Resident: Cho
Author(s): Burgess et al.
Journal: Pediatric Dentistry
Year. Volume (number). Page #’s: 2002. 24. 465-479.
Major topic: resin-based composite restoration
Type of Article: Literature Review
Main Purpose: To review current posterior resin-based composite products
Findings:
Compomers or polyacid modified composite resins:
A compomer is a polyacid-modified, resin-based composite with constituents derived from composite and glass ionomer. They contain etchable glass fillers that release fluoride. Less wear resistance and mechanical than composite resin, but the fluoride release and uptake are greater and it is easy to use.
Resin-based composite composition and improvement:
Resin-based composite consists mainly of a resin matrix and inorganic filler particles. The resin matrix is made up of resin monomers and initiator/catalyst system for polymerization. Most common monomers are bis-GMA and urethane dimethacrylate (UDMA). The filler particles are silicon dioxide based. Macrofilled developed in 1960s range from 10-100um. Microfilled developed in 1970s average less than 0.1um and have extremely smooth surface but lower fracture toughness and mechanical properties. Midsize-filled particles range from 1.0-10um. Minifilled particles range from 0.1um-10um, which have high strength and better polish than midsize-filled. In the 1980s, hybrids containing midsize-filled or minifilled and microfilled particles were made to be used in posterior bearing surfaced.
In the past, resin based composites (RBC) required mixing and were chemically activated. Now, resin-based composites are visible-light cured, single-paste, no mixing required, have fewer voids, greater strength, better color stability, and higher surface polymerization rates than chemically activated RBC. With present-day RBC, polymerization shrinkage ranges from 2%-3%. Shrinkage of the composite resin transfers stress to the walls of the cavity and can tear the adhesive bond to the tooth or pull opposing cusps together by deforming the tooth. Shrinkage of the RBC can subsequently cause post-op sensitivity, increased microleakage, staining, and recurrent caries.
The current American Dental Association Council of Scientific Affairs recommends that posterior resin-based composites should be radiopaque.
Flowable resin-based composite:
Flowable RBC’s have 37%-53% less filler volume compared to conventional minifilled hybrids. In a study conducted comparing flowables with minifilled hybrids, flowables had inferior mechanical properties. Flowables are recommended only in low-stress areas or very conservative occlusal restorations. Flowable RBCs are recommended as a liner of proximal box for class II restorations in order to adapt to surface irregularities. However, no clinical trials have been yet to be reported on the superiority of this technique compared to using only a RBC.
Packable resin-based composite:
“Packable” or “condensable” RBCs were introduced with the expectation that they would handle or condense like amalgam. These RBCs had high filler loading. Leinfelder and others have reported that overall, the mechanical properties of packable composites are not substantially better than most conventional minifilled hybrids. Packable composites do not polish as well as conventional RBC.
Clinical trials:
The results of clinical trials using resin composite as a direct restorative material for posterior restorations have shown increasing success with newer more highly filled products.
Key points/Summary: Composites and their accompanying adhesives are unforgiving compared to amalgam. With low- to moderate-caries-risk patients, resin-based composite should be the initial material used to restore a small carious lesion in the posterior region. Flowable or hybrid RBC would be ideal in this situation. Hybrid or packable RBC is indicated for small to large posterior restorations. Compomers should be limited to Class III or V restorations in the permanent dentition.
Assessment of Article: Great article! Very good overview how composite properties have changed over time and acknowledges that more research needs to be conducted using current composite materials. At the end of the article noted that oftentimes clinical trials are inaccurate due to incorrect sample size, no power analysis, and materials and methods were not listed.
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