Time dependence of 2.5% nitric acid solution as an etchant on human dentin and enamel

On the method of revealing enamel structure by acid etching. Aspects of optimization and interpretation

The study aimed at finding an optimal combination of acid concentration and etching time when nitric acid is used as etchant for the study of the finer details of human dental enamel structure. Four hundred 2-3-mm-thick segments of facio-lingually sectioned human third molar crowns were assigned to 20 groups with 20 specimens in each group, each group differing with respect to acid concentration (0.1, 1, 2.5, and 5%) and etching time (15, 30, 45, 90, and 180 s). After etching and preparation, specimens were observed in the scanning electron microscope (SEM). Surface roughness/topography increased with increasing acid concentration and increasing etching time, but not in a linear fashion; generally, prisms tended to go from flat-surfaced to cone-shaped and prism sheaths from fissure-like to wedge-shaped. Intragroup variations and intergroup similarities were considerable. The two major enamel factors determining the etch effect are crystal orientation and prism sheath properties. Other factors, such as distribution of porosities and crystal quality, also contribute probably. Slight to moderate topography is best for observing the finer enamel structure, for example, etching with concentrations in the range 0.1-1% and with etching times in the range 15-90 s, the stronger the acid, the shorter the time. The depth effect of nitric acid is judged to be relatively small. Considerable variations in expression of prism cross-striations were observed. SEM observations of acid-etched enamel in carefully selected planes are a powerful method for the study of enamel structure, bearing in mind the artifactual aspects of the observed surface.

A 48-month Clinical Evaluation of Fissure Sealants Placed With Different Adhesive Systems

Aim

To compare the retention rates of a nanofilled occlusal fissure sealant placed with the use of an etch-and-rinse or a self-etch adhesive over 48 months.

Materials and Methods

The authors enrolled 244 teeth, each with no restoration or sealant and no detectable caries, from 16 patients. The sealants were placed with Solobond M two-step etch-and-rinse adhesive or Futurabond NR one-step self-etch adhesive by four previously calibrated dentists using a table of random numbers. After completion of the adhesive application, a nanofilled sealant, Grandio Seal, was applied and light-cured. Two other calibrated examiners, who were unaware of which adhesive had been used, independently evaluated the sealants at baseline and at 12-, 24-, 36-, and 48-month recalls. Each sealant was evaluated in terms of caries formation being present or absent and retention using the following criteria: 1 = completely retained, 2 = partial loss, and 3 = total loss. The Pearson χ2 test was used to evaluate differences in retention rates among the sealants used with different adhesives for each evaluation period.

Results

The retention rates for sealants in the Solobond M group were significantly higher than those in the Futurabond NR group in all periods of evaluation (p<0.05). No statistically significant difference between the retention rates for premolars and molars was found at each evaluation period (p>0.05). There was no new caries formation throughout the 48-month recall period.

Conclusion

Fissure sealants placed with etch-and-rinse adhesive showed better retention rates than those placed with self-etch adhesive.

Primary dentin etching time, bond strength and ultra-structure characterization of dentin surfaces

OBJECTIVES

To evaluate the effect of shortening the etching time on roughness, microhardness and bond strength of three adhesive systems to primary tooth dentin.

METHODS

Flat dentin surfaces from primary molars were randomly assigned to six experimental groups. Three different adhesive systems were used: an etch-and-rinse adhesive (Single Bond), a two-step self-etching (Clearfil SE Bond), and a one-step self-etching (One-Up Bond F) adhesive. In half of the specimens, the recommended etching time was used, in the other half the etching time was 50% reduced. After applying the adhesive, resin composite build-ups were constructed and stored in a humid environment for 24h at 37 degrees C. Specimens were sectioned into 1mm(2) beams and tested for microtensile bond strength (MTBS). Debonded surfaces were analyzed by scanning electron microscopy (SEM). Additional surfaces were conditioned for microhardness measurements (KHN) and for atomic force microscopy (AFM) analysis. Intertubular and total surface roughness (Ra) were recorded. Results were analyzed with ANOVA and Student-Newman-Keuls tests (P<0.05).

RESULTS

Single Bond and Clearfil SE Bond showed higher MTBS than One-Up Bond F. Bond strength and intertubular roughness increased when Single Bond and One-Up Bond F were used with a reduced etching time. For Clearfil SE Bond no differences in MTBS were detected when reducing the etching time. The application of phosphoric acid, Clearfil SE Bond primer and One-Up Bond F decreases dentin microhardness.

CONCLUSIONS

Shortening One-Up Bond F application time and reducing the etching time of phosphoric acid to one-half of the manufacturer's recommended etching time when using Single Bond are recommended when bonding to primary dentin.

Effects of rotary instrumentation and different etchants on removal of smear layer on human dentin

STATEMENT OF PROBLEM

Various methods of rotary preparation and conditioning of teeth affect surface topography and may affect the retention of dental restorations.

PURPOSE

This study microscopically evaluated dentin surfaces prepared by different rotary instruments and etched using several types of acid etchants that have been deemed suitable dentin conditioners.

MATERIAL AND METHODS

Occlusal surfaces of 35 extracted human molars were ground wet with 320-grit silicon carbide paper to the depth of the central groove and then prepared with diamond (n = 5) and finishing burs (n = 30). Five specimens from each group were used for SEM evaluation of mechanical preparation effects. Dentin specimens (n = 5) prepared with finishing burs were then etched with 1 of 5 etchants (25% polyacrylic acid, 10% phosphoric acid, 10% citric acid, 20% lactic acid, or 32% phosphoric acid) for 10 seconds. Specimens were critical-point dried and freeze fractured for SEM analysis.

RESULTS

Diamond rotary instruments created more undulating surfaces than finishing burs. Fine grooves were observed running perpendicular to undulations and parallel to the direction of instrument rotation. Specimens prepared with finishing burs exhibited a smooth surface interrupted by only a slight granularity. The amorphous smear layer was partially removed after the application of 25% polyacrylic acid (pH 1.53), but all dentinal tubules contained plugs. The number of dentin tubules containing plug material and the amount of material in the tubules decreased noticeably with 10% phosphoric acid (pH 0.86), and the dentin surface had an appearance similar to the specimen etched with 10% citric acid (pH 1.70). The surfaces treated with 20% lactic acid (pH 1.40) produced a clearly etched surface with minimal demineralization. Etching of dentin with 32% phosphoric acid (pH 0.16) revealed significant changes in dentin with the evidence of increased tubule diameter.

CONCLUSION

Differences related to the method of instrumentation were found in the surface characteristics of dentin. The degree of smear layer removal was related to the pH of the acid etchant.

The effect of pretreatment with an oxalic acid solution on marginal adaptation to enamel in vivo

STATEMENT OF PROBLEM

New acids such as oxalic acid have been introduced as a conditioning agent in the total-etch technique. There is concern about long-term retention of the acid on enamel in relation to the superficial etch effect.

PURPOSE

This in vivo study evaluated the marginal adaptation to enamel conditioned with either and oxalic acid solution or a phosphoric acid with SEM replica technique.

MATERIAL AND METHODS

Twenty-four patients received one of each of three class III restorations. Two cavity preparations were pretreated with aluminum nitrate/oxalic acid/glycine solution 1 of the Gluma 2000 system. The first cavity was primed and sealed with Gluma 2000 solution 2, the second cavity with Gluma 3 and 4. The third cavity was conditioned with phosphoric acid (Gluma 1) and sealed with the bonding resin Gluma 4. All three cavities were restored with a hybrid resin composite (Pekafill). At baseline and after 1 year, replica impressions were made to study the margins with SEM. Semiquantitative analysis of the enamel interfaces was performed (x200 and x1000 magnifications). Marginal quality of the three restorative systems were compared and tested intraindividually.

RESULTS

The three restorations exhibited good enamel marginal adaptation and a high percentage of gap-free margins at baseline, 96% to 97% of the total length of margins investigated. Marginal quality decreased significantly after 1 year for all three groups. Gap-free margins were observed in 81% to 85% of the marginal length. No significant differences were found among the groups.

CONCLUSION

Despite a less pronounced etch pattern created by conditioning of enamel with the oxalic acid solution, a good enamel marginal quality was observed at both evaluation times, comparable to the marginal adaptation of the phosphoric acid conditioned cavities.

Influence of concentration and application time of maleic acid on dentin permeability

OBJECTIVES

Since dentin permeability ultimately affects bond strength, the purpose of this study was to compare the effects of different concentrations of maleic acid, and different exposure times on dentin permeability.

METHODS

One hundred and thirty freshly extracted human non-carious third molars were used. Hydraulic conductance was determined after various treatments. The teeth were divided into five groups. In the first group, the smear layer was untreated. In three other groups, 0.10, 0.25, or 0.5 M aqueous solution of maleic acid was applied on dentin slices for 15, 30, or 60 s. In the last group, the Scotchbond Multi-Purpose dental adhesive system (3M Dental Products) conditioner was applied for 15, 30, or 60 s.

RESULTS

After a 60 s exposure time, the Scotchbond Multi-Purpose dentin conditioner or the 0.1 M solution of maleic acid was as effective at increasing dentin permeability as the 0.25 M and 0.5 M maleic acid solutions. The maximum dentin permeability was reached after 15 s with 0.25 M and 0.5 M solutions of maleic acid, after 30 s with Scotchbond Multi-Purpose and after 60 s with the 0.1 M solution of maleic acid. During the first 30 s, the 0.1 M solution of malic acid did not increase dentin permeability and did not completely remove the smear layer; a SEM examination of the dentin slices corroborated the functional results.

SIGNIFICANCE

The manufacturer's recommendation of 15 s of etching using Scotchbond Multi-Purpose conditioning gel produced a moderate amount of etching which increases dentin permeability to about one-half its maximum value.

Bond strengths of ceramic brackets using different bonding techniques

A series of laboratory investigations was carried out to compare the shear-type bond strengths and site of bond failure of ceramic orthodontic brackets bonded to etched enamel. When light-cured composite resin was used as the luting agent, there was no reduction in bond strength when using 2.5 per cent nitric acid to etch the enamel, compared to 37 per cent phosphoric acid. The use of the two resin modified glass ionomer cements were found to give rise to significantly lower bond strengths than composite resin when used for placing ceramic brackets. Significantly less composite resin remained on the enamel surface following bracket removal in those samples etched with nitric acid.

Correlation of bond strength with surface roughness using a new roughness measurement technique

OBJECTIVES

The correlation between shear bond strength and surface roughness was investigated using new surface measurement methods.

METHODS

Bonding agents and associated resin composites were applied to set amalgam after mechanically roughening its surface. Surface treatments were noe (as set against glass), 80 grit, and 600 grit abrasive paper. Surface roughness (R(a) as measured parallel and perpendicular (+) to the direction of the polishing scratches and true profile length were measured. A knife-edge was applied (rate = 2.54 mm/min) at the bonding agent/amalgam interface of each sample until failure.

RESULTS

Coefficients of determination for mean bond strength vs either roughness (R(a), of profile length were significantly higher for measurements in parallel directions than for those measurements in (+) directions. The shear bond strength to set amalgam for a PENTA-containing adhesives system (L.D. Caulk Division) was not significantly different from that of a PENTA-free adhesive (3M Dental Products Division), even though PENTA has been reported to increase bond strength to nonprecious metals.

SIGNIFICANCE

The shear bond strength of resin composite to amalgam is correlated to surface roughness when it is measured parallel to the polishing scratches. This correlation is significantly lower when surface roughness is measured in the typical manner, perpendicular to the polishing scratches.

Three-year clinical evaluation of Tenure dentine bonding agent

Twenty cervical abrasion lesions in five patients of mean age 58 years were restored with Tenure dentine bonding agent and Silux composite, without enamel etching. The cumulative loss rates of restorations were 5 per cent, 5 per cent, and 11 per cent after 1 year, 2 years and 3 years, respectively, and there was a slight increase of marginal staining. The results are in agreement with other authors.

One-year clinical performance of PMDM-based dentine bonding agents

Two PMDM-based dentine bonding agents and a microfilled composite were used to restore a total of forty non-undercut caries-free cervical abrasion lesions without enamel etching. Restorations were evaluated over one year and the loss rate calculated using a life table analysis. Marginal staining was assessed from colour photographs on a continuous linear rating scale. After one year, 5 per cent of Tenure bonded restorations were lost compared with 52 per cent of Mirage bonded restorations. Slight marginal staining was evident around Tenure bonded restorations after one year.

Morphological aspects of the resin-dentin interdiffusion zone with different dentin adhesive systems

Cross-sections of resin-dentin interfaces were etched with an argon-ion beam to make their substructure detectable by scanning electron microscopy. The dentin adhesive systems were categorized morphologically into three groups, and an attempt was made to clarify their adhesive mechanism. The first group of products removed the smear layer. The argon-ion bombardment clearly disclosed a hybrid or resin-impregnated dentin layer. It is hypothesized that conditioning with acidic or chelating agents demineralized the dentin surface-layer to a certain depth, leaving behind a collagen-rich mesh-work. Hydrophilic monomers are then believed to alter this collagen-fiber arrangement in a way that facilitates penetration of the adhesive resin, resulting in a mechanical, intermingled link between collagen and the adhesive resin. The second group preserved the smear layer. In this case, the dentinal tubules were obliterated with globular particles at their orifices and remained patent underneath these smear plugs. This type of adhesive system aims at the incorporation of the smear layer into the hydrophilic monomers, which have an affinity for the organic and/or inorganic components of the underlying dentin. Finally, a third, small group only partly dissolved the smear layer, creating a thin resin-impregnated dentin layer and a resin-impregnated smear plug. This study clearly showed that the application of recent adhesive systems induced structural changes in the dentin surface morphology, creating a retentive interface, called the inter-diffusion zone, between the deep, untouched dentin layers and the composite filling material. This resin-dentin interdiffusion zone offers bonding sites for copolymerization with the resin composite and, concurrently, might have protective potential for the pulp tissues.

Effect of trichloracetic acid on the microhardness and surface morphology of human dentin and enamel

Trichloracetic acid is recommended for the treatment of external cervical root resorption. The present study examined the effect of 90% trichloracetic acid on the microhardness and surface morphology of human dentin and enamel. Intact extracted human teeth were sectioned and embedded in acrylic resin. Each tooth was grinded and highly polished exposing a flat surface of dentin and enamel. The teeth were treated with 90% trichloracetic acid for 30, 60 and 90 s. Vicker's microhardness of the dentin and enamel was assessed for each tooth before and after each treatment. In addition the surface morphology of a trichloracetic acid treated tooth was examined via SEM. The results showed that 90% trichloracetic acid caused a second order type reduction of the microhardness, as well as structural changes in both dentin and enamel.