Socket shield technique concurrent with immediate implantation- A Review ABSTRACT Socket shield technique done simultaneously with an immediate implant is the progressive improvement over other concepts for preservation and maintenance of healthy hard and soft tissues around a dental implant

Socket shield technique concurrent with immediate implantation- A Review
ABSTRACT
Socket shield technique done simultaneously with an immediate implant is the progressive improvement over other concepts for preservation and maintenance of healthy hard and soft tissues around a dental implant. It is a method in which instead of completely removing the tooth; a buccal root fragment is left in the socket, as the implant is inserted behind it. Enamel matrix derivative (Emdogain) may or may not be used for the formation of new cementum.
Osseointegration is achieved without any inflammatory or resorptional responses. Buccal cortical bone is well-preserved with the formation of periodontal ligament and cementum around the implant surface, the peri-implant junctional epithelium was seen at a greater final length than in conventional implantation. It is an appropriate choice in cases of high esthetic concern which manages risks of extraction and preserves post extraction tissues in aesthetically challenging areas. It is a safe technique to preserve alveolar bone, as it decreases horizontal and vertical bone loss and preserves it with minimal invasion in comparison to conventional implantation. The purpose of this review is to study the benefits of the immediate implant executed concurrently with socket shield technique.
KEYWORDS: Socket shield technique, Papilla preservation
INTRODUCTION
Modern dentistry has grown proficient enough for replacing a missing tooth in any form the patient requires. In the aesthetically challenging anterior area, restoration is mandatory and necessity. Extraction of the tooth is followed by damage to the periodontium, then alveolar bone undergoes remodelling process leading to loss of ridge dimension. The unfavourable consequences of tooth extraction have been prevailed by various treatment approaches such as graft materials and/or barrier membranes, augmentation procedures, more palatal placement of the implant, immediate implants and so on. Immediate implantation achieves osseointegration but by some means, gingiva undergoes a remodelling process and ultimately volumetric changes occur; especially in buccal tissues in the horizontal direction. Augmentation procedures bring about tissue shrinkage, while the use of bone grafting materials and collagen barriers compensated for this but could not avoid the resorption process. In spite of these additional substitutes, placing only an implant does not overcome the drawbacks of extraction; furthermore, the recession of interdental area and surrounding tissues is a risk with immediate implants which are the basic requirement for the maintenance of the gingival structure.
The concept of retaining a root for minimum tissue alteration after tooth extraction originated in the 1950s. Successful researches were carried out with submerged tooth roots to preserve alveolar ridge under complete dentures (Miller 1958, Marrow 1969) as well as submerged endodontically treated tooth root showed regeneration of alveolar bone (Bjorn 1963), in addition to histological and radiographic evidence of new cementum and connective tissue over the coronal surface of the submerged root, separating dentin from the new bone (O’Neal et al 1978). This technique not only maintained existing bone volume but also facilitated vertical bone growth coronally to the decoronated root. Assessment of uncalcified root sections placed in close proximity to the implant revealed cementum layer on the implant surface with inserting collagen fibres (Buser 1990). Discretionary use of enamel matrix derivative possesses an important role in the development of periodontal tissues which was illustrated by the formation of new periodontal attachment on the inside of the root fragment (Hammarstrom 1997, Heijl 1997, Sculean 2000). Submerged ankylosed tooth fragment preserved the alveolar bone (Malmgren 2000, Filippi 2001, Malmgren 2002); while non-ankylosed tooth fragment did not undergo a resorptional process (Hürzler 2010).
“Socket shield technique” is the term coined by Hürzler et al in the year 2010 with regard to preservation of buccal bone plate. It is the technique used in combination with immediate implant cases. The Principle of Socket Shield Technique is to prepare the root of a tooth with intact facial periodontal tissues which require extraction by leaving facial root fragment in place and maintain its physiological relationship to the facial plate. Periodontal attachment apparatus remains vital and undamaged which prevents the expected post-extraction socket remodelling and supports the facial tissues (Gluckman 2015). The prepared root fragment acts as a socket-shield and prevents the recession of tissues facial to an immediately placed implant (Gluckman 2015) (Fig 1).
Socket shield technique used in combination with immediate implant placement is indicated for non-smokers, a hopeless anterior tooth with neighbouring teeth on the mesial and distal aspects, a tooth with intact periodontal tissues as far as preoperatively diagnosable with thin, normal or thick phenotype and patient with good oral hygiene. Correspondingly, it is contraindicated for teeth with present or past periodontal disease, vertical root fractures on the buccal aspect, horizontal fractures at or below bone level, presence of pathologies affecting buccal part of the root (e.g. External or internal resorptions), mobile tooth or with wide periodontal ligament (Kan and Rung 2013), pregnancy or breastfeeding and all the restrictions of oral surgical procedures such as Bisphosphonate medication, Immunosuppression, Radiation therapy, Anticoagulation etc (Bäumer 2017).
This technique has known to be a less invasive method which does not use bone substitute material making it much more cost-effective; furthermore, avoids resorption process in horizontal and vertical direction while maintaining healthy periodontium, original level of crestal bone and eventually gingival tissues.
LITERATURE REVIEW
ANIMAL STUDIES
The first ever socket shield experiment conducted on a beagle dog by Hürzler et al in 2010 used third and fourth mandibular premolars, which were prepared by retaining a buccal fragment of distal root 1 mm coronal to the buccal bone plate and enamel matrix derivative (Emdogain) gel smeared over it. Enamel matrix derivative prevents epithelial proliferation and has anti-microbial property (Bosshardt 2008). The implant was placed lingually to the retained root fragment with or without contact in between them; this favoured osseointegration into the alveolar bone and formed connective tissue in the gap between the dental implant and retained root fragment. In contrast, this outcome was not perceived when Emdogain was not applied (Bäumer 2015). Dentin surface of the root fragment was covered with newly formed acellular cementum. There was the absence of resorption process at the apical end of the tooth fragment which also showed a thin layer of newly formed cementum and formation of new woven bone (Hürzler 2010).
Tooth with vertical fracture line has been contraindicated to be used as a socket shield because it would form a recess for bacteria which is inaccessible to the immune system and consequently lead to infection. Hence, the experiment was performed again by Bäumer et al in 2015 to confirm the use of socket shied in the vertically fractured tooth with only a modification of splitting the prepared root fragment into two pieces in a vertical direction. This resulted in vertically drilled outline filled with new bone without any signs of resorption and absence of remodelling in buccal crestal bone (Bäumer 2015).
A further experiment was operated in 6 foxhound dogs by preparing the root fragment at the crestal level and the samples obtained were studied in 6 groups. The experiment was done in the same manner as the previous ones with only a variation of involving different sizes of retained root fragment which governs the amount of remaining bone around the implant with its proper placement and affects the result. Attempts to preserve thick root fragment showed poor results with the increased apical migration of bone and unfavourable connective tissue attachment. Preservation of 3mm of surrounding bone evidenced for apposition of connective tissue, minimal apical migration of bone with a better bone to implant contact illustrating thin and short roots give better results because it avoids resorption, modification on bundle bone and preserves the volume of soft tissues (Guirado 2016).
CLINICAL STUDIES
A retrospective clinical study on 10 successive patients estimated volumetric changes of the affected facial structures and its esthetic outcome. Concurrent to the animal studies the implants healed without adverse effects and clinical manifestation of peri-implant tissues showed healthy site with the mean tissue loss on the facial side of 0.21 ± 0.18 mm, mean loss of the marginal bone level at the implant shoulder was 0.33 ± 0.43 mm at the mesial aspect and 0.17 ± 0.36 mm at the distal aspect of the implants. The average recession at implant area was 0.33 ± 0.23 mm and at adjoining teeth was 0.38 ± 0.27 mm in addition to a mean pink esthetic score of 12 was recorded from photographs (Bäumer 2017). Volumetric changes were demonstrated by socket shield technique in different clinical reports. While comparing, the maximum loss of 1.67mm in labial direction was seen in a study by Bäumer et al 2013 to maximum horizontal loss of 0.72mm was noted by Chen and Pan in 2013. Different subject, measurement method and tooth position were recognized as the reason for this dissimilarity.
In a recent randomized controlled trial of 40 dental implants placed in the anterior region, its marginal bone level and pink aesthetic score (PAS) was compared between socket shield technique in combination with immediate implantation and conventional immediate implantation at 3 years follow up (Table 1). Clinically, socket shield technique showed higher aesthetic score but the survival rate of the dental implant was same as that of conventional method which proved that socket shield technique has better aesthetic outcome than the conventional technique. In this study, retained root fragment was prepared 1mm below the bone crest without flap elevation which helped in sustaining blood supply to the buccal bundle bone and the jump gap was filled with allograft in contrast to the original approach, thus preserving the increased amount of alveolar ridge volume (Bramanti 2018).
Socket shield technique used in combination with immediate implant also overcomes the challenge of proximal bone loss. Papillary position relies on proximal bone level whose loss can be expected after the extraction of the adjacent tooth. In a study of proximal socket shield for interimplant papilla preservation (Kan 2013) maxillary right central incisor was sectioned buccopalatally, and mesial half of the root was removed, while distal root fragment was prepared 2mm coronal to the distal marginal bone which was hollowed out creating a 1.5-2mm thick C-shaped root fragment extending from disto-buccal to disto-palatal line angles and rest of the procedure was carried out in similar fashion. At 1-year follow-up aesthetic results were up to the mark accompanied by well maintained interimplant papilla between the central incisors. This study revealed that leaving a portion of the root fragment adjacent to an existing implant restoration along with existing coronal portion of the root fragment with supracrestal cementum (2mm above the proximal bone) where dentogingival fibres are attached also contributed to the preservation of the level of the interimplant papilla (Kan 2013).
In a case report by Cherel et al, the root of right maxillary central incisor was sectioned in 3 parts with preservation of mesial root only. The coronal portion of the root fragment was left intact whereas the apical section was removed. This displayed complete preservation of papilla and well-maintained bony peak (Cherel). Retention of buccal root fragment does not compensate papillae preservation but it is obtained with retention of proximal root fragment. The modified socket shield technique allows the full three-dimensional preservation of alveolar structure (Cherel) (Fig 7).
The other modification of this technique includes socket shield applied as a part of a delayed implantation which is carried out after 6 months. A delayed implantation is an alternative approach used to preserve the buccal bundle bone over a longer period of time with reduced risks and complications. During the preparation height of the shield is maintained to the bone level and the overlying gingiva is tunnelled by 2 mm to allow the insertion of collagen cone. Absorbable collagen cone is inserted into the shield prepared socket and is secured with a criss-cross suture. The minimal invasive flap is used for re-entry during delayed implantation. Along with preservation of bone volume, it also promotes vertical bone growth and meets the expectation of the ideal method (Glocker 2014) (Fig 8).
Similarly, an alternative to the original technique was attempted by preparing the shield with a long shank root resection bur and filling the jump gap with a xenogenic bone particulate (Fig 9) while skipping the application of Emdogain. Provisional crown was prepared in such a manner that there was enough space between the socket shield and the restoration creating an ‘S’ shaped profile emergence increasing the growth of soft tissue in between them. If this step is neglected it would lead to socket shield which is not covered with soft tissue. Regardless of the alternatives used soft tissue contour remained comparable with the neighbouring structure (Fig 10) (Gluckman). Model-guided flapless socket shield technique was used to maintain buccal bone and prevent a gingival recession in the esthetic area. Model-guided surgery is recognised as an accurate practice and flapless surgery reduces pain as well as a recession in the anterior region. These in combination with socket shield technique proved to be precise with its final outcome (Holbrook 2016).
Socket shield technique used along with CAD/CAM surgical guide and custom healing abutment assisted in the correct and precise positioning of the implant with the retained root fragment allowing the additional fabrication of the individual healing abutment (Fig 11). Root fragment was prepared 1 mm above gingival level and Emdogain was applied over it. This technique eased the entire procedure by reducing the time and cost as there was no need for augmentation or reconstructive surgical treatment with high esthetic results (Hürzler 2017). These studies point to the success of the socket shield technique done in combination with immediate implant placement.
MECHANISM OF SOCKET SHIELD TECHNIQUE
During extraction of a tooth, a periodontal ligament which is responsible for the formation of buccal bundle bone is lost and blood supply to the bundle bone is discontinued affecting its nourishment and eventually causing its total or partial resorption. Retained root fragment preserves periodontal ligament and supracrestal attachment of tooth avoiding buccal bone remodelling. Decoronation of the tooth is considered as a type of guided bone regeneration as remaining residual root undergo a resorptive process by osteoclasts from adjacent bone marrow which is gradually replaced by new bone (Malmgren et al 1984). The proven experiments have shown the end results as attachment of retained root to the buccal bone plate by a physiologic periodontal ligament, osseointegration of implant to alveolar bone along with peri-implant soft tissue revealing a physiologic junctional epithelium-free of any inflammatory reaction. The internal surface of root fragment also showed a thin layer of junctional epithelium and dentin surface was covered by a thin layer of newly formed acellular cementum both in an apical direction (Hürzler 2010¬). Formation of new bone was also seen in between implant and dentin when enough space was created to allow new cell migration and bone remodelling process in this area. Retained root fragment prevents the resorption of bundle bone and conserves soft tissue in the esthetic zone as height and thickness of facial and interproximal bone plays a very important role in this region (Hürzler 2010).
THE CLINICAL PROCEDURE OF SOCKET SHIELD TECHNIQUE
The procedure of socket shield technique includes decoronation of tooth followed by odontosection in mesio-distal direction then tooth root is sectioned vertically using a long tapered fissure diamond bur with the subsequent conservative extraction of palatal root fragment. After osteotomy preparation for implant placement, debridement of granulation tissue is done then the implant is placed lingually to the root fragment more towards the palatal side.
Generally, fissure bur is used to cut the tooth along the long axis but the modification to this has been executed with the use of the trephine bur. Trephine bur created an organized cylindrical shaped tooth fragment on the buccal side to support the buccal bone while the separation of root was done using a bone trephine. It was recognized as a less sensitive technique and easier to stay in track determined preoperatively. During extraction of a tooth, trephine bur also extracts a bone fragment which can be used as a graft material (Haseeb 2015).
The shield should be prepared in such a manner that it is thick enough for longevity (strength/ durability), yet thin enough so that it does not interfere with implant placement (Cherel) as well as the use of tapered implant has shown to be more beneficial (Kan and rung 2013). Best results were observed when the socket shield was reduced to bone crest level and chamfer was created in the crestal 2mm of the shield (GST 2017).
COMPLICATIONS AND MANAGEMENT
Despite the fact that socket shield technique showed excellent aesthetic result with complete tissue preservation, few cases were noted with complications which show its technique sensitivity (Gluckman 2017). Smoking and history of periodontitis is a contributing factor to implant failure (Karoussis et al 2007). Limiting or reducing smoking habits will decrease this risk. Preparation of shield by sectioning the root in mesial-distal direction, and removing the palatal half of the root (Kan and Rung 2017) along with the apex and pulp (Cherel) eliminated the potential complications of this technique. Mucositis and peri-implantitis were noted in few cases (Guirado 2016). The comparative study between the conventional immediate implant placement and immediate placement with socket shield technique showed bone loss of 12% and 2% respectively with soft tissue volume loss (attached gingiva) of 18% and 2% for the same in a follow up of 2 years duration (Abadzhiev 2014).
In a retrospective assessment of 125 socket shield cases, 25 underwent complications out of which 5 failed to osseointegrate. Unsuccessful implants were removed and rest 20 were managed.
1. Implant failure
The implants which failed to osseointegrate were removed and replaced. Socket shield was intact and uninfected. Replaced implants osseointegrated and were restored.

2. Infection
Mobile socket shields developed an infection and were removed. GBR procedure was done and the implant was restored. Immobile socket shield site was cleaned, rinsed with saline and the new implant was placed.

3. Socket shield exposure
Internal exposure of socket shield was the most common complication noted which is due to the lack of adequate space between the coronal edge of the shield and the subgingival contour of the crown. The author recommends correcting this before final restoration. The shield can be reduced to bone level and all sharp edges also smoothened. Small connective tissue graft is to be added into the sulcus to assist soft tissue closure. The second most common complication is the external exposure which is due to an overextension of the shield’s coronal aspect that perforates the overlying soft tissue. It can be managed using the same method.

4. Migration
The migrated socket shield was restored without reduction and was monitored without any additional complication. (GST 2017)
In spite of these complications witnessed, it should be known that none of the experiments can be observed with 100% accuracy and minute obstacles can be well managed. Comparatively, socket shield technique with immediate implant placement has fewer complications and failure rate so it can be used on a regular basis.
CONCLUSION
Hence, socket shield technique with immediate implant placement has proven to be cost-effectively an excellent method for ridge preservation with the maintenance of aesthetics in the anterior region and complete osseointegration of implant without any resorptional responses and signs of inflammation. It has created a benchmark in the preservation of gingival harmony including interproximal papilla. Even though it is technique sensitive, with correct clinical skill it can and should be used in daily practice due to its superior outcome as mentioned afore. This technique not only replaces the conventional implantation technique with its standard approach but also reduces the stress of the clinician and the patient simultaneously with its less invasive method. Along with all the benefits of this technique, it also has its own shortcomings due to insufficient long-term studies and the long-term results are still unknown.