Download The Correlation Between Tooth Size-Basal Bone

THE CORRELATION BETWEEN TOOTH SIZE-BASAL BONE
SIZE DISCREPANCY AND LONG TERM STABILITY
OF THE LOWER INCISORS IN CLASS II
DIVISION 1 PATIENTS
Wael Kanaan, D.D.S.
A Thesis Presented to the Faculty of the Graduate School
Of Saint Louis University in Partial Fulfillment
Of the Requirements for the Degree of
Master of Science in Dentistry
2006
ABSTRACT
The purpose of this study was to evaluate the effect
of tooth size-basal bone size discrepancy on long term stability of mandibular anterior teeth in a large group of
Class II, Division 1 patients.
The study searched for a
reliable way to measure the length of basal bone by employing an elliptical formula and tested its validity on 36
casts.
After proven to be reliable, the basal bone dis-
crepancy was measured utilizing the records of 105 patients.
On these patients, photocopies of study models and
cephalograms were available pretreatment (T1), at the end
of active treatment (T2), and a mean of 14.8 years posttreatment (T3).
Irregularity was calculated according to
the method of Little (1975).
The data failed to show a
correlation between basal bone discrepancy at T1 and relapse.
However, it was demonstrated that a weak but sta-
tistically significance correlation (r=-.198) exists between basal bone discrepancy at T2 and incisor irregularity
at T3.
Furthermore, the correlation was stronger between
basal bone discrepancy at T3 and incisor irregularity at T3
(r=-.318)
Over the nearly 15 years, basal bone discrepancy
increased an average of 2.96 mm implying a continual reduction of basal bone length.
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CHAPTER I: INTRODUCTION
Crowded, irregular and protruding teeth are major
problems facing the contemporary orthodontist.
To provide
effective treatments for patients, diagnosis and treatment
planning is a cornerstone for long-term success. To this
end, measuring the amount of crowding is one factor in the
process of developing an adequate diagnostic database.
Dental crowding is defined as the discrepancy between
tooth size and jaw size that results in a misalignment of
the tooth row (van der Linden and McNamara 2000).
Tooth
size could be measured directly from the plaster cast, but
the literature has not yet described a reliable way to
measure the jaw size.
Crowding, therefore is commonly
measured relative to the perimeter of the dental arch, but
not relative to the basal bone that is holding the teeth.
Basal bone and apical base are synonyms for the bone
that supports and is continuous with the alveolar process,
as well as with the maxillary and mandibular bodies.
The
term “apical base” was first introduced by Axel Lundström
in 1923.
Tweed (1944) considered the treatment to be suc-
cessful when the mandibular incisors were positioned on basal bone implying that a functional mechanical balance exists.
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Relapse is a major concern for orthodontists, and many
factors had been suggested to explain it.
One of the fac-
tors involves Lundström’s apical base concept which has
been adopted by many clinicians.
Basically, the basal bone
is held to be relatively immutable and any attempt to move
the roots outside the boundary of the basal bone is thought
to enhance relapse (Brodie 1950).
The purpose of this study is to:
1. Establish a reliable way to measure the size of basal bone.
and
2. To study the relationship between post-treatment relapse and the discrepancy between tooth size and basal bone size, (basal bone discrepancy), in the mandibular arch in Class II division 1 patients.
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CHAPTER II: REVIEW OF THE LITERATURE
Long-term retention and stability of orthodontically
treated patients has been a concern nearly as long as orthodontic correction of malocclusion has been performed.
As early as the turn of the last century, authors of orthodontic texts were concerned with factors that led to instability.
Guilford expressed this apprehension in 1893 when
he stated:
The natural tendency of a tooth to return to its former
position, aided by the tension of the parts that have resisted its movement, will certainly move a tooth from its
new position unless the newly formed process has become
thoroughly calcified, and is thus by its strength and
density able to resist the opposing forces. Numberless
failures to retain the good results of regulation are attributable to this cause alone.
Angle (1907) said that retention was considered too
lightly.
He was of the opinion that it was far easier to
lay down rules governing tooth movement than to establish
rules for retention that would lead to stability.
Other
authors of this period, such as Dewey (1914) and Lischer
(1912), each devoted an entire chapter to issues of retention in their texts.
Dewey felt that retention was the
main problem of orthodontics.
Furthermore, Hawley said in
1919 “If anyone would take my cases when they are finished,
retain them and be responsible for them afterward, I would
gladly give them half the fee.”
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Case (1920) reiterated the
point when he stated that the permanent retention of the
“regulated” teeth was absolutely indispensable to the success of the specialty.
Oppenheim (1934) stated, “Retention
is the most difficult problem in orthodontia; in fact it is
the problem.”
Neither time nor research has given us strict rules
for retention, and, as a result, long term stability has
remained one of the foremost challenges facing the specialty.
As the consensus of many authors, orthodontists real-
ize that stability of the end results is one of the prime
objectives of orthodontic treatment, without it neither
proper function nor optimal esthetics can be maintained.
Unfortunately, given the present state of knowledge regarding relapse, stability of the obtained result cannot be assured.
Etiology of Relapse
The etiology of relapse is a complex problem that includes various factors.
It is important for orthodontists
to be aware of current concepts regarding relapse and, in
so doing, attempt to devise treatments that minimize this
problem. In reviewing the literature, a number of factors
are commonly invoked such as tooth size, arch form, treatment modalities, occlusion, gingival fiber respond, treat-
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ment timing, growth potential, muscular function and the
position of the teeth in relation to the basal bone.
Tooth Size
It has been reported that large teeth are more likely
to be crowded than small teeth.
Fastlicht (1970) searched
for the relationships between tooth size and crowding in
treated and nontreated patients and found that “the correlation between the mesiodistal widths of the mandibular and
the maxillary incisors with crowding was very significant
in both cases.
This indicates that where there was a larg-
er mesiodistal width, there was more crowding.”
The effect
of tooth size on crowding has been further supported by
subsequent studies (Norderval, Wisth and Boe 1975; Smith,
Davidson and Gipe 1982; Rhee and Nahm 2000) that reported a
strong correlation between tooth size and crowding.
Con-
versely, other studies have failed to show a significant
correlation between tooth size and crowding (Howe, McNamara
and O’Connor 1983; Puneky, Sadowsky and BeGole 1984;
Radnzic 1988).
It has also been suggested that tooth shape may have
more of an effect on incisor irregularity than tooth size.
Peck and Peck (1972) found that well-aligned lower incisors
had a significantly reduced mesiodistal dimension (MD) and
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a significantly enlarged faciolingual dimension (FL).
Based on their findings, the so-called “Peck’s Ratio”
(MD/FL) was said to be used as a predictor of long term
stability.
Accordingly, “reproximation” (stripping) was
recommended as a method to enhance stability (Barrer 1975;
Betteridge 1981; Williams 1985).
Although their results
were later corroborated by some authors (Rhee et al. 2000;
Shah et al. 2003), others have failed to show significant
correlation between the Peck’s Ratio and stability (Smith
et al. 1982; Gilmore and Little 1984, Puneky, Sandowsky and
BeGole 1984; Bernabe, delCastillo and Flores-Mir 2005).
Even though Peck and Peck recognized the importance of
tooth shape on long term stability, they thought that relapse is still a multifactorial phenomenon and tooth shape
alone would not assure long term stability (Peck and Peck
1972).
Arch Form
Historically, many have assumed that arch form, especially in the mandible, cannot be altered permanently by
appliance therapy.
Although generally held as an important
concept, some strongly believe that arch form can undergo
stable alteration.
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Case (1921) recognized that patients he had treated
with various degrees of expansion tended not to exhibit
long term stability, but rather showed relapse of crowding
in the mandibular anterior segment.
Case began to extract
teeth in conjunction with his treatment in an attempt to
achieve more balance between the teeth and the bone that
supported them.
Case’s belief that teeth occasionally
needed to be extracted so that arch form could be maintained and stability enhanced was a major deviation from
the leadings of Angle.
In support, Tweed (1944) provided extensive documentation that stability was enhanced if arch form was maintained. Tweed reviewed many cases that he had treated according to the nonextraction principles of Angle and noted
a high incidence of relapse after treatment.
He concluded
that the relapsed cases were out of balance with the face
because teeth were not properly placed over basal bone.
Tweed retreated these patients with premolar extractions to
eliminate the need for expansion that he had used to make
space for the full complement of teeth.
With extractions,
he felt that he could place the mandibular incisors upright
over basal bone into what he thought would be a more stable
position.
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Nance (1947) agreed with this conclusion.
He found
that attempts to alter arch form generally lead to relapse.
Similarly, Strang (1952) stated that “the width from one
mandibular canine to another was an accurate index of the
muscle balance of each individual and, therefore, this distance determines the limit of the denture expansion and enhances stability of the finished result.”
Strang argued
that a slight expansion of the inter-canine width could be
tolerated only if it was accomplished by moving the canines
distally into the slightly wider premolar extraction site.
Bishara and colleagues (1973) examined 30 first premolar extraction cases that were on average 1.2 years out of
retention.
They reported that over 70% of any expansion in
the lower intercanine widths had already relapsed.
Shapiro
(1974) also found that an expanded mandibular intercanine
width has a strong tendency to return to its pretreatment
width, but that Class II division 2 patients could maintain
approximately 1 mm of intercanine expansion. Subsequently,
Little, Wallen and Riedel (1981) reported on the long term
follow-up of 65 cases with extraction of first premolars.
The lower intercanine width had been increased by more than
1 mm during treatment in 60% of the cases but, after treatment, constriction in the intercanine width occurred in 60
of 65 cases, usually by more than 2 mm.
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Felton and colleagues (1987) used a forth degree polynomials to asses dental arch form and found poor posttreatment stability in 70% of their nonextraction sample.
Glenn, Sinclair and Alexander (1987) assessed the long term
stability of nonextraction orthodontic treatment performed
on 28 patients who were out of retention for 8 years.
They
reported a decrease in the intercanine width, despite minimal change during treatment.
Similarly, Taner, Ciger and
Germec (2004) evaluated arch width changes in 21 Class II
Division 1 patients who where out of retention for an average of 3 years.
They found a significant reduction in the
mandibular intercanine width and the inter-first bicuspid
width.
It has also been reported that arch width decreases
after retention regardless whether orthodontic treatment
involved expansion or not (Little et al. 1981); however,
they also found that width changes were not an accurate
predictor of later mandibular anterior arch crowding or
post-retention irregularity.
They concluded that the issue
of expansion versus nonexpansion of the arch was not a
critical factor in postretention stability.
This assertion corresponds to the observations of
Sillman (1964) and DeKock(1972).
They studied individuals
who did not undergo any orthodontic treatment and found
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that arch width decreases in both the anterior and the posterior regions of the mandibular arch occur after the eruption of the permanent canines.
Similarly, Henrikson,
Persson and Thilander (2001) studied the changes in dental
arch form over 18 years in a sample of 30 individuals with
normal occlusion.
They found that age changes in the den-
tal arch form occur from adolescence to adulthood, with the
tendency of the mandibular arch to become more rounded.
These changes were correlated significantly with an increase in lower incisor irregularity.
Based on these studies, it can be argued that arch
constriction after orthodontic treatment is a normal function of aging, rather than a by-product of certain types of
orthodontic treatment.
It is necessary therefore to dis-
tinguish between changes induced by appliance therapy from
those that occur as a part of normal growth and development.
Although many experts have suggested that it is necessary to maintain the mandibular pretreatment dental arch
from, others have suggested using the basal bone to determine mandibular dental arch form.
Hew (1966) studied the
correlation between dental arch form, basal arch form, and
relapse and found that “Similarity in form of the dental
and basal arches seems to prevent some relapsing tenden-
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cies.” Based on his findings, he suggested using the shape
of the basal arch to determine the dental arch form especially in the lower arch.
Treatment Strategy: Extraction vs. Nonextraction
The question of extraction in orthodontics has always
been controversial.
Extraction of teeth for orthodontic
treatment was prevalent before 1900, but from the turn of
the last century to the mid-1930s, under the influence of
Angle’s beliefs, orthodontics to abandon extraction.
Sub-
sequently, Tweed and others deferred the specialty back to
extraction after they had become dissatisfied with relapse
seen in their nonextraction patients.
Later, orthodontists
realized that relapse can occur whether teeth were extracted or not.
The influence of the two treatments on the long-term
stability of the mandibular incisors has been studied extensively.
Although most authors have studied the effect
of one treatment on long-term stability, only few authors
have compared the outcome of extraction and nonextraction)
in the same study.
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Nonextraction Studies
It has been suggested by many authors (Kingsley 1880,
Angle 1907; Cetlin and Ten Hoeve 1983; Damon 2005) that the
best way to achieve stability is to retain all permanent
teeth.
Unfortunately, most studies failed to prove long-
term stability in nonextraction patients (Glenn et al.
1987; Little, Riedel and Stein 1990; Sadowsky et al. 1994).
Therefore, extraction of teeth did not answer the question
of long-term stability.
Extraction Studies
As might be expected, many have disagreed with the
nonextraction approach and have turned to extraction as an
adjunct to orthodontic treatment with an eye toward enhancing long-term stability (Case 1921; Lundström 1925 and
Tweed 1944).
The extraction of premolars, however, does
not assure long-term lower-incisor stability.
This failure
was further documented by recent longitudinal studies that
showed variable degrees of relapse (Little et al.. 1981;
Sandusky 1983; McReynolds and Little 1991; Vaden, Harris
and Gardner 1997).
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Extraction vs. Nonextraction studies
Paquette, Beattie, and Johnston (1992) compared the
long term effects of extraction and nonextraction edgewise
treatments in 63 patients (33 extraction and 30 nonextraction) for whom the 2 strategies were equally appropriate.
They found that the mean postretention increase in the irregularity index of the mandibular incisors for the extraction group (2.3 mm) was smaller than that for the nonextraction group (2.9 mm).
The difference, however, was of
little clinical value.
Luppanapornlarp and Johnston (1993) reported similar
results in a study of postretention stability in 62 patients who were clearly either extraction (33) or nonextraction (29) candidates.
The postretention increase in
mandibular incisor irregularity was 2.6 and 3.1 mm for the
extraction and nonextraction groups, respectively.
Fur-
thermore, Kahl-Nieke, Fischbach and Schwarze (1995) carried
out a long-term follow-up study of 226 orthodontically
treated patients (91 extraction and 135 nonextraction) and
found that the mean increases in the irregularity index
from posttreatment to postretention was 1.8 mm in the extraction and 2.3 mm in the nonextraction groups.
However,
this 0.5 mm difference between the groups was not statistically significant.
Rossouw and colleagues (1993) assessed
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88 subjects (44% nonextraction, 56% extraction) with respect to relapse and reported that no significant differences were recorded between extraction and nonextraction
groups regarding long term stability of the lower arch.
To this end, relapse often occurs regardless of treatment strategy.
Thus, dental stability is a complex problem
that depends on factors other than treatment strategy, itself.
Functional Balance
It has been suggested that an imbalance of orofacial
muscles may play an important role in malocclusion and in
the relapse after treatment (Strang 1952; Salzmann 1974).
As examples, it is well accepted that habits such as thumb
sucking, lip biting, and tongue thrusting can cause malocclusion.
In the same way, orthodontic treatments, such as
excessive proclination of the lower incisors, may upset the
balance between soft tissue and teeth resulting in relapse.
Mills (1966) stated that the lower incisors lie in a narrow
zone of stability in equilibrium between opposing muscular
pressure, and that the labiolingual position of the incisors should be accepted and not altered by orthodontic
treatment.
Similarly, Reitan (1969) claimed that teeth
tipped either labially or lingually during treatment are
14
more likely to relapse as the resulting unbalance muscular
forces tend to return the teeth toward their original position.
Moss’ functional matrix theory has provided a basis
for many practitioners’ belief that alteration of teeth position either facially or lingually could be maintained.
Moss believed that his research has indicated that the
form, position and maintenance of the denture are secondary
responses to the primary demands of the muscle acting on it
(Moss and Salentijn 1959).
Those who hold to this theory
advocate that alteration of tooth position can be maintained if the muscular forces are altered.
However, the
functional matrix theory does not support the idea that the
mechanical alteration of tooth position can be stable because the original teeth were in balance with the muscles
and this mechanical alteration would then be out of balance
with the original muscular forces which have not changed.
On the other hand, it supports the use of functional appliances to retrain the musculature so that the alteration of
tooth position will be in harmony with the forces acting on
the teeth and therefore be stable.
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Gingival Fiber Response
One type of relapse is the tendency for a previously
rotated tooth to move toward its former position.
It has
been suggested that overcorrection would enhance stability,
but there is little evidence to indicate that it is a successful method of preventing relapse.
Reitan (1959) re-
ported that the collagenous supporting fibers of the gingiva appeared taut and directionally deviated after tooth rotation.
According to Edwards (1968), this tautness does
not alleviate itself even after a long period of retention
and, accordingly, it is a factor that could account for the
relapse tendencies of rotated teeth.
In response to Reitan’s work, surgical procedures to
control or lessen rotational relapse in orthodontic treatment have been suggested.
Based on Bauer’s (1963) thesis,
Edwards (1970) advocated a simple surgical procedure designed to sever the supercrestal fibers in the gingiva to
allow the gingival fibers to reattach at a position of
equilibrium, free from tension.
He provided strong clini-
cal evidence that this procedure would reduce rotational
relapse.
To evaluate the efficacy of this surgical proce-
dure, Edwards (1988) studied 320 patients who had received
orthodontic treatment 15 years previously.
Half of the pa-
tients received the surgical procedure, whereas the other
16
half served as a control.
He found a highly significant
difference between the mean relapses of the control and the
surgical patients.
Further, he found that the surgical
procedure was more successful in reducing relapse in the
maxillary anterior segment than in the mandibular anterior
segment.
This finding was confirmed by Taner and associ-
ates (2000), who found a significant difference in irregularity index between patients who received the surgical
procedure and the controls.
With the growing evidence that
surgery might reduce rotational relapse, Gottlieb, Nelson
and Vogels (1996) undertook a national survey of 1032 orthodontists to determine the extent of this surgical procedure as an adjunct to retention procedures.
They found
that only 20.5%1 of the orthodontists used fiberotomy as a
strategy to improve posttreatment stability.
In conjunction with the surgical procedure, interproximal enamel reduction of the lower anterior teeth has been
suggested as an adjunct to enhance long term stability.
Boese (1980) performed enamel reduction and circumferential
supracrestal fiberotomy (CSF) on 40 patients.
He found
that all patients had excellent results (postretention irregularity index of 0.62 mm) 4 to 9 years postretention
1
In fact, only 1.8% of orthodontists performed this procedure in their
clinic. The rest were completed by periodontists, oral surgeons or general practitioners.
17
without retention appliances.
It should be pointed out,
however, that interproximal reduction was performed twice,
immediately posttreatment, and a second time during the 4
to 9 years posttreatment period.
Occlusion
Occlusion is considered a potent factor in maintaining
stability.
Kingsley in 1880 stated that “The occlusion of
the teeth is the most important factor in determining the
stability of teeth in the new position.”
Angle (1907) also
stated that orthodontic corrections would remain stable if
the teeth were in proper occlusion.
He thought that the
influence of each jaw upon the other maintained the form
and the size of the dental arches.
A good occlusion, how-
ever, may not guarantee that a case will not need retention.
The role of proper occlusion has been assessed by Andrews (1972).
Andrews examined 120 non-treated patients
with excellent occlusion to determine the common characteristics of normal occlusion and found the so-called “the six
keys to normal occlusion.”
In addition, he found that, in
unsatisfactorily treated orthodontic cases, at least one of
the six keys was absent.
Andrews suggested that patients
who exhibited all six keys had a stable occlusion and that
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retention was not necessary for these patients after the
third molars were removed and growth had ceased.
Ras and
coworkers (1992) studied the relation between occlusion and
relapse and found that “The group of patients with relatively good results after active treatment showed less relapse than the group with relatively moderate results after
active treatment.”
Roth (1981) highlighted the importance of the functional occlusion as well as the static occlusion to prevent
relapse.
He believed that “the answer to stability of the
treated orthodontic case would at least partially rest in
the functional dynamics of occlusion.”
Although many or-
thodontists today believe in many Roth’s ideas, it has never been documented that cases treated in accord with this
philosophy have a lesser degree of relapse.
Treatment Timing
It has been suggested that corrections carried out
during periods of growth are less likely to relapse (Riedel
1960).
Therefore, orthodontic treatment should be started
at the earliest possible age.
Riedel stated that, from a logical view point, this
idea has merit if the orthodontists influence the growth
and development of the maxilla and the mandible.
19
Riedel
believed that changes in muscle balance in a normal direction would allow for more normal development of the dentition.
Salzmann (1974) also suggested that treatment of
very young children had advantages in term of stability.
If orthodontics is performed when muscles are still growing, then the origins and insertions of the muscles may actually change in order to reach a state of balance with the
new tooth position.
Salzmann did not provide any evidence
to support this idea.
Growth Potential
Growth can be a potentially important factor in relapse, especially mandibular growth.
The concept that some
relapse occurs as the mandible outgrows the maxilla (Bjork
and Skieller 1972; Johnston 1986) is supported by Harper’s
report (1986) that the extra growth of the mandible relative to the maxilla bears a significant correlation to
changes in the buccal segment during retention.
Schudy (1974) studied 74 adolescents and found that
during the growth period the mandible moved forward more
than the maxilla resulting in a more upright lower incisors
and crowding.
Also, several other studies have found a re-
lationship between facial growth and lower incisor relapse
(Sinclair and Little 1983; Shields, Little and Chapko
20
1985). Unfortunately, none of the studies have shown a statistically significant correlation between mandibular
growth and relapse.
Mandibular crowding has not only been correlated with
anterior-posterior facial growth, but also to vertical
growth.
Alexander (1996) studied the relationship between
vertical growth and incisor irregularity in 97 Class I extraction patients 10 years postretention.
He found greater
incisor irregularity in patients with greater vertical
growth displacement of the molars and the incisors.
Dris-
coll-Gilliland, Buschang and Behrents (2001) confirmed this
finding, stating that “the subjects who had greater growth
in the vertical dimension and lower incisor eruption had
larger increases in space irregularity.”
Behrents (1985) has shown that craniofacial growth and
change does not cease in the late teens but continues
throughout life.
He has suggested that an expected pa-
tient’s future growth may lead either to relapse or an enhancement of the correction.
His findings suggested that
Class II females’ malocclusion may be more prone to relapse
after treatment than Class II males. Similarly, Class III
males may be more prone to relapse than Class III females.
This continued growth of the mandible in both treated and
21
nontreated patients may be the most important factor in the
developing of incisor uprighting and crowding.
Basal Bone
The concept of placing the lower incisors “upright
over basal bone” to enhance long-term stability was introduced by Tweed in 1944.
It was argued that, in this posi-
tion, teeth were in mechanical balance and could best resist the forces that could cause displacement.
Although practitioners have come to define “upright”
as plus or minus five degrees from a perpendicular to the
mandibular plane, there has been no experimental evidence
to show what “basal bone” is or where it begins or ends
(Reidel 1960).
Defining Basal Bone
According to common authors, basal bone is the bone
that underlies, supports, and is continuous with the alveolar process (Daskalogiannakis 2000).
The “apical base”
concept was first introduced by Lundström in 1923 as the
“immediately adjoining section upon which the region that
is limited to the apical zone (of the teeth) rests or to
which it is attached.”
This concept failed to stimulate a
sufficient response until Tweed presented it again in 1944
22
as basal bone.
Thus, basal bone and apical base are syno-
nyms (Daskalogiannakis 2000).
Tweed (1944) defined basal bone as “the bony ridge
over which the mandibular central incisors must be situated
to produce permanence of orthodontic results.”
Salzmann
(1948) defined the basal bone as “the area in the jaws
which begins at the most constricted point on the body of
the maxilla and mandible when seen on the profile cephalograms.
It includes Downs’ Point A, Point B and Lundström’s
apical base and it extends around the body of the maxilla
or mandible at the most constricted portions parallel to
the alveolar processes.”
Many years after the introduction of the basal bone
concept, however Brodie (1950) noted that this term has
never been satisfactory defined, although it seems to be
accepted by most as the skeletal bone which supports alveolar bone.
Changes in Basal Bone
The question whether basal bone is immutable or not
has been debated ever since the days of Edward Angle, and
perhaps even earlier.
Angle (1900) believed that each
tooth positioned in its proper place has a definite role in
23
the development of the jaws and that “bone growing” is possible under the concept of functional development.
Moss (1959), who introduced the Functional Matrix
Hyptheis, suggested that the tooth is a functional matrix
for alveolar growth; the growth and eruption of the tooth
is able to induce alveolar growth and hence the formation
of an adequate bony support.
Furthermore, he argued that
by changing the muscular forces applied to the denture, expansion occurs as a secondary response and therefore can be
stable if the new functional matrix supports this change.
It should be emphasized, however, that the functional matrix theory does not support the concept that mechanical
expansion of the denture is stable.
It was also suggested by Frankel (1974) that the dynamics of eruption could be utilized to increase alveolar
growth by using vestibular shields.
He proposed that his
functional regulator appliance displaces the attachment of
the lips and cheeks at the sulci in an outward direction
and as a result, enhances the development of the basal
bone.
Damon (2005) suggested using light forces in crowded
cases to expand the alveolar bone and maintain its integrity.
He stated “If orthodontists maintain force levels in
the optimal force zone, the alveolar bone and tissue can be
moved.”
24
On the other hand, many authors oppose the concept of
modifying basal bone.
Lundström (1925) made a landmark
contribution to orthodontics when he proposed a theory that
the apical base did not change to fit the normal occlusion,
but rather that establishment of normal occlusion was controlled by the apical base.
Brodie (1950) reported that
the “Apical base ... is relatively immutable.”
He further
stated that extractions were used to accommodate the dentition to the osseous base, genetically predetermined in
size.
Howes (1960) surveyed the apical base on models from
a longitudinal sample of treated and untreated cases. He
found that “The basal arch outline, from mandibular first
molar to mandibular first molar, alters little if any after
the age of 5 years or perhaps, as Hunter indicated, much
earlier.”
The findings of a recent study by Vanarsdall and
associates (2005) confirmed the fact that standard edgewise
orthodontic treatment does not have any effect on the basal
structure of the maxilla or the mandible.
Current Methods to Locate Basal Bone
Although the definition of basal bone clearly describes an area that underlies the teeth apices, different
studies have used different methods to measure it.
Downs
(1948) searched for an accurate method to determine the
25
limits of the basal bone.
He introduced two cephalometric
landmarks, point A and point B that represented what he
called the denture base.
He used these two points, along
with other points, to study the skeletal pattern of the
face as a part of his famous cephalometric analysis.
To
study the discrepancy in apical base relationships, Riedel
(1952) adapted Downs’ points, A and B, and used them in two
angular measurements, SNA and SNB.
Ever since, points A
and B have been used extensively in cephalometric evaluations and in many studies to determine the apical base relationship.
Howes (1947) used dental casts to analyze the relationship between tooth size and the supporting bone.
He
found that the supporting bone was above the palatal shelf
and over the apices of the teeth.
By using a survey line
above the apices of the teeth without impinging on the mucobuccal fold and sectioning horizontally on this line, he
was able to remove the alveolar process and expose the supporting bone.
He found the basal arch to be in the apical
one-third of the alveolar bone.
In the mandibular arch it
is 8 mm below the gingival margin.
Rees (1953) also found
the apical base to be 8 to 10 mm apical to the gingival
margin.
Falck (1969) defined the apical base as “the area
resulting from the peripheral connection of two reference
26
points located 14 mm away from the buccal cusps of the
first primary molars/premolars.”
Miethke and associates
(2003) argued that Falck’s method locating the apical base
was inaccurate for comparing treatment outcomes, given that
the primary molars have shorter cusps than the premolars.
The difference in the crown height between these two tooth
types would change the reference points and thus change the
apical base level.
To overcome this limitation, Miethke’s
group agreed with Howes (1947) and Rees (1953) by using the
gingival margins as a reference point instead of the buccal
cusps; however, they defined apical base as the area resulting from the peripheral connection of six reference
points located 5 mm below the most apical points of the
gingival margins of the lower lateral incisors, canines and
second primary molars/premolars (Figure 1).
In their opin-
ion, the 5 mm distance from the gingival margins was not a
true reflection of the apical base.
Although some authors have used the gingival margins
as a reference to locate basal bone, Sergl, Kerr, and
McColl (1996) used the most concave contour of the buccal
surface of the casts to measure the basal bone area.
Not surprisingly, confusion exists concerning the location of basal bone, largely because of the absence of
27
agreement among the authors who simply used their opinion
and speculation to locate basal bone.
Fig 1. Additional reference points for defining the apical base. These were located 5 mm below the most apical
point of the gingival margin of the described teeth
(Miethke et al. 2003).
Basal Bone and Tooth Size-Arch Size Discrepancy
It has been shown that, over a period of many years,
there has been discussion of, and concern for, stability by
placing teeth “over basal bone.”
Unfortunately, one of the
difficulties in orthodontic treatment planning has been the
estimation of the size or dimensions of basal bone.
Angle’s (1900) “line of occlusion” was readily accepted by early clinical orthodontists.
It prompted a search
for meaningful measurements of dental arch dimensions that
could be utilized in diagnosis and treatment planning.
It
was not until 1923 that the potential relationship between
Lundström’s apical base and dental arch form began to be
understood, as well as the realization that one of the most
28
important diagnostic dental arch dimensions was dental arch
perimeter.
Lundström’s theory was effectively translated
into clinical practice by Nance in 1947.
In his classic work, Nance (1947) described a method
for measuring the “outside” arch perimeter by using a piece
of a 0.010 inch brass wire placed along the buccal surfaces
of the teeth from the mesial of one permanent molar to the
mesial of the opposite permanent molar (Figure 2).
Alt-
hough most clinicians today do not measure the “outside perimeter” as advocated by Nance, the use of brass wire to
determine the available dental arch perimeter is still a
popular method.
Fig 2. Arch perimeter is measured along the buccal surface of the dentition as illustrated by the solid line
(Nance 1947).
Carey (1958) adopted, with some modification, Nance’s
method.
He used an 0.020 inch soft brass wire bent to a
symmetrical arch form that was placed over the contact
point region of the posterior teeth and over the incisal
edges of the anterior teeth.
He placed a mark where the
29
wire crossed the mesial contact point of the first permanent molars; the dental arch length could then be measured
between these two marks.
Even though he used the incisal
edges of the anterior teeth to measure the dental arch perimeter, he suggested that in certain cases it was necessary to pass the wire over the incisal edges “at a point
where we judge them to belong.”
Moorrees (1959) presented a variation of the brass
wire method for measuring dental arch perimeter.
He used
stainless steel tubes welded to a flange (Figure 3).
The
flange served as a mean of attaching a wire guide to a
plaster model at the mesial aspect of the first permanent
molar, and the tubes allowed the soft 0.15 mm stainless
steel wire to be guided through them.
Sticky wax was used
to fix the flange to the cast, and the wire was bent along
the buccal cusps or the incisal edges of the teeth, stabilized to the tube with hot wax, straightened, and measured
with a sliding caliper.
30
Fig.3. Moorrees apparatus to measure arch perimeter
(Moorrees 1959).
Huckaba (1964) described a similar brass-wire approach
to measure the dental arch length.
He used a 0.025 inch
brass wire and centered the wire over the contact points in
the posterior dentition.
In the anterior region, he dis-
tinguished between three situations when contouring the
brass wire:
1. If the lower anterior teeth are upright over the
basal bone, the wire is positioned directly over
the incisal edges;
2. If the lower anterior teeth are tipped to the
lingual, the wire should be extended to the labial of the incisors; and
3. If the lower anterior teeth are tipped to the labial, the wire should be positioned to the lingual.
The wire is then cut and straightened with the fingers
and measured with a boley gauge.
31
Musich and Ackerman (1973) introduced a new apparatus,
the catenometer, to measure the dental arch perimeter based
on a catenary curve.
The catenometer (Figure 4) consists
of a modified vernier gauge with a fine chain attached to
the points.
The device is mounted vertically on a clear
plastic sheet with the chain hanging freely.
The study
models are placed vertically against the plastic with the
interproximal guides on the distal aspect of each first
permanent molar.
The chain hangs freely and the caliper is
adjusted to find the best fit to the arch shape.
Fig 4. The catenometer is placed on the study model with
hanging chain adjusted to estimate the arch perimeter
(Musich et al. 1973)
In addition to the brass wire and chain techniques,
Lundström (1955) suggested calculating the dental arch perimeter with a caliper by measuring and adding straightline segments of the arch in six sections (Figure 5).
This
method, however, ignores the fact that the dental arch is
32
curved and therefore the summation of these straight-line
measurements has an inherent error, in that it shows less
space than is actually present in the arch.
Fig 5. Dental arch perimeter obtained by measuring the
arch in six sections (Lundstrom 1955).
BeGole (1979) took the advantage of improvements in
computer-science and wrote the first program to perform
dental model analyses, including tooth size/arch size discrepancy.
The program, MODELS, uses a set of 118 inputs to
perform the analyses.
These inputs are dental landmarks
that may be digitized from a photocopy of the study model.
Arch perimeter is calculated as “the sum of various connecting line segments drawn around the dental arch”; The
four segments start from the mesial surface of the first
molar to the distal surface of the lateral incisor, to the
mesial surface of the central incisor on the opposite side,
to the distal surface of the lateral incisor, to the mesial
surface of the first molar.
33
Direct measurement of photocopied three-dimensional
objects has a high potential for error in cases with severe
tipping.
Champagne (1992) reported that photocopies are an
unreliable method for arch length measurement and space
analysis determination.
On the other hand, Tran and col-
leagues (2003) compared the manual measurement of the irregularity index to computer measurements based on photocopies of models.
They concluded that the computer method
is a valid and reliable alternative for assessing mandibular incisor alignment.
To overcome the unreliability of 2-dimensional measurements, 3-dimensional model analyses were introduced
based on scanner-based 3-dimensional digitizers, laserbased scanners, or mechanical 3-dimensional digitizers.
Yamamoto and associates (1989) described an optical method
for creating 3-dimensional computerized models with a laser-beam scan of the dental casts.
Later, other attempts
were made to transfer the dental cast into a 3-dimensional
virtual model. Kuroda and colleagues (1996) introduced a
three-dimensional dental cast analyzing system that employs
laser scanning.
This computerized model can be used to
calculate distances and perimeters from the 3-dimensional
virtual model.
OrthoCad (Cadent, Fairview, NJ) is such a
34
system that is commercially available and transforms impressions or plasters into 3-dimensional virtual models.
Dental arch length is commonly measured at the level
of the teeth, not at the basal bone level.
Some years ago,
Rees (1953) described a method of measuring the bony apical
base from dental casts:
1. The lip and cheek frena are ground away from the
casts;
2. Three lines perpendicular to the occlusal plane (mesial to the first permanent molars and at the contact point of the central incisors), are constructed. These lines are extended by 8-10 mm from the
dental papilla toward the vestibular fold.
3. With the aid of a piece of thin adhesive tape, the
distance from the mesial of one first permanent molar around to the other is measured through the tips
of the vertical lines.
Because Rees’ method measured the outer border of the
basal bone, Howes (1960) stated that “This is a circumferential or a perimeter measurement and, in my opinion, is a
confusing or misleading term.”
He suggested measuring the
arch length as “the midline length of the basal arch, from
distal aspect of the first molars to the most anterior
point of the basal arch.
This is Point A in the maxillary
35
arch and Point B in the mandibular arch.” This method of
measuring basal arch length did not gain popularity because
it depends on two points, Point A and Point B.
Holdaway
(1956), for example, documented significant changes in the
maxillary and mandibular apical base relationship as a result of orthodontic treatment.
Payne (1966) studied 33 pa-
tients treated with the Begg technique and found a significant improvement in the maxillary and mandibular apical
base relationship.
Most of the improvement in the apical
base relationship was primarily accomplished by the posterior movement of Point A.
Fig 6. The four segments that represent basal arch (*)
(after Hew 1966)
Hew (1966) divided the basal bone into four segments
and measured the length of each segment individually (Fig-
36
ure 6).
The total length of the four segments was believed
to represent the perimeter of the basal bone.
He studied
the correlation between tooth mass and available basal arch
and found a high correlation between relapse and basal arch
deficiency.
He further indicated that “the reduction of
dental units improve the correlation between tooth mass and
basal arch length in relapsed cases.”
Stanton (1918), along with engineers, developed several instruments for accurately measuring dental casts.
Among these instruments was a surveying instrument, embodying the principles of a pantograph, capable of projecting
accurately to a plane any and all points of interest of the
dental cast.
Kleuglein (1985) used a modified pantograph
(Figure 7) to measure basal bone.
Sergl (1996) used the
same apparatus to measure the area within the borders of
basal bone.
These measurements were based on the principle
of tracing the contour of the basal bone.
Fig 7. Modified pantograph used by Kleuglein (Sergl
1996).
37
Purpose of the Study
Despite the numerous methods that have been developed
to measure arch length, most do not measure the actual
length of the basal bone.
Therefore, crowding has been
commonly measured relative to the perimeter of the dental
arch, but not relative to the basal bone that houses the
teeth.
Even with the methods that attempt to measure the basal bone, they are either dependent on complicated apparatus or time consuming methods.
On the other hand, relapse is still a concern for orthodontists and it might be helpful to study additional
factors in hope of finding a correlation with these factors
and relapse.
It is the purpose of this study to:
1.
Seek a reliable method to measure the perimeter of basal bone; and
2.
To study the relationship between posttreatment relapse and tooth size-basal bone perimeter deficiency in the mandibular arch in Class
II division 1 patients.
38
CHAPTER III: PATIENTS AND METHODS
Measuring Basal Bone
The most reliable way to measure basal bone perimeter
presumably would be through the use of a cone beam, 3D CAD
SCAN or a CT SCAN.
Given contemporary standards of radia-
tion hygiene, it would be difficult to utilize these methods solely for the sake of orthodontic “diagnosis.”
Ac-
cordingly, this study will explore the relationship between
three methods of measuring mandibular basal bone perimeter
from traditionally available orthodontic records: the dental casts and the lateral cephalometric radiograph.
The
first two methods will measure basal bone perimeter from
dental casts with a stainless steel wire.
The third method
will estimate the perimeter from a formula utilizing two
variables: one lateral cephalometric measurement and one
cast measurement.
Source of the Sample
A sample of eighteen patients with pre-treatment (T1)
and post-treatment (T2) records was collected from the
files of the Orthodontic Department of Saint Louis University.
The patients’ records were collected on the basis of
their having good impressions of the lower arch that reveal
most of the depth of the alveolar process.
39
Each record was
assigned a number so that the possibility of patient identification would be eliminated.
Measuring Basal Bone from the Cast
Preparing the Casts
The pretreatment and posttreatment study casts of the
lower arch were duplicated and trimmed to a level that represented the beginning of the basal bone.
The following
methods were used:
1. An impression was made for each model with Biostar machine (Biostar, Great lakes Orthodontics, LTD, Tonawanda, NY) and 3 mm mouthguard material;
2. The impression was poured with orthodontic stone and
allowed to set for one day;
3. Two lines were drawn perpendicular to the functional
occlusal plane from the mesial contact point of the
mandibular permanent first molar into the basal bone
area (Figure 8);
4. with the lateral cephalogram and the functional occlusal plane as a reference, the vertical distance between the averaged mandibular molar mesial cusp tip
and Point B was measured (Figure 9).
This measurement
was reduced by 9.6% to eliminate magnification.
40
Fig 9. The vertical distance between the averaged mesial cusp of the
lower molar and Point B.
Functional occlusal
plane was used as a reference
Fig 8. Terminal planes
marked on the model
5. The corrected measurement was transferred to the dental cast as a cross mark on the two terminal planes
using the mesial buccal cusp of the lower first molar
as a vertical reference point.
6. A horizontal line, Line X (Figure 10) was drawn around
the sulcus to connect these two cross marks along the
basal bone and parallel to base of the models.
This
procedure assumes that the base of the model was
trimmed parallel to the functional occlusal plane.
7. The area above line X and mesial to the terminal
planes was trimmed away with a wheel stone mounted on
41
a lathe.
This procedure will expose the basal bone
shelf.
8. Two lines were drawn perpendicular to the basal bone
shelf from the two mesial buccal contact points of the
first molars (Figure 11).
Fig 10. The grained area
represents the area to be
trimmed as described by
the terminal lines and
the X line
Fig 11. Projecting the
buccal contact point
to the basal bone area
9. A line was drawn to connect the labial section of the
right and left sides of the basal arches over the labial frenum area.
The center is marked as point FF
which represents the midline of the Labial basal arch
(Figure 12).
42
FF
Fig 12. Connecting the
right and left sides of
the basal arches over the
labial frenum area. The
midline is marked as FF
Fig 13. The Model is
ready for basal bone
measurement after exposing the basal shelf.
After all models were prepared (Figure 13). basal bone
perimeter was measured in two ways (Figure 14):
1. The center of the basal shelf (center basal bone); and
2. From the center of the basal shelf posteriorly around
the outer surface in the anterior segment (anterior
basal bone).
Fig 14. Basal bone perimeter estimated along
the basal shelf.
43
Selecting a Proper Geometrical Shape
For the purpose of measuring basal bone perimeter, it
was necessary to employ some defined curve.
After review-
ing several different curves (parabola, catenary curve,
circle, ellipse and oval), the ellipse curve was chosen for
the following reasons:
1. Unlike other shapes that require a complex formula to
calculate the perimeter, the perimeter of an ellipse can
be estimated by a simple formula that utilizes two variables, the length of the major and minor axes.
In the
current study, the major axis can be measured from the
cephalogram and minor axis from the study models.
2. Eccentricity (e) is a number that describes the degree of
roundness of the ellipse.
For any ellipse, 0 < e < 1.
The smaller the eccentricity, the rounder the ellipse.
If e = 0, it is a circle and if e = 1, it is a parabola.
Henrikson and colleagues (2001) studied the eccentricity
of the mandibular arch in a sample of 30 subjects with
normal occlusion.
They found that eccentricity varied
from .71 to .98. Thus, all mandibular arches studied were
elliptical.
44
Measuring Anterior Basal Bone
Basal bone perimeter was measured with a graded measurement wire (See appendix I for wire fabrication) from the
prepared models by trial-and-error method as followings:
1. The operator (WK) selected one of the preformed
wires where both ends coincide with the two lines
that were drawn perpendicular to basal bone shelf
from the two mesial buccal contact points of the
first molars.
2. The middle of the preformed wire coincided with
point FF.
When it did not, a shorter or longer wire
is selected until the center of the wire laid over
point FF.
3. On occasion, it was necessary to change the shape of
arch form from one eccentricity to another based on
the template, or from the greater curvature to the
lesser curvature (Figure 15).
Fig 15. The left SS wire was bent over the lesser curvature while the right one was bent over the greater curvature. Note that both arches have the same perimeter
45
4. When the actual estimate of the basal bone was between two sizes, the average was recorded (Figure
16).
Fig 16. A case where one wire is shorter “54 mm”
and the next wire is longer “56 mm.” Thus, the average was recorded “55 mm.”
Measuring Central Basal Bone
1. The operator (WK) selected one of the preformed
wires where both ends coincide with the two lines
that were drawn perpendicular to basal bone shelf
from the two mesial buccal contact points of the
first molars.
2. The middle of the preformed wire coincided anteriorly with the center of the basal bone thickness.
When it did not, a shorter or longer wire is selected until the center of the wire laid over the center
of basal bone.
46
Formulaic Estimation of Basal Bone Perimeter
Because the graded measurement wires were contoured as
an ellipse, this method used the formula for an ellipse to
estimate basal bone perimeter.
The formula is as follows:
P= Pi (X + Z)/2
Where:
P = the perimeter of an ellipse shape
Pi = 3.14
X = half the length of the major axis
Z = half the length of the minor axis (Figure 17).
Fig 17. A diagram representing the major and minor axes of an ellipse
The length of the major axis was measured from the
lateral cephalogram, whereas the length of the minor axis
was measured directly from the cast:
1. For measuring the anterior basal bone, the length of
the major axis (X), basal bone depth, was measured as
the distance from the averaged mesial contact points
of the lower molars to point BO (Jacobson 1975) measured parallel to the functional occlusal plane (Figure
47
18). Point B has a vertical distribution in the envelope of error.
Thus, the average error introduced
will be small (Baumrind and Frantz 1971). For the central basal bone measurement, the length of the major
axis was measured as the distance from the averaged
mesial contact points of the lower molars to a point
perpendicular to the apex of the lower incisor parallel to the functional occlusal plane.
This measure-
ment was reduced by %9.6 to eliminate the cephalometric magnification; and
Fig 18. Measuring the length of the major axis
(X), along the functional occlusal plane for the
anterior basal bone method (upper arrow) and for
the central basal bone method (lower arrow)
2. The length of the minor axis (Z), basal bone width, is
the distance between the buccal contact point of the
lower second bicuspids and the first molars (Figure
19).
The buccal extent of the contact point was se-
48
lected rather than the middle of the contact point because of the lingual inclination of the lower molar
(Figure 20).
If the contact point was open, then the
inner mesio-buccal line angle of the lower permanent
first molar was used.
All measurements were taken to the nearest 0.1 mm with
a digital caliper.
Data were stored in a commercial
spreadsheet program (Microsoft Excel 2003, Microsoft Co,
Redmond WA).
Fig 19. The length of
the minor axis (Z) as
measured from the dental cast
Fig 20. Because of the lingual inclination of the lower
molar, the buccal contact
point represents the center
of the basal bone better than
the middle contact point
Error of the Method
A reliability test was performed to evaluate measurement error.
Four out of 36 cases were randomly selected,
duplicated, trimmed to the basal bone level, and measured
49
with the graded measurement wire technique.
Also, the four
corresponding cephalograms were retraced and remeasured
again.
Intraclass Correlation Coefficient (ICC) was executed
on the repeated measures.
A perfect score equals 1.00;
however, a Cronbach’s Alpha ≥ 0.8 is considered an indicator of a reliable technique. Cronbach’s alpha was calculated from the formula:
where N is equal to the number of items and r-bar is the
average intra-item correlation among the items.
Posttreatment Relapse and Basal Bone Discrepancy
The correlation between post-treatment relapse and
tooth size, basal bone perimeter and the tooth size-basal
bone size discrepancy at the end of treatment were studied
using the records of 105 patients for whom complete pretreatment, immediate posttreatment and posttreatment records (approximately 15 years after treatment) were available.
These patients were part of the Saint Louis Universi-
ty recall study that was completed in 1990.
50
Source of the Sample
This 105 patients was part of a study conducted by
Paquette, Beattie, Luppanapornlarp and Johnston (1990).
The sample consisted of pretreatment (T1), immediate posttreatment (T2) and posttreatment (T3) records.
The inclu-
sion criteria were: Caucasian, at least a “half-step” Angle
Class II, division 1 malocclusion, no missing permanent
teeth prior to treatment, treatment completed between 1969
and 1980, complete records, including pre- and posttreatment lateral cephalograms and dental models and a willingness to return to the Orthodontic Clinic for complete follow-up records.
Of the 2500 patients who met the criteria, 238 expatients agreed to participate in the study.
Not everyone
who agreed to participate actually did and some records
could not be located. In the end, the sample consisted of
105 individuals, 51 extraction and 54 nonextraction patients (Table 1).
The average posttreatment interval was
14.88 years, with a range of 8.95 to 22.50 years.
The
posttreatment records obtained from each subject were a
lateral cephalogram and study models.
51
Table 1. Disposition of Paquette’s sample
Disposition
Main Sample
Refused to participate
Failed appointment
Pregnant
Would not return phone calls
Unable to contact
Retreated recently
Record incomplete
Participate
Total
26
10
9
24
28
1
35
105
238
Model Analysis
The model analysis for this sample was completed by
Beattie (1991) and Luppanapornlarp (1992).
All models were
photocopied from the occlusal surface. A 100 mm ruler was
included in the image for reference. To make contact points
easier to see, an enlargement of 122% was introduced by the
photocopy machine.
The photocopies were then digitized ac-
cording to a custom 68 point regimen (designed with Tools,
a customization of Dentofacial Planner, Version 5.32, Dentofacial software, Toronto, Canada).
All measurements, ex-
cept one, were generated by the cephalometric software that
include arch length required, Intercanine width and Irregularity index (Figure 21).
Arch width from 5-5 (Figure 22)
52
was measured manually with a digital caliper to the nearest
0.1 mm.2
Fig 21. Irregularity Index = A+B+C+D+E (Little
1975).
Fig 22. Lower arch width
measurements: 3-3 intercuspid width; 5-5 distance between the buccal
contact point of the lower first molar and the
second bicuspid.
Cephalometric Technique
Given that the purpose of this study was to measure
basal bone discrepancy and relapse, certain measurements
from the lateral cephalogram were essential to an estimate
of basal bone perimeter.
All tracings were completed by Beattie (1991) and
Luppanapornlarp (1992) and checked by a second observer3
prior to execution of the analysis.
2
All lateral cephalo-
Of the 105 patients, the digitized models of 23 patients could not be
obtained. Thus the operator (WK) performed all the measurements on the
photocopies of these models.
3
Dr. L.E. Johnston
53
grams were traced on a light box with a sharp 3H drafting
pencil on 0.003 inch matte acetate.
For each film, standard anatomical landmarks were
traced (Figure 23).
Molars and incisors were traced with a
template and the long axis was transferred from the template to the tracing based on the “best fit” superimposition.
Mesial contact points of the right and left upper
and lower molars were then averaged and marked with dots.
The functional occlusal plane (FOP) was used rather than
the Downs’ occlusal plane, because the former is less affected by changes in incisor position and thus more stable
reference plane (Harris, Johnston, and Moyers 1963).
The
FOP was drawn according to Jenkins (1955), who defined it
as a line bisecting the radiolucent areas between the occlusal surfaces of the upper and lower first molars and bicuspids.
Cephalometric Technique and Analysis
All tracings were digitized by Beattie (1991) and Luppanapornlarp (1992) with a transparent digitizer (Scriptel
RDT-1212, Scriptel Corporation, Columbus OH) and a commercial software package (Dentofacial Planner, Version 5.32,
Dentofacial Software, Toronto, Canada).
54
Fig 23. Cephalometric tracing points: diagram adapted from
Broadbent and Broadbent (1975).
Based on the digitized landmarks, the program executed
a suite of cephalometric measurements for each tracing.
A
custom analysis was written (designed with Tools, a customization of Dentofacial Planner, Version 5.32, Dentofacial
software, Toronto, Canada) to generate the measurement of
basal bone depth (M6-BO) that is required for the formulaic
estimation.
This measurement was reduced by 9.6% to elimi-
nate cephalometric magnification.
In addition to the meas-
urement of basal bone depth, other measurements were col-
55
lected to study any possible correlation between these
measurements and postretention relapse (Table 2).
Table 2. Cephalometric measurements generated by the
customized analysis.
Measurement
Abbreviation
Angular (º)
Sella-Nasion-Point A
Sella-Nasion-Point B
Point A-Nasion-Point B
Mandibular plane-Frankfort plane
Mandibular plane- Sella- Nasion
Lower 1-Nasion-Point B
Lower 1-Mandibular Plane
Lower 1-Frankfort plane
SNA
SNB
ANB
FMA
SN-GoGn
L1-NB
IMPA
FMIA
Linear (mm)
Lower 6- Point BO
Lower 6- Lower 1
Lower 1- Point A- Pogonion
Lower 1- Nasion- Point B
AO-BO
Nasion-Menton
L6-BO
L6-L1
L1- APg
L1-NB
Wits
N-Me
Error analysis of the cephalometric method
To assess error (specifically random error,) double
determinations (Dahlberg 1940) were preformed by Beattie
(1991) and Luppanapornlap (1992) with 10 sets of lateral
cephalograms and models (5 extraction and 5 nonextraction)
chosen with the aid of a table of random numbers (Dixon and
Massey 1969).
Each film was retraced and redigitized and
the models were rephotocopied and redigitized.
The error
standard deviations from the double determinations were
generated according to Dahlberg’s formula, √ [∑d2/2N], where
56
d is the difference between double determination and N is
the number of double determinations.
Because the digitized photographs of 23 patients were
not available, Intraclass Correlation Coefficient (ICC) was
executed on 3 sets of records and Cronbach’s alpha was calculated for the repeated measurements.
Statistical Analysis
Standard descriptive statistics (arithmetic mean,
range and standard deviation) were computed for each variable assessed at T1, T2 and T3.
Relapse was assessed by the
irregularity index (Little 1975).
The irregularity index
measures displaced contact points and provides an objective
value to quantify relapse of the lower incisors. Pearson’s
formula was used to study the correlation between tooth
size, basal bone size and tooth size-basal bone size deficiency at T1, T2, T3 and posttreatment relapse at T3.
Al-
so, the irregularity index was correlated with all cephalometric measurements generated by the custom analysis.
Be-
cause it is assumed that teeth would be aligned properly at
T2, tooth size was measured individually from the photographs at T2.
Occasionally, tooth size was measured from
the photographs at T3 if teeth at T2 still have bands on
them.
57
CHAPTER 4: RESULTS
Basal Bone measurements
Descriptive statistics were calculated for the 18 patients at T1 and T2.
The range, mean, and standard devia-
tions for each measurement are presented in Tables 3 to 4.
Basal bone depth was on average 18.3 mm, while basal bone
width was on average 39.6 mm.
Based on the vertical cut
level, basal bone was located on average 15.6 mm apical to
the functional occlusal plane.
The center basal bone
length was 8.5 mm less than the formulaic measurement; the
anterior basal bone length overestimated the length of basal bone by 0.8 mm compared to the formulaic measurement.
The anterior basal bone measurement displayed a higher
significant correlation (r=.98) with the formulaic measurement than the center basal bone methods (r=.93).
Both
methods, however were highly and significantly correlated
with the formulaic measurement (Table 5 and Figure 24).
Intraclass Correlation Coefficient (ICC) was calculated from error measurement on four patients’ records (Table
6).
Fortunately, It was proven that the formula’s estima-
tion was highly repeatable (α=.99)
58
Table 3. Descriptive statistics for the 18 patients at T1
and T2.
Measure
N
L6-BO
18
Minimum
T1
T2
15.4
11.8
Maximum
T1
T2
22.2
22
Mean
T1
T2
19.3
5-5
18 36.0 31.4 48.2 43.2 40.9
Formulaic
18 56.6 46.9 70.4 67.0 62.4
measurement
Central meas50
40
64
60
52.5
16
urement†
Anterior meas18 57.0 47.0 72.0 68.0 63.6
urement
Vertical cut
18 12.7 11.8 19.2 20.8 15.5
level
† Central measurements of two sets were not
cause of improper lingual depth.
S.D.
T1
T2
17.3
1.80
3.22
38.2
1.71
1.40
57.2
3.88
6.74
50.3
4.42
5.67
57.6
4.04
6.79
15.7
2.03
2.22
completed be-
Table 4. Overall descriptive statistics for the 18 patients.
Measure
N Minimum Maximum
Mean
11.8
22.2
18.3
L6-BO
18
31.4
48.2
39.6
5-5
18
46.9
70.4
59.8
Formulaic measurement
18
40.0
64.0
51.3
Central measurement†
16
47.0
72.0
60.6
Anterior measurement
18
11.8
20.8
15.6
Vertical cut level
18
†Central measurements of two sets were not completed
cause of improper lingual depth.
S.D.
2.51
1.56
5.31
5.04
5.42
2.13
be-
Table 5. Pearson’s correlation for the central measurement
and anterior measurement to the formulaic measurement
R
Central measurement/ formulaic measure- 0.93
ment
Anterior measurement/ formulaic meas- 0.98
urement
59
Approx. Sig.
<.0001
<.0001
75
Graded wire measurement
70
65
60
55
50
45
40
35
40
45
50
55
60
65
70
75
Formulaic estimation
Fig 24. A scattergram that compares the formulaic measurement to the center basal bone measurement (dash shape) and
to the anterior basal bone measurement (box shape)
Table 6. Cronbach’s Alpha for Intraclass Correlation Coefficient
Measure
L6-BO
5-5
Estimated perimeter
1st method measurement
2nd method measurement
Vertical
Cronbach’s Alpha
0.99
0.95
0.99
0.96
0.98
0.94
60
Posttreatment Relapse and Tooth Size-Basal Bone
Size Discrepancy
For the 105 patients, descriptive statistics (means,
standard deviations and range) for age, treatment time and
posttreatment interval are presented in Table 7.
Because
the retention period was approximately 4 years, these patients have been out of retention an average of 10.8 years.
Descriptive statistics for cephalometric and cast
measurements were also calculated for the 105 patients at
T1, T2 and T3 and all summarized in Table 8.
The formulaic
measurement was .93 mm on average less than the tooth mass
at the end of treatment.
On average, basal bone discrepan-
cy decreased from T1 to T2 by 2.35 mm, but increased at T3
by 2.95 mm.
In a comparison between the changes of basal
bone depth (M6-BO) and the dental arch depth (M6-L1), both
decreased 1.9 mm and 2.3 mm respectively from T2 to T3.
The study presented a weak, but statistically significant correlation between basal bone discrepancy at T2, T3
and relapse at T3 (r=-.198, r= -.318 respectively)(Table 8
and Figures 25-27).
There was no statistically significant
correlation between relapse and tooth size or basal bone
size at T1, T2, and T3.
The correlation between postreten-
tion irregularity index and different variables that may
contribute to relapse is presented in Table 10.
61
The error studies for Luppanapornlarp, Beattie and
this study are presented in Tables 11-13.
Intraclass Cor-
relation Coefficients were calculated on the records of 10
patients. Cronbach’s Alpha for different measurements are
presented in Table 14.
Table 7. Descriptive statistics of the 105 patients
Time point
Start of Tx
End of Tx
Recall
Treatment
Posttreatment
Mean
S.D.
Age (Years)
12.72
1.47
14.53
1.56
29.42
3.32
Interval (Years)
1.81
0.57
14.88
3.31
62
Minimum
Maximum
10.42
12.09
22.64
16.75
19.08
36.25
0.5
8.95
3.89
22.5
Table 8. Descriptive statistics for the 105 patients at T1, T2 and T3.
Measurement “angular”
N
Minimum
T2
72.5
T3
73.1
T1
89.2
Maximum
T2
86.4
T3
87.3
T1
80.6
Mean
T2
78.9
T3
79.6
T1
3.23
S.D.
T2
3.09
T3
3.23
SNA
105
T1
73.2
SNB
105
72.3
71.1
72.7
83.7
82.6
84.5
75.8
75.6
76.3
2.83
2.98
3.57
ANB
105
-0.1
-2.0
-2.8
9.7
9.7
9.6
4.8
3.3
3.2
1.96
2.00
2.35
FMA
105
10.2
8.8
0.7
41.7
40.2
41.6
22.0
22.4
20.6
5.55
5.96
7.59
SN-GoGn
105
20.5
18.6
13.1
50.3
49.5
51.8
37.1
36.0
33.9
5.46
5.85
7.43
L1-NB
105
9.3
9.3
6.8
39.5
40.0
39.2
24.8
28.0
23.1
5.49
5.78
5.72
IMPA
105
74.1
75.9
75.5
110.2
111.7
114.1
94.2
98.8
95.1
6.45
6.95
7.24
M6-BO
105
12.4
9.91
7.27
24.7
23.4
22.1
19.6
17.4
15.5
2.05
2.90
2.90
5-5
105
40.9
40
38.0
57.3
57.3
56.8
49.4
47.3
47.1
2.99
3.59
4.03
Basal bone perimeter
105
46.1
41.6
36.6
73.9
70.8
70.3
62.5
57.7
54.7
4.10
6.30
6.50
Space required
105
56.0
48.4
*
75.6
72.2
*
65.8
58.6
*
3.42
6.47
*
Basal bone discrepancy
105
-18.1
-8.8
-13.8
8.7
5.1
2.6
-3.3
-0.9
-3.9
4.51
2.58
2.86
Irregularity index
105
0.2
0.0
0.2
14.2
1.9
9.2
4.69
0.5
3.3
2.66
0.46
1.91
3-3 width$
105
19.4
22.1
22.6
36.1
36.0
34.3
28.2
29.4
28.3
3.98
3.48
3.32
L6-L1
105
17.3
14.6
12.4
27.0
26.1
25.4
22.5
20.4
18.1
2.13
2.95
2.73
L1-APg
105
-4.1
-3.3
-4.1
5.1
6.1
4.9
0.24
1.48
.0
1.82
1.85
1.79
Measurement “linear”
* Measurement not completed at the timeframe
63
Table 9. Pearson’s correlation for tooth size, basal bone
size and basal bone discrepancy and irregularity index at
T3
Studied variable
Tooth size at T1
Tooth size at T2
Basal bone size at T1
Basal bone size at T2
Basal bone size at T3
Basal bone discrepancy at T1
Basal bone discrepancy at T2*
Basal bone discrepancy at T3*
R
Sig.
-0.162
0.159
-0.121
0.082
0.022
0.013
-0.198
-0.318
0.098
0.105
0.218
0.405
0.823
0.447
0.021
<0.001
* Significant correlation at 95% level
12
Irregularity Index @ T3
10
8
6
4
2
-20.00
-15.00
-10.00
0
0.00
-5.00
5.00
10.00
15.00
Basal Bone Discrepency @ T1
Fig 25. A scattergram that presents the relationship between basal bone discrepancy at T1 and irregularity index
at T3 (r = .013)
64
12
Irregularity index at T3
10
8
6
4
2
-10.00
-8.00
-6.00
-4.00
-2.00
0
0.00
2.00
4.00
6.00
Basal bone discrepency at T2
Fig 26. A scattergram that presents the relationship between basal bone discrepancy at T2 and irregularity index
at T3 (r = -.198)
12
Irregularity Index @ T3
10
8
6
4
2
-16.00
-14.00
-12.00
-10.00
-8.00
-6.00
-4.00
-2.00
0
0.00
2.00
4.00
Basal Bone Discrepency @ T3
Fig 27. A scattergram that presents the relationship between basal bone discrepancy at T3 and irregularity index
at T3 (r =-.318)
65
Table 10 Pearson’s correlation for different variables and
irregularity index at T3.
Measure
R
Sig. Measure
SNA at T1*
-.312 <.001 FMIA at T1
SNA at T2*
-.313 <.001 FMIA at T2
SNA at T3*
-.353 <.001 FMIA at T3
SNB at T1*
-.269
.005 IMPA at T1*
SNB at T2*
-.282
.004 IMPA at T2
SNB at T3*
-.258
.007 IMPA at T3*
ANB at T1
-.130
.186 FMA at T1
ANB at T2
-.064
.516 FMA at T2
ANB at T3
-.094
.340 FMA at T3*
Wits at T1
-.036
.715 SN-GoGn at T1
Wits at T2
.041
.680 SN-GoGn at T2*
Wits at T3
-.116
.240 SN-GoGn at T3*
L1-NBº at T1*
-.249
.010 N-Me at T1
L1-NBº at T2
-.113
.250 N-Me at T2
L1-NBº at T3
-.154
.120 N-Me at T3
L1-NB mm at T1*
-.196
.050 L6-L1 mm at T1
L1-NB mm at T2
.051
.600 L6-L1 mm at T2
L1-NB mm at T3
-.069
.484 L6-L1 mm at T3
L1-APg mm at T1
-.189
.053 5-5 width at T1
L1-APg mm at T2
.054
.580 5-5 width at T2
L1-APg mm at T3
-.029
.769 5-5 width at T3
Pg-NB mm at T1
.148
.130 3-3 width at T1
Pg-NB mm at T2
.120
.220 3-3 width at T2
Pg-NB mm at T3
.061
.540 3-3 width at T3
* Significant correlation at 95% level
R
.131
.000
.027
-.201
-.146
-.212
.157
.182
.203
.123
.202
.221
.014
.080
.126
-.087
.018
.000
-.114
.191
.056
-.007
.074
.028
Sig.
.180
.000
.780
.039
.137
.029
.110
.060
.040
.210
.040
.020
.890
.420
.201
.377
.860
.000
.240
.051
.570
.941
.450
.780
Table 11. Error standard deviations for double determination (N=30) (Modified after Luppanapornlap 1992)
Measure
IMPA
FMA
L1-APg
S.D.
Angular
1.58
0.44
Linear
0.40
66
Table 12. Double determinations for model measurements
(N=30): Descriptive and inferential statistics; study model
error (SDE)(Modified after Luppanapornlap 1992)
Measure
Mandibular intercanine width
Mandibular arch
length
Irregularity
Index
Replication 1
Mean
S.D.
Replication 2
Mean
S.D.
24.84
1.73
25.25
2.64
1.33
57.10
5.78
57.19
5.88
0.39
3.30
2.81
3.13
2.68
0.69
SDE
Table 13. Error standard deviations for double determination (N=30) (Modified after Beattie 1991)
Measure
IMPA
FMA
L1-APg
S.D.
Angular
1.07
1.16
Linear
0.54
Table 14. Double determinations for the 23 missing measurements. Cronbach’s Alpha values for Intraclass Correlation
Coefficient.
Measurement
5-5 width*
3-3 width
Tooth size
Irregularity index
* remeasured for the 105 patients
67
Cronbach’s Alpha
0.91
0.94
0.89
0.96
CHAPTER 5: DISCUSSION
The present study was designed to characterize the
long term effect of tooth size-basal bone size discrepancy
on relapse in Class II, Division 1 patients.
To assess the
discrepancy, it was first necessary to develop a reliable
method to measure basal bone perimeter from conventional
data source; models and cephalograms.
Basal Bone Measures
Because basal bone can be seen as a 2D geometrical
shape, it was possible to estimate the length of basal bone
by a formula with high reliability.
Because of its unique
features, the ellipse was selected as the basis of the present method to study basal bone length.
It was the question whether to measure the perimeter
at the center of basal bone or the center in the posterior
segment and the outer surface in the anterior segment.
Be-
cause the anterior measurement revealed a higher correlation (r= .98) with the formulaic measurement than the central measurement (r=.93), the anterior method was selected
in this study.
In the central measurement, it was noticed that the
anterior placement of the wire varied with the variation of
basal bone thickness, the thinner the basal bone is the
68
larger the measurement and vice versa (Figure 28).
This
variation may account for the lower correlation achieved by
central method.
A
B
C
Fig 28. The effect of basal bone thickness on basal bone
perimeter as measured centrally. Note that the thicker the
basal bone is anteriorly, as in A, the shorter the perimeter is. Note the difference between the two perimeters of A
and B as superimposed in C.
With the anterior method, basal bone perimeter measured with the graded measurement wires was 0.8 mm longer
than the formulaic measurement.
This difference could be
explained by:
1. Measurements completed on the dental casts did not
take into consideration the soft tissue thickness that
covers the alveolar ridge anteriorly.
Rees (1953)
considered the effect of soft tissue thickness on basal bone perimeter to be minimum and that “the buccal
mucosa is included in the measurement, but, it is very
thin in this area, the deviation is relatively small
and is relatively consistent in all patients.” Studies
69
have reported, however, that the thickness of facial
gingiva in the mandible at the incisors region averaged 0.7 mm (Muller and associates 2000).
2. Facial displacement of the soft tissue during the impression procedure could increase the length of basal
bone when measured from the casts.
Soft tissue dis-
placement is not expected to happen at the level of
the attached gingiva or the mucogingival junction;
however the tissues start to displace gradually apical
to the mucogingival junction.
Because basal bone lev-
el in this study was on average 2.6 mm4 apical to the
mucogingival junction, soft tissue displacement is assumed to be minimal.
Clinical Importance of Measuring Basal Bone with a Formula
The potential clinical importance of measuring basal
bone with a formula is thought to facilitate basal bone
measurement from conventional records regardless of the
quality or the vestibular depth of the casts.
Only few
methods have been suggested to measure basal bone length
(Rees 1953, Howes 1960 and Hew 1966).
4
However, these meth-
Based on the fact that the lower incisor’s crown length is 9 mm and the
width of the attached gingiva is 4 mm. Thus, basal bone is located 15.6
mm (the vertical cut) – 13 mm = 2.6 mm apical to the mucogingival junction.
70
ods require dental casts with deep vestibule to perform basal bone measurement.
Also, the study found that the formulaic estimation is
consistent if the landmarks are correctly placed.
However,
the formulaic measurement should not be considered in patients with lingual inclination of the buccal segments as
the inclination hides the actual width of basal bone and
leads to an underestimated basal bone perimeter.
Tooth Size and Basal Bone Size relationship
Because there is a difference between the size of the
crowns and the size of the root apices that are located in
basal bone, the perimeter of basal bone, from a theoretical
stand-point, is expected to be less than tooth size.
How-
ever, Rees (1953) found the mandibular basal bone perimeter
to be on average 4.47 mm larger than the tooth size, with a
range of 1.97 to 6.97 mm.
Stifter (1958) also found the
mandibular basal bone to be 2.83 mm on average larger than
tooth size, with a range of -3.7 to +8.6 mm.
It should be
emphasized that Rees and Stifter measured basal bone perimeter along the outside surface of the alveolar ridge that
lead to an overestimation of basal bone size.
On the other
hand, the present study reported that basal bone size, at
the end of treatment, is about 1 mm lesser than tooth size
71
with a range of -8.8 mm to 5.1 mm.
This wide range (about
14 mm) reiterates the fact that basal bone host the root
apices, not the crowns themselves and therefore, basal bone
length is not an indicator for dental arch length.
Basal Bone Location
In terms of locating basal bone, basal bone was 15.6
mm apical to the buccal cusp tip of the mandibular first
molar.
This distance was 1.6 mm longer than the 14 mm sug-
gested by Falck (1969). With triangular calculation (Figure
32), it was possible to estimate that basal bone level in
this study was 2.4 mm occlusal to the root apex and 6.6 mm
apical to the gingival margin.
This position corresponds
to the finding of Howes (1947) that basal bone is located
in the apical one third of the alveolar bone.
On the other
hand, basal bone level in this study was 1.4-3.4 mm less
than what Rees (1953) found (8-10 mm).
72
Fig 32. Since the lower incisor has an average inclination to the occlusal plane of 65º and the average incisor’s length is 20 mm, this is
expressed as 18 mm of true vertical height of the incisor.
Posttreatment Relapse and the Amount of Tooth SizeBasal Bone Size Discrepancy
Because the present study has developed a method to
measure basal bone perimeter, basal bone discrepancy at T1,
T2 and T3 was correlated with the amount of relapse at T3.
It would be reasonable to think that patients who have
larger basal bone at the beginning of treatment would have
less relapse posttreatment.
Unfortunately, the present
study failed to show a correlation between basal bone discrepancy at T1 and relapse (r=.013, p=.447).
On the other
hand, the study found a weak but statistically significant
negative correlation (r=-.198, p<.05; r=-.318, p<.0001) between relapse and basal bone discrepancy at T2 and T3, respectively.
The difference in the correlation could be ex-
plained by the fact that about half of the patients had two
bicuspids extracted that would decrease basal bone perimeter.
Tooth Size and Relapse
Even though some studies have reported a significant
correlation between tooth size and relapse (Fastlicht 1970;
73
Norderval, Wisth and Boe 1975; Smith, Davidson and Gipe
1982; Rhee and Nahn 2000), the present study failed to show
a statistically significant correlation between relapse and
tooth size at T1 and T2 (r= -.162 and r=.159), respectively.
This finding corresponds to the finding of other stud-
ies that failed to presents such a relationship (Howe,
McNamara and O’Connor 1983; Puneky, Sadowsky and BeGole
1984; Radnzic 1988).
Mandibular Arch Depth Change
Dental arch depth and basal bone depth decreased 5 mm
and 4.1 mm, respectively from T1 to T3.
Because 48% of the
sample had two lower bicuspids extracted, forward movement
of the lower molars to close the extraction space and to
aid in achieving Class I molar relationship would account
for that decrease in the dental arch depth and the basal
bone depth during treatment.
When comparing changes between dental arch depth and
basal bone depth between T2 and T3, dental arch depth decreased on average 2.3 mm while basal bone depth decreased
1.9 mm.
This decrease could be interpreted as a forward
movement of the lower molars of 1.9 mm and a backward movement of the lower incisors in the amount of 0.4 mm.
Sever-
al other studies supported these findings of continual de-
74
crease in arch depth (Simons and Joondeph 1973; Sinclair
and Little 1983; Little and associates 1990).
Little
(1990) stated that “As teeth erupted after treatment, mesial molar movement and lingual tipping of incisors were the
most common cephalometric findings.”
Other factors that might contribute to the forward
movement of the molars include the anterior component of
force, as well as the mesial drifting tendency of teeth
when in occlusion (Van Beek 1978).
Cephalometric Variables
As a side note, various cephalometric measurements
have been correlated with relapse.
Following the trend
found in previous stability studies (Bishara, Chada, and
Potter 1973; Little, Wallen and Riedel 1981), most of the
variables failed to show any significant correlation with
relapse.
However, some variable showed a weak significant
correlation with relapse such as SNA and SNB at T1, T2, and
T3.
Other variables showed a weak significant correlation
only at T1 such as L1-NBº, L1-NB mm, L1-APg and IMPA.
Limitation of the Study and Suggestions
The study had some limitations.
The sample in this
study received orthodontic treatment during the 1960s and
75
70s when extraction was a common procedure to alleviate
crowding.
Thus, our sample does not have patients with big
basal bone discrepancy at the end of treatment.
It would
be interesting to conduct a similar study on patients with
severe crowding treated as nonextraction and correlate basal bone discrepancy with long term stability in these patients.
On the other hand, one might study the relationship
between basal bone discrepancy and relapse on patients with
minimal dental crowding and proclined incisors.
This may
exclude other initial factors, such as rotation, that may
contribute to relapse in the future and magnify the importance of basal bone discrepancy.
Summary
The purpose of this study was to evaluate the effect
of basal bone discrepancy on long term stability of mandibular anterior teeth in a large group of Class II, Division
1 patients.
The study searched for a reliable way to meas-
ure the length of basal bone by employing an elliptical
formula and tested its validity on 36 casts.
After proven
to be reliable, the basal bone discrepancy was measured
utilizing the records of 105 patients.
On these patients,
photocopies of study models and cephalograms were available
76
pretreatment (T1), at the end of active treatment (T2), and
a mean of 14.8 years posttreatment (T3).
Irregularity was
calculated according to the method of Little (1975).
The
data failed to show a correlation between basal bone discrepancy at T1 and relapse.
However, it was demonstrated
that a weak but statistically significance correlation (r=.198) exists between basal bone discrepancy at T2 and incisor irregularity at T3.
Furthermore, the correlation was
stronger between basal bone discrepancy at T3 and incisor
irregularity at T3
(r=-.318)
Over the nearly 15 years,
basal bone discrepancy increased an average of 2.96 mm implying a continual reduction of basal bone length.
77
APPENDIX I
Fabricating Hemi-Elliptical Wires
Sixteen different lengths of stainless steel wire
(graded measurement wires) that measured from 40 mm to 70
mm, in 2 mm increments, were bent into a hemi-elliptical
shape as followings:
1. Using a straight 14 inch 0.032 inch stainless steel
wire, the desired length was cut 0.5 mm longer. Stainless steel wire was preferred over brass wire to maintain the elliptical shape and resist distortion.
2. Both ends were ground with a blue stone mounted on a
slow speed handpiece to have a flat end instead of a
smashed end and produced wires of the desired lengths.
A digital caliper was used to check for accuracy.
3. With a fine Sharpie® marker, a mark was placed in the
middle of the wire. This mark aided in forming the
hemi-elliptical shape of the wire as well as placing
the wire, later, over the approximate midline of the
basal bone.
4. The wire was contoured on an ellipse template (Figure
30) using the 30º ellipse shape for the best fit (Figure 31).
Fig 30. The elliptical
template being used in
the study
Fig 31. The graded
measurement wire is
bent to the best fit
78
5. Each wire was labeled with its length (Figure 32).
Fig 32. The graded meaurement wire is
ready for basal bone measurement
79
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VITA AUCTORIS
Wael Kanaan was born on the 2nd of July 1978 in
Volfsburg, Germany. Dr. Kanaan is the oldest of three boys
and a girl of an educated Syrian family who believed in
science and education.
He moved with his family to Saudi Arabia in 1986 and
graduated from King Fahd High School in 1995. After that,
he moved to Aleppo, Syria, to start his dental education at
Aleppo University and received his Doctor of Dental Surgery
degree in July, 2000.
After gaining some orthodontic expe-
rience at Damascus University and the University of Michigan, he was accepted into the orthodontic residency program
at Saint Louis University.
The best day of his life was when he met his wife, Siba Tabbakh, and married her early January 2004.
Dr. Kanaan will eventually practice in his country,
Syria, after spending some years in the US.
90