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Accelerated Orthodontic Treatment byRapid Canine Retraction in VariousMalocclusions

Eric Jein-Wein Liou; Taiwan

ORTHODONTIC TOOTH MOVEMENT

PAPERS & ABSTRACTS: 6TH INTERNATIONAL ORTHODONTIC CONGRESS70

Rapid canine retraction is a technique of retracting

the canine through distraction of the periodontal

ligament. This approach is based on the principles of

distraction osteogenesis and sutural expansion osteogene-

sis, such as rapid maxillary expansion. By surgically under-

mining and reducing the thickness of the interseptal bone

distal to the canine, the canine–interseptal bone complex

is distalized with a dental distractor in 1 month (Figs 1a to

1c). It has been revealed experimentally and clinically that

rapid stretching of the periodontal ligament initiates osteo-

genesis. This technique corrects various malocclusions,

especially dentoalveolar protrusion, in a shorter period of

time with minimal loss of anchorage and greater scale of

improvement (Fig 1d). Its effectiveness is even greater

when it is combined with the use of miniscrews.

Pre-distraction Preparation: SequentialActivation

The anterior teeth are bonded and a segment of 0.016 �

0.022-inch nickel-titanium archwire is placed for activation

of the periodontal ligaments; no archwire is placed and no

anchorage preparation is performed on the posterior teeth.

To minimize anchorage loss during rapid canine retraction,

the anchor teeth should be left undisturbed before extrac-

tion of the first premolars. The period of sequential activa-

tion is 1 month.

Surgical Procedure for Undermining theInterseptal Bone Distal to the Canine

The surgical procedure is performed inside the extraction

socket of the first premolar. No mucoperiosteal flaps are

raised and no osteotomy is made at the buccal or lingual

plate of the canine. The surgical procedure consists of the

following steps:

1. Extract the first premolar and measure its exact length.

2. Estimate the exact length of the canine based on the

exact length of the first premolar and the ratio of the

radiographic length of the canine to the first premolar

on the periapical radiograph.

3. Deepen the socket of the first premolar to the exact

length of the canine with a 4-mm round carbide bur. The

bur should be held parallel to the long axis of the canine.

4. Reduce the thickness of the interseptal bone distal to

canine with a cylindrical carbide bur. This procedure is

critical. The thickness of the interseptal bone distal to

the canine is estimated on the periapical radiograph.

The bur is held parallel to the long axis of the canine and

moved buccolingually while shaving the interseptal

bone. Ten buccolingual (back-and-forth) shaving move-

ments will reduce the thickness of the interseptal bone

by approximately 1 mm. The interseptal bone is reduced

to 1 to 1.5 mm in thickness. To make sure the socket is

deepened and the interseptal bone reduced adequate-

ly, periapical radiographs may be taken again after this

procedure.

5. Undermine the interseptal bone distal to the canine.

Two vertical grooves, at the mesiobuccal and mesiolin-

gual corners of the interseptal bone, are made inside the

extraction socket with a 1-mm carbide fissure bur. These

two vertical grooves extend obliquely toward the base

of the interseptal bone and become a V-shaped groove.

The interseptal bone is not cut through to the canine.

6. Place a 0.016 � 0.022-inch stainless steel archwire from

first molar to first molar. No bracket is bonded on the

second premolars for ease of insertion of the archwire.

7. Insert the dental distractor into the headgear tube on

the first molar and engage it by the mesial of the canine

KEYNOTE LECTURE

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ORTHODONTIC TOOTH MOVEMENT L07

71DOCTORS’ PROGRAM

bracket so that the canine can be retracted along the

archwire. The distractor is activated 0.6 mm per day until

the canine is retracted into the desired position and

amount. The canine can usually be retracted 5 to 6 mm

per month.

Post-distraction Anchorage Preparation forthe Anterior Retraction

1. Incorporate the second molars into the anchor unit.

2. Reinforce the first molars with a 0.036-inch TMA trans-

palatal or lingual arch with mesial angulation and lingual

crown torque.

3. Reinforce the first molar with a pair of TMA lever arms

(also for intrusion of the anterior teeth).

4. Alternatively, miniscrews may be placed.

Indications

Although this technique could also be used in cases of

severe dental crowding, it is specifically indicated in adult

cases with severe dentoalveolar protrusion, such as Class I

bimaxillary, Class II, division 1, and Class III mandibular den-

toalveolar protrusion. It has also been combined with the

use of miniscrews for an orthognathic-like improvement of

dentoalveolar protrusion by a great scale of anterior retrac-

tion and posterior teeth distalization and/or intrusion.

This technique accelerates orthodontic tooth movement

and improves the treatment results in two ways. First, it

shortens the period of canine retraction and saves more

time for the finishing details; second, it retains more

anchorage for a greater improvement of the dentoalveolar

protrusion and torque control.

Long-Term Results

In a clinical study of 54 patients, treatment results remained

stable at 5 years after the rapid canine retraction, and no

periodontal defects or endodontic compromises were

noted. The pulpal responses of all the canines recovered

gradually within 3 years of the retraction. The apical root

resorption was acceptable in all the retracted canines. In

conclusion, the rapid canine retraction has no detrimental

effects on the periodontal and pulpal tissues and has no

excessive root resorption in the long-term results.

a b c

d

Figs 1a to 1c By surgically undermining andreducing the thickness of the interseptalbone distal to the canine, the canine–inter-septal bone complex is distalized with a den-tal distractor in 1 month.

Fig 1d This technique corrects various mal-occlusions, especially dentoalveolar protrusion,in a shorter period of time with minimal lossof anchorage and greater scale of improve-ment.

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Rapid Orthodontic Treatment by UsingDentoalveolar Distraction Osteogenesis

Haluk Iseri, R. Kisnisci, G. Kurt; Turkey

ORTHODONTIC TOOTH MOVEMENTL08


It is a well-known fact that most orthodontic cases imply

shortage of space and crowding. Although nonextrac-

tion treatment has became quite popular during the last

decade, a considerable number of cases still require treat-

ment based on tooth extraction. The first phase of the treat-

ment in premolar extraction cases is retraction of the

canines; this phase usually lasts about 6 to 9 months. In addi-

tion, extraoral and/or intraoral anchorage mechanics are

required to keep the obtained space safe during canine

retraction, particularly in cases in which maximum anchor-

age is required. Therefore, under normal circumstances, con-

ventional treatment with fixed appliances is likely to last

about 20 to 24 months. However, the use of extraoral

anchorage appliances and the duration of the orthodontic

treatment result in the most complaints, especially from

young adult and adult subjects. To overcome this problem, a

technique of rapid canine retraction using distraction osteo-

genesis, the dentoalveolar distraction (DAD) technique, has

been described and used by Iseri et al1 and Kisnisci et al.2 The

effects of DAD on the dentofacial structures are presented in

this lecture.

Materials and Methods

Class I or II malocclusion patients who needed fixed appli-

ance orthodontic treatment based on tooth extraction were

selected for this study. All of the patients were in the perma-

nent dentition and demonstrated moderate to severe

crowding and/or increased overjet at the start of treatment.

The study sample consisted of 20 maxillary canines from 10

growing or adult subjects with a mean age of 16.53 years

(13.08 to 25.67).

Surgical Procedure

The maxillary and mandibular canines were moved rapidly

into the cavity of the extracted first premolars, following a

surgical procedure lasting about 30 minutes for each canine.

Complete vertical and horizontal corticotomies were per-

formed around the root of canine tooth, followed by splitting

of the spongy bone around it. By using this surgical tech-

nique, the dentoalveolus was designed as a bone transport

segment for rapid posterior movement of the canines. Then

the first premolar was extracted and the base of the extrac-

tion socket was weakened. The design of the surgical tech-

nique, therefore, did not rely on stretching and widening of

the periodontal ligament, which would prevent overloading

and stress accumulation in the periodontal tissues. Moreover,

neither the buccal and apical bone through the extraction

site nor the palatal cortical plate interfered the movement of

the canine-dentoalveolus segment during the distraction

procedure because of the surgical procedure and distal

movement vector of the canine along the guidance burs of

the distractor through the extraction cavity. The surgery and

the device after the surgery were well tolerated by all of the

patients.

Appliance Design and Distraction Protocol

A custom-made, rigid, tooth-borne, intraoral distraction

device was designed, produced, and used for rapid tooth

movement with DAD. The DAD device is made of stainless

steel and mainly constructed of one distraction screw and

two guidance bars. The canines and first molars were band-

ed and the distractor was soldered on the canine and first

INVITED LECTURE

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molar bands, as high as possible on the buccal sides in order

to minimize the tipping effect. The device was placed 1 to 2

mm distant from the alveolar mucosa for patient comfort. No

other appliances were used on the second premolars and

the incisors during the distraction procedure. The distraction

device was fixed to the canine and first molar by cement at

the end of surgery and activated by turning the screw in the

clockwise direction with a special apparatus. The canine was

moved distally by closure of the screw during distraction. The

distraction device was activated twice a day, once in the

morning and once in the evening, with a total amount of 0.8

mm per day. Immediately after the canine retraction was

completed, fixed appliance orthodontic treatment was initi-

ated and leveling of the maxillary and mandibular dental

arches began.

Results

The canines were moved rapidly into the socket of the

extracted first premolars in compliance with distraction oste-

ogenesis principles, and the distraction procedure was com-

pleted in 8 to 14 days with a rate of 0.8 mm per day (Fig 1).

Full retraction of the canines were achieved in 10.05 ±

2.01 days, and the anchorage teeth were able to withstand

the retraction forces without any anchorage loss. The mean

sagittal and vertical posterior anchorage losses were 0.19

and 0.51 mm, respectively. The mean change in canine

inclination was 13.15 ± 4.65 degrees, and the anterior face

height and mandibular plane angle increased and overjet

decreased significantly at the end of dentoalveolar distrac-

tion. No clinical and radiographic evidence of complica-

tions such as root fracture, root resorption, ankylosis, peri-

odontal problems, and soft tissue dehiscence were

observed. Periodontal status was normal in all cases at the

end of the 1-year orthodontic treatment time following the

DAD. The plaque and gingival index values were increased

following the surgery and then gradually decreased

through the 1-, 6-, and 12-month periods. The pocket

depth measurements on three sites other than the buccal

site were increased significantly by DAD (P < .05 and P <

.001, respectively) but significantly decreased during the

follow-up period. Patients demonstrated minimal to mod-

erate discomfort following the surgery, and edema was

observed in some of the patients.

Clinical Implications and Conclusions

The concept of distraction osteogenesis for rapid orthodon-

tic tooth movement seems promising, especially in severe

cases in which a long treatment time is necessary. By using

the DAD technique, the canines can be fully retracted in 8 to

14 days as compared to the regular rate of orthodontic tooth

movement of about 1 mm per month. Therefore, the DAD

technique is an innovative method since it reduces the over-

all orthodontic treatment time by up to 6 to 10 months even

in severe extraction cases, with no need for extraoral or intra-

oral anchorage mechanics and without any unfavorable

short- and long-term effects on the periodontal tissues and

surrounding structures.

Patients who had compliance problems for social and

professional reasons; older adolescent and adult patients;

patients with moderate and severe crowding; adult Class II

overjet cases; bimaxillary dental protrusion cases; orthog-

nathic surgery cases who need dental decompensation;

and cases having root shape malformations, short roots,

periodontal problems, or ankylosed teeth are good candi-

dates for tooth movement by using DAD.

References

1. Iseri H, Bzeizi N, Kisnisci R. Rapid canine retraction using den-

toalveolar distraction osteogenesis [abstract]. Eur J Orthod

2001;23:453.

2. Kisnisci R, Iseri H, Tuz H, Altug A. Dentoalveolar distraction osteo-

genesis for rapid orthodontic canine retraction. J Oral Maxillofac

Surg 2002;60:389–394.

Fig 1 Using the DAD technique, the distraction procedure wascompleted in 8 to 14 days with a rate of 0.8 mm per day.

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INVITED LECTURE


T he ability of periodontal alveolar and periosteal

sutural cell populations to respond to mechanical

forces is the key to current orthodontic and dento-

facial orthopedic therapy.

Major advances in appliance design and orthodontic

materials such as wire alloys have facilitated the fabrication

of lower load:deflection ratios in force systems. However,

despite attempts to provide “lighter” forces that are deliv-

ered by orthodontic appliances, there is no evidence that

the mechanical stress experienced by the tissue has been

reduced significantly, because of the tremendous moments

of force due to tipping that is always produced. Above a

certain stress level, orthodontic force systems may be cre-

ating tissue necrosis while causing physical repositioning of

roots or bone.

The following tissue changes would then be tissue

regeneration as part of the wound healing process. Theo-

retically, a repeated cycle of tissue necrosis and wound

healing may cause root resorption. Similarly, these non-

physiologic force levels may result in poor correlation with

appliance activation and the rate of tooth or bone move-

ment. Various orthodontic and orthopedic force systems

using organ and cell cultures have been utilized to explore

the relationship of mechanical force to tissue response. Ini-

tially, collagen synthesis was measured as a reflection of

organ culture viability and responsiveness to mechanical

force. Increase in type III collagen was demonstrated to be

a significant change in remodeling periodontal and sutural

tissue. Subsequently, we followed the regeneration of

blood vessels subsequent to orthodontic strain on the

periodontal ligament because of the possible relationship

between type III collagen synthesis and blood vessel

growth. Tartrate-resistant acid phosphatase–positive stain-

ing cells indicative of future resorptive cells were closely

associated with blood vessels. Mechanical stress of peri-

odontal and bone cell layers in culture similarly demon-

strated increase of type III collagen synthesis.

Finally, recent studies demonstrated a relationship

between mechanical strain and integrin expression in iso-

lated cells. This suggests a possible signal transduction

pathway for biomechanical force in which change of shape

in the extracellular matrix results in cell membrane strain,

which in turn activates cell response through integrin sites

on the cell membrane surface and changes in the cellular

cytoskeleton.


Biomolecular Mechanics: The New Orthodontist

Edwin H. K. Yen; Canada

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KEYNOTE LECTURE


T his presentation systematically analyzes the variety

and potency of aging variables affecting the mor-

phology, structure, and mechanical properties of

polymeric and metallic orthodontic materials, with emphasis

on associated clinical implications. The materials reviewed

will include adhesives and bonding with conventional and

self-etching acid etching; nickel-titanium (NiTi) wire alloys;

elastomeric modules; and brackets. A critical, evidence-based

approach will be utilized. It is surprising that for most of the

proposed applications of materials, there is a striking lack of

supporting evidence. Hence, the effectiveness and aging of

active self-ligating brackets, the kinetics of fluoride release

from adhesives, and friction variants with bracket-archwire

combinations, among others, have not been studied in vivo,

although these issues constitute standard marketing tools in

relevant promotional material.

Recent studies revealing the aging pattern of orthodontic

materials in vivo have furnished critical evidence that greatly

impacts the clinical efficiency of materials. Thus, intraoral ag-

ing of adhesives may modify their physical and mechanical

properties, possibly leading to bond failure at loads of lower

magnitude than those sustained at the initiation of treat-

ment. Because in vitro testing cannot reveal this effect, stan-

dard laboratory bond strength protocols must be modified

to become clinically meaningful, whereas research protocols

should be complemented with in vivo failure rate studies.

Self-etching adhesives have been shown to present simi-

lar bond strength and roughly the same failure rate relative

to conventional acid-etching. However, retention of the

acidic residues that result from the application of self-etching

may impose two main effects on the interfacial characteris-

tics of enamel: It can react with calcium to form calcium

phosphate complexes with potential undesirable effects on

the solubility of the polymer network, and it can increase the

thickness of the adhesive layer. The biocompatibility of these

systems remains unexplored; therefore, further proof of the

long-term efficacy and safety of these systems is necessary.

For NiTi wire alloys, the force transferred from an activat-

ed archwire to a preadjusted bracket slot, as well as sliding

mechanics, seems to be affected by the surface modification

and mechanical profile alteration of materials induced by

intraoral aging. Only recently, after more than a decade of

global scale application of these wires, has this information

become available. These wires have shown substantial altea-

tions following exposure to the intraoral environment, where-

as currently available evidence on the role of friction in effec-

tively altering the rate of tooth movement in vivo is lacking.

In addition, there is no consensus on the effect of intraoral

environmental conditions on the superelastic properties of

NiTi archwires and coil springs, and further evidence is needed

to establish the true spectrum of alterations. It is known, how-

ever, that intraoral temperature variations may transiently affect

their properties, whereas the fracture resistance of NiTi wires

is significantly reduced by their exposure to the oral cavity.

In the field of elastomerics, mechanics, which rely on elas-

tomeric ligation or traction such as correction of rotations,

torque expression, or space closure, may be adversely

affected by the aging-induced increase in the creep of these

appliances. Clinicians should either shorten the time periods

between appointments or use alternative means, ie, steel

ligatures and coil springs, for engaging and retracting teeth,

respectively.

Further evidence addressing the relaxation and fatigue

variants of the spring component of active self-ligating

brackets is necessary before the advantageous pattern of

engagement of these appliances over conventional brackets

is established.

Overall, the objective of this presentation is to promote a

skeptical and strenuously screened incorporation of advance-

ments and newly introduced orthodontic auxiliaries and util-

ities. This approach may be implemented by adopting the

paradigm of therapeutic agents from associated medical

fields rather than treating orthodontic materials as cosmet-

ic products.


Orthodontic Materials: IntegratingResearch Evidence in Chairside Applications

Theodore Eliades; Greece

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INVITED LECTURE

Bone Biomechanics of Tooth Movement:PDL and Periosteal Responses

W. Eugene Roberts; United States


Bone modeling and remodeling are independent

adaptive mechanisms that allow a tooth to move

relative to basilar bone. In orthodontics, the term

remodeling is often applied inappropriately. Changes in

bone shape or size due to surface resorption and formation

are modeling processes. Remodeling is the physiologic term

for turnover of mineralized tissue without a change in

external form. It is a coupled sequence of catabolic and

anabolic events to repair aged and damaged mineralized

tissue. Properly distinguishing bone modeling from remod-

eling is an important semantics issue. Tooth movement is

controlled by bone modeling events. Remodeling plays an

indirect role.

Frost’s mechanostat (Fig 1) is useful for understanding the

fundamental biomechanics of orthodontic tooth move-

ment. Natural tooth position is dictated by the equilibrium of

all forces acting on the dentition. Superimposition of thera-

peutic force is thought to elevate the biomechanical envi-

ronment from steady-state turnover into the hypertrophic

and fatigue failure ranges of bone biomechanics. As a tooth

moves, strain patterns within the supporting bone elicit spe-

cific patterns of subperiosteal bone formation and resorption.

Tooth movement is an inflammatory adaptation of the

periodontium to applied loads.

Orthodontics is the adaptive response of the alveolar

process and its periodontal tissues to therapeutic loads

superimposed on function. The initial periodontal ligament

(PDL) response involves displacement of a tooth root within

the PDL space, resulting in compression of the PDL in the

direction of tooth movement, occlusion of its blood supply,

and necrosis. In the area of maximal compression, the cush-

ioning effect of the PDL is lost and the heavy loads of func-

tional occlusion are transferred directly into the adjacent

alveolar bone. Thus, the initial necrotic areas of the PDL

become stress risers, elevating the peak functional loading of

resisting bone into the fatigue failure range (greater than

4,000 microstrain). This scenario results in undermining

resorption to remove bone in the path of tooth movement.

The rates of tooth movement and adaptation of the alve-

olar process are manifestations of anabolic and catabolic

modeling along bone surfaces of the PDL and periosteum.

The thickness of the alveolar process is controlled by func-

tional strain (flexure). As a tooth moves into alveolar bone,

catabolic modeling (resorption) occurs at the bone-PDL

interface, resulting in thinning of the alveolar process. Con-

current functional loading of the tooth exposes the weak-

ened alveolar plate to excessive strain, which is expressed as

compressive loading of the subperiosteal surface in the


Fig 1 Frost’s mechanostat is a clinically oriented expression ofthe biomechanics of bone physiology.

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direction of tooth movement. This sequence of events

results in anabolic modeling to increase the thickness of the

alveolar plate. In effect, the alveolar process moves ahead of

the tooth until the flexure, due to functional loading, is back

in equilibrium.

The thickness of the plate of alveolar bone trailing a mov-

ing tooth is also controlled by bone flexure. As the root is dis-

placed, the PDL thickens and anabolic modeling (bone for-

mation) occurs along the bone-PDL interface. As the plate of

alveolar bone thickens, it becomes more rigid and the func-

tional flexure drops below the optimal steady state range.

This scenario triggers a disuse atrophy reaction, and cata-

bolic modeling (bone resorption) occurs along the trailing

periosteal surface. The resorption continues until the func-

tional flexure of the alveolar plate returns to the optimal

range.

In brief, tooth movement is a therapeutic manifestation of

the principal adaptive mechanisms of bone biomechanics:

atrophy, hypertrophy and fatigue failure. Clinical correlations

are that: (1) periodontally healthy teeth can be moved into

atrophic edentulous spaces; (2) augmentation bone grafts

prior to orthodontics are usually contraindicated; (3) in the

presence of active periodontitis, the osteogenic response of

the periosteum is inhibited, resulting in loss of alveolar crest

height as a tooth is moved; and (4) in general, the rate of

tooth movement in the maxilla is about twice that in the

mandible.

T he superelasticity of the new superwires and

microimplants is perhaps the most important

advance of the last 10 years in the orthodontic field.

Superelastic wires have very large reversible strains and a

nonelastic stress-strain or force-deflection curve. The two

main clinical implications of superelasticity are that the wire

can be bent or deformed without the risk of producing

heavy forces and that the wires can be selected independent

of size and force. We know that part of the force we apply

with our wires can be lost or altered due to friction or the

appearance of undesired forces, for which reason the design

of new brackets must provide optimal transmission of force.

New superwires need new bracket designs. We need friction

during the torque and finishing phases. It is very important

to understand the clinical concept of friction selection con-

trol. It is also very important to comprehend that the friction

is not always bad and that in many clinical occasions it is nec-

essary, for example, to control the rotations during the align-

ment phase or the control of torque during the closing and

finishing phase.

The straight wire low friction (SWLF) technique com-

bines the use of low friction brackets with the latest high

technology wires (thermal nickel titanium [NiTi] and beta III

titanium) and the use of microscrews. The Synergy bracket

(Rocky Mountain Orthodontics) is similar to a conventional

bracket, but it has some technical innovations. For instance,

it has three pairs of wings instead of two. The central wings

are overelevated, preventing contact between the wire and

the ligature. The other two wings allow for excellent control

of rotations. In addition, the slot is not straight; it has a

curved surface to improve the sliding of the archwire, and

the ends of the sides are not at a 90-degree angle. This

design allows better sliding when we put the ligature only

in the central wings, good control of the rotations and the

torque of the roots when we place the ligature in the later-

al wings, early insertion of rectangular thermoelastic wires

L48

Straight Wire Low Friction Technique

David Suárez Quintanilla; Spain

INVITED LECTURE

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(a great advantage in reducing the length of the alignment

phase), and increased interbracket width because of the

curve of the edges of the slot. The SWLF has simple biome-

chanics, and its main advantages are to apply low and con-

stant forces to improve the orthodontic tooth movement

and to reduce the risk of orthodontic radicular resorption

(Figs 1 and 2).

The aim of this lecture is to relate clinical practice to

recent research in the field of orthodontic tooth move-

ment. We will examine the type of forces used in the SWLF

technique (eg, intensity, duration, direction, rhythm of

application, distribution of stress), the biological response

(eg, bone deformation, changes in the periodontal liga-

ment, stress and strain, blood flow, cell differentiation and

biochemistry), and the degree of tooth movement

achieved. We will compare different techniques through

clinical and experimental studies and the finite element

method. Finally, we will study, on the basis of recent

research, the clinical aspects of orthodontically induced

inflammatory root resorption (OIIRR). Heavy forces not only

reduce the amount and speed of orthodontic tooth move-

ment, but they can also produce orthodontic radicular

resorption. OIIRR is a big problem in orthodontics because

it compromises the future stability and survival of the den-

tition. Histologic investigation provides evidence that the

same resorptive process also occurs on other areas of the

root surface. OIIRR is a multifactorial problem associated

with patient characteristic such as age, sex, systemic condi-

tions, and malocclusion, as well as with treatment factors

such as type of appliance, duration of treatment, orthodon-

tic force magnitude, and type of tooth movement.

Figs 1 and 2 The SWLF technique combinesthe use of low friction brackets with thelatest high technology wires and micro-screws.

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KEYNOTE LECTURE


What happens to our hard-won occlusions years

after we have left the scene? This question has

teased and frustrated orthodontic clinicians

and researchers over many years. It would be valuable to

know the answer to this question as it is a fundamental

issue challenging our very effectiveness in providing

acceptable clinical results—results that we hope will

remain esthetic and functional over time.

This lecture presents a critical evaluation of a series of

cases treated by the presenter using the long-term follow-

up records to gain an insight into the dental and cephalo-

metric changes occurring over time. It refers largely to four

published papers from the Orthodontic Department of the

University of Melbourne, Australia. These independently

conducted research projects drew information and data

from the records of some 70 cases to gain an in-depth pic-

ture of the treatment changes, but also, more interestingly,

the posttreatment changes in dental arrangement and

facial pattern that had occurred some 11 years later.

Various statistical tests were used in these four projects

to search for factors that may relate to posttreatment

change. These factors included the standard of occlusal fin-

ish, pretreatment vertical facial pattern, and mandibular

rotational and incisal changes occurring during and after

active treatment. Much of the information highlights the

unpredictable nature of long-term posttreatment change

(Fig 1). Some findings question long-held beliefs relating to

orthodontic stability.


Tooth Movement—The Sort That Happens After Orthodontic Treatment

Ted Crawford; Australia

Long-term PAR score change

Time (years)

PAR

sco

re

0 2.1 13

25.5

3

7

30

25

20

15

10

5

0

Fig 1 PAR score changes in a sample group

of 75 patients.

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INVITED LECTURE


T he treatment of various dentofacial anomalies in

orthodontics requires the application of mechanical

forces to teeth. It has been shown that mechanical

forces regulate bone development and remodeling and

that orthodontic tooth movement is a result of alveolar

bone remodeling. During orthodontic tooth movement,

external forces are applied to teeth that, in turn, are trans-

mitted to the surrounding tissues, such as the periodontal

ligament and alveolar bone. The final acceptor of these

forces are the cells that reside within the periodontal liga-

ment and alveolar bone. Clinical observations show that

ankylosed teeth, which lack a periodontal ligament, fail to

move. Moreover, dental implants that are placed as teeth

replacements are bound to alveolar bone (osseointegra-

tion) and cannot be moved, as they also lack a periodontal

ligament. The complete resorption of alveolar bone that

follows tooth extraction and complete destruction of the

periodontal ligament is a phenomenon that needs further

investigation. All the above clinical situations reveal the

pivotal role of the periodontal ligament in the remodeling

of the surrounding alveolar bone. This remodeling is well

balanced throughout life and results from the equal action

of two sets of cells: osteoblasts and osteoclasts. It also func-

tions in a cycle: As osteoblasts mature, they produce cyto-

kines that induce osteoclasts to resorb bone. During

resorption, osteoclasts release other cytokines that cause

further maturation to osteoblasts and apposition of new

bone.

It seems that orthodontic tooth movement is a peri-

odontal ligament phenomenon and occurs only in its pres-

ence. The periodontal ligament is a connective tissue that

holds the tooth in place and contains cells and extracellu-

lar matrix. The cells are predominantly fibroblasts and are

the end targets of external force application. It seems that

these cells receive the external signal of mechanical forces

and respond in a biologic manner that finally causes alveo-

lar bone remodeling and local change in the architecture of

the area as the tooth moves. The biologic response of these

cells is not clear, but in recent years more and more informa-

tion is accumulating in an effort to elucidate orthodontic

tooth movement phenomena. Periodontal ligament fibro-

blasts have the properties of osteoblastic cells and under

certain cell culture conditions can form bone. Cell culture

experiments simulating the application of mechanical

forces during orthodontic tooth movement showed that

periodontal ligament fibroblasts sense mechanical forces

and respond by activation of certain transcription factors

that are either associated (c-Jun, c-Fos) or specific for bone

development (Runx2). Activation of transcription factors

causes changes or reprogramming in transcription of genes

related to bone apposition (eg, ALP, Col1, osteocalcin) and

protein production accordingly. These products reach the

extracellular matrix, mineralization occurs, and, finally, new

bone is formed. It seems that during this process the peri-

odontal ligament acts as a source of undifferentiated mes-

enchymal cells that under the signal of mechanical forces

enter the differentiation pathway, maturing into pre-

osteoblasts. These newly formed preosteoblasts enter the

balanced bone remodeling cycle, causing a temporary

imbalance and turning the cycle of bone remodeling more

rapidly until the tooth is moved in its new place and no

more external forces are acting on it. Today, some of the key

factors operating after mechanical force application on the

periodontal ligament have become evident, but much

more research is necessary in order to elucidate the signal-

ing pathway of bone remodeling after force application.

The thorough understanding of the molecular events that

are involved will aid in future pharmaceutical intervention

and absolute control of therapeutic parameters such as

treatment time and anchorage problems.


From Force Application to Tooth Movement: The “Biological” Connection

Efthimia K. Basdra; Greece

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Orthodontics is probably the only dental specialty that

actually uses the inflammatory process as a mean of

solving functional and esthetic problems. Force appli-

cation initiates an extracellular and intracellular sequential

process. We know exactly how and when it is evoked, but

we are unable to predict its actual overall outcome.

Orthodontically induced inflammatory root resorption

(OIIRR) or, as it is better known, root resorption, is an

unavoidable pathologic consequence of orthodontic tooth

movement. It is a certain adverse effect of an otherwise

predictable force application. Although it is rarely serious, it

is a devastating event when it is radiographically recog-

nized. The extent of this inflammatory process depends on

many factors, such as the virulence or aggressiveness of the

different resorbing cells and the vulnerability and sensitivi-

ty of the tissues involved (Fig 1).

Individual variation and susceptibility, which are related

to this process, still remain beyond our understanding. We

are therefore unable to predict the incidence and extent of

OIIRR after force application.

During the last decade, there has been an increased

interest in OIIRR primarily due to two reasons: the mapping

of the human genome, which has led to the idea that this

may assist in better understanding the pathologic process,

and the increasing number of legal claims against ortho-

dontists, mainly because of root shortening. In the Decem-

ber 2002 issue of Seminars in Orthodontics, the most com-

monly discussed legal examples were related to OIIRR.

Root shortening is measured using different imaging

techniques. The most common one is the parallel periapi-

cal radiographic technique. This technique hides several

problems that might affect the image seen on the film and,

hence, the conclusions, especially the legal ones, that are

drawn from it.

The lecture discusses the clinical aspects of OIIRR, point-

ing to new ideas published in the current literature as well

as attempts to answer the following questions:

• What is the best way to accurately measure the amount of

apical root resorption?

• Can a special jig with an external wire attached to the

tooth surface and parallel to its long axis contribute to this

measurement?

• What are the effects of the angular changes between the

tooth and the film on measuring the amount of OIIRR?

(Angular changes are usually the consequence of the

orthodontic treatment as well as the result of technical

problems.)

• Is there a known way to avoid or prevent OIIRR during

orthodontic treatment?

Orthodontists should take all known measures, if any exist,

to reduce the occurrence of OIIRR. The evidence that we

present suggests several procedures known today that

might prevent this phenomenon; however, none of them

can be relied on to completely prevent OIIRR.

We believe that future studies might clarify the exact

cause and course of OIIRR and, hopefully, will help to elim-

inate it.

KEYNOTE LECTURE



The Myth of Orthodontically InducedInflammatory Root Resorption

Naphtali Brezniak, Atalia Wasserstein; Israel

Fig 1 The root resorption process.

Hyalinizedzone

Force CementoidDentinCement

Bone Osteoid

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INVITED LECTURE

T his paper reports several new aspects of root resorp-

tion in human premolars based on a series of ongo-

ing investigations at the University of Sydney, Aus-

tralia, from 1997.

Phase I investigated the hardness and elastic modulus of

cementum and the most suitable storage media for the ex-

tracted samples. A jig was developed that allowed survey-

ing of teeth on all surfaces under the Ultra Micro Indentation

System (UMIS). This newly developed methodology per-

mitted a three-dimensional evaluation of root cementum

without any embedding or sectioning. Hardness and elastic

modulus along the root surface as well as on the buccal and

lingual enamel surfaces were mapped on a pilot sample of

nine human premolars derived from six subjects. It was

found that the hardness of cementum gradually increased

from apical to cervical regions.1 Twenty additional human

first premolars were collected and stored according to five

storage/disinfection protocols. The results showed that Milli-

Q (Millipore) could be used as a reliable storage medium.

Phase II involved studies on a core sample of 36 human

premolars collected from 16 orthodontic patients who

were subjected to either controlled light (25 g) or heavy

(225 g) buccally directed orthodontic forces on one side,

while the contralateral side served as control. This core

sample was investigated for alterations in physical proper-

ties, mineral composition, and location and volume of re-

sorption craters consequent to application of two force

levels vis à vis controls. Hardness and elastic modulus

showed a significant decrease from the cervical to the api-

cal regions; however, there was no consistent trend in the

data to indicate a statistically significant difference be-

tween the control and force application groups.

For quantitative analysis of mineral contents, teeth were

analyzed using the electron probe microanalysis (EPMA)

technique. The calcium, phosphorus, and fluorine concen-

trations were measured on intact cementum at 90 points

per tooth along the buccal and lingual surface at the mid-

point of the cervical, middle, and apical third of the root.

Results have highlighted a significant interindividual varia-

tion in the calcium, phosphorus, and fluorine concentrations

(P = .024, .017, and .000, respectively) in cementum. There

was no significant difference in the calcium, phosphorus, and

fluorine concentrations of cementum between buccal and

lingual surfaces, except for a significantly higher fluorine con-

tent at the cervical region on the buccal surface (P = .000).

A newly developed software allowed three-dimensional

volumetric quantitative analysis of the resorption craters.

The mean volume of the resorption crater in the light-force

group was 3.49-fold greater than the controls, and in the

heavy-force group it was 11.59-fold more than the controls.

The heavy-force group had 3.31-fold greater total resorp-

tion volume than the light-force group. The buccal cervical

and lingual apical regions demonstrated more root resorp-

tion as compared to the other regions.

The amount of root resorption when controlled light

and heavy intrusive force magnitudes were applied to

human premolars was also evaluated on another sample of

54 first maxillary premolar teeth using a micro CT scan X-ray

system (SkyScan-1072) and specially designed in-house soft-

ware for volumetric measurements (Chull2D). Heavy forces

demonstrated significantly more resorption, and the mean

volume of the resorption craters in the light- and heavy-

force groups were two and four times greater, respectively,

than in the control group.

Phase III investigated the prevention of root resorption

in an animal sample. An investigation on whether fluoride

has a beneficial effect in reducing the incidence of root

resorption on 32 8-week-old Wistar rats was performed.

Scanning of the resorption crates was performed using the

micro CT and software as described. The resorption sites

were significantly increased (P < .05) in the groups receiving

orthodontic tooth movement. Fluoride on average reduces

the size of resorption craters, but the effect is variable and

was not found to be statistically significant (P > .05).

Reference1. Sameh Malek M, Darendeliler A, Swain M, Tyler K. A New Method

for 3-Dimensional Evaluation of the Physical Properties of Root

Cementum. Available at: http://oldsite.vislab.usyd.edu.au/gallery/

dentistry/cementum.html. Accessed 3 May 2005.


Exploring the Dimensions of RootResorption: Can We Prevent It?

Ali Darendeliler; Australia


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T he purpose of this study was to compare the palatal

implant-supported bone-borne anchorage (BBA)

with a conventional intraoral tooth-borne anchor-

age (TBA) during upper canine retraction in extraction

cases requiring maximum distal anchorage.

Based on an ongoing randomized clinical trial, 18 ado-

lescent patients (mean age, 14.2 ± 1.37 years) were treated

with two upper first premolar extractions with maximal

posterior anchorage indication. The orthodontic treatment

was carried out using the Alexander fixed orthodontic

appliance. All subjects were informed and signed a consent

form agreeing to both of the treatment protocols that was

previously approved by the Regional Research Ethics Com-

mission (No. 236/2000). In the BBA group (n = 9; mean age,

13.8 ± 0.92 years) osseointegrated palatal implants

(Orthosystem, Straumann) were used for maximal anchor-

age; in each case, a 1.2-mm square stainless steel rigid

transpalatal wire was fixed to the implant and to the molar

bands by laser welding. In the TBA group (n = 9; mean age,

14.5 ± 1.68 years) the conventional anchorage was provid-

ed by a 0.017 � 0.025-inch heat-treated SS utility arch com-

bined with a transpalatal bar (TPB). For the canine retraction

a superelastic closed-coil spring (150 cN) was used beside a

0.016 � 0.022-inch SS segment arch to ensure torque con-

trol in both groups. The duration of the canine retraction in

both groups was determined. At the start and at the finish

of retraction the 6-PTV distances were measured on the lat-

eral cephalograms.

There was no significant difference in the duration of the

extraction gap closure by canine retraction, which was 5.25

± 1.73 months for the TBA group and 4.97 ± 1.62 months

for the BBA group. An insignificant difference was found in

the average mesial movement of the upper first molars

between the two groups; the 6-PTV distance increased by

0.5 ± 1.0 mm in the BBA group and 1.6 ± 1.8 mm in the TBA

group (Table 1).

It is known that during maxillary growth, the first perma-

nent molars undergo a downward and mesial drift along

the facial axis, so that the 6-PTV distance increases on aver-

age 1 mm per year with the skeletofacial growth in adoles-

cents. The measurements in the BBA group seem to agree

with this observation: An average 0.5 mm increase in the

6-PTV distance was found over the 5.25 months. Normal

growth is also presumable in the TBA group; therefore, the

tendency of an anchorage loss is to be supposed, for, on

average, three times more mesial molar movement during

the 4.97 month period was measured in the TBA group. The

advantage of using the palatal implant as anchorage is not

in the generally accepted shortening of the canine retrac-

tions timeframe and thus the overall treatment period.

ORTHODONTIC TOOTH MOVEMENTSL005

Maxillary Canine Retraction Using Bone-borne Versus Tooth-borne Anchorage in Growing Patients

Gabriella Borsos; Hungary; K. A. Schlegel; Germany; A. Vegh; Hungary

Table 1 Duration of extraction gap closure (canine retractions) and the concurrent mesialization of theupper first molars

Maxillary Implant group (n = 9) Control group (n = 9) Significancecanine retraction Mean SD Mean SD (Student t test)

T (mo) 5.25 1.73 4.97 1.62 ns (P = .621)

6-PTV (mm) 0.5 1.0 1.6 1.8 ns (P = .164)

ns = not significant

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T he skeleton is an efficient feedback-controlled,

steady-state system that continuously integrates sig-

nals and responses. The local structural adaptation

of bones to mechanical loads is the basis for almost all

osteointegratory procedures.

Increased mechanical load stimulates bone formation,

ie, inducing osteoblast activity. Orthodontic force brings

about remodeling processes in the attachment apparatus,

primarily bone resorption on the pressure side and new

bone formation on the tension side. Intraoral force affects

both the extracellular matrix (ECM) and the cells. However,

the cells respond both to the force, probably via specific

mechano-signal transduction pathways, and to the changes

(tissue injury) in the ECM. Only an in vitro cell culture model

can evaluate the direct cellular response to force excluding

cell-ECM interactions.

Mechanical loading affects the expression of RUNX2, the

master gene of bone development and bone homeostasis.

Its function is essential for the differentiation of osteoblasts

from undifferentiated progenitor cells. RUNX2 transcripts are

translated into protein at sites of bone and cartilage forma-

tion. Similar distribution patterns during intramembranous

and enchondral ossification in human fetal oro-craniofacial

tissues have been reported. Its involvement was elucidated

since mutations in the RUNX2 gene cause cleidocranial

dysplasia (CCD; MIM 119600), characterized by an over-

shooting development of tooth germs in the permanent

dentition and a dysplastic bone formation, particularly in

the craniofacial skeleton.

The objective of this study was to examine the effect of

pressure-type force, simulating orthodontic force on

RUNX2 and other genes’ expression in osteoblasts.

We simulated pressure mechanical load on mature

human osteoblasts in vitro using a centrifugal gravity field

of 200�g and varying load times. This force corresponds to

40.3 g/cm2, a typical intraoral occurring force. Before (pre-

load) and at defined times after force application (post-

load), total RNA was isolated. Gene expression of RUNX2

and other genes was measured using quantitative real-

time reverse transcriptase polymerase chain reaction (RT-

PCR). In comparison, unstimulated cells grown under iden-

tical conditions and processed in parallel were used as

negative controls.

The application of centrifugal force for 90 minutes

induced no significant response of the RUNX2 gene over a

period of 32 minutes postload. Only after 30 minutes of

force application a stimulatory effect was observed: At 2.5

minutes postload, an increase in RUNX2 expression by 1.7 ±

0.14 was detectable. This increase diminished rapidly with-

in the next 2 minutes. During the next 30 minutes postload,

the RUNX2 expression reached its pre-centrifugal level.

Our results showed a clear transient increase in RUNX2

gene expression caused by mechanical pressure followed

by a fast down-regulation back to its preload expression

level. RUNX2 gene expression behavior after mechanical

stimuli could be determined with a simple laboratory

setup. In a previously reported pilot study only the duration

of pressure was varied, which caused an immediate gene

Rather, the importance of the palatal implant seems to

come in the next step of the conventional treatment guid-

ance, namely during the incisors’ en masse contraction

phase when compared to the use of the intraoral tooth-

borne anchorage possibilities. In conclusion, it is not the

treatment time that is the main advantage of palatal

implants, but rather a predictable and high-quality treat-

ment outcome.

SL006

Pressure Simulation of OrthodonticForce

Uwe Baumert, I. Golan; Germany; M. Redlich, H. A. Roos, A. Palmon; Israel; D. Müssig; Germany

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ORTHODONTIC TOOTH MOVEMENT SL083


response. Now we have widened our research on human

gingiva and periodontal ligament fibroblasts using the

same stress protocol and extend the gene expression stud-

ies to other genes directly or indirectly controlled by

RUNX2.

With the knowledge of each additional variable the use

of standard values can be reduced when calculating indi-

vidual optimized force applications.

Objective

The purpose of this retrospective study was to identify and

quantify the effect of factors that influence orthodontic

treatment time.

Method

The sample consisted of 366 orthodontic patients (220

females and 146 males) age 10 to 20 years who were treat-

ed by one orthodontist, had undergone a complete course

of orthodontic treatment, and were treated in a single

stage with fixed appliances. Four categories of data

(sociodemographic characteristics, malocclusion character-

istics, treatment method, and patient cooperation) were

collected and analyzed.

Results

The average treatment time was 23.5 months (range, 12 to

37 months; SD, 4.7). A multiple regression model explained

38% of the variance and identified nine significant vari-

ables. Five of these variables were pretreatment character-

istics: male gender, maxillary crowding of 3 mm or more,

Class II molar relationships, and a proposed treatment plan

involving extractions or delayed extractions. The remaining

variables (three of which were associated with patient co-

operation) were poor oral hygiene, poor elastic wear, brack-

et breakages, and brackets rebonded for repositioning.

Conclusions

Orthodontic treatment time is influenced by a number of

patient characteristics and clinical decisions. It is possible to

predict estimated treatment time for a patient using a small

number of personal characteristics and treatment plan

decisions.

SL083

Factors Influencing Treatment Time inOrthodontic Patients

Kirsty Skidmore, W. M. Thomson, W. J. Harding, K. J. Brook; New Zealand

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SHORT LECTURE


Aim

The prefabricated archwire ICKARE is an original system

that allows simultaneous or step-by-step retraction and

intrusion of incisors with fine-tuning of the incisors’ torque.

Subject and Description

The ICKARE archwire system consists of three segments

(available in 0.18 and 0.22 inches). The anterior segment of

the archwire is full-sized for torque control and is connect-

ed to two smaller rectangular steel lateral segments, thus

allowing sliding mechanics. However, according to clinical

requirements, it is possible to choose between different

sizes for the anterior segment. The anterior segment is con-

nected to the lateral segments via crimping components.

Two additional power arms (0.32 inches; vertical part, 5

mm, horizontal part, 7 mm, ending with a small hook) are

soldered to the rectangular crimping components.

Operation

A power chain is attached from the molar band to the

power arm hook. The under-dimensioned lateral segments

of the archwire slide posteriorly with low friction. A

typodont study shows any possible incisor movement

(intrusion, extrusion, lingual tipping, lingual root torque or

translation) during retraction according to the positioning

and shaping of the horizontal part of the power arm, which

allows the desired bowing effect of the archwire. It is then

possible to decide where the resultant forces will pass:

above, under, or through the center of resistance of the

incisor unit.

Results

The findings of a study involving 200 cases treated with the

ICKARE archwire confirm the typodont study results.

Conclusion

Just one archwire is enough to perform any incisor move-

ment desired during incisor retraction. The ICKARE archwire

makes orthodontic therapy easier, more efficient, and more

reliable.


The ICKARE Cranium-Arch System forIncisor Retraction and Intrusion

Jean-Francois Ernoult, R. Bonnefont, J. Casteigt, C. Charron; France

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Using randomized controlled trial methodology, the

aim of this study was to evaluate and compare the

treatment effects of an extraoral appliance (EOA)

and an intraoral appliance (IOA) for distal movement of

maxillary first molars.

A total of 40 patients (mean, 11.5 years; SD, 1.29) at the

Orthodontic Clinic, National Health Service, Skane County

Council, Malmö, Sweden, were randomized to receive treat-

ment with either extraoral traction (cervical headgear) or

an IOA using superelastic coils for distal movement of max-

illary first molars. The inclusion criteria were a nonextraction

treatment plan, a Class II molar relationship, and maxillary

first molars in occlusion with no erupted maxillary second

molars. The outcome measures to be assessed in the trial

were treatment time; cephalometric analysis of distal molar

movement; anterior movement of maxillary central inci-

sors, ie, anchorage loss; and sagittal and vertical skeletal

positional changes of the maxilla and mandible.

In the IOA group, the molars were distalized during an

average time of 5.2 months, whereas in the EOA group the

corresponding time was 6.4 months (P < .01). The mean

amount of distal molar movement was significantly higher

in the IOA group than in the EOA group (3.0 vs 1.7 mm; P <

.001). Moderate anchorage loss was produced, with the IOA

implying increased overjet (0.9 mm), whereas the EOA cre-

ated decreased overjet (0.9 mm).

It can be concluded that the IOA was more effective

than the EOA in creating distal movement of the maxillary

first molars.

SHORT LECTURE



Extraoral Versus Intraoral Appliance for Distal Movement of Maxillary FirstMolars: A Randomized Controlled Trial

Lars Bondemark, I. Karlsson; Sweden

Aim

To monitor the global response of periodontal ligament

(PDL) fibroblast cells to simulated orthodontic force. The

cellular global response was evaluated on two levels: gene

response (genomics) and protein synthesis (proteomics).

Materials and Methods

Human PDL fibroblasts (the primary tissue that responds to

orthodontic force) were subjected to either pressure- or

tension-type in vitro mechanical forces resembling ortho-

dontic force.

SL101

Genomics and Proteomics Response ofPeriodontal Cells to Orthodontic Force

Meir Redlich; Israel; I. Golan, D. Müssig; Germany; A. Palmon, E. Reichenberg, I. Bar Kana; Israel

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Genomics

In contrast to conventional methods for gene expression

profiling, by which only the expression of one or a few

genes can be analyzed in one assay, a gene array technique

enables analysis of the expression of multiple genes in a

single assay. More than 8,000 human genes can be

assessed in a single experiment.

Proteomics

Recently, in the post-genome era, proteome analysis has

rapidly developed and is now widely accepted as a tech-

nology complementing genetic profiling. Proteomics appli-

cation on protein mixtures provides information about

multiple gene products by means of expression levels and

posttranslational modifications and is very powerful in the

characterization of diseased versus normal cells.

Results

Genomics

Hundreds of genes were immediately affected by the sim-

ulated orthodontic force. The most conspicuous finding

was up-regulated genes associated with signal transduc-

tion events. Other genes affected by the force in either up-

or down-regulation were inflammatory and bone remodel-

ing genes.

Proteomics

In response to force, the PDL cells expressed about 900

new proteins not expressed by the controls; an increase in

the expression of many other proteins also occurred. The

force down-regulated a few proteins while others remained

unchanged. Thus, the effect of force seems to be global.

The expression of various isoforms of vimentin, a cytoskele-

ton protein directly associated with both signal transduc-

tion processes and maintaining cell integrity, is highly

important.

Conclusions

The immediate cellular response to orthodontic force is

dual. First, the mechanical stimulus is transduced to biolog-

ical signals, and second, self-defense mechanisms are

recruited to maintain cell vitality.

SL102

Slow Maxillary Expansion with NickelTitanium

Derek Mahony; Australia

T here is uniform agreement among prominent ortho-

dontic researchers, such as Burstone and Ricketts,

about the need to correct mesiopalatal rotations of

the maxillary first molars to gain 1 to 2 mm of arch length

per side and prevent the overeruption of the mandibular

second permanent molar that is so frequently observed

during Phase 1 treatment.

The problem has been to find an appliance that allows

molar rotation and facilitates arch development simultane-

ously. McNamara has stated that an estimated 25% to 30%

of all orthodontic patients can benefit from maxillary

expansion, and 95% of Class II cases can be improved by

molar rotation, distalization, and expansion.

The traditional forms of maxillary expansion such as the

Haas and Hyrax appliances can correct transverse maxillary

discrepancies but will not rotate or distalize molars. Further-

more, Hicks has shown rapid maxillary expansion to pro-

duce heavy forces that result in bone fragments, bleeding,

microfractures, cyst formation, vascular disorganization,

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ORTHODONTIC TOOTH MOVEMENT SL118


and connective tissue inflammation in the suture site dur-

ing the rapid expansion.

Story and Ekstrom have suggested that slow expansion

procedures allow physiologic adjustments and reconstitu-

tion of the sutural elements over a 30-day period. Increased

fibroblastic, osteoclastic, and osteoblastic activity seems to

occur when the maxilla is widened slowly. Furthermore, the

neuromuscular adaptation of the mandible to the maxilla

in slow expansion allows for normal vertical closure.

This presentation discusses a new fixed-removable nick-

el-titanium appliance, the NPE2, which delivers a uniform,

slow, continuous force for maxillary expansion, molar rota-

tion, molar distalization, and arch development. The appli-

ance expands at a rate that maintains tissue integrity dur-

ing remodeling of the teeth and bone. To put it simply, as

the palate expands, the bone regeneration matches the

rate of expansion.

The NPE2 delivers a force of 350 g in 3-mm increments,

and, as the force application is preprogrammed, it is self

limiting. This action is made possible by harnessing the

unique property of nickel-titanium in regard to shape

memory and transition temperature. This allows the NPE2

to constantly return to a set shape after deformation.

The benefits of the NPE2 include:

• Better physiologic response and stability

• Less tipping of abutment teeth

• Buccal or distal rotation of molars

• Shorter retention period

• No need for laboratory procedures

• Frequent operator or patient adjustments not required

• Less patient discomfort

• Improved hygiene

• Less problematic effects on speech and eating

It is well known from the literature that when an ortho-

dontic force is applied on a tooth, that tooth may

undergo some root resorption. For example, after rapid

palatal expansion (RPE), extensive root resorption may

occur on the teeth through which the expansion force was

transmitted to the maxilla, namely the anchored teeth. As

the RPE treatment proceeds, movement of the central inci-

sors, to which no force was directly applied, has been

described. This movement consists of a mesial tipping fol-

lowed by a recovery of the original axial root angulation.

However, to date, no extensive research has been pub-

lished concerning root resorption of the nonanchored inci-

sors to which forces are possibly applied indirectly during

expansion, since movement of these teeth occurs. Four-

teen cats were divided into a treated group (n = 10) and a

control group (n = 4). Animals in the treated group received

a RPE treatment consisting of an active phase of 25 days, a

retention phase of 60 days, and a relapse phase of 60 days.

Standardized occlusal radiographs were taken periodically.

At the end of the relapse phase, all animals were sacrificed.

The maxillary block was decalcified and sequential frontal

slides were prepared. The root resorption was assessed

from the histologic preparations. The changes in mesiodis-

tal tip angle and in root proximity were measured from the

radiographs taken during four time points: pretreatment,

active, retention, and relapse phases.

Results

Extensive apical root resorption developed on the nonan-

chored first maxillary incisor. The root resorption area on

SL118

Maxillary Incisor Root Resorption After Rapid Palatal Expansion in Cats

Thierry Levy; France; A. D. Vardimon, M. Weinreb; Israel

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the first maxillary incisor was more than 750-fold greater in

the treated group than in the control group (P < .001).

The root resorption area on the second maxillary incisor

was slightly greater in the treated group than in the control

group, but the difference was not significant (eg, on the left

side it was 1.43-fold greater in the treated group than in

the control group, P = .499). The maxillary incisors tipped

mesially during the active and the retention phases. This

tipping was accompanied with an increase in root proxim-

ity. Partial recovery toward the original axial root angulation

occurred during the relapse phase. The extent of tipping of

the first maxillary incisor, which reached 27 degrees (P <

.001), was more than 2.5-fold greater than that of the sec-

ond maxillary incisor (P < .001), and it resulted in a more

than 17-fold greater increase in root proximity for the first

maxillary incisor than for the second maxillary incisor (P <

.01 on the right side and P < .05 on the left side). The study

clearly demonstrates that there is a high susceptibility of

the first maxillary incisor to undergo root resorption during

RPE treatment and that excessive root proximity between

apices of the first and the second maxillary incisors, which

presumably results in an excessive pressure on the apical

root surface of the first maxillary incisor, is involved in the

process of root resorption of the first maxillary incisor. This

is corroborated by the increased sensitivity to root resorp-

tion on the distal side of the root of the first maxillary

incisor (the distal side was 5-fold more affected than the

mesial side), and by the correlations found for the first max-

illary incisor between root resorption and root proximity

(eg, r = 0.723 and P < .01 on the right side) and between

root resorption and mesiodistal tip angle (eg r = –0.927 and

P < .001 on the right side).

T he aim of this retrospective analysis was to study the

relationship between initial position of impacted

maxillary canines (as seen in panoramic radiographs)

and treatment length, periodontal status of canines after

orthodontic treatment, and possible root resorption of

neighboring teeth.

Fifty impacted canines (n = 50) randomly selected from

three private practices were chosen for this study. Thirty-

one were located palatally and 19 labially. In 46 impacted

canines an open surgical approach was used. Results show

a relationship between initial position as seen in the

panoramic radiographs and traction length. We considered

traction length the time from surgical exposure until the

canine was leveled. The more initial canine inclination, the

longer the duration of traction, and we found a cut-off

value of 35 degrees with at least 12 months of orthodontic

traction time.

Canines in area 2 (between the roots of the lateral and

central incisors) presented more root resorption in the lat-

eral incisor. Labially positioned impacted canines showed a

poor periodontal outcome in terms of gingival recession,

gingival inflammation, and loss of bone support. These

probably would have improved with a different surgical

technique.

The most important aspect of this study is the new data

given for predicting treatment time, possible periodontal

problems, and root resorption risk in neighboring teeth

from the study of the initial position of the canine.

SL119

Impacted Canines: Treatment Duration,Periodontal Status, and Root Resorption.Analysis of 50 Cases

Ignacio Zamalloa Echevarria; Spain

SHORT LECTURE

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Osteopontin Deficiency Enhances ToothMovement and Suppresses RootResorption

Chooryung Judi Chung; Japan; S. R. Rittling, D. T. Denhardt; UnitedStates; A. Nifuji, M. Noda, K. Soma; Japan

SHORT LECTURE


Osteopontin (OPN) is a major noncollagenous bone

matrix protein known to induce mechanical

stress–related bone remodeling. Therefore, we elu-

cidate the role of OPN as a candidate regulator of ortho-

dontic tooth movement in vivo by comparing tooth move-

ment between OPN-deficient mice (N = 41, age greater

than 10 weeks) and wild-type mice (N = 27, age greater

than 10 weeks). Tooth movement was induced by connect-

ing a nickel-titanium (NiTi) coil spring to the maxillary right

first molar, which induces mesial tooth movement for peri-

ods of 7 to 21 days. The maxillary left first molar served as

an untreated internal control. The amount of tooth move-

ment was compared between wild-type and OPN-deficient

mice using soft X-ray and micro CT scanning. In addition,

new bone formation, bone resorption, and root resorption

were compared between wild-type and OPN-deficient mice

by using bone histomorphometry and micro CT scanning.

Statistical analysis was performed based on the Mann-

Whitney U-test. A p-value less than 0.05 was considered sig-

nificant.

As a result, tooth movement was significantly enhanced

in OPN-deficient mice during the intermediate period

compared to the wild-type controls (P < .05). OPN deficien-

cy significantly enhanced new bone formation induced by

tooth movement based on the quantification of mineral

apposition rate (MAR; P < .05) and bone formation rate (BFR;

P < .05) compared to the wild-type controls. Although the

numbers of osteoclasts were similar between the two

groups, the number of odontoclasts was significantly

reduced in the OPN-deficient group (P < .05) compared to

the wild-type controls. Micro CT scanning of the root also

indicated reduction of root resorption in OPN-deficient mice

compared to the wild-type mice (P < .05).

These results indicate that OPN is a negative regulator of

tooth movement and new bone formation in vivo. In addi-

tion, OPN also increases the level of root resorption. There-

fore, targeted regulation of OPN may provide smooth and

secure tooth movement.


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