SDF Action in Proximal Caries Lesions

Written by: Drs. Theodore P. Croll, Joel H. Berg, Gerald A. Ferreti, and Steven R. Jefferies



Silver diammine fluoride (SDF) solution is easily applied to caries lesions that meet the eye of the dentist. However, lesions that develop on approximal surfaces of contacting posterior teeth and are detected radiographically pose a unique challenge. Croll and Berg1,2 have suggested the use of soft dental picks dipped in 38% SDF solution to soak such caries lesions to attenuate progression of the caries infections. Since 2015, we have much bite-wing radiographic evidence that the soft dental pick SDF application method is successful in abating the progress of beginning Class II caries lesions. 

To show photographic efficacy of our method, an extracted third molar was abutted in dental stone, against a newly exfoliated, primary second molar that had a carious mesial surface.2 A segment of shoelace, to simulate the gingival papilla, was placed in the “interproximal” site. We then inserted an SDF-soaked soft dental pick and left it in place for 2 minutes. The third molar was then cut away, and the caries lesion was photographed before and after several millimeters of the tooth surface was trimmed away. That way, the depth of SDF penetration could be assessed. Fluoride varnish was not used in this demonstration. This report documents a similar experimental model with other extracted teeth using different steps in the procedure.


An extracted maxillary primary first molar that had a large distal surface caries lesion (Figure 1) and a smaller mesial surface caries infection. The tooth was embedded in Mortite Weatherstrip and Caulking Cord (Thermwell Products Co, Inc) with the carious distal surface abutted firmly against a proximal surface of an extracted third molar. With a thick cloth shoelace occupying the interproximal space to simulate the gingival papilla, the SDF/fluoride varnish procedure was achieved as follows:

Figure 1. Primary molar with large distal caries lesion.

Figure 2. Examples of soft dental picks coated with silver diammine fluoride (SDF) solution.

Figure 3. Molar embedded in Mortite Caulking and abutted against the third molar. The pick was inserted, and the sluiceways were painted with more SDF.

Figure 4. After 60 seconds, fluoride varnish was applied, and the system was untouched for about 60 seconds.

Figure 5. The primary molar was tipped backward in soft caulking material.

  • About 1 to 2 cm of a soft dental pick was immersed in 38% SDF in a dappen dish. The tip was observed to be covered with fluid like the ones pictured in Figure 2.
  • The pick was then inserted into the “interproximal space” such that a small section of the tip extended beyond the contact space. A small applicator painted extra SDF solution all along the sluiceway to ensure ideal saturation of the caries lesion (Figure 3). The pick was moved in and out slightly several times to assist the spread of the SDF over and into the caries lesion physically and by capillary action.
  • After 60 seconds, the treatment field was blanketed with 5% fluoride varnish, and the experimental model was left untouched for 3 minutes (Figure 4). (This step differs from the prior laboratory demonstration.)2
  • The primary molar was then tipped back into the soft Mortite caulking base (Figure 5), removed, and photographed (Figure 6).
  • Using coarse aluminum oxide discs, about 3 mm of the distal tooth surface was trimmed away (Figure 7). An occlusal view shows the amount of trimming (Figure 8).
  • Figure 9 demonstrates deep black coloration of the caries lesion, indicating the amount of penetration achieved by the 38% SDF fluid.

Figure 6. An SDF-soaked caries lesion with a fluoride cover in place.

Figure 7. Fluoride varnish was rinsed away, and aluminum oxide abrasive discing is shown.

Figure 8. The mesial surface was reduced about 3 mm.

Figure 9. SDF penetration deep into the caries lesion.

Figures 10 and 11. The 5-year-old’s left primary molars were treated with SDF.

Figures 12 and 13. Left primary molars, photographed 6 months after SDF treatment.

Figure 14. Comparative bite-wing films over 29 months.

This exact procedure was completed for the 4 left primary molars in September 2020 for a 5-year-old boy, requiring no local anesthetic injections (Figures 10 to 13). Photographs of the 4 treated molars were recorded on March 23, 2021 (Figures 12 and 13). The black SDF stain was apparent in the photographs but not consequential cosmetically. Bite-wing radiographs in September 2020, March of 2021, and February 2023 revealed no obvious enlargement of the proximal radiolucencies (Figure 14). Observation of the successive bite-wing radiographs shows that the caries lesions had not progressed radiographically in 29 months. The mother reported that she had flossed her son’s teeth nightly before she brushed them at bedtime.


The findings we observed in the 7-year-old over 29 months are consistent with those observed in the senior author’s child and teen patient population since dental soft pick SDF insertion was started in 2016.1-7 A review article examined the effect of SDF on microbial activity in caries lesions.8 Not only does the soft dental pick interproximal SDF insertion method work, as evidenced by radiography, but this laboratory demonstration, by physical observation, also gives evidence of the effectiveness of that treatment. It is noteworthy that successful chemical attenuation of the caries lesions in this patient occurred with only one SDF application. Frequency of subsequent applications, we believe, should be customized for each patient depending upon flossing habits and ongoing caries susceptibility.

We believe the fluoride varnish coating, after application of the SDF, not only shields the SDF from dilution by saliva, prolonging its action, but also has a usual remineralizing effect on all associated enamel surfaces. In practice, we consider it critical for the dentist and clinical staff to instruct patients and parents about the importance of daily flossing so that the interproximal acid challenge to proximal tooth surfaces is eliminated or at least minimized. How flossing is achieved also needs to be taught to older children and teens, and parents need to be shown how to floss younger children until those youngsters have the manual dexterity and understanding to do the job for themselves. That commonly occurs between 9 and 11 years of age. Vivid, large photographs of what flossing accomplishes, and what non-flossing leads to, are also quite helpful in this preventive dentistry teaching quest.

Fair criticism of our experimental model and observations of the depth of penetration of the SDF liquid could be that the extracted tooth was drier than a caries lesion in a tooth in the mouth. SDF in a wetter tooth and lesion would probably take a longer time to penetrate so deeply into tooth structure. The fluoride varnish coating protecting the SDF action perhaps affords that additional time. This question could be answered by an in vitro study with saliva or an artificial saliva-soaked extracted tooth.


1. Croll TP, Berg JH. Delivery of fluoride solutions to proximal tooth surfaces. Part II: Caries interception with silver diamine fluoride. Inside Dentistry. 2017;13(9):56–8. 

2. Croll TP, Berg JH. Delivery methods of silver diammine fluoride to contacting proximal tooth surfaces and history of silver in dentistry. Compend Contin Educ Dent. 2020;41(2):84–9. 

3. Croll TP, Berg JH, Donly KJ. Silver in medicine and dentistry. Inside Dentistry. 2020;16(10):35-40. 

4. Croll TP, Berg JH, Donly KJ. SDF saturation of carious proximal tooth surfaces. Dent Today. 2021;40(3):64–5.

5. Croll TP, Berg JH. Radiographic verification of silver diammine fluoride action on proximal dental caries lesions in a teenager. Dent Econ. 2021;111(5):52–3. 

6. Croll TP, Berg JH, Christensen GJ. SDF for managing open gingival floor margins in Class II restorations. Inside Dentistry. 2021;17(5):20–4. 

7. Croll TP, Berg JH. SDF application on posterior contacting axial surfaces in orthodontic patients. Dental Economics. 2023;113(5):38–9. 

8. Zhang JS, Chen Z, Chu CH, Yu OY. Effect of silver diamine fluoride upon the microbial community of carious lesions: A scoping review. J Dent. 2023;134:104554. doi:10.1016/j.jdent.2023.104554 


Dr. Croll is clinic director of Cavity Busters Doylestown in Doylestown, Pa; adjunct professor of pediatric dentistry at the University of Texas Health Science Center at San Antonio (Dental School); and clinical professor of pediatric dentistry at Case Western Reserve School of Dental Medicine. He can be reached at 

Dr. Berg is Professor Emeritus and former Dean of the University of Washington School of Dentistry. He can be reached at

Dr. Ferretti is the Anne Hunter Jenkins Endowed Master Clinician in Pediatric Dentistry and Orthodontics and chief of dentistry at Rainbow Babies and Children’s Hospital and professor, chair, and program director of pediatric dentistry at Case Western Reserve School of Dental Medicine. He can be reached at

Dr. Jefferies is a guest researcher in the Department of Applied Materials Science at Uppsala University in Uppsala, Sweden. He can be reached at

Disclosure: The authors report no disclosures.