Dental Asia March/April 2019

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Clinical Feature 7 TH GENERATION ADHESIVE SYSTEMS By George Freedman DDS, FAACD, FIADFE, Dipl.ABAD Over the past five decades, the evolution of adhesive techniques has transformed the scope of dental practice. The vast majority of direct and indirect restorations are bonded to natural tooth structure rather than cemented or mechanically retained. Extensive research and product development have improved adhesives, concurrently with patient demands for improved oral appearance. The widespread demand and use of dental adhesives has fueled an intensive development of better and easier dental adhesives in rapid succession; inundating dentists with successive “generations” of adhesive materials. While the term “generation” has no scientific basis in the realm of dental adhesives and is to a great extent arbitrary, it has served a useful purpose in the organisation of the myriad of commercially available materials into more comprehensible categories. The “generational” definitions assist in identifying the chemistries involved, the strengths of the dentinal bond, and the ease of clinical use. Ultimately, this type of classification benefits both dentist and patient by simplifying the clinician’s chairside choices. The beginning of the generational adhesive systems The 1 st generation adhesives in the late 1970s were rather unsuccessful. While their bond strength to enamel was high, their dentinal adhesion was pitifully low at typically less than 2 MPa. Generally, all the adhesive generations bond well to the microcrystalline structure of enamel; it is their bond strength to the semi-organic dentin that is the greater concern. “Bonding” was achieved through chelation of the bonding agent to the calcium component of the dentin. While tubular penetration did occur, it contributed little to the retention of the restoration. It was common to see debonding at the dentinal interface within several months. 1 These bonding agents were recommended for small, retentive Class III and Class V cavities. 2 Post-operative sensitivity was common when these bonding agents were used for posterior occlusal restorations. 3 In the early 1980s, a distinct 2 nd generation of adhesives was developed, attempting to use the smear layer as a bonding substrate. 4 This layer bonded to the underlying dentin at a negligible level of 2-3 MPa. The weak 2-8 MPa dentinal bonding strength of 2 nd generation adhesives meant that mechanical retention form was still required. Restorations with margins in dentin saw extensive microleakage, and posterior occlusal restorations were likely to exhibit significant post-operative sensitivity. The long-term stability of 2 nd generation adhesives was problematic; one-year retention rates were as low as 70%. 5,6 In the late 1980s, revolutionary twocomponent primary/adhesive systems were introduced. Their marked clinical improvement warranted their classification as 3 rd generation adhesives. Significant increases in dentin bonding strength (8-15 MPa) diminished the need for cavity retention form. Erosion, abrasion, and abfraction lesions were treatable with minimal tooth preparation, hence the beginning of ultraconservative dentistry. A noticeable decrease in postoperative sensitivity with posterior occlusal restorations was very welcome. 3 rd generation adhesives were the first “generation” that bonded not only to tooth structure, but (weakly) to dental metals and ceramics as well. The downside of 3 rd generation bonding agents was their lack of longevity; intraoral adhesive retention started to decrease after three years. Despite significant levels of postoperative sensitivity, patient demands for tooth-coloured restorations convinced some dentists to begin providing posterior composite fillings routinely. 7,8,9 The transformation and popular generations of the adhesive systems In the early 1990s, 4 th generation bonding agents transformed dentistry. Their high bond strength to dentin (17-25 MPa) and limited post-operative sensitivity in posterior occlusal restorations encouraged many dentists to switch from amalgam to direct posterior composite fillings. 4 th generation is characterised by the process of hybridisation at the dentin-composite interface. Hybridisation is the replacement of the hydroxyapatite and the water in the surface dentin by resin. This resin, in combination with the remaining collagen fibres, constitutes the hybrid layer. Hybridisation involves both the dentinal 44 DENTAL ASIA MARCH / APRIL 2019
Clinical Feature tubules and the intratubular dentin, dramatically improving bond strength to dentin. 13-16 Total etching and moist dentin bonding, concepts developed by Fusayama and Nakabayashi in Japan in the 1980s, introduced to North America and popularised by Gwinnett and Bertolotti are the innovative hallmarks of the 4 th generation adhesives. 17-20 The materials in this group are distinguished by their components; there are two or more ingredients that must be mixed, preferably in very precise ratios, easy in the research laboratory, but rather more complicated chairside. The number of mixing steps and precise measurements tend to confuse the process, consequently reducing the dentin bonding strengths. The very popular 5 th generation dental adhesives first appeared in the mid 1990s. These materials adhere well to enamel, dentin, ceramics and metal, but most importantly, are characterised by a single adhesive component. Etching is still required but there is no mixing, and thus, less possibility for error. Bond strengths to dentin are in the 20-25+ MPa range, suitable for all dental procedures (except in conjunction with self-curing resin cements and self-curing composites). Dental procedures tend to be both stressful and technique sensitive. Where some of this stress can be eliminated, dentists, staff and patients all benefit. 5 th generation bonding agents are easy to use and predictable. There is little technique sensitivity in a material that is applied directly to the prepared tooth surface and post-operative sensitivity is appreciably reduced. byproducts are permanently incorporated into the dental-restorative interface. In the early versions of 6 th generation adhesives, the dentin bond (18-23 MPa) remained strong after time, while the unetched, unprepared enamel bond was prone to failure. Additionally, the multiple components and multiple steps in some 6 th generation techniques can cause confusion. The current formulation of the dental adhesive systems A new, simplified adhesive system, the 7 th generation, was introduced in 2002. Just as the 5 th generation bonding agents made the leap from previous multi-component systems to a rational and easy-to-use single bottle, the 7 th generation simplified the 6th generation materials into a single component, single bottle system. Both 6 th and 7 th generation adhesives are available for self-etching, self-priming adhesion for improved procedures with minimal technique sensitivity, and no post-operative sensitivity (Fig. 1). No-mix, self-etching, self-priming, single bottle 7 th generation adhesives represent the most current formulation of dentinal adhesives on the market. The elimination of mixing uncertainty eliminates technique sensitivity. There is no etching step. Priming and bonding of the dental surfaces are accomplished simultaneously, greatly simplifying the adhesive procedure. It is a predictable one-step, one-bottle system for the complete etching and bonding of both enamel and dentin surfaces. Its specifications include an excellent dentin bonding (18-35 MPa) and similar adhesion to both prepared and unprepared enamel. It can be used effectively for both direct and indirect composite restorations and it adheres relatively well to ceramic. Further, 7 th generation adhesives are insensitive to the amount of residual moisture on the surface of the preparation. The bond strength to both dentin and enamel are essentially the same, regardless of the moisture or lack of moisture on the prepared surfaces. Thus, moist bonding is not required. 7 th Generation Adhesive Technique The following is an abbreviated technique description for the use of 7 th generation adhesives: Dentists and researchers have sought to eliminate the etching step, or to include it chemically in one of the other steps. The 6 th generation adhesives, introduced in 2000, require no separate etching step, at least at the dentinal surface. They have a dentin-conditioning liquid in one of their components; the acid treatment of the dentin is self-limiting, and the etch Fig. 1 MARCH / APRIL 2019 DENTAL ASIA 45
Page 4 and 5: CONTENTS MARCH / APRIL 2019 18 24 2
Page 6: First Words The New Age of Digitali
Page 10 and 11: Dental Updates New VOCO Prophylaxis
Page 12: Dental Updates AACD Welcomes 2019 C
Page 15 and 16: Periodontal Disease Bacteria Linked
Page 18 and 19: Dental Updates Henry Schein One Acq
Page 20 and 21: Under the Spotlight 18 DENTAL ASIA
Page 22 and 23: Under the Spotlight It is easy for
Page 24 and 25: Word of Mouth by Dr. Christoper Ho
Page 26 and 27: CELEBRATING DIGITAL TRANSFORMATION
Page 28 and 29: Dental Profile achieve very good re
Page 31 and 32: Dental Profile TAKING DIGITAL IMPRE
Page 33 and 34: Dental Profile The high-precision S
Page 35 and 36: Dental Profile MARCH / APRIL 2019 D
Page 37 and 38: Clinical Feature The importance of
Page 39 and 40: Fig. 8: X-ray after extraction show
Page 42 and 43: Clinical Feature Glass Ionomer Seal
Page 44 and 45: Clinical Feature Fig. 1.1: An erupt
Page 48 and 49: Clinical Feature 1. Decay is noted
Page 50 and 51: User Report CENTION N: REDEFINING D
Page 53 and 54: User Report Amalgam GIC Cention N P
Page 56: User Report Fig. 15: Teeth 46 and 4
Page 59 and 60: User Report initial drilling channe
Page 61 and 62: User Report Fig. 16: Postoperative
Page 64 and 65: Behind the Scenes REPLACEMENT OF EX
Page 66 and 67: Behind the Scenes angles due to the
Page 68 and 69: Behind the Scenes and silanated for
Page 70 and 71: Behind the Scenes A JOURNEY THROUGH
Page 72 and 73: Behind the Scenes Fig. 11 Fig. 15 r
Page 74 and 75: Behind the Scenes The overall aesth
Page 77 and 78: In Depth With Fig. 1: Primescan - t
Page 79 and 80: In Depth With The blue light used b
Page 81: In Depth With The first set of data
Page 85 and 86: In Depth With Extending Dental Oper
Page 87 and 88: In Depth With combines the cutting-
Page 89 and 90: Product Highlight BRAVIA ® XL Spec
Page 91 and 92: Product Highlight COLTENE Unveils t
Page 93 and 94: Product Highlight 3Shape launches T
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Show Preview 9 th -12 th June 2019
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Giving Back to Society February is
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Dental Asia March/April 2019

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