For many years stainless steel crowns have been a significant part of the restorative armamentarium in paediatric dentistry. By definition they are prefabricated crown forms that are adapted to individual teeth and cemented with a biocompatible luting agent.1 If some logical sequences of steps in tooth preparation and crown adaptation are followed it is a relatively simple restorative treatment modality to employ. The principal indications for their use is in those primary and permanent teeth that are either hypocalcified or that have multiple and extensive carious lesions and whose pulps have been removed. As a result stainless steel crowns continue to be the restoration of choice for compromised primary molar teeth although they are not aesthetically pleasing. The eventual exfoliation of primary teeth ensures that aesthetics will ultimately be restored while the integrity of the dentition is maintained through its mixed dentition stage of development. In the case of permanent molar teeth, stainless steel crowns are a useful semi-permanent restoration that can be used until the tooth fully erupts and more permanent and aesthetic coronal restorations can be selected. The full coronal coverage that stainless steel crowns supply virtually ensures that re-decay will not occur and, furthermore, their smooth surfaces renders the tooth easier to clean using routine oral hygiene procedures.
TYPES OF STAINLESS STEEL CROWNS
There are, currently, three types of stainless crowns that are available to the practitioner and these are:
Crowns with straight sides with margins that follow the gingival contours of the tooth. The gingival margins can be trimmed where necessary but also need contouring and crimping to ensure gingival adaptation to the prepared tooth.
Crowns that have been pre-formed and pre-crimped that, as a result, are more difficult to adapt since trimming will result in the removal of the manufacturers' gingival crimp. The ensuring of a proper fit usually requires modification of the prepared tooth rather than the crown.
Aesthetic crowns have recently been introduced but they have been assessed to promote poor gingival health, they appear bulky, do not possess a natural appearance and are very expensive.2
INDICATIONS FOR USE
Stainless steel crown restorations are indicated for the restoration of primary and permanent molar teeth with1,3
Extensive carious lesions which undermine cusps and expand beyond line angles
Developmental defects such as hypoplasia and hypocalcification
Failure of other available restorative materials is likely
Following pulpotomy or pulpectomy
For restoring a primary molar tooth to be used as an abutment for a space maintainer
The intermediate restoration of fractured teeth
CONTRA-INDICATIONS FOR USE
Stainless steel crowns are contra-indicated when
More than two thirds of the roots are resorbed
There is clinical and/or radiographic evidence of radicular pathology
The tooth exhibits excessive mobility
AIMS, OBJECTIVES AND OUTCOME INDICATORS
The stainless steel crown is a durable restoration and its clinical success is predicated upon the following.1,3
Its surface is smooth and polished and remains intact
Crown margins are closely adapted to the tooth and do not cause gingival irritation
All excess cement is removed from around the margins
Contact with adjacent teeth is appropriately established
Crown is in proper occlusion
Where possible the vitality of the tooth is maintained
The restoration should not interfere with the eruption of the succadaneous tooth
The restoration enables the patient to adequately maintain oral hygiene
TOOTH PREPARATION AND CROWN ADAPTATION
Since teeth that require stainless steel crown restorations invariably have large carious lesions and there is, as a result, the possibility of a pulp exposure it is recommended that once adequate local anaesthesia is achieved the initial stages of tooth preparation are performed under rubber dam isolation.4 The first step in tooth preparation is to reduce the occlusal surface by at least 2mm. This step may be carried out before rubber dam application to ensure that the tooth is out of occlusion. Since the cuspal anatomy of stainless steel crowns is shallow there is no need to follow the cuspal outlines so that the occlusal table may be flattened.
Following occlusal reduction all caries should be removed. It is recommended that caries removal should start at the periphery and progress towards the pulp. This sequence ensures that if the pulp is exposed the operator is ensured that the tooth is not only caries free but a pulpotomy or pulpectomy can be performed in a clean uncontaminated field. In the absence of a pulp exposure the exposed dentin can be protected by calcium hydroxide or glass ionomer cement.
Remembering that stainless steel crowns gain their retention from engaging the crown-root undercut smooth surface reduction can be achieved by using a tapered diamond fissure bur. With the bur angled at 10° to 15° the buccal and lingual surfaces are reduced to just below the free gingival margin of the tooth ensuring that the crown-root undercut is left intact. The mesial and distal surfaces are prepared in a similar manner making sure that a dental explorer may be freely passed between the adjacent teeth. Buccal and lingual reduction is recommended before proximal surface reduction because primary molar teeth have broad contact areas and this sequence minimizes the risk of damaging the adjacent tooth. The preparation should now be carefully examined and any sharply angled corners at the mesial and distal buccal and lingual aspects of the preparation should be rounded off (Figs. 1 & 2). The rubber dam can now be removed and a crown adapted.
A stainless steel crown of the correct mesial distal width is selected and tried on the tooth. The crown height should be checked to ensure proper occlusion. If a preformed and precrimped crown is being used it must be remembered that this crown can only tolerate a minimal amount of adjustment to ensure an adequate marginal fit. It is thus the authors' opinion that the uncrimped straight sided crown is more versatile, although more time consuming, since it can be cut and contoured to fit.
The initial trying on of the crown may indicate that it is in supra occlusion and the reason for this may be that the occlusal reduction of the tooth was insufficient or that the crown is too long. In the case of the former further occlusal reduction can be carried out and in the latter the length of the crown can be reduced by using crown and bridge scissors at its gingival margin or by the use of abrasive stones. When reducing the height of the crown an even width band of stainless steel should be removed from its periphery. This ensures that the finished crown will follow the gingival contour of the tooth. All cut and abraded margins should be polished.
The crown can then be adapted to fit the tooth by the selective use of pliers. Open contacts are eliminated by the use of a ball and socket plier at the mesial and distal (Fig. 3). If necessary, the marginal circumference can be reduced by the use of a band contouring plier (Fig. 4). The final mandatory gingival crimp is achieved by the use of a gingival crimping plier (Fig. 5). The margins of the crown are engaged by the top two thirds of its beak and bent inwards. It is important to even out the crimp as one progresses round the periphery of the crown so the final margin is smooth with no kinks and unwanted projections.
A contoured and crimped crown should be placed on the tooth by engaging the lingual surface and then wedged over to the buccal. A well adapted crown should audibly snap into place without the application of an excessive amount of force. The margins should be checked with an explorer to check the marginal adaptation and appropriate adjustments made in cases of deficiency (Fig. 6). Before final cementation the occlusion should also be checked again.
A polycaboxylate or glass ionomer cement can be used for the crowns final cementation and the clinician must ensure that any excess cement is removed. Any deficiencies in the coronal hard tissues will be made up by the cement itself so that coronal build up is not necessary.
FURTHER CONSIDERATIONS IN CASE SELECTION
The stainless steel crown is an important restorative modality for the treatment of special needs children and children from remote areas who do not have ready access to regular dental care. Furthermore, many of these children also require the adjunctive use of general anaesthesia for their dental care. A general anaesthetic is indicated when the dental health of the patient has, or has the potential to, interfere with their general health particularly when they do not have the capability to tolerate treatment in a conscious state, or when distance from care precludes multiple appointments. The use of general anaesthesia in paediatric dentistry is generally indicated under the following conditions:
Extreme non cooperation, anxiety and fearfulness
Patients with medical conditions who are in need of significant dental treatment
Mental and physical disabilities
Patients with extensive dental needs from remote areas where access to regular dental care is not available
Allergy to local anaesthetics
Very young patients with extensive caries i.e. Nursing bottle caries.
The availability of general anaesthetic facilities to dentists and their child patients is extremely limited and the waiting lists for these services are extensive. As a result, the majority of these children, particularly those living in remote areas, have irregular and infrequent access to dental treatment and their teeth often present with caries that affects multiple surfaces. Stainless steel crowns are indicated in these children in order to restore their dentitions to a healthy state not only because of their durability and reliability but also because of their long-term effectiveness in preventing recurrent caries. Similarly in those patients who demonstrate an inability to maintain good oral hygiene because of either physical or mental disability the full coverage provided by the stainless steel crown significantly reduces the incidence of recurrent caries. Children who are on chronic doses of pharmaceutical agents for a multitude of medical conditions are also at risk for caries because many of these preparations contain large amounts of sucrose in order to make them more palatable.
The findings of Randall et al5 in their analysis of ten studies showing that stainless steel crowns demonstrated superior clinical success rates over the long term when compared with Class II restorations adds further support for the use of stainless steel crowns in all of these children. In fact if it is determined that the patient is at high risk for developing new caries in the future the dentists' use of stainless steel crowns rather than more conservative Class II restorations may be justified.
The authors believe that for children with high caries rates who match the criteria cited above, serious consideration should be given to full coronal coverage of primary molar teeth with stainless steel crowns particularly when restorative treatment under general anaesthetic is a necessity. This rationale applies even if teeth are only minimally affected by caries. The use of this crown and its effectiveness in preventing recurrent caries may further prevent or decrease the number of future treatments requiring general anaesthesia particularly since the availability of these services are limited. The risks of morbidity and mortality associated with the use of general anaesthesia are similarly reduced.
It is the authors' opinion that there is a general under-use of the stainless steel crowns in paediatric dentistry and that this can largely be attributed the lack of familiarity with the indications for their use, the procedures involved in tooth preparation and their adaptation. The intent of this review is to assist the practitioner in gaining an insight of their effectiveness, ease of use and the multitude of indications for their use in the maintenance of the integrity of the developing dentition particularly in children who exhibit a high caries risk.
Keith Titley is Professor, Department of Paediatric Dentistry, University of Toronto.
David Farkouh is a MSc candidate, Department of Paediatric Dentistry, University of Toronto.
Robert Chernecky is Senior Technician, Department of Biomaterials, University of Toronto.
Oral Health welcomes this original article.
1. Academy of Pediatric Dentistry. Special issue. Reference Manual. 21(5): 105, 1900-00.
2. Fuks AB., Ram D., Eidelman E. Clinical performance of esthetic posterior crowns in Primary molars: a pilot study. Ped. Dent. 21:445-448, 1999.
3. Academy of Pediatric Dentistry. Pediatric Dentistry Handbook. AJ Nowak ed.: 86-87, 1999.
4. Paediatric Dentistry Manual. Faculty of Dentistry, Department of Paediatric Dentistry, University of Toronto. Sigal MJ ed.: Seventh Edition:168-177, 1998.
5. Randall RC., Vrijhoef MMA., Wilson NHF. Efficacy of preformed metal crowns vs amalgam restorations in primary molars: a systematic review. J.A.D.A. 131: 337-343, 2000.