Robin Yong

Application of three‐dimensional computed tomography in craniofacial clinical practice and research

Following the invention of the first computed tomography (CT) scanner in the early 1970s, many innovations in three-dimensional (3D) diagnostic imaging technology have occurred, leading to a wide range of applications in craniofacial clinical practice and research. Three-dimensional image analysis provides superior and more detailed information compared with conventional plain two-dimensional (2D) radiography, with the added benefit of 3D printing for preoperative treatment planning and regenerative therapy. Current state-of-the-art multidetector CT (MDCT), also known as medical CT, has an important role in the diagnosis and management of craniofacial injuries and pathology. Three-dimensional cone beam CT (CBCT), pioneered in the 1990s, is gaining increasing popularity in dental and craniofacial clinical practice because of its faster image acquisition at a lower radiation dose, but sound guidelines are needed to ensure its optimal clinical use. Recent innovations in micro-computed tomography (micro-CT) have revolutionized craniofacial biology research by enabling higher resolution scanning of teeth beyond the capabilities of MDCT and CBCT, presenting new prospects for translational clinical research. Even after four decades of refinement, CT technology continues to advance and broaden the horizons of craniofacial clinical practice and phenomics research.

Dental phenomics: advancing genotype to phenotype correlations in craniofacial research

The field of dental phenomics provides many opportunities to elucidate the roles of genetic, epigenetic and environmental factors in craniofacial development. To date, research findings have helped to clarify the pathogenesis of many conditions, aiding diagnosis and clinical management. This paper provides an overview of dental phenomics research in some commonly encountered oral diseases in everyday clinical practice, as well as research relating to craniofacial growth and development. Clinically, advances in cariology and periodontology have led to better diagnostic capabilities and treatment provision. In the study of growth and development, important information regarding the varying clinical presentation and pathogenesis of many disorders is now apparent through the accurate quantification of phenotypes. Improvements in two-dimensional (2D) and three-dimensional (3D) imaging and analytical techniques have allowed for accurate dental phenotyping, and efforts are ongoing to apply these in vitro techniques to the in vivo setting. The field of dental phenomics represents an exciting avenue that links research findings to practical application, and collaboration between researcher and clinicians will help advance the field further.

Nanoscratch testing for the assessment of enamel demineralization under conditions simulating wine erosion

BACKGROUND Erosive tooth wear and dentinal hypersensitivity are common problems affecting professional wine tasters. By using nanoscratch testing, the aim of this in vitro study was to assess enamel softening under conditions simulating 10 one-minute episodes of wine erosion. METHODS Ten enamel specimens were bathed in artificial saliva for 2 hours before being eroded for 10 episodes, with each episode comprising one minute of wine erosion followed by one minute of remineralization in artificial saliva. Nanoscratches were placed with a spherical tip (20 μm radius) in a nanoindenter under a load of 100 mN at baseline (stage 1), after a one-erosion episode (stage 2) and after 10-erosion episodes (stage 3). RESULTS There were significant effects of erosion stages on both scratch depth (p<0.001) and surface roughness (p<0.001). Post hoc tests showed significant differences in both scratch depths and surface roughness between stages 1 and 3 (p<0.001), and between stages 2 and 3 (p<0.01). CONCLUSIONS Enamel softening occurs at an early stage of wine tasting, emphasizing the need to implement early preventive strategies in professional wine tasters. Further research elucidating the fundamental mechanisms involved in early stages of erosion has the potential to lead to development of more effective preventive strategies.

VARIATIONS IN DENTAL ARCH MORPHOLOGY ARE OUTCOMES OF THE COMPLEX ADAPTIVE SYSTEM ASSOCIATED WITH THE DEVELOPMENTAL VARIATION OF HYPODONTIA

Development of the human facial structures including the jaws and dentition occurs in a process that has the characteristics of a complex adaptive system (CAS) influenced by epigenetic, genetic and environmental factors. Earlier studies have suggested dental arch development to be reduced in size in subjects with hypodontia when compared with controls. Hypodontia is a variation of development and presents with a reduced number of teeth together with several other phenotypic changes. This study uses enhanced 3D imaging techniques to increase the accuracy of the measurements of dental arches. The sample consists of orthodontic patients, 60 with hypodontia (thirty males and thirty females), and 60 controls matched for age, gender and ethnicity. One operator using an Amann Girrbach Ceramill Map400 3D scanner recorded the 3D images from dental models. The 3D images were then viewed on MeshLab and the accuracy of the measurements were determined through repeat measurement of the same images; this was undertaken with intraand inter-operator reproducibility. Ten repeat measurements were taken on 10 different models. Validation of the new system was undertaken by repeating the measurements using the standard 2D caliper technique. Arch dimension measurements were determined from distance between the left-hand side first molar to the right-hand side first molar. Similar measurements were also made for the inter-canine width. The results for average intraoperator measurements were 0.33 mm for the maxillary arch and 0.40 mm for the mandibular arch. The difference in average inter-operator reproducibility was also measured for inter-molar arch dimensions at 0.31 and 0.23 mm for maxillary and mandibular arches, respectively. This novel method provides an increased range of measurement of similar accuracy to standard techniques. This study will proceed to establish the variations on the 3D images between the hypodontia subjects and the control group.

Extensive phenotyping of the orofacial and dental complex in Crouzon syndrome

OBJECTIVES Fibroblast growth factor receptor 2 (FGFR2) C342Y/+ mutation is a known cause of Crouzon syndrome that is characterised by craniosynostosis and midfacial hypoplasia. Our aim was to conduct extensive phenotyping of the maxillary, mandibular and dental morphology associated with this mutation. MATERIALS AND METHODS Morphometric data were obtained from 40 mice, representing two genotypes (Crouzon and wild-type) and two sexes (males and females) (n=10 in each group). Dental analysis further categorised the first molars into the two jaws (maxillary and mandibular) (n=20 in each group). Maxillary, mandibular and dental morphology was compared by analysing 23 linear landmark-based dimensions in three-dimensional micro-computed tomography reconstructions. RESULTS Compared with wild-type, Crouzon (FGFR2C342Y/+) maxillae were significantly shorter in maximum height, anterior and posterior lengths and middle width, but larger in posterior width (p<0.05 for height; p<0.001 for other comparisons). In the Crouzon mandible, the ascending and descending heights, effective and mandibular lengths, and intercoronoid and intercondylar widths were significantly shorter, whereas intergonial width was larger (p<0.01 for intercondylar width; p<0.001 for other comparisons). Crouzon teeth were significantly smaller mesiodistally, but larger in crown height (p<0.001 for each comparison). All Crouzon mice presented with bifid mandibular condyles and a quarter presented with expansive bone lesions in the mandibular incisor alveolus. CONCLUSIONS Our findings of hypoplasia in all three planes in Crouzon maxillae and mandibles, together with the presence of bifid mandibular condyles and expansive bone lesions, may be relevant to maxillofacial surgery and orthodontics. Beyond skeletal effects, the FGFR2C342Y/+ mutation is now implicated in affecting tooth development. This studys skeletal phenomics data also provides baseline data against which the effect of various treatments can now be assessed.

Technical Note: The use of 3D printing in dental anthropology collections

OBJECTIVES Rapid prototyping (RP) technology is becoming more affordable, faster, and is now capable of building models with a high resolution and accuracy. Due to technological limitations, 3D printing in biological anthropology has been mostly limited to museum displays and forensic reconstructions. In this study, we compared the accuracy of different 3D printers to establish whether RP can be used effectively to reproduce anthropological dental collections, potentially replacing access to oftentimes fragile and irreplaceable original material. METHODS We digitized specimens from the Yuendumu collection of Australian Aboriginal dental casts using a high-resolution white-light scanning system and reproduced them using four different 3D printing technologies: stereolithography (SLA); fused deposition modeling (FDM); binder-jetting; and material-jetting. We compared the deviations between the original 3D surface models with 3D print scans using color maps generated from a 3D metric deviation analysis. RESULTS The 3D printed models reproduced both the detail and discrete morphology of the scanned dental casts. The results of the metric deviation analysis demonstrate that all 3D print models were accurate, with only a few small areas of high deviations. The material-jetting and SLA printers were found to perform better than the other two printing machines. CONCLUSIONS The quality of current commercial 3D printers has reached a good level of accuracy and detail reproduction. However, the costs and printing times limit its application to produce large sample numbers for use in most anthropological studies. Nonetheless, RP offers a viable option to preserve numerically constraint fragile skeletal and dental material in paleoanthropological collections.

AGENTS WITHIN A DEVELOPMENTAL COMPLEX ADAPTIVE SYSTEM: INTRAUTERINE MALE HORMONES AND DENTAL ARCH SIZE IN HUMANS

Oral development is a complex adaptive system influenced by genetic, epigenetic and environmental factors. The dental arch develops from 6 weeks in utero until adult life, forming an accessible record to study general growth and development. Increased tooth size in female dizygotic opposite-sex (DZOS) twins compared with female dizygotic same-sex (DZSS) twins provides evidence for the masculinisation of females gestated with a male co-twin, possibly due to the intrauterine influence of male sex hormones: the “Twin Testosterone Transfer” (TTT) hypothesis. This study aimed to investigate the potential influence of intrauterine male hor mones on dental arch size of female DZOS twins. Serial dental models of the primary and permanent dentitions of 69 female DZOS and DZSS twins were examined. Intercanine width, intermolar width, arch length and arch circumference were measured using a customised 2D image analysis system. Unpaired t-tests showed signifi cant differences for mandibular intercanine width (p = 0.03; effect size = 0.6) and borderline differences for mandibular intermolar width and arch circumference (p = 0.05; effect size = 0.5). No significant differences were found in the permanent dentition. These findings provide support for the TTT hypothesis with some arch dimensions being larger in female DZOS twins. We have developed a model of assessing the effects of intrauterine male hormones on the epigenetic changes that last into postnatal life. Our evidence suggests that this is a moderate effect possibly interacting with numerous other environmental factors that may influence arch size.