Surface and vertical dimensional changes of mineral trioxide aggregate and biodentine in different environmental conditions

Abstract Surface changes in biological environments are critical for the evaluation of physical and biological activity of biomaterials. Objective: This study investigated surface alterations of calcium silicate-based cements after exposure to different environments. Material and Methods: Forty-eight cylindrical cavities were prepared on root surfaces. The cavities were filled using ProRoot MTA or Biodentine and assigned to four subgroups (n=6): dry, wet, acidic, and blood. Surface topographies were evaluated using an optical profilometer for 28 days, and the roughness of the material surfaces was quantified. Vertical dimensional change was measured by determining the height difference between the material surface and the flat tooth surface. Data were compared with a two-way repeated measures ANOVA and Bonferroni tests. Results: In dry condition, the surface roughness of MTA or Biodentine was constant up to 3 days (p>0.05) but decreased after 28 days (p<0.05). In dry condition, ProRoot MTA presented constant surface level through time, while Biodentine showed decreased surface level after 28 days. In wet condition, the roughness and the surface levels of both materials increased after 1 day (p<0.05). Neither the surface roughness nor the levels of the materials showed significant changes in acidic conditions (p>0.05). Both materials showed the highest roughness in blood conditions on the 1st day (p<0.05), while the surface roughness in blood decreased dramatically after 28 days. The roughness of Biodentine was higher in wet conditions up to 3 days compared with ProRoot MTA (p<0.05). Likewise, in blood condition, Biodentine showed higher roughness on the 28th day than ProRoot MTA (p<0.05). Conclusions: Dry, wet, and blood conditions had a time-dependent effect on the surface roughness and vertical dimensional changes of the materials. However, acidic conditions did not affect the roughness and the surface level of the materials.


Introduction
Mineral trioxide aggregate (MTA) and Biodentine are mostly used calcium silicate-based cements (CSCs) in several endodontic procedures, such as retrograde filling, coronal barrier, pulp capping agent, and perforation repair material. 1 Both materials consist of tricalcium silicate and dicalcium silicate as main components. MTA also contains calcium sulfate and bismuth oxide (radiopacifier), and Biodentine contains calcium carbonate and zirconium oxide (radiopacifier).
Hydration of the materials forms calcium silicate hydrate gel and calcium hydroxide. 2 MTA completes the initial setting after 40 min and solidifies completely in 140 min. 3 Biodentine has a smaller particle size that increases the surface area and density of the material compared with MTA. 4 Biodentine has a relatively short setting time and showed initial setting after 9-12 min and solidifies after 45 min. 5 The local physicochemical environment determines the suitability of the materials for clinical applications. 6 MTA and Biodentine generally come into contact with body fluids and moisture when used for endodontic applications, and both materials can solidify in blood, plasma, and other fluids. 7 However, when these materials are used as cavity liners and bases under final adhesive restorations, they are placed in relatively dry conditions. 8 In addition, the materials can be exposed to blood during endodontic applications, such as apical surgery and revascularization procedures. 9 The pH of the environment becomes acidic during endodontic treatment of necrotic teeth with periapical lesions or the repair of teeth with perforating furcal lesions, which may affect the properties of the materials. 10 Different oral conditions may affect the surface characteristics of the materials. 11 Surface roughness is a component of the surface texture and is also the measure of vertical (positive or negative) deviations of the surface from an ideal flat surface. The biocompatibility and bioactivity of these materials provide a microenvironment for cell attachment and odonto-/osteogenic activity during pulp capping procedures, 12 regenerative endodontics, 13 or periapical healing after apical plug formation. 14 According to previous studies, a rough surface may promote the attachment and proliferation of the cells by increasing material-cell interactions. 15,16 In addition, the materials can release calcium ions, and the accumulation of the calcium on the surface increases surface roughness, which leads to the formation of hydroxyapatite on the surface. 17 However, excessive surface roughness might have a negative impact on the strength and sealing of materials. 18 MTA and Biodentine have a similar surface roughness in wet conditions. 15 However, no comparable data on the effects of different conditions on the roughness of MTA or Biodentine were found in literature.
Setting conditions could also affect the dimensional stability of these materials. 19 The dimensional stability of a material should be adequate to improve its adaptation and prevent leakage. Slight expansion might contribute to the adaptation of the material, but excessive shrinkage or expansion during setting may lead to leakage, lack of marginal integrity, or cracks in the root canal walls. 20 Recently, an optical profilometer was used to measure the physical properties of dentin or the rotary instruments, as well as the adaptation of root end-filling materials. 21 The optical profilometer acquires a computer-based three-dimensional

Material and Methods
The crowns of 24 human maxillary canine teeth were removed, and the root halves were obtained by sectioning the roots longitudinally. The middle part of each root half was used for the experiments. using 600-and 1000-grit abrasive discs (Buehler, Lake Bluff, IL, USA) was used to polish the surface of the blocks. 22 Irrigation was performed during 3 min using 2.5% sodium hypochlorite (NaOCl), followed by 1 min of 17% ethylenediaminetetraacetic acid (EDTA) to remove any debris in the cavity. The media were refreshed three times per week.

Measurement of surface roughness
The surface of each specimen was scanned using