Panavia EX Research Articles

Micro-CT Detection and Characterization of Porosity in Luting Cements.

To evaluate porosity volume and localization in luting cements under fixed dental prostheses after cementation using micro-computed tomography (CT). Seventy-seven sound molars were circumferentially prepared to receive all-ceramic crowns, and IPS e.max ceramic copings were fabricated according to the manufacturer's instructions. For this study, different dental luting cements were used: eight resin-based cements (Variolink II, RelyX ARC, Clearfil Esthetic, BisCem, RelyX U100, Panavia EX, Super Bond C&B, and Multilink Automix), one resin-modified glass ionomer (Ketac Cem Plus), one glass ionomer (Ketac Cem), and one polycarboxylate (Durelon). Specimens were scanned with a micro-CT (SkyScan) for detection and comparison of the cements' porosities. Statistical analyses were performed using Kruskal-Wallis one-way ANOVA and Bonferroni's adjusted Mann-Whitney U tests. Multilink Automix (Volume = 0.11 ± 0.08 mm3 ; Surface Area = 1.63 ± 1.31 mm2 ), Ketac Cem Plus (Volume = 0.22 ± 0.21 mm3 ; Surface Area = 4.32 ± 3.71 mm2 ), and Variolink II (Volume = 0.34 ± 0.38 mm3 ; Surface Area = 6.47 ± 5.10 mm2 ) contained less porosity (p < 0.001) than all other cements. All other cements were not significantly different from one another (p > 0.05); however, the volume and surface area of the porosity found in the other tested luting cements were significantly greater than those of the Multilink Automix, Ketac Cem Plus, and Variolink II (p < 0.001), all of which demonstrated no significant differences (p > 0.05). The liquid and powder forms prepared by manually mixing the cements were found to cause greater porosity.

Longevity of conventional and bonded (sealed) amalgam restorations in a private general dental practice

To compare and contrast the longevity of conventionally placed dental amalgam restorations with those placed using bonding techniques. Retrospective survival analysis (Kaplan Meier) of dental amalgam restorations placed by a single operator in a private general dental practice. The records relating to dental amalgam restorations placed between 1 August 1996 and 31 July 2006 were sourced. The details of these were placed into a database that permitted flexible interrogation. Survival data on conventionally placed amalgams (C) and those bonded with either Panavia Ex (PE) or Rely X ARC (RX) were exported into a statistical package to permit survival analysis by the method of Kaplan and Meier.Results The number of restorations available for analysis were C = 3,854, PE = 51 and RX = 1,797. Percentage survival at one year was C = 96.29, PE = 95.65, and RX = 97.58. Percentage survival at five years was C = 86.21, PE = 76.35 and RX = 82.59. A Log Rank test demonstrated no statistically significant difference (p >0.05) in survival between the restoration types. Amalgam restorations bonded with PE or RX exhibited an acceleration of failure rate around 1,000 days post-placement. Further survival analyses of the method of restoration versus type of restored teeth (molar/premolar) and cavity preparation (Class I/II) showed no significant difference in the survival curves in respect of type of restored tooth. In the comparison of Class I and II cavities, the survival curves for the restorations differed significantly (p <0.0001), however when the curves for the Class I restorations alone were compared, no significant difference was found (p = 0.2634). This was also the case for the Class II restorations (p = 0.2260). Within the limitations of the study, bonding amalgams, compared to placing them conventionally, afforded no significant benefit upon restoration longevity. This, coupled with the emerging trend of an accelerating decline in longevity of bonded amalgams from 1,000 days onwards and with the greater cost, challenges the justification for routine bonding of amalgams.

Effect of surface treatment on the initial bond strength of different luting cements to zirconium oxide ceramic

The objective of this study was to compare the shear bond strength to zirconium oxide ceramic of adhesive-phosphate-monomer-containing (APM) and non-APM-containing (nAPM) luting cements after different surface treatments. nAPM cements: Bifix QM, Dual Cement, Duo Cement Plus, Multilink Automix, ParaCem Universal DC, PermaCem Smartmix, RelyX ARC, Variolink Ultra, and Variolink II; APM cements: Panavia EX, Panavia F2.0, and RelyX UniCem. Groups of ten test specimens were each prepared by layering luting cement, using cylindrical Teflon molds, onto differently treated zirconium dioxide discs. The surface treatments were airborne-particle abrasion with 110 mum alumina particles, silica coating (SC) using 30 mum alumina particles modified by silica (Rocatec System) or SC and silanization. Bifix QM and Multilink Automix were used in combination with an additional bonding/priming agent recommended by the manufacturers. After 48 h of water storage, each specimen was subjected to a shear test. Combinations involving APM-containing cements (14.41-23.88 MPa) generally exhibited higher shear bond strength than those without APM (4.29-17.34 MPa). Exceptions were Bifix QM (14.20-25.11 MPa) and Multilink Automix (19.14-23.09 MPa) in combination with system-specific silane or priming agent, which were on the upper end of shear bond strength values. With the use of the Rocatec system, a partially significant increase in shear bond strength could be achieved in nAPM cement. Modified surface treatment modalities increased the bond strength to zirconium oxide, although the most important factor in achieving a strong bond was the selection of a suitable cement. System-specific priming or bonding agents lead to further improvement.

Effect of groove placement on the retention/resistance of resin-bonded retainers for maxillary and mandibular second molars

Statement of problem. Lack of retention/resistance form in the clinical preparation of teeth for resin-bonded retainers may lead to clinical failure. Purpose. This study investigated the effect of proximal grooves on the retention/resistance of cast resin-bonded retainers for maxillary and mandibular second molar teeth. Material and methods. Two ivorine teeth (a maxillary and a mandibular second molar) were prepared for resin-bonded retainers. Twenty metal replicas of the prepared teeth were made (10 for each tooth morphotype). Resin-bonded retainers 0.5 mm thick were made for the 40 replicas and luted with Panavia EX cement. Forces for dislodgment of the retainers were applied along the long axes of the teeth. Forces recorded at the time of dislodgment were analyzed with 2-way analysis of variance and the post hoc Scheffé test. Results. Grooves resulted in substantial increases in debonding forces for maxillary molars (P<.001). The effect of grooves on mandibular second molars was not significant (P=.13). Conclusion. Grooves placed in tooth preparations of maxillary molar teeth for resin-bonded retainers had a significant effect on retention/resistance. The effect of grooves on mandibular second molars was less pronounced. (J Prosthet Dent 2001;85:472-8.)

New method for the in vitro evaluation of dental alloy bonding systems

Statement Of Problem: Bonding systems are used in some fixed prosthetic devices with base alloys. However, different studies of the same dental alloy bonding agents, under similar circumstances, have yielded disparate results in bond strength testing. Purpose: This study compared directly 2 dental alloy bonding systems through a “duel” type of confrontation, which basically is a 2-way tensile force test. Material And Methods: Ninety Wiron 88 base alloy cylinders (diameter of 8 mm length 15 mm) were sandblasted on both sides with Al203 powder (particle size 50 μm) during 10 seconds at an approximate distance of 5 mm, at an air pressure of 60 psi determined before sandblasting procedures. The surface of each cylinder was cleaned from Al203 powder with a strong burst of oil-free air from a chairside air syringe. Thirty cylinders were randomly assigned to 1 of 3 groups for direct bond strength comparison: (1) Panavia 21 to Panavia EX, (2) Panavia 21 to Metabond, or (3) Panavia 21 to a combination of a resin bonding agent plus Panavia 21. Each group was composed of 10 specimens that used 3 cylinders for each specimen. Each side of the sample cylinder received the same quantity of cement and 1 cylinder at a time was bonded to it. Cylinder alignment was verified with a Boley gauge during luting procedures. The bonded 3-piece block was held together for 24 hours under a compressive force of 2 kg/cm2 using a hydraulic press. Excess cement was removed with a brush, and the pertinent air sealant was applied to allow for autocuring of the cement. Specimens were later stored in water at room temperature for 48 hours before thermocycling procedures. Each specimen was thermocycled for 100 cycles with a 5-minute dwelling time in water at 4°C and 60°C. Specimens were subject to tensile force testing until debonding in 1 of the cylinders. Results: The opposing pull duel test (OPDT) showed that the Panavia EX failed (40.3 MPa) 10 of 10 duels against Panavia 21, whereas Panavia 21 failed (49.7 MPa) 9 of 10 duels against Metabond, and Panavia 1 failed (50.1 MPa) 10 of 10 duels against Photobond+Panavia 21. ANOVA revealed significant differences (P <.05) between PAN-EX group and MET and PHB+P21 groups. However, no significant differences were found between MET and PHB+P21 groups. Conclusion: The opposing pull duel test was a valid method to directly compare bond strengths of 2 bonding systems to dental base alloys. There was a small dispersion of the values even though cement mixing and thickness variables were difficult to control. Duel tensile testing provides meaningful information on the superiority of one bonding system over another in this controlled environment. (J Prosthet Dent 2000;84:217-21.)

Adhesion of bonded orthodontic attachments to dental amalgam: In vitro study

Bonding orthodontic attachments to molars is difficult in the presence of extensive buccal amalgam restorations. The purposes of this study were (1) to examine different amalgam surface preparations, (2) to examine properties of adhesive cements to amalgam, (3) to determine the most shear-resistant bonding technique and (4) to discuss whether these shear bond strengths were of adequate magnitude to be of clinical acceptability. The sample consisted of 108 standardized amalgam cylinders divided into 9 groups of 12 based on surface treatment technique and resin type. SPEED brackets (Strite Industries, Cambridge, Ontario) were bonded to amalgam surfaces that were either polished, sandblasted with 50 μm aluminium oxide, or chemically corroded. Adhesives used were Phase II (Reliance Orthodontic Products Inc, Itasca, Ill), Panavia EX (J Morita USA Inc, Tustin, Calif), or C & B Metabond (Parkell, Farmingdale, NY). After thermocycling from 10°C to 50°C 10,000 times, all samples were tested for shear bond strength with the Universal Testing Machine (Instron Corporation, Canton, Mass). The results show significantly higher bond strengths for all of the resin systems when sandblasting of the amalgam surface is used ( P < .0001). Only Panavia EX bonded strongly to polished samples, suggesting the presence of a chemical bond. Laboratory acceptable bond strengths to amalgam are possible. The surface characteristics of the amalgam appear to be more influential in the strength of the bond than does the nature of the resin. (Am J Orthod Dentofacial Orthop 1999;116:506-13)

キャスタブルセラミックス（ＯＣＣ）の予後調査

The purpose of this study was to evaluate the clinical strength of castable glass-ceramic (OCC, Olympus Optical Co., Japan) restorations.On 38 patients, from February 8, 1994 to December 19, 1996 at Aichi-Gakuin University Dental Hospital, 154 castable glass-ceramic restorations were cemented.These restorations were reexamined February 1998 and an analysis of fractures in the restorations was performed. Observed fractures as well as cracking or chipping and 22.7% of the restorations were considered fractured, and the longest survival time until now has been 48 months. The Kaplan-Meier survival probability calculated for these restorations was 0.86 using Panavia 21 and 0.90 using Panavia EX after a time interval of 24 months, and 0.66 using Panavia 21 and 0.82 using Panavia EX after a time interval of 36 months. There were no significant differences in the survival between the two cements.It was then con cluded that castable glass-ceramic restorations are suitable for clinical use, although some problems remain, especially with the successful lifetime of the castable glass-ceramics.

Microleakage along apical root fillings and cemented posts

Statement of problem. Coronal leakage of endodontically treated teeth has been found to result in a high failure rate. Purpose. This study tested leakage along apical root fillings remaining after post space preparation and cemented posts in root canals. Material and methods. A total of 120 human roots were used in the study and divided into six groups, 20 roots for each group. By using a modified fluid transport model, leakage (in μL/hr) along ParaPost dowels that were cemented in the coronal 7 mm of root canals with Fuji Duet, Ketac Cem, Panavia EX, or zinc phosphate cements was compared with that along the coronal 7 mm of conventional root canal fillings. Leakage along the apical 4 mm of root filling remaining after post space preparation was compared with that along the 11 mm root filling before post space preparation. Results. More leakage was recorded along the apical 4 mm of root filling than along the 11 mm of original root filling ( p = 0.0325). ParaPost dowels cemented with any test cement did not produce more leakage than the 7 mm coronal root filling ( p = 0.2145). Conclusions. The apical 4 mm of root canal filling remaining after post space preparation leaks statistically significantly more than the original full-length root canal filling. The leakage created by removal of the coronal part of root canal filling during post space preparation may be compensated by the cemented posts. (J Prosthet Dent 1998;79:264-9)

Long-term monitoring of microleakage of cavity varnish and adhesive resin with amalgam

Statement of problem. The penetration of oral fluids and bacteria at the interface between the cavity walls and amalgam restorations, which is known as marginal leakage, is one of the problems facing restorative dentistry today. This may cause secondary caries and the irritation of the pulp. Purpose. This in vitro study tested and compared the sealing ability of a cavity varnish and a dental adhesive for decreasing the marginal leakage of high copper amalgam fillings by chemical diffusion technique. Material and methods. The samples were randomly divided into three groups. The cavities in the first group were filled with high copper amalgam. In the second and third groups, the cavities were treated with Copalite and Panavia EX adhesives, respectively, before the amalgam fillings were performed. After the periods of 2 hours, 48 hours, 1 week, and 1.5 and 6 months, the amount of calcium diffused through the interface area into the deionized water was measured with inductively coupled plasma. Results. Six-month results revealed that using a dental adhesive as an interfacial sealer had significant advantages to reduce microleakage when compared with a conventional copal varnish. (J Prosthet Dent 1998;79:136-39.)

各種接着試験法における接着界面の破面解析および応力解析

To clarify the differences in fracture mechanism when different modes of load were applied, two types of dental adhesives were used in various tests-for tensilestrength, compressive shear strength, flexural strength and cleavage strength-and fractographical analyses of the bonding surface after breakage were perfomed by SEM. Furthermore, the distribution of stress in the adhesive layer subjected to tensile, compressive shear and torsion loads was examined by three-dimensionalphotoelastic analysis. The results were as follows:1. The kind of fracture occurring in two types of adhesive was cohesive fracture due to a force induced in the adhesive layer.2. Fractographical analysis of Panavia EX by SEM revealed the occurrence of a brittle fracture characterized by a river-like pattern inall but one of the tests for tensile strength.3. Super Bond C & B presented a ductile fracture featuring elongated dimples in tests for tensile strength, 4-point flexural strength, and compressive shear strength. In cleavage strength and 3-point flexural strength test, the ductile fracture had tear dimples.4. The compressive shear strength test revealed that the amount of stress was the smallest in the central area of the bonding surface and tended to increase toward the upper and lower margins.5. In the torsion test, stress gradually increased from the center outward.

Bond strengths of maxillary anterior base metal resin-bonded retainers with different thicknesses

Purpose. This study evaluated the effect of three different thicknesses of base metal resin-bonded retainers on retention/resistance. Material and methods. Three ivorine teeth, a central incisor, lateral incisor, and canine, were prepared to receive resin bonded retainers. Fifteen metal replicas of prepared teeth were made (five for each tooth morphotype). A total of 45 metal retainers were cast in three different thicknesses, 0.3, 0.5, and 0.7 mm, with 15 for each thickness. Retainers were cemented to metal die replicas with Panavia EX luting agent. After 24 hours, forces to dislodge the retainers were applied at 45 degrees to the vertical mesiodistal plane at the proximolingual line angle. Results. An increase in thicknesses resulted in elevation of dislodging forces that were almost linear for the three thicknesses of canine retainers. The central incisor exhibited the greatest increase in resistance to dislodgment between retainers that were 0.3 and 0.5 mm thick, whereas increased thickness for the lateral incisor retainer resulted in minimal or no benefit. (J Prosthet Dent 1997;78:281-5.)

In vitro shear strength of bonded amalgam cores with and without pins

This study compared the shear bond strength of resin-bonded amalgam with and without pins. The coronal third of 240 embedded posterior teeth was removed to expose a flat, nonretentive surface. Three Minikin pins were placed in the dentin in a triangular pattern 1 mm apart. Amalgam was condensed into a Delrin mold (4.2 mm in diameter and 3 mm in height) positioned over each tooth. The adhesives Amalgam-bond, All-bond, Amalgambond with high-performance additive, Panavia EX, and Panavia with Photobond were the materials used to bond the amalgam to the dentin. Half of the samples were immersed in normal saline solution for 7 days and the others for 30 days. Shear bond strengths were recorded as the maximum load per cross-sectional area of the bonded surface with a testing machine with 1 kN load cell and crosshead speed of 0.5 mm/min. A three-factor analysis of variance and Student-Newman-Keuls test (p = 0.05) identified Amalgambond with high-performance additive as the strongest adhesive in this study. The use of pins with or without adhesives increased the shear strength of amalgam samples significantly more than samples that used adhesives alone.

Durability of resin bonds to a cobalt-chromium alloy

Common nickel-chromium-beryllium alloys used for resin-bonded fixed partial dentures have possible health hazards due to leaching of nickel and beryllium. For resin-bonded restorations corrosion resistant cobalt-chromium alloys (CoCr) are a suitable alternative material without sacrificing physical properties. This study evaluated the bond strength and bond durability of new adhesive systems to a CoCr alloy. Plexiglas (acrylic) tubes filled with composite were bonded to CoCr alloy discs. Groups of 24 samples were bonded using six different bonding systems. Subgroups of eight bonded samples were stored in an isotonic artificial saliva solution (37 °C) either for 1 day, 30 days or 150 days. In addition the 30- and 150-days samples were subjected to 7500 or 37 500 thermal cycles, respectively. The bond strength of a conventional BisGMA composite (Twinlook) to sandblasted CoCr was significant lower than when using chemomechanical bonding systems and decreased continuously during the storage time of 150 days. The additional use of silane on the sandblasted alloy resulted in an insignificant increase in bond strength. Statistically significant higher and more durable bonds to CoCr alloy were achieved either with the combination of silica coating and use of the conventional BisGMA composite or with the combination of sandblasting and the use of a composite modified with a phosphate monomer (Panavia EX). In the latter systems, the bond strengths were mainly limited by the cohesive strength of the resin composites; partial adhesive failures were only observed for a tribochemical silica coating system. A new composite also containing the active phosphate monomer (Panavia TPN-S) exhibited a significant decrease in cohesive strength over time.

各種合着用セメントの諸性質

The purpose of this study was to evaluate and compare the mechanical properties, water sorption and solubility and shear bond strengths of eight commercially available luting agents to silver-palladiumcopper-gold (Ag-Pd-Cu-Au) dental alloy. Five adhesive resin cements, Bistite Resin Cement, Imperva Dual, Panavia EX, Panavia 21 and Super-Bond C & B and three conventional luting agents, zinc phosphate (Elite Cement 100), carboxylate (HY-bond Carbo Cement) and glass ionomer (Fuji Bond) were used. In general, resin cements except for Super-Bond C & B showed higher values of Knoop hardness and compressive, diametral and transverse strengths than conventional luting agents. Adhesive resin cements showed much less water sorption and solubility than ordinary cements. Adhesive luting agents maintained excellent bond strengths of approximately 27-37 MPa to Ag-Pd-Cu-Au alloy after 50, 000 thermocycles while alternately immersing the specimen in 4°C and 60°C water for one minute each. These results suggest that resip cements may be more clinically useful for cementing restorations than conventional luting agents.

Use of an adhesive resin for bonding orthodontic brackets

To date, most successful bonding agents used in orthodontics rely on mechanical retention to both the enamel and bracket base. Chemical adhesion to enamel as seen with glass ionomer cements, and to the silanated base of ceramic brackets have been tried. Recent developments in resin formulation have led to the production of adhesive diacrylate resins capable of forming adhesive bonds to certain metals including stainless steel. The aim of this experiment was to compare such a resin, Panavia EX, with a more conventional 'no-mix' orthodontic bonding resin. Two different base retention mechanisms were used, and the effect of rebonding and differing environmental conditions were also investigated. The results indicated that Panavia EX could produce greater bond strengths than the more conventional bonding resin. Of the two base retention systems tested, braised mesh bases gave consistently greater bond strengths than the cast base, although no base/resin specificity could be detected. Re-using the same brackets showed rebound strengths to be significantly lower than initial bond strength although the results indicated the adhesive resin was still able to bond more effectively to these used brackets than the conventional resin. Environment had the greatest effect on bond strength, such that following environmental exposure there was no significant difference between the two resins. This latter factor, and in particular the more complex bonding technique required for the adhesive resin, means that Panavia EX cannot be recommended for orthodontic use in its present form.

Adding Retentive Features in the Rebonding of Cast Metal Resin‐Bonded Prostheses

Many methods have been used to improve retention in resin-retained fixed prostheses, such as electrolytic etching of the retainer, the labial wrap design, proximal grooves, cast pin retention, and the use of improved adhesive resins such as Panavia EX (Kuraray Co, Osaka, Japan). Insufficient retentive features often lead to debonding of resin-retained fixed prostheses. Debonded prostheses may occasionally be recemented and successfully retained by the addition of retentive features to the prosthesis and abutment teeth. When recementing a debonded prosthesis with questionable retention, additional retention may be added to the retentive wings of the prosthesis by using a Rochette retentive hole in combination with pin retention or enamel/dentinal slots in the abutment teeth.

コンポジットレジンによる支台築造の実験的研究 その２ 根菅内象牙質処理法がレジンコアの維持力と辺縁封鎖性に及ぼす影響

In this study we investigated the effect of two different dentin pretreatments on the retention of prefabricated posts and on the microleakage of the composite resin cores.The dentin surfaces of both post space and root face of extracted human single-rooted teeth were treated with either 1) 37% phosphoric acid solution or 2) 37% phosphoric acid solution and then 10% sodium hypochlorite solution. Then, a prefabricated post (AD Post®, Kuraray Co.) was cemented with an adhesive resin cement (Panavia EX®, Kuraray Co.) after application of dentin bonding agent (Clearfil New Bond®, Kuraray Co.). And a composite resin core was built up with light-cured composite resin (Clearfil Photo Core®, Kuraray Co.).The retention of prefabricated posts was measured after one day immersion into 37°C water, 5, 000 times and 10, 000 times of thermalcycles between 4° and 60°C of water bath. The microleakage was measured after 2, 500 times of thermalcycles between 4° and 60°C in 0.2% aqueous solution of basic fuchsin dye.The results obtained indicated that phosphoric acid etching was ineffective both on the retention and on the marginal sealing of posts and composite resin cores. Meanwhile, removing of the collagen layer exposed by phosphoric acid etching (30 s) with sodium hypochlorite solution (60 s or 120 s) effectively increased adhesive strength of the adhesive resin to dentin, i. e. the retention of prefabricated posts significantly increased and the microleakage of the composite resin cores was significantly reduced.These results were supported by SEM observation of interface between adhesive resin and dentin.

Shear strength of resin developed by four bonding agents used with cast metal restorations

The evolution of the acid etch technique has made possible a more conservative approach to the fabrication of cast metal restorations. The resin bonding technique, however, places a greater burden for success on the selection of a bonding agent. This study examined the shear bond strength durability of cast metal restorations bonded to tooth structure with one of four metal adhesive bonding agents. Results indicated stronger bonds for restorations cemented with Panavia EX bonding agent than with any of the other bonding agents tested, both with and without exposure to thermal stress. Although it was one of the easier materials with which to work, Panavia EX bonding agent requires the additional step of applying an agent to prevent oxygen contact in the setting process.

Fracture resistance of composite and amalgam cores retained by pins coated with new adhesive resins

This study determined the effects of coating pins with either Panavia EX or with 4-META (Cover-Up) materials on the fracture resistance of pin-retained amalgam and composite cores. Gold-plated stainless steel (TMS) and titanium (Filpin) self-threading pins were used. Findings of this study corroborated the findings of several other studies that the use of pins reduces the fracture resistance of restorations. However, coating the pins with adhesion promoters such as Panavia EX and 4-META materials has been found to be effective in improving the fracture resistance. Cross-preference was observed between TMS and Filpin pins; that is, Panavia material coating was more effective with TMS pins, while 4-META was more effective with Filpin pins.

Comparison in shear bond strength of orthodontic brackets between five bonding systems related to different etching times: An in vitro study

New adhesives are continuously being marketed. The adhesive-bracket bond is still the weakest point in orthodontic bonding. A new device for the measurement of shear bond strength values (SBS) of orthodontic brackets is presented in this article. With this device, five commercial products were evaluated for their SBS: Lee Bond (LB), Concise (C), Super C (SC), Achieve-no-mix (ANM), and Panavia Ex (PE). After applying Begg brackets of laminated minimesh on lower human incisors, the specimens were thermocycled. The products investigated produced high bond strengths. The products tested showed shear bond strengths that were significantly lower than those stained with PE. The application of PE yielded the highest shear values. Nevertheless, some characteristics of this product might be clinically somewhat inconvenient. There was no significant difference in shear bond strength between 15 and 60 seconds enamel etching before bond application.