| Objective:The clinically short crown of the teeth caused by various reasons is a problem that dentists often face in clinical work.The main reasons are the residual roots and residual crown caused by trauma and caries,aesthetic problems caused by gingiva covering too many crowns.The common method to solve such problems is crown lengthening surgery(CLS).The most important principle of CLS is to achieve a stable biological width through gingival cutting and alveolar bone removing.Avoiding persistent damage to biological width(BW)while leaving enough space for post-repair to ensure retention and aesthetics To ensure postoperative outcomes,the current CLS method requires a distance of at least 3mm from the new gingiva’s position to the modified alveolar crest,including a 2 mm BW and a 1 mm sulcus depth.However,in clinical work,the following phenomenon is often observed,that is,the same criteria are followed for all patients undergoing CLS,and after the same period of recovery,the patient shows a different prognosis when preparing for final repair.In some patients,the position of the gingival margin can meet the requirements for the protection of BW and the position of the edge of the prosthesis.In some patients,the position of the gingival margin is too extended to the crown,resulting in the clinical crown still too short to meet the requirements of repair.This problem not only plagues the physicians in the periodontal and prosthetic departments,but also brings additional time and economic costs to the patients.Through consulting the literature,we have learned that foreign countries are constantly researching this issue,but the results of relevant reports are not consistent,the views on this issue are quite different,and domestic research on this issue is rare.In previous studies on this issue,there seems to be a consensus that the gingival biotype has different effects on the postoperative effects of related operations involving gingival resection.Therefore,we intend to further study and analyze the effects of gingival biotypes on BW and the location of posterior margin of CLS.It is preliminary to explore that different patients follow the same operating standards when exercising CLS,and the position of postoperative margins is different.The reason is whether the gingival tissue recovery process of different gingival biotypes is different,or the BW of different gingival biotypes is different,and then there are different manifestations in the process of postoperative gingival recovery.The value of BW is the main basis for the operation of CLS.The effect of postoperative is self-evident,and how to accurately obtain the data of patient BW before surgery is particularly important.For the measurement method of BW,many scholars at have carried out a lot of research.The traditional method is to observe and measure after making a slice by corpse,or use a periodontal probe to measure the distance from the bottom of the sulcus to the AC.None of these methods can measure the BW of patients without preoperative noninvasiveness.Cone-beam computed tomography(CBCT)has been used in various fields of the oral cavity for a long time with its high-precision development of hard tissues,short operating time,small amount of radiation,and three-dimensional reconstruction to obtain all information.It is also one of the purposes of this study to determine whether the BW data obtained by using the current measurement method is consistent with the BW data obtained by CBCT measuring the distance from the enamel cementum boundary to the same slice AC.If the measured BW data is not different from the BW data measured using the periodontal probe,the CBCT can be used to obtain the patient’s BW non-invasive before surgery.At the same time,according to the relatively accurate BW value of each patient’s surgical site position,the dental doctor can provide reference for individualized operation of different patients.This study would focus on the following issues:1.All the teeth used were measured with a periodontal probe to measure the BW value during the operation,and the data of the coronal displacement of the gingival margin were measured at 3 fixed time points after surgery(1 month after CLS,3 months after surgery,and 6 months after surgery).After statistical analysis,whether there was a difference in the amount of marginal gingiva displacement between different gingival biotypes at a fixed time point after CLS and the time point at which the gingival margin of different gingival biotypes was finally stabilized after CLS and whether the difference in BW values of different gingival biotypes were observed.2.Whether other factors such as the difference between the upper and lower teeth,will affect the position of the gingiva margin after CLS.3.All the teeth were tested by CBCT before CLS.The BW values ??were measured using CBCT matching software.The consistency of the two methods of measuring BW with periodontal probe and CBCT was compared.Methods:27 crown lengthening patients(age: 37.59±13.71 years old,Gender: 13 males,14females)with a total of 40 teeth(14 front teeth and 26 posterior teeth,16 upper teeth and 24 lower teeth)were involved in this study after screening.All the subjects were divided into two groups by their ginigival biotypes:thin gingival biotype(13 cases,age:40.23±15.01 years old,gender: 5 males,8 females,21 teeth)and thick gingival biotypes(14 cases,age: 35.14±11.87 years old,gender: 8 cases).All the teeth were checked before the CLS by using CBCT,and the BW and SD were measured during the surgery by using a periodontal probe.And the displacement of the gingival tissues of the teeth was measured at 1,3,and 6 months after CLS.All the data were recorded and making statistical analysis.Results:1.The results of the comparison of the gingival margin displacement of the median site and the adjacent site at the 3 time points after operation were as follows: there were statistically significant differences at 1 month after CLS(1.11±0.18 vs 1.25±0.20 mm,P=0.00),the 3 months after CLS(1.28±0.30 vs 1.55±0.28 mm,P=0.00)and the 6months after CLS(1.37±0.33 vs 1.61±0.26 mm,P=0.00).The amount of displacement of median site was significantly smaller than that of the adjacent site.2.The results of comparing thin gingival biotype and thick gingival biotype at the 3 time points after operation were as follows: there were no statistically significant differences at 1 month after CLS(1.18±0.17vs1.23±0.11 mm,P=0.27).There were statistically significant differences at the 3 months after CLS(1.27±0.15 vs 1.68±0.14 mm,P=0.00)and the 6 months after CLS(1.32±0.14vs1.76±0.12 mm,P=0.00),the thin gingival biotype showed less amount of gingival margin displacement after surgery.3.The results of gingival margin displacement of thin gingival biotypes were compared at 3 fixed time points after CLS: there was no significant difference between 1 month and 3 months after CLS(1.18±0.17 vs 1.27±0.15 mm,P=0.09)and between 3 months and 6 months(1.27±0.15vs1.32±0.14 mm,P=0.20).The results of gingival margin displacement of thick gingival biotype were compared at each time point as follows:there was a statistically significant difference between 1 month and 3 months after CLS(1.23±0.11 vs 1.68±0.14 mm,P=0.00),there was no significant difference between 3 months and 6 months(1.68±0.14 vs 1.76±0.12 mm,P=0.06).4.The results of the comparison of the gingival margin displacement of the buccal sites and the lingual sites at 3 fixed time points after CLS were as follows: there was no significant difference at 1 month after CLS(1.20±0.16vs1.20±0.16 mm,P=0.82),3months after CLS(1.48±0.23vs1.44±0.31 mm,P=0.54)and 6 months CLS(1.57±0.24vs1.50±0.31 mm,P=0.29).5.The results of the comparison of the gingival margin displacement of the upper and lower teeth at 3 fixed time points after CLS were as follows: there were no significant differences at 1 month after CLS(1.20±0.16vs1.20±0.12 mm,P=0.90),3 months after CLS(1.46±0.23vs1.47±0.29 mm,P=0.94)and 6 months after CLS(1.50±0.24vs1.58±0.29 mm,P=0.38).6.There were statistically significant differences between the results of BW(1.49±0.19vs1.80±0.21 mm,P=0.00)and SD(1.93±0.28vs2.24±0.41 mm,P=0.00)of thin and thick gingival biotypes measured by using periodontal probes.7.There was no statistically significant difference in the results of the measurement of the BW,whether it was the overall comparison of all the teeth or the further division into the 2 groups of thin-thickness biotype.[All tested teeth(1.64±0.26 mmvs 1.69 ±0.20 mm,P=0.11),thin gingival biotype(1.49±0.19mmvs1.57±0.12 mm,P=0.07),thick gingival biotype(1.80±0.21mmvs1.87±0.18 mm,P=0.61)].8.There were no statistically significant difference in the results of the measurement of the BW(1.59±0.15vs1.67±0.29 mm,P=0.42)and SD(2.00±0.28 vs 2.11 ± 0.43 mm,P=0.44)of the anterior teeth and posterior teeth.Conclusions:1.After the CLS,the gingival margin displacement of the median site and the adjacent site were different.The former was significantly smaller than the latter.2.The amount of gingival margin displacement of the thin gingival biotype and the thick gingival biotype showed a difference in the beginning of 3 months after CLS,and the difference was more obvious in the 6 months after CLS.3.In the thin gingival biotype,the gingival margin displacement was stable in 1 month after CLS,and the gingival margin displacement of the thick gingival biotype was stable in the 3 months after CLS.4.The difference between the buccal lingual site and the position of the upper and lower teeth was not a factor influencing the change of the position of the gingival margin after CLS.5.The BW and SD of the thin gingival biotype and the thick gingival biotype were different.The BW and SD of the thin gingival biotype were smaller than the BW and SD of the thick gingival biotype.6.The BW data measured using CBCT was consistent with the BW data measured using periodontal probes. |
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