Dental Composite Classification in Pediatric Dentistry: Types, Curing Methods and Clinical Applications

Composite Classification

In this section we are going to classify composite according to filler size, curing modes and clinical applications.

Composite-Filler Size

A wide range of dental composite filler sizes were developed such as Macrofill-10-50μm, Minifill-0.1-1.1μm, Microfill 0.05-0.5μm, Nanofill 0.005-0.01μm and Hybrids 10–50 μm & 10–50 nm. (Lutz & phillips, 1983).

Macrofill Composite

Due to the high filler-resin ratio, with Filler loading of 70-80% by weight. (Donly & Browning, 1992). This allow macrofill composite to sustain high compressive strength and low coefficient of thermal expansion. (Donly & Browning, 1992).

Clinical considerations of using macrofill composite include polishing difficulties, rough surface that tends to stain (Donly & Browning, 1992) and poor resistance to occlusal wear due to selective wear of resin matrix. (Donly & Browning, 1992).

Microfill Composite

Microfill composite was fostered to overcome rough surfaces of macrofill resin composites with two hundred to three hundred times smaller fillers than the filler in macrofill composite. (Buen et al., 2007). Smoother surface was reported thanks to Colloidal silica microfillers. (Buen et al., 2007). Better aesthetics and polish-ability was also reported as an advantage of microfill composites. (Buen et al., 2007). However, in terms of compressive and flexural strength, it shows reduced physical and mechanical qualities to conventional composites. (Zhou et al., 2019).

Nanofill Composite

Developed in effort to have better smoothness of surfaces and to enhance physical and mechanical qualities of traditional composites. (Rinastiti et al., 2010). Due to the fact that nanofill composite have higher filler volume, the physical and mechanical qualities are superior to traditional composite. (Rinastiti et al., 2010). It also stood out with the best aesthetics and surface smoothness in composite. (Rinastiti et al., 2010). However, difficulty in adaptation of nanofill composite to the cavity margins were observed due to high filler content. (Rinastiti et al., 2010).

Hybrid Composite

Developed in an effort to combine the properties of both macrofilled and microfilled fillers. (Rinastiti et al., 2010). Composed of 2 different sizes of fillers (0.5–1.0 μm and 10–50 nm); colloidal silica which present in concentrations of 10 – 20% and heavy metal glasses constituting of 75%. (Zhou et al., 2019). Hybrid composite features less thermal expansion and higher compressive strength. (Zhou et al., 2019).

However, it presents increased polymerization contraction due to a higher content of diluent monomer which governs the handling and viscosity of resin composition. (Chan et al., 2010). In contrast, paralleled to the inadequate range of shades of early macrofilled and microfilled composites. (Zhou et al., 2019). Present hybrid composites with tailored opacity and translucency are idyllic for aesthetic tooth fillings of anterior teeth. (Hientze et al., 2015).

Composite According to Curing Modes

A range of activation systems are utilized to generate a free radical that initiates the polymerization process. (Zhou et al., 2019). Because it affects the kinetics of polymerization, they also affect the properties of the restoration. (Zhou et al., 2019).

Composite curing is classified into; self-cured, Light-activated and Dual-cured composites. (Kwon et al., 2015).

Chemically initiated composites contain activators for polymerization like benzoyl peroxide (BPO) and tertiary amines. (Shin & Rawls, 2009). Here hardening process of composite is activated by an oxidation–reduction initiator system at room temperature. (Shin & Rawls, 2009). On the other hand, Light-activated composites contain activators such as Camphorquinone (CQ) and amine complex initiation. (Shin & Rawls, 2009). This is initiated by either UV light or visible light absorption of energy activates the CQ and amine. (Shin & Rawls, 2009).

Curing Lights

A dental curing light is a dental apparatus utilized for polymerization of light-cure resin-based composites. (Mallman et al., 2005). Light Emitting Diode (LED), Quartz-Tungsten-Halogen (QTH) and Plasma arc curing light (PAC) light are examples of different types of curing lights used in dentistry. (Mallman et al., 2005).

Tungsten-Halogen light curing unit were stumbled on as a more reliable method for polymerization. (Dunn & Bush, 2002), with wider emission spectrum and cure different photo-initiators. However, they produce loud noises because of the cooling fans, additionally, they have high start-up cost. (Mallman et al., 2005).

LED require less power to operate curing units because of their unfiltered, narrow emission spectrum. (Yoshikawa et al., 2001). Consequently, they may be powered with rechargeable batteries, making them available in lightweight and cheaper cost. (Yoshikawa et al., 2001).

Depth of Cure and Exposure Time

Degree of conversion and power density is governed by the light absorption and scattering of light in resin composite. Consequently 1-2mm depth of curing is a standard for adequate curing intensity. (Yoshikawa et al., 2001). Light rarefication differs depending on opacity, filler size, filler concentration and pigment shade. (Yoshikawa et al., 2001). Darker shades require longer curing time. (Alpino et al., 2006). Curing light intensity can vary drastically, depending on quality and age of light source, light tip orientation and direction, distance between light tip and tooth, lastly, presence of contamination on the light source. (Alpino et al., 2006).

In spite of the many pros of light cured resins, self-cured resin composites can be used with consistent results as luting agent under metallic restorations. (Alpino et al., 2006).

Polymerization Shrinkage

Gab formation between the tooth surface and composite bonded interface caused by shrinkage stresses. (Davidson & Feilzer, 1997). This subsequently leads to marginal staining, postoperative sensitivity, secondary caries and finally restoration failure (Davidson & Feilzer, 1997). Composite resin exhibit shrinkage while hardening with average of 2% to 6% at 30 min. (Kleverlaan & Feilzer, 2005). Factors affecting polymerization shrinkage include; the volume of filler content, Intensity of curing light, thickness of composite resin, shade, and opacity of composite. (Kleverlaan & Feilzer, 2005). Shrinkage is highest with ramp curing modes and high intensity modes, whereas it is lesser with step-curing and low intensity modes. However, the most important factor regarding the effects of polymerization shrinkage is the C-factor. (Watts & Satterthwaite, 2008).

C-factor stands for the ratio of bonded to unbonded or free surfaces of the composite restoration to the tooth surface. (Watts & Satterthwaite, 2008).

This is calculated as bonded walls divided by unbonded walls. The higher the c-factor the more the susceptibility of the restoration for polymerization shrinkage. (Watts & Satterthwaite, 2008).

Class IV restoration is reported as the low-risk filling for polymerization shrinkage with c-factor of 0.2. On the other hand, Class I with C-factor 5 is at a comparatively high risk. (Van Dijken, 2010).

Longevity of Composite Filling

Multiple factors such as the size of the resin composite filling, tooth number/position and patient risk assessment for caries have been shown to affect the longevity of composite fillings. (Bohaty et al, 2013). In addition, properties of the material used, adequacy of the bond to the tooth surface and experience of the operator can determine the quality of the seal at the composite-tooth interface. (Bohaty et al, 2013). As a whole the general findings advocate that at least 60% of resin composite fillings will be sustained for more than 10 years when material and technique is used correctly. (Kubo, 2011).

Composite Clinical Applications

In this section we are going to classify composite according to their clinical use in different clinical scenarios.

Flowable Composite

Flowable composite was introduced in dentistry for the first time in 1996. (Garcia et al., 2006). The reduced filler loading from 50–70% by volume to 37–53% (volume) (Baroudi & Rodrigues, 2015) allow decreased viscosity and increased flowability of the composite. (Baroudi & Rodrigues, 2015). Flowable composite can go in minute spaces or areas of a restorative cavity by an injection syringe, thus increase the operation simplicity and shorten the working time. (Baroudi & Rodrigues, 2015).

First-generation flowable resin composites, were only applied as a cavity liner or pits and fissure sealants owing to its lower filler volume and its modulus of elasticity (Boruziniat et al., 2016).

Newer generations retain a broader range of purposes such as, preventive resin restoration (PRR), minimally invasive class III & class V restorations and abfraction lesions. (Baroudi & Rodrigues, 2015). However, flowable composites are suggested to be operated only in low-stress bearing fillings due to its low compressive and flexural strength compared to conventional composite. (Zhou et al., 2019).

Bulk-Fill Composites

Conventional composite is classically cured every 1 mm increment, This type of composite was created to reduce the time consuming drawback of incremental technique in cavity filling. (Kim et al., 2015). Bulk-fill composites allow depth of polymerization to be sufficient for 4 mm increments by utilizing high translucent shades. (Zorzin et al., 2014). Complex activator systems are used to shorten the light curing time. (Orłowski et al., 2015). A study by Al-Harbi et al. (2015) found that bulk-fill composites offer improved cervical contact and comparable marginal quality of bulk-fill restoration versus incremental-fill class-II fillings.

Compomers – Polyacid Modified Resin Composites

A combination of composite and glass ionomer cement (polyalkenoate acid and glass components). Compomers possess a dual-setting mechanism, of which the major setting reaction is the resin photopolymerization, then the acid–alkali reaction takes place in presence of water. (Pummer et al., 2020). Developed in faith of conveying the favourable qualities of resin composites and GIC. (Pummer et al., 2020). As a result of its ease of handling and fluoride release, compomers transpired quickly and received acceptability by the dental communities. (Ruse, 1999). However, compomers convey a number of drawbacks like brittleness, lower compressive strength, longer curing time, and water sensitivity. (Mousavinasab & Meyers, 2009). Compomers were also reported to have a high polymerization shrinkage (Mousavinasab & Meyers, 2009). A study by Moodley & Grobler (2003) found that resin modified GIC released larger volume of fluoride compared to compomers. When compomers were used as fissure sealants, compomer sealant showed a lower retention rate than conventional sealants. (Ram et al., 2005). Therefore, it was appropriate as a temporary sealant for molar teeth. (Ram et al., 2005).

Flowable compomer E.g. Dyract Flow are easily adapted to the cavity walls, are indicated for minimal invasive restorations and are used in marginal repair of resin restorations. (Ehlers et al., 2019).

In class I & II restorations, high success rates of 91.2% and 94% for Dyract compomer were achieved after 3 years. Class III restorations were also reported successful. (Ehlers et al., 2019). However, high fracture rate and its inferior aesthetics to composite discouraged its use in class IV restorations. (Ehlers et al., 2019).

Clinically, failure of compomers is related to poor moisture control, retention loss and secondary caries. (Kramer & Frankenberfer, 2015). However, under a correct application protocol like moisture control and compliance of the patient compomers demonstrated high success rates. (Kramer & Frankenberfer, 2015). Therefore, the patients must be judged individually specially in the deciduous dentition, according to the patient’s caries risk, tooth location and cavity shape. (Campagna et al., 2018).

References

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• 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.

• D Alpino, P.H., Wang, L., Rueggeberg, F.A., Svizero, N.R., Pereira, J.C., Pashley, D.H. and Carvalho, R.M., 2006. Bond strength of resin-based restorations polymerized with different light-curing sources. Journal of Adhesive Dentistry, 8(5), p.293.

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• Mousavinasab, S.M. and Meyers, I., 2009. Fluoride release by glass ionomer cements, compomer and giomer. Dental research journal, 6(2), p.75. (Mousavinasab & Meyers, 2009)

• Pummer, A., Cieplik, F., Nikolić, M., Buchalla, W., Hiller, K.A. and Schmalz, G., 2020. Longevity of posterior composite and compomer restorations in children placed under different types of anesthesia: a retrospective 5-year study. Clinical oral investigations, 24(1), pp.141-150.

• Rinastiti, M., Özcan, M., Siswomihardjo, W. and Busscher, H.J., 2010. Immediate repair bond strengths of microhybrid, nanohybrid and nanofilled composites after different surface treatments. Journal of dentistry, 38(1), pp.29-38.

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• 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.