Malwina Kolasa1, Joanna Szczepańska2
Direct pulp capping in permanent teeth in children – tertiary dentin formation, materials used. Part II
Bezpośrednie pokrycie miazgi w zębach stałych u dzieci – tworzenie zębiny trzeciorzędowej, stosowane materiały. Część II
1Doctoral studies, Department of Developmental Age Dentistry, Medical University of Łódź
Head of Department: Professor Joanna Szczepańska, MD, PhD
2Department of Developmental Age Dentistry, Medical University of Łódź
Head of Department: Professor Joanna Szczepańska, MD, PhD
Pokrycie bezpośrednie polega na aplikacji środka leczniczego na miazgę obnażoną mechanicznie lub urazowo. Nadrzędnym warunkiem powodzenia terapii jest odpowiedni stan kliniczny miazgi, która powinna być zdrowa lub objęta odwracalnym procesem zapalnym. Metoda jest szczególnie polecana w leczeniu młodych zębów stałych ze względu na wysoki potencjał regeneracyjny miazgi. U jej podstaw leży zdolność odontoblastów do tworzenia mostu zębinowego poprzez odkładanie zębiny trzeciorzędowej. W przypadku obnażenia miazgi warstwa odontoblastów obumiera i musi być zastąpiona przez nową populację odontoblastów wyróżnicowaną z komórek macierzystych miazgi pod wpływem działania leku aplikowanego na miazgę. Stosowana do pokrycia miazgi substancja, poza właściwościami odontotropowymi oraz zdolnością stymulacji do wytwarzania zadowalającego jakościowo mostu zębinowego, powinna być biozgodna, przylegać do tkanek zęba oraz ich nie przebarwiać, a także nie rozpuszczać się w płynie z kanalików zębinowych ani w wodzie. Dotychczas nie odkryto środka, który spełniałby wszystkie wyżej wymienione warunki, dlatego niezwykle istotne jest ciągłe prowadzenie badań mających na celu wynalezienie substancji dającej najlepsze rezultaty w pokryciu bezpośrednim miazgi.
Direct pulp capping involves placing therapeutic material on mechanically or traumatically exposed pulp. The most essential requirement of therapeutic success is clinical state of the pulp which should be healthy or in reversible pulpitis. The method is particularly recommended for young permanent teeth due to the high regenerative potential of dental pulp. The mechanisms underlying these repair processes involve the ability of odontoblasts to form dentin bridges via tertiary dentin deposition. If pulp exposure occurs, a layer of odontoblasts is killed and must be replaced with a new odontoblastic population, which differentiates from pulpal stem cells under the influence of a therapeutic agent applied on the pulp. In addition to odontotropic properties and the ability to stimulate production of qualitatively satisfying dentinal bridge, the substance used for pulp capping should be biocompatible, not stain dental tissues, exhibit good adhesion to them, and insolubility in dentin tubule fluid or water. So far an agent which meets all the requirements mentioned above has not been invented. It is crucial to continue research to develop a substance that will yield the best effects in direct pulp capping.
Biological pulp treatment plays a particularly important role in the exposure of pulp in young permanent teeth. Direct pulp capping in teeth with incomplete root development is characterised by high success rates and allows for the continuation of apexogenesis. Direct pulp capping is used only in certain clinical situations, which are indications for the procedure. Pulp exposure should have traumatic or mechanical aetiology, and the dental pulp should be either healthy or reversibly inflamed. If the above-mentioned criteria are met, no pathological clinical symptoms or lesions are revealed by the X-ray and tooth separation from the oral environment is possible, there is a good chance of therapeutic success of direct pulp capping.
Tertiary dentin formation
In order to fully understand the mechanisms of pulp treatment using biological methods, it is necessary to analyse the processes leading to the formation of tertiary dentin, a tissue that underlies the success of the discussed therapy.
Tertiary dentin is a type of dentin that forms in response to pathological external stimuli. Its role is to protect the pulp. Lesot et al. (1) were the first to postulate that two types of tertiary dentin need to be distinguished. According to the author, tertiary dentin formed by primary osteoblasts should be referred to as reactive dentin, while dentin produced by newly differentiated odontoblasts or odontoblast-like cells should be referred to as reparative dentin. The classification was widely accepted due to its possible use in the histological context (2). Since the mechanisms underlying the formation of these two types of tertiary dentin vary, it is necessary to use different treatment strategies. These strategies will depend on the degree of pulp destruction as well as on whether the layer of primary osteoblasts was destroyed.
Reactive dentin forms in pulpal response to an early or slowly progressing stimulus, such as caries, non-cariogenic lesions or dental materials/medications. This type of dentin is formed by healthy odontoblasts at the site of the stimulus action between the pulp and the physiological dentin. If pulp irritation by the stimulus is only minor, as in the case of physiological tooth wear, reactive dentin grows slowly and its structure may not differ significantly from secondary dentin. In the case of stronger stimuli, the structure of dentin is more irregular; however, it is always more or less tubular (2). Indirect capping is a treatment method that affects the formation of reactive dentin.
In the case of major damage or severe pulp irritation, the superficial layer of primary odontoblasts is killed. Undifferentiated mesenchymal cells or dental pulp stem cells are transferred into newly-differentiated generation of odontoblasts, which, along with odontoblast-like cells, form a non-tubular structure, i.e. reparative dentin (2, 3). This mechanism underlies pulp treatment by means of direct capping. Therefore, dental material used for this purpose should be able to stimulate pulp stem cells to differentiate into a new population of odontoblasts.
Materials currently used for direct pulp capping
Perfect material for direct pulp capping should stimulate reparative processes within the pulp, tightly adhere to dental tissues, as well as be biocompatible, cause no dental tissue discolouration and be insoluble in water and dentin tubule fluid. So far, no material has been developed that would meet all these criteria.
The history of introducing calcium hydroxide as an agent used for direct pulp capping dates back to the early 1930s. The material was introduced into medical practice by Herrmann and for many decades it was considered to be the gold standard in direct pulp capping (4). Calcium hydroxide is used in dentistry in a setting or a non-setting form, with the latter one used in direct pulp capping.
The action of calcium hydroxide involves the release of hydroxyl ions, which alkalise the environment and have antibacterial effects. The development of superficial necrosis is the initial result of its direct contact with the pulp. Minor inflammation develops under the necrotic layer, which stimulates the pulp to defence, i.e. odontoblast differentiation and the formation of dentin bridge (5-7).
Disadvantages of calcium hydroxide include its poor mechanical and physical properties, formation of irregular and porous dentin bridge with evident defects as well as its solubility in dentinal fluid and acids. Also, calcium hydroxide does adhere to hard tissues. The above listed factors contribute to bacterial microleakage, which is one of the main causes of direct pulp capping failure. Calcium hydroxide initiates calcifying processes in the pulp, leading to pulp chamber mineralization, which may hinder the potential future endodontic treatment. Long-term success rates for direct pulp capping with the use of Ca(OH)2 range between 13% and 96%, depending on the author (8). The long-term use of calcium hydroxide as the only agent for biological dental procedures revealed its many advantages, but also many drawbacks, which motivated the search for alternative products described below.
Mineral trioxide aggregate (MTA) is a material with significantly improved physical properties and lower complication rates compared to calcium hydroxide, which has recently gained popularity. Calcium hydroxide is the main reaction product of MTA and water.
MTA shows good mechanical strength as well as odontotropic, antibacterial and antifungal properties. Due to its limited solubility in tissue fluids, MTA does not undergo resorption as opposed to Ca(OH)2, which improves its sealing efficacy and reduces the risk of microleakage. Furthermore, it is non-toxic towards pulp cells and produces X-ray contrast owing to the addition of bismuth oxide. There are two types of MTA: Grey Mineral Trioxide Aggregate (GMTA) and White Mineral Trioxide Aggregate (WMTA), which was developed to avoid dental discolouration, which occurs after GMTA. WMTA presents longer setting time and, according to some authors, worse physical properties of the formed bridge than GMTA. Other researchers found no statistically significant differences in the thickness of GMTA and WMTA-induced dentin bridge (9).
A more rapid formation of a thicker and more homogeneous dentin bridge is an advantage of MTA over Ca(OH)2 (9, 10). Furthermore, MTA-induced inflammation is milder and short-lasting compared to Ca(OH)2 (9-11). In most studies, long-term success rates for MTA are higher compared to Ca(OH)2 (10, 12).
Biodentine is one of promising alternatives for the commonly used direct pulp capping agents. It is marketed in the form of ready-to-use capsules containing powder and ampoules containing calcium chloride solution, which requires agitation in a vortex mixer. The reaction produces hydrated calcium silicate and calcium hydroxide. Addition of calcium chloride in Biodentine reduces the setting time. Like Ca(OH)2 and MTA, Biodentine has odontotropic activity, stimulating the formation of reactive and reparative dentin. This was confirmed in in vitro studies, which demonstrated that Biodentine stimulates pulpal cells to release TGF-β1, which promotes the differentiation of pulpal stem cells into odontoblasts (13). In vivo studies demonstrated the ability of Biodentine to produce dentin bridge of satisfactory quality and thickness (14). Long-term marginal tightness preventing bacterial microleakage is an important advantage of this material. Furthermore, Biodentine may be used not only as an odontotropic agent, but also as dentin substitute to reconstruct the missing crown portion without the need for conditioning (13).
Attempts to use other direct pulp capping preparations
BioAggregate (likewise MTA and Biodentine) belongs to the group of bioceramic calcium silicate-based cements. The material is available in the form of white powder consisting mainly of calcium silicate, calcium phosphate and hydroxyapatite. As opposed to MTA, BioAggregate releases no toxic substances, such as aluminium. Tantalum (V) oxide instead of bismuth oxide is used in the material as a contrast agent (15).
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Płatny dostęp do wszystkich zasobów Czytelni Medycznej
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