Full-Coverage Restoration for Primary Molars

Jane A. Soxman, DDS Diplomate American Board of Pediatric Dentistry

Stainless steel crowns (SSC’s) are deemed to be the most durable and reliable treatment for primary molars with multi-surface caries when the restoration should survive more than two years or the child is under six years of age.1 SSC’s are also indicated for interproximal caries extending beyond line angles, for restoration of a primary molar that is to be an abutment for a space maintainer, and following pulpotomy or pulpectomy.2

If sedation or general anesthesia are necessary to treat a child with extensive caries, stainless steel crowns have been shown to reduce the risk of repeated sedation or general anesthesia. In a study by Azadani et al., probability of survival for SSC’s was 98% by 84 months after general anesthesia. Preventive or restorative treatment other than SSC’s resulted in recurrent caries in a substantial number of patients.3

Caries risk status, particularly with high-risk children, should be considered when making decisions regarding a treatment plan in the primary dentition. Both the distal surface of the primary second molar and the occlusal surface of the first permanent molar impact the incidence of caries on the mesial surface of the first permanent molar.4 Once the distal surface of the second primary molar and the mesial surface of the first permanent molar are in contact, the mesial surface of the first permanent molar becomes a susceptible surface for carious involvement due to spread of caries from distal surface of the second primary molar. For this reason, a stainless steel crown may be indicated when restoring the mesial surface of the second primary molar in a child with occlusal caries on the first permanent and with high caries risk or severe early childhood caries. Additionally, recurrent caries around the margins of a disto-occlusal composite resin restoration in a second primary molar may result in mesial caries in the adjacent first permanent molar.

Armamentarium

  • Mirror & Explorer
  • Pre-contoured/pre-crimped SSC’s
  • Local anesthesia
  • Rubber dam with slit technique
  • #7, 8, or 8A rubber dam clamp lighted with floss for second primary molars with the first permanent molar unerupted
  • #14 or 14A rubber dam clamp for first permanent molar

Crown Selection

  • Pre-contoured SSC’s require no buccal or lingual tooth reduction.
  • If new to this procedure, measure the mesio-distal width of the primary molar with a millimeter ruler or Boley gauge to help in determining the crown size. Size 4 is the most common size.
  • For a maxillary first primary molar with unusual morphology or space loss due to interproximal caries, finding the correct size crown may be more difficult. If unable to find a crown that fits, try a crown from opposite side/opposite arch. For instance, if you cannot find a crown to fit a maxillary right first primary molar, use a mandibular left first primary molar crown.
  • With inter-proximal space loss, the mesio-distal dimension of the SSC may be decreased with Howe plier (Figure 1).
  • Crown and band contouring and crimping pliers may be used to reduce the crown size if size needed is ½ size smaller (Figure 2).

Preparation

  • #6 or #8 round carbide bur or coarse tapered round-end diamond in high-speed for 1mm occlusal reduction (Figures 3, 4).
  • If the first permanent molar is erupted and contacting the distal of the second primary molar, place a wooden wedge to separate the second primary molar from the first permanent molar, opening the interproximal area to avoid disking the mesial of the first permanent molar (Figure 5).
  • If the first permanent molar is unerupted, and the rubber dam clamp is on the second primary molar, the rubber dam is retracted with a spoon excavator while doing the distal reduction to avoid catching the bur in the rubber dam (Figure 6).
  • #170 or 169L carbide bur for interproximal sub-gingival reduction. Start on buccal or lingual surface and cut just inside the marginal ridge (Figure 7).
  • Do not have the patient bite the crown into place during the try-in. With a tight “snap” fit, removing the crown after seating will be very difficult. For try-in, place the crown over the occlusal. If the entire occlusal and marginal ridges are covered by the SSC, the crown should fit.
  • After interproximal reduction, check for ledge with explorer. A ledge will impede seating of the crown (Figure 8).
  • Bite stick for a “snap” fit with patient’s occlusal force biting on the stick (Figure 9).
  • Cement – Glass Ionomer, polycarboxylate, or *self-adhesive resin cement (dual cure and do not over-dry tooth).
  • Wet cotton tipped applicators or wet 2×2’s to remove excess cement on buccal and lingual.
  • Floss with 4–5 knots segmentally tied to remove excess interproximal cement (Figure 10).

Esthetic Crowns

Zirconia and pre-veneered stainless steel crowns offer a more esthetic alternative, but have their drawbacks. Both require more tooth reduction than a stainless steel crown, and one must prepare for a pulp exposure, particularly on a first primary molar. Both types of crowns are seated passively with digital pressure, unlike the “snap” fit of a pre-contoured SSC that is achieved with a bite stick and occlusal force. Zirconia crowns have exceptional durability and esthetics but are expensive, cannot be contoured to the primary molar and require more preparation time for placement (Figure 11). Dental insurance may reimburse more for a stainless steel crown than an esthetic crown. With bruxing, zirconia crowns do not cause excess enamel loss to occluding primary molars.5 If hemostasis cannot be achieved, zirconia is not a good choice. Blood may show through the crown (one manufacturer claims this does not occur in their crown). Zirconia crowns may be sterilized. Nu-Smile’s pink “try-in” crowns can be used to determine the correct size, avoiding contaminating the internal surface of the crown to be cemented with blood or saliva (Figure 12). Pre-veneered stainless steel crowns are stainless steel crowns with a resin facing (Figure 13). Two shades are typically available. The darker shade is usually a better match (Figure 14). These too offer better esthetics than stainless steel but are not recommended with bruxing or short clinical crowns; because the acrylic facing may fracture and chip off (Figure 15). Informed consent should include this potential with or without bruxing. Another limitation is greater removal of tooth structure to accommodate the facing and crimping is limited to the lingual surface. As with zirconia, pre-veneered stainless steel crowns are more expensive than SSC’s and require increased time for preparation.6

Selection of Zirconia Versus Pre-veneered

  • Bruxing – zirconia
  • Deep bite with short clinical crown – zirconia
  • Unable to control gingival bleeding – pre-veneered
  • Need a smaller size – pre-veneered can be crimped on lingual
  • Minimal tooth structure remaining – pre-veneered due to smaller crown size with interior dimensions

As the body of evidence grows, nonsurgical caries management techniques are gaining popularity and acceptance. This approach may not only avoid sedation in order to treat the young or uncooperative child, but also conserves tooth structure, slows or arrests the disease process, interrupts biofilm activity, and maintains pulp vitality. The Hall technique is performed with a pre-contoured SSC and without the use of local anesthesia, tooth preparation or caries removal. Criteria include no radiographic evidence of pulpal involvement and an asymptomatic primary molar. This technique has been shown to be cost-effective with high clinical and radiographic success rates when compared to traditional technique with caries removal.7,8,9,10,11,12,13 With no interproximal spacing, an orthodontic separator may be placed for a few days prior to crown placement (Figures 16, 17, 18). The airway must be protected; this technique is not recommended for a child who is uncontrollable without the use of a rubber dam. Although the occlusal may be “high” due to no occlusal reduction, this should adjust to a normal occluso-vertical dimension within 15–30 days.14

Full coverage restorations are “once and done.” Stainless steel crowns are the restoration of choice for large interproximal carious lesions, for children with multiple early childhood caries whose restorations must survive for two or more years, and for avoiding repeated sedations or general anesthesia due to recurrent caries or additional involved surfaces. Zirconia and pre-veneered crowns offer an esthetic option to stainless steel as shown with a maxillary first primary molar restored with a zirconia crown and the mandibular first primary molar restored with a SSC (Figure 19). Hall technique may provide an alternative, avoiding sedation or general anesthesia, yet providing a durable restoration that is simply performed.

Dr. Jane Soxman will be one of the featured speakers at the 2022 PEAK Track II Spring Meeting at Bedford Springs.
Go to www.pagd.org to learn more.


References

  1. Maupopome G, Yepes JF, Galloway M, Tang Q, Eckert GJ, Downey T, Vinson L. Survival analysis of metal crowns versus restorations in primary mandibular molars. J Am Dent Assoc. 2017;148:760–766.
  2. American Academy of Pediatric Dentistry. Pediatric restorative dentistry. The Reference Manual of Pediatric Dentistry. Chicago, Ill.: American Academy of Pediatric Dentistry; 2020;21:371–383.
  3. Azadani EN, Peng J, Kumar, A, Casamassimo PS, Griffen A, Amini H. A survival analysis of primary second molars in children treated under general anesthesia. J Am Dent Assoc. 2020;151:568–575.
  4. Lim LZ, Preisser J, Benecha HK, Zandona AF. Longitudinal assessment on the impact of caries status of nearby surfaces on caries progression on the mesial surface of first molars. Int J Paediatr Dent. 2020;30:775–781.
  5. Johnson-Harris D, Chiquet B, Flaitz C M, Badger, G. Wear of primary tooth enamel by ceramic materials. Pediatr Dent. 2016;38:519–522.
  6. Soxman, JA (2015) Full coverage restoration for primary molars. In: Soxman, JA (ed), Handbook of Clinical Techniques in Pediatric Dentistry, 1st edn. Wiley Blackwell, Oxford, pp. 39–50.
  7. Innes NP, Evans DJ, Stirrups DR. Sealing caries in primary molars: randomized control trial, 5-year results. J Dent Res. 2011;90:1405–1410.
  8. Ludwig KH, Fontana M, Vinson LA, Platt, JA, Dean JA. The success of stainless steel crowns placed with the Hall technique. J Am Dent Assoc. 2014;145:1248–1253.
  9. Innes NP, Evans DJ, Bonifacio CC, Geneser M, Hesse D, et al. The Hall technique 10 years on: Questions and answers. Br Dent J. 2017;222:478–483.
  10. Clark W, Geneser M, Owais A, Kanellis M, Qian F. Success rates of Hall technique crowns in primary molars: a retrospective pilot study. Gen Dent. 2017;65:32–35.
  11. Boyd DH, Page LF, Thomson WM. The Hall technique and conventional restorative treatment in New Zealand children’s primary oral health care – Clinical outcomes at two years. Int J Paediatr Dent. 2018;28:180–188.
  12. Schwendicke F, Krois J, Robertson M, Splieth C, Santamaria R, Innes N. Cost-effectiveness of the Hall technique in a randomized trial. J Dent Res. 2019;98:61–67.
  13. Midani R, Splieth CH, Mustafa Ali M, Schmoeckel J, Mourad SM, Santamaria RM. Success rates of preformed metal crowns placed with the modified and standard hall technique in a paediatric dentistry setting. Int J Paediatr Dent. 2019;29:550–556.
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