Cone beam computed tomographic analysis of the spatial limitation during mandibular arch distalization.

BACKGROUND: In the literature, attempts are seldom made to quantify spatial limitation during mandibular arch distalization. This study aimed to investigate the spatial limitations associated with cortical contact with the mandibular second molar during mandibular arch distalization. METHODS: The study population included 67 individuals who had undergone cone beam computed tomography (CBCT) (34 male and 33 female; mean age: 23.9 ± 2.72 years). The total ridge width, alveolar housing width, and root width were measured to evaluate the buccolingual limit. The space distal to the molar root represented the mesiodistal limit. The influence of sex, right versus left side, root-contact condition, malocclusion category, and presence of wisdom teeth were evaluated. RESULTS: The rate of cortical contact was 49.3% before any orthodontic movement. No significant differences were observed in the alveolar width according to sex (male vs female), side assessed (right vs left), wisdom teeth (present vs absent), or malocclusion category. The ridge width and the alveolar width were smaller in the contact group than in the non-contact group (P < 0.01). The group with wisdom teeth showed a larger available distalization distance, but a significant difference was observed only near the alveolar crest. CONCLUSIONS: Both ridge width and available distalization distance were limiting factors for mandibular teeth distalization. For cases in which whole-arch distalization is planned, CBCT is recommended before treatment, especially for non-extraction treatment. This approach ensures safe and predictable tooth movement.

Recognizing the peak bone mass (age 30) as a cutoff point to achieve the success of orthodontic implants.

The aim of present study was to investigate the critical risk factor (age 30: peak bone mass) to evaluate the success of orthodontic implants. A total of 426 orthodontic implants were placed in 270 patients as orthodontic anchorages. Data were analyzed according to patient's characteristics, location of placement, implant categories, and orthodontic force. The young patients were the age ≤ 30 years and the older patients were the age > 30 years. Statistical analysis was performed and a p value < 0.05 was considered to indicate statistical significance. The Chi-square or Fisher exact test was used depending on sample sizes. The null hypothesis was no statistically significant correlation between age ≤ 30 years and age > 30 years. The overall success rate (with and without predrill) was 89.2%. The success rate of orthodontic implants was significantly larger in younger patients (89.9%) than in older patients (76.1%). Recognizing age-related factor in the success rates, older patient (> 30 years) were significant lower than young patients (≤ 30 years) in the gender (female and male), malocclusion (Class II), facial pattern (ortho and hyperdivergent), location (infrazygomatic crest), jaw (maxilla), side (right), material (titanium and stainless), length (9 mm and 10 mm), diameter (2 mm), load (< 3 weeks), and force (intrusion). Therefore, the null hypothesis was rejected. Age 30 is a cutoff point to achieve the success of orthodontic implants. The success rates of older patients (age > 30 years) were significant lower than young patients (age ≤ 30 years), especially in female.

Morphometric analysis of the cranial base in Asians.

This study tested the hypothesis that developmental heterogeneity in cranial base morphology increases the prevalence of Class III malocclusion and mandibular prognathism in Asians. Thin-plate spline (TPS) graphical analysis of lateral cephalometric radiographs of the cranial base and the upper midface configuration were compared between a European-American group (24 females and 31 males) and four Asian ethnic groups (100 Chinese, 100 Japanese, 100 Korean and 100 Taiwanese; 50 females and 50 males per group) of young adults with clinically acceptable occlusion and facial profiles. Procrustes analysis was performed to identify statistically significant differences in each configuration of landmarks (P < 0.001). The TPS graphical analysis revealed that the greatest differences of Asians were the horizontal compression and vertical expansion in the anterior portion of the cranial base and upper midface region. The most posterior cranial base region also showed horizontal compression between the basion and Bolton point, with forward displacement of the articulare. Facial flatness and anterior displacement of the temporomandibular joint, resulting from a relative retrusion of the nasomaxillary complex and a relative forward position of the mandible were also noted. These features that tend to cause a prognathic mandible and/or retruded midface indicate a morphologic predisposition of Asian populations for Class III malocclusion.

Trueness of intraoral scanning for different tooth-size arch-length deficiencies.

Background/purpose: As science and technology continue to advance, the utilization of intraoral scanners (IOSs) has become increasingly popular in the orthodontic workflow. The aim of this study was to discuss whether the degree of crowded arches affects scan accuracy. Materials and methods: Three different crowding levels of dental models (model MI: mild, model MO: moderate, and model SE: severe) were scanned using both an IOS and desktop scanner. Stereolithographic files were obtained and superimposed via CAD software to calculate differences between each measuring point of a model and the farthest corresponding point. The deviations from three models were compared with statistical analysis. Results: The trueness of different crowding arches showed that the deviation value of model SE was the maximum, followed by model MI, and model MO in the maxillary arch. In the mandibular arch, the order of the deviation from greatest to least was firstly model SE, then model MO, and model MI. Significant differences were observed among the maxillary models (P < 0.001), but there was no significant difference between models in the mandible (P = 0.669). Conclusion: The trueness of the three crowded arches is in the clinically acceptable range. The degree of crowding increases, the trueness of scanning at each position decreases. In the maxillary arch, more severe crowding corresponds to higher deviations. In the mandible, the degree of crowding is not explicitly related to the maximum deviation; therefore, the clinician should notice the deviation when using IOSs for crowding cases.

Orthodontic treatment for a mandibular prognathic girl of short stature under growth hormone therapy.

This report presents a case of a 12-year-old girl with maxillary deficiency, mandibular prognathism, and facial asymmetry, undergoing growth hormone (GH) therapy due to idiopathic short stature. Children of short stature with or without GH deficiency have a deviating craniofacial morphology with overall smaller dimensions; facial retrognathism, especially mandibular retrognathism; and increased facial convexity. However, a complete opposite craniofacial pattern was presented in our case of a skeletal Class III girl with idiopathic short stature. The orthodontic treatment goal was to inhibit or change the direction of mandibular growth and stimulate the maxillary growth of the girl during a course of GH therapy. Maxillary protraction and mandibular retraction were achieved using occipitomental anchorage (OMA) orthopedic appliance in the first stage of treatment. In the second stage, the patient was treated with a fixed orthodontic appliance using a modified multiple-loop edgewise archwire technique of asymmetric mechanics and an active retainer of vertical chin-cup. The treatment led to an acceptable facial profile and obvious facial asymmetry improvement. Class I dental occlusion and coincident dental midline were also achieved. A 3½-year follow-up of the girl at age 18 showed a stable result of the orthodontic and dentofacial orthopedic treatment. Our case shows that the OMA orthopedic appliance of maxillary protraction combined with mandibular retraction is effective for correcting skeletal Class III malocclusion with midface deficiency and mandibular prognathism in growing children with idiopathic short stature undergoing GH therapy.

Modern therapy for severe alveolar ridge atrophy.

This clinical report illustrates a modern method for oral rehabilitation of severe edentulous atrophic ridge. Shallow vestibule and small denture-bearing area of the maxilla provide insufficient retention, and only the symphyseal region of the mandible has obvious alveolar ridge. The surgery of deepening vestibule of the maxilla ridge was done by using tentative miniscrew combined with old denture and soft liner. The osseointegrated dental implants were installed over symphyseal region of the mandible to act as retentive devices for prostheses. In addition, functional reline with rebase material to build buccal-tongue contact over the retromolar area after denture delivery obtained high satisfaction from the patient. Many clinical conditions cannot be managed solely with implants or preprosthetic surgery alone, whereas a combination of the 2 can achieve successful outcome.

Correlation between facial asymmetry of skeletal class III jaw relationship and morphology of the temporomandibular joint: A cone beam computed tomography study.

Background/purpose: Facial asymmetry is a common dentofacial deformity especially in skeletal Class III jaw relation. The purpose of this study was to evaluate the condylefossa relationship of Taiwanese people in skeletal Class III jaw relation with or without facial asymmetry by CBCT image. Materials and methods: CBCT images were collected from Kaohsiung Medical University Hospital and then divided into symmetric Class III group (Menton [Mn] deviation â‰¦ 4 mm) and asymmetric Class III group (Menton [Mn] deviation > 4 mm). Maxilla deviation, upper and lower dental midline deviation, joint space, condylar axial angle and condylar volume was measured. Independent t test was used for comparison between groups, and paired t test was applied for comparison between both condyles within each group. The Pearson correlation coefficient was used to analyze the correlation between skeletal midline deviations and joint morphology. Results: No significant difference was found in joint space between groups or between sides within each group, but we can find a significant difference in axial condylar angle easurement which was greater on the non-deviation side of condyle. Significant lesser condylar volume was also found on the deviation side in asymmetric group. There had a significant positive correlation between Mn point deviation, geometric center difference and condylar volume ratio. Conclusion: These results demonstrated that in the side with greater mandibular growth potential, the axis rotation in axial plane would be greater. In the side with lesser mandibular growth potential, the total condyle volume would be lesser, even though with large variation.

Biomechanical analysis of alveolar bone stress around implants with different thread designs and pitches in the mandibular molar area.

Threaded implants have been shown to play an important role in increasing mechanical osseointegration. The aim of this study was to determine bone stress distribution when using different types of implant thread pitches and designs. Five 3D finite element models were constructed to simulate bone stresses induced in implant bodies with two types of thread form: triangular ("Tri" prefix) and trapezoidal ("Trap" prefix). The former had thread pitches of 0.8, 1.2, and 1.6 mm, while the latter had thread pitches of 1.2 and 1.6 mm. A biting load of 143 N was applied vertically and obliquely to the occlusal central fossa of the crown. The main effects of each level of the three factors investigated (loading type, pitch, and thread form) in terms of the stress value were computed for all models. Results indicated that the loading type was the main factor of influence on the peak compressive stress of the alveolar bone. Optimal thread pitch was 1.2 mm for a triangular-thread implant, and a trapezoidal-threaded implant with thread pitch of 1.6 mm had the lowest stress value among trapezoidal-threaded implants. This study concluded that each thread form has its unique optimal thread pitch with regard to lower concentration of bone stress. Clinically, this study suggests that in biomechanical consideration, thread pitch exceeding 0.8 mm is more appropriate for a screwed implant. For clinical cases that require greater bone-implant interface, trapezoidal-threaded implants with thread pitch of 1.6 mm provide greater primary stability and lower concentration of bone stress under different loading directions.

Changes in Facial Profile after Modified Anterior Maxillary Subapical Osteotomy.

(1) Background: This study explored the effects of modified anterior maxillary subapical osteotomy (AMSO) on facial profile changes in patients with bimaxillary protrusion. (2) Methods: Cephalograms of patients were collected preoperatively and over 2 months postoperatively. The following landmarks were recorded: pronasale (Prn), subnasale (Sn), labrale superius (Ls), anterior nasal spine (ANS), and incisor superius (Is). The following distances and angles were measured: ANS-Prn, ANS-Sn, ANS-Ls, Is-Sn, Is-Ls, SNA angle, and nasolabial (NLA) angle. (3) Results: Is and ANS were significantly retracted by 7.3 and 2.3 mm, respectively. Soft tissue landmarks (Prn, Sn, and Ls) were significantly retracted (1.2, 1.6, 4.4 mm, respectively). Postoperative changes in soft/hard tissue ratios were 0.54, 0.72, 0.31, and 0.60 for Prn/ANS, Sn/ANS, ANS/Is, and Ls/Is, respectively. The NLA angle was increased significantly by 7.1°. (4) Conclusions: The horizontal soft/hard tissue ratios of Sn/Is, ANS/Is, and Ls/Is were 0.22, 0.31, and 0.60, respectively. The NLA angle was increased significantly by 7.1°. The modified AMSO provides an increased blood supply, allows for direct vision, and results in fewer complications than other AMSO methods.

Craniofacial skeletal dysplasia of opposite-sex dizygotic twins.

Craniofacial skeletal dysplasia can lead to different skeletal malocclusions. Both environmental factors and heredity contribute to the formation of malocclusions. There are strong familial tendencies in the development of Angle's Class II and III malocclusions. Cases such as opposite-typed (Class II and III) malocclusions with skeletal and dentoalveolar discordance in siblings or dizygotic (DZ) twins have seldom been reported. We describe the rare case of a pair of opposite-sex DZ twins with completely different skeletal malocclusions, and discuss the clinical considerations for treatment. The patients were twins aged 13 years and 4 months. The girl had mandibular prognathism and a Class III dentoskeletal relationship, whereas the boy had skeletal Class II with mandibular retrusion. Several morphological traits have been implicated with hormonal effect. However, there was no evidence of whether the masculinization effect had any impact on jaw size in the female fetus or whether this effect lasted into adolescence. We suggest that, although DZ twins share the same growth environment, genetic or other unknown extrinsic factors can result in discordance of characteristics of the craniofacial skeleton, dentition, and occlusion.

Treatment of adult Class III malocclusions with orthodontic therapy or orthognathic surgery: receiver operating characteristic analysis.

INTRODUCTION: The aim of this study was to distinguish between orthodontic patients with skeletal Class III malocclusions requiring surgery and those not requiring surgery by conducting a receiver operating characteristic analysis of cephalometric variables. METHODS: We used lateral cephalometric radiographs of 80 subjects (40 nonsurgical and 40 surgical patients) with Class III malocclusions and obtain 25 cephalometric measurements using computerized cephalometry. Of these, 14 measurements showed statistically significant differences between the 2 groups. Receiver operating characteristic analysis was used to determine the ability of the 14 cephalometric measurements in distinguishing between the 2 groups. Six statistically validated and clinically relevant measurements were used to obtain the optimum discriminant effectiveness. RESULTS: For a Class III malocclusion patient with any 4 of these 6 measurement criteria, the sensitivity was 88% and the specificity was 90% in determining the need for surgical treatment: overjet, ≤-4.73 mm; Wits appraisal, ≤-11.18 mm; L1-MP angle, ≤80.8°; Mx/Mn ratio, ≤65.9%; overbite, ≤-0.18 mm; and gonial angle, ≥120.8°. CONCLUSIONS: We selected 6 cephalometric measurements as the minimum number of discriminators required to obtain the optimum discriminant effectiveness of diagnosis between surgical and nonsurgical treatment of skeletal Class III malocclusions.

Changes in Tongue Area, Pharyngeal Area, and Pharyngeal Airway Velocity after Correction of Mandibular Prognathism.

This study aimed to investigate the correlation between the amount of mandibular setback, and the related changes of the tongue area, pharyngeal area, and pharyngeal airflow velocity. Twenty-five patients treated for mandibular prognathism, and serial cephalograms were obtained (T1: preoperation, T2: more than one year postoperation). The postoperative area of the tongue, pharyngeal airway space, and pharyngeal airflow velocity were investigated. Statistical analysis was performed with the Student t-test and Pearson correlation. The amount of mandible setback was significant after surgery (12.8 mm; p < 0.001). The pharyngeal area was significantly reduced 115.5 mm2 (p = 0.046). There was a slight reduction of the tongue area (43.2 mm2; p = 0.305) and an increase of pharyngeal airflow velocity (0.3 m/s; p = 0.133). The Pearson correlation coefficient test showed no statistical significance among the amount of horizontal setback and vertical movement of the mandible, such as the reductions in the tongue area, the pharyngeal airway space, and the increase in pharyngeal airflow velocity. Larger amounts of mandibular setback caused a significant reduction of pharyngeal airway area, but without significant changes of the tongue area and pharyngeal airflow velocity.

Differences in the Buccal Bone Marrow Distance of ≤0.8 mm in the Mandible of Patients Undergoing Sagittal Split Ramus Osteotomy among the Different Skeletal Patterns: A Retrospective Study.

This study investigated the relationship between the thickness of the ramus and skeletal patterns using cone-beam computed tomography (CBCT) for sagittal split ramus osteotomy. Ninety participants were categorized into three skeletal patterns (Class I, Class II, and Class III). The first vertical slice (slice 0) was observed in the intact mandibular canal, and then moved forward to 40 mm (slice 21) with a 2 mm interval. The thickness of buccal bone marrow (B value) was measured. A B value of ≤0.8 mm was considered to be the major risk factor causing the occurrence of postoperative lower lip paresthesia. There were 461 sides with a B value of ≤0.8 mm. There was a significant difference in the skeletal patterns [Class III (198 sides: 15.7%) > Class I (159 sides: 12.6%) > Class II (104 sides: 8.3%)]. Class II participants had significantly larger B values (2.14 to 3.76 mm) and a lower occurrence rate (≤0.8 mm) than those of Class III participants (1.5 to 3 mm) in front of the mandibular foramen (from 6 mm to 20 mm). Class III participants had significantly shorter buccal bone marrow distance and a higher occurrence rate of B values (≤0.8 mm) than Class II.

Importance in the Occurrence Distribution of Minimum Oropharyngeal Cross-Sectional Area in the Different Skeletal Patterns Using Cone-Beam Computed Tomography.

PURPOSE: Obstructive sleep apnea is a condition involving repetitive partial or complete collapse of the pharyngeal airway, especially in patient with mandibular hypoplasia. The present study investigated the differences between the volume of the oropharyngeal airway and the minimum axial area in three skeletal patterns through the use of cone-beam computed tomography (CBCT). MATERIALS AND METHODS: CBCT scans of 147 patients were collected to measure the upper oropharyngeal airway volume (UOV), lower oropharyngeal airway volume (LOV), upper oropharyngeal airway area (UOA), minimum upper oropharyngeal airway area (MUOA), lower oropharyngeal airway area (LOA), minimum lower oropharyngeal airway area (MLOA), anatomical structures (orbitale, Or; porion, Po; pogonion, Pog; hyoid, H; second cervical vertebra, C2; fourth cervical vertebra, C4), and relevant angles. Statistical analysis was performed using analysis of variance and Pearson's test. RESULTS: Compared with patients in Class II, those in Class III and Class I exhibited a significantly anterior position of H and Pog. The vertical positions of H and Pog revealed no significant difference between the three skeletal patterns. Patients in skeletal Class III exhibited significantly larger oropharyngeal area (UOA, MUOA, LOA, MLOA) and oropharyngeal airway (UOV and LOV) than those in skeletal Class II did. The horizontal position of Pog had a moderately significant correlation with UOA (r = 0.471) and MUOA (r = 0.455). CONCLUSION: Patients in skeletal Class II had significantly smaller oropharyngeal airway areas and volumes than those in Class III did. The minimum oropharyngeal cross-sectional area had a 67% probability of occurrence in the upper oropharyngeal airway among patients in Class I and Class II and a 50% probability of occurrence among patients in Class III.

Bone stress analysis of various angulations of mesiodistal implants with splinted crowns in the posterior mandible: a three-dimensional finite element study.

PURPOSE: Ideally, implants for dental prostheses should be placed parallel to each other. However, anatomic limitations sometimes make nonparallel implants necessary. The purpose of this study was to determine the bone stresses on implants tilted at various angles and to determine what arrangements might carry a higher risk of failure. MATERIALS AND METHODS: Three-dimensional finite element models were constructed using the mean values measured for the Asian mandible in the first and second molar areas. Eight implants were divided into three tilting types: parallel implants (P1(PP), P2(MM), and P3(DD)), convergent implant apices (C1(PD) and C2(MP)), and divergent implant apices (D1(DP), D2(DM), and D3(PM)). A biting load of 200 N was applied vertically and obliquely on the occlusal central fossa of the splinted crowns. The main effects of each level of the three investigated factors (loading type, relationship of implant apices, and distal tilting of one or both implants) in terms of the stress values were computed for all models. RESULTS: The loading type was the main factor affecting the stress in bone when comparing implant apices and distal tilting of the implant body. When loading was combined with distal tilting, the stress values were significantly increased, especially in models P3(DD) and C1(PD). CONCLUSION: The loading type is the main factor affecting the stress distribution for different implantation arrangement. Moreover, placement of the implants with distal tilting should be avoided in the posterior mandible.

Comparison of Different Cervical Finish Lines of All-Ceramic Crowns on Primary Molars in Finite Element Analysis.

This study aimed to conduct a stress analysis of four types of cervical finish lines in posterior all-ceramic crowns on the primary roots of molar teeth. Four different types of finish lines (shoulder 0.5 mm, feather-edged, chamfer 0.6 mm, and mini chamfer 0.4 mm) and two all-ceramic crown materials (zirconia and lithium disilicate) were used to construct eight finite element primary tooth models with full-coverage crowns. A load of 200 N was applied at two different loading angles (0° and 15°) so as to mimic children's masticatory force and occlusal tendency. The maximum stress distribution from the three-dimensional finite element models was determined, and the main effect of each factor (loading type, material, and finish line types) was evaluated in terms of the stress values for all of the models. The results indicated that the loading type (90.25%) was the main factor influencing the maximum stress value of the primary root, and that the feather-edged margin showed the highest stress value (p = 0.002). In conclusion, shoulder and chamfer types of finish lines with a 0.4-0.6 mm thickness are recommended for deciduous tooth preparation, according to the biomechanical analysis.

Fracture Resistance of Monolithic Zirconia Crowns in Implant Prostheses in Patients with Bruxism.

The aim of this study is to determine the minimum required thickness of a monolithic zirconia crown in the mandibular posterior area for patients with bruxism. Forty-nine full zirconia crowns, with seven different occlusal thicknesses of 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 mm, were made by using a computer-aided design/computer-aided manufacturing system (CAD/CAM). Seven crowns in each group were subjected to cyclic loading at 800 N and 5 Hz in a servohydraulic testing machine until fracture or completion of 100,000 cycles. Seven finite element models comprising seven different occlusal thicknesses of 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 mm were simulated using three different loads of vertical 800 N, oblique 10 degrees 800 N, and vertical 800 N + x N torque (x = 10, 50, and 100). The results of cyclic loading tests showed that the fracture resistance of the crown was positively associated with thickness. Specimen breakage differed significantly according to the different thicknesses of the prostheses (p < 0.01). Lowest von Mises stress values were determined for prostheses with a minimal thickness of 1.0 mm in different loading directions and with different forces. Zirconia specimens of 1.0 mm thickness had the lowest stress values and high fracture resistance and under 800 N of loading.

Comparison of Pharyngeal Airway between Mandibular Setback Surgery Patients (Skeletal Class III) and Nonsurgery Patients (Skeletal Classes I and II).

PURPOSE: We investigated the pharyngeal airway dimensions and their correlations in patients who underwent mandibular setback surgery versus those who did not. MATERIALS AND METHODS: One hundred and sixty cephalometric radiographs (120 patients) were obtained from patients with three skeletal malocclusion classifications: Class I and Class II in the nonsurgery group and Class III in the surgery group (preoperative and postoperative cephalograms). The following dimensions were measured: nasopharyngeal airway (NOP), uvulopharyngeal airway (UOP), shortest distance from the posterior tongue to the pharyngeal wall (TOP), and distance from the epiglottis to the pharyngeal wall (EOP). Paired t test, one-way analysis of variance, and Pearson correlation coefficients were used for statistical analysis. RESULTS: Preoperatively, UOP and TOP of skeletal Class III patients (15.2 mm and 16.6 mm) were significantly larger than those of skeletal Class II (11.5 mm and 12 mm) and Class II (12.3 mm and 12.9 mm) patients, respectively. No differences were observed in EOP between the three skeletal patterns. The hyoid bone of Class III patients was significantly anterior to that of Class I/II patients. Furthermore, UOP had a moderate negative correlation with soft palate length. Postoperatively, no significant difference (UOP, TOP, EOP, soft palate width, and hyoid bone) was found between the skeletal classes. CONCLUSION: Preoperatively, UOP and TOP of skeletal Class III patients were significantly wider than those of skeletal Class I/II patients. Pre- and postoperatively, EOP did not exhibit significant differences among the three skeletal classifications. No differences were found in all postoperative pharyngeal airway dimensions between Class III patients and nonsurgery patients (Class I and Class II).

Effects of cortical bone thickness and trabecular bone density on primary stability of orthodontic mini-implants.

BACKGROUND/PURPOSE: Mini-implant screws are now routinely used as anchorage devices in orthodontic treatments. This study used synthetic bone models to investigate how the primary stability of an orthodontic mini-implant (OMI) as measured by resonance frequency (RF) is affected by varying cortical bone thickness and trabecular bone density. MATERIALS AND METHODS: Three synthetic cortical shells (thicknesses of 1, 2, and 3 mm) and three polyurethane foam blocks (densities of 40, 20, and 10 pound/cubic foot) were used to represent jawbones of varying cortical bone thicknesses and varying trabecular bone densities. Twenty-five stainless steel OMIs (2 × 10 mm) were sequentially inserted into artificial bone blocks to depths of 2, 4, and 6 mm. Five experimental groups of bone blocks with OMIs were examined by Implomates® RF analyzer. Statistical and correlation analyses were performed by Kruskal-Wallis test, Wilcoxon rank-sum test, and simple linear regression. RESULTS: As trabecular bone density decreased, RF decreased; as cortical bone thickness decreased, RF also decreased. Simple linear regression analysis showed highly linear correlations between trabecular bone density and RF (R 2 > 0.99; P < 0.0001) and between cortical bone thickness and RF (R 2 > 0.98; P < 0.0001). CONCLUSION: The stability of an OMI at the time of placement is influenced by both cortical bone thickness and trabecular bone density. Both cortical bone thickness and trabecular bone density have strong linear correlations with RF.

Dental implant navigation system guide the surgery future.

No study has investigated the effect of learning curves on the accuracy of dental implant navigation systems. This study evaluated the accuracy of the dental implant navigation system and established the learning curve according to operation site and operating time. Each dental model was used for drilling 3 missing tooth positions, and a patient tracking module was created. The same dentist performed the drilling test for 5 sets of dental models. CT back scanning was performed on the dental models. Customized implants based on the drilled holes were inserted. The relative error between the preoperative planning and actual implant was calculated. Using the dental navigation system could help dentists position implants more accurately. Increasing the frequency with which a dentist used the navigation system resulted in shorter operations. Longitudinal and angular deviation were significantly (P < 0.0001 and P = 0.0164). We found that the same level of accuracy could be obtained for the maxilla and mandible implants. The Student's t test demonstrated that the longitudinal error, but not the total or angular error, differed significantly (P = 0.0012). The learning curve for the dental implant navigation system exhibited a learning plateau after 5 tests. The current system exhibited similar accuracy for both maxillary and mandibular dental implants in different dental locations. The one-way ANOVA revealed that the total, longitudinal, and angular errors differed significantly (P < 0.0001, P < 0.0001 and P = 0.0153). In addition, it possesses high potential for future use in dental implant surgery and its learning curve can serve as a reference for dentists.