Download post-treatment change of overbite as related to incisal inclination

Medicine magisterexamen i
odontologi
Master of Medical Science in
Odontology
Postretention change of overbite as related to
incisal inclination and position
Anahita Rashedi
Odontologiska Institutionen
Stockholm 2006
Nr 102
A dissertation submitted for fulfilment of master degree as part of the
orthodontic postgraduate program
ACKNOWLEDGEMENTS
With highest gratitude to Professor Lennart Lagerström and Professor Jan
Huggare, the Head of Department of Orthodontics at Karolinska Institutet,
for their time, excellent guidance and support throughout the study and for
making this study possible.
Special thank to Halmstad Orthodontic Clinic providing all the patient
records and for their welcome to the clinic for measurements and access to
facilities in accordance with this study.
DECLARATION
This thesis has not been submitted elsewhere for any other Degree or
Qualification. Except where acknowledged this thesis is my original work.
SIGNATURE:
DATE:
2
TABLE OF CONTENTS
ABSTRACT
CHAPTER I
INTRODUCTION
AIMS OF THE STUDY
HYPOTHESIS
CHAPTER II
MATERIAL AND METHODS
METHODS
STATISTICS
CHAPTER III
RESULTS
CHAPTER IV
DISCUSSION
CHAPTER V
CONCLUSIONS
CHAPTER VI
REFERENCES
APPENDIX I
3
ABSTRACT
AIM: to investigate post-treatment overbite relapse as related to incisal
inclination and interocclusal position changes (according to Backlund’s
index, 1958). Furthermore, to identify cephalometric variables for prediction
of posttreatment overbite relapse.
MATERIAL AND METHODS: Study models and roentgen-cephalograms
from 97 orthodontically treated patients were analysed in regard to
- Incisal inclination and interocclusal position on the palatal surface of the
upper incisors (Backlund´s index, 1958)
- Vertical skeletal relation before treatment (T1), at retention (T2) and at
post-retention at age of 19 years (T3).
RESULTS: There was a significant overbite change at T3 compared to T2
(p < 0.05). No correlations could be found between the overbite relapse at
T3 and incisor inclination, interincisal angle, interocclusal position, or with
any other variables at T2. At T1, none of the included variables except
ML/NSL and interocclusal position 4 (Backlund´s index) could predict
overbite relapse at T3 (p < 0.05).
CONCLUSIONS: This study indicates that the orthodontic treatment
outcome, as far as interincisal relation, incisal inclination and interocclusal
position are concerned, is not related to the long term overbite relapse.
Dentitions characterized by an initial low mandibular plane angle and a
gingivally located lower anterior occlusal position (Backlund´s index 4) are
prone to overbite relapse.
4
INTRODUCTION
The overbite is defined as vertical overlapping of the anterior incisors with
the average of being equal to one third the length of the maxillary incisor
crown (Strang 1934, 1950).
During the past 10 000 years of the history of mankind, this definition has
changed. Due to an altered lifestyle from hunting to agriculture and the
transform to the industrial world, the dental occlusion has adopted to the
environmental need. The overbite such as the contemporary definition above
only existed in the ancient population immediately after the eruption of the
permanent teeth. With extensive tooth wear due to non-processed food, it
was then soon after, to edge to edge relationship. (Thilander et al 1991,
Varrela 1992, Kaifu 2000).
Rowlett et al (1923) described the incisors of primitive man occluding in an
edge-to-edge relationship with the molars in normal occlusion. The vertical
overlapping, known as “overbite” has prevailed since only 2000 years ago
and is believed to be due to transformation to the civilized diet (Rowlett et al
1923).
In the ancient populations, the edge to edge anterior occlusion was due to
the tooth wear and its effect on interproximal wear creating spaces. Lingual
tipping of anterior teeth to an edge to edge relationship was to compensate
and maintain the contacts between adjacent teeth (Kaifu, 2000, Silness et al
1993).
The prevailing definitions of contemporary malocclusions are dynamic and
the norms of what is believed to be ideal, might change in the future (Kaifu
2000).
5
In the study of Moyers (1960), it is claimed that there is no complete
agreement on the normal range of overbite and that it may vary with the age
and facial pattern and time.
An important criteria for a successful orthodontic treatment result, is to
achieve a normal overbite and to maintain it permanently. The overbite in
long-term is dependent on several factors. According to Backlund (1958)
one of the causes of the increased overbite is the inclination of the upper and
lower incisors in relation to their supporting jaw bone and to each other.
Retroclined incisors give rise to an enlarged interincisal angle with poor
vertical support for the anterior occlusion. The anterior teeth may therefore
reach excessive vertical levels and overlapping. Eruption goes on until the
vertical growth force of the alveolar bone has ceased or is balanced by
masticatory axial forces or forces exerted by soft tissue or until impingement
of the gingival tissues occurs. The incisor angle is by definition of Backlund
(1958) the angle formed by lower incisors with the lingual surface of upper
incisors. Another major assumable factor of importance for stabilization of
the incisors, is the morphology of the horizontal plateau, the so called
cingulum of the upper incisors. The extent of this plateau and its
morphology are important, to allow contact with the lower incisors and
balance for small lateral and forward movement (Backlund 1958).
To increase the vertical stability, it would then be important to pay attention
to a proper finishing of the incisor angle and interincisal relation during
orthodontic treatment.
Payne et al (1964) investigated the relation of overbite change to postretention growth, indicating that post-retention ramus growth tended to
6
decrease the mandibular plane angle, resulting in increased posterior facial
height and forward positioning of the symphysis and therefore considered
this phenomenon as partially responsible for overbite relapse.
There have also been studies about different treatment modalities such as the
role of extraction versus non extraction on the stability of the overbite.
Hernandez et al (1969) found greater incidence of relapse in an extraction
than a non extraction sample.
Magill (1960) found that one half of the overbite relapse occurred within
two years out of retention. There was no significant difference with regards
to different Angle classes of malocclusion or mode of treatment when it
comes to extraction versus non extraction.
Bishara and Jakobsen (1998) indicate that despite significant correlations
between overbite and facial height based on untreated long-term follow up
of 40 years, they are low and not useful for predictive purposes. They
claimed that normal growth changes in the vertical dimension of the face,
does not play a clinically significant role in determining the amount of the
overbite on an individual. Other factors such as growth of the alveolar
processes might also influence changes in overbite.
The relation of the upper incisors to the lower incisor is of great importance
as they erupt towards each other to their final position which is determined
by their inclined planes. This inclined plane regulates the lower incisors, by
which angle they meet the upper incisors “the incisal angle” and where they
occlude on the lingual surface of the upper incisors. Therefore there might
be a stabilizing area where the lower incisors will occlude optimal with the
upper incisors (Backlund 1958). Finding the best interrelation between the
7
upper and lower incisors would help to maintain the orthodontic treatment
results. Mills (1966) stated that the lower incisors lay in a narrow zone of
stability in equilibrium between the opposing muscular pressure, that of
their labio-lingual position should not be altered dramatically. Reitan
claimed that tipping of the incisors labially or lingually during orthodontic
treatment will most likely relapse (Reitan 1969).
Adequate interincisal contact and angle with good posterior intercuspidation
may prevent overbite relapse (Kahl-Nieke et al 1995, Reitan 1969 and
Shudy 1974).
The purpose in this study therefore, is to examine whether the incisor
inclination and position and their interrelation at retention, is related to the
overbite relapse at postretention and if so, what would be the most stable
relation and inclination of the incisors at the final treatment. Another
purpose of the study is to identify if there are any predictive factors for the
overbite relapse at postretention and if so can those patients prone to relapse
be identified at the initial treatment phase in an orthodontic practice.
The aim of the study is to investigate post-retention overbite change related
to incisal inclination and interocclusal position.
MATERIAL AND METHOD
The material consists of 97 patients with full records of study casts and
lateral cephalograms from a group of randomized 1554 orthodontic patients
reaching to 520 treated by orthodontists in the city of Halmstad in southwest
of Sweden. The patients were all treated by specialists in orthodontics with
8
fixed appliance with or without removable appliance as part of the
treatment.
The sample of the study is ethically approved in prior studies (Lagerström et
al 1998, 2000 and Berset et al 1998).
The material comprises of complete lateral cephalograms and study casts
from the initiation of treatment T1, at retention T2 and at post-retention T3
The mean (SD) age at the initial treatment T1 was 12.5 (1.5 years), at T2
14.5 (SD 1.5) and at T3 18.6 years (1.8 years).
Inclusion criteria:
•
Swedish adolescent patient population in Halmstad
•
No palatal or labial clefts, no facial trauma
•
No diseases that could affect the growth
•
Treatment being carried out in the Specialty Clinic of Halmstad with
prior malocclusions of Angle class I, II, III with the
presence/absence of crowding reflecting orthodontic patients in
general, all with homogenous routines for treatment such as fixed
appliances and retention such as two years after treatment and out of
retention with control at the age of 19 years.
•
Complete patient records, lateral cephalograms and available study
models at all three stages such as pre-treatment T1, Posttreatment
T2, Postretention T3.
•
Post-retention of minimum 2 years
9
Study model analysis:
In order to compare the changes from post-treatment to post-retention, all
the study models at all three stages were evaluated and measured with a
digital caliper measuring the following variables by one observer:
•
Overbite: as the greatest amount of vertical overlap of the incisors in
centric occlusion
•
Anterior occlusion according to Backlund (1956), as to where the
lower incisors occlude on the lingual surface of the upper incisors :
Grade 1 2 3 4 (FIG 1):
1
the first part is the acutely inclined incisal part with inclination of
4° to axial line
2
The plateau of cingulum with the 30° to axial line directly after
the lingual surface curves called the border.
3
The third and cervical part consists of convex surface represented
by an angle 6° to axial line.
4
Behind the tooth representing the palatal gingival.
FIG. 1
10
•
Intercanince distance (the distance between the tip of the cusps)
•
Irregularity index (Little 1975)
•
Overjet : Amount of greatest horizontal overlap in centric occlusion
Cephalometric Analysis:
All cephalograms were performed with the same magnitude of
magnification and in the same clinic in Halmstad using standardized
procedures.
All three stages were measured by the same observer with manual digitizing
using a mechanical pencil with 0.5 mm lead, tracing on a transparent sheat
and a millimetric orthodontic ruler (FIG II.).
The following parameters were measured:
•
Interincisal angle
•
Upper incisor inclination to NL
•
Lower incisor inclination to ML
•
ANB
•
ML/NSL
•
ML/NL
11
FIG. 2
10 randomly selected patients were recalculated and retraced by the
observer and traced by another observer to control the intra-observer and
inter-observer errors.
Statistics:
The statistical methods used, are the Dahlberg´s Method of Error, Wilcoxon
Matched Pairs Test and the Multiple Correlation Analysis, conveyed with
help of statistician Margareta Krook Brandt at the Karolinska Institutet.
The significant level at p < ,050 is used in this study.
12
RESULT
There was a significant overbite change at T3 compared to T2 (p < 0.005).
(Wilcoxon Matched Pairs Test p=0,032965)
No correlations could be found between the overbite relapse at T3 and
incisor inclination, interincisal angle, interocclusal position, or with any
other variables at T2.
At T1, none of the included variables except ML/NSL and interocclusal
position 4 (Backlund´s index) could predict overbite relapse at T3 (p <
0.05).
Hereby the results are presented in table I and the following graphs:
TABLE 1.
Mean and SD of all the measured variables at T1, T2, and T3:
T1
T2
T3
MEAN (SD)
MEAN (SD)
MEAN (SD)
Overbite
mm
Backlund Index
1,2,3,4
Intercanine distance (Lower arch) mm
Irregularity Index mm
Overjet
mm
2.,8
3.8
26,6
-2,2
6,2
(1,8)
(1,0)
(1,9)
(3,2)
(9,9)
1.8
1,8
26,8
-0,2
2,8
(1,0)
(0,7)
(1,9)
(0,6)
(0,9)
2.0
2,0
26,4
-0,7
3,4
(1,1)
(0,8)
(2,1)
(0,9)
(1,2)
ML/NSL
ML/NL
ANB
U1/NL
L1/ML
Interincisal Angle
28,3
32,5
4,4
110,2
95,2
126,3
(5,5)
(5,2)
(2,3)
(6,6)
(7,4)
(11,2)
27,9
32,4
3,8
109,1
95,9
127,0
(5,3)
(5,1)
(2,0)
(6,2)
(8,2)
(10,6)
26,6
31,3
3,7
109,9
96,3
127,7
(5,4)
(5,6)
(2,1)
(6,1)
(7,8)
(10,0)
VARIABLE
UNIT
◦
◦
◦
◦
◦
◦
13
Vertical overbite at T1, T2, T3
Box Plot (Stat1 51v *118c)
8
6
4
2
0
-2
Median
25%-75%
Non-Outlier Range
Outliers
-4
v öb T1
v öb T2
v öb T3
Significant difference between T2 and T3, the vertical overbite relapse at retention
and its change to postretention (p<0,05).
Vertical overbite change T2-T3 with ML/NSL at T1
Scatterplot (Stat1 51v*97c)
Diff T 2-T 3 = 1,5464-0,0392*x
4
3
Diff T2-T3
2
1
0
-1
-2
-3
20
22
24
26
28
30
32
34
36
38
40
42
44
46
ML/NSL T 1
ML/NSL T 1:Diff T 2-T 3: r = -0,2272, p = 0,0252
14
No correlations could be found between the vertical overbite relapse and all
the measured variables as described above and in Table 1.
The null hypothesis of the study that final treated interincisal relationship,
inclination and position will not interfere with the overbite stability was
accepted in this study.
DISCUSSION
The incisor angle and the angle formed by the lower incisors with the
lingual surface of upper incisors together with the morphology of the
horizontal plateau, cingulum of the upper incisors where the lower incisors
occlude, have been advocated for stability of the vertical dimension
(Backlund 1958).
To increase the vertical stability, it has been suggested to pay attention to a
proper finishing of the incisor angle and interincisal relation during
orthodontic treatment.
Payne et al (1964) investigated the relation of overbite change to postretention growth, indicating that post-retention ramus growth tended to
decrease the mandibular plane angle, resulting in increased posterior facial
height and forward positioning of the symphysis and therefore as partially
responsible for overbite relapse.
There have also been studies about different treatment modalities such as the
role of extraction versus non extraction on the stability of the overbite.
Hernandez et al (1969) found greater incidence of relapse in an extraction
than a non extraction sample. However in this study the prevalence of
15
extraction versus non-extraction did not imply any significant differencial
influence on overbite relapse.
Magill (1960) found that one half of the overbite relapse occurred within
two years out of retention. There was no significant difference with regards
to different Angle classes of malocclusion or mode of treatment when it
comes to extraction versus non extraction. In this study the ANB angle did
not have any relation with the vertical overbite relapse. Since the patients
were followed up til the age of 19 years almost all patients were out of
retention for a minimum of 2 years at T3. Bishara and Jakobsen (1998)
indicate that despite significant correlations between overbite and facial
height based on untreated long-term follow up of 40 years, they are low and
not useful for predictive purposes. They claimed that normal growth
changes in the vertical dimension of the face, does not play a clinically
significant role in determining the amount of the overbite on an individual.
Other factors such as growth of the alveolar processes might also influence
changes in overbite.
Nanda and Nanda (1992) found that the prepubertal growth spurt for
patients with skeletal deep bite occurs on average 1.5 - 3 years later than in
cases with open bite. For this reason advocating a longer retention period for
patients with skeletal deep bites, counteracts the effect of late dento-facial
growth.
In the current study as the prior studies the only putative predictive
significant factors for overbite relapse were, initial skeletal deep bite at T1
and/or Backlund index 4, meaning dentoalveolar deep occlusion with
gingival impingement. These patients are susceptive to vertical relapse and
16
should be in retention and for a longer and monitored more often when out
of treatment for retention controls. The patients and the parents should also
be informed about the relapse risk in beforehand, when there is evident
initial skeletal deep bite or when dentoalveolar deep bite with gingival
impingement is present.
However it is important to bear in mind that the current study is
retrospective with short term follow-up only to the age of 19 years. The
patient groups are treated with fixed appliances with different treatment
modalities and individual variations such as the initial malocclusion, growth
pattern, patient compliance during treatment and final treatment results
which make all more complicated. Long term follow-ups are difficult to
convey since many of the patients move and are difficult to trace after 10-15
years. There are more favourable with long term studies in exposing the act
of overbite change beyond the growth into adulthood.
Mills (1966) stated that the lower incisors lie in a narrow zone of stability in
equilibrium between the opposing muscular pressure and that of their labiolingual position should not be altered dramatically. Reitan claimed that
tipping of the incisors labially or lingually during orthodontic treatment will
most likely relapse (1969).
Adequate interincisal contact and angle with good posterior intercuspidation
may prevent overbite relapse (Kahl-Nieke et al 1995, Reitan 1969 and
Shudy 1974).
In this study the incisor inclinations, the interincisal angle and the
interocclusal position at T2 did not demonstrate any statistical significant
relevance to the overbite relapse.
17
As the sample of the study comprised of 97 patients it was adequate for
statistical comparisons according to the statistician acquired to convey this
study. However to have certain conclusions, this study should be conveyed
as a prospective study with broader follow up.
The measurements were done by the same observer and 10 randomized
patients were retraced by the observer and by another observer and the
measurement were compared to access the accuracy in measuring and to
access the intra and interobserver change. The error of the method was
assessed by the Dahlbergs formula.
The measurements did not differ from the acceptable range of 0,6 mm on
linear measurements and 0,8 ◦ on angular measurements.
The accuracy of the measurements coincided well with the control
measurements and is considered reliable and reproducible.
As individuals are different and there is a large variation it is also difficult to
collect a large homogenous sample in one study.
The age of the patients in all three groups were within the same age ranges
with small standard deviations, representing acceptable homogenous groups.
This study implies that the incisor inclinations and interincisal relation and
position might not play an important role for the overbite stability as
believed before and that there are far more complex and multifactorial
reasons behind together with the large variation of the growth.
18
CONCLUSION
There is a vertical relapse taking place from retention to postretention at the
age of 19 years.
Overbite relapse was not affected by final incisor inclination, interincisal
angle, interocclusal position at rentetion.
Overbite relapse is due to multiple factors more complex than the incisor
inclination and position at the final treatment results.
Initial skeletal deep relation and initial dento-alveolar deep bite with
gingival impingement at T1, were associated with vertical relapse at T3 and
may be considered as putative predictive factors for vertical relapse.
Patient with the above mentioned diagnosis characteristics, should receive
the correct retention, maintain their retention longer and monitored for postretention controls with information of the risk for relapse.
19
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