Multiple Reflection Symmetry Detection via Linear-Directional Kernel Density Estimation

Symmetry is an important composition feature by investigating similar sides inside an image plane. It has a crucial effect to recognize man-made or nature objects within the universe. Recent symmetry detection approaches used a smoothing kernel over different voting maps in the polar coordinate system to detect symmetry peaks, which split the regions of symmetry axis candidates in inefficient way. We propose a reliable voting representation based on weighted linear-directional kernel density estimation, to detect multiple symmetries over challenging real-world and synthetic images. Experimental evaluation on two public datasets demonstrates the superior performance of the proposed algorithm to detect global symmetry axes respect to the major image shapes

3D imaging and nonparametric function estimation methods for analysis of infant cranial shape and detection of twin zygosity

Abstract The use of 3D imaging of craniofacial soft tissue has increased in medical science, and imaging technology has been developed greatly in recent years. 3D models are quite accurate and with imaging devices based on stereophotogrammetry, capturing the data is a quick and easy operation for the subject. However, analyzing 3D models of the face or head can be challenging and there is a growing need for efficient quantitative methods. In this thesis, new mathematical methods and tools for measuring craniofacial structures are developed. The thesis is divided into three parts. In the first part, facial 3D data of Lithuanian twins are used for the determination of zygosity. Statistical pattern recognition methodology is used for classification and the results are compared with DNA testing. In the second part of the thesis, the distribution of surface normal vector directions of a 3D infant head model is used to analyze skull deformation. The level of flatness and asymmetry are quantified by functionals of the kernel density estimate of the normal vector directions. Using 3D models from infants at the age of three months and clinical ratings made by experts, this novel method is compared with some previously suggested approaches. The method is also applied to clinical longitudinal research in which 3D images from three different time points are analyzed to find the course of positional cranial deformation and associated risk factors. The final part of the thesis introduces a novel statistical scale space method, SphereSiZer, for exploring the structures of a probability density function defined on the unit sphere. The tools developed in the second part are used for the implementation of SphereSiZer. In SphereSiZer, the scale-dependent features of the density are visualized by projecting the statistically significant gradients onto a planar contour plot of the density function. The method is tested by analyzing samples of surface unit normal vector data of an infant head as well as data from generated simulated spherical densities. The results and examples of the study show that the proposed novel methods perform well. The methods can be extended and developed in further studies. Cranial and facial 3D models will offer many opportunities for the development of new and sophisticated analytical methods in the future.Tiivistelmä Pään ja kasvojen pehmytkudoksen 3D-kuvantaminen on yleistynyt lääketieteessä, ja siihen tarvittava teknologia on kehittynyt huomattavasti viime vuosina. 3D-mallit ovat melko tarkkoja, ja kuvaus stereofotogrammetriaan perustuvalla laitteella on nopea ja helppo tilanne kuvattavalle. Kasvojen ja pään 3D-mallien analysointi voi kuitenkin olla haastavaa, ja tarve tehokkaille kvantitatiivisille menetelmille on kasvanut. Tässä väitöskirjassa kehitetään uusia matemaattisia kraniofakiaalisten rakenteiden mittausmenetelmiä ja -työkaluja. Työ on jaettu kolmeen osaan. Ensimmäisessä osassa pyritään määrittämään liettualaisten kaksosten tsygositeetti kasvojen 3D-datan perusteella. Luokituksessa hyödynnetään tilastollista hahmontunnistusta, ja tuloksia verrataan DNA-testituloksiin. Toisessa osassa analysoidaan pään epämuodostumia imeväisikäisten päiden 3D-kuvista laskettujen pintanormaalivektorien suuntiin perustuvan jakauman avulla. Tasaisuuden ja epäsymmetrian määrää mitataan normaalivektorien suuntakulmien ydinestimaatin funktionaalien avulla. Kehitettyä menetelmää verrataan joihinkin aiemmin ehdotettuihin lähestymistapoihin mittaamalla kolmen kuukauden ikäisten imeväisten 3D-malleja ja tarkastelemalla asiantuntijoiden tekemiä kliinisiä pisteytyksiä. Menetelmää sovelletaan myös kliiniseen pitkittäistutkimukseen, jossa tutkitaan pään epämuodostumien ja niihin liittyvien riskitekijöiden kehitystä kolmena eri ajankohtana otettujen 3D-kuvien perusteella. Viimeisessä osassa esitellään uusi tilastollinen skaala-avaruusmenetelmä SphereSiZer, jolla tutkitaan yksikköpallon tiheysfunktion rakenteita. Toisessa osassa kehitettyjä työkaluja sovelletaan SphereSiZerin toteutukseen. SphereSiZer-menetelmässä tiheysfunktion eri skaalojen piirteet visualisoidaan projisoimalla tilastollisesti merkitsevät gradientit tiheysfunktiota kuvaavalle isoviivakartalle. Menetelmää sovelletaan imeväisikäisen pään pintanormaalivektoridataan ja simuloituihin, pallotiheysfunktioihin perustuviin otoksiin. Tulosten ja esimerkkien perusteella väitöskirjassa esitetyt uudet menetelmät toimivat hyvin. Menetelmiä voidaan myös kehittää edelleen ja laajentaa jatkotutkimuksissa. Pään ja kasvojen 3D-mallit tarjoavat paljon mahdollisuuksia uusien ja laadukkaiden analyysityökalujen kehitykseen myöhemmissä tutkimuksissa

A scale space approach for exploring structure in spherical data

Abstract A novel scale space approach, SphereSiZer, is proposed for exploring structure in spherical data, that is, directional data on the unit sphere of the three-dimensional Euclidean space. The method finds statistically significant gradients of the smooths of the probability density function underlying the observed data. Bootstrap is used to establish significance and inference is summarized with planar maps of contour plots of smooths of the data, overlaid with arrows that indicate the directions and magnitudes of the significant gradients. An effective way to explore such maps is a movie where each frame corresponds to a fixed level of smoothing, that is, a particular spatial scale on the sphere. The SphereSiZer is demonstrated using simulated data as well as two real-data examples. The first example examines the distribution of infant head normal vector directions. The presence of local maxima in the normal vector distribution may indicate head deformity, such as severe flatness or asymmetry. The second example considers the distribution of earthquakes in the Northern Hemisphere

Suuskannerien hyödyntäminen oikomishoidossa

Tiivistelmä Lähtökohdat: Suuskannereita alettiin hyödyntää oikomishoidossa vuosituhannen vaihteessa, ja nykyään skannerien markkinat kasvavat jatkuvasti sitä mukaa, kun kalvo-oikominen yleistyy. Artikkelissa käsitellään suuskannerien toimintaperiaatteita ja käyttömahdollisuuksia ortodontiassa sekä vertaillaan niitä perinteisiin jäljentämismenetelmiin. Lisäksi luodaan katsaus skannauksen kehitykseen ja tämänhetkisiin markkinoihin. Menetelmät: Tutkimusmenetelmänä käytettiin kirjallisuuskatsausta. Aihetta käsitteleviä tuoreita artikkeleita etsittiin PubMed- ja Scopus-tietokannoista. Tulokset ja johtopäätökset: Markkinoilla olevat skannerit hyödyntävät hyvin monenlaisia teknologioita. Suuskannerien tarkkuudessa on eroavaisuuksia: eräät skannerit tuottavat tarkempia digitaalisia jäljennöksiä kuin muut. Eroista huolimatta skannerien on osoitettu olevan kliinisesti riittävän tarkkoja, mutta niiden hinnat ovat vielä korkeita. Monissa tutkimuksissa on todettu, että opetteluvaiheen jälkeen työn tehokkuus ja potilastyytyväisyys ovat skannerilla työskenneltäessä merkittävästi paremmat kuin perinteisiä jäljennösmenetelmiä käytettäessä. Hammaslääkärin työhön kuuluu jatkuva oman ammattitaidon kehittäminen. Uusi oikojasukupolvi on edellistä valmiimpi hyödyntämään digitaalisia laitteita, ja kynnys niiden käyttöönottoon madaltuu arkisen viestintäteknologian yleistyessä

Reproducibility of Natural Head Position assessed with stereophotogrammetry

Abstract Objective: The aim of this study was to assess the stability of Natural Head Position (NHP) over time using the 3dMDface System. Setting and sample population: This was an experimental study. Three‐dimensional facial images of 40 students were captured on two different occasions, with an interval of at least two weeks. Materials and Methods: The images were taken using a stereophotogrammetric device (3dMD). The mirror positioned NHP was obtained in a standing position and then replicated in a sitting position for capturing. The self‐balanced NHP was taken in a sitting position. Rapidform 3D software was used for position angle calculations. The angle changes between the positions were calculated for rotations around the x‐, y‐ and z‐axes. Results: The differences between NHP in the self‐balanced and mirror positions recorded on the first and second occasions were 2.43 and 1.75 degrees, respectively, around the x‐axis. The average changes in NHP around the x‐axis between the self‐balanced and mirror balanced positions exceeded 3 degrees at the two‐week interval. The differences were smaller for the rotations around the y‐ and z‐axes. Some subjects consistently tended to hold their heads in a more extended position when self‐balanced, while others did this when mirror balanced. There was no difference in the reproducibility of NHP between men and women. Conclusion: The reproducibility of NHP for consecutive stereophotogrammetric captures is generally acceptable. The reproducibility of NHP using the mirror position was slightly better compared with NHP in the sitting self‐balanced position

Facial asymmetry and chewing sides in twins

Abstract Objective: To resolve how the preferred chewing side (PCS) affects facial asymmetry in twins, whether there are differences between monozygotic (MZ) and dizygotic (DZ) twins, and whether the twins with PCS have more asymmetric faces compared to symmetrically chewing twins. Material and methods: The study included 106 Lithuanian twin pairs of the same sex, 59 MZ and 47 DZ pairs. The data were analysed from facial 3D images and manually added landmarks. 3D images were analysed by Rapidform2006 software and statistical analyses were done by using the R software environment version 4.1.0. Results: The contralateral effect of PCS and larger chin side was dominant among right and non-right side chewing twins. Being female increased the whole face symmetry. Conclusion: The volume of the chin becomes larger on the side opposite to the twins’ habitual chewing side. As the results are quite similar in both twin types, functional factors are more prominent than heredity

Effect of cervical headgear on dental arch area, shape and interarch dimensions:a randomized study

Abstract Purpose: The goal was to study the effects of early cervical headgear treatment on maxillary and mandibular dental arch area, shape and interarch dimensions. Methods: The total study group comprised 67 children aged 7.6 years (standard deviation 0.3) with Angle class II malocclusion collected between 1992 and 1996. The children were randomly divided into two groups of equal size. In the first group, cervical headgear treatment was started immediately and undertaken for 2 years. The remaining patients served as untreated controls. Dental casts were taken and scanned at the beginning of treatment (T0) and at the 2‑year (T1) and 4‑year follow-up (T2). Three-dimensional landmarks describing the positions of maxillary and mandibular incisors, canines, first and second premolars and first molars were used to calculate and visualize the maxillary and mandibular dental arch area and shape using the polynomial equation y = Ax⁶ + Bx². Results: Significant changes in the shape and area of both maxillary and mandibular dental arches were induced with cervical headgear. The headgear increased dental arch area, sagittal dimensions at the mid-sagittal line and transversal dimensions at all of the measured levels in both dental arches compared to the control group. Conclusions: Cervical headgear is an effective treatment device to gain space in both dental arches. Furthermore, when used as an early phase treatment, relapse is relatively small compared to the gained space.Zusammenfassung Zielsetzung: Ziel dieser Studie war es, die Auswirkungen einer frühen zervikalen Headgear-Behandlung auf den Bereich des Ober- und Unterkieferzahnbogens, die Form und die Interbogendimensionen zu untersuchen. Methoden: Die Studiengruppe umfasste insgesamt 67 Kinder im Alter von 7,6 Jahren (Standardabweichung 0,3) mit Angle-Klasse-II-Malokklusion, die zwischen 1992 und 1996 behandelt wurden. Die Kinder wurden randomisiert in 2 gleich große Gruppen aufgeteilt. In der ersten Gruppe wurde sofort mit der zervikalen Headgear-Behandlung begonnen und sie wurde 2 Jahre lang durchgeführt. Die übrigen Patienten dienten als unbehandelte Kontrolle. Zu Beginn der Behandlung (T0), beim 2‑ (T1) und beim 4‑Jahres-Follow-up (T2) wurden Abdrücke genommen und gescannt. Dreidimensionale Landmarken zur Darstellung der Positionen von Schneidezähnen, Eckzähnen, ersten und zweiten Prämolaren und ersten Molaren im Ober- und Unterkiefer wurden zur Berechnung und Visualisierung des Bereichs und der Form des Zahnbogens des Ober- und Unterkiefers unter Verwendung der Polynomgleichung y = Ax⁶ + Bx² verwendet. Ergebnisse: Mit dem zervikalen Headgear wurden signifikante Veränderungen in Form und Fläche sowohl der Ober- als auch der Unterkieferzahnbögen induziert. Das Headgear vergrößerte im Vergleich zur Kontrollgruppe die Zahnbogenfläche, die sagittalen Dimensionen an der mittleren sagittalen Linie und die transversalen Dimensionen auf allen gemessenen Ebenen in beiden Zahnbögen. Schlussfolgerungen: Das zervikale Headgear ist eine wirksame Behandlungsvorrichtung, um in beiden Zahnbögen Platz zu gewinnen. Wenn sie als Frühphasentherapie eingesetzt wird, ist das Rezidiv im Vergleich zum gewonnenen Platz relativ gering

Evaluation of facial soft tissue asymmetric changes in Class III patients after orthognathic surgery using three-dimensional stereophotogrammetry

Abstract The aim of this study was to investigate changes in facial soft tissue asymmetry over time after orthognathic surgery in Class III patients using three-dimensional stereophotogrammetry. The study included 101 patients with a skeletal Class III malocclusion (72 female, 29 male; age range 19–53 years, mean age 28.6 years) who underwent orthognathic surgery. The minimum follow-up was 12 months. Three-dimensional photographs were acquired using the 3dMDtrio stereophotogrammetry system, and 21 anthropometric landmark positions were evaluated at three time points: before surgery (T0), 6 months (T1) and 12 months (T2) after surgery. Facial asymmetry was assessed and classified as follows: 0–2 mm, mild; 2–5 mm, moderate;> 5 mm, severe. The average distance for whole face asymmetry differed between T0 (median 0.76 mm) and T1 (median 0.70 mm); however, there was no statistically significant difference at any time point. The chin volume asymmetry score differed significantly between T0 (median 1.11 mm) and T1 and T2 (median 1.08 mm for both; P < 0.001 and P = 0.001, respectively), but not between T1 and T2 (P = 0.061). The study findings indicate that the asymmetry of the facial soft tissues has the potential to return after 6 months, without reaching the baseline

The association between dental and facial symmetry in adolescents

Abstract Introduction: Facial aesthetics have become one of the most important objectives of orthodontic treatment. The correction of dental arches should be performed in accordance with the face. This study explored the association between occlusal and facial asymmetries in adolescents, particularly emphasizing a Class II subdivision. Methods: Eighty-one adolescents (43 males, 38 females) with a median age of 15.9 (interquartile range, 15.17–16.33) years were enrolled. Of these patients, 30 had a Class II subdivision (right side, n = 12; left side, n = 18). Three-dimensional facial scans were analyzed using surface- and landmark-based methods. Chin asymmetry was determined using the chin volume asymmetry score. Three-dimensional intraoral scans were analyzed to assess occlusal asymmetry. Results: The surface matching scores were 59.0% ± 11.3% for the whole face and 39.0% ± 19.2% for the chin. Chin volume was larger on the right side than on the left side in most patients (n = 51, 63%), and it was associated with a dental midline shift to the corresponding subdivision side. A correlation between dental and facial asymmetries was noted. In addition, the dental midline shifted to the left in patients with a Class II subdivision, regardless of the side, and to the right in those with a symmetrical Class II subdivision. However, several patients did not possess asymmetrical occlusal traits sufficient for statistical analysis. Conclusions: Dental asymmetry was weak but significantly correlated with facial asymmetry

Associations of sagittal malocclusions with dental arch characteristics and crowding in Northern Finland Birth Cohort 1966

Abstract Objective: To analyse the associations between the widths and forms of dental arches, malocclusions and crowding in middle-aged adult population. Materials and Methods: The study material is part of the Northern Finland Birth Cohort 1966 (NFBC1966); the subjects were examined at the age of 46 years. A total of 781 adults with full dentition and no orthodontic treatment history were included. Overjet, overbite, cross-bite and scissor bite were examined during clinical examination. The widths and forms of dental arches, molar relationships and crowding were measured using three-dimensional (3D) dental models. Results: Dental arches were significantly larger in males than in females. Class II (CII) occlusion and increased overjet (≥6 mm) were associated with narrow maxilla (P < .001, P < .05 respectively). Subjects with lateral cross-bite had significantly narrower maxilla and wider mandible (P < .05) than subjects with normal lateral occlusion. In subjects with CII occlusion, square or tapered maxilla and tapered or ovoid mandible were significantly more frequent compared to subjects with Class I (CI) occlusion (P < .05). CII occlusion was significantly associated with crowding in the maxilla (P < .01). Conclusions: Narrow and tapered-shaped maxilla was related to CII occlusion, which was associated with dental crowding in the maxilla. Malocclusions were more likely to be found together with other malocclusions than alone