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The preservation of the hard and soft tissues for superior esthetic and biomechanical outcomes has become an integral part of any treatment plan intended to replace a tooth intended for extraction. With the introduction of the four techniques that constitute the Partial Extraction Therapy (PET) concept; the preservation of the tissues is more promising than ever. This review collates the reports from 1942 up to 2020 on the Root Submergence, Socket Shield, Proximal Socket Shield, and Pontic Socket Shield techniques, stating the complications and modifications made since the innovation of each technique alongside the advantages and disadvantages. It was concluded that definitive protocols for implementing and evaluating the success of each technique are needed to ensure the long-term success of any treatment plan that includes a technique of the PET.
Keywords: Partial extraction therapy, periodontal ligament, pontics, socket
| Introduction | |  |
Tooth loss comes with many complications due to a vital structure being removed from the body, thereby initiating a process of loss at the vascular level leading to the remodeling, resorption, and in some cases complete loss of the supporting bone and soft tissues. This encouraged clinicians to discover techniques that mimic the natural teeth in their preservation of the hard and soft tissues, without inflicting a negative effect on the restorative treatment intended to replace the missing teeth.[1] Thus, the concept of partial extraction therapy (PET) was introduced, which combined 4 different techniques that aimed to preserve part of the tooth in the bone, thereby reducing the loss of the bone vasculature and periodontal ligament (PDL) attachment and in turn reducing or eliminating the remodeling and resorption of the hard and soft tissues associated with tooth extraction. The root submergence technique (RST), the Socket Shield Technique (SST), the Proximal SST (PSST), and the pontic shield technique (PST) are the 4 technique included in the concept of PET.[2] This review looks into the history of each technique as well as discuss their various applications, complications, and modifications in clinical and histological human studies, including randomized clinical trials, case series, and case reports, that have reported on the various techniques of the PET.
| Root Submergence Technique | | |
The concept of RST has been present in the literature since 1942 in the form of studying remaining fractured roots rather than intentionally submerging the root for bone preservation or formation.[3] The main advantage of RST is the inexpensive preservation of the alveolar bone dimensions in order to provide a better retentive surface area for the removable denture prosthesis,[4],[5] or to preserve the alveolar bone for a future dental implant,[6] or to preserve the tissues' dimensions in the pontic's area under a tooth supported fixed dental prosthesis,[7] with a chance of developing bone and new cementum and connective tissue coronal to the submerged segment. It also preserves the tissues next to a dental implant and improves the predictability of the interdental papillae height in dental implant therapy. On the other hand, the main reported disadvantages are the loss of vestibular depth, the resorption of the submerged roots, dehiscence of the soft tissues over the roots due to the pressure of the removable dentures, pain in some cases owing to root caries and pulpitis, eruption of the roots out of the bone and soft tissue in cases where the removable dentures were not continuously used, poor esthetic outcomes because of a stretched lip appearance caused by the pressure from the dentures on the vestibule after the coronal flap displacement.[8]
| Socket Shield Technique | | |
Based on the previously discussed RST and its benefits in maintaining the alveolar bone dimensions without causing damage or being considered a risk factor to the surrounding tissues when retained, the concept of socket shielding was introduced in a 2010 study, initially on dogs, followed by a single implant placement in a human as a proof-of-concept.[9] In the human case report, the maxillary left central incisor was deemed unrestorable due to vertical root fracture and so the lingual, mesial and distal segments were removed retaining only the buccal segment at 1 mm apical to the gingival margin and consisting of the tooth's enamel and 0.5 mm of the dentin. The implant was placed lingual to the segment and extended apically beyond it with the spaces around the implant being filled with an enamel matrix protein derivative.[10],[11] Finally, a fabricated screw-retained abutment was placed with an out-of-occlusion provisional crown. After 6 months, both the bone and gingival tissues were well preserved around the implant and no interference with the osseointegration process was observed. A second and a third human case report were done in 2013 following the same technique and supporting the results as only 1 implant was placed with the SST and after 4–5 months, there was successful osseointegration without any signs of inflammation or resorption around the buccal root fragment or the implant. A study comparing the results of 10 implants placed with the SST and 16 with conventional implants placement showed that the bone loss was less, the soft-tissues volume was more, and the esthetics according to the operator and patient were better with the SST compared to the conventional immediate implant therapy. It is only appropriate to end the SST section in this review with a group study that included the author who first described the technique, Dr. Markus Hürzeler. The study reported a complication with an implant placed for 6 years utilizing the SST and came with deep pockets and signs of inflammation in the area. The examination revealed mobility of the buccal fragment and the surgeon opted to remove the fragment and graft the area using a xenograft bone substitute. The buccal fragment had followed the normal growth of the maxilla in the antero-caudal direction and eventually came in contact with the prosthesis, after which the occlusal forces were transferred to it, causing it to fail. A method suggested to minimize the movement of the buccal fragment and causing such complications is to place the implant as close as possible to the buccal fragment, thus creating some bony connection between the fragment and the implant that prevents the effect of the antero-caudal maxillary growth on the implant and buccal fragment.[12],[13],[14]
| Proximal Socket Shield Technique | | |
As the maintenance of the interdental papilla between two implants in the esthetic zone is one of the major challenges of implant therapy, the PSST was first suggested and reported by following the same principles of the SST but they utilized the distal root fragment rather than the buccal one. The 12 months of follow-up showed a well-maintained interdental papilla and bone between the new and old implants. In a case of 2 central incisors being replaced utilizing the (PSST), only the coronal mesial fragments of the roots were kept and the implants were placed apical to the crest of the bone by 1 mm; after 11 months the interproximal and buccal soft tissues showed optimal healing results. In a report where the SST was utilized in the buccal side only, it was noted after 6 months that the horizontal and vertical bone dimensions were preserved, while the interproximal papilla was starting to show signs of papillary loss and black triangles. Nevertheless, the use of the PSST requires excellent case selection and flawless surgical execution; and as the fragment of the root is located 2 mm above the margin of the bone, the risk of fracture is possible which has not been assessed yet. These might be the reasons why there are not many reports in the literature on the PSST.[15],[16]
| Pontic Shield Technique | | |
Initially known as the Modified SST and then named the PST, it is a technique introduced to preserve the hard and soft tissues in the pontic areas following the same technique as the SST but instead of placing an immediate implant in the socket, a bone grafting material is used to fill the socket and the socket is closed by either a repositioned flap, gingival graft, or membrane. The first human studies on PST revealed successful preservation of the bone and surrounding soft tissues in all dimensions. In a report where the SST was combined with the PST in the management of multiple implants placement in the esthetic area, showed soft tissue coverage over the sockets and perfect preservation of the tissues and bone that were treated using the PST even in the area where the apex was kept due to the inability of its removal without causing excessive trauma.[14] Filling the sockets that are treated with the PST with nothing but a collagen sponge in combination with implant placement in the adjacent sockets utilizing the SST, yielded excellent results as the sockets were fully covered with soft tissue and the bone contour was preserved in all the surgical sites; which seems to indicate that the blood clot formed in the socket can achieve the desired regeneration while the buccal fragment can prevent the buccal bone remodeling. The reported advantages of the PST is that there's no need to cover the exposed segment with the repositioned flap or a gingival graft as the buccal segment is already covered by the buccal soft tissue, and thus the risk of carious infections is minimum to nonexistent. Furthermore, even if there's an apical pathology, the buccal fragment can be preserved while all the other tooth structures and apical lesions are removed, which overcomes an issue that was identified with the use of the RST.[2]
| Discussion | | |
Osseointegration by itself is not the only criteria to determine the success of implant therapy nowadays, the preservation of the soft tissue and bone volume around the implant as well as the long-term esthetic results are equally important. Previous reviews were done on the Socket Shielding Technique when it was still in the infancy stage and there was not enough evidence to support the long-term success of the technique. Even more recent reviews stated that more randomized clinical trials are needed and that the Socket Shielding Technique should be used with caution and only in selective cases. The excellent results of the PET techniques can be attributed to the preservation of the vascular architecture of the buccal bone and soft tissues due to the presence of an intact PDL between the root/fragment and the bone. Complete preservation of the bone was not possible even with the SST as it was reported. However, the higher the thickness of the buccal bone and fragment, the better the results were; a histological study on dogs concluded that if the buccal bone thickness is 3 mm and the remaining buccal segment is 2 mm then the successful outcome of the SST can be predictable, and it was reported that a thickness of the buccal wall and the buccal root fragment of more than 2 mm can yield predictable results. [17,18] In 2020, Gluckman and his fellow researchers introduced a standardized protocol of the steps used in the SST, which can also be utilized in the PSST and PST, to improve the repeatability and predictability of the protocol and procedure followed, and also provide a better platform for the operators to report their data. Meanwhile, another protocol was also introduced in 2020 by multiple authors including Dr. Markus Hürzeler, the creator of the SST. The main differences being that Gluckman's group recommending the placement of the buccal fragment's coronal edge at the level of the crest of the bone and thinning the most coronal 2 mm to a chamfer design, while Staehler's group recommended that the buccal fragment be placed 0.5 mm coronal to the level of the bone crest without the chamfer design of the coronal 2 mm of the fragment. Another difference was the positioning of the implant, where Gluckman's group recommended the submergence of the implant 1.5 mm below the level of the buccal fragment without touching the buccal fragment and the space grafted with a bone substitute, while Staehler's group recommended the placement of the implant at the level of the crest of the bone with the implant being in contact with the buccal fragment. The differences were attributed to two factors; the first being the supracrestal connective tissue barrier being lost when the tooth structure was prepared to the level of the crest of the bone, thus causing the loss of 1 mm of the buccal bone height as a space for the new connective tissue barrier to inhabit. Therefore, by keeping the buccal fragment at 0.5 mm supracrestally, the connective tissue barrier is preserved and in turn the vertical bone height is also preserved, while at the same time avoiding the complications that arise from having the margin of the buccal fragment 1 or 2 mm supracrestally.[19] The second factor was the lifelong growth of the maxilla in the antero-caudal direction, and by having a space between the implant and the buccal fragment the risk of complications to the fragment over time is increased, thereby, by having the implant in close proximity to the buccal fragment it becomes almost ankylosed with the implant and thus decreasing any complications that might arise with the growth of the maxilla. The prosthesis over the implant placed with the SST needs to be planned and prepared well, in order to avoid any unnecessary complications such as internal exposure of the buccal fragment that can be prevented by fabricating the prosthesis in an S-shape to allow maximum fill of the soft tissues and thus reducing the possibility of internal exposure; as well as evaluating the biomechanical aspect of the SST in comparison to conventional implant placement, where it was found that the SST neither provides any negative or positive effects on the biomechanical aspect of the placed implant, and the main benefit of the technique lies in its preservation of the PDL fibers, thus maintaining the vascular architecture of the bone. The majority of the SST, PST, and PSST cases were done in the anterior teeth and the premolars, and only one report was done on a molar site, which might be due to the complexity of preparing an ideal buccal fragment to be used as a shield as the mesial and distal roots might be diverged or curved; and might also be because the esthetic areas are where the practitioners think of the PET techniques, while in the molar areas the conventional augmentation techniques are favored. A recent report showed the presence of a periapical lesion in an implant placed utilizing the SST, although the stability of the implant was not affected. After debridement and grafting of the periapical area, the tissues showed good healing and stability. Nevertheless, the presence of such issues without a clear cause further raises the need for long-term randomized control trials on the PET techniques.[20],[21]
| Conclusion | | |
The various PET techniques have provided excellent mechanical, biological, and esthetic outcomes in the hands of experienced operators with meticulous treatment planning and case selection. A standardized evaluation of the PET outcomes needs to be developed based on objective findings, as well as a standardized protocol for the preparation of the root fragment and for the placement of the implants in the ideal position to ensure long-term success of the treatment.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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Correspondence Address:
Rakan Saifuddin Shaheen,
Department of Preventive Dentistry, College of Dentistry, Riyadh Elm University, Riyadh
Kingdom of Saudi Arabia
 Source of Support: None, Conflict of Interest: None DOI: 10.4103/ijpcdr.ijpcdr_2_21
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