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ORIGINAL ARTICLE

Dental arch width in Class II Division 2 deep-bite malocclusion

Todd M. Walkow, DMD, MS,a and Sheldon Peck, DDS, MScDb

Newport Beach, Calif, and Boston, Mass

A severe phenotype of Angles Class II Division 2 (II/2) malocclusion with extremely deep overbite has been

called cover-bite, or Deckbiss in its early German descriptions. This distinctive occlusal variation is

characterized by skeletofacial hypodivergence, mandibular dentoalveolar retrusion, excessive bony chin

projection, reduced mesiodistal tooth size, maxillary incisor retroclination, and at least 100% overbite,

covering at least 1 mandibular incisor in occlusion. In this study, maxillary and mandibular dental arch widths

measured at the first molars and the canines were recorded from dental casts of 23 subjects with II/2

cover-bite malocclusions. The data were compared with a control-reference sample of 46 orthodontic

patients matched for age and gender. In the cover-bite group, the intermolar widths in both arches and the

intercanine width in the maxilla were comparable with those in the control sample. However, mandibular

intercanine width in the II/2 cover-bite group was significantly less than that of the controls (P .01). Thesefindings suggest that II/2 deep overbite malocclusion is characterized by normalized and relatively

compatible transverse dimensions in the maxilla and in the mandibular posterior segments. The transverse

underdevelopment that this study identified in the mandible from canine to canine is probably responsible for

mandibular incisor compression and crowdingnatural sequelae of the deep overbite in II/2 cover-bite.

Thus, a reasonable orthodontic treatment plan for the mandibular dentoalveolar compensation often seen in

II/2 deep-bite patients would be anterior expansion of the mandibular arch width, usually reducing the need

for orthodontic tooth extractions and increasing the desirability of fixed retention. (Am J Orthod Dentofacial

Orthop 2002;122:608-13)

At the beginning of the 20th century, Edward H.

Angle1-3 differentiated between the first and

second divisions of his Class II type of maloc-clusion. In contrast to Class II Division 1 (II/1) patients

with characteristically narrowed upper arches, Class

II Division 2 (II/2) patients were observed by Angle to

have more nearly normal maxillary arch widths. Other

features of II/2 he described were retrusion of the

maxillary incisors, deep impinging vertical overbites,

and relatively normal nasal and lip functions.

Although Angle astutely noted these distinguishing

features 100 years ago, current scientific notation often

blurs or ignores the distinction between these 2 ana-

tomically different Class II subtypes. For instance,

Enlow and Hans4 discuss generic Class II skeletodentalfeatures and facial growth without differentiating II/2

from II/1. According to them, Class II patients have

long, narrow anterior cranial bases that affect the

nasomaxillary complex and result in long, narrow

palates and maxillary arches. Their conceptual Class II

subject appears to be modeled around the features of

the II/1 dentofacial type, but this was never established.

In an effort to identify some anatomical features

that make the II/2 deep-overbite discrepancy unique,

Peck et al5 investigated characteristics of a severe

expression of II/2 overbite: the cover-bite malocclu-

sion. The II/2 cover-bite condition was first recorded in

1912 in the German literature (as Deckbiss).6 This

occlusal phenotype is characterized today by conceal-

ment or complete covering of the mandibular incisor

crowns due to excessive overbite and retroclination of

the maxillary incisors

5

(Fig 1, A-D). The cephalomet-ric and odontometric study of Peck et al5 identified the

following additional morphological attributes of a II/2

cover-bite malocclusion: (1) craniomandibular skeletal

hypodivergence, (2) excessive bony chin projection due

to an anteriorly well-developed basal bone region of the

mandibular body, and (3) reduced mesiodistal size of

the maxillary and mandibular incisors.

Angles3 clinical observation of the nearly nor-

mal width of both arches in II/2 malocclusion rarely

has been examined in controlled studies. Peck et al5

also commented anecdotally on the apparently adequate

aPrivate practice, Newport Beach, Calif.bAssociate clinical professor of Oral and Developmental Biology (Orthodon-

tics), Harvard School of Dental Medicine, Boston, Mass.

Reprint requests to: Dr Todd M. Walkow, 360 San Miguel #706, Newport

Beach, CA 92660; e-mail, [email protected].

Submitted, February 2002; revised and accepted, April 2002.

Copyright 2002 by the American Association of Orthodontists.

0889-5406/2002/$35.00 0 8/1/129189

doi:10.1067/mod.2002.129189

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transverse jaw dimensions observed in patients with

II/2 deep-bite malocclusions. Moorrees et al7 used

serial dental casts of untreated Class II malocclusions tocompare arch dimensions of II/1 and II/2 subgroups.

Compared with dental-cast measurements from a con-

trol-reference population, II/2 dental casts had maxil-

lary and mandibular intercanine distances greater than

average, and intermolar distances with a normal distri-

bution. In contrast, intercanine and intermolar distances

in II/1 patients measured less than average. Buschang et

al,8 in a cross-sectional study of 386 white women,

found that II/2 patients had greater maxillary interca-

nine and intermolar distances than did II/1 patients.

However, the II/2 patients showed mandibular interca-

nine and intermolar widths less than the Class I and II/1patients. Neither of the previously mentioned arch-

width studies7,8 of II/2 patients considered the amount

of overbite in the sample group.

Knowledge of arch-width characteristics associated

with severe II/2 deep bite (cover-bite) malocclusion

would be helpful in determining orthodontic treatment

goals and likely posttreatment sequelae for this partic-

ular skeletodental dysmorphology. The purpose of this

study was to assess dental arch width in II/2 cover-bite

subjects. The null hypotheses to be tested states that

there is no mean difference in maxillary and mandibu-

lar intercanine and intermolar distances between II/2

cover-bite subjects and a control-reference sample.

MATERIAL AND METHODS

Pretreatment dental casts of 23 orthodontic patients

having II/2 cover-bite malocclusions were collected

from patient records at the Harvard School of Dental

Medicine in Boston and at a private orthodontic prac-

tice in the northeastern United States. The subjects

ages ranged from 8.4 to 33.9 years (median, 12.4

years). Males predominated over females in the II/2

cover-bite sample with 20 subjects (87%). A control

sample of 46 subjects matched according to age and sex

was selected from orthodontic patient records at the

Harvard School of Dental Medicine: for each II/2subject, the pretreatment dental casts of 2 matched

control patients were used (Table I). All private prac-

tice patients said they had European ethnicities. Ethnic-

ity and race data were not obtainable for the dental

school clinic patients.

The following diagnostic criteria were used for

inclusion in the experimental sample of II/2 cover-bite

subjects: (1) Class II molar relationship on at least 1

side in centric occlusion, (2) Class II deciduous or

permanent canine relationship, (3) retroclination of 2 or

more maxillary incisors, and (4) a vertical relationship

Fig 1. Typical Class II Division 2 deep overbite (cover-bite) malocclusions at diagnosis: A, B,

9.2-year-old boy; C, D, 11.3-year-old boy.

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in which at least 1 mandibular incisor crown is coveredcompletely by the corresponding maxillary incisor

(overbite 100%).

The arch-width measurements were recorded from

each subjects pretreatment dental casts by 1 examiner

(T.M.W.), using an odontometric dial caliper and re-

cording the data to the nearest 0.1 mm. To reduce

examiner bias, the examiner measured the 138 casts in

random order. Four arch-width measurements (Fig 2),

using methods similar to those of earlier studies,8-12

were taken from the casts of all 69 subjects in this

study:

Maxillary and mandibular intercanine width: the

distance between the cusp tips of the right and left

canines, or the center of the wear facets in cases of

attrition.

Maxillary intermolar width: the distance between theapices of the mesial triangular fossae of the right and

left first molars. This point is relatively easy to find,

because it is the mesial termination of the central

groove. From clinical experience, we have found this

point to be located without difficulty in restored

teeth.

Mandibular intermolar width: the distance between

the central pits of the right and left first molars. This

reference point was most accessible because all

developmental grooves converge at this point on the

occlusal surface.

A double-determination method13 applied to thearch-width measurements gave results that had small

variability relative to the mean, producing a minimal

measurement error (Table II). The low error-of-the-

method results confirms the strong reliability of the

measurement technique and the selected arch-width

measurement reference points.

A 2-sample t test was used to determine whether

there was a statistically significant difference in mean

intercanine and intermolar widths between the II/2

sample and the controls. The level was set at 0.05.

RESULTSAn exploratory analysis confirmed that the data

were normally distributed, and that the variances be-

tween the groups were equal. With a 2-sample t test, a

statistically significant difference in the mean mandib-

ular intercanine width for the II/2 sample compared

with the control sample was found (Table III). Thus, the

null hypothesis for the mandibular intercanine width

variable can be rejected. The mean mandibular interca-

nine width for the II/2 cover-bite sample is signed with

negative value, indicating that it measures significantly

smaller than that of the controls.

DISCUSSION

Of the 4 main categories in Edward H. Angles

ubiquitous classification of malocclusions, the II/2 type

of discrepancy occurs the least often. Obtaining data on

II/2 patients has always been challenging because of the

low prevalence rates. In a study of 2758 white North

American adolescents between 14 and 18 years of age,

Massler and Frankel14 found the prevalence rate of II/2

to be 2.7%. Using that same method of examination,

Altemus15 found a prevalence rate of 1.6% for II/2

among 3289 black students in the District of Columbia.

Fig 2. Maxillary and mandibular intercanine width and

intermolar width measurements.

Table I. Distribution and relative frequency of Anglemalocclusion classes in control sample

Malocclusion

Class

Number of

subjects

Relativefrequency

(%)

Class I 16 34.8

Class II Division 1 22 47.8

Class II Division 2 4 8.7

Class III 4 8.7

Total 46 100.0


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Prevalence data for II/2 cover-bite malocclusion have

been reported only by Peck et al,5 who found a

prevalence rate of 1.7% in a North American orthodon-

tic patient population.

The case-control method is the most suitable and

efficient investigative approach to study conditions of

infrequent occurrence, such as the cover-bite phenotype

of the II/2 malocclusion. In this study, we collected a

sufficient number of cases by combining pretreatment

subjects from 2 different sample sources. The experi-

mental sample of 23 II/2 deep-overbite patients favored

males over females by a ratio greater than 6 to 1. A

natural bias for male expression in deep-bite malocclu-

sion has been reported earlier.5

Our measurements of arch width in II/2 cover-bite

patients found mandibular intercanine width signifi-

cantly less than that in the control-reference sample. A

possible explanation of this phenomenon might be that

the extreme deep bite in cover-bite patients inhibits

anterior development of the mandibular dentoalveolar

segment. The mandibular incisors could be compressedby the lack of available space resulting from a forward

growth rotation of the mandible. Thus, mandibular

anterior crowding and dentoalveolar extrusion are pos-

sible sequelae to the mandibular intercanine width

constriction. Another view could be based on the nature

of holding cusps in stabilizing arch form and tooth

position over time: the molars and the premolars meet

their antagonists naturally in a solid, interlocking oc-

clusion, but the canines and the incisors do not have

this advantage and thus would be more likely to shift

position in time.

Bjork16 found the forward (bite-closing) rotation of

the mandible, associated with the II/2 deep bite maloc-

clusion, to be characterized by decreased maxillary

arch length, anterior dental crowding, and deepening of

the anterior dental and skeletal vertical relationships.

The reduced mesiodistal diameters of the mandibular

incisors in II/2 cover-bite patients require a smaller

anterior arch perimeter, actually helping to accommo-

date the reduced mandibular intercanine width to min-

imize the crowding potential of the incisors.5

The small sample size in this study might have

decreased its power. Increasing the sample size would

most likely lead to a greater probability of establishing

statistical significance for the observed trends in the

maxillary intercanine, maxillary intermolar, and man-

dibular intermolar arch-width measurements.

CLINICAL IMPLICATIONS

The skeletodental peculiarities of the II/2 deep-bite

patient often present unique clinical challenges. These

patients have a distinct dentofacial dysmorphology andthus should not be treated simply as a variation of the

more common II/1 malocclusion. Nonetheless, some

clinicians have reported similar treatment modalities

for all patients in the Class II category.17,18

Treatment planning to address the sagittal and

vertical discrepancies observed in II/2 cover-bite pa-

tients has featured varied approaches. Successful re-

sults have used Class II elastics with extraoral traction

and bite planes,19 or with a functional appliance,20 or

combinations of functional and fixed orthodontic appli-

ances.21,22 Litt and Nielsen23 orthodontically treated

Table II. Error analysis with 10 double determinations

Measurement (mm)

Meanabsolute

difference

Meansigned

difference

SD of thesigned

difference

Error ofthe

method

Maxillary intermolar 0.12 0.02 0.14 0.04

Maxillary intercanine 0.20 0.14 0.26 0.08

Mandibular intermolar 0.10 0.04 0.12 0.04

Mandibular intercanine 0.15 0.07 0.19 0.06

Table III. Arch width measurements and t test for equality of means

Measurement (mm)

II/2 sample Controls

t P valueMean SD Mean SD

Maxillary intermolar 45.2 2.7 44.2 3.1 1.30 .20

Maxillary intercanine 33.0 2.4 33.9 3.3 1.09 .28

Mandibular intermolar 41.1 2.4 40.4 3.1 0.94 .35Mandibular intercanine 25.6 1.5 26.8 1.8 2.65 .01*

*P .05.



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identical twin boys with II/2 malocclusions: 1 under-

went extraction treatment, and the other had nonextrac-

tion expansion treatment. Both approaches produced

acceptable outcomes.

Results of this study demonstrate collapsed man-dibular intercanine width in II/2 cover-bite patients,

probably because of mandibular anterior confinement

from severe overbite. During II/2 orthodontic treat-

ment, the maxillary incisors are usually proclined to

permit a posteriorly displaced mandible to reposition

anteriorly.24 The mandible is thus allowed to develop

more favorable sagittal and vertical postures, and man-

dibular anterior teeth often have fresh space for de-

crowding. In this way, nonextraction arch development

is usually the most reasonable treatment approach for

the overcompensated dentition in severe II/2 discrep-

ancies.Consideration of mandibular dentoalveolar arch-

width expansion for the treatment of II/2 problems

might generate concern about the increased potential

for unstable orthodontic results. Little et al25 found the

mandibular intercanine width to decrease postorthodon-

tically, regardless of whether this dimension was ex-

panded. During the retention period, no significant

differences in the amount of mandibular anterior

crowding among the different malocclusion classes

were noted. However, II/2 patients demonstrated the

least relapse. Canut and Arias26 retrospectively studied

30 II/2 treated patients for outcome stability. They

found that almost all showed some crowding of man-

dibular incisors at 3 years postretention. Maintenance

of the original mandibular intercanine width and arch

length during treatment proved to be no guarantee for

stability of the anterior teeth in their II/2 sample.

Thus, some overbite rebound seems to be inevitable

in the II/2 deep-bite orthodontic patient.26,27 A post-

treatment increase in overbite could provoke a reduc-

tion of the mandibular intercanine distance and subse-

quent mandibular incisor crowding. Therefore, it might

be prudent to place fixed lingual retention on themandibular anterior teeth of cover-bite patients. The

bonded retainer might also help to maintain the overbite

correction by not allowing mandibular anterior arch-

width collapse.

In the current study, the II/2 cover-bite patients had

arch-width measurements comparable with those re-

corded for the control-reference sample, except for

mandibular intercanine width. Based on these findings,

it is unlikely that an interarch transverse discrepancy

would develop during treatment of the typical II/2

cover-bite patient.

CONCLUSIONS

Based on the results of this study, dental arch form

in the II/2 deep-overbite patient might be characterized

as normal, except in the mandibular intercanine width

dimension, which is reduced. The decrease in themandibular anterior arch width is probably a result of

the severe overbite that inhibits forward mandibular

dentoalveolar growth but cannot inhibit the strong basal

and symphyseal growth in the II/2 mandible.5 Decom-

pensating the dentition by expanding the mandibular

intercanine width after bite-opening procedures would

appear to be an acceptable treatment approach, espe-

cially for II/2 deep-bite patients with mandibular ante-

rior crowding.

According to our findings, the posterior arch widths

in the maxilla and the mandible of II/2 cover-bite

patients are the same as those of other orthodonticpatients. The postcanine dental arches also appear to be

well related to one another occlusally. Therefore, trans-

verse maxillomandibular discrepancies would not be

suspected as a cause of II/2 deep-bite malocclusions.

We thank Dr Blaine Langberg for his kind help with

the graphics.

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