Improving retention of dental veneers fabricated from an experimental enamel-based biopolymer compared with CAD/CAM hybrid materials

Objectives

CAD/CAM hybrid materials have become increasingly utilized in restorative dentistry. However, their low tensile bond strength (TBS) may lead to the detachment of minimally invasive restorations. When prepared, an experimental enamel-based biopolymer prosthesis provided a honeycomb-like interfacial layer with luting adhesives leading to a higher TBS than Ni-Cr-Be based alloy, lithium disilicate-based ceramic, and cured-resin-composite. This study aimed to compare TBSs of dental veneers fabricated from experimental biopolymer and commercial hybrid materials bonded to enamel using two different luting adhesives.

Methods

Laminate veneers (4 × 4 mm) 1 mm thick were prepared from commercial CAD/CAM blocks: VITA ENAMIC, SHOFU Block HC, KATANA AVENCIA, and an experimental biopolymer. The flat bonding surface of the veneers was ground to 600-grit, followed by 50-μm alumina air-abrading for standardization. Each veneer was fixed on flat ground bovine enamel using either Super-Bond C&B or RelyX™ U200 resin (n = 10). The surface treatment and bonding procedures were treated as recommended by the manufacturers. All bonded specimens were stored in water at 37 °C for 24 h before tensile testing with a universal testing machine at a cross-headed speed of 1.0 mm/min. The fractured surface was examined with a stereomicroscope and scanning electron microscope. TBS data were statistically analyzed using two-way ANOVA and Tukey's HSD test (α = 0.05).

Results

Experimental biopolymer veneers demonstrated the highest mean TBS with cohesive failure in the luting agents. Adhesive failure at the veneer side interface was found in other groups. There was no significant difference between the two luting agents.

Conclusion

The results indicate that the experimental biopolymer veneer bonded to enamel provided the best retention. The TBS at the enamel-resin interface is higher than at the veneer-resin interface for all commercial CAD/CAM hybrid materials.

Clinical significance

An experimental enamel-based biopolymer veneer can provide better retention than CAD/CAM hybrid materials in clinical treatment.

Marginal Micro-Seal and Tensile Bond Strength of a Biopolymer Hybrid Layer Coupled with Dental Prosthesis Using a Primerless-Wet System

The aim of this study is to compare the marginal seal and tensile bond strength (TBS) of prostheses fixed to enamel-dentin using different adhesive systems. Resin-composite inlays directly fabricated from Class V cavities of extracted human molars/premolars and mini-dumbbell-shaped specimens of bonded enamel-dentin were prepared for microleakage and tensile tests, respectively. Four adhesive systems were used: primerless-wet (1-1 etching for 10-, 30-, or 60-s, and 4-META/MMA-TBB), primer-moist (All-Bond2 + Duolink or Single-Bond2 + RelyX ARC), self-etch (AQ-Bond + Metafil FLO), and dry (Super-Bond C&B) bonding. Dye penetration distance and TBS data were recorded. Failure modes and characteristics of the tooth-resin interface were examined on the fractured specimens. All specimens in 10-, 30-, and 60-s etching primerless-wet, Super-Bond, and AQ-Bond had a microleakage-free tooth-resin interface. Primer-moist groups showed microleakage at the cementum/dentin-resin margin/interface. Significantly higher TBSs (p < 0.05) were recorded in primer-less-wet and Super-Bond groups with the consistent hybridized biopolymer layer after the chemical challenge and mixed failure in tooth structure, luting-resin, and at the PMMA-rod interface. There was no correlation between microleakage and TBS data (p = −0.148). A 1−3 µm hybrid layer created in the 10−60 s primerless-wet technique, producing complete micro-seal and higher tensile strength than enamel and cured 4-META/MMA-TBB, may enhance clinical performances like Super-Bond C&B, the sustainable luting resin.

An Enamel Based Biopolymer Prosthesis for Dental Treatment with the Proper Bond Strength and Hardness and Biosafety

Although dental prosthesis materials such as metal alloys, ceramics, and cured resin composite have long been utilized to restore teeth, their bond strength and hardness values are not well matched to human enamel. Prosthesis detachment and opposing enamel wear are major concerns in restorative dentistry. An experimental biopolymer, hybridized enamel, was synthesized and utilized as a dental prosthesis to compare hardness and tensile bond strength (TBS) with those of commercial materials. Vickers hardness (VHN) with a 100 g loading for 15 s at eight indentations on each specimen (n = 20) was measured. TBSs between prostheses and two types of resin luting agents (n = 10), Super-Bond C&B and All-Bond2 + Duo-Link, were tested. Fractured surfaces and the luting resin-prosthesis interface were examined under a stereomicroscope or a scanning electron microscope (SEM). Statistically significant differences in the TBS and hardness were revealed (p < 0.05). The experimental biopolymer provided a hardness value comparable with human enamel and the highest TBS for both luting agent types. The SEM micrograph demonstrated a honeycomb-like pattern interface between the experimental biopolymer and luting resin. These results suggest that this experimental biopolymer may be a better restorative material to protect from natural enamel loss from tooth reduction or attrition and prevent prosthesis detachment during mastication.

Impact of hybrid layer formation on the 15-year survival, complications and failures of full-coverage retainers

PURPOSE

To compare the effect of 4-META/MMA-TBB resin, which can provide hybrid layer formation, and acid-base cements on survival, complications, and failure risks of full-coverage retainers evaluated for 15 years.

METHODS

A total of 1,161 abutment teeth in 260 patients treated with at least one single crown or fixed partial denture were recalled for clinical examination. Survival was defined as not having undergone extraction of abutments or renewal of prostheses. Secondary caries, pulp necrosis, or prosthesis detachment were recorded as complications. Survival and complications rates were analyzed using the Kaplan-Meier method and log-rank test. Multivariable analysis of factors associated with failure or complications using Cox's proportional hazard regression model was performed (α = 0.05).

RESULTS

Significant differences were observed in survival ( p = 0.007), secondary caries (p = 0.000), and prosthesis detachment (p = 0.025) complications between luting agents. The 5-, 10-, and 15-year survival rates for 4-META/MMA-TBB resin were 95.2%, 90.5%, and 90.5%, while those of acid-base cements were 93.2%, 80.6, and 67.4%, respectively. Secondary caries and prosthesis detachment complications for 4-META/MMA-TBB resin were 1.9% and 0.5%, whereas those for acid-base cements were 15.2% and 4.3% respectively. Acid-base cements were associated with a 1.664-, 2.950-, 3.333-, and 4.444-times greater risk of failure, prosthesis renewal, secondary caries and prosthesis detachment, respectively.

CONCLUSIONS

4-META/MMA-TBB resin has higher long-term survival rate with lesser caries and prosthesis detachment than acid-base cements. The ability of this resin to create an acid-base resistant hybrid layer may contribute to a life-long function of tooth abutment.

Effect of strong tooth-bleaching with 38% hydrogen peroxide on marginal seal of dental restorations using self-etch and total-etch adhesives

The purpose of this study was to evaluate the distance and/or thickness of dye penetration at enamel and cementum/dentin margins of restorations before and after vital bleaching. Class V cavities were prepared on extracted human premolars and restored with light-cured resin composite using either AQ-Bond or Single-Bond2 adhesives. Four conditions: no bleaching (control), restored before bleaching (RB), bleached and immediately restored (BIR), bleached and stored in artificial saliva for 7 days then restored (B7R), were used for each adhesive group. After soaking in basic fuchsin dye for 24 hours, all specimens were vertically sectioned through the middle of restorations to measure the distance and/or the thickness of dye penetration. No microleakage was found either on enamel and cementum/dentin margins of control group using AQ-Bond. Whereas leakage was found in the control group using Single-Bond2 and bleached groups. Statistically significant differences in leakage distance and/or thickness were found among groups at the cementum/dentin margin (P < .05). Dye could penetrate into the pulp chamber of BIR (60%) and B7R (15%) specimens.

CLINICAL SIGNIFICANCE

The negative control or leakage-free group is very important when discussing the effects of bleaching on marginal seal or microleakage. Bleaching using 38% H₂ O₂ increases the microleakage distance and dye penetration area of cementum/dentin margin more than that of enamel margin. The bleached tooth is not a good substrate for reliable bonding and complete seal and it is also a channel for external stimuli reaching the pulp.

Prognosis test by visualization of demineralized dentin under restorations to prevent initial wall-lesions initiated by lactic acid

PURPOSE

To visualize the complete protection of restored dentin in the acidic environment by the complete impregnation of resin into demineralized dentin.

METHODS

Class V cavities prepared in extracted human molars composed of enamel, cementum and dentin surfaces were sealed using either 4-META/MMA-TBB resin with conditioning periods of 10, 30, 60 seconds with 10% citric acid and 3% ferric chloride mixed aqueous solution (10-3) or Single-Bond 2 adhesives prior to restoration with light-cured resin-composite. Specimens were either immersed in artificial saliva or 0.1 mol/L buffered lactic acid solutions at 37°C for 14 days. After immersion in 0.5% basic fuchsin dye for 24 hours, the extent of dye penetration at the margin was measured. SEM micrography was used to investigate the quality of hybridized dentin when immersed in HCl followed by NaOCl solutions.

RESULTS

After lactic acid exposure, dye penetration into the adjacent demineralized cementum/dentin was found to be significantly lower than the leakage distance under 30 and 60 seconds and Single-Bond 2 specimens. Leakage-free margins were found in 10-second conditioning period specimens for both control and after soaking in buffered lactic solution with the stable hybridized dentin after chemical challenge.

CLINICAL SIGNIFICANCE

A leakage-free interfacial layer, provided by complete hybrid layer formation, can block lactic acid penetration. Using this novel prognosis test for visualization of demineralized dentin, clinical restorations are likely to be more reliably predictable in the prevention of initial wall-lesions, post-operative hypersensitivity and/or pulpal infection.

A 10-Year Clinical Evaluation of Resin-Bonded Fixed Dental Prostheses on Non-Prepared Teeth

This study evaluated the conditions of the non-invasive resin-bonded fixed dental prostheses (FDP) and patient satisfaction up to 10 years of clinical function. A total of 23 patients who required fixed prostheses in the areas of mandibular anterior and premolar, and maxillary anterior region received resin-bonded restorations between 1999-2003. In 13 patients with 14 edentulous areas were restored with an adhesive pontic (natural tooth, acrylic and porcelain). Two indirect proximal veneers using resin composite were placed in each space in 10 patients having 13 edentulous spaces. All prostheses were bonded to the proximal surface of adjacent teeth using resin cement based on 4-META/MMA-TBB. No debonding of proximal veneers but 4 pontic debonding was observed which were rebonded and remained functional until final follow up. The abutments in pontic and proximal veneer groups were free of caries and hypersensitivity. Periodontal health was improved after treatment and was maintained for 10 years except for 4 abutments that still showed some bleeding on probing. Non-invasive resin-bonded FDPs are simple, pain-free, less costly treatment procedures that could provide acceptable clinical longevity with high patient satisfaction.

Dentin protection by a primer-less adhesive technique

PURPOSE

To identify the remaining demineralized dentin (the permeable layer that allows leakage) when using primer-less wet bonding with a total etching period of 10 to 60 seconds compared with contemporary resin adhesives.

METHODS

Extracted human molars were selected and Class V cavities were prepared on the axial surfaces at the CEJ, providing margins in enamel and dentin for leakage testing using a basic dye (n = 10). Seven groups of conditioned teeth [1-1 etched for 10, 30, and 60 seconds (primer-less wet), All-Bond 2 and Single-Bond 2 (wet), AQ-Bond (self-etched), Super-Bond C&B (dry)] were used as bonding systems for resin composite restoration. All specimens were stored in water at 37 degrees C for 24 hours before soaking in a 0.5% basic fuchsin solution for 24 hours. The distance of dye penetration was measured using stereomicroscopy.

RESULTS

No leakage at the enamel- and dentin-resin interfaces was found for all etching periods of 1-1 primer-less, Super-Bond C&B, and AQ-Bond specimens. However, leakage was observed at dentin margins in two wet with primer systems, All-Bond 2 (1.31 +/- 1.39 mm) and Single-Bond 2 (0.37 +/- 0.28 mm), which required phosphoric etching to remove a weak smear layer on prepared dentin.

Influence of dentin substrates to simplify wet-bonding: a leakage-free and reliable tensile strength interface for long-lasting restorations

The wet-bonding procedure can be simplified by eliminating the primer. An aqueous mixture of 1% citric acid and 1% ferric chloride (1-1) was hypothesized as providing an easier dehydratable thinner substrate to which 4-META/MMA-TBB resin can adhere reliably. The 1-1 was applied for 10 s and rinsed off with water for 10 s. Demineralized dentin under four conditions was prepared before bonding to PMMA rod using 4-META/MMA-TBB resin: air-dried 10 s (D-NP); air-dried 10 s, primed 60 s with 5% 4-META in acetone (D-P); blotted dry 10 s (W-NP); blotted dry 10 s, primed 60 s (W-P). The tensile strengths (MPa) using mini-dumbbell specimens were 4.0 ± 2.4 for D-NP, 10.6 ± 5.4 for D-P, 38.3 ± 4.4 for W-NP, and 42.9 ± 3.3 for W-P. There was no significant difference between W-NP and W-P with cohesive failure in the dentin and the cured resin. In the wet groups, the hybridized dentin was stable against both HCl and NaOCl challenges. TEM examination and a leakage tests confirmed a perfect seal with a leakage-free interface of W-NP. These results suggest that this primer-less wet-bonding is promising method to protect the underlying intact dentin and pulp, thus providing long-lasting dental treatment.

Marginal integrity between a prefabricated composite block and enamel, DEJ, and dentin

PURPOSE

To evaluate the stability of the interfacial layer and leakage patterns between enamel, DEJ, dentin and three adhesive systems as demonstrated by either a dye or a silver nitrate technique to understand the marginal integrity of restored tooth substrates.

METHODS

Extracted human molars were cross-sectioned to prepare enamel, DEJ and dentin surfaces. Areas with the DEJ aligned in the middle were restored with prefabricated flat composite blocks using either Superbond C&B (SB), Panavia Fluorocement (PN) or Variolink II (VL) cements. 7 restored specimens for each cement were prepared to investigate the interfacial layer after chemical challenge using SEM. Restored and control specimens for each cement were prepared for leakage tests by soaking either in 0.5% basic fuchsin or 50% silver nitrate solutions for 24 hours (n = 8). The penetration depth of tracer was measured using stereoscopy and a digital micrometer. SEM backscattered electron image and energy dispersive x-ray spectrometry were used to detect the location of the silver.

RESULTS

Prepared SB hybridized enamel, dentin and DEJ were stable against soaking in HCl followed by NaOCl solutions whereas prepared DEJ- and dentin-resin interfacial layers were degraded, detached and thinner than that of enamel in VL and PN specimens. No leakage was found at the enamel-resin interface for all cements and at the DEJ- and dentin-resin interfaces for SB specimens. VL specimens showed significantly greater leakage at the interface of dentin and DEJ than did PN specimens.

Compressive Fracture Resistance of Porcelain Laminates Bonded to Enamel or Dentin with Four Adhesive Systems

PURPOSE

To measure the compressive strength of porcelain laminates of 0.5 or 1.0 mm thickness when bonded to enamel or dentin using these resin cements: All-Bond 2 + Choice, Panavia 21, Scotchbond + Opal, and Super-Bond C&B.

MATERIALS AND METHODS

The buccal and lingual aspects of human molars were sectioned to prepare specimens at least 3 x 3 x 3 mm in size. Thirty horizontally flat enamel surfaces were prepared with a diamond disc for each group using a milling machine. Ten enamel specimens were randomly selected to test the fracture strength of 0.5-mm thick porcelain laminates without resin cement, and the data were recorded for a control group. The enamel specimens of each group were divided into two subgroups of 15 specimens to bond with either 0.5- or 1.0-mm thick porcelain laminates. Four resin cements were used for bonding of individual groups. All bonded specimens were stored in 37 degrees C for 24 hours before fracture testing. The horizontally flat dentin surfaces were prepared on the fractured bonded specimens using a diamond disc for each group. Ten 0.5 mm porcelain laminates were randomly selected to test the fracture strength on dentin (control group). The bonded laminates to dentin were prepared using the same procedure as for enamel. The fracture strengths were statistically analyzed at alpha= 0.05.

RESULTS

Statistically significant differences in mean fracture strengths between groups were revealed. No significant difference in fracture strengths of control specimens between enamel and dentin was found. Super-Bond C&B provided a higher fracture resistance of porcelain than the other resin cements. Increasing the thickness of porcelain laminate increased the fracture strength. The 0.5-mm thick porcelain bonded to enamel had higher fracture strength than that of 1.0-mm thick porcelain bonded to dentin when using Super-Bond C&B and Scotchbond + Opal cements.

CONCLUSIONS

Bonding techniques and curing systems of resin cements influenced the fracture resistance of porcelain laminates. Dry bonding with auto-polymerization of Super-Bond C&B resin provided the highest fracture resistance of porcelain. Porcelain bonded to enamel with this resin had a much higher fracture strength than when bonded to dentin.

Effect of tooth-bleaching on the tensile strength and staining by caries detector solution on bovine enamel and dentin

PURPOSE

To evaluate the tensile strength and staining of enamel and dentin after extracoronal or intracoronal bleaching using conventional bleaching agents.

METHODS

Extracted bovine incisors were divided into eight groups of 10 specimens. Individual groups were treated by extracoronal bleaching (E) using in-office and home techniques with different concentrations of hydrogen peroxide (H2O2) and carbamide peroxide (CP); no bleaching (EN), 35% H2O2 and 10% CP (E35H-10C), 35% H2O2 and 20% CP (E35H-20C), 35% CP and 10% CP (E35C-10C), 35% CP and 20% CP (E35C-20C). Intracoronal "walking bleaching" (I) was performed after 24 hours of root canal treatment in the three remaining groups; no bleaching (IN); sodium perborate dissolved in 35% H2O2 (ISP-35H); and sodium perborate in distilled water (ISP-W). Mini dumbbell shapes of enamel and dentin with central cross-section diameters of 1.5 x 0.5 mm and 3 x 1 mm respectively were prepared for tensile testing using an Instron machine. Fracture surfaces were examined using SEM. Bleached enamel and dentin specimens were stained and evaluated using Caries Detector solution. Staining scores were analyzed using Kruskal-Wallis H and Mann-Whitney test (P < 0.05).

RESULTS

Tensile strengths (mean +/- SD) of enamel and dentin respectively for each group in MPa were: EN = 30.5 +/- 3.3 and 85.4 +/- 3.0, E35H-10C = 14.8 +/- 2.3 and 58.9 +/- 2.0, E35H-20C = 10.6 +/- 2.6 and 55.5 +/- 2.2, E35C-10C = 25.4 +/- 3.4 and 70.8 +/- 2.5, E35C-20C = 20.3 +/- 4.1 and 67.2 +/- 3.3, IN = 26.5 +/- 4.1 and 85.9 +/- 2.5, ISP-35H = 13.6 +/- 3.1 and 46.7 +/- 2.3, ISP-W = 21.7 +/- 3.3 and 68.3 +/- 4.4. ANOVA and Tukey HSD test found statistically significant differences among and between groups respectively (P < 0.05). No significant difference was found between non-bleached groups (IN and EN) of enamel and dentin. Mean tensile strengths of all bleached groups were significantly lower than those of non-bleached groups. Fracture surfaces demonstrated the different morphologies for bleached and non-bleached enamel and dentin.

Effect of remaining demineralised dentine on dental microleakage accessed by a dye penetration: how to inhibit microleakage?

OBJECTIVES

To demonstrate that microleakage has taken place at the defect, which was analysed previously by a tensile test using dumbbell shaped specimens trimmed from bonded resin/dentine restorations, and to suggest how microleakage can be inhibited reliably in dental treatment.

METHODS

A total of 60 Class V box cavities were prepared at the cemento-enamel junction on fresh bovine incisors and randomly divided into four groups of 15 specimens each. Exposure times of etching for 10:3 conditioner were set at 10, 30 or 60 s, and for 10% phosphoric acid (positive control) at 10 s. The cavity walls were rinsed with water for 10 s, air-dried for 10 s and hybridised with 4-META/MMA-TBB resin. All the cavities were filled with a light cured resin composite and stored in 37 degrees C water for 24 h and then immersed in 15% methylene blue for 2 h. The length of dye penetration along the interface was graded by defined criteria and analysed using Kruskal-Wallis and Mann-Whitney tests. The dye penetration patterns were examined by light microscopy and the remaining demineralised dentine was analysed by Transmission Electron Microscopy (TEM).

RESULTS

The least leakage score was obtained in 10s-10:3 etched group with 12 out of 15 specimens demonstrating no leakage. Leakage was significantly lower at the cementum margin than for the other three groups. No significant difference in the extent of greatest dye penetration was found between the 60s-10:3 and 10s-phosphoric etched groups. Dye penetration along the cementum margins was significantly higher than that of the enamel margins in all groups, except the 10s-10:3 etched group. TEM examination confirmed that there were exposed collagen fibrils in the remaining demineralised dentine, where microleakage had taken place.

SIGNIFICANCE

It could be concluded from this study that microleakage has taken place at the defect in the bonded specimens which has correlations with zones of incompletely infiltrated demineralised dentine that was observed using TEM. A reliable method of inhibiting microleakage is the presence of well prepared hybridised dentine.

Influence of dentinal polyelectrolytes on wet demineralized dentin, a bonding substrate

The objective of this study was to show the influence of dissolved dentinal polyelectrolytes on the characteristics of dentin (bonding substrate) demineralized by citric acid in the absence or presence of ferric chloride. The demineralizing agent was an aqueous mixture of 0, 1, 3, or 10% ferric chloride in 10% citric acid (10-0, 10-1, 10-3, 10-10, respectively). The hypothesis was that the concentration of dissolved dentinal noncollagenous substances, mainly polyelectrolytes soluble in water, must be decreased by their aggregation with ferric ions, which changes the characteristics of demineralized dentin, the rates of demineralization, and dehydration. Cervical bovine dentin was prepared in 3 x 2 x 2-mm blocks, each weighing 20.0 +/- 0.5 mg. The rate of demineralization was investigated by measuring the weight loss resulting from demineralization by immersion in 10 mL of conditioner at 2-h intervals. The dehydration rate of wet demineralized dentin was determined using two methods: (1) weight loss in a desiccator under 263 Pa pressure and (2) differential scanning calorimetry (DSC). Twenty, 12, 8, and 4 h were required to complete demineralization of the blocks with the 10-0, 10-1, 10-3, and 10-10 solutions, respectively. The 10-10 wet demineralized dentin showed the highest rate of dehydration, followed in descending order by the 10-3, 10-1, and 10-0 specimens. Ferric chloride in dentin conditioners provided both a higher rate of dentin demineralization and a higher dehydration rate of wet demineralized dentin. These results suggest that in the presence of ferric chloride, a decreasing amount of dissolved polyelectrolytes aggregated with ferric ions in the substrates may increase the permeability of dentin to water and citric acid. Improvement of monomer permeability is essential to the preparation of good hybridized dentin, providing a more stable and reliable bonding and also protecting the dentin and pulp from infection. A further study of bonding substrates is required in order to understand the role of hybridized dentin in improved dental treatment.

Comparison of microleakage of three acid-base luting cements versus one resin-bonded cement for Class V direct composite inlays

STATEMENT OF PROBLEM

Demineralized dentin beneath set cement may adversely affect microleakage under fixed restorations.

PURPOSE

Microleakage of direct composite inlays cemented with acid-base cements and a methyl methacrylate resin cement were evaluated to determine their effect on the integrity of the underlying hybridized dentin.

MATERIALS AND METHODS

Sixty Class V box preparations (3 mm x 3 mm x 1.5 mm) were precisely prepared in previously frozen bovine teeth with one margin in enamel and another margin in dentin. Direct composite inlays (EPIC-TMPT) for each preparation were divided into 4 groups of 15 specimens each and cemented with 3 acid-base cements (control group): Elite, Ketac-Cem, Hy-Bond Carbo-Cem, and 1 adhesive resin cement: C&B Metabond. All specimens were stored in distilled water for 24 hours at 37 degrees C before immersion in 0.5% basic fuchsin for 24 hours. The dye penetration was measured on the sectioned specimens at the tooth-cement interface of enamel and cementum margins and recorded with graded criteria under light microscopy (Olympus Vanox-T) at original magnification x 50, 100, and 200. A Kruskal-Wallis and the Mann-Whitney test at P<.05 were used to analyze leakage score.

RESULTS

All cementum margins of the 3 acid-base cements tested demonstrated significantly higher leakage scores than cementum margins for inlays cemented with the resin cement tested(P<.01). No leakage along the tooth-cement interface was found for inlays retained with the adhesive resin cement.

CONCLUSIONS

Within the limitations of this study, the 3 acid-base cements tested exhibited greater microleakage at the cementum margins than did the adhesive resin cement that was tested.

Effect of dentin conditioners on wet bonding of 4-META/MMA-TBB resin

PURPOSE

By altering either ferric chloride concentration in 10% citric acid (1% ferric chloride = 10-1; 5% ferric chloride = 10-5; 10% ferric chloride = 10-10) or conditioning periods with an aqueous mixture of 1% citric acid and 1% ferric chloride (1-1), the influence of dentin substrate on bond strength and hybridized dentin in wet bonding of 4-META/MMA-TBB resin was examined.

MATERIALS AND METHODS

Dentin surfaces of fresh bovine incisors were conditioned either with 10-1, 10-5, or 10-10 mixtures for 10 s (10-1-10s, 10-5-10s, 10-10-10s groups) or with a 1-1 mixture for 5, 10, 30 or 60 s (1-1-5s, 1-1-10s, 1-1-30s, 1-1-60s groups). Rinsed, demineralized dentin samples were kept wet, primed with 5% 4-META in acetone for 60 s, and bonded with 4-META/MMA-TBB resin. Bonded specimens were trimmed to a mini-dumbbell shape for tensile testing. The cross sections of bonded specimens were modified with HCl and NaOCl in order to assess the hybrid layer. The fractured surfaces of specimens and the hybridized dentin were investigated with SEM.

RESULTS

No significant difference (p > 0.01) in tensile strength was identified between 10-1-10s and 10-5-10s groups (30 MPa), 10-10-10s and 1-1-5s groups (15 MPa), and the three groups conditioned by 1-1-10s, -30s and -60s (40 MPa). The thickness of the hybrid layer increased with increasing either ferric chloride or conditioning periods.

CONCLUSION

The concentration of ferric chloride in 10% citric acid for wet bonding must be less than 5% in order to provide a reliable bond. When applied from 10 to 60 s, the 1-1 conditioner provided hybridized dentin with reliable tensile bond strength. The thickness of the hybrid layer did not influence the tensile bond strength.

Effect of seating force, margin design, and cement on marginal seal and retention of complete metal crowns

PURPOSE

The purpose of this study was to determine the marginal discrepancy and retention of silver-palladium crowns cemented with zinc phosphate (Phosphacap) and glass-ionomer cement (Fuji Cap 1) using different seating forces on preparations with various margin designs.

MATERIALS AND METHODS

Crown preparations with three finish lines--chamfer, shoulder, and shoulder with a 45-degree bevel--were sequentially prepared on a dentoform premolar. A metal die for each of the three finish lines was constructed. Complete metal crowns were fabricated for each metal die using a silver-palladium alloy. Three different seating forces--25, 100, and 300 N--were used to load the crowns until initial set of the cement. The marginal discrepancy was calculated by measuring the change in crown height before and after cementation using a digimatic indicator. Retention was determined by measuring the tensile strength using the Lloyd universal testing machine.

RESULTS

The higher seating forces produced better crown seating but had no significant effect on crown retention. The shoulder and shoulder with bevel finish lines provided better crown retention than the chamfer. Glass-ionomer cement provided greater crown retention than zinc phosphate cement. No significant correlation between marginal seating and crown retention was revealed using a Pearson analysis.

CONCLUSION

Marginal seal was not influenced by either margin design or type of luting cement, but was improved with higher seating force. Crown retention was affected by the margin finish line and the luting agent.