Radiographic Assessment Before Cementation—Detecting the “Misfit” of Indirect Restorations

During my Restorative Design workshop on Spear campus, I always survey the participants by asking the question, “Who uses radiographs to check the fit/misfit of the indirect restoration before cementation?” Overwhelmingly, 50-75 percent of participants use radiographs to conduct this procedure.

I have never used radiographs for this purpose. The only area that may be possible to evaluate by this technique is the interproximal—not the buccal or lingual—aspect of the tooth-restorative interface.

There are many variables that must be considered when checking the fit/misfit of the indirect restoration before cementation, which make radiographic assessment highly unpredictable—and therefore, not recommended.

These variables include:

• The horizontal and vertical angle of the x-ray beam relative to the tooth preparation finish line and the intaglio surface of the restoration at the margin. To be accurate, the x-ray beam would have to be exactly parallel to these surfaces.¹
• Improper angulation of the censor/film relative to the x-ray beam will cause distortion of the radiographic image.
• Radiographic differences in appearance of the enamel and dentin at the preparation finish line.
• Anatomic variation in tooth/root form interproximally.
• Radiographic differences in appearance of restorative materials. The relative opacity of the restorative materials is highly variable between metal, zirconia, lithium disilicate, and other glass ceramic materials and milled composite resins.
• There is no standard of what a “closed” margin looks like radiographically.
• There is questionable stability of the tooth during the try-in procedure and the manipulation that occurs while taking the radiograph.

Radiographic Assessment Before Cementation—A Literature Review

Because such a high percentage of dentists in my courses use radiographic evaluation to check for the misfit of indirect restorations, I thought I was unaware that this was a current clinical standard. I decided to do a literature review on the topic using PubMed as my resource.

There was no literature which supported using radiographic assessment for evaluation or marginal integrity.

There was one systematic review published in 2014 which examined the period 1950-2014². This review initially identified 446 potential studies for inclusion, which was reduced to 14 based on the review criteria they had established.

Six of the 14 papers were evaluating implant restorations, so only eight related to restorations on teeth. Two studies were in-vivo and only one study published by Assif D. (1985), evaluated the marginal gap of crowns to a tooth. The remaining studies were evaluating amalgam, composite, overhang of luting agents, and caries.

The conclusion of the review authors was there were no clinically relative outcomes related to the use of radiographs to evaluate restorative fit. The studies included in the review were too few and rated as low to moderate quality based on QUADAS criteria.

QUADAS is a tool to assess the quality of diagnostic accuracy studies included in systematic reviews. It is concerned with the quality of the internal and external validity of a study.

The most recent relevant article I was able to identify was by Wahle et al. (2018), which evaluated ceramic crown margins with digital radiography. They evaluated lithium disilicate, fluorapatite and metal-ceramic crown fit on a maxillary premolar.

Two radiographic angles were used to evaluate marginal gap increment of 0 to 20 µm and increasing by 20 µm to a maximum of 200 µm. Twenty-one dentists evaluated the radiographs to identify “acceptable” and “unacceptable” margins. For the purposes of this study, a marginal discrepancy greater than 80 µm was considered “unacceptable”.

The correct overall radiographic marginal assessments for all crown materials was 66 percent. Here is a breakdown relative to materials:

• Metal ceramic – 48.8 percent
• Lithium disilicate – 72.1 percent
• Fluorapatite – 76.9 percent

In addition, 78.6 percent of metal-ceramic crowns were incorrectly scored as “acceptable” (false positives) for open margins. When evaluating the other materials, 66.1 percent of lithium disilicate and 45.8 percent of fluorapatite crowns were evaluated incorrectly as “unacceptable” (false negatives) for closed margins. The authors of this study concluded that care is needed in evaluating crown margins with digital radiographs.

Final thoughts

Radiographic evaluation of indirect restorations is highly variable, and a normal radiographic appearance of a margin does not necessarily mean that the margin of the restoration is sufficient.

If anyone has read a current peer-reviewed study from a quality journal to support the practice of using radiographs to evaluate margins, I would love to hear about it.

Robert Winter, D.D.S., is a member of Spear Resident Faculty.

References:

1. Sailer BF, Graibel MA. Comparative analysis of intraoral radiographs with variation of tube angulation to detect insufficient crown margins. International Journal of Computerized Dentistry 2013; 16: 201-207.
2. Liedke GS, Spin-Neto R, DaSilveira HED, Wenzel A. Radiographic diagnosis of dental restoration misfit: A systematic review. Journal of Oral Rehabilitation 2014; 41: 957-967.
3. Wahle WM, Masri R, Driscoll C, Romberg E. Evaluating ceramic crown margins with radiography. J Prosthet Dent 2018; 119(5): 777-782.