Introduction

Composite resin restorations help achieve the ideal of minimal intervention (MI) dentistry of tooth structure. Unquestionably, both dental experts and the general public have become more aware of the MI concept and its treatment. Innovations in products and treatment methods backed by adhesive dentistry research allow for highly predictable results with esthetic success. However, the complexities of clinical practice often disrupt attempts to obtain its maximum potential. This article re-examines bonding systems, which support composite resin restoration, and their applications.

1. Bonding systems

[Self-etching vs. Total etching]

Today's bonding systems can be roughly classified into two types: self-etching systems and Total etching systems. Functional monomers in a self-etching system have recently been confirmed to bond chemically with hydroxyapatite in the tooth substance.¹ The secondary caries model also shows the formation of acid-base resistant zone (ABRZ) immediately below the resin hybrid-layer, something not observed with total etching system.² These research results are considered to indicate the advantage of self-etching systems over total etching systems with respect to long-term durability. Tokuyama Bond Force, a self-etching system, has also been confirmed to form an ABRZ.³ These characteristics are believed to improve the long-term durability of composite resin restoration.

[One-step self-etching system]

One-step self-etching systems have been developed by improving on two-step self-etching systems. The convenience of one-step systems has led to the expansion of its use in the clinical practice. Characteristically, these systems contain water and organic solvent: water is required to provide the bonding agent with the etching function, while the organic solvent (alcohol or acetone) is required to mix several types of resin monomer components evenly. However, water and organic solvent inhibit the polymerization of the bonding agent. They have the potential to degrade the mechanical properties of the bonding agent after curing and are associated with the possibility of causing degradation in the adhesive restoration.⁴ Thus, a one-step self-etching system requires thorough air drying to remove these solvents. While the advantage of one-step self-etching systems reduce the number of steps required to achieve simplicity in the protocol associated with the pretreatment of the tooth surface, they demonstrate their full potential only when the pretreatment of the tooth surface is performed in exact compliance with the manufacturer's instructions.⁵

2. Selecting bonding systems

There are many commercial bonding systems currently available. Dentists typically select one or more bonding systems for their clinical practice. An effective method for evaluating these systems is the micro-tensile bonding strength test.⁶ Our hope is that dentists will use the results (bond strength values) in selecting bonding systems.

After the test sample (tooth) is treated with adhesive, the composite resin is built up and polymerized. The test sample is then sliced to create several specimens with small bonding areas. The specimens are subjected to tensile testing.

A bond strength of 30 MPa means the bond will not fail if a weight of approximately 300 kg per square centimeter is attached (For these purposes, the crown of the mandibular first molar tooth is considered to be 11.4 mm wide⁷. The occlusal surface is close to 1 cm² for the largest cases). For comparison, the tensile bond strength of the dentin-enamel junction, a naturally occurring bonding interface, is reported to be 51.5 MPa.⁸ The initial bond strengths of one-step self-etching systems, having become increasingly popular in recent years are considered to be roughly equivalent to the conventional bonding systems requiring two or more steps. When comparing the bond strength values of different products, note that bond strength test results may differ under different conditions; be careful to compare test results measured under identical conditions.⁹

3. Why do composite resins de-bond?

Recent improvements and developments in bonding systems have expanded the application range of the composite resin restorations to include cases involving microdontia, open bite, and diastema (Figures 1 to 4). These advances have increased the range of treatment options available to patients who choose not to have orthodontic treatment or large-scale prosthetic treatments involving the removal of healthy tooth structure. However, clinicians are convinced, even with all the research available, that composite resins will eventually de-bond.

Figure 1: A 46-year-old male patient, presenting-. An open bite. "I'm embarrassed about the gap between my front teeth. I don't want orthodontic or prosthetic treatments." The photograph shows the appearance following occlusal adjustment in the molar region in centric relation.

Figure 2: The patient was satisfied with the composite resin restorations and showed no problems one year after the treatment.

Figure 3: A 22-year-old female patient.- having gone through orthodontic treatment, the space remains and tooth separation is visible after treatment. The UR2-UL2 teeth were treated with direct composite resin restoration.

Figure 4: After treatment. Tooth substrate was not cut at all.

There is little laboratory bond test evidence suggesting composite resins de-bond in the clinical practice.

When bond tests are performed on many of the bonding systems currently available, fractures are observed not in the bonding surface, but rather in the dentin. Thus, the de-bonding of the composite resin is believed to occur when various factors prevent the product from excuting its inherent adhesive performance. Typical causes include residual caries, contamination of the bonding surface by exudates or water, and insufficient light irradiation. It is our hope that all readers will remember that all bonding-based composite resin restorations require accuracy in all steps, from diagnosis to postoperative management.

* Cavity preparation

Carious dentin is classified in two categories: carious-infected dentin (outer layer of carious dentin), which is extensively decalcified and softened by bacterial infection and cannot be recalcified; and caries-affected dentin (inner layer of carious dentin), which is moderately decalcified and softened, but without bacterial infection and capable of being remineralized. The former type of carious-infected dentin must be removed; caries-affected dentin should be preserved. The extent of caries removal is determined by comprehensively evaluating hardness, color, wetness, and degree of staining with a caries-detecting dye.¹⁰ For appropriate cavity preparation, a caries detector dye is essential, and the use of loupes or a microscope is recommended. Bond strength to caries-affected dentin is lower than to intact dentin. However, according to research by Nakajima et al., a brief application of NaClO solution improves bond strength to caries-affected dentin¹¹. Although this smear layer is removed by the etching effects of the bonding system, a thick smear layer is believed to prevent penetration of the resin monomer into the dentin. Since grinding with a rough regular-grit diamond bur thickens the smear layer and decreases bonding strength, it is preferable to finish the cavity preparation using a round steel bur or super-fine diamond bur. The bonding agent flows evenly over a smoothly finished cavity surface and creates a uniform bonding layer. It is believed that one advantage of this uniform bonding layer that it improved bond strength. A round bevel is generally preferred in regards to the preparation of the enamel margin, particularly the bevel. However, do not form a bevel on the occlusal surface of a molar tooth to preserve as much as occlusal enamel; rather, smooth the margin using a superfine bur. Even a fine bur requires care to avoid generating fine cracks in the enamel. Preparing the margin facilitates margin control from filling and polishing to the postoperative management. For margins of the labial surfaces of anterior teeth, select an appropriate bevel, such as a straight bevel or long straight bevel, based on esthetic requirements.

* Moisture prevention, saliva, and blood

Satisfactory bonding in the interface between the tooth structure and biomaterials necessitates protecting the tooth surface after cavity preparation from all factors that inhibit adhesion, including saliva, exudates, and blood, before and during the bonding treatment. Reports suggest moisture does not influence bond strengths with high-grade bonding systems.¹² Nevertheless, in the case of incremental fillings associated with highly esthetic requirements that take time, although difficult to place at times, rubber dam isolation is highly recommended, where possible. We believe such cases require further improvements in the adhesive restoration technique.

Figure 5: Many patients visit a dental clinic because they prefer composite resin restoration and dislike the look of metal that is visible when they smile.

Figure 6: Depending on the case, only the affected tooth is protected against moisture.

Figure 7:
Incremental filling was performed with Estelite Pro.

* Primary teeth

In composite resin restoration for a child, a one-step self-etching system, which can reduce the time required for the procedure, is useful. On the other hand, we often encounter cases in which the composite resin is de-bonded from the primary teeth. Many reports state that bond strengths to a primary tooth are indistinguishable from that of a permanent tooth;¹³ and the use of resin on a primary tooth cannot be correlated to the de-bonding of the resin. Many cases of de-bonding appear to be due to inadequate removal of caries, insufficient moisture prevention, or inadequate tooth surface treatment. Since caries in a primary tooth has a pale color and children have significantly more excretion of saliva and exudate than adults, we recommend using a caries detector dye and a rubber dam, as in the treatment for a permanent tooth. If it appears that there is insufficient procedure time or irradiation time, the dentists should consider a glass ionomer filling as another treatment option.

* Wedge-shaped defects

Typical cases of composite resin de-bonding often accompany wedge-shaped defects. The causes of wedge-shaped defects is considered to be abrasion, abfraction, erosion, and the combination of all these factors. Abfractions are believed to occur due to the stress applied by occlusal force. The stress concentration has been identified as a possible cause of composite resin de-bonding. However, wedge-shaped defects occur in the cervical region of the tooth, this location likely allows large amounts of exudates and blood to enter the tooth surface. De-bonding of the material is more likely if cleansing of the tooth surface or the condensing pressure of the filling is inadequate. Even with a wedge-shaped defect, we believe appropriate bonding can be achieved in a restoration that integrates with the tooth structure.

* Importance of air drying

As mentioned earlier, a one-step self-etching system generally contains water and an organic solvent, such as ethanol or acetone. These are the components required to etch the tooth substance and to stabilize the product. However, they are no longer needed in the bonding layer after curing and may damage the long-term durability of the bond. Removing water and the solvent by air drying is vital. Bonding systems based on different viscosities use different solvents and different monomers, and require different methods for efficient solvent removal. For this reason, the dentist must implement air drying in strict in accordance with the instructions provided by the manufacturer. On the other hand, if air drying scatters the bonding agent to the gingiva as well as to the tooth surface and cures there, the patient may complain of a white discoloration to the gingiva, due to protein coagulation, or discomfort to the tongue, caused by the film of bonding agent cured on the gingiva. Carefully remove excess bonding agent before and after light irradiation (Figures 8 and 9). You may also use a microbrush to remove the spattered bonding agent.

Figure 8: With one-step self-etching systems, thoroughly remove any bonding agent scattered on the gingiva prior to light-curing.

Figure 9: Rubber dam sheet after the treatment. Although air drying is important for one-step self-etching systems, it also causes significant spatter.

* Use time (phase separation)

Certain one-step bonding agents undergo phase separation of the resin monomer components and water after the material is dispensed on the type of solvent or components. To ensure secure tooth surface treatment, it is preferable to dispense the bonding agent immediately before use, regardless of the product.

* Maintenance

Examine the restoration approximately one week after placing the restoration. Check for protrusions of the bonding agent not recognized immediately after placing the restoration. Chencking for protrusionsof the bonding agent not recognized immediately after placing the restoration. Inspect the condition of the margins, the polish of the surface of the restoration and for food impaction. Since teeth treated for caries are at the highest risk for future caries,¹⁴ the placement of the restoration does not complete the caries treatment. Rather, caries treatment includes the management program subsequent to restorative treatment.

4. Tokuyama Bond Force

Tokuyama Bond Force is a one-step self-etching bonding agent. It offers the following features: (1) a strong bond to dentin and enamel; (2) formation of a thin, uniform bonding layer; (3) no phase separation, although this is generally a concern for one-step systems; and (4) low susceptibility to air drying. These features are likely to the product's adhesive self-reinforcing (SR) monomer. The monomer combines with the apatite component of the tooth substance interface to form a three-dimensional cross-linked structure via eluded calcium ions, when polymerized it forms a strong bonding layer that provides high bond strength.

Recently, an innovative pen-type dispenser has been introduced to the Tokuyama Bond Force product line. The pen like container allows users to consistently dispense drops of equal amounts-a simple operation that reduces the stress of dispensing the liquid. In response to the smaller cavity preparation of the MI concept, the volume of an individual drop is reduced by 1/3 compared to conventional bottle type dispensing products, increasing its cost effectiveness. The content indicator enables users to monitor the amount of liquid remaining in the container. This product is bound to please both clinicians and staff.

Diagram of a Tokuyama Bond Force bonding layer, showing a uniform bonding layer in all areas, including corners and edges.

The newly released Tokuyama Bond Force Pen uses a pen like container and reduces drop volumes by 1/3 compared to conventional bottle- type dispensing products. It also provides ease of use and reduces the stress associated with dispensing the liquid.

1)

Comparative study on adhesive performance of functional monomers. Yoshida Y, Nagakane K, Fukuda R, Nakayama Y, Okazaki M, Shintani H, Inoue S, Tagawa Y, Suzuki K, De Munck J, Van Meerbeek B. J Dent Res. 2004 Jun; 83(6); 454-8.

2)

Assessment of the nanostructure of acid-base resistant zone by the application of all-in-one adhesive system; Super dentin formation. Nikaido T, Weerasinghe DD, Waidyasekera K, Inoue G, Foxton RM, Tagami J. Biomed Mater Eng. 2009; 19(2-3); 163-71.

3)

SEM observation of acid-base resistant zone in all-in-one adhesive systems. Toru Nikaido, Miho Nishimura, Yasuhiro Iida, Go Inoue, and Junji Tagami , Adhesive dentistry 25; 197-203, 2007

4)

Relationship between mechanical properties of one-step self-etch adhesives and water sorption. Hosaka K, Nakajima M, Takahashi M, Itoh S, Ikeda M, Tagami J. Pashley DH. Dent Mater 2010 Apr; 26(4):360-7

5)

45 Points for avoiding failures in bonding treatment -- Why doesn't it bond, why doesn't it cure? --(Japanese) written and edited by Noboru Yasuda, Toru Nikaido, Naotake Akimoto, and Yoshiyuki Toyama, Quintessence Publishing Co., Inc, 2010

6)

Relationship between surface area for adhesion and tensile bond strength-evaluation of a micro-tensile bond test. Sano H, Shono T, Sonoda H, Takatsu T, Ciucchi B, Carcalho R, Pashley DH. Dent Mater. 1994 Jul; 10(4):236-40.

7)

Dental Anatomy (Japanese), 22nd edition, Tsunetaro Fujita, Kanehara & Co., LTD., 1995

8)

Physical properties of the dentin-enamel junction region. Urabe I, Nakajima S, Sano H, Tagami J. Am J Dent. 2000 Jun;13(3):129-35.

9)

Direct comparison of the bond strength results of the different test methods: a critical literature review. Scherrer SS, Cesar PF, Swain MV. Dent Mater. 2010 Feb; 26(2):e78-93.

10)

Caries Treatment Guidelines based on Evidence and Consensus under the MI (Minimal Intervention) Concept (Japanese), written and edited by the Caries Treatment Guidelines Preparation Committee of the Japanese Society of Conservative Dentistry, Nagasue Shoten, 2009

11)

Improving the effect of NaOCl pretreatment on bonding to caries-affected dentin using self-etch adhesives. Taniguchi G, Nakajima M, Hosaka K, Iwamoto N, Ikeda M, Foxton RM, Tagami J. J Dent. 2009 Oct;37(10):769-75.

12)

Effective bond strength of current adhesive systems on deciduous and permanent dentin. Senawongse P, harnirattisai C, Shimada Y, Tagami J. Oper Dent. 2004 Mar-Apr; 29(2):196-202.

13)

Microtensile bond strength of different adhesive systems to primary and permanent dentin. Soares FZ, Rocha Rde O, Raggio DP, Sadek FT, Cardoso PE, Peditr Dent. 2005 Nov-Dec; 27(6):457-62.

14)

Cariology -- Chair-side Prevention and Recovery Programs --(Japanese) Junji Tagami, Nobuhiro Hanada, and Yasuko Momoi, Nagasue Shoten, 2008

Tokuyama Bond Force Pen Dental adhesive for dentin bonding Single component bonding agent in which the "3D SR technology" enables strong bonding (Controlled medical device) Certification number 218AFBZX00117000