Extraction of a tooth triggers a cascade of events to start up the healing of the socket .Bone remodeling starts in a three dimensional fashion. This normal healing event results in a minimal loss of width of the bone first followed by loss of the bone height. Loss of around 1mm of vertical height of bone, and a substantial (4-6mm) loss of width in the buccal-lingual plane occurs. Loss has been shown to be significant during the first three months of extraction resulting in both soft and hard tissue deformity thus affecting the prosthesis to provide satisfactory esthetic results. So to reduce the restorative process certain procedures have been shown to be predictable and potentially capable of eliminating secondary surgery for site preparation when implant therapy is planned. The key element is prior planning by the dental therapist to act at the time of extraction to prevent the collapse of the ridge due to the loss of the alveolus.
To better manage these risks and unaesthetic result. Several techniques have been employed in literature as ridge preservation procedures involving the use of bone grafts, barrier membranes,preserving the root section and biologics to provide a better restorative outcome. This review will explore the evidence behind each technique and their efficacy in accomplishing site preparation. The literature does not identify a single technique as superior to others; however, all accepted therapeutic procedures for ridge preservation have been shown to be more effective than blood clot alone in randomized controlled studies
Keywords: Bone grafts, root membrane technique, socket shield technique.
INTRODUCTION
Ontogenetically alveolar process is a tooth-dependent tissue that means its development is directly related to the eruption of teeth. Anchorage of the tooth to the jaws is provided by the bundle bone, that bone in which principle fibers of the periodontal ligament are anchored.Form of the teeth, their axis of eruption and eventual inclination are certain parameters which affects or determine the volume as well as shape of the alveolar process (Schroeder 1986). Ultimate consequence of loss of tooth is atrophy of the alveolar process (e.g. Atwood 1957, Hedegard 1962, Tallgren 1972). With the emergence of osteoclast, at 3rd week restorative of bundle bone starts and it with time it starts losing its function and disappear.More bundle bone in the crest of the buccal than the lingual wall is the reason behind more pounced loss of hard tissue in buccal wall (Botticelli et al. 2004, Arau´jo&Lindhe 2005, Arau´jo et al. 2008).
Most common dental procedure in our day to day life is tooth extraction. Generally, healing of the extraction socketoccurs in an uneventfulmanner. And the loss in horizontal dimension is more as compared to vertical bone loss and facial aspect ridge is more affected. Also loss of vertical ridge height, which hasbeen described to be most pronounced on the buccal aspect (Lekovic et al. 1997, 1998, Arau´jo&Lindhe 2005).Thus a narrower and shorter ridge is produced due to the restorative cascades (Pinho et al. 2006) and due the effect of thisrestorative pattern relocation of the ridge occurs to a more palatal / lingual position. Defect becomes more dramatic or challenging if it’s associated with the previous bone loss due to periodontal disease, endodontic lesions,or a traumatic episode.
If a tooth requires extraction, implant therapy is often considered one of the best options to replace a tooth functionally and esthetically. Loss of tooth and subsequent ridge collapse continue to burden restorative implant treatmentto obtain optimal functional and aesthetic prosthetic reconstructions.However sufficient alveolar bone volume andfavorable architecture of the alveolar ridge are essential forideal functional and esthetic reconstruction following implant therapy.Therefore, knowledge about the healing process at extraction sites, including contour changes causedby bone resoprtion, is essential for treatment planningso post extraction tissues should be carefully managed to preserve the alveolar ridge. In-lieu of surgical augmentation to correct aridge defect, various methods has been used in the literature. The purpose of this review paper is to highlight the benefits of ridge preservation at the time of extraction and provide an evidence-based rationale for adding this procedure to the implant protocol in site preparation.
TYPES OF BONE GRAFTS TO BE PLACED IN EXTRACTION SOCKET
First step in the ridge preservation is placing various bone graft materials inside the thoroughly debrided fresh extraction socket. Based on the source of origin these grafts have been classified as follows: auto graft (oral or extra oral), allograft (e.g. human freeze-dried bone), xenograft (bovine or porcine), and alloplasts or synthetic materials (hydroxyapatite, tricalcium phosphate, bioactive glass).
• Intraoral autogenously bone grafts
Maxillary tuberosity, post-extraction healing sites, and tori or exostoses are the various intraoral sites from where intraoral autogenouslygrafts have been harvested. The source of intraoral bone also is important.Osteogenic potential of cortical bone is very little and when the bone is cancellous in nature its provides better osteogenic potential since this bone contains hematopoietic marrow, such as red bone marrow from the maxillary tuberosity or from healing tooth sockets (8 to 12 weeks after extraction).Various techniques have been used to harvest particulate bone. Blood mixed with the bone obtained by using low or high speed but is known as Osseous Coagulum2.Triturated cortical or cancellous bone kept in amalgamcapsule for 60 seconds is known as bone blend. Hand instrumentsuch chisel, osseous collection device, or back action hoe can also be usedto collect bone. As an alternative to these auto grafts, allografts, xenografts, and alloplasts, usually available in a block or particulate form, can also be used (Iasella et a. 4), demonstrated the benefit of using alternative bone graft materials for site preservation following tooth removal.
• Iliac bone and marrow autograftshave shown to be the most predictable graft materials for bone growth. Because of the necessity of harvesting from a secondary surgical site and the possible morbidity associated with the procedures they are no longer popular5. Root resorption and ankylosis, in regards to bone grafting around teeth are various complications associated with use of fresh bone graft and marrow6. Later, to minimize these complications bone graft were by either freezed by keeping the bone graft in a storage medium or adding autologous intraoral bone to the harvested iliac crest bone graft mixture.
• Allografts consist of tissue transferred from one individual to another genetically dissimilar individual of the same species. Lack of secondary surgical site and decreased host morbidity are the advantagesprovided by these grafts. Unlimited amounts of graft material can be obtained. These grafts can be categorized as demineralized frozen or freeze-dried bone (DFDBA) or mineralized frozen or freeze-dried bone (FDBA). When implanted in mesenchymal tissue. FDBA provides an osteoconductive scaffold and elicits slower resorption than DFDBA7. Urist suggested in his study the added advantage of exposure of bone morphogenic proteins (BMPs) by using demineralized cortical bone causingit to be osteoinductive as well as osteoconductive.
When implanted in a well vascularized bone Osteoinduction involves the elicitation of mesenchymal cell migration, attachment and osteogenesis and when implanted in tissues induction of endochondral bone formation that would otherwise not form bone8. Schwartz et al. studied DFDBA samples from six different b
one banks and different lots within the same b
ank, the authors concluded there was a large variation between bone banks as well as between lots within the same bank. Possible reasons for the disparities were attributed to age, sex and medication taken by the donor, processing of the sample (demineralization time, sterilization method, particle size, etc.) and the time between death and harvest from the donor9.
Shapoff et al. Carriedout a study to determine if particle size is considered to be a factor in the evaluation of the osteogenic activity of freeze-dried bone allografts (FDBA) and if so,whether small particles have any enhancing or inhibiting effect on osteogenesis, within the parameters of the study it was concluded that,ostegenesis is enhanced by small particles of FDBA. This study also demonstrated that when comparing the osteogenic potential of freeze-dried bone allograftthe particle size is a variable to be considered10.
Zaner and Yukna also studied particle sizes of autogenous bone obtained by different collection methods and FDBA. Guided tissue regeneration around was also used in his study. They found that the smallest and most uniform particle size was seen of bone blend (21 x 105 um), osseous coagulum and FDBA had particle sizes of 300-500um, and chiseled bone chips had the largest and least uniform particle size (789 x 1559 um). They also suggested that the most appropriate graft particles size was 380 um. This particle size would produce the minimal pore size of 100 um needed between particles to allow for vascularization and bone formation to occur11.
DFDBA is also available in various sizes from 20-100 um and 100-300 um (lamellar bone or laminar bone) and as blocks of ilium12.
There have been no reports of viral contamination or acquired pathology from DFDBA or FDBA, although donor tissue has the potential to transmit disease12 – 13. Risk of disease transfer is reduced to one in eight million by freezing the bone allograft14. Mellonig et al. demonstrated safety of DFDBA byevaluating HIV-spiked human cortical bone and bone obtained from an AIDS patient by testing for the presence of HIV both before and after processing13.
Wood and Mealey conducted a study in which 40 extraction sockets were divided into 2 groups.Extraction sockets were grafted by either randomly selected DFDBA or FDBA.Post graft Histologic samples were obtained at 4-5 months, during implant placement.When changes in alveolar ridge dimension were compared there were no significant differences. DFDBA had a significantly greater percentage of vital bone at 38.42% versus FDBA at 24.63%. Significantly lower mean percentage of residual graft particles at 8.88% was seen in DFDBA compared to FDBA at 25.42%. The authors concluded that this study provided the first histologic and clinical evidence directly comparing ridge preservation with DFDBA versus FDBA in humans and demonstrated significantly greater new bone formation with DFDBA15.
In a recent study by Eskow and Mealey16comparison between the uses of cortical versus cancellous. FDBA from a single donor in ridge preservation was made. At 18 weeks histology of cortical samples showed more residual graft material present in and only 13-16% new bone formation respectively for cancellous and cortical FDBA. The dimensional ridge changes for both materials were similar and both showed loss of ridge height and width with the cortical FDBA preserving more lingual/palatal ridge height than the cancellous FDBA. In 11 of 35 patients the residual ridge at implant placement required additional bone grafting on the buccal aspect due to thin remaining bone or dehiscence, thus confirming other studies showing ridge preservation techniques will improve the outcome for site preparation for implants with some loss of bone still expected17.
Rummelhart et al.18 Found no difference in clinical parameters when DFDBA was compared to FDBA in periodontal defects. Furthermore, Sanders et al.19 concluded that mixing DFDBA with autogenous bone can increase the volume of bone available for grafting as well as enhance clinical outcomes when attempting to regenerate bone, especially in 1- and 2-walled periodontal defects.
• Xenografts
When tissue grafts are transferred from one species to a different species it’s called xenograft. In some short-term studies it has been observed that the placement of biomaterial in alveolar sockets may promote bone formation and ridge preservation, the graft may also delay healing. Long term effect on bone formation and amount of ridge augmentation that can occur by placement of Bio-Oss collagen(GeistlichPharma North America, Inc.) was made in a study. A xenogeneic graft in extraction sockets in five beagle dogs was completed. Non-grafted sites served as the control. The Bio-Oss collagen served as a scaffold for tissue modeling, but not new bone formation. When compared to the non grafted sites. Improved preservation of the alveolar process and ridge profile was shown in the Bio-Oss collagenplaced into the extraction sockets.Conclusions were made that the placement of a biomaterial in an extraction socket may modify remodeling and counteract normal marginal ridge contraction following tooth removal20.
Deproteinized bovine bone mineral (DBBM) more commonly known by the brand name Bio-Oss(GeistlichPharma) is the most common xenograft used today. In 2000 a study was conducted in which extraction sockets grafted with DBBM at 9 months were evaluated. Specimens were analyzedhistologically in the coronal, mid, and apical third of the sockets. The average amount of vital bone ranged from 26.4 – 35.1% with the most vital bone present in the apical portions and the least present in the coronal portion. The coronal portion of the socket was mostly connective tissue (63.9%). The DBBM graft material was still present at 9 months. The authors noted that it was present uniformly throughout the socket and averaged an overall 30% residual graft21.
Follow up study was then conducted by same author later in whom they analyzed the amount of woven versus lamellar bone present in the 3 socket regions. Also In authors found that while DBBM still remained in the socket at 9 months, no connective tissue was in contact with the graft, thus allowing the authors to claim that DBBM is biocompatible socket filler that can be used in ridge preservation procedures22. Another study that found DBBM as a favorable graft for ridge preservation compared DBBM to irradiated cancellous allograft (ICA), and to solvent-dehydrated allograft (SDA) when used to preserve extraction sockets23.
• Alloplasts are a synthetic graft material which is inert and implanted into tissue. Most common examples of alloplast are Hydroxyapatite, tricalcium phosphate, calcium sulfate and bioactive glass polymers24.This graft material has osteoconductive property which serves as a nisus or scaffold for new bone formation.Defect fill, stabilization of the remaining osseous structure, clinical attachment gain, and decreased probing depths are the result which has been shown by using alloplast24, 25.
Study was conducted in 1988 in which 3 groups were classified and treated with bioactive glass. The first group of patients had class II or class III residual ridge defects (Siebert classification). Ridge augmentation procedure was done in this group.
The second group had extraction sockets in which bioactive glass was used for ridge preservation at the time of tooth extraction.
The third group was treated as the control and the teeth were extracted and allowed to heal without any graft.
No significant difference in the ridge preservation group versus the ridge augmentation group was seen. The bioactive glass was able to maintain the alveolar ridge width and gain enough width in the augmentation cases. The control g
roup did not show significant differences in buccal-
lingual dimension; however the vertical resorption was significant26.
Another common synthetic bone graft used is hydroxyapatite.Froum et al in 2004. Evaluated extraction sockets grafted with hydroxyapatite and noted approximately 31% vital bone present at 6-8 months27. In that same study, bovine bone yielded an average of 29.75% vital bone. All of the extraction sites had buccal defects and there was no attempt to gain primary closure27.
Finally, another alternative that can be used in ridge preservation is sponges made of collagen or polylactic/polyglycolic acid. Serino et al. conducted studies with Fisiograft a synthetic co-polymer composed of polylactic and polyglycolic acids, used as space filler during ridge preservation. After the reflection of full thickness flapssponges were filled in half of the extraction socket and other half was left to heal by blood clot alone. No attempt was made to achieve primary closure. After 6 months the implants were placed histological analysis was made. No significantly different in ridge dimension between any of the groups was obtained. Histologically new mineralized and well structured bone was seen at the test sites. At extraction socket no residual graft material was detected in the extraction sites28.
Bio–col technique described by Sclar involved the placement of DBBM particles in the extraction socket and then covered with a collagen plug or membrane sutured into place. Results yielded an adequate ridge preservation that allowed implant placement29.
Collagen sponges have also been used as carriers for placing other graft materials.
DEVELOPMENT OF SITE THROUGH RIDGE PRESERVATION
A guided tissue regeneration principle is the principal behind implant site development, including guided bone regeneration and ridge preservation. Barrier membrane can be used at extraction site or deficient alveolar ridge. Augmentation of socket can be made by using with graft material and sealed with a barrier membrane or a membrane may be used without graft material in the socket. This procedure was termed ridge preservation by Rose et al.
Guided bone regeneration (GBR) a dental surgical procedure that use barrier membrane to direct the growth of new bone and gingival tissue at sites with insufficient volumes or dimensions of bone or gingival for proper function, esthetics or prosthetic restoration. An alveolar ridge with a volumetric deficiency can be improved with the use of graft material and a barrier membrane30 ,31.
If implant therapy is the desired course of treatment is therapy, main goal is to give the patient a stable replacement for their tooth (teeth) with the most esthetic outcome possible. Soft tissue contour of the tooth being restored with the Single tooth restorations should be identical to the natural tooth contour. Height of alveolar bone and thickness of facial plate after extraction are the most important factors which should be considered in implant therapy.
The use of ridge preservation techniques are used to prevent residual ridge defects, and thus increase satisfaction with respect to esthetics and function. Key component of successful and esthetic implant therapyis adequate buccal plate thickness at the time of implantplacement. During implant placement thickness of facial bone should be at least 1.8 mm after the final osteotomy is drilled resulted in significantly less bone resorption than facial plates that were less than 1.8 mm32.
Braut et al. In his study evaluated the thickness of facial bone in the anterior maxilla in 125 cone beam CT scans. They measured the width at two points; at middle of root and 4 mm from the CEJ in 498 teeth. Their results showed the majority of teeth had <1 mm of bone thickness (62.9% at 4 mm from the CEJ, 80.1% at the midroot) with a statistically significant decrease in facial bone thickness from the first premolar to the central incisors.At the crest facial bone was either missing or thin in 90% of the teeth evaluated by CBCT33. This study confirms the value of ridge preservation at the time of extraction and the need to support that thin alveolus to reduce buccal bone resorption.
BARRIER MEMBRANES
Many types of materials were developed to serve as barrier membranes. These different membranes are distinguished as either non-resorbable or resorbable membranes.
NON RESORBABLE MEMBRANES
First commercial membrane was produced from Teflon, an expanded polytetrafluoroethylene (e-PTFE) following Nyman and colleagues membrane constructed from Millipore(cellulose acetate) filters. This membrane consisted of 2 parts: a collar portion and an occlusive portion, collar portion have open pores to allow in-growth of connective tissue and to prevent epithelial migration; and an occlusive portion, prevents the flap tissues from coming into contact with the root surface. Later, to treat osseous defect the membrane was redesigned with a stiff central portion with the understanding that the space defined and protected by the membrane determined the volume of the tissue to be regenerated34 ,35. For the treatment of both osseous and periodontal defects titanium was then built into the membrane35. Successful use of non-resorbable membranes in GTR therapy led to application of these membranes in GBR procedure.
First clinicians to report successful ridge augmentation with GBR in humans using an e-PTFE membrane and tenting pins wasBuser et al.36To provide tenting support to the overlying e-PTFE membrane titanium mini – screws were placed in the defect. Following six to ten months of healing, the authors demonstrated bone volume increased to allow placement of dental implants in nine of the twelve sites. 1.5 to 5.5 mm gain in new bone was observed. The authors concluded that the biologic principle of osteopromotion by exclusion was highly predictable for ridge enlargement or defect regeneration under the prerequisite of complication-free healing.
However, complications are common to occur during the healing following placement of non-resorbable membranes. Recovering of the non-resorbable membranes at second surgery leads disturbs healing30. Membrane exposure created by variable amounts of flap sloughing during healing has been a recurrent post-surgical complication associated with the use of non-resorbable membranes37. Adhesion of bacteria is common to occur on the exposed porous membrane.In one study GBR failures, as high as 31%, due to membrane exposure have been reported38. There is a communication made between oral environments and newly forming tissues due to membrane exposure increasing the possibility for infection and decreasing the probability of regeneration.
Development of a high-density polytetrafluoroethylene (d-PTFE) non-porous membrane used specifically for ridge preservation following extraction has been utilized to counteract some complications due to non-resorbable porous membrane (e-PTFE). A retrospective study based in a private practice demonstrated the use of d-PTFE left exposed following extraction and maintained in place for 4 weeks resulted in significant retention of the alveolar ridge in 276 sockets. Although no controls were used in this study, measurements were taken at baseline and one year later to verify the amount of bone loss at specific points using a stent. The advantage of the d-PTFE over e-PTFE was that no primary coverage was attempted and therefore, no releasing incisions to manipulate the flap were used. Outcome was not affected by the use of exposed d-PTF and the non-porous membrane appears impenetrable to bacteria due to its surface characteristics [60].
RESORBABLE MEMBRANES
There are three types of biologically resorbable membranes:
1) Polyglycoside synthetic copolymers: polylactic acid –Guidor(Sunstar Americas, Inc.), pol
yglactide– Resolute(W.L. Gore and Associates Inc.),
polyglactin 910 –Vicryl(Ethicon division Johnson & Johnson Medical),
2) Collagen and 3) Calcium sulfate – CalcigenOral (Biomet 3i).
Second surgery for retrieval is not required normally in collagen as well as all resorbable membranes, so in addition to less morbidity and the elimination of a second surgery,patient is more satisfied with resorbable membranes. Principal constituent of connective tissue is Collagen and it provides structural support for tissues throughout the body30. Homeostatic action is provided by Collagen and also it possesses the ability to stimulate platelet attachment and enhance fibrin linkage, which may assist initial clot formation and stabilization, leading to enhanced regeneration39. Collagen also has chemotactic property for fibroblasts in vitro. This property could possibly enhance cell migrationin vivo40. Manipulation and adaptation of Collagen membranes are easy and appreciated. Patients tolerate collagen, a weak immunogenic, very well30,41- 43.
Luczyszyn et al.44 used ADM as a membrane for ridge preservation. Role of acellular dermal matrix (ADM), associated with a resorbable hydroxyapatite (RHA) bone graft in regeneration to prevent bone loss after tooth extraction was evaluated in his study.
Acellular dermal matrix (ADM) is derived from human donor skin tissue. It is commercially available from tissue banks sanctioned by the American Association of Tissue Banks (AATB). The donor tissue undergoes multiple washing steps to remove the epidermis and the various cells that may cause graft rejection. The tissue is then preserved through a patented freeze-drying process that prevents ice crystals from forming. ADM was initially known for its use in skin grafting for burn patients, and various plastic and orthopedic reconstructive procedures. In dentistry, ADM is utilized in primarily in root coverage procedures. Extensive studies have proven its efficacy in these procedures.
Luczyszyn et al.44concluded in his study that the ADM was successful and have the ability to preserve ridge thickness and that the additional use of RHA favored the preservation of the ridges along with an increase in the width of keratinized tissue.
ROOT PRESERVATION TECHNIQUE – to prevent bone loss
▪ Submucosal vital and non-vital root retention45have been described.From an ontogenetic perspective, this technique is most physiological approach to the prevention of alveolar ridge resorption is to naturally preserve the inflammation-free dental root—if possible.
▪ Salama.46 Root submergence technique was demonstrated by Salama topreserves the natural periodontium, thereby completely preventing bone resorption.
▪ Davarpanah& Szmukler-Moncler47reported a series of five casesthat implant osteotomy preparation and placement were through the ankylosed roots. No interference in implant integration was observed by the deliberately left root fragments.
▪ Recently a novel approach48was introduced where only a portion of root is retained and subsequently submerged in proximity to an immediately placed implant.
➢ Root membrane technique
➢ Socket shield technique
▪ In 2010, Hürzeler et al.48 introduced a new method, the socket shield technique, in which a partial root fragment was retained around an immediately placed implant with the aim of avoiding tissue alterations after tooth extraction.Observed histologically the absence of inflammation and of bone resorbtion around the 4 implants placed in the 3rd and 4th premolars of the dogs after 4 months follow-up. All implants presented osteointegration.
▪ Kan e Rungcharassaeng (2013)49 placed implants with immediate loading using this technique at the aesthetic zone and was able to maintain the anterior aesthetics preserving the interimplantarypapillae.
▪ Cherel e Etienne (2014)50registered the preservation of papillae between 2 implants with immediate loading in adjacent teeth after an 11-month follow-up.
▪ Lagas et al (2015)51performed this technique in the upper incisors of 16 patients without any bone grafting and proved its success without any bone loss.
▪ Baumer et al (2015)52used this technique in pre-molars of 3 dogs and registered a healthy periodontal ligament around the buccal fragments and a good osteointegration of implants with no osteoclastic activity. Buccal bone volume was also maintained.
CONCLUSION
The literature is substantial in support of site preparation for implant therapy, not just in the esthetic zone but throughout the mouth. Clinicians have long known the benefit of preserving the ridge at the time of extraction to reduce the resorptive process and in many cases to avoid an additional surgical procedure to augment a deficient ridge. This review has given the evidence behind these statements and shown techniques commonly used today. It is apparent that the specific materials are not the key element to successful ridge preservation. Many choices are available to the clinician and success is based on the care at the time of extraction to preserve the remaining walls of the alveolus (extraction socket) through minimal trauma. Ridge preservation is merely one aspect of successful implant therapy, but one that needs to be considered early in the treatment plan by the restorative doctor. It is a cost-effective measure when compared to the need for guided bone regeneration as an additional surgical procedure to treat the resulting ridge defect through augmentation.