Shade selection and reproduction remain among the most technique-sensitive procedures in prosthodontics. Achieving an acceptable color match is influenced by multiple variables, including observer perception, lighting conditions, surrounding colors, and the intrinsic optical properties of restorative materials. Although visual shade matching is widely practiced, it is inherently subjective and has been shown to present considerable variability, even among experienced clinicians [1]-[3].

Acrylic resin–based artificial teeth are routinely used in complete dentures, removable partial dentures, overdentures, and fixed detachable hybrid prostheses. In conventional complete denture therapy, shade selection is often performed within a single material category, which may reduce matching complexity. However, significant esthetic challenges arise in mixed rehabilitations where acrylic artificial teeth must harmonize with ceramic restorations. In such situations, precise chromatic correspondence becomes critical. This difficulty is largely explained by fundamental differences in optical behavior between polymer-based materials and ceramics, including light scattering, translucency gradients, and pigment integration [4].

Despite these limitations, universal shade guides—particularly the Vita Classic^® system—are commonly used in daily practice as reference tools for artificial tooth selection. However, these shade guides were primarily developed for ceramic-based workflows and may not be calibrated to correspond to acrylic resin artificial teeth manufactured using different pigments, fillers, and layering technologies. Consequently, reliance on ceramic-oriented shade guides may lead to clinically perceptible mismatches when applied to acrylic teeth.

In addition, the interpretation of color differences in dentistry should rely on objective numeric parameters, particularly ΔE values, which are widely reported for dental materials and commonly used in denture tooth color studies. These metrics enable a standardized quantification of perceptible and clinically acceptable differences. In this context, Paravina et al. proposed clinically relevant perceptibility and acceptability thresholds, providing a practical framework for translating instrumental color differences into clinical decision-making [5].

Another contemporary investigation demonstrated that acceptability thresholds vary significantly depending on chromatic regions of the dental color space, indicating that observer tolerance is not uniform across lightness and chroma combinations [6]. These findings highlight the need for context-specific interpretation of color differences in dentistry.

Parallel to these developments, the growing integration of instrumental shade assessment reflects the need for greater reproducibility and reduced operator-dependent variability. Recent systematic and scoping reviews have shown that digital shade matching methods, including spectrophotometry, generally provide improved repeatability and reliability compared with purely visual approaches, particularly under standardized conditions [7][8].

Given the widespread clinical use of acrylic resin artificial teeth and the routine reliance on universal shade guides, it remains essential to determine whether true chromatic correspondence exists between these materials and commonly used shade guide systems.

The aim of the present in vitro study was therefore to evaluate the chromatic properties of commercially available acrylic resin–based artificial teeth on the Moroccan market and to compare them with the Vita Classic^® shade guide tabs and manufacturer-specific shade guides, using spectrophotometric measurements expressed in the CIE Lab* color space.

The results of this study show that Vita Classic^® shade guide tabs are not a reliable method to match the color of acrylic resin denture teeth. This matches what other researchers have found: even within a single commercial shade guide system, the actual color values (Lab*) can vary from one guide to another [10]. That means using just one guide as a “gold standard” can create mismatches that aren’t actually there.

Beyond the variability of the guides themselves, there’s a bigger issue: do any shade guide systems really match natural teeth? Large spectrophotometric studies comparing human teeth to Vita Classical and Vita 3D-Master systems have shown that these shade guides don’t always represent the full range of natural tooth colors found in real people, and that the mapping between different shade systems isn’t perfect [11]. This supports our finding (Table 3) that the common “A1-A3” labels on artificial teeth often don’t line up with the actual Vita shades.

From a methodological perspective, using a spectrophotometer in this study follows the current best practices, as instrument-based shade assessment has been shown to be more reliable than visual selection [7][8][12][13]. This is especially important when working on complex cases where acrylic denture teeth need to match ceramic restorations.

When we looked at the effect of layering, we found that simply increasing the number of resin layers doesn’t guarantee a better match to Vita Classic^®. That makes sense, since the final color depends on many factors—like how the resin is formulated, how pigments are distributed, the degree of translucency, and the surface finish [14]. Studies show that color and optical properties can vary widely among denture teeth brands and materials, and that things like aging or exposure to staining drinks can change the color further [15][16].

A new challenge comes from digitally fabricated teeth, like those made by milling or 3D printing with PMMA. Recent research suggests that how these teeth are made, and what materials are used, can affect their color stability and how they wear over time [14]. These studies have also reported significant inter-brand chromatic variability in PMMA-based artificial teeth [14]-[16].

This means that, for best results, it’s better to pick the denture tooth brand and shade first (using its own calibrated guide and checking with a spectrophotometer), then match any other restorations to that choice, rather than assuming all shade guides are interchangeable.

This study has several limitations. Only one specimen per brand and shade was analyzed. Measurements were limited to technical replicates. Aging procedures and clinical lighting variability were not simulated. Results should therefore be interpreted as exploratory pilot data.

This study found that there are significant color mismatches between most acrylic resin artificial teeth commercially available in Morocco and the Vita Classic^® shade guide. Most manufacturer-specific guides also didn’t consistently match their own artificial teeth. The main exceptions were the Ivoclar^® system, which showed strong internal consistency, and the Acrylux^® range, which performed relatively well. These findings apply specifically to A1-A3 shades and should not be generalized to other chromatic groups.

Importantly, neither the number of resin layers nor the manufacturing technology predicted how closely a tooth would match a shade guide. This suggests that the most important factor is the manufacturer’s color quality control and how materials, pigments, and processing are handled.

From a clinical perspective, these findings suggest several practical steps. When planning mixed prosthetic cases, it’s wise to prioritize systems that have demonstrated better chromatic consistency (like Ivoclar^® and Acrylux^®). It’s also strongly recommended to use the manufacturer’s own shade guide, rather than relying on universal guides meant for ceramics. Another good approach is to select the artificial teeth first, then try to match ceramic restorations to them, rather than the other way around. Lastly, using digital shade recording in daily clinical practice can greatly improve precision and help minimize mistakes that come from traditional visual shade selection [7][8][12][13].