JADA Continuing Education
THE CLINICAL PERFORMANCE OF LABORATORY-FABRICATED CROWNS PLACED ON FIRST PERMANENT MOLARS WITH DEVELOPMENTAL DEFECTS
MARTIN J. KOCH, M.D., D.M.D. and
FRANKLIN GARCÍA-GODOY, D.D.S., M.S.
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ABSTRACT
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Background. Young permanent molars with developmental enamel defects commonly are treated with stainless steel crowns. However, allergic reactions to nickel and chromium have been reported by some patients. The literature contains no evaluations of alternative treatments.
Methods. In a retrospective study, the authors evaluated the clinical performance of cast gold crowns and tooth-colored composite or ceramic crowns placed on first permanent molars with developmental defects in children 6 to 8 years of age. A total of 41 molars were prepared. After crown preparation, an impression was made, and crowns of cast gold, Artglass (J.F. Jelenko & Co.) composite or Empress (Ivoclar) leucite-containing ceramic were fabricated and clinically evaluated every six months for a period ranging from two to five years postoperatively (mean three years).
Results. After two to five years, all crowns were fully retained. The marginal adaptation of 39 of the 41 crowns was rated excellent, and the marginal adaptation of the remaining two crowns (both gold) received acceptable ratings. In two cast gold crowns, the margins were subgingival at cementation; the remaining 39 crowns had supragingival margins at the time of luting. By the end of the second year, all margins were supragingival. All teeth were vital and asymptomatic at all evaluation points. No secondary caries was recorded. Neither gingival inflammation nor loss of vertical dimension was recorded in any case. All crowns were well-accepted by the patients and their parents.
Conclusions. Laboratory-fabricated crowns can be used for the treatment of young permanent molars with developmental defects.
Clinical Implications. Cast gold, composite or ceramic crowns can be used successfully to treat developmental defects of first permanent molars in children.
Developmental dental defects of enamel—such as amelogenesis imperfecta, dentinogenesis imperfecta or extensive enamel hypoplasia—can undermine the occlusal surfaces of permanent teeth, producing pain and leading to dental caries. These developmental conditions also can predispose the dentition to excessive wear and loss of the tooth’s vertical dimension.
The nature and location of developmental defects does not always permit the placement of a traditional conservative restoration. In such situations in the young permanent dentition, stainless steel crowns are used commonly as a semipermanent restoration. After adjacent permanent teeth erupt to the occlusal plane, cast metal crowns then are used to replace the stainless steel crowns.
If not properly adapted, stainless steel crowns may produce open bite, gingivitis or both.1–3 Perhaps more significantly, nickel allergy has been associated with stainless steel orthodontic appliances4–6 and stainless steel crowns containing nickel and chromium.7
A previous study evaluating the retention of stainless steel crowns in primary teeth reported some adverse reactions associated with the crowns.8 It is possible that these adverse reactions were due to nickel or chromium allergy. Approximately 9 percent of female and 6 percent of male children demonstrated nickel allergy, and in another study, children 8 years of age and older with nickel-chromium crowns had a significantly higher positive patch test than children without these crowns.7 In yet another study by García-Godoy and Landry,9 the use of different cements created no gingival reactions. It may be that some types of cements interact with the crowns, producing a greater release of their components. Interestingly, the clinical performance of stainless steel crowns in permanent molars has not been reported.
The use of laboratory-fabricated crowns traditionally has not been recommended in children, owing to the crowns’ cost and the difficulty in finishing margins before permanent teeth are fully erupted—and, perhaps, also because of the fear of pulp exposures during crown preparation. However, no clinical study has shown this to be a problem of clinical significance in young permanent molars.
Gold and ceramic crowns have properties different from those of stainless steel crowns. This makes them ideal as restorations for permanent molars with developmental defects, especially in children with allergy to nickel or chromium. Occlusal adjustments in seated restorations are easy and safe. Conventional cementation might be preferable to adhesive procedures in teeth with defective enamel. In addition, crown margins often are subgingival during cementation, and this makes adhesive procedures difficult.
Although the properties of cast gold, ceramic and composite crowns are well-accepted in general, there is no recent information available on the use of any of these crowns in children. We therefore hypothesized that laboratory-fabricated crowns might perform adequately when placed in hypoplastic permanent molars in children.
Because stainless steel crowns are used routinely in primary teeth, they are assumed to perform satisfactorily also in permanent teeth. We undertook a retrospective study to evaluate the clinical performance of cast gold crowns, tooth-colored ceramic crowns and resin-based composite crowns placed on first permanent molars with developmental defects in children 6 to 8 years of age, some with nickel and chromium allergy, as no data or clinical experience in this area has been reported.
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MATERIALS AND METHODS
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During the years 1992 through 1996, a dentist (M.J.K.) at a university dental clinic (University of Heidelberg, Germany) treated 41 first permanent molars with developmental defects in 12 children 6 to 8 years of age. The dentist performed all crown preparations and cementations. Underlying defects were localized opacities (eight patients, n = 25), localized enamel hypoplasia (three patients, n = 12), or generalized hypomineralized amelogenesis imperfecta (one patient, n = 4).
The dentist prepared all teeth under local anesthesia with high-speed burs and copious amounts of water. The gingiva was gently retracted with a rubber dam. He used a modified partial crown preparation to avoid extending the outline (mainly in the proximal areas) under the rubber dam, thereby avoiding gingival bleeding and also pulp exposure.
To allow adequate retention of each temporary crown, the dentist made two dimple preparations lingually and facially on the occlusal surface. After crown preparation, he made an impression with a polyether impression material (Impregum, ESPE, Germany).
Temporary crowns were made from a chemically cured composite material (ProTemp, ESPE, Germany) and seated with an easily removed, eugenol-free temporary cement (Opotow Trial Cement, Waterpik Technologies).
Gold crowns (n = 29) were made of Degulor M (Degussa, Germany) and seated with zinc phosphate cement (Harvard Cement, Richter & Hoffmann, Germany).
Tooth-colored crowns (n = 4) were made of composite (Artglass, Kulzer, Germany) or from leucite-containing heat-press ceramic (n = 8) (Empress, Ivoclar, Liechtenstein). The dentist seated them using rubber dam isolation after etching the tooth with 37 percent phosphoric acid for 20 seconds (Email Preparator, Vivadent, Liechtenstein). After etching, he rinsed the teeth and luted them by applying Syntac II Primer, Heliobond and Tetric (all from Vivadent, Liechtenstein). The dentist silanized Empress crowns by using Monobond S (Ivoclar, Liechtenstein).
During seating of the tooth-colored crowns, the dentist used ultrasound to allow the cement to flow better, as described by Patyk and Scherer10 and Judge and Wilson.11
The dentist examined the teeth clinically every six months. In a few, but not all, cases, he took radiographs to augment the clinical evaluation in assessing the outcome of the restorations. The evaluation period ranged from two to five years postoperatively (mean = three years).
The examining dentist used five criteria to assess the crowns’ clinical performance:
- – retention;
- – marginal adaptation;
- – location of margins;
- – vitality;
- – presence of secondary caries.
The criteria are described in more detail in Table 1
. A t-test was used to evaluate the results.
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RESULTS
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Table 2 shows the results. After two to five years of service, all crowns were fully retained.
We rated the marginal adaptation of the crowns using the U.S. Public Health Service criteria, in which Alfa = excellent margins, Bravo = acceptable margins (if only one site of the margin was not excellent), Charlie = unacceptable margins (if more than one site of the margin was not excellent). The marginal adaptation of 39 of the 41 crowns was rated Alfa. Two gold crowns on one patient received Bravo ratings, which could have been improved if the crowns were polished. No crown received a Charlie rating.
In two of the gold crowns, the margins of the crowns were subgingival at baseline; the remaining 39 crowns had supragingival margins. After two to five years, all crowns showed supragingival margins.
All crowned teeth were vital and asymptomatic at all evaluation times, and no secondary caries was recorded on any tooth. Neither gingival inflammation nor loss of vertical dimension was recorded in any case.
All crowns were well-accepted by the patients and their parents. The parents preferred the ceramic and composite crowns to the gold crowns. Artglass crowns appeared to be slightly discolored at their final evaluation as compared with their baseline appearance.
Of the five criteria we used for clinical evaluation, marginal adaptation was the only one in which change was observable during the course of the study for any of the 41 crowns. Thirty-nine crowns retained their Alfa rating, while two crowns deteriorated slightly from Alfa to Bravo. The rate of change in marginal adaptation was not statistically significant according to the sign test (P = .5).
Figures 1–6 illustrate the results.
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DISCUSSION
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This study showed that laboratory-fabricated crowns can perform satisfactorily when placed on young permanent molars that have developmental defects.
From a marginal adaptation standpoint, all crowns were made (at baseline) with the gingival margins seated at the gingival level. After the crown had been in service for two to five years, the gingival margins were more supragingival than at baseline and showed more tooth structure, owing to the continuous eruption of the permanent molars. From a clinical standpoint, this did not present any problems or disadvantages, as the margins of the crowns were accessible during brushing and flossing. After two to five years of service, all crowns were well-accepted by the patients and their parents.
No secondary caries was detected around any restoration. However, the use of these crowns should be considered carefully in patients with high caries risk, especially if these patients are not likely to follow a good oral hygiene program.
Another issue to consider in future studies is the recent introduction of sonoabrasive preparation instruments (such as SonicSys, KaVo, Germany), which allow atraumatic subgingival preparation. This technique is much more conservative and may improve the success of crown preparation procedures in children.
Because this was a retrospective study with no actual "control" group, it was difficult to compare the different materials used. The sample size was small, especially for the tooth-colored restorations, and the restorations were not placed under the conditions of a randomized prospective study. Tooth-colored crowns were used only in situations in which all defective enamel could be removed, crown margins were accessible and the parents requested an esthetically acceptable treatment (Figure 3
). Gold crowns were used for teeth with more extensive defects and teeth with limited occlusal space due to wear, as well as when parents had no objections to the treatment. In this study, we were not able to analyze wear of opposing teeth, because some opposing teeth also were treated with a crown, and others already had signs of wear before the treatment (owing to the underlying developmental defect of enamel).
There are some limitations to the use of cast crowns for the treatment of first permanent molars in children younger than 10 years of age. Placement may be difficult owing to short crowns, large pulps, previous loss of enamel and subgingival placement of crown margins. The impression material must allow for good wetting of dental surfaces. Polyether impression materials (which appear to be ideal for these cases) require a long setting time. The treatment requires the fabrication of a temporary crown, and the patient must cooperate, maintain a good oral hygiene status and, preferably, have a low risk of developing caries.
From an esthetic standpoint, the use of gold crowns may be an acceptable treatment, even if the final result might give the appearance of a gold onlay, because of the supragingival margins that will occur with the continuous eruption of the permanent molar. If a ceramic crown is used and the color has been chosen properly, the supragingival margins should not offer an esthetic problem. Even if there is a slight discoloration, the esthetic result will be far superior to that rendered by a gold or stainless steel crown.
One advantage of adhesive crowns (ceramic or composite) can be a clinical situation in which the preparation will not retain a conventionally cemented restoration. The use of gold, ceramic or composite crowns may be particularly useful in patients who are allergic to nickel and chromium, as stainless steel crowns contain both of these elements. However, although gold crowns have been well-accepted in dentistry and have not been reported to have any major clinical complications, a recent study involving Degulor M high noble alloy showed the material to be cytotoxic,12 probably owing to the copper released from the alloy.13 This recent finding also may be a reason to consider the use of ceramic or composite crowns, as they are more biocompatible than both stainless steel crowns and certain gold alloys.
In this study, postoperative radiographs were not taken if there was no clinical justification for them.
A long-term, prospective, controlled clinical evaluation of these types of crowns used for this purpose in children is advisable. However, it must be noted that the literature contains no reports of short-term or long-term clinical evaluation of stainless steel crowns placed on permanent molars with developmental defects. The use of stainless steel crowns in permanent teeth with developmental defects has been assumed anecdotally to be successful.
Another consideration that has not been reported in the literature is the potential problem that a stainless steel crown preparation on permanent teeth with developmental defects may impose on the final preparation of the tooth for a cast gold, ceramic or composite crown in the future. This needs further evaluation.
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CONCLUSIONS
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Developmental defects of first permanent molars in young children can be treated by using cast gold crowns. The few ceramic and composite crowns in this study also showed excellent clinical performance.
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FOOTNOTES
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Dr. Koch is a consultant for Pediatric Dentistry, Department of Conservative Dentistry and Periodontology, Dental School, University of Heidelberg, Heidelberg, Germany.
Dr. García-Godoy is a professor and the director, Clinical Materials Research, Department of Restorative Dentistry, University of Texas Health Science Center at San Antonio, and visiting professor, Department of Conservative Dentistry and Periodontology, Dental School, University of Heidelberg, Heidelberg, Germany. Address reprint requests to Dr. García-Godoy at University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, Texas 78284.
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REFERENCES
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ABSTRACT
MATERIALS AND METHODS
