The effects of ageing on the biomechanical properties of root dentine and fracture.

OBJECTIVES: Knowledge of the mechanical behaviour of root dentine can facilitate better understanding of spontaneous vertical root fracture (VRF), an age-related disease initiated mainly at the root apex. We tested the hypothesis that the biomechanical properties of root dentine change with ageing. METHODS: Sixteen human premolars were divided into "old" (17-30 years) and "young" (50-80 years) groups. The elastic modulus, nano-hardness, micro-hardness, elemental contents, tubular density/area of root dentine in cervical, middle and apical root regions were evaluated using atomic force microscopy-based nano-indentation, Knoop indentation, scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. RESULTS: The apical dentine showed a lower nano-hardness, a lower elastic modulus, a lower calcium content, a lower calcium-to-phosphorus ratio and a smaller tubular density/area than the cervical dentine in both age groups, whereas spatial differences in micro-hardness were observed only in old roots. Compared with young dentine, old dentine showed a greater hardness, a higher elastic modulus, a greater mineral content and a smaller tubular size in the cervical portion, whereas the age-induced changes in tubular density were insignificant. Finite element analysis revealed that due to its higher elastic modulus, old apical dentine has a higher stress level than young dentine. CONCLUSIONS: The intrinsic material properties of root dentine have spatial variations, and they are altered by ageing. The higher stress level in old apical dentine may be one reason, if not the most important one, why spontaneous VRFs are more likely to occur in the elderly population.

Scanning electron microscopic analysis to compare the cleaning efficiency of three different irrigation systems at different root canal levels: an in vitro study.

AIM: This study compared the efficacy of conventional, endovac and ultrasonic irrigation system for the removal of debris from root canal walls, using scanning electron microscopy (SEM) at cervical, middle and apical 3rd. MATERIALS AND METHODS: A total of 30 freshly extracted human mandibular premolars with complete root formation were selected and divided into group 1 endovac, group 2 conventional and group 3 ultrasonic. After instrumentation and irrigation, the teeth were sectioned in buccolingual direction and analyzed by SEM and the results were analyzed statistically by students unpaired 't' test. RESULTS: There was significant difference between mean values of cervical (CV), middle (M), and apical (A) when endovac compared with conventional and conventional compared with ultrasonic group (i.e. < 0.05) and no significant difference between mean values at CV, M and A when endovac compared with ultrasonic group. CONCLUSION: Among all groups ultrasonic and endovac group showed cleaner canal walls and less amount of debris than conventional group. CLINICAL SIGNIFICANCE: Application of ultrasonic and endovac can be used effectively for irrigation of canals leading to least debris and better prognosis.

In vitro evaluation of dentin tubule occlusion by Denshield and Neodymium-doped yttrium-aluminum-garnet laser irradiation.

INTRODUCTION: This in vitro study evaluated the efficacy of bioglass (Denshield; Novamin Technology, Alachua, FL) and Neodymium-doped yttrium-aluminum-garnet (Nd:YAG) laser irradiation on dentinal tubuli orifice occlusion (DOO) by comparing samples examined under environmental scanning electron microscope (ESEM) after applying each desensitizing approach separately and in combination. METHODS: Forty-eight human molars were collected, randomly organized in 4 equal groups, and had their cervical dentin exposed. Additionally, in half of the specimens of each experimental group, the smear layer was removed (subgroups A1, B1, C1, and D1). Group A received NovaMin paste treatment for 5 minutes (NM) to the experimental surface. Group B received Nd:YAG laser irradiation (0.5 w, 10 Hz, and 50 mJ) (L). Group C received NM followed by L. Group D was treated with L followed by NM. All specimens were stored for 24 hours and evaluated for DOO under ESEM by 4 blinded observers. RESULTS: The presence of a smear layer significantly contributed to DOO regardless of the treatment modality (ordinal logistic regression, P < .001). Compared with group A, all other treatments delivered significantly more occluded dentin orifices (P < .001 for groups B and D and P < .05 for group C). A layer formation was observed in subgroups C2 and D2. CONCLUSIONS: Under these experimental conditions, a smear layer was essential for successful DOO. Laser irradiation alone and combined with NovaMin proved superior to NovaMin alone on DOO. This combined approach has the potential to improve the outcome of treatment for cervical dentin hypersensitivity. The biological significance of this newly formed layer needs to be elucidated.

Evaluation of push-out bond strength of surface treatments of two esthetic posts.

OBJECTIVES: To evaluate the push-out bond strength of two surface treatments of a glass fiber and zirconia ceramic post. MATERIALS AND METHODS: Sixty samples were fabricated and divided into two main groups according to the type of esthetic post indicated for maxillary central incisor: glass fiber post and zirconia ceramic post. Each group was subdivided to two subgroups according to the type of bond strength test either between post and root or between post and core. Each subgroup was further subdivided into three classes according to surface treatment: no treatment (control), sandblasting in conjunction with silica particles then silane coating (SB+SIC+SC), etching using hydrofluoric acid then silane coating (E+SC). For the subgroups of the bond strength between post and root, each class was subdivided into two subclasses according to the location of the sample (cervical or apical). RESULTS: Bond strength to root canal or resin core were affected by the type of post, glass fiber post recorded significant higher bond strength than zirconia ceramic. Surface treatment recorded higher values for bond strength, SB+SIC+SC gave higher bond strength than E+SC. Cervical section recorded significant higher bond strength than apical section. CONCLUSIONS: Glass fiber posts recorded higher bond strength than glass ceramic post to both root canal and resin core. Surface treatments increase bond strength for glass fiber and zirconia ceramic posts to both root canal and resin core. SB+SIC+SC gave higher bond strength than E+SC. Bond strength at the cervical section is higher than at the apical section.

Efficacy of final irrigation--a scanning electron microscopic evaluation.

The purpose of this in vitro study was to determine the degree of removal of pulpal remnants and smear layer from root canals after final irrigation with three different solutions. During instrumentation the step-back preparation and 1% NaOCl were used. The final 4-min, 30-ml irrigation varied as follows: group I, 10 ml of 1% NaOCl + 10 ml of 10% citric acid + 10 ml of distilled water; group II, 15 ml of 0.5% NaOCl + 15 ml of EDTA-T; and group III, 10 ml of 5% NaOCl + 10 ml of 3% H2O2 + 10 ml of 5% NaOCl. Scanning electron microscopic photomicrographs were evaluated for the mean number of visible open dentinal tubules by three observers. The largest number of visible tubules in the three groups was in the cervical third, followed by the middle and apical thirds. There was no statistically significant difference between groups I and II when third was compared with third; however, groups I and II had significantly more visible dentinal tubules than group III.

In vitro dentin pretreatment: surface roughness and adhesive shear bond strength.

The aim was to define the morphology and roughness of dentin from different tooth areas after various pretreatments to identify the effect of hybrid layer, resin tags, and mineralised dentin surface on shear bond strength. Thirty-eight extracted molars were used, each providing two sections of cervical (c) and lateral (l) dentin. Five pretreatments were performed: A) 0.2% EDTA; B) abrasion with Al2O3 particles, 0.2% EDTA; C) 10% H3PO4; D) 10% H3PO4 and immersion in a collagenase solution; E) control: no treatment. Z100 composite resin cylinders were bonded to the specimens with All Bond 2 bonding resin and tested for shear bond strength. Twelve other specimens from each group were analysed with an optical profilometer and an atomic force microscope, and four were further examined by scanning electron microscopy (SEM). Mean shear strength values in MPa were: Ac: 8.36 +/- 4.23; Al: 8.77 +/- 3.68; Bc: 6.05 +/- 3.62; Bl: 8.39 +/- 4.60; Cc: 6.87 +/- 3.45; Cl: 9.00 +/- 5.62; Dc: 13.30 +/- 5.45; Dl: 8.44 +/- 4.47; Ec: 4.10 +/- 1.54; El: 6.09 +/- 4.34. No statistically significant difference for cervical versus lateral dentin was found within treatments except for group D. Treatments performed on lateral dentin did not differ significantly. In cervical dentin, A differed from E; C from E; and D from A, B, C and E. An increased surface roughness was found in group D. Shear bond strength to dentin did not seem to depend on a hybrid layer formation, but on the direct contact of the adhesive with the mineralised dentinal surface and partly on the orientation of the dentinal tubules.