Evaluation of tissue oxygen saturation of the masseter muscle during standardised teeth clenching.

BACKGROUND: Haemodynamics during recovery after teeth clenching is poorly understood. OBJECTIVE: To clarify factors influencing tissue blood oxygenation recovery after clenching with altered muscle activity and duration, but constant total muscle activity. METHODS: The following tasks were based on constant maximum voluntary clenching (100% MVC): (a) 50% MVC × 30 seconds; (b) 30% MVC × 50 seconds; and (c) 10% MVC × 150 seconds. Tissue oxygenated (oxy-Hb), deoxygenated (deoxy-Hb) and total haemoglobin (total-Hb) were recorded using near-infrared spectroscopy in the masseter muscle during recovery after each task. Participants rested for 30 seconds before each task; average resting values were set as baseline. Respective ratios to baseline at 20, 60, 120 and 180 seconds after each task were calculated; the tasks were compared at each time point using one-way repeated-measures ANOVA. RESULTS: Oxy-Hb and total-Hb decreased and deoxy-Hb increased during the tasks and recovered thereafter. For Task 3, not all values recovered to baseline, even after 180 seconds (oxy-Hb: 96.85%, total-Hb: 98.31%, deoxy-Hb: 102.98%). Oxy-Hb (after 180 seconds, Task 1-Task 3: P < .001, Task 2-Task 3: P = .013) and total-Hb (after 180 seconds, Task 1-Task 3: P < .001, Task 2-Task 3: P = .005) were significantly lower, and deoxy-Hb (after 180 seconds, Task 1-Task 3: P < .001, Task 2-Task 3: P = .005) was significantly higher for Task 3 than other tasks, at all times during and after recovery. CONCLUSION: Despite the same total muscle activity, weak-force, long-duration clenching is more harmful than strong-force, short-duration clenching, suggesting a greater effect of awakening bruxism than sleep bruxism on myalgia.

Stability of secondarily inserted orthodontic miniscrews after failure of the primary insertion for maxillary anchorage: Maxillary buccal area vs midpalatal suture area.

INTRODUCTION: Few studies have examined the secondary insertion of orthodontic miniscrews after failure of the first insertion. We investigated both the primary and secondary success rates of miniscrews used for maxillary anchorage and compared the stability of the maxillary buccal area (MB) and the midpalatal suture area (MP). METHODS: In total, 387 miniscrews were primarily inserted into the MB (between the second premolar and first molar); of these, 81 (20.9%) miniscrews lacked stability and were reinserted into the MB (same position or more distal position) or the MP. Additionally, 84 miniscrews were primarily inserted into the MP; 13 (15.5%) of those lacked stability and were reinserted into the MP. We calculated and compared the primary and secondary success rates in each area. Moreover, we investigated the factors affecting clinical success. RESULTS: Although the success rate of the secondary insertion was significantly lower than that of the primary insertion into the MB, miniscrews inserted into the MP were stable in both primary and secondary insertions. The screw length was significantly associated with the stability of miniscrews inserted into the MB. CONCLUSIONS: For secondary insertions, miniscrews placed in the MP may be more stable than those inserted in the MB.

Prognosis of primary and secondary insertions of orthodontic miniscrews: What we have learned from 500 implants.

INTRODUCTION: Although the success of using orthodontic miniscrews for primary insertion has been reported in the literature, few studies have followed up on secondary insertions after failure of the first insertion. In this study, we investigated not only the primary but also secondary success rates of miniscrews and considered the risk factors influencing their stability. METHODS: Five hundred miniscrews were inserted for orthodontic anchorage in 240 patients. Ninety-eight miniscrews lacked stability; thus, 77 of these were removed and reinserted. We calculated and compared the primary and secondary success rates of insertion. Moreover, we investigated which clinical parameters affected the stability of miniscrews. RESULTS: The success rate of secondary insertion (44.2%) was significantly lower than that of primary insertion (80.4%). The screw length and jaw receiving the insertion were significantly associated with the stability of miniscrews. The 8.0-mm miniscrews were significantly more stable than the 6.0-mm miniscrews, and the success rate for insertions into the maxilla was significantly higher than that for the mandible. CONCLUSIONS: Secondary insertions lack stability; therefore, clinicians should be aware of the reduced success rate of reinsertion and know the risk factors to avoid failure of secondary insertions.

Features in subjects with the frontal occlusal plane inclined toward the contralateral side of the mandibular deviation.

INTRODUCTION: The frontal occlusal plane of the maxilla generally inclines toward the ipsilateral side of the mandibular deviation in subjects with facial asymmetry; however, a few patients with facial asymmetry have their frontal occlusal planes inclined toward the contralateral side. We aimed to investigate the morphologic and functional features of such patients. METHODS: The subjects were 40 patients with facial asymmetry divided into 2 groups based on the inclination of the frontal occlusal plane toward the ipsilateral or the contralateral side. We analyzed lateral and posteroanterior cephalometric radiographs and occlusal variables and evaluated temporomandibular joint symptoms. Statistical comparisons were performed between the 2 groups (P <0.05). RESULTS: The posteroanterior cephalometry significantly differed between the ipsilateral and contralateral groups. Occlusal force and occlusal contact area were significantly larger, and temporomandibular joint symptoms were more frequently found on the side of the upward-inclined frontal occlusal plane than on the opposite side in both groups. CONCLUSIONS: The features in the contralateral group in terms of occlusal force and temporomandibular disorders were clinically significant. Clinicians should note that the conditions associated with the contralateral group require less presurgical decompensation.

Retrospective study of 100 autotransplanted teeth with complete root formation and subsequent orthodontic treatment.

INTRODUCTION: Autotransplantation has become a major therapeutic option for replacing missing teeth in adult orthodontic patients. However, little systematic information is available about the long-term stability of autotransplanted teeth with complete root formation after the application of an orthodontic force. The objective of this study was to investigate the outcomes of autotransplanted teeth with complete root formation that underwent orthodontic treatment. METHODS: One hundred teeth, autotransplanted in 89 patients, were examined over a mean observation period of 5.8 years. Orthodontic force was applied with nickel-titanium wires 4 to 8 weeks after autotransplantation. Root resorption, ankylosis, mobility, pocket depth, and inflammation at the recipient site were investigated clinically and with radiographs. RESULTS: The survival rate of the autotransplanted teeth was 93.0%. Abnormal findings were found in 29 teeth, including 7 lost teeth, for a success rate of 71.0%. Donor tooth type and occlusal condition of the donor tooth before transplantation were associated with abnormal findings. CONCLUSIONS: The early application of orthodontic force may increase the success rate of autotransplanted teeth, and the type and presurgical occlusal condition of donor teeth affect the success rate.

Unilateral maxillary central incisor root resorption after orthodontic treatment for Angle Class II, division 1 malocclusion with significant maxillary midline deviation: A possible correlation with root proximity to the incisive canal.

Root resorption can be caused by several factors, including contact with the cortical bone. Here we report a case involving a 21-year-old female with Angle Class II, division 1 malocclusion who exhibited significant root resorption in the maxillary right central incisor after orthodontic treatment. The patient presented with significant left-sided deviation of the maxillary incisors due to lingual dislocation of the left lateral incisor and a Class II molar relationship. Cephalometric analysis demonstrated a Class I skeletal relationship (A pointnasion-B point, 2.5°) and proclined maxillary anterior teeth (upper incisor to sella-nasion plane angle, 113.4°). The primary treatment objectives were the achievement of stable occlusion with midline agreement between the maxillary and mandibular dentitions and appropriate maxillary anterior tooth axes and molar relationship. A panoramic radiograph obtained after active treatment showed significant root resorption in the maxillary right central incisor; therefore, we performed cone-beam computed tomography, which confirmed root resorption along the cortical bone around the incisive canal. The findings from this case, where different degrees of root resorption were observed despite comparable degrees of orthodontic movement in the bilateral maxillary central incisors, suggest that the incisive canal could be an inducing factor for root resorption. However, further investigation is necessary to confirm this assumption.

Differential growth of craniofacial and tibial bones to sympathetic hyperactivity-related hypertension in rats.

OBJECTIVE: To evaluate the effect of sympathetic nervous system hyperactivity on craniofacial skeletal growth in growing spontaneously hypertensive rats (SHRs). DESIGN: Craniofacial skeletal growth was compared between male SHR and Wistar-Kyoto rats (WKR) using linear measurements on lateral and transverse cephalometric radiographs at the age of 12 weeks. Tibia length was measured as an index of whole body growth. Body weight　and blood pressure were measured from 3 to 12 weeks of age. Bone microstructure in the mandibular condyle and tibia between the two groups was compared at the age of 12 weeks using microcomputed tomography. RESULTS: The SHRs had a significantly lower body weight than WKRs from 7 weeks of age, and tibial length was significantly smaller in the SHRs than in the WKR at 12 weeks of age. In all SHRs, blood pressure was significantly higher than in WKRs from 3 to 12 weeks of age. Cephalometric analyses revealed decreased measurements of the neurocranium, viscerocranium, and mandible in SHRs, and mandibular growth was most negatively affected in this group. Lastly, in SHRs, microcomputed tomography analyses revealed decreased bone mineral density and bone volume/tissue volume in the mandibular condyle but not in the tibia. CONCLUSION: In growing SHRs, hypertension related to the hyperactivity of the sympathetic nervous system reduced craniofacial skeletal growth more than the growth of the tibia.

Cone-beam computed tomography-based diagnosis and treatment simulation for a patient with a protrusive profile and a gummy smile.

For patients with bimaxillary protrusion, significant retraction and intrusion of the anterior teeth are sometimes essential to improve the facial profile. However, severe root resorption of the maxillary incisors occasionally occurs after treatment because of various factors. For instance, it has been reported that approximation or invasion of the incisive canal by the anterior tooth roots during retraction may cause apical root damage. Thus, determination of the position of the maxillary incisors is key for orthodontic diagnosis and treatment planning in such cases. Cone-beam computed tomography (CBCT) may be useful for simulating the post-treatment position of the maxillary incisors and surrounding structures in order to ensure safe teeth movement. Here, we present a case of Class II malocclusion with bimaxillary protrusion, wherein apical root damage due to treatment was minimized by pretreatment evaluation of the anatomical structures and simulation of the maxillary central incisor movement using CBCT. Considerable retraction and intrusion of the maxillary incisors, which resulted in a significant improvement in the facial profile and smile, were achieved without severe root resorption. Our findings suggest that CBCT-based diagnosis and treatment simulation may facilitate safe and dynamic orthodontic tooth movement, particularly in patients requiring maximum anterior tooth retraction.