The current four classification categories based on timing of implant placement after tooth extraction initially were proposed at the third ITI consensus conference and were modified by Chen and Buser in 2018 [1, 9]. Immediate placement of an implant after extraction was classified as type 1 and has several advantages, including reduction of treatment duration and procedures, high patient satisfaction, and optimized use of existing bone. In contrast to healing of the extraction socket with a substantial amount of bone loss, the significant increase in bone level observed 3 months after implant installation on the mesial sides in our study illustrated bone regeneration around immediately installed implants. We also hypothesize that immediate placement of an implant can also decrease alveolar ridge resorption to a variable degree.

Osseointegration is characterized histologically by direct bonding of bone to the implant surface and clinically by fusion of the implant with the surrounding bony structure. Interactions between implant surfaces and bone tissue are crucial for osseointegration [2]. Elias et al. reported that implant shape, size, and surface morphology, as well as surgical technique, all play a significant role [10]. SLA surface is one of the most documented rough surfaces in implantology, demonstrating both macro and micro surface roughness. Abrahamsson et al. [11] in 2004 conducted an in vivo experiment in canine and proved the effectiveness of SLA-surfaced implants with higher bone to implant contact and bone formation around the implant by contact osteogenesis. In a study by Donos et al. in 2011 [12], genes associated with regeneration, such as Notch-1, exhibited increased expression on the SLA surface compared to the machined group, and the Wnt signaling pathway is believed to play a significant role as a regulator in regenerative responses to various titanium surfaces. Several clinical studies have illustrated the clinical effectiveness of SLA-surfaced implants rehabilitated in healing sites [2, 4, 13].

As for the implant size, Heimes et al. concluded on the review in 2023 that the larger diameter increases the contact area and provides better primary stability while the linear relationship between implant length and primary stability ends at 12 mm [14]. We recommended choosing the implant length and diameter according to the position of implant placement, anatomical considerations of the area, space and bone availability, and load distribution. From aspect of shape of implant, tapered implant has the advantages of increased primary stability by exerting lateral compressive force on the cortical bone and better load distribution and osseointegration than straight design, which stabilize implant by transmitting static frictional force along implant axis [14]. In addition, the tapered implant can reduce surgical trauma during implant installation and subsequently increase bone-to-implant contact [15].

The implant used in our study possesses the internal connection with hexagon shape with morse taper, which seems to be more efficient concerning biological aspects, allowing lower bacterial leakage with the best sealing ability and present better result in crestal bone loss than external connections. In addition, the internal connection type shows the advantage of high mechanical stability. According to these authors, the internal morse taper type of connection showed higher reliability in the esthetic region [16].

The study conducted by Sodnom-Ish et al. on the survival rate of 105 tissue-level tapered SLA surface implants, which were placed with delayed implantation in 61 patients, demonstrated a survival rate of 98.1% [4]. The higher survival rate observed for tissue-level implants compared to bone-level implants in this study may be attributed to the uneven distribution of samples and timing of implant placement. However, it is important to note that the survival rate of tissue-level implants with immediate placement remains limited in the current literature.

In MBL analysis of our installation of tapered, sand-blasted, and acid-etched internal submerged implants from Shinhung Implant System, the significant regeneration of bone around the implant at 3 months after implant installation suggests the immediate efficacy of SLA surface on bone formation. Even though one of our previous studies of immediate implantation in the posterior maxilla showed fluctuation in bone regeneration and bone loss [17], a consecutive increase in bone level until 5 years after installation was observed in the present study indicating the medium-term effectiveness of SLA-surfaced implants. Several factors have been identified associated with survival and MBL in a 5-year retrospective study. According to Song et al. [18], MBL during 5 years of implant installation is significantly influenced by factors such as smoking status, type of abutment connection, and implant surface. Marginal bone gain in our study can also be influenced by other factors like bone grafting during implant installation. However, most of the cases (91.8%) have not performed additional bone grafting at the time of implant placement. Rather than additional bone graft, positioning the implant fixture below the adjacent crestal bone level in case of premolar and anterior region. In the molar region, we recommended to follow the bone grafting guideline prescribed by Mustakim et al. [17] depending on the presence of interradicular septum and ABH.

In the assessment of MBL around implant, although cone-beam computed topography (CBCT) has the advantage of 3-dimensional assessment, the application of CBCT for post-operative implant assessment is not generally recommended due to titanium artifact and higher radiation dose compared to 2-dimentional radiograph. On the other hand, based on a study of prediction of dental implant failure from deep learning of periapical and panoramic radiograph [19], the diagnostic accuracy and precision of periapical radiograph was 78.6% and 0.84, while that of panoramic radiograph was 78.7% and 0.87, respectively. Moreover, panoramic radiograph is valuable for patients with multiple implants along the jaws with different timepoints.

Success of an immediate implant depends on the primary stability acquired from apical and lateral bone [17]. The clinical result is highly predictable when the ideal conditions for immediate placement are met. The general considerations for successful immediate implant placement are an extraction socket free of acute infection, atraumatic extraction with a flapless procedure, intact facial bone with sufficient thickness (1.5 mm), availability of > 5 mm basal or palatal bone to allow primary stability, three-dimensional implant positioning in relation to existing socket morphology, a sufficient gap between implant and facial wall (> 2 mm), and choice of implant according to location and availability of bone.

In addition to general considerations, the positional rationale concerning the location of implant placement also needs to be addressed. For immediate implant placement in the maxillary anterior region, factors such as a single tooth socket with thin buccal bone, high esthetic demand, and the relationship with anatomical structures (nasal floor, nasopalatine canal, hyper-pneumatized maxillary sinus) are major concerns. The adequacy of facial bone thickness (≥ 1 mm) and apical bone (≥ 5 mm) should be assessed before deciding on immediate placement. Subsequently, palatal positioning of the implant in relation to the extracted socket, with an at least 2 mm gap between the implant and facial bone with bone graft during flapless extraction enhances esthetic outcomes [20]. A single- or double-rooted maxillary premolar area, particularly when dealing with relatively low bone quality, can pose challenges, especially in cases of maxillary sinus hyperpneumatization. In our present study, the premolar region exhibited significantly high survival rates (100%), emphasizing the importance of adhering to general considerations for implant placement and appropriate choices regarding implant diameter and length.

Immediate placement of implants in the maxillary molar region requires special considerations owing to its multi-rooted nature, low bone density, and proximity to the maxillary sinus. Essential factors to be considered include the presence of an adequate interradicular septum, the remaining alveolar bone height (ABH), and the absence of maxillary sinus infection. It is advisable to perform tooth sectioning during extraction to prevent injury to the interradicular septum. Mustakim et al. [17] have proposed guidelines for immediate implant placement in the maxillary molar region, considering adequate interradicular bone and ABH. The study classified sockets into types I, II, and III based on interradicular bone and types A, B, and C based on ABH. Immediate placement can be performed in type I sockets with adequate interradicular bone, eliminating the need for additional bone grafting. For type II sockets, immediate implant placement with bone grafting is recommended, while use of wide-diameter implants is suggested for a type III interradicular septum with inadequate lateral support. ABH determines the need for sinus lifting, where type A (ABH > 8 mm) allows immediate implant placement without sinus lifting, type B ABH indicates need for sinus lifting or consideration of short dental implant, and type C (ABH < 6 mm) can be suitable for implant installation after sinus lifting.

When contemplating immediate implant placement in the narrow ridge of the anterior mandible, a narrow-diameter implant can be chosen to maintain adequate facial bone width. Consideration of flap design is essential to prevent injury to the mental foramen during implant installation in the premolar region. If a vertical incision is necessary for visualization, it is recommended to place the incision between the mandibular canine and the first premolar. For immediate implant placement in mandibular molars, use of short dental implants in a deeper restoration-guided implant position is recommended to avoid injury to the inferior alveolar nerve. Tooth sectioning, as in maxillary molars, is also advisable for mandibular molars to maintain the interradicular septum for apical primary stability. Our study shows that immediate implant placement has a high survival rate in all regions of the mandible when adhering to the presented considerations.

All three failure cases in our study were associated with maxillary sinus pathology. Our previous study on structural analysis of sinusitis-related implant failure demonstrated metal contaminants on the surfaces of the failed implants. Additionally, inflammatory infiltrates and high osteoclastic activity were observed in the surrounding bone graft materials [21]. The possible etiologies of implant failure in the present study could include pre-existing sinusitis and Schneiderian membrane perforation, insufficient residual alveolar bone height, implant surface contamination, graft material-related reactions, and uneven distribution of occlusal force.

The previous study of implant success and survival rate in 1019 Luna® implants in medically compromised patients revealed the comparable survival rate (97.0%) with those of healthy patients [3]. The review literature by Sbricoli et al. concludes for no association between diabetes, cardiovascular diseases, hypertension, or osteoporosis and the risk of peri-implantitis [22]. This agrees with the population-based study in 6384 patients during 31-year follow-up periods [23]. Among the three failure cases, the patient with one implant failure at #16 has hypertension and received renal transplantation without taking immunosuppressant medication. However, another immediate implant at mandibular molar region of the same patient was functioning without bone loss until the time of assessment.

The limitations of the present study include the retrospective nature and the fact that all surgeries were carried out by a single surgeon. Moreover, future study with the extended follow-up duration, larger sample size and comparative study design with delayed implant placement outcomes could yield valuable insights.