This study compared 3D-printed crowns and CAD/CAM crowns with prefabricated zirconia crowns—commonly used in pediatric dentistry—to evaluate changes in surface hardness, surface roughness, TP, and ΔE following exposure to an acidic solution. Previous studies have indicated that prolonged contact with acidic beverages can deteriorate surface characteristics, reduce color stability, and impair the mechanical properties of restorative materials [13]. Therefore, the comparative evaluation of these parameters among different crown types holds clinical relevance. In the present study, statistically significant differences were observed in all evaluated parameters following acidic exposure, and the null hypothesis was rejected.

Although long-term performance is often emphasized for restorative materials, this concept should be interpreted differently in pediatric dentistry compared to adult dentition. In pediatric patients, the clinical service period of crowns is limited by physiological exfoliation and craniofacial growth. Therefore, in pediatric dentistry, “long-term” performance refers to the material’s ability to maintain mechanical integrity and esthetic stability throughout the remaining lifespan of the primary tooth rather than the decades-long service expected of permanent restorations [14].

The long-term clinical success of esthetic restorative materials is closely linked to their physical and optical properties, including surface hardness, roughness, translucency, and color stability [15, 16]. Surface hardness is a key indicator of resistance to mechanical forces; insufficient hardness increases susceptibility to wear, abrasion, and surface degradation due to mastication and oral hygiene practices [17, 18]. The Vickers microhardness test is frequently employed to assess surface hardness changes following acidic exposure [19, 20]. In the present study, prefabricated zirconia crowns exhibited the highest baseline hardness, followed by CAD/CAM crowns and 3D-printed crowns, which aligns with previous findings reporting superior hardness in Y-TZP-based materials such as prefabricated zirconia crowns [21,22,23]. The CAD/CAM crowns results are consistent with those of Colombo et al. [12], who reported a reduction in hardness after 7 days, likely due to water absorption and surface solubility [24, 25]. 3D-printed crowns displayed the lowest initial Vickers hardness and the highest proportional loss following acidic exposure, suggesting that the material composition significantly affects the chemical stability and acid resistance. These findings align with previous studies reporting reduced hardness in resin-based 3D-printed materials [26, 27]. All the groups experienced statistically significant hardness reductions after immersion in Coca-Cola, with prefabricated zirconia crowns demonstrating the least proportional change, supporting its greater resistance to acidic degradation.

In addition to acidic challenge, changes in surface hardness may also be influenced by water imbibition, which is a well-documented phenomenon in resin-based restorative materials. Water diffusion into the polymer matrix can lead to plasticization, reduced intermolecular forces, and subsequent decreases in mechanical properties such as hardness. Although water sorption was not directly quantified in the present study, its potential contribution should be acknowledged when interpreting hardness alterations, particularly for resin-containing CAD/CAM and 3D-printed crown materials [28,29,30].

In pediatric applications, wear resistance is crucial not only for material longevity but also for maintaining compatibility with the physiological wear patterns of primary teeth. In this context, hybrid ceramics and resin-based materials may offer advantages in mimicking natural wear and supporting occlusal development [31, 32].

Surface roughness plays a critical role in both biofilm accumulation and esthetic longevity. Increased roughness enhances bacterial adhesion and staining, compromising the durability of the restoration [33]. The literature defines a threshold surface roughness of 0.2 µm, above which bacterial colonization significantly increases [34]. Therefore, maintaining roughness below this value is strongly recommended to ensure clinical success.

In the present study, the initial surface roughness values of the tested 3D-printed (VarseoSmile® TriniQ) and CAD/CAM resin nano-ceramic (GC Cerasmart 270) materials were already close to or above the 0.2 µm threshold. Following acidic beverage exposure, these values increased further. This finding suggests that acidic challenge may exacerbate surface irregularities, potentially increasing the risk of plaque retention. Considering the association between surface roughness and biofilm accumulation, these materials may require greater attention to oral hygiene maintenance, particularly in pediatric patients with frequent acidic beverage consumption. However, it should be emphasized that biofilm formation is multifactorial and influenced by clinical polishing procedures, salivary factors, and individual oral hygiene practices. Therefore, while increased roughness may indicate a potential predisposition to plaque retention, its actual clinical impact should be interpreted cautiously and validated through long-term in vivo studies.

Zirconia crowns are known for their high biocompatibility and smooth surface characteristics, which contribute to reduced gingival irritation and resistance to plaque accumulation [35]. Studies on anterior pediatric zirconia crowns have reported that prefabricated zirconia crowns exhibit the highest gloss and lowest surface roughness (Ra), whereas Kinder Krowns® and EZCrowns® have higher Ra values [36]. In a comparative study on posterior deciduous molars, NuSmile® crowns presented Ra values close to clinically acceptable thresholds and lower than those of other brands. Although that study focused on posterior restorations, the use of the same brand of material supports the consistency of our anterior findings with previous reports [37].

Similar trends have been observed in surface treatment studies. Go et al. [38] reported that the surface roughness of zirconia samples polished with various systems did not differ significantly from that of untreated controls, indicating that appropriate polishing can achieve a smooth surface. Similarly, Shin et al. [39] reported minimal roughness changes after simulated tooth brushing on prefabricated pediatric zirconia crowns. Although the initial and post-brushing values differed slightly among the NuSmile®, Sprig®, and Kinder® groups, the magnitude of change was clinically negligible. These findings align with our results, where prefabricated zirconia crowns demonstrated Ra values near the acceptable clinical limit.

The literature also highlights the polishability of CERASMART270. Matzinger et al. [40] reported Ra values of 0.11–0.13 µm following chairside polishing, whereas Neiva & Valcanaia [41] reported values of 0.11 ± 0.01 µm via the brush-paste method, which are significantly lower than those of Vita Enamic (0.42 ± 0.06 µm). In contrast, untreated or coarsely finished CERASMART270 samples have shown much higher Ra values, ranging from 0.54 ± 0.10 µm to over 1.0 µm, underscoring the importance of surface finishing protocols [42, 43]. Acidic environments are known to degrade resin-based materials. Scotti et al. [44] reported significant increases in the surface roughness of CERASMART270 following exposure to Coca-Cola and Red Bull. The Ra value of 0.48 µm obtained in our study supports these findings and indicates surface deterioration due to acidic exposure.

To date, no specific study has evaluated the surface roughness of the TriniQ resin. However, the literature suggests that 3D-printed resins generally exhibit greater surface roughness than CAD/CAM-processed materials do [45]. Furthermore, compared with conventional blocks, newly introduced permanent 3D printing resins have demonstrated inferior surface quality and mechanical performance [46, 47]. These findings suggest that the higher Ra values observed with the 3D-printed crowns may be attributed to the inherent characteristics of 3D printing technology and polymerization protocols.

The success of aesthetic restorative materials depends not only on their mechanical properties but also on their optical characteristics, such as translucency and color stability [48]. Translucency refers to a material’s ability to transmit light and is essential for achieving a natural tooth-like appearance. It is influenced by both the material composition and thickness. The TP of 1-mm-thick human enamel typically ranges from 15 to 19 [49]; therefore, restorative materials with TP values near this range are more likely to yield natural aesthetic outcomes. Moreover, color stability ensures that the restoration maintains its initial shade over time by resisting staining from dietary pigments and environmental exposure [48].

In the present study, the initial TP of the 3D-printed crowns (20.72 ± 1.96) was the highest and closest to the enamel reference range. Other materials also demonstrated baseline TP values within or near the natural enamel range. However, exposure to an acidic environment resulted in different optical responses among the materials. In the CAD/CAM group, TP increased significantly (from 24.65 to 28.75, p < 0.001). This increase may be associated with water sorption by the resin matrix, leading to matrix swelling and alterations at the matrix–filler interface. Water uptake has been reported to influence color stability and optical behavior in resin composites, potentially affecting internal light transmission and translucency [50]. In contrast, the 3D-printed crowns exhibited a significant decrease in TP (from 20.72 to 19.38, p = 0.002). This reduction may be related to acid-induced surface degradation and possible filler–matrix debonding, which can increase light scattering and reduce translucency, as previously observed in resin-based restorative materials exposed to acidic conditions [51]. For the prefabricated zirconia crowns, no significant change in TP was observed. This finding may be attributed to the material’s dense polycrystalline structure and minimal water sorption, contributing to greater optical stability under acidic challenge.

Although statistically significant differences were detected, TP values remained within clinically acceptable limits. These findings suggest that, beyond baseline translucency, the long-term optical stability of restorative materials may depend on their compositional characteristics and resistance to environmental degradation. Translucency is influenced primarily by material thickness and composition, but environmental conditions and duration of use can also affect optical behavior [48].

Color stability is defined as a material’s ability to maintain its initial shade over time [52]. While intrinsic factors such as filler content and particle size are influential, extrinsic factors—particularly the consumption of pigmented, acidic beverages—can contribute to discoloration. For example, drinks such as Coca-Cola may cause pigment absorption or adherence on the surface of restorations [53].

In general, a ΔE*ab value ≤ 3.3 is considered the clinical threshold for perceptible ΔE [52]. Although all the tested materials significantly increased ΔE following Coca-Cola exposure, these changes remained below the 3.3 threshold, indicating acceptable clinical performance under acidic conditions.

Among the evaluated materials, the prefabricated zirconia crowns group exhibited the lowest ΔE (white background: ΔE = 2.28 ± 1.30; black background: ΔE = 1.58 ± 0.87). This may be attributed to the dense crystalline microstructure and low water absorption of monolithic zirconia, which confer resistance to pigment infiltration. Consistent with our findings, previous studies reported lower ΔE values for zirconia-based materials (approximately 1.7), supporting their superior color stability in aesthetic restorations [54]. Similarly, Duymuş et al. confirmed the resistance of zirconia materials to ΔE following exposure to beverages such as Coca-Cola [55].

3D-printed crowns presented higher ΔE values, particularly on white backgrounds, suggesting greater susceptibility to external environmental factors. CAD/CAM crowns demonstrated a moderate ΔE, positioned between 3D-printed crowns and prefabricated zirconia crowns, likely due to its hybrid composite structure. Notably, background color influenced ΔE measurements: white backgrounds amplified ΔE in the 3D-printed crowns and prefabricated zirconia crowns groups, whereas black backgrounds did so in the CAD/CAM crowns. These differences are attributed to each material’s unique light absorption and reflection characteristics in relation to background contrast.

It should be noted that the experimental design represents an accelerated aging model rather than a direct simulation of clinical conditions. In daily life, pediatric crowns are exposed to acidic beverages intermittently and for short durations, rather than continuous immersion. Continuous exposure was intentionally applied to exaggerate degradation mechanisms within a limited experimental timeframe. Therefore, the outcomes should be interpreted cautiously and regarded as indicators of relative material behavior under extreme conditions, rather than absolute predictors of in vivo performance [56, 57].

While the present findings provide valuable insight into the color stability of restorative materials, the limitations of the methodology must be acknowledged. The exposure of both internal and external surfaces to staining agents may overestimate clinical discoloration. Furthermore, as an in vitro study, the direct applicability of the results to clinical practice is inherently restricted. Although crown-shaped samples offer a more realistic morphological representation, their complex geometry poses challenges for standardized measurements. Therefore, to better validate these findings and relate them to clinical performance, further long-term, prospective clinical studies are warranted. Furthermore, the absence of dynamic oral factors such as salivary buffering, masticatory forces, and thermal cycling may limit the direct extrapolation of the results to clinical conditions.

While 3D-printed crowns demonstrated certain disadvantages in terms of surface roughness and color stability, their clinical accessibility, lower cost, and ease of fabrication make them a promising alternative in settings with limited resources. However, such considerations should be interpreted as contextual observations rather than definitive clinical recommendations.