch.  

CuSil dentures are not the best solution for people with numerous, evenly distributed, stable natural teeth.  They are advertised mostly as "transitional" dentures meaning that they are especially recommended when the remaining teeth are likely to be lost (eventually) for any reason, or in cases where stable teeth are poorly distributed about the dental arch (as in the case below).  A CuSil denture can stabilize loose teeth and, with care, can extend their lives.  It is also easy to replace lost natural teeth on the CuSil denture, and the denture can be relined like any other standard denture.  In other words, the CuSil denture can eventually be transformed into a regular full denture if the patient loses all the natural teeth.  I have found them to be especially useful for upper dentures, but more of a problem for lowers.  Lower CuSil dentures are prone to breakage if the patient is a heavy bruxer (grinder), especially if the remaining natural teeth are located in the front of the arch.  This is because the holes that allow the penetration of the natural teeth weaken the architecture of a lower denture.   

Cu-Sil denture	Cu-Sil from side
Case before removal of 2 teeth	After extractions and insert

The images above show a Cu-Sil denture which was used as an immediate denture.  The patient's two front central teeth were extracted, leaving the natural canine and molar on the patient's left side in position.  The image on the lower right shows the case immediately after the two central teeth were extracted and the denture inserted.  The black arrow points to one of the patient's two remaining natural teeth.   Cases like this tend to result in an extremely stable and retentive denture.

Overdentures

Overdentures are defined as any removable tooth replacement device that is inserted over existing teeth or their remnants, replacing these teeth with false teeth.  Prior to modern dentistry, overdentures were very nearly the universal tooth replacement device since surgical removal of teeth was painful, dangerous, and frequently impossible without modern anesthetics.  In those days, dentures were made to fit over the rotting stumps of decayed or broken teeth.  

Today, non restorable teeth are generally removed prior to the placement of a removable prosthesis, however, there are still instances where these teeth can be maintained to the patient's advantage.  The most frequently seen overdenture today involves teeth that have had root canal therapy.  If the roots of these teeth are still serviceable, the crown may be cut off at gum line and a removable appliance may be placed over the stumps.  Sometimes, the stumps are themselves covered with filling material or cast metal copings in order to protect them from decay.  The advantage to this is that the roots of these teeth can maintain the bone that supports them.  This bone would otherwise resorb away leaving less tissue to support the denture.  In addition, the root itself can serve as a "rest", or a vertical support for the denture allowing for more stability than would otherwise be available.

The addition of a soft denture material such as CuSil on the denture surface that immediately overlies the rigid root stumps allows the overdenture to nestle more snugly into the soft tissue on the roof of the mouth.  This allows for more suction to develop and can frequently improve the retention of an overdenture.  

Implant retained dentures 

Implants , as mentioned elsewhere, are quite expensive but quite effective in retaining an otherwise non retentive denture.  A titanium "screw" is actually placed into a hole drilled into the bone to approximate the position of teeth.  After several months, the titanium has integrated (attached) into the bone, and the implant is then uncovered and a post which "pokes" through the gums into the mouth is attached to the implant.  This post may support a porcelain tooth, or it may support an attachment for a denture.  If the patient has NO teeth at all in any given arch (upper or lower), a full mouth of individual implants attached to porcelain teeth and bridges could cost about what an expensive automobile costs.  

On the other hand, a minimum of 2 implants can maintain a lower denture which would not otherwise be tolerated by that patient.  More than two implants are needed for upper implant retained dentures.  Although the dentures that fit over implants are considerably more expensive than standard dentures, they offer the added advantage of allowing upper dentures to be built in the shape of an arch instead of having to cover the entire palate. This is of special significance to people who otherwise cannot wear full dentures because they make them gag.  

Implant retained dentures have special significance for people who cannot wear lower dentures. As an edentulous (toothless) person ages, and the bone continues to resorb away, lower ridges frequently disappear entirely.  Thus there is no vertical bone underlying the gums to stabilize a lower denture.  These people frequently cannot wear a lower denture at all.  The addition of two implants in the front of the lower jaw can make it possible to retain a lower denture which would otherwise be impossible for the patient to tolerate. The image on the left below shows a pair of ball attachments on implants, and the denture that fits over them is shown in the image on the right.

Mini implant retained dentures
When a new full denture is first made, it is possible to make a duplicate, or an exact copy of the denture cheaply and quickly.  This is a "quick and dirty" method of obtaining a second denture for emergencies.  Duplicate dentures are made by flowing liquid "agar" around the finished denture and allowing it to harden.  (Agar is a gelatin-like material made from seaweed which is liquid when hot, but cools to form a flexible rubbery substance similar to very dense Knox Jell-O.  When agar is used in dentistry, it is generally called "reversible hydrocolloid".  It is one of the oldest, but still one of the most accurate impression materials known.)   The original denture is removed from the agar mold (the agar is cast around the denture in two halves) leaving a hole in the agar where the denture used to be.  The hole is then filled with liquid plastic; white plastic in the tooth indents and pink to form the base and flanges.  The two halves of the agar form are placed back together and the liquid plastic is allowed to harden.  Duplicate dentures are not especially high quality since the flowable plastic used to make them tends to be porous and less resistant to wear, and the delineation between the tooth colored plastic in the tooth indents and the pink base plastic may not always be exactly at the margins of the teeth, but these dentures make it possible to keep a spare set of dentures tucked away just in case the regular denture must be sent out for repair, or is lost and a new denture must be made.  They are frequently delivered to the patient without adjusting them for sore spots or any other technical modifications to make them more affordable.  Duplicate dentures are only an adjunctive service and are not intended to take the place of the real thing.  Adjustments cost money, and if the dentist were to spend as much time and effort on them as he did on the primary service, the duplicate could end up costing as much as the primary dull denture.