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Objective:To explore the clinical application effect of open vertical helical loop to correct ectopic eruption of the first permanent molar, and to provide reference for the selection of treatment timing and methods for ectopic eruption of the first permanent molar.Methods:A total of 30 patients with unilateral or bilateral ectopic eruption of maxillary first permanent molars, aged from 7 to 8.5 years old, who visited the Affiliated Hospital of Jining Medical University from 2020 to 2021, were retrospectively selected. The first permanent molars were moved to their normal positions by bonding buccal tubes between the second primary molars and the first permanent molars with a vertical loop. We compared and analyzed the mesial inclination angle of the first permanent molar, the length of the lateral dental arch, and the root resorption status of the second deciduous molar before and after treatment.Results:All 30 patients underwent complete orthodontic treatment, with the first permanent molar adjusted to its normal position. The inclination angle of the first permanent molar after treatment was (91.3±5.1)°, which was statistically significant compared to (78.1±6.3) ° before treatment ( t=-10.023, P=0.014); The length of the lateral dental arch after treatment was (34.0±1.0)mm, which was significantly increased compared to (31.61±1.1)mm before treatment, and the difference was statistically significant ( t=-25.96, P=0.007). After treatment, the degree of root resorption of the affected second molar significantly increased compared to that before treatment (χ 2=12.002, P<0.001); There was no statistically significant change in root resorption before and after treatment of the healthy second molar ( P=0.818). Conclusions:The use of open vertical helical loop correction for ectopic eruption of maxillary first permanent molar can effectively adjust the mesial inclination angle of patients with ectopic eruption of maxillary first permanent molar. However, close attention should be paid to the root resorption of the second primary molar, and early detection and treatment should be carried out in clinical practice. If the root resorption of the second primary molar is severe after treatment, a retainer should be made in a timely manner to maintain the arch length.
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BACKGROUND: The number of roots and morphology of the root canal system of permanent mandibular first molars vary greatly among different populations; therefore, it is important to be familiar with the variations in the root and root canal for the location and negotiation of the canals. OBJECTIVE: To investigate the variations in the roots and root canal of permanent mandibular first molars in the Han population of southwest Shandong Province by cone-beam CT. METHODS: 656 patients undegoing cone-beam CT examination at the Department of Stomatology, Affiliated Hospital of Jining Medical University, from September 2012 to October 2015 were recruited, and all patients had healthy, well-developed, and untreated bilateral permanent mandibular first molars with normal appearance. Subsequently, the three-dimensional reconstruction based on cone-beam CT data was performed using Planmeca Romexis software to observe the variations in the root and root canal system of permanent mandibular first molars in the Han population of southwest Shandong Province. RESULTS AND CONCLUSION: Among 1312 permanent mandibular first molars, the incidence of permanent mandibular first molars with three roots was 70.66% (927/1312); the majority of root canal variations involved two roots and three root canals, accounting for 48.09% (631/1312). The incidence of distal root was 35.37% (232/656), the incidence of distal root was 29.34% (385/1312) in total teeth, and the incidence of distal root bilaterally was 68.95% (153/232). There was a significantly increased incidence of distal root on the right side than on the left side (P < 0.05), and the incidence in the male was significantly higher than that in the female (P < 0.05). These results suggest that most of Han populations in southwest Shandong Province have permanent mandibular first molars with two roots, and the root canal variations mainly involve two roots and three root canals, with the high incidence of distal root. Moreover, cone-beam CT is available for detecting the variation in roots and root canal system, which can provide references for root canal treatment.
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BACKGROUND:The design of post and core of the molar is affected by various factors,including the effect of the number of posts on the retention force and the effect of the number of posts on the dentin stress and distribution.OBJECTIVE:To make a mechanical analysis on the three-dimensional finite element models of the mandibular first molar defect restored with different numbers and locations of gold alloy posts,cores and all-ceramic crown.METHODS:Cone-beam CT based three-dimensional finite element models of post and core restored first mandibular molars were established,with seven different post designs.According to the numbers and location of gold alloy post inserted into root canal,a single post was placed at the mesial buccal root in group A,a single post at the mesial tongue root in group B,a single post at the distal root in group C,two posts at the mesial buccal root and the distal root in group D,two posts at the mesial buccal root and mesial tongue root in group E,two posts at the mesial tongue root and the distal root in group F,one post respectively at the mesial buccal root,mesial tongue root and distal root in group G.The von Mises criterion was applied for comparing the maximum yon Mises stress value of dentin and stress concentration areas in the seven models which restored with golden alloy posts and cores with all-ceramic crown under the maximum (600 N),vertical (225 N),inclined (225 N) and horizontal (225 N) loads.RESULTS AND CONCLUSION:Under vertical,inclined and horizontal direct loads,the maximum stresses on the remaining dentin in group C were significantly lowest,compared with the groups A and B.The maximum stresses on the remaining dentin changed irregularly with the variation of the numbers and location of posts,when the mandibular first molar defect was restored with all-ceramic crown with gold alloy posts and cores.Under the horizontal load,the maximum Von Mises stress value of the dentin increased remarkably.Under the horizontal load,the maximum stresses on the remaining dentin in group E were the highest.To conclude,the numbers and location of posts and cores have influence on magnitude and distribution of stress,when the mandibular first molar defect is restored with all-ceramic crown with gold alloy post and core.
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Objective To evaluate the effects of flapless versus flap implant surgery on the tissues surrounding the implants in the esthetic zone.Methods A controlled study was conducted in 20 patients with a single implant in the anterior esthetic zone,as compared with the flapless and traditional flap implant placement.6 and 12 months after the implant ation,the vertical reduction of labial and lingual bone were assessed by cone beam computed tomography (CBCT);6 and 12 months after the crowns restoration,the peri-implant soft tissues were examined by probing depth (PD),modification sulcus bleeding index (mSBI),papillary index (PPI) and evaluated by pink esthetic score (PES) standard.Results The vertical reduction of the flapless labial and lingual bone was lower than that of the flap,in which the change of labial bone was statistical differences at 6 months after implant surgery between groups (P ＜ 0.05).The differences of PES between two groups were not statistically significant,although PES increased over time in both groups,which the flapless group had a significantly change in PES from crown placement to 12 months (P＜0.05).Conclusions A flapless implant surgery in sufficient bone support may provide a better short-term esthetic result,whereas the longterm effects need further studies.
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<p><b>OBJECTIVE</b>To make a mechanical analysis on three-dimensional finite element models of the mandibular first molar defect restored with post core and all-ceramic crown, and to provide a guideline for planning restoration for such kind of tooth structure defect.</p><p><b>METHODS</b>Cone-beam CT based three dimensional finite element models of post and core restored first mandibular molars were established, with 6 different ferrule designs (the ferrule with only 180 axial wall on different locations). The von Misses criterion was applied for comparing the maximum von Misses stress value of dentin and stress concentration areas in six models which restored with fiber post or cast NiGr alloy post core or Au alloy post core under the maximum, vertical, inclined and horizontal direct loads.</p><p><b>RESULTS</b>The restoration effects in six models were compared, and the maximum von Misses stress concentration areas were not obviously different. The maximum von Misses stress value of NiCr alloy post core and crown was 62.81 MPa. Under horizontal load, the maximum von Misses stress value of dentin increased remarkably.</p><p><b>CONCLUSIONS</b>The location of residual dentin has little influence on the stress distribution, when restored by post core and crown. Au alloy post core and crown or fiber post core and crown are superior to NiCr alloy post core and crown.</p>
Subject(s)
Chromium Alloys , Cone-Beam Computed Tomography , Crowns , Dental Porcelain , Dental Restoration, Permanent , Dental Stress Analysis , Dentin , Physiology , Finite Element Analysis , Molar , Post and Core TechniqueABSTRACT
BACKGROUND:The location of residual dentin may affect stress distribution of tooth root. ＜br> OBJECTIVE:To make a three-dimensional finite element analysis of gold al oy post-core and al-ceramic crown in the repair of structure defects of the mandibular first molar, and to provide a guideline for planning restoration for such kind of tooth structure defects. ＜br> METHODS:Three-dimensional finite element models of the restored first mandibular molars were constructed by CT image reconstruction technique. Then MIMICS software was used to separate the areas and finish the three-dimensional calculation. GEOMAGIC software was also applied to modify and generate a NURBS surface in each patch. Al components of the models were assembled under the ANSYS preprocessor. The Mohr strength theory was applied for comparing the maximum Mohr stress value of dentin and stress concentration areas in six models under different simulating loads. ＜br> RESULTS AND CONCLUSION:The restoration effects in six models were compared, the maximum Mohr stress value of dentin and stress concentration areas were not obviously different. The location of residual dentin has little influence on the stress value and distribution, when restored by gold al oy post-core and and al-ceramic crown.
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BACKGROUND:Hydroxyapatite/gel nano-composite has the same mechanical strength to the natural bone, but its ability to repair bone defects and osteogenic effect need to be confirmed by further studies. OBJECTIVE:To explore the repair effect of hydroxyapatite/gel bionic composite in skul defects of rabbits. METHODS: The hole-like calvarium defect models were established in rabbits, and treated with hydroxyapatite/ gel composites (hydroxyapatite/gel group), autologous skul as positive control (autologous bone group) and nothing as negative control (blank group). The repairing condition in the skul defect areas were observed and analyzed by X-ray and CT at 4, 8, 12 weeks after implantation. RESULTS AND CONCLUSION: After 8 weeks, X-ray assessment showed that normal-like bone tissue appeared in the defect region of the autologous bone group; in the hydroxyapatite/gel group, dense bone with similar morphology to normal bone tissue was found in the central site of defect region, and the boundary was slightly blurred. After 12 weeks, the hydroxyapatite/gel showed blurred edge compared with autologous bone, and the center of the composite was disconnected; in the blank group, a clear and regular transmitted shadow was observed. After 12 weeks, CT examination showed that the hydroxyapatite/gel was connected tightly with the surrounding normal bone tissue. As a new bionic composite, the hydroxyapatite/gel can achieve good effect in repairing skul defects of rabbits.
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Objective To evaluate the alteration of labial bone mass one year after immediate implant or delayed implant placement in esthetic zone.Methods From June 2009 to June 2012,22 patients with 11 immediate implant and 11 delayed implant in the maxillary anterior region were followed up.CBCT images were obtained immediately after surgery and one year after implant placement,the horizontal and vertical alterations of the labial bone were evaluated by image analysis software.Results The 1-year vertical reduction of labial bone after immediate implant placement was statistically significant (P＜0.05),and no significant difference in delayed implant (P＞0.05).The 1-year horizontal reduction of labial bone was statistically significant at coronal and middle of implant,without significant difference at apical of implant.Conclusions Immediate implant can not stop the physical absorption of labial alveolar ridge,and the study can provide reference to achieve esthetics in the anterior region.
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BACKGROUND:As the rapid development of oral implantation and restoration techniques, as wel as the increasing enlargement of indications, angulated abutments have been widely used. Posterior teeth region, as the weight-loading region of occlusion, can bear great force from the implants, the assessment of angulated abutments in posterior teeth region has clinical value. OBJECTIVE:To evaluate the short-term clinical efficacy of angulated abutments on the implant denture in posterior teeth region. METHODS:From January 2008 to January 2013, 114 patients with 175 ITI implants in the posterior teeth region were included in this study and they al underwent single-crown restoration. The involved patients were divided into angulated abutment group and straight abutment group. Periodontal probing depth, modified plaque index, modified sulcus bleeding index and peri-implant crestal bone loss in two groups were recorded at 6 months and 2 years after restoration. Cumulative survival rate of the implant denture was calculated by life-table analysis. RESULTS AND CONCLUSION:There was no significant difference in periodontal probing depth, modified plaque index, and modified sulcus bleeding index between two groups (P>0.05). The annual crestal bone loss showed no significant difference between two groups (P>0.05). Moreover, the 5-year cumulative survival rate with 15° and 20° abutments was 95.6%, and that with straight abutment was 96.4%. The angle of abutments has no correlation with peri-implant soft tissue and peri-implant crestal bone loss, implant restorations with 15° and 20° angulated abutments may be successful y used in the posterior region, whereas the long-term effects need further research.