May I Do An Amalgam?
Dr. Arlene Koloma, Pedodontist
As a student in dental school, one of the first things we are taught is conservation of tooth structure. We were taught to memorize this rule and apply it on a daily basis- first on our typodonts and then on our patients. I was thus very surprised when I started my pediatric dentistry training and I saw so many stainless steel crowns while doing hygiene checks. Maybe they didn't learn the same rules I did, I thought to myself. As a neophyte during my first week in the clinic, the thought of placing a stainless steel crown petrified me. After all, we prepared so many more amalgam restorations than crown preparations in dental school. Furthermore, preparing a crown took so much longer with more steps along the way which also allowed more room for error. There were enough variables in treating children that I was determined to delay the procedure for a stainless steel crown for as long as possible.
My first patient for restorative treatment was in the chair and I proudly told the floor instructor that I was going to do a MO amalgam on tooth "I". I was relieved that I was going to do a procedure that I was familiar with for my first operative treatment. After all, I was nervous enough having a child in the chair! My relief was short lived as my instructor then informed me that I was going to do a stainless steel crown on the tooth instead. I looked at my assistant and then at my four year old patient in the chair. They both seemed to look at me with compassion as if they knew what I was thinking. After administering the anesthetic, I attempted to place the rubber dam. My instructor finally came over and placed the rubber dam probably fearing that so much time had elapsed that the anesthetic was wearing out! I asked my assistant for a selection of the diamond burs that I faithfully used for crown preparations in dental school. My assistant gave me a blank stare, shook her head and proceeded to the supply room. She returned and told me that we had two patients waiting. I rather timidly took hold of the handpiece and started preparing the tooth knicking the rubber dam repeatedly. After completing my axial reductions and checking the occlusion, I was ready to place the restoration. I then attempted to try the crowns my assistant handed me but none seemed to fit. Despite my efforts to apply my textbook knowledge in this situation, my attempts were futile. I trimmed, I contoured and I crimped repeatedly and the crowns were either too short or would just wobble on the tooth. The instructor came over to check to see how we were doing. He seemed perplexed to see the same patient in the chair. He looked even more amazed when he saw the twenty or so crowns on the table. I showed him my preparation and I told him I just could not get the crown's margin to be flush with the tooth's margin. He smiled, asked one of the second year residents to see my next patient, sat down and showed me how to do a stainless steel crown ... the right way. Throughout my residency, my stainless steel crown preparation with the chamfer margin became a private joke between us.
Humphrey introduced stainless steel crowns to pediatric dentistry in 1950. These preformed crowns have been one of the most useful materials for the restoration of primary teeth. Since then many studies have been done as to the choice of restoration between amalgams and stainless steel crowns. In a clinical study conducted by Braff in 1975, a total of 79 stainless steel crowns and 150 multisurface amalgams were placed in 74 children by one pediatric dentist in private practice. The restorations were followed from placement (mean age of child was 4.2 years) until the the teeth were either exfoliated, extracted or the patient did not return for care. In 1975, Braff determined success of the restoration by lack of replacement need of the first restoration placed. Using this criteria, he reported a success rate of 70% for crowns and 11% for amalgams. He thus concluded stainless steel crowns were superior to multisurface amalgam restorations in primary molars. When taking retreatment into consideration, he suggested the crowns were more economical. Another study by Dawson and his colleagues in 1981 was completed to compare the lifespan of stainless steel crowns and two surface amalgams. In this retrospective study, there were 280 restorations in 114 patients. The average lifetime of the crowns for first and second primary molars was 40.2 months and 38.2 months. In contrast, the average lifespan of the Class II amalgams was 22.9 months for first molars and 22.7 months for second primary molars. Prior to the age of 8 years, 71.4% of class two amalgams needed replacement while 12.8% of first molars and 11.8% of second primary molars which were crowned needed to be replaced. It was determined that the stainless steel crown was the restoration of choice for primary molars, especially for multisurface restorations in the first molar before the eruption of the first permanent molar. A data pool was collected in a case history study (Gordon 1978, Lilienfeld and Lilienfeld 1980). This data pool, consisting of 2229 restorations in 226 pediatric patients, was used to study the durability and lifespan of a restoration and predict long range success of these restorations in primary molars. Observations for amalgam and stainless steel crown restorations were made by Messer and Levering (1988). 331 stainless steel crowns and 1898 amalgams were studied. The data pool enabled Messer and Levering to statistically show that crowns placed in children age 4 or younger demonstrated a success rate approximately twice that of Class II amalgams, for each year up to 10 years of service.
So when is a stainless steel crown the preferred form of treatment? First of all, stainless steel crowns are used when primary or young permanent teeth have extensive decay. Primary teeth with decay on three or more surfaces and primary teeth where decay has encroached and extended past the line angles are examples. Because of the anatomy of the first primary molar, those with mesial interproximal decay are included in this group. Their anatomy does not allow for sufficient support of MO restorations. Stainless steel crowns are also valuable for restoring primary or permanent teeth which are hypoplastic. Furthermore, those teeth affected by conditions such as dentinogenesis imperfecta and amelogenesis imperfecta need full coverage for their restoration. The stainless steel crown is also used for individuals who for one reason or another have significant difficulty with their oral hygiene regimen and placement of other restorative materials would probably be unsuccessful. Primary teeth that have undergone pulpotomy or pulpectomy procedures also are candidates for stainless steel crowns. Stainless steel crowns are also used when needed as an abutment for space maintainers or prosthetic appliances. In individuals who have a high caries rate, the stainless steel crown can also be used preventively against recurrent caries in teeth that have amalgam restorations. When a child bruxes his teeth severely, the child may lose his interarch vertical dimension or the child may have pulp exposure and a stainless steel crown may be needed in these cases. Finally, the stainless steel crown may be used as a temporary restoration for a tooth that is fractured.
The following is the general procedure for tooth preparation, crown selection and placement of stainless steel crowns. Adaptations may be made to suit each practitioner's needs. First, the occlusion is evaluated bilaterally. A rubber dam is then placed following local anesthetic administration. Wooden wedges may then be placed to depress the rubber dam, protect the gingiva and the rubber dam from the bur and improve access. The decay is first removed with a No. 330 bur in the highspeed handpiece and then with a large round bur in the slow speed handpiece. (This is in reverse to the amalgam preparation.) Reduction of the occlusal surface is next with a No. 169L or tapered thin diamond. Depth cuts of 1.0-1.5 mm are made on the occlusal grooves. The occlusal surface is then reduced by 1.5 mm following the inclines of the cusps. Proximal reduction then occurs with the same bur where contact is broken gingivally and buccolingually. There is slight convergence of the proximal walls occlusally. The margin for a stainless steel crown preparation is feather edge. All line angles should be slightly rounded and the occlusobuccal and occlusolingual line angles are beveled at a 30-45 degree angle to the occlusal surface. This beveling is restricted to the occlusal third of the crown and is all that is necessary for the buccal and lingual reduction.
Crown selection is the next step. There are two types of stainless steel crowns frequently used. Pretrimmed crowns (Unitek Stainless Steel Crowns, 3M Co., St. Paul, MN; and Denovo Crowns, Denovo Co. Arcadia, CA) are festooned and follow the line parallel to the gingival crest. These crowns, which have straight sides, will need contouring and some trimming. Precontoured crowns (Ni-Chro Ion Crowns and Unitek Stainless Steel Crowns, 3M Co., St. Paul, MN) are festooned and precontoured. The trimming and contouring needed is minimal, if at all. If trimming of these crowns is necessary, one must be careful to recontour the crown as trimming will cause loss of the existing precontour and the crown will have a larger circumference and thus fit more loosely. The aim for the proper crown is to select the smallest crown that can be seated on the tooth and for the proximal contacts to be re-established. The crown is seated on the lingual first and then pressure is applied buccally. Resistance should be encountered as the crown is seated over the buccal bulge. Adjacent marginal ridge heights should be at the same level. If there is a discrepancy in marginal ridge heights, the following situations may exist. The selected crown may be too long , a gingival ledge may be present, contact may still exist between the adjacent teeth or there may be inadequate occlusal reduction. If the crown is too long or overcontoured, considerable blanching will occur. The crown should be trimmed 1 mm into the gingival sulcus. To determine this, place the crown on the tooth and mark the level of the crest of the gingiva on the crown. Trim the crown 1 mm below this mark with the crown's margins trimmed parallel to the contour of the gingiva. Contour the crown with a No. 114 ball and socket pliers or a No. 137 Gordon pliers. Contouring consists of curving the gingival third of the crown to reduce the marginal circumference of the crown. Finally, the crown is crimped with the 137 pliers or the No. 800-417 crimping pliers. This crimping is done for the entire circumference of the crown at a length of 1 mm. The completed contouring and crimping will ensure a tightly fitting crown. The explorer is then used to check the fit of the crown on the tooth. The rubber dam is then removed so the final check for occlusion can be performed. The crown is then polished with a heatless stone at a 45 degree angle to make sure the margins are smooth and slightly thinned. A rubber wheel is then used for final polish. The tooth is dried, the crown is filled approximately two thirds with cement and cemented. Recommended cements are a zinc phosphate, polycarboxylate or glass ionomer cement. The excess cement is removed with an explorer and a knotted piece of floss is used to ensure all cement is removed interproximally. Occlusion is checked once again bilaterally.
When placing full coverage restorations on permanent teeth, we are able to check our margins on the die and thus can be quite confident about the placement and adequate adaptation of our margins. When we place stainless steel crowns, however, we do not have this device available to check our margins. There are two principles that we follow to ensure our margins are well adapted to the existing tooth. These two principles were described by Spedding and they are (1) crown length and (2) shape of the crown's gingival margins. The stainless steel crown should extend slightly apical to the tooth's height of contour which in primary teeth is just above the gingival crest. Therefore when the margins of the crown approximates the greatest diameter of the tooth (the heights of contour) the space between the tooth and the restoration is minimal and close adaptation of the crown to the tooth can be accomplished. The shape of the gingival margin of the crown is the other principle. The proper outline for the buccal and lingual gingiva for second primary molars is similar to a smile. The buccal gingiva of the first primary molar is that of a stretched out S in a horizontal position. The margin of the lingual gingiva of the first primary molars resembles a smile. The proximal contours of the primary teeth approximates that of a frown. These shapes aid greatly when trimming stainless steel crowns to allow for superior marginal adaptation.
So now you are an expert at placing stainless steel crowns on primary teeth. The next step is convincing the parent that his or her child needs a crown. Often it is a task in itself to convince the parent that the child needs treatment on the tooth since the baby tooth is going to fall out anyway. Then we must explain the important function of the primary tooth is to hold space for the permanent tooth underneath until it erupts. Then once they understand that they will ask why can't a filling be placed in the tooth since it won't be present forever anyway. Then you must explain the cost-effectivenss of the crown and why it is the preferred choice of treatment. More often than not, when a patient comes in for emergency treatment or when I notice a missing restoration it is that of a multisurface amalgam. Now, however, there is pulpal involvement as well. Due to the structure of the tooth, adequate retention was not possible and the filling was displaced. Now the tooth needs a pulpotomy and a stainless steel crown at best or perhaps an extraction and a space maintainer if the tooth cannot be saved. The child then needs to be treated twice for the same tooth. Thus it would have been more cost and time efficient to the parent to have treated the tooth with a stainless steel crown at the first appointment. Most importantly, the child would not have to undergo treatment twice on the tooth. Redoing restorations repeatedly is definitely not impressive to your patients.
I have shared the story of my first personal adventure with stainless steel crowns repeatedly in hopes that others will in turn be encouraged to use this material in their restorative armamentarium for children. I did everything wrong at my first attempt at a stainless steel crown procedure and now can do so with much greater ease. Now if only someone could simplify the procedure for full veneer fabrication for me!
Dr. Arlene Koloma, Pedodontist
- Braham RL, Morris ME:
- Textbook of Pediatric Dentistry, 2nd ed. Baltimore, Williams and Wilkins, 1985, pp 551-554.
- Braff MH:
- A comparison between stainless steel crowns and multisurface amalgams in primary molars. J Dent Child 42:474-78, 1975.
- Dawson LR, Simon JF, Taylor PP:
- Use of amalgam and stainless steel restorations for primary molars. J Dent Child 48:420-22, 1981.
- Gordon JE:
- Epidemiological insights on malnutrition. J Clin Nutr 31:2340-44, 1978.
- Humphrey WP:
- Use of chronic steel in children's dentistry. Dent Surv 26:945-94, 1950.
- Levering NJ, Messer LB:
- The durability of primary molar restoration: I: Observations and predictions of success of amalgams. Pediatr Dent 10:74-80, 1988.
- Lilienfeld AM, Lilienfeld DE:
- Foundations of Epidemiology, 2nd ed. New York, Oxford University Press, 1980 chapter 8.
- Messer LB, Levering NJ:
- The durability of primary molar restorations: II. Observations and predictions of success of stainless steel crowns. Pediatr Dent 10(2):81-85, 1988.
- Pinkham JR, Casamassimo PS, Fields HW, McTigue DJ, Nowak A:
- Pediatric Dentistry: Infancy Through Adolescence, 2nd ed. Philadelphia, WB Saunders, 1994, pp 312-317.
- Spedding RH:
- Two principles for improving the adaptation of stainless steel crowns to primary molars. Dent Clin N Am 28(1):157-175, 1984.