Conventional Versus Digital Implant Impression Techniques: A Comprehensive Narrative Review

ABSTRACT

Accurate transfer of intraoral implant position is a critical determinant of the success of implant-supported prostheses. The evolution from conventional elastomeric impressions to digital intraoral scanning has significantly transformed prosthodontic workflows. However, controversy persists regarding the comparative accuracy and clinical applicability of these techniques, particularly in complex cases such as full-arch rehabilitations. This narrative review aims to critically evaluate conventional and digital implant impression techniques with respect to accuracy (trueness and precision), clinical efficiency, patient-centered outcomes, and influencing variables. Evidence from recent in vitro studies, randomized clinical trials, and systematic reviews was analyzed, including the studies provided. The findings suggest that while digital impressions demonstrate advantages in patient comfort, workflow efficiency, and data management, conventional techniques—particularly splinted open-tray methods—continue to exhibit superior precision in full-arch implant scenarios. Digital impressions are clinically reliable for single-unit and short-span restorations but remain technique-sensitive. Future advancements in scanner technology and digital workflows may bridge existing limitations.

Keywords: Implant impressions, digital dentistry, intraoral scanners, accuracy, CAD/CAM, prosthodontics

INTRODUCTION

Implant-supported prosthetic rehabilitation has become a predictable and widely accepted treatment modality for partially and completely edentulous patients. A fundamental prerequisite for the long-term success of such restorations is the passive fit of the prosthesis, which is directly dependent on the accuracy of implant impressions. Any discrepancy in recording the three-dimensional spatial orientation of implants may lead to misfit of the prosthesis, resulting in mechanical complications such as screw loosening, screw fracture, or framework distortion, as well as biological complications including peri-implantitis.

Traditionally, implant impressions have been made using elastomeric materials such as polyvinyl siloxane (PVS) and polyether. These conventional techniques have been considered the gold standard due to their established accuracy and long-term clinical success. However, the introduction of digital dentistry, particularly intraoral scanners (IOS), has revolutionized prosthodontic workflows by enabling direct digital capture of implant positions.

Digital implant impressions utilize scan bodies attached to implants and convert intraoral data into standard tessellation language (STL) files, which can be used for computer-aided design and manufacturing (CAD/CAM). This approach eliminates several steps inherent in conventional workflows, thereby reducing potential sources of error.

Despite these advantages, the literature presents conflicting evidence regarding the accuracy of digital impressions compared to conventional methods, particularly in full-arch implant restorations. Therefore, a comprehensive understanding of both techniques is essential for evidence-based clinical decision-making.

1. CONVENTIONAL IMPLANT IMPRESSION TECHNIQUES

Conventional implant impressions involve transferring the intraoral position of implants to a definitive cast using impression copings and elastomeric materials. These techniques are broadly categorized into:

• Open tray (pick-up) technique
• Closed tray (transfer) technique
• Splinted and non-splinted approaches

Among these, the splinted open-tray technique is often regarded as the most accurate for multiple implant cases, as it minimizes micromovement of impression copings during impression removal.

1.1Factors Affecting Accuracy

The accuracy of conventional impressions is influenced by multiple variables, including:

• Impression material (polyether vs PVS)
• Implant angulation and depth
• Number and distribution of implants
• Splinting technique
• Tray design and rigidity
• Stone expansion during cast pouring

Errors may occur at any stage of the process, including material distortion, coping displacement, and laboratory procedures.

1.2 Evidence from Literature

A recent in vitro study demonstrated that conventional impressions using A-silicone and polyether materials exhibited superior precision compared to digital impressions, although trueness values were comparable. This highlights the reliability of conventional methods in reproducing consistent results.

Another study emphasized that inaccuracies in conventional impressions may increase with implant angulation, as removal of the impression material can cause distortion.

Despite these limitations, conventional techniques remain highly reliable, especially in full-arch and complex implant scenarios.

1.3 Advantages

• High precision and reproducibility
• Well-established clinical protocol
• Less dependence on advanced technology
• Superior performance in full-arch restorations

1.4 Limitations

• Technique-sensitive and multi-step process
• Increased chairside time
• Patient discomfort (gag reflex, unpleasant taste)
• Risk of material distortion
• Laboratory-dependent errors

2. DIGITAL IMPLANT IMPRESSION TECHNIQUES

Digital implant impressions involve capturing intraoral data using intraoral scanners after attaching scan bodies to implants. The captured images are processed into 3D digital models, eliminating the need for physical impressions.

2.1 Digital Workflow

The digital workflow includes:

1. Placement of scan bodies
2. Intraoral scanning
3. Generation of STL files
4. Virtual articulation and prosthesis design
5. CAD/CAM fabrication

This streamlined process reduces procedural steps and enhances efficiency.

2.2 Factors Affecting Accuracy

Digital impression accuracy depends on:

• Scanner type and resolution
• Scan body design and material
• Scanning strategy
• Operator experience
• Environmental factors (saliva, lighting, movement)

Additionally, accuracy decreases as the scanning span increases, particularly in full-arch cases.

2.3 Evidence from Literature

A randomized clinical trial demonstrated that digital and conventional implant impressions exhibited comparable accuracy in distal extension cases.

Another clinical study reported that digital impressions provided superior patient comfort, reduced chairside time, and comparable precision to conventional methods.

However, some studies suggest that digital impressions may be less accurate in long-span restorations and cases with significant implant angulation.

2.4 Advantages

• Enhanced patient comfort
• Reduced chairside time
• Elimination of impression materials
• Improved infection control
• Easy data storage and transfer
• Possibility of rescanning without repeating entire procedure

2.5 Limitations

• High initial cost of equipment
• Technique sensitivity
• Learning curve for clinicians
• Reduced accuracy in full-arch cases
• Dependence on software and hardware

Accuracy: Trueness and Precision

Accuracy in implant impressions is defined by two key parameters:

• Trueness: closeness of the measured value to the actual value
• Precision: reproducibility of repeated measurements

Conventional impressions generally demonstrate higher precision due to consistent material behaviour, whereas digital impressions often show comparable trueness but variable precision depending on scanner technology.

Studies indicate that deviations in both techniques are within clinically acceptable limits; however, differences become more pronounced in full-arch restorations.

Digital implant impressions utilize scan bodies attached to implants and convert intraoral data into standard tessellation language (STL) files, which can be used for computer-aided design and manufacturing (CAD/CAM). This approach eliminates several steps inherent in conventional workflows, thereby reducing potential sources of error.

Despite these advantages, the literature presents conflicting evidence regarding the accuracy of digital impressions compared to conventional methods, particularly in full-arch implant restorations. Therefore, a comprehensive understanding of both techniques is essential for evidence-based clinical decision-making.

DISCUSSION

The comparison between conventional and digital implant impression techniques continues to be a subject of debate, as both approaches demonstrate distinct advantages depending on the clinical context. Conventional impressions, particularly the splinted open-tray technique, have long been regarded as the gold standard due to their high precision and reproducibility. Evidence suggests that elastomeric materials such as polyvinyl siloxane and polyether provide consistent results, especially in full-arch implant rehabilitations where passive fit is critical.¹ Precision is particularly important in multi-unit prostheses, as inaccuracies can lead to biomechanical complications such as screw loosening or framework misfit.

Digital impressions, on the other hand, have gained significant popularity due to advancements in intraoral scanning technology and CAD/CAM workflows. Clinical studies indicate that digital impressions demonstrate comparable accuracy to conventional techniques in partially edentulous cases and short-span restorations.² In addition to accuracy, digital workflows offer several advantages, including improved patient comfort, reduced chairside time, elimination of impression materials, and efficient data storage and transfer.⁴ These factors have contributed to increased patient acceptance and clinician preference for digital techniques in routine practice.

Despite these benefits, limitations of digital impressions remain evident, particularly in full-arch implant cases. One of the primary concerns is the accumulation of stitching errors during the scanning process, which can compromise accuracy over long spans. This limitation is more pronounced in edentulous arches due to the lack of stable anatomical landmarks for reference. Additionally, factors such as scanner type, scan body design, operator experience, and intraoral conditions (e.g., saliva, movement, and lighting) significantly influence the accuracy of digital impressions.²

Implant angulation also plays a critical role in determining impression accuracy. Conventional impressions may be affected by distortion during material removal, especially in cases of divergent implants. Conversely, digital impressions, although less affected by material distortion, may still show reduced accuracy in complex angulated configurations.³

Overall, current evidence indicates that both conventional and digital impression techniques are clinically acceptable, with their selection largely dependent on case complexity and clinical requirements. Conventional techniques remain preferable for full-arch and complex implant cases, while digital impressions are highly suitable for single-unit and short-span restorations. A hybrid approach integrating both techniques may provide optimal clinical outcomes.

CONCLUSION

Both conventional and digital implant impression techniques play significant roles in modern prosthodontics. Conventional methods remain the gold standard for full-arch and complex implant cases due to their superior precision. Digital impressions, however, offer substantial advantages in patient comfort, efficiency, and workflow simplification, making them highly suitable for routine clinical applications.

The choice of technique should be guided by clinical requirements, operator experience, and available technology. As digital systems continue to evolve, they are expected to overcome current limitations and potentially become the standard of care in implant prosthodontics.

REFERENCES