EVOLUTION AND CURRENT TRENDS IN COMPOSITE RESINS

EVOLUTION AND CURRENT TRENDS IN COMPOSITE RESINS

• CURRENT TRENDS AND EVOLUTION ON DENTAL COMPOSITES

Received for arbitration: 20/04/2007

Accepted for publication: 10/05/2007

Authors: G. Douglas R. RODRIGUEZ Associate Professor in Dental Biomaterials subject of Basic Dental Sciences, Faculty of Dentistry, University of Carabobo.

• PEREIRA S. Natalie A. Professor hired in the course of Operative Dentistry Department of Prosthodontics and Occlusion of the Faculty of Dentistry at the University of Carabobo

Abstract: 
The introduction of composite-based resin technology to restorative dentistry was one of the most significant contributions to dentistry in the last twenty year. The advantages of bonded restorations include conservation of sound tooth structure, reduction of microleakage, prevention of postoperative sensitivity, tooth reinforcement and the transmission / distribution of functional stress across the bonding interface of the tooth. Today, improvements in formulations, development of new placement techniques and the optimization of physical and mechanicals properties had made the direct composite restoration more reliable and predictable.

The main objective of this article was analyzing the advances of resin composites restoration material. Trought an exhaustive literature revision. Valuing aspect as composition, classification, phisycal and mechanical properties, manipulation and current trends of this material. 

Key words: Dental restoration materials, Composite Resins, Bis-GMA.

NTRODUCTION

The rich history associated with the development of composite resins had its beginnings during the first half of the twentieth century (Fig . 1). At that time , the only materials that had tooth color and could be used as material for aesthetic restoration were silicates . These materials had major drawbacks being the main , the damage suffered shortly be placed. ( 1) In the late 40s , acrylic resins, polymethylmethacrylate ( PMMA) replaced the silicates. These resins have a tooth -like color, were insoluble in the oral fluids , were easy to handle and inexpensive . Unfortunately, these acrylic resins have low wear resistance and very high polymerization shrinkage and very marginal leakage accordingly . ( 2)

The era of modern resins begins in 1962 when Dr. Ray . L. Bowen ( 3) developed a new type of composite material . The main innovation was the matrix resin Bisphenol -A- glycidyl methacrylate ( Bis -GMA ) and a silane coupling agent or between the resin matrix and the filler particles . Since then , composite resins have witnessed numerous developments and its future is even more promising , since they are investigating prototypes that exceed their main shortcomings , especially to resolve the polymerization shrinkage and stress associated with this

COMPOSITE RESINS

According Anusavice , (5) three dimensional composites are combinations of at least two chemically different materials , with a different interface , yielding properties superior to those with constituents individually.

Dental composite resins are a complex mixture of polymerizable resins mixed with particles of inorganic fillers . To attach the filler particles to plastic resin matrix , the filler is coated with silane, a connection or coupling agent . Other additives included in the formulation to facilitate the polymerization , to adjust the viscosity and improve the radiographic opacity.

Composite resins are modified for color, translucency and opacity, to thereby imitate the color of natural teeth , making them the most aesthetic direct restoration material . Initially , composite resins are indicated only for aesthetic restoration of anterior sector. Later, thanks to advances in materials , the indication was extended to posterior . Among the advances of composite resins , improved properties such as wear resistance , handling and aesthetics are recognized . ( 6)

Similarly, adhesive techniques have been refined so that the adhesion between the composite resin and the tooth structure is more reliable , reducing marginal leakage and secondary caries . Furthermore, composite restorations being adhesive to tooth structure cavity preparations allow more conservative , preserving the valuable dental structure. However , despite all these advantages, the placement of composite resins is a sensitive technique and requires more time placement , and to be controlled factors such as humidity of the operative field and polymerization shrinkage. ( 7)

Composite RESIN COMPOSITION

The Basic Structural Components of Composite Resins son (5.8 )

1. Matrix : Material plastic resin That form of a continuous phase.

2. Filling: Particles / reinforcing fibers Forming A dispersed phase.

3. Agent connection or coupling , which favors the union of the filling with the matrix ( Known As Silano ) .

4. activator system - the polymerization initiator

5. Pigments They allow the Get Color Such teeth .

6. polymerization inhibitors , which extend the life of storage and increase the Working Time .

Resinous matrix : This consists of aliphatic or aromatic monomers dimethacrylate . The most commonly used base monomer over the past 30 years has been the Bis -GMA (Bisphenol -A glycidyl methacrylate ) . Compared with methylmethacrylate , Bis- GMA has higher molecular weight which implies that their polymerization shrinkage is much lower, also shows less volatility and less diffusivity into tissues. (9)

However , high molecular weight is a limiting feature as it increases its viscosity , tack and leads to an undesirable rheology that compromise the handling characteristics . Furthermore, in common polymerization conditions, the conversion of Bis -GMA is low. (10) To overcome these deficiencies , low viscosity monomers such as TEGDMA ( triethylene glycol dimethacrylate ) are added . Currently the Bis -GMA / TEGDMA system is one of the most used in composite resins. (11 ) In general this system shows relatively satisfactory clinical results , but there are still properties that need improvement , such as resistance to abrasion. ( 12)

On the Other Hand , the molecule Bis -GMA , has two hydroxyl groups which promote water sorption . An Excess water sorption in Resin Has Negative Effects on Properties and PROMOTES ITS A Possible hydrolytic degradation. ( 13) CURRENTLY monomers Less viscous As the Bis - EMA6 (Bisphenol A dieter Polyethylene glycol dimethacrylate ) , have been incorporated into Some Resins , What causes a reduction TEGDMA . The Bis - EMA6 possesses molecular weight and Mayor Fewer units have double bonds by weight , in consequence produce a reduction of polymerization shrinkage , gives a more stable matrix hydrophobicity Also mayor, which decreases its sensitivity and Alteration Of The humidity . (14)

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