Immediate dentures part 2: denture construction

Impression taking

Master impression

The aim of a master impression is to record contours of the teeth present, the remainder of the arch and the functional depth and width of all the areas of the oral cavity accurately. A special tray fabricated in the laboratory is used for this purpose. (Figure 2). The tray should be checked on both the cast and in the mouth to assess its adequacy and any overextension or deficiency corrected (as mentioned before) prior to the master impression being taken. Molding may be indicated for the intended saddle areas with green stick tracing compound to determine the functional width and depth of the buccal and lingual sulci prior to the master impression being taken.¹ The reproduction of the remaining dentition is obtained by capturing the coronal and occlusal aspects of the remaining teeth accurately, including any prepared surfaces.¹ Stabilizing primary disease along with a thorough scale and polish will ensure such an outcome.

A variety of commonly used materials include alginate, addition or condensation silicones or polyethers. The authors advise the choice of impression material to be made on a case by case basis, taking into account various factors such as number of remaining teeth present, any undercuts present, extent of alveolar ridge resorption, etc.

Challenges with taking impressions

When taking impressions for immediate dentures there is a risk, particularly when there are periodontally involved teeth, cavitated carious lesions or bridge work, that the impression material can engage the undercut around these teeth and/or fixed prosthesis. This can lead to potential iatrogenic removal upon withdrawal of the impression. There are a number of techniques that can be used to minimize this which include:

Blocking out the undercuts using wax or another appropriate material which can be removed after impressions are taken to stop the impression material from flowing and engaging the undercut³ (Figure 3);

Splinting mobile teeth, which may commonly be achieved using direct composite at the chairside;²

Applying a layer of vaseline to act as a lubricant and making the withdrawal of the impression easier;

Impression material selection – alginate is an ideal impression material to use in such cases as the material is less rigid and more prone to tearing which can be a favourable characteristic in these situations.

Jaw registration

The jaw registration procedure may vary depending on whether it is decided to conform to the patient's current OVD or to re-organize the occlusion. In general, conforming to the current OVD is less clinically and technically demanding, is more predictable, and tends to be better tolerated by the patient in general.

In situations where the OVD is to be maintained and patients retain most of their natural teeth with multiple stable contacts which are easily located, jaw registration can be taken using an appropriate bite registration material. However, where multiple teeth are missing and the OVD is planned for re-organization, it is necessary to use wax record blocks that are well fitted and adapted nicely to the underlying edentulous saddle. This will ensure that no movement or distortion of the rim occurs during the jaw registration.² If needed, stability can be enhanced by fixing wire clasps to the wax bases in order to engage the remaining standing teeth.⁴ The wax rim is then reduced and shaped to determine the proposed occlusal plane and OVD. The registration is taken with the patient manipulated into the retruded arc of closure at the proposed OVD. This may be challenging, particularly as there may often be no tooth to tooth contact present. A bite registration material is then used for the final registration so that the technician is able to articulate the study casts without any movement or rocking of the casts.

The proposed aesthetics should be assessed in the form of the tooth size, shape, set-up and shade. An advantage of teeth being present is that one can assess if the patient is keen to maintain the appearance. This can serve as a guide, otherwise the selection is done in the same way as it is for conventional dentures. The setting up of the teeth should closely mimic the position occupied by their natural predecessors. However, there will be situations where replicating the natural appearance may not be desirable due to malocclusion or mal-alignment (Figure 4). Such patients may benefit from altering tooth position, size and shape. This decision is made jointly with the patient and prescribed to the technician.

Wax try-in/trial

A wax try-in of the prosthesis should be carried out where possible. This may not be possible in all cases due to the fact that the teeth have not been extracted and, in such situations, the patient should be shown the waxed-up prosthesis on the articulated casts to give an idea of what the final result is likely to be. This should be approved prior to construction.²

Where a wax try-in is possible, this should be fitted and assessed in the same way as a conventional denture. Any clinical, technical or aesthetic issues should be addressed prior to construction of the prosthesis. Where changes are required, these should be carried out and the wax try-in re-tried. Once the clinician and patient are both happy, the denture can then be prescribed for construction.

Extraction of teeth and immediate denture fit

Prior to extraction of any teeth, the prosthesis should be present and checked to ensure that it is as prescribed and will replace those teeth that are planned for extraction. A large part of the success attributed to immediate dentures lies with a good extraction technique.² The extractions should be carried out as atraumatically as possible, preserving as much bone as possible, particularly the buccal and lingual plate so that bone loss and subsequent resorption is minimized (Figure 5). However, this is not always possible. In the past, there was a tendency to carry out alveolotomy and alveolectomy procedures in order to remove any undercuts in the labial sulcus.^5,6 However, these procedures are rarely favoured today due to their destructive nature, and the onus is now on fabricating a denture that overcomes this issue.⁷ These procedures can also create challenges in the long term as treatment options can become limited. For example, implant placement may be difficult due to limited bone being available at the surgical site.

Once the teeth are removed, the denture should be tried in and checked that it sits in the correct position properly. Any interference from teeth as well as gross overextensions should be corrected. The denture should be checked for retention, support and stability. The occlusion should be checked both in a static and dynamic relationship and any interference corrected. Where there are no stable occlusal contacts, this will normally be in the retruded contact position. Since a large part of fabrication of an immediate denture involves guesswork to ascertain the level of alveolar ridge after extraction, it is likely that the denture may require significant adjustment prior to fit. Therefore, it is important to book sufficient time on the day of surgery in order to provide the patient with a comfortable, well-fitting denture prior to the patient leaving the surgery, otherwise the patient is less likely to wear the prosthesis. This can be challenging as the patient is ‘numb’ from the local anaesthetic used for the extractions, therefore the patient should be subsequently reviewed soon after, to re-assess the prosthesis. Patients may also be anxious and emotionally drained after the procedure, therefore, offering them extra support from the entire team will help them significantly as patients often appreciate care and attention at this critical stage. Providing them with written leaflets on post-operative instructions is useful as they may not be able to recall information correctly, especially if the extractions have been carried out under conscious sedation.

Post-operative instruction and review

It is recommended that patients should be advised to keep the dentures in the mouth for the first 24 hours.^8,9 This is so that the soft tissue oedema does not prevent the denture from seating well. After that, the denture should be worn during the day and removed and stored correctly at night whilst the patient sleeps.

While there are no specific guidelines regarding the recall period, it would be sensible to review the patient 24 hours after the extraction to reassess the prosthesis and carry out adjustments as appropriate. After this the patient can be reviewed at one week and then one month. However, this needs to be determined on a case by case basis as various factors will influence the decision, including the number of extractions, fit of the prosthesis, patient compliance, etc. Once reviewed, adjustments may be carried out as appropriate. Resorption and bony remodelling will occur over time, which is likely to affect the retention and stability of the prosthesis and a reline often becomes necessary. This is particularly common and occurs sooner where multiple teeth have been extracted or where extractions were traumatic. Relines can be required as early as 4–6 weeks¹⁰ and can be carried out either chairside or in the laboratory. After 3–6 months post-extraction, the denture may loosen further and require rebasing or fabrication of a new prosthesis.¹⁰ Where possible, this should be delayed until the clinician feels that further bone resorption is unlikely to occur, otherwise this rebased or new prosthesis will quickly suffer the same fate. However, there may be certain situations where a reline or re-base would not be feasible for an immediate denture and a new denture may need to be made quite early, for example, where a large amount of early bone resorption may cause significant loss of retention. In such cases, a new denture can serve as a transitional/interim denture till bony remodelling is complete, at which stage a new permanent conventional removable prosthesis can be fabricated.

Some of the common problems with immediate dentures over time include compromised aesthetics and poor retention. Aesthetics is of particular concern in the anterior region where a gap may start to show between the alveolar ridge and the denture, especially when an open faced or partial flange has been used. For this reason it is prudent to review such patients in order to identify these issues regularly.

Addition to immediate dentures

It may become necessary to add teeth to the existing immediate dentures as and when subseqent teeth are lost due to various factors. The ability to add teeth to a prosthesis is dependent on the design of the prosthesis and the material used. Where possible, dentures should be designed to accommodate additions where teeth have a guarded or poor prognosis, as this will make addition to the prosthesis relatively straightforward.

The addition of teeth to acrylic immediate dentures can be carried out in the laboratory or chairside. For laboratory addition, an impression is taken of the arch with the immediate denture in situ and sent to the laboratory prior to extraction. The lab then casts the impression and adds the tooth/teeth to the prosthesis. This is then returned, the tooth/teeth extracted and the prosthesis fitted. The disadvantage of using this technique is that the patient is without the prosthesis for a period whilst this is carried out but, if it is planned in advance and arranged with the lab, then it can often be carried out within a few hours. The advantage with such a repair is that it saves chair time and the materials that can be used in the laboratory are often superior in quality to the ones that can be utilized within the dental surgery.

A chairside technique described in the literature can circumvent the issue of the patient being without the prosthesis.¹¹ In this case, an impression is taken of the mouth with the denture in situ, the impression is then cast and the tooth/teeth planned for extraction are removed from it. The tooth/teeth are then extracted. Acrylic denture tooth/teeth are placed onto the cast where the missing teeth are and wax used to secure the acrylic teeth to the denture. This is then tried in the mouth for position, colour and shape. Any readjustments required are carried out. The denture is placed back on the cast and a putty index is made to record the position of the acrylic tooth in the arch. The modelling wax is then removed and vaseline applied onto the study cast. Using the putty index, the tooth is placed in position and fixed to the denture using auto-polymerizing acrylic resin. Once set, the denture is tried in the patient's mouth for any final adjustments.¹¹ The advantage of this technique is that the patient does not have to be without his/her denture. However, this process takes time clinically and there is a need to have the ability to cast impressions within the practice, which may not always be possible.

Conclusion

Immediate dentures form a significant part of prosthetic dentistry and continue to provide patients with replacement of their natural teeth in the post-extraction period. They not only allow maintenance of appearance and function, but also help to prepare patients psychologically for the edentulous phase of their life. With the use of correct techniques, immediate dentures can be quite retentive and stable in the interim period and provide a rewarding experience both for the clinician as well as the patient.