In Search of Novel Degradation-Resistant Monomers for Adhesive Dentistry: A Systematic Review and Meta-Analysis

Abstract

This study aimed to assess whether degradation-resistant monomers included in experimental dental adhesives can improve long-term bond strength compared to conventional monomers. This study followed the latest PRISMA guidance (2020). The search for the systematic review was carried out in four electronic databases: PubMed/Medline, Scopus, SciELO and EMBASE, without restrictions on the year of publication and language. The last screening was conducted in July 2022. Interventions included were in vitro studies on experimental dental adhesives that tested short-term and long-term bond strength, but also water sorption and solubility data when available, in extracted human molars. Meta-analyses were performed using Rstudio v1.4.1106. A summary table analyzing the individual risk of bias was generated using the recent RoBDEMAT tool. Of the 177 potentially eligible studies, a total of 7 studies were included. Experimental monomers with acrylamides or methacrylamide−acrylamide hybrids in their composition showed better results of aged bond strength when compared to methacrylate controls (p < 0.05). The experimental monomers found better sorption and solubility compared to controls and were significantly different (p < 0.001). It is possible to achieve hydrolytically resistant formulations by adding novel experimental monomers, with chemical structures that bring benefit to degradation mechanisms.

Keywords: acrylate monomers; degradation-resistant; dental adhesion; dentin bonding agents; hybrid layer; hydrolysis: hydrolytically resistant; resin-based materials.

Figure 1

Flowchart in compliance with the PRISMA statement guidelines, showing the steps followed in each stage of the systematic review. Out of 177 potentially relevant papers, after screening, eligibility, and inclusion, 7 remained.

Figure 2

Forest plot of the immediate microtensile bond strength, including 7 distinct studies with different strategies and 3 commercial controls, which do not have any symbol, purposefully—Adper Single Bond 1, Adper Single Bond 2 and Solobond M. Symbol legend: ★ eugenyl methacrylate derivatives; ● methacrylamide derivatives; ◆ urushiol derivatives; ⬟ CBA monomer derivatives.

Figure 3

Forest plot of the bond strength difference after real aging in distilled water (6 months), by subtracting the final from the initial bond strength value. Symbol legend: ★ eugenyl methacrylate derivatives; ● methacrylamide derivatives. Statistical significance (difference to 0) is shown in asterisks, where * p ≤ 0.05 ** p ≤ 0.01 *** p ≤ 0.001.

Figure 4

Forest plot of the bond strength subsequent to artificial aging (thermocycling—5000 cycles) subtracted from the initial bond strength values. Symbol legend: ◆ urushiol derivatives. Statistical significance (difference to 0) is shown in asterisks, where * p ≤ 0.05 ** p ≤ 0.01 *** p ≤ 0.001.

Figure 5

Forest plot that includes data of the water solubility measured in 4 individual studies. Symbol legend: ★ eugenyl methacrylate derivatives; ● methacrylamide derivatives.

Figure 6

Forest plot that includes data of the water sorption measured in 4 individual studies. Symbol legend: ★ eugenyl methacrylate derivatives; ● methacrylamide derivatives.

Figure 7

Graph of treatment network in pairs of immediate bond strength.