Partial Dentures
 

What is the Procedure for Having a Partial Denture?

Initial Examination and Discussion

This gives the dentist an opportunity to find out all about you: your medical history, your needs and expectations and to examine your mouth.

They will screen you for oral cancer; look for any problems with your soft tissues, teeth and gums .

X-rays may be required to check individual teeth or a screening X-ray (OPG) to give them a good general appreciation of what's going on.

Further special tests may be performed to help with the diagnosis.

Once this has been done, they will have a good idea of your situation and be able to discuss the advantages and disadvantages of the various alternatives for restoring your space or spaces and any other treatment that is required.

It may be that they need to take a couple of study models in order to plan things more carefully and to look at your bite in more detail on an articulator.
If so, two quick impressions of your top and bottom teeth would be needed in a suitably sized tray. This is usually done in Alginate- a rapidly setting material that is pink or green in colour.

I’m always asked what it tastes of and to be honest- not a lot! I guess chewing gum that had lost nearly all of its flavour may be a fair description. If the dentist does this, they are likely to arrange an appointment a week or so later. This will give them time to study and analyse which options would be best for you.

At this point a treatment plan will be written or printed out for you to consider and come back with any questions.

In this section we are assuming that a partial denture has been decided on.

1st Appointment – First or Primary Impressions

The first thing we need to do is take a basic impression to make special trays for a more accurate secondary impression a little later. See Partial denture procedure part 2.

To get a good impression of your teeth, the dentist places a 'gooey' material over your teeth- it sets firm over the next couple of minutes. The first impression is similar to that for study models described above. If you have had study models- these may be adequate and mean this stage can be skipped.

Modern materials are elastic or flexible, meaning that even though they can be a bit tough to remove on occasions, we can always get them out!

It is highly, highly unlikely, yet theoretically possible that a dentist could pull out an incredibly loose tooth (and I mean 'waving in the wind' kind of loose), when taking your impression. We can take precautions such as putting vaseline on teeth or blocking out spaces between teeth, to make the impression easier to remove.

When we take top impressions, the material can tickle your soft palate or back of your throat and potentially make you want to retch. This generally isn't a problem unless you have a strong gag reflex- you will know if you have an issue with gagging, as anything in your mouth can cause this reflex- even your own toothbrush.

When having your top impression taken, your dentist may encourage you to lean forward with your chin down towards your chest. This causes the material to flow forwards not backwards. You may also find it helps to focus on nice slow, deep tummy breaths- in and out through your nose, or twiddling your toes or making a slow circle with your foot; different dentists have their own methods for taking your mind off the impression!

Certain materials are more accurate than others and can take that little bit longer to set. Silicone impression materials needed for crown, bridge and implant work must be very accurate and often (but not always) takes a good few minutes to set. Such impressions are also commonly used for the final impression for cobalt chrome partial dentures.

2nd Appointment – Recording your Bite

The dentist needs to transfer the way you bite your teeth together accurately to an articulator; a special machine that acts like your jaw so we can observe how your teeth bite and move across each other. This helps ensure that the denture will fit accurately and that the bite on the natural and artificial teeth will be correct.

There are two main positions of your bite the dentist can record:

  • ICP(Inter Cuspal Position)
This is the way you normally bite, with the maximum number of teeth coming into contact with each other- it is the way you automatically bite- without thinking. This is the position that is used, when you have enough teeth to accurately bite in the same position over and over again.

To record this, the dentist may squirt in a bit of a silicone impression material and ask you to 'bite', until the material sets; they may use wax instead, which again you 'bite into'. Alternatively, if you have a lot of teeth and the position is obvious, they may need nothing at all. If you have a reproducable bite but only on a few teeth- wax rims or blocks will be needed. These are made in the laboratory and then softened for you to bite into to produce an accurate record.

  • RCP (Retruded Contact Position)
Where you don’t have a stable bite, (generally just a few teeth that don’t meet) this position must be used. It is the only way the dentist can get you to bite in a reproducible way.

You can move your jaw forwards varying amounts, but when your jaw is as far up and back as it can go- you have a position that can be recreated. If you have no teeth i.e. need complete dentures- they must also be made to this position and it's the same if you have no stable bite.

It is not always easy to get you into this position- when you open your mouth, your jaw rotates a little to begin with in the socket- this is the first part of your opening. You can feel this, if you put your fingers on your jaw joint, just in front of your ear, and open and close just a small amount. If you open wider you will feel your lower jaw actually begin to slide forward down your top jaw.

Wax rims; occlusal rims, or bite blocks- 3 names for the same thing will be softened under a bunsen burner flame and used to record this position of your bite- when your jaw is right back and just rotating.

The dentist may try to get you into position (RCP) in one of the following ways:

(i) Ask you to curl your tongue as far back in the roof of your mouth as it will go. Essentially resetting your jaw backwards.

(ii) They may add a little bit of wax to the back of the top bite- block for you to aim for with your tongue.

(iii) They may ask you to relax the muscles of your jaw completely and go floppy; as if you were starting to fall asleep and your mouth was beginning to open slightly.

(iv)They may ask you to swallow, after which you are completely relaxed.

(v) Alternatively, they may hold you on the chin and push your jaw gently backwards and upwards to find the position.

Or some combination of the above!

Lab Stage- Designing Your Denture

This is very important and quite a time- consuming stage that you don’t really see.

After reading this, you will probably have a new found appreciation for, not just the process, but also the cost of dentures.

This same basic design process is followed in order to come up with the best possible solution given your particular circumstances. The ultimate success of your RPD (removable partial denture) will depend on many factors- the design is one important aspect.

First the impressions are poured up to give a replica model of your teeth and these are mounted on an articulator. The record of your bite is used to make sure the top and bottom model fit together as they do in your mouth.

The teeth are then surveyed using a special machine, called rather unsurprisingly a 'Surveyor'- this helps to identify the following:

  • The best way for the denture to be put in and taken out.
  • Areas that can be used for retention (clasps) to help hold the denture in.
  • Areas next to teeth which need to be adjusted in the mouth, or blocked out before the denture is made, to allow it to be put in and taken out easily. Elastic impression materials will stretch over a bulbous area of your tooth or ridge, but the hard acrylic or metal of a cobalt chrome denture won’t. If we do not relieve things in this area as you try to put it in, it will scrape over your gums- not very nice!

The denture is then designed by the dentist (ideally), technician or both in communication together.

The following must be planned:


  • Saddle areas
This is a term for the teeth that are to be replaced.

  • Support
How will the denture resist forces towards your gums during eating? Will it be from teeth... in which case it is known as a ‘tooth borne’ denture' or from your gums/ridges, known as a ‘mucosal borne’ denture or a combination of both.

The decision depends on the number and position of the missing teeth, as well as the quality of the remaining teeth. If all spaces have good teeth either side, then a tooth borne design can usually be used- this is much preferred as teeth are better at taking the forces of your chewing and don’t resorb in the same way that your ridges do.

Tooth-borne dentures must be cobalt-chrome dentures. Mucosa- borne dentures must be made entirely of acrylic. 'Tooth and mucosa borne' will be a cobalt chrome denture with an area that rests just on the gum.

  • Retention
How will your denture stay up or down (if it is a bottom denture)?

Retention stops the denture coming away from your gums. Grip or retention for your denture can be obtained by using metal clasps, guide planes, precision attachments, and, if undercuts are present, sometimes by the shape of your ridge.

All of these technical aspects need to be carefully thought through and considered- it is not just as simple as saying- "Yep let's chuck a clasp on that tooth". For example, the surveying procedure described above will identify if there is enough undercut on the tooth for a clasp and if not, the way the denture is put in may be changed to create this. A bit of white filling material might be used to change the shape of the tooth in the mouth and create one.

How deep is the undercut? If it is too deep, the clasp may grip too much and not come out. Two major types of clasp exist: the clasp might come down from the top of the tooth (occlusally approaching clasp) into the undercut, or possibly up from the bottom upwards (gingivally approaching clasps)- and that’s just the possibilities for one simple clasp… You can see that this is a very involved process! The British Dental Journal books dedicate a thick clinical guide just to this designing process!

  • Bracing
How will the denture be prevented from moving sideways and rocking? Bracing will help prevent lateral movement and can be got from:

(i) A metal arm on the other side of the tooth to the clasp.

(ii) The connector of the denture- the part of the denture that holds or connects everything togther e.g. the metal framework.

(iii) The saddle- the bit of the denture on which the missing teeth sit – it can either be entirely acrylic or a metal framework with acrylic on top.

  • Connector
Which type and design of connector will be used? There are many, if not endless variations and the choice will depend on the number and position of the missing teeth; how high your smile is; if there gaps between your teeth where metal may show through; if are you likely to loose more teeth which will need to be added in the near future and more!

Where possible the choice should keep the denture away from the margins of your teeth to help cleaning. On the bottom the decision is generally between a lingual bar and a lingual plate. Bars are generally preferred because they are healthier, but only possible if there is enough room (over 7mm of space).

Plates provide great stability, support and retention- the only downside is they cover the margins of your teeth.

  • The look
You can have the most beautifully designed denture that will stay in your mouth perfectly and not rock and move but if you have a high smile, visible metal near the front may be unacceptable.

If you have a low smile, you can often have the extra retention and clasps even onto your front incisors and no-one except you and the dentist will ever know.

If you have a high or gummy smile, you are often faced with a choice and it is just a matter of deciding what is most important.

The clasp is there to provide added retention to stop the denture moving and coming down; removing this would certainly improve the look, but is that worth it? It depends on the rest of the design? Is this the only grip? Will losing it be catastrophic? Can a smaller, less visible clasp be used to provide some support? These are all things which will need to be discussed your dentist during the design phase.

Will my Teeth be Prepared for Partial Dentures?

If you are having a basic acrylic denture, there is often little tooth modifying for the dentist to do.

With chrome dentures however, the fit and way the forces of chewing are directed down through your teeth can be considerably improved by adjusting the shape of teeth. As such, before the final impressions are taken, your teeth may need to be modified slightly according to the design of the denture.
This can be done by shaping the tooth or preferably filling slightly with a drill, or bonding white composite material to the tooth- it all depends on the situation.


The main preparations your dentist could make include:

  • Rest Seats
These are small indentations that allow a ‘rest’ from a cobalt chrome denture to direct the forces appropriately down the tooth. They are placed where possible into existing fillings or incorporated into crowns. They are not always needed, but where you have a particularly close bite, putting a 'rest' straight on the tooth would prop you open; this creates a little bunker into which it can fit- meaning you can continue to close your teeth normally.

  • Guide Surfaces
These 'guide' the denture in and out of place; as well as making it more stable and improving the appearance.

  • Create Retentive Areas
Dentures can have clasps to help grip the teeth, but to work effectively there must be a slight bulbous part on the tooth that they have to flex over. Without this, the clasps are not really active and the denture will not have the same grip.

  • Reduce/ Remove big Undercuts on Teeth
Small undercuts or retentive areas (as mentioned above) are generally a good thing; big ones however are not. Clasps can only flex so much and the solid base of a denture can't fit into these areas. By modifying them, you can improve the fit, look and stop areas where food could get packed and cause problems.

So if your dentist starts drilling your teeth a little before taking the impression, it's these things that they are working on. Sometimes there will not be space in your bite for a clasp or rest on the denture; in these cases, the dentist may need to smooth down the opposing tooth or filling a little to create more space. All efforts are made to keep these little tooth adjustments in enamel so that you don’t get any sensitivity.