Cortical bone thickness of the alveolar process measured with cone-beam computed tomography in patients with different facial types

Architectural changes in alveolar bone for dental decompensation before surgery in Class III patients with differing facial divergence: a CBCT study

This study aimed to investigate alveolar bone change around mandibular anterior teeth during orthodontic decompensation in patients with skeletal Class III malocclusion and different vertical facial patterns. The records of 29 consecutive Class III patients selected from those pending two-jaw orthognathic surgery were divided into low (≤ 28°), average (30°-37°), and high (≥ 39°) mandibular plane angle (MPA) groups. The DICOM files of CBCT scans and STL files of digital dental models, taken before (T1) and after (T2) presurgical orthodontic treatment, were imported into Dolphin imaging software to reconstruct dentoskeletal images. T1 and T2 images were superimposed and analyzed for bone thickness and height at the level of root apex on each mid-sagittal slice of six mandibular anterior teeth. Differences between T1 and T2 were analyzed by non-parametric tests and mixed-effect model analysis. The results showed that the measurements of alveolar bone height generally decreased after treatment, regardless of MPA. The facial divergence, incisor irregularity, tooth site, treatment time, and change in proclination were identified as the significant factors affecting alveolar bone thickness and height during treatment. The presurgical orthodontic treatment to decompensate mandibular anterior teeth should be very careful in all MPA groups.

Overcoming compact bone resistance to tooth movement

The general boundaries to tooth movement are within the adjacent compact and trabecular bones, gingiva, mucosa, and muscular envelope. Findings from finite element analysis of maxillary posterior teeth distalization against mini-implants suggest that stiff outer and interproximal compact bone resists tooth movement, regardless of bone thickness, and that teeth should be steered away from this bone during orthodontic treatment. However, individual variation in the tooth-bone interface dictates the course and outcome of treatment, offering the basis for inferences on the limits of mini-implant anchorage and the presumed influence of the regional acceleratory phenomenon through decortication and microperforation, 2 modalities advocated to effect faster tooth movement.

Sex-, growth pattern-, and growth status-related variability in maxillary and mandibular buccal cortical thickness and density

Objective

The primary objective of this study was to quantitatively analyze the bone parameters (thickness and density) at four different interdental areas from the distal region of the canine to the mesial region of the second molar in the maxilla and the mandible. The secondary aim was to compare and contrast the bone parameters at these specific locations in terms of sex, growth status, and facial type.

Methods

This retrospective cone-beam computed tomography (CBCT) study reviewed 290 CBCT images of patients seeking orthodontic treatment. Cortical bone thickness in millimeters (mm) and density in pixel intensity value were measured for the regions (1) between the canine and first premolar, (2) between the first and second premolars, (3) between the second premolar and first molar, and (4) between the first and second molars. At each location, the bone thickness and density were measured at distances of 2, 6, and 10 mm from the alveolar crest.

Results

The sex comparison (male vs. female) in cortical bone thickness showed no significant difference (p > 0.001). The bone density in growing subjects was significantly (p < 0.001) lower than that in non-growing subjects for most locations. There was no significant difference (p > 0.001) in bone parameters in relation to facial pattern in the maxilla and mandible for most sites.

Conclusions

There was no significant sex-related difference in cortical bone thickness. The buccal cortical bone density was higher in females than in males. Bone parameters were similar for subjects with hyperdivergent, hypodivergent, and normodivergent facial patterns.

Correlation between facial growth patterns and cortical bone thickness assessed with cone-beam computed tomography in young adult untreated patients

Background

The vertical facial growth pattern is one of the most important issue in the orthodontic diagnosis and treatment. Previous studies investigated the association between interdental bone thickness and facial divergence using mainly bidimensional analysis. When two-dimensional dental radiographic views are not sufficient for diagnosis and measurements, cone-beam computed tomography (CBCT) images should be used to assess the alveolar bone structure three-dimensionally and with high accuracy and reliability.

The aim of the present study was to evaluate the correlation between alveolar bone thickness and facial divergence in young adults untreated patients using a three-dimensional method analysis with CBCT images.

Methods

Records of 30 untreated patients (mean age 16 ± 2 years) with Angle Class I and mild to moderate crowding were analyzed. Subjects were classified as hypodivergent (<39˚), normodivergent (41 ± 2˚), and hyperdivergent (>43°). according to the inter-maxillary angle between the sagittal maxillary plane (ANS-PNS) and the mandibular plane (GN-ME). The alveolar bone thickness measurements were taken for the buccal and palatal/lingual surfaces of maxillary and mandibular anterior teeth. Axial-guided navigation (AGN) was used to locate all landmarks using a specific software (Horos 3.0).

Results

The statistical analysis showed a significant difference between the hypodivergent and hyperdivergent group regarding buccal bone height (P = 0.005), buccal apical bone thickness (P = 0.003) and palatal mid-root bone thickness (P = 0.006). Moreover, buccal bone height (P = 0.006) was found to be statistically significant different in normodivergent compared with hypodivergent individuals.

Conclusions

Facial types were found to be correlated with alveolar bone thickness. The hyperdivergent subjects presented thinner alveolus bone in the anterior maxilla and at almost all sites in the mandible. Clinicians should be aware of the possibility of thin cortical bone plates in hyperdivergent patients, reducing antero-posterior movements to avoid fenestration and dehiscence.

The thickness of posterior buccal attached gingiva at common miniscrew insertion sites in subjects with different facial types

INTRODUCTION

The purpose of this study was to assess the thicknesses of maxillary and mandibular posterior buccal approximal attached gingiva at common miniscrew insertion sites, which has critical importance in determining miniscrew length, in subjects with different facial types.

METHODS

One hundred seventy-four subjects with no transversal skeletal discrepancy were included in this study. The facial types of these subjects were evaluated in the sagittal and vertical directions. In the sagittal direction, the subjects were assigned into 3 groups: skeletal Class I, II, and III. Also, each of these groups was divided into subgroups in the vertical direction: low angle, norm, and high angle. Transgingival probing was used to measure the thickness of the buccal attached gingiva.

RESULTS

The thickness of the buccal attached gingiva between the second premolar-first molar ranged from 1.18 ± 0.33 to 1.46 ± 0.28 mm and from 1.28 ± 0.30 to 1.58 ± 0.37 mm in the maxilla and mandible, respectively. The thickness of the buccal attached gingiva between the first-second molars ranged from 1.31 ± 0.41 to 1.60 ± 0.62 mm and from 1.36 ± 0.43 to 1.72 ± 0.52 mm in the maxilla and mandible, respectively. In terms of the thicknesses of the buccal attached gingiva of second premolar-first molar and first-second molars, no statistically significant difference was found between subjects with different facial types.

CONCLUSIONS

It was determined that the thicknesses of maxillary and mandibular posterior buccal approximal attached gingiva varied between 1.18-1.72. At this point, the insertion of miniscrews of 7-8 mm in length was recommended for maxillary and mandibular posterior buccal regions, in order to obtain adequate insertion depth.

Failure rates of miniscrews inserted in the maxillary tuberosity

Introduction:

Anchorage conservation in orthodontics has always been a challenge.

Objective:

The aim of this current study was to find out the failure rate of miniscrews inserted in the maxillary tuberosity (MT) region.

Methods:

This pilot study consisted of 40 patients (23 female, 17 male; mean age = 20.1±8.9 years) that had received 60 MT miniscrews for orthodontic treatment. Clinical notes and pictures were used to find out the primary outcome of miniscrew failure. Independent failure factors were also investigated. Logistic regression analysis was done for predictor’s relation with MT miniscrews failure.

Results:

There was no significant correlation in failure rate according to various predictor variables, except for miniscrews installed by lesser experienced operators, which showed significantly more failure. The odds ratio for miniscrew failure placed by inexperienced operators was 4.16.

Conclusion:

A 26.3% failure rate of mini-implants inserted in the MT region was observed.

Anatomical relationship between the maxillary posterior teeth and the sinus floor according to an anterior overbite

OBJECTIVE

To evaluate the vertical relationship between the maxillary sinus floor (MSF) and the maxillary posterior teeth (MPT) according to an anterior overbite.

SETTINGS AND SAMPLE POPULATION

The patients were divided into three groups according to an anterior overbite. The open bite group (OBG) included patients with an anterior overbite of ≤0 mm, the normal overbite group (NBG) included patients with an overbite of 0-3 mm, and the deep bite group (DBG) included patients with an overbite ≥3 mm. Thirty patients were randomly matched into each group based on age and sex.

MATERIALS AND METHODS

The distances and vertical relationship between the MSF and the MPT was analysed using cone-beam computer tomography. The vertical relationship between the two was classified as either favourable or unfavourable for the intrusion of the posterior teeth.

RESULTS

A higher ratio of patients in the OBG had MPT positioned close to the MSF than the DBG. Intrusion of the posterior teeth was unfavourable for an average of 87.2%, 77.2% and 70.2% molars in the OBG, NBG and DBG, respectively.

CONCLUSIONS

The vertical distance between the MSF and the MPT is associated with an anterior overbite. The posterior teeth were in an unfavourable position for the orthodontic intrusion in the OBG as compared to the other groups. Additional caution is needed when planning orthodontic intrusion treatment for patients with an anterior open bite. But, there were some individual variations within each group.

Dentoalveolar changes in adults promoted by the use of auxiliary expansion arch: A cbct study

Background

The objective of this study was to evaluate the dentoalveolar effects and the changes of buccal cortical bone in the posterior area after expansion obtained with TMA auxiliary expansion arch in adult patients.

Material and Methods

A retrospective analysis of CT scans of 13 patients (6 male, 7 female) treated at a private clinic, taken immediately before and after the use of an auxiliary expansion archwire, was performed. Mean age at installation of TMA auxiliary expansion arch was 29.23 years (s.d.=9.13) and the mean age when the auxiliary arch was removed was 29.52 years (s.d.=9.16). Mean time of the use of the TMA auxiliary expansion arch was 0.29 years (s.d.=0.09). The patients used fixed appliances and after leveling and alignment, a TMA auxiliary expansion arch was installed, combined with the primary 0.017x0.025-inch thermoactivated Ni-Ti archwire. CBCT scans were taken at T1 and T2. Linear and angular measurements regarding the positioning of maxillary molar, premolars and canines were performed. Intragroup comparison of the variables at T1 and T2 was performed with dependent t tests.

Results

There was statistically significant transverse increase and buccal inclination of all teeth. The cortical bone showed adaptability and displacement in the same direction of tooth movement, but in smaller amounts.

Conclusions

The auxiliary expansion arch proved to be effective to correct dentoalveolar constriction in adult patients, by increasing the buccal dental inclination with larger displacements than the bone crest adaptation and with significant transverse gains.

Key words:Cone-Beam Computed Tomography, Maxillary Expansion, Adult treatment.

Distribution and amount of stresses caused by insertion or removal of orthodontic miniscrews into the maxillary bone: A finite element analysis

OBJECTIVE

Initial stability of miniscrews is an important factor in their success as orthodontic anchorages. One of the factors affecting this stability is the stresses exerted to the bone by the screw. Since the distribution and extent of stresses and strains produced during insertion or removal of miniscrews had not been measured before, this study used finite element analysis (FEA) to measure these parameters in tapered versus cylindrical screws with or without pilot sockets.

MATERIALS AND METHODS

An FEA model of maxilla, pilot hole, and tapered/cylindrical miniscrews were created from 875 CT scan data. The bone cortex was considered 2mm thick. The cancellous bone was reconstructed below the cortical bone. Miniscrews were modelled on the basis of commercial titanium tapered and cylindrical miniscrews (1.6mm wide, 8mm long). The diameter and length of the guiding hole were considered to be 1.1 and 1.5mm, respectively. The miniscrews were inserted (and removed) between the maxillary second premolar and first molar. Stress/strain produced in the bones or screws were measured.

RESULTS

During screw insertion, in all setups, the highest stress existed within both the bone and screw, when the screw was in the cortical bone; after insertion into the cancellous bone, the stress suddenly dropped. In cylindrical screws, the highest amount of stress was distributed around the neck which was used for screw driving. In tapered screws, the stress was mostly distributed around the front one-third of the screw. During screw removal, the results of four setups were rather similar with stresses concentrated around screw necks, in the depth of the screw hole, and around the bone surface. The greatest bone stress during insertion was caused by the pilot-less tapered screw (10.18MPa) and the lowest stress was exerted by a pilot-less cylindrical screw (0.74MPa).

CONCLUSION

Most of the stress and strain is tolerated by the cortical bone and not the cancellous one. Using cylindrical miniscrews might be more bone-friendly. However, all cases had stresses below tolerable thresholds, and hence are safe.

Relationship between alveolar bone thickness, tooth root morphology, and sagittal skeletal pattern : A cone beam computed tomography study

PURPOSE

The goal of this work was to examine the relationship between sagittal facial pattern and thickness of alveolar bone in conjunction with root morphology of teeth by using cone beam computed tomography (CBCT).

METHODS

The study was carried out on the CBCT scans from 3 group of patients (n = 20 in each group). The first group involved skeletal class 1, the second group involved skeletal class 2, and the third group involved skeletal class 3 patients. In all, 14 permanent teeth and interdental regions in the maxilla and mandible were evaluated. Root length and root width were measured on each tooth. Buccal cortical bone thickness, cancellous bone thickness, and lingual cortical bone thicknesses were measured in each interdental region. Analysis of variance, Kruskall-Wallis H and Mann-Whitney U tests were used for statistical comparisons.

RESULTS

No significant difference was found between the groups for root length, root width, buccal cortical bone and lingual cortical bone thickness. A significant difference was observed between the groups for cancellous bone thickness as it was thicker in skeletal class 2 group. Cortical bone was thicker in the mandible compared to maxilla on both buccal and lingual sides and it was thicker in the posterior region compared to the anterior region on the buccal side.

CONCLUSIONS

Differences in cancellous bone thickness between different sagittal facial patterns and differences in cortical bone thickness between different alveolar regions should be taken into consideration when planning orthodontic tooth movements and anchorage mechanics.

Kate S, S. Potnis S, E. Kolge N. A simplified method for measurement of palatal bone thickness to select the optimum length of orthodontic mini-implant

Introduction

The palatal bone is a suitable site for mini-implant placement due to it being a “rootless area” with dense bone. This application has increased with mini-implant-assisted rapid palatal expansion becoming the preferred method of expansion. It is necessary to measure the vertical bone height with a reasonable accuracy, at the implant insertion site, to utilize the maximum available bone support, and to avoid the risk of perforations. As an accepted method, full-volume cone-beam computed tomography (CBCT) scan is advised for the same. This requires an additional procedure, further, radiation exposure, and cost to the patient. The aim of the study was to establish the utility of lateral cephalogram as a simple and reliable method to measure palatal bone thickness for placement of mini-implants in the 1st premolar and 1st molar region, which are the most common sites of mini-implant placement.

Materials and Methods

A total of 30 CBCT scans and digital lateral cephalograms of patients were selected and analyzed at the 1st premolar and molar region and were statistically evaluated using Student’s t-test and Wilcoxon rank-sum test.

Results

The results obtained indicated a highly significant correlation between the measurements obtained on lateral cephalograms at both the 1st premolar and 1st molar areas, P < 0.001.

Conclusion

The data presented show that lateral cephalometry provides a reliable assessment of the quantity of vertical bone for paramedian insertion of a palatal implant.

Failure rates of mini-implants inserted in the retromolar area

OBJECTIVE

Anchorage reinforcement is an important issue in orthodontic treatment. There is a lack of evidence regarding the failure rate of mini-implants inserted in the retromolar (RM) area, therefore the purpose of this present study was to evaluate the failure rates of mini-implants inserted in the RM area and to evaluate the factors affecting their stability.

MATERIAL AND METHODS

This retrospective cohort study of 102 patients (52 female, 55 male; mean age: 18.6years; SD: 5.2years) that had received 110 RM mini-implants for orthodontic treatment from 1.2.2012 to 1.6.2017 was conducted after IRB approval at the department of orthodontics. Clinical notes and photographic images of the patients were analysed to evaluate the dependent and independent variables. The primary outcome was mini-implant failure. Independent variables of patient related factors, mini-implant related factors, orthodontic related factors, surgical related factors, and maintenance-related factors were evaluated by logistic regression models for association to failure rates.

RESULTS

A 23.2% failure rate of mini-implants inserted in the RM area was observed. The patient's right side and inflammation were significantly associated with RM mini-implant failure. The odds ratios (relative risk) for mini-implant failure in the right side, and in mini-implants with inflammation around them were 0.166 and 0.188, respectively.

CONCLUSIONS

Failure rate for RM mini-implants were found to be 23.2%. To minimize RM mini-implant failure, clinicians should attempt to reduce inflammation around the mini-implants, especially for mini-implants placed on the right RM area.

Proximity of the roots of posterior teeth to the maxillary sinus in different facial biotypes

INTRODUCTION

Orthodontists consider facial growth pattern and oral function when developing a treatment plan. Less attention is given to the relationship between the maxillary posterior teeth and the maxillary sinus. We aimed to evaluate the relationship between the roots of the maxillary posterior teeth and the floor of the maxillary sinus.

METHODS

Proximity of the roots to the maxillary sinus was scored for the left and right first and second premolars and molars (scores, 0-3). Mean scores per patient and per tooth type were calculated. The influences of age, sex, and facial biotype on mean scores per patient and tooth were analyzed.

RESULTS

The mean scores per patient and the second molar scores were significantly lower in the normodivergent subjects compared with the hypodivergent subjects, and in the hypodivergent vs the hyperdivergent groups, indicating that the hypodivergent biotype had significantly fewer second molar roots into the sinus than the normodivergent and hyperdivergent biotypes. Age had no effect on mean score per patient, but in the hyperdivergent group, the second molar score increased with age, meaning that second molar roots tend to be closer to the sinus floor.

CONCLUSIONS

In a young population (7-24 years), the positions of the apices of the maxillary second molar roots in relation to the maxillary sinus floor are associated with the facial biotype. In a hypodivergent biotype, the roots of the second molars are located farther from the sinus floor compared with the normodivergent and hyperdivergent facial patterns.

Correlation between tooth size-arch length discrepancy and interradicular distances measured on CBCT and panoramic radiograph: an evaluation for miniscrew insertion

INTRODUCTION

The selection of appropriate sites for miniscrew insertion is critical for clinical success.

OBJECTIVES

The aim of the present study was to evaluate how interradicular spaces measured on panoramic radiograph compare with Cone-Beam Computed Tomography (CBCT), and how crowding can influence the presence of available space for miniscrew insertion, in order to define a new "safe zones" map.

METHODS

A total of 80 pre-treatment panoramic radiographs and 80 CBCT scans with corresponding digital models were selected from the archives of the department of Dentistry, Aarhus University. Crowding was measured on digital models, while interradicular spaces mesial to the second molars were measured on panoramic radiographs and CBCTs. For panoramic radiographs, a magnification factor was calculated using tooth widths measured on digital models. Statistical analyses were performed to investigate the correlation between the amount of crowding and the available interradicular space. Visual maps showing the amount of interradicular spaces measured were drawn.

RESULTS

The most convenient interradicular spaces are those between the second molar and the first premolar in the mandible, and between the central incisors in the maxilla. However, some spaces were revealed to be influenced by crowding.

CONCLUSIONS

Calibration of panoramic radiographs is of utmost importance. Generally, panoramic radiographs underestimate the available space. Preliminary assessment of miniscrew insertion feasibility and the related selection of required radiographs can be facilitated using the new "safe zone" maps presented in this article.

Performance of Cone Beam Computed Tomography Systems in Visualizing the Cortical Plate in 3D Image Reconstruction: An In Vitro Study

INTRODUCTION

Cortical bone is an important anatomical structure and its thickness needs to be determined prior to many dental procedures to ensure treatment success. Imaging modalities are necessarily used in dentistry for treatment planning and dental procedures. Three-dimensional image reconstruction not only provides visual information but also enables accurate measurement of anatomical structures; thus, it is necessarily required for maxillofacial examination and in case of skeletal problems in this region.

AIMS

This study aimed to assess the ability of three Cone Beam Computed Tomography (CBCT) systems including Cranex 3D, NewTom 3G and 3D Promax for Three-Dimensional (3D) image reconstruction of the cortical plate with variable thicknesses.

METHODS

Depending on the cortical bone thickness, samples were evaluated in three groups of ≤ 0. 5 mm, 0.6 -1 mm and 1.1-1.5 mm cortical bone thickness. The CBCT scans were obtained from each sample using three systems, their respective FOVs, and 3D scans were reconstructed using their software programs. Two observers viewed the images twice with a two-week interval. The ability of each system in the 3D reconstruction of different thicknesses of cortical bone was determined based on its visualization on the scans. The data were analyzed using SPSS and Kappa test.

RESULTS

The three systems showed the greatest difference in the 3D reconstruction of cortical bone with < 0.5 mm thickness. Cranex 3D with 4×6 cm2 FOV had the highest and 3D Promax with 8×8 cm2 FOV had the lowest efficacy for 3D reconstruction of cortical bone. Cranex 3D with 4×6 cm2 and 6×8 cm2 FOVs and NewTom 3G with 5×5 cm2 and 8×5 cm2 FOVs showed significantly higher efficacy for 3D reconstruction of cortical bone with 0.6-1mm thickness while 3D Promax followed by NewTom 3G with 8×8 cm2 FOV had the lowest efficacy for this purpose.

CONCLUSION

Most CBCT systems have high efficacy for 3D image reconstruction of cortical bone with thicknesses over 1 mm while they have poor efficacy for image reconstruction of cortical bone with less than 0.5 mm thickness. Thus, for accurate visualization of anatomical structures on CBCT scans, systems with smaller FOVs and consequently smaller voxel size are preferred.

Quantitative evaluation of palatal bone thickness for the placement of orthodontic miniscrews in adults with different facial types

Objectives:

To quantitatively evaluate palatal bone thickness in adults with different facial types using cone beam computed tomography (CBCT).

Methods:

The CBCT volumetric data of 123 adults (mean age, 26.8 years) collected between August 2014 and August 2016 was retrospectively studied. The subjects were divided into a low-angle group (39 subjects), a normal-angle group (48 subjects) and a high-angle group (36 subjects) based on facial types assigned by cephalometric radiography. The thickness of the palatal bone was assessed at designated points. A repeated-measure analysis of variance (rm-ANOVA) test was used to test the relationship between facial types and palatal bone thickness.

Results:

Compared to the low-angle group, the high-angle group had significantly thinner palatal bones (p<0.05), except for the anterior-midline, anterior-medial and middle-midline areas.

Conclusion:

The safest zone for the placement of microimplants is the anterior part of the paramedian palate. Clinicians should pay special attention to the probability of thinner bone plates and the risk of perforation in high-angle patients.

Quantitative evaluation of palatal bone thickness in patients with normal and open vertical skeletal configurations using cone-beam computed tomography

Purpose

To perform a comparative analysis of the palatal bone thickness in Thai patients exhibiting class I malocclusion according to whether they exhibited a normal or open vertical skeletal configuration using cone-beam computed tomography (CBCT).

Materials and Methods

Thirty CBCT images of Thai orthodontic patients (15–30 years of age) exhibiting class I malocclusion with a normal or open vertical skeletal configuration were selected. Palatal bone thickness was measured in a 3.0-mm grid pattern on both the right and left sides. The palatal bone thickness of the normal-bite and open-bite groups was compared using the independent t-test. The level of significance was established at P<.05.

Results

The palatal bone thickness in the normal-bite group ranged from 2.2±1.0 mm to 12.6±4.1 mm. The palatal bone thickness in the open-bite group ranged from 1.9±1.1 mm to 13.2±2.3 mm. The palatal bone thickness was lower at almost all sites in patients with open bite than in those with normal bite. Significant differences were found at almost all anteroposterior sites along the 3 most medial sections (3.0, 6.0, and 9.0 mm lateral to the midsagittal plane) (P<.05).

Conclusion

Class I malocclusion with open vertical skeletal configuration may affect palatal bone thickness, so the placement of temporary anchorage devices or miniscrew implants in the palatal area in such patients should be performed with caution.

Tomographic Evaluation of the Lower Incisor's Bone Limits in Mandibular Symphysis of Orthodontically Untreated Adults

The amount of available bone in the lower incisor region is critical for periodontal preservation when planning large anteroposterior dental movements. The aims of this study were to evaluate bone limits of the lower incisors in the mandibular symphysis and to verify whether they are influenced by facial growth patterns, lower incisor inclinations, skeletal anteroposterior relationships, or patient age. Tomographic images of 40 orthodontically untreated patients were evaluated and measurements of width and height of the mandibular symphysis, thickness on the lingual and labial sides of the alveolar bone, and thickness of the entire alveolar bone were performed in sagittal view. The following cephalometric measurements were also evaluated: growth pattern (FHI), lower incisor inclination (IMPA), and skeletal anteroposterior relationships (AO-BO). Pearson's correlation test was used to assess associations among bone measurements, cephalometric measurements, and patients' ages. Weak to moderate positive correlations between FHI and bone measurements on the labial side of the incisors and total alveolar width were found. The height of the symphysis had a moderate negative correlation with FHI. It was concluded that patient age, FHI, and IMPA influenced bone limits of the lower incisors in the mandibular symphysis, while AO-BO had no influence.

Effect of incisal loading during orthodontic treatment in adults: A randomized control trial

OBJECTIVE

To measure the changes in tooth mobility, alveolar bone, and receptor activator of nuclear factor kappa-B ligand (RANKL)/osteoprotegerin (OPG) in the gingival crevicular fluid (GCF) during orthodontic treatment to regain incisal function in the presence and absence of biting exercises.

MATERIALS AND METHODS

Thirty-six females (42.3 ± 6.5 years old) with periodontally compromised upper incisors received orthodontic treatment to obtain ideal incisor relationships. Eighteen subjects in the experimental biting exercise group were instructed to bite a soft plastic roll for 5 min/d; the 18 control subjects were not given plastic rolls. Alveolar bone thickness, height, and density around the upper incisors were assessed at three root levels using cone-beam computed tomography. GCF was collected at the labial and palatal sites of the upper incisors at pretreatment (T0), end of treatment (T1), 1 month after T1 (T2), and 7 months after T1 (T3). RANKL/OPG was determined using enzyme-linked immunosorbent assays.

RESULTS

Labial and palatal bone thickness significantly increased (>twofold) from T1 to T3 in the experimental group at all three root levels (all P < .05). Bone thickness correlated negatively with RANKL/OPG ratio between T1 and T2 ( P < .05). Tooth mobility, bone height, and density were not significantly different between T1 and T3.

CONCLUSIONS

Biting exercises significantly increased bone thickness but did not affect tooth mobility, bone height, or density. The RANKL/OPG ratio decreased 1 month after treatment (T2) and correlated with increased bone thickness. ( ClinicalTrials.in.th TCTR20170625001).

Relationship between anterior mandibular bone thickness and the angulation of incisors and canines-a CBCT study

OBJECTIVES

The morphology of the maxillary and mandibular alveolar cortex plays an important role in the planning of orthodontic treatment. Cone-beam computed tomography (CBCT) provides a precise demonstration of anatomical structures. Therefore, the aim of this paper was to evaluate what influence the position of incisors and canines have on the dimensions of the cortical and spongious bone of the anterior mandibular alveolar process.

MATERIALS AND METHODS

The material consisted of 100 CBCT volumes (61 females and 39 males, aged 18-71 years) obtained by means of a Gendex GXCB-500 machine and analysed using i-CAT Vision and CorelDRAW 9 software. Several linear and angular measurements were taken of cortical and spongious mandibular, vestibular and lingual alveolar bone.

RESULTS

The thickness of the vestibular spongious bone increased around lateral incisors and canines together with dental axis inclination, as did the thickness of the lingual spongious bone around central incisors and canines with greater angles of vestibular cortex curvature. In all teeth, the thickness of lingual cancellous bone decreased along with increase of the angle of tooth inclination. In the case of almost all groups of teeth, the thickness of lingual cancellous bone around teeth declined as the angle of curvature of the cortical bone decreased. The rotation of mandibular incisors and canines did not affect the thickness of the surrounding bone.

CONCLUSIONS

The position of teeth has little influence on vestibular bone thickness and is only significant around central incisors. In the case of almost all groups of teeth, the thickness of lingual spongious bone around teeth declined as the angle of curvature of the cortical bone decreased.

CLINICAL RELEVANCE

CBCT is a diagnostic tool that provides detailed information on the dimensions of the anterior dentate mandibular alveolar process.

Insertion torque and Periotest values are important factors predicting outcome after orthodontic miniscrew placement

INTRODUCTION

Approximately 14% of orthodontic anchor screws (miniscrews) become dislodged regardless of the accuracy of placement. It is therefore important to investigate the factors causing dislodgement. We evaluated the stability of miniscrews after placement to identify factors influencing outcome in orthodontic treatment using miniscrews.

METHODS

We investigated 120 miniscrews (Dual-top Auto Screw III; Jeil Medical, Seoul, Korea) (diameter, 1.4 mm; length, 6 mm) placed on the buccal or lingual side between the maxillary second premolar and the first molar in women. Patient age and rate and time of screw dislodgement were examined. Insertion torque values and Periotest (Tokyo Dental Industrial, Tokyo, Japan) measurements indicating horizontal and vertical mobility of the inserted screws were compared between groups with and without dislodgement (failure and success groups, respectively).

RESULTS

Mean insertion torque values were 10.7 ± 1.9 N·cm and 8.5 ± 2.1 N·cm in the failure and success groups, respectively. Cortical bone thickness measurements (success group, 1.34 ± 0.35 mm; failure group, 0.99 ± 0.09 mm) were significantly higher, whereas Periotest values at placement (success group, horizontal, 4.9 ± 1.4; vertical, 4.7 ± 1.3; failure group, horizontal, 7.0 ± 0.8; vertical, 7.1 ± 0.9) were significantly lower in the success group than in the failure group.

CONCLUSIONS

The Periotest value, together with insertion torque and cortical bone thickness, could serve as an index of initial stability for predicting the outcome of miniscrew placement.

Bone availability for mandibular molar distalization in adults with mandibular prognathism

OBJECTIVES

To investigate the retromolar space available for molar distalization in patients with mandibular prognathism.

MATERIALS AND METHODS

Using cone-beam computed tomography, the posterior mandibular dimensions in 110 consecutive patients with Class I or Class III malocclusion were measured (mean age, 27.0 ± 7.1 years). The shortest linear distances from the distal root of the right mandibular second molar to the inner border of the mandibular cortex were measured at the level of root furcation and 2, 4, and 6 mm apical to the furcation along the sagittal line and the posterior line of occlusion. The retromolar distances were compared between the Class I and Class III malocclusion groups using general linear mixed models.

RESULTS

The retromolar space measured through the sagittal line showed no significant intergroup difference. Among the distances measured through the posterior line of occlusion, the space measured at depths 0 and 2 mm to the furcation were significantly greater in the Class III group than in the Class I group.

CONCLUSIONS

Patients with Class III malocclusion have greater retromolar space for mandibular molar distalization along the posterior line of occlusion only at the level of the second molar furcation.

Facial Growth Patterns and Insertion Sites of Miniscrew Implants

INTRODUCTION

We aimed to evaluate the associations between the craniofacial growth pattern with interradicular distances (IRDs), cortical widths (CWs), and jaw heights (JHs). Also, we mapped safe zones for miniscrew implantation.

METHODS

Cone-beam computerized tomography data pertaining to 60 Class-I patients were divided into 3 growth groups: normal, horizontal, and vertical. IRDs and CWs were measured for bimaxillary canines to second molars, on buccal and lingual sides, at 3 transverse planes (1, 3, and 5 mm apically to the alveolar crest). JHs were measured in both jaws, between canines and second molars. The role of growth patterns and other variables were analyzed; also, safe zones were mapped with statistical substantiation.

RESULTS

IRDs were greater in the mandible, males, at points more distant from the ridge crest, and on the lingual side. Cortexes were thicker in the horizontal growth pattern, mandible, males, older patients, and lingual sides. JHs were greater in vertical growth pattern, mandible, and males.

CONCLUSIONS

The cortex might be thicker in patients with a horizontal growth pattern. The height might be greater in vertical growth pattern. IRDs might not be affected by growth pattern.

Influence of basis images and skull position on evaluation of cortical bone thickness in cone beam computed tomography

OBJECTIVES

The aim of this study was to assess the influence of the number of basis images and the orientation of the skull on the evaluation of cortical alveolar bone in cone beam computed tomography (CBCT).

STUDY DESIGN

Eleven skulls with a total of 59 anterior teeth were selected. CBCT images were acquired by using 4 protocols, by varying the rotation of the tube-detector arm and the orientation of the skull (protocol 1: 360°/0°; protocol 2: 180°/0°; protocol 3: 180°/90°; protocol 4: 180°/180°). Observers evaluated cortical bone as absent, thin, or thick. Direct observation of the skulls was used as the gold standard. Intra- and interobserver agreement, as well as agreement of scoring between the 3 bone thickness classifications, were calculated by using the κ statistic. The Wilcoxon signed-rank test was used to compare the 4 protocols.

RESULTS

For lingual cortical bone, protocol 1 showed no statistical difference from the gold standard. Higher reliability was found in protocol 3 for absent (κ = 0.80) and thin (κ = 0.47) cortices, whereas for thick cortical bone, protocol 2 was more consistent (κ = 0.60). In buccal cortical bone, protocol 1 obtained the highest agreement for absent cortices (κ = 0.61), whereas protocol 4 was better for thin cortical plates (κ = 0.38) and protocol 2 for thick cortical plates (κ = 0.40).

CONCLUSIONS

No consistent effect of the number of basis images or head orientation for visual detection of alveolar bone was detected, except for lingual cortical bone, for which full rotation scanning showed improved visualization.

Is There a Difference in Stability After Intraoral Vertical Ramus Osteotomy Between Vertically High-Angle and Normal-Angle Patients?

PURPOSE

Few studies have evaluated the relapse pattern of intraoral vertical ramus osteotomy (IVRO) for the correction of mandibular prognathism with a high angle. The aim of this study was to measure the association between vertical facial types (high and normal mandibular plane angle) and relapse after IVRO for the management of mandibular prognathism.

MATERIALS AND METHODS

The retrospective cohort study sample (skeletal Class III patients) was divided into 2 groups according to the angle of the sella-nasion plane relative to the mandibular plane (SN-MP) at the initial examination. Lateral cephalograms were analyzed for the predictor (facial type) and outcome (cephalometric changes over time) variables before surgery, 7 days after surgery, and 12 months after surgery. The 2 groups were matched for sample size (n = 20 in each). Data were analyzed using repeated-measures analysis of variance with Bonferroni correction.

RESULTS

The normal-angle group (group N, SN-MP from 27° to 37°) and high-angle group (group H, SN-MP >37°) were not significantly different in terms of gender and age at the initial examination. Seven days after surgery, the mandibles in group H moved 2.5 mm more superiorly than those in group N (P = .013); consequently, the amount of overbite correction in group H was approximately 2 mm greater than that in group N (P = .002). Nevertheless, 12 months after surgery, there was no statistically significant difference in relapse of the maxilla and mandible between the 2 groups. In the 2 groups, the mandible moved approximately 0.7 mm superiorly during retention.

CONCLUSIONS

These findings suggest that IVRO is a clinically acceptable and stable treatment modality for mandibular prognathism with a high angle.

Three-dimensional mapping of cortical bone thickness in subjects with different vertical facial dimensions

BACKGROUND

The purpose of this study was to determine differences in cortical bone thickness among subjects with different vertical facial dimensions using cone beam computed tomography (CBCT).

METHODS

From 114 pre-treatment CBCT scans, 48 scans were selected to be included in the study. CBCT-synthesized lateral cephalograms were used to categorize subjects into three groups based on their vertical skeletal pattern. Cortical bone thickness (CBT) at two vertical levels (4 and 7 mm) from the alveolar crest were measured in the entire tooth-bearing region in the maxilla and mandible.

RESULTS

Significant group differences were detected with high-angle subjects having significantly narrower inter-radicular CBT at some sites as compared to average- and low-angle subjects.

CONCLUSIONS

Inter-radicular cortical bone is thinner in high-angle than in average- or low-angle subjects in few selected sites at the vertical height in which mini-implants are commonly inserted for orthodontic anchorage.

Performance of cone-beam computed tomography and multidetector computed tomography in diagnostic imaging of the midface: A comparative study on Phantom and cadaver head scans

PURPOSE

To compare multidetector computed tomography (MDCT) and cone-beam computed tomography (CBCT) regarding radiation, resolution, image noise, and image quality.

METHODS

CBCT and 256-MDCT were compared based on three scan protocols: Standard-dose (≈24 mGy), reduced-dose (≈9 mGy), and low-dose (≈4 mGy). MDCT images were acquired in standard- and high-resolution mode (HR-MDCT) and reconstructed using filtered back projection (FBP) and iterative reconstruction (IR). Spatial resolution in linepairs (lp) and objective image noise (OIN) were assessed using dedicated phantoms. Image quality was assessed in scans of 25 cadaver heads using a Likert scale.

RESULTS

OIN was markedly higher in FBP-MDCT when compared to CBCT. IR lowered the OIN to comparable values in standard-mode MDCT only. CBCT provided a resolution of 13 lp/cm at standard-dose and 11 lp/cm at reduced-dose vs. 11 lp/cm and 10 lp/cm in HR-MDCT. Resolution of 10 lp/cm was observed for both devices using low-dose settings. Quality scores of MDCT and CBCT did not differ at standard-dose (CBCT, 3.4; MDCT, 3.3-3.5; p > 0.05). Using reduced- and low-dose protocols, CBCT was superior (reduced-dose, 3.2 vs. 2.8; low dose, 3.0 vs. 2.3; p < 0.001).

CONCLUSION

Using the low-dose protocol, the assessed CBCT provided better objective and subjective image quality and equality in resolution. Similar image quality, but better resolution using CBCT was observed at higher exposure settings.

KEY POINTS

• The assessed CBCT device provided better image quality at lower doses. • Objective and subjective image quality were comparable using higher exposure settings. • CBCT showed superior spatial resolution in standard-dose and reduced-dose settings. • Modern noise-reducing tools are used in CBCT devices currently. • MDCT should be preferred for assessment of soft-tissue injuries and oncologic imaging.

[Bone-based anchorage failure]

The aim of this article is to list the circumstances likely to give rise to failure of orthodontic temporary bone-supported anchorage and, hence, to attempt to define criteria for correct miniscrew usage. Our study was based on a review of the literature and analyses of clinical cases. Our findings show that, with a sound knowledge of the indications for screw selection and positioning and of the insertion protocols combined with a clear understanding of orthodontic mechanics, bone-based anchorage can henceforth provide orthodontists with an essential tool to enable formerly unachievable dental movements and to stabilize unwanted movements, thus making treatment both more reliable and more effective.

Short-term effects of strain produced on a split palatal screw-type hyrax appliance after rapid maxillary expansion: A clinical trial

INTRODUCTION

The aim of this study was to establish an accumulated strain pattern in different parts of rapid maxillary expansion appliances and relate them to different vertical growth patterns. A clinical study was conducted of 40 patients with posterior crossbite who required rapid palatal expansion.

METHODS

Patients (mean age, 8.48 years) were recruited and treated at the Dental Hospital of Bellvitge, Hospitalet de Llobregat, Barcelona, Spain. Strain gauges were placed on the arms of the RME hyrax screw appliance to record deformation (strain) during the expansion and the retention phases for 75 days. A finite element model was used to place the gauge at the point where the strain was most expressed. The vertical coefficient of variation was used to classify the patients by their vertical growth pattern. P = 0.05 was considered to be statistically significant.

RESULTS

During the expansion phase, the highest values of accumulated strain were measured in the posterior part of the appliance for all facial biotypes, but these values passed to the anterior area at the end of the retention phase of the mesocephalic and brachycephalic patients. There was statistically significant difference in the strain of the posterior arms in accordance with the vertical growth pattern (P = 0.05) during the retention phase. At 75 days of retention, 61.25% of the arms had already begun to have strain dissipation.

CONCLUSIONS

The accumulated strain pattern in the rapid maxillary expansion appliance can vary depending on the facial biotype. In the future, orthodontists should try to tailor the activation and retention protocol based on each patient's characteristics.

Failure rates of mini-implants placed in the infrazygomatic region

Background

The purpose of this pilot study was to evaluate the failure rates of mini-implants placed in the infrazygomatic region and to evaluate factors that affect their stability.

Methods

A retrospective cohort study of 30 consecutive patients (55 mini-implants) who had infrazygomatic mini-implants at a University Clinic were evaluated for failure rates. Patient, mini-implant, orthodontic, surgical, and mini-implant maintenance factors were evaluated by univariate logistic regression models for association to failure rates.

Results

A 21.8 % failure rate of mini-implants placed in the infazygomatic region was observed. None of the predictor variables were significantly associated with higher or lower odds for failed implants.

Conclusions

Failure rates for infrazygomatic mini-implants were slightly higher than those reported in other maxilla-mandibular osseous locations. No predictor variables were found to be associated to the failure rates.

Relationship Between the Thickness of Cortical Bone at Maxillary Mid-palatal Area and Facial Height Using CBCT

INTRODUCTION

Orthodontic mini-implants have been incorporated into orthodontic treatment modalities. Adequate bone at mini-implant placement site can influence the success or failure of anchorage. The present study was to determine the thickness of cortical bone in the maxillary mid-palatal area at predetermined points for the placement of orthodontic mini-implants using Cone Beam CT technique in order to evaluate the relationship of these values with the facial height. Materials and Methods : A total of 161 patients, consisting of 63 males (39.13%) and 98 females (60.87%), were evaluated in the present study; 38% of the subjects had normal facial height, 29% had short face and 33% had long face. In order to determine which patient belongs to which facial height category, i.e. normal, long or short, two angular and linear evaluations were used: the angle between S-N and Go-Me lines and the S-Go/N-Me ratio. Twenty points were evaluated in all the samples. First the incisive foramen was located. The paracoronal cross-sections were prepared at distances of 4, 8, 16 and 24 mm from the distal wall of the incisive foramen and on each cross-section the mid-sagittal and para-sagittal areas were determined bilaterally at 3- and 6-mm distances (a total of 5 points). The thicknesses of the cortical plate of bone were determined at the predetermined points. Results : There was a significant relationship between the mean cortical bone thickness and facial height (p<0.01), with significantly less thickness in long faces compared to short faces. However, the thickness of cortical bone in normal faces was similar to that in long and short faces. Separate evaluation of the points showed that at point a16 subjects with short faces had thicker cortical bone compared to subjects with long and normal faces. At point b8 in long faces, the thickness of the cortical bone was significantly less than that in short and normal faces. At point d8, the thickness of the cortical bone in subjects with short faces was significantly higher than that in subjects with long faces. Conclusion : At the point a16 the cortical bone thickness in short faces was significantly higher than normal and long faces. The lower thickness of the cortical bone in the palatal area at points b8 and d8 in subjects with long faces might indicate a lower anchorage value of these points in these subjects.

An anatomical radiographic evaluation of the posterior portion of the mandible in relation to autologous bone harvest procedures

The purpose of the study was to evaluate the course of the mandibular canal and the thickness of the vestibular cortical plate in the posterior region of the mandible in relation to autologous bone harvest procedures. The study was performed on a cohort of 30 cone-beam computed tomography hemimandible images. For each hemimandible, the course of the mandibular canal and the thickness of the vestibular cortical plate have been evaluated in 4 regions: the retromolar region, the second molar region, the first molar region, and the second premolar region. The analyzed variables show a characteristic trend: the thickness of the cortical vestibular plate and the horizontal distance of the canal from the cortical vestibular plate are higher in the second molar region specifically in the area bordering on the retromolar region. In fact, the maximum thickness reaches the average value of 3.46 mm on 30 hemimandibles for slice (SD, 0.56 mm; range, 2.36-4.83 mm), and the horizontal distance reaches the average value of 6.06 mm on 30 hemimandibles for slice (SD, 1.34 mm; range, 3.65-9.27 mm); both variables decrease in more distal slices of the retromolar region. The vertical distance of the canal from the cortical crest shows the average value of 14.25 mm on 22 slices of the second molar and retromolar regions (SD of average values, 1.03 mm; range of average values, 12.92-16.25 mm; range of absolute values, 7.11-22.92 mm) exactly in regions potentially suitable for procedures of bone harvest (second molar and retromolar regions).

A CBCT atlas of buccal cortical bone thickness in interradicular spaces

OBJECTIVE

To provide a road map of buccal cortical bone thickness in interradicular locations where miniscrew implants are commonly placed.

MATERIALS AND METHODS

Cone-beam computed tomography images from 100 study quadrants (50 maxillary and 50 mandibular) were studied. Cortical bone thickness was measured at the most mesial point, the midpoint, and the most distal point in interradicular areas from the canine to the first molar in both arches at 4 mm and 6 mm from the alveolar ridge. Indicator variables of whether the cortical bone thickness was thinner than 1 mm and thicker than 1.5 mm were constructed and analyzed in a general linear mixed model.

RESULTS

Buccal cortical bone was significantly thinner at a point bisecting two teeth than the bone adjacent to the teeth (P < .0001). The site with the greatest percentage of measurements <1 mm (20%) was at the midpoint bisecting the mandibular canine and the first premolar. The site with the highest percentage of measurements >1.5 mm (50%) was in the mandible adjacent to the first molar (distal to the midpoint of the second premolar and first molar) at 6 mm from the alveolar crest.

CONCLUSION

Cortical bone thickness is significantly thinner centrally between two teeth than in the areas adjacent to the roots.

Comparison of molar intrusion efficiency and bone density by CT in patients with different vertical facial morphology

The purpose of this study is to examine the relationship between molar intrusion efficiency and bone density in patients with different vertical facial morphology. Thirty-six female patients, with overerupted upper first molars, were divided into two groups according to mandiblular plane angle (FH-MP): hyperdivergent, FH-MP>30° (G1), hypodivergent, FH-MP<22° (G2). Mini-screw implants with elastic chains were used to intrude upper first molars. Spiral CT was used to measure the intrusion degree of upper first molar and bone density, and molar intrusion efficiency was calculated as amount/duration (mm month(-1) ). In addition, each tooth was divided into three portions (cervical, furcation and apical) to measure the bone density. It was found in this study that treatment duration was 3·13 and 4·71 months in G1 and G2 and that the intrusion efficiency was 1·57 and 0·81 in G1 and G2 with significant difference (P < 0·05). There were significant differences in cervical, furcation and apical bone density between two groups (P < 0·05). The bone density was significantly reduced after molar intrusion. In addition, the bone density change was greater in G1 than in G2 (P < 0·05). It was concluded that molars were more easily to be intruded in hyperdivergent than in hypodivergent patients. The difference of bone density and bone density changes during intrusion may account for the variation of molar intrusion efficiency.

Maxillary buccal cortical plate inclination at mini-screw insertion sites

OBJECTIVE

To evaluate whether buccal cortical bone inclination varies for the maxillary alveolar processes of adult patients with decreased, normal, and increased facial heights.

MATERIALS AND METHODS

Cone-beam computed tomography images of 135 adult patients, including 49 hypodivergent subjects (26 women, 23 men), 40 hyperdivergent subjects (24 women, 16 men), and 46 normodivergent (25 women, 21 men) were analyzed. Cortical bone inclination measurements were made relative to the occlusal plane. Cross-sectional slices of the maxilla were taken at interdental sites from the distal aspect of maxillary canine to the mesial aspect of maxillary second molar.

RESULTS

Analysis of variance indicated significant differences (P < .05) between the angles formed by the line tangent to the cortical bone and the occlusal plane among the vertical facial types for the regions between canine and first premolar and between second premolar and first molar at miniscrew insertion sites.

CONCLUSION

The results of this study indicate that vertical facial pattern should be taken into consideration when adjusting the insertion angle of miniscrews at the maxillary buccal region.

Mandibular posterior anatomic limit for molar distalization

INTRODUCTION

The purpose of this study was to investigate the mandibular posterior anatomic limit for molar distalization.

METHODS

Three-dimensional computed tomography scans were obtained on 34 adults with a skeletal Class I normodivergent facial profile and a normal occlusion. Posterior available space was measured at the crown and root levels along the posterior occlusal line connecting the buccal cusps of the first and second molars on the axial slices. It was also measured at the occlusal level on the lateral cephalograms derived from the computed tomography scans. The measurements on the cephalograms were used to predict the actual posterior available space determined by computed tomography and to determine the presence of root contact with the inner lingual cortex by linear regression and discriminant analyses, respectively.

RESULTS

The posterior available space was significantly smaller at the root level than at the crown level. Root contact was observed in 35.3% of the 68 roots. The posterior available space measured on the lateral cephalograms resulted in a regression equation with a coefficient of determination of 0.261 to predict actual available space and correctly identified root contact in 66.2% of cases with a threshold value of 3.9 mm.

CONCLUSIONS

The posterior anatomic limit appeared to be the lingual cortex of the mandibular body. Computed tomography scans are recommended for patients who require significant mandibular molar distalization.

Finite element analysis of rapid canine retraction through reducing resistance and distraction

Objective

The aims of this study were to compare different surgical approaches to rapid canine retraction by designing and selecting the most effective method of reducing resistance by a three-dimensional finite element analysis.

Material and Methods

Three-dimensional finite element models of different approaches to rapid canine retraction by reducing resistance and distraction were established, including maxillary teeth, periodontal ligament, and alveolar. The models were designed to dissect the periodontal ligament, root, and alveolar separately. A 1.5 N force vector was loaded bilaterally to the center of the crown between first molar and canine, to retract the canine distally. The value of total deformation was used to assess the initial displacement of the canine and molar at the beginning of force loading. Stress intensity and force distribution were analyzed and evaluated by Ansys 13.0 through comparison of equivalent (von Mises) stress and maximum shear stress.

Results

The maximum value of total deformation with the three kinds of models occurred in the distal part of the canine crown and gradually reduced from the crown to the apex of the canine; compared with the canines in model 3 and model 1, the canine in model 2 had the maximum value of displacement, up to 1.9812 mm. The lowest equivalent (von Mises) stress and the lowest maximum shear stress were concentrated mainly on the distal side of the canine root in model 2. The distribution of equivalent (von Mises) stress and maximum shear stress on the PDL of the canine in the three models was highly concentrated on the distal edge of the canine cervix.

Conclusions

Removal of the bone in the pathway of canine retraction results in low stress intensity for canine movement. Periodontal distraction aided by surgical undermining of the interseptal bone would reduce resistance and effectively accelerate the speed of canine retraction.

Quantitative evaluation of alveolar cortical bone density in adults with different vertical facial types using cone-beam computed tomography

OBJECTIVE

The purpose of this study was to quantitatively evaluate the cortical bone densities of the maxillary and mandibular alveolar processes in adults with different vertical facial types using cone-beam computed tomography (CBCT) images.

METHODS

CBCT images (n = 142) of adult patients (20-45 years) were classified into hypodivergent, normodivergent, and hyperdivergent groups on the basis of linear and angular S-N/Go-Me measurements. The cortical bone densities (in Hounsfield units) at maxillary and mandibular interdental sites from the distal aspect of the canine to the mesial aspect of the second molar were measured on the images.

RESULTS

On the maxillary buccal side, female subjects in the hyperdivergent group showed significantly decreased bone density, while in the posterior region, male subjects in the hyperdivergent group displayed significantly decreased bone density when compared with corresponding subjects in the other groups (p<0.001). Furthermore, the subjects in the hyperdivergent group had significantly lower bone densities on the mandibular buccal side than hypodivergent subjects. The maxillary palatal bone density did not differ significantly among groups, but female subjects showed significantly denser palatal cortical bone. No significant difference in bone density was found between the palatal and buccal sides in the maxillary premolar region. Overall, the palatal cortical bone was denser anteriorly and buccal cortical bone was denser posteriorly.

CONCLUSION

Adults with the hyperdivergent facial type tend to have less-dense buccal cortical bone in the maxillary and mandibular alveolar processes. Clinicians should be aware of the variability of cortical bone densities at mini-implant placement sites.

Evaluation of alveolar cortical bone thickness and density for orthodontic mini-implant placement

Objective: Mini-implant stability is primarily related to bone quality and quantity. This study evaluated alveolar cortical bone thickness and density differences between interradicular sites at different levels from the alveolar crest, and assessed the differences between adolescents (12-18 years of age) and adults (19-50 years of age), males and females, upper and lower arch, anterior and posterior region of jaws and buccal and oral side. Study Design: In this retrospective study, 48 Computed Tomography scans, performed for oral surgery purposes were selected from dental records of 3,223 Caucasian orthodontic patients. The SimPlant software (Materialise, Leuven, Belgium) was used to measure cortical bone thickness and density at 13 interradicular sites and four bone levels ( 2,4,6 and 8 mm ). For the statistical analysis descriptive statistics, Student’s t-test and Pearson correlation coefficient were used. Results: Statistically significant differences in alveolar cortical bone thickness and density between age, gender, sites and sides were found (P<0.05). The Pearson correlation coefficient demonstrated a significant linear increasing of thickness and density from crest to base of alveolar crest (P≤0.05). Conclusion. Adults show a thicker alveolar cortical bone than adolescents. Alveolar cortical bone thickness and density were greater in males than in females, in mandible than in maxilla, in the posterior region than the anterior, in oral than buccal side. There is an increase of thickness and density from crest to base of alveolar crest.

Key words:Orthodontics, cortical bone thickness, cortical bone density, mini-implant, computed tomography, temporary anchorage devices.

Location of the mandibular canal and thickness of the occlusal cortical bone at dental implant sites in the lower second premolar and first molar

The objective of this study was to evaluate the location of the mandibular canal and the thickness of the occlusal cortical bone at dental implant sites in the lower second premolar and lower first molar by using dental cone-beam computed tomography (CBCT). Seventy-nine sites (47 second premolar and 32 first molar sites) were identified in the dental CBCT examinations of 47 patients. In this study, 4 parameters were measured: (1) MC—the distance from the mandibular canal to the upper border of the mandible; (2) CD—the distance from the mandibular canal to the buccal border of the mandible; (3) MD—the distance from the mandibular canal to the lingual border of the mandible; (4) TC—the thickness of the cortical bone at the occlusal side. A statistical analysis was employed to compare the size and differences between these 4 parameters at the lower second premolar and lower first molar. Regarding the MC and MD, the experimental results showed no statistical difference between the first molar and second premolar. However, the TC for the second premolar was greater than that of the first molar. Thus, careful consideration is necessary in choosing the size of and operation type for dental implants.

A report on the use of Er:YAG laser for pilot hole drilling prior to miniscrew insertion

The aim of the present in vitro study was to investigate the required time period of the Er:YAG laser that is used for drilling through cortical bone when pilot hole drilling is needed before miniscrew insertion. Even though Er:YAG laser is used in various in vivo and in vitro studies, there is no accepted procedure of laser for depth control during drilling through cortical bone. The study sample consisted of 120 cortical bone segments having 1.5 and 2.0 mm of cortical bone thickness. An Er:YAG laser, with a spot size of 1.3 mm and an air-water spray of 40-50 ml/min, was used. The laser was held 2 mm away from and perpendicular to the bone surface with different laser settings. Twelve specimens were prepared for each subgroup. As the cortical bone thickness increased, the time needed to drill through the bone increased. Frequency increase directly caused a decrease in irradiation duration. When three different frequency, three different energy, and four different power values were tested for both the 1.5- and 2-mm cortical bone thicknesses, the shortest duration needed to drill through cortical bone was seen in the 3.6-W (300 mJ-12 Hz) setting. When pilot holes are drilled prior to miniscrew placement in 1.5 to 2 mm of cortical bone using Er:YAG laser, the most appropriate value is found with the 3.6-W (300 mJ-12 Hz) setting.