Cilj ovog retrospektivnog istraživanja bio je ispitati promjene zubnih lukova nakon ortodontske
terapije i dugoročnu stabilnost tih promjena.
Istraživanje je obuhvaćalo dentalne modele 103 ispitanika adolescentne dobi s malokluzijama
klase I i klase II, koji su tretirani fiksnim ortodontskim napravama s ekstrakcijom zubi i bez
ekstrakcije zubi. Dentalni modeli uzeti su prije ortodontske terapije (T1), nakon ortodontske
terapije (T2) i u dugoročnom postretencijskom razdoblju od barem 5 godina (T3). Zatim su
skenirani u digitalni oblik. Digitalna linearna i angularna gnatometrijska mjerenja provedena
su u računalnom programu „Matlab“: Indeks nepravilnosti (LII), interkanina širina (IK),
intermolarna širina (IM), interdentalni kut (ID), kontaktni kut (CA), rotacijski kut (RA).
Uzorak se sastojao od 70,9 % ispitanica i 29,1 % ispitanika. Klasa I bila je prisutna u 71,8 %
slučajeva. Prosječan postretencijski period trajao je 17,2 (± 6,5) godina. Zubi su ekstrahirani u
53,4 % ispitanika. Bonferronijev Post Hoc test pokazao je da se LII značajno smanjio
ortodontskom terapijom u ekstrakcijskim i neekstrakcijskim slučajevima. Uz neznatan rast
zadržao se i u postretencijskom razdoblju, iako je nešto veći u ekstrakcijskim slučajevima,
zadržao se ispod 2,05 mm (p < 0,001). Interkanina širina u oba luka ponaša se slično, raste u
periodu T1-T2, te se vraća na početne vrijednosti u periodu T2-T3, a kod ispitanica i kod
ekstrakcijskih slučajeva nešto je izraženija. Intermolarna širina pokazala se kao najstabilnija
linerana varijabla. Indeks nepravilnosti u T2 u oba luka pokazao je negativnu korelaciju s
gornjom intermolarnom širinom (Pearson, N = 103, p = 0,047), dok interkanina širina u oba
luka negativno korelira s intermolarnom u T3 (N = 103, p < 0,001). Angularni parametri
pokazali su veće vrijednosti u neekstrakcijskim slučajevima, iako ta razlika nije uvijek bila
statistički značajna. Ekstrakcijski slučajevi imali su uže lukove prije početka ortodontske
terapije. Postretencijske promjene interdentalnih i kontaktnih kutova nisu bile značajno
izražene. Rotacijski kutovi prednjih zubi gornjeg i donjeg zubnog luka pokazali su se izrazito
stabilnima u dugoročnom postretencijskom periodu.
Klinički značajna dugoročna stabilnost postignuta je u ekstrakcijskim i neekstrakcijskim
slučajevima u oba zubna luka. Intermolarna širina i njezina promjena za vrijeme ortodontske
terapije prediktori su stabilnosti rezultata u ekstrakcijskim slučajevima.
|Abstract (english)|| |
Aim: to investigate changes in the upper and lower dental arches caused by orthodontic
treatment and changes that occured in long-term postretention period. Another aim was to
compare the differences in different time periods between dental arches treated with and
without extraction as well as to establish predictors of long-term stability after orthodontic
treatment with and without extraction.
Materials and methods: This retrospective study included 103 patients with Class I and
Class II malocclusions treated with fixed appliances in both arches with and without extraction.
Inclusion criteria were treated patients with dental and skeletal class I and class II, at least 5
years out of retention with full documentation and study models of satisfiying quality.
Exclusion criteria were patients with dental and skeletal class III, orthognathic patients, patients
with congenitally missing teeth (except third molars), patients with circumferential supracrestal
fiberotomy performed and patients who had prosthetic work done in T3 time period.
The sample was collected from a database of a private orthodontic office and the patients
were treated by an experienced orthodontist during the 1970s and 1980s with comprehensive
orthodontic treatment with fixed appliances in both arches. After orthodontic treatment, the
dental arches were retained with a lower bonded retainer from canine to canine and a
Wraparound retainer in the upper arch. The retention period lasted for three years. After three
years, all retention appliances were removed and interproximal reduction was performed on the
lower incisors (the intercanine segment) where this had not been done during treatment.
The dental casts were obtained at pretreatment (T1), posttreatment (T2), and long- term
postretention period of at least 5 years (T3). The study models were scanned with Ortho Insight
3D scanner (Motion View LLc, Hixon, USA), digitalized and converted to STL files. Linear
and angular measurements were evaluated in Mathlab enviroment, a programme specifically
constructed for this purpose. The measurments were determined for the upper and lower arch
in three time periods as follows: the intercanine width (IK), intermolar width (IM), Little's
Irregularity Index (LII), the interdental angle (ID), contact angle (CA) and rotational angle
(RA). The measurements were performed by an experienced and calibrated examiner . Thirty
days after the initial measurements, 40 dental casts were randomly selected to check for
Statistical analyses were performed in STATISTICA 64, version 10 for Windows.
Results: The study sample comprised 70.9% female and 29.1% male patients. Class I in
71.8% of cases and class II in 28.2%. The average postretention time was 17.2 years (±6.5)
with an average retention time of 3.4 (±1.17) years. Extraction was performed in 55 patients
while 48 (46.6%) received nonextraction treatment. The Bonferroni Post Hoc test showed that
LII in the upper and lower arch in T1 was statistically significantly higher in the extraction
group (p<0,001). In T3 in the upper and lower arch LII was slightly higher in extraction cases
but remained under 2.05mm. In the upper arch 92.2% of patients and 82.5% in the lower arch
showed satisfactory alignment under 3mm. Average LII at T3 in upper arch was 1.69 ± 1.27
mm in extraction and 1.10 ± 0.79 mm in nonextraction cases. Average LII at T3 in the lower
arch was 2.05 ± 1.64 mm in extraction and 1.52 ± 1.27 mm in nonextraction cases.
Average LII in postretention period (T3) in the upper and lower arch showed a negative
correlation with IM T3 in the upper arch (Pearson,N=103, p=0.047), while IK in the upper and
lower arch in T3 correlated with IM T3 in the upper and lower arches (N=103, p<0,001).
Intercanine width in both arches showed similar changes, it increased during orthodontic
treatment period (T1-T2) , and returns to initial values in the posttreatment and postretention
period (T2-T3). Females and extraction cases show more posttreatment changes. Intermolar
width has been shown as the most stable variable.
The angular parameters showed greater values in nonextraction cases, even though this
difference hasn't proved statistically significant. The extraction cases showed narrower arches
before orthodontic treatment. The postretention changes of interdental and contact angles didn't
show any significant differences. In extraction cases, the initial ID of lower canines showed a
negative correlation with LII posttreatment change in the lower arch (Pearson, N=48, p=0.02).
In nonextraction cases, the initial ID of upper canines showed a negative correlation with LII
in the upper arch in T3 (Pearson, N=47, p=0.045). In the extraction cases treatment change of
the interdental angle of lower canines showed positive correlation with lower LII (Pearson,
In the lower arch rotational angles in the postretention period showed a tendency to return
to initial values. This was not registered in the upper arch. The long-term rotational changes of
upper and lower anterior teeth were under 3 degrees and clinically insignificant.
Conclusion: Clinically relevant long-term stability was found in extraction and nonextraction cases in both arches twenty years after orthodontic treatment with Little's Irregularity
Index value under 3mm. The lower arch, both in extraction and nonextraction cases, showed
In the postretention period, intercanine width in extraction cases showed a tendency to
return to initial values, while in nonextraction cases intercanine width showed better stability.
In females treated with extractions, intercanine width tended to return to initial values, while
males showed stable results.
Intermolar width changes during orthodontic treatment were bigger that postretention
changes of intermolar changes. Intermolar width in nonextraction cases showed to be the most
stable linear variable.
After orthodontic treatment, the smallest contact angle in the lower arch was measured
between canines and lateral incisors and, in the upper arch, smallest contact angle was measured
between central incisors. The initial arch form in extraction cases was tapered, while in
nonextraction cases it was more ovoid.
Rotational angles in the lower arch showed a tendency to return towards initial values,
while this was not shown in the upper arch. Postretention changes of rotational angles were less
than three degrees and can be considered clinically insignificant.
Long- term postretentional changes of dental arches were inevitable, but in a clinical sense
those changes are insignificant. Intermolar width and its change during orthodontic treatment
can be a good predictor of stability in extraction cases.