Dental Asia Mar/Apr 2018

42 Clinical Feature DENTAL ASIA MARCH / APRIL 2018 Introduction The word “bioactivity” is one of the latest buzz words in the dentistry. It is highlighted as a feature inmany restorative products with di ơ erent and conƪicting claims. This has stirred up confusion and controversy surrounding the concept. This article will attempt to provide clarity for the practicing restorative dentist: What is bioactivity? What are bioactive products? How can they be used to provide the best dental care? The term “bioactive material” originated with Dr. Larry Hench in 1969. He was looking for an improved graft material for bone reconstruction needed by injured returning soldiers of the Vietnam war. Hench was searching for a material that could form a living bond with tissues in the body. All the available materials at the time were rejected by the body. He developed bioglass (calcium silicophosphate glass), a completely synthetic material that chemically bonds to bone. 1 Table 1 lists some examples of bioactive restorativematerials by their mechanism of action. Some examples of bioactive restorative materials by their mechanism of action, bioactivity increasingwith eachmechanismas you go down. Materials that remineralise, only remineralise. Materials that deposit hydroxyapatite also remineralise. Materials that stimulate pulpal regeneration also remineralise and deposit hydroxyapatite. Materials that mineralise Dental decay is the cumulative result of consecutive cycles of demineralisation and remineralisation at the interface between bioƤlm and the tooth surface. Oral bacteria excrete acid after consuming sugar, leading to demineralisation. Hydroxyapatite crystals are dissolved from the subsurface. Remineralisation is the natural repair process for non-cavitated lesions . It relies on calcium and phosphate ions, assisted by ƪuoride, to rebuild a new surface on the existing crystal remnants in the subsurface. 5 Under normal physiological conditions at pH 7, saliva is supersaturated with calcium and phosphate ions, making caries progress slow. As the pH is lowered, higher concentrations of calciumandphosphate are required to reach saturationwith respect to hydroxyapatite. 5 This is called the “critical pH”, the point where equilibriumexists and there is nomineral dissolution and nomineral precipitation. The critical pH of hydroxyapatite is around 5.5 and that of ƪuorapatite is around 4.5. This varieswith individual patients. Below critical pH, demineralisation occurs while above critical pH, remineralisation occurs (Figs. 1-2) 43 . Cycling of oral pH during cariogenic challenges in naturally occurring hydroxyapatite Hench deƤned a bioactive material as “one that elicits a speciƤc biological response at the interface of a material which results in the formation of a bond between the tissues and the material”. 2 Today there are many di ơ erent deƤnitions of bioactivity found in the dental literature, dependant on the research and on the researcher. The deƤnition Ƥts the research, whereas it should Ƥt the concept. To achieve clarity of meaning, it is best to go with what can be most easily understood by clinicians and patients alike - the deƤnition found in the dictionary. Bioactivity: noun - any effect on, interaction with, or response from living tissue Historically dental materials were designed to have a “neutral” e ơ ect on the tooth. 3 Many current dental materials are not neutral. They are “active”, not “passive”, participants in the restorative process. New materials are being developed to harness this potential behavior. These are “bioactive” materials. For simpliƤcation and clarity in discussing bioactive restorative materials it is best to separate them according to their mechanism of action. There are three separate mechanisms that are demonstrated by bioactive restorative materials. A bioactive restorative material can display one or more of the following actions: 1. Remineralises and strengthens tooth structure through ƪuoride release and/or the release of other minerals 2. Forms an apatite-like material on its surface when immersed in body ƪuid or simulated body ƪuid (SBF) over time 4 3. Regenerates live tissue to promote vitality in the tooth By Dr. Fay Goldstep D , E/^D K& d/KE D d Z/ > d 'KZz WZK h d y DW> ^ EKEͲ /KͲ d/s /E d/s &/>>/E' Z ^dKZ d/KE D >' D^ KDWK^/d Z ^/E^ /KͲ d/s Z D/E Z >/ d/KE '> ^^ /KEKD Z^ ^ /ͲZŝǀĂ ^ĞůĨ ƵƌĞ͕ ' Ͳ ƋƵŝĂ &ŽƌƚĞ '> ^^ /KEKD Z Z/s d/s ^ WƵůƉĚĞŶƚͲ d/s ŝŽ d/s '/KD Z^ ^ŚŽĨƵͲ ĞĂƵƟĮů // ĂŶĚ &ůŽǁ WůƵƐ WK^/d/KE K& ,z ZKyz W d/d > /hD >hD/E d ^ ŽdžĂͲ ĞƌĂŵŝƌ ĞŵĞŶƚ Wh>W Z ' E Z d/KE > /hD ^/>/ d ^ DŝŶĞƌĂů dƌŝŽdžŝĚĞ ŐŐƌĞŐĂƚĞ ;Dd Ϳ ͲďĂƐĞĚ ŵĂƚĞƌŝĂůƐ ŶĚŽ ƌĞƉĂŝƌ ĐĞŵĞŶƚ EŽƚ ĚĞŶƟŶ ƐƵďƐƟƚƵƚĞ ^ĞƉƚŽĚŽŶƚͲ ŝŽĚĞŶƟŶĞ ƌŽǁŶ ĂŶĚ ƌŽŽƚ ĚĞŶƟŶ ƌĞƐƚŽƌĂƟǀĞ ƐƵďƐƟƚƵƚĞ͘ WƵůƉĂů ŚĞĂůŝŶŐ ĂŶĚ ĞŶĚŽ ƌĞƉĂŝƌ /E Z ^/E' /K d/s/dz z D , E/^D