Coordinated Arch Development Versus Expansion

For more than a century, the controversy of treating tooth size/arch length discrepancies, with or without extraction of permanent teeth, has been at the forefront of diagnosis and treatment planning.^1-6

So here we are at the beginning of the 21st century, back to a predominantly nonextraction approach—an approach that was discarded 70 years ago. What changes have taken place to influence our profession to such a degree? Certainly, our philosophy of treatment timing has changed radically. Instead of waiting for the completion of second molar eruption and missing the pubertal growth spurt, we generally believe that basal discrepancies are positively impacted when we use the greatest growth increments to our advantage. Beginning in the 1960s, and after encountering significant resistance for almost 15 years, extraoral appliances, such as headgears and functional appliances to temporarily redirect growth, gained widespread popularity and considerable support in the literature.^7-16

That said, the management of nonextraction cases has seen the introduction of a plethora of appliances for both maxillary and mandibular (basal) discrepancies. When treating a Class II skeletal discrepancy in a growing patient, the clinician may have to rely on cephalometrics and facial analyses to discern whether a protruded maxilla or retruded mandible is the primary cause. Most cases do not present a clear picture as to which one is the primary cause, especially in a growing patient.

Two Class II Approaches

One camp of orthodontists uses mostly mandibular propulsive appliances to reposture the mandible forward and simultaneously redirect maxillary growth.^17-22 This philosophy is somewhat similar to Angle’s philosophy more than 100 years ago. In denying the effectiveness of extraoral force, he relied on heavy Class II elastics to favorably influence growth.¹ While providing positive orthopedic effects, side effects of this method include a displacement of the anterior teeth labially, which is true with any Class II system. If lower anterior teeth are upright, crowded, or procumbent to begin with, this appliance will further displace these teeth beyond the “neutral zone,” resulting in a significant long-term relapse. If lower incisors are initially recumbent, these appliances can certainly produce a positive result. Therefore, proper case selection is imperative.

Another camp uses extraoral forces such as headgears to redirect maxillary growth and allow mandibular growth to “catch up.”^7,8,23 This method, while very effective, relies on patient compliance, and therefore the results will vary. Since the headgear is a maxillary arch appliance, the mandibular incisor position is essentially unaffected. Thus, one could argue that isolating the mandibular arch during Class II skeletal correction may have a positive effect on the long-term stability of mandibular incisor position.

Tooth-Size and Arch-Size Discrepancies

This leads us to the treatment of tooth-size/arch-size discrepancies in the nonextraction case. In extraction treatment, significant crowding is corrected with the removal of permanent dental units—usually bicuspids. However, in the nonextraction case, the deficiency in arch length or arch perimeter is treated with expansion of the arch and/or interproximal reduction. Interproximal reduction is usually relegated to moderate discrepancies (2 mm to 4 mm), while greater discrepancies are treated with expansion.

Types of Expansion

Expansion, according to McNamara,²⁴ can be subdivided into arbitrary categories such as orthodontic, passive, and orthopedic.

“Orthodontic” expansion could also be described as any “mechanical” expansion that employs brackets and archwires, finger springs, removable expansion plates, or quad-helix-type appliances. Generally, these devices tip the crowns labially and the roots lingually. If these movements violate the “neutral zone,” the surrounding musculature may provide an opposing force, leading to long-term relapse.^25,59 To help retain the position of the crowns, the roots should be torqued underneath the crowns to establish the forces of occlusion through the long axes of the teeth.

“Passive” expansion refers to the blocking of the labial and buccal musculature from the arches. When the orthodontist temporarily removes their influence on the teeth, a widening of the dental arches will frequently occur. This expansion is not produced via biomechanical forces, but rather intrinsic forces such as the tongue. Appliance examples include the lip bumper^26,27 and the FrÄnkel appliance.²⁸

“Orthopedic” expansion refers to changes that primarily occur in the underlying skeletal structures rather than the movements of teeth within the alveolus.^29-34 Orthopedic expansion not only separates the midpalatal suture, but it also affects the circumzygomatic and circummaxillary sutural systems.³⁵ New bone is deposited at the expansion site within 3 to 6 months to re-establish the integrity of the suture.³⁰

Orthopedic expansion, similar to orthodontic expansion, does not directly influence the opposing forces of the surrounding soft-tissue envelope. Thus, the general consensus of the orthodontic community, realizing the possibility of significant relapse, is to “overexpand” the maxilla to almost a complete buccal crossbite. The greatest efficacy of maxillary expansion, at both the skeletal and alveolar levels, is usually during the mixed and adolescent dentitions, prior to the pubertal peak of growth and development.

When comparing rapid maxillary expansion to “slow” maxillary expansion long-term, there were no clinically significant differences in anteroposterior and vertical maxillary changes³⁶ or mandibular behavior.³⁷ One adolescent dentition study initially used rapid maxillary expansion (RME) at one quarter-turn twice a day until the suture was determined to be opened from occlusal films (5 to 7 days). The screw was then turned three times a week until a 2-mm overexpansion was achieved (about 4 months). After evaluating the patient sample about 2½ years after retention, the dental and skeletal changes in the transverse dimension exhibited a high degree of stability.³⁸ Their hypothesis was that slower expansion produced less tissue resistance and stimulated the adaptation process in the circummaxillary structures. These events would minimize any relapse tendency in the long term.

Maxillary expansive forces appear not to be restricted to intermaxillary sutures, but are also distributed to the sphenoid and zygomatic bones and other related structures in the craniofacial complex.³⁹ Histologic studies on animals have also demonstrated signs of increased cellular activity at various cranial sutures.^40-44 The available data on suture mechanics appears to have a common theme that mechanical forces regulate sutural growth by inducing sutural mechanical strain. Various orthopedic devices, including headgears, facemasks, and functional appliances, may induce sutural strain, resulting in a modification of natural sutural growth.^45,46

Using the effects of expansion on modifying natural, sutural growth, several investigators have applied various headgears for the treatment of skeletal Class II and Class III malocclusions.^47-54 Although studies have emphasized the importance of starting earlier in the growth cycle to gain a maximum effect,^55-58 there do not appear to be any statistically significant differences between specific entry points in the growth cycle.⁴⁹ With the exception of one investigation,⁴⁹ most studies applied the headgears after the rapid maxillary expansion (at two quarter-turns per day) had been completed.^47,50-52

Coordinated Arch Development Versus Expansion

Coordinated Arch Development® (CAD) is a term I introduced at the 1996 AAO scientific session, together with my partner of 30 years, Jerry Klein, DDS. It is a combined orthopedic/orthodontic approach to long-term stability, applied during periods of optimum growth and development. The approach is based on the following:

1. Early treatment of maxillomandibular skeletal discrepancies, preferably in the late mixed dentition. The roots of the “CAD” philosophy are credited to my friend and mentor Norman Cetlin, DMD, of Boston. He emphasized the importance of first molar position over incisor position as the cornerstone of long-term stability. He also preferred the late mixed dentition as the entry point of treatment to utilize “E” space for tooth-size/arch-size discrepancies, when distal movement of first molars could be enhanced by the absence of the unerupted second molars.
2. Uprighting upper and lower posterior segments sagittally and transversely, using slow expansion for a greater effect in the same time frame. Uprighting is done in equal increments to prevent the violation of the “neutral zone” during expansion, with the goal of placing the segments well within cancellous bone to allow the optimization of axial inclinations to accept and distribute the functional forces of occlusion through their long axes.
3. Controlling the functional occlusal plane by advocating intra-arch mechanics, thereby minimizing the side effects of mechanotherapy.
4. Re-educating the intraoral musculature during dimensional changes to the arches by utilizing lip bumpers, inner bows of facebows, and myofunctional therapy when necessary.

CAD distinguishes itself from expansion by the following;

1. CAD addresses all three dimensions simultaneously. Expansion focuses on the transverse dimension.
2. CAD distalizes the arches during expansion to create a wider dimension of the arch, thereby reducing the amount of necessary expansion. Expansion solely relies on transverse changes.
3. CAD coordinates upper arch dimensional changes with lower arch dimensional changes to maximize intercuspation throughout treatment. Maxillary expansion tends to overcorrect the maxillary arch with no corresponding changes in the lower arch.
4. CAD attempts to place and maintain the teeth in the “neutral zone” throughout treatment. RME or orthodontic expansion tends to violate the “neutral zone” by placing the teeth into the space of the surrounding musculature. If the musculature cannot adapt to the new transverse dimension, relapse of the teeth toward the “neutral zone” may occur in the long term.
5. CAD emphasizes the importance of placing the teeth well within cancellous bone during expansion by slowly and simultaneously expanding and distalizing in relatively equal increments. This allows the integrity of the periodontium to be maintained. In mesially displaced arches (Class II), expanding teeth that have already been placed in areas of narrower cancellous bone could certainly compromise the integrity of the periodontium.
6. CAD attempts to “re-educate” the surrounding musculature back to its original resting length by utilizing lip bumpers and the inner bows of facebows. There is no attempt to re-educate the soft tissue envelope in pure expansion.

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Raphael L. Greenfield, DDS, MScD, has been in private practice for more than 30 years. He is a diplomate of the American Board of Orthodontics and a referee for the American Journal of Orthodontics and Dentofacial Orthopedics. This article was supported by an educational grant from Ortho Classic. He can be reached at

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