Micro-computed Tomography Evaluation Of Ceramic Crowns Fabricated By CAD/CAM Systems And The Traditional Techniques,a Meta-analysis

Background:With the development of repair technology and biomaterials,all-ceramic crowns are gradually replacing other materials and are favored by doctors and patients.The adaptation of prostheses,including marginal fit and internal fit,especially the marginal fit has an important impact on the prosthetic restoration success rate and longivity.The edge gap is the core of marginal fit.Inaccurate margin may lead to the accumulation of bacteria and plaque,the dissolution of luting materials,and the introduction of unfavorable inflammation or the periodontal tissues.The suitability of restorations can currently be evaluated by a variety of different techniques.Clinically,the marginal adaptation can be assessed objectively by direct observation,direct probe inspection,radiographic techniques,etc.However,these methods can just be used to evaluating the edge condition excludingthe status of the interior in the restoration,which are easily influenced by the experience of the observer.The precision is also lower.The impression replica technique is to use an impression material to reproduce the gap between the prosthesis and the preparation.The silicone replica impression can be measured in vivo or in vitro for internal and edge gap measurements.The impression replica technique is suitable for measuring crowns,inlays,implant prosthesis,and all-ceramic fixed partial denture.The impression replica technique has the characteristics of simple operation,low cost,low equipment requirements,no damage to the model,no need of special cutting tools,etc.However,the impression may be teared in the process of the assessment,which may cause thelack of the required measurement site.The microscope may also cause inaccurate measurement of the value of the restorations adaptation.In addition,traditional fractional-based stereomicroscope,electronmicroscope,optical microscope,and atomic force microscopy that can provide nano-scale scanning levels,can evaluate sectioned specimens by using a microscope.However,the assessment of the stereomicroscope technique is to measure the cross-sections of the prosthesis and the preparation,the process of section may lead to deformation.And,if the angle of the sample measured by the electronmicroscope is incorrect,the analysis result may also not be accurate.The Micro-CT technique is a novel method for measuring the suitability of prosthesis in recent years.Because of its advantage of non-destructiveness and reliability,the Micro-CT technique has been more and more widely used in the evaluation of suitability of all-ceramic crowns.Domestic and foreign scholars have conducted extensive researches on the suitability of all-ceramic crowns manufactured by different methods,but there is no the systematic evaluation on suitability by using the Micro-CT technique.This study is to uses evidence-based medicine methods to conduct a meta-analysis of studies published on the applicability of the Micro-CT technique by assessing the suitability of all-ceramic crowns manufactured by different methods,and to provides scientific guidance for clinical and experimental studies.Methods:The following databases were searched : Pubmend,OVID,Cochrane library,CBM,CNKI,Wanfang etc.Searching articles about all-ceramic crowns fabricated by using CAD/CAM systems or the conventional techniques,in which crown adaptation were assessed by the Micro-CT technique.The last related articals of suitability research was done in January 2018,and the language was limited to Chinese andEnglish,according to the PICOS principles and the literature inclusion and exclusion criterias.Two individuals extracted data by reading the literature titles and abstracts individually,and graded literature quality of the selected literature.The Meta-analysis was peformed by Revman5.3 software.The standardized mean difference(SMD),95%(confidence interval)were used to combine the statistical datas.The statistical results were represented by the forest plots.Publication bias between studies were represented by funnel plots.Results:A total of 835 related articles were searched,and only 8 articles met the inclusion criterias,including 119 CAD/CAM cases and 89 traditional technology cases.The overall quality score of RCTs was moderate,as none of the studies involved participants double-blind,or blinded assessment of the results.The results of the analysis showed that there was no statistical difference about crown adaptation assessed by the Micro-CT method,which was fabricated by the conventional techniques and the CAD/CAM systems.At the same time,there was no statistical difference in the adaptation evaluation of all-ceramic crowns between the CAD/CAM groups.Conclusions:1.The marginal gap values of the all-ceramic crown restorations fabricated by the traditional lost-wax heat-pressing and slip-casting technology and CAD/CAM systems were within the clinically acceptable ranges,and there was no statistical difference.2.Studies have shown that there is no statistical difference in the marginal gap value of the all-ceramic crowns produced by the CAD/CAM system.3.As a novel evaluation method for the adaptation of ceramic prostheses,the Micro-CT technique is reliable.