Post Preparation Research Articles

Effect of post preparation on the apical seal of teeth obturated with plastic thermafil obturators

The effect of post canal preparation on the apical seal of endodontically obturated teeth with plastic Thermafil obturators was studied in vitro. Fifty-four extracted human maxillary anterior teeth were divided into four experimental and two control groups. Two groups were obturated with lateral condensation or plastic Thermafil obturator techniques; this was followed by post space preparation. Two groups were obturated as described above except that post space was not prepared. Apical leakage was determined with the use of 2% methylene blue dye solution at an absolute pressure of 75 mm Hg. There were no statistically significant differences between any of the groups. The clinical implication of these findings is discussed.

The proton magnetic resonance study for hydrogen behavior in three hydrogenated silicon films

Abstract The proton magnetic resonance spectrum of three hydrogenated silicon films (nc-Si:H, a-Si:H, annealed a-Si:H) were presented, which confirm the compositional inhomegeneity for hydrogen in the dilute and clustered phase. The deposition or post preparation condition was important for the formation of the clustered SiH phase, not only for the spatial distance between SiH bond, but for some subtle structure in NMR spectrum. The hydrogen glass behavior in silicon films was essential for the explanation of experimental results.

Post preparation techniques and their effect on the apical seal

It is accepted clinical procedure to extend post preparations to such a depth that 3 mm to 5 mm of gutta-percha remains at the apex of the tooth. Clinicians use numerous techniques to achieve this goal. This investigation quantitatively analyzed the effect of the method of gutta-percha removal on the apical seal and evaluated apical leakage in teeth with different levels of remaining gutta-percha. The methods evaluated included the GPX instrument, heated pluggers, and Gates-Glidden drills. Groups of 25 extracted teeth were prepared with each of the three methods leaving 3 mm or 5 mm of gutta-percha remaining apically. Spectrophotometry (optical density) was used to assess apical leakage. Significantly less leakage was observed with the heated plugger technique at the 3 mm and 5 mm levels when compared to the 3 mm and 5 mm levels in both the GPX and Gates-Glidden groups.

Interface Morphology, Nucleation and Island Formation of Tisi2 on Si(111).

ABSTRACTIn this study we investigate the formation mechanisms and morphology of TiSi2 formed by deposition of Ti on atomically clean silicon substrates. Ti films of 50–400 Å thickness were deposited in ultra-high vacuum on Si (111) wafers and annealed to temperatures between 500–900°C. Films were monitored in situ with AES and LEED, and post preparation characterization was accomplished with SEM, TEM and Raman scattering. The results show that for films of thickness ≤, 100 Å the C49 TiSi2 phase is stable over the entire 600-800°C temperature range. However, for films of 200-400 Å thickness, the C49 to C54 phase transition occurs at temperatures varying from 700 to 800°C dependent upon film thickness. The high temperature annealing results in flat interface structures, and island formation is observed for all films with the C54 structure. The interface morphology and the mechanisms of TiSi2 island and phase formation are discussed in terms of surface and bulk free energies considerations based on nucleation theory.

Evaluation of dowel space preparation on the apical seal using an image processing system.

The effect of post preparation on the apical seal of endodontically treated specimens was studied. The canals prepared in bovine bone were instrumented and obturated using five obturation techniques: the silver point technique, the lateral condensation of gutta-percha technique, the warm vertical condensation of gutta-percha technique, the Hygenic Ultrafil injection system and the Obtura technique. In addition to these five control groups, the five experimental groups were also subjected to post preparation. In the latter group, the gutta-percha was removed with an engine-driven root canal reamer 48 hours after obturation. Both the control and experimental groups were suspended in a 0.5 per cent crystal violet solution for 48 hours. After dye penetration, the specimens were immersed in liquid nitrogen and then split longitudinally. Linear measurements of the resultant apical dye leakage were determined by image processing. For each obturation technique, all specimens in both the control and experimental groups were recorded if they showed leakage. Using Fisher's exact probability test, it was shown that there was no significant difference between the obturation techniques used.

ポスト先端部の不適合が歯根歯質に及ぼす力学的影響

Reconstruction of the crowns of non-vital teeth with posts can be a very useful technique. However, there are many cases where the length of the posts are insufficient, resulting in a poor fit and dead space at the apex of the post. The purpose of this study was to compare the post length to the depth of the post preparation using parallel X-ray films of 31 teeth (incisors, canines and premolars) and to locate the dead space at the apex of the post. In addition, stress analysis of the post-reconstructed upper central incisor models having five types of posts with dead space at the apex and two levels of supporting conditions were calculated using the finite element method. The results obtained were as follows: 1. From the roentogenographic survey, the depth of the post preparations averaged two thirds of the remaining root length, and one half the length of the root in bone. However, lengths of the posts were on the average 20% shorter than the depth of the post preparation. 2. As the dead space increased and supporting levels diminished, stresses of post-reconstructed teeth were found to increase gradually and to concentrate in the remaining dentin near the apex of the post.

Characteristics of disorder in defective layered semiconductor α-In2Se3

In2Se3 which crystallizes in layer structure has been studied at different post preparation temperatures. The presence of a large number if intrinsic defects affects strongly its electrical and optical properties. Our experiments aimed at measuring the influence of the post-preparation annealing on conductivity and anisotropy. From FIR spectroscopy the reflectivity spectrum is found to be influenced by crystal disorder. Photoluminescence measurements are also included and provide valuable information concerning the crystal degree of ordering.

A comparative study of post preparation diameters and deviations using para-post and gates glidden drills

Para-post and Gates Glidden drills are commonly used to create post space in endodontically treated teeth. The purpose of this study was to compare post preparation diameters and deviations for the Para-post and Gates Glidden drills. Thirty extracted mandibular canine teeth were endodontically treated and embedded in resin blocks. Buccolingual and mesiodistal long-cone radiographs were made using a jig to assure repeatability. Three operators randomly prepared post space in five teeth using Para-post drills and in five teeth using Gates Glidden drills. The post spaces were filled with a contrast medium and the blocks were reradiographed. Drill deviation and post space diameter were measured from the radiographs with a traveling stage microscope. The mean Para-post space diameter was 1.32 mm and deviation from the center of the canal was 0.34 mm. The Gates Glidden was 1.38 and 0.17 mm, respectively. The differences in drill deviation were statistically significant (p

Kinetics of cellular oncogene expression in mouse lymphocytes. II. Regulation of c-fos and c-myc gene expression.

Newly isolated lymphocytes from mouse spleens express the c-fos oncogene even in the absence of mitogen with maximal mRNA levels 60 min post preparation of single cell suspension, whereas c-myc mRNA levels increase only after mitogenic stimulation with maximal mRNA levels 6 h post stimulation. The half-lives of c-fos mRNA are generally very short; they increase from 14 min (after 30 min of culture) to 70 min (after 2 h of culture). The half-lives of c-myc mRNA decrease from 50 min (at 2 and 6 h post stimulation with concanavalin A) to 12 min (at 48 h post stimulation). The c-fos gene transcription is already turned on in time-0 lymphocytes 10 min after disruption of the organ structure of the spleens and is down-regulated after 2 h and later. In nuclear run-on experiments with nonstimulated lymphocytes there is already significant transcription of the first exon of c-myc, but almost no elongation of the transcript to exon 2 and 3. In concanavalin A-treated lymphocytes elongation is stimulated about 5-fold within 6 h and returns to background levels at 48 h post stimulation. The nuclear run-on analyses of nonactivated lymphocytes showed a signal for RNA complementary to c-myc mRNA detected with a probe specific for the exon 1/intron 1 boundary of c-myc, which disappeared with increasing time of concanavalin A stimulation. This anti-sense transcription may play a role in regulating the elongation of c-myc transcripts.

Root canal posts--some prosthodontic aspects.

Abstract Prosthodontic treatment of non‐vital teeth following endodontic therapy faces problems originating from the fact that such teeth generally have damaged clinical crowns, necessitating retention beyond the remaining coronal portions of the teeth. Additional intraradicular retention can be obtained by means of root canal posts. The total need for retention shows wide variations. Each case, therefore, should be carefully analyzed before decisions arc made about post types, post designs and post dimensions. The need for retention is dependent upon intermaxillary relations, type of prosthetic appliance, position of tooth, and volume and shape of remaining tooth substance. At least 3 mm of well‐sealed root canal should be left apically to the post preparation, but normally the post preparation should not extend into the apical one‐third of the root. Sufficient additional retention through a post is usually achieved when the extention of the post into the root canal at least equals the difference between the mean height of the prepared coronal dentin and the height of an ideal crown preparation of the tooth.

Root curvature localizations as indicators of post length in various tooth groups.

Abstract The straight line length available for post preparations in pulps of 957 human teeth was evaluated. Analysis of radiographs in both buccolingual and mesiodistal directions showed that only 2.7% of the teeth studied were straight to the apex in both views. Average straight line lengths were calculated for the different types of teeth and used to offer guidelines for the length of post preparation. Buccal roots of maxillary molars and the mesial roots of the mandibular molars frequently showed straight line lengths insufficient for post preparations.

Effect of root curvature on post length in the restoration of endodontically treated premolars

Abstract Two hundred and eighteen bi‐rooted maxillary premolars were examined radio graphically to determine the length from the apex at which root curvature occurred. The information may serve as a guide in determining post preparation length. The results of the study indicated that the lingual root was slightly straighter than the buccal root. The curvature of the root was on the average 6.47 mm from the apex on the buccal root and 5.18 mm from the apex on the lingual root.

Effect of the dentin smeared layer on tensile strength of cemented posts

The tensile strengths for post lengths of 4 and 7 mm were compared in vitro with 3 different cementing media. In one group, the post preparation was rinsed with 5.25% NaOCl and in the other with 17% EDTA followed by 5.25% NaOCl. The EDTA-NaOCl flush had a profound effect when unfilled resin was used to cement the posts. A 4 mm post cemented with resin in the EDTA-NaOCl group was one and one-half times as retentive as a 7 mm post cemented with zinc phosphate and twice as strong as the 7 mm post with polycar☐ylate cement. The 7 mm post cemented with the resin after the EDTA-NaOCl rinse was twice as resistant to displacement as the 7 mm post cemented with zinc phosphate and three times stronger than the polycar☐ylate cement.

Linear and volumetric analysis of apical leakage in teeth prepared for posts

The effect of post preparation on the apical seal of endodontically treated teeth was studied. The canals of extracted human teeth were instrumented and obturated with gutta-percha using the lateral condensation technique. Post spaces were prepared immediately or 48 h after obturation by removing the gutta-percha with either heated endodontic pluggers, chloroform and files, or Peeso reamers. Linear and volumetric measurements of resultant apical dye leakage revealed that no significant differences existed between the gutta-percha removal techniques at either of the two time intervals studied.

Effect of post preparation on the apical seal

Apical leakage was analyzed quantitatively in extracted teeth with varied levels of remaining gutta-percha. The effect of the method of gutta-percha removal on the apical seal was also evaluated. Ninety teeth were prepared so that 30 teeth had 3 mm of gutta-percha, 30 teeth had 5 mm, and 30 teeth had 7 mm. An additional 75 teeth were divided into three groups of 25 each. A different method of gutta-percha removal was used for each group: hot instrument, mechanical rotary instrument, and chemical solvent. An electrochemical method was used to analyze apical microleakage. Measurements of leakage of each sample were obtained at 24-hour intervals for 30 days. The data suggest that the mechanical method is the most desirable for gutta-percha removal in post preparation. As the level of gutta-percha increased to 7 mm the degree of leakage decreased. At least 5 mm of gutta-percha is necessary for an adequate apical seal.

Pulpal dystrophic calcification

During routine dental examination, a 36-yr-old white male presented with two asymptomatic and uninvolved maxillary incisors. No treatment was provided for 12 yr until an accidental shearing off of the crown of #7 at the cervical level. An artificial canal was made with engine-driven burs and root canal hand instruments for placement of a dowel, cast core, and crown. The post preparation procedure produced a labial perforation. This defect was repaired with amalgam and we elected to do apical retrograde amalgams in both apices while the flap was laid open. Ten years later, both teeth are functioning in excellent health. The literature review suggests that dystrophic calcification is being overtreated and reports higher success for nontreated cases as compared with treated cases.

The prevalence of facial asymmetry in healthy male white adults

An indirect post and core technique in which the core is waxed and invested with the die has been described. The post and core are cast directly into the invested die, which has the advantage of an accurate casting of the post preparation obtained with less laboratory time and without the disadvantages of retrieving an intact wax pattern. This technique is particularly suited for long, narrow post preparations; short preparations where precise fit is necessary for retention; and multiple adjacent post preparations.

A modified indirect cast post and core technique

An indirect post and core technique in which the core is waxed and invested with the die has been described. The post and core are cast directly into the invested die, which has the advantage of an accurate casting of the post preparation obtained with less laboratory time and without the disadvantages of retrieving an intact wax pattern. This technique is particularly suited for long, narrow post preparations; short preparations where precise fit is necessary for retention; and multiple adjacent post preparations.

Drying post preparation canals prior to cementation.

material should express all elastomeric material along the bevel. This is evident with this technique (Figs. 1 and 2). 8. Adjust areas of the casting that project through the elastomeric material, causing incomplete seating of the castings, and then repeat until a marginal seal is attained. This technique could also be used to determine if splinting is necessary for multiple-unit restorations. 9. Determine that the castings are seated, and reconfirm the occlusal relationships and interproximal contacts. 10. Complete porcelain application and, prior to final cementation, repeat this procedure to assure marginal seal.

The prosthodontic use of endodontically treated teeth: Theory and biomechanics of post preparation

It is impossible to state that any given system is better than another system for any and all situations. In all systems it is advisable to leave at least 3 to 5 mm of root canal filling to preserve the integrity of the apical seal. From a retentive standpoint, the parallel-sided posts have a greater retention than the tapering-sided posts but, because they are placed within a tapering root, they require more finesse on placement. In all teeth the length of the post is important since it is directly proportional to the amount of support offered by the post and its resistance to root fracture.