Can We Improve the Laser Etching with the Digitally Controlled Laser Handpiece-Xrunner?

OBJECTIVE: The aim of this study was to compare the shear bond strength (SBS), enamel surface characteristics, and the adhesive remnant index (ARI) scores of different etching methods. BACKGROUND DATA: Laser etching changes the physical characteristics of the enamel surface and these alterations hold promise for the conditioning of enamel for bonding procedures. A new Er:YAG laser handpiece is unique in its ability to digitally control size, shape, and depth of irradiated enamel area. MATERIALS AND METHODS: Ninety-eight premolar teeth were used in this study. Eighty of 98 teeth were divided into four experimental groups of 20 teeth each for SBS testing: (1) 37% phosphoric acid, (2) manual Er:YAG laser (120 mJ, 10 Hz, and 1.2 W), (3) manual Er,Cr:YSGG laser (45 mJ, 50 Hz, and 2.25 W), and (4) digitally controlled Er:YAG laser (Xrunner; 100 mJ, 10 Hz, 1 W). The SBS values and ARI scores were recorded. Eighteen teeth were used to evaluate the surface morphology with scanning electron microscopy and atomic force microscopy after etching and following debonding and restoration. RESULTS: Mean SBS value was 7.75 ± 2.5 MPa for Xrunner and 8.11 ± 3.5, 9.47 ± 3.3, and 7.11 ± 3.7 MPa for the acid, Er,Cr:YSGG, and Er:YAG groups, respectively (p = 0.148). However, the acid etching group demonstrated significantly higher ARI scores (p < 0.001). CONCLUSIONS: All etching methods caused enamel surface irregularities and were effectively restored to its original gloss. Laser etching was found to be an alternative to acid etching; however, the clinical success should be evaluated with further studies.

Relationship between head posture and the severity of obstructive sleep apnea.

INTRODUCTION: The objective of this study was to compare the head posture of patients with obstructive sleep apnea (OSA) having different levels of severity with that of control subjects. METHODS: One hundred subjects participated in this study. Seventy-five subjects underwent overnight polysomnography in a sleep laboratory and were allocated into "mild," "moderate," or "severe" OSA groups, and 25 subjects with no complaints regarding OSA were allocated into 1 group and served as the controls. Cephalometric radiographs were obtained from all participants in natural head position. Craniocervical, craniovertical, and cervicovertical angles were measured in the groups. Data were analyzed using the least significant difference. RESULTS: The results showed significant differences between the OSA groups and the control group, and among the test groups, in all craniocervical, craniovertical, and cervicovertical angles (P <0.05), except for 1 craniovertical measurement (P >0.05). There were no significant differences in this measurement among the test groups and in any measurement between the mild and moderate OSA groups (P >0.05). CONCLUSIONS: Head posture showed significant differences in patients with OSA. In general, the more severe the OSA, the more extended the natural head position as indicated by increases in the craniocervical angles. The cervical posture parameters may indicate existing OSA.

Effects of Different Combinations of Er:YAG Laser-Adhesives on Enamel Demineralization and Bracket Bond Strength.

OBJECTIVE: The purpose of this study was to investigate the demineralization around brackets and shear bond strength (SBS) of brackets bonded to Er:YAG laser-irradiated enamel at different power settings with various adhesive systems combinations. METHODS: A total of 108 premolar teeth were used in this study. Teeth were assigned into three groups according to the etching procedure, then each group divided into three subgroups based on the application of different adhesive systems. There were a total of nine groups as follows. Group 1: Acid + Transbond XT Primer; group 2: Er:YAG (100 mJ, 10 Hz) etching + Transbond XT Primer; group 3: Er:YAG (200 mJ, 10 Hz) etching + Transbond XT Primer; group 4: Transbond Plus self-etching primer (SEP); group 5: Er:YAG (100 mJ, 10 Hz) etching + Transbond Plus SEP; group 6: Er:YAG (200 mJ, 10 Hz) etching + Transbond Plus SEP; group 7: Clearfil Protect Bond; group 8: Er:YAG (100 mJ, 10 Hz) etching + Clearfil Protect Bond; group 9: Er:YAG (200 mJ, 10 Hz) etching + Clearfil Protect Bond. Brackets were bonded with Transbond XT Adhesive Paste in all groups. Teeth to be evaluated for demineralization and SBS were exposed to pH and thermal cyclings, respectively. Then, demineralization samples were scanned with micro-CT to determine lesion depth values. For SBS test, a universal testing machine was used and adhesive remnant was index scored after debonding. Data were analyzed statistically. RESULTS: No significant differences were found among the lesion depth values of the various groups, except for G7 and G8, in which the lowest values were recorded. The lowest SBS values were in G7, whereas the highest were in G9. The differences between the other groups were not significant. CONCLUSIONS: Er:YAG laser did not have a positive effect on prevention of enamel demineralization. When two step self-etch adhesive is preferred for bonding brackets, laser etching at 1 W (100 mJ, 10 Hz) is suggested to improve SBS of brackets.

Natural head position and lower incisor irregularity: Is there a relationship?

OBJECTIVE: The aim of this study was to assess the relationship between dynamic measurements of natural head position (NHP) and lower incisor irregularity to identify potential gender differences. MATERIALS AND METHODS: A total of 103 plaster models and dynamic NHP measurements were taken from 51 male (mean age: 14.20 ± 2.51 years) and 52 female (mean age: 15.02 ± 2.67 years) subjects. The dynamic NHP data were gathered by using an inclinometer device and a portable data logger. Lower incisor irregularity was measured with Little's irregularity index. The Mann-Whitney U and Kruskal-Wallis rank tests were used at a significance level of p < 0.05. To evaluate the correlation between NHP and lower incisor irregularity, Spearman correlation coefficients (r) were calculated. RESULTS: There were significant gender differences in the sagittal measurements of NHP (p = 0.031) and incisor irregularity (p = 0.023). A Kruskal-Wallis test revealed no significant difference in NHP measurements between subjects presenting different levels of irregularity. Females displayed no significant correlation between incisor irregularity and any NHP measurement. However, in the males high correlation coefficients between incisor irregularity and sagittal NHP measurements (r = 0.369; p = 0.008) were noted. CONCLUSION: Significant correlations between lower incisor irregularity and sagittal NHP measurements in males were observed. Females had a more forwardly inclined NHP than males. Moreover, male subjects displayed greater incisor irregularity than female subjects.

Temperature rise caused in the pulp chamber under simulated intrapulpal microcirculation with different light-curing modes.

OBJECTIVE: To evaluate and compare intrapulpal temperature rise with three different light-curing units by using a study model simulating pulpal blood microcirculation. MATERIALS AND METHODS: The roots of 10 extracted intact maxillary central incisors were separated approximately 2 mm below the cement-enamel junction. The crowns of these teeth were fixed on an apparatus for the simulation of blood microcirculation in pulp. A J-type thermocouple wire was inserted into the pulp chamber through a drilled access on the palatal surfaces of the teeth. Four measurements were made using each tooth for four different modes: group 1, 1000 mW/cm(2) for 15 seconds; group 2, 1200 mW/cm(2) for 10 seconds; group 3, 1400 mW/cm(2) for 8 seconds; and group 4, 3200 mW/cm(2) for 3 seconds. The tip of the light source was positioned at 2 mm to the incisor's labial surface. RESULTS: The highest temperature rise was recorded in group 1 (2.6°C ± 0.54°C), followed by group 2 (2.57°C ± 0.62°C) and group 3 (2.35°C ± 0.61°C). The lowest temperature rise value was found in group 4 (1.74°C ± 0.52°C); this value represented significantly lower ΔT values when compared to group 1 and group 2 (P  =  .01 and P  =  .013, respectively). CONCLUSIONS: The lowest intrapulpal temperature rise was induced by 3200 mW/cm(2) for 3 seconds of irradiation. Despite the significant differences among the groups, the temperature increases recorded for all groups were below the critical value of 5.6°C.

Temperature changes of pulp chamber during in vitro laser welding of orthodontic attachments.

The use of lasers has been suggested for orthodontists to fabricate or repair orthodontic appliances by welding metals directly in the mouth. This work aimed to evaluate the temperature changes in the pulp chamber during welding of an orthodontic wire to an orthodontic molar band using Nd : YAG laser in vitro. A freshly extracted human third molar with eliminated pulpal tissues was used. J-type thermocouple wire was positioned in the pulp chamber. A conductor gel was used in the transferring of outside temperature changes to the thermocouple wire. An orthodontic band was applied to the molar tooth and bonded using light cured orthodontic cement. Twenty five mm length of 0.6 mm diameter orthodontic stainless steel wires was welded to the orthodontic band using Nd : YAG laser operated at 9.4 watt. Temperature variation was determined as the change from baseline temperature to the highest temperature was recorded during welding. The recorded temperature changes were between 1.8 and 6.8°C (mean: 3.3±1.1°C). The reported critical 5.5°C level was exceeded in only one sample. The results of this study suggest that intraoral use of lasers holds great potential for the future of orthodontics and does not present a thermal risk. Further studies with larger samples and structural analysis are required.

Effects of water flow rate on shear bond strength of orthodontic bracket bonded to enamel surface after Er:YAG laser ablation.

OBJECTIVE: The aim of present study was to evaluate the effect of water flow rate on enamel surface roughness and shear bond strength (SBS) of orthodontic brackets after Er:YAG laser ablation. BACKGROUND DATA: It is well known that external water supply is a fundamental requirement for Er:YAG laser efficiency on dental hard tissues. However, there is no consensus considering the water flow rate used during Er:YAG laser ablation. METHODS: Eighty sound human upper premolar teeth were used in the present study. Seventy-six teeth were assigned into four groups according to surface treatments. The 37% phosphoric acid-etched group served as the control. Er:YAG laser irradiation was performed in three subgroups with water flow rates of 25, 36, and 48 mL/min, respectively. All specimens were subjected to a SBS test. One specimen from each different surface treatment modality was examined by scanning electron microscopy. Kruskal-Wallis test was used to compare the SBS value of each group. RESULTS: Although the control group had the highest SBS value, statistically no significant differences were found among groups. CONCLUSIONS: Er:YAG laser application with a water flow rate of 48 mL/min produced better enamel surface alterations without any thermal damage to yield higher SBS values.

Effect of enamel laser irradiation at different pulse settings on shear bond strength of orthodontic brackets.

OBJECTIVE: To compare the effect of laser irradiation at two different pulse settings and acid etching on the shear bond strength (SBS) of orthodontic brackets to enamel. MATERIALS AND METHODS: Thirty-six premolars were allocated to three groups (n  =  12): (1) 37% phosphoric acid etching, (2) erbium-doped yttrium aluminum garnet (Er:YAG) laser etching with medium-short pulse mode (MSP; 100 µs, 120 mj, 10 Hz, 1.2 W), and (3) Er:YAG laser etching with quantum-square pulse mode (QSP; 120 mj, 10 Hz, 1.2 W). Metallic brackets were bonded with Transbond XT. After photopolymerization, the samples were subjected to 5000 thermal cycles and debonded with a universal testing machine, and the SBS values were recorded. Surface morphology was evaluated with profilometric examination, scanning electron microscopy, and atomic force microscopy. The adhesive remnant index (ARI) was evaluated to assess the remaining adhesive. RESULTS: The results of SBS testing were analyzed by one-way analysis of variance and Tukey honestly significant diffference tests. The mean SBS values of QSP and MSP laser groups were 11.80 ± 2.7 MPa and 10.10 ± 4.5 MPa, respectively, and the QSP group demonstrated significantly higher SBS (P < .01) than that of the acid-etched group (6.6 ± 2.4 MPa). No significant difference was observed between the SBS values of the two laser groups (P < .05). The difference between the ARI scores of the laser groups and the acid-etched group was statistically significant (P < .05). CONCLUSION: Laser etching at MSP and QSP modes present successful alternatives to acid etching; however, long-term clinical studies are required to verify clinical success.

Inadequate shear bond strengths of self-etch, self-adhesive systems for secure orthodontic bonding.

This study evaluated the shear bond strength (SBS) of a traditional orthodontic bracket bonding agent (Transbond XT) against two self-etch, self-adhesive systems (Maxcem Elite and Vertise Flow). Sixty premolar teeth and sixty brackets were randomly and equally divided into five groups: Transbond XT (TXT) as the control, Maxcem Elite (ME) without etching, ME with etching (ME/ Etch), Vertise Flow (VF) without etching, and VF with etching (VF/Etch). Respective SBS results of the five groups were 9.86±3.20, 4.67±2.94, 7.82±2.56, 2.55±0.77, and 7.89±1.17 MPa. SBS values of the new self-etch adhesive systems were significantly lower than the traditional etch-and-rinse control (p<0.005). However, no significant differences were found between TXT and the self-adhesives applied with etching (p>0.005). After debonding, ARI scores "0" and "1" were predominant in non-etched ME and VF groups. It was concluded that new self-etch, self-adhesive bonding systems require additional phosphoric acid application to achieve comparable SBS values as the traditional orthodontic bonding agent.

Effects of modified and conventional facemask therapies with expansion on dynamic measurement of natural head position in Class III patients.

INTRODUCTION: The aim of this prospective clinical trial was to assess the effects of varying force directions on the dynamic measurement of natural head position and orofacial airway dimensions of Class III patients during maxillary orthopedic protraction compared with an untreated control group. METHODS: The conventional facemask group comprised 15 patients (8 girls, 7 boys; mean age, 9.6 ± 1.3 years), the modified facemask group comprised 15 patients (7 girls, 8 boys; mean age, 9.5 ± 1.5 years), and the control group comprised 15 subjects (7 girls, 8 boys; mean age, 9.8 ± 1.6 years). Natural head position measurements and cephalometric records were obtained from all subjects before and after treatment or the control period (approximately 1 year). An inclinometer and a portable data logger were used to collect the dynamic natural head position data. For statistical comparisons, paired samples t tests, analysis of variance (ANOVA), and post-hoc Tukey tests were used at the P <0.05 level. RESULTS: Both treatment groups showed statistically significant changes in the sagittal (pitch) measurements of natural head position and upper pharynx, aerial, and total area of airway measurements during the treatment period. In the control group, the only statistically significant change was an increased upper pharynx measurement (P = 0.020). According to the intergroup comparisons, statistically significant natural head position differences were found in the conventional (6.4° flexion) and the modified (5.7° flexion) facemask groups when compared with the controls. The modified facemask group also showed significant changes in aerial (P = 0.003) and total (P <0.001) areas of the airway measurements compared with the control group. No statistically significant differences were observed between the 2 treatment groups. CONCLUSIONS: These findings suggest that modified and conventional facemask therapy with expansion have significant cranial flexion effects on the dynamic measurements of natural head position. Additionally, the modified facemask procedure showed significant effects on the orofacial airway dimensions compared with the initial values and the values of the untreated controls.

Rapid maxillary expansion effects on dynamic measurement of natural head position.

OBJECTIVE: To identify the effect of rapid maxillary expansion (RME) procedure on dynamic measurement of natural head position (NHP). MATERIALS AND METHODS: The treatment group comprised 23 patients, 12 girls and 11 boys (mean age: 10.1 ± 1.1 years), and the control group comprised 15 subjects, 8 girls and 7 boys (mean age: 9.7 ± 1.4 years). The test subjects underwent RME treatment using full cap acrylic device, and the mean amount of expansion was 5.48 mm. An inclinometer and a portable data logger were used to collect the NHP data. Intragroup changes were evaluated by using nonparametric Wilcoxon test, and intergroup changes were analyzed with Mann-Whitney U-test. P values less than .05 were considered statistically significant. RESULTS: The mean difference between initial and final NHP was 0.31°, and this difference was not statistically significant. Also, there were no statistically significant differences between the RME and control groups before and after treatment. CONCLUSION: Treatment with the RME procedure showed no statistically significant effects on dynamic measurement of NHP when compared with initial values or untreated control.

In-vitro assessment of temperature rise in the pulp during orthodontic bonding.

INTRODUCTION: In this in-vitro study, we evaluated the temperature changes in the pulp chamber during bracket bonding using 4 different light sources. METHODS: Eighty intact extracted maxillary central incisors were used. The teeth were divided into 4 groups of 20 teeth each. Brackets (Mini Twin, Dentaurum, Ispringen, Germany) were bonded with Transbond XT (3M Unitek, Monrovia, Calif) adhesive and light cured with low-intensity halogen light for 40 seconds, high-intensity halogen light for 40 seconds, light-emitting diode (LED) light for 20 seconds, and plasma arc light (PAC) for 6 seconds. Light curing was performed 5 mm from tooth surfaces. A J-type thermocouple wire was positioned in the center of the pulp chamber. The results were analyzed with analysis of variance (ANOVA) and the Tukey HSD test. RESULTS: ANOVA and the Tukey HSD test showed that pulp chamber temperature changes were influenced by the type of light source. All groups showed significant differences between each other (P <0.001). The intrapulpal temperature changes induced by different light sources were the following: high-intensity halogen (6.84 degrees C +/- 2.44 degrees C), low-intensity halogen (4.71 degrees C +/- 0.96 degrees C), LED (2.95 degrees C +/- 1.12 degrees C), and PAC (0.96 degrees C +/- 0.83 degrees C). CONCLUSIONS: High- and low-intensity halogen light induced significantly higher intrapulpal temperature changes than did the LED and PAC. Except for the high intensity halogen light, orthodontic bonding with light-curing units did not exceed the critical 5.5 degrees C rise in temperature reported to produce pulpal damage.

Flowable composites for bonding orthodontic retainers.

OBJECTIVE: To test the null hypothesis that there are no statistically significant differences between flowables and an orthodontic adhesive tested in terms of shear bond strength (SBS) and pullout resistance. MATERIALS AND METHODS: To test the SBS of Light Bond, FlowTain, Filtek Supreme, and Tetric Flow were applied to the enamel surfaces of 15 teeth. Using matrices for application, each composite material was cured for 40 seconds and subjected to SBS testing. To test pullout resistance, 15 samples were prepared for each composite in which a wire was embedded; then the composite was cured for 40 seconds. Later, the ends of the wire were drawn up and tensile stress was applied until the resin failed. Findings were analyzed using an ANOVA and a Tukey HSD test. RESULTS: The SBS values for Light Bond, FlowTain, Filtek Supreme, and Tetric Flow were 19.0 +/- 10.9, 14.7 +/- 9.3, 22.4 +/- 16.3, and 16.8 +/- 11.8 MPa, respectively, and mean pullout values were 42.2 +/- 13.0, 24.0 +/- 6.9, 26.3 +/- 9.4, and 33.8 +/- 18.0 N, respectively. No statistically significant differences were found among the groups in terms of SBS (P > .05). On the other hand, Light Bond yielded significantly higher pullout values compared with the flowables Filtek Supreme and Flow-Tain (P < .01). However, there were no significant differences among the pullout values of flowables, nor between Light Bond and Tetric Flow (P > .05). CONCLUSIONS: The hypothesis is rejected. Light Bond yielded significantly higher pullout values compared with the flowables Filtek Supreme and FlowTain. However, flowable composites provided satisfactory SBS and wire pullout values, comparable to a standard orthodontic resin, and therefore can be used as an alternative for direct bonding of lingual retainers.

Evaluation of mineral content of enamel prepared by erbium, chromium:yttrium-scandium-gallium-garnet laser.

The aim of this study was to evaluate the mineral content of enamel etched at two different power settings with an erbium, chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser. Buccal, lingual and mesial or distal surfaces of five premolar teeth were cut, and three enamel slabs were obtained from each tooth. Fifteen enamel specimens were divided into three groups (1 W, 2 W and control) of five specimens each and subjected to Er,Cr:YSGG laser. The mean percentage weights of the five elements [calcium (Ca), potassium (K), magnesium (Mg), sodium (Na) and phosphorus (P)] in each slab were measured by inductively coupled plasma-atomic emission spectrometry (ICP-AES). One way analysis of variance (ANOVA) was used to analyze differences among the groups (1 W, 2 W and control). There were no significant differences among the groups (1 W, 2 W and control) for Ca, K, Mg, Na, or P, or for the Ca/P ratio (P > 0.05). Scanning electron microscopy (SEM) photographs indicated that the surface irregularities increased with increased power setting. Laser treatment did not affect the mean percentage weights of Ca, K, Mg, Na, and P, or the Ca/P ratio, in any group.

Microleakage under lingual retainer composite bonded with an antibacterial monomer-containing adhesive system.

OBJECTIVE: To determine and compare the microleakage of a conventional acid-etched, light-cured lingual retainer adhesive system with a recently developed antibacterial monomer-containing adhesive with and without etching. METHODS: Sixty human mandibular incisors were separated into three groups of 20 teeth each, which received the following treatments: group 1 (control) = Transbond LR (3M Unitek), conventional lingual retainer bonding; group 2 = Clearfil Protect Bond (Kuraray Medical) with acid-etching; and group 3 = Clearfil Protect Bond without acid-etching. The wire in each was 0.0215-inch multistranded PentaOne (Masel Orthodontics). Samples were sealed with nail varnish, stained with 0.5% basic fuchsin, and sectioned. Transverse sections were evaluated under a stereomicroscope and scored for microleakage in millimeters at the composite-enamel interface. Statistical analysis was performed by Kruskal-Wallis and Mann-Whitney tests with Bonferroni correction. RESULTS: Group 2 had less microleakage (0.11 ± 0.19 mm) than group 1 (0.26 ± 0.30 mm) or group 3 (0.24 ± 0.27 mm). However, the difference in the microleakage of the composite-enamel interface among all investigated groups was not significant (P>.05). CONCLUSION: The findings of this study do not speak against using an antibacterial monomer-containing self-etching adhesive to bond lingual retainers.

Correction of Mandibular Retrognathia and Laterognathia by Distraction Osteogenesis: Follow up of 5 cases.

This article evaluates the use of distraction osteogenesis in the treatment of mandibular retrognathia and laterognathia and the long term treatment results of the patients treated with this technique. The procedure was carried out in 5 subjects (3 males and 2 females, mean age 18.4 years) aged between 14 years and 27 years. In patients treated with bilateral mandibular distraction, it was observed that the ANB angle decreased by a mean of 5 degrees , the mandibular corpus length increased by a mean of 14.5 mm and the overjet decreased by a mean of 12.2 mm after treatment. In patients treated with unilateral mandibular distraction, a mean of 3.5 degrees reduction was achieved in ANB angle, the mandibular corpus length increased by a mean of 5.5 mm and a mean of 7 mm correction was achieved in relation to craniofacial midline with treatment. One of these patients showed an increase of 10 mm in ramus height on the affected side and a decrease of 5 degrees in gonial angle whereas the other one showed an increase of 12.5 degrees in gonial angle and an increase of 11 mm in ramus height on the affected side after treatment. The most significant long term relapse was observed in one of the patients treated with bilateral mandibular distraction. Long term relapse seen in the rest of the patients was within clinically acceptable limits. It can be concluded that distraction of the deformed mandible is a feasible and effective technique for treating mandibular retrognathia and laterognathia. However, it must be borne in mind that accurate placement of the distractors and determining the correct distraction vector are crucial factors that have an influence on long term clinical success.

Microleakage between composite-wire and composite-enamel interfaces of flexible spiral wire retainers. Part 2: comparison of amorphous calcium phosphate-containing adhesive with conventional lingual retainer composite.

The aim of this study was to test the hypothesis that there is no difference in the microleakage values of a newly developed amorphous calcium phosphate (ACP)-containing adhesive and a conventional lingual retainer composite at the composite-enamel and composite-wire interfaces of flexible spiral wire retainers (FSWRs). Sixty freshly extracted human mandibular incisors separated into three equal groups were used in this study. Multi-stranded 0.0215 inch diameter wire was bonded to enamel using conventional orthodontic adhesive (Transbond LR, 3M Unitek) and ACP-containing composite (Aegis Ortho, Harry J. Bosworth Co.), with or without the use of a primer. The specimens were sealed with nail varnish, stained with 0.5 per cent basic fuchsine for 24 hours, sectioned and examined under a stereomicroscope, and scored for microleakage at the composite-enamel and composite-wire interfaces from the mesial and distal margins. Statistical analyses were performed with Kruskal-Wallis and Mann-Whitney U-tests with a Bonferroni correction. Little or no microleakage was observed between the composite-enamel interface for any of the three groups, and any difference was not statistically significant. The amount of microleakage at the wire-composite interface was higher than that at the enamel-composite interface. Multiple comparison testing showed statistically significant differences in microleakage between Transbond LR and the ACP-containing adhesive used with primer at the composite-enamel and composite-wire interfaces (P < 0.001). ACP-containing adhesive used with primer showed the highest microleakage scores at the composite-enamel (mean: 0.39 +/- 0.42 mm) and composite-wire (mean: 1.66 +/- 0.47 mm) interfaces. The hypothesis is rejected. The ACP-containing composite used with or without primer showed significantly higher leakage at the composite-wire interface, while conventional lingual retainer composite showed lower microleakage scores.

Microleakage between composite-wire and composite-enamel interfaces of flexible spiral wire retainers. Part 1: comparison of three composites.

The aim of this investigation was to test the hypothesis that there is no difference in microleakage between composite-enamel and composite-wire interfaces, when different composites are used. Forty-five freshly extracted human mandibular incisors separated into three groups were used in the study. Multi-stranded 0.0215 inch diameter wire was bonded to enamel using two conventional (Transbond XT and Transbond LR) and a flowable (Venus Flow) orthodontic composite. The specimens were sealed with nail varnish, stained with 0.5 per cent basic fuchsine for 24 hours, sectioned and examined under a stereomicroscope, and scored for microleakage at the composite-enamel and composite-wire interfaces from the mesial and distal margins. Statistical analysis was performed using Kruskal-Wallis and Mann-Whitney U-tests with a Bonferroni correction. Little or no microleakage was observed between the composite-enamel interfaces for the three investigated composites, and any difference was not statistically significant. However, statistically significant differences were found between microleakage at the composite-wire interface for both the conventional and flowable composite groups (P < 0.001). Flowable composite showed the highest leakage (mean: 4.8 +/- 0.8 mm), while Transbond XT (mean: 0.5 +/- 0.3 mm) and Transbond LR (mean: 1.1 +/- 1.2 mm) showed significantly lower and comparable results. The amount of microleakage at the wire-composite interface was significantly greater than that at the enamel-composite interface of flexible spiral wire retainers (FSWRs). The null hypothesis is therefore rejected. Flowable composites may not be appropriate for bonding FSWRs.

Gingival response to mandibular incisor extrusion.

INTRODUCTION: The aims of the study were to evaluate the rate of accompanying gingival movement and changes in the widths of the attached gingiva (AG) and the keratinized gingiva (KG) after orthodontic extrusion of the mandibular incisors. METHODS: The study was carried out with 10 subjects whose mandibular incisors were orthodontically extruded to correct a dental open bite. Periodontal indices and the widths of the AG and the KG were recorded before and after treatment. The gingival movement in relation to orthodontic extrusion was determined by radiopacity with a specially designed metal device indicating the position of the gingival margin (GM) and the mucogingival junction (MGJ) on the cephalograms before and after extrusion. RESULTS: The widths of the AG and the KG, and the clinical crown length increased significantly after treatment (P <0.05). The GM and the MGJ moved in the same direction as the teeth by 80% and 52.5%, respectively. The sulcus depth decreased significantly (P <0.05). CONCLUSIONS: Orthodontic extrusion leads to increases in the widths of the AG and the KG. The gingiva moves in the same direction as the tooth, but less. Clinically, increased gingival width can lead to a gummy smile in patients with a low lip line. Gingival corrective procedures cannot be performed in such cases due to risk for root exposure. Nevertheless, long-term follow-up is suggested to determine the final sulcus depth and the position of the GM and the MGJ.

Biomechanical evaluation of chincup treatment with various force vectors.

INTRODUCTION: The aim of this study was to evaluate the biomechanical effects of chincup treatment by using a 3-dimensional finite element model. METHODS: Three-dimensional models of the mandible and the temporomandibular joint were modeled and analyzed. The final mesh consisted of 1572 solid elements with 5432 nodes. The chincup with 500 g of force was applied in a direction from the chin toward the mandibular condyle, the coronoid process, and a point anterior to the coronoid process. Then, the mechanical responses in terms of displacement and von Mises stresses are evaluated. RESULTS: The mandible was displaced backward and downward with the vector passing through the condyle. Forward and upward displacement was recorded with the force vector passing through or anterior to the coronoid process. The mandibular condyle and the coronoid process showed minimal displacement for all force vectors. The highest stress levels were observed in the condylar and posterior ramus regions and increased as the force vector was transferred away from the condyle. CONCLUSIONS: With the limitations of modeling, boundary conditions, and solution assumptions, chincups applied in various directions produce different force vectors, which induce different stress locations and displacements. The force vector is an important determinant of the orthopedic effects of the chincup and therefore should be carefully considered.