Interfacial assessment of cention forte vs. equia forte and two forms of calcium silicate cements at two time intervals

Layering dissimilar dental materials is common in procedures such as pulpotomies in primary and young permanent teeth, where a well-sealed permanent restoration over a calcium silicate cement (CSC) base is critical to success. Traditional bases (e.g., zinc oxide–eugenol, calcium hydroxide) have been largely replaced by CSCs due to their biocompatibility, bioactivity, hydrophilicity, sealing ability, and low solubility, as well as their promotion of pulp healing and reparative dentin. MTA’s hydration produces an alkaline pH favorable for healing; MTA Angelus has a shorter setting time (about 15 minutes) compared with traditional formulations. Bio-C Repair is a ready-to-use bioceramic putty with higher plasticity but lower calcium content than other CSCs and includes zirconium. New restorative options include Equia Forte (a reinforced high-viscosity glass ionomer cement suitable for load-bearing restorations) and Cention Forte (an alkasite with alkaline fillers and ion release). The study evaluates how timing (immediate vs delayed) and the presence of a primer influence the interfacial integrity and mechanical impact (microhardness) when these restorations are layered over two CSC forms (MTA Angelus powder and Bio-C Repair putty). The null hypothesis stated that immediate contact of the evaluated CSCs with different restorative materials would not affect interfacial properties.

Prior work highlights CSCs’ favorable properties and clinical success due to bioactivity and sealing, driven by hydration reactions producing calcium hydroxide and calcium silicate hydrates (Camilleri, 2007). MTA Angelus exhibits shortened setting time relative to traditional MTA due to reduced calcium sulfate. Bio-C Repair shows distinct composition (notably zirconium) and handling benefits but lower calcium content compared to other CSCs. Reinforced high-viscosity GICs such as Equia Forte demonstrate improved mechanical properties and suitability for load-bearing applications. Cention materials (e.g., Cention-N) have shown high flexural strength and ion release profiles. Interfaces between CSCs and restoratives can be sensitive to timing and moisture dynamics, potentially influencing hydration, ion exchange, and bond formation; SEM studies have documented interface behavior and water exchange effects when GICs contact CSCs. These insights motivated assessing interfacial gaps and microhardness at defined distances from the interface when different timing and priming protocols are used.

Design: Randomized in vitro study following CRIS guidelines with ethical approval (Al-Azhar University, Cairo, Egypt; primary code P-PD-22-27; final code REC-PD-23-19). Sample size: 72 extracted primary molars (n=12 per group) based on prior data (power 80%, alpha 0.05). Grouping: Teeth randomly allocated (random.org) into six groups by restorative material and CSC, each with two subgroups by timing (immediate A; delayed B): - C/M: Cention Forte over MTA Angelus powder (n=12; A n=6, B n=6) - C/P: Cention Forte over Bio-C Repair Putty (n=12) - Cx/M: Cention Forte without primer over MTA Angelus powder (n=12) - Cx/P: Cention Forte without primer over Bio-C Repair Putty (n=12) - EQ/M: Equia Forte over MTA Angelus powder (n=12) - EQ/P: Equia Forte over Bio-C Repair Putty (n=12) Preparation: Standard coronal cavity preparation in cleaned extracted primary molars. CSC placement (MTA Angelus powder or Bio-C Repair putty) over canal orifices at 3–4 mm thickness using wetted cotton pellet. Timing protocols: Subgroup A (immediate): restorations placed before CSC sets. For C: apply Cention primer to CSCs and cavity walls, light cure 30 s; place Cention Forte. For Cx: place Cention Forte without primer. For EQ: place Equia Forte directly. Subgroup B (delayed): restorations placed after 2 h to allow complete CSC setting. Storage: All specimens incubated at 37 °C and 100% humidity for 1 week prior to testing. SEM and EDX: Specimens sectioned longitudinally and polished to expose interfaces. SEM (FEI Quanta 3D 200i) under low vacuum, 20–30 kV, WD 15–17 mm; low magnification screening for marginal gaps; gaps >5 µm wide and >20 µm long at 1000× deemed significant. EDX performed at the interface and at 200 µm and 400 µm from the interface to evaluate elemental migration. Microhardness: Vickers microhardness testing (HVS-50) with 50 g load for 15 s using a diamond indenter and 20× objective. Three indentations per specimen spaced ≥0.5 mm. HV calculated as HV = 1.85 P/d^2, where P is load (kgf) and d is diagonal length (mm). Measurements focused on restorative materials at 200 µm and 400 µm from the interface. Statistics: Normality assessed by Shapiro–Wilk and Kolmogorov–Smirnov (P>0.05). Paired t-tests for within-group timing comparisons (A vs B); independent t-tests for comparisons of HV where applicable; one-way ANOVA with Tukey post hoc for multiple group comparisons. Significance threshold P<0.05.

- SEM: No significant interfacial gaps detected for any combination of CSC (MTA Angelus powder or Bio-C Repair putty) with restorations (Cention Forte with or without primer; Equia Forte) at either time interval. A minor gap in two EQ/P immediate samples was observed but considered statistically insignificant. - EDX (uncontaminated materials): Equia Forte mainly O, F, Al, Si with lower Na, K, P. Cention Forte: high C, plus O, F, Al, Si, Ca, Ba; primer contained C, O, Si, P, trace K. MTA Angelus and Bio-C Repair comprised mainly O and Ca, with Al and Si; Bio-C Repair also contained Zr. - Microhardness at 200 µm: In Cention Forte groups (C/M and C/P), immediate application (A) yielded significantly lower HV than delayed (B): P=0.002 (MTA powder) and P=0.03 (Bio-C putty). Other group comparisons at 200 µm were not significantly different between A and B. - Microhardness at 400 µm: In Cx/M (Cention without primer over MTA powder), immediate (A) was significantly higher than delayed (B), P=0.003. In EQ/P (Equia over Bio-C putty), immediate (A) was significantly higher than delayed (B), P<0.0001. - Overall trends: Delayed application of Cention Forte over both CSCs improved HV near the interface (200 µm). Immediate application without primer (Cx) over MTA powder produced higher HV at deeper level (400 µm). For Equia Forte, delayed application over MTA powder tended to yield higher HV than immediate, whereas over Bio-C putty, immediate application produced higher HV than delayed but remained lower than over MTA powder.

Interfacial integrity was generally excellent across materials and timing, with only minor, non-significant gaps observed for Equia Forte immediately over Bio-C Repair putty. The absence of a primer between Cention Forte and CSCs allowed intimate blending at the interface, likely due to shared alkaline chemistry and the presence of similar ions (Ca, Si, P, K), favoring ionic exchange. In contrast, primer use created distinct layers without gaps, potentially limiting intermixing. For Equia Forte (a hydrophilic, high-viscosity GIC), immediate placement on Bio-C Repair putty showed slight separation likely from water withdrawal, whereas delayed placement mitigated this. Equia Forte on MTA Angelus showed intimate contact at both intervals, aided by MTA Angelus’s rapid set and lower moisture demand. Microhardness behavior reflected material interactions and timing. At 200 µm, delayed placement of Cention Forte over either CSC increased HV, consistent with allowing CSCs to complete setting and maintain alkaline conditions beneficial for MTA hydration; primer’s acidity could transiently depress pH, influencing immediate-set interactions. Without primer, immediate placement over fresh CSCs may enhance interlocking and ion exchange, explaining higher HV in Cx/M at 400 µm for immediate versus delayed. For Equia Forte, delayed application over MTA powder generally improved HV, possibly via development of interfacial silicate salts and (fluoro)hydroxyapatite over time; Equia’s immediate placement can absorb water from MTA, compromising its surface if applied too soon. Over Bio-C putty, immediate Equia application showed higher HV than delayed, possibly due to different rheology and water requirements of the putty, though still lower than values with MTA powder. Collectively, findings address the hypothesis by demonstrating that timing and the presence or absence of primer significantly influence interfacial microhardness at specified depths, while interfacial gaps are largely absent. Clinical implications include optimizing timing and adhesive protocols to enhance restoration longevity when layering over CSCs.

- Delayed application of Cention Forte over MTA Angelus powder or Bio-C Repair putty yields higher microhardness (HV) near the interface, supporting improved durability. - When using Cention Forte, apply primer only to tooth walls and avoid contact with MTA; immediate placement of Cention Forte without primer over either CSC can maximize HV, but absence of primer may risk tooth–restoration microleakage. - For Equia Forte, delayed application over MTA Angelus powder provides optimal hardness conditions; over Bio-C Repair putty, immediate application yields higher HV than delayed but remains lower than over MTA powder. - Interfacial SEM revealed no significant gaps for any material combination at either time interval, supporting reliable interfacial adaptation. Future work should evaluate clinical performance, microleakage at tooth–restoration interfaces, and longer-term aging effects across more CSC and restorative systems.

- In vitro design using extracted primary molars; clinical behavior and long-term outcomes were not assessed. - Microhardness measurements were performed only on the restorative materials at 200 µm and 400 µm from the interface; other mechanical properties and deeper gradients were not evaluated. - Only two CSCs (MTA Angelus powder, Bio-C Repair putty) and two restoratives (Cention Forte with/without primer, Equia Forte) were tested; results may not generalize to other materials. - Restorations in delayed groups were placed after 2 hours; different delay intervals were not explored. - Storage period was 1 week; extended aging, thermocycling, and fatigue were not included.