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PubMedDate not supplied

Fracture behavior of human mandibular incisors following endodontic treatment and porcelain veneer restoration.

PURPOSE: Because of existing controversy, the present study investigated the individual and combined effects of endodontic treatment and porcelain veneer restoration on the fracture behavior of human mandibular incisors. MATERIALS AND METHODS: Forty extracted intact human mandibular incisors were assigned to four groups of ten with a similar range of labiolingual widths at the cementoenamel junctions. Group A consisted of intact teeth; group B consisted of endodontically treated teeth; group C teeth were restored with labial porcelain veneers; and those of group D were endodontically treated and had labial porcelain veneers. All teeth were subjected to a slow continuous loading test at 30 degrees to the long axis of the teeth and 1 mm below the incisal edge on the labial side. RESULTS: Fracture forces were 415 +/- 220 N, 370 +/- 89 N, 420 +/- 128 N, and 448 +/- 156 N for groups A, B, C, and D, respectively. Root fracture was the most common mode of failure. There were no statistically significant differences between the groups in terms of fracture forces and modes of failure. CONCLUSION: Human mandibular incisors with endodontic treatment and/or porcelain veneer restorations were able to withstand the same magnitude of oblique loading as intact teeth. Endodontic treatment and/or porcelain veneer restoration did not affect the mode of failure of mandibular incisors.

Acid Etching, Dental↗
PubMed2005

Fracture resistance of human root dentin exposed to intracanal calcium hydroxide.

The purpose of the present study was to determine if exposure to intracanal calcium hydroxide [Ca(OH2)] alters the fracture resistance of human root dentin. One hundred and two freshly extracted single rooted human teeth divided into three groups of 34 teeth each. Coronal access and endodontic instrumentation using round burs, stainless steel files, and Profile GT rotary files were completed for each tooth. The prepared root canal system of each tooth was filled with saline solution (group 1), USP Ca(OH)2 (group 2), or Metapaste (group 3). The apicies and access openings were sealed with composite resin and the teeth were immersed in saline. After 30 days, the roots of 17 teeth from each group were sectioned horizontally into 1-mm thick disks and each disk was loaded to fracture at 2.5 mm/min with a SATEC universal-testing machine. After 180 days the same procedure was performed on the remaining 17 teeth in each of the 3 groups. The peak load at fracture was measured for each dentin disk. Data were analyzed using one-way ANOVA and a post hoc Student-Newman-Keuls test. After 30 days exposure to the test solution, there was no difference in the peak load at fracture for the three groups of teeth. However, after 180 days, the roots of the teeth exposed to USP Ca(OH)2 showed a significant decrease in peak load at fracture when compared to the 30-day groups and the 180-day groups exposed to saline or Metapaste.

Calcium Hydroxide↗
PubMed2004

Surface debris of canal walls after post space preparation in endodontically treated teeth: a scanning electron microscopic study.

PURPOSE: To evaluate surface cleanliness of root canal walls along post space after endodontic treatment using 2 different irrigant regimens, obturation techniques, and post space preparation for adhesive bonding. STUDY DESIGN: Forty teeth, divided into 4 groups, were instrumented, using Ni-Ti rotary files, irrigated with NaOCl or NaOCl+EDTA and obturated with cold lateral condensation (CLC) or warm vertical condensation (WVC) of gutta-percha. After post space preparation, etching, and washing procedure, canal walls were observed using a scanning electron microscope (SEM). Amount of debris, smear layer, sealer/gutta-percha remnants, and visibility of open tubules were rated. RESULTS: Higher amounts of rough debris, large sealer/gutta-percha remnants, thick smear layer, and no visibility of tubule orifices were recorded in all the groups at apical level of post space. At middle and coronal levels areas of clean dentin, alternating with areas covered by thin smear layer, smaller debris, gutta-percha remnants, and orifices of tubules partially or totally occluded by plugs were frequently observed. CONCLUSIONS: After endodontic treatment, obturation, and post space preparation SEM analysis of canal walls along post space shows large areas (covered by smear layer, debris, and sealer/gutta-percha remnants) not available for adhesive bonding and resin cementation of fiber posts.

Acid Etching, Dental↗
PubMed2004

[Full crown preparation of a vital tooth is outdated].

The restorative solutions for esthetic problems are becoming minimal invasive. Adhesive technology and materials as composite luting cements are biocompatible and therefor less harmfull for vital pulps. Necrosis of vital pulps hardly occurs and the survival of porcelain veneers is very good. The esthetic result is also quite impressive, although marginal discoloration is frequently reported. Full crown preparations can be avoided, but replacement of failing crowns is not banned out in dental practice. Full ceramic crowns however can also be luted with adhesive cements and the amount of hard tissue that has to be removed for optimal esthetic results is much less than for porcelain fused to metal crowns. Saving hard and soft tooth tissues is promoted and advocated as a quality standard. Longevity of treatment outcome has been reported and should be an evidence-based decision in the future.

Biocompatible Materials↗
PubMed1998

Dimensional changes during veneering procedures on discoloured teeth.

OBJECTIVES: The aim of the study was to determine the dimensional changes of teeth when veneering procedures are involved. METHODS: Fifteen discoloured central incisors were selected from a group of 180 veneer restorations (VRs) composed of three different types of materials (direct resin composite, indirect resin composite and porcelain). Impressions and dies were made before treatment, after preparation and after placement and finishing the restoration. Contact stylus profilometry and subsequent analysis of the 3-D surface images provided quantitative data of the differences between the various treatment phases. RESULTS: The preparation reduction was the most for indirect resin composite VRs and the least for direct resin composite VRs. All veneer restorations showed nearly the same thickness and dimensional change after treatment, except one, which resulted in an additional increase of volume of the tooth. CONCLUSION: From the results of this study it is concluded that the dimensions of a discoloured tooth treated with a veneer restoration unintentionally increased, resulting in overcontour.

Analysis of Variance↗
PubMed2004

Effect of sono-abrasion in the microleakage of a pit and fissure sealant.

PURPOSE: To assess the microleakage of a pit and fissure sealant after preparing enamel with sono-abrasion, used alone or associated with acid etching. This technique was compared with classical enamel preparations i.e. acid etching and diamond bur associated with etching. MATERIALS AND METHODS: Ninety 3rd molars were used. In the mesial halves, the fissures were prepared with sono-abrasion and acid etching for 15 seconds. Then, the samples were randomly assigned to three groups of 30. They were either treated with acid etching alone (group 1), widened mechanically with a bur and etched for 15 seconds (group 2) or prepared with sono-abrasion alone (group 3). Then, the resin-based sealant was applied according to the manufacturer's recommendations. The teeth were thermocycled and placed in a 1% solution of methylene blue. The teeth showing microleakage and the means of infiltration were assessed with an image analysis system. RESULTS: The poorest results were obtained with sono-abrasion alone which showed a greater number of specimens with microleakage (73.3%) (p < 0.001). They also showed the highest mean of microleakage (0.85+/-0.79 mm vs 0.1+/-0.26 for acid; 0.35+/-0.85 for bur associated with etching p < 0.0001); and 0.19+/-0.45 for sono-abrasion associated with etching. CONCLUSION: No significant difference was noted between the three types of enamel preparation using etching. Sono-abrasion can be used for preparing dental enamel prior to sealing the tooth but it does not eliminate the need for etching.

Acid Etching, Dental↗
PubMed2002

Artefacts of electron paramagnetic resonance dosimetry caused by a mechanical effect on samples of tooth enamel.

It has been ascertained that in the process of the mechanical preparation of tooth enamel, two types of paramagnetic centres are formed. The centres of one type, the long-lived ones, occurred in the process of friction of dental borers against the enamel. Their number grew with an increase of the treated surface area and the rotation rate of the borers. The electron paramagnetic resonance signal of such radicals looked like a symmetric singlet with the width deltaHpp=0.094 mT and g=2.0029. The other, short-lived centres, occurred when tooth enamel was crushed into small granules, which caused an increase in the background signal intensity. The mechanism of formation of paramagnetic centres in enamel during the process of teeth treatment and prepartion has been considered. The estimation of an increase in the reconstructed absorbed dose due to the contribution from the mechanically induced signal has been made. Contamination of tooth enamel samples with diamond crumb during diamond borer preparation has been shown to lead to an imaginary increase in radiation-induced signal intensity and, consequently, to an increase in the reconstructed dose.

Artifacts↗
PubMed2004

Preparing anterior teeth for indirect restorations.

Practitioners have many techniques available for the indirect restoration of anterior teeth. There is some confusion, however, as to what preparation technique is appropriate for each type of restoration, let alone which material to select for the production of the restoration. This article considers the different types of preparation recommended for veneers and resin-bonded, all-ceramic and porcelain fused to metal crowns and gives an indication when each technique may be used.

Aluminum Silicates↗
PubMed1994

The relationship between preparation convergence and retention of extracoronal retainers.

PURPOSE: Although traditional ideal convergence (the sum of taper of the opposite sides) for crown preparation has been arbitrarily set at 4 degrees to 10 degrees, some believe absolute parallelism yields the highest retention. This study examined the relationship between the degree of convergence of a machined metal die and the retention of its casting. MATERIALS AND METHODS: The method used was that of cementing cast metal crowns onto full crown preparations on brass dies with varying convergence angles, and then recording the force required to remove the crowns from the dies in a vertical direction using a Tate-Emery Testing Machine and Load Indicator. RESULTS: It was found that retention (i.e., the force needed to remove the cemented castings from the die in their common long axis) increases from 0 degree convergence to peak between 6 degrees to 12 degrees convergence. It also seems that a critical film thickness does exist for optimum retention, and that film thicknesses smaller than the critical thickness may be responsible for the phenomenon that we have observed and directly related to the convergence angle itself. CONCLUSIONS: There seems to be experimental data supporting the use of traditionally taught convergence. Our study found that convergence angles between 6 degrees and 12 degrees seem to be optimum for tooth crown preparation when one plans to use zinc phosphate cement. Convergence angles of less than 6 degrees may not be desirable even if they can be clinically achieved. The results of our study indicate that a relationship exists between the convergence angle and the critical cement thickness that is necessary to realize the maximum strength properties of zinc phosphate cement.

Analysis of Variance↗
PubMed1997

The resin-bonded cast post core: technical preparation and cementation protocols.

Post and core restorations have been widely utilized in the reconstruction of endodontically treated teeth. This study compares the traditional cast post core with the bonded type, and reviews the restoration of devitalized teeth without imposing frictional forces within the root canal walls. Clinical and laboratory aspects are discussed, with emphasis on the cementing procedure. Several resin cements are evaluated and compared to traditional zinc oxide phosphate cement techniques; microleakage test results are presented. The learning objective of this article is to outline the clinical indications, advantages, disadvantages, and the clinical techniques employed for resin-bonded cast post core restoration. A case of an endodontically treated maxillary left central incisor following a direct trauma is used to illustrate the procedure of resin-bonded post core placement. Biocompatibility of the cast post core is confirmed by a radiograph 2 years postoperatively.

Adult↗
PubMed2003

Contraction stress of composite resin build-up procedures for pulpless molars.

PURPOSE: The purpose of this study was to photoelastically evaluate contraction stresses associated with various resin composite build-up procedures for pulpless molars. MATERIALS AND METHODS: Photoelastic models of endodontically treated mandibular molars were fabricated to simulate a preparation for a full-cast crown. The model configuration included three lateral walls, but no post space. The buildups were made with dual-curing resin composite using the following procedures: 1) bulk dual cure, 2) bulk chemical cure, 3) horizontal two increments, dual cure, and 4) indirect. Five specimens were fabricated for each condition. The stresses developed in the models were recorded photographically in the field of a circular polariscope. RESULTS: The build-up procedures tested generated widely different stress distributions and intensities. The highest stresses were seen with the bulk dual-cure method. The slower polymerization chemical-cure group developed distributions similar to the bulk dual-cure group with a significantly lower fringe order. The two horizontal increments dual-cure techniques developed an individual group of fringes for each layer. Compared with the bulk dual-cure group, stresses around the occlusal margin were reduced by incrementalization, while fringes were more closely spaced at the line angles with a slightly lower fringe order. The indirect method demonstrated the lowest stress which extended over the smallest area. CONCLUSION: Contraction stress in resin composite buildups varied significantly depending upon the procedures of fabrication. The bulk dual-cure method developed the most severe contraction stresses, while the indirect technique resulted in significantly lower contraction stresses than the other techniques tested.

Analysis of Variance↗
PubMed2002

[Analysis the stress variations of the root canal wall of pulpless tooth by different root canal preparation with finite-element method].

OBJECTIVE: To analyze the stress variations of the root canal wall of pulpless tooth by different root canal preparations. METHODS: On the basis of the set up model of the mandibular first molar, modified model was established by simulation of the routine or step-back root canal preparation and filling in. Then the maximum mises stress of each part of teeth and wall of root canal were calculated by special finite-element software. RESULTS: The stress-changing tendency is similar between two modified models but the maximum mises stress of the model by step-back technique is a little greater than one by routine. The stress of wall of mesial-buccal root canal was the greatest and one of mesial-lingual root canal was the least at three root canals. The stress-changing tendency of modified models was similar to original model. The maximum mises stress of modified models was near or less than one of original model except that of amalgam layer because of material property alteration. CONCLUSION: Not only routine but step-back technique is an effective and safe method. Dentist can choose them in practice.

English Abstract↗