Prosthodontics

Completely Dentures Again

In this month’s tips I should like to return to three aspects of complete denture construction. In ‘Dentures done right’ I looked at the timing of choosing teeth and mould for complete dentures to avoid costly and time consuming retrys.

First, where are teeth set? They are set in the position of the natural dentition in the neutral zone, and definitely not ‘to the ridge’. I have found a very useful pointer to the placement of maxillary canines. Their mid point is at the line of the first palatal ruga. Please check on any model that you have. When I set up teeth I often found that it was easiest to start with this fixed canine position. Canines turn the corner of the arch, and when viewed from directly in front only the anterior part of this tooth should be visible. For some reason, canines are most often set showing too much of the labial face, and I think this is due to the palatal shape that may well require a little selective grinding when lower anterior teeth are set up to allow for tucking in the distal aspect of the denture tooth into the line of the arch. If your patient has an old partial denture, because the palatal tissues hardly change, this can be used to give tooth position guidance also.

Secondly to look the part, the vertical dimension must be correct. By way of reminder the occlusal vertical dimension (OVD) should be 3 – 4mm less than the rest vertical dimension (RVD) anteriorly. The challenge is therefore to determine the correct RVD. Various suggestions such as licking lips, relaxing or even humming have been proposed. However, there are a significant minority of patients who continue to close their lower jaw and persistently give a reduced and erroneous RVD. I have found that if I place a small piece of tissue paper and ask patients to just hold it between their lips, this magically stops continual closure and gives the correct result. I suspect that there is an interruption to some of the proprioceptive pathways. Always be prepared to take the RVD on several occasions if your measurements vary by more than a millimetre or so.

If you want further evidence of the importance of correct OVD look at some of the later programmes from one of my favourite television presenters – Fred Dibnah. On closing his jaw, his mandible protrudes, his masseters bulge, his maxillary incisors are set to the incorrect axial inclinination and are tipped back towards the ridge, and it should be obvious to any clinician that there is a significant, 7 or 8mm, reduction in the OVD. This also shows how, if the OVD is reduced, the mandibular closing muscles have to work harder. It follows that I cannot agree with a recent correspondent in Dental Practice who routinely advocated a 2mm reduction from the normal complete denture OVD.

My third comments refer to the denture bearing tissues. In ‘On the move’ I discussed the case of an edentulous maxilla against mandibular anterior teeth, and how the baseplate moves during taking the bite. I also mentioned that there was often an enlarged maxillary tuberosity. Space at the time precluded discussions about how to treat an enlarged tuberosity, so here goes!.

Your clinical examination will have showed if the tuberosities are flabby and move from side to side when palpated, or if they are placed lower than the natural line of the residual maxillary ridge or exhibit bony undercuts. Is there sufficient space between the tuberosity and the retromolar pad for the correct extension of the denture base? Try my ‘little finger test’. Ask your patient to sit upright and remove their dentures, andadopt the resting mandibular postural position. The tip of your left little finger palpates the region of the normal space between the lateral surface of the tuberosity and the anterior border of the ascending ramus on your patient’s right side.   If the tip of the little finger can be inserted into the space, there will be sufficient room, at the OVD for the correct extension of the mandibular denture base over the retromolar pad and the maxillary base over the tuberosity for maximum retention and stability of both. When using this test keep a sharp lookout the your patient does not open their mouth. Use your right little finger on the left side.

Supplement your clinical examination with radiographs of the area. These will show the size and position of the maxillary antrum, the thickness of the alveolar bone and the depth of the enlarged soft tissues forming the tuberosity.

If the tuberosity is enlarged, then for optimum denture base extension and your patient is fit, the treatment of choice is tuberosity reduction. This is best carried out under local anaesthesia, and is a simple surgical procedure suitable for general dental practice.

There are three possible surgical treatments:

1. Where there is a buccal bony undercut and a normal thickness of overlying mucosa.

This is the simplest problem to correct. An incision is made along the crest of the ridge together with a buccal relieving incision anteriorly (Fig 1). The flap is raised and retracted whilst the excess bone can be trimmed away using a tapered fissure bur. When you think the correct amount of bone has been removed, replace the flap, and palpate the ridge through the flap. Any irregularities will be apparent and can be corrected. Sometimes when the flap is replaced, for ideal tissue approximation, it will be necessary to trim excess tissue using sharp scissors whilst holding the flap in tissue forceps. The wound is closed with simple interrupted sutures with the first suture placed at the junction of the ridge and relieving incisions.

1. Where there is enlargement of the soft tissues and no buccal bony undercut.

The aim of the surgery is to reduce the height of the soft tissues by wedge resection. An incision of elliptical shape, down to bone , is made just palatal to the crest of the ridge, extending from the hamular notch to 5mm anterior to the anterior edge of the fibrous mass, as determined by palpation and probing, and angling the scalpel blade as shown in the diagram. It is usual to find a ‘gritty’ feeling from this dense white fibrous tissue. A second matching buccal incision is made.. The mass of fibrous tissue thus defined is removed. Sometimes, if the two incisions have not met at the crest of the ridge it is necessary to do a little sharp dissection to remove any remaining fibrous tissue from the bone.. It is easier to do this starting anteriorly and working distally as vision into the wound will be better.. The next stage is to carefully thin the buccal and palatal flaps by removing more fibrous tissue by sharp dissection with a scalpel. This require care to ensure that sufficient fibrous tissue is removed to give the necessary reduction in vertical height without ‘buttonholing’ the flap, or on the palatal aspect dissecting too deeply and involving the palatal neurovascular bundle. The flap can be approximated as before, any excess trimmed and then closed, this time with mattress sutures to slightly evert the edges of the wound.

1. Where there is both enlargement of the soft tissues and a buccal bony undercut.

The procedure outlined in (b) above must be carried out first to reduce both the height and thickness of the soft tissues. Whilst it is sometimes possible to raise the buccal mucoperiosteum sufficiently to gain access to the bone, more commonly safe access can only be achieved by making a relieving incision as described in (a) from the anterior end of the elliptical incisions. This approach gives excellent direct vision for any buccal bony reshaping. Please note, if you carry out the preceedure for this presentation in the reverse order you will encounter considerable surgical difficulties and your result will be unacceptably poor. Suturing is by one simple suture at the angle of buccal to ridge incisions, then mattress sutures along the ridge.

In all cases the usual post-operative instructions apply. Antibiotic cover should not be necessary. For patients who already wear dentures apply a local reline in the surgical area using ‘Viscogel’

Pain after surgery is rarely a problem and should be controllable by mild analgesics. I remove sutures at one week, rebase the denture at 3-4 weeks with viscogel and expect the tissues to be sufficiently healed for impression taking for new dentures in about 8 weeks.

In summary, tuberosity reduction is a very useful pre-prosthetic surgical operation. It greatly reduces problems of denture construction and enhances the fit, retention and stability of the completed prostheses.

I am grateful to Professor Chris Deery, Dean of Dental Studies and the University of Sheffield for permission to attach the video showing the techniques described above.