A clinical case was chosen to present the step-by-step procedures that enables measuring the pressure exerted on the gingiva by the implant-supported crown.

A 64-year-old male patient attended to rehabilitate his edentulous first left mandibular molar site (#36) that displayed a thick biotype gingiva. After clinical and 3D radiological examination implant therapy involving a 2-stage surgery protocol was proposed; it consisted into placing a Top DM implant of 4.0 × 10 mm (Bioner, San Just Desvern, Spain) in a 1.5 mm subcrestal position. The patient signed an informed consent to allow his data serve a publication purpose on the condition of anonymity.

The implant is designed with an internally indexed hexagonal conical connection [15] and presents a regular honeycomb like macro- and microsurface texture obtained by etching only, without sandblasting [16]. After achieving a primary stability superior to 35 Ncm, the implant was left to heal for 3 months in a submerged fashion. Three months later, the implant was uncovered and standard clinical and radiologic examinations assessed its osseointegration. A transepithelial abutment of 3 mm in height designed with a hexagonal head was screwed into the implant neck with a 25 Ncm torque. This abutment served simultaneously as a transgingival healing abutment while receiving a healing cap, and as a prosthetic abutment while receiving a screw-retained crown over its hexagonal head.

After 6 weeks of soft tissue healing (Fig. 1a) an intraoral scan (IOS) was taken with the healing cap in place (IOS#1). Immediately after, the healing cap was removed and an IOS was taken with the scan-body placed on top of the transepithelial abutment. The intra-oral scan was sent to the dental lab and the dental technician designed and produced by CAD-CAM a screw-retained crown (DentalCAD, Exocad, Darmstadt, Germany; MillBox CIMsystem, Balsamo, Italy). The single crown was affixed to the transepithelial abutment; strains exerted by the prosthesis on the healed gingiva led to various intensities of gingival blanching (Fig. 1b). After 30 min, the presence of blanching was checked as having completely vanished (Fig. 1c). Following prosthesis delivery, a second IOS (IOS #2) was taken with the crown in place. After 3 months of function and soft tissue conditioning, the crown was unscrewed and a third IOS (IOS#3) was taken; this recorded the emergence profile that was shaped under the implant-supported crown (Fig. 2a, b).

Presentation of the case. a) Radiographic control of the implant by the end of the soft tissue healing period. Note the bone grown over the shoulder of the Top DM implant, in contact with the concave shape of the transepithelial abutment. b) Blanching of the gingiva upon delivery of the implant-supported crown. Note the various blanching intensities. c) Vanished blanching that led the patient to be safely discharged

Views of the emergence profile after unscrewing the crown. a) Vestibulo-occlusal view of the soft tissue of the emergence profile after 3 months of function. b) Occlusal close-up view. The mesial gingiva participated mostly to the emergence profile conditioned under the crown

The digital merging procedure previously described by Szmukler-Moncler et al. [17] was applied. On top of the 3 above mentioned IOSs, it involves on one hand the STL (Standard Tessellation Language) files of the healing cap, the transepithelial abutment and the implant, all provided by the manufacturer and on the other hand the STL file of the crown designed by the dental technician.

Figure 3 lists the various steps of the digital protocol. First the STL of the healing cap, the transepithelial abutment and the implant were superposed according to the drawings of the manufacturer in a single STL (Fig. 4a); then, it was merged with IOS#1 until matching (Fig. 4a-c). Figure 4d represents a section of the merging of the superposed implant items with IOS#1; it shows how the healing cap seats on the transepithelial abutment.

>Diagram showing the various superpositions and merging steps. IOS#1 was first handled with the various STLs; the aim was to merge appropriately the healing cap with IOS#1. Then, IOS#2 was handled with the various STLs; the aim was to merge the STL of the crown with IOS#2. This succession of superpositions and merging allows reading the distances the crown compresses and stretch the gingiva

Merging the healing cap with IOS#1. a) Importation of the STL of the healing cap, the transepithelial abutment and the implant while preparing the merging with IOS#1. b) Steady point referencing in preparation of the automatic merging between the STL and IOS#1 by selecting 5 similar reference points. c) Successful result of the automatic merging of the STL of the healing cap. d) Vestibulo-lingual section of the merging of the STL of the healing cap-transepithelial abutment-implant with IOS#1. The green line refers to IOS#1; the yellow line highlights the external delimitation of the healing cap and the further gingiva. Note how the healing cap seats on the transepithelial abutment

As for the prosthetic part, the first step was to superimpose the STL of the crown with the STL of the titanium base of the crown, the transepithelial abutment and the implant in a single STL (Fig. 5a, b); this STL was then merged with IOS#2 to place the crown and its related items in its correct position (Fig. 5c, d). Then, this STL was merged with IOS#1; it now allows measuring the distance the crown squashes and stretches the gingiva (Fig. 5e, f). Completing this procedure of successive merging and superpositions allows measuring the distance the crown is squeezing the peri-implant gingiva and stretching it at every place of the emergence profile, from the most coronal part of the crown to the most apical one.

Merging of the crown with IOS#2. a) Image of the superposition of the crown, the Ti base, the transepithelial abutment and the Top DM implant. b) Close-up of the connection between the crown and the transepithelial abutment as read on the STL. c) Referencing the STL of the crown in preparation of the automatic merging with IOS#2. d) Successful result of the automatic merging of the STL of the crown. e) Mesio-distal view of the superposition of the STL of the crown and its related items with IOS#1 (in orange). The STL of the healing cap is not shown here in order to allow for a better reading of the figure. The yellow dot lines are delimiting the external envelope of the healing cap. An apical limit of the crown below the orange line means that the crown squashes and displaces the healed gingiva. The distance of the squeezing can be measured at every point of the gingiva. e) Measure of the displacement distances the crown brought to the healed gingiva. The mesio-distal axis where the displacements were measured is shown in the occlusal view of the crown (left). The highest displacement distance the crown is triggering on the gingiva is 1.7 mm on the mesial side. On the distal side, pressure of the crown was over 0.4 mm (in yellow) and stretching was over 0.1 mm (in red)

The measurements on the digitally merged files were performed at the sites of the various blanching intensities (Fig. 1b), at the vestibulo-mesial side where the gingiva exhibited the most severe blanching, at the mid-vestibular side where blanching was moderate, at the vestibulo-distal side where blanching was absent, on the mesial side where blanching was severe and on the distal side where blanching was absent.

After 3 months of function and soft tissue conditioning of the emergence profile, the crown was unscrewed and a scan (IOS#3) was taken to get the exact shape of the emergence profile (Fig. 6).

View of IOS#3 taken after unscrewing the crown. Note the hexagonal head of the transepithelial abutment and the emergence profile that has been conditioned under the crown

To visualize the places where the gingiva was strained in order to lead to the actual emergence profile, IOS#1 and IOS#3 were superposed while subjecting IOS#3 to a partial transparency.

The IOSs were performed with the Trios 3 scanner (3Shape, Copenhague, Denmark); the superposition and merging steps as the distance measurements were performed with the Exocad software (Exocad, Darmstadt, Germany).

The soft tissue displacements caused by the crown that led to the various intensities of blanching are shown in Fig. 7a and b. Severe blanching appeared when the crown strained the gingiva over a distance of 1.3 to 1.7 mm; moderate blanching was seen upon a displacement of 0.9 mm and lack of blanching was found up to a displacement of 0.6 mm.

Results of the measurements. a) Occlusal representation on the crown of the plans where the displacement distances were recorded. Five sites have been measured; each one corresponds to a distinct blanching response of the gingiva to the strains yielded by the prosthetic crown. b) Measurements corresponding the various blanching intensities of the gingiva during crown delivery. On the vestibular site, the most intense bleaching was due to a displacement of 1.3 mm, the moderate blanching responded to a pressure of 0.9 mm. No blanching was observed when compression was 0.6 mm. On the mesial side, blanching is masked by the crown but the pressure was there the highest with 1.7 mm

The mesio-distal length of the emergence profile was 10.1 mm (Fig. 8) and the vestibulo-lingual width was 5.9 mm; this is to compare with the Ø 5.0 mm external diameter of the healing cap of the transepithelial abutment. This means that the initial emergence profile shaped by the healing cap was increased by twice in the mesio-distal direction. Figure 9a and b are showing the evolution of the topography of the gingiva from the end of the healing period to its final conditioning under the crown. They are evidencing that, in the present case, the gingiva (in white) was mostly squeezed in the mesial portion of the actual emergence profile.

Mesio-distal measurement of the emergence profile read on IOS#3. The mesio-distal distance of the emergence profile is 10.1 mm. It has been enlarged compared to the initial Ø 5.0 mm emergence profile reached around the healing cap

Superposition of IOS#1 and IOS#2 showing the topography of the soft tissue conditioning under the crown. a, b. Vestibular and vestibulo-occlusal view of the location of the strained gingiva. IOS#3 (in brown) was rendered partially transparent to allow identifying the initial topography of the gingiva (in white) given by IOS#1. These images reveal that pressure was mostly exerted by the crown on its mesial side and much less on its vestibular one