Implant placement immediately after extraction has been advocated for its advantage of reduced overall treatment period and number of appointments as well as cost-efficiency higher than delayed implant placement [1~3]. However, due to unavoidable morphological and structural change of soft and hard tissue on the extraction sites [1], immediate implant placement may result in unexpected post-operative remodeling of soft and hard tissue after surgery such as mid-facial mucosal recession, papillary height loss due to resorption of the facial and interproximal bone, and vertical and horizontal bone resorption [4~6].

When the commercial healing abutment(HA) is applied after immediate implant surgery, it is usually difficult to completely seal the extraction socket area, which causes the area to be healed by secondarily. In particular, unlike the anterior region, the diameter of the extraction socket in the posterior area is much larger than the implant fixture diameter. Thus, it is a challenge to maintain the bone graft material placed in the gap between the extraction socket wall and the fixture and to prevent the peri-implant soft tissue from collapsing [5,7,8]. These problems can be resolved by applying the interim restoration which allows to optimize the outcome in the regenerative and esthetic aspects, however, clinicians may face the mechanical complications, such as provisional crown fracture or loosening of the abutment, as well as the biological complications, i.e. mucosal inflammation or marginal bone loss due to excessive cement or food impaction [9]. In addition, especially for the single implant placement in the posterior region, it is difficult to consider the immediate restoration unless the primary stability is sufficient to endure immediate loading [10], since it has been reported that the failure rate of implant after immediate loading may increase due to the micromotion and masticatory force [11].

Regarding the forementioned shortcomings of immediate restoration, several previous research have recently introduced a customized healing abutment designed which fits the extraction socket entrance after immediate implantation [12,13]. By covering the extraction socket, it can maintain the graft materials surrounding immediately placed implants and capture the existing soft tissues while eliminating the adverse effects of immediate restoration such as micromotion and cement leakage. In the early days, the concept of creating a sealing socket abutment(SSA) was proposed by adding composite resin directly to the ready-made abutment at the chair-side to secure the graft materials in the gap around the fixture, which not only increased chair time and lab work but also damaged soft tissue to the residual monomers [14]. Nowadays, computer-aided design and manufacturing(CAD/CAM) technology has enabled the clinicians to create SSA in a more comfortable way by taking optical impression with intraoral scanner, designing the abutment with computer software and fabricating it with a three-dimensional(3D) printer or milling machine, and the scientific evidence of this novel treatment modality is getting established by the recent publications [15~17]. Among many restorative materials, polymethylmethacrylate(PMMA) and poly etheretherketone(PEEK) are commonly used for their physical and mechanical advantages [18]. While SSA appears to be attractive in immediate implantation to maintain natural tooth profile, cost-effectiveness and additional steps to fabricate SSA are some of inconvenient factors to consider.

To help this, this case report presents the cases treated by the HA or SSA fabricated by CAD/CAM technology to compare the soft tissue healing and volumetric change in peri-implant mucosal contour after the immediate implantation in the posterior region.

The present case report includes the cases of the patients who were treated at Department of Periodontology, Yonsei University Dental Hospital, Seoul, Republic of Korea. The retrospective data collection, except for any personal information of the patients, was ethically approved by the Institutional Review Board at Yonsei University Dental Hospital, Seoul, Republic of Korea(Approval No. 2-2024-0042).

Of the four patients immediately implantation in the posterior area, two patients(case 1 and case 2) had HA connected and the other 2 patients(case 3 and case 4) had SSA for 3 months before final prosthesis delivery. All four patients were recommended for extraction and implantation due to endodontic problem(root fracture, root canal failure), and all had a buccal wall thickness of 1 mm or more. All of the treatment procedures were conducted by a single practitioner(S.-W.Y.), and Table 1 presents demographic information for four patients.

All site numbers used in the present case report are based on FDI(Fédération Dentaire Internationale) World Dental Federation notation.

In terms of horizontal contour change, the cases 1 and 2 that the HAs were applied demonstrated reduction of approximately 1mm after final prosthesis delivery when compared to the pre-surgical state, while the cases 3 and 4 which the SSA were used showed a smaller reduction less than 0.5mm during the same time period.

In the aspect of vertical contour change, the cases 2, 3 and 4 did not present any change, whereas the mucosal margin of the case 1 receded 0.7mm after loading compared to the pre-surgical state.

All measurements are summarized in Table 2.

The cases described in the present report showed that the mucosal contour change could be minimized by sealing the extraction socket entrance with HA or SSA following the immediate implant placement after the posterior tooth extraction, however, there was a difference between using the HA and SSA.

In terms of both horizontal and vertical change, the SSA resulted in less change compared to the HA, which implies that the SSA was better in optimizing the maintenance of soft tissue contour. In the recently published papers, it was also demonstrated that there was a benefit in terms of maintaining soft tissue contour, keeping papilla index and minimizing ridge dimension change when SSA was used [21~23] just as the outcomes from the cases 3 and 4 of the present study. Furthermore, a retrospective study done by Tarnow et al. emphasized on the use of bone graft and provisional restoration to minimize the ridge contour change [24]. On the contrary, the cases 1 and 2 with HA resulted in larger reduction of horizontal soft tissue dimension eventually having peri-implant mucosal margin unmaintained and even though there was a compensation of mucosal level of approximately 0.5mm in the vertical direction achieved after the final prosthesis installation, more reduction of mucosal level occurred in both horizontal and vertical aspects compared to the SSA-applied cases.

In the immediate implantation, mucosal level may change after a surgery depending on a patient's periodontal phenotype, which may cause an unexpected recession in marginal mucosa [1]. Based on the previous studies [21~23] and the outcome from the present report, SSA could assist to minimize the unexpected mucosal level change and it was also previously reported that both not only the soft tissue but also the hard tissue could be better maintained with SSA [22,23,25]

Unlike the immediate implantation in the anterior region, the size of gap defect used to be wider when the implant is immediately placed in the extraction socket of the posterior tooth. Therefore, the amount of bone graft material needs to be increased as well, which eventually makes the stability of the graft material more crucial [14,26]. Taking this notion into account, the SSA would be more useful in the posterior, since there used to be a larger discrepancy in the size between the HA and socket entrance. Not only the increase of the wound stability, but the peri-implant marginal mucosa with a physiologic emergence similar to that of a natural tooth could be obtained by the SSA during the early healing stage.

In the present cases, the fabricating methods for the SSA in the case 3 and that in the case 4 were different to each other. In the case 3, the SSA was made by applying 3D-printed PMMA crown over the non-hex type PEEK abutment, which was designed and fabricated before the implant surgery, whereas in the case 4, the provisional crown and customized titanium abutment were designed and milled after the implant placement according to the mucosal profile, resembling the appearance of natural teeth. Since the pre-fabricated provisional crown needed to be relined by resin to fill the gap between the mucosa and the PEEK abutment, the chair time spent for delivering the SSA took longer in the case 3 compared to the case 4. This implies that the pre-fabricated SSA could be beneficial in terms of reducing the number of visits, but on the other hand, it may increase the discomfort of both the clinicians and patients due to the longer chair time.

Recently published randomized controlled clinical have shown the efficacy of applying the SSA following the immediate implant placement in the anterior site [23,27]. Perez et al [23]. reported that the SSA resulted in better outcomes in terms of preserving the papilla contour and preventing the peri-implant marginal bone loss for a year after the implant placement. Meanwhile, the study of Fernandes et al [27]. demonstrated that the SSA and HA did not show significant difference for a year, but the peri-implant tissue volume shrinkage in the early healing stage(between the immediate implant placement and one month post-surgery) was significantly lower when the SSA was applied. This implies that the SSA would provide a benefit in terms of preserving the peri-implant marginal bone level and mucosal contour and volume in the posterior area as well. However, the well-designed clinical study dealing with this issue is still scarce. Despite the limitations of the present case report in the aspect of small number of patients, the present case report has suggested that the SSA may prevent mucosal volume shrinkage and it could be thought that the present case report provides a cornerstone and starting point for the future research which will investigate the efficacy of the SSA in the immediate implant placement in the posterior region.

Within the limitation of the present case report, to resemble the emergence profile of natural tooth, the SSA could be promptly prepared pre- or post-operation through digital dentistry and maintain peri-implant mucosal contour in the immediate implantation in the posterior site.