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International journal of oral science 9(3), 174-184 (2017). doi:10.1038/ijos.2017.34, Published by West China College of Stomatology, Sichuan Univ. Press, Chengdu, Sichuan

Fluoride-containing adhesives for enamel sealing are commonly used for the prevention of white spot lesions during fixed orthodontic treatment. Thus, we examined whether enamel sealing with L.E.D. ProSeal® (Reliance Orthodontic Products Inc., Itasca, IL, USA) before bracket bonding increases the rate of bond failure during orthodontic treatment. In 20 adolescents (11–16 years, 10 male/10 female) at the start of fixed therapy, self-ligating SmartClip™SL3 metal brackets (3M Unitek, Monovia, CA, USA) were bonded to cleaned and conditioned (40% H3PO4, 30 s) buccal enamel surfaces of all permanent teeth except molars using Transbond™ XT (3M Unitek). In a split-mouth design, either L.E.D. ProSeal® (1st/3rd quadrant) or Clinpro™ XT Varnish (2nd/4th quadrant; 3M Unitek) was applied to enamel surfaces before (ProSeal®) or after (Clinpro™ XT Varnish) bracket bonding (200 teeth each; light curing: 20 s, Ortholux™ Luminous, 3M Unitek). Cumulative bond failure as total number of teeth with bracket detachment since start of therapy was documented every 3 months for a total of 12 months. Cumulative bond failure was higher for enamel sealing before bonding from 6 months onward reaching significance at 12 months (34/200) compared to sealing after bonding (24/200): p = 0.038; Cramer’s V = 0.488; odds ratio (OR) = 1.5; relative risk (RR) = 1.4. The higher loss rate was limited to the lower arch, but evident within 3 months reaching significance at 9 and 12 months (p = 0.019/0.011, V = 0.636/0.630; OR = 1.7/1.75, RR = 1.5/1.6). In general, cumulative bond failure at 12 months was higher in the lower arch, but this was only significant for teeth sealed before bonding (p = 0.001, V = 0.303, OR = 3.4, RR = 2.8). Enamel sealing with L.E.D. ProSeal® should be performed after bracket bonding to prevent increased bond failure and bracket loss in the lower dental arch.

The anchorage mechanisms currently used in orthodontic treatment have various disadvantages. The objective of this study was to determine the applicability of the osteoporosis medication strontium ranelate in pharmacologically induced orthodontic tooth anchorage. In 48 male Wistar rats, a constant orthodontic force of 0.25 N was reciprocally applied to the upper first molar and the incisors by means of a Sentalloy(®) closed coil spring for two to four weeks. 50% of the animals received strontium ranelate at a daily oral dosage of 900 mg per kilogramme of body weight. Bioavailability was determined by blood analyses. The extent of tooth movement was measured both optometrically and cephalometrically (CBCT). Relative alveolar gene expression of osteoclastic markers and OPG-RANKL was assessed by qRT-PCR and root resorption area and osteoclastic activity were determined in TRAP-stained histologic sections of the alveolar process. Compared to controls, the animals treated with strontium ranelate showed up to 40% less tooth movement after four weeks of orthodontic treatment. Gene expression and histologic analyses showed significantly less osteoclastic activity and a significantly smaller root resorption area. Blood analyses confirmed sufficient bioavailability of strontium ranelate. Because of its pharmacologic effects on bone metabolism, strontium ranelate significantly reduced tooth movement and root resorption in orthodontic treatment of rats. Strontium ranelate may be a viable agent for inducing tooth anchorage and reducing undesired root resorption in orthodontic treatment. Patients under medication of strontium ranelate have to expect prolonged orthodontic treatment times.

Orthodontic force application is well known to induce sterile inflammation, which is initially caused by the compression of blood vessels in tooth-supporting apparatus. The reaction of periodontal ligament cells to mechanical loading has been thoroughly investigated, whereas knowledge on tissue reactions of the dental pulp is rather limited. The aim of the present trial is to analyze the effect of orthodontic treatment on the induction and cellular regulation of intra-pulpal hypoxia. To investigate the effect of orthodontic force on dental pulp cells, which results in circulatory disturbances within the dental pulp, we used a rat model for the immunohistochemical analysis of the accumulation of hypoxia-inducible factor-1α in the initial phase of orthodontic tooth movement. To further examine the regulatory role of circulatory disturbances and hypoxic conditions, we analyze isolated dental pulp cells from human teeth with regard to their specific reaction under hypoxic conditions by means of flow cytometry, immunoblot, ELISA and real-time PCR on markers (Hif-1α, VEGF, Cox-2, IL-6, IL-8, ROS, p65). In vivo experiments showed the induction of hypoxia in dental pulp after orthodontic tooth movement. The induction of oxidative stress in human dental pulp cells showed up-regulation of the pro-inflammatory and angiogenic genes Cox-2, VEGF, IL-6 and IL-8. The present data suggest that orthodontic tooth movement affects dental pulp circulation by hypoxia, which leads to an inflammatory response inside treated teeth. Therefore, pulp tissue may be expected to undergo a remodeling process after tooth movement.

Summary Objective The aim of the study has been to describe the normal range of mandibular movements and condylar kinematics in children as well as to test the null hypothesis that these variables are not associated with gender, facial type and weight. Materials and methods The sample was comprised of 92 healthy children (7.2–10.6 years old) and 40 adult controls (18–34.7 years old). Examinations included the maximal mouth opening capacity and laterotrusion to the right and to the left. The condylar path inclination angle was calculated at 3 mm and 5 mm protrusion of the mandible. Kinematic variables were registered using the ultrasonic JMA system. Results Maximal mouth opening capacity averaged 46.73 mm for the children and 53.53 mm for the adults. The mean values of the lateral movements were 9.36 mm to the right and 9.62 mm to the left for the boys, and 9.91 mm and 9.68 mm for the girls, respectively. Mean condylar path inclination in the children was 36.5° (right) and 36.2° (left) at 3 mm of protrusive movement, and 34.3° (right) and 34.0° (left) at 5 mm of protrusive movement. Associations of the kinematic variables with gender, weight, or facial type were insignificant. Conclusion Younger school children have not yet reached the maximum mouth-opening capacity. Correlation analysis suggests some weak, but insignificant associations of gender, facial type and weight with mouth opening, laterotrusion and the condylar path inclination angle. The null hypothesis was not rejected.

The aim of this study was to compare the shear bond strength and Adhesive Remnant Index of four different veneering ceramic materials to metal brackets. Additionally, it should be examined whether it is possible to overcome the etching method using hydrofluoric acid which is noxious. Instead of this treatment, air particle abrasion with 25 μm aluminium trioxide, silane coupling application and etching with 37.0 per cent orthophosphoric acid as pre-treatment procedures of the veneering ceramics before bonding was investigated. Two surface conditioning methods of four ceramic materials before bonding brackets were examined: in group 1 an air particle abrasion with 25 μm aluminium trioxide (4 seconds at a pressure of 2.5 bars) and subsequently a silane coupling agent (Espe Sil, 3M Unitek, Monrovia, USA) was applicated on one side of each ceramic specimen (10 per group). In group 2 one side of each sample (10 per group) was etched with 37.0 per cent orthophosphoric acid for two minutes and was followed by a silane application (Espe Sil, 3M Unitek, Monrovia, USA). After this procedure the self-ligating metal brackets SmartClip (3M Unitek, Monrovia, USA) brackets were bonded to the ceramic blocks and a thermocycling process started (5°C - 55°C, 6000 cycles). Then, shear bond strength and Adhesive Remnant Index (ARI) were measured. To determine statistical differences Oneway-ANOVA and Tukey Post-hoc test were performed. The level of significance was set at α = 0.05. On the basis of the results of the current study, it could be concluded that sandblasting with 25 μm aluminium trioxide and the use of orthophosphoric acid (37.0 per cent) seem to prepare the surface of the ceramic restoration sufficiently before bracket bonding. The found level of shear bond strength values seem be sufficient for bracket bonding. Hydrofluoric acid seems not to be justifiable anymore for preparing the surface of dental ceramic restorations before bracket bonding.

Strontium represents a new generation of anti-osteoporotic agents that exert anti-catabolic and anabolic effects on bone cells at once. We used strontium in vitro in order to examine its potential to stimulate bone marker transcription and hydroxyapatite formation on isolated Runx2(+/-) osteoblasts from a patient with cleidocranial dysplasia. This disease is evoked by heterozygous mutations of Runx2, an important transcription factor for osteoblast maturing and transcription of osteogenic genes, which results in insufficient gene dosage of Runx2. This genetic defect is responsible, for example, for patent fontanels, sometimes throughout the life, supernumerary teeth, and aplasia or hypoplasia of clavicles and mimics symptoms of hypophosphatasia. In this trial, we investigated the effect of strontium on gene expression of bone marker proteins, the formation of hydroxyapatite and the cell proliferation of strontium-treated Runx2(+/-)-osteoblasts. Unlike normal osteoblasts, gene expression of bone marker proteins was not affected in strontium-treated Runx2(+/-) osteoblasts, while improved hydroxyapatite formation was noted in the extracellular matrix. A WST-1 cell proliferation assay with strontium-treated Runx2(+/-)-osteoblasts showed that strontium induces cell proliferation and growth. This effect might be responsible for the improved mineralisation of the extracellular matrix of strontium-treated Runx2(+/-)-osteoblasts observed.

The spheno-occipital synchondrosis is part of the cranial base growth plate and is of crucial importance in craniofacial development. In this investigation, we studied changes in collagen gene expression in the spheno-occipital synchondrosis in order to identify the developmental stages most important for extracellular matrix production and ossification of the rat cranial base growth plate. Gene transcripts of type II and X collagen were most abundant at day 10 postnatally in the spheno-occipital synchondrosis. This observation is assumed to be due to intrinsic genetic factors and local environmental factors.

Objective: To test the null hypothesis that there are no differences between children and adults in the condylar path inclination angle on the right and left sides. Materials and Methods: A group of 80 children aged 6 to 10 years (subgroups I through V, according to chronologic age) was compared with an adult group with regard to the condylar path inclination angle (CPIA) on the right and left sides. The CPIA was measured using the ultrasonic JMA-System for registration. Results: During development of the temporomandibular joint the condylar path inclination angle increased with age in the subgroups of children. A significant difference was found in the CPIA between the groups of adults and children. In the group with the oldest children (mean age: 10.3 years) the condylar path inclination angle had reached 81.87% on the right side and 78.85% on the left side compared with the adult group at a 5 mm protrusive path. In the pooled group of children the CPIA amounted to 73.08% on the right side and 72.13% on the left side compared with the values for the adults. No significant difference was found between the right and left CPIA in any group. Conclusion: The hypothesis is rejected. The CPIA on the right and left sides increased with age in the group of children and was significantly smaller in the group of children compared with the group of adults.

The purpose of this study was to compare the frictional properties of four self-ligating metal brackets, Speed, Damon 2, In-Ovation, and Time, with those of three conventionally ligated metal brackets, Time, Victory Twin, and Discovery. The self-ligating Time bracket can also be used as a conventionally ligated bracket. Friction was tested 20 times for each bracket/wire combination using a Zwick testing machine with stainless steel wires in three different wire dimensions (0.017 x 0.025, 0.018 x 0.025, and 0.019 x 0.025 inches). All brackets had a 0.022 inch slot and the prescription of an upper first premolar. The data were statistically analysed with unsigned comparisons of all bracket/wire combinations using the Mann-Whitney U-test and the Games-Howell post hoc test. The results showed almost all brackets to have the lowest frictional force with a wire dimension of 0.018 x 0.025 inch. Friction of the self-ligating brackets using wire with a dimension of 0.018 x 0.025 inches was 45-48 per cent lower than with 0.017 x 0.025 and 0.019 x 0.025 inch wires. Friction of the conventionally ligated brackets showed a 14 per cent or less reduced friction with 0.018 x 0.025 inch wire compared with 0.017 x 0.025 and 0.019 x 0.025 inch wires. The self-ligating metal brackets showed lower frictional forces with a 0.018 x 0.025 inch wire than conventionally ligated brackets, whereas conventionally ligated brackets showed lower friction with 0.017 x 0.025 and 0.019 x 0.025 inch wire. Friction values vary with different bracket/archwire combinations and, therefore, the choice of a bracket system for treatment should consider the correct wire dimension to produce the lowest possible frictional forces.

SUMMARY Enamel discolouration after debonding of orthodontic attachments could occur because of irreversible penetration of resin tags into the enamel structure. Adhesives could discolour because of food dyes or ultraviolet irradiation. The aim of this study was to investigate the colour stability of adhesives during ultraviolet irradiation and exposure to food colourants. Four different adhesives were exposed in a Suntest CPS+ ageing device to a xenon lamp to simulate natural daylight (Transbond XT, Enlight, RelyX Unicem, and Meron Plus AC). Tomato ketchup, Coca Cola©, and tea were chosen as the food colourants. After 72 hours of exposure, colour measurements were performed by means of a spectrophotometer according to the Commission Internationale de l’Eclairage L*a*b* system and colour changes ( ∆ E*) were computed. Statistical differences were investigated using two-way analysis of variance (ANOVA) and Friedman test. Unsatisfactory colour stability after in vitro exposure to food colourants and ultraviolet light was observed for the conventional adhesive systems, Transbond XT and Enlight. RelyX Unicem showed the least colour change and the resin-reinforced glass-ionomer cement (GIC), Meron Plus AC, the greatest colour change. The investigated adhesives seem to be susceptible to both internal and external discolouration. These in vitro fi ndings indicate that the tested conventional adhesive systems reveal unsatisfactory colour stability which should be improved to avoid enamel discolouration.

To evaluate the effect of different filler contents of orthodontic adhesives on shear bond strength and Adhesive Remnant Index (ARI).Four experimental adhesive groups were created: group 1 was an unfilled urethane-dimethacrylate (UDMA) adhesive, group 2 consisted of UDMA and a filler content of 30 vol%, group 3 consisted of UDMA and a filler content of 50 vol%, and group 4 was manufactured with a filler level of 70 vol% in a UDMA matrix. The embedded filler was silicon dioxide. After etching and priming, stainless steel brackets were bonded to extracted human third molars (n = 60) with the experimental adhesives (15 teeth per group). After storage in distilled water for 72 hours, shear bond strength and ARI scores were evaluated. Kruskal-Wallis and post hoc test were performed for statistical analysis.Shear bond strength of UDMA-based adhesives depends on filler content. Higher adhesive filler levels reveal greater bond strength between enamel and stainless steel brackets. ARI scores showed no significant difference among the groups. However, higher filled adhesives (filler content 70 vol%) seem to present higher ARI scores.Highly filled UDMA adhesives offer greater bond strength than do lower filled or unfilled resins.

Animal experiments are used in embryological and teratological studies of matters relevant to humans. In gravid rats, a decrease in the levels of folic acid and vitamin B12 was observed in maternal blood and in amniotic fluid. At the time of secondary palatal closure (14th day of pregnancy), the folic acid level of the amniotic fluid was 73% lower than that of the maternal blood. A drop in vitamin B12 in conjunction with an increase in amniotic homocysteine levels is seen as a risk factor for malformation of the palate. The understanding of causes of cleft generation could lead to a prophylactic treatment approach.

The development of white spot lesions around orthodontic brackets and gingivitis is a common problem during orthodontic treatment with fixed appliances. This prospective randomized double-blind controlled clinical trial investigated the preventive efficacy of a one-time application of two commonly used fluoride varnishes in patients with low to moderate caries risk. Ninety adolescent orthodontic patients with a low to moderate caries risk were prospectively randomized to three groups of 30 patients each: (1) standardized dental hygiene with fluoride toothpaste and one-time application of placebo varnish (control) or (2) of elmex® fluid or (3) of Fluor Protector S on all dental surfaces at the start of fixed therapy. The extent of enamel demineralization and gingivitis was determined with the ICDAS and the gingivitis index (GI) at baseline and after 4, 12, and 20 weeks. Each treatment group showed a significant increase of the ICDAS index, but not of the GI over the course of time with no significant intergroup differences detectable. A one-time application of fluoride varnish at the start of orthodontic treatment did not provide any additional preventive advantage over sufficient dental hygiene with fluoride toothpaste with regard to formation of white spots and gingivitis in patients with a low to moderate caries risk. In dental practice, patients often receive an application of fluoride varnish at the start of orthodontic treatment with fixed appliances. However, the efficacy of this procedure is still unclear.

Nicotine is considered an etiologic factor for chronic inflammatory phenomena within the periodontal ligament that may result in loss of periodontal attachment. Considering that smokers account for 26 % of adult and 12 % of adolescent patients in orthodontic practice, we performed in vivo and in vitro studies as to whether orthodontic forces may add to the nicotine-induced loss of periodontal bone. Fourteen male rats (Fischer 344 inbred) were used. Seven of these served as controls, while the other seven received daily subcutaneous injections of 1.89 mg L-nicotine per kg body weight. Both groups were exposed to orthodontic mesialization of the first two upper left molars using a NiTi closed-coil spring, the contralateral side serving as control. Periodontal bone loss was assessed by cone-beam computed tomography (CBCT). Human periodontal fibroblasts were stressed by compression (2 g/cm2) and/or nicotine (3/5/7.5 µmol), and the expression of cyclooxygenase-2 (COX-2), prostaglandin E2 (PGE2), interleukin-6 (IL-6), osteoprotegerin (OPG), and receptor activator of nuclear factor κB ligand (RANKL) was determined at the transcriptional level by quantitative real-time polymerase chain reaction (qRT-PCR) and at the translational level by enzyme-linked immunosorbent assay (ELISA). In addition, differentiation of co-cultured murine RAW264.7 cells to osteoclast-like cells was quantified by tartrate-resistant acid phosphatase (TRAP) staining. Orthodontic force application in vivo led to a significant increase in nicotine-induced periodontal bone loss, and cell compression in vitro to increased COX-2, PGE2, IL-6, and RANKL expression, reduced OPG expression, and enhanced differentiation of RAW264.7 cells to osteoclast-like cells compared to nicotine alone. Additional loss of periodontal bone must be expected during orthodontic treatment of smokers. Clinicians should inform their patients of this increased risk and refrain from performing tooth movements before cessation of smoking.

The belief of many orthodontists that premolar extraction therapy leads to a loss of vertical dimension and an aggravated facial profile often predetermines a non-extraction approach. We investigated the short-term effects of systematic premolar extraction in borderline cases for extraction therapy on dentofacial parameters, especially vertical dimension and facial profile. Of 50 juvenile borderline cases for extraction treatment with a distinct sagittal overjet of 6–9 mm and dental crowding of >6 mm, 25 had all first premolars extracted, whereas the 25 control patients received non-extraction orthodontic treatment with corresponding fixed and removable appliances. Patient selection by multivariate cluster analysis ensured homogeneity at baseline regarding dentoskeletal parameters. Parameter changes were determined with radiographic cephalograms and compared between the extraction and non-extraction group. The systematic extraction of premolars in borderline patients with a distinct sagittal overjet and crowding did not significantly influence sagittal or vertical skeletal dimension, while leading to a slightly more concave lip profile due to incisor retraction compared to the non-extraction control group. The influence of premolar extractions on facial profile is often overestimated, since only slight changes in lip profile are to be expected. In integrated treatment planning, the extraction decision should not be primarily based on concerns about the aggravation of facial profile and loss of vertical dimension. The decision, whether to extract healthy premolars in borderline patients for extraction therapy, is difficult to make. Our study clarifies the repercussions on cephalometric dentofacial parameters, facilitating future orthodontic extraction decisions.

SUMMARY Introduction During the early development, numerous histological and morphometric changes occur in the cranial sutures the exact knowledge of which is of fundamental significance for understanding clinically relevant cranial anomalies. In this paper a histological and histomorphometric longitudinal study of the coronal, sagittal and lambdoid sutures in the rat is reported in relation to age. Material and methods Forty-eight male Wistar rats (Rattus norvegicus Berkenhout) were raised under standard conditions. Eight animals each were sacrificed at defined time points (10, 14, 28, 42, 70, 98 days post partum) for specimen preparation. Histological preparations of the sagittal, coronal and lambdoid sutures were produced and examined morphologically and histomorphometrically (suture width, height, and area). Results Histologically, three phases of sutural growth with characteristic structural features were found. Histomorphometry reveals a quasi linear increase in height from the 30th to the 98th day post partum. Suture width remained relatively constant in the area of dura mater and periosteum. Conclusion The sutures of the test animals studied had a similar growth behaviour primarily consisting of an increase in height with almost constant width. The three-phases of development could be demonstrated histologically in all sutures.

A 3-point skeletal anchorage with taping screws for distraction osteogenesis after a Le Fort III osteotomy was applied for the first time in a severely mentally impaired patient where intraoral devices had to be avoided. All 3-force application points included the center of resistance, which allowed an optimal control on the resulting moment. A novel device for skeletal long-term retention into the nasal dorsum prevented a relapse, whereas adjustment of the midface position was observed. Fusioned three-dimensional computed tomography analysis revealed real movements not accessible by a conventional cephalometry.

Introduction We aimed to compare the shear bond strength (SBS) of three different retainer wires and three different bonding adhesives in consideration of the pretreatment process of enamel surface sandblasting. Methods 400 extracted bovine incisors were divided into 10 groups of 20 paired specimens each. 10 specimens of each group were pretreated by enamel sandblasting. The retainer wires Bond-A-Braid™, GAC-Wildcat®-Twistflex and everStick®ORTHO were bonded to the teeth with the adhesives Transbond™-LR, Tetric-EvoFlow™ and Stick®FLOW and then debonded measuring the SBS. Results While sandblasting generally increased SBS for all tested combinations, the retainer wires bonded with Transbond™-LR showed the highest SBS both with and without prior sandblasting. Significantly lower SBS were found for Tetric-EvoFlow™ that were comparable to those for everStick®ORTHO. Conclusions Pretreatment of enamel surfaces by sandblasting increased the SBS of all retainer-wires. Transbond™-LR showed the best results compared to Tetric-EvoFlow™ and everStick®ORTHO, while all combinations used provided sufficient bonding strengths for clinical use.

The purpose of this study was to investigate whether the mechanical properties of polymer brackets can be improved without discoloration by electron beam (EB) irradiation applied with a Rhodotron electron accelerator using standard high-energy parameters including a 10 MV acceleration voltage and 100 kGy of energy. We analyzed polymer samples and several commercially available brackets. The first group included three polymeric base materials (polyoxymethylene, polycarbonate, polyurethane) currently used in various bracket systems. The second group included five bracket types, three of which are on the market (Aesthetik-Line and Brillant by Forestadent; Envision by Ortho Organizers) while the other two were experimental brackets containing urethane dimethacrylate as a monomer matrix and functional silane-treated SiO2 fillers with a filler content of 10 or 40 vol%. Each category included 40 specimens previously irradiated by a commercial provider (Beta-Gamma-Service, Bruchsal, Germany) and another 40 nonirradiated controls. The polymer specimens were analyzed for fracture toughness, Vickers hardness, and wear resistance, and the bracket specimens for Vickers hardness and color stability. The Wilcoxon–Mann–Whitney U test was used for pairwise comparison to identify significant differences (p ≤ 0.05). Significant increases in fracture toughness and Vickers hardness were observed in polycarbonate and polyurethane after EB irradiation, while EB irradiation of polyoxymethylene resulted in a significant decrease in these parameters. The polyurethane samples demonstrated significantly less postirradiation wear. All the commercially available brackets except for Brillant revealed significant increases in Vickers hardness. Significant discoloration was observed in all brackets after irradiation. Although our evaluation of polymer brackets revealed considerable improvements in mechanical properties after EB irradiation, this benefit was marred by very obvious discoloration. We cannot therefore recommend industrial scale EB irradiation for any polymer bracket currently on the market.

The aim of the study was to investigate the effect of bleaching on the colouration of tooth enamel and shear bond strength of orthodontic ceramic brackets based upon current whitening practice. The bleaching and bonding techniques were performed on extracted bovine teeth for the investigation of their colorimetric spectrum and the adhesive bond strength on surface enamel. One group was designated as the control group with no pre-treatment. Another group was treated with a 45% hydrogen peroxide solution prior to bonding. The difference in colour was expressed as the Euclidian distance ΔE. The resulting shear bond strength was analyzed and evaluated by scores of Adhesion Remnant Index. Statistical analysis was performed using the Kruskall-Wallis and post-hoc test. The colorimetric analysis revealed statistically significant differences between original and bleached as well as bleached and debonded teeth setting off a blue colour shift. Furthermore, statistically there was no significant difference noted in bonding strength between non-treated surfaces and those treated with peroxide. It can be concluded that peroxide pre-treatment does result in colour differences of teeth. Bonding and debonding procedures seem to have no statistically significant influence on the enamel colour using current materials.

Objective Methionine is an essential amino acid and pivotal for normal growth and development. However, previous animal studies have shown that excessive maternal intake of methionine causes growth restrictions, organ damages, and abnormal growth of the mandible in newborn animals. However, the effect of excessive methionine on the development of the cranial growth plate is unknown. This study investigated histological alterations of the cranial growth plate induced by high methionine administration in newborn rats. Design Twenty pregnant dams were divided into a control and an experimental group. The controls received a diet for rats and the experimental group was fed from the 18th gestational day with a special manufactured high methionine diet for rats. The high methionine diet was maintained until the end of the lactation phase (day 20). The offspring of both groups were killed at day 10 or 20 postnatally and their spheno-occipital synchondroses were collected for histological analysis. Results The weight of the high-dose methionine treated experimental group was considerably reduced in comparison to the control group at day 10 and 20 postnatally. The cartilaginous area of the growth plate and the height of the proliferative zone were markedly reduced at postnatal day 10 in the experimental group. Conclusions In summary, the diet-induced hypermethioninemia in rat dams resulted in growth retardations and histomorphological changes of the spheno-occipital synchondrosis, an important craniofacial growth centre in newborns. This finding may elucidate facial dysmorphoses reported in patients suffering from hypermethioninemia.

Electron beam irradiation can be used to improve the mechanical properties of polymers. The aim of this study was to investigate the influence of electron beam irradiation with an energy dose of 100 kGy on the mechanical properties and colour stability of conventional polymer brackets and experimental filled composite brackets. The conventional brackets tested were Aesthetik-Line, Brillant, and Envision. The experimental brackets contained urethane dimethacrylate, as a monomer matrix and functional silane-treated SiO2 fillers with a filler content of either 10 (Exper 1) or 40 (Exper 2) vol per cent. The influence of electron beam post-curing on Vickers hardness (VH) of the polymer brackets was investigated. Additionally, a possible discolouration of the brackets after electron beam irradiation was determined according to the three-dimensional L * a * b * colour space. The irradiated brackets were compared with untreated control groups. Statistical analysis was performed using the Wilcoxon test. With the exception of Brillant brackets, all investigated brackets showed a significant enhancement of VH after electron beam post-curing. However, the brackets suffered a significant increase in discolouration. Aesthetik-Line brackets showed the highest discolouration, Δ E , and Exper 2 brackets the lowest Δ E values. The discolouration of the examined brackets differed significantly. These results demonstrate that the mechanical properties of polymer brackets could be modified by electron beam irradiation. Nevertheless, clinical use of electron beam post-curing might be restricted because of unacceptable colour changes.

This study was designed to investigate the effect of strontium on human PDL cells in vitro. Strontium is used to treat osteoporosis because of its bone formation promoting effect on osteoblast cells. This investigation presents evidence that strontium promotes PDL cell proliferation. Simultaneously, strontium suppresses the expression of the inflammation-promoting cytokine IL-6. The observed effect of strontium on PDL cells supports its use it in guided dental tissue regeneration.

Summary We conducted a temporal gene expression analysis with type I collagen in the coronoid process, alveolar process and mandibular angle of the rat. We observed gene expression cross-sectionally across different important physiological time points in the rat postnatal life in order to observe in which developmental stage mandibular development mainly occur. This study indicates prominent type I collagen expression at day 10 postpartum in the mandibular ramus and at day 21 in the alveolar process. These findings correspond well with previously obtained data from proliferation studies in facial bone suggesting that craniofacial growth in the rat occurs mainly between days 10 and 21.

Introduction Electron-beam irradiation can be used to influence the properties of polymers. Electron beams cause cross-linking that enhances the molecular mass of the polymer; this leads to branched chains until, ultimately, a 3-dimensional network is formed. The aim of this study was to evaluate the effect of electron-beam irradiation on polymer bracket materials. Methods Since polymers are commonly used materials for brackets, polyoxymethylene, polycarbonate, and polyurethane were chosen for this study. The acceleration voltage of the electron-beam device was 10 MeV, and the energy dose was 100 kGy with an electron accelerator (BGS beta gamma service, Rhodotron, Bruchsal, Germany). Three-medium wear, fracture toughness, and Vickers hardness tests were performed. The irradiated samples were compared with untreated control groups. Results Polycarbonate and polyurethane bracket materials have enhanced fracture toughness and Vickers hardness after electron-beam irradiation of 100 kGy and 10 MeV. Polyoxymethylene bracket materials showed significantly lower fracture toughness values after irradiation compared with the untreated control group. Polyoxymethylene had the best mechanical properties, followed by polycarbonate and polyurethane. Almost the same effects could be measured during the 3-medium wear test. Conclusions Electron-beam postcuring improved Vickers hardness and fracture toughness of polymers with lower mechanical properties (polycarbonate and polyurethane). Polyoxymethylene, with sufficient hardness and fracture toughness, could not be improved with electron-beam postcuring.

Orthodontic miniscrews are exposed to three mechanical loading phases during clinical use: torsional loading upon insertion, flexural loading during anchorage function, and torsional loading upon removal. The aim of this study was to simulate clinical loading conditions for different types of orthodontic miniscrews in vitro to quantify the effects of combined torsional and bending stress. Various orthodontic miniscrew systems (Lomas, Dual-top, Aarhus anchorage, Tomas-pin and T.I.T.A.N.-pin) comprising 10 samples each were subjected to the following loading sequences in vitro: a torsional load corresponding to manual insertion with limited torque; and flexural loading at two different insertion depths. For all screw systems with torsional pre-loading (simulating insertion), subsequent flexural loading (simulating anchorage) yielded permanent deformations of approximately 0.15-0.25 mm, depending on the insertion depth. Since EDX analysis revealed comparable elemental compositions for the different screw systems, the differences in mechanical properties are attributed to screw design. Torsional loading during screw insertion may cause premature mechanical weakening and needs to be minimized. Unless fully inserted, screws show pronounced plastic deformation and hence fracture risk under subsequent flexural loading.

To assess the usefulness of different post and core materials and systems, in vitro testing of fracture strength and fatigue resistance is a useful tool. However, the literature does not present coherent results as to which system can withstand the highest loads. With a geometrical model, the effects of load angulation and contact point location on the generated forces were calculated. To validate the mathematical model, a set of measurements was performed with a set-up that made it possible to measure the critical forces on a post and core restoration. A high level of correlation between the predictions of the model and the measurements was found. It was shown that the resulting forces are strongly dependent on the precise design of the test set-up and results from different geometries cannot be compared directly. Very strong sensitivity to small misalignment was found, all of which serves to explain the large differences in the literature.

Human teeth with substantial coronal defects are subject to reconstruction by means of post and core restorations. Typically, such a restoration comprises a slightly cylindrical post onto which an abutment of varying shape, depending on the designated restoration, is attached. As clinical results are not satisfactory to date, we proposed a new proprietary post and core design which makes use of positive locking. As this prefabricated system is not customised to an individual root's cross-sectional geometry (usually oval), a varying amount of radicular dentin is left in periphery of the core's outer edge. The aim of this study was to assess the implications of this fact, i.e., whether the root has to endure higher overall stress levels which ultimately may lead to failure of one of the components involved. A series of finite element simulations were performed to evaluate stress and strain on the system, in which the proposed post and core was embedded into a virtual dentin cylinder of different diameters, ranging from flush mounting of the restoration to a dentin excess of 4 mm, and subsequently loaded with forces with two angles of attack (90 degrees and 130 degrees ). The results show that flush mounting yields an agreeable stress and strain distribution within the radicular dentin, but overall stress levels drop significantly with an excess of 0.5 mm of surrounding dentin. More than 1 mm excess was not found to have profound positive effects.

Objective: To test the null hypothesis that there are no differences between children and adults in maximum laterotrusion and maximum retrusion on the right and left sides. Materials and Methods: This population-based study included 81 randomly selected children between the ages of 6 and 10 years and 67 adults. Kinematic variables were measured with the ultrasonic JMA-System for registration. Results: The mean maximum laterotrusion of the children's group (10.6 ± 1.5 mm on the left, 11.0 ± 1.7 mm on the right) was significantly smaller than that of the adult group (11.7 ± 2.0 mm on the left, 12.2 ± 1.7 mm on the right). The maximum laterotrusion of the children's group corresponded to about 90% on the left and right sides of that of the adult group. The mean maximum retrusion of the children's group was significantly bigger than that of the adult group. There, the adult values corresponded to 66.7% on the left and 50% on the right side of the children's values. No significant difference in maximum laterotrusion and retrusion was noted on the right and left sides, and no significant differences according to gender specificities were observed in either group. Conclusions: The hypothesis is rejected. In development of the temporomandibular joint, maximum laterotrusion on the right and left sides increases significantly with age, and maximum retrusion decreases significantly with age.

In orthodontics, adhesive failures can occur because of saliva contamination during bonding. However, most in vitro studies concerning bond strength of saliva-contaminated enamel disregard the influence of temperature changes in a wet environment. The aim of the present study was to compare the influence of saliva, blood and etching gel remnant contamination on shear bond strength (SBS) after thermocycling. After etching of extracted human third molars (n = 80), a conventional primer (Transbond XT) and a moisture-insensitive primer (Transbond MIP) were evaluated using the adhesive, Transbond XT, under dry conditions and after contamination with saliva, blood and etching gel remnants. To simulate temperature changes and the moisture of saliva in the oral cavity, all samples were thermocycled (6,000 x 5 degrees C/55 degrees C) in a mastication device before SBS testing. A Mann-Whitney U test was used to determine statistical differences. Under dry conditions Transbond XT and Transbond MIP showed no significant difference in SBS. However, clinically unacceptable (P = 0.005) bond strength was observed using Transbond XT after saliva and blood contamination. In wet conditions only Transbond MIP showed sufficient bond strength. If contamination during bonding is expected, a hydrophilic primer should be used. Under dry conditions hydrophilic or hydrophobic primers could be applied. Blood contamination seems to be a more serious problem for bond strength than saliva or etching gel contamination.

The purpose of this study was to compare the frictional properties of two self-ligating aesthetic brackets, Opal (Ultradent Products) and Oyster (Gestenco Int.), with those of four conventionally ligated aesthetic brackets, Transcend (3M Unitek), Inspire (Ormco), Allure (GAC Int.), and Image (Gestenco Int.). Friction was tested with different wire dimensions and qualities [stainless steel (SS) wire 0.017 x 0.025 inches; SS 0.019 x 0.025 inches; TMA 0.019 x 0.025 inches] using a Zwick testing machine. All brackets had a 0.022-inch slot and the prescription of an upper first premolar of the Roth system (tip: 0 degrees, torque: -7 degree). Each bracket/archwire combination was tested 10 times and each test was performed with a new bracket/wire sample that was pulled through twice. Additionally, two sets of 30 Opal brackets each were aged with an ageing machine under standardized conditions for 9-10 and 18-20 months, respectively. Friction of the aged brackets was tested with identical wire dimensions and qualities using the same testing procedure. All data were statistically analysed with unsigned comparisons of all bracket/wire combinations using GLM and the Games-Howell post hoc test. The results showed Opal brackets to have the lowest frictional forces for all wire dimensions and qualities. Furthermore, friction was lower at a significant level (P

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Introduction The purpose of this study was to compare the shear and tensile bond strengths of 8 common adhesive systems for bonding in orthodontics. Methods One hundred sixty freshly extracted bovine mandibular permanent incisors were randomly divided into 8 groups. Self-ligating esthetic Damon 3 brackets (Ormco, Orange, Calif) were bonded by using the following adhesive systems: Quick Bond (chemically and light-cured; Forestadent, Pforzheim, Germany), Blugloo (Ormco), Enlight LV (Ormco), Kurasper F (Kuraray Dental, Frankfurt, Germany), Transbond LR (3 M Unitek, Monrovia, Calif), Light Bond (Reliance Orthodontic Products, Itasca, Ill), and Fuji Ortho LC (GC America, Alsip, Ill). After 24 hours, half of each group was debonded measuring the shear bond strength and half measuring the tensile bond strength. Results Blugloo showed the best shear bond strength values, whereas Transbond LR and Quick Bond (chemically and light-cured) had the lowest. Tensile strength was the highest with Fuji Ortho LC and the lowest with Quick Bond (chemically and light-cured) and Kurasper F. The tensile strength of light-cured Quick Bond was about 47% lower than that of Fuji Ortho LC. Conclusions Blugloo, Fuji Ortho LC, Light Bond, and Enlight LV are among the materials of choice for bonding fixed orthodontic appliances to teeth. All bond strength values were clinically satisfactory except for the tensile strength of chemically and light-cured Quick Bond and Kurasper F.

Introduction The purpose of this study was to compare the shear and tensile bond strengths of 8 common adhesive systems for bonding in orthodontics. Methods One hundred sixty freshly extracted bovine mandibular permanent incisors were randomly divided into 8 groups. Self-ligating esthetic Damon 3 brackets (Ormco, Orange, Calif) were bonded by using the following adhesive systems: Quick Bond (chemically and light-cured; Forestadent, Pforzheim, Germany), Blugloo (Ormco), Enlight LV (Ormco), Kurasper F (Kuraray Dental, Frankfurt, Germany), Transbond LR (3M Unitek, Monrovia, Calif), Light Bond (Reliance Orthodontic Products, Itasca, Ill), and Fuji Ortho LC (GC America, Alsip, Ill). After 24 hours, half of each group was debonded measuring the shear bond strength and half measuring the tensile bond strength. Results Blugloo showed the best shear bond strength values, whereas Transbond LR and Quick Bond (chemically and light-cured) had the lowest. Tensile strength was the highest with Fuji Ortho LC and the lowest with Quick Bond (chemically and light-cured) and Kurasper F. The tensile strength of light-cured Quick Bond was about 47% lower than that of Fuji Ortho LC. Conclusions Blugloo, Fuji Ortho LC, Light Bond, and Enlight LV are among the materials of choice for bonding fixed orthodontic appliances to teeth. All bond strength values were clinically satisfactory except for the tensile strength of chemically and light-cured Quick Bond and Kurasper F.

Introduction: Despite their popularity in satisfying esthetic demands, plastic brackets still have some disadvantages because of decreased wear resistance and hardness. Our aim in this study was to investigate the mechanical properties of an alternative bracket—polymer urethane-dimethacrylate (UDMA) reinforced by silicon dioxide fillers with several filler levels. Methods: Three bracket groups were created: (1) unfilled UDMA, (2) UDMA with a filler content of 40% by volume, and (3) UDMA with a filler content of 70% by volume. Flexural strength, fracture force, and Vickers hardness of the bracket groups were tested. In addition, a 3-medium wear test was performed. Results: The filler-reinforced brackets showed increased hardness, greater stiffness, and improved wear resistance compared with unfilled brackets. Higher filler concentrations in a polymer matrix result in greater stiffness of the polymer. Despite this, the filled composite brackets were not statistically more susceptible to fractures than the unfilled plastic brackets. Conclusions: Experimental UDMA brackets reinforced with silicon dioxide fillers showed an obvious trend for improved mechanical properties compared with unfilled UDMA brackets.