Clinical Study Of The Keratinized Mucosa Augmentation At The Buccal Site Of Adjacent Multi-implants In The Posterior Mandible

Background:The healthy peri-implant soft tissue is important for long-term stability of implant restoration.Autogenous free gingival grafts(FGG)are the most effective method for keratinized mucosa augmentation around implants but also exhibit the disadvantages of high morbidity.Recently,soft tissue substitutes are used for peri-implant keratinized mucosa augmentation.The lack of keratinized mucosa is common in the adjacent multi-implants of the posterior mandible.Some studies showed that the predictability of keratinized mucosa augmentation was lower in the mandibular posterior region than the other sextants as a result of the local anatomical limitation.However,the prognostic evidence regarding the clinical effect of keratinized mucosa augmentation at the buccal site of adjacent multi-implants in the posterior mandible is scarce.Clinical studies are insufficient in this sextant.Objective:1.To evaluate the effect of FGG at the buccal site of adjacent mandibular molar implants and compare the difference between the first molar site(M1)and second molar site(M2)with a 3-year retrospective study to elucidate the influence of implant location on the clinical effect of FGG.2.To compare the clinical outcomes and patient-reported outcome measures(PROMs)after augmentation with xenogeneic collagen matrix(XCM)or FGG during different postoperative phases with a 6-month prospective study to provide clinical evidence for the application of XCM at the buccal site of adjacent multi-implants in the posterior mandible.Materials and methods:1.The retrospective study:from January 2019 to December 2019,twenty-one patients treated with FGG at the buccal site of adjacent mandibular molar implants from January 2016 to December 2016 at Department of Oral Implantology of Peking University Hospital of Stomatology were recalled for examination.The keratinized mucosa width(KMW)was measured at baseline and immediately after surgery and then at 6 months and 3 years after surgery.The probing depth,modified bleeding index,modified plaque index,modified gingival index,and marginal bone loss were assessed at 3 years.Peri-implant parameters were measured and compared between M1 and M2.2.The prospective comparative study was conducted from November 2018 to December 2019 at Department of Oral Implantology of Peking University Hospital of Stomatology.Forty-two patients with KMW of<2 mm at the buccal site of adjacent multi-implants in posterior mandible were enrolled.All underwent vestibuloplasty and were allocated to FGG(control)or XCM(test)group,21 patients per group.The buccal KMW were evaluated at baseline and immediately after surgery and then at 3 months and 6 months after surgery.The other peri-implant soft tissue parameters were also evaluated.PROMs were evaluated using questionnaires and visual analog scales immediately after surgery,2 weeks postoperatively,and 6 months postoperatively.Intraoperative morbidity of pain,stress,nausea,tolerance to time,and acceptance of surgery were evaluated immediately after surgery.The severity and duration of daily subjective pain,swelling,and bleeding were compared within a 2-week postoperative period.Pain severity between groups during daily oral activities and pain perception from donor sites and recipient sits of control group were compared.The willingness to retreat and satisfaction were assessed at 6 months.Results:1.In the 3-year retrospective study,the mean increase in the KMW was 2.35±1.33 mm,and the mean KMW shrinkage rate was 58 ± 23%.M1 showed a significantly greater increase in the KMW than M2(M1:2.87 mm ± 1.40 mm,M2:1.83 ± 1.06 mm,p<0.05).M2 exhibited more FGG shrinkage than M1(M1:50 ± 26%,M2:68 ± 20%,p<0.05).However,other peri-implant parameters did not show significant differences when compared between different sites.2.During the 6-months follow-up study,the gain of KMW was significantly higher in FGG than XCM(XCM:1.57±1.69 mm,FGG:2.68 ± 1.80 mm,p=0.003).XCM showed higher mean KMW shrinkage rate than FGG(XCM:65±21%;FGG:47±23%,p=0.000).No significant between-group differences were observed in the parameters immediately after surgery,except acceptance of surgery(0,0-30.0 vs.30,0-50.0,p=0.025).At 2 weeks,pain severity(46.7 ± 25.9 vs 61.9 ± 20.2,p=0.040)and duration(5.52 ± 3.57 vs 8.48 ± 2.80,p=0.005)were significantly lower in the test group,and pain perception during speaking and chewing was significantly higher for FGG,with no significant between-group differences in swelling and bleeding.Most patients(76%)reported higher pain perception at donor sites than recipient sites in control group.At 6 months,the test group showed a higher willingness to retreat(76%vs 43%,p=0.021);however,satisfaction with treatment outcomes was similar in both groups.Other peri-implant parameters did not show significant difference.Conclusions:1.FGG at the buccal site of adjacent multi-implants in posterior mandible are effective and stable.M1 was associated with a more stable KMW than M2,but no difference in other peri-implant parameters was found between the sites.The implant location may affect the increase in the KMW after FGG,suggesting remarkable shrinkage of FGG as a result of shallow vestibules,restriction from the external oblique line and muscle attachment,and absence of support from the adjacent teeth.2.At the buccal site of adjacent multi-implants in posterior mandible,the mean KMW at 6 months was greater than 2mm following XCM.FGG exhibited more predictable outcome in terms of gain of KMW than XCM.XCM demonstrated higher acceptance of surgery,less postoperative morbidity,and a higher willingness to retreat than FGG during different postoperative phases,mainly for less and shorter pain perception during the early healing stage.