Is trabecular bone related to primary stability of miniscrews?

Effects of exposure length, cortical and trabecular bone contact areas on primary stability of infrazygomatic crest mini-screws at different insertion angles

BACKGROUND

The infrazygomatic crest mini-screw has been widely used, but the biomechanical performance of mini-screws at different insertion angles is still uncertain. The aim of this study was to analyse the primary stability of infrazygomatic crest mini-screws at different angles and to explore the effects of the exposure length (EL), screw-cortical bone contact area (SCA), and screw-trabecular bone contact area (STA) on this primary stability.

METHODS

Ninety synthetic bones were assigned to nine groups to insert mini-screws at the cross-combined angles in the occlusogingival and mesiodistal directions. SCA, STA, EL, and lateral pull-out strength (LPS) were measured, and their relationships were analysed. Twelve mini-screws were then inserted at the optimal and poor angulations into the maxillae from six fresh cadaver heads, and the same biomechanical metrics were measured for validation.

RESULTS

In the synthetic-bone test, the LPS, SCA, STA, and EL had significant correlations with the angle in the occlusogingival direction (rLPS = 0.886, rSCA = -0.946, rSTA = 0.911, and rEL= -0.731; all P < 0.001). In the cadaver-validation test, significant differences were noted in the LPS (P = 0.011), SCA (P = 0.020), STA (P = 0.004), and EL (P = 0.001) between the poor and optimal angulations in the occlusogingival direction. The STA had positive correlations with LPS (rs = 0.245 [synthetic-bone test] and r = 0.720 [cadaver-validation test]; both P < 0.05).

CONCLUSIONS

The primary stability of the infrazygomatic crest mini-screw was correlated with occlusogingival angulations. The STA significantly affected the primary stability of the infrazygomatic crest mini-screw, but the SCA and EL did not.

Evaluation of safe areas for miniscrew use according to various skeletal anomalies with CBCT

OBJECTIVES

We aimed to determine safe areas to apply miniscrews in the interradicular region of the maxilla and mandible in individuals with various sagittal skeletal malocclusions.

MATERIALS AND METHODS

Cone beam-computed tomography images of 159 individuals were used. Individuals were divided into three groups: Class I, Class II, and Class III. In the sagittal plane, 3-6-9-mm apical sections were determined from the alveolar crest apex. The buccal cortical bone thickness, interradicular distance, and buccolingual bone distances were measured.

RESULTS

In the buccal cortical bone thickness, we observed statistically significant differences between the classes except for the 1-1 region in the maxilla and all regions and sections in the mandible (p < 0.05). The differences in the buccolingual bone distance between classes were statistically significant, except for the 3-mm and 6-mm sections in the 3-4 and 4-5 regions of the maxilla, the 9-mm sections in the 1-2 and 2-3 regions, the 6-mm and 9-mm sections in the 3-4 region, and the 6-mm section in the 4-5 regions of the mandible (p < 0.05). The differences in the interradicular bone distance were statistically significant between the classes in all regions and sections of the mandible except the 6-mm sections in the 1-2 region and in all sections of the maxilla except the 6-mm sections in the 3-4 region (p < 0.05).

CONCLUSIONS

We observed significant differences in the buccal cortical bone thickness, interradicular bone distance, and buccolingual bone distance among individuals.

CLINICAL RELEVANCE

Understanding the anatomy of interradicular regions and preventing complications.

Three-dimensional evaluation of the cortical and cancellous bone density and thickness for miniscrew insertion: a CBCT study of interradicular area of adults with different facial growth pattern

AIM

The purpose of this study was to evaluate the effect of the density and the thickness of the cortical and the cancellous bone at selected inter-radicular areas in subjects with different facial growth patterns using cone beam computed tomography (CBCT) in order to choose the optimal area for miniscrew insertion.

MATERIALS AND METHODS

From 150 CBCT scans, 45 scans were included in the study. The subjects were categorized into three groups based on their skeletal growth pattern according to SN-GoMe angle and facial height index. Cortical and cancellous bone density and thickness were measured at the selected inter-radicular areas.

RESULTS

Compared to the other two groups, the hyperdivergent group had thinner cortical bone in the anterior region of the maxilla between the central and the lateral incisors on the buccal side at 4 mm from the alveolar crest (P-value: 0.012) and on the palatal side at 7 mm from the alveolar crest (P-value: 0.030). Cancellous bone density values in these areas were higher in subjects with hypodivergent and hyperdivergent growth pattern. Furthermore, in hyperdivergent group less dense cortical bone in the posterior region of the maxilla on the palatal side between the second premolar and the first molar (p-value: 0.020) and on the buccal side between the first molar and the second molar (p-value: 0.038 & 0.047) was observed. No significant differences were found in the mandible between the three groups. No significant differences were found between the male and the female subjects.

CONCLUSION

Hyperdivegents presented thinner cortical bone in the anterior of the maxilla between the central and the lateral incisors. Less dense cortical bone was found between maxillary second premolar and first molar on the palatal side and also between the maxillary first molar and the second molar on the buccal side in this group too. Normal showed higher density values in the posterior of the maxilla compared to the other two groups. No significant differences were found among three groups in mandible.

On the material dependency of peri-implant morphology and stability in healing bone

The microstructural architecture of remodeled bone in the peri-implant region of screw implants plays a vital role in the distribution of strain energy and implant stability. We present a study in which screw implants made from titanium, polyetheretherketone and biodegradable magnesium-gadolinium alloys were implanted into rat tibia and subjected to a push-out test four, eight and twelve weeks after implantation. Screws were 4 mm in length and with an M2 thread. The loading experiment was accompanied by simultaneous three-dimensional imaging using synchrotron-radiation microcomputed tomography at 5 μm resolution. Bone deformation and strains were tracked by applying optical flow-based digital volume correlation to the recorded image sequences. Implant stabilities measured for screws of biodegradable alloys were comparable to pins whereas non-degradable biomaterials experienced additional mechanical stabilization. Peri-implant bone morphology and strain transfer from the loaded implant site depended heavily on the biomaterial utilized. Titanium implants stimulated rapid callus formation displaying a consistent monomodal strain profile whereas the bone volume fraction in the vicinity of magnesium-gadolinium alloys exhibited a minimum close to the interface of the implant and less ordered strain transfer. Correlations in our data suggest that implant stability benefits from disparate bone morphological properties depending on the biomaterial utilized. This leaves the choice of biomaterial as situational depending on local tissue properties.

Evaluation of stresses on mandible bone and prosthetic parts in fixed prosthesis by utilizing CFR-PEEK, PEKK and PEEK frameworks

Fixed prostheses are appropriate treatment solutions for edentulous patients. In fixed prostheses, following "All on four", titanium frameworks are commonly used to support the implants. However, the limitations of titanium have prompted researchers to search for alternative materials (e.g. polymers). This study applied finite element investigation to evaluate the stress distribution in the parts of fixed prosthesis and the surrounding bone tissue, using polymeric frameworks in place of titanium, and different densities of spongy bone. As, the success of fixed prosthesis was predicted to be influenced also by bone quality, particularly spongy bone density. Fixed prosthesis was constructed on edentulous mandible, then different frameworks (CFR-PEEK 60%, CFR-PEEK 30%, PEKK, and PEEK) were stimulated instead of titanium, under 300N unilateral and bilateral forces. Three densities of spongy bone were stimulated which are normal, low and high. The choice of framework material depended on the density of spongy bone. Moreover, PEEK framework showed the lowest stress values on bone tissues and the highest stress values on mucosa. All frameworks could be used in the fixed prosthesis, in the cases of normal and high densities of spongy bone. In low-density case, soft frameworks (PEKK and PEEK) were recommended to reduce the stresses generated on bone tissues.

A novel auxiliary device enhances miniscrew stability under immediate heavy loading simulating orthopedic treatment

OBJECTIVES

To evaluate miniscrew stability and perform a histomorphometric analysis of the bone around the miniscrew under a load corresponding to orthopedic force.

MATERIALS AND METHODS

Thirty-two miniscrews were implanted into eight rabbit tibias. Auxiliary group rabbits received auxiliary devices with miniscrews (n = 8, 28 days; n = 8, 56 days), and those in the nonauxiliary control group received miniscrews without auxiliary devices (n = 8, 28 days; n = 8, 56 days). Elastics were placed between miniscrews to apply a load of 5 N. Miniscrew stability was evaluated using a Periotest. Bone-to-implant contact (BIC) and spike implantation depth were measured histomorphologically.

RESULTS

Periotest values in the auxiliary group were significantly lower than those in the nonauxiliary group at all time periods. There was no significant difference in BIC between the auxiliary and nonauxiliary groups at 28 or 56 days postimplantation. The implantation spike depth in the auxiliary group was significantly greater at 56 days compared to that at 28 days. Newly formed bone was observed around the spike of the auxiliary device at 56 days.

CONCLUSIONS

The results suggest that the use of miniscrews in conjunction with auxiliary devices provides stable skeletal anchorage, which may be useful in orthopedic treatments.

Bone quality affects stability of orthodontic miniscrews

The objective of this study was to evaluate the effect of bone–miniscrew contact percentage (BMC%) and bone quality and quantity on orthodontic miniscrew stability and the maximum insertion torque value (ITV). Orthodontic miniscrews of five different dimensions and several bovine iliac bone specimens were used in the evaluation. Miniscrews of each dimension group were inserted into 20 positions in bovine iliac bone specimens. The experiment was divided into three parts: (1) Bone quality and quantity were evaluated using cone-beam computed tomography (CBCT) and microcomputed tomography. (2) The 3D BMC% was calculated. (3) The ITVs during miniscrew insertion were recorded to evaluate the stability of the orthodontic miniscrews. The results indicated that longer and thicker miniscrews enabled higher ITVs. CBCT was used to accurately measure cortical bone thickness (r = 0.939, P < 0.05) and to predict the bone volume fraction of cancellous bone (r = 0.752, P < 0.05). BMC% was significantly influenced by miniscrew length. The contribution of cortical bone thickness to the ITV is greater than that of cancellous bone structure, and the contribution of cortical bone thickness to BMC% is greater than that of cancellous bone structure. Finally, the higher is BMC%, the greater is the ITV. This study concludes that use of CBCT may predict the mechanical stability of orthodontic miniscrews.

Interradicular distance and alveolar bone thickness for miniscrew insertion: a CBCT study of Persian adults with different sagittal skeletal patterns

Background

This study aimed to assess the interradicular distance and alveolar bone thickness of Persian adults with different sagittal skeletal patterns for miniscrew insertion using cone-beam computed tomography (CBCT).

Methods

This cross-sectional study was conducted on maxillary and mandibular CBCT scans of 60 patients (18–35 years) in three groups (n = 20) of class I, II and III sagittal skeletal pattern. Anatomical and skeletal parameters were measured at 2, 4 and 6 mm apical to the cementoenamel junction (CEJ) by one examiner. The intra- and inter-class correlation coefficients were calculated to assess the intra, and interobserver reliability. Data were analyzed by ANOVA and Tukey’s test (alpha = 0.05).

Results

The intra- and interobserver reliability were > 0.9 for all parameters. The largest inter-radicular distance in the maxilla was between the central incisors (1–1) in classes I and III, and between premolars (4–5) in class II patients. The largest inter-radicular distance in the mandible was between molar teeth (6–7) in all three classes. The buccal cortical plate thickness was maximum at the site of mandibular first and second molars (6–7). The posterior maxilla and mandible showed the maximum thickness of cancellous bone and alveolar process. Wide variations were noted in this respect between class I, II and III patients.

Conclusions

The area with maximum inter-radicular distance and optimal alveolar bone thickness for miniscrew insertion varies in different individuals, depending on their sagittal skeletal pattern.

Effect of Microimplant Neck Design with and without Microthread on Pullout Strength and Destruction Volume

The microthread neck concept has been applied to dental implants. This study investigated the pullout strength and destruction volume of orthodontic microimplants with and without the microthread neck design. Fifteen microimplants (diameter: 1.5 × 10 mm) of three types (Types A and B: without microimplant neck; Type C: with microimplant neck) were tested. The insertion torque (IT), Periotest value (PTV), horizontal pullout strength (HPS), and horizontal destruction volume (HDV) of each type were measured. Kruskal–Wallis H test and Dunn’s post-hoc comparison test were performed to compare the measured values of the three types of microimplants. The correlations of the measured values were used to perform the Spearman’s correlation coefficient analysis. The ITs of Types B (8.8 Ncm) and C (8.9 Ncm) were significantly higher than those of Type A (5.2 Ncm). Type B yielded the lowest PTV (4.1), and no statistical differences in PTV were observed among the three types. Type A had a significantly lower HPS (158.8 Ncm) than Types B (226.9 Ncm) and C (212.8 Ncm). The three types did not exhibit any significant differences in the HDV. The results of the Spearman’s correlation coefficient test revealed that HDV (ρ = 0.710) and IT (ρ = 0.813) were strongly correlated with HPS, whereas for PTV and HPS, it was not. HPS was strongly and significantly correlated with HDV. The orthodontic microimplant with a microimplant neck design did not perform better than that without a microthread in the mechanical strength test.

Computed tomography assessment of maxillary bone density for orthodontic mini-implant placement with respect to vertical growth patterns

OBJECTIVE

To quantitatively measure and report bone density of maxilla in the interradicular (alveolar and basal bone) and infrazygomatic crest (IZC) region in various growth patterns among Dravidian individuals.

DESIGN

This was a retrospective spiral computed tomography (CT) study.

SETTING

The study was conducted at the Department of Orthodontics, Saveetha Dental College and Hospital, Tamil Nadu, India.

METHODS

Sixty CT scans (24 men, 36 women; mean age = 25.3 years and 23.8 years, respectively) divided equally into three groups based on vertical facial proportions were included. Bone density measurements in Hounsfield units (HU) were performed using Philips and RadiAnt DICOM viewers. Buccal cortical, palatal cortical and cancellous bone regions were analysed in a Philips DICOM viewer and IZC region was analysed in a RadiAnt DICOM viewer. Statistical analysis with one-way ANOVA and post-hoc Tukey HSD test was done.

RESULTS

The hypodivergent group had a significantly higher bone density at the buccal cortex in posterior region (P < 0.05) when compared to the normodivergent and hyperdivergent groups. Buccal basal bone was denser than buccal alveolar bone (P < 0.05) in all three groups. In the IZC region, hypodivergent groups had significantly higher density values when compared to the normodivergent and hyperdivergent groups (P < 0.05).

CONCLUSION

The present study concluded that cancellous bone density in the interradicular regions was greatest in the anterior sites and was not influenced by growth pattern. Hypodivergent groups tend to have higher density in the posterior regions (buccal and palatal cortical bone) and at the IZC region compared to normodivergent and hyperdivergent groups.

Determination of sex dimorphisms of the thickness of the hard palate in adolescence using computed tomography: Pilot study

BACKGROUND

In addition to traditional craniometric techniques, computer craniometry has been used in recent decades, including stereometric methods, which make it possible to determine the microanatomical spatial relationships and dimensional features of various structures of the skull, in particular the thickness of the inert palate of the maxilla.

AIM

Determination of the gender-specific variability of the thickness of the bony palate at the age of 18-20 years using CT.

MATERIAL AND METHODS

The material of the pilot study were 40 computed tomograms of young males and females aged 18-20 years. The method of computer craniometry was used to measure the thickness of the bony palate in sagittal projection taking into account the gender. A graphic raster map was created to identify the palatal areas, then analyze their thickness and determine the safe zones for the mini dental implants.

RESULTS

In young males and females (18-20 years) the thickness of the bony palate decreases at different levels from front to back and from the median suture to the alveolar process. The greatest thickness of the bony palate corresponds to its anterior third and reliably predominates in young males at all levels compared to young females. In the middle and posterior third palate, the averages do not show gender differences and their variation is insignificant.

CONCLUSIONS

The greatest thickness of the bony palate can be used as the most favorable zone for the fixation of orthodontic mini dental implants. The variability in the thickness of the bony palate should be considered when selecting the most optimal zones and depth of mini-implant placement.

[The experimental study of a Russian orthodontic mini-screw]

BACKGROUND

The aim of this research is the experimental study measuring stability of the orthodontic miniscrews «Turbo» designed in Russia in comparison with its foreign analogues, namely, «Vector Tas» (USA) and «BioRay» (Taiwan).

MATERIAL AND METHODS

Four self-drilling orthodontic miniscrews of each manufacturer, i.e. «Vector Tas», USA, (10-mm length, 2-mm diameter), «BioRay», Taiwan, (10-mm length, 2-mm diameter), «Turbo», Russia, (9-mm length, 2-mm diameter), a total of 12 items, were inserted into native pig mandible sample. Their stability was estimated by torques using a dynamometer (Zahoransky AG, Germany) and «Periotest» device («Periotest M», Germany). This experiment was conducted in native pig mandible sample immediately after the screws' placement and in 7 days after loading at an angle 70°.

RESULTS

After application of a load, the decreased torque values and increased Periotest values were registered in all orthodontic miniscrews.

CONCLUSION

Orthodontic miniscrews «Turbo» designed in Russia are slightly inferior to «VectorTas» miniscrews and superior to «BioRay» miniscrews in primary stability and stability after 7 days under loading.

Effects of Intrabony Length and Cortical Bone Density on the Primary Stability of Orthodontic Miniscrews

Miniscrews have gained recent popularity as temporary anchorage devices in orthodontic treatments, where failure due to sinus perforations or damage to the neighboring roots have increased. Issues regarding miniscrews in insufficient interradicular space must also be resolved. This study aimed to evaluate the primary stability of miniscrews shorter than 6 mm and their feasibility in artificial bone with densities of 30, 40, and 50 pounds per cubic foot (pcf). The primary stability was evaluated by adjusting the intrabony miniscrew length, based on several physical properties: maximum insertion torque (MIT), maximum removal torque (MRT), removal angular momentum (RAM), horizontal resistance, and micromotion. The MIT and micromotion results demonstrated that the intrabony length of a miniscrew significantly affected its stability in low-density cortical bone, unlike cases with a higher cortical bone density (p < 0.05). The horizontal resistance, MRT, and RAM were affected by the intrabony length, regardless of the bone density (p < 0.05). Thus, the primary stability of miniscrews was affected by both the cortical bone density and intrabony length. The effect of the intrabony length was more significant in low-density cortical bone, where the implantation depth increased as more energy was required to remove the miniscrew. This facilitated higher resistance and a lower risk of falling out.

Primary Stability of Orthodontic Titanium Miniscrews due to Cortical Bone Density and Re-Insertion

The increasing demand for orthodontic treatment over recent years has led to a growing need for the retrieval and reuse of titanium-based miniscrews to reduce the cost of treatment, especially in patients with early treatment failure due to insufficient primary stability. This in vitro study aimed to evaluate differences in the primary stability between initially inserted and re-inserted miniscrews within different cortical bone densities. Artificial bone was used to simulate cortical bone of different densities, namely 20, 30, 40, and 50 pound per cubic foot (pcf), where primary stability was evaluated based on maximum insertion torque (MIT), maximum removal torque (MRT), horizontal resistance, and micromotion. Scanning electron microscopy was used to evaluate morphological changes in the retrieved miniscrews. The MIT, MRT, horizontal resistance, and micromotion was better in samples with higher cortical bone density, thereby indicating better primary stability (P < 0.05). Furthermore, a significant reduction of MIT, MRT, and horizontal resistance was observed during re-insertion compared with the initial insertion, especially in the higher density cortical bone groups. However, there was no significant change in micromotion. While higher cortical bone density led to better primary stability, it also caused more abrasion to the miniscrews, thereby decreasing the primary stability during re-insertion.

Bone Damage Evolution Around Integrated Metal Screws Using X-Ray Tomography - in situ Pullout and Digital Volume Correlation

Better understanding of the local deformation of the bone network around metallic implants subjected to loading is of importance to assess the mechanical resistance of the bone-implant interface and limit implant failure. In this study, four titanium screws were osseointegrated into rat tibiae for 4 weeks and screw pullout was conducted in situ under x-ray microtomography, recording macroscopic mechanical behavior and full tomographies at multiple load steps before failure. Images were analyzed using Digital Volume Correlation (DVC) to access internal displacement and deformation fields during loading. A repeatable failure pattern was observed, where a ∼300–500 μm-thick envelope of bone detached from the trabecular structure. Fracture initiated close to the screw tip and propagated along the implant surface, at a distance of around 500 μm. Thus, the fracture pattern appeared to be influenced by the microstructure of the bone formed closely around the threads, which confirmed that the model is relevant for evaluating the effect of pharmacological treatments affecting local bone formation. Moreover, cracks at the tibial plateau were identified by DVC analysis of the tomographic images acquired during loading. Moderate strains were first distributed in the trabecular bone, which localized into higher strains regions with subsequent loading, revealing crack-formation not evident in the tomographic images. The in situ loading methodology followed by DVC is shown to be a powerful tool to study internal deformation and fracture behavior of the newly formed bone close to an implant when subjected to loading. A better understanding of the interface failure may help improve the outcome of surgical implants.

Investigating the Mechanical Characteristics of Bone-Metal Implant Interface Using in situ Synchrotron Tomographic Imaging

Long-term stability of endosseous implants depends on successful bone formation, ingrowth and adaptation to the implant. Specifically, it will define the mechanical properties of the newly formed bone-implant interface. 3D imaging during mechanical loading tests (in situ loading) can improve the understanding of the local processes leading to bone damage and failure. In this study, titanium screws were implanted into rat tibiae and were allowed to integrate for 4 weeks with or without the addition of the growth factor Bone Morphogenetic Protein and the bisphosphonate Zoledronic Acid. Samples were subjected to in situ pullout using high-resolution synchrotron x-ray tomography at the Tomcat beamline (SLS, PSI, Switzerland) at 30 keV with 25 ms exposure time, resulting in a total acquisition time of 45 s per scan, with a 3.6 μm isotropic voxel size. Using a custom-made loading device positioned inside the beamline, screws were pulled out with 0.05 mm increment, acquiring multiple scans until rupture of the sample. The in situ loading protocol was adapted to ensure short imaging time, which enabled multiple samples to be tested with short loading steps, while keeping the total testing time low and reducing dose deposition. Higher trabecular bone content was quantified in the surrounding of the screw in the treated groups, which correlated with increased mechanical strength and stiffness. Differences in screw implantation, such as contact between threads and cortex as well as minor tilt of the screw were also correlated to the mechanical parameters. In situ loading enabled the investigation of crack propagation during the pullout, highlighting the mechanical behavior of the interface. Three typical crack types were observed: (1) rupture at the interface of trabecular and cortical bone tissues, close to the screw, (2) large crack inside the cortex connected to the implant, and (3) first failure away from the screw with cracks propagating toward the screw-bone interface. Mechanical properties of in vivo integrated bone-metal screws rely on a combination of multiple parameters that are difficult to identify and separate one from the other.

Histomorphometric evaluation of the bone surrounding orthodontic miniscrews according to their adjacent root proximity

Objective

This study was conducted to perform histomorphometric evaluations of the bone surrounding orthodontic miniscrews according to their proximity to the adjacent tooth roots in the posterior mandible of beagle dogs.

Methods

Four male beagle dogs were used for this study. Six orthodontic miniscrews were placed in the interradicular spaces in the posterior mandible of each dog (n = 24). The implanted miniscrews were classified into no loading, immediate loading, and delayed loading groups according to the loading time. At 6 weeks after screw placement, the animals were sacrificed, and tissue blocks including the miniscrews were harvested for histological examinations. After analysis of the histological sections, the miniscrews were categorized into three additional groups according to the root proximity: high root proximity, low root proximity, and safe distance groups. Differences in the bone–implant contact (BIC, %) among the root proximity groups and loading time groups were determined using statistical analyses.

Results

No BIC was observed within the bundle bone invaded by the miniscrew threads. Narrowing of the periodontal ligament space was observed in cases where the miniscrew threads touched the bundle bone. BIC (%) was significantly lower in the high root proximity group than in the low root proximity and safe distance groups. However, BIC (%) showed no significant differences among the loading time groups.

Conclusions

Regardless of the loading time, the stability of an orthodontic miniscrew is decreased if it is in contact with the bundle bone as well as the adjacent tooth root.

Comparison of Early Implant Failure Rates Between Subjects With and Without Orthodontic Treatment Before Dental Implantation

The present study compared early dental implant failure rates between patients with and without orthodontic treatment before dental implantation. The data of adults who had undergone dental implantation between January 2007 and December 2016 were analyzed retrospectively. A total of 124 subjects with 255 implants were divided into a treatment group (46 subjects, 85 teeth) consisting of patients who had undergone implant surgery after orthodontic treatment and a control group of patients who had not undergone preimplant orthodontic treatment. Implants that failed before permanent crown fabrication were defined as failures. No significant differences in gender or age were found between the treatment group and controls. No significant differences were found in implant failure rates in either jaw between the treatment and control groups. However, the failure rate was still higher in the treatment group (14.81%) than in the control group (3.28%) for the maxilla. Results of this study demonstrate an increased implant failure rate only in the maxilla of patients who underwent orthodontic treatment before dental implantation, especially implant surgery combined with a sinus lift procedure. Further study with a larger sample size and longer follow-up period is necessary to confirm results of the present study and identify other confounding factors.

Gripping and Anchoring Effects on the Mechanical Strengths of Orthodontic Microimplants

PURPOSE

The aim of this study was to evaluate the mechanical strengths in 5 different designs of orthodontic microimplants by analyzing their configuration of structure.

MATERIALS AND METHODS

Thirty microimplants of 5 types (diameter 1.5 mm: type A, B, and C; diameter 1.3 mm: type D and E) were assessed. All microimplants were manually driven into the artificial bones at a 7-mm depth. The anchor area (AA), gripping area (GA), insertion torque (IT), Periotest value (PTV), and pullout strength (PS) were measured. Intergroup and intragroup comparisons were used to detect their significant differences.

RESULTS

In the intergroup comparison, type D had a least IT (4.5 Ncm). In the PTV analysis, type B had the largest AA (7.76 mm) and its PTV (1.6) was significantly least than the others. In the PS test, type C had the largest GA (2.40 mm) and its PS was the largest. Intragroup comparisons (IT and PS), type A, and type E presented positively significant correlation. GA revealed positive with PS, and AA showed reverse tendency with PTV.

CONCLUSION

The more AA of microimplants, the more stable they are. The more GA of microimplants, the more PS they are. Therefore, type C was better than the others because it had the largest GA and second largest AA.

Effects of implant tilting and the loading direction on the displacement and micromotion of immediately loaded implants: an in vitro experiment and finite element analysis

Purpose

The purpose of this study was to investigate the effects of implant tilting and the loading direction on the displacement and micromotion (relative displacement between the implant and bone) of immediately loaded implants by in vitro experiments and finite element analysis (FEA).

Methods

Six artificial bone blocks were prepared. Six screw-type implants with a length of 10 mm and diameter of 4.3 mm were placed, with 3 positioned axially and 3 tilted. The tilted implants were 30° distally inclined to the axial implants. Vertical and mesiodistal oblique (45° angle) loads of 200 N were applied to the top of the abutment, and the abutment displacement was recorded. Nonlinear finite element models simulating the in vitro experiment were constructed, and the abutment displacement and micromotion were calculated. The data on the abutment displacement from in vitro experiments and FEA were compared, and the validity of the finite element model was evaluated.

Results

The abutment displacement was greater under oblique loading than under axial loading and greater for the tilted implants than for the axial implants. The in vitro and FEA results showed satisfactory consistency. The maximum micromotion was 2.8- to 4.1-fold higher under oblique loading than under vertical loading. The maximum micromotion values in the axial and tilted implants were very close under vertical loading. However, in the tilted implant model, the maximum micromotion was 38.7% less than in the axial implant model under oblique loading. The relationship between abutment displacement and micromotion varied according to the loading direction (vertical or oblique) as well as the implant insertion angle (axial or tilted).

Conclusions

Tilted implants may have a lower maximum extent of micromotion than axial implants under mesiodistal oblique loading. The maximum micromotion values were strongly influenced by the loading direction. The maximum micromotion values did not reflect the abutment displacement values.

The effects of bone density and crestal cortical bone thickness on micromotion and peri-implant bone strain distribution in an immediately loaded implant: a nonlinear finite element analysis

Purpose

This study investigated the effects of bone density and crestal cortical bone thickness at the implant-placement site on micromotion (relative displacement between the implant and bone) and the peri-implant bone strain distribution under immediate-loading conditions.

Methods

A three-dimensional finite element model of the posterior mandible with an implant was constructed. Various bone parameters were simulated, including low or high cancellous bone density, low or high crestal cortical bone density, and crestal cortical bone thicknesses ranging from 0.5 to 2.5 mm. Delayed- and immediate-loading conditions were simulated. A buccolingual oblique load of 200 N was applied to the top of the abutment.

Results

The maximum extent of micromotion was approximately 100 μm in the low-density cancellous bone models, whereas it was under 30 μm in the high-density cancellous bone models. Crestal cortical bone thickness significantly affected the maximum micromotion in the low-density cancellous bone models. The minimum principal strain in the peri-implant cortical bone was affected by the density of the crestal cortical bone and cancellous bone to the same degree for both delayed and immediate loading. In the low-density cancellous bone models under immediate loading, the minimum principal strain in the peri-implant cortical bone decreased with an increase in crestal cortical bone thickness.

Conclusions

Cancellous bone density may be a critical factor for avoiding excessive micromotion in immediately loaded implants. Crestal cortical bone thickness significantly affected the maximum extent of micromotion and peri-implant bone strain in simulations of low-density cancellous bone under immediate loading.

Bone density effects on the success rate of orthodontic microimplants evaluated with cone-beam computed tomography

INTRODUCTION

The purpose of this study was to evaluate the effect of bone densities on the success rate of orthodontic microimplants with cone-beam computed tomography images.

METHODS

We examined 127 orthodontic microimplants implanted into the maxillary buccal alveolar bone of 71 patients (53 female, 18 male; mean age, 19.2 years) with malocclusion. The cortical, cancellous, and total bone densities were measured with Simplant Pro 2011 software (version 13; Materialise, Leuven, Belgium), and the correlations between these measurements and the orthodontic microimplant success rates were evaluated with cone-beam computed tomography.

RESULTS

The overall success rate was 85.0% (108 of 127). Sex, age, and side of placement were not significant factors for success in the results (P >0.05). The density of the cortical bone increased apically (3, 5, and 7 mm) from the alveolar crest, but in the cancellous bone it decreased. Whereas the orthodontic microimplant success rates significantly increased as cancellous bone density and total bone density increased (P <0.01), cortical bone density did not have a significant effect on the success rate (P >0.05).

CONCLUSIONS

The success rate of orthodontic microimplants significantly increased with higher cancellous and total bone densities, whereas cortical bone density did not have a significant effect.

Mechanical influence of thread pitch on orthodontic mini-implant stability

The aim of this study was to evaluate the effect of pitch distance on the primary stability (PS) of orthodontic mini-implants (MIs) in artificial bone. Twenty experimental MIs were allocated to two groups, according to their geometric design: G1 (30o X 0.6 mm) and G2 (45o X 0.8 mm), and inserted into artificial bone of different densities: D1 (0.32 g/cm3) and D2 (0.64 g/cm3). The maximum insertion torque (IT) and removal torque (RT) values were recorded in N.cm. Loss of torque (LT) values were obtained by calculating the difference between the IT and RT. MI mobility was measured by means of a Periotest assessment. Normality and homogeneity were determined by means of the Kolmogorov-Smirnov and Shapiro-Wilk tests, respectively. A two-way ANOVA was used to detect differences between the mini-implant design and density factors. The ANOVA/Tukey tests were used to determine the intergroup difference. Higher IT values were observed for G2 (p ≤ 0.05) in D2. No statistical difference for RT was observed between the groups, whereas G2 presented higher values only for LT (p ≤ 0.05). The Periotest values (PTV) were higher for G1, in comparison with G2, in D1. G1 presented better PS in D2 (IT, RT and LT), whereas G2 was found to be more stable in D1, after evaluation with Periotest.

Interradicular trabecular bone density of the lateral maxilla for temporary anchorage devices--a histomorphometric study

OBJECTIVE

To analyze the interradicular trabecular bone density of the lateral maxilla regarding the insertion of temporary anchorage devices (TADs).

MATERIAL AND METHODS

The material consisted of tissue blocks of autopsy material from 20 subjects (17 male, 3 female, 16 - 63y). The specimens comprised the dentated alveolar bone of the lateral maxilla. The interradicular areas (IRA) from canine to distally of the second molar (IRA 3-4, 4-5, 5-6, 6-7, 7d) were histomorphometrically measured with respect to the hard tissue fraction of the trabecular bone (HTFTB, %) and statistically analyzed.

RESULTS

Histomorphometric measurements showed the following results: Mean HTFTB of IRA 3-4 was 44.08%, of IRA 4-5 31.07%, of IRA 5-6 33.96%, of IRA 6-7 36.33% and of IRA 7d 25.40%. Only the difference between the HTFTB of IRA 3-4 and the other IRAs was statistically significant (p < 0.05). Regarding the minimum and maximum HTFTB value of each IRA, there was a great amount of difference, especially for IRA 3-4: minimum HTFTB was 17.20% and maximum 67.03%.

CONCLUSION

Apart from the IRA between canine and first premolar, the HTFTB in the IRAs of the lateral maxilla have to be classified as low or even moderate. IRA 3-4 should also be considered cautious regarding its minimum values. Thus, it seems that the interradicular trabecular bone density of the lateral maxilla is unfavorable to achieve a good primary stability of TADs.