November 29, 2018
by Zeeshan Sheikh, Dip.Dh, BDS, MSc, PhD; Nader Hamdan, BDS, MSc, MDent (Perio); Michael Glogauer, DDS, PhD, Dip.Perio
In order for implant therapy to be successful there is a need for the dental implant to be adequately integrated into host bone in the proper position in three dimensions. For this to be achieved, adequate height and volume of alveolar bone is required. However, the alveolar ridge is prone to resorption following extraction of teeth which results in inadequate bone volume and unfavorable alveolar ridge architecture which ultimately limits the successful placement of dental implants. 1,2 Although immediate placement of dental implants is a successful form of therapy, 3 it has been reported that implants do not adequately preserve the alveolar ridge. 4,5 This could be due to the early disappearance of the thin bundle bone with an average thickness of 0.5 to 0.7 mm 6 as a consequence of losing blood supply from the periodontal ligament space palatally and due to blood supply disruption buccally due to elevation of a flap. 7
Socket Healing and Changes Following Tooth Extraction
Following tooth extraction, socket healing is characterized by internal changes that lead to formation of bone within the socket, and external/dimensional changes that lead to loss of alveolar ridge height and width. 1 Various factors affect the healing process of sockets that are left empty and/or undisturbed. Wider extraction sockets necessitate more time for defect bone bridging when compared with narrower sockets. It is known that it takes longer to completely form bone at molar sites compared to single-rooted sites. 1 In addition, sockets of teeth with horizontal bone loss heal more quickly as the lower level of the alveolar bone means less bone infill is required. 1 Internal changes following tooth extraction are characterized by:
Externally, it has been observed that height reduction is more pronounced at the buccal wall and is accompanied by a horizontal loss on both buccal and lingual walls. 11 Resorption of the external buccal and lingual walls of the socket results in dimensional changes of the ridge. 12 The most rapid changes are found in the early post-extraction period, from six months to two years. 13 It has been seen that there are differences in the rate of resorption between maxillary and mandibular sites, with the changes being about four times greater in the mandible than the maxilla. 13 The effect of a single tooth extraction of a premolar or a molar tooth on bone healing has been studied by Schropp et al. and they revealed that major changes take place in the first 12 months after extraction with an average of 50% reduction in the width of the alveolar ridge (Fig. 1). 1
However, two-thirds of this reduction usually occurs within the first three months, and although it is not always possible to retain teeth due to pain and infection, if possible, teeth should be retained for as long as possible to coincide with the chosen time for implant placement. 1,14
Alveolar Ridge Preservation
This includes any procedure undertaken at the time of or following teeth extraction that is designed to minimize external resorption of the alveolar ridge and maximize bone tissue formation within the extraction socket. Literature suggests that ridge preservation should be considered if an implant is to be placed more than six to eight weeks after tooth extraction. 10 However, as evidence also suggests that major bone loss occurs during the first three months after extraction, it might be also prudent to consider socket preservation whenever immediate implant placement is not planned. Some preservation techniques are based on the principles of guided bone regeneration (GBR). Others include minimally traumatic tooth extraction, soft and hard tissue grafting with and without the use of barrier membranes (Figs. 2 & 3).
Several clinical and preclinical studies have reported and demonstrated that ridge resorption can be limited when alveolar ridge preservation procedures are used versus the placement of no graft material in freshly extracted non-intact sockets. 15 It has been noted that with ridge preservation procedures, horizontal resorption of just over 1 mm still occurs with relative preservation of vertical height, whereas a lack of any preservation results in more than 3 mm of horizontal loss and at least 1 mm or more of vertical loss. 15 Although extraction of a tooth inherently is a traumatic procedure, the use of appropriate instruments with minimal force is recommended and can limit damage to the hard and soft tissues. 15 It has to be kept in mind that in presence of acute infection it is advisable to not perform ridge preservation at the time of extraction and preservation may be delayed by six to eight weeks 10 (Fig. 4).
Socket debridement and socket wall decortication: Some research studies advise to perform debridement to physically remove anything that may interfere with socket healing. 10,16 Other studies suggest that a round bur should be used to perforate the socket walls to allow greater access for blood vessels to improve bony infill. 17 Conversely, it has been shown that retention of the periodontal ligament along the socket walls may aid retention of the clot during the early stages of socket healing. 17
Soft tissue coverage of the extraction socket: Soft tissue coverage procedures are employed to retain, stabilize and protect grafting materials. A plethora of techniques have been suggested such as rotating grafts from adjacent tissue to cover the defect, coronal advancement of buccal flaps or using free gingival or subepithelial connective tissue grafts18,19 (Fig. 5).
Conversely, the site may be left to allow healing and regeneration of mucosa over the socket for six to eight weeks and at this stage the added soft tissue volume may assist optimal closure over the socket along with ridge preservation procedure being performed 20 (Fig. 4).
Use of bone or bone-replacement graft materials: Many bone replacement grafting materials have been investigated and used for extraction socket preservation and these include autologous bone, allografts (mineralized and demineralized freeze-dried bone allografts, FDBA and DFDBA), xenografts, bioactive glass, and synthetic hydroxyapatite. 21 Both Becker et al. 21 and Froum et al. 22 showed little new bone formation around DFDBA and a study revealed that DFDBA cannot speed up bone formation. 23 A study using porous bovine bone graft (Bio-Oss) reported that there was around 82% bone fill achieved. 24 The use of a xenograft, allograft and alloplasts does not require a donor site, hence eliminating donor site morbidity following harvesting and also simplifies the procedure. Although published literature shows different graft materials and techniques for improving bone healing in extraction sockets 25, the important question is of the clinical relevance. Does a particular bone graft material have the ability to successfully preserve the extraction socket and predictably achieve a level of bone fill that allows for tissue loss to be kept to a minimum? Although all alveolar ridge preservation studies demonstrated beneficial results, no one particular grafting material has proven superior to others.
The use of barrier membranes: Barrier membranes are used as occlusive barriers in order to prevent the soft tissue from proliferating into the defect. This will stabilize the newly formed blood clot and will also provide space for some bone healing to take place. Barrier membranes are commonly classified as being resorbable or non-resorbable and can either be synthesized using natural or synthetic materials. 26,27 The most commonly used non-resorbable barrier membrane to maintain the alveolar ridge after tooth extraction is dense polytetrafluoroethylene (dPTFE). 28 The resorbable membranes are generally formulations of collagen procured from various animal sources with or without chemical modifications to improve the handling characteristics and in vivo efficacy. 29 The rationale behind using bone replacement graft biomaterials under barrier membranes is to prevent the collapse of membranes that do not have sufficient structural integrity and also to allow for bone formation to take place around and within the graft biomaterials. Heterogeneity exists among the studies regarding barrier use for alveolar ridge preservation procedures. Although results among the studies were relatively similar, no clear benefit was demonstrated with or without a barrier in the context of the studies examined. Use of barrier membranes may prove beneficial in cases where extraction socket walls are either partially or completely missing. Additional controlled and comparative studies are needed to confirm this. In fact the general consensus is that neither a bone graft material nor a membrane is needed if all extraction socket walls are intact and the thickness of the buccal plate of bone is 2 mm or more (which is usually rare).
A reasonable suggestion to clinicians attempting extraction socket preservation would be to use an osteoconductive bone graft material (xenograft or alloplast) covered with a connective tissue graft or a resorbable barrier membrane which may be tacked into place. This is expected to preserve sufficient alveolar ridge volume and contour to permit implant placement after four to six months with acceptable clinical and aesthetic results. However, if the clinician is planning to place the implant within six to eight weeks post-extraction, then using a resorbable collagen sponge to aid with initial clot stabilization is recommended. This would allow for clot stabilization sufficiently but would not promote bone fill and preserve the ridge.
Some specific recommendations to perform extraction socket preservation are:
If the dental implants can be placed at the time of extraction this eliminates the need for extensive ridge preservation.
However, this is not the case always and there are several clinical considerations that need to be kept in mind before attempting to preserve the alveolar ridge. Additionally, relatively recent techniques have been proposed with the aim of maintaining adequate blood supply to the usually thin buccal wall of bone. These techniques depend on partial extraction of the root of the tooth to allow maintenance of the periodontal ligament space associated with the buccal bone (Fig. 6).
This ultimately allows for adequately maintaining sufficient bone for optimal implant placement. However, it has to be kept in mind that not all extraction sockets need to be preserved. In addition, it is challenging to predict how extractions will heal as some sockets heal with minimal resorption but conversely, some lose a lot of soft and hard tissue. Based on the evidence presented in literature there is no one material technique that meets all the criteria to successfully preserve the ridge after extraction. Finally, further long-term studies are required, especially to assess the ridge dimension following preservation and implant placement. OH
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About the Authors
Dr. Zeeshan Sheikh works at the Faculty of Dentistry/Faculty of Medicine, University of Toronto and at Mt. Sinai Hospital. He was trained as a clinician scientist from institutions like Queen Mary University of London, McGill University and University of Toronto. His expertise lies in developing novel biomaterials for bone grafting and regeneration for dental and orthopaedic applications.
Dr. Nader Hamdan is an Assistant Professor and Director of the Graduate Periodontics Program, Faculty of Dentistry at Dalhousie University. Besides his academic full-time position, Dr. Hamdan treats his own patients in multiple private practices limited to periodontics and Dental Implant Surgery in Canada. Dr. Hamdan is a member of the American Academy of Periodontology, the Canadian Academy of Periodontology, the Atlantic Society of Periodontists, and the Steering Committee of the Network for Canadian Oral Health Research (NCOHR).
Dr. Michael Glogauer works at the University of Toronto. His research and clinical interests focuses on developing novel bone grafting approaches prior to implant placement and the role of the oral innate immune system in maintenance of health. He is currently focusing on using oral innate immune biomarkers to detect early stages of periodontal diseases through his role as Scientific Director at the Mt. Sinai Hospital’s Centre for Advanced Dental Research and Care. He is a periodontist at OMGPerio.ca.