| Objective: In clinical work,it is found that the "free hand" implant of mandibular second molar is easily limited by oral conditions and jaw anatomical structure.The possibility of deviation is higher when implant is implanted,which will have adverse effects on the implant restoration and the long-term stability of the implant.Therefore,this study used the method of imaging analysis,compared with the mandibular first molar,to measure the related anatomical factors of alveolar bone in the implant area of mandibular second molar and evaluate the effect of clinical implant,so as to provide the basis for the design of mandibular second molar implant.Methods:Part one: CBCT measurement of alveolar bone in mandibular molar area:Choose from June 2017 to January 2020 with 193 cases who have taken CBCT(Cone beam CT)and want to implant restoration of the first or second molars of the mandible in Stomatological Hospital Affiliated to Dalian Medical University,of which there are 105 mandibular first molars,88 second molars,79 males and 114 females,aged from 23 to 75 years old,with an average of(45.7±5.21)years old.Ondemand 3D and SPSS23.0 software were used to measure and compare the differences of alveolar bone in inclination,alveolar bone width,the distance from alveolar crest to mandibular nerve canal,alveolar bone density and alveolar bone morphology in the implant area of mandibular first and second molars.The inspection standard is α=0.05。Part two: Evaluation of the implant effect of mandibular second molars: 89 patients with mandibular first and second molars were selected in part one,including58 mandibular first molars and 31 mandibular second molars,43 males and 46 females,aged 26～80 years,with an average of(47.8±3.46)years old.Ondemand3 D and SPSS23.0 software were used to measure and compare the neck deviation,apical deviation,depth deviation and implant angle deviation of mandibular first and second molar implants and simulated implants,and the deviation / failure rate of one-stage implant surgery were measured and compared.And the survival rate,marginal bone resorption and the proportion of complications of mandibular first and second molars were compared immediately,6 months and 12 months after restoration.The inspection standard is α=0.05。Results:Part one1 The inclination of alveolar bone and the distance from alveolar crest to mandibular nerve canal of mandibular first and second molars: The inclination of alveolar bone and the distance from alveolar crest to mandibular nerve canal of mandibular first molar were greater than those of mandibular second molar(P<0.05),but the inclination of alveolar bone and the distance of canal crest of mandibular first and second molar had no significant difference in different gender and the existence or no of the third molar(P>0.05).2 Alveolar bone width and alveolar bone density of mandibular first and second molars: The alveolar bone width W1 and alveolar bone density of mandibular first molars were greater than those of the second molars,while the alveolar bone width W2 and W3 were less than those of the second molars(P<0.05).The alveolar bone density in the implant area of mandibular second molar with third molar was higher than that in the implant area without third molar(P<0.05);There was no significant difference in the width of alveolar bone between the existence or no of the third molar(P>0.05).3 Alveolar bone morphology: The incidence of lingual depression of mandibular first molar(53.3%)was lower than that of mandibular second molar(84.1%).Part two1 Implant deviation:The neck deviation,apical deviation and implant angle deviation of mesial distal and buccolingual direction of mandibular second molar were larger than those of mandibular first molar(P<0.05).However,there was no significant difference in buccolingual and mesial distal depth deviation between the first and second mandibular molars(P>0.05).2 Deviation / failure rate and influencing factors: 58 mandibular first molars were implanted,and the deviation and failure rate were 0%;A total of 31 mandibular second molars were implanted,and 5 of them were deviated / failed.The rate of deviation and failure was 16.1%.When alveolar inclination < 70°or the width of alveolar crest < 6mm,the deviation / failure rate were higher when compared with the absence of these factors(P<0.05).3 The implant retention rate,marginal bone resorption and postoperative complications: The implant retention rate of mandibular first molar in immediate restoration,6 months and 12 months after restoration were 100%;The implant retention rate of mandibular second molar in immediate restoration,6 months and 12 months after restoration were 96.7%.The amount of marginal bone resorption at 6months and 12 months after restoration,and the proportion of postoperative complications at 12 months after restoration of mandibular second molars were larger than those of mandibular first molars,and the differences were statistically significant(P<0.05).Conclusion:1 After the extraction of mandibular first and second molars,the implant conditions of alveolar bone in the implant area of mandibular first molars were better than those of the second molars in terms of inclination,width of alveolar crest,the distance from alveolar crest to mandibular nerve canal,density and morphology,which indicated that from the anatomical point of view of mandible,the implant operation of the second molars would be more difficult than that of the first molars.2 When the mandibular third molar exists,the alveolar bone density of the mandibular second molar implant area is higher,which is beneficial to obtain higher initial stability of the mandibular second molar implant.3 In the case of "free hand" implant,the implant accuracy and post restoration evaluation(marginal bone resorption,post restoration complications)of the mandibular first molar were better than those of the second molar,suggesting that implant guide should be used in the implant operation of the mandibular second molar.4 Alveolar bone inclination and width of alveolar crest are the risk factors for the deviation / failure of the first stage of mandibular second molar implant surgery.It is suggested that doctors need to accurately grasp the alveolar bone inclination and the width of alveolar crest in the first stage of mandibular second molar implant surgery. |
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