| Recently, tooth fracture receives more and more attention of dentisties and patients. It is related with root canal therapy. This preliminary study provides three parts including article review, clinical survey and laboratory experiment to research the posterior tooth fracture .Part one ReviewMethods Retrieve the Medline and VIP database in the past decade(2001.1～2010.12) by using key words such as"endodont"and"tooth fracture"to gain the articles on tooth fracture after RCT published in Chinese and English. Further articles were gleaned from references listed in the publications and related articles and from searching selected journals. Articles on dental trauma, diagnosis/diagnoses and treatment/management were excluded. Pooled analysis the Chinese and English, years, risk factors of the satisfactory articles.Results 142 related articles were found.10 of them were expert opinion or literate reviews,37 were case reports and another 95 were studies. There were no vacancy in quantity of every year. In 96 studies, 84(88.4%) were involved to risks for potential frature in endodontically treated teeth. The potential risks were present in access cavity preparation, instrumentation and irrigation of the root canal, obturation of the instrumented root canal, post-space preparation, post selection, and coronal restoration and from inappropriate selection of tooth abutments for prostheses.The articles on post and artifical crown were the most and the constituent ratio is 48.8%(41).11(11.5%) articles were related to prevalence and incidence of tooth fracture.But of these articles, we could not identify any high-level randomized control study.Most of them(66.9.1%) were mid-level studies(LOE-2,3) and some (19.0%) were low-level studies(LOE-5).Conclusions Tooth fracture received attention in the past decade. Some scholars consided tooth fracture was related with root canal therapy.However, there were no high-level articles.Part two Clinical SurveyMethods Collect cases of tooth fracture from Endodontic department of Jiangsu provincal Stomatological hospital during Sep 1st ,2009 to Sep 1st,2010. If the cases were that posterior teeth were diagnosised tooth fracture and had particular, relative inforamation of them were gathered. Meanwhile, analysis the typical cases.Result 171 cases of postetior teeth fracture were collected. Premolar and molar were 44 and 127,respectively. Maxillary and mandiblar teeth were 119 and 52,respectively. On fracture location, maxillary first molar were most(57/171) and mandibluar first molar were second(33/171) and mandibluar fisrt and second premolar were least(2/171 and 4/171,respectively).On failure mode, crown fracture, root fracture and crown and root fracture were 60, 12 and 99, respectively. On biting hard food, biting were most(93/171), doubtfull biting were second(61/171) and no biting were least(17/171). On pulp condition,there were no significant difference between vital pulp and root canal therapy. Male and female were 90 and 81,respectively.18- ,45-and 60-years were 62,61 and 48,respectively.Besides, show 4 typical cases.Conclusion On fracture location, maxillary first molar were most and mandibular first premolar were least.The failure mode is major in crown and root fracture and fracture were always companied with biting hard food.There were no significant relationship between tooth fracture and root canal therapy,gender and age.Part three Laboratory experimentThe following are one-factor experiments to study the relationship between tooth fracture resistance and cavities,root canal preparation and crown restoration, respectively.1 Three types of cavitiesMethods Forty mandibular premolars were divided into four groups by randomized bolck .Group A were treated with nothing and served as control group. Group B,C,D were prepared to form three different cavities (occlusal, mesio-occlusal and mesio-occlusal-distio cavities) and endodontically treated. A compress load was applied at 45°to the long axis with an Instron machine until fracture at a crosshead speed of 1mm/min. Data were analyzed by Stata 10.0 software(heterogeneity of variance,Chi2(3)=16.2123 Prob>chi2=0.001). The failure mode can be classified as restorable and unrestorable with blinding methods.Results The maximum fracture resistances of each group were (870.3±313.4)N, (600.2±224.0)N,(493.5±102.5)N and (262.6±100.0)N.There were no significant difference between A and B groups(P=0.068) and between B and C groups(P=0.818). However,there were significant difference betweent A and C groups(P=0.001), A and D groups (P=0.000),B and D groups(P=0.000) and C and D groups(P=0.002).If the fracture resistances of group A were 100%, then the fracture resistances of group B,C,D were reduced to 69.0%, 56.7% and 30.2%, respectively. Tooth fracture occurred in every group. Unrestorable failure mode were happened in group A and B (2 and 3,respectively).Conclusions The fracture resistance of teeth were reduced after root canal therapy.The cavities more larger ,the teeth easier fracture. The teeth with small cavities were not easy to fracture.But,once fracture,the root will be involved in.2 Two types of root canal preparation methodsMethods Ten mandiblur molars were randomly divided into two groups by casting lots.Group A (hand preparation) were prepared to size 30 .02 taper by stainless steel K-files with step-back.Group B (rotary technique preparation) were prepared by progressively tapered systems ProTaper with crown-down.Sharper files (Sx,S1,S2) were used to prepared root canals and Finisher files(F1,F2) were used to fine apcial repair to size30 .09 taper. Both receive root canal filling by cold lateral compaction, zinc-phosphate cement base and amalgam repair of endodontic access cavity preparations. All the teeth were embedded in superhard stone.A compress load was applied parallel to the long axis with an Instron machine until fracture at a crosshead speed of 1mm/min. Data were analyzed by SPSS 17.0 software. Root fractures were observed by magnifier afer remove the superhard stone.Result The maximum fracture resistances of Group A were (920±62.8)N and Group B were (741±356.4)N. There were no significant difference between two groups (P=0.51).No root fracture was observed.Conclusion No significant difference between fracture resistances reduced by hand preparation and rotary technique preparation were observed.3 One Crown restoration methodsMethods Twelve mandiblur molars were prepared to size 30 .02 taper by K-files with step-back and received root canal filling by cold lateral compaction, zinc-phosphate cement base and amalgam repair of endodontic access cavity preparations.All the teeth were randomly divided into two groups. Group A were restored without casting crowns and group B were with cobalt-chromium alloy casting crowns. The embedding,fracture resistance determining and fracture observation of all samples were the same as experiment 2. Data were analyzed by SPSS 17.0 software.Results The fracture resistance of Group A (818.05±100.06)N were lower than Group B(1079.06±195.05)N (P=0.015). Teeth restored with casting crowns were observed no tooth fracture but all superhard stone fracture.However, teeth without casting crowns were observed crown fracture.No root fracture was observed.Conclusion The fracture resistance can be increased by cobalt-chromium alloy casting crown restoration.
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