Clinical evaluation of tooth angle and peripheral bone thickness considering sex and age for implant placement in the maxillary anterior region.

STATEMENT OF PROBLEM: Consideration of the thickness of alveolar bone on both the palatal and labial sides and the inclination angle of teeth is important for immediate implant placement in the maxillary anterior region. However, comprehensive research exploring how sex and age influence the thickness of bone and tooth angle in the maxillary anterior region is lacking. PURPOSE: The purpose of this clinical study was to investigate the effect of sex and age on the thickness of labial and palatal bone and on the tooth inclination angle of maxillary central and lateral incisors using cone beam computed tomography (CBCT) images in an Asian population. MATERIAL AND METHODS: The labial and palatal bone thickness and the inclination angle of maxillary central and lateral incisors were measured from the CBCT images of 149 participants aged between 20 and 65 years. The correlation between the angles of the maxillary central and lateral incisors and sex and age on the tooth angles and thicknesses of labial and palatal bone was determined statistically. RESULTS: A high correlation (R=0.73) was found between the angle of maxillary central and lateral incisors. Men had higher angles of the maxillary central and lateral incisors and thicker palatal bone at the middle and root of the teeth compared with women. In both sexes, the angle and palatal bone thickness of maxillary central incisors were significantly higher than those of maxillary lateral incisors. The angle of both maxillary central and lateral incisors decreased gradually with age, with a difference in angle of over 10 degrees. CONCLUSIONS: The study revealed that women exhibited relatively thinner palatal bone compared with men. Additionally, participants aged between 40 and 65 years exhibited significantly thicker palatal bone compared with younger age groups, potentially providing a larger site for implant placement. Furthermore, tooth angle gradually decreases with age in the maxillary anterior region.

Design and Biomechanical Analysis of Customized Angled Abutment Based on Tooth Inclination Angle for Immediate Implant Placement on Maxillary Anterior Region.

PURPOSE: Finite element analysis and an in vitro experiment were employed to investigate the loading effects of angled abutments, comparing various customized angled abutments derived from the average angle of incisors in patients with a commercial 15°∆ angled abutment, on both the implant and surrounding bone. METHODS: Four customized angled abutment models (21.9°∆, 24.15°∆, 20.22°∆, 33°∆) were developed using cone-beam computed tomography (CBCT) images of incisor inclination from various age groups of patients. 3D maxillary bone models were created from CBCT images of four individual patients. Finite element analysis and in-vitro strain gauge experiments were conducted, applying 100N or 50N of axial or oblique force, to assess the differences in stress/strain between the customized and the commercial 15°∆ angled abutments in both the implants and surrounding bone. RESULTS: Under axial loading, the stress values in the dental implant and surrounding bone were elevated due to the relatively higher angles of the customized angled abutments (21.9°∆, 24.15°∆, 20.22°∆, 33°∆) when compared to the commercial 15°∆ angled abutment; however, under oblique loading the commercial 15°∆angled abutment exhibited higher stress values in both the implant and surrounding bone. For in vitro experiment, there is no statically difference in bone strain between the customized (21.9°∆) and the commercial 15°∆ angled abutments in axial loading. Nevertheless, in oblique loading using a commercial 15°∆ angled abutment induced the higher bone strains. CONCLUSION: Customized angled abutments offer lower stress/strain under oblique loads but higher stress/strain under axial loads compared to commercial ones. Therefore, in the design and application of angled abutments, careful consideration of the occlusal load direction is paramount for achieving biomechanical success of dental implant.

Preoperative assessment of bone density for dental implantation: a comparative study of three different ROI methods.

BACKGROUND: Dental cone beam computed tomography (CBCT) is commonly used to evaluate cancellous bone density before dental implant surgery. However, to our knowledge, no measurement approach has been standardized yet. This study aimed to evaluate the relationship between three different regions of interest (ROI) methods on cancellous bone density at the dental implant site using dental CBCT images. METHODS: Patients' dental CBCT images (n = 300) obtained before dental implant surgery were processed using Mimics (Materialise, Leuven, Belgium). At the potential implant sites, the rectangle, cylinder, and surrounding cylinder ROI methods were used to measure bone density. Repeated measures one-way analysis of variance was performed to compare the three ROI methods in terms of measurement results. Pearson correlation analysis was performed to identify the likely pair-wise correlations between the three ROI methods. RESULTS: The density value obtained using the surrounding cylinder approach (grayscale value [GV],523.56 ± 228.03) was significantly higher than the values obtained using the rectangle (GV, 497.04 ± 236.69) and cylinder (GV,493 ± 231.19) ROI methods in terms of results. Furthermore, significant correlations were noted between the ROI methods (r > 0.965; p < 0.001). CONCLUSIONS: The density measured using the surrounding cylinder method was the highest. The choice of method may not influence the trends of measurement results. TRIAL REGISTRATION: This study was approved by the Institutional Review Board of China Medical University Hospital, No. CMUH111-REC3-205. Informed consent was waived by the Institutional Review Board of China Medical University Hospital, CMUH111-REC3-205, owing to the retrospective nature of the study.

Effects of diameters of implant and abutment screw on stress distribution within dental implant and alveolar bone: A three-dimensional finite element analysis.

Background/purpose: Few studies have investigated the effects of abutment screw diameter in the stress of dental implants and alveolar bones under occlusal forces. In this study, we investigated how variations in implant diameter, abutment screw diameter, and bone condition affect stresses in the abutment screw, implant, and surrounding bone. Materials and methods: Three-dimensional finite element (FE) models were fabricated for dental implants with external hex-type abutments measuring 4 and 5 mm in diameter. The models also included abutment screws measuring 2.0 and 2.5 mm in diameter. Each implant model was integrated with the mandibular bone comprising the cortical bone and four types of cancellous bone. In total, 12 finite element models were generated, subjected to three different occlusal forces, and analyzed using FE software to investigate the stress distribution of dental implant and alveolar bone. Results: Wider implants demonstrated lower stresses in implant and bone compared with standard-diameter implants. The quality of cancellous bone has a minimal impact on the stress values of the implant, abutment screw, and cortical bone. Regardless of occlusal arrangement or quality of cancellous bone, a consistent pattern emerged: larger abutment screw diameters led to increased stress levels on the screws, while the stress levels in both cortical and cancellous bone showed comparatively minor fluctuations. Conclusion: Wider implants tend to have better stress distribution than standard-diameter implants. The potential advantage of augmenting the abutment screw diameter is unfavorable. It may result in elevated stresses in the implant system.

Effects of an augmented reality aided system on the placement precision of orthodontic miniscrews: A pilot study.

Background/purpose: Augmented reality (AR) is gaining popularity in medical applications, which may aid clinicians in achieving improved clinical outcomes. The purpose of this study was to determine the positional and angle errors of orthodontic miniscrew placement by using a self-developed AR aided system. Materials and methods: Cone beam computed tomography (CBCT) and patient printed models were used in in vitro experiments. The participants were divided into a control group and an AR group, in which traditional orthodontic methods and the AR-aided system were used respectively. After the information obtained from the CBCT images and navigation system was combined on the display device, the AR-aided system indicated the planned miniscrew position to guide the clinicians during the placement of miniscrews. Both methods were compared by a senior and a junior dentist, and the position and angle of miniscrew placement were statistically analyzed using Wilcoxon's signed-rank and Mann-Whitney U tests. Results: When the AR-aided system was used, the accuracy of miniscrew placement in the mesiodistal position considerably increased (83%) when the procedure was performed by a senior clinician. In addition, the accuracy of miniscrew placement in the mesiodistal position and the angle of miniscrew placement considerably increased by approximately 67% and 72%, respectively, when the procedure was performed by a junior clinician. The position error of miniscrew placement was smaller for the junior clinician when the AR-aided system was used than for the senior clinician. Conclusion: The AR-aided system improved the accuracy of miniscrew placement regardless of the clinician's level of experience.

Analysis of mandibular molar anatomy in Taiwanese individuals using cone beam computed tomography.

Background/purpose: Before periapical surgery in the mandibular posterior teeth is performed, the thicknesses of the buccal alveolar bone wall and buccolingual root might be a critical issue. This study aimed to assess the anatomical structure of the posterior region of the mandible in Taiwanese individuals using cone-beam computed tomography (CBCT). Materials and methods: The CBCT images of 96 Taiwanese individuals (51 male and 45 female), which included 192 mandibular first molars and 192 mandibular second molars, were imported into medical imaging software to measure the buccal alveolar bone thickness and buccolingual root thickness at 3 mm above the root apex. Statistical analysis was conducted to examine the impact of tooth position, gender, and age on the anatomical position of mandibular molars. Results: The buccal alveolar bone thickness at 3 mm above the root apex of the mandibular second molar demonstrates a significantly higher value when compared to that of the first molar. Nonetheless, concerning the buccolingual root thickness, no significant differences were observed between these two teeth. In addition, the buccal alveolar bone thickness and buccolingual root thickness at 3 mm above the root apex may not be influenced by gender and age. Conclusion: The anatomical structures of the posterior region of the mandible in Taiwanese individuals exhibited variations between the mandibular first and second molars. However, these differences were not influenced by gender or age.

Influence of implant length and insertion depth on primary stability of short dental implants: An in vitro study of a novel mandibular artificial bone model.

Background/purpose: Dental implants are a mainstream solution for missing teeth. For the improvement of dental implant surface treatment and design, short dental implants have become an alternative to various complex bone augmentation procedures, especially those performed at the posterior region of both the maxilla and mandible. The objective of this study was to evaluate the effect of various insertion methods on the primary stability of short dental implants. Materials and methods: Commercial dental implants were inserted into artificial mandibular bone specimens using various insertion methods (equicrestal position, subcrestal position 1.5 mm, and lateral cortical anchorage) in accordance with an implant surgical guide. Insertion torque value (ITV) curves were recorded while implant procedures were performed. Both maximum ITVs (MITVs) and final ITVs (FITVs) were evaluated. Subsequently, Periotest values (PTVs) and implant stability quotients (ISQs) were measured for all specimens. A Kruskal-Wallis test was conducted to analyze the results for four primary stability parameters, and the Dunn test was used for a post hoc pairwise comparison when a difference was identified. Results: For all groups, their mean MITVs ranged from 33.6 to 59.4 N cm, whereas their mean FITVs ranged from 17.5 to 43.5 N cm. Insertion torque value, ISQ, and PTV decreased significantly when implants were inserted into subcrestal positions. When implants were inserted in the lateral bicortical position, the four aforementioned parameters yielded greater values. Conclusion: When 6-mm short implants were inserted in a lateral cortical anchorage position, high primary stability was yielded.

Comparison sealing ability in three bioceramic sealers applied in hydraulic condensation technique by using micro-computed tomography.

Background/purpose: Sealing ability in root canal obturation has always been a key concern for endodontic success. The purpose of this study was to analyze the percentage of voids in root canal space obturated by using single cone hydraulic condensation with different root canal sealers and to compare those with AH Plus sealer. Materials and methods: Experiments were conducted using twenty 3D-printed upper first premolars. After the buccal root canals were prepared using Ni-Ti rotary instruments, the teeth were divided into four groups: the AH Plus, BC sealer, BC sealer HiFlow, and Endoseal MTA groups. All buccal canals were obturated by single-cone hydraulic condensation. All specimens were scanned using micro-computed tomography and the percentage volume of the voids inside and outside the filled materials (Vin and Vout) at three different canal depth intervals were calculated by a Bruker micro-CT software. Differences according to root canal sealers were evaluated statistically using the Kruskal-Wallis test and the Wilcoxon Rank Sum test at a significance level of 0.05. Results: The results indicated that most of the voids were presented near the interface (Vout), the Vin is very small and not significant different between groups. The Vout decreased in the following order: AH Plus(1.837% ± 1.226%)≅BC sealer (1.225% ± 0.836%)>BC sealer Hiflow(0.349% ± 0.071%)>Endoseal MTA(0.203% ± 0.049%). Conclusion: For the percentage volume of voids between the root canal filling material and root canal surface, though the BC sealer Hiflow is slightly larger than Endoseal MTA, which is still much less than BC sealer and AH Plus.

New classification for bone type at dental implant sites: a dental computed tomography study.

OBJECTIVE: This study proposed a new classification method of bone quantity and quality at the dental implant site using cone-beam computed tomography (CBCT) image analysis, classifying cortical and cancellous bones separately and using CBCT for quantitative analysis. METHODS: Preoperative CBCT images were obtained from 128 implant patients (315 sites). First, measure the crestal cortical bone thickness (in mm) and the cancellous bone density [in grayscale values (GV) and bone mineral density (g/cm3)] at the implant sites. The new classification for bone quality at the implant site proposed in this study is a "nine-square division" bone classification system, where the cortical bone thickness is classified into A: > 1.1 mm, B:0.7-1.1 mm, and C: < 0.7 mm, and the cancellous bone density is classified into 1: > 600 GV (= 420 g/cm3), 2:300-600 GV (= 160 g/cm3-420 g/cm3), and 3: < 300 GV (= 160 g/cm3). RESULTS: The results of the nine bone type proportions based on the new jawbone classification were as follows: A1 (8.57%,27/315), A2 (13.02%), A3 (4.13%), B1 (17.78%), B2 (20.63%), B3 (8.57%) C1 (4.44%), C2 (14.29%), and C3 (8.57%). CONCLUSIONS: The proposed classification can complement the parts overlooked in previous bone classification methods (bone types A3 and C1). TRIAL REGISTRATION: The retrospective registration of this study was approved by the Institutional Review Board of China Medical University Hospital, No. CMUH 108-REC2-181.

Effect of Implant Length and Insertion Depth on Primary Stability of Short Dental Implant.

Purpose: To evaluate the effect of insertion depth, bone type, and implant diameter on the primary stability of short implants. Materials and Methods: Commercial dental implants with different lengths (6 and 8 mm; BLX, Straumann) were inserted into artificial bone specimens of good and poor quality at three different depth positions: equicrestal, 1-mm subcrestal, and 2-mm subcrestal. Insertion torque values were recorded spontaneously during the implant procedure. Both maximum insertion torque values (MITVs) and final insertion torque values (FITVs) were recorded. Subsequently, Periotest values (PTVs) and implant stability quotients (ISQs) were measured for all specimens. Results: The mean MITVs of all groups ranged from 31.8 to 46.2 Ncm. However, the mean FITVs of all groups ranged from 8.8 to 29 Ncm. Torque values decreased significantly when the implants were inserted into their final positions. When insertion depth was increased, the PTV and ISQ decreased. Long implants and implants inserted into good-quality bone yielded greater primary stability, and bone quality appeared to have a greater effect on primary stability. Conclusion: When 6-mm short implants are inserted in a subcrestal position, low primary stability may be yielded, particularly in poor-quality bone.

Biomechanical Evaluation of Bone Atrophy and Implant Length in Four Implants Supporting Mandibular Full-Arch-Fixed Dentures.

Residual alveolar ridge resorption often occurs after tooth extraction, which causes issues requiring further prothesis rehabilitation. A treatment concept referred to as all-on-four, involving fixed dentures supported with four implants, was recently developed. The current study aimed to determine the effect of changing bone atrophy and implant length in all-on-four treatments on stress and strain in the surrounding bone of the implant. A three-dimensional finite element method was used in this research. The stress analysis was conducted with von Mises stress values. Two types of synthetic jawbone models with mild and moderate atrophy were used. Furthermore, two different implant lengths with a similar implant design and diameter were selected, and they were classified into eight models. Then, the bone model was assessed via a computed tomography (CT) scan and was transformed into a virtual model in Geomagic and SolidWorks with implant rebuilding. After modifying bone atrophy, the von Mises stresses in the surrounding bone of the implant were as follows: mild type 2 < mild type 3 < moderate type 3 < moderate type 4. The bone quantity change rate increased more than when bone conditions were limited. Compared with changes in implant lengths, the stresses in the peri-implant surrounding bone were generally higher in the 9 mm implant length group than in the 11.5 mm group. However, the results did not significantly differ. In conclusion, the von Mises stress and strain increased in the models with moderate atrophy and low-density trabecular bone. Hence, bone atrophy and its presurgical diagnosis in long-term implant prognosis are crucial.

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.

The Effects of Insertion Approach on the Stability of Dental Implants.

Dental implant surgery involves the insertion of a dental implant into the alveolar bone; the success of the surgery depends on the initial stability of the implant. The objective of this study was to examine the effects of dental implant insertion approaches in clinical surgery and in accordance with the standards of American Society for Testing and Materials on initial implant stability. Three insertion approaches were used for dental implant placement (Branemark Systems NobelSpeedy Groovy, Nobel Biocare AB, Gothenburg, Sweden) in two types of artificial bone-good bone (GB) and poor bone (PB). The three insertion approaches were as follows: (1) continuous rotation insertion (CRI): using a torque testing machine to continuously screw in an implant to completion and (2 and 3) intermittent rotation insertion (IRI)_90 and IRI_80: using CRI to bury an implant to 90% and 80% of its full length followed by IRI to complete the implantation, respectively. The maximum insertion torque value (ITV), periotest value (PTV), and implant stability quotient (ISQ) were measured and compared. The results indicated that bone quality and insertion approach both affected implant stability. Insertion approaches affected all three implant stability indicators differently in the GB and PB groups (p = 0.008). In GB groups, the insertion approach primarily affected ITV, whereas in PB groups, it primarily affected PTV. The effect of the insertion approach was less apparent for ISQ. Overall, in both the GB and PB groups, the implant stability for IRI_80 was greater than that for IRI_90, and the implant stability for IRI_90 was greater than that for CRI. Future in vitro studies should adopt an insertion approach that complies with the clinical practice for dental implant surgery. Dentists should adjust the timing for IRI in dental implant surgery to achieve greater initial dental implant stability.

Biomechanical Analyses of Porous Designs of 3D-Printed Titanium Implant for Mandibular Segmental Osteotomy Defects.

Clinically, a reconstruction plate can be used for the facial repair of patients with mandibular segmental defects, but it cannot restore their chewing function. The main purpose of this research is to design a new three-dimensionally (3D) printed porous titanium mandibular implant with both facial restoration and oral chewing function reconstruction. Its biomechanical properties were examined using both finite element analysis (FEA) and in vitro experiments. Cone beam computed tomography images of the mandible of a patient with oral cancer were selected as a reference to create 3D computational models of the bone and of the 3D-printed porous implant. The pores of the porous implant were circles or hexagons of 1 or 2 mm in size. A nonporous implant was fabricated as a control model. For the FEA, two chewing modes, namely right unilateral molar clench and right group function, were set as loading conditions. Regarding the boundary condition, the displacement of both condyles was fixed in all directions. For the in vitro experiments, an occlusal force (100 N) was applied to the abutment of the 3D-printed mandibular implants with and without porous designs as the loading condition. The porous mandibular implants withstood higher stress and strain than the nonporous mandibular implant, but all stress values were lower than the yield strength of Ti-6Al-4V (800 MPa). The strain value of the bone surrounding the mandibular implant was affected not only by the shape and size of the pores but also by the chewing mode. According to Frost's mechanostat theory of bone, higher bone strain under the porous implants might help maintain or improve bone quality and bone strength. The findings of this study serve as a biomechanical reference for the design of 3D-printed titanium mandibular implants and require confirmation through clinical investigations.

Biomechanical Evaluation and Factorial Analysis of the 3-Dimensional Printing Self-Designed Metallic Reconstruction Plate for Mandibular Segmental Defect.

PURPOSE: Reconstruction plates are frequently used to treat mandibular segmental defects. The aim of this study is to compare the biomechanical performance of a 3-dimensional-printed self-designed titanium alloy reconstruction plate with that of the traditional reconstruction plate in mandible reconstruction. The analyzed parameters of the self-designed reconstruction plate, including plate length (100 mm and 125 mm), plate thickness (2.1, 2.4, and 2.7 mm), and bone mass (100, 75, and 50%), were also evaluated. METHODS: An artificial mandible with anatomical geometry was used to develop the self-designed reconstructed plate. Both in vitro experiments and finite element simulations were performed for the biomechanical comparison of the self-designed and traditional reconstruction plates. In finite element analysis, 3 major muscle forces of mandible movement were set as the loading condition, and the displacement of the condyle was fixed in all directions as the boundary condition. RESULTS: The biomechanical performances (stresses in the plate and strains in bone) of the self-designed reconstruction plate were superior to those of the traditional plate. Factorial analysis indicated that plate length and thickness had significant effects on decreasing stresses of the plate and mandibular bone. CONCLUSIONS: The self-designed reconstruction plate might have a benefit to reduce the stresses/strains in plate itself and surrounding bone.

Incisor liability and its effects among East Asian children.

BACKGROUND/PURPOSE: Incisor liability is the discrepancy in the sum of the mesiodistal crown width between the primary and permanent incisors. Incisor liability affects the integrity and eruption of the permanent incisors during the transition from the primary to permanent dentition. This study investigated the incisor liability in the primary dentition of Taiwanese children. METHODS: The digital periapical films of 203 upper arches of 105 boys and 98 girls and 195 lower arches of 119 boys and 76 girls aged between 3 and 6 years were selected in this retrospective study. The mesiodistal crown widths of the primary and permanent incisors were measured using the medical imaging software for both arches. Differences in incisor liability values were statistically analyzed. RESULTS: The mean ± standard deviation of the incisor liability values were 8.32 ± 1.88 and 6.91 ± 1.13 mm for the upper and lower arches, respectively, in all children. The incisor liability was closely related with the total crown widths of the permanent incisors for upper and lower arches. The incisor liability values were higher among boys than girls for the upper but not lower arch. CONCLUSION: Incisor liability differs depending on ethnicity. In Taiwanese children, incisor liability was closely related with the crown widths of the permanent incisors. The incisor liability values of boys were higher than those of girls in the upper arch but not the lower arch.

Effects of Gender and Age in Mandibular Leeway Space for Taiwanese Children.

PURPOSE: Leeway space is clinically crucial in pediatric dentistry because it is utilized to resolve tooth crowding and allow the first molars to drift mesially to establish a Class I molar relationship in the later stages of mixed dentition. This study investigated leeway space in the mixed dentition of Taiwanese children of different sexes and ages. MATERIALS AND METHODS: The digital panoramic dental films of 182 lower arches of 119 boys and 63 girls aged 5-10 years were analyzed in this retrospective study. The mesiodistal crown widths of the primary canines and first and second molars and the permanent canines and first and second premolars were measured using medical imaging software. Differences in leeway space were statistically analyzed. RESULTS: The average leeway space was 1.29 ± 1.48 mm on each side of the lower arch. The leeway space of children aged 5-6 years was significantly greater than that of children aged 7-8 years. No gender difference in crown width was discovered, except with regard to the primary first molar. Although no gender difference in leeway space was observed, permanent teeth affected leeway space more for girls than for boys. CONCLUSION: In Taiwanese children, although leeway space does not differ by sex, age affects leeway space. However, permanent tooth size has an influence on the leeway space of girls.

Biomechanical Effect of Orthodontic Treatment of Canine Retraction by Using Metallic Orthodontic Mini-Implant (OMI) Covered with Various Angles of Revolving Cap.

OBJECTIVE: This study evaluated the biomechanical effects of a metallic orthodontic mini-implant (OMI) covered with various types of angled revolving cap on the peri-OMI bone and the canine periodontal ligament (PDL) by finite element (FE) analyses. MATERIALS AND METHODS: Three-dimensional FE models included comprised cortical bone and cancellous bone of the maxilla, and the OMIs were created. The forces (0.98 N) pulled in both the canine hook and the revolving cap, pulling towards each other in both directions as loading conditions. The upper surface of the maxilla was fixed as a boundary condition. RESULTS: The bone stresses were increasing in the models by using OMI covered with a revolving cap as compared with that in the conventional model (in which only the OMI was placed). However, no obvious differences in bone stresses were observed among the models with various types of angled revolving cap. The minimum principal strain in the canine PDL was highest for condition 180T, followed by condition 180L. However, the maximum differences in the values between each experimental model and the conventional model were around 5%. CONCLUSION: This study showed no obvious effects in decreasing or increasing stress/strain in bone and PDL by using various types of angled revolving cap covered metallic mini-implant in orthodontic treatment of canine retraction.

Assessment of the Retromolar Canal in Taiwan Subpopulation: A Cross-Sectional Cone-Beam Computed Tomography Study in a Medical Center.

The retromolar canal is an anatomical variation that occurs in the mandibular bone. The retromolar canal typically originates in the mandibular canal on the distal side of the third molar and extends forward and upward to the retromolar foramen (RMF), which contains the neurovascular bundle. Accidentally damaging the neurovascular bundle in the retromolar canal during the extraction of the third molar, dental implant surgery, or maxillofacial orthognathic surgery may lead to subsequent complications such as incomplete local anesthesia, paresthesia, and bleeding during operation. The objective of this study was to investigate the prevalence of the RMF in the Taiwanese population in a medical center by using dental cone-beam computed tomography (CBCT) and to identify the position of the RMF in the mandibular bone. The dental CBCT images for the mandibular bone of 68 hemi-mandible were uploaded to the medical imaging software Mimics 15.1 to determine the prevalence of the RMF in the Taiwanese population and the three positional parameters of the RMF in the mandibular bone: (1) The diameter of the RMF, (2) the horizontal distance from the midpoint of the RMF to the distal cementoenamel junction of the second molar, and (3) the vertical distance from the midpoint of the RMF to the upper border of the mandibular canal. Seven RMFs were observed in the 68 hemi-mandibles. Thus, the RMF prevalence was 10.3%. In addition, the diameter of the RMF was 1.41 ± 0.30 mm (mean ± standard deviation), the horizontal distance from the midpoint of the RMF to the distal cementoenamel junction of the the second molar was 12.93 ± 2.87 mm, and the vertical distance from the midpoint of the RMF to the upper border of the mandibular canal below second molar was 13.62 ± 1.3487 mm. This study determined the prevalence of the RMF in the Taiwanese population in a medical center and its relative position in the mandibular bone. This information can provide clinicians with a reference for posterior mandible anesthesia and surgery to ensure medical safety.

Can Male Patient's Age Affect the Cortical Bone Thickness of Jawbone for Dental Implant Placement? A Cohort Study.

Dental implants are among the most common treatments for missing teeth. The thickness of the crestal cortical bone at the potential dental implant site is a critical factor affecting the success rate of dental implant surgery. However, previous studies have predominantly focused on female patients, who are at a high risk of osteoporosis, for the discussion of bone quality and quantity at the dental implant site. This study aimed to investigate the effect of male patients' age on the crestal cortical bone of the jaw at the dental implant site by using dental cone-beam computed tomography (CBCT). This study performed dental CBCT on 84 male patients of various ages to obtain tomograms of 288 dental implant sites at the jawbone (41 sites in the anterior maxilla, 95 in the posterior maxilla, 59 in the anterior mandible, and 93 in the posterior mandible) for measuring the cortical bone thickness. A one-way analysis of variance and Scheffe's test were performed on the measurement results to compare the cortical bone thickness at implant sites in the four jaw areas. The correlation between male patient age and cortical bone thickness at the dental implant site was determined. The four jaw areas in order of the cortical bone thickness were as follows: posterior mandible (1.07 ± 0.44 mm), anterior mandible (0.99 ± 0.30 mm), anterior maxilla (0.82 ± 0.32 mm), and posterior maxilla (0.71 ± 0.27 mm). Apart from dental implant sites in the anterior and posterior mandibles, no significant correlation was observed between male patients' age and the cortical bone thickness at the dental implant site.