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I. Introduction
Immediate implant placement in the maxillary molar offers several advantages including (1) reduction of treatment time and cost, (2) fewer surgical interventions, (3) alveolar ridge preservation, (4) patient satisfaction and comfort, and (5) better osseointegration provided by fresh socket healing potential1-3. However, compared with the mandible, immediate implant placement in the maxillary molar is challenging due to biomechanical factors and anatomical features including wide alveolar socket, poor quality of bone, and close proximity to the maxillary sinus3-5.
Immediate implant placement in the maxillary molar extraction socket as a predictable treatment is questionable, although high survival and success rates have been reported2,6,7. The main challenge for this procedure is primary stability of the implant in the fresh socket. Several studies have discussed failure of immediate implant and its possible causes8-10. However, there is no guideline regarding proper case selection and surgical technique for successful immediate implant placement in the maxillary molar.
In this study, We evaluated 26 cases and selected eight representative cases of immediate maxillary molar implant placement to present the step by step of the procedure. We also classified alveolar bone height (ABH) and socket morphology of the maxillary molar to establish guidelines for immediate implant placement.
II. Materials and Methods
1. Case selection
Reporting of this study follows the STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) guidelines11,12. A retrospective study was conducted on 148 implants in 106 patients who received immediate implant placement at the Department of Oral and Maxillofacial Surgery, Seoul National University Dental Hospital from 2011 to 2019. The study protocol and access to patient records were approved by the Institutional Review Board of Seoul National University, Seoul, Korea (No. S-D20200007). All methods were performed in accordance with the relevant guidelines and regulations of the Declaration of Helsinki.
The following inclusion criteria were applied:
(1) Immediate implant placement following tooth extraction in the maxillary molar region.
(2) No contraindications to surgical procedures.
(3) Implant treatment using tapered, sand-blasted, large-grit, and acid-etched (SLA) surfaced internal dental implants.
The exclusion criteria were as follows:
(1) Simultaneous sinus augmentation via the lateral window technique.
(2) Lack of pre- and postoperative clinical and radiographic data.
Informed consent was obtained from patients, and clinical and radiograph examinations were carried out. Preoperative radiographs were obtained to check the root configuration, periapical condition, maxillary sinus condition, proximity of roots with the maxillary sinus, and ABH.
2. Classification of ABH
ABH is important in achieving primary stability vertically and is measured from the crestal bone to the maxillary sinus floor through the radiograph. The result will determine the indication for socket lifting.(Fig. 1) Classification of ABH is as follows:
• Grade A: ABH>8.0 mm; sufficient to contain the fixture in the vertical dimension and does not require socket lifting.
• Grade B: 6.0 mm≤ABH≤8.0 mm; may or may not require socket lifting, socket lifting is required for a longer implant.
• Grade C: ABH<6.0 mm; insufficient ABH, socket lifting is mandatory.
3. Classification of socket interradicular septum
To achieve lateral primary stability, the morphology of the socket plays an important role. Following the extraction procedure, the interradicular septum of the socket was confirmed clinically to determine the need for bone grafting or a wide-diameter implant (Fig. 1):
• Type I: Interradicular septum can support and integrate well with the implant. Bone grafting is not mandatory.
• Type II: Interradicular septum support for the implant is available but weak; bone grafting is required for primary stability of the implant fixture.
• Type III: The interradicular septum bone is absent to provide primary stability within the socket, and fixture stabilization only depends on the socket wall. In this type, a wide implant diameter can replace most of the extraction socket.
After applying the inclusion and exclusion criteria, the final group contained 26 patients. We presented eight representative cases each of ABH and interradicular septum type; two cases with Grade A Type I including one (Fig. 2) and two immediate implants (Fig. 3); one case with Grade B Type I (Fig. 4); three cases with Grade C Type I (two of which required reinstallation with and without sinus lifting) (Fig. 5); one case with Grade A Type II (Fig. 6); and one case with Grade A Type III.(Fig. 7)
4. Surgical procedures
After obtaining informed consent, surgery was performed under local anesthesia using 2% lidocaine with 1:100,000 epinephrine. Atraumatic tooth extraction was performed without flap elevation, and a diamond bur was used to separate the roots to preserve the interradicular septum and the buccal bone. The socket was debrided thoroughly using a surgical curette and sterile saline irrigation.
For Grade C cases, the socket was tapped using a blunt sinus osteotome with a proper force to elevate the sinus floor.(Fig. 5) We chose the length and the diameter of SLA implants based on the bone height and width measurements. The fixture was placed in the mid-point of the interradicular septum parallel to the central fossa line of the adjacent teeth and lower than the lowest extraction margin.(Fig. 2, 4) In the Grade A Type III case, the wide diameter Anyone (Megagen, Seoul, Korea) bone level implant (6.5 mm×8.5 mm) was used to occupy most of the extraction socket.(Fig. 7) The primary stability of the implant was confirmed. In the Grade A Type II case, bone grafting was performed using particulate allogeneic bone Oragraft (LifeNet Health, Virginia Beach, VA, USA) to fill the gap between the fixture and the surrounding bone, followed by application of a resorbable collagen bilayer membrane, Bio-Gide (Geistlich, Princeton, NJ, USA).(Fig. 6) Sutures were placed with proper tension using 4-0 polyglactin 910 Vicryl (Johnson & Johnson, New Brunswick, NJ, USA) in cases without bone grafting to maintain the convexity of the buccal bone. Tension-free suturing using 4-0 polyglactin 910 Vicryl was performed in cases of bone grafting to fix the membrane.
5. Reinstallation for the failed implant
In one of the Grade C Type I cases, pus discharge and fistula formation occurred several months after implant placement. After removing the failed implant, a wide diameter Luna implant (5.0 mm×7 mm) was installed along with allogeneic bone graft without membrane.(Fig. 5. E-H)
6. Reinstallation for the failed implant with sinus lifting
In another Grade C Type I case, the implant was immediately installed in #16, but signs of sinusitis were observed five months later. Therefore, reinstallation was performed using a Luna implant (4.5 mm×7 mm) with sinus lifting and bone graft using cortical bone and Oragraft.(Fig. 5. I-L)
7. Installation of two immediate maxillary molar implants
In one mixed Grade A Type I (#26 area) and Type II (#27 area) case, the teeth was extracted, and two 4.1 mm×10 mm ITI Straumann implant fixtures (Institut Straumann AG, Basel, Switzerland) were installed. Bone grafting with Oragraft was performed after the installation.(Fig. 3)
8. Re-entry procedure and prosthetic fabrication
The re-entry procedures were performed six months after fixture placement to connect the healing abutment. Three months following the re-entry procedure, prostheses were installed.
9. Follow-up visits
Follow-up visits were scheduled at one month after fixture installation and at one month, six months, and one year after prosthesis loading. The patients were educated on oral hygiene at each visit, and implant stability, surrounding tissue condition, and calculus presence were assessed. Marginal bone level (MBL) changes were checked periodically through panoramic radiographs.
10. Implant failure evaluation
The International Congress of Oral Implantologists (ICOI) Pisa Consensus implant health scale13 was used to determine the failure criteria of the implants:
• Pain or tenderness during function.
• Implant mobility.
• Radiographic bone loss of more than half of the implant length.
• Uncontrolled exudate.
• Implant loss.
11. MBL evaluation
MBL was measured using panoramic radiographs obtained immediately after fixture placement (T0), one month after fixture placement (T1), after the re-entry procedure (six months after fixture placement, T2), and one month (T3) and one year (T4) after prosthesis loading. The distance of the implant shoulder to the most coronal bone-to-implant contact on the mesial and distal sides of the implant was measured three times, and the mean value was used for analysis. The change in MBL from T0 to follow-up visits and changes between consecutive visits were calculated. The measurements were performed using PACS calibration system (PiView-Star, ver. 5.0.1; Infinitt, Seoul, Korea) with a positive number or increased MBL indicating bone loss.
12. Statistical analysis
Both descriptive and quantitative data were collected. For analyzing MBL, mean and standard deviation were calculated. The Shapiro–Wilk test was used to test the normality of variables. The differences between follow-up periods were tested by paired Student’s t-test. All analyses were carried out using IBM SPSS Statistics (ver. 25.0; IBM, Armonk, NY, USA). A P-value <0.05 was considered statistically significant.
III. Results
1. Patients
The study group included 26 patients, consisting of 11 males and 15 females; a total of 29 SLA implants was installed. The mean patient age was 64.88 years (range, 16-86 years). Among the 29 implants, 10 implants were installed in #16, 5 implants in #17, 10 implants in #26, and 4 implants in #27.
Among the 29 SLA implants, 14 were Luna (Shinhung, Seoul, Korea) with sizes of 4 mm×7 mm (n=4), 4 mm×8.5 mm (n=7), 4 mm×10 mm (n=2), and 4.5 mm×10 mm (n=1); 14 implants were Straumann (Institut Straumann AG) with sizes of 3.3 mm×8 mm (n=1), 4.1 mm×6 mm (n=1), 4.1 mm×8 mm (n=3), and 4.1 mm×10 mm (n=4); and one implant was Anyone (Megagen, Seoul, Korea) with a size of 6.5 mm×8.5 mm. In the reinstallation case, two Luna implants with sizes of 4.5 mm×7 mm and 5 mm×7 mm were used. Based on type, 20 implants were bone level (BL) and nine were tissue level (TL).(Table 1)
2. Failure evaluation
Among 26 patients, two showed signs of implant failure before the re-entry procedure. One patient showed peri-implantitis signs and symptoms including pain, exudate discharge, and fistula formation, and the other patient experienced sinusitis. These two implants were removed, resulting in a success rate after initial treatment of 93.10%.
Following removal of the implant, re-installation procedures were performed immediately using wider diameter implants with bone graft and sinus lifting. The two re-installed implants showed favorable outcomes and continue to function well after prosthesis delivery.
3. MBL evaluation
MBL at T1, T2, T3, and T4 changed significantly in comparison with that at T0. Bone gain was recorded on the mesial side at T1 (–0.44±0.62 mm) and on the distal side at T2, T3, and T4 (–0.27±0.52 mm, –0.16±0.60 mm, –0.28±0.52 mm, respectively) in comparison with T0.
Compared with previous follow-up measurements, the mean MBL at T2 was significantly higher than that at T3 and T4. The mean MBL at T3 was significantly higher than that at T4 on the distal side. The mean MBL at T3 and T4 did not differ significantly on the mesial side (P<0.05).(Table 2)
IV. Discussion
Our study showed significant MBL changes between installation and follow-up. A fluctuating change indicating bone regeneration and bone loss was observed in the first year following installation but was stable after one year of prosthesis loading. In the first month following installation, significant bone regeneration was observed, and bone loss started six months following installation. This fluctuating change can be explained by wound healing and remodeling of the bone. A previous study showed that remnants of the periodontal ligament following tooth extraction harbor Wnt-responsive osteoprogenitor cells, which are responsible for extraction socket healing and supporting osseointegration of the immediately placed implant14. Another study suggested that osteogenesis takes place in the first six weeks after implant installation, followed by remodeling15. In contrast to delayed implant placement, in the first 4 months following immediate implant placement in a fresh socket, healing is incomplete and hard tissue alteration occurs16. At this period, the implant may fail to counteract buccal ridge alterations that follow tooth loss17. Matarasso et al.18 performed surgical re-entry six months following immediate molar implant placement and found completely healed marginal defects through de novo bone formation. Therefore, for maxillary molar immediate implant, it is highly recommended to wait for six months of healing before proceeding to the re-entry procedure.
In delayed implant placement, marginal bone loss often is observed in the first year of function and remains stable afterward19. We also observed stable MBL after one year of loading, with an average of 0.01±0.01 mm bone loss on the distal side and 0.03±0.03 mm bone loss on the mesial side. For MBL, the pattern of immediate placement following osteogenesis is similar to that of delayed placement.
Our study showed a 93.10% survival rate, which is higher than that of previous studies8-10. Such a successful outcome depends on primary stability of the implant with apical and lateral bone4,20. This stability is determined by the interradicular septum and the quality and quantity of bone to mechanically engage the implant fixture laterally21,22. Therefore, preserving the interradicular septum and buccal bone integrity through atraumatic extraction and flapless procedures play a vital role. A traumatic or pathologic process in one or more bony walls of the socket may alter the bone resorption pattern and rate through invasion of fibrous tissue in the socket23. As the interradicular septum has a close relation to the sinus membrane, trauma to the septum during extraction may lead to perforation or tearing of the sinus membrane. We previously conducted a study on early failed implant surfaces24 and found that the main cause of failure was non-infectious and comprised metal contamination or inflammatory reaction involving fibrosis, lymphocytic and macrophage infiltrates, and high activation of osteoclasts in the tissue surrounding the failed implant. The inflammatory product and reaction induced by the sinus and fractured interradicular septum may prolong the healing process and impede osseointegration of bone to the implant. To preserve the interradicular septum, use of a diamond fissure bur to separate the roots is recommended with meticulous irrigation to wash away any metal debris from the bur.
The flapless procedure is suggested to minimize postoperative peri-implant tissue loss, accelerate post-surgical healing, and increase patient comfort. In a previous study, raising the flap and absence of buccal bone resulted in significantly higher marginal bone loss than with a flapless procedure and preserved buccal bone7.
Classification of molar sockets for lateral primary stability in immediate implant placement was described in a previous study4. In our study, we highly suggest bone grafting in type II sockets for optimal primary stability regardless of jumping distance. Following extraction, a gap between the interradicular septum and buccal/palatal wall is formed. When placing the implant, the horizontal dimension of the available bone should be at least 3 mm greater than the implant diameter25. Therefore, bone grafting in type II sockets is important for maintaining the dimension of the alveolar bone and minimizing marginal bone loss26. A previous study showed that particulate allogeneic bone grafting material demonstrated higher potential for horizontal gain in comparison with other synthetic materials27. The use of a collagen membrane together with a particulate bone graft can reduce the risk of infection and enhance the healing process of the socket by promoting undisturbed migration and proliferation of osteoblastic lineage cells; it can also provide space for new bone formation by preventing collapse of soft tissue into the wound28,29. We suggest using the membrane when primary wound closure cannot be optimized in a wide extraction socket. We also highly suggest bone grafting in cases of immediate placement of two implants regardless of the amount of remaining interradicular septum to compensate for simultaneous bone resorption by the two implants and to maintain inter-implant papilla integrity.
In choosing the most suitable implant for maxillary molar immediate implant, tapered SLA implant is most reliable. Previous studies demonstrated the superiority of tapered SLA in achieving primary and secondary stability compared with other types of implants due to its advantageous properties in improving osteoblast differentiation; producing osteogenic factors, growth factors, and cytokines; and increasing bone-implant contact30-32. Tapered SLA dental implants such as Straumann, Shinhung Implant System, and Anyone by Megagen also provide self-cutting effects, which are favorable in preserving crestal bone level especially in immediate implant placement33. The high success rate of these implants was shown in rehabilitation of diverse pathologies of the jaw and in well-integrated grafted bone following management of oroantral fistula and odontogenic maxillary sinusitis34,35.
To maintain healthy peri-implant tissues, choice of BL or TL implant also plays an important role. TL is known for the smooth surface of the neck that minimizes plaque retention, and platform-switched BL experiences weaker effects of biological width, decreasing the likelihood of progressive bone resorption36,37. However, considering mucosal thickness, the BL implant resulted in significantly greater marginal bone loss when the soft tissue was thin (less than 2 mm), whereas the TL resulted in a similar amount of loss in thin and thick soft tissue36. In cases of poor oral hygiene, TL may provide benefit for implant maintenance. However, one of the disadvantages of the TL implant is that it is not suitable for limited mesio-distal and vertical dimensions. Therefore, in choosing the type of implant, mucosal thickness, oral hygiene, and dimension of the edentulous region of the patient should be considered. When choosing the length of the implant, we prefer a size range of 6 to 10 mm, as an implant shorter than 6 mm has greater risk of not achieving primary stability and an implant longer than 10 mm may impart risk of perforation of the sinus membrane.
For the type III socket and re-installation case, we highly suggest a wide- or ultra-wide-diameter implant. The high survival rate of such implants (diameter greater than 6 mm) placed immediately has been reported in several studies, with the longest follow-up period of up to 12 years38-40. In our case, the type III socket benefited from the ability of an ultra-wide-diameter implant to engage the bony walls of the extraction socket. Other benefits offered by the ultra-wide diameter are preservation of bone and soft tissue, reduced buccal bone resorption, and better suitability in cases of sinus pneumatization38. As a wide-diameter implant is appropriate for posterior regions with poor bone quality, it also has been suggested for replacing previously failed implants, such as in our re-installation case2,38.
Immediate implant installation in the maxillary molar is complex and requires more than simple understanding of the characteristics of a socket. It also requires full comprehension of the ABH characteristics and the proximity of the maxillary molar to the maxillary sinus. Studies that classify ABH in the maxillary molar for achieving apical primary stability in immediate implant placement are lacking. Our study describes the classification of ABH to help clinicians achieve apical primary stability through socket lifting. Presence of the sinus floor and interradicular cortical layer help fix the implant body and guarantee good primary stability through engagement of the implant’s apical part and sinus floor23,41. Previous studies reported successful outcome of sinus floor intrusion using a hand osteotome without bone graft using “up-fracture” of the interradicular bone superior to the sinus to achieve an extra vertical dimension of approximately 4 mm23,42. However, in previous studies, the sockets were left to heal for four months before implant placement after socket lifting. In our study, the implants were placed immediately after socket lifting in Grade B and C, and the outcomes were favorable without complications. High success of simultaneous immediate implant following socket lifting was reported in a previous study, in agreement with our findings43.
In the 1996 consensus conference on sinus grafts, socket lifting was recommended in cases with 8 mm of ABH or less44. When the ABH is 4 mm or less, sinus floor elevation should be performed through a lateral approach with consideration of delayed implant placement; when the ABH is greater than 5 mm, socket lifting is suggested45. In Grade B ABH, a short dental implant (SDI, length <8 mm) can also be considered. In our cases, we immediately installed an SDI in five patients, including two re-installation cases. Nguyen et al.46 reported a high survival rate of SDI in medically compromised patients and considered SDI as a reliable treatment in avoiding sinus lifting or vertical bone grafting. In a previous systematic review and meta-analysis, no significant differences in implant survival, marginal bone loss, complications, and prosthesis failure were found between SDI and standard dental implants in posterior jaws. However, SDI should be used with caution, especially in the posterior maxilla47. A previous study46 showed that direction is easily distorted when drilling for an SDI and requires more skill and accuracy. Second, drilling with counterbore should not be too deep. Last, the implant-supported prosthesis should not be too large relative to the crown-to-implant ratio46. Considering these points, either a single crown or multiple fixed prosthesis (splinted) are adequate for SDI in the posterior maxilla.
In regard to the position of the implant, most clinical reports chose the lowest level of the surrounding bone crest. However, in some studies, the implants were intentionally placed 1.5 to 2 mm below the bone crest2. Javaid et al.20 stated that the implant shoulder should be placed 2 to 3 mm apical from the gingival margin to compensate for the expected vertical resorption. In our cases, we placed all implants lower than the lowest extraction margin to compensate for resorption of alveolar bone and to optimize primary wound closure. A previous study48 demonstrated that marginal bone loss around non-submerged implants is associated with changes in the salivary microbiome during bone healing. Increased severity of bone loss was related to increased proportions of periodontal pathogenic species48. Optimized primary closure allows healing of an extraction socket and regeneration of bone without intervention from oral microbiota.
Immediate implant placement in the maxillary molar is an acceptable and predictable treatment. However, this modality is complex and requires full comprehension regarding the rationale and appropriate technique for a favorable outcome. Achieving primary stability laterally and apically is the main goal for immediate implants. Atraumatic extraction, socket lifting consideration, selection of appropriate bone grafting material, and implant type and size according to patient condition are the prognostic factors for favorable outcome, even in cases of re-installation. Routine clinical and radiographic follow-up also help in detecting early failure of the implant and in management measures. Oral hygiene maintenance plays a key role in implant longevity.
V. Conclusion
This clinical study demonstrated the significance of immediate implant placement in maxillary molar as a reliable treatment with a high survival rate using tapered SLA implants, as shown by clinical and radiological outcomes. The results of this study suggest that in-depth knowledge of the maxillary molar and surrounding anatomical characteristics help the clinician choose and use the appropriate technique and material. The socket lifting procedure is a fast and conservative approach in achieving vertical primary stability of an implant without direct interference to the maxillary sinus. Bone grafting with allogeneic particulate material or use of wide-diameter implants helps engage the fixture in the lateral direction for good stability. Six months is the optimal time to achieve osseointegration of a maxillary molar immediately placed implant before the re-entry procedure. Hence, full comprehension of socket morphology variations and timely management according to wound healing are cornerstones for primary stability in an immediately placed implant. In this study, we classified maxillary molar socket morphology and ABH and demonstrated the rationale with a step-by-step technique to help achieve favorable outcomes with an immediately placed implant. With an accurate approach to immediate implantation, surgical intervention and treatment time can be reduced, supporting patient satisfaction and comfort.
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