Intermittent loading improves resultsin mandibular alveolar distractionosteogenesis

Ugo ConsoloCarlo BertoldiDavide Zaffe

Authors’ affiliations:Ugo Consolo, Carlo Bertoldi, Department ofNeurosciences, Head–Neck, Rehabilitation, Sectionof Dentistry and Maxillofacial Surgery, Universityof Modena and Reggio Emilia, Modena, ItalyDavide Zaffe, Department of Anatomy andHistology, Section of Human Anatomy Universityof Modena and Reggio Emilia, Modena, Italy

Correspondence to:Prof. Davide ZaffeDipartimento di Anatomia e IstologiaSezione di Anatomia Umana NormaleVa Del Pozzo71- 41100 ModenaItalyTel.:þ þ39-0594224800Fax: þ þ 39-0594224861e-mail: zaffe@unimore.it

Key words: alveolar distraction, bone structure, histology, osteogenesis

Abstract

Aim: To evaluate clinical and morphological effects on distractive callus after application of

an original protocol of bone stimulation.

Material and methods: Traditional or mechanically stimulated alveolar-distraction

osteogenesis was studied on 16 highly selected subjects subdivided into two groups.

Clinical, radiological, densitometric and histological (on biopsies) analyses were performed

6, 8 and 12 weeks after distraction was completed.

Results: In subjects undergoing stimulated alveolar-distraction osteogenesis, bone density

was higher and at histology, bone with ordered structure was observed after 6 weeks.

Moreover, bone trabeculae with oriented architecture and greater amounts of lamellar

bone were observed after 8 and 12 weeks in the same subjects.

Discussion and conclusions: In conclusion, although osteogenic processes were similar in

both groups, they were induced earlier and were better structured in subjects undergoing

stimulated alveolar-distraction osteogenesis. These encouraging results can only be

achieved and preserved by strict monitoring of distractive vectors.

Alveolar distraction osteogenesis (ADO) is

a process of new bone formation (Zaffe

et al. 2002) subjected to two fundamen-

tal biological principles (Ilizarov 1989a,

1989b, 1997): (1) tension/stress effects, in

which a force produces stress or strain and

induces growth of soft tissue and bone and

(2) load/morphology effects, in which load-

ing and blood supply influence the shape

and mass of skeletal segments. These prin-

ciples are defined as Ilizarov effects.

Ilizarov’s method has been successfully

applied in the oral and maxillo-facial field.

After initial animal studies (Snyder et al.

1973; Micheli & Miotti 1977), the method

was applied in humans starting in 1992

(McCarthy et al. 1992; Klein & Howaldt

1995; Molina & Monasterio 1995). The

vector in these distractive methods was

applied along the direction of the longitu-

dinal bone axis.

In relation to the longitudinal axis of the

bone, Block et al. (1996) on animals, and

subsequently Chin & Toth (1996) and

Chin (1999a, 1999b, 1999c) in humans,

studied a method of distraction with

transverse vectors. These studies were

fundamental to ADO development and

particularly suitable for corrections of eden-

tulous–alveolar–ridge defects. This pre-

prosthetic surgical method represented an

innovative approach for achieving newly

formed bone build-up in the short term at

a ‘moderate biological and surgical cost.’

The implementation of ADO for correct-

ing alveolar ridge defects is constrained by

general and local conditions. The lack of

these conditions can cause complicationsCopyright r Blackwell Munksgaard 2006

Date:Accepted 13 June 2005

To cite this article:Consolo U, Bertoldi C, Zaffe D. Intermittent loadingimproves results in mandibular alveolar distractionosteogenesis.Clin. Oral Impl. Res. 17, 2006; 179–187doi: 10.1111/j.1600-0501.2005.01213.x

179

such as dehiscence of soft tissues, fracture

and infection of the distracted bony seg-

ment, lesions to vessels or nerves, devia-

tion of the distraction vector, delayed

consolidation, unsatisfactory osteogenesis

and poor final therapeutic outcomes.

ADO is most effective when combined

with implant-based prostheses. This type of

prosthesis helps obviate the resorption of

new bony volumes and ensures a therapeu-

tic continuity by effectively reproducing

the type of loads propagated through teeth

to the surrounding bony tissue. Neverthe-

less, the combination of ADO and implant-

based prosthesis requires that implant alloca-

tion be meticulously planned temporally and

spatially to obtain a correct distribution of

masticatory loads in relation to implants and

through implants to the underlying bone.

At present, additional knowledge is re-

quired to achieve a more rational planning

of rehabilitation. An exhaustive under-

standing of callus stimulation procedures

suitable for achieving adequate bone induc-

tion (qualitatively and quantitatively struc-

tured and correlated to masticatory load)

would pave the road toward improvement.

The purpose of this work is to apply an

original system of bone stimulation to repro-

duce (after prosthetic rehabilitation) loading

of regenerated bony segment and to evaluate

its clinical and morphological effects.

Material and methods

Screening

Patients for the present study were selected

according to inclusion and exclusion cri-

teria, listed below, and typified according

to the classification of Lekholm & Zarb

(1985), supplemented by that of Cawood &

Howell (1988), considering the whole jaw

and intraforamina area, respectively, when

included in the defect.

Patients undergoing ADO accomplished

the following general indications: a medical

history of good health, particularly ruling

out bone disease; no medical history of

systemic therapy, e.g. chemotherapy, ra-

diation therapy, etc.; no respiratory, masti-

catory or swallowing disorders; no tobacco

and/or alcohol abuse; and suitable oral

hygiene and compliance. Oral hygiene

was estimated using the plaque index (PI)

(Silness & Loee 1964) and gingival index

(GI) (Loee & Silness 1963), when possible,

and in any case was considered as the

absence of signs of inflammation signs or

food traces.

Patients also showed the following spe-

cific indications: alveolar vertical atrophy

(greater than 3 mm) with more than 7 mm

of residual bone covering the lower alveolar

nerve; vertical thickness of the distractive

fragment greater than 4 mm; good bone

quality (by densitometry and clinically

confirmed at surgery); and no diseases

affecting the site metabolism; no spatial

obstacle to the use of the distractor. On the

contrary, patients were excluded from the

study if they fulfilled the following general

criteria: systemic conditions not allowing

distractive therapy; neurotic and psychotic

disorders; tetracycline or non-steroidal

anti-inflammatory drugs (NSAID) allergy;

pregnancy or lactation; and underage or

uncooperative. Patients were also excluded

if they fulfilled the following specific

criteria: poor oral hygiene; chronic or

pre-chronic infective diseases; chronic sto-

matitis in the surgical field; cancerous or

pre-cancerous lesions, treated within the

last 5 years; dental treatments unrelated to

the study; and parafunctions.

Sixteen patients matched for gender, age

and type of alveolar ridge defect were se-

lected; all subjects gave their informed

consent to the ADO procedure.

Control group (CG)

Ten patients, five males and five females,

aged 15–71 years (mean� SD¼ 42.8�19.9), were selected. Four (40%) were

completely edentulous and the rest were

partially edentulous. The alveolar bone

defect had a mesiodistal dimension of 27–

60 mm (mean� SD¼ 46.8� 12.2) and a

vertical dimension of 6.6–14 mm (mean

SD¼10.4� 3). According to Lekholm &

Zarb (1985), the degree of the defect was B/

2–3 in five patients and C/2–3 in the

remaining five. Cawood & Howell (1988)

degree 4 defects were present in two

patients and degree 5 in three patients.

According to clinical intraoperative and

densitometric criteria, the bone quality of

the patients was defined as degree 1–2

(Lekholm & Zarb 1985).

Loaded device group (LDG)

This group contained three males and

three females, aged 20–63 years (mean

SD¼38.7� 16.5). Two patients (33%)

were completely edentulous and the rest

were partially edentulous. The alveolar

bone defect had a mesiodistal dimension

of 30–60 mm (mean� SD¼ 49.5� 12.7)

and a vertical dimension of 6.6–14 mm

(mean� SD¼ 10.4� 3.3). According to

Lekholm & Zarb, the degree of the defect

was B/2–3 in three patients and C/2–3 in

the remaining three. Cawood & Howell

degree 4 defects were observed in one

patient and degree 5 in two patients. The

bone quality of the patients was degree 1–2.

Operative protocol

The same team carried out all clinical

evaluations during the pre-distractive, dis-

tractive and post-distractive phases. De-

scriptive criteria were used to classify the

initial appearance of tissue changes during

the ADO procedure and final results, since

indexes or classifications for alveolar dis-

tractive therapy are lacking.

Alveolar sites were examined by conven-

tional radioscopy (orthopantomography,

etc), Computer tomography (CT) with

transverse image digital reconstructions

(maximum slice¼1 mm) and densitome-

try. Densitometric evaluations (Kalander et

al. 1990), carried out by an auto-standar-

dizing apparatus (3-CTcytec, General Elec-

tric Healthcare Technologies, Waukesha,

WI, USA), were computed as Hounsfield

units (HU). A complete radiographic study

was performed before surgical inter-

ventions by the distractive protocol. The

radiologist, permitting reproducible, com-

parable and reliable evaluations, carefully

checked anatomical reference points for

each patient and apparatus collimation on

the basis of previous radiographs.

Pre-surgical phase

Chalk models of the dental arches, stan-

dard radiographies and CT with high-reso-

lution transverse reconstructions were

performed on patients to plan the therapy

of implant-based prosthesis.

Surgical phase

The surgical distraction protocol was per-

formed using the Hidding intra-oral extra-

alveolar distractor (Hidding et al. 1999;

Lazar et al. 1999) TRACK (Tissue Regen-

eration by Alveolar Callus distraction –

Koln) model (Martin, Tuttlingen, Ger-

many) under general anesthesia as pre-

viously described (Hidding et al. 1999;

Lazar et al. 1999; Consolo et al. 2000;

Consolo et al . Loading effect on distracted bone

180 | Clin. Oral Impl. Res. 17, 2006 / 179–187

Raghoebar et al. 2002; Zaffe et al. 2002).

To maintain the distractive vector constant

and to prevent lesions, a suitable TRACK

device was chosen depending on the degree

of correction of alveolar dismorphism. The

same surgical team performed surgery and

device application, according to the tar-

geted prosthetic outcomes.

Post-surgical phase

The protocol (traditional ADO – TADO)

recommended for the TRACK device was

followed for treating the CG (Table 1). A

protocol of stimulated ADO (SADO) de-

rived from our previous studies (Consolo

et al. 2000; Zaffe et al. 2002) was followed

for treating the LDG (Tables 1 and 2).

Moreover, the SADO protocol schedules

early implant insertion at removal of the

distraction device. Callus stimulation was

performed by cyclical distractive activa-

tions and deactivations for 8 weeks after

distraction was completed (Table 2).

In the two groups, clinical evaluations

were also repeated at the same time during

the latency, distractive and post-distractive

periods. An additional complete set of

radiographic examinations was performed

after distractor removal.

The postponed implant insertion of the

CG (TADO) calls for fewer radiographic

examinations. Nevertheless, radiographic

examinations were needed at implant in-

sertion in CG, 4 weeks after the end of

distraction. Simultaneous implant inser-

tion with distractor removal of the LDG

(SADO) required radiographic examina-

tions at 8 weeks but not at 12 weeks after

the end of distraction. Orthopantomogra-

phies and teleradiographies and plain radio-

graphic examinations were also performed

as required.

To mark newly formed bone during the

post-surgical phases, patients were given

tetracycline antibiotic (Bassado (doxycy-

cline) – 100 mg twice a day, for 3 days

starting 5 days prior to biopsy –Pharmacia

Upjhon, Nerviano, Italy).

Morphofunctional analysis of the tissues

was performed on cylindrical biopsies (two

biopsies for each patient) obtained by

means of a hollow mill (2 mm diameter),

operating at 600 rpm. under saline jet, at 8

and 12 weeks after the distraction proce-

dure. Biopsies were taken from the center

of the mesiodistal side of the callus, at a

right angle to the distractive membrane.

Due to causes unrelated to the study, four

patients (two for each group) were also

biopsied at 6 weeks after distraction was

completed. Unscheduled soft tissue surgi-

cal correction in 3 patients of the LDG

allowed an additional biopsy 12 weeks after

the end of distraction.

Statistics

Densitometric data were evaluated (Glantz

2003) with the Wilcoxon (matched pairs)

test, Mann–Whitney test (2 groups) or the

Kruskal–Wallis test (three groups). If P was

equal or inferior to 6% (P�0.06) groups

were considered statistically different and

then analyzed parametrically. Data were

evaluated by the paired Student’s t-test,

unpaired Student’s t-test (2 groups) or AN-

OVA test (three groups), both followed by

the Student–Newman–Keuls test when

the distribution was Gaussian. Groups

were considered statistically different if P

was equal or inferior to 5% (P�0.05).

Histology

Biopsies were fixed in 4% paraformalde-

hyde in 0.1 M phosphate buffer pH 7.2 for

1 h at room temperature and then dehy-

drated and embedded in methyl methacry-

late (PMMA) at 41C, as reported elsewhere

(Zaffe et al. 2002). Longitudinal thin

(5-mm-thick) and thick (200-mm-thick) sec-

tions were obtained from biopsies using an

Autocut 1150 bone microtome (Reichert-

Jung GmbH, Nussloch, Germany) and a

Leica 1600 diamond saw microtome (Leica

Microsystems, Wetzlar, Germany), respec-

tively (Zaffe et al. 2002). Thin sections

were stained with toluidine blue, tri-

chrome Gomori stain, total alkaline phos-

phatase (TAP) and tartrate-resistant acid

phosphatase (TRAP) methods, as reported

elsewhere (Zaffe et al. 2002). Thick sec-

tions were reduced to 100mm and X-ray

microradiographed (Zaffe et al. 2002).

Microradiographs and thin sections were

analyzed and photographed using an Axio-

phot Zeiss microscope (Carl Zeiss AG,

Oberkochen, Germany) under ordinary or

polarized light. New bone formation was

checked in thick sections using the micro-

scope under fluorescent light.

Trabecular bone volume (TBV, index of

bone tissue content – Parfitt et al. 1987)

and bone tissue structure (woven vs. la-

mellar bone) were evaluated by means of

a suitable image analyzer (VIDAS, Carl

Zeiss) on microradiographs and stained

sections, under polarized light, respective-

ly. Data were evaluated (Glantz 2003) with

the Mann–Whitney test (two groups).

Results

Clinical

The distraction procedure was successful

without serious complications in almost all

patients. No infection, dehiscence or neu-

rovascular injuries were observed. A satis-

factory post-surgical course was achieved

in all patients. Due to good vascularization,

soft tissues were trophic after suture

removal.

Pain was only reported in a few patients

of both groups during the activation phase.

The distraction procedure in these patients

Table 1. Distractive protocol

TADO ODP ! 1 week ! DS ! DE ! 8 weeks ! DR ! 4 weeks ! ISADO ODP ! 1 week ! DS ! DE ! 8 weeks ! DRI

TADO, traditional alveolar distraction osteogenesis; SADO, stimulated alveolar distraction osteogenesis; ODP, osteotomy and distractor positioning; DS,

distraction start; DE, distraction end; DR, distractor removal; DRI, distractor removal and implantology; I, implantology.

Table 2. SADO treatment schedule

Week Day

1 2 3 4 5 6 7

1 A D A D2 A D A3 D a d a4 d a d5 a d a d6 a d7 a d8 a d ###

A, 1 turn activation; D, 1 turn deactivation; a,

1/2 turn activation; d, 1/2 turn deactivation;

### , distractor removal and implant inser-

tion.

Consolo et al . Loading effect on distracted bone

181 | Clin. Oral Impl. Res. 17, 2006 / 179–187

was made more bearable by increasing the

frequency (4 daily activations to spread out

distraction) and, if needed, decreasing the

amount of activation (less than 1 mm per

day). Despite reduction of the treatment

scheduled by protocol (Table 2), some pa-

tients in the LDG reported pain during the

final activation–deactivation cycle.

Oral surgery was required 6 weeks after

the end of distraction in three patients (two

CG and one LDG). The latter LDG patient

and six other patients (four CG and two

LDG) underwent soft tissue treatment 12

weeks after the end of distraction to deepen

the oral vestibule and/or obtain keratinized

gingival buildup.

The planned angle of the distraction

vector was changed in four patients (two

CG and two LDG). In three of these pa-

tients (two CG and one LDG), the amount

of deviation was compatible with that

needed in implant-based prosthetic rehabi-

litation.

Unscheduled corrective surgery, required

due to the loss of anchorage of the distrac-

tion device and major deviation, was re-

quired 6 weeks after the end of distraction

in one patient (LDG). This clinical compli-

cation excluded the results obtained 6

weeks after distraction was completed in

this patient.

In all patients, the alveolar ridge was

suitable for the successive pre-prosthetic

surgical procedure at the end of the distrac-

tive protocol.

The distracted fragments ranged between

27 and 60 mm (mean� SD¼ 46.8� 12.2),

and bone buildup (verified at TC) ranged

from 6.6 to 14 mm (mean� SD¼ 10.4

� 3) in CG patients. The distracted frag-

ments (Fig. 1) ranged from 30 to 60 mm

(mean� SD¼ 49.5� 12.7), and the ach-

ieved bone buildup (CT verified) ranged

from 6.6 to 14 mm (mean� SD¼ 10.4

� 3.2) in patients of the LDG.

Due to the roughly triangular section of

the distracted bony segments, the actual

bone thickness could not be reliably and

exactly evaluated in either group; these

measurements were purposely omitted

since they would have produced arbitrary

results and were substantially of little clin-

ical importance. The longitudinal size

(P¼ 0.697) of the defect and consequently

of the distracted bone, and the height

(P¼ 0.956) of the defect and of the corre-

sponding correction were not statistically

different in the CG and LDG (Mann–

Whitney rank-sum test).

Radiograms clearly showed all skeletal

distracted segments and the hard tissue,

which originated from the cut edges. Quite

often radiograms did not show conspicuous

differences when the two groups were

compared at the same observation interval

(Fig. 1).

Densitometry

Bone densitometry (P¼ 0.871) was not

statistical by different at non-parametric

statistical analysis (Mann–Whitney rank-

sum test) between the LDG (n¼6, mean

SD¼792.5� 642.7 HU) and CG (n¼10,

mean� SD¼ 847.9� 527.5 HU) prior to

surgery (Fig. 2).

When the distraction device was re-

moved (8 weeks after distraction was com-

pleted), values in the LDG (mean� SD

¼1210� 547.5 HU) differed significantly

from those in the CG (mean� SD¼670.1

� 424.5 HU) (P¼0.044 – Student’s t-

test). In compensation, densitometric va-

lues (mean� SD¼ 755.1� 357.1 HU) in-

creased in the CG at implant insertion

(12 weeks after distraction was completed).

No statistical differences (P¼ 0.062 –

Student’s t-test) were found when compar-

ing the correspondent densitometric values

of the patients at implant insertion, i.e. the

values obtained 12 weeks after distraction

for CG vs. those obtained 8 weeks after

distraction for LDG.

Longitudinal comparisons (before sur-

gery vs device removal vs implant inser-

tion) of densitometric values of each group

did not reach statistical significance in CG,

at non-parametric statistical analysis

(Kruskal–Wallis test) (P¼ 0.532). On the

contrary, the correspondent values were

statistically significant in LDG, at non-

parametric statistical analysis (Wilcoxon

test) (Po0.032). These values were highly

significant in the LDG, at parametric sta-

tistical analysis (paired Student’s t-test)

(P¼0.001).

Histology

Six weeks after the end of distraction, the

regenerated tissue in subjects undergoing

TADO (CG) was almost exclusively com-

posed of fibrous tissue, in accord with our

previous study (Zaffe et al. 2002). How-

ever, several islands of high angiogenic

activity were found inside the soft callus.

A feeble osteogenetic activity was ob-

served, and a limited number of isolated

and small trabeculae surrounded by vessels

could be seen in the fibrous tissue. Osteo-

blasts were not laid down on the trabeculae

surface, since these small bony formations

were the result of a static osteogenetic

process (Ferretti et al. 2002). The bone

Fig. 1. Computed tomography with transverse im-

age digital reconstructions of subjects undergoing

traditional alveolar distraction osteogenesis (a) and

simulated alveolar distraction osteogenesis (b) at the

distractor removal step. Note the absence of large

radiographic differences between these subjects.

2000

1000

0CG LDG

before8 weeks

12 weeks

HU

Fig. 2. Graph showing the densitometric behavior in

all subjects of the two groups, before surgery, 8 and

12 weeks after the end of distraction. Note that 8

weeks after distraction was completed, values were

higher in loaded device group and lower in control

group than those before surgery.

Consolo et al . Loading effect on distracted bone

182 | Clin. Oral Impl. Res. 17, 2006 / 179–187

had a woven structure, containing charac-

teristic globe-shaped osteocytes.

Six weeks after the end of distraction,

biopsies showed large amounts of bony

tissue (Fig. 3) in subjects undergoing

SADO (LDG). As a result of the dynamic

osteogenesis process (Ferretti et al. 2002),

bony trabeculae mainly had a woven struc-

ture, but also small parts with an ordered

structure (Fig. 3). This parallel-fibered bone

contained the characteristic ellipsoid-shaped

osteocytes, with a cellular density much

lower than woven bone. Fluorescent bone

labeled by tetracycline, i.e. the bone formed

from the fifth to second day before biopsy

(Fig. 3), had a woven or parallel-fibered

structure, although the former prevailed.

The TRAP histochemical reaction high-

lighted active osteoclasts eroding the bony

trabeculae, almost always having a woven

structured tissue due to its abundance.

Eight weeks after the end of distraction,

often about 1/3 of the biopsy core (corre-

sponding to the inner portion of biopsy)

was fibrous and not yet transformed into

bone in subjects undergoing TADO (CG).

Bony trabeculae formed a disordered net-

work of woven structured bone with sev-

eral irregular, globe-shaped osteocytes (Fig.

4a). Ordered bone (OB) and ellipsoid-

shaped osteocytes were scanty. Medullary

cavities expressed an appreciable TAP re-

activity, whereas the biopsy portions not

transformed into calcified tissue (i.e.

formed by only fibrous tissue) expressed

TAP solely in their outer rim, i.e. in tissue

adjacent to bone. TRAP highlighted a lim-

ited number of osteoclasts actively eroding

the previously formed bone. All trabeculae

(Figs 4b and 6) were formed by woven bone

(ordered bone – parallel-fibered or lamellar

– OB%I0).

Eight weeks after the end distraction,

bony trabeculae formed a well-anasto-

mosed, dense network in subjects under-

going SADO (LDG). Some trabeculae

displayed a parallel disposition. The bone

showed portions with a woven structure,

particularly if recently formed, but a cer-

tain amount of ordered tissue was also

apposed to the pre-existing woven bone

(Fig. 4e). Morphometry (Fig. 6) highlighted

that about one-fifth of the whole bone had

a parallel-fibered or lamellar structure. Wo-

ven bone (Fig. 4c) was sometimes found in

the obliterated primitive haversian cavities,

and then in the transformation of trabecu-

lar into compact bone. TAP (Fig. 4d) was

strongly expressed around active osteo-

blasts but also inside the fibrous tissue

surrounding them. Osteoclasts, as identi-

fied by TRAP, were scanty.

A very high statistical difference of the

amount of ordered bone percent (P¼ 0.001)

was found at non-parametric statistical

analysis (Mann–Whitney rank-sum test)

between the LDG (n¼ 6, mean� SD¼20.6� 4.9) and CG (n¼10, mean� SD

¼ 0� 0) 8 weeks after distraction (Fig. 6).

Twelve weeks after the end of dis-

traction, good bone content (mean

TBV¼35.4%) was observed in subjects

undergoing TADO (CG), with an abun-

dance of ordered bone (Fig. 5b). The trabe-

culae displayed a bone core, woven

structure, with many irregularly shaped

osteocytes, wrapped by a sheath of more

ordered bone, sometimes lamellar, with

fewer ellipsoid-shaped osteocytes (Fig. 5a).

The amount of ordered bone reached a

mean value of about 30% in the CG (Fig.

6). TAP expression was greater than in

8-week-old biopsies. Resorption activity

by a high number of TRAP-positive osteo-

clasts was good (Fig. 5a). Even if the

ordered bone might appear resorbed, the

osteoclast action was mainly addressed to

woven bone (Fig. 5a and b).

Twelve weeks after the end of distrac-

tion, the biopsied bone was more abundant

(mean TBV¼ 44.2%) than in TADO in

subjects undergoing SADO (LDG). Tra-

beculae were longer and wider than those

at 8 weeks (Fig. 5c). Trabeculae were

preferentially ordered in a stretched out

orientation, and had a low-density cel-

lular bone with a mainly lamellar stru-

cture (Fig. 5e and f). Even though some

trabeculae of newly formed bone had

Fig. 3. Microradiographs (a, b, d) and fluorescences (c, e) of a loaded device group biopsy, 6 weeks after the end

of distraction. Note the great amount of newly formed bone of the biopsy. Note also the new (fluorescent) bone

recently formed in apposition to woven (green arrows – with many irregular-shaped osteocytes) or parallel-

fibered (blue arrows–with ellipsoid-shaped osteocytes) previously formed bone. Field width a¼ 3600 mm;

b¼c¼960 mm; d¼e¼ 850 mm.

Consolo et al . Loading effect on distracted bone

183 | Clin. Oral Impl. Res. 17, 2006 / 179–187

a woven structure, woven bone gen-

erally formed the core of trabeculae

enwrapped in lamellar bone (Fig. 5F).

The amount of ordered bone was very

high in this group, reaching a mean value

of 51% (Fig. 6). TAP expression, i.e. os-

teogenesis marker, was reduced, although

consistently found around the few flat-

tened osteoblasts (Fig. 5d). On the con-

trary, TRAP-positive osteoclasts were

sometimes found to remove bone, gener-

ally woven structured.

On performing a non-parametric statis-

tical analysis (Mann–Whitney rank-sum

test), a statistical difference was found

in the percent amount of ordered bone

(P¼ 0.014) between the LDG (n¼ 3, mean

SD¼51.0� 10.5) and CG (n¼10, mean

SD¼28.9� 6.3) 12 weeks after dis-

traction (Fig. 6).

Discussion

Several authors (Widmark et al. 1998,

2001; Bahat & Fontanessi 2001) consider

regenerated bone as unreliable and ill-

suited, as compared with native bone, for

maintaining long-term stability for im-

plant-supported prosthetic rehabilitation.

Masticatory forces greatly affect native

oral bone during its formation. On the

contrary, regenerated alveolar bone is

formed without any mechanical load on

the distracted segment. The availability of

methods able to influence bone formation

positively might help transform the fea-

tures of regenerated bone into those of the

native ones.

Technical problems, arising when con-

siderable bony buildup is achieved by

distraction of segments, may underlie the

dearth of studies in this field. Several

variables affect the outcome of alveolar

distraction. We selected patients according

to strict criteria using few and well-defined

parameters that were amenable to statistic

evaluation in order to limit the number of

variables. Patients were split into groups,

matched for gender, age and type of

ridge defect to be corrected. However, the

small sample size forced us to apply non-

parametric methods. This analysis revealed

the absence of statistical significance

in the size of bony defects of the two

groups. Moreover, the clinical classifica-

tions of Lekholm & Zarb (1985) and

Cawood & Howell (1988), which are

still largely correlated to techniques for

correcting ridge deformities irrelevant to

our study, were not used to define clinical

outcome. These two classifications are

reliably inherent to a less narrow grate of

resolvable bony defects.

Clinical, radiological and cast pre-surgi-

cal evaluations were performed in order to

calculate the distractive vector suitable

for prosthetic needs. The bony defect

was vertically solved in all the patients.

On the contrary, four (sagittal and

horizontal) vectorial deviations in were

achieved. The recorded vectorial deviations

seem to be attributable to the two

respective sample sizes rather than the

different protocols applied in the two

groups.

Contrary to TADO, in SADO, activa-

tion (one turn) followed by deactivation

(one turn) were performed every 2 days

Fig. 4. Morphology (a, c, toluidine blue stain; b, e, under polarized light, trypan blue stain) and histochemistry

(d, total alkaline phosphatase) of the bone in control group (a, b) and loaded device group (c, d, e), 8 weeks after

distraction was completed. Note in b the woven structure of the trabeculae. The ordered bone (lamellar or

parallel fibered), in apposition to the previously formed woven bone, has been outlined by a light-blue broken

line in e, to point out the method used for bone morphometry. Field width a¼b¼c¼d¼ 306mm; e¼ 408 mm.

Consolo et al . Loading effect on distracted bone

184 | Clin. Oral Impl. Res. 17, 2006 / 179–187

for the first 2 weeks after distraction was

completed. The callus was adequately soft

to undergo these loading cycles without

stress reactions in the tissues, in particular,

bony tissue, surrounding the device fixing

screws. Activation and deactivation were

then reduced both in amplitude and fre-

quency over the following 6 weeks to avoid

stress reactions.

Clinical requirements leading to un-

scheduled surgical corrections over the

treatment period underscore the need to

harmonize the protocol for prosthetic reha-

bilitation. Obliteration of the oral vestibule

(displayed in four CG and three LDG

patients), and the consequent need for

surgical deepening, may be attributed to

the TRACK device used rather than to

reduced oral vestibule depth or to the

different (stimulation) protocol. These

‘first-generation’ devices have two metallic

guides that parallel the distractive screw,

and the guides may produce soft tissue

drag. This side effect along with a shallow

vestibule was common in patients who

required surgical deepening.

Algesthesia reported by some patients in

the final stages of stimulation was never so

intense as to require suspending the stimu-

lation or distractive procedure. Pain in the

LDG patient who dropped out of the study

due to high distractive vector deviation was

caused by buccal orthodontic traction dur-

ing vector correction. This finding and the

well-known problems related to internal

rigid fixation and soft tissue expansion

lead us to believe that ADO algesthesia is

probably related to an inappropriate effect

on the newly formed bony callus. The good

clinical results achieved must in part be

attributed to the psychological motivation

of the patients included in this study and to

the low rate of individual side effects,

despite the complex activities that the

patients were forced to perform.

The matched densitometric values

across the LDG and CG were a categorical

pre-operative condition for this study. A

decreasing densitometric trend was ob-

served in the CG (TADO). The small

number of patients in this group does not

allow a statistical significance to emerge

between protocol steps. On the contrary,

the lower variability of densitometric va-

lues leads to a statistically significant dif-

ference between protocol steps in the LDG

(SADO). Bone ridge densitometric values

have clinic and prognostic significance

(Schnitman el al. 1988; Hutton et al.

1995; Misch et al. 1998, 1999a, 1999b;

Misch 1999), and, if they exceed 800–

850 HU, they are an important factor for

implant insertion and success rate. In the

LDG, densitometries of the second step

essentially fulfill this densitometric re-

quirement and were statistically greater

than those of CG. The variability of the

distribution was probably the cause of the

statistical parity of densitometries of the

second step of the LDG as compared with

those of the third step of CG. This may

reflect a late acquisition of bone density in

the CG, whereas similar results are

achieved in a shorter time in the LDG.

Fig. 5. Morphology (c, microradiograph; e, toluidine blue stain; b, f, under polarized light, trypan blue stain)

and histochemistry (d, total alkaline phosphatase; a, tartrate-resistant acid phosphatase) of the bone in control

group (a, b) and loaded device group (c, d, e, f), 12 weeks after distraction was completed. Note in a and b how

osteoclasts (red) erode both woven and lamellar bone. In c the new bone surrounds fragments of (elder) bone

(arrows) having a lower radiotransparence, i.e. a higher mineralization. Note also in e and f how the two

trabeculae are mainly formed by lamellar bone containing the typical ellipsoid-shaped osteocytes. Field width

a¼b¼e¼ f¼ 408 mm; c¼563 mm; d¼ 306 mm.

50

40

30

20

10

CG LDG

OB

%

8 weeks

12 weeks

0

Fig. 6. Graph showing the mean amount of the

ordered (lamellar or parallel-fibered) bone percent

(OB%) of control group (CG) and loaded device

group, 8 and 12 weeks after the end of distraction.

The value in 8-week CG (OB%¼ 0) was adapted to

allow plotting.

Consolo et al . Loading effect on distracted bone

185 | Clin. Oral Impl. Res. 17, 2006 / 179–187

Histology highlights relevant differences

between the LDG (SADO) and CG (TADO)

as early as 6 weeks after distraction was

completed. Despite good angiogenesis, new

bone formation is only occasionally found

in TADO, whereas new bone formation is

often found in SADO. In TADO, all bone

has a woven structure due to the static os-

teogenesis processes (Ferretti et al. 2002).

On the contrary, the more abundant newly

formed bone of SADO also had zones with a

more ordered structure (mainly parallel-fi-

bered structure). This bone is formed in app-

osition to the previously formed tissue

(therefore also woven ‘static’ bone) by dyna-

mic osteogenesis (Ferretti et al. 2002). As

showed at fluorescence microscopy, appreci-

able amounts of this type of bone were found

after only 6 weeks in SADO. At histology,

the process of bone formation is accelerated,

increasing after 6 weeks in SADO as com-

pared with conventional TADO.

Bone processes proved to be progressing

well in TADO 8 weeks after the end of

distraction. The bone was structured

mainly as woven tissue and showed a good

osteogenic index, in term of alkaline phos-

phatase expression, even if some (inner)

parts of the biopsies were still made up of

fibrous tissue. Alkaline phosphatase expres-

sion was higher and ordered bone was

greater in SADO 8 weeks after distraction

was completed. The bone shows small parts

with a woven structure and many parts

with a parallel-fibered or lamellar structure.

Unlike TADO, where deposition is archi-

tecturally disordered, bone trabeculae begin

to show preferential trajectories (probably

due to feeble loads) in SADO. Histology of

8-week-old biopsies seems to confirm the

previous results and points out both osteo-

genic processes, with structural and archi-

tectural bone improvement, in relation to

stimulated distraction as compared with

conventional TADO.

Even if bone with an ordered structure

was adequate, several parts of bone had a

woven structure in TADO 12 weeks after

the end of distraction. The trabeculae with a

fully woven structure are due to bone re-

sorption, which osteoclasts brought about

from the 8th to 12th week (Zaffe et al.

2002). To counterbalance resorbed tissue,

new bone with a woven structure is rapidly

formed (Consolo et al. 2000; Zaffe et al.

2002). The high osteogenic activity of

TADO produces new bone with an ordered

structure in apposition to previously formed

bone but also produces new bone with a

woven structured (new trabeculae). A re-

markable amount of bone with an ordered

(mostly lamellar) structure was found in

SADO 12 weeks after the end of the dis-

traction. Bone formation processes were

noticeably reduced: active osteoblasts were

scanty and bone surfaces were covered by

flattened osteoblasts or isolated cells (bone

lining cells). A small amount of bone resorp-

tion activities were detectable in SADO 12

weeks after the end of the distraction. The

results seem to highlight an advanced steady

state in SADO as compared with TADO.

The amount of ordered bone increases

in both groups 12 vs. 8 weeks after distrac-

tion. Morphometry reveals a statistical

significance and a consistently higher

amount of ordered bone in LDG vs. CG,

both 8 and 12 weeks after distraction.

Briefly, histological results highlight a

similar behavior in the two groups. All

morphostructural findings were anticipated

in subjects undergoing stimulated alveolar

distraction (SADO) and are tardily expressed

in subjects undergoing customary alveolar

distraction (TADO). From a qualitative

standpoint, the results of SADO biopsies

are fundamentally the same as those in

TADO biopsies. However, bone formation

and structure modification are realized be-

latedly and to a lower extent in conven-

tional distraction treatment (TADO).

Quantitative evaluations show that not

only are osteogenetic processes anticipated

in SADO but also bone formation time is

controlled. Osteogenetic processes (Ferretti

et al. 2002) begin with disordered layers of

osteoblasts that form woven bone in SADO

when angiogenic processes are not yet rea-

lized in TADO. Bone formation speed de-

celerates in both groups; ordered osteoblasts

layers form lamellar bone, but due to the

relatively shorter time, the slope of the

deceleration curve is steeper in TADO.

With a lower bone formation speed, great

ordered bone is formed.

The applied stimulative distraction

(SADO) protocol derives from the sugges-

tions of Prof. J. Hidding on the need to

stimulate the distractive callus properly to

prompt its evolution. We preferred to apply

a stimulation protocol, with extended and

mild cycles, from when distraction was

completed to avoid ‘overstimulation’ that

could modify the osteogenetic processes.

Even though we operated on selected pa-

tients with reduced loads, a moderate degree

of pain was recorded in some patients in the

terminal phases of stimulation. As early as

6 weeks after distraction, we clinically es-

tablished the tenacity of the stimulated

callus (SADO) during distractor removal in

the patient excluded from the study (LDG).

Callus stiffness was indirectly confirmed by

the ineffectiveness of the orthodontic trial,

in an attempt to correct vector deviation,

and the subsequent pain that followed.

In conclusion, our results provide firm

evidence for early formation, superior

structure quality and architectural displa-

cement of bone in patients undergoing

stimulated alveolar distraction osteogen-

esis. Bone displacement appears to be

more fitted to prosthetic implant-based

rehabilitation. Control of the distractive

vector, from which the congruence of al-

veolar stimulation and implant insertion

derives, and respect of the principles of

occlusal-based prosthetic rehabilitation ap-

pear to be particularly important. Since our

findings relate to a rather limited number

of patients, further studies will be neces-

sary to confirm our results.

Acknowledgements: We wish to

thank Dr John Pradelli, MD for assistance

in manuscript draft and revision. The

MIUR (Cofin 2003) Research Fund

supported this investigation.

Consolo et al . Loading effect on distracted bone

186 | Clin. Oral Impl. Res. 17, 2006 / 179–187

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