01 - Space Management in Preadolescent Children

Mixed Dentition Analysis Review

Mixed Dentition Analysis Review

The most readily identifiable orthodontic problem in the early mixed dentition is dental crowding. Parents initially become concerned when the larger permanent incisors replace nicely aligned and spaced primary incisors in the early mixed dentition and crowding/malalignment is obvious. Parents want to know how this will impact the long-term alignment of the permanent teeth and usually seek advice from their family dentist initially. Family dentists should be able to

• Provide an answer based on their knowledge of dental development,
• Perform a mixed dentition space analysis,
• Interpret the results of the analysis, and
• Suggest appropriate interventions.

The normal condition in the primary dentition is interdental spacing of the primary incisors (image 1). The primate spaces between the lateral incisors and canines in the maxillary arch, and between the canines and first molars in the mandibular arch of the primary dentition, provide space that is important in allowing alignment of the larger permanent incisors (image 2). As a general rule, children who present with crowded primary incisors will have major crowding problems in the permanent dentition (image 3). Spacing in the primary dentition is the norm. Perfectly aligned primary teeth with no spacing or crowded teeth are not normal.

Image 1, Spacing of the primary incisors: Interdental spacing of the primary incisors, as in this child, is normal.	Image 2, Primate spaces in the primary dentition: The crowns of the developing permanent incisors lie lingual to crowns of the primary incisors.
Image 3, Crowding of the primary incisors: This child has significant crowding of the primary dentition, which is indicative of significant future crowding in the permanent dentition.

Mixed Dentition Transition

During the early mixed dentition the larger permanent incisors replace the smaller primary incisors, and the majority of children develop some degree of incisor crowding.

Graphs from Moorrees and Chadha (Angle Orthodontist 35, 1965) illustrate the amount of average crowding or spacing present in the incisor segments for males and females during the transition from the primary dentition to the early mixed dentition (Images 1-5). In each of these graphs, M represents the eruption of the permanent molar; I1 and I2 represent the eruption of the central and lateral incisor, and C the eruption of the permanent canine.

Prior to the eruption of the first permanent molars there is an average of about 2 mm of spacing in the maxillary incisor segment (images 1 and 2) and about 1 mm of spacing in the mandibular incisor segment (images 3 and 4). As the first permanent molars erupt, they drift forward, closing some of the interdental spacing found in the primary dentition. This is called the early mesial shift.

As the larger permanent incisors erupt and replace the primary incisors, additional crowding occurs. In the maxillary arch, males (image 1) tend to have no incisor crowding, while most females (image 2) develop minor incisor crowding (<1 mm) when the permanent incisors erupt. In the mandibular arch both males (image 3) and females (image 4) appear to develop 2 mm of incisor crowding with the eruption of the lateral incisors. In all four cases, once the primary canines exfoliate this initial incisor crowding resolves.

Some parents may become quite concerned when the nicely aligned and spaced primary incisors are replaced by crowded and irregular permanent incisors in the early mixed dentition. This information can be used to reassure parents that some degree of initial crowding is quite normal in the early mixed dentition (image 5).

Image 1, Maxillary Arch Crowding – Males: Maxillary crowding in males in the early mixed dentition.	Image 2, Maxillary Arch Crowding – Females: Maxillary crowding in females in the early mixed dentition.
Image 3, Mandibular Arch Crowding – Males: Mandibular crowding in males in the early mixed dentition.	Image 4, Mandibular Arch Crowding – Females: Mandibular crowding in females in the early mixed dentition.
Image 5, Crowding by Gender and Arch: Crowding in males and females in both arches in the early mixed dentition.

Dimensional Changes

Dental crowding is a function of two things: (1) the size of the teeth, and (2) the size of the dental arch supporting the teeth. Many parents are mystified when orthodontists or dentists suggest that extraction of teeth is required in young children who have not started their pubertal growth spurt and have a lot of growth potential remaining. Dentists must have a basic understanding of the growth and development of the dental arches to answer these concerns.

One can graphically summarize the dimensional changes in the maxillary and mandibular dental arches from ages 6-18 years. In the maxillary arch (image 1) there is a slight decrease in arch length and a slight increase in arch circumference (+1 mm). The maxillary incisors erupt into a more facial position, which increases arch length, but the loss of leeway space also reduces arch length. In the mandibular arch (image 2) there is a reduction in both arch length (-1 mm) and arch circumference (-4 mm) with a slight increase in canine and molar width. The mandibular incisors tend to upright over this period of time, which supplements effects due to the loss of leeway space.

In patients with moderate and more severe crowding, these average growth changes in the dental arches are insufficient to accommodate the larger teeth in both arches (image 3).

Image 1, Growth changes in the maxillary arch.: Growth changes in the maxillary arch between 6-18 years of age.	Image 2, Growth changes in the mandibular arch.: Growth changes in the mandibular arch between 6-18 years of age.
Image 3, Comparison of maxillary & mandibular arch changes: Comparison of growth changes in the dental arches between 6-18 years of age.

Space Analysis Assumptions

In the early mixed dentition, we know that incisor crowding is very common, especially in the lower arch, and that future growth of the dental arches will most likely not accommodate a significant amount of dental crowding. The Mixed Dentition Space Analysis gives dentists some ability to predict future dental crowding (image 1).

As you recall from earlier courses, mixed dentition space analysis has a number of underlying assumptions:

1. there is a reasonably good correlation between the size of the erupted mandibular incisors and the permanent canines and premolars
2. prediction tables are valid for your patient’s sex and ethnicity
3. all succedaneous teeth are present and developing normally
4. arch dimensions do not change appreciably during growth
5. molar position is stable.

Think about these assumptions before you begin the space analysis—for some patients all the assumptions are not correct, and you’ll have to take that into account as you interpret the results.

Size of Unerupted Permanent Teeth

The UNC Space Analysis Form uses the Tanaka and Johnston space analysis procedure to predict the mesio-distal width of the unerupted canines and premolars. No radiographs or prediction tables are required to perform this analysis, an advantage over in other analyses. Upper and lower dental casts with erupted permanent incisors and a measuring device (i.e., Boley gauge) are all that are needed.

The first step in the Tanaka and Johnston space analysis is the measurement of the erupted lower incisors using a Boley gauge or dividers (image 1). The mixed dentition analysis (MDA) assumes that there is a correlation between the width of the lower incisors and unerupted canines and premolars in both arches.

The width of the unerupted permanent canine and premolars in each buccal segment is determined by the following simple calculation:

Mandible: half the sum of the widths of the mandibular incisors + 10.5 mm

Maxilla: half the sum of the widths of the mandibular incisors + 11.0 mm

The key assumption, of course, is that there is a good correlation between the size of the mandibular incisors and the unerupted canines and premolars. If there is an obvious discrepancy between the size of the mandibular centrals and laterals, as sometimes occurs, that would produce an over-estimate of the size of the unerupted teeth.

Available vs. Required Space

The space available in the dental arch is determined by measuring the arch segments between the mesial surfaces of both first permanent molars (image 1). One must estimate an ideal dental arch where the teeth are arranged in a stable position in the alveolar bone. Using a Boley gauge or dividers, the arch segments are as follows:

1. Mesial of first permanent molar to mesial of primary canine
2. Mesial of primary canine to the mesial of the permanent central
3. Mesial of permanent central to mesial of primary canine
4. Mesial of primary canine to mesial of first permanent molar.

The space required to accommodate the permanent teeth is determined in each arch by adding together:

1. The sum of the incisor widths (image 2)
2. The predicted widths of the unerupted left canine and premolars
3. The predicted widths of the unerupted right canine and premolars

Space discrepancy (crowding or spacing) is calculated in the mandibular arch (image 3) and the maxillary arch (image 4) by:

Discrepancy = Total Space Available – Total Space Required

Image 1, Space Available in the maxillary and mandibular arch: The space available in the dental arch is determined.	Image 2, Incisor width in the maxillary and mandibular arch: The width of the four incisors in the maxillary and mandibular arches is recorded.
Image 3, Mandibular Space Analysis: The discrepancy (crowding or spacing) in the mandibular arch is calculated.	Image 4, Maxillary Space Analysis: The discrepancy (crowding or spacing) in the maxillary arch is calculated.

Considerations in Interpreting Results

The endpoint of the analysis is a number for each arch that may be either positive (spacing) or negative (crowding). As you learned previously, these numbers have very limited significance when viewed alone. The practitioner must now refocus on other relationships to interpret the results for each individual patient. These relationships are included in sections 7-10 of the UNC Space Analysis Form (image 1) and include:

• Lip posture
• Lip competence
• Incisor position
• Skeletal jaw relationship
• Future molar shift (leeway space)
• Occlusal relationship of the 1st permanent molars

The facial profile analysis (image 2) is used to assess skeletal jaw relationship and lip posture. These relationships are used in sections 7 to 10 of the space analysis to interpret the results of the space analysis.

The results of the profile analysis are crucial in assessing crowding and incisor position. Protrusive lips, significant lip incompetence (>4 mm) and proclined incisors indicate dental crowding even if the teeth are aligned on the dental arches. These patients usually require extraction of permanent teeth to position the lips in acceptable positions, reduce lip incompetence, and upright the incisors in the alveolar bone. The profile view on the right shows lip and mentalis strain, while the view on the left shows lip incompetence (image 3). These relationships must be considered alongside the space analysis numbers.

Image 1, Interpretation of Numerical Results: Sections 7-10 of the UNC Space Analysis.	Image 2, UNC Facial Profile Analysis: The UNC Facial Profile Analysis assesses skeletal jaw relationship and lip posture.
Image 3, Lip incompetence and incisor protrusion: Lip protrusion and incompetence due to protrusive incisors.

Interpretation of Results

Now that you have completed a mixed dentition analysis and determined the amount of predicted crowding or spacing for a patient, how do you interpret the numbers and use the information in planning treatment?

When classifying generalized crowding (where the discrepancy numbers would be negative) the following clinical descriptions can be used:

• 0-2 mm/arch: mild crowding
• 2-4 mm/arch: moderate crowding

• 4 mm/arch: severe crowding

• 10 mm/arch: very severe crowding

The type of intervention depends on:

• Amount of crowding (mild, moderate, or severe)
• Location of crowding (localized or generalized)

Important questions should be considered:

• Was there initially sufficient space, and loss of a primary tooth resulted in localized crowding?
• Will a primary tooth have to be extracted, and will intervention to prevent space loss be required?
• In mild cases of crowding, can the leeway space be used to align the teeth?

Types of Treatment for Space Problems

To effectively diagnose and treat space problems in the mixed dentition, dentists must be familiar with four terms:

1. Space maintenance
2. Space regaining
3. Space management
4. Serial extraction

The definition of each of these terms is based on the results of the mixed dentition analysis. The degree and location of crowding will determine which of the above strategies is employed in the mixed dentition.

The first three techniques are suggested for children in the mixed dentition with mild crowding, and serial extraction is suggested for children with severe crowding who will receive later treatment with a fixed orthodontic appliance. Using these techniques during the mixed dentition may simplify future comprehensive orthodontic treatment in the permanent dentition. Each one of these terms will be explained in separate sections of this module to help clarify the differences.

Children with more severe generalized crowding in the mixed dentition will need comprehensive fixed orthodontic treatment, involving arch expansion or extraction of permanent teeth, and may be best treated by an orthodontist.

Space Maintenance

Space Maintenance

In a patient with adequate space for the permanent teeth, space maintenance is the intervention used to prevent loss of space after extraction of a primary first or second molar. Once a primary molar is extracted, mesial drift and distal tipping of adjacent teeth will occur, reducing the space available for eruption of the underlying permanent premolars.

A number of factors must be evaluated prior to the initiation of space maintenance:

1. Space analysis should confirm that there is adequate space available.
2. When was the primary molar extracted? Space loss almost always starts immediately after the loss of a primary molar. If the tooth was lost more than 3 months previously, space loss probably has occurred, and then space regaining will be required rather than space maintenance.
3. When will the underlying permanent tooth erupt? If the permanent tooth will require more than 6 months to erupt, space maintenance will be required. Eruption charts give average values for the general population; one must remember that individual variation exists (image 1). Dental age as determined by assessing the general eruption schedule and root development (image 2) is more informative than chronological age. A permanent tooth normally erupts when 2/3 to 3/4 of root development is complete, and in general, a permanent tooth takes about 1 month to erupt through 1 mm of overlying bone. Extraction of primary teeth can also either accelerate or slow the eruption of underlying permanent teeth depending on root development.
4. Is there a permanent successor tooth present (image 3)? If not, long-term maintenance of the space for eventual prosthetic replacement may or may not be the best plan. This must be weighed against the possibility of closing the space orthodontically or forgoing space maintenance and allowing the permanent teeth to drift into the extraction site to close the space.

Image 1, Tooth eruption and development chart.: Tooth eruption and development chart.	Image 2, Incomplete root development: Eruption usually occurs when the root is 2/3rds to 3/4th complete. These erupting central incisors are at that stage.
Image 3, Congenitally missing second premolar: Note that despite the congenitally missing 2nd premolar is missing, resorption of the mesial root of this 2nd primary molar has already begun.

Removable vs. Fixed Space Maintainers

A number of different types of space maintainers can be used after the loss of primary teeth. Generally the appliances can be classified as:

• Fixed (cannot easily be removed by the patient or adjusted in the mouth) (image 1)
• Removable (can be removed by the practitioner for minor adjustments or can be removed by the patient to allow easier access for oral hygiene)(image 2)

With any type of appliance, adequate follow-up is crucial. Space maintainers are not an “insert it and forget it” type of treatment. All patients must be on a regular recall schedule and have adequate oral hygiene to ensure success.

Patients with space maintainers are instructed to avoid hard, sticky, and chewy foods to decrease the chance of damage and loosening of appliances. Fixed appliances reduce the chance of failure, but some children do not follow these suggestions very well and damage even the best-designed fixed space maintainers.

The adaptation of orthodontic bands on primary teeth, especially first primary molars, can be difficult. This reduces the effectiveness of fixed banded appliances on these teeth. But this is even more of a problem with removable appliances, since primary teeth do not have a pronounced height of contour that can be used to engage retentive elements such as wire clasps.

In general, fixed space maintainers are more effective in children than removable space maintainers.

Image 1, Fixed space maintainers: Crown-and-loop and band-and-loop appliances are examples of fixed space maintainers.	Image 2, Removable space maintainers: A removable appliance is an alternative design for bilateral space maintenance.

Fixed Space Maintainers

Fixed space maintainers require minimal cooperation by the patient (beyond not deliberately breaking them), and usually are preferred for that reason. There are several types:

1. Loss of a single tooth. Band and loop space maintainers are most commonly used after the extraction of a single primary first molar in the primary or mixed dentition (image 1). Bilateral band and loop space maintainers are indicated if both first primary molars are lost in an arch prior to the eruption of the permanent incisors. A variation of this appliance is the crown and loop space maintainer (image 2).

2. Loss of multiple teeth. If multiple primary teeth are lost and both the permanent incisors and first permanent molars have erupted, a lingual arch contacting the incisors (mandible) (image 3) or a lingual arch with a palatal button that does not contact the incisors (Nance appliance, maxilla) (image 4) can be used to prevent posterior space loss. Both appliances require the use of cemented orthodontic bands to attach the appliance to the 1st permanent molars. Variations of both appliances can be made to be removable by the use of special lingual attachments on the molars. The appliances can also include adjustment loops that can be activated to procline the incisors and tip the molars distally.

Lower lingual arches are contraindicated prior to the eruption of the permanent mandibular incisors. Remember, the permanent lower incisors tend to erupt lingual to the primary incisors. A lingual arch that is contoured to the lingual surfaces of the primary teeth can impede the eruption of the permanent teeth (image 5).

Image 1, Band and loop space maintainer: Band and loop space maintainers replacing first primary molars.	Image 2, Crown and loop space maintainer: Crown and loop space maintainers replacing primary molars.
Image 3, Lower lingual arch space maintainer: A lower lingual arch cemented to the first permanent molars.	Image 4, Lower lingual arch impeding eruption of incisors: A lower lingual arch impeding the eruption of lower incisors.

Distal Shoe Maintainers

A distal shoe space maintainer is used in the primary dentition or early permanent dentition after the extraction of a 2nd primary molar before the 1st permanent molar has erupted (image 1). The goal is to prevent the first molar from drifting mesially as it erupts, which is likely to occur. If at all possible, the 2nd primary molar should be maintained through endodontic intervention (i.e., pulpectomy) even if the prognosis is guarded, because the intact tooth is a much better space maintainer than a distal shoe appliance.

Radiographs are used to construct the appliance, which uses a blade to engage the mesial surface of the 1st permanent molar to guide its eruption (Image 2). As the erupting permanent molar engages the blade, it is guided into the correct position in the arch. Distal shoe space maintainers can fail to guide the eruption of the first permanent molar. In this radiograph (image 3) the molar has drifted forward underneath the blade of the space maintainer and become positioned underneath the wire loop. The space maintainer must be removed and the tooth allowed to erupt into the mouth. Space regaining may then be used to reposition the tooth distally into a normal position.

Image 1, Distal shoe space maintainer: A distal shoe space maintainer designed to guide the eruption of the first permanent molar.	Image 2, Radiograph of a distal shoe space maintainer: Radiograph of a successful distal shoe space maintainer.
Image 3, Failure of distal shoe space maintainer: Failure of a distal shoe space maintainer. The appliance must be removed to allow the molar to erupt, and then it will be necessary to move it distally to re-open space for the 2nd premolar.

Removable Space Maintainers

The major indication for use of removable acrylic partial denture space maintainers is when multiple primary molars have been lost (image 1). In these cases, long spans of wire make band and loop space maintainers impractical, and unerupted or partially erupted permanent incisors make the use of a lingual arch problematic. Clasps are used to retain the appliances, and acrylic can be placed into the extraction sites to prevent tooth movement.

The appliances allow ready access for oral hygiene in patients with a high caries rate. Compliance with wearing the appliance can then become an issue. If the appliance is not worn all the time, space loss will occur.

Flowchart for Space Maintenance Types

A structured sequence helps in the decision-making process when planning space maintenance in the primary and mixed dentitions, and a flow chart is the best way to understand the sequence.

The first part of the flow chart (image 1) deals with treatment options for loss of a single primary molar. The next part (image 2) shows the treatment options when there is loss of multiple primary molars, the first permanent molars are erupted, and the permanent incisors are not erupted. The last section of the flow chart illustrates treatment options when there is loss of multiple posterior permanent teeth and the first permanent molars and incisors are erupted (image 3).

Image 1, Loss of one primary molar: Decisions when only one primary molar has been lost prematurely.	Image 2, Loss of multiple primary molars: Decisions when multiple primary teeth are missing and the first permanent molars have erupted.
Image 3, Loss of multiple primary molars (cont.): Decisions when the permanent molars have not erupted.

Space Regaining

Localized Space Loss

If space maintenance is not instituted after extraction of a primary tooth, space loss will occur during the next few months. Repositioning the teeth to regain space, not just space maintenance, is required to stabilize the situation. Up to 3 mm of space can be reestablished in a localized area with relatively simple appliances. Localized space loss greater than 3 mm constitutes a severe problem and is more difficult to manage.

In this case (image 1) localized space loss of about 3 mm has occurred in the maxillary arch after the premature loss of the upper left second primary molar. The first permanent molar has drifted forward into the extraction space and rotated mesio-lingually as it erupted. A removable acrylic appliance (image 2) was used to regain the space by distalizing the permanent molar with a wire spring that contacted the tooth on the mesio-buccal corner, to both distalize and de-rotate it. The space for the second primary molar was regained (image 3), and a fixed space maintainer (image 4) was placed to maintain the regained space. Space maintenance always is required after space has been regained, otherwise it will be quickly lost again. The sequence of steps in this space regaining treatment are shown together in image 5.

Image 1: Maxillary left 1st molar has drifted mesially after early loss of 2nd primary molar.	Image 2: Removable space regaining appliance with a finger spring to move the molar distally.
Image 3: Space has been opened with 3 months wear of the regaining appliance.	Image 4: Band and loop space maintainer in place.
Image 5: The sequence of space regaining

Appliances for Maxillary Space Regaining

Image 1 illustrates an example of a simple single-tooth space regaining appliance that resembles a band and loop space maintainer. There are two coil springs on the wire loop, which is free to slide through the tubes attached to the orthodontic band. The springs are compressed when the appliances is cemented and apply a force to push the teeth apart.

Space regaining is easier in the maxillary than the mandibular arch, and removable appliances can be designed to utilize springs (image 2) or expansion screws (image 3) to reposition the teeth. At the same time these forces tend to dislodge the appliance, stressing the retention elements, which limits the amount of force that can be applied to the teeth. Removable appliances generally are designed to apply forces to a single point on a tooth surface resulting in tipping of the tooth and de-rotation if desired. As a majority of space loss manifests itself as tipping and rotation, these types of forces can be used with removable appliances to reposition teeth to their normal position.

If an expansion screw is used to regain space, the screw should be activated slowly (1/4 turn 2-3 times per week). When the screw is activated too quickly, the teeth will not move at the same rate as the screw is activated and the appliance may not seat correctly.

Extraoral forces can be applied to maxillary molars through the use of headgear. Unilateral space loss in the maxillary arch can be treated using an asymmetric headgear (image 4) in which the outer bow of the headgear on the side with space loss is longer than the unaffected side. A cervical pull neck strap is used along with the asymmetric outer bow to distalize the first permanent molar and upright the molar at the same time if mesial tipping is present, and the inner bow can be used for de-rotation.

Image 1: Simple single tooth space regaining appliance.	Image 2: Space regaining appliances with various wire spring designs.
Image 3: Space regaining appliances with expansion screws, which must be activated very slowly.	Image 4: An asymmetric cervical pull headgear to regain maxillary space unilaterally.

Mandibular Space Regaining

In the mandibular arch, removable space regaining appliances are less efficient due to frequent problems with irritation of the lingual tissues, breakage, and lack of retention (image 1). They are recommended infrequently because poor compliance becomes a major problem.

More effective appliances in the mandibular arch are:

• Active lingual arch
• Lip bumper

A passive lingual arch is the best choice for space maintenance in the mandibular arch when multiple posterior teeth have been lost and the first molars have erupted. Lingual arches can also be designed to actively apply a distal force to the molars and procline the incisors, thus regaining space bilaterally in the mandibular arch. Adjustable loops of wire, fabricated into the posterior sections of the lingual arch, can be opened to expand the length of the lingual arch (image 2). Since lingual arches are usually constructed of heavy round steel wire that fits into lingual sheaths on the molar bands, large single activations generate excessive large forces. The loops must be opened only a little at the time, and this is done by the dentist after removing the lingual arch. It fits tightly enough that the patient cannot remove it.

A lip bumper (image 3) is attached to the lower first molars. It can be soldered or welded to the molar bands, or can be made to fit into tubes on the orthodontic bands (so the patient can remove it for meals and tooth brushing—which of course introduces compliance issues). The anterior portion of this heavy wire is coated with acrylic and is positioned off the labial surface of the teeth so it actively stretches the lower lip away from the teeth. The lip in turn puts force on the wire and the wire transfers the force to the molar teeth.

Both the active lower lingual arch and the lip bumper regain space by tipping the mandibular molars distally while proclining the incisors. With a lip bumper, even though the device does not touch the incisors, tongue forces procline the incisors when it eliminates lip pressure against them.

Image 1: Removable mandibular space regaining appliance.	Image 2: An adjustable lingual arch can be used for mandibular space regaining.
Image 3: A lip bumper with an anterior acrylic shield.

Space Management

Space Management

In patients with generalized rather than localized crowding predicted to be less than 4 mm, space management uses leeway space to align the teeth. The mixed dentition space analysis shows the amount of crowding that could be alleviated if mesial shifting of the permanent molars were prevented.

Leeway space (image 1) is the difference in the mesial-distal widths of the teeth in the primary buccal segments (canine, first molar, and second molar) and the permanent buccal segments (canine, first premolar, and second premolar). The late mesial shift occurs with the exfoliation of the primary second molars around 11-12 years of age. Since the primary molars are larger than the premolars that replace them, the permanent first molars can move mesially with the loss of the primary second molars. In the majority of cases the leeway space is larger in the lower arch than the upper arch, which allows the lower molar to shift further anteriorly than the upper molar and establish a Class I occlusal relationship.

On average the leeway space per arch is:

• Maxillary arch = 0.9 mm/quadrant
• Mandibular arch = 1.8 mm/quadrant

These are average values, and there may be significant variations among individual patients. If leeway space is maintained, however, the average patient has nearly 4 mm of space in the mandibular arch that can be used for the relief of incisor crowding.

Treatment Steps in Space Management

In space management, prior to loss of the primary second molars a lingual arch is placed to prevent the late mesial shift (the mesial drifting of the permanent molars following exfoliation of the primary teeth). The lingual arch can also be activated slightly to tip the molars distally and the incisors facially, slightly expanding the arches to gain additional space. Image 1 shows a series of slides depicting space management in the late mixed dentition. Initially there is a mild amount of incisor crowding (image 1). A lingual arch is placed and the second primary molars are disked to increase the space available (image 2), which facilitates eruption of the first preolars and alignment of the anterior teeth. Once the premolars have erupted (image 3), the lingual arch can be removed and the incisors are relatively well aligned (image 4).

Disking primary canines as well as primary molars can also be used to provide space for alignment of the permanent teeth. A one-sided end-cutting diamond disk can be used to reduce the width of the primary canines and create sufficient space to allow the permanent incisors to realign in the early mixed dentition when a mild amount of crowding is present (image 5).

The mandibular leeway space allows the lower first permanent molars to shift mesially into a Class I molar relationship. If a lower lingual arch is placed to utilize the leeway space to align the permanent mandibular teeth, a Class I molar relationship may not result. In cases where a lower lingual arch is used for space management, headgear or other appliances may be required to distalize the maxillary molars to establish a Class I molar relationship.

Image 1: Moderate crowding in late mixed dentition child, with a small space discrepancy if mesial shift of the first permanent molars is prevented.	Image 2: The incisors have been tipped facially with the lingual arch, and the mesial of the primary second molars have been disked to provide space.
Image 3: After eruption of all the succedaneous teeth, the lingual arch can be removed.	Image 4: The mandibular teeth now are in reasonable alignment.
Image 5: A one-sided diamond disk can be used to reduce the width of the primary teeth.

Early Loss of Primary Canines

A common sign of severe crowding in the early mixed dentition is early unilateral loss of a mandibular primary canine, which results in a shift of the dental midline (image 1). Initially there is inadequate space for the eruption of the permanent mandibular lateral incisor. As the incisor erupts it causes extensive resportion of the mesial surface of the primary mandibular canine, which causes increased mobility and early loss of the tooth. After the canine is lost unilaterally, the incisors are free to shift toward the side where the canine was lost.

In these cases it is best to extract the contralateral primary canine and place a lingual arch. This prevents the incisors from moving lingually and allows self-correction of the midline shift, which can occur if the incisors have not drifted too far laterally. A partial fixed appliance may be used to actively create space and correct the midline shift. A lower lingual arch can be used to maintain the leeway space in the mandibular arch while a fixed orthodontic appliance (first molar bands, bonded brackets on incisors—often called a 2x4 appliance) is used to align the mandibular incisors and correct the midline shift. The 2x4 appliance along with the LLA can be activated to create arch length by advancing the incisors and distally tipping the lower molars (image 2).

In the maxillary arch, early unilateral loss of a primary canine also is an indication for extraction of the contralateral one, but placement of a lingual arch to hold space usually is unnecessary.

Image 1, Early unilateral loss of a mandibular primary canine: Early unilateral loss of a mandibular primary canine with a shift of the midline.	Image 2, Lingual arch and 2x4 appliance: A lower lingual arch and fixed 2x4 appliance used to align mandibular incisors.

Crowding >4 mm.

Patients with >4 mm of crowding/arch will require more extensive treatment and may best be referred to an orthodontist.

The critical treatment decision in these patients is whether to expand the dental arches to create space to align the teeth or to extract permanent teeth in each quadrant (usually, first premolars) to make room for the others. This subject is covered in detail in the Level IV teaching program To Extract Or Not To Extract, Part 1, which you will be studying in the near future. Expansion of the dental arches to create space must not cause excessive incisor protrusion, compromise alveolar bone support or periodontal attachment, or exceed the tolerance of the soft tissues (i.e., produce lip incompetence and protrusion).

Nonextraction treatment may require dental and/or skeletal expansion, distalization of posterior teeth, alteration of incisor position or angulation, and interproximal reduction (IPR) of tooth widths to provide additional space. A complete fixed appliance and 18-24 months of treatment time usually are necessary.

Serial Extraction

Serial Extraction

In some children, potentially severe crowding is obvious (images 1-3), and the mixed dentition analysis quantified the space discrepancy as 7-8 mm in both arches. For this child, the mandibular lingual arch was placed to maintain leeway space to keep crowding from getting worse, in the hope that nonextraction treatment might be possible, and serial extraction was not done—but if the space discrepancy is large enough, intervention to gain sufficient space to align all the permanent teeth in a stable position will be futile.

Sequential extraction of primary teeth during the mixed dentition can reduce crowding and irregularity of the incisors, and if followed by extraction of first premolars in the late mixed dentition, can allow the permanent canines and second premolars to erupt through keratinized tissue into more normal positions in the alveolus at the appropriate time and in the correct sequence. Serial extraction can be defined as the orderly removal of selected primary and permanent teeth in a predetermined sequence to alleviate crowding.

Historically, serial extraction was developed in the hope of providing a way to treat severe crowding while eliminating the need for future appliance therapy. Time has shown that it does not result in ideal tooth positions or eliminate the need for future orthodontic treatment. The main advantages of serial extraction is that it potentially makes future orthodontic treatment less complicated and decreases periodontal problems due to eruption of teeth outside the dental arch. Perhaps it also improves long-term stability.

Image 1: Severe maxillary crowding, with one permanent canine blocked out and the other one displaced facially.	Image 2: Severe mandibular crowding, with canines and 2nd premolars ready for eruption.
Image 3: Note that in the mandibular arch the canines and 2nd premolars are ready for eruption, but the distal roots of the 2nd primary molars have not resorbed. These primary teeth should be extracted at this point.

Ideal Patient for Serial Extraction

The ideal patient for serial extraction should have:

1. Early mixed dentition with a large amounted of predicted crowding, 8-10 mm of discrepancy per arch. If the amount of crowding is less than 10 mm, serial extraction alone is not recommended because more residual spacing and more uncontrolled tipping of the teeth will occur (image 1).
2. No skeletal disproportions.
3. Class I molar relationship.
4. Normal overbite. Serial extractions will deepen the bite.
5. No congenitally missing permanent teeth.

Even in the ideal situation, a later phase of comprehensive orthodontic treatment is almost always required to correct the sequelae of serial extraction. In clinical practice where comprehensive follow-up treatment is available, patients with a discrepancy of 8 mm or more often are candidates for serial extraction.

Serial Extraction Sequence

The sequence followed during serial extractions is designed to allow the first premolars to erupt ahead of the canines so that the first premolars can be extracted early to allow eruption of the canines and second premolars. If severe crowding exists, the result is that in each quadrant, the canine and second premolar share the space vacated by the first premolar.

Normally, in the maxillary arch the first premolar erupts before the permanent canine, which is ideal for serial extractions. However in the lower arch, the first premolar erupts along with or after the permanent canine. This makes serial extractions in the lower arch trickier. If the primary 1st molar is extracted when the root of the underlying first premolar is approximately 1/2 to 2/3 developed, the eruption of the first premolar can be accelerated.

Step 1 of serial extraction sequence Primary canines are extracted first to allow the permanent incisors to align (image 1). A lower lingual arch may be placed to prevent the lower incisors from retroclining and deepening the bite prior to the eruption of the permanent canines.

Step 2 of serial extraction sequence The first primary molars are extracted when the roots of the lower first premolars are about 2/3 formed and the crown is about to penetrate into the gingiva (image 2). This will accelerate the eruption of the first premolars so they erupt before the canines.

Step 3 of serial extraction sequence The first premolars are then extracted soon after they erupt. This allows the canine and second premolars to erupt into this space.

Image 1: The first step in the serial extraction process is extraction of the primary.	Image 2: The second step in the serial extraction process is extraction of the first primary molars.

Serial Extraction Outcomes

Serial extraction is not a panacea for the treatment of severe crowding. In the vast majority of patients, future comprehensive orthodontic treatment is required to treat the tipping, residual spacing, and increased overbite that usually occurs after serial extraction. The advantage of serial extraction is that the comprehensive treatment usually is shorter and less complicated than if serial extractions had not been done.

In cases with very severe crowding, the amount of residual tipping and drifting may be minimal after serial extractions, as shown in this panoramic radiograph of a patient who had serial extractions but no orthodontic treatment (image 1). Even in this favorable situation, a period of fixed appliance treatment would improve both alignment and root positions.

The panoramic radiograph in image 2 also shows a favorable result of serial extraction, but you can see that one of the maxillary canines has been displaced facially because even with extraction in the quadrant of the dental arch, there was not quite enough room for it. Again, a period of fixed appliance treatment will be needed to finish the job.

Once the sequence of serial extraction has been initiated, a prudent dentist might repeat the mixed dentition analysis space analysis and/or refer the patient for an orthodontic consult prior to extracting the first premolars. As a general rule, extraction of the permanent teeth should not be done before arrangements for future fixed appliance treatment are in place.

Image 1, Tipping and drifting of the teeth after serial extraction: Tipping of teeth is common after serial extraction.	Image 2, Panorex of reasonable result after serial extractions: Reasonable results after serial extraction without orthodontic treatment.

Self-Test Referral

The self-test section of this program is designed to help you be sure you have understood the material.

Now that you have gone through the module, do the assigned reading in Contemporary Orthodontics(pages 147-184 in 5th ed.; pages 163-201, 4th ed.) Then take the self-test, and use it as a guide for further study and review.

Copyright 2013, UNC Dept. of Orthodontics

Self-Test

Instructions

1. View the teaching program.
2. Use the mouse to mark the correct answer(s) to each question.
3. Review the feedback from the program—it will tell you if you’re right or wrong, and why.

Reading: Contemporary Orthodontics, 3rd edition, pages 165-170, 418-429, and 452-462.

Question 1

Which of the following is not an underlying assumption of a complete mixed dentition space analysis (like the UNC analysis)?

1. All succedaneous teeth are present and developing normally.
2. Males have larger teeth than females.
3. Molar position is predictable. ✓
4. The size of the erupted mandibular incisors is well correlated with the unerupted buccal segments.
5. Prediction tables are valid for all patients.

Correct

That’s right; even though males do have larger teeth than females, that is not one of the assumptions of the UNC mixed dentition space analysis. Mesial drift of the 1st permanent molars is assumed to occur when 2nd primary molars are lost, and calculating the amount of drift to correct the molar relationship is an important part of the space analysis procedure. It is assumed that all teeth are present and will erupt, that the size of the incisors can be used to predict the size of the unerupted canine, premolars can be used to predict the size of the unerupted teeth, and that prediction tables for this purpose will be valid.

Incorrect

No, that’s wrong. Even though males do have larger teeth than females, that is not one of the assumptions of the UNC mixed dentition space analysis. Mesial drift of the 1st permanent molars is assumed to occur when 2nd primary molars are lost, and calculating the amount of drift to correct the molar relationship is an important part of the space analysis procedure. It is assumed that all teeth are present and will erupt, that the size of the incisors can be used to predict the size of the unerupted canine, premolars can be used to predict the size of the unerupted teeth, and that prediction tables for this purpose will be valid.

Question 2

Which of the following additional factors are evaluated during interpretation of the numerical results in sections 7-10 of the UNC Space Analysis Form?

a. Lip posture

b. Molar shift

c. Facial profile analysis results

d. Depth of the curve of Spee

1. a and b
2. a and c
3. b and d
4. a, b, and c ✓
5. all of the above

Correct

That’s right; all of these factors are evaluated in sections 7 through 10 of the UNC Space Analysis Form except the depth of the curve of Spee. The facial profile analysis is used to analyze lip posture, mandibular incisor position, and skeletal jaw relationship, which all have a direct relationship on space analysis in the dental arches. The depth of the curve of Spee, although it does have implications to the space required to align the teeth in the mandibular arch, is not part of the UNC Space Analysis Form.

Incorrect

No, that’s wrong. All of these factors are evaluated in sections 7 through 10 of the UNC Space Analysis Form except the depth of the curve of Spee. The facial profile analysis is used to analyze lip posture, mandibular incisor position, and skeletal jaw relationship, which all have a direct relationship on space analysis in the dental arches. The depth of the curve of Spee, although it does have implications to the space required to align the teeth in the mandibular arch, is not part of the UNC Space Analysis Form.

Question 3

(A) A lower lingual arch is recommended for bilateral space maintenance in the mixed dentition prior to the eruption of the mandibular permanent incisors, because (B) The mandibular permanent incisors erupt lingually to the primary incisors.

1. A true, B true, A and B related
2. A true, B true, A and B not related
3. A true, B false
4. A false, B true ✓
5. A and B false

Correct

That’s right, the first statement is false, but the second one is true. A lower lingual arch is contraindicated for use in the primary or early mixed dentition prior to the eruption of the mandibular permanent incisors. Bilateral band and loop space maintainers are indicated in these situations. The second statement is true as the mandibular incisors usually erupt lingual to the primary incisors. A lower lingual arch would impede the eruption of the mandibular permanent incisors.

Incorrect

No, that’s wrong. The first statement is false, but the second one is true. A lower lingual arch is contraindicated for use in the primary or early mixed dentition prior to the eruption of the mandibular permanent incisors. Bilateral band and loop space maintainers are indicated in these situations. The second statement is true as the mandibular incisors usually erupt lingual to the primary incisors. A lower lingual arch would impede the eruption of the mandibular permanent incisors.

Question 4

Which of the following can be used as space regaining appliances?

a. Distal shoe

b. Lower lingual arch

c. Transpalatal arch

d. Band and loop

1. a and b
2. a and c
3. b and c ✓
4. a, b, and c
5. all of the above

Correct

That’s right. Lower lingual arches and transpalatal arches can be used as passive space maintenance appliances, but they can also be used as active appliances to regain space in the maxillary or mandibular arches. Omega loops in the lingual arch can be opened that will distally tip the molars and procline the lower incisors. Transpalatal arches can be adjusted to derotate and distalize a maxillary molar. The band and loop and distal shoe appliances are passive space maintainers and cannot be adjusted to regain space.

Incorrect

No, that’s wrong. The correct answer is b and c. Lower lingual arches and transpalatal arches can be used as passive space maintenance appliances, but they can also be used as active appliances to regain space in the maxillary or mandibular arches. Omega loops in the lingual arch can be opened that will distally tip the molars and procline the lower incisors. Transpalatal arches can be adjusted to derotate and distalize a maxillary molar. The band and loop and distal shoe appliances are passive space maintainers and cannot be adjusted to regain space.

Question 5

Space regaining should be limited to cases with

1. 0-3 mm of generalized space loss.
2. 3-5 mm of generalized space loss.
3. 0-3 mm of localized space loss. ✓
4. 3-5 mm of localized space loss.
5. bilateral space loss.

Correct

That’s correct. If space maintenance is not instituted after extraction of a primary tooth, space loss will occur in a number of months. Repositioning the teeth to regain space is then required. Up to 3 mm of space can be reestablished in a localized area with relatively simple appliances. Localized space loss greater than 3 mm constitutes a severe problem and is more difficult to manage.

Incorrect

No, that’s wrong. If space maintenance is not instituted after extraction of a primary tooth, space loss will occur in a number of months. Repositioning the teeth to regain space is then required. Up to 3 mm of space can be reestablished in a localized area with relatively simple appliances. Localized space loss greater than 3 mm or generalized space loss constitute severe problems and are more difficult to manage.

Question 6

(A) Space management can be used to accommodate up to 4 mm of crowding in the transition from the mixed dentition to the permanent dentition, because (B) This much space typically is lost as the permanent first molars shift mesially after exfoliation of the primary second molars.

1. A true, B true, A and B related ✓
2. A true, B true, A and B not related
3. A true, B false
4. A false, B true
5. A and B false

Correct

That’s right; both statements are true and related. Space management uses a lingual arch to prevent loss of the leeway space during the late mixed dentition. The leeway space, which can be up to 4 mm in the mandibular arch, can then be used to accommodate mild crowding in the permanent dentition. Loss of the leeway space occurs when the primary second molars are exfoliated and the permanent molars shift mesially.

Incorrect

No, that’s wrong, both statements are true and related. Space management uses a lingual arch to prevent loss of the Leeway space during the late mixed dentition. The Leeway space, which can be up to 4 mm in the mandibular arch, can then be used to accommodate mild crowding in the permanent dentition. Loss of the leeway space occurs when the primary second molars are exfoliated and the permanent molars shift mesially.

Question 7

A lower lingual arch that utilizes the mandibular leeway space to align the mandibular teeth may

a. interfere with the early mesial shift.

b. require that the maxillary molars be distalized to obtain a Class I molar relationship.

c. be indicated for use in cases with a mild amount of crowding.

d. be indicated for use in cases with a moderate amount of crowding.

1. a and b
2. a and c
3. b and c ✓
4. a, b, and c
5. a, b, and d

Correct

That’s correct. During space management the late mesial shift of the mandibular molars is prevented. The late mesial shift and loss of the mandibular leeway space usually allows the lower first permanent molars to shift mesially into a Class I molar relationship. If a lower lingual arch is placed to utilize the leeway space to align the permanent mandibular teeth, a Class I molar relationship may not result. In cases where a lower lingual arch is used for space management, headgear may then be required to distalize the maxillary molars to establish a Class I molar relationship. Space management is indicated for use in cases with mild crowding. The leeway space is not sufficient to accommodate moderate crowding.

Incorrect

No, that’s wrong. During space management the late mesial shift of the mandibular molars is prevented. The late mesial shift and loss of the mandibular leeway space usually allows the lower first permanent molars to shift mesially into a Class I molar relationship. If a lower lingual arch is placed to utilize the leeway space to align the permanent mandibular teeth, a Class I molar relationship may not result. In cases where a lower lingual arch is used for space management, headgear may then be required to distalize the maxillary molars to establish a Class I molar relationship. Space management is indicated for use in cases with mild crowding. The leeway space is not sufficient to accommodate moderate crowding. The early mesial shift occurs with the eruption of the first permanent molars (approximately age 6 years) and the closure of the primate spaces in the early mixed dentition.

Question 8

In the early mixed dentition, premature unilateral loss of a primary mandibular canine

a. indicates significant incisor crowding.

b. results in a shift of the dental midline to the affected side.

c. occurs during the eruption of the adjacent permanent lateral incisor.

d. requires no intervention.

1. a and b
2. a and c
3. b and c
4. a, b, and c ✓
5. all of the above

Correct

That’s right. Premature unilateral loss of a primary mandibular canine usually indicates significant incisor crowding. There is insufficient space for the eruption of the adjacent permanent lateral incisor. As the lateral incisor erupts, it prematurely resorbs the mesial surface of the primary canine, which causes it to be lost early. The unilateral loss of the primary canine then results in a shifting of the dental midline to the affected side. Intervention is usually recommended in these cases. The contralateral primary is extracted and a lingual arch is placed to encourage self-correction of the midline. Active correction of the midline can also be done.

Incorrect

That’s wrong. Intervention is usually recommended in these cases. The contralateral primary is extracted and a lingual arch is placed to encourage self-correction of the midline. Active correction of the midline can also be done. Premature unilateral loss of a primary mandibular canine usually indicates significant incisor crowding. There is insufficient space for the eruption of the adjacent permanent lateral incisor. As the lateral incisor erupts, it prematurely resorbs the mesial surface of the primary canine, which causes it to be lost early. The unilateral loss of the primary canine then results in a shifting of the dental midline to the effected side.

Question 9

(A) The normal eruption sequence in the maxillary arch makes serial extractions more challenging in the maxillary arch because (B) The eruption of a maxillary permanent tooth can be accelerated if the extraction of the overlying primary tooth is timed correctly.

1. A true, B true, A and B related
2. A true, B true, A and B not related
3. A true, B false
4. A false, B true ✓
5. A and B false

Correct

That’s right. The first statement is false while the second statement is true. A major objective of serial extraction is to extract the first premolars before the permanent canines erupt. In the maxillary arch the first premolars usually erupt before the canines, which is favorable. The mandibular arch is more challenging because the canines often erupt before the first premolars. It’s true that the eruption of a permanent tooth can be accelerated if the overlying primary tooth is extracted when this uncovers the underlying permanent tooth, so timely removal of first primary molars can accelerate the eruption of first premolars, allowing their extraction before canines erupt.

Incorrect

No, that’s wrong. The first statement is false while the second statement is true. A major objective of serial extraction is to extract the first premolars before the permanent canines erupt. In the maxillary arch the first premolars usually erupt before the canines, which is favorable. The mandibular arch is more challenging because the canines often erupt before the first premolars. It’s true that the eruption of a permanent tooth can be accelerated if the overlying primary tooth is extracted when this uncovers the underlying permanent tooth, so timely removal of first primary molars can accelerate the eruption of first premolars, allowing their extraction before canines erupt.

Question 10

Serial extractions are done to

a. accelerate the eruption of the first premolars.

b. prevent loss of the leeway space.

c. eliminate the need for future orthodontic treatment.

d. allow early alignment of the permanent incisors.

1. a and b
2. a and c
3. a and d ✓
4. a, c, and d
5. all of the above

Correct

That’s right. One of the objectives of serial extractions is the early resolution of permanent incisor crowding. The extraction of the primary canines creates space for the permanent incisors to erupt into normal positions and align early. Another objective is to accelerate the eruption of the first premolars, so they can be removed early. Serial extractions do not eliminate the need for future orthodontic treatment. First premolars are removed during serial extractions, and leeway space is not relevant since these teeth have been removed.

Incorrect

No, that’s wrong. One of the objectives of serial extractions is the early resolution of permanent incisor crowding. The extraction of the primary canines creates space for the permanent incisors to erupt into normal positions and align early. Another objective is to accelerate the eruption of the first premolars, so they can be removed early. Serial extractions do not eliminate the need for future orthodontic treatment. First premolars are removed during serial extractions, and leeway space is not relevant since these teeth have been removed.