classification of alveolar bone width

Classification of the Alveolar Ridge Width: Implant-DrivenTreatment Considerations for the Horizontally DeficientAlveolar RidgesLen Tolstunov, DDS, DMD1

Among many techniques advocated for the horizontally deficient alveolar ridges, ridge-split has many

advantages. Here, treatment management strategies of the horizontally collapsed ridges, especially the ridge-

split approach, are discussed and a clinically relevant implant-driven classification of the alveolar ridge width is

proposed, with the goal to assist an operator in choosing the proper bone augmentation technique.

Comparison and advantages of two commonly used techniques, ridge-split and block bone graft, are presented.

Key Words: ridge-split, block bone graft, alveolar ridge

INTRODUCTION

It has been shown that although bone collapseafter tooth loss is usually three dimensional(3D), the horizontal deficiency or width lossdevelops to a larger extent.1,2 Alveolar widthdeficiency can represent loss of buccal (labial)

cortical or medullary bone, or both. Deficiency ofthe buccal cortex (cortical plate) after toothextraction can present significant difficulty inimplant reconstruction.3,4 The buccal cortical platewith a thickness ,2 mm next to an implant appearsto have a higher risk of subsequent resorption.5

A variety of implant-driven bone augmentationtechniques for the deficient alveolar bone havebeen proposed.6–8 Four of these techniques arefrequently performed: (1) guided bone regeneration(GBR)/particulate bone grafting;9,10 (2) onlay (ve-neer) block bone grafting with intraoral sources,such as chin, ramus, posterior mandible, zygomaticbuttress, and maxillary tuberosity;11–13 (3) ridge-split/bone graft procedure;14–16 and (4) alveolardistraction osteogenesis.17–19 Most of these tech-

niques are designed to improve horizontal bone

loss before or simultaneously with dental implant

placement.

DIAGNOSIS AND TREATMENT PLANNING

It is important to establish a proper diagnosis based

on the alveolar ridge assessment before initiation of

the treatment plan. Initial clinical evaluation sup-

plemented by radiographic images helps in most

cases to distinguish two-dimensional (2D) versus 3D

alveolar bone deficiency. Although minimal bone

loss and patient’s lack of desire to go through

grafting surgical procedure(s) can be circumvented

with restorative means, extensive bone atrophy

usually requires surgical correction for a proper

implant placement.

Alveolar bone should be initially assessed

clinically (visually) for a rough width and height

analysis and interarch-occlusal relationships. In

some cases, although 7–8 mm of bone width is

present, it could be lingually (palatally) positioned

and therefore might require an additional buccal

bone grafting for a proper restoratively driven

implant insertion.

Alveolar width can be measured with different

calipers on top of the thin mucosa or by ridge

1 Private practice, Oral and Maxillofacial Surgery, San Francisco,Calif, and Departments of Oral and Maxillofacial Surgery,University of the Pacific, Arthur A. Dugoni School of Dentistryand University of California San Francisco, San Francisco, Calif.Corresponding author, e-mail: [email protected]: 10.1563/AAID-JOI-D-14-00023

Journal of Oral Implantology 365

CLINICAL

FIGURES 1 AND 2. FIGURE 1. Cone beam computerized tomography scan of the horizontally deficient edentulous maxillaryalveolar ridge. Alveolar bone width and height, as well as thickness of the buccal and palatal cortical and medullary boneare demonstrated. This alveolar ridge is a class III ridge according to the classification presented in the article. FIGURE 2. Axialcone beam computerized tomography scan of the horizontally collapsed edentulous right maxillary alveolar ridge showingvaried thickness of the alveolar ridge.

TABLE 1

Classification of alveolar ridge width

Alveolar ridge width (mm),

based on CBCT* scan

.10 8–10 6–8 4–6

Alveolar ridge deficiency No deficiency Minimal Mild Moderate

Class 0 I II III

Schematic diagram

Comments

Indications for surgery Hard tissue surgery is

not indicated.Occasionally,

alveolar width(buccal convexity)

can be improved foresthetic reasons

with a soft tissuegraft.

Hard tissue surgery is

rarely indicated.Occasionally,

alveolar width canbe improved by

particulate bonegraft or palatal soft

tissue graft foresthetic and

prosthetic reasons.

Particulate (GBR)

grafting or ridge-split is often needed

to improve labialbone projection and

proper occlusalimplant position.

An ideal width for the

ridge-splitprocedure that can

be done in a single-or two-stage

approach (seeFigure 3). Block

graft or GBR canalso be done.

Immediate insertion Yes Yes Yes/no, depends on

presence of apicalbone for primary

implant stability

Yes/no, depends on

presence of apicalbone for primary

implant stability (seeFigure 4)

Operator experience Basic Basic Basic Basic to advanced

*CBCT, cone beam computerized tomography.�GBR, guided bone regeneration.

366 Vol. XL / Special Issue / 2014

Classification of the Alveolar Ridge Width

mapping (with local anesthesia) through it. Pano-

ramic and other 2D radiographic images are often

sufficient in some implant cases, although an

implant-driven bone analysis often implies need

for a 3D or volumetric bone evaluation with cone

beam computerized tomography (CBCT) scans.

CBCT improves the ability for precise measurement

of the ridge on all levels as well as evaluation of

both cortical and medullary portion of the bone for

primary implant stability (Figures 1 and 2).

TABLE 1

Extended

2–4 ,2 6–10/2–4 2–4/6–10

Severe Extreme ‘‘Hourglass’’ (undercut)(buccal or lingual)

‘‘Bottleneck’’

IV V VI VII

GBR� at the mid ridge

level can be done

Ridge reshaping or GBR

at the top of the ridgecan be done

Ridge-split or block bonegraft is a graft of

choice (surgeon’sexperience).

Large extraoral block graftis a preferable surgical

choice. Alternative ismultiple and sequential

augmentationprocedures.

Not recommended No Yes/no, depends on theseverity of the undercut

Usually yes, can dependon the morphology of

the top portion of theridge

Advanced Advanced Basic Basic

FIGURES 3 AND 4. FIGURE 3. Intraoperative photograph of the ridge-split procedure demonstrating the mobilization andrepositioning of the buccal muco-osteo-periosteal flap. FIGURE 4. Intraoperative photograph of the ridge-split procedure thatis done simultaneously with the implant insertion.


Tolstunov

CLASSIFICATION OF THE ALVEOLAR RIDGE WIDTH

In 1988, Cawood and Howell20 suggested an

anatomic classification of the edentulous jaws for

the preprosthetic surgery. It proposed six classes

and detailed the changes that the edentulous

alveolar process in anterior and posterior maxilla

and mandible undergo after teeth extraction (the

pattern of resorption). In 1989, Jensen21 proposed

an implant-driven site classification by bone quality

and quantity and proximity to vital structures. In

2002, Wang and Al-Shammari22 described a practi-

cal (therapeutically oriented) classification of alveo-

lar ridge defects, that is, horizontal, vertical, and

combination defects, proposing the edentulous

ridge expansion approach (ridge-split) for the

horizontal and combination defects of the alveolar

ridge.

TABLE 2

Ten-point comparison of ridge-split and monocortical block bone graft techniques

Comparison Monocortical Block Grafting (Intraoral) Ridge-split Procedure

1 Type of grafting Onlay: external, ‘‘cortex to cortex’’;donor cortical graft is added to the

collapsed recipient buccal cortical

bone, resulting in the grafted bonethat has cortical environment on

one side and periosteum on theother side

Inlay: internal (like an ‘‘open book’’);cortical envelope is preserved and

expanded and a particulate grafting

is done ‘‘from within,’’ resulting in abilateral proximity of the grafted

bone to both cortices (similar to a 4-wall defect of extraction socket)

2 Graft resorption Free (devascularized) graft; the graftedbone may contain a substantial

amount of nonvital bone that didnot survive detachment,

devascularization, and transportation;an increased risk of postoperative

graft resorption27; slow andincomplete neovascularization rate28

Vascular bone flap (muco-osteo-periosteal flap) (see Figure 3),

vascularization is preserved at alltimes; ‘‘cancellous bone grafts are

more rapidly and completelyrevascularize than cortical grafts’’29

Decreased risk of postoperative graftresorption16

3 Donor site morbidity Yes: pain, swelling, IAN* injury(posterior mandible, ramus),

‘‘wooden teeth sensation’’ (chin),sinus perforation (zygomatic

buttress), others

No

4 Recipient site morbidity Soft tissue dehiscence and graft

exposure, loose fixation screws andgraft mobility; graft loss

Soft tissue dehiscence and graft

exposure, buccal plate malfracture;inadequate split

5 Wound closure Primary wound closure is mandatory Closure by secondary intention ispreferred

6 Buccal soft tissue flap Buccal flap is lifted and oftenstretched; tension-free primary

closure is important, but can bechallenging

Buccal flap is not compromised; it isnot lifted and left attached to the

buccal periosteum

7 Wound healing By plasmatic imbibition from the host(recipient) tissue

Internal ‘‘coagulum’’ is easily convertedin the woven bone due to

protection and excellentvascularization from both cortices

throughout the whole process8 Immediate implant insertion Traditionally not done Can be done in some cases (see Figure

4)

9 Delayed implant insertion Implants are placed into the corticalbone interface 4 to 6 months later

Implants are placed into the cancellousbone interface 4 to 6 months later

10 Environmental factors andlong-term stability of a

graft

More subject to a postoperative injury(‘‘external’’ grafting); less long-term

stability and more long-termresorption28

Less subject to a postoperative injuryduring mastication; it is more

protected (‘‘internal’’ orinterpositional grafting); less long-

term resorption and more long-termstability30,31

*IAN, inferior alveolar nerve.



Here, a clinically relevant implant-driven classi-

fication of the alveolar ridge width based on

precise measurement of the alveolar width with

computerized tomography/CBCT scans is recom-

mended; it is presented in the Table 1. The

classification attempts to match the specific ridge

(its width and topography) with the appropriate

surgical technique (GBR, ridge-split, or block graft)

that can be used in the particular case of

horizontal bone atrophy. Although each opera-

tor’s experience ultimately determines the chosen

surgical technique, it is important to compare

benefits and drawbacks of different surgical

procedures for certain ridges to improve the

selection process.

COMPARISON OF THE RIDGE-SPLIT AND BLOCK BONE GRAFTING

TECHNIQUES

A literature review showed few similarities and

many differences between autogenous intraoral

monocortical (veneer) block graft and ridge-split/

bone graft techniques. Both procedures require a

skilled surgical practitioner equipped with knowl-

edge of regional anatomy and vascularization and

prepared for risks and complications of the proce-

dure. Both the ridge-split and block grafting

techniques are used mainly for a 2D horizontal

alveolar ridge augmentation (alveolar bone widen-

ing; some height gain can also be achieved with

both techniques).

Autogenous block bone grafting demonstrates

high osteogenic potential and effective in severe

anterior alveolar atrophy in maxilla and mandi-

ble.23–25 Two main disadvantages of monocortical

block grafts are donor site morbidity and late-term

graft resorption.26 The monocortical block bone

resorption has been reported to have up to 5%

early bone loss and up to 40% late bone loss of the

entire graft volume due to remodeling and

inadequate consolidation.27

Table 2 shows differences (10-point comparison)

between the ridge-split procedure and autogenous

intraoral monocortical block bone grafting. Factors

that are presented include donor- and recipient site

morbidity, type of wound closure, buccal flap

integrity and vascularity, specifics of wound healing,

type of bone interface, and possibility of an

immediate implant placement.

CONCLUSION

Knowledge of 3D bone anatomy with CBCT scan

helps to establish a proper ridge diagnosis before

initiation of implant treatment. The recommended

ridge width classification for the horizontally

deficient alveolar ridges is designed to be a clinically

relevant implant-driven anatomic guide for choos-

ing an appropriate surgical modality for the specific

collapsed alveolar ridge. Operator experience and

surgical comfort ultimately determines the choice of

the technique. The ridge-split approach tends to

have many advantages, including lack of donor site

morbidity and a graft stability over time.

ABBREVIATIONS

CBCT: cone beam computerized tomography

GBR: guided bone regeneration

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