Precision of orthodontic cephalometric measurements on ultra low dose-low dose CBCT reconstructed cephalograms.

OBJECTIVES: To analyze differences in variation of orthodontic diagnostic measurements on lateral cephalograms reconstructed from ultra low dose-low dose (ULD-LD) cone beam computed tomography (CBCT) scans (RLC) as compared to variation of measurements on standard lateral cephalograms (SLC), and to determine if it is justifiable to replace a traditional orthodontic image set for an ULD-LD CBCT with a reconstructed lateral cephalogram. MATERIAL AND METHODS: ULD-LD CBCT images and SLCs were made of forty-three dry human skulls. From the ULD-LD CBCT dataset, a lateral cephalogram was reconstructed (RLC). Cephalometric landmarks (13 skeletal and 7 dental) were identified on both SLC and RLC twice in two sessions by two calibrated observers. Thirteen cephalometric variables were calculated. Variations of measurements, expressed as standard deviations of the 4 measurements on SLC and RLC, were analyzed using a paired sample t-test. Differences in the number of observations deviating ≥ 2.0 mm or degrees from the grand mean between SLC and RLC were analyzed using a McNemar test. RESULTS: Mean SDs for 7 out of 13 variables were significantly smaller for SLCs than those for RLCs, but differences were small. For 9 out of 13 variables, there was no significant difference between SLC and RLC for the number of measurements outside the range of 2 mm or degrees. CONCLUSIONS: Based on the lower radiation dose and the small differences in variation in cephalometric measurements on reconstructed LC compared to standard dose LC, ULD-LD CBCT with reconstructed LC should be considered for orthodontic diagnostic purposes. CLINICAL RELEVANCE: ULD-LD CBCT with reconstructed LC should be considered for orthodontic purposes.

Effect of voxel size in cone-beam computed tomography on surface area measurements of dehiscences and fenestrations in the lower anterior buccal region.

OBJECTIVES: This study aims to assess whether different voxel sizes in cone-beam computed tomography (CBCT) affected surface area measurements of dehiscences and fenestrations in the mandibular anterior buccal region. MATERIALS AND METHODS: Nineteen dry human mandibles were scanned with a surface scanner (SS). Wax was attached to the mandibles as a soft tissue equivalent. Three-dimensional digital models were generated with a CBCT unit, with voxel sizes of 0.200 mm (VS200), 0.400 mm (VS400), and 0.600 mm (VS600). The buccal surface areas of the six anterior teeth were measured (in mm2) to evaluate areas of dehiscences and fenestrations. Differences between the CBCT and SS measurements were determined in a linear mixed model analysis. RESULTS: The mean surface area per tooth was 88.3 ± 24.0 mm2, with the SS, and 94.6 ± 26.5 (VS200), 95.1 ± 27.3 (VS400), and 96.0 ± 26.5 (VS600), with CBCT scans. Larger surface areas resulted in larger differences between CBCT and SS measurements (- 0.1 ß, SE = 0.02, p < 0.001). Deviations from SS measurements were larger with VS600, compared to VS200 (1.3 ß, SE = 0.05, P = 0.009). Fenestrations were undetectable with CBCT. CONCLUSIONS: CBCT imaging magnified the surface area of dehiscences in the anterior buccal region of the mandible by 7 to 9%. The larger the voxel size, the larger the deviation from SS measurements. Fenestrations were not detectable with CBCT. CLINICAL RELEVANCE: CBCT is an acceptable tool for measuring dehiscences but not fenestrations. However, CBCT overestimates the size of dehiscences, and the degree of overestimation depends on the actual dehiscence size and CBCT voxel size employed.

Phagocytosis and macrophage polarization on bacterially contaminated dental implant materials and effects on tissue integration.

Bacterial contamination is hard to avoid during dental implant surgery. Macrophages and their polarisation play a decisive role in bacterial colonisation and tissue integration on bacterially contaminated dental implants. The present study investigated the role of macrophages in stimulating tissue coverage overgrowth of contaminating oral bacteria on polished titanium (Ti-P) and acid-etched zirconium dioxide (ZrO2-MA) dental implant materials. Different co-culture models were employed to determine phagocytosis rates of Streptococcus mitis or Staphylococcus aureus contaminating a dental implant surface and the influence of contaminating bacteria and osteoblasts (U2OS) on macrophage polarisation. S. aureus was phagocytized in higher numbers than S. mitis in bi-cultures on smooth Ti-P surfaces. Contaminating S. mitis stimulated near full polarisation of macrophages from a non-Ym1-expressing- to a Ym1-expressing-phenotype on smooth Ti-P, but on ZrO2-MA both phenotypes occurred. In tri-cultures with U2OS-cells on smooth Ti-P, a larger percentage of macrophages remained in their non-Ym1-expressing, "fighting" M1-like phenotype to clear Ti-P surfaces from contaminating bacteria. On ZrO2-MA surfaces, more macrophages tended towards their "fix- and-repair" M2-like phenotype than on Ti-P surfaces. Surface coverage of smooth, bacterially contaminated Ti-P surfaces by U2OS-cells was more effectively stimulated by fighting, M1-like macrophages than on ZrO2-MA surfaces. Comprehensive guidelines are provided for the development of infection-resistant, dental implant materials, including bacteria, tissue and immune cells. These guidelines point to more promising results for clinical application of Ti-P as compared with ZrO2-MA.

[Questionnaire survey on the application of polypropylene mesh and sling in pelvic floor reconstruction surgery in Chinese IUGA members].

Objective: To investigate the similarities and differences between Chinese International Urogynecological Association (IUGA) members and international IUGA members on the treatment of pelvic organ prolapse (POP) and stress urinary incontinence (SUI) with polypropylene (PP) mesh and sling. Methods: Questionnaires were sent to Chinese IUGA members by Email. The contents of the questionnaires included POP mesh, SUI slings, abdominal sacrocolpopexy (ASC), complications, patients' awareness of rights protection, litigation and database use.Chi-square test was used to compare the proportion of Chinese IUGA members and international IUGA members to the problem alternatives. Results: A total of 31 Chinese IUGA members (100%, 31/31) responded to the questionnaire. All Chinese IUGA members (100%, 31/31) recognized and used PP sling to treat SUI, 98% (917/936) of international IUGA members had used and continued to use PP sling. For ASC surgery, 81% (25/31) of Chinese IUGA members and 82% (768/936) of international IUGA members agreed with and implemented the operation (P=0.841), while 94% (29/31) of Chinese IUGA members and 72% (674/936) of international IUGA members had the same or increased surgical volume as before (P=0.019). For the treatment of POP by transvaginal implantation of PP mesh, Chinese IUGA members had significant differences with international IUGA members in terms of whether they had used (P=0.002), were using (P<0.001), reasons for not using mesh (P<0.001), and indications of mesh implantation (P<0.001). Totally 81% (25/31) of Chinese IUGA members used various databases for monitoring and follow-up, while only 62% (580/936) of international IUGA members used databases, but there was no statistical difference (P=0.092). Conclusion: There are great differences in the concept and clinical application of transvaginal PP mesh implantation for POP between Chinese IUGA members and international IUGA members.

Soft tissue coverage on the segmentation accuracy of the 3D surface-rendered model from cone-beam CT.

OBJECTIVES: The aim of this study is to investigate the effect of soft tissue presence on the segmentation accuracy of the 3D hard tissue models from cone-beam computed tomography (CBCT). MATERIALS AND METHODS: Seven pairs of CBCT Digital Imaging and Communication in Medicine (DICOM) datasets, containing data of human cadaver heads and their respective dry skulls, were used. The effect of the soft tissue presence on the accuracy of the segmented models was evaluated by performing linear and angular measurements and by superimposition and color mapping of the surface discrepancies after splitting the mandible and maxillo-facial complex in the midsagittal plane. RESULTS: The linear and angular measurements showed significant differences for the more posterior transversal measurements on the mandible (p < 0.01). By splitting and superimposing the maxillo-facial complex, the mean root-mean-square error (RMSE) as a measurement of inaccuracy decreased insignificantly from 0.936 to 0.922 mm (p > 0.05). The RMSE value for the mandible, however, significantly decreased from 1.240 to 0.981 mm after splitting (p < 0.01). CONCLUSIONS: The soft tissue presence seems to affect the accuracy of the 3D hard tissue model obtained from a cone-beam CT, below a generally accepted level of clinical significance of 1 mm. However, this level of accuracy may not meet the requirement for applications where high precision is paramount. CLINICAL RELEVANCE: Accuracy of CBCT-based 3D surface-rendered models, especially of the hard tissues, are crucial in several dental and medical applications, such as implant planning and virtual surgical planning on patients undergoing orthognathic and navigational surgeries. When used in applications where high precision is paramount, the effect of soft tissue presence should be taken into consideration during the segmentation process.

[Analysis of a Chinese Charcot-Marie-Tooth disease type 2D pedigree].

Objective: To achieve definite diagnosis in a clinically diagnosed Charcot-Marie-Tooth disease (CMT) pedigree and broaden the mutational diversity of CMT-related mutations in Chinese Han population. Methods: Patients clinically diagnosed with CMT were recruited from Department of Neurology, Chinese PLA General Hospital between December, 2012 to June, 2016. Clinical examination, laboratory tests, nerve conduction studies, and molecular and bioinformatics analyses were performed on a clinically diagnosed CMT pedigree. Results: In the pedigree, a GARS mutation (c.794C>T, p. S265F) was identified and CMT2D was diagnosed. Conclusion: The newly identified GARS mutation has broaden the mutational diversity of CMT2D in Chinese Han population.

The implant infection paradox: why do some succeed when others fail? Opinion and discussion paper.

Biomaterial-implants are frequently used to restore function and form of human anatomy. However, the presence of implanted biomaterials dramatically elevates infection risk. Paradoxically, dental-implants placed in a bacteria-laden milieu experience moderate failure-rates, due to infection (0.0-1.1%), similar to the ones of joint-arthroplasties placed in a near-sterile environment (0.1-1.3%). Transcutaneous bone-fixation pins breach the immune-barrier of the epidermis, exposing underlying sterile-tissue to an unsterile external environment. In contrast to dental-implants, also placed in a highly unsterile environment, these pins give rise to relatively high infection-associated failure-rates of up to 23.0%. Herein, we attempt to identify causes as to why dental-implants so often succeed, where others fail. The major part of all implants considered are metal-made, with similar surface-finishes. Material choice was therefore discarded as underlying the paradox. Antimicrobial activity of saliva has also been suggested as a cause for the success of dental-implants, but was discarded because saliva is the implant-site-fluid from which viable bacteria adhere. Crevicular fluid was discarded as it is largely analogous to serum. Instead, we attribute the relative success of dental-implants to (1) ability of oral tissues to heal rapidly in the continuous presence of commensal bacteria and opportunistic pathogens, and (2) tolerance of the oral immune-system. Inability of local tissue to adhere, spread and grow in presence of bacteria and an intolerant immune-system are identified as the likely main causes explaining the susceptibility of other implants to infection-associated failure. In conclusion, it is the authors' belief that new anti-infection strategies for a wide range of biomaterial-implants may be derived from the relative success of dental-implants.

Success, clinical performance and patient satisfaction of direct fibre-reinforced composite fixed partial dentures - a two-year clinical study.

To evaluate the success, clinical performance and patient satisfaction of directly placed fibre-reinforced composite (FRC) fixed partial dentures (FPDs) in 2 years. One hundred sixty-seven FRC FPDs (120 subjects) were directly fabricated to restore a single missing tooth by six Advanced Education in General Dentistry (AEGD) residents. The FRC FPDs recipients were randomised into two groups according to the fibre materials (pre-impregnated glass or polyethylene). Clinical performance was evaluated at baseline (2 weeks), 6, 12 and 24 months by two calibrated evaluators for prosthesis adaptation, colour match, marginal discoloration, surface roughness, caries and post-operative sensitivity using modified United State Public Health Service (USPHS) criteria. Prosthesis appearance, colour, chewing ability and overall satisfaction were evaluated by patients using a visual analogue scale (VAS). Kaplan-Meier estimation was used to estimate the prosthesis success. Ninety-four patients with 137 FRC FPDs returned (21·67% attrition rate for study subjects, 17·94% for FRC FPDs). Seventeen FRC FPDs failed, due to one-end (n = 4) or two-ends (n = 4) debonding or pontic fracture (n = 9). The cumulative 2-year success rate was 84·32% and survival rate was 92·7%; there were no statistically significant differences between the groups according to different missing tooth location, retention type or fibre materials (P > 0·05). Patient satisfaction regarding prosthesis appearance, col-our, chewing ability and overall satisfaction was rated high on the VAS (mean >80 mm) for all criteria at all time points. The FRC FPDs (restoring single tooth) fabricated by AEGD residents achieved acceptable success and survival rates in a 2-year follow-up.

[Expression characteristics of epithelial markers in human embryonic stem cells differentiating into keratinocytes].

OBJECTIVE: To differentiate human embryonic stem cells (hESCs) into keratinocytes (K-hESCs) and analyse the expression characteristics of biomarkers of K-hESCs. METHODS: The hESCs of line H9 were seeded on matrigel in mTeSR1 medium. The hESCs were directly differentiated into keratinocytes in epithelial differentiation medium with bone morphogenetic protein 4, retinoic acid and N2 supplement. The karyotype of K-hESCs was analyzed, comparing the gene expression differences of K-hESCs with human gingival epithelial cells (HGECs), human immortalized oral epithelial cells (HIOECs) and HaCaT by Real-time PCR. Molecular characteristics of the cell differentiation were observed throughout the process by immunocytochemical techniques. RESULTS: H9-hESCs were successfully differentiated into the cells that exhibited characteristics of keratinocytes in epithelial differentiation medium. The karyotype of K-hESCs was 46, XX; and the keratinocyte gene p63 expression in K-hESCs was significantly lower than that in HaCaT (P < 0.05), but there was no significant difference of p63 expression in K-hESCs, comparing with that in HGECs and HIOECs (P > 0.05). CONCLUSION: H9-hESCs could be directly differentiated into K-hESCs. The gene expression of K-hESCs was similar to that of epithelial cells in the early stage of monolayer cells differentiation with high proliferative activity.

[Accelerated orthodontic treatment]. / De versnelde orthodontische behandeling.

An orthodontic treatment usually involves a long process which often represents an obstacle for patients. To overcome this problem, surgical techniques have been developed to support and accelerate the orthodontic treatment. Two systematic reviews of the literature on clinical research and animal experiments were carried out in order to draw reliable conclusions about the effectiveness of the various surgical techniques. A total of 18 clinical studies and 22 animal experimental studies were analysed. In both reviews of the literature, a study was made of whether the surgical techniques resulted in an accelerated rate of tooth movement and which complications may be observed. In addition, which biological mechanisms take place during surgically facilitated orthodontics was investigated. Both reviews reported accelerated tooth movement with minimal complications after surgical procedures in comparison to conventional orthodontics. An increase in catabolic and anabolic activities was observed. It has to be concluded that based on the quality of the current literature there is still insufficient information for general conclusions and that more standardised prospective research is necessary for a reliable conclusion about the optimal method of treatment.

Antimicrobial penetration in a dual-species oral biofilm after noncontact brushing: an in vitro study.

OBJECTIVES: Oral biofilm is inevitably left behind, even after powered brushing. As a special feature, powered brushing removes biofilm in a noncontact mode. When the brushing distance becomes too large, biofilm is left behind. We hypothesize that biofilm left behind after brushing has different viscoelastic properties than before brushing, impacting antimicrobial penetration. MATERIALS AND METHODS: In vitro grown dual-species biofilms were subjected to 20 % mechanical deformation before and after powered brushing at 4-mm brushing distance. Biofilm thickness and stress relaxation were measured for unbrushed and brushed biofilms. Stress relaxation was analyzed with a three-element Maxwell model. Antimicrobial penetration from five mouthrinses was microscopically evaluated for unbrushed and brushed biofilms. RESULTS: Thicknesses of unbrushed and brushed biofilms were similar. Brushing decreased the prevalence of fast and increased the prevalence of slow relaxation elements, which was accompanied by deeper penetration of chlorhexidine and cetylpyridinium chloride. Penetration of antimicrobials from other mouthrinses was relatively low in unbrushed and brushed biofilms. CONCLUSIONS: This confirmation of our hypothesis points to an additional advantage of powered toothbrushing in a noncontact mode, changing the viscoelastic properties of biofilm in a direction that increases antimicrobial penetration of chlorhexidine and cetylpyridinium. CLINICAL RELEVANCE: The biofilm left behind after noncontact powered toothbrushing may have less recalcitrance toward penetration of chlorhexidine and cetylpyridinium chloride than prior to brushing.

Atomic pair distribution functions analysis of disordered low-Z materials.

Results of high-energy X-ray diffraction experiments coupled to atomic pair distribution function analysis of disordered low-Z materials are presented. Several scientifically and technologically important classes of disordered low-Z materials such as small and large organic molecules, graphitic powders, polymers and liquids are intentionally explored to certify the technique's performance. Results clearly show that disordered low-Z materials can be well characterized in terms of material's phase identity, relative abundance in mixtures and atomic-scale structure. The demonstrated efficiency of the technique provides the scientific community with much needed confidence to apply it more often than now.

Cone beam computed tomography volumetric airway changes after orthognathic surgery: a systematic review.

The aim of this systematic review was to provide a structured overview of three-dimensional airway volume changes in relation to various orthognathic surgeries. Clinical human studies performing pre- and postoperative three-dimensional airway volume assessments to investigate volumetric changes of the airway after orthognathic surgery were included. Pre-determined inclusion and exclusion criteria were applied in an extensive search of the PubMed, Embase, and Web of Science electronic databases. The cut-off date was set to January 1, 2022. Forty-one articles reporting retrospective and prospective case-control and case series studies were included. All studies were determined to be of medium quality (moderate risk of bias). The included studies were categorized by type of intervention. Pre- and postoperative volumes were extracted from the available data, and volume changes as a percentage of the preoperative levels were calculated. Isolated mandibular setback surgery generally decreased the airway volume. Isolated maxillary or mandibular advancement, bimaxillary advancement, and surgically assisted maxillary expansion generally increased the airway volume in the total airway and oropharynx, among which the effect of bimaxillary advancement surgery appeared most significant. High heterogeneity exists in the terminology and definitions of the airway and its segments. A more uniform methodology for airway volume measurement is needed to provide an insight into the impact on the airway of specific types of surgical intervention. In conclusion, airway volumes are affected after orthognathic surgery, which may be of clinical significance, especially in patients who are predisposed to obstructive sleep apnoea.

[Introduction and application of European Academy of Paediatric Dentistry judgment criteria and scoring system for molar-incisor hypomineralization].

Molar-incisor hypomineralization (MIH) is defined as an enamel mineralization defect caused by systemic factors, which is characterized by demarcated opacities. These opacities are liable to result in brittle hypomineralized enamel breakdown, which expediting the eventual development of cavities, even tooth loss. Early diagnosis and prompt intervention are essential. The MIH scoring system based on the diagnostic criteria of the European Academy of Paediatric Dentistry (EAPD) is internationally recognized. This system is particularly helpful to diagnose and evaluate the MIH, as well as conductive to the performance of epidemiological investigations. This paper gives a presentation on the EAPD judgment criteria and scoring system as well as their applications, based on the current situation of MIH studies and our findings of MIH epidemiological investigation.

[Validity and reliability of digital diagnostic measurements on digital three-dimensional dental models]. / Validiteit en betrouwbaarheid van digitale diagnostische metingen op digitale driedimensionale gebitsmodellen.

Digital three-dimensional dental models are widely used for orthodontic diagnosis. The aim of this clinical study was to assess the validity and reliability of digital diagnostic measurements on digital three-dimensional dental models. Two types of digital three-dimensional dental models and a plaster dental model were made of 10 volunteers. Digital measurements of the tooth width were compared with the physical measurements of the plaster models. None of the digital diagnostic measurements appeared to differ significantly from the physical measurements.

Methodology and models in erosion research: discussion and conclusions.

This paper summarises the discussions which took place at the Workshop on Methodology in Erosion Research in Zürich, 2010, and aims, where possible, to offer guidance for the development and application of both in vitro and in situ models for erosion research. The prospects for clinical trials are also discussed. All models in erosion research require a number of choices regarding experimental conditions, study design and measurement techniques, and these general aspects are discussed first. Among in vitro models, simple (single- or multiple-exposure) models can be used for screening products regarding their erosive potential, while more elaborate pH cycling models can be used to simulate erosion in vivo. However, in vitro models provide limited information on intra-oral erosion. In situ models allow the effect of an erosive challenge to be evaluated under intra-oral conditions and are currently the method of choice for short-term testing of low-erosive products or preventive therapeutic products. In the future, clinical trials will allow longer-term testing. Possible methodologies for such trials are discussed.

Ventilation Assessment by Carbon Dioxide Levels in Dental Treatment Rooms.

It is important for dental care professionals to reliably assess carbon dioxide (CO2) levels and ventilation rates in their offices in the era of frequent infectious disease pandemics. This study was to evaluate CO2 levels in dental operatories and determine the accuracy of using CO2 levels to assess ventilation rate in dental clinics. Mechanical ventilation rate in air change per hour (ACHVENT) was measured with an air velocity sensor and airflow balancing hood. CO2 levels were measured in these rooms to analyze factors that contributed to CO2 accumulation. Ventilation rates were estimated using natural steady-state CO2 levels during dental treatments and experimental CO2 concentration decays by dry ice or mixing baking soda and vinegar. We compared the differences and assessed the correlations between ACHVENT and ventilation rates estimated by the steady-state CO2 model with low (0.3 L/min, ACHSS30) or high (0.46 L/min, ACHSS46) CO2 generation rates, by CO2 decay constants using dry ice (ACHDI) or baking soda (ACHBV), and by time needed to remove 63% of excess CO2 generated by dry ice (ACHDI63%) or baking soda (ACHBV63%). We found that ACHVENT varied from 3.9 to 35.0 in dental operatories. CO2 accumulation occurred in rooms with low ventilation (ACHVENT ≤6) and overcrowding but not in those with higher ventilation. ACHSS30 and ACHSS46 correlated well with ACHVENT (r = 0.83, P = 0.003), but ACHSS30 was more accurate for rooms with low ACHVENT. Ventilation rates could be reliably estimated using CO2 released from dry ice or baking soda. ACHVENT was highly correlated with ACHDI (r = 0.99), ACHBV (r = 0.98), ACHDI63% (r = 0.98), and ACHBV63% (r = 0.98). There were no statistically significant differences between ACHVENT and ACHDI63% or ACHBV63%. We conclude that ventilation rates could be conveniently and accurately assessed by observing the changes in CO2 levels after a simple mixing of household baking soda and vinegar in dental settings.

[Clinical characteristics of patients with odontogenic sinusitis underwent endoscopic sinus surgery].

Objective: To analyze the clinical features of patients with odontogenic sinusitis (OS) treated by endoscopic sinus surgery (ESS). Methods: A retrospective investigation was carried out in our 27 (16 males and 11 females) cases with OS aged (49.74±14.42) years old. Subjects were hospitalized between January 2018 and November 2020 from Department of Otorhinolaryngology Head and Neck Surgery, Beijing Chaoyang Hospital. The medical history, symptoms, result of nasal endoscopy and paranasal sinus computed tomography (CT) were analyzed statistically by SPSS 19.0. Results: OS mainly occured on unilateral sinuses, with a duration of (8.56±11.79) months. Seventy point four percent (19/27) of the patients had a course within six-month, only 11% was over 12 months (3/27). Symptoms mostly showed as nasal obstruction (88.9%; 24/27), runny nose (81.5%; 22/27), nasal stinks (16/19) and postnasal drip (10/10). Sixty-three percent (17/27) of the OS patients had a dental history. Nasal endoscopic examination revealed a swelling of the ostiomeatal complex (77.8%; 21/27), medial wall interhal displacement of maxillary sinus (55.6%; 15/27), white emulsion-like purulent secretion in the middle meatus (70.4%; 19/27) and nasal polyps (59.3%; 16/27). Etiology of OS included implant-related problems (14.8%; 4/27) and periodontal disease (85.2%; 23/27). Conclusions: OS is usually unilateral sinusitis with a short history. Its clinical features show nasal stinks, white emulsion-like purulent secretion in the middle meatus and imaging findings of unilateral maxillary sinusitis with tooth-related lesions.

Melting of polymer single crystals studied by dynamic Monte Carlo simulations.

We report dynamic Monte Carlo simulations of lattice polymers melting from a metastable chain-folded lamellar single crystal. The single crystal was raised and then melted in an ultrathin film of polymers wetting on a solid substrate, mimicking the melting observations made by using Atomic Force Microscopy. We observed that the thickness distribution of the single crystal appears quite inhomogeneous and the thickness increases gradually from facetted edges to the center. Therefore, at low melting temperatures, melting stops at a certain crystal thickness, and melting-recrystallization occurs when allowing crystal thickening; at intermediate temperatures, melting maintains the crystal shape and exhibits different speeds in two stages; at high temperatures, fast melting makes a melting hole in the thinnest region, as well as a saw-tooth-like pattern at the crystal edges. In addition, the linear melting rates at low temperatures align on the curve extrapolated from the linear crystal growth rates. The temperature dependence of the melting rates exhibits a regime transition similar to crystal growth. Such kinetic symmetry persists in the melting rates with variable frictional barriers for c -slip diffusion in the crystal as well as with variable chain lengths. Visual inspections revealed highly frequent reversals upon melting of single chains at the wedge-shaped lateral front of the lamellar crystal. We concluded that the melting kinetics is dominated by the reverse process of intramolecular secondary crystal nucleation of polymers.

[Enlargement of the gingiva during treatment with fixed orthodontic appliances]. / Zwelling van de gingiva bij orthodontische behandeling met volledig vaste apparatuur.

Gingival enlargement commonly occurs in patients treated with fixed orthodontic appliances. In a study, 25 patients were monitored during and after treatment with fixed orthodontic appliances. The extent of the enlargement of the gingiva was determined by means of intra-oral photographs made shortly before the placement of the appliances, immediately after their removal and at 3 and 6 months after the appliances had been removed. The enlargement of the gingival was determined using a Visual Analogue Scale. During orthodontic treatment the average degree of gingival enlargement increased significantly. After removal of the appliances a significant decrease in the degree of gingival enlargement occurred. Within 3 months after debonding the gingival enlargement was at the same level as before starting the orthodontic treatment. The conclusion was that the enlargement of the gingiva that takes place during treatment with fixed orthodontic appliances was reversible.