The custom alveolar ridge splitting (cars) technique for predictable horizontal ridge augmentation in the atrophic posterior mandible a case report

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397

The Custom Alveolar Ridge-Splitting (CARS)
Technique for Predictable Horizontal Ridge
Augmentation in the Atrophic Anterior Maxilla:
A Retrospective Case Series Study
Stuart J. Froum, DDS1
Raed O. Kadi, BDS2
Buddhapoom Wangsrimongkol, DDS3
Parnward Hengjeerajaras, DDS2/Natacha Reis, DDS2
Paul Yung Cheng Yu, DDS4/Sang-Choon Cho, DDS2

Implant-supported restorations have proven to be a predictable option for
replacing missing teeth. In cases of inadequate bone quantity, the bone volume
can be increased by bone augmentation procedures. Several factors can affect
bone regeneration, including the morphology of the defect at the implant
site. A defect surrounded by bony walls (an intraosseous defect) is known to
yield a highly successful regeneration. The purpose of this retrospective case
series study was to present a new step-by-step surgical procedure known as
the Custom Alveolar Ridge-Splitting (CARS) technique for maxillary anterior
ridge augmentation. This technique creates an intraosseous defect while
splitting and augmenting an atrophic ridge. Sixteen consecutive cases were
treated with the CARS procedure. All implants were restored and followed
for 12 to 24 months after loading, and all cases were effectively treated with
successful implant placement. According to this retrospective study, the CARS
procedure is simple, successful, and predictable and may be used as a surgical

option for horizontal alveolar ridge augmentation in the anterior maxilla. Int
J Periodontics Restorative Dent 2021;41:397–403. doi: 10.11607/prd.5411

Ashman Department of Periodontology and Implant Dentistry, New York University College
of Dentistry, New York, New York, USA; Private Practice, New York, New York, USA.
2Advanced Program for International Dentists in Implant Dentistry, Ashman Department of
Periodontology and Implant Dentistry, New York University College of Dentistry, New York,
New York, USA.
3Advanced Program for International Dentists in Implant Dentistry, Ashman Department of
Periodontology and Implant Dentistry, New York University College of Dentistry; Master of
Science in Oral Biology, New York University College of Dentistry, New York,
New York, USA.
4Ashman Department of Periodontology and Implant Dentistry, New York University College
of Dentistry, New York, New York, USA.
1

Correspondence to: Dr Stuart J. Froum, 17 West 54th Street, Suite 1c/d, New York,
NY 10019, USA. Email: dr.froum@verzion. net
Submitted September 2, 2020; accepted September 13, 2020.
©2021 by Quintessence Publishing Co Inc.

Implant-supported
restorations
have been proven to be a predictable option for replacing missing
teeth.1–3 To obtain successful, longterm outcomes, a sufficient volume
of bone is required with at least
2 mm of bone on the facial and oral
aspects of the implant.4 In the anterior maxilla, the goal of therapy is
to restore esthetics as well as function, which can present a challenge
when the edentulous alveolar ridge

is deficient in quantity and quality of
bone.5 Alveolar bone loss, including contour changes, can occur by
bone resorption and remodeling
after tooth extraction, or it may occur pathologically prior to tooth
extraction because of periodontal disease, periapical pathology,
or trauma to teeth and bones.6 In
cases of inadequate bone quantity,
the bone volume can be increased
by bone augmentation procedures
in conjunction with or followed by
implant placement.7
Ridge-splitting techniques have
been described in one-, two-, and
three-stage approaches.8–10 However, the technique described herein
differs from each of these and is potentially more predictable.
To achieve an esthetic and functionally stable implant-supported
fixed prosthesis, a combination of
soft and hard tissue augmentation
procedures is often necessary.4,11–13
Despite advancements in bone

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398

Fig 1  Initial drilling is performed with the
guide.

regeneration techniques, the outcomes in many cases are not highly
predictable.14 Several factors can affect bone regeneration. One of those
is the morphology of the defect at
the implant site, which has been reported to be a critical factor for the
success of bone augmentation.14 A
defect surrounded by bony walls is
an intraosseous defect, and this type
of defect is known to yield a highly
successful regeneration due to good
blood and osteoblast supply in addition to being well contained.15–17 In
contrast, an extraosseous defect with
fewer bony walls has been shown to
be less predictable for bone augmentation procedures.15–17
The purpose of this retrospective case series study was to present
a new step-by-step surgical procedure known as the Custom Alveolar
Ridge-Splitting (CARS) technique
for maxillary anterior ridge augmentation, document the results in 16
patients, and discuss the advantages and limitations of this technique.

Materials and Methods
Clinical data was obtained from
the Implant Database (ID) at New

Fig 2  The guide cylinder in place.

Fig 3  A trephine bur is used, guided by
the guide cylinder.

York University College of Dentistry

(NYUCD). This data set was extracted as de-identified information from
the routine treatment of patients at
the Ashman Department of Periodontology and Implant Dentistry
at NYUCD. The ID was certified by
the Office of Quality Assurance at
NYUCD. This study is in compliance
with the Health Insurance Portability and Accountability Act requirements.
Sixteen consecutive cases were
selected from patients who desired
dental implants with a fixed prosthesis to replace their missing teeth
in the anterior maxillary arch and
had implants placed with the CARS
procedure. Eleven women and 5
men (age range: 22 to 65 years;
mean age: 45 years) were included.
All 16 cases were effectively treated
with successful implant placement.
Follow-up times were recorded for
each of the implants placed.
The CARS procedure follows
a specific set of steps and can be
modified according to the surgical scenario. Following a CBCT of
the surgical site, the point of entry
of the trephine guide and trephine
are determined on an axial section
of the site. After elevation of a full-

thickness flap, the initial drilling is
made with the help of a guide (Fig
1), and a guide cylinder is placed

into this first osteotomy, which was
prosthetically selected for future
implant placement (Fig 2). A circular vertical cut is then created by
an appropriately sized trephine bur
(with the bur diameter similar to the
diameter of the future implant) and
guided by the guide cylinder (Fig 3).
The guide cylinder is then removed,
and the final cut is made with the
same trephine bur to the planned
length (2 mm more than the future
implant length). During cutting, the
surgeon evaluates the stability of
the split segment. If the segment
is stable, the second stage can be
performed in the same surgery. If it
is not stable, the flap is sutured, and
reentry is performed 3 to 4 weeks
later. At the second stage, a greenstick fracture is created by the same
trephine bur (or a small periosteal
elevator or small bone carrier), and
the segment is moved buccally and
wedged in the surrounding buccal
bone plate. Again, the stability of
the segment is evaluated. If good
stability is achieved, implant placement can then be attempted. Otherwise, bone grafting is performed

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399
to maintain the space, and the flap
is sutured. The patient then returns
3 to 4 weeks later, and the last stage
is performed, including osteotomy
and implant placement. Tapered
implants are the most indicated for
this technique.
In the present study, implants
were loaded 6 to 21 months after
implant placement. In 11 cases, the
CARS procedure was performed 3
to 4 weeks before implant placement. In 3 cases, the CARS procedure was performed simultaneously with implant placement and
guided bone regeneration (GBR).
In 1 case, the CARS procedure
was performed 3 months prior to
implant placement. In 1 case, the
segment was fractured, and successful retreatment was performed
2 months later. The technique for
all cases included in this study was
first performed on a 3D model
of the patient, printed from the
CBCT scan file. Using these models for surgical simulation familiarized the surgeon with the actual
site and procedure that was to be
performed on the patient. It also
allowed the clinicians to experience the risks and helped them
evaluate whether the site was more
amenable to a two- or three-stage

approach and whether the site required augmentation by a GBR
procedure or any other procedure
to manage any associated conditions.
The following two case reports
are examples to illustrate the technique with its various aspects and
procedures.

Case 1

A 22-year-old woman presented to
the Ashman Department of Periodontology and Implant Dentistry at
NYUCD missing her maxillary right
canine. She had a high smile line,18
malocclusion, and parafunctional
habits. The patient was first treated
orthodontically (at the NYUCD’s
Orthodontic Department) to manage the malocclusion and parafunctional habits before she was referred
to restore her missing tooth (Figs
4a and 4b). For this patient, the
CARS technique was performed 4
weeks prior to implant placement.
All procedures were performed under local anesthesia (2% lidocaine,
1:100,000; Henry Schein).
The initial surgery was performed with a crestal incision made
at the edentulous site, extending
from the maxillary right lateral incisor to the maxillary right first premolar, with intrasulcular incisions
around the buccal aspects of the
maxillary right lateral incisor and
right first premolar. This was followed
by two vertical labial releasing incisions at the mesial aspect of the right

lateral incisor and distal aspect of the
right first premolar. A full-thickness
flap was then elevated. Initial drilling
was performed, and a guide cylinder
was placed in the area that had been
prosthetically selected for a future
implant. A circular vertical cut was
created with a 4.3-mm–diameter
trephine bur (Straumann) guided by
the guide cylinder. The guide cylinder was then removed, and the
final cut was made with the same
trephine bur with copious irrigation
to the planned length (Figs 4c and

4d). During the cutting, the stability
of the split segment was evaluated,
and the decision was made to perform the second stage of the CARS
procedure. A greenstick fracture was
created using a small bone carrier,
and the segment was moved buccally and wedged in the surrounding buccal bone plate. The stability
of the segment was then evaluated
and was found to be poor. Therefore,
a bone graft consisting of small particles of cancellous bovine bone (BioOss, Geistlich) was moistened with
normal saline and packed in the newly created intraosseous defect (Fig
4e). The flap was then repositioned
and adapted, and tension-free closure was achieved and stabilized by
simple interrupted resorbable sutures (chromic gut 4/0 suture, Ethicon, Johnson & Johnson).
The patient returned 4 weeks
later for the second surgery, and the
last stage of the CARS procedure

was performed under local anesthesia. A crestal incision was made
at the edentulous site on the maxillary right canine with intrasulcular
incisions around the buccal aspect
of the right lateral incisor and the
right first premolar. A full-thickness
flap was then elevated without any
vertical incisions. An osteotomy
was made, and the implant (4.1 ×
10 mm, BLT SLActive Roxolid, Straumann) was placed following the
specific implant protocol (Fig 5a). A
periapical radiograph was then taken. The flap was then repositioned
and adapted, and tension-free closure was achieved and stabilized by
interrupted resorbable 4/0 chromic
gut sutures. The implant was successfully restored 9 months after

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400

a

b

c
Fig 4  Case 1. (a) Clinical and (b) periapical
radiographic views of the missing maxillary
right canine. (c) The final cut was created

by the same trephine bur as before (Fig 3).
(d) Clinical view after the final trephine cutting and (e) after bone grafting.

d

e

implant placement (Figs 5b and 5c).
The patient returned for follow-up
every 3 months for 15 months (Fig
5d). During this time, 2 years after
implant placement, the implant and
bone levels remained stable, with
excellent function of the restoration
(Figs 5e to 5g).

Case 2

A 29-year-old woman presented to
the Ashman Department of Periodontology and Implant Dentistry
at NYUCD missing a maxillary left
central incisor (Figs 6a and 6b). The
CARS technique was performed 4
weeks prior to implant placement.
All procedures were performed using the same steps and materials
used in Case 1, except the current
patient received GBR simultaneously with implant placement.
The implant (4.1 × 10 mm, BLT
SLActive Roxolid, Straumann) was

placed at the central incisor site, and
a GBR procedure was performed on
the buccal aspect using bone graft
material (Bio-Oss, particle size 1 cc,
Geistlich) and a resorbable membrane (Bio-Gide, Geistlich) with
tacks. Healing was uneventful (Fig
6c). The implant was successfully
restored 12 months after placement
and was followed for an additional
12 months (up to 2 years postplacement), and stable bone and soft tissue levels were seen at 24 months
postplacement (Figs 6d and 6e).

Results
In the 16 cases followed, all implants
were successfully placed and restored (6 to 21 months after implant
placement), and were followed up
for 12 to 24 months after loading.
In 1 case, the segment was fractured, and successful retreatment
was completed 2 months later: The

implant was successfully placed and
restored (6 months after implant
placement), and was followed for an
additional 24 months after loading.
To date, all 22 implants have functioned well with no failures or complications. Appendix Table 1 summarizes the placement, procedure,
time of loading, and follow-up information of all 16 consecutive cases
treated with the CARS technique
(all Appendix Tables can be found
in the online version of this article
available at quintpub.com/journals).

Patients 8 and 1 represent the first
and second case reports, consecutively.

Discussion
The present study introduces a new
technique for horizontal ridge augmentation of atrophic ridges that
can be used for single or two adjacent edentulous sites in the anterior

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401

a

b
c

d

e

f

Fig 5  Case 1. (a) Clinical view of the implant placed 4 weeks after the first surgery.
(b) Occlusal and (c) periapical radiographic views of the final screw-retained crown at 1
month postloading. (d) Occlusal view at 1 year postloading. (e) Occlusal, (f) facial, and
(g) periapical radiographic views at 2 years postloading.

g

a

b

c

d

e

Fig 6  Case 2. (a) Occlusal and (b) frontal
views of the missing maxillary left central
incisor. (c) Occlusal view after the CARS
technique, GBR, and implant placement.
(d) Clinical and (e) periapical radiographic
views of the final screw-retained crown at
24 months postplacement.

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402
maxilla, in cases where the mesiodistal space is narrow for alveolar
ridge-splitting, with a minimum narrow ridge width of 2 mm. It can also
be used in the anterior mandible

with the same minimum bone width.
In 2018, Hu et al published a modification of the alveolar ridge-splitting technique recommending the
three-stage alveolar ridge-splitting
technique.10 The CARS technique
is a modification of the alveolar
ridge-splitting technique. The goal
of the CARS technique is to create an intraosseous bony defect
produced by designed cuts in the
residual alveolar bone, which then
becomes the future implant site after creating a greenstick fracture of
the patient’s native bone based on
those customized cuts. The created
intraosseous bony defect will contain a fresh blood clot rich in cells
that can stimulate the osseous tissues healing and bone formation according to the regional acceleratory
phenomenon and the buccal gap
distance.19–21 The addition of a bone
graft can prevent the collapse of the
created space.22 These advantages
and changes in the technique do not
require the periosteum supply to be
maintained on the transported segment, as recommended in the original ridge-splitting technique.8
The CARS technique can simplify alveolar ridge augmentation
surgical techniques, enhance the
results of GBR, enable a more predictable and prosthetically oriented
implant placement, be less invasive,
and possibly minimize patient morbidity.11 However, it may require two
to three staged procedures (but
when conditions are optimum, the

CARS technique can be done in one

stage). In addition, the trephined
bony segment could fracture, which
occurred in one case in the present
study: The fractured segment was
repositioned and allowed to heal,
and the implant and restoration
were then successfully placed and
continued to function well with 24
months of follow-up.
Currently, a wide range of surgical procedures are available for
ridge augmentation. However, it
is difficult to demonstrate that any
one of these can offer better outcomes than another.23 A comparison
between GBR, block grafts, ridgesplitting, and the CARS techniques is
presented in Appendix Table 2. The
ridge-splitting and the CARS techniques create intraosseous defects
with horizontal and vertical incisions,
respectively. These intraosseous
defects have demonstrated more
predictable outcomes than extraosseous ones.15–17 Moreover, the CARS
technique improves both soft and
hard tissue morphology.12 However,
all techniques are operator-sensitive
and require surgical skill. Training
for the CARS technique presents an
easy learning curve with the use of
3D models, which can be printed
from the patient’s CBCT scan file.
Comparison with other augmentation procedures demonstrates
that the CARS technique requires a

smaller flap size, reducing surgical
time and patient morbidity, thus potentially decreasing patient discomfort.

Conclusions
Within the limitations of this case
series, it can be concluded that the
CARS technique may present another option for horizontal alveolar
ridge augmentation in the anterior
maxilla in cases of atrophic alveolar ridges. Further research with a
greater number of patients and
case-controlled comparison studies
are necessary to determine the success and advantages of the CARS
technique compared to those conventionally used for horizontal ridge
augmentation.

Acknowledgments
An application for patent has been filed to
protect the novel instruments and techniques described in this article. The authors
declare no conflicts of interest.

References
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MA. A retrospective evaluation of endosseous titanium implants in the partially edentulous patient. Int J Oral Maxillofac Implants 1992;7:195–202.
3.
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Brånemark PI, Jemt T. Long-term followup study of osseointegrated implants
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Treatment planning 2000: An esthetically oriented revision of the original implant protocol. J Esthet Dent 1997;9:55–
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technique: Review of the literature

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Three-stage split-crest technique: Case
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Int J Periodontics Restorative Dent
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12.Levine RA, Huynh-Ba G, Cochran DL.
Soft tissue augmentation procedures
for mucogingival defects in esthetic
sites. Int J Oral Maxillofac Implants
2014;29(suppl):s155–s185.
13. Simion M, Baldoni M, Zaffe D. Jawbone
enlargement using immediate implant
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technique and guided tissue regeneration. Int J Periodontics Restorative Dent
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14.Muchhala S, Unozawa M, Wang WCW,
Robins CG. Treatment options for atrophic ridges based on anatomical locations of the missing teeth. J Oral Biol
2018;5:6.
15. Misch C, Misch CE. Bone augmentation
by deficit six and topography: The twoto five-bony wall defects. Dentaltown
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16.Misch CM, Misch CE. The repair of localized severe ridge defects for implant
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17.Cortellini P, Tonetti MS. Clinical concepts for regenerative therapy in intrabony defects. Periodontol 2000
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19.Frost HM. The regional acceleratory
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Bissada NF, Bouquot JE. Accelerated
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403a
Appendices
Appendix Table 1 Case Details of All 16 Patients with Implants Placed Using the CARS Technique
Implant sitea

Age, y

Gender

Additional
procedure

Filling
material

Loading
time, mo

Follow-up
time, mo

1

23

29

F

GBR

Bio-Oss

12

12

2

14

45

M

None

Bio-Oss

15

12

3

12, 22

65

M

None

Bio-Oss

15

12

4

21

22

M

None

Bio-Oss

13

12

5

13

60

M

None

Bio-Oss

12

15

6

11, 21

29

M

GBR

Bio-Oss

9

18

7

12

35

F

None

Bio-Oss

9

18

8

13

22

F

None

Bio-Oss

9

24

9

12

29

F

None

Bio-Oss

9

24

10

11, 21

34

F

None

Bio-Oss

9

18

11

11, 21

62

F

None

Bio-Oss

9

18

12

13

50

F

None

Bio-Oss

9

24

13

11, 21

51

M

GBR

Bio-Oss

6

18

14

24

65

F

Fractured

Bio-Oss

6

24

15

11, 21

50

F

None

None

6

18

16

12

30

F

None

Bio-Oss

6

18

Patient no.

CARS = Customized Alveolar Ridge-Splitting; F = female; GBR = guided bone regeneration; M = male.
All Bio-Oss (Gesitlich) filling material used small particle sizes (1 cc).
a
FDI numbering system.

Appendix Table 2 Comparison Between GBR and Block Grafts, Ridge Splitting, and CARS Techniques
GBR and block graft

Ridge splitting

CARS

Osseous defect

Intra- or extraosseous

Intraosseous

Intraosseous

Cutting direction

Decortication

Horizontal cutting

Vertical cutting

Wound size

Large

Large

Small

Technique

Operator-sensitive

Operator-sensitive

Operator-sensitive (easy
learning curve with 3D
models)

High

High

TBD

Incidence of use

CARS = Customized Alveolar Ridge-Splitting; GBR = guided bone regeneration; TBD = to be determined.

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