Article
“Why is it that teeth decay? You don‧t always have to go to the doctor‧s to have holes in your arm stopped up do you? It‧s a flaw in the design.”
Standards in healthcare are of fundamental importance. Evidence-based dentistry, audit and peer review are essential components of effective clinical practice. To assist with these processes, the BSRD perceives a need for guidelines on acceptable levels of care in restorative dentistry. Some guidance is already available from our sister organizations, the British Endodontic Society, the British Society of Periodontology and The British Society of Prosthodontics, within their spheres of interest. This document is intended to act as a stimulus to members of the Society and to the profession to seek attainable targets for quality in fixed prosthodontics. It is hoped that this document from the Society will assist in the pursuit and maintenance of high standards of clinical practice.
These guidelines should not be considered prescriptive or didactic. Obviously, there will be circumstances, encountered during patient management, when the ‘ideal’ treatment may not be possible nor the outcome optimal. In addition, new techniques and materials will become available which will bring about change. However, it is the Society‧s belief that these standards can and should be the goal during management of the majority of clinical cases.
Indications
The decision to provide a crown or fixed bridge, whether tooth- or implant-supported, depends on many factors, including:
In all situations, the clinical advantages and long-term benefits of crowns and fixed bridges should justify such treatment and outweigh their disadvantages. They should only be undertaken in those situations in which such advanced restorative care will clearly contribute to the oral health and welfare of the patient.
The replacement of failed crowns and bridges and the teeth or implants which support them should be conditional on an understanding of the aetiology and successful preventive management of the cause(s) of failure.
Alternatives to crowns and fixed prostheses
Modern dentistry offers many opportunities to provide direct and indirect restorations which satisfy aesthetic and functional requirements of patients without the need for significant, if any, tooth preparation.
Vital bleaching, composite resins, ceramic inlays and onlays and resin-retained bridges frequently have major roles in any treatment plan. Where teeth are minimally or moderately restored at the time of presentation, adhesive restorations are generally most appropriate. For example, in the management of the worn dentition, particularly that damaged by erosive substances, the use of full coverage crowns has little to commend it as the first option for treatment.
Dental implants may frequently be the treatment of choice when missing teeth are to be replaced. The biological cost to the patient is low when sufficient bone is available to house them. Aspects of the provision of implant-based restorative dentistry are similar to those for teeth, whilst others require different considerations and skills. These guidelines will refer to implant-supported crowns and fixed prostheses as necessary.
The development of adhesive techniques and the predictability of dental implants reduce the need for the removal of sound tissue as part of restorative treatment.
Definition of a fixed bridge
Any dental prosthesis that is luted, screwed or mechanically attached or otherwise securely retained to natural teeth, tooth roots, and/or dental implant abutments that furnish the primary support for the dental prosthesis.
The Glossary of Prosthodontic Terms. J Prosthet Dent 2005; 94: 10–92.
The rationale for the use of crowns
The rationale for the use of fixed bridges
Assessment
Aims
The clinical examination may be supported by special tests, which may include:
Other forms of special test may include:
Diagnoses may take time to establish and require the use of additional special tests including dental investigations to stabilize or determine a prognosis for one or more teeth. Any case considered to be beyond a clinician's capabilities and experience should be referred for further assessment, advice and possibly treatment.
Many clinical situations benefit from the involvement of additional dental specialists or those with particular skills. Such involvement should take place prior to the establishment of a treatment plan and may increase the options available to the patient. Implant-based treatment may be provided either by a single competent operator or by a team led by a prosthodontist and including a surgeon. The need for inter-disciplinary provision and restoration of implants is based on the complexity of the case and the skill and wishes of the dentist providing the restorative care. It is important that the whole dental team is knowledgeable about dental implants. Training of dental nurses, technicians and reception staff is mandatory.
Treatment planning
Aims
Design
The design for tooth-supported fixed bridges should:
The choice of material(s) should:
Implant-supported crowns and fixed bridges should use an implant system which:
Treatment planning is facilitated by:
Before finally agreeing to a particular treatment strategy, patients should be made aware of the implications, possible sequelae and anticipated life-expectancy of the work and other options for their continuing care. In addition, patients must understand and accept that the success of the treatment will be highly dependent on their subsequent commitment to oral healthcare maintenance. This constitutes an essential part of the process of obtaining informed consent from the patient prior to treatment.
All treatment plans should be kept under continual review throughout all stages of patient management. Contingency treatment options should form part of the overall strategy for patient care.
While not always essential, pre-operative photographic records may assist in the provision of treatment and form part of a baseline record.
Consent
It is important to obtain written informed consent for all forms of fixed prosthodontic treatment: this should include a clear understanding of the financial cost of treatment. Consent may only be obtained following a full discussion of the proposed treatment with the patient.
Clinical records
In common with all other documentation related to the patient, clinical records detailing the provision of crowns and bridges should be complete, unambiguous and prepared in a legible form.
Preparatory management
Preparatory management should, where indicated, include demonstrable completion of:
Dental implants
Space requirements for dental implants
The number and position of implants
The number and position of implants is influenced by the type of prosthesis provided, the quantity and quality of bone and the occlusal loads expected. For edentulous patients the following may be a guide:
| ▪ Fixed bridge: | – Maxilla |
– 6 implants |
| ▪ Overdenture: | – Maxilla |
– 4 implants |
Surgical protocols for implant placement
Single versus two-stage surgery
There is no evidence of improved outcomes between single and two stage surgical treatments. Single stage surgery is convenient for patients and reduces treatment times. A two-stage procedure, whereby the implant is buried and subsequently uncovered after an appropriate healing time, should be considered under the following circumstances:
Immediate placement
In this type of treatment the dental implant is placed immediately into the tooth socket following dental extraction.
Immediate loading
Healing times
Healing times refer to the time that the implant needs to osseointegrate in the jawbone.
Cemented or screw-retained restorations
The decision on whether to provide a restoration that is cemented or screw-retained depends on the following factors:
A screw-retained prosthesis may have a visible screw access hole but it provides the most secure retention and simplifies any future maintenance. The angulation of the implant may prevent the use of screw-retention of the restoration.
Determination of colour and form of restorations
Shade determination should involve consideration of the hue, chroma and value for the body, cervical and incisal portions of the proposed crown and bridge. This should involve:
Shade determination is best completed pre-operatively to minimize errors related to eye fatigue, dehydration of teeth and apparent shifts in shade following the removal of tooth tissues.
Details of features, such as areas of opacity and translucency, cracks and any special staining effects required should be recorded as part of the shade determination. A written and diagrammatic prescription will facilitate the transfer of information between the dentist and the technician.
Where appropriate, the patient and, whenever possible, the technician who will construct the restorations, should participate in the completion of the prescription of colour and form. Clinical photographs may be of value in assisting a technician who is unable to examine the patient in person. Electronic colour determination using scanning devices may be helpful but an appreciation of their limitations is required.
Where teeth are to be replaced, the use of a diagnostic wax-up is beneficial and may be used to construct a provisional prosthesis to facilitate patient and dentist understanding of the final form of the restoration prior to beginning definitive prosthodontic treatment. In the case of implant-supported restorations and some tooth supported fixed prostheses, the contours of the provisional restoration may be used to develop soft tissue form adjacent to the crown or fixed prosthesis.
Tooth preparations
All preparations should be planned taking account of access and with reference to radiographs and study casts.
The equipment for tooth preparation should be well maintained and include an appropriate range of instrumentation.
Decisions regarding the form and dimension of preparations should take account of:
If pulp vitality/integrity of the tooth is likely to be put in jeopardy by the extent of the preparation required, then additional preparatory treatment involving orthodontic realignment or elective root canal therapy may be indicated. Specific consent must be sought prior to elective root canal therapy.
When it is intended to remove a finite amount of tooth tissue a guide or pre-operative index is a valuable aid to avoid excessive preparation.
Impressions
Master impressions
Purpose
To obtain an accurate, dimensionally-stable, fully-supported impression of the prepared teeth, any dental implants and associated soft tissues.
Materials
Impression trays
Whether custom-made or of the stock variety, impression trays should:
Technique
Completed impressions should be:
Opposing arch impressions
Impressions of the opposing arch are critical to the success of crown and bridgework. While such impressions may generally be successfully completed using alginate, great care is required to avoid the introduction of significant errors in their use.
Impressions of the opposing arch should be handled, decontaminated, protected and stored with the same care adopted for master impressions.
Occlusal registration for working casts
The purpose of occlusal registration is to allow opposing casts to be related accurately either in a cast relator or an articulator. A formal registration may not be required if a small number of teeth is being restored and there are sufficient remaining contacts between the unprepared teeth to allow the technician to establish adequately the intercuspal position (ICP) or centric occlusion (CO). Sufficient information informing the technician which teeth make contact in the patient's mouth on mandibular closure will facilitate this.
Materials
The material selected to record occlusal registrations should:
In situations where patients have lost posterior occlusal support, it may only be possible to make an occlusal registration by using wax occlusion rims. However, the limitations of these for fixed prosthodontic work should be recognized.
Technique
Principal mandibular positions
When adopting a conformative approach (ie the crown or bridge is to be in harmony with existing jaw relationships), the intercuspal position (ICP)/centric occlusion (CO) should be recorded. When a reorganized approach has been planned, it is advantageous if the change in the jaw relationship has been made prior to making the tooth preparations such that ICP/CO and the Retruded Axis Position (RAP)/Centric Relation (CR) coincide. This makes the recording of jaw relationships easier.
Functional relationships
Correct functional relationships are of considerable importance to the clinical success of crown and bridgework. To facilitate correct functional relationships, registration procedures should include a facebow transfer. Lateral and protrusive registrations are often recommended, but in the dentate patient confer little benefit where there is reasonable anterior guidance. Appropriate records to allow the duplication of the anterior guidance may be helpful for the restoration of anterior teeth: this is particularly the case where multiple restorations are planned.
The use a functionally-generated path (FGP) technique can create an inter-occlusal record of assistance in providing information about the relationship of antagonist teeth to posterior preparations on mandibular closure and mandibular excursions.
The accuracy of inter-occlusal records should be confirmed by the dentist and technician. The use of shimstock foil, a split-cast technique or copings are all techniques which may assist in achieving accuracy in relating working casts. However, the quality of the inter-occlusal record remains paramount.
Temporary, provisional and interim restorations in fixed prosthodontics
Purpose
Temporary restorations
To restore, protect and maintain the position of prepared teeth between appointments and until the placement of the final restoration.
Interim prostheses
Interim prostheses may be required to maintain form and function during treatment involving the use of dental implants. Tooth-supported prostheses are preferable in this respect.
Qualities
Provisional restorations
Temporary restorations may also be used to test form and function and develop soft tissue contours adjacent to the restoration: these are more appropriately termed ‘provisional restorations’. Provisional crowns and bridges should incorporate most of the qualities of the final restorations which will replace them. These should include:
Technique
There is much to commend a replica technique for the fabrication of provisional crown and bridgework in situations in which tooth form and function should remain unchanged. However, there are a number of methods which may all give acceptable results. Practitioners nonetheless need to be aware of the advantages and limitations of the method selected.
When planning a significant change in form or function the diagnostic wax-up can be used to produce an index for the production of provisional restorations. This approach allows the clinician to assess the patient‧s response to the proposed changes prior to the construction of the definitive restorations.
During the fabrication and placement of provisional crown and bridgework, care is required to ensure:
Temporary and provisional restorations should be cemented to the teeth with a material that provides an adequate marginal seal but has physical properties that allow removal of the provisional restoration without damage to underlying preparation.
Laboratory prescriptions
Purpose
To record and communicate precise details of all aspects of the crown and bridgework required.
Laboratory prescriptions are best completed together with the technician. In situations in which this is impractical, misunderstandings and omissions in prescriptions may be minimized by effective clinician/technician liaison, including the clinician inspecting various stages of the laboratory work, notably working casts and wax-ups.
Requirements
Laboratory prescriptions should include:
The use of labelled diagrams together with study casts, diagnostic wax-ups and impressions of temporary or provisional restorations greatly facilitates communication. Clinical photographs may assist the technician in the design of crowns particularly with aspects of form and surface texture but should not be relied upon to communicate colour accurately.
Try-in
Purpose
To confirm the clinical acceptability of completed or partially completed crowns or fixed bridges in terms of:
Principles
Final placement of restorations
The final placement of tooth-supported and implant-supported restorations has a number of common elements but also significant differences.
Tooth-supported restorations
Aim
To cement/bond crowns and bridges considered to be satisfactory by both the operator and the patient at the time of try-in or following a period of temporary cementation.
Technique
The luting system should be chosen with the following in mind:
The preparations should be cleaned, isolated and, where indicated, primed and conditioned as required for the cement selected. The luting system should be dispensed, mixed and applied in strict accordance with manufacturer‧s instructions whilst the operating field should be controlled.
The final restorations must be fully seated within the available working time using appropriate techniques to overcome the effects of hydraulic forces. While it is highly desirable to have some excess luting material present along the entire margin of the restoration, completely filling the restoration with cement will impede the seating of crowns and fixed bridges. The restorations must not be allowed to move relative to the underlying preparation(s) during the critical initial set or polymerization of the lute. At this time special precautions may be required to isolate and protect the luting material used.
When set, the excess luting material should be removed using instruments and techniques least liable to cause damage. It is of particular importance to ensure that no excess cement is left in interproximal or subgingival sites.
Newly cemented/bonded crowns and bridges must be examined with particular regard to:
Where indicated, suitable adjustments should be completed, including refinishing of roughened areas.
Implant-supported crowns and fixed prostheses
Aim
To attach securely crowns and bridges considered to be satisfactory by both the operator and the patient at the time of try-in or following a period of temporary use.
The final restoration may be screw-retained or cemented to an abutment attached to the implant.
Screw-retained crowns and prostheses:
Cement-retained crowns and prostheses:
For all restorations
Before discharging a patient, following the placement of crowns and bridgework, suitable instructions should be given regarding immediate care, action to be taken in the event of post-operative pain or discomfort, and appropriate oral hygiene measures.
Initial review
Purpose
To assess the patient‧s response to the restorations and to deal with any post-operative difficulties, concerns, pain or discomfort which arise after placement.
Procedure
Long-term review
Long-term reviews of crowns and fixed prostheses should form part of routine recall examinations. These examinations should, from time to time, include radiographic examinations using intra-oral films.
Care needs to be taken during long-term review to ensure that the cement lute remains intact for all tooth-supported indirect restorations. This is of particular importance for fixed bridges or linked crowns where failure of the cement lute may lead to rapid and extensive dental caries.
Follow-up of implant patients is just as important as for those who have received tooth-supported crown and bridgework: radiographs are advisable one year following treatment to check that coronal bone levels have been maintained. All patients should be reviewed at least annually. They should be encouraged to return to the provider of the implant treatment if they feel that there has been any deterioration.
To monitor clinical performance and any deterioration in acceptability, detailed records should be kept of clinical observations made during reviews of crown and bridgework.
When a dental hygienist or other dental care professional is part of the dental team undertaking long-term care of crowns and bridges he/she must be aware of the specific maintenance issues and potential modes of failure.
Concluding remarks
The provision of crowns and fixed bridges to a high standard is an exacting task for the whole dental team, clinician, technician, nurse and other support staff, as well as for the patient. Provision of high-quality crown and bridgework accompanied by excellent maintenance can produce long-term success which is rewarding for both the patient and the dental team.
The Society hopes that these guidelines are helpful and act as a practical reminder of the standards that we try to achieve. Guidance notes are never complete, and these are no exception. The Society will be reviewing this document at regular intervals for accuracy and in the light of contemporary thinking. Any comments you may have would be gratefully received and should be addressed to the Honorary Secretary of the Society.