CDE0211

28 I I industry report _ compobonds cosmeticdentistry 2_2011 clinical errors. This is because the inorganic phase of dentine is dissolved, leaving the organic collagen matrix unsupported. If this organic matrix is not re-hydrated by the primer and adhesive, the dentine bond is severely compromised. Ensuring that the collagen fibres are hydrated necessitates leaving the dentine moist, which is difficult to assess clinically. Alternately, the DBA should contain a solvent to re-hydrate the collagen fibres, for example water or ethanol, so that the adhesive can impregnate thespacesonceoccupiedbytheinorganicphaseand form a resin-collage complex, or a hybrid layer. DBAs containing the solvent acetone are partic- ularly likely to cause desiccated dentine, since ace- tone evaporates rapidly, leaving collapsed collagen fibres.11 Therefore,iftheadhesivebondingtechnique isincorrectlyexecuted,thedentinebondwillbeinfe- rior, causing poor adhesion, marginal leakage, dis- colourationandpost-operativesensitivity.Oneofthe reasons for post-operative sensitivity is inadequate sealing of the dentine tubules following etching during the dentine bonding procedure.12 The latter is duetoinadequateclinicalprotocolscitedabove,and particularly plagues TE, multi-step bonding agents. After the etching phase, the dentine tubules are exposed and at risk after removal of the inorganic matrix and the smear layer. If the next two stages, primingandintroductionoftheadhesive,areincom- petently performed to seal the tubules by formation of an adequate hybrid layer, post-operative sensi- tivity is an inevitable result. On the other hand, SE DBAs dissolve, rather than removethesmearlayer,whichisincorporatedwithin the collagen fibres and the resin monomer to form a viable hybrid layer. Therefore, the reduced post- operative sensitivity reported by some studies with SEagentscouldbeattributedtoincorporationofthe smearlayerintothehybridlayer,andthereforenever leaving the dentine tubules exposed.13 Other studies have reported no difference in dentine hypersensi- tivity using either TE or SE systems, and poor clinical technique has been mentioned as the most signifi- cant factor, rather than the type of DBA, in causing post-operative symptoms.14 To summarise, the advantages of SE systems are: 1.less technique sensitive; 2.degree of dentine moisture not a concern; and 3.depth of etching and adhesive penetration are similar,sincebothprocessesoccursimultaneously. One of the drawbacks of the SE systems high- lightedbysomestudiesistherelativelyhighpH(≈2), comparedwithtraditionalphosphoricacidwithapH ≈ 1, resulting in inferior bond strengths compared with TE systems.15,16 However, other studies have failed to find significant differences between the two systems,17 and current research is inconclusive. The SE agents are divided into strong or mild groups, the former having a pH of 1 and the latter a pH of 2. Although the milder versions are less aggressive and form thinner hybrid layers, a thinner hybridi- sation zone does not appear to compromise bond strength.18 It is the integrity (absence of voids, tears) rather than the thickness of the hybrid layer that appears more significant to a viable dentine bond. Another possible drawback with the one-step SE agents is residual water that may remain in the Fig. 8_Vertise Flow is an excellent base lining, acting as a shock absorber due to its low MOE. Fig. 9_Vertise Flow is ideal for intra-oral repairs of fractured porcelain. Fig. 10_The Translucent shade of Vertise Flow is invaluable for detecting future decay underneath fissure-sealed teeth. Fig. 11_The lower first permanent molar is isolated with a rubber dam using a SoftClamp (KerrHawe SA). Notice the remnants of an old fissure sealant resin within the fissures. Fig. 12_The tooth is air abraded with aluminium-oxide powder to remove plaque and decay, including remnants of old fissure sealants. Fig. 13_A prophylaxis brush is used to clean the tooth with a slurry of pumice. Fig. 9 Fig. 10Fig. 8 Fig. 12 Fig. 13Fig. 11