Bevacizumab-Associated Implant Presence-Triggered Osteonecrosis: A Case Report and Literature Review.

The effect of bevacizumab-related osteonecrosis of the jaw on previously osseointegrated dental implants has not been adequately studied. Here, we report a case of osteonecrosis of the jaw detected around dental implants placed before bevacizumab therapy. A 66-year-old woman undergoing bevacizumab therapy for metastatic triple-negative breast cancer developed malocclusion after buccal gingival swelling and pain in the #18, #19, and #20 tooth region. The patient visited a local dental clinic, where existing implants in relation to #19 and #20 were removed. Subsequently, the patient visited our department, and intraoral examination revealed necrotic bone in the region corresponding to #19 and #20. Radiographic examination showed a pathologic fracture in this region that was considered to result from osteonecrosis of the jaw. Bevacizumab therapy was suspended temporarily until the acute inflammation had subsided. In addition, treatment with antibacterial agents and conservative surgery was considered. Complete soft tissue coverage was observed 14 days after surgery. In recent years, the number of patients receiving bevacizumab treatment has increased. Because bevacizumab-related osteonecrosis of the jaw could occur around previously osseointegrated dental implants as well, this case report suggests an effective treatment regimen based on a combination of antibacterial agents and conservative surgery.

Maxillofacial Fractures Associated With Interpersonal Violence.

Interpersonal violence is a major cause of maxillofacial fractures. The aim of this study was to analyze the characteristics of these fractures associated in an effort to develop more effective management. The clinical records and radiographs of 272 patients with maxillofacial fractures associated with interpersonal violence collected during a 36-year period were retrospectively analyzed. Two hundred and nineteen patients were male (80.5%) and 53 (19.5%) were female. The patients ranged in age from 1 to 77 years. Two hundred and two patients (74.3%) were aged 10 to 29 years. The injury was the result of impact by a fist/hand/elbow in 224 patients (82.3%). The fracture site was the mandible in 191 patients (70.2%), the midface in 78 (28.7%), and both sites in 3 (1.1%). One hundred and eight (39.6%) of 273 mandibular fractures were in the angle, 75 (27.5%) were in the symphysis, and 90 (33.0%) were at other sites. Forty-three (53.1%) of 81 fractures in the midface were in the zygoma, 19 (23.5%) were in the maxilla, and 19 (23.5%) were at other sites. Fractures were more common on the left side. Nine patients (3.3%) also had injuries at other body sites. Ninety-five patients (34.9%) were treated by maxillomandibular fixation, 84 (30.9%) by open reduction and internal fixation, 59 (21.7%) by observation, 14 (5.1%) by intramaxillary splinting, 14 (5.1%) by transcutaneous reduction, and 6 (2.2%) by other procedures. Interpersonal violence-related maxillofacial fractures have characteristic features, especially with regard to site and laterality.

Trends and characteristics of maxillofacial fractures sustained during sports activities in Japan.

BACKGROUND/AIM: Sports activity increases the risk of maxillofacial fractures. The aim of this study was to analyze trends and characteristics of maxillofacial fractures sustained during sports activity to develop more effective treatments and possibly to prevent injury. MATERIALS AND METHODS: Data of 248 patients with maxillofacial fractures sustained during sports activity were retrospectively analyzed based on their clinical records and radiographs. RESULTS: The patients were 226 males (91.1%) and 22 females (8.9%). Their ages ranged from 6 to 70 years and the majority were in their second decade. The fractures were sustained in various sports which included baseball in 85 patients (34.3%), rugby in 40 (16.1%), soccer in 30 (12.1%), softball in 22 (8.9%), golf in 10 (4.0%), hockey in 8 (3.2%), combat sports in 28 (11.3%), and others in 29 (11.7%). The cause of injuries was collision with another player in 97 patients (39.1%), hit by a ball in 89 (35.9%), intended attack in 20 (8.1%), hit by equipment of another player in 15 (6.0%), a fall in 14 (5.6%), and collision with ground equipment in 13 (5.2%). The site of fractures was the mandible in 145 patients (58.5%), midface in 100 (40.3%), and both in 3 (1.2%). Among 210 fracture sites in the mandible, 77 (36.6%) were in the angle, 68 (32.4%) in the symphysis, and 65 (30.9%) in others. Among 103 fractures in the midface, 58 (56.3%) were in the zygoma, 26 (25.2%) in alveolar bone, and 19 (18.4%) in others. Treatment was observation in 67 patients (27.0%), maxillomandibular fixation in 64 (25.8%), open reduction and internal fixation in 63 (25.4%), intramaxillary splinting in 40 (16.1%), transcutaneous reduction in 10 (4.0%), and other procedures in 4 (1.6%). CONCLUSION: Maxillofacial fractures sustained during sports activity showed characteristic features dependent on the type of sport and cause of injury.

Computed Tomography-Based 3-Dimensional Finite Element Analyses of Various Types of Plates Placed for a Virtually Reduced Unilateral Condylar Fracture of the Mandible of a Patient.

PURPOSE: This study was performed to evaluate stresses in various types of plates placed for a virtually reduced unilateral condylar fracture of the mandible using computed tomography-based 3-dimensional finite element (FE) models of a patient to select the optimal plate system. MATERIALS AND METHODS: A computed tomography-based FE model of the mandible of a patient with a unilateral condylar fracture was constructed. The fracture was virtually reduced and fixed with 1 straight titanium plate; 2 straight titanium plates; 2 straight poly-L-lactic acid plates; and 4-hole (box), 5-hole (strut), and 7-hole (lambda) condylar plates. Stresses developing in these plates were analyzed by applying 478.1 N of bite force at the first molar of the contralateral side of the mandible. RESULTS: The magnitudes of tensile stress were within the tensile strength in all types of plates. However, the magnitudes of compressive stress in 1 straight titanium plate and 2 straight poly-L-lactic acid plates were beyond the compressive strength. The tensile and compressive stresses of the 5-hole (strut) plate were the smallest among the 3 types of condylar plates. CONCLUSIONS: Fixation by 2 straight titanium plates or any type of condylar plate was biomechanically indicated for the condylar fracture of this patient. Among these plates, the 5-hole (strut) plate was considered optimal. FE analysis is useful in selecting the optimal fixation method in the individual patient.

Biomechanical analysis of poly-L-lactic acid and titanium plates fixated for mandibular symphyseal fracture with a conservatively treated unilateral condylar fracture using the three-dimensional finite element method.

The purpose of this study was to investigate stress on poly-L-lactic acid (PLLA) plates with a thickness of 1.4 mm and titanium plates with a thickness of 1.0 and 1.4 mm placed for mandibular symphyseal fractures with or without conservatively treated, unilateral condylar fractures using finite element analysis. The symphyseal fracture region was defined by the following three conditions: the defect, the callus, and the contact condition. Stress on the plates was analyzed by an applying occlusal force of 478.1 N on the first molar of the non-condylar fracture side. In the model of isolated symphyseal fracture, the maximal stresses were below the material strength in all plate types and conditions. In the models with condylar fracture, the maximal stresses on these plates were much higher than those in the models of isolated symphyseal fracture, especially for the defect condition. Although the maximal stresses on all types of plates in the contact condition were below the material strengths, some of those in the defect condition were higher than these strengths. These results suggest that a PLLA plate can theoretically withstand stress under good reductions of symphyseal fractures, even for condylar fractures; however, both the PLLA plate and titanium miniplate may be at risk of fracture under poor reduction.

Influence of bone parameters on peri-implant bone strain distribution in the posterior mandible.

OBJECTIVES: The success rate of dental implants depends on the type of bone at the implant site. The purpose of the present study was to investigate the effects of the bone parameters at the implant-placement site on peri-implant bone strain distributions. STUDY DESIGN: The morphologies and bone densities of seventy-five potential implant sites in the posterior mandible were measured using computed tomography (CT). Based on the CT data, we defined bone parameters (low and high in terms of cancellous-bone density and crestal-cortical bone density, and thin and thick in terms of crestal-cortical bone thickness), and we constructed finite-element models simulating the various bone types. A buccolingual oblique load of 200 N was applied to the top of the abutment. The von Mises equivalent (EQV) strains in the crestal-cortical bone and in the cancellous bone around the implant were calculated. RESULTS: Cancellous-bone density greatly affected the maximum EQV strain regardless of the density and thickness of the crestal cortical-bone. The maximum EQV strains in the crestal cortical-bone and the cancellous bone in the low-density cancellous-bone models (of 150 Hounsfield units (HU)) were 1.56 to 2.62-fold and 3.49 to 5.31-fold higher than those in the high-density cancellous-bone models (of 850 HU), respectively. The crestal cortical-bone density affected the maximum EQV strains in the crestal cortical-bone and in the cancellous bone in the low-density cancellous-bone models. The crestal cortical-bone thickness affected the maximum EQV strains in the cancellous bone and in the crestal cortical-bone in the low-density cancellous-bone models. CONCLUSIONS: Our results confirm the importance of bone types for the peri-implant bone strain distribution. Cancellous-bone density may be a critical factor for peri-implant bone strain.

Maxillofacial fractures in children.

Maxillofacial fractures in Japanese children were retrospectively analyzed. The subjects were 287 patients aged 15 years and younger seeking treatment for maxillofacial fractures in the Department of Oral and Maxillofacial Surgery, Nara Medical University. The patients were 186 males and 101 females. Injuries most frequently occurred as a result of traffic accidents in 125 patients, 92 of which were bicycle-related accidents. Injuries by falling from one level to another were found in 49, primarily in younger children. One hundred seventy-nine fractures occurred in the mandible, 100 in the midface, and 8 in both. In the mandible, fractures most frequently occurred in condyle followed by symphysis. In the midface, alveolus was mostly involved. The facial injury severity scale ranged from 1 to 9 with an average of 1.83 and was higher in traffic accidents. Injury to other sites of the body was found in 33 patients, 28 of which occurred in traffic accidents. Observation was most frequently chosen in 84 patients. Intramaxillary fixation was chosen in 79, primarily for alveolar fractures and in younger children. Maxillomandibular fixation was chosen in 62 for mandibular fractures in older children. Open reduction and internal fixation was performed in 40, primarily in older children. The facial injury severity scale was higher in patients treated by open reduction and internal fixation and maxillomandibular fixation. Maxillofacial fractures in Japanese children showed characteristic features primarily depending on their age in terms of etiology, patterns, and treatment modalities.

Changes in strain energy density in the temporomandibular joint disk after sagittal split ramus osteotomy using a computed tomography-based finite element model.

PURPOSE: We evaluated the changes in the strain energy density (SED) in the temporomandibular joint (TMJ) disk after sagittal split ramus osteotomy (SSRO) at three time points. A finite element model (FEM) based on real patient-based computed tomography (CT) data was used to examine the effect of SSRO on the TMJ. METHODS: Measurements of the condylar position and angulation in CT images and FEM analyses were performed for 17 patients scheduled to undergo SSROs at the following time points: before surgery, immediately after surgery, and 1 year after surgery. SED on the entire disk was calculated at each of the three time points using FEM. Furthermore, the relationship between individual SED values and the corresponding condylar position was also evaluated. RESULTS: No significant change was observed in the condylar position at the three time points. The FEM analysis showed that SED was the highest and lowest immediately after and 1 year after surgery, respectively. A possible SED distribution imbalance between the left and right joints was improved 1 year after SSRO. Concerning the effect of fossa morphometry and condylar position, wide and deep glenoid fossae and a more posterior condylar position tended to show lower SED. CONCLUSION: SED in the articular disk temporarily increased after surgery and significantly decreased 1 year after surgery compared with that before surgery. SSRO generally improved the imbalance between the left and right joints. Thus, SSRO, which improves maxillofacial morphology, may also improve components of temporomandibular disorders.

Impalement injuries of the oral cavity in children.

PURPOSE: The purpose of this study was to analyze impalement injuries of the oral cavity in children. PATIENTS AND METHODS: Data on 144 children with impalement injuries in the oral cavity at the Department of Oral and Maxillofacial Surgery, Nara Medical University were analyzed retrospectively. RESULTS: The patients were 93 boys and 51 girls (age range, 7 months to 10 years). One hundred thirty-two patients (91.7%) were younger than 5 years. Injuries occurred frequently by falling onto an object held in the mouth in 77 patients (53.5%). The impaled objects were a toothbrush in 30 patients (20.8%), a cylindrical toy in 27 (18.8%), and chopsticks in 19 (13.2%). The soft palate was frequently involved in 64 patients (44.4%), followed by the hard palate in 26 (18.1%). Computed tomographic examination was performed in 16 patients (11.1%). Observation with or without medication was most frequently chosen in 98 patients (68.1%). Surgical intervention was performed in 46 patients (31.9%), 41 under local anesthesia and 5 under general anesthesia. Admission was required in 12 patients (8.3%). No complications, such as deep infection or neurologic sequelae, were observed. CONCLUSIONS: Most impalement injuries in the oral cavity in children heal spontaneously or with minimal intervention. These children can be followed on an outpatient basis with instructions to their parents about possible complications, except for a few selected cases.

Maxillofacial fractures in older patients.

PURPOSE: The purpose of the present study was to analyze the trends and characteristic features of maxillofacial fractures in older patients. PATIENTS AND METHODS: The data from 247 patients aged 65 years old or older, who were treated for maxillofacial fractures at the Department of Oral and Maxillofacial Surgery, Nara Medical University, from October 1981 to March 2010, were retrospectively analyzed. RESULTS: Of the 247 patients, 127 were men and 120 were women; 50 patients had been treated in the first third of the period, 87 in the second, and 110 in the third. Injury had most frequently occurred because of falling on a level surface (n = 126), followed by a traffic accident (n = 84). Of the fractures, 140 were in the mandible, 90 in the midface, and 17 in both. In the mandible, the fracture lines were most frequently observed at the condyle, followed by the body, exclusively in edentulous patients. In the midface, the zygoma was mostly involved. The facial injury severity scale score ranged from 1 to 10 (average 1.81). Injury at other sites of the body was found in 45 patients. Observation was most frequently chosen (n = 127), primarily for those of older age, followed by open reduction and internal fixation in 46 and maxillomandibular fixation in 41 patients. The facial injury severity scale score was greatest in patients treated by open reduction and internal fixation, followed by those treated by maxillomandibular fixation. CONCLUSION: Maxillofacial fractures in older patients have been increasing and showed the characteristic features of etiology, patterns, and treatment modalities.

Maxillofacial fractures sustained in bicycle accidents.

PURPOSE: The purpose of this study was to analyze maxillofacial fractures sustained in bicycle accidents by demographics, cause of injury, site and severity of fractures, injuries to other sites of the body, and treatment modalities. PATIENTS AND METHODS: Data on 307 patients treated for maxillofacial fractures sustained in bicycle accidents in the Department of Oral and Maxillofacial Surgery, Nara Medical University from 1981 through 2009 were analyzed retrospectively. RESULTS: The patients were 166 males and 141 females (average age, 30.9 years). Causes of injury were a fall on a level surface in 169 patients, an automobile accident in 56, fall from 1 level to another in 28, and a motorcycle accident in 24. One hundred seventy-five fractures were observed in the mandible, 117 in the midface, and 15 in the mandible and midface. In the mandible, fracture lines were exclusively observed at the condyle. In the midface, the zygoma was most frequently involved. The Facial Injury Severity Scale ranged from 1 to 7 (average, 1.88). Injuries at other sites of the body were found in 47 patients and were frequently found in automobile and motorcycle accidents. Maxillomandibular fixation was most frequently chosen in 81 patients, followed by observation in 76 and open reduction and internal fixation in 71. The Facial Injury Severity Scale was highest in patients treated by open reduction and internal fixation, followed by those treated by maxillomandibular fixation. CONCLUSIONS: Maxillofacial fractures sustained in a bicycle accident frequently occurred by falling on a level surface and were not so serious in most cases; however, in accidents with motor vehicles, injuries to other sites of the body were observed at a higher rate.

A mandibular body fracture related to mouth-opening training in a dialysis patient.

A mandibular body fracture related to mouth-opening training in a dialysis patient is reported. A 61-year-old male patient had noticed pain in the right mandibular body and difficulty in mouth opening a week previously. The patient had been performing mouth-opening training for a couple of weeks. The right lower face was slightly swollen with tenderness at the right lower border of the mandible. Hypoesthesia of the right lower lip was also observed. A bone step was palpable on the alveolar ridge of the right mandible, but mobility was not marked. The mandible was atrophic in the body region with only four anterior teeth left. Panoramic X-ray examination revealed a moderately displaced fracture in the right molar region of the mandible. The patient had no severe pain or difficulty in eating using a partial denture. The patient had received dialysis for 17 years and had also been treated by warfarin and aspirin. The patient was followed up under restricted mouth opening. Osteosynthesis with bone remodeling was confirmed after 6 months by X-ray examination. No complication requiring further treatment occurred during the follow-up period. In this patient, a medically compromised condition under long-term dialysis is considered a predisposing factor, which made the atrophic mandible more susceptible to the stress related to mouth-opening training.

Maxillofacial fractures resulting from falls.

PURPOSE: The purpose of this study was to analyze maxillofacial fractures resulting from falls in terms of the demographics, the circumstance of injury, the site and severity of fracture, and the treatment. PATIENTS AND METHODS: Data of 457 patients treated for fall-related maxillofacial fractures at the Department of Oral and Maxillofacial Surgery, Nara Medical University, Nara, Japan, from 1981 to 2007 were retrospectively analyzed. RESULTS: Patients were 163 males and 116 females with an average age of 51.3 years who had fallen on a level surface (simple fall), and 110 males and 68 females with an average age of 31.9 years in falls from a greater height (fall from height), respectively. Fractures of the mandible were more frequently observed than those of the midface. In the mandible, fracture lines were exclusively observed at the condyle, especially in simple falls. In the midface, the zygoma was most frequently involved. Facial Injury Severity Scale ranged from 1 to 6, with an average of 1.78 in simple falls, and from 1 to 9, with an average of 2.04 in falls from height, respectively. These were dependent on the causes and height of the fall. Fractures at the other sites of the body were found in 14 patients (5.0%) with simple falls and 38 (21.3%) with falls from height. Maxillomandibular fixation was most frequently chosen for mandibular fractures and observation for midface fractures. Open reduction and fixation was more frequently chosen in patients with falls from height than those with simple falls and in patients with a higher Facial Injury Severity Scale score. CONCLUSIONS: Maxillofacial fractures resulting from falls showed characteristic features in the demographics, the circumstance of injury, and the site and severity of fracture. Treatment was chosen according to these features.

Fate of developing tooth buds located in relation to mandibular fractures in three infancy cases.

The fate of developing tooth buds located in relation to mandibular fractures was investigated in three infancy cases. Three infants, 2 girls and a boy, aged from 1 year and 5-months old to 2 years and 6-months old, were treated for dislocated mandibular fracture in the symphyseal region by manual reduction and fixation with a thermoforming splint and circumferential wiring under general anesthesia. Fracture healing was uneventful in all cases. A few years later, no obvious deformity of the jaw or malocclusion was observed; however, malformation of the crown was found in one of the permanent teeth on the fracture line in the first case. In the second case, no abnormality was observed in one of the permanent teeth on the fracture line, but the effect on the other tooth could not be evaluated due to abnormality of the tooth probably not related to the injury. In the third case, root formation was arrested in one of the permanent teeth on the fracture line and the tooth was lost early after eruption. The development of tooth buds on the fracture line is not predictable and therefore, should be monitored by regular follow up.

Study of Treatment Methods for Surrounding Soft Tissues of Implants Following Mandibular Reconstructions with Fibula-Free Flaps.

In maxillofacial reconstruction implant treatment, unsatisfactory soft tissue treatment of the area around the implant may lead to inflammation. As a result, appropriate soft tissue treatment is critical. To the best of our knowledge, there are no studies that compare the different tissue treatment methods available. Hence, in this study, we compare three soft tissue treatment methods around implants after mandibular reconstruction is achieved with a fibula-free flap. Out of 33 patients who underwent mandible reconstruction using fibula-free flaps between 2006 and 2015, 5 were selected for this study. A total of 17 implants were used for treatment by the final prosthetics of the five patients. Three soft tissue treatment methods with free gingival graft (FGG) were evaluated, namely, installing a splint in a modified abutment to protect the wounded area during a palatal mucosa transplant (method 1), installing a splint or dentures to a locator abutment (method 2), and the use of screw-in fixed dentures (method 3). The method that could guarantee the widest keratinized mucosa was the screw-in fixed denture method. The results of our study indicated that employing screw-in fixed dentures for FGG may be a useful soft tissue treatment for mandible reconstruction implants.

Evaluation of Primary Stability of Cylindrical and Tapered Implants in Different Bone Types by Measuring Implant Displacement: An In vitro Study.

AIMS: The purposes of this study were to investigate the primary stability of cylindrical and tapered implants in different bone types by measuring implant displacement and to examine the relationship between insertion torque value (ITV) and implant displacement. MATERIALS AND METHODS: Four different polyurethane bone models consisted of low-density or low-to-medium-density cancellous bone with or without a cortical bone layer. A total of 120 cylindrical and tapered implants were placed into bone blocks (n = 15 in each group), and the ITV was measured. A lateral load of 15 N was applied to the top of the abutment, and implant displacement was recorded. RESULTS: Implant displacement was significantly affected by cancellous bone density and to a lesser degree by cortical bone thickness. The displacement of tapered implants was significantly smaller than that of cylindrical implants in the presence of cortical bone. However, both implant groups showed similar ITV in the low-density cancellous bone model with the cortical bone layer. There was a correlation between ITV and displacement in the cylindrical and tapered implants. However, no correlation was observed between ITV and displacement within each bone type. CONCLUSIONS: Implant stability depended mainly on the bone type, whereas implant design had a limited influence on primary stability. The use of tapered implants may be advantageous for improving primary stability in patients with low-density cancellous bone only when crestal cortical bone exists. The same ITV of cylindrical and tapered implants did not necessarily represent similar primary stability in the bone type.

Micromotion analysis of different implant configuration, bone density, and crestal cortical bone thickness in immediately loaded mandibular full-arch implant restorations: A nonlinear finite element study.

BACKGROUND: Excessive micromotion may cause failure of osseointegration between the implant and bone. PURPOSE: This study investigated the effects of implant configuration, bone density, and crestal cortical bone thickness on micromotion in immediately loaded mandibular full-arch implant restorations. MATERIALS AND METHODS: A finite element model of the edentulous mandible was constructed. Four implants were inserted in two different configurations, which were four parallel implants or tilted distal implants according to the all-on-four concept. Different cancellous bone densities and crestal cortical bone thicknesses were simulated. The framework was made of acrylic resin. A vertical load of 200 N was applied at the cantilever or on the distal implant (noncantilever loading). RESULTS: The maximum extent of micromotion was significantly influenced by the density of cancellous bone and to a lesser extent by implant configuration and the crestal cortical bone thickness. The all-on-four configuration showed less micromotion than the parallel implant configuration in some circumstances. The maximum micromotion detected with noncantilever loading was less than 1/3 of that with cantilever loading. CONCLUSIONS: Implant configuration had a limited influence on micromotion. Avoiding cantilever loading during the healing period should effectively reduce the risk of excessive micromotion in patients with low-density cancellous bone and thin crestal cortical bone.

Immune Thrombocytopenic Purpura Detected with Oral Hemorrhage: a Case Report.

Immune thrombocytopenic purpura (ITP) is an immune-mediated acquired disease found in both adults and children. It is characterized by transient or persistent decreases in the platelet count. We report a case of ITP detected based on oral hemorrhagic symptoms. The patient was a 79-year-old female with no significant past medical history. She presented with sudden onset of gingival bleeding and hemorrhagic bullae on the buccal mucosa. Gingival bleeding was difficult to control. Laboratory tests revealed severe thrombocytopenia with a platelet count as low as 2000/µL. Under a provisional diagnosis of a hematological disorder, she was referred to a hematologist. A peripheral smear showed normal-sized platelets. A bone marrow examination revealed increased numbers of megakaryocytes without morphologic abnormalities. The patient was diagnosed with ITP and treated with a combination of pulsed steroid therapy and high-dose immunoglobulin therapy. However, her severe thrombocytopenia was refractory to these treatments. Then, a thrombopoietin receptor agonist was begun as a second-line treatment. Her platelets rapidly increased, and no bleeding complications were reported. Because oral symptoms can be one of the initial manifestations of ITP, dentists should be familiar with the clinical appearance of ITP, and attention must be paid to detect and diagnose unidentified cases.

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.

Biomechanical analysis of immediately loaded implants according to the "All-on-Four" concept.

PURPOSE: The purpose of this study was to investigate the biomechanical behavior of immediately loaded implants in an edentulous mandible according to the "All-on-Four" concept. METHODS: A 3D-finite element model of an edentulous mandible was constructed. Four implants were placed between the bilateral mental foramen according to "All-on-Four" concept. A framework made of titanium or acrylic resin between the bilateral first molars was modeled. Immediate loading and a delayed loading protocol were simulated. A vertical load of 200N was applied at the cantilever or on the abutments region of the distal implants, simulating the absence of a cantilever. RESULTS: The peak principal compressive strains in the immediate loading models resulted in 24.0-35.8% and 26.4-39.0% increases compared with the delayed loading models under non-cantilever loading and cantilever loading, respectively. The loading position greatly affected the principal compressive and tensile strain values. The peak principal compressive strains in non-cantilever loading resulted in a 45.3-52.6% reduction compared with those in cantilever loading. The framework material did not influence the peak compressive and tensile strain. The maximum micromotion at the bone-implant interface in the immediate loading models was 7.5-14.4µm. CONCLUSIONS: Mandibular fixed full-arch prostheses without cantilevers may result in a favorable reduction of the peri-implant bone strain during the healing period, compared with cantilevers. The maximum micromotion was within the acceptable limits for uneventful implant osseointegration in the immediate loading models. Framework material did not play an important role in reducing the peri-implant bone strain and micromotion at the bone-implant interface.