Biomechanical Effect of an Exposed Dental Implant's First Thread: A Three-Dimensional Finite Element Analysis Study.

BACKGROUND The purpose of this study was to assess the effect of different exposure levels of a dental implant's first thread on adjacent bone stress and strain using the finite element analysis method. MATERIAL AND METHODS Three-dimensional models of 2 threaded implants and abutments with a mandibular bone segment were constructed to represent the covered (C) and exposed models. In the exposed models, the implant was first placed in the bone, and rotated around its axis a quarter-turn each time to simulate 4 different levels of first thread exposure at the mid-lingual side: Upper Flank (UF), Thread Crest (TC), Lower Flank (LF), and Thread Root (TR) models. Oblique forces were applied and analysis was performed. RESULTS Maximum compressive stress magnitude and distribution varied according to the exposed thread profile. In the exposed group, peak stress ranged from 136 MPa to 197 MPa in TC and LF models, respectively, compared to 141 MPa in C model. In LF, UF, and C models, peak stress was observed at the mid-lingual side of the crestal region, while in TC and TR models, peak stress shifted distally in accordance with thread profile. However, alveolar bone volumes which exhibited compressive microstrain levels within the physiological loading and maintenance windows were relatively close in all models. CONCLUSIONS Results suggest that the exposed thread profile influences stress and strain outcomes in the adjacent bone; however, this influence is only limited to a small region around the exposed thread.

Comparison of mesiodistal space measurements of single-implant sites on panoramic and oblique images generated by cone-beam CT.

PURPOSE: To compare the mesiodistal space measurements of single-implant sites on panoramic and oblique images generated by cone-beam CT (CBCT). METHODS: CBCT images for 101 single-implant sites of 66 patients referred for pre-surgical radiographic implant planning were selected for the study; 15-mm-thickness panoramic images were reformatted and used for measuring mesiodistal space dimensions. The measurements were repeated and compared with those of thin oblique images (200-300 µ) using Wilcoxon signed rank test. The correlation between measurements in addition to intra-observer agreement was evaluated by Pearson's correlation coefficients. RESULTS: All mesiodistal space measurements on panoramic and oblique images generated by CBCT were strongly correlated and there were no statistically significant differences between them (P < 0.05). CONCLUSIONS: Both panoramic and oblique images generated by CBCT can be used for measuring mesiodistal space dimensions of single-implant sites.

Impact of Bone Augmentation of Facial Bone Defect around Osseointegrated Implant: A Three Dimensional Finite Element Analysis.

(1) Background: When dental implants are placed at the esthetic zone, facial bone fenestration might be expected. This study aimed to evaluate the biomechanical effect of bone augmentation around implants with facial bone fenestration defects using the finite element method. (2) Methods: An anterior maxillary region model with facial concavity was constructed with a threaded implant inserted following the root direction, resulting in apical threads exposure to represent the fenestration model. Several bone coverage levels were simulated by gradually shifting the deepest concavity point buccally, mimicking bone augmentation surgeries with different bone fill results. Oblique forces were applied, and analysis was performed. (3) Results: Peak compressive stress magnitude and distribution varied according to the level of exposure and facial concavity depth. The fenestration model demonstrated a slightly lower peak peri-implant bone stress, smaller implant displacement, and smaller bone volume with strain levels above 200 µ strain. A gradual increase in compressive stress, implant displacement, and bone volume exhibited strain level above 200 µ strain was observed with the increased bone fill level of the facial bone fenestration. (4) Conclusions: Exposure of implants apical threads at the maxillary anterior region does not significantly affect the peri-implant stress and strain results. However, increasing the buccolingual width and eliminating the buccal concavity might increase the peri-implant bone volume exhibited favorable loading levels.

Morphologic classification and stress analysis of the mandibular bone in the premolar region for implant placement.

PURPOSE: The objective of this study was to assess the influence of mandibular morphology on the stress and strain distributions in the bone supporting an implant. MATERIALS AND METHODS: Subjects were selected from patients with missing mandibular premolar teeth. Computed tomographic scans of the premolar region were classified into nine groups based on the overall bone morphology and the relative position of the alveolar crest. Finite element models of the bone on the basis of this classification, with inserted implants and superstructures, were constructed. A load of 200 N applied 30 degrees buccal from the vertical axis was directed toward the occlusal surface. RESULTS: One hundred two partially (n = 98) and completely (n = 4) edentulous subjects were recruited. Their ages ranged from 40 to 79 years (mean age, 60.5 years; 41 men and 61 women). Approximately 56% of the patients showed bone widening in the caudal direction. The maximum compressive stresses were shown in the lingual cervical regions. An influence of overall bone morphology on stress distribution was not observed; however, the alveolar crest contour clearly affected the maximum stress and strain values. Compressive microstrain above 4,000 was observed only when the alveolar crest was lingually located relative to the body of the mandible. These high strain levels were concentrated at the lingual cervical margin, with volumes ranging from 0.04 to 0.07 mm3. CONCLUSION: The contour of the alveolar crest potentially plays a critical role in maintaining the bone levels surrounding implants.

Effect of calibration of a medical review monitor on the visibility of mandibular canal at dental implant sites: A cone beam CT study.

OBJECTIVES: The aim of this study was to assess the visibility of mandibular canal (MC) on cone beam CT (CBCT) images using a medical review monitor under two different calibration modes. The effect of age, gender, and location of the dental implant site was also assessed. MATERIALS AND METHODS: CBCT images of 428 dental implant sites were selected for the study. Images were displayed twice on a medical review monitor using two different calibration modes: standard and DICOM, and two observers evaluated the visibility of the MC using four-point scoring scale (1-4, poor to excellent). Cohen Kappa was used to assess intra and inter-rater reliability. Chi-square test was used to compare proportions of MC visibility by gender and location and one-way ANOVA was used to compare mean age and MC visibility. RESULTS: Each observer classified the visibility of MC with a total agreement of 100% between DICOM mode and standard mode (Kappa = 1, P < 0.001 for each observer). In each mode, a strong agreement (inter-rater reliability) was detected between the observers (Cohen's kappa = 0.88 for both modes, P < 0.001) with a percent agreement of 95.3% for each mode. Gender and location were not statistically associated with MC visibility (P > 0.05). Age, however, was a significant predictor of MC visibility (P < 0.05). CONCLUSIONS: DICOM calibration had no added value over standard calibration for assessing the visibility of MC at dental implant sites on a medical review monitor. Only the age had significant effect on the visibility.

Predictability of bone density at posterior mandibular implant sites using cone-beam computed tomography intensity values.

OBJECTIVE: The aim of this study was to investigate the predictability of bone density at posterior mandibular implant sites using cone-beam computed tomography (CBCT) intensity values. MATERIALS AND METHODS: CBCT cross-sectional images for 436 posterior mandibular implant sites were selected for the study. Using Invivo software (Anatomage, San Jose, California, USA), two observers classified the bone density into three categories: low, intermediate, and high, and CBCT intensity values were generated. RESULTS: Based on the consensus of the two observers, 15.6% of sites were of low bone density, 47.9% were of intermediate density, and 36.5% were of high density. Receiver-operating characteristic analysis showed that CBCT intensity values had a high predictive power for predicting high density sites (area under the curve [AUC] =0.94, P < 0.005) and intermediate density sites (AUC = 0.81, P < 0.005). The best cut-off value for intensity to predict intermediate density sites was 218 (sensitivity = 0.77 and specificity = 0.76) and the best cut-off value for intensity to predict high density sites was 403 (sensitivity = 0.93 and specificity = 0.77). CONCLUSIONS: CBCT intensity values are considered useful for predicting bone density at posterior mandibular implant sites.

Volatile sulphur compounds in exhaled air of dental students smoking the waterpipe: a nested case control study.

BACKGROUND: This study aims at investigating a potential adverse effect that waterpipe tobacco smoking may cause by comparing levels of volatile sulphur compounds in exhaled air of male dental students who smoke the waterpipe with those who do not smoke. METHODS: Dental students were categorized into waterpipe smokers and non-smokers. Volatile sulphur compounds were measured using a halimeter following the completion of questionnaire on smoking and oral hygiene habits and self-perceived halitosis. Statistics were carried out using ANOVA and relevant post hoc tests, associations were investigated using cross tabulation with the χ2 test. RESULTS: Results showed significantly higher levels of volatile sulphur compounds in: waterpipe smokers who smoke at least once a month when compared with non-smokers regardless their oral hygiene habits; subjects who do not brush their teeth; and subjects who self-perceive halitosis. There were no significant differences in these levels for similar groups on the basis of: use of floss, or use of mouth wash. CONCLUSIONS: It seems that waterpipe tobacco smoking results in increased volatile sulphur compounds levels in exhaled air. Oral hygiene practices like the use of tooth brush, dental floss, and mouth wash also seem to result in lower levels.

Oral health status in children with acute lymphoblastic leukemia.

UNLABELLED: Leukemia is a malignancy of the bone marrow. Acute lymphoblastic leukemia (ALL) is the most common pediatric malignancy and accounts for nearly 75% of all newly diagnosed leukemias and 25% of all malignancies in childhood. The aim of the present study was to review the oral health status in children with ALL. Databases were explored using various combinations of the following keywords: "acute lymphoblastic leukemia", "children", "inflammation", "pediatric", "periodontal disease" and "periodontitis". Oral inflammatory conditions including chelitis, gingivitis, herpetic gingivostomatitis, mucositis, oral candidiasis, periodontitis and ulcerations are common manifestations in children with ALL. RESULTS: Periodontal inflammatory conditions and oral mucositis were reported to be significantly higher in children with ALL as compared to healthy controls. Tooth morphological disorders including agenesis, microdontia, short roots and developmental defects in the enamel and dentin were more often observed in children with ALL as compared to healthy controls. Children with ALL have a reduced salivary flow rate, which makes them more susceptible to dental caries as compared to healthy children. Malocclusion due to microdontia may also trigger temporomandibular joint disorders in children with ALL; however, this relationship needs further investigations. CONCLUSION: Oral inflammatory conditions including mucositis and gingivitis are common in children with ALL as compared to healthy children. Tooth morphological disorders including microdontia and enamel and dentin are common manifestations in children with ALL.

Magnitude and direction of mechanical stress at the osseointegrated interface of the microthread implant.

BACKGROUND: The mechanism by which the microthread implant preserves peri-implant crestal bone is not known. The objective of this research is to assess the effect of microthreads on the magnitude and direction of the stress at the bone-implant interface using finite element analysis modeling. METHODS: Three-dimensional finite element models representing the microthreaded implant (microthread model) and smooth surface implant (smooth model) installed in the mandibular premolar region were created based on microscopic and computed tomography images. The mesh size was determined based on convergence tests. Average maximum bite force of adults was used with four loading angles on the occlusal surface of the prosthesis. RESULTS: Regardless of the loading angle, principal stresses at the bone-implant interface of the microthread model were always perpendicular to the lower flank of each microthread. In the smooth model, stresses were affected by the loading angle and directed obliquely to the smooth interface, resulting in higher shear stress. The interfacial stresses decreased gradually in the apical direction in both models but with wavy pattern in the microthread model and smooth curve for the smooth model. Although peak principal stress values were higher around the microthread implant, peri-implant bone volume exhibiting a high strain level >4,000 µ was smaller around the microthread implant compared to the smooth implant. CONCLUSION: Stress-transferring mechanism at the bone-implant interface characterized by the direction and profile of interfacial stresses, which leads to more compressive and less shear stress, may clarify the biomechanical aspect of microthread dental implants.