Three-dimensional radiographic assessment of the mandibular retromolar donor site in different vertical facial growth types

PURPOSE

To assess volumetrically, the impact of vertical facial growth types (VGFT) on the retromolar area as a bone donor site MATERIAL AND METHODS: 60 cone beam computed tomography (CBCT) scans of adult individuals were classified in three groups according to their SN-GoGn angle: hypodivergent group (hG) (33.33%), normodivergent group (NG) (30%) and hyperdivergent group (HG) (36.67%). Total harvestable bone volume and surface (TBV and TBS respectively), total cortical and cancellous bone volume (TCBV and TcBV respectively) and the percentage of cortical and cancellous bone volume (CBV and cBV respectively) were evaluated.

RESULTS

The whole sample showed a mean TBV of 1220.99±448.81mm³ and a mean TBS of 940.29±259.93mm². Statistically significant differences were found between the different outcome variables and the vertical growth patterns (p<0.001). TBS differs for the different vertical growth patterns with the highest mean of TBS observed in the hG group. TBV also significantly differs between the different vertical growth patterns (p<0.001) with the highest mean observed for the hG individuals. Significant differences in percentages of cBV and CBV were present between the hyper-divergent groups and the other groups (p<0.001) with the hyper-divergent group having the lowest percentage of CBV and the highest percentage of cBV.

CONCLUSION

hypodivergent individuals tend to have thicker bone blocks that can be used in onlay technique while thinner bone blocks harvested from hyperdivergent and normodivergent individuals can be used in three-dimensional grafting approach.

Multinational study on profile preference of laypersons

BACKGROUND

This study aimed to assess the facial profile preferences of lay people in seven locations from different countries and whether their place of residence, sex, age, race, education, or income influenced the decision.

METHODS

After altering the lip and nose in 1 mm increments in the sagittal and sagittal/vertical directions, 50 profile silhouettes with white-like facial features were rated by evaluators. The soft tissue values were integrated into the profiles, and profile preferences were identified for each location. An ANOVA with post hoc Tukey test was used to compare the differences in mean preference in each location. A multivariable regression model was used to assess the effect of the demographics of the evaluator on preference.

RESULTS

Thirteen profiles were ultimately analyzed. The mean for profile preference was significantly different across locations (P < 0.0001). For evaluators in the United States and Lebanon, the most preferred profile had the original lip and original nose. In Switzerland and South Africa, retrusive lips, and a small and less upturned nose was most preferred. In Japan and Saudi Arabia, the most preferred profile had the original lip and a protrusive nose that was less upturned. A protrusive lip with a small, upturned nose was preferred in Turkey. Profile change (P < 0.0001), location (P < 0.0001), sex (P < 0.0001), and race (P = 0.02) were significant confounders; in contrast, age, education, and income were not significant.

CONCLUSIONS

Profile preference is different among the seven locations. For the most part, lay people prefer profiles within one SD from white norms. Also, an upturned nose is the least favored in most of the locations. Sex and race are also significant confounders.

CLINICAL RELEVANCE

An orthodontic treatment plan decision is affected by an individual's preference for their facial appearance. This study helps clinicians understand how racial and regional differences may affect patients' preferences and, therefore, their expectations for orthodontic treatment results.

Effect of head rotation on two-dimensional cephalometric measurements using cone beam-computed tomography

OBJECTIVE

The purpose of this study was to identify the variation of bi-dimensional cephalometric measurements following real head rotation.

MATERIAL AND METHODS

Thirty cone beam-computed tomography (CBCT) head films were oriented according to three axes: horizontal Frankfort plane, transverse bi-orbital plane, and Opisthion-Nasion median plane. Axial rotation of 2°, 4°, 6°, and 8° from the Odontoïdale point were performed. Horizontal and vertical linear and angular measurements were studied on lateral cephalograms derived from each rotation T0, T2, T4, T6, and T8. A paired t-test was applied to compare the measurements between T0 and each rotational angle.

RESULTS

Of the 18 measurements, 55% showed statistically significant differences (P < 0.05) and 22% showed clinically significant differences, mostly at T6 and T8. Horizontal linear measurements Ba-A and N-Ba decreased, and vertical linear measurement G-Sn increased gradually, as the angle of head rotation increased. Angular measurements studied did not vary.

CONCLUSIONS

Head malpositions during X-ray acquisition should be avoided and rotated lateral CBCT cephalograms should be corrected and recentered to prevent any variation in linear measurements.

Assessment of lower third molar space: A comparative radiographic study

Objective:

The aim of this study was to assess lower third molar space using four different radiographic reconstructed Cone Beam Computed Tomography (CBCT) images: orthopantomogram, lateral cephalogram, multiplanar CBCT and a newly introduced three-dimensional (3D) simulation technique.

Methods:

The CBCT scans of 32 individuals (20.97 ± 2.152 years) with a total of 50 lower third molars were collected and analyzed. The ratio between the necessary space and available space for lower third molars was calculated on each radiographic reconstructed image. Repeated-measure analysis of variance followed by multiple comparison tests were used.

Results:

The mean ratio was significantly smaller with cephalograms (0.611 ± 0.263), followed respectively by orthopantomograms (0.756 ± 0.221), multiplanar CBCT (0.789 ± 0.191) and 3D simulation technique (0.807 ± 0.193) (p < 0.001). The lowest mean difference was recorded between multiplanar CBCT and 3D simulation technique (0.017). Intra class correlation coefficient was strong (>0.90) for all techniques except cephalograms.

Conclusions:

The assessment of the lower third molar space differs according to the adopted imaging technique. 3D simulation technique is a useful novel technology that allows an exploration of the crown in many different dimensions and orientations, giving more predictable results than the conventional methods.

Three-dimensional radiographic assessment of the mandibular interforaminal donor site in different vertical facial growth types

PURPOSE

To assess volumetrically, the impact of vertical facial growth types (VFGT) on the mandibular interforaminal region as a potential bone donor site.

MATERIAL AND METHODS

60 cone beam computed tomography (CBCT) scans of adult individuals were classified in three groups according to their SN-GoGn angle: hypodivergent group (hG) (N=20), normodivergent group (NG) (N=19) and hyperdivergent group (HG) (N=21). Total harvestable bone volume (TBV), cortico-cancellous bone volume (CBV-cBV), and cortical bone surface (CBS) were evaluated. ANOVA test followed by Tukey post hoc tests were used to compare the mean continuous outcomes according to their VFGT.

RESULTS

The whole sample showed a mean TBV of 1376.32±541.01mm³, CBV of 468.52±121.54mm³ and cBV of 908.73±474.71mm³. The mean CBS amounted to 782.58±146.80mm². The comparison between the groups stated a significantly different mean TBV and cBV (-p-value<0.001). The mean CBS was significantly different (-p-value=0.015): the smallest for the NG, but not significantly different (-p-value<0.001): the highest for the HG, intermediate for the NG and the smallest for the hG.

CONCLUSION

Hypodivergent individuals have the thickest cancellous bone suitable for an onlay bone graft, while hyperdivergent individuals have the thinnest bone ideal for a 3D grafting approach.

Three-dimensional evaluation of the nasomaxillary complex before and following rapid maxillary expansion compared to normal subjects

Objectives:

The objectives of the study were to evaluate the nasomaxillary complex (NMC) measurements before and following rapid maxillary expansion (RME) compared to normal subjects.

Materials and Methods:

Thirty consecutive patients (14 males and 16 females) with a mean age of 9.5 ± 1.8 years for males and of 11.8 ± 1.7 years for females, who underwent RME to correct their posterior unilateral or bilateral crossbite, were selected. Computed tomography (CT) scans done before treatment (BT) formed the Group BT and those after treatment constituted the Group AT. An untreated normal sample (Group NC) presenting a normal transverse occlusion and needing a cone beam CT for other purposes was formed by 30 subjects (14 males and 16 females) with a mean age of 10 ± 0.9 years for males and of 11.6 ± 1.0 years for females. The CT scans were compared between both groups BT and AT with Group NC and measurements were performed on scanned images. The mean differences between measurements were compared using the t-test (α = 0.05).

Results:

No significant differences in volumetric measurements representing the NMC were found between groups BT and NC. By comparing Group AT to NC, we found that all volumetric variables displayed statistically significant differences with an increase of those of Group AT. Linear transverse variables were increased in Group NC compared to Group BT and their differences were statistically significant. However, the same variables were larger in Group AT compared to Group NC.

Conclusion:

RME produces an increase of the NMC dimensions compared to normal controls, which supports the principle of overcorrection, needed to compensate the post-treatment relapse.

Evaluation of upper airway volume and craniofacial volumetric structures in obstructive sleep apnoea adults: A descriptive CBCT study

OBJECTIVE

The aim of this investigation was to assess, with a descriptive three-dimensional evaluation, the volume of upper airway (UAWV) and the volume of craniofacial structures in adult patients suffering from obstructive sleep apnoea (OSA) and compare them to the corresponding findings in adults with no sleep disorders.

MATERIALS AND METHODS

The sample consisted of 54 adult males, 27 suffering from OSA diagnosed by means of the Apnoea Hypopnea Index and 27 with no history of sleep disorders. All subjects had a cone beam computerized tomography scan performed with the same head position. UAWV was assessed with the Amira® software, and craniofacial volumes by means of a specially developed data-processing program, which allowed the construction of tetrahedrons using anatomical landmarks. Assessed volumes were naso-maxillary, cranium upper anterior, oral cavity, post-oral cavity, hyoid to mandible, and post-hyoid. SPSS (version 19.0) was used for the statistical analysis. The Levene's test for Equality of Variance, the t-test for Equality of Means and the Mann-Whitney test were used to evaluate the variables. The level of significance was set at P ≤ 0.05.

RESULTS

The mean value of UAWV was smaller in the OSA group. The post-hyoid volume, the calculated posterior volume, and the ratio of posterior to total volume showed differences between the groups.

CONCLUSIONS

Craniofacial structures did not show significant differences between the groups, but in the OSA group the posterior space released for upper airway was significantly bigger and UAWV was significantly smaller.

Evaluation of shear bond strength of orthodontic molar tubes bonded using hydrophilic primers: An in vitro study

OBJECTIVE

To evaluate and compare the shear bond strength (SBS) of orthodontic molar tubes bonded using two hydrophilic primers along with a moisture tolerant adhesive system to dry and saliva-contaminated enamel surfaces; and to assess the mode of their bond failure.

MATERIALS AND METHODS

A total of 60 extracted human mandibular molars were randomly divided into three major groups according to the primer used, each consisting of 20 molars: XT group acts as a control and bonded with the conventional hydrophobic Transbond XT primer, OS group bonded with the hydrophilic Ortho Solo primer, AP group bonded with the hydrophilic Assure Plus all surface bonding resin. Each major group was further divided into two subgroups, of 10 molars each, according to presence or absence of saliva. All the specimens were thermocycled 500 cycles between 5̊ and 55°C. Shear forces were applied to the specimens with a universal testing machine at a crosshead speed of 1mm/min and SBS was measured in megapascals (MPa). The mode of failure was determined using the adhesive remnant index (ARI). Data were analysed using two-way analysis of variance (ANOVA) followed by univariate analysis and Bonferroni post hoc tests.

RESULTS

The three tested primers did not show a significant difference in the mean SBS in dry conditions (P=0.137); the mean SBS of OS and AP primers were 15.60±5.879MPa and 12.51±2.583MPa respectively which were comparable to that of the hydrophobic XT primer (12.76±2.952MPa). In saliva-contaminated conditions, the mean SBS values were 10.41±4.457MPa and 9.22±3.422MPa for OS and AP primers respectively, which were significantly higher than that of XT primer (4.82±2.050MPa) (P=0.004). When comparing the mean SBS for each group according to the bonding condition, it was significantly higher in dry bonding compared to saliva-contaminated bonding for the three primers; XT (P<0.001), OS (P=0.003) and AP (P=0.011). In the dry field, most of the bond failures of the three primers were adhesive (score 3), whereas in the saliva-contaminated field, most of the failures were cohesive (score 1).

CONCLUSION

Dry bonding yielded the highest SBS for the three primers. Saliva contamination significantly decreased the bond strength of both hydrophilic primers; however, the values were above the clinically acceptable limit. The hydrophilic primers tested in the present study can be successfully used for bonding orthodontic molar tubes under dry and saliva-contaminated enamel surface conditions.

The inflection point: a torque reference for lingual bracket positioning on the palatal surface curvature of the maxillary central incisor

Background

Contrary to buccal orthodontics, lingual orthodontics has no reference for vertical bracket positioning on the maxillary central incisor. The aim of this study was to provide a reference point in relation to torque for lingual bracket positioning on the palatal surface curvature (PSC) of the maxillary central incisor.

Methods

Cone beam computed tomography (CBCT) radiographs of 50 right maxillary central incisors from archives of a dental radiographic center were transferred to Photoshop, where their PSC was traced using pen-tool. The PSC torque angle values of the incisors were calculated in Excel using cubic poly-Bezier curves at 0.5-mm increments and at the inflection point of PSC. Descriptive statistics for the torque angle values of the increments and for the inflection point for the 50 incisors were then calculated. One-way ANOVA test was used to detect systematic differences between the increments, and Tukey test was used post-hoc.

Results

For all incisors, increments incisal to inflection point exhibited progressive decrease in torque angle values from the first-calculated increment to inflection point while increments cervical to inflection point exhibited progressive increase from inflection point to last-calculated increment. Mean torque angle values of all the increments and inflection point showed high standard deviations and vast range of values. One-way ANOVA test was highly statistically significant (p < 0.0001) and most pairwise comparisons of the increments using Tukey test were significant.

Conclusions

Inflection point can be used as a reference for bracket positioning on PSC. Cervically oriented shifts in vertical bracket position cause crown labial/root palatal movement cervical to inflection point and crown palatal/root labial movement incisal to it. A scientific mathematical justification for customized bracket torque prescriptions on PSC of maxillary central incisor was also provided.

Electronic supplementary material

The online version of this article (10.1186/s40510-018-0234-0) contains supplementary material, which is available to authorized users.

Assessment of the efficiency of Erbium-YAG laser as an assistant method to rapid maxillary expansion: An in vivo study

INTRODUCTION

Maxillary transverse deficiency (MTD) is one of the most pervasive and common skeletal problems in the craniofacial complex. This study aimed to evaluate the effect of associating the application of Erbium-YAG laser with rapid maxillary expansion (RME) for treating MTD in young adult patients with permanent dentition in regard to skeletal and dental effects.

METHODS

Twenty-four subjects, aged from 15.5 to 19 years and needing RME as a therapeutic procedure, were randomly assigned to either the laser group (n=12) or the control group (n=12). The RME was realized by a two bands hyrax expander cemented on upper first molars. Patients in the laser group were undergone mucosal-bony perforations along the midpalatal suture every month, for three consecutive months, using Erbium-YAG laser. Postero-anterior cephalograms were taken for all patients. Skeletal and dental changes before and after RPE as well as at the end of the retention phase were collected and compared for both groups. Total time needed for expansion and retention were recorded and compared.

RESULTS

The findings showed more significant changes in most maxillofacial components in the laser group after the expansion phase. However, there was no significant differences with respect to retention or total treatment duration.

CONCLUSIONS

Laser assisted rapid maxillary expansion (LARME) can be a good approach to use for improving skeletal effects in young adult patients suffering from MTD.

Association between normative and self-perceived orthodontic treatment need in a Lebanese population

The aims of this study were to investigate the association between normative and perceived orthodontic treatment need in a Lebanese population and the effect of sociodemographic status on orthodontic treatment need. A prospective cross-sectional clinical study was designed using a sample of 150 subjects (81 males and 69 females) aged 11-18years seeking dental treatment at Beirut Arab University. Normative orthodontic treatment need was scored using the two components of the Index of Orthodontic Treatment Need (IOTN), the Dental Health Component (DHC) and the Aesthetic Component (AC). Perceived need for orthodontic treatment was evaluated by scoring the AC of the IOTN. A total of 31.3% of the sample were in great need of orthodontic treatment according to the DHC of the IOTN. On the other hand, only 9% of the sample perceived their need to be definite. A significant positive but weak correlation was found between the normative and perceived need for orthodontic treatment. There was also a significant association between age and normative treatment need.

Soft tissue norms: Conventional and based on true vertical in a Lebanese population

INTRODUCTION

The aim of this study was to establish cephalometric soft tissue norms in a Lebanese population of young adults and profile differences between males and females.

MATERIALS AND METHODS

Ninety subjects divided into 43 women and 47 men, aged from 18 to 30 years, were selected based on specific criteria. The lateral cephalograms were taken in the natural head position. Holdaway, Steiner, Merrifield, Ricketts, Epker and Fish analyses were applied as conventional analyses. Scheideman, Spradley, Cooke, Arnett, Bergman, Farkas and Viazis analyses were applied as analyses based on the true vertical.

RESULTS AND CONCLUSION

The specific soft tissue measurements of this sample are reported in six grids. The differences between males and females related especially to the lower facial height and lip thickness, which had higher values in males, who also presented a more retruded lower lip and more protruded nasal tip. Women had higher values for mentolabial and frontonasal angles.

Asymmetric Head Gear: A Comparison between Unilateral Outer Bow Expansion and Unilateral Outer Bow Shortening - an Energy Approach using the Finite Element Method

OBJECTIVE

To compare the influence of outer bow length difference and unilateral outer bow expansion on the 'asymmetric effect' of the headgear.

METHODS

Twelve 3D finite element models of a headgear with two tubes were designed, which were similar except for the outer bow length or the degree of unilateral expansion in Solid-Works 2011. A 3N force was applied to the outer bow ends in ANSYS Workbench 12.1 and the distalising, lateral forces to molars, moments and the energy of the system were evaluated.

RESULTS

As the degree of unilateral expansion increased, the net differences in all findings were increased up to a point, and then changed. There was an increasing pattern in the length difference group. Buccal movement was observed in the intact/shorter side molar.

CONCLUSION

Unilateral shortened outer bow asymmetric headgears are more efficient and more predictable in clinical application than the unilateral outer bow expansion.

The importance of using the entire face to assess facial profile attractiveness

INTRODUCTION

The aim of this study was to evaluate the importance of using the entire face to assess facial profile attractiveness. The secondary objective was to assess the facial profile preferences of orthodontists, dentists and laypeople.

METHODS

Two original cephalometric radiographs of two subjects (one man and one woman meeting the normality criteria) and 16 modified samples of these radiographs were used. The 18 radiographs were then converted into silhouettes and printed twice: the entire profile (A) and the lower third alone (B). The silhouettes were randomly distributed into two binders A and B. A survey was conducted using three panels of evaluators: orthodontists, dentists and laypeople. The esthetic appreciation was quantified according to the Visual Analogue Scale (VAS).

RESULTS

Pearson's correlation coefficient was calculated to compare the scores of the entire profile with the scores of the lower third alone. The results showed that the orthodontists panel presented a much better correlation between A and B compared to dentists and especially to laypeople. A comparison of profile scores with the correlation coefficients shows that the profiles with the highest scores present the lowest correlations. The three panels of evaluators preferred the orthogonal profiles or profiles with upper lip protrusion over profiles with lower lip protrusion.

CONCLUSION

For profiles with values close to the norm, the lower face alone does not reveal the attractiveness of the entire facial profile. Hence, the importance of using the entire facial profile to assess the beauty of the face.

Evaluation of Three-Dimensional Volumetric Changes After Sinus Floor Augmentation with Mineralized Cortical Bone Allograft

AIM

The aim of this retrospective study was to quantify three-dimensional (3D) volumetric bone changes over a two-year period in maxillary sinuses augmented with a mineralized cortical bone allograft material (MCBA) material.

PATIENTS AND METHODS

Eleven patients (6 males and 5 females) with mean of age of 51.6 (range: 46-61) years were treated to increase the vertical dimension of the alveolar crest by maxillary sinus floor augmentation procedure. Study data were collected from patient records and by analyzing preoperative radiographs and cone beam computed tomography (CBCT) scans taken within the first two weeks after maxillary sinus lift (T0), immediately before implant placement four months after grafting (T1), and after one year of implant loading (T2). All DICOM-formatted images were rendered into volumetric images using software that automatically calculated the volume of the grafted material in cubic centimeters.

RESULTS

Mean graft volume was 16.24 ± 1.54 cm(3) at T0, 14.48 ± 1.48 cm(3) at T1 and 13.06 ± 1.39 cm(3) at T2. Mean volume retraction resulted in 1.76 ± 0.34 cm(3) ΔV1 (T0-T1) and 1.42 ± 0.4 cm(3) ΔV2 (T1-T2) and was 10.83 % of the initial total volume at (T0-T1) and 9.8 % of the total volume (T1-T2).

CONCLUSION

The present retrospective investigation demonstrated a 20.63 % decrease in graft volume. Volumetric 3D assessment of CBCT scans with the selected software appeared to be a promising approach to quantifying long-term changes in the grafted area.

Bone stress and strain modification in diastema closure: 3D analysis using finite element method

The aim of this study was to analyse the stress and strain distribution in the alveolar bone between two central incisors in the process of diastema closure with a constant force. A 3-dimensional computer modeling based on finite element techniques was used for this purpose. A model of an anterior segment of the mandible containing cortical bone, spongy bone, gingivae, PDL and two central incisors with a bracket in the labial surface of each tooth were designed. The von Mises stress and strain was evaluated in alveolar bone along a path of nodes defined in a cresto-apical direction in the midline between two teeth. It was observed that stress and strain of alveolar bone increased in midline with a constant force to close the diastema regardless of the type of movement in gradual steps of diastema closure, however the stress was higher in the tipping movement than the bodily so it can be suggested that a protocol of force system modification should be introduced to compensate for the stress and strain changes caused by the reduced distance to avoid the unwanted stress alteration during the diastema closure.

Three-dimensional changes of the naso-maxillary complex following rapid maxillary expansion

OBJECTIVE

To assess the volumetric changes and the maxillary response of the naso-maxillary complex (NMC) following rapid maxillary expansion (RME).

MATERIALS AND METHODS

Thirty consecutive patients (14 males and 16 females) with a mean age at first observation of 9.5 ± 1.8 years for males and of 11.8 ± 1.7 years for females, presenting a posterior unilateral or bilateral crossbite and requiring RME, were selected for the study. Each patient underwent expansion to correct the transverse occlusal relationships. Computed tomography scans were taken before RME (T1) and at the end of the active expansion phase (T2). Measurements were performed on scanned images. The Kolmogorov-Smirnov test was performed; the mean differences between measurements at T1 and T2 were compared using the t-test (α = .05).

RESULTS

All volumetric, maxillary, transverse skeletal anterior and posterior variables as well as all dental anterior and posterior linear and angular variables representing the NMC displayed statistically highly significant increases after RME (P < .001).

CONCLUSIONS

After RME the total volume of the NMC increased by 12%, the nasal volume by 17%, and the maxillary volume by 10.6%. The maxillary and the nasal contributions represented 69.75% and 30.25%, respectively.

Effects of buccal and lingual enamel sandblasting on shear bond strength of orthodontic brackets bonded with a self-etching primer

The purpose of this study was to evaluate the effects of sandblasting on the initial shear bond strength (SBS) and on the bracket/adhesive failure mode of orthodontic brackets bonded on buccal and lingual enamel using a self-etching primer (SEP). The brackets were bonded using a SEP and composite resin on the buccal and lingual surfaces of 30 premolars with intact enamel and 30 premolars pretreated by sandblasting with 50 μm aluminum-oxide. Student's paired t-test was used to compare the groups for differences in SBS and a multiple Chi(2) test was performed to compare the bond failure mode. It was shown that sandblasting increases significantly SBS of the SEP on the buccal surfaces but the increase on the lingual surfaces is not statistically significant. A comparison of the adhesive remnant index scores indicated that there was more residual adhesive remaining on the teeth that were treated by sandblasting than on the teeth with intact enamel. Besides, there is no statistical difference between SBS of the SEP on buccal and lingual surfaces with intact enamel. Therefore, we can conclude that sandblasting improves the bond between buccal and lingual enamel and resin ant that the SEP provides the same SBS on buccal and lingual intact surfaces.

Effect of a two-year fluoride decay protection protocol on titanium brackets

INTRODUCTION

Fluoride ion can attack titanium, causing its corrosion. Orthodontic patients being high-risk caries developers and in need of fluoride protection, the Center for Disease Control has developed a Fluoride Decay Prevention (FDP) protocol, consisting of a 6-minute tooth-brushing, followed by a 1-minute daily mouthwash, in addition to an in-clinic trimestrial topical fluoride gel application. This study aimed at evaluating gravimetrically, by scanning electron microscopy (SEM), and by sliding mechanics analysis, the consequences of FDP at 6, 12, 18, and 24months on titanium brackets corrosion.

METHODS

One hundred and fifty titanium brackets were randomly divided into five groups of 30. Group 1 was the control group. Groups 2, 3, 4, and 5 each received an equivalent of 6, 12, 18, and 24months of FDP treatment respectively. All groups were placed in artificial saliva for 2months and then rinsed. Subsequently, the brackets were dried, for 48hours, using Silica gel in a desiccator maintained at 37°C before testing.

RESULTS

SEM analysis showed that numbers and dimensions of pits gradually increased due to corrosion as we moved from group 1 to group 5. Gravimetrical and sliding mechanics results revealed no statistical difference between groups 2 and 3, and a significant difference between groups 4 and 5 upon comparison with the control group.

CONCLUSION

Surface changes due to corrosion were detected at 6 and 12months of FDP but had no clinical effects. However, the increase in sliding resistance and bracket weight loss became significant at 18 and 24months of FDP.

[Sexual dimorphism and facial cavities: a 3D imaging volumetric study]

INTRODUCTION

The aim of this study was to investigate the sexual dimorphism in facial cavity's volumes of untreated young adults.

METHODS

Sixty subjects, ages between 18 to 30 years, were selected and divided in two groups according to the gender. Volumes of orbital, nasal, sinusal and buccal cavities were measured from CT scans with AMIRA(®)software. The statistical studies were performed using Kolmogorov-Smirnov test for normality followed by Student "t" test (p < 0.05).

RESULTS

The gender comparison reflected statistically significant differences between the volumes of orbital, nasal, sinusal and buccal cavities, volumes being larger in males. Sexual dimorphism did not appear in the ratio of each cavity volume on the total facial volume.

CONCLUSION

Absolute volume of facial cavities are larger in males, but no sexual dimorphism is detected comparing volume ratios. A difference in size, but not in shape, between genders might exist.

[Facial volumes and vertical facial type: a three dimensional comparative study]

INTRODUCTION

The purpose of this study was to compare the volume of facial cavities in untreated young subjects with long- and short-faces.

METHODS

Two groups of thirty subjects each, one with low (GoGn-SN < or = 28 degrees), and the other with high (GoGn-SN > or = 36 degrees) mandibular plane angles, ages between 18 to 30 years, were selected. For each subject, volumes of orbital, sinusal and buccal cavities were measured from CT scans with the AMIRA software. The statistical studies were performed using Kolmogorov-Smirnov, followed by Student "t" test (p < 0.05).

RESULTS

Results suggest that there is no statistically significant difference between the volume of facial cavities in long- and short-face subjects. Only the ratio of nasal cavity volume to the total volume is significantly smaller in the short-face group.

CONCLUSION

A compensatory phenomenon might exist between the three directions of growth to equilibrate an excess or deficit of the vertical dimension, thus maintaining constant the volume of facial cavities.