Table of Contents      
INVITED REVIEW
Year : 2015  |  Volume : 7  |  Issue : 3  |  Page : 94-112

Ridge augmentation in implant dentistry


Department of Oral and Maxillofacial Surgery, Santosh Dental College and Hospital, Ghaziabad, Uttar Pradesh, India

Date of Web Publication31-Dec-2015

Correspondence Address:
Manoj Goyal
Santosh Dental College and Hospital, No. 1 Santosh Nagar, Pratap Vihar, Ghaziabad, Uttar Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2231-0754.172939

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   Abstract 

Dimensional changes in the alveolar ridge after extraction often compromises on achieving optimal implant stability and placement of implants in the right prosthodontic positions. These situations demand augmentation of the residual ridge to achieve successful implant placement and long-term survival. Although the available literature speaks of an overabundance of techniques and agents for ridge augmentation, there is a relative paucity of quality evidence to guide the selection of suitable techniques and material. Henceforth, this paper is an endeavor to develop and describe an evidence-based decision pathway for the selection of suitable techniques for various clinical situations. Additionally, a descriptive overview of various techniques and materials is presented.

Keywords: Bone grafts, ridge augmentation, socket grafting, socket preservation


How to cite this article:
Goyal M, Mittal N, Gupta GK, Singhal M. Ridge augmentation in implant dentistry. J Int Clin Dent Res Organ 2015;7, Suppl S1:94-112

How to cite this URL:
Goyal M, Mittal N, Gupta GK, Singhal M. Ridge augmentation in implant dentistry. J Int Clin Dent Res Organ [serial online] 2015 [cited 2018 Dec 17];7, Suppl S1:94-112. Available from: http://www.jicdro.org/text.asp?2015/7/3/94/172939


   Introduction Top


The fast pace of soaring popularity of implants in dentistry by clinicians and patients alike is substantiated by the existence of a booming share of implants in the global dental market, i.e., worth approximately US$7 billion with a perceived annual growth rate of 9%.[1] This existent profitability of implants is incumbent on high success rates of approximately 95% for placing prosthesis in completely as well as partially edentulous jaws.[2] However, the local conditions may not always be favorable for implant placement as in cases of deficient bone volume after extraction. The sufficient horizontal as well as vertical bone dimensions are a prerequisite to warranty the success of implants.[3],[4] But the fact that the maintenance of the alveolar bone is dependent on the presence of teeth explains the high prevalence of paucity of sufficient bone after extraction.[5],[6] Hence, often there is the need to augment the available atrophic bone to make it amenable to implant placement in suitable prosthetic positions with desirable stability and aesthetics. To feed this need for augmentation, a plethora of agents and techniques are available with volumes of literature; yet there is an absence of consensus for the efficacy of any of these surgical techniques.[7],[8],[9] The present paper will attempt to summarize the evidence on changes in the alveolar bone after extraction, efficacy of ridge augmentation, comparative efficacy of various techniques and graft materials, and short implants versus ridge augmentation. Further, this paper will give a descriptive insight into various bone graft materials, techniques, and physiologies of regeneration. Also, an algorithm to guide the selection of suitable techniques and materials in commonly presented clinical conditions would be presented.


   Postextraction Dimensional Changes in Ridge Morphology Top


As the quantity and quality of the bone is a key determinant for success of implant prosthesis, it is imperative that the clinician be aware of postextraction dimensional changes in ridge/socket morphology. The presence of the tooth and physiological stimulation is a prime factor for maintenance of the alveolar bone and thus, following extraction of the tooth rapid resorptive changes take place.[5],[6] A recent systematic review summarized that dimensional changes are rapid in the first 2-3 months after extraction and thereafter resorption is gradual. It was reported that horizontal bone loss (3.79 ± 0.23 mm; 29-63%) was more extensive than vertical bone loss (1.24 ± 0.11 mm on buccal, 0.84 ± 0.62 mm on mesial, and 0.80 ± 0.71 mm on distal sites; 11-22%).[6] However, the extent of bone loss is affected by multiple factors,[6] i.e., elevation of flap (full-thickness, split thickness, or none)[1],[10] systemic health status (e.g., diabetes), lifestyle (e.g., smoking), number of roots, and preextraction dimensions of alveolar bone, etc.[6],[10],[11],[12],[13],[14],[15] Vertical bone loss is dependent on the phenotype of the buccal bone wall; it is greater and extensive in amount in thin-walled phenotypes than in thick-walled phenotypes. In fact, it has been reported to be 3.5 times more severe when facial wall thickness is <1 mm [1]


   Evidence on Ridge/socket Preservation Top


The data presented in this section is an overview of the recently published systematic reviews and meta-analyses investigating the outcomes of various techniques as well as materials for ridge/socket augmentation [Table 1]. Although definitive outcomes for clinical guidance could not be extracted from the published literature primarily owing to heterogeneity, a few conclusions yet noteworthy. The heterogeneity existed mainly owing to variable research methods (randomized controlled trials, case series, and/or retrospective records), heterogeneous outcomes of interest as well as poorly defined outcomes and short follow-up periods, etc.
Table 1: Evidence from recent systematic reviews

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Rationale of ridge augmentation

It can be safely concluded that ridge/socket augmentation is an efficient procedure for augmenting atrophic/deficient bone. Statistically significant alveolar volume gains in preserved/augmented versus nonpreserved sites have been reported, i.e., +1.89 mm in terms of buccolingual width, +2.07 mm for midbuccal height, +1.18 mm for midlingual height, +0.48 mm for mesial height, and +0.24 mm for distal height [16] Even greater alveolar bone volume gain has been reported with use of Ti-mesh as barrier in combination with autogenous/allogenic/xenogenic bone grafts, i.e., ≈4.91 mm of vertical regeneration and ≈4.36 mm of horizontal regeneration.[17] On the other hand, it is quite interesting as well as contrasting to note that similar rates of implant success and survival have been reported for implant placement in augmented versus naive bone.[18] This seriously questions the rationale of ridge augmentation. Also, the existing literature points toward the need for simultaneous augmentation at the time of implant placement.[7],[17] So, instead of routine use, socket grafting procedures should be performed when there is a possibility of extended treatment time between extraction and implant placement. Also, it has been recommended that socket grafting should be performed in aesthetic areas in case of buccal bone thickness≤2 mm or when there is a proximity to anatomic structures, i.e., maxillary sinus or mandibular canal.[7]

Comparative evaluation of types of bone grafts

Although theoretical assumptions state that autogenous bone grafts are superior to other bone substitute materials, the literature fails to substantiate this fact.[20],[21],[22],[23] The recent systematic reviews reported no superior clinical outcomes with autogenous bone graft over other bone substitute material for routine augmentation, guided bone regeneration (GBR), or maxillary sinus floor augmentation [20],[21],[22],[23]

Comparative evaluation of various techniques of ridge augmentation

There is no clear evidence supporting any of the specific techniques but GBR.[24],[25],[26] GBR has been shown to be a predictable technique, especially when Ti-mesh is employed for horizontal as well as vertical augmentation [mean implant survival rate (MISR) of 100%].[18] Milinkovic and Cordaro (2014)[25] extracted data from 53 publications for partially edentulous patients and 15 publications for edentulous patients. Although owing to heterogeneity of included studies, no clear-cut indications could be extracted for specific bone augmentation procedures, a few suggestions could be drafted on the basis of magnitude of the mean implant survival rate. The evidence suggested that dehiscence and fenestrations can be treated successfully with GBR at the time of implant placement [MISR 92.2%, mean complication rate (MCR) 4.99%]. In partially edentulous ridges, when a horizontal defect is present, procedures such as staged GBR (MISR 100%, MCR 11.9%), bone block grafts (MISR 98.4%, MCR 6.3%), and ridge expansion/splitting (MISR 97.4%, MCR 6.8%) have been proved to be effective. Vertical defects can be treated with simultaneous and staged GBR (MISR 98.9%, MCR 13.1% and MISR 100%, MCR 6.95%, respectively), bone block grafts (MISR 96.3%, MCR 8.1%), and distraction osteogenesis (MISR 98.2%, MCR 22.4%). In edentulous patients, there is evidence that bone block grafts can be used (MISR 87.75%), and that Le Fort I osteotomies can be applied (MISR 87.9%) but are associated with a high complication rate. Further, the addition of platelet-rich plasma (PRP) has been reported to confer no additional benefit on either bone volume gain or implant survival.[20],[27]

Short implants in nonaugmented sites versus long implants in vertically augmented sites

Esposito et al. (2010)[26] performed a meta-analysis to compare if vertical augmentation procedures were more advantageous that short implants. The analysis revealed that vertical

augmentation procedures resulted in [odds ratio (OR) = 5.74] and more statistically significant complications (OR = 4.9). Thus, if possible short implants seem to be a better alternative to vertical augmentation for implant placement.[28],[29]


   Physiology of Bone Grafts and Regeneration Top


There are three basic mechanisms [8],[9] by which bone grafts augment recipient bone site, i.e., osteogenesis, osteoinduction, and osteoconduction. In osteogenesis, surviving residual cells in the bone graft differentiate into osteoblasts and stimulate the formation of new bone. Osteoinduction is a process where the bone graft stimulates the formation of new bone by virtue of bone growth factors contained in it. In osteoconduction, the bone graft possesses neither the ability to regenerate bone nor stimulate the recipient bone to form new bone. Here, the donor graft merely acts as a scaffold for ingrowth of vascular and connective tissues. Eventually, all transplanted grafts are replaced by new bone.


   Types of Bone Grafts Top


On the basis of origin, there are mainly four categories of bone grafts:[33] autografts, allografts, xenografts, and alloplastic materials. All of these possess distinct as well as overlapping advantages and disadvantages [Table 2].
Table 2: Comparative summary of different types of grafts

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Autografts

These refer to grafts transplanted from one place to other within the same individual. These are referred to as the “gold standard” owing to the only graft types with all three mechanisms of bone regeneration, i.e., osteogenesis, osteoconduction, and osteoinduction as well.[30],[33],[34],[35] These can be harvested from neighboring intraoral sites [Figure 1] or remote extraoral sites.[35] Usually, the intraoral sites, i.e., mandibular symphysis (chin), ramus, and tuberosity, etc., are preferred over distant extraoral sites, i.e., anterior iliac crest, tibial plateau, and proximal ulna [Table 3]. This is mainly owing to the ease of harvest and the low morbidity associated with intraoral grafts.[35] On the other hand, extraoral graft may require a second surgery or even a second surgical team, which often extrapolates to increased cost and management in “in-patient settings.” Also, grafting from the extraoral donor site is associated with greater risk of complications and longer periods of postoperative management [35] [Table 3].
Figure 1: sources of intraoral grafts

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Table 3: Autogenous grafts from intraoral and extraoral origins

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Autogenous grafts can be cortical, cancellous, or corticocancellous.[8],[35] The prime difference between cortical and cancellous (particulate) bone grafts is with respect to healing and the ability to be contoured and adapted to the recipient site.[8],[35] Cancellous grafts undergo rapid incorporation (within weeks to months) and have greater osteogenetic potential compared to cortical grafts.[8],[35] On the other hand, incorporation of cortical grafts is rather a slower process known as creeping substitution where the revascularization starts from periphery toward the center. In fact, the remnant pieces of donor graft may persist as necrotic areas walled off by new bone.[8] It is easier to achieve primary stabilization with cortical grafts while cancellous grafts often require to be contained within membranes or titanium mesh due to the lack of rigidity.[8]

Harvesting autogenous grafts

Ramus graft

Local anesthesia

Mandibular nerve trunk anesthesia is supplemented with local infiltration in the area of coronoid process, mental foramen, and buccal part of the mandibular body reaching toward the mandibular base.

Surgical technique [Figure 2]

Theincision extends from the medial aspect of the external oblique ridge to the first molar area. The concavity where the external oblique ridge meets the ramus is the prime landmark to facilitate locating the starting point of this incision. A mucoperiosteal flap is reflected to visualize the border between the external oblique ridge and ascending ramus. The lateral border of the ramus and the external oblique ridge is dissected free. The soft tissues are retracted along the anterior border of the ramus till the insertion fibers of the temporalis muscle are identified. The donor area is identified and the borders of the osteotomy cuts are marked by drilling holes through the cortex till the cancellous bone is identified by marrow bleeding. The superior border of osteotomy cut is made on external oblique ridge along the anterior border of the ramus approximately till one-third of the width of the ramus. The anterior cut is placed along the distal aspect of the first permanent molar. The inferior cut is placed approximately 4-5 mm superior to the mandibular canal. Medially, the osteotomy cut is placed in the lateral cortex. After delineating the margins of the osteotomy cuts by drilling holes, the cuts are completed with either rotary or osteotome or piezotome. The latter is considered to be the best owing to inherent low risks associated with its use while osteotome is least preferred due to poor patient acceptance.[35] Following this, the lateral bone block is fractured with due care to avoid damage to the inferior alveolar neurovascular bundle.
Figure 2: mandibular ramus graft; (a) mucoperiosteal flap raised and exposure of donor site (b) harvesting of graft (c) preparation of recipient site (d) fixing the harvested block onlay graft

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Care of donor area and graft

A collagen membrane is used the fill the donor area defect, which is closed by running sutures after hemostasis. The graft is stored in blood-soaked gauze till it is particulated or transplanted.

Chin/symphysis graft

Local anesthesia

Mandibular nerve block is supplemented with local infiltration in the anterior mandibular labial vestibule.

Surgical technique

The mucoperiosteal flap can be raised by vestibular or sulcular incision. The former is preferred as the latter is associated with postoperative gingival recession. The two-layer vestibular incision is made through the deepest part between the vestibule and lip. The lateral extent of the incision depends on the purpose of harvest. For local grafts, the incision is limited till the canines. On the other hand, for maxillary sinus grafting the incision in extended till the premolars to locate the mental nerves. The superior osteotomy cut is placed at least 5 mm inferior to the apex of the mandibular teeth and the inferior cut is placed approximately 4 mm superior to the inferior border of the mandible [Figure 3]. Often, the graft is given a cut in the midline and is harvested in two parts using an osteotome.
Figure 3: symphyseal graft; (a) atrophic ridge with deficient horizontal dimensions (b) exposed symphyseal area (donor site) (c) completed osteotomy (d) harvesting graft (e) fixation of veneer graft to the recipient site and filling the residual voids with particulate graft (f) immediate postoperative view

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Care of donor area and graft

As described for ramus graft, the residual symphyseal cavity is packed with collagen membrane after achieving hemostasis. The closure is performed in two layers, i.e., periosteum and muscle layer followed by mucosa. The graft is handled in same way as described for ramus graft.

Tuberosity graft

Local anesthesia

Posterior superior alveolar nerve block.

Surgical technique

The mid-crestal incision extending from the hamular notch to the second molar area is employed to gain access to maxillary tuberosity. Only a little amount of bone (1-3 mL) is removed using a rongeur or piezotome. The latter is again a preferred approach owing to lesser risks.[35]

Care of donor area and graft

For maxillary tuberosity, primary closure can be achieved due to small residual defect. The graft should be harvested keeping a minimum of 2 mm clearance from the maxillary sinus. In case of oroantral communication, the closure can be achieved using either of the buccal sliding flap, buccal fat pad, or palatal finger flap.

Allografts

The grafts are harvested from the same species but from a different donor (genetically heterogeneous).[33] These can be fresh-frozen, freeze-dried bone allografts (FDBAs) or demineralized freeze-dried bone allografts (DFDBAs).[8],[33] FDBA and DFDBA are preferred over fresh-frozen allografts in the wake of their low immunogenicity.[33] Essentially, allografts are osteoconductive with the exception being DFDBA, which may possess some osteoinductive potential. This is possibly because of the exposed organic content (might be growth factors) after demineralization. The mechanism of incorporation of allografts involves creeping substitution similar to autogenous cortical grafts.[33] FDBA undergoes faster replacement and osseointegration compared to DFDBA and thus enables earlier implant placement.[33] Whenever it is osseointegration is desired to be delayed as in cases of poor confines, i.e., sinus augmentation, DFDBA is preferred over FDBA.[33]

Xenografts

These grafts are derived from genetically dissimilar species, i.e., bovine, porcine, equine, and coralline, etc.[8],[9],[33] The bovine grafts are preferred over other sources of xenografts. Mainly, inorganic portion of the bone is used. Commercially, these grafts are available in block or particulate form. Unfortunately, high failure rates (higher rates of connective tissue ingrowth, poor vascularization, delayed osseointegration) are associated with these grafts.[33]

Alloplastic grafts

These are synthetic grafts of nonbiologic origin available in a range of porosities and densities, i.e., hydroxyapatite, calcium sulfate, tricalcium phosphate, and bioactive glass. For clear reasons, these are osteoconductive. When used alone, these types of materials often yield suboptimal bone turnover and this fact limits their use.[33] However, these can be combined with autogenous grafts in various proportions to yield optimal results.[23]


   Decision Pathway for Ridge Augmentation and Socket Preservation Top


The suitable technique and material for ridge augmentation is dependent on clinical characteristics of the patients, i.e., location and type of defect and the surgeon's own preference. Latter is often affected by surgeon's clinical skill and expertise, and financial aspects but mostly it is dictated by principles laid by evidence. Here, in this section simplified evidence-based decision pathways for the selection of suitable techniques for socket preservation and ridge grafting are presented [Figure 4] and [Figure 5].
Figure 4: flowchart: decision pathway for ridge augmentation; (a) ridge augmentation in the maxilla (b) ridge augmentation in the mandible

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Figure 5: decision pathway for socket preservation

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The foremost step in treatment planning, i.e., selection of the right technique as well biomaterial and timing of augmentation (staged versus simultaneous) is preoperative patient assessment. These preoperative considerations include systemic health status and local factors, i.e., morphology of soft tissues and bone. Although it is advisable to employ cone beam computed tomography to scan the defect in three dimensions, panoramic radiographs in combination with suitable intraoral radiographs may also be used. It is essential to have sufficient soft tissue coverage to ensure primary tension-free closure over the planed area of augmentation. In cases of probable inadequacy of soft tissues, the augmentation of soft tissues must be planned prior to augmenting hard tissues. Assessment of bone morphology at the planned site of implant placement include adequacy of bone volume, ridge contour, and position of marginal bone of neighboring teeth.


   Socket Preservation Top


The alveolar bone uneventfully resorbs after extraction and results in residual ridge morphology with compromised horizontal and vertical bone volume to receive implant and a lingually positioned crest due to greater resorption on the buccal aspect.[5],[6],[7] Socket grafting at the time of extraction is a preventive procedure, which does not inhibit the resorption but limits it.[17] Moreover, the minimal amount of resorption after socket grafting happens in a predictable fashion. Also, the magnitude of volume loss is less in the grafted socket versus the naive socket. This has been substantiated by a recent meta-analysis where ≈1.4 mm lesser horizontal bone loss and ≈1.8 mm lesser vertical bone loss were reported in grafted sites compared to nongrafted sites.[21] However, it is interesting to note that similar mean implant survival rates has been reported for implants placed in preserved sites versus naive sites. Additionally, the bone grafting may still be needed at the time of implant placement as it is only possible to limit the alveolar bone resorption and yet not possible to completely eliminate it.[17] These facts question the rationale of socket preservation. In the light of these facts, it is recommended that it should be performed in aesthetic areas in case of buccal bone thickness≤2 mm or when there is a proximity to anatomic structures, i.e., maxillary sinus or mandibular canal. Also, overaugmentation may help, especially in aesthetically sensitive areas where the buccal bone contour is critical.[7]

There is a lack of evidence regarding the choice of techniques and biomaterials for socket preservation. Benic and Hämmerle (2014)[36] beautifully described the grafting protocol on the basis of class defect. The authors described six phenotypes on the basis of morphology of defects [Table 4] and [Figure 6] and they also provided guidance on choice of biomaterial and technique for socket preservation [Figure 6].
Table 4: Classification of bone defects[36]

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Figure 6: classification of bone defects.[36]

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   Techniques of Ridge Augmentation Top


The various techniques of ridge augmentation can be differentiated either on the basis of the form of graft, i.e., block or particulate, guidance or use of membrane, i.e., GBR, transportation of vital structures, i.e., maxillary sinus lift and inferior alveolar nerve transportation.[8],[9],[36] None of these techniques are free from complications and all possess their unique advantages. A few of the technical considerations need to be borne in mind ubiquitously for all grafting procedures [Box 1].{Inline 1}

Onlay grafting

Onlay grafting can either be block onlay grafting or particulate onlay grafting. The latter can further be categorized as subperiosteal tunnel grafting or direct particulate onlay grafting.

Particulate onlay grafting

Direct particulate onlay grafting

Indications: The direct particulate onlay grafting [Figure 7] is employed for correcting horizontal deficiencies in the anterior maxilla and for saddle depressions, i.e., vertical deficiency. The recipient sites with three-walled and four-walled defect morphology with an apical stop are considered to be best amenable to direct particulate onlay grafting.
Figure 7: particulate graft

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Technique: The direct particulate onlay grafting can be performed as a staged or simultaneous procedure. The planned recipient area is exposed by raising a mucoperiosteal flap to visualize the defect. It is important to place releasing incisions to ensure direct visualization of the defect and tension-free closure. After drilling holes in the recipient bed to ensure osseointegration, the particulate graft is condensed over the defect. For defects with poorly contained boundaries, (i.e., maxillary sinus) demineralized grafts are preferred over mineralized grafts due to their slower resorption.[33] The coverage with membranes is often recommended but can be omitted for small defects with sufficient neighboring walls to provide volume stability.[36],[44] The malleability and workability of particulate graft can be enhanced with tissue adhesives, i.e., fibrin sealants or protein-based regenerative gels (Emdogain; Straumann, Andover, MA, USA).

Subperiosteal tunnel grafting

Indications

Small to moderate buccal plate defects are best open to subperiosteal tunnel grafting. The morphology of such defects is characterized by wider buccal base with narrow crestal width (≤4 mm) and intact lingual wall with optimum vertical dimensions.[8]

Technique

After administration of local anesthesia, access incision is placed distant (often mesially) from the recipient site. Subperiosteal tunneling from the incision to graft site is performed with the help of a periosteal elevator. The demineralized particulate bone graft is placed in this subperiosteal tunnel with the help of modified 1 mL carrier syringe. The graft may need digital manipulation to conform to the recipient bed in the desired form. The mesial incision is closed in a tension-free manner to ensure uneventful healing with minimal risks of dehiscence and graft exposure.

Block onlay grafting

Indications

Horizontal or vertical deficiency or combined horizontal and vertical deficiency.

Technique

This is one of the most commonly employed techniques for horizontal as well as vertical ridge augmentation. The block graft can be autogenous graft harvested from neighboring intraoral donor sites, distant extraoral donor sites, or commercially available xenografts or alloplastic grafts.[33] After raising the mucoperiosteal flap, the recipient bed is prepared by drilling multiple holes till the underlying spongiosa is reached. Depending on the type of defect, the graft is contoured to adapt in proximity to the recipient site as veneer [Figure 8] and [Figure 10], block [Figure 9] and [Figure 10], or inverted J Block graft is employed for the vertical defects while veneer graft is used in the case of horizontal defects. For combined defects, the graft is modified to the shape of the inverted letter J. Another modification is lamellar technique where only the cortical part of the graft is used as veneer, whereas the underlying defect is filled with particulate graft. After ensuring proper adaptation of the graft to the recipient bed, the voids can be filled with particulate bone graft material. It is imperative to stabilize the graft with two screw fixations to allow unimpeded integration while avoiding shearing of microvasculature and tender connective tissues.[37],[38] Due care should be taken to fix the screws passively as lateral pressure from screws may either fracture the block graft or result in undue resorption and graft failure. In case of insufficient soft tissue coverage, a membrane may be used for barricading from unwanted connective tissue and epithelial ingrowth. However, often the block grafts do not require the use of barrier membrane as the cortical part of the graft prevents the soft tissue from creeping into the grafted area.[44],[45]
Figure 8: veneer graft

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Figure 9: block onlay graft

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Figure 10: block and veneer graft; (a) shaping of harvested graft (b) shaped graft (c) fixation of graft as block and veneer for combined horizontal and vertical augmentation

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These grafts require a little longer time to integrate with the recipient bone and thus, it is recommended that the staged approach of implant placement be preferred. It is preferable to allow healing 4-6 months prior to functional loading. However, if the basal bone is sufficient and the implant stability is not to be relied on the graft bone immediate placement of the implant can be performed.[43],[45],[46]

Interpositional bone graft (Sandwich grafting)

Indications

Vertical deficiency with preexisting minimal vertical alveolar dimensions of 4-5 mm and without any soft tissue deficit.[8]

Technique

A vestibular incision is placed in nonkeratinized mucosa to expose the facial aspect of the planned area of augmentation. First, vertical corticotomies and osteotomies are performed using micro reciprocating and sees to the preservation of ≈2 mm of bone around the roots of neighboring teeth. This is followed by horizontal corticotomy and osteotomy to mobilize the segment. A minimum clearance of ≈3-5 mm from vital structures such as the maxillary sinus or mandibular canal is essential. It is crucial to perform only as much advancement as permitted by the soft tissue envelope to achieve tension-free closure. The free segment can also be advanced buccally or lingually to achieve the desired prosthodontic position. After careful transportation preserving soft tissue attachments, the bone graft block (usually corticocancellous autogenous graft) is sandwiched between the transported segment and basal bone [Figure 11] and [Figure 12]. The graft fixation is achieved with miniplates. Periosteal releasing incisions may be placed to aid tension free closure.
Figure 11: interpositional bone graft

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Figure 12: case presentation: interpositional ridge graft; (a) recipient site (b) incision placed (c) flap raised (d) osteotomy and splitting (e) interpositioning of bone graft (f) closure

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Ridge split technique (book bone flap)

Indications

Horizontal deficiency requiring 2-5 mm of augmentation.[8],[45]

Technique

This technique can be utilized in case of alveolar width ≥4 mm so that a minimum of 2 mm thickness of outfractured buccal and lingual walls can be achieved.[8],[45] This is essential for maintaining the vascularity of the outfractured segments. The mucoperiosteal flap to expose the donor area is raised by a crestal incision. A vertical osteotomy ≈10-12 mm in length is performed on the recipient alveolar crest with a clearance of 2 mm from the roots of adjacent teeth. After osteotomy is complete, the facial and lingual walls are spread apart by using osteotomes to make space for placement of the implant [Figure 13]. Residual voids are filled with particulate graft and the implant is submerged at least 1 mm apical to the alveolar ridge crest [Figure 14]. The closure must be tension-free and in case of soft tissue deficit, collagen membrane with soft tissue graft can be used to close the defect.
Figure 13: ridge split technique

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Figure 14: ridge split; (a) thin alveolar ridge (b) ridge split using MCT disk (3-mm radius) (c) expansion using rigid osteotome (d) flexible chillet (e) MCT ridge splitter (gentle separation) (f) bone expanders (g) implant placement (h) closure

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The technique described above is conventional ridge split technique where immediate implant placement is performed. It can be performed when horizontal deficiency exists at the crestal part and the ridge widens apically. However, it is not uncommon to encounter challenging ridge morphology, i.e., deficient ridge crest combined with severe facial concavity.[45] This may exist in case of chronic periapical infection where longstanding inflammation caused resorption of the labial cortical plate in the apical region. In such a condition, ridge-splitting may lead to sudden fracture of the cortical plate at the apical region. Fortunately, with a little modification, the ridge split technique is still feasible. The flap is raised only in the crestal part to be expanded and the dehiscence in the apical area is left undisturbed. The crestal part is expanded and particulate graft is packed over facial dehiscence by the subperiosteal tunnel technique. The advantages of this technique include being less invasive and abolishing the need for placement of the barrier membrane.

The best suited histological bone type amenable to ridge-splitting and expansion is bone with medium density (maxillary bone), i.e., porous cortical bone with coarse/fine trabecular bone (D3/D4 bone).[45] It is tricky to perform ridge-splitting in case of dense cortical bone, i.e., the mandible where sudden fracture of cortical plates may happen during expansion. In mandibular ridge with dense cortical plates, ridge-splitting can be performed using either two-stage or one-stage approach.[45] The choice between the two depends on the availability of armamentarium and surgeons' skill. The one-stage conventional approach is preferred only when the surgeon has adequate experience supported with suitable armamentarium, e.g., piezosurgery. Only modification here in one stage ridge-splitting for mandibular ridge compared to conventional ridge split is raising flap from either buccal or facial side compared to both sides in conventional technique. Here, the intact mucoperiosteal flap protects in case of sudden fracture of the cortical plate. In two-stage approach of ridge-splitting, an osteotomy is performed similar to the conventional ridge split procedure. But expansion is not performed at this stage; rather the flap is sutured back. After a healing period of 3-4 weeks, the osteotomy area is accessed again. The new bone formed at the osteotomy site during this healing period is soft and expandable. Thus, ridge-splitting and implant placement at reentry after 3-4 weeks becomes easier. Due care is taken to raise the flaps only minimally. The periimplant spaces are filled with particulate graft and the lingual flap is coronally advanced and sutured back. Uncovering of implants and functional loading is done after 4-6 months.

Ridge expansion

Indications

≤6 mm width of the alveolar ridge crest.[47]

Technique [Figure 15] and [Figure 16]

The alveolar ridge crest is exposed by raising a mucoperiosteal flap. Horizontal osteotomy is performed extending from 1 mm distance from neighboring tooth to 8-10 mm distal to the axis of the last implant.[47] The horizontal osteotomy is extended as deep as the length of the implants to be placed. Following this releasing, vertical osteotomy is performed. This is essential in case of dense cortical bone. The vertical osteotomy cuts are placed at the mesial and distal ends of the horizontal osteotomy cut. With a pilot drill, osteotomy holes (1.2-2 mm) corresponding to each implant site are placed. Then immediately expansion screws are placed. The maximum diameter of these screws is 2.5 mm and ≈1 mm expansion of the buccal cortical plate is achieved. Next, differential preparation of the implant site is done by reducing the width of the lingual and sometimes buccal cortical plate to reduce the need of expansion. This is possible if width of the alveolar crest is ≈4-5 mm. Second, expansion screws of 3.5 mm diameter are inserted in differentially prepared pilot osteotomy sites to enable additional expansion by 0.5 mm. Lastly, implants corresponding to 4 mm diameter are placed. This results in an additional expansion of 0.5 mm and a net total expansion of 2 mm. The final outcome is net total alveolar crest width of 6 mm with 1 mm thickness of the buccal as well as lingual cortical plate.
Figure 15: ridge expansion; (a) measuring the thickness of the alveolar crest using periodontal probe (b) horizontal osteotomy (c) drilling first holes every 7.5 Mm (d) first 1 mm of expansion (e) differential preparation (f) placement of implants (at this stage 2 mm of expansion is observed)[47]

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Figure 16: ridge split and expansion; (a) atrophic ridge (b) mucoperiosteal flap raised and osteotomy performed (c) gradual staged expansion (d) implants in position (e) healing abutments placed

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Distraction osteogenesis

Indications

Significant vertical deficiency.

Technique

This technique allows significant augmentation of both hard and soft tissues in areas with extensive tissue loss in a staged manner.[47],[48],[49],[50] A transport segment is mobilized in a similar manner as for interpositional bone grafting, preserving attachment to the crestal and lingual tissues [Figure 17].[49] The transport segment can be mobilized in multiple planes to allow simultaneous correction of buccolingual postions as well. The distractor is fixed to transported and basal bone segments with approximately 1-2 mm gap between the two segments. This is left in situ for a latency period of 5-7 days to allow the formation of soft tissue callus between the two segments and then activation is started at the rate of 0.5-2 mm/day for periodic distraction. After completion of the desired amount of distraction, the distraction device is removed and quality of the bone is explored. The newly formed bone is hourglass shaped and placement of additional grafts may be required for proper implant placement at this time. The implant placement is performed after a period of 4-6 months.
Figure 17: distraction osteogenesis

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Inferior alveolar nerve transportation

Indications

To allow placement of dental implants in atrophic mandible with deficient vertical height as a substitute for grafting [51],[52],[53]

Technique

This method involves lateral translocation of the contents of the mandibular canal to soft tissues of the mandibular vestibule. The implants can then be placed traversing the empty mandibular canal. This technique allows placement of 8-12 mm long implants without any grafting.[51],[52]

Maxillary sinus lift with and without bone graft

Indications

≤10 mm of bone height in the posterior maxilla [54],[55]

Technique

Lateral wall of the maxillary sinus is exposed by raising a trapezoidal flap with anterior releasing incision adjacent to the last tooth and posterior releasing incision in the posterior part of the infrazygomatic crest. A midcrestal incision is placed and mucoperiosteal flap is reflected. A bone window approximately 15 mm × 10 mm in size is created at least 5 mm superior to the sinus floor. A small round bur is used to outline the margins of the window by placing holes in the bone with due care to leave the underlying membrane intact. The holes are connected and the window is created by infracture of the outlined bone. The membrane is dissected free from the bone, i.e., anterior wall and floor of the sinus. After dissection and ensuring intactness of the mucosa, it is lifted and bone graft in particulate form is condensed to fill the created cavity, which is then closed by replacing the oral mucosa [Figure 18]. Postoperative care includes refraining from sneezing and blowing of the nose and decongestants and antibiotic coverage. A modification of this technique involves filling the cavity with blood instead of graft material. The implant is placed traversing through the created cavity with the membrane resting on its top. A consolidation period of 3-4 months is recommended.
Figure 18: local sinus lift with bone graft

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Guided bone regeneration

This technique is based on the principle of creating a barrier to the ingrowth of connective tissue and epithelial cells and space maintenance for osteogenesis. GBR, also known as guided tissue regeneration, is an evidence-based predictable approach for separating the bone graft material (usually particulate) from neighboring soft tissues to allow unimpeded bone formation.[36] In this technique, a membrane is secured covering the graft material to stabilize the material, parting it from adjacent connective tissues, and limiting resorption [Figure 19] and [Figure 20]. A plethora of membranes, resorbable/nonresorbable and moldable or stiff are available [Figure 21].[36]
Figure 19: guided bone regeneration; (a) recipient site, (b) raising mucoperiosteal flap, (c) osteotomy for implant placement, (d) implant placed with particulate graft, (e) barrier membrane placed and stabilized, (f) healed site, (g) healing abutment, (h) final prosthesis

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Figure 20: guided bone regeneration, (a) pre-operative clinical view, (b) pre-operative ct showing extensive bone loss, (c) reflecting mucoperiosteal flap, (d) implant placement, (e) particulate bone graft, (f) membrane placement, (g) closure, (h) implant, (i) immediate post-operative view

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Figure 21: types of membranes

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The choice of membrane mainly depends on volume stability of the graft in defect. Stiff membranes such as titanium mesh or metal supported expanded polytetrafluoroethylene (e-PTFE) are suitable for complex defects, i.e., vertical defects. For small to moderate defects, resorbable collagen membrane or platelet-rich fibrin (PRF) membranes [Figure 22] are preferred. Nonresorbable membranes such as Ti-mesh and e-PTFE have an inherent problem of requiring second surgery to remove them. Further, with Ti-mesh there is a risk of fibrous ingrowth and exposure of membrane through the gingiva. To limit this unwanted outcome, use of collagen membrane to cover Ti-mesh as an adjuvant barrier is recommended. Another problem associated with membranes is premature exposure of membrane resulting in infection and exposure of graft. This is observed more commonly with alloplastic membranes, which are occlusive and may interfere with blood supply. Although mainly used in conjunction with particulate graft, the barrier technique may also be used for block graft.
Figure 22: (a) PRF membranes (b) membrane over particulate graft

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   Conclusion Top


In this paper, a simplified algorithm has been presented to serve as a clinical guide for decision-making in ridge augmentation as well as socket preservation. As the evidence suggests, GBR is the most predictable technique. The continued thrust of active research in this area may result in development of more simplified and promiscuous methods of regeneration.

Acknowledgement

The authors are thankful to Dr. Anuj Aggarwal (former postgraduate student, Department of Oral and Maxillofacial Surgery, Santosh Dental College and Hospital, Ghaziabad, Uttar Pradesh, India) for contributing a few of the clinical photographs.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14], [Figure 15], [Figure 16], [Figure 17], [Figure 18], [Figure 19], [Figure 20], [Figure 21], [Figure 22]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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    Evidence on Ridg...
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