From Amalgam to Dental Composites: The Evolution of Pediatric Restorative Dentistry

Dental amalgam fillings were frequently used in paediatric dentistry due to its simple technique, moderate moisture control and low cost. (Fuks, 2002). Up until the last decade, extensive research about the hazards of the mercury content in amalgam have developed concerns about murcury toxicity. (Fuks, 2002). Those apprehensions together with advancements in tooth-colored materials raised concerns on the use of amalgam restorations in pediatric dentistry. (Fuks, 2002).

This led to changes in the utilization of amalgam in dental communities, and to the transition to use tooth-colored fillings as alternative materials for carious teeth restoration (Zwicker et al., 2014) such as dental composite, compomers, Glass Ionomer cement (GIC) and resin modified GIC. (Zwicker et al., 2014).

In this paper however we are going to focus on dental composite and compomers composition, classifications and their applications in paediatric dentistry.

History of Dental Composite Restorations

In 1936, the use of poly(methylmethacrylate) (PMMA) as a denture material was first recorded. (Chan et al., 2010). In 1960s where R. L. Bowen led the invention of composites from Bis-GMA (bisphenol A-glycidyl methacrylate). (Rueggeberg, 2020).

Recently, the popularity and predictability of dental composite resin material have increased. (Velo et al., 2016). Surpassing the esthetics of other dental fillings with preservation of tooth structure in relative to indirect fillings, ability to repair and lower cost comparatively. (Fagundes et al., 2006). Made composite fillings the preffered choice of restorative material. (Fagundes et al., 2006).

Composition of Dental Composite

Classically, a resin composite is composed of three major parts; resin matrix and cross-linking agents, inorganic fillers, coupling agent. (Makvandi et al., 2019). Additionally, inhibitors E.g. Butylated Hydroxytoluene are used to prevent spontaneous polymerization. (Klauer et al., 2019). On the other hand, several initiator-activator systems are added to the composite for the polymerization reaction to take place such as Camphorquinone. (Klauer et al., 2019).

Resin Matrix

Organic resin matrix consists of the monomers that bond together to form a solid polymer in a proccess called polymerization. (Klauer et al., 2019). It is composed of bisphenol glycidylmethacrylate (BIS-GMA) which functions as the base of the composite. (Klauer et al., 2019). Diluents such as methylmethacrylate (MMA), bisphenol dimethacrylate (BIS-DMA) plus urethane dimethacrylate (UDMA) are inserted in composite to increase flow and handling characteristics of the composite. (Klauer et al., 2019). Cross link diluents like triethylene glycol dimethacrylate (TEGDMA) and ethylene glycol dimethacrylate (EGDMA) are also added to the resin matrix because it can accept pigments to form a tooth colored polymer. (Makvandi et al., 2019). Resin matrix was shown to be responsible for the setting contraction/polymerization shrinkage of composite filling material. (Makvandi et al., 2019).

In the past several decades cytotoxicity and genotoxicity of methacrylate related to methacrylate uncured monomers on the pulp tissue has been confirmed. (Zhou et al., 2019). However, based on current evidence dental sealants or composites with low-level BPA causes no known health hazards. (American Dental Association, 2011).

Inorganic Filler

Composite fillers are found in different sizes and are made of different materials such as Silicon dioxide Colloidal silica, Quartz. (Hervás García et al., 2006). Silicate glass in composite fillers usually contain barium, strontium, and zirconium which acts as Radio-opaquers this allow the composite to be visible under X-ray. (Hervás García et al., 2006)

Inorganic fillers function as support for the resin matrix, bringing about, increased toughness, strength, and decreased wear. (Hervás García et al., 2006). Increasing the number of fillers show decrease in polymerization contraction and decrease in thermal expansion and shrinkage. (Zhou et al., 2019). Additionally, fillers provide superior manipulation by enhancing the viscosity, decrease the water sorption and staining. (Zhou et al., 2019).

Silane Coupling Agent

Silane couplng agent acts by joining the resin matrix and the inorganic fillers. (Lung & Matinlinna, 2012). This mediator bonds with methacrylate groups of the resin matrix to produce siloxane bond and hydroxyl groups of the filler. (Lung & Matinlinna, 2012).

References

• Chan, K.H., Mai, Y., Kim, H., Tong, K.C., Ng, D. and Hsiao, J., 2010. Resin composite filling. Materials, 3(2), pp.1228-1243.

• VELO, M.M.D.A.C., COELHO, L.V.B.F., BASTING, R.T., AMARAL, F.L.B.D. and FRANÇA, F.M.G., 2016. Longevity of restorations in direct composite resin: Literature review. RGO-Revista Gaúcha de Odontologia, 64(3), pp.320-326.

• Gonçalves, F., Azevedo, C.L., Ferracane, J.L. and Braga, R.R., 2011. BisGMA/TEGDMA ratio and filler content effects on shrinkage stress. Dental Materials, 27(6), pp.520-526.

• Hervás García, A., Lozano, M., Cabanes Vila, J., Barjau Escribano, A. and Fos Galve, P., 2006. Composite resins: a review of the materials and clinical indications.

• Lung, C.Y.K. and Matinlinna, J.P., 2012. Aspects of silane coupling agents and surface conditioning in dentistry: an overview. Dental materials, 28(5), pp.467-477.

• Zhou, X., Huang, X., Li, M., Peng, X., Wang, S., Zhou, X. and Cheng, L., 2019. Development and status of resin composite as dental restorative materials. Journal of Applied Polymer Science, 136(44), p.48180.