Title	Amalgam May Not Be More Stable Than Composite Resin When Used As Rest Seat
Clinical Question	For a patient requiring a cast removable partial denture, is amalgam more stable than composite resin when used as a rest seat?
Clinical Bottom Line	There is limited evidence supporting a definitive answer. Some of the evidence is conflicting, however the only clinical study comparing amalgam with composite resin found that there was no significant difference between the stability of these materials when used for rest seats. (See Comments on the CAT below)
Best Evidence
PubMed ID Author / Year Patient Group Study type (level of evidence) 22182224 de Aquino/2011 30 individuals with RPD's and a total of 193 rest seats in either Enamel, Amalgam or Composite Resin Clinical Study Key results Application of the Pearson test (p = 0.289) found no statistically significant differences among the materials on which the rest seats were prepared. Out of 83 amalgam rest seats, 74 (82.9%) were intact and 9 (10.8%) were deemed non-intact after 2 years of regular use. Out of 54 resin composite rest seats, 50 (92.6%) were deemed intact and 4 (7.4%) were deemed non-intact after 2 years of regular use. 22173722 Pospiech/2011 60 human molars in which standardized mesial-occlusal-distal cavities were prepared. The cavities were restored with the following materials: Definite, Tetric Ceram, SureFil, Heliomolar RO, Ariston pHc, and Oralloy, and provided with a rest seat. In Vitro Study Key results Fracture analysis found that 80% amalgam rest seats showed no sign of fracture, compared to 80-100% of composite resin rest seats with either hairline or total fractures. Wear was determined by measuring loss of volume. Amalgam rest seats lost a mean of 0.056mm^3 (+/- 0.018), which was comparable to Definite (composite resin) which lost a mean of 0.058 mm^3 (+/- 0.028), but less than the remainder of composite resins tested. Margin analyses were performed before and after cycling and the difference was compared. The number of “gap-free margins” was reduced for all materials after cycling. Amalgam performed comparably to several of the composite resins tested. However, the decline in marginal quality of Definite (40%) was higher than that of amalgam. 18350944 Maeda/2008 28 patients with RPD's; 31 cingulum rest seat prepared with composite resin Clinical Study Key results There was no failure of bonded rest seats, however, some abrasion was noted in 3. Regarding periodontal measures (probing depths, bleeding on probing and tooth mobility), there was no significant difference in the post-insertion data from the baseline values for either abutments or controls. Study found that there is no risk in damaging the periodontium by using bonded composite resin cingulum rest seats.
Evidence Search	removable[All Fields] AND ((restorative[All Fields] AND material[All Fields]) OR ("composite resins"[MeSH Terms] OR ("composite"[All Fields] AND "resins"[All Fields]) OR "composite resins"[All Fields] OR ("composite"[All Fields] AND "resin"[All Fields]) OR "composite resin"[All Fields]))
Comments on The Evidence	The first clinical study analyzed rest seats for shape, rest adaptation, wear, caries, fracture and surface type. Patients were followed up once every three months for 2 years. Though there was a significant difference between enamel and restorative material for rest seats, it was found that for retentive areas, enamel was 14 times more stable than restorative material (composite resin or amalgam). For the in vitro study, rest seats were prepared entirely in restorative material. A simulation of 5 years worth of mastication was performed (1,200,000 cycles of thermo-cycling and mechanical loading). Each restoration was analyzed for fracture, wear and margin. Specimens that were fractured could not be used for wear and margin analysis (dropping the number of specimens that could be examined from 60 to 48).
Applicability	The conclusions drawn would be applicable for patients who have existing restorations or need restorations in potential rest seat areas on abutment teeth for removable partial dentures, however the evidence regarding this topic is scarce, and more research needs to be done before favoring any specific treatment modality.
Specialty	(General Dentistry) (Prosthodontics)
Keywords	rest seat, amalgam, composite resin, RPD, removable partial denture
ID#	2169
Date of submission	02/12/2012
E-mail	khanaa@livemail.uthscsa.edu
Author	Anwar Khan
Co-author(s)
Co-author(s) e-mail
Faculty mentor	Joseph Bartoloni, DDS
Faculty mentor e-mail
Basic Science Rationale (Mechanisms that may account for and/or explain the clinical question, i.e. is the answer to the clinical question consistent with basic biological, physical and/or behavioral science principles, laws and research?) None available
Comments and Evidence-Based Updates on the CAT (FOR PRACTICING DENTISTS', FACULTY, RESIDENTS and/or STUDENTS COMMENTS ON PUBLISHED CATs) by Paul Hansen (Lincoln, Nebraska) on 06/26/2012 Nice CAT. Always a great question on rest seats. Ideal vs. what we must do in the clinical setting.