OBJECTIVETo study the effect of bleaching on the mechanical properties of human dentin.

METHODSThe finite element method (FEM) based the cohesive zone model had been employed to study the fracture resistance of human dentin. There types of dentin were considered, i.e. original dentin, dentin after direct-bleaching and indirect-bleaching.

RESULTSThe bleaching treatments had large impact on the crack growth resistance of human dentin. The initiation toughness (1.48 MPa x square root of m), growth toughness (3.90 MPa x square root of m x mm(-1)) and plateau toughness (3.25 MPa x square root of m) of human dentin were reduced to 1.29 MPa x square root of m, 3.45 MPa x square root of m x mm(-1) and 2.71 MPa x square root of m respectively after indirect-bleaching. The worst case was the direct-bleaching which causes significant reductions in the growth toughness (0.14 MPa x square root of m x mm(-1)) and plateau toughness (1.63 MPa x square root of m) respectively, while the initiation toughness remained the same as that after indirect-bleaching.

CONCLUSIONThe cohesive zone modeling is an effective tool in characterizing the fracture behavior of human dentin. Bleaching treatments reduce the crack growth resistance of human dentin and increase the risk of fracture of teeth.

Dentin ; Humans ; Tooth Root

Inflammatory external root resorption (IERR) refers to the pathological process of dissolving the hard tissue on the outer surface of the tooth root by the body's own immune system under the stimulation of various physical and chemical factors such as infection, stress, trauma and orthodontic treatment. Severe IERR can lead to endodontic and periodontal diseases, and even the loss of teeth. Therefore, understanding the etiology and the pathogenic mechanism of IERR are of importance in its prevention and treatment. This article will review the etiology and the regulation mechanisms of IERR.
Dental Cementum ; Humans ; Root Resorption ; Tooth Root

OBJECTIVETo investigate the effects of root canal preparation treated by endodontists of different levels in different difficulty associated with the root canal anatomy factors.

METHODSTotally 422 teeth with 901 root canals were randomly selected from the Conservative Dentistry Department, West China Stomatology Hospital, and these teeth were respectively treated by junior specialist postgraduates, senior specialist postgraduates and endodontic specialists. Grading criteria of root canal risk factor and root canal therapy difficulty assessment were found based on 6 items: Tooth type, working length, root curvature, calcification, number of canals, and the previous endodontic treatment. The effects of root canal preparation with different difficulty in different groups were analyzed with RxC Chi-square test.

RESULTSSuccess rates of root canal preparation in junior group and senior group during three difficulty groups were statistically different (P < 0.05), and the root canal therapy difficulty group I > group II > group III. The operator factors in root canal therapy difficulty group I and group II were not significantly different P > 0.05). But in root canal therapy difficulty group III, the endodontic specialist group have highest success rate in root canal preparation.

CONCLUSIONThe cases of root canal treatment should be treated by endodontist of corresponding level according to the difficulty. In difficult cases, endodontic specialist can provide better root canal preparation result.

China ; Humans ; Root Canal Preparation ; Root Canal Therapy ; Tooth Root

Humans ; Root Canal Therapy ; Tooth Apex ; Tooth Root ; injuries

The management of the third molar tooth in mandibular angle fracture is still controversial. Retrospective analysis of 197 cases of mandibular angle fractures associated with third molar tooth was undertaken. Selective prophylactic extraction of the third molar teeth were undertaken in 66 cases. The third molar teeth were retained in 131 fractures. The indication of extraction of the third molar teeth in mandibular angle fracture were as follows: 1) interfering with reduction of the fracture; 2) excessive mobility; 3) exposure of tooth root due to distraction of the fracture; 4) fractured teeth; 5) severely carious tooth 6) infected supporting structure. There were no significant differences between the complication rate in the "tooth removed" group and "tooth retained" group. Complications were minimal. Therefore proper management of the third molar tooth in mandibular angle fracture will minimize complication.
Molar, Third* ; Retrospective Studies ; Tooth Root ; Tooth*

The aim of this study was to evaluate the microleakage of teeth according to root canal preparation with & without apical enlargement in various size of apical foramen. 60 extracted one canal roots were cross-cutted at 5 mm from root apex and divided into two groups according to their apical foramen size of large (L) and small (S). Each group was subdivided into two groups accordance with their cross-sectional configuration at 5 mm from apex, round (R) and ovoid (O); SR Group, SO Group, LR Group, LO Group. Each group was shaped in .02 taper by Quantec series Nickel-Titanium (NiTi) rotary file, obturated by lateral condensation method. Leakage was measured using a fluid transport model under 40 cmH2O pressure. After the leakage test, blocks which had showed the leakage retreated with .04 taper and .06 taper and evaluated the degree of fluid filtration in each group. The data was analysed statistically using chi-square test and fisher's exact test. The results obtained were as follows: 1. Significant difference in leakage was found in groups which had different apical foramen size in .02 taper instrumentation (p < 0.05), but not in .04 taper instrumentation (p > 0.05). 2. The difference in microleakage according to the shape of canal was not evident at 5 mm from apex (p > 0.05). 3. There was correlation between .02 taper instrumentation and .04 taper instrumentation in LR group , LO group (p < 0.05).
Filtration ; Root Canal Preparation ; Tooth Apex ; Tooth*

OBJECTIVETo discuss orthodontic extrusion of crown-root fractured teeth before restoration.

METHODS3 cases with fractured teeth and 2 cases with root caries were performed canal therapy.

RESULTSOrthodontic extrusion of the root was carried out before restoration. All cases were satisfactory after treatment.

CONCLUSIONSOrthodontic extrusion of remaining root before restoration not only can maintain the remaining root but also obtain functional and esthetic results.

Humans ; Root Canal Therapy ; Root Caries ; therapy ; Tooth Crown ; injuries ; Tooth Fractures ; therapy ; Tooth Movement Techniques ; methods ; Tooth Root ; injuries

Tooth preparation design is essential for successful laminate veneer treatment. Preservative tooth preparation limited on enamel, supra-margin advantageous for plaque control, and maintaining contact points known as a standard concept. However, the tooth preparation design has been the controversial issue. In biomechanical considerations, the incisal coverage should be decided on esthetic needs and necessity for the anterior guidance reconstruction. In occasion for sufficient enamel thickness, preparation can prolong to the palatal side but not recommended at palatal concavity. Elongation to contact point is selective option according to the cases. If an old resin restoration located at contact area, laminate veneer should cover over half area of that after surface treatment. The laminate veneer can be also selected at a partially discolored tooth root canal therapy (RCT) and at this occasion, the fiber-reinforced composite (FRC) posts are recommended.
Dental Enamel ; Dental Veneers* ; Tooth Preparation* ; Tooth Root ; Tooth*

Humans ; Tooth Crown ; Tooth Diseases ; diagnosis ; therapy ; Tooth Root

Humans ; Tooth Crown ; pathology ; Tooth Diseases ; therapy ; Tooth Root ; pathology