RESIN-MODIFIED GLASS IONOMER

RESIN-MODIFIED GLASS IONOMER

COMMENTARY LETTERS grams while our privatepayment and other patients may be subject to higher fees. I would appreciate clarification as to the ethic...

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COMMENTARY

LETTERS

grams while our privatepayment and other patients may be subject to higher fees. I would appreciate clarification as to the ethics of charging different fees for the same procedure in the case of prior arrangements made with insurance companies or other organizations. Thank you. William W. Weller, DDS Jacksonville, Ill.

1. American Dental Association. American Dental Association principles of ethics and code of professional conduct, with official advisory opinions revised to April 2012. www. ada.org/sections/about/pdfs/code_of_ethics_ 2012.pdf. Accessed Aug. 14, 2013.

Author’s response: My thanks to Dr. Weller for his response and for providing the opportunity to clarify the difference between the fee charged and the actual reimbursement received. Negotiating a fee discount on a case-by-case basis with

patients or with a particular carrier is not inherently problematic. What does raise concern, however, is when a dentist is increasing his or her usual treatment fee for patients who are not insured. The practical impact of such a practice is fee shifting, wherein insured patients get treatment at a lower rate but where uninsured patients are making up the difference. In an effort to promote both justice and veracity, having one across-the-board usual fee for a particular treatment is necessary. While circumstances may arise in which a dentist is willing to accept less than the established usual fee either because he or she has negotiated a lower rate of reimbursement with an insurance carrier or with a patient who may have, for example, lost his or her job,

all patients are starting out at the same baseline and the fee represents the treatment provided rather than the means or method of payment. Douglas A. Auld, DDS McAlester, Okla.

RESIN-MODIFIED GLASS IONOMER

Upon reading the “Conclusions” section of Dr. Brad Strober and colleagues’ August JADA article, “Effectiveness of a Resinmodified Glass Ionomer Liner in Reducing Hypersensitivity in Posterior Restorations: A Study From the Practitioners Engaged in Applied Research and Learning Network” (Strober B, Veitz-Keenan A, Barna JA, et al. JADA 2013;144[8]:886897), I was astounded that the authors wrote, “These findings suggest that the time, effort and expense involved in placing

1224 JADA 144(11) http://jada.ada.org November 2013 Copyright © 2013 American Dental Association. All Rights Reserved.

COMMENTARY

an RMGI [resin-modified glass ionomer] liner in RBC [resinbased composite] restorations may be unnecessary, as the representative liner used did not improve hypersensitivity outcomes.” That short-sighted comment assumes that the only reason one uses an RMGI base is to avoid “hypersensitivity.” (This writer would like to know the difference between hypersensitivity and sensitivity.) If the authors had sought out the full value of a dentin replacement liner or base in the literature, they might have encountered the work of Ruiz and Mitra,1 who detailed the following advantages to that restorative approach: dRMGI liners bond chemically to dentin and do not eventually hydrolyze as time goes by, the way dentin/resin bonds do. dRMGI liners counteract contraction stresses of overlying resin-based composite during resin polymerization. Cusp deformation, therefore, is decreased. dTooth sensitivity after tooth repair is decreased with an RMGI liner in place. dRespective coefficients of thermal expansion of tooth structure and glass-ionomer cement systems are similar. The chemical bond of glass-ionomer to tooth structure along with similar dimensional changes related to thermal challenge decrease marginal opening and leakage. dThe presence of the fluoride ion in the calcium-aluminum fluorosilicate glass filler of glass-ionomer cements decreases acid solubility of associated tooth structure, and the fluoride also has an antimicrobial effect. One other benefit of a glassionomer cement system as an “underfilling” that I have experienced since the early 1980s is

that when an enamel/RBC margin opens, years after a tooth is repaired, new caries appears to be self-limiting when the infection approaches the liner/base margin. Such defects can often be repaired simply, rather than requiring complete removal of the RBC material.2,3 The full implications of this phenomenon would make for a valuable in vitro study in a lab that has an artificial caries system. When one carefully considers the properties of RMGI cements, along with those of RBCs, the logical conclusion is that the RMGI cements are the best direct placement dentin restorative substitute we currently have, and the RBCs are the best direct application enamel replacement. The fact that the two materials have resin in common and that they chemically combine during restorative stratification gives an added attraction to this type of tooth repair. If the Practitioners Engaged in Applied Research and Learning Network is seeking another project, they might consider a survey of practicing endodontists to ascertain those specialists’ experiences and opinions of posterior Class I and Class II tooth repair with and without glass-ionomer liners or bases. Theodore P. Croll, DDS Doylestown, Pa.

1. Ruiz JL, Mitra S. Using cavity liners with direct posterior composite restorations. Compend Contin Educ Dent 2006;27(6): 347-351. 2. Croll TP. Repair of defective Class I composite resin restorations. Quintessence Int 1990;21(9):695-698. 3. Croll TP. Repair of Class I resincomposite restoration. ASDC J Dent Child 1997;64(1):22-27.

Authors’ response: We appreciate Dr. Croll’s concerns with our statements regarding lack of effectiveness for resinmodified glass-ionomer (RMGI) liners. In response to his question, we consider vital teeth as having sensitivity to cold and

LETTERS

heat and little sensitivity to air flow, and hypersensitive teeth as having an exaggerated response to cold, heat or air stimulation (we tested cold and air). Dr. Croll has provided a list of supposed advantages to the use of RMGI liners/bases in resin-based composite (RBC) restorations. We contend that none of these has been shown to be of clinical importance. Regarding RMGI chemical bond stability and the proposed degradation of resin to dentin bonds, a recent 10-year retrospective study of RMGI/glass ionomer (GI) and RBC cervical restoration found equivalent rates of retention.1 This suggests no clinical difference in bond reduction. RMGI liners are suggested to reduce contraction stress, have a coefficient of thermal expansion similar to tooth structure and be antimicrobial. These advantages should lead to better clinical performance with GI as a restoration as well as a liner. However, this appears not to be the case. A systematic review has failed to support the contention that under clinical conditions GI restorations have a cariostatic effect.2 The recent Namgung and colleagues’ study1 found that secondary caries rates for GI and RBC were similar. Unfortunately, RMGI liners lead to higher rates of bulk fracture in posterior RBC restorations. Opdam and colleagues,3 in a large retrospective study, compared the longevity of GI-closed sandwich with total-etch (no liner) RBC restorations. The GI-liner restorations had a higher failure rate overall, primarily owing to bulk fracture, and this became more prevalent with three to four years of clinical service. Odds ratios for failure were 4.08 liner versus total-etch and

JADA 144(11)  http://jada.ada.org  November 2013 1227 Copyright © 2013 American Dental Association. All Rights Reserved.