The document discusses treatment strategies for horizontally deficient alveolar ridges, focusing on the ridge-split approach and proposing a clinically relevant implant-driven classification system for alveolar ridge width. It compares the advantages of ridge-split and block bone graft techniques for addressing horizontal bone loss before or during dental implant placement. The classification aims to guide practitioners in selecting appropriate surgical methods based on the specific ridge morphology and operator experience.

1. ClassificationoftheAlveolarRidgeWidth:Implant-Driven
Treatment Considerations for the Horizontally Deficient
Alveolar Ridges
Len 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
I
t has been shown that although bone collapse
after tooth loss is usually three dimensional
(3D), the horizontal deficiency or width loss
develops to a larger extent.1,2
Alveolar width
deficiency can represent loss of buccal (labial)
cortical or medullary bone, or both. Deficiency of
the buccal cortex (cortical plate) after tooth
extraction can present significant difficulty in
implant reconstruction.3,4
The buccal cortical plate
with a thickness ,2 mm next to an implant appears
to have a higher risk of subsequent resorption.5
A variety of implant-driven bone augmentation
techniques for the deficient alveolar bone have
been proposed.6–8
Four of these techniques are
frequently 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, zygomatic
buttress, and maxillary tuberosity;11–13
(3) ridge-
split/bone graft procedure;14–16
and (4) alveolar
distraction 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 Dentistry
and University of California San Francisco, San Francisco, Calif.
Corresponding author, e-mail: tolstunov@yahoo.com
DOI: 10.1563/AAID-JOI-D-14-00023
Journal of Oral Implantology 365
CLINICAL

2. FIGURES 1 AND 2. FIGURE 1. Cone beam computerized tomography scan of the horizontally deficient edentulous maxillary
alveolar ridge. Alveolar bone width and height, as well as thickness of the buccal and palatal cortical and medullary bone
are demonstrated. This alveolar ridge is a class III ridge according to the classification presented in the article. FIGURE 2. Axial
cone beam computerized tomography scan of the horizontally collapsed edentulous right maxillary alveolar ridge showing
varied 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 for
esthetic reasons
with a soft tissue
graft.
Hard tissue surgery is
rarely indicated.
Occasionally,
alveolar width can
be improved by
particulate bone
graft or palatal soft
tissue graft for
esthetic and
prosthetic reasons.
Particulate (GBR)
grafting or ridge-
split is often needed
to improve labial
bone projection and
proper occlusal
implant position.
An ideal width for the
ridge-split
procedure that can
be done in a single-
or two-stage
approach (see
Figure 3). Block
graft or GBR can
also be done.
Immediate insertion Yes Yes Yes/no, depends on
presence of apical
bone for primary
implant stability
Yes/no, depends on
presence of apical
bone for primary
implant stability (see
Figure 4)
Operator experience Basic Basic Basic Basic to advanced
*CBCT, cone beam computerized tomography.
ÀGBR, guided bone regeneration.
366 Vol. XL/Special Issue/2014
Classification of the Alveolar Ridge Width

3. 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
GBRÀ at the mid ridge
level can be done
Ridge reshaping or GBR
at the top of the ridge
can be done
Ridge-split or block bone
graft is a graft of
choice (surgeon’s
experience).
Large extraoral block graft
is a preferable surgical
choice. Alternative is
multiple and sequential
augmentation
procedures.
Not recommended No Yes/no, depends on the
severity of the undercut
Usually yes, can depend
on the morphology of
the top portion of the
ridge
Advanced Advanced Basic Basic
FIGURES 3 AND 4. FIGURE 3. Intraoperative photograph of the ridge-split procedure demonstrating the mobilization and
repositioning of the buccal muco-osteo-periosteal flap. FIGURE 4. Intraoperative photograph of the ridge-split procedure that
is done simultaneously with the implant insertion.
Journal of Oral Implantology 367
Tolstunov

4. 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 bone
that has cortical environment on
one side and periosteum on the
other side
Inlay: internal (like an ‘‘open book’’);
cortical envelope is preserved and
expanded and a particulate grafting
is done ‘‘from within,’’ resulting in a
bilateral proximity of the grafted
bone to both cortices (similar to a 4-
wall defect of extraction socket)
2 Graft resorption Free (devascularized) graft; the grafted
bone may contain a substantial
amount of nonvital bone that did
not survive detachment,
devascularization, and transportation;
an increased risk of postoperative
graft resorption27
; slow and
incomplete neovascularization rate28
Vascular bone flap (muco-osteo-
periosteal flap) (see Figure 3),
vascularization is preserved at all
times; ‘‘cancellous bone grafts are
more rapidly and completely
revascularize than cortical grafts’’29
Decreased risk of postoperative graft
resorption16
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 and
graft 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 is
preferred
6 Buccal soft tissue flap Buccal flap is lifted and often
stretched; tension-free primary
closure is important, but can be
challenging
Buccal flap is not compromised; it is
not lifted and left attached to the
buccal periosteum
7 Wound healing By plasmatic imbibition from the host
(recipient) tissue
Internal ‘‘coagulum’’ is easily converted
in the woven bone due to
protection and excellent
vascularization from both cortices
throughout the whole process
8 Immediate implant insertion Traditionally not done Can be done in some cases (see Figure
4)
9 Delayed implant insertion Implants are placed into the cortical
bone interface 4 to 6 months later
Implants are placed into the cancellous
bone interface 4 to 6 months later
10 Environmental factors and
long-term stability of a
graft
More subject to a postoperative injury
(‘‘external’’ grafting); less long-term
stability and more long-term
resorption28
Less subject to a postoperative injury
during mastication; it is more
protected (‘‘internal’’ or
interpositional grafting); less long-
term resorption and more long-term
stability30,31
*IAN, inferior alveolar nerve.
368 Vol. XL/Special Issue/2014
Classification of the Alveolar Ridge Width

5. 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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