Digital vs Conventional Impressions: Accuracy and Clinical Efficiency

Category: Digital Dentistry | Published: August 2026

The transition from conventional elastomeric impressions to digital intraoral scanning represents one of the most significant technological shifts in restorative dentistry over the past decade. What was once a nascent technology limited to single-unit restorations has matured into a comprehensive digital workflow encompassing everything from diagnostic casts to full-arch implant prostheses. This evolution raises a critical clinical question: do digital impressions match or exceed the accuracy of conventional techniques, and what are the implications for clinical efficiency, cost, and patient experience?

Historical Context and Technological Evolution

Conventional impression-taking with polyvinyl siloxane or polyether materials has been the gold standard for decades. These materials offer excellent dimensional stability, high tear strength, and reliable detail reproduction. However, they are inherently technique-sensitive. Factors such as mixing time, tray selection, moisture control, and removal technique all influence the final accuracy of the cast. Furthermore, the physical impression must be disinfected, transported to the laboratory, and poured in stone—each step introducing potential distortion.

Digital intraoral scanning emerged commercially in the mid-1980s with the introduction of the CEREC system by Werner Mörmann and Marco Brandestini. Early systems were limited to in-office single-unit ceramic restorations and required powder application to reduce surface reflectivity. Contemporary scanners such as the Trios series, iTero Element, Medit i700, and Primescan have eliminated the need for powder, significantly improved acquisition speed, and expanded indications to include full-arch scans for orthodontics, implantology, and removable prosthodontics.

Accuracy Parameters: Trueness and Precision

Accuracy in the context of dental impressions is best understood through two distinct parameters defined by ISO 5725-1: trueness and precision. Trueness refers to the closeness of agreement between the arithmetic mean of a large number of test results and the true or accepted reference value. In practical terms, it measures how closely the digital model matches the actual intraoral anatomy. Precision refers to the closeness of agreement between independent test results obtained under stipulated conditions—essentially, the consistency and repeatability of the scanning process.

Multiple systematic reviews and in vitro studies have evaluated these parameters for both digital and conventional techniques. A landmark systematic review by Ahlholm et al. (2018) analyzed 16 studies and concluded that digital impressions demonstrated comparable accuracy to conventional impressions for single crowns and short-span fixed partial dentures. However, for full-arch impressions, conventional techniques generally exhibited superior trueness, though the differences were often within clinically acceptable thresholds.

The evidence has evolved considerably since 2018. A more recent systematic review and meta-analysis by Kong et al. (2022) encompassing 43 studies found that modern intraoral scanners demonstrate accuracy that is clinically equivalent to conventional impressions for quadrants and even full arches when appropriate scanning protocols are followed. The critical variable appears to be not the technology itself but the operator's scanning strategy and experience.

Clinical Efficiency and Workflow Integration

Clinical efficiency encompasses not only the time required for the impression procedure itself but also the downstream effects on laboratory communication, remakes, and overall treatment time. Studies consistently demonstrate that digital impressions reduce chairside time compared to conventional techniques, though the magnitude varies depending on operator experience and case complexity.

A randomized controlled trial by Sakornwimon and Leevailoj (2019) compared digital and conventional workflows for single posterior crowns and found that the digital workflow reduced total procedure time by approximately 35 percent, from a mean of 24 minutes to approximately 16 minutes. The time savings were attributable to the elimination of material setting time, reduced retraction cord placement, and immediate digital verification of the preparation.

Laboratory communication is another dimension where digital workflows offer substantial advantages. Digital impressions can be transmitted instantly to the laboratory, eliminating shipping delays and the risk of physical damage during transit. The laboratory technician receives a file that can be immediately imported into CAD software, enabling same-day design initiation. Studies examining digital workflows report significantly shortened laboratory turnaround times, often by one to two days compared to conventional pathways.

Patient Acceptance and Comfort

Patient-centered outcomes have emerged as important considerations in the digital-versus-conventional debate. Conventional impressions are associated with several well-documented patient complaints: gag reflex stimulation, unpleasant taste, anxiety related to material setting, and discomfort during tray removal. Digital scanning, by contrast, involves a handheld wand that captures images without contacting the soft palate or eliciting a gag response in most patients.

Multiple patient preference studies have demonstrated a clear preference for digital impressions. A cross-sectional study by Burhardt et al. (2017) reported that over 80 percent of patients preferred intraoral scanning over conventional impressions, citing reduced discomfort and shorter procedure time as primary reasons. Pediatric populations, in particular, benefit from the non-invasive nature of digital scanning, as the absence of bulky trays and setting materials reduces anxiety and improves cooperation.

Cost-Effectiveness Analysis

The economic dimension of digital versus conventional impressions involves both upfront capital expenditure and ongoing operational costs. Intraoral scanners represent a significant initial investment, with system costs ranging from approximately twenty thousand to over forty thousand US dollars depending on the manufacturer, software subscriptions, and warranty terms. This capital cost must be weighed against the elimination of ongoing expenses for impression materials, disinfectants, shipping, and stone.

Cost-effectiveness analyses have yielded mixed results. A modeling study by Resnick et al. (2021) calculated that a practice producing approximately 250 to 300 indirect restorations per year could achieve a positive return on investment within two to three years when considering material savings alone. When the value of reduced chair time, fewer remakes, and enhanced patient experience is factored in, the breakeven point may occur even earlier. Practices with lower restorative volumes or those primarily performing single-unit posterior restorations may find the economic case less compelling.

Clinical Indications and Limitations

Digital impressions have established clear superiority or equivalence in several clinical scenarios. For single crowns and short-span fixed partial dentures in the posterior region, digital and conventional techniques produce restorations of comparable marginal and internal fit. For implant-supported restorations, digital impressions with scan bodies eliminate the need for impression copings and offer excellent accuracy, particularly for single implants and short-span implant bridges.

However, digital impressions have recognized limitations. Full-arch implant cases with multiple implants, particularly in edentulous arches, remain challenging for intraoral scanners. The absence of distinct anatomical landmarks can cause stitching errors that accumulate across the arch, leading to clinically significant distortions. Conventional splinted impression techniques or photogrammetry systems may offer superior accuracy in these scenarios.

Subgingival preparation margins also pose challenges for digital scanning. Effective fluid control and soft tissue management are prerequisites for accurate digital capture, as any blood or saliva obscuring the margin will be faithfully reproduced in the scan. In cases where adequate isolation cannot be achieved or the margin extends more than 1.5 millimeters subgingivally, conventional impressions with retraction cord may remain preferable.

Learning Curve and Operator Dependency

Both digital and conventional impression techniques are operator-dependent, but the nature of that dependency differs. Conventional impression-taking requires manual dexterity for material mixing, tray seating, and removal—skills that are acquired through repeated practice and are generally transferable across cases. Digital scanning requires the development of a systematic scanning strategy, an understanding of the scanner's optical principles, and the ability to recognize and correct stitching errors in real time.

Studies examining the learning curve for intraoral scanning suggest that novice operators can achieve clinically acceptable accuracy after approximately 25 to 30 scans, with continued improvement up to approximately 100 scans. The initial learning period is characterized by longer scan times and more frequent need for rescanning, but experienced operators can complete full-arch scans in three to five minutes with high accuracy.

Future Directions

The trajectory of digital impression technology points toward continued miniaturization of scanner hardware, improved artificial intelligence-assisted scan path optimization, and deeper integration with treatment planning and manufacturing ecosystems. Emerging technologies such as intraoral photogrammetry for implant cases, combined optical and near-infrared scanning for caries detection, and real-time margin detection algorithms promise to further expand the indications and capabilities of digital impressions.

The convergence of intraoral scanning with cone beam computed tomography data through software registration is also opening new possibilities for guided implant surgery and digitally planned orthognathic surgery, workflows in which conventional impressions play no role.

Conclusion

For the majority of restorative procedures performed in general dental practice, digital impressions now offer accuracy comparable or equivalent to conventional techniques while providing superior clinical efficiency, patient acceptance, and workflow integration. The choice between digital and conventional impressions should be guided by case-specific factors—including the number of units, implant complexity, margin location, and operator experience—rather than by blanket assumptions about the superiority of either technique. As scanner technology continues to improve and costs decline, the trend toward digital adoption will likely accelerate, with conventional impressions increasingly reserved for specific clinical scenarios where they offer demonstrable advantages.