Precision of the emergence profile: optical impression versus customised transfer

The aesthetic success of an implant in the anterior region relies on a triad: surgical positioning, prosthetic restoration and stability of the peri-implant tissues. In the practice, the provisional crown serves as a guide to sculpt the gingival architecture and implant emergence. The crucial challenge lies in the exact transfer of this morphology to the laboratory. This case report details the treatment of a 26-year-old patient for an upper left central incisor (#9), where a satisfactory emergence profile was achieved following a temporisation phase on a thick gingival biotype.

The objective of this study is to quantify the discrepancy between two capture protocols: the traditional PVS impression with a customised impression coping (ensuring mechanical tissue support) and the direct optical impression (Dentsply Sirona Primescan). The study specifically seeks to evaluate the collapse of peri-implant tissues following the removal of the provisional restoration, a phenomenon suspected of altering the accuracy of the digital model compared to the stabilised clinical situation.

The authors test the hypothesis that an optical impression taken without physical support, even within less than 30 seconds after crown removal, results in measurable tissue collapse. To verify this, they use the GeoMagic Control X software to perform a 3D comparison between the STL files derived from the plaster model (reference) and those from the intraoral scan (measurement), thereby identifying precise volumetric deviations in the emergence zone.

Methodology: Digital vs analogue comparison

This case report documents the management of a 26-year-old patient for the restoration of an implant at the upper left central incisor (tooth #9). The patient presented with a thick gingival biotype and a stable provisional restoration during the second surgical phase.

The comparison protocol was based on two distinct acquisition methods:

• The analogue approach (Reference): Taking a final impression using a custom impression tray, addition silicone (PVS) and a customised impression coping (custom impression coping) to support the peri-implant tissues. The working model was poured in type 4 dental stone.
• The digital approach (Measurement): Acquisition of an intra-oral optical impression via the Primescan (Dentsply Sirona) scanner, performed less than 30 seconds after the removal of the provisional crown.

For the comparative analysis, the plaster model was scanned to generate a reference STL file. The data (reference vs measurement) were imported into the GeoMagic Control X software. Following an initial alignment and registration via best fit matching, the region of interest (emergence profile and gingival contours) was isolated. The analysis used the 3D comparison tool to measure the mean, maximum and minimum distance deviations between the data points.

Results of the three-dimensional comparison

The evaluation of the reproduction accuracy of peri-implant soft tissues was performed by superimposing the STL files (Best-fit alignment) in the GeoMagic Control X software. The data from the plaster model (PVS impression with customised transfer) served as a reference against the data measured by the Primescan intraoral scanner.

The quantitative results highlight dimensional discrepancies between the two techniques, summarised in the following table:

The qualitative analysis via the 3D comparison tool reveals major clinical observations:

• Tissue collapse: Colourimetric mapping indicates a collapse of the peri-implant tissues on the intraoral scan compared to the conventional physical impression.
• Modification kinetics: This change in tissue position is observed despite an extremely short scanning delay of less than 30 seconds after the removal of the provisional restoration.
• Location of deviations: The most significant deviations (reaching a maximum of 0.5291 mm) are located at the emergence profile and gingival contours, critical areas for the aesthetic success of the final restoration.

The study highlights that, unlike the physical impression where the customised transfer mechanically supports the gingival architecture during the polymerisation of the material, the intra-oral scan captures a gingiva free of any support. This lack of immediate structural support leads to a measurable modification of the emergence profile compared to the clinical situation stabilised by the provisional.

Analysis of tissue stability: Digital vs Conventional

This clinical case report highlights an often underestimated technical reality: the rapidity of peri-implant soft tissue collapse following the removal of a provisional crown. Although digital imaging with the Primescan system is renowned for its precision, 3D analysis via GeoMagic Control X reveals a mean deviation of 0.0391 mm and a maximum discrepancy of 0.5291 mm compared to the physical impression. These figures demonstrate that, even in a patient presenting with a thick gingival biotype, the tissue undergoes immediate collapse as soon as the physical support of the restoration is removed.

The major interest of this study lies in the timing: the scan was performed less than 30 seconds after the removal of the provisional. Despite this speed, the 3D comparison diagram confirms tissue collapse compared to the Hinds technique (customised PVS transfer), which mechanically maintains the emergence profile. For the practitioner, this means that the technological accuracy of the scanner does not (yet) compensate for the lack of physical support for the gingival cradle during acquisition.

The limitations of this report lie in its single sample (n=1) and the patient's favourable biotype. The authors aptly note that these deviations could be significantly amplified in the case of a thin biotype or if the scanning delay exceeded 30 seconds. Based on current data, while the efficiency of the digital workflow is undeniable, customised transfer remains the gold standard for accurately capturing the gingival architecture sculpted by the provisional.

Summary of results

This case report, focusing on the restoration of a single central incisor in a 26-year-old patient, demonstrates that an intraoral scanner used less than 30 seconds after the removal of the provisional restoration does not prevent tissue collapse. The 3D comparative analysis reveals a mean deviation of 0.0391 mm and a maximum discrepancy of 0.5291 mm, confirming a collapse of the peri-implant tissues compared to the PVS impression technique with a customised impression coping.

In practical terms, for the practitioner:

• Prioritise the customised impression coping: In the aesthetic zone, the physical impression with a custom-made coping remains the gold standard to mechanically support and accurately record the emergence profile shaped by the provisional.
• Manage the time variable: Gingival collapse begins instantly; even a digital capture of less than 30 seconds is insufficient to guarantee the stability of soft contours without adequate physical support.
• Adapt to the biotype: If a discrepancy is observed on a thick biotype, caution is imperative on thin biotypes where the distortion of the gingival cradle is potentially faster and more pronounced during the scan.

Technical glossary of the study

Custom impression coping: Modified prosthetic device to accurately reproduce the soft tissue contours shaped by the provisional restoration. In this study, it is used to prevent the collapse of the emergence profile during physical impression taking.

Emergence profile: Architecture of the transition zone between the implant head and the gingival margin. This profile is sculpted by the provisional crown to guide the growth of the interdental papillae and establish the definitive gingival contours.

Gingival biotype: Morphological classification of periodontal tissues. The patient in the study presented a thick biotype, a factor that influences the stability of the soft tissues and their resistance to collapse upon removal of the prosthetic components.

GeoMagic Control X: 3D metrology software used by the authors for STL file alignment and comparative analysis of volumetric deviations between the traditional impression (reference data) and the intraoral scan (measured data).

Scan body: Digital transfer device screwed onto the implant to allow the intraoral scanner to precisely locate the position and spatial orientation of the implant platform.

"Best fit" alignment (Best fit matching): Algorithmic process of superimposing digital surfaces aimed at minimising overall deviations between two point clouds (STL), making it possible here to compare the exact position of the peri-implant tissues according to the two impression methods.

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