Intraoral Scanners vs. Impressions: Accuracy Compared

Which is more accurate: intraoral scanners or conventional impressions?

Both methods are accurate for most dental procedures, but each has its strengths depending on the case. Here’s a quick breakdown:

• Intraoral Scanners:
  • Great for single-tooth restorations and orthodontics.
  • Offers real-time error correction and faster workflows.
  • More comfortable for patients – no messy materials or gag reflex triggers.
  • Less accurate for long-span restorations or complex implant cases.
• Conventional Impressions:
  • Better suited for complex cases like full-arch restorations or intricate implant work.
  • Handles subgingival areas and high-moisture environments well.
  • More prone to human error and requires more steps, increasing the risk of inaccuracies.

Quick Comparison

Takeaway: Use intraoral scanners for comfort, speed, and routine procedures. Opt for conventional impressions in complex cases requiring maximum detail. A combined approach often works best.

Intraoral Scanners: How They Work and Their Benefits

How Intraoral Scanners Work

Intraoral scanners create detailed 3D models by projecting laser or structured light onto the surfaces of teeth. The reflected data is then processed into high-resolution images, capturing intricate details with impressive precision ^[10].

One commonly used method is triangulation. This involves projecting a fringe pattern and calculating 3D coordinates by measuring angles and distances between specific points ^[6]. Such techniques allow for highly accurate data capture, which is essential for producing reliable results.

Modern scanners are incredibly fast. For example, the TRIOS scanner captures 2,500 images per second, generating around 25 sub-scans and approximately 2.5 GB of data every second ^[9]. This speed enables real-time capture of complex details, including tooth surfaces and surrounding soft tissues.

Some devices even utilise multiple wavelengths to improve point recognition ^[7]. The resulting 3D model can be edited and validated immediately, giving dental practitioners the ability to assess the scan’s quality and make adjustments on the spot ^[10].

This precise and efficient data collection forms the foundation for the benefits of digital impressions.

Benefits of Digital Impressions

Digital impressions come with several advantages over traditional methods, particularly in terms of accuracy and dimensional stability. Unlike putty-based impressions, which are prone to distortion, digital scans remain consistent and precise throughout the treatment process ^[3].

These scans not only improve accuracy but also enhance patient comfort. The elimination of messy impression materials and the reduced need for retakes make the process far more pleasant for patients. Additionally, digital workflows streamline operations by cutting out setting times and allowing for rapid data sharing ^[3][11]. Studies have shown that digital impressions are generally quicker and better received by patients ^[1].

The efficiency of digital impressions also translates to reduced chair time and faster turnaround for orthodontic appliances ^[12][13]. Furthermore, the digital format makes it easier for practitioners, specialists, and lab technicians to collaborate seamlessly, as data can be shared instantly ^[3]. From an environmental standpoint, digital scans eliminate the waste associated with traditional impression materials, aligning with eco-conscious practices ^[3].

While the benefits are clear, it’s important to consider the limitations of intraoral scanners.

Drawbacks of Intraoral Scanners

Despite their many strengths, intraoral scanners are not without challenges. Full-arch scans, for instance, can show greater deviations compared to partial-arch scans. Research indicates discrepancies ranging from 100 to 200 micrometres, particularly in the molar regions.

Certain technical hurdles also arise. Scanning subgingival areas, reflective surfaces, or maintaining a dry field during the process can be tricky. As one expert put it:

"teeth are exotic surfaces to scan." ^[9]

The accuracy of scans can be heavily influenced by the operator’s experience, scanning technique, and the software being used. Regular updates to the system are essential for maintaining optimal performance. As highlighted:

"Maintaining updated software and understanding factors beyond scanner resolution are crucial for optimal accuracy. Conversely, smaller IOS tips, fast scanning speeds, and specific scanning patterns compromise the accuracy and precision." ^[14]

Cost is another factor to consider. Lower-priced scanners may struggle with challenging surfaces compared to their more advanced counterparts ^[9]. Additionally, as the scanned area increases, merging individual images becomes more complex, potentially affecting accuracy. Environmental conditions, such as lighting, scanning distance, and the properties of the scanned material, can further impact performance ^[15].

Conventional Impressions: Methods and Precision

Overview of Conventional Impression Materials

Conventional dental impressions use physical materials to create a mould of a patient’s oral structures. These impressions are critical for producing accurate restorations ^[17]. For best results, the materials used must be stable, rigid, biocompatible, and hydrophilic, ensuring they capture both teeth and soft tissue details with precision ^[17]. Two of the most commonly used materials in dental practices today are polyether (PE) and polyvinyl siloxane (PVS), also known as A-silicone ^[16][17].

Polyether materials, such as 3M™ Impregum™ Polyether Impression Material, are particularly valued for their clinical benefits. Dr. Carlo Arcara, DDS, PhD, shares his perspective:

"I prefer polyether (PE), like 3M™ Impregum™ Polyether Impression Material, in most cases because it has a very long working time, so you have enough time to remove the retraction cord and load and seat the impression tray." ^[17]

This longer working time makes polyether especially useful for complex procedures that demand precise timing. For implant cases, a double impression technique is often employed – using heavy or medium body material first, followed by a light body material – to ensure soft tissue details are captured accurately ^[17]. These qualities contribute to the reliability of conventional impressions, as explored further below.

Strengths of Conventional Impressions

Conventional impressions offer distinct advantages in specific clinical situations. Studies have shown that when performed correctly, these methods deliver exceptional precision. For instance, research found that polyvinyl siloxane impressions achieved a precision of 14.06 ± 2.01 µm and a trueness of 16.15 ± 2.07 µm ^[16]. Gypsum cast scans were noted to have the highest accuracy, followed by conventional impressions and then digital scans ^[16].

Among materials, A-silicone stands out for its minimal deviation and top-tier accuracy, with polyether coming next. Both have demonstrated better precision than digital scanners in many cases ^[18]. Laboratory findings suggest that conventional impressions can match the accuracy of intraoral scanners, while clinical data have shown similar results for fixed dental prostheses with fewer than four units ^[19]. For larger fixed solutions or removable prostheses, conventional methods are often preferred due to their superior accuracy in these more complex applications ^[19]. Over the years, the workflow for conventional impressions has been refined, creating a dependable process that dental laboratories are well-equipped to handle.

Problems with Conventional Impressions

Despite their precision, conventional impressions come with challenges. One of the biggest issues is the potential for human error, which has driven the development of intraoral scanners ^[14]. Unlike digital approaches that simplify workflows, conventional methods involve multiple steps, each introducing opportunities for mistakes ^[20]. Errors such as poor tray selection, improper material mixing, surface contamination, internal bubbles, or patient movement can compromise the final restoration. These mistakes often result in longer chairside adjustments and costly remakes ^[5].

A critical concern is the accuracy of margin details. As David Hudnall, DMD, explains:

"The most important aspect of any impression are the fine details that indicate exactly where the restoration should end. The absence of clear delineation of details is the bane of any lab tech’s existence and jeopardises the final restoration’s fit." ^[22]

Comparative studies highlight the accuracy gap between conventional and digital methods. For example, conventional polyether impressions showed a mean distance deviation of 454.24 ± 334.70 µm, which is significantly higher than the 160.98 ± 204.48 µm to 255.56 ± 395.89 µm range observed with intraoral scanners ^[21]. Additionally, the mean angular deviation for conventional impressions was recorded at 1.82 ± 1.51° ^[21]. Factors such as the impression technique, transportation conditions, tray selection, and mixing procedures can further affect accuracy ^[21]. Errors at the impression stage are difficult to correct later in the lab, ultimately impacting the internal and marginal fit of prostheses ^[21]. These limitations underline the importance of weighing patient experience and practicality when deciding between conventional and digital options.

Patient Experience and Practical Factors

Patient Comfort and Convenience

When it comes to choosing an impression method, comfort is a major consideration for patients. Research highlights a clear preference for digital scanning over traditional methods. One study found that patients rated their discomfort at 6.66 for conventional impressions, compared to 9.03 for digital scanning on a 10-point scale ^[23].

Traditional impressions involve using putty-like materials and bulky trays, which often cause gag reflexes and discomfort due to their taste and texture ^[24][4]. These factors can make the experience unpleasant for many patients.

Digital impressions, on the other hand, bypass these issues entirely. Without the need for messy materials, the process feels cleaner and less invasive. This not only reduces anxiety but also leads to higher satisfaction among patients ^[24][25].

Speed and Workflow Integration

The time savings with digital impressions are significant. They can cut procedure times nearly in half, reducing them from about 24 minutes to just 12 minutes – or from 605 seconds to 248 seconds ^[27].

Another key advantage of digital workflows is the ability to identify and correct errors in real time ^[26]. This makes the process not only faster but also more efficient. As Dentsply Sirona USA explains:

"Digital scans provide a faster and more comfortable approach for taking impressions than analog methods that are associated with unpleasant tasting materials, bulky trays and possible gagging."

• Dentsply Sirona USA ^[26]

Digital impressions also allow instant sharing with dental labs and specialists, speeding up the treatment timeline. The FDI World Dental Federation supports this, stating:

"The use of digital impressions eliminates a number of clinical and laboratory steps, leading to fast and effective delivery of the final custom-made medical device."

• FDI World Dental Federation ^[8]

In fact, studies show digital workflows can reduce both chairside time and overall case turnaround by up to 50%. This results in fewer appointments and more efficient treatments ^[25]. While digital methods are becoming the go-to choice, conventional impressions still hold their place in certain clinical situations.

Conventional Methods: Patient Perspective

Despite the growing preference for digital scanning, some patients may still require conventional impressions. Those with excessive salivation or very limited mouth opening can face challenges with digital scanning ^[25]. Similarly, while modern intraoral cameras are now more compact, their size may still pose difficulties for some patients ^[25].

Traditional methods also come with their own set of drawbacks, like the unpleasant taste and texture of the materials used. However, studies consistently show that most patients favour digital techniques due to the overall comfort, reduced gag reflex, and ease of breathing during the procedure ^[3]. This improved experience often leads to higher acceptance rates for treatments in practices that have adopted digital technology.

Direct Comparison: Intraoral Scanners vs Conventional Impressions

Comparison Table

Here’s a side-by-side look at how intraoral scanners stack up against conventional impressions:

The data highlights how the choice between these methods often comes down to specific clinical needs. For instance, research by Zarbakhsh et al. demonstrated that digital impressions deliver greater precision, with internal gaps ranging from 51.88 to 88.93 μm, compared to 120.23–188.66 μm for conventional techniques ^[28].

In clinical scenarios, the average difference in accuracy between digital and conventional methods was reported to be approximately 317.86 microns ^[1]. However, the effectiveness of digital methods can vary due to operator-related factors like scanner type, head size, scanning strategy, and the operator’s level of experience ^[2]. Notably, scanners using active wavefront sampling technology have been shown to achieve higher precision compared to other scanner types ^[2].

For implant cases, where precision is critical, the choice of method becomes even more nuanced. Conventional impressions are often favoured in partially edentulous cases with implants and for extensive fixed or removable prostheses ^[2][19]. Additionally, caution is recommended when inter-implant angles exceed 15°. In completely edentulous cases without implants, digital methods generally match the accuracy of conventional ones only when bony structures are covered with attached mucosa ^[2].

Understanding these differences helps clinicians choose the most suitable approach for each unique case.

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Clinical Uses and Recommendations

When to Use Intraoral Scanners

Intraoral scanners shine in specific clinical situations, especially when precision and patient comfort are priorities. Studies reveal that 51% of patients prefer intraoral scans over traditional impressions, with 75% of those who tried both favouring digital scanning ^[31]. These tools not only improve accuracy but also streamline treatment workflows.

Orthodontics is a prime example where digital impressions excel. They’re ideal for tasks like diagnostic setups, fabricating aligners, and producing removable appliances ^[31]. For adults undergoing clear aligner therapy, these scanners provide precise digital models that form the foundation for custom-fit devices ^[32].

Patients who struggle with gag reflexes, anxiety, or breathing difficulties also benefit significantly from digital scanning ^[30][31]. Additionally, intraoral scanners are well-suited for single-tooth restorations and short-span fixed reconstructions. On top of that, the digital workflow offers an environmental edge by cutting down on material waste and eliminating the need to transport physical moulds to labs, reducing the carbon footprint ^[3].

When Conventional Impressions Are Preferred

While digital technology has advanced, there are still scenarios where conventional impressions are the better choice. For example, long-span reconstructions often demand the superior accuracy that traditional methods provide. Clinical data consistently shows that conventional impressions outperform intraoral scanners for extensive fixed solutions or removable prostheses ^[2].

Complex implant cases also require careful consideration. When inter-implant angles exceed 15°, digital scanning can struggle to capture the necessary details reliably ^[2]. Similarly, conventional impressions are often favoured for partially edentulous cases with implants, as they can more effectively capture intricate anatomical features.

Another area where traditional methods shine is in capturing subgingival finish lines, especially when bleeding is present ^[1]. For patients with excessive salivation, conventional impressions can be more practical, as they function well in high-moisture environments ^[3].

When it comes to removable prosthetics, fully digital workflows are generally limited to simpler, tooth-bounded cases like Kennedy Class III and IV. More complex prostheses often require the tactile feedback that only conventional impressions can provide ^[2]. Lastly, cost can be a deciding factor. Traditional impressions involve lower upfront costs, making them a more accessible option for many practices ^[3].

These distinctions often lead clinicians to adopt a combined approach, using each method where it’s most effective.

Modern Practices Using Both Methods

Today’s dental practices are increasingly blending traditional and digital techniques to deliver the best outcomes for their patients. By 2025, 57% of dental practices in the USA had adopted intraoral scanners, illustrating the growing role of digital tools alongside conventional methods ^[34].

To make this hybrid approach work, staff training and clear communication with dental labs are essential. Teams need to stay skilled in both traditional and digital methods to ensure they can provide evidence-based care ^[31]. Additionally, maintaining detailed prescriptions and sharing thorough patient information with labs enhances outcomes, regardless of the impression technique used ^[33].

Patient education is another key element. With 78% of patients valuing personalised guidance and 90% appreciating digitally visualised outcomes ^[34], clinicians can explain the advantages of each method based on the treatment. Typically, intraoral scanners are used for routine single-unit restorations, orthodontic cases, and situations where patient comfort is a priority. Meanwhile, conventional impressions are reserved for more complex multi-unit cases, challenging implant scenarios, and treatments requiring maximum detail.

Digital vs conventional impressions – how does the accuracy compare?

Conclusion: Key Points

When it comes to accuracy, both intraoral scanners and traditional impression techniques perform on a similar level for most dental applications. Research, including systematic reviews, confirms that digital impressions fall within clinically acceptable accuracy ranges, making them a reliable choice for routine procedures ^[35].

Digital impressions also offer distinct advantages, such as improving patient comfort and cutting down working time, which can lead to more efficient workflows. However, traditional impressions still hold their ground, especially in full-arch restorations. Studies highlight that high-quality materials like polyvinyl siloxane can deliver superior accuracy in these cases ^[1].

Operator expertise plays a crucial role in the success of both methods. With digital scanning, accuracy improves as practitioners gain experience, while traditional impressions demand precise handling of materials and techniques. For example, modern scanners like the TRIOS 3 can achieve a precision of about 10 micrometres when used correctly and in line with manufacturer guidelines ^[29].

A hybrid approach often works best, allowing treatment strategies to be tailored to the specific needs of each case. Digital scanning is ideal for routine procedures and orthodontic cases, while traditional impressions are better suited for more complex restorations. This flexibility ensures that the chosen method aligns with the demands of the treatment.

For dental practices in Australia, the key takeaway is that both methods can deliver comparable accuracy when properly executed. Therefore, the decision between intraoral scanners and conventional impressions should hinge on considerations like patient comfort, workflow efficiency, and the complexity of the case, rather than accuracy alone.

FAQs

What should dentists consider when deciding between intraoral scanners and traditional impressions?

When choosing between intraoral scanners and traditional impressions, dentists should weigh a variety of important factors. One of the most important is accuracy. Modern intraoral scanners can often match or even exceed the precision of traditional methods, though this can vary based on the case and the specific scanner being used.

Another key consideration is patient comfort. Digital scans are generally quicker and less invasive, which can make the experience much more pleasant for patients compared to traditional impressions.

Time efficiency is another benefit of digital scanning. These systems can help streamline workflows, potentially speeding up processes. However, cost is an important factor to keep in mind. While the initial investment in an intraoral scanner can be substantial, it may save time and resources over the long run. Additionally, the dentist’s level of experience with the technology and the scanner’s compatibility with existing systems in the practice are crucial points to evaluate.

In the end, the decision should strike a balance between precision, patient comfort, and the overall efficiency of the dental practice.

Why are intraoral scanners more comfortable than traditional dental impressions?

Intraoral scanners bring a far more comfortable alternative to traditional dental impressions. Gone are the bulky trays and messy materials that often cause discomfort or trigger gag reflexes. Instead, the process involves quick, non-invasive digital scans, making the entire experience much smoother.

Patients frequently mention feeling less anxious and more at ease during the procedure. The faster, gentler approach of intraoral scanning avoids the unpleasant sensations tied to older methods. This shift has made these scanners a popular choice among both patients and dental professionals for creating precise dental impressions.

When might investing in an intraoral scanner be worth the cost?

Investing in an intraoral scanner can pay off in the long run when its advantages lead to savings and smoother operations. These benefits include quicker case processing, shorter chair time, better patient comfort, and faster lab turnaround – all of which can enhance both productivity and patient satisfaction.

On top of that, the precision offered by intraoral scanners helps cut down on errors, resulting in better clinical results. For dental practices moving towards digital workflows or aiming to remain competitive in today’s landscape, the upfront cost can provide lasting benefits over time.

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