Dental composite
Synthetic resins evolved as restorative materials since they were insoluble, of good tooth-like appearance, insensitive to dehydration, easy to manipulate and inexpensive.
Composite resins are most commonly composed of Bis-GMA and other dimethacrylate monomers (TEGMA, UDMA, HDDMA), a filler material such as silica and in most applications, a photoinitiator.
[4] The first light-curing units used ultra-violet light to set the material, however this method had a limited curing depth and was a high risk to patients and clinicians.
It was decided, after further research, that this type of composite could be used for most restorations provided the acid etch technique was used and a bonding agent was applied.
[5] Initially, resin-based composite restorations in dentistry were very prone to leakage and breakage due to weak compressive strength.
The dentist should place composite in a deep filling in numerous increments, curing each 2–3 mm section fully before adding the next.
Modern techniques vary, but conventional wisdom states that because there have been great increases in bonding strength due to the use of dentin primers in the late 1990s, physical retention is not needed except for the most extreme of cases.
Primers allow the dentin's collagen fibers to be "sandwiched" into the resin, resulting in a superior physical and chemical bond of the filling to the tooth.
Modern bonding techniques and the increasing unpopularity of amalgam filling material have made composites more attractive for Class II restorations.
Opinions vary, but composite is regarded as having adequate longevity and wear characteristics to be used for permanent Class II restorations.
Whether composite materials last as long or have similar leakage and sensitivity properties when compared to Class II amalgam restorations was described as a matter of debate in 2008.
[10] Glass fillers are found in multiple different compositions allowing an improvement on the optical and mechanical properties of the material.
Matrices such as BisHPPP and BBP, contained in the universal adhesive BiSGMA, have been demonstrated to increase the cariogenicity of bacteria leading to the occurrence of secondary caries at the composite-dentin interface.
BisHPPP has furthermore been shown to regulate bacterial genes, making bacteria more cariogenic, thus compromising the longevity of composite restorations.
[citation needed] An initiator package (such as: camphorquinone (CQ), phenylpropanedione (PPD) or lucirin (TPO)) begins the polymerization reaction of the resins when blue light is applied.
Final restoration is difficult to polish adequately leaving rough surfaces, and therefore this type of resin is plaque retentive.
Designed to decrease clinical steps with possibility of light curing through 4-5mm incremental depth, and reduce stress within remaining tooth tissue.
Polymerization is accomplished typically with a hand held curing light that emits specific wavelengths keyed to the initiator and catalyst packages involved.
Indications include: the restoration of class I, II and III and IV where aesthetics is not paramount, and the repair of non-carious tooth surface loss (NCTSL) lesions.
Compared to universal composite, flowables have a reduced filler content (37–53%) thereby exhibiting ease of handling, lower viscosity, compressive strength, wear resistance and greater polymerisation shrinkage.
Contraindications include: in high stress-bearing areas, restoration of large multi-surface cavities, and if effective moisture control is unattainable.
Unlike flowable composite, they exhibit a higher viscosity thereby necessitating greater force upon application to 'pack' the material into the prepared cavity.
Indirect composite is cured outside the mouth, in a processing unit that is capable of delivering higher intensities and levels of energy than handheld lights can.
As a result, they are less prone to shrinkage stress and marginal gaps[28] and have higher levels and depths of cure than direct composites.
[9] According to a 2012 review article by Demarco et al. covering 34 relevant clinical studies, "90% of the studies indicated that annual failure rates between 1% and 3% can be achieved with Class I and II posterior [rear tooth] composite restorations depending on the definition of failure, and on several factors such as tooth type and location, operator [dentist], and socioeconomic, demographic, and behavioral elements.
"[31] This compares to a 3% mean annual failure rate reported in a 2004 review article by Manhart et al. for amalgam restorations in posterior stress-bearing cavities.
Reclassifying repairable minor defects as successes rather than failures is justifiable: "When a restoration is replaced, a significant amount of sound tooth structure is removed and the preparation [i.e. hole] is enlarged".
[28] Another study concludes that although there is a lower failure rate of composite inlays it would be insignificant and anyway too small to justify the additional effort of the indirect technique.
[36] Also in the case of ceramic inlays a significantly higher survival rate compared to composite direct fillings can not be detected.
[37] In general, a clear superiority of tooth coloured inlays over composite direct fillings could not be established by the review literature (as of 2013).
