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EFFECT OF EARLY CLASS II TREATMENT ON THE INCIDENCE OF INCISOR
DAVID RUEY CHEN
A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE
UNIVERSITY OF FLORIDA
O 2007 David Ruey Chen
I thank the members of my supervisory committee, for their mentoring; my family and
friends, for their continual support and encouragement.
TABLE OF CONTENTS
ACKNOWLEDGMENTS .............. ...............3.....
LIST OF TABLES .........__... ......._. ...............5....
LIST OF FIGURES .............. ...............6.....
AB S TRAC T ......_ ................. ............_........7
1 INTRODUCTION ................. ...............9.......... ......
2 MATERIALS AND METHODS ................. ...............11.......... ....
Subj ects ................. ...............11.................
Inclusion Criteria ................. ...............11.......... .....
M ethods ................. ...............11.......... .....
Data Analysis............... ...............12
3 RE SULT S ................. ...............14.......... .....
4 DI SCUS SSION ................. ...............2.. 1......... ....
5 CONCLUSIONS .............. ...............24....
LIST OF REFERENCES ................. ...............25................
BIOGRAPHICAL SKETCH .............. ...............28....
LIST OF TABLES
3-1 Subj ect characteristics by treatment group. ..........__......__ ....___ ..........1
3-2 Incidence of incisor injury maxillaryy incisors) ................. .......___ ...... .........16
LIST OF FIGURES
2-1 Modified Ellis Classification. ............. ...............13.....
3-1 Maxillary incisor injury distribution and severity. ............. ...............17.....
3-2 Mandibular inci sor inj ury di stribution and severity ................. ...............18.............
3-3 Incidence of injury in males vs. females throughout treatment. = P < 0.05. ........._........19
3-4 Incidence of injury in sex between treatment groups from DC1-F maxillaryy
incisors). = P < 0.05. ............. ...............20.....
Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science
EFFECT OF EARLY CLASS II TREATMENT ON THE INCIDENCE OF INCISOR
David Ruey Chen
Chair: Calogero Dolce
Major: Dental Sciences
Many studies have demonstrated the frequency of dental injuries in children and
adolescents. The purpose of this study was to evaluate the prevalence and the effect on
incidence of incisor trauma in patients that participated in a clinical trial designed to investigate
early growth modifications in the treatment of CLII malocclusion. The subjects were categorized
into 3 groups based on the type of treatment during phase-1: (1) headgear/biteplane, (2) bionator,
(3) no treatment observation group. All 3 groups underwent phase-2 treatment with fixed
appliances. Incisor injury was scored at every data collection point with the Ellis index by a
single-blinded examiner using dental casts, intraoral photos, panoramic and periapical x-rays.
Twenty-five percent of the subj ects had some level of incisor trauma at baseline exam. No
significant differences were found in regards to sex and prevalence of injury at baseline, but
males did show higher incidence of injury throughout the course of treatment. No differences in
incidence of trauma were found between the 3 groups throughout treatment. The maj ority of the
injuries were minor and consisted of enamel fractures only (80%). Seventy-eight percent of the
injuries occurred in the maxillary incisors with central incisors being the most common. Early
orthodontic treatment does not seem to affect the incidence of incisor injury. The maj ority of the
injuries prior to and during treatment were minor, therefore the cost benefit ratio of orthodontic
treatment in order to prevent incisor trauma is doubtful.
Dental injuries are common and present an important dental public health problem.
Many epidemiological studies during the last three decades have shown the frequency of dental
injuries in children and adolescents. -" The occurrence of dental injuries in a population can be
defined by its prevalence and incidence. The prevalence of incisor injury has been reported to
range from 6% to 34%.9-11 Falls, collisions, sporting activities, and traffic accidents have been
reported to be the main cause of most dental injuries.12,13 Variables such as age, gender, socio-
economic status, and behavioral problems may also influence the frequency of dental trauma.
Bauss et al.12 and Caliskan et al.13 both found that patients aged 8-11 years exhibited the
highest prevalence of dental trauma. It has been shown that incisor injuries occur more
frequently in males.14,15 Socio-economic influences can also have a significant effect on a
child's experience with dental injuries.16,17 Studies have shown a positive correlation between
the frequency of incisor trauma with increased protrusion,18,19 Class II malocclusion,3,20
increased overjet,21-24 and lip incompetence.19,25 Early orthodontic treatment for children with
such characteristics has been recommended in order to prevent incisor trauma and its
sequelae.22,25 Nguyen et al.23 had suggested the incorporation of overj et as a malocclusion item
into orthodontic treatment indices because of its potential correlation with dental trauma.
Although the indications for early orthodontic treatment in order to diminish the
likelihood of trauma to permanent incisors have been presented by several authors,
Koroluk et al.26 found the maj ority of injuries to be minor and easily treated at low cost and with
good long-term prognosis. They concluded that early growth modification might have some
effect on the incidence of trauma but the expected cost of trauma per child to be less for those
who had a 2-phase orthodontic treatment.
The efficacy of early intervention is largely dependent on the timing of treatment and
peak occurrence of injury. Orthodontic intervention could be ineffective with minimal benefits if
dental trauma occurs before the start of treatment. Currently, few reports are available regarding
the effectiveness of early orthodontic treatment in order to reduce the incidence of incisor
The purpose of this study was to evaluate the prevalence and the effect on incidence of
incisor trauma in patients that participated in a clinical trial designed to investigate early growth
modifications in the treatment of CLII malocclusion.
MATERIALS AND METHODS
The subj ects were part of a previous prospective, longitudinal, randomized clinical trial
designed to examine and report the effectiveness of early treatment with headgear/biteplane
(HG/BP) or with bionator (B) in patients with Class II malocclusion and compare results with
changes over a similar time period in an observation (C) group. A stratified block randomization
procedure was used to assign a treatment protocol (HG/BP, B, C) during Phase-1 for each
patient. Strata were defined by severity of Class II malocclusion, need for preparatory treatment,
mandibular plane angle, race, and gender. After completing Phase-1, all groups underwent fixed
appliances in Phase-2, followed by a retention/follow-up period. The study design and subject
selection are described in detail in the previous publication.27
The inclusion criteria included: bilateral greater than or equal to one-half-cusp Class II
molars, or unilateral greater than one-half-cusp Class II molars, fully erupted permanent first
molars, not more than 3 permanent canines or premolars, positive overj et and overbite, and good
general and dental health.
Incisor injury was assessed at all data collection (DC) points using the Modified Ellis
Classification (Figure 2-1). Maxillary (#7-10) and mandibular (#23-26) incisors were scored.
Study models, intraoral/extraoral photos, x-rays (lateral cephlogram, panoramic, and periapicals
taken during Phase-2) obtained at each DC point was used to inspect incisor injury. Any existing
or new restorations on each tooth were noted. One trained and reliability tested examiner [DRC]
recorded all injuries. The records for all DC points of each patient were evaluated at the same
time in order to eliminate the chance of recording errors over time.
Overj et was assessed for each patient at all DC points using the lateral cephalograms
taken at each data collection period.
Statistical comparisons were performed at baseline (DC 1), end of Phase 1 (DC 5),
baseline at Phase 2 (DC 7), and end of Phase 2 (DC F). Relationships between outcomes and
covariates were examined with chi-square and Fisher exact tests. For all analyses, a p-value less
than 0.05 was considered statistically significant. Pearson's correlation coefficient was used to
examine any relationship between initial overj et and trauma.
Score Injury Description
0 Non injured tooth
1 Fracture of the crown involving enamel only
2 Fracture of the crown involving enamel and dentin
3 Fracture of crown involving pulp (untreated, pulp cap,
pulpotomy, root filling)
4 Nonvital without crown fracture
5 Root fracture
6 Lost due to trauma
7 Missing tooth
Figure 2-1. Modified Ellis Classification.
Table 3-1 presents the subject characteristics by treatment group. At DC 1, 64 of the 261
participants (25%) had some level of incisor trauma (B=27 (31%), HG/BP=18 (19%) C=19
(23%)). The differences in the distribution of subj ects with trauma to each treatment group were
not statistically significant (P = 0.18). Figures 3-1 and 3-2 shows the distribution and severity of
injury to maxillary and mandibular teeth. The majority (80%) of the injuries were scored as a
minor fractures involving enamel only. Fractures involving enamel and dentin consisted of 19%
and only 1 subject had trauma with pulpal exposure. The maxillary incisors had the highest
number of injuries (77%), with central incisors being the most common. The prevalence of
incisor trauma at DC 1 were not statistically significant between males and females (P = 0.27),
with 21% of females and 27% of males having some degree of incisor trauma.
Since the maj ority of the injuries occurred in the maxilla, further analysis focused on the
incidence of only maxillary incisor injury. As shown in Table 3-2, there were no differences in
the incidence of new trauma between treatment groups during phase-1 (DC 1-5), between
treatment phases (DC5-7), during phase-2 (DC7-F), and overall (DC1--F). As seen in Figure
3-3, there was a statistically significant higher incidence of trauma in males compared with
females during the entire study. During the entire course of the study, only the control group and
not the HG/BP or bionator groups showed a statistically significant higher incidence of trauma in
males than females (Figure 3-4).
Overj et was measured to determine if overj et correlated with trauma in males. The mean
overj et value at baseline was 5.81Imm (A 2.77 SD; range, 0.87-13.2) for males and 5.48mm (A
2.30 SD; range, 0.5 1-1 1.2) for females. No correlation was found between initial overj et value
and amount of upper incisor trauma at baseline (Pearson Correlation Coefficient = 0.02; P =
0.75). When evaluating baseline overjet and change in upper incisor injury as continuous
variables throughout treatment between DC 1 to DC F, a borderline significant correlation of
0.23 (P = 0.0549) was found in the control group, but not detected in the headgear or bionator
groups (correlations -0. 11, -0.06, respectively).
Table 3-1. Subject characteristics by treatment group.
B C HG/BP
Characteristic (n= 87) (n= 81) (n= 93) P-value
Sex (% female) 40% 38% 38% 0.93
Race (% white) 87% 93% 95% 0.20
Age at baseline: mean (s.d.) 96(.) 9.5 (0.8) 9.7 (0.8) 0.74
Initial molar class severity#
% mild 26% 30% 31%
% moderate 26% 26% 23% 0.95
% high 47% 44% 46%
# definition of initial molar class severity: mild (bilateral 1/2 cusp), moderate (at least 1 side 3/4 cusp), or
severe (at least 1 side full cusp).
Table 3-2. Incidence of incisor injury maxillaryy incisors).
(% new injury)
Time point B HG/BP C P
DC 1 DC 5 22.1 17.7 22.5 0.69
DC 5 DC 7
DC 7 DC F
DC 1 -DC F
S20 -1IEllis Score
O 15 0 3
7 8 9 10
Figure 3-1. Maxillary incisor injury distribution and severity.
3-( 5 Ellis Score
23 24 25 26
Figure 3-2. Mandibular incisor injury distribution and severity.
4 20 i
Figure 3-3. Incidence of injury in males vs. females throughout treatment. = P < 0.05.
C B HGIBP
Figure 3-4. Incidence of injury in sex between treatment groups from DC1-F maxillaryy
incisors). = P < 0.05.
In this study, we found 25% of the subj ects had some level of incisor trauma at the
baseline exam which falls in the range of previously reported prevalence of incisor injury of 6%
to 34%.9-11 This shows that a significant number of patients already had some form of dental
trauma during early childhood. In a study of Brazilian preschool children from birth to 6 years
old, 35.5% of the children already had signs of dental trauma.28 Therefore, if orthodontic early
treatment is to have any effect on the incidence of this early incisor trauma, orthodontic
treatment would most likely need to be initiated soon after the eruption of the permanent
incisors. Thus, determination of the initial onset of trauma would be pertinent to prevention.
The prevalence of incisor injury at baseline was not statistically different between boys
and girls at the mixed dentition stage. This is similar to the results found by Koroluk et al.26
Marcenes et al.29 also found no difference in prevalence between boys and girls at 9 years of age
living in Syria. However, we observed that males had a higher incidence of trauma during the
phase-2 treatment period. This finding is consistent with several investigators. 12,14,15 This could
be due to increased activity of boys at this age.
Throughout the trial, the incidence of incisor trauma was not statistically significant
between the 3 treatment groups. All three groups showed a trend of decreased incidence
between phase 1 and phase 2. Bauss et al.12 and Caliskan et al.13 both found that children aged 8
-11 years, an age range where phase I treatment usually occurs, exhibited the highest prevalence
of dental trauma. Children at these ages may exhibit increased risk-taking behaviors and
physical leisure activities such as school sports30, therefore increasing the risk of injury during
treatment. Nonetheless, the decrease in incidence between phase 1 and phase 2 may implicate
the potential benefit of early treatment in order to reduce risks of trauma later on.
During early childhood, several nondental factors may also play a role in affecting dental
trauma and should be considered. Socio-economic influences can also have a significant effect
on a child's experience with dental injuries." Nicolau et al.16 found that adolescents who
experienced adverse psychosocial environments, such as non-nuclear families, paternal
punishments, and poor school performance along the life course had more traumatic dental
injuries than their counterparts who experienced more favorable environments.
Mercenes et al.14 discovered a higher incidence of incisor injury in children from mothers with
higher educational background. Odoi et al.31 associated behavioral problems such as peer
rel ati onship problems, hyperactivity/inattenti on, and emoti onal di stores s with occurrence of
traumatic dental injury. Perheentupa et al.32 attributed increased tooth trauma to high alcohol
consumption and overweight.
We observed that approximately 78% percent of total incisor injury occurred in the
maxillary incisors while 22% occurred in the mandibular incisors. Most of the injuries involved
the maxillary central incisors followed by maxillary lateral incisors. This is in agreement with
previous studies.12,13,33 It is very likely that the susceptibility of teeth to trauma is related to their
position in the dental arch. Maxillary incisors are usually the most anteriorly positioned teeth,
therefore it is conceivable that they will have the highest frequency of trauma.
Some studies found enamel-dentin fractures without pulpal involvement to be the most
common form of injury. 4,13 Other investigations, in contrast, report enamel fracture or luxation
to be the most common fracture type. 1,5,6 Our investigation revealed the maj ority of trauma
consisted of enamel fractures. Only 19% of the injuries involved dentin, and only 1 subject had
trauma with pulpal exposure. Fortunately, this shows that the maj ority of trauma is minor and
could be fixed with composite restorations with good long term prognosis.34 Therefore, the cost
of treating an injured tooth with restorations versus cost of orthodontic prevention must be
considered in order to determine the optimal cost/benefit ratio.
The reports on whether increased overj et may play a significant predisposing factor for
incisal trauma are conflicting. Bauss et al.12 found higher prevalence of trauma in subj ects with
overj et values greater than 3mm. Jarvinen24 attributed increased trauma to overj et values 6mm or
greater. However, some studies found that increased overjet may not be positively correlated
with the risk of dental injury.22,35 Koroluk et al.26 found no differences between mean overj et of
patients with and without incisor trauma at baseline. In this study, we found no correlation
between initial overj et and prevalence of trauma. In addition, we found no correlation between
changes in overj et with incidence of trauma throughout treatment. The conflicting results
reported by the literature may be due to several factors such as trauma classification, dentition
studied, geographical and behavioral differences between study locations and countries.
Nonetheless, it seems logical that patients with severe overj et may be at greater risk of injury
simply because the incisor protrusion.
In conclusion, we have found that a significant number of patients already had some level
of incisor injury prior to any treatment. No correlations were found between initial overj et
values and prevalence of trauma. Early orthodontic treatment did not seem to have a significant
effect on the incidence of trauma. The maj ority of the injuries that occurred prior to and during
treatment were minor and consisted of enamel fractures. Most of the injuries occurred in the
maxillary central incisors and in general, males showed higher risk of trauma than females.
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David Ruey Chen was born in Taichung, Taiwan in 1978. He received his BS in
biological sciences from the University of California Davis in 2000. He graduated from the
University of California San Francisco in 2004 obtaining a Doctor of Dental Science degree and
was inducted into the Omicron Kappa Upsilon National Dental Honor Society. He continued his
dental education at the University of Florida and received a degree of Master of Science with a
certificate in orthodontics in 2007.