Bond strengths to endodontically-treated teeth

PURPOSE

To evaluate the bond strengths of three different types of resin bonding systems to teeth prepared for endodontic treatment.

MATERIALS AND METHODS

Access cavity preparation and removal of pulpal tissue were performed in bovine incisors. The root canals were chemically irrigated with saline (control), 5% sodium hypochlorite, 3% hydrogen peroxide, or combinations of both for 60 s. After storage in water for 1 d, the dentin surface was ground to a flat surface with 600-grit SiC under water. The area for bonding was demarcated with a vinyl tape (4 mm-in-diameter hole), and bonded using either Clearfil Liner Bond II, Single Bond, or Superbond C&B. After storage in 37 degrees C water for 1 d, tensile bond strengths were measured using a universal testing machine at a crosshead speed of 2 mm/min. Ten teeth were tested for each group.

RESULTS

One-way ANOVA and Fisher's PLSD test revealed that Single Bond and Superbond C&B had a statistically lower (P < 0.05) bond strengths in the chemical irrigation groups compared with the control group.

Connective tissue responses to calcium hydroxide-based root canal medicaments

AIM

The objective of the present study was to evaluate the tissue inflammatory response induced by calcium hydroxide pastes, with or without paramonochlorophenol and camphor.

METHODOLOGY

Isogenic BALB/c mice were inoculated into the subcutaneous tissue with either 0.1 mL of a suspension of Calen, Calen with camphorated paramonochlorophenol, Calen with paramonochlorophenol, Calasept paste or phosphate-buffered saline (control). After 6, 12 and 24 h and 2, 3, 5, 7 and 15 days, three animals in each group were sacrificed and the excised lesions processed for histopathological evaluation of the inflammatory response. Events monitored and graded included the assessment of vascular congestion, oedema, haemorrhage, inflammatory infiltrate, necrosis and tissue repair.

RESULTS

The pastes induced an inflammatory response at every observation period, although the intensity, duration and extension of inflammation varied. Calen paste always produced an initial short-term inflammatory response whilst the other pastes produced extended reactions. All pastes allowed repair to take place by the end of the experimental period, although the speed of this process varied between the materials. Calen presented the best biocompatibility; the phenolic compound caused greater tissue response, which was even more severe in the absence of camphor. Calasept paste was damaging and the repair process slower.

CONCLUSIONS

All calcium hydroxide formulations caused an inflammatory response. The severity and longevity of the responses varied between pastes as a result of the various antiseptic agents. Although irritating, repair was apparent with all formulations.

Dentinal tubule penetration of root canal sealers after root canal dressing with calcium hydroxide

The purpose of this study was to evaluate the dentinal tubule penetration of root canal sealers after root canal dressing with calcium hydroxide (Ca(OH)2). Forty-two single-rooted teeth were instrumented to size 60. Six teeth served as the control group, and the remaining teeth were assigned to two groups. Root canals of the first group were filled with the Ca(OH)2 paste; the second group was filled with TempCanal, and all were incubated for 7 days. The samples were either irrigated with only NaOCl or with EDTA, followed by NaOCl to remove Ca(OH)2. All of the teeth were obturated with CRCS, AH26, and Ketac Endo by a lateral condensation technique. The specimens were then kept at the same conditions for another 7 days, and then all of the roots were prepared for scanning electron microscopic evaluation. Scanning electron microscopic examination revealed that Ca(OH)2 was not completely removed from the root canal surfaces, and root canal sealers did not penetrate into the dentinal tubules when only NaOCl was used. EDTA followed by NaOCl irrigation resulted in complete removal of Ca(OH)2 and root canal sealers penetrated into the dentinal tubules.

pH changes and calcium ion diffusion from calcium hydroxide dressing materials through root dentin

The purpose of this study was to evaluate Ca2+ and OH- diffusion properties through root dentin by using different calcium hydroxide (CH) dressing materials. Twenty-eight single-rooted teeth were instrumented and external defects were created on the root surface. 17% EDTA was used to eliminate the smear layer. All surfaces except the external defects were sealed, and the teeth were placed in normal saline. Ca2+ concentrations and the pH in the saline were determined for 3 days as the control period. After removing the teeth from normal saline, they were filled with: (i) DT Temporary Dressing CH; (ii) CH powder and normal saline; (iii) TempCanal; and (iv) CH points. The teeth were then placed in normal saline, and Ca2+ concentrations and pH values were measured at 1, 3, 7, 14, and 28 days. Nonsetting CH pastes gradually released Ca2+, whereas this increase was absent from CH points. None of the test materials induced a pH increase in the media during the observation period. This study demonstrated that, when nonsetting CH pastes are applied to the root canal, diffusion of Ca2+ without an increase in pH to the surrounding media occurs. This implies that these type of material are more suitable than CH points for treatment of external root resorption.

Removal efficiency of calcium hydroxide dressing from the root canal

The aim of this study was to investigate whether differences in the composition of calcium hydroxide (Ca(OH)2) preparations influence the removal efficiency of irrigation solutions used in combination with filing of the canal. Three Ca(OH)2 preparations were used: Calxyl, Pulpdent paste, and chemically pure Ca(OH)2 mixed with distilled water. Fifty-one single-rooted extracted human teeth were prepared with a step-back technique and divided into groups A, B, and C. In each group, 15 teeth were assigned to each Ca(OH)2 preparation while the remaining two served as positive and negative controls. Each group of treated teeth was divided into three subgroups of five teeth each: subgroup I--canals were irrigated with saline, filed with a #25 file, and finally flushed with saline; subgroup II--canals were irrigated with NaOCl, filed with a #25 file, and finally flushed with NaOCl; and subgroup III--canals were irrigated with NaOCl, filed with a #25 file, and finally flushed with tetrasodium EDTA. Canal sections were then photographed, and the percentage ratios of Ca(OH)2 coated area to the total canal surface area were calculated by image processing analysis. Results revealed: (a) none of the methods efficiently removed all dressing from the walls, and (b) concentration of the paste used had little effect on the efficacy of the methods applied for the removal of the dressing. Excipients (i.e. methylcellulose contained in Pulpdent) possibly effect retention of Ca(OH)2.

Sodium hypochlorite and its use as an endodontic irrigant

Sodium hypochlorite has been used as an endodontic irrigant for more than 70 years, and is now one of the most common solutions for this purpose. The chemical properties and production of commercial sodium hypochlorite are reviewed. Domestic bleaches and an infant sanitizer are compared from the point of view of cost and ease of use--Milton being recommended where a 1% solution is required. The cost of syringes and needles for endodontic irrigation is many times greater than the hypochlorite they contain, and total annual practice costs for hypochlorite are low. Brief guidelines for clinical use, storage, handling and disposal are included.

Effects of sodium hypochlorite on nickel-titanium Lightspeed instruments

Sodium hypochlorite is a major irrigant in endodontics, and nickel-titanium instruments are gaining in popularity. This paper investigated the corrosion of nickel-titanium Lightspeed instruments in 1% and 5% NaOCl solutions. The instruments were immersed in ultrasonicated NaOCl solutions for varying times up to 1 h. Corrosion was determined by electrothermal absorption spectrometry in 100 microL aliquots of NaOCl. Background contamination of nickel in the 1% and 5% NaOCl solutions used was low, but high enough to interfere in detecting any increases in nickel after immersing the instruments. The amounts of titanium recorded in the 1% NaOCl solutions were insignificant. However, a statistically significant amount of titanium was detected from the Lightspeed instruments after immersion times of 30 and 60 min in 5% NaOCl. Clinically such instruments do not have an 'in situ' time of 30 min, and this corrosion may be considered irrelevant clinically.

Chemical stability of heated sodium hypochlorite endodontic irrigants

Several previous studies have investigated the advantage of temperature on tissue-dissolving and antimicrobial properties of sodium hypochlorite. However, it is known that the chemical stability of sodium hypochlorite is adversely affected by exposure to high temperature. The purpose of this study was to investigate the effect of heating sodium hypochlorite to 50 degrees C on the stability of the solution. An iodometric titration test was used to evaluate the decomposition rates of heated and nonheated solutions over 30 days. Results showed that all specimens exhibited a minimal, gradual degradation versus time. However, no statistically significant difference (p < 0.05) was noted between the two groups. After 30 days, both heated and non-heated solutions maintained high available chlorine content and pH values consistent with excellent tissue-dissolving and antibacterial properties.

Determination of impedance changes at varying frequencies in relation to root canal file position and irrigant

This study was conducted on 10 anterior and premolar teeth that were scheduled for endodontic treatment. After length of tooth determination, a series of test K-file handles were locked at lengths varying from 3 mm short to 0.5 mm long of the foramen. Samples of impedance were taken at each length with a digital signal processor at six different frequencies and for each of seven different irrigants or canal conditions. A total of five different root canal irrigants were used in each tooth (RC Prep, 70% isopropyl alcohol, 14.45% EDTA sodium solution, normal saline, and 5.25% NaOCl), along with two variations of a dry canal. The greatest impedance changes occurred +/- 0.25 mm from the foramen. No significant difference was noted in prediction error at different frequencies (p > 0.05); however, prediction error was significant with respect to different irrigants (p < 0.02). Conductive irrigants demonstrated less change of electrical characteristics with length than nonconductive irrigants, thus allowing a greater prediction of file position in relation to the foramen using electrically nonconductive irrigants.

Interaction of calcium hydroxide with zinc oxide-eugenol type sealers: a potential clinical problem

When a ZnOE type sealer was placed in root canals treated previously with calcium hydroxide dressing, an accelerated sealer setting rate occasionally occurred. This clinical observation led to the present experimental design aiming to investigate the effect of calcium hydroxide on a ZnOE cement and ZnOE type sealers and to preliminarily assess the removal efficiency of a calcium hydroxide preparation from root canal systems. Micro-MIR FTIR spectroscopy was used to quantify the effect of calcium hydroxide on the setting reactions of a ZnOE cement and two ZnOE type sealers. The removal efficiency of calcium hydroxide from root canal systems was evaluated after treatment with NaOCl; NaOCl and filing; and NaOCl plus EDTA and filing. Calcium hydroxide preferentially interacted with eugenol inhibiting the ZnO-eugenol chelate formation. The Ca(OH)2-eugenol interaction was rapid, and kinetically dependent, leading to residual eugenol in the set product. The set ZnOE cement and the ZnOE type sealers in contact with calcium hydroxide were brittle in consistency and granular in structure. Although none of the treatments tested completely removed calcium hydroxide from root canals, treatment with EDTA significantly reduced the extent of residual calcium hydroxide.

Removal of smear layer in the root canal using oxidative potential water

We investigated oxidative potential water (OPW) for its ability to remove the smear layer using a scanning electron microscope. OPW has been studied mainly in Japan and is known to suppress bacteria and viruses without harming living systems. We found that OPW used as in irrigant during and after root canal instrumentation is as effective as 5% NaOCl or 17% EDTA for opening and keeping patent the dentinal tubules.

Intracanal pH changes of calcium hydroxide pastes exposed to carbon dioxide in vitro

It has been suggested that the main benefit of using calcium hydroxide as an intracanal medicament lies in its bactericidal effect, provided that the pH of the paste is above 12.5. The purpose of this study was to measure changes in the pH of several calcium hydroxide pastes sealed in root canals for 30 days. Sixty-two extracted, single-rooted human teeth were endodontically prepared using K-files up to size 60. The teeth were separated at random into six equal groups to be filled with either Calxyl, Hydrocalcium, or a paste made by mixing calcium hydroxide powder with either distilled water, camphorated p-monochlorophenol, local anesthetic solution, or Solvidont. Cavidentin was used to seal the coronal orifice of the teeth that were placed individually in vials containing 10 mL distilled water. Five vials of each group were exposed to air at room temperature, whereas the other five vials were exposed to carbon dioxide in a closed container. The pH of the paste in the root canal was measured after 30 days. There was no significant (p > 0.01) change in the pH (mean 13.11) of the pastes placed in teeth before and after exposure to air, whereas the pH of the pastes in teeth exposed to carbon dioxide was significantly (p < 0.01) reduced (mean 12.54). There was no significant difference in pH between the six preparations. After 30 days of exposure to carbon dioxide, they still maintained a purportedly bactericidal pH within the root canal.

Chemical analysis of the liberation of calcium and hydroxyl ions from calcium hydroxide pastes in connective tissue in the dog--Part I

The objective of this research is to chemically analyze calcium hydroxide pastes added to three hydrosoluble vehicles having different acid-base characteristics using polyethylene tubes implanted in subcutaneous connective tissue in a dog, evaluating the liberation of calcium and hydroxyl ions over a period of 7, 30, 45 and 60 days. The three vehicles were saline, anesthetic, and polyethylene glycol 400. Chemical analysis of the liberated calcium ions was done by means of conductimetry using EDTA for titration. Liberation of hydroxyl ions was determined by analogy of calcium ions liberated, which are in direct proportion to the molecular weight of calcium hydroxide.

Evaluation of various methods of removing gutta-percha and endodontic sealer

Extracted human teeth were studied to evaluate three methods of removing gutta-percha and endodontic sealer from previously obturated canals. The results showed that: (1) Each method of removal left debris in the canals. (2) Significantly more debris remained in the apical third than in the middle or coronal thirds. Likewise, significantly more debris remained in the middle than in the coronal third. (3) Use of the GPX instruments enabled gutta-percha to be removed as effectively as the other methods. (4) Use of the GPX instruments required significantly less time for gutta-percha removal, compared to removal by the other methods.

Stability of various sodium hypochlorite solutions

Although the manufacturers use at least a 2-yr expiration date for sealed undiluted NaOCl solutions, chemical stability of NaOCl may be adversely affected by many factors. The purpose of this study was to investigate the effects of storage temperature, concentration, and time on the stability on three different brands of commercial household bleaching agents as a source of NaOCl, and to compare the stability of these brands. All solutions showed degradation versus time; however, this degradation occurred very slowly except for the group of solutions containing 5% available chlorine stored at 24 degrees C. Solutions containing 0.5% available chlorine stored at 4 degrees C and 24 degrees C and 5% solutions stored at 4 degrees C showed satisfactory stability at 200 days. No significant difference was found among three brands in respect to their chemical stability.

Application of root canal cleaning agents having dissolving abilities of collagen to the surface treatment for enhanced bonding of resin to dentin

Commercial root canal cleaning agents with the ability to dissolve collagen were used for the surface treatment to enhance the bonding of dental resins. These agents increased the bond strength of a dental bonding agent to dentin. For example, the tensile bond strength to bovine dentin was 10.7 +/- 3.9MPa following the joint use of M and N and 8.8 +/- 2.2MPa following the combined use of P-S and N. In these cases, the damage to the tooth surface was very small and was equal to or less than damage caused by EDTA. These results demonstrate the usefulness of commercial root canal cleaning agents for dentin surface treatment due to their ability to enhance the bonding of dental resin.

In vitro release of calcium and hydroxyl ions from two types of calcium hydroxide preparation

Non-setting and setting pastes are the most common forms of calcium hydroxide, used in endodontics. The aim of this study was to investigate the differences in the availability of calcium and hydroxyl ions from some commercial preparations of both types. In vitro released calcium and hydroxyl ions were determined by a potentiometric method, after diffusion through sintered glass. The non-setting pastes evaluated were Calcipulpe, Calxyl Red, Calxyl Blue and Cinacal; while setting base materials were represented by Dycal, Nu-Cap and Reolit. The data obtained showed significantly higher availability of calcium and hydroxyl ions from non-setting pastes, compared with 'alkaline cements' (P < 0.05). Great variations in the amount of released ions were also found among samples of the same material.

Effective shelf-life of prepared sodium hypochlorite solution

Although the tissue solvent and bactericidal properties of sodium hypochlorite are well known, the effective shelf-life of prepared sodium hypochlorite solutions is not known. The stability of sodium hypochlorite is adversely affected by exposure to high temperature, light, air, and the presence of organic and inorganic contaminants. The purpose of this study was to investigate the variables of storage conditions and time on the tissue-dissolving capacity of three different concentrations of sodium hypochlorite. Fresh frozen human umbilical cord was used as the tissue sample for this experiment. Tissue samples were dissolved at time intervals ranging from 1 day to 10 wk in 5.25%, 2.62%, and 1.0% solutions of sodium hypochlorite. The tissue-dissolving ability of 5.25% sodium hypochlorite remains stable for at least 10 wk. The tissue-dissolving ability of 2.62% and 1.0% sodium hypochlorite remains relatively stable for 1 wk after mixing, then exhibits a significant decrease in tissue-dissolving ability at 2 wk and beyond.