There are many ways to affix a restoration to a tooth, with adhesion approaches mainly divided into adhesive bonding techniques or conventional Luting. While the end goal is the same, Luting and adhesive bonding differ in several ways.
Adhesive bonding works on a chemical level to produce a bond and micromechanical retention between the restoration and the tooth. This is accomplished by substituting inorganic tooth materials with resin monomers; essentially, minerals in the enamel and/or dentin are replaced by resin monomers. Through polymerization, these become micromechanically interlocked into the resulting porosities.1 These adhesive bonding procedures can be completed through 2 different approaches: etch-and-rinse and self-etch.
However, cementation uses good prep design and resistance to connect the underlying tooth structure with a restoration. The cement creates a hard cement layer to adhere to both surfaces. With cementation, no matter how good the cement is, there must be adequate preparation, including good retention form and resistance.
If conventional cementation is the chosen method, clinicians still have to decide which cement is the right one for the job—and with so many options available on the market, it can be a tricky choice. The best way to narrow down the pool is to consider the numerous factors that affect cement selection. These include required bond strength, prep design, chosen restorative material, ability to isolate, and the importance of esthetics.
Dental cement can be broken down into three main primary categories: glass ionomers (GI), resin-modified glass ionomers (RMGIs), and resin cement (SARC & ARC).
Glass ionomer
Glass ionomer cement followed closely behind its polycarboxylate peers, emerging on the market in 1977. First introduced by Wilson and Kent in 1972, they designed this cement to be a hybrid that combined silicate cement’s fluoride release and translucency with polycarboxylates’ chemical bond to the tooth structure and good seal. As a result, glass ionomers have excellent translucency and very low film thickness. They are used primarily for metallic and porcelain-fused-to-metal (PFM) restorations, as they can chemically bond to stainless steel, tin-plated noble metals, and base metals.2
Glass ionomer cement are some of the most resistant to salivary contamination, as they are extremely moisture tolerant, have low solubility, and are water-based. Their bond strength is considerably reduced when the tooth’s surface is dry. This, along with a low initial pH level, can increase the rate of postop sensitivity. Although glass ionomers can have a remineralization effect (due to their fluoride release), their use has seen a decline, as their moderate retention rates are similar to that of zinc phosphate.2
RGMIs
RGMI cement was built upon its glass ionomer predecessors but substituted part of glass ionomer cement’s polyacrylic acid with hydrophilic methacrylate monomers.4 Thanks to their insolubility, RGMI cements are ideal for cases where isolation is difficult, including areas where salivary flow, crevicular fluid, or tongue control can be problematic. Additionally, when applied to moist dentin, they incur little postop sensitivity and have low microleakage.
Like glass ionomers, RGMIs are indicated for metallic and PFM restorations, as well as zirconia and alumina-based ceramics and lithium-disilicate CAD/CAM inlays and onlays. However, they are contraindicated for all-ceramic restorations, as there is a risk of clinical fracture.
Resin cement
The most popular option on the market today, resin cements were available in the early 1990s. Their popularity stems from an array of advantages, including their mechanical properties, high translucency, shade selection, insolubility, high retention, and low film thickness.
Since they are methacrylate-based, resin cements require that the tooth surface be pretreated with 37% phosphoric acid. This acid-etch technique to enamel and dentin produces high adhesion levels as a result of the polymerization process. Resin cements need to be paired with a bonding agent and the cement and bonding agent must be compatible. Bonding agents come in total-etch or self-etch varieties.
With total-etch bonding systems, phosphoric acid is applied to the enamel, while the inside surface of the restoration is treated with hydrofluoric acid. While this technique provides high levels of adhesion, it can also induce postop sensitivity. Self-etch systems are simpler since they don’t require any pretreatment of the tooth, making them appealing to many clinicians. However, self-etching cement does not provide bond strengths as high as total-etch systems.
The adhesion process with resin cement is facilitated through polymerization through light, chemicals, or a dual-cure process. Resin cements come in light-cure, dual-cure, and self-cure varieties. Light-cured cement is ideal when the restoration is located in an easily accessible location that provides adequate isolation. Most manufacturers offer multiple shades of these cement, ideal for ceramic restorations with thin thickness, enabling them for use with esthetic restorations.
Dual-cure cements are technique-sensitive but are a good choice for restorations that are not easily accessible (making them difficult to light cure) or are too thick for effective light penetration. Alternatively, self-cured cement does not cure through light but rather achieves polymerization through a chemical reaction. While these cements typically have lower bond strength than light- or dual-cure options, self-cure cements are easier to use. Since self-cure cements are not available in a wide range of shades or translucency, they are best indicated for use with metal or opaque ceramics restorations.
Postop sensitivity is a concern with resin cement, with one study finding that 37% of patients reported sensitivity in the first year after a resin-cemented crown.5 The sensitivity is largely attributed to a failure to seal the dentinal tubules exposed by the acid etching process. Additionally, although resin cement provides good bond strength and retention, multiple steps and challenging cleanup can make the process cumbersome.
Conclusion
Regardless of cement selection, it is critical to remember that cement is likely to fail without proper preparation. Even with advances in cement and increased retention and bond strength, inadequate prep can still spell disaster for restorations. While resin cement has exploded in popularity due to the current prevalence of all-ceramic restorations, clinicians should always be deliberate in selecting cement and the indications of each particular case.
References
1. Yoshida Y, Inoue S. Chemical analyses in dental adhesive technology. Jpn Dent Sci Rev. 2012;48(2):141–152. doi:10.1016/j.jdsr.2012.03.001
2. Burgess JO, Ghuman T. A practical guide to the use of luting cement. Accessed October 19, 2020. http://www.ineedce.com/courses/1526/PDF/APracticalGuide.pdf
