Mechanical principles retention and stability
Download 35.66 Kb.
|
BBBB
Restav, Химия в таблицах Стахеев А.Ю.1998г., лекции, 2 5318752383990239969, Kimyoviy termodinamika-fayllar.org, Kimyoviy termodinamika-fayllar.org
|
MECHANICAL PRINCIPLES RETENTION AND STABILITY. It should be noted that even though retention and stability are defined separately, they depend on each other and are alway sintertwined. The difference between these properties is the direction of the forces exerted on the preparation. Retention is the ability of a restoration to resist a displacement in the opposite direction to its insertion axis when subjected to tensile forces. This basically depends on the existing contact between the internal surfaces of the restoration and the external surface of the prepared tooth, which is called frictional resistance46(Fig3-1). Fig3-1The retention is dependent on the parallelism of the opposed walls in different restorations. Extracoronal restoration(A). Intracoronal restoration(B). Thus, retention is closely related to the parallelism obtained by the walls and the prepared area. The more parallel the axial walls and the greater the surface contact, the greater the resultant retention(Fig3-2). Fig3-2 Illustration of the relation between retention and the angulation of the preparation^ The retentiveness of preparations of the same size decreases when the preparation angle increases. As such, it seems reasonable to make the preparation as parallel as possible to enable better frictional retention. However, a more parallel preparation complicates the cementation procedure because the flow of the cement is hindered. This causes a misfit of the restoration and increased thickness of the cement film, especially on the occlusal and cervical portions of the preparation. Another factor of secondary importance that improves the retention is the action of the cement. Zinc phosphate-based cement aids the mechanical interlocking as it takes advantage of the micro roughness of the preparation and restoration. Glass ionomer and resin cements act through micromechanical union, in addition to the adhesive properties. The type of cement used has a direct effect on the cementation of the restorations. It has been found that the bond strength of adhesively cemented preparations is superior to that of preparations with zinc phosphate and glass ionomer cements.5 A good preparation should have a wall inclination with adequate frictional retention, complete seating with the lowest possible cement thickness, and resistance to displacement from different masticatory forces(Fig3-3). Fig-3-3 The action of the cement is secondary to the retention. However, adequate cementation is important for the longevity of the restorative treatment.
Teeth with short clinical crowns require less convergence to provide greater retention, and teeth with long clinical crowns require greater convergence(Fig3-4). Fig3-4 Existing relationship between the height and angulation of the preparation. Shorter teeth should have a smaller0(A). Longer teeth should have a larger0(B).
QO'LLASH VA BARQAROLIK. Shuni ta'kidlash kerakki, ushlab turish va barqarorlik alohida belgilanadigan bo'lsa ham, ular bir-biriga bog'liq va har doim bir-biriga bog'langan. Ushbu xususiyatlar orasidagi farq - bu preparatga tatbiq etiladigan kuchlarning yo'nalishi. Saqlash - bu tiklash kuchlari ta'sirida tortish kuchiga ta'sir qilganda uning joylashtiruvchi o'qiga teskari yo'nalishda siljishga qarshi turish qobiliyati. Bu asosan tiklanishning ichki yuzalari va tayyorlangan tishning tashqi yuzasi orasidagi mavjud bo'lgan aloqaga bog'liq bo'lib, u ishqalanish qarshiligi deb ataladi46 (3-1-rasm). Shakl 3-1 Saqlash turli xil restavratsiyalarda qarama-qarshi devorlarning parallelligiga bog'liq. Ekstrakoronal tiklash (A). Intrakoronal tiklash (B). Shunday qilib, ushlab turish devorlar va tayyorlangan maydon tomonidan olingan parallellik bilan chambarchas bog'liq. Eksenel devorlar qanchalik parallel bo'lsa va sirt bilan aloqa qanchalik katta bo'lsa, natijada ushlab turish shunchalik katta bo'ladi (3-rasm). Shakl 2-3 Preparatni ushlab turish va angulyatsiya qilish o'rtasidagi bog'liqlikning tasviri ^ Tayyorlash burchagi oshganda bir xil o'lchamdagi preparatlarning saqlanib qolish qobiliyati pasayadi. Shunday qilib, ishqalanishni yaxshiroq ushlab turish uchun tayyorgarlikni iloji boricha parallel qilish maqsadga muvofiq ko'rinadi. Shu bilan birga, ko'proq parallel tayyorgarlik sementlash jarayonini murakkablashtiradi, chunki tsement oqimiga to'sqinlik qiladi. Bu, ayniqsa, preparatning okklyuziya va serviks qismlarida tsement plyonkasining tiklanishi va qalinligi oshishiga olib keladi. Tarkibni yaxshilaydigan ikkinchi darajali ahamiyatga ega bo'lgan yana bir omil bu tsement ta'siridir. Sinkli fosfat asosidagi tsement mexanik ravishda blokirovkalashga yordam beradi, chunki u tayyorlash va tiklashning mikro pürüzlülüğünden foydalanadi. Shisha ionomer va qatronlar tsementlari yopishqoqlik xususiyatlaridan tashqari mikromekanik birikma orqali ham harakat qiladi. Amaldagi tsement turi restavratsiya tsementatsiyasiga bevosita ta'sir qiladi. Yopishqoq sementlangan preparatlarning bog'lanish kuchi sink fosfat va shisha ionomer tsementlari bilan preparatlarnikidan ustun ekanligi aniqlandi.5 Yaxshi preparat etarli darajada ishqalanish saqlanib qolgan devor moyilligiga ega bo'lishi kerak. mumkin bo'lgan eng past tsement qalinligi va turli chaynash kuchlarining siljishiga qarshilik (3-3-rasm) bilan o'tirish. Shakl-3-3 Tsementning ta'siri ushlab turishdan keyin ikkinchi darajali hisoblanadi. Shu bilan birga, etarli sementlash restorativ davoning uzoq umr ko'rishlari uchun muhimdir.
Qisqa klinik kronlari bo'lgan tishlar ko'proq tutilishini ta'minlash uchun kamroq konvergentsiyani, uzoq klinik kronlari bo'lgan tishlar esa ko'proq konvergentsiyani talab qiladi (3-4-rasm). Shakl 3-4 Preparatning balandligi va burchakli tomoni o'rtasidagi mavjud munosabatlar. Qisqa tishlar kichikroq bo'lishi kerak0 (A). Uzunroq tishlarda kattaroq0 (B) bo'lishi kerak.
Thus, when the teeth are long, the inclination of the walls can be increased to achieve greater occlusal convergence, sufficient to maintain adequate retention. On the other hand, the walls of shorter teeth should be prepared close to parallel to maintain an effective retention. It has been proposed that the anterior teeth and premolars should have a minimum occlusocervical dimension of 3mm, and the molars a minimum dimension of 4mm. Teeth that do not have these minimum dimensions should be modified to increase their retention through additional retention.23 Goodacre et al(2001)22 found that a minimum preparation height of 3mm was necessary to provide sufficient resistance to lateral displacement of the restoration when the occlusal convergence angle does not exceed 10 degrees. In preparations with a height of 5mm, changing the convergence angle from 2 to 10 degrees decreases the surface areaby 13.9%. An increase of just1 mm in preparation height results in a considerable gain in surface area. Since the surface area increases, increasing the height of the preparation and reducing the angulation may result in improvement in the function of the luting agent, the resistance to lateral displacement, and the retention of the fixed prosthesis9(Fig3-5). Fig3-5 Existing relationship between surface area and retention of the preparation. In the same tooth, a partial preparation has less retentiveness than a total preparation. Preparation for partial crown(A). Preparation for crown(B). With teeth of the same height, the same preparation in a premolar will be less retentive than in a molar. Preparation for a full crown on a premolar(C). Preparation for a crown on a molar(D). shqalanish tutilishi preparat sirtlari bilan tiklanishiga bog'liq bo'lgani uchun, tayyorlangan tishning klinik toji qanchalik katta bo'lsa, aloqa yuzasi shuncha katta bo'ladi va natijada oxirgi ushlanib qoladi. Shunday qilib, tishlar uzun bo'lganda, etarli tutilishni saqlab qolish uchun etarli bo'lgan okluzal konvergentsiyaga erishish uchun devorlarning moyilligini oshirish mumkin. Boshqa tomondan, qisqaroq tishlarning devorlari samarali ushlab turishni ta'minlash uchun parallel ravishda tayyorlanishi kerak. Old tishlar va premolarlar minimal okklyuzotservik o'lchamlari 3 mm, tishlar esa 4 mm gacha bo'lishi kerakligi taklif qilingan. Ushbu minimal o'lchamlarga ega bo'lmagan tishlarni qo'shimcha ushlab turish orqali ularning tutilishini oshirish uchun o'zgartirish kerak Goodacre va boshq (2001) 22 okluzal konvergentsiya burchagi 10 darajadan oshmasa tiklashning lateral siljishiga etarlicha qarshilik ko'rsatish uchun minimal 3 mm tayyorgarlik balandligi zarurligini aniqladi. Balandligi 5 mm bo'lgan preparatlarda konvergentsiya burchagini 2 dan 10 gradusgacha o'zgartirish yuzaning pasayishini 13,9% ga kamaytiradi. Tayyorgarlik balandligining atigi 1 mm ga ko'tarilishi sirt maydonida sezilarli darajada o'sishga olib keladi. Sirt kattalashganligi sababli, preparat balandligini oshirish va angulyatsiyani kamaytirish lute agentning ishini yaxshilashi, lateral siljishga qarshilik va qattiq protezni ushlab turishiga olib kelishi mumkin9 (3-5-rasm). Shakl 3-5 Sirt maydoni va preparatni ushlab turish o'rtasidagi mavjud munosabatlar. Xuddi shu tishda qisman preparat umumiy tayyorgarlikka qaraganda kamroq tutuvchanlikka ega. Qisman tojga tayyorgarlik (A). Tojga tayyorgarlik (B). Xuddi shu balandlikdagi tishlar bilan premolardagi bir xil preparat molga qaraganda kamroq saqlanib qoladi. Premolar (C) bo'yicha to'liq tojga tayyorgarlik. Molar (D) ustidagi tojga tayyorgarlik. The angulation or occlusal convergence of the preparation was one of the first aspects of crown preparation to receive specific attention. The convergence angles between the opposed surfaces of a full-crown preparat ioninfluence their retention and resistance to rotation, with the angle being theoretically optimal between 2 and 4 degrees. Due to the difficulty in fitting and preparing a crown with these angles, angles between 2 and 22 degrees are considered acceptable. 22^,54,65 when different inclinations of occlusal convergence (12 or 20 degrees ) and different preparation heights (4 and 6 mm) of crowns made by a computer-aided design/computer-aided manufacturing (CAD/CAM) system were compared, it was shown that preparations with a 12- degree convergence angle show better internal adaptation compared to those with a 20-degree convergence angle.38 The pursuit of a well-executed preparation requires the clinician's dexterity and concentration. Studies report a significant variation in convergence values (between 14 and 20 degrees) in preparations made by different profession- als3^,56 Stability is the property of a preparation to withstand the displacement of a restoration due to oblique forces. These can lead to rotation of the restoration, such as during mastication or in the presence of parafunctional habits. Preparations with a high degree of convergence or short preparations can be subjected to dislodging forces in various directions. The shorter the preparation, the more important the occlusal convergence angle. All measures taken to limit the freedom of movement of restorations subjected to torsional and rotational forces in a horizontal plane will increase their stability. To obtain stability in a preparation, two alternatives can be employed: decreased convergence of surfaces, and adding grooves to occlusal surfaces(Fig3-6). Fig3-6 To avoid displacement of a crown, it is necessary for the tangent point to be located on the lower half of the crown. High angulation of the preparation will result in a crown with low resistance to displacement. This can be verified by the position of the tangent point located above the half of the crown(A). An alternative for correcting the angle is by reducing the diameter of the base, making the surfaces more parallel and improving stability (B). Another alternative for improving stability is the realization of additional grooves, creating smaller displacement arcs(C). Shillingburg et al (2007) 54 suggest that the length of the tooth should always be greater than its base to ensure stability. Based on the principles of the height/width ratio of the preparation, Pegoraro et al (2004) 46 suggested that if the width is greater than the height, the radius of rotation increases, impairing adequate stability. For the same height, crowns with larger diameters have comparatively less stability(Fig3-7). Fig3-7 Existing relationship between the height and diameter of the preparation. Tooth with smaller diameter(A). Tooth with larger diameter(B). Some theories consider the relationship between angle, diameter, and preparation time as regards a restoration's retention and stability. According to Lewis and Owen, 29 when you draw a line from the center of rotation perpendicular to the line that forms the axial wall of the preparation at the opposite end of the preparation, you will find intersection point "B". All points located above "B" are stabilizers. Another equally applicable theory was proposed by Zukerman, 69 who said that if you draw a circle with the floor of the preparation as the diameter, all points above the "B" intersection, located between the circumference and the axial wall of preparation, are stabilizers (Fig3-8). Fig3-8 Illustration of the theories of Lewis and Owen 29 and Zukerman. 69 Preparatning angulyatsiya yoki okluzal konvergentsiyasi tojni tayyorlashga alohida e'tibor berishning birinchi jihatlaridan biri edi. To'liq tojli preparatning qarama-qarshi sirtlari orasidagi yaqinlashish burchaklari ularning tutilishiga va aylanishiga chidamliligiga ta'sir qiladi, burchak nazariy jihatdan 2 dan 4 darajagacha optimal bo'ladi. Ushbu burchaklar bilan tojni o'rnatish va tayyorlash qiyinligi sababli, 2 dan 22 darajagacha burchaklar qabul qilinadi. 22 ^, 54,65 kompyuter yordamida loyihalash / kompyuter yordamida ishlab chiqarish (SAPR / CAM) tizimi tomonidan qilingan har xil okluzal konvergentsiya moyilligi (12 yoki 20 daraja) va har xil tayyorlanish balandliklari (4 va 6 mm) tojlari solishtirilganda 12 daraja yaqinlashish burchagi bilan 20 daraja yaqinlashish burchagiga qaraganda yaxshiroq ichki moslashuvni namoyish etadi.38 Yaxshi bajarilgan tayyorgarlikka intilish klinisyenning epchilligi va kontsentratsiyasini talab qiladi. Tadqiqotlar shuni ko'rsatadiki, turli xil kasblar tomonidan tayyorlangan preparatlarda yaqinlashuv qiymatlarining (14 dan 20 darajagacha) sezilarli o'zgarishi3 ^, 56 Barqarorlik - tiklanishning qiyshaygan kuchlar ta'sirida siljishiga bardosh beradigan tayyorgarlik xususiyati. Bu tiklanishning aylanishiga olib kelishi mumkin, masalan, mastatsiya paytida yoki parafunktsional odatlar mavjud bo'lganda. Yuqori darajadagi yaqinlashuvga ega bo'lgan preparatlar yoki qisqa muddatli preparatlar turli yo'nalishlarda ajralib chiqadigan kuchlarga duch kelishi mumkin. Tayyorgarlik qancha qisqa bo'lsa, okluzal konvergentsiya burchagi shunchalik muhim bo'ladi. Gorizontal tekislikda burama va aylanma kuchlarga duchor bo'lgan restavratsiyalarning harakatlanish erkinligini cheklash bo'yicha barcha choralar ularning barqarorligini oshiradi. Preparatdagi barqarorlikni olish uchun ikkita alternativadan foydalanish mumkin: sirtlarning yaqinlashuvining pasayishi va okluzal yuzalarga oluklar qo'shilishi (3-6-rasm). Shakl 3-6 Tojni siljishini oldini olish uchun tojning pastki yarmida teginish nuqtasi joylashgan bo'lishi kerak. Tayyorgarlikning yuqori angulyatsiyasi siljishga nisbatan past qarshilikka ega bo'lgan tojga olib keladi. Buni tojning yarmidan yuqori qismida joylashgan A (A) teginish nuqtasi holati bilan tekshirish mumkin. Burchakni to'g'rilash uchun alternativ - bu taglikning diametrini kamaytirish, sirtlarni yanada parallel qilish va barqarorlikni yaxshilash (B). Barqarorlikni yaxshilashning yana bir alternativasi - bu kichikroq siljish kamonlarini (C) yaratib, qo'shimcha oluklarni amalga oshirishdir. Shillingburg va boshq (2007) 54 tishning uzunligi barqarorlikni ta'minlash uchun har doim uning tagidan kattaroq bo'lishi kerak. Pegoraro va boshq (2004) 46 preparatning balandligi / kengligi nisbati printsiplariga asoslanib, agar kenglik balandlikdan katta bo'lsa, aylanish radiusi oshib, etarli barqarorlikni buzadi. Xuddi shu balandlik uchun katta diametrli tojlar nisbatan kamroq barqarorlikka ega (3-7-rasm). Shakl 3-7 Preparatning balandligi va diametri o'rtasidagi mavjud munosabatlar. Diametri kichikroq bo'lgan tish (A). Diametri kattaroq (B) bo'lgan tish. Ba'zi nazariyalar, tiklanishni ushlab turish va barqarorlikka nisbatan burchak, diametr va tayyorgarlik vaqti o'rtasidagi bog'liqlikni ko'rib chiqadi. Lyuis va Ouenning so'zlariga ko'ra, 29, aylanish markazidan preparatning qarama-qarshi uchida preparatning eksenel devorini tashkil etuvchi chiziqqa perpendikulyar ravishda chiziq tortganingizda, kesishish nuqtasi "B" ni topasiz. "B" dan yuqorida joylashgan barcha nuqtalar stabilizatorlardir. Yana bir xil tatbiq etiladigan nazariyani 69 yoshli Zukerman taklif qilgan va agar u preparatning tagligi diametri bilan aylana chizib qo'ysangiz, "B" kesishmasidan yuqorida, aylana va tayyorlashning o'qi devori o'rtasida joylashgan barcha nuqtalar stabilizatorlar deb aytgan. (Shakl 3-8). Shakl 3-8 Lyuis va Ouen 29 va Tsukerman nazariyalarining tasviri. 69 Whenever possible, the teeth should be prepared in such away that they have circumferential irregularity. When teeth are anatomically reduced, they have characteristic geometric shapes. For example, when maxillary molars are prepared, they have a rhomboid shape when viewed from the occlusal side; mandibular molars have a rectangular shape, and most of the anterior teeth and premolars have an oval shape. These forms provide circumferential irregularity. 23 The value of these irregularities was assessed by comparing the areas of conical and pyramidal preparations. The pyramidal preparations showed increased resistance. 24 Therefore, it is important to preserve the "edges" of a preparation. When a prepared tooth does not have "edges" because of its morphology or an existing condition, it must be modified by additional retentions to ensure resistance to displacement. All means to increase the contact surfaces result in the increase of retention and are called auxiliary retentive features. They are categorized as grooves, boxes, and pinholes 10 (Figs3-9and3-10). Fig-3-9 Preparation of additional grooves. Fig3-10 The grooves must have slightly rounded margins(A). Occlusal view of the same tooth prepared with and with out circumferential irregularity; an example of the application of additional grooves(B). The difference in wear between a partial and full crown causes a difference in stability of the restoration; the additional grooves are an alternative to increase the stability (C,D). An interesting aspect of the groove is that the rotation direction forms an arc away from one of the walls of the groove, and the arc from the other wall causes stabilization, providing resistance in both directions of movement (Fig3-11). Fig-3-11 Mechanical principle of the action of the grooves. The structure of the tooth in which the groove is placed must be able to withstand the forces to prevent rotation of the crown, so they should be placed in structurally sound regions. 45 Another alternative is to reconstruct the lost walls through core buildup with composite or glass ionomer (Fig3-12). Fig-3-12 Coronal reconstruction, allowing the creation of additional grooves(A,B).
Ular oluklar, qutilar va teshikchalar 10 deb tasniflanadi (3-9 va 3-10-rasmlar). Shakl-3-9 Qo'shimcha oluklarni tayyorlash. Shakl 3-10 Oluklar biroz yumaloq qirralarga ega bo'lishi kerak (A). Atrof-muhit tartibsizliklari bilan va tashqarisida tayyorlangan xuddi shu tishning okklyuziv ko'rinishi; qo'shimcha oluklarni (B) qo'llash namunasi. Qisman va to'liq toj o'rtasidagi aşınma farqi tiklash barqarorligining farqini keltirib chiqaradi; qo'shimcha oluklar barqarorlikni oshirish uchun alternativ (C, D). Yivning qiziqarli tomoni shundaki, burilish yo'nalishi yivning devorlaridan biridan kamon hosil qiladi va boshqa devordan yoy barqarorlashuvga olib keladi va bu harakatning har ikki yo'nalishida ham qarshilikni ta'minlaydi (3-rasm). Shakl-3-11 Oluklar ta'sirining mexanik printsipi. Yiv joylashtirilgan tishning tuzilishi tojning aylanishiga to'sqinlik qiladigan kuchlarga bardosh bera olishi kerak, shuning uchun ular tizimli ravishda mustahkam mintaqalarga joylashtirilishi kerak. Yo'qotilgan devorlarni yadro birikmasi yordamida kompozitsion yoki shisha ionomer bilan tiklash (45-1-rasm). Shakl-3-12 Qo'shimcha oluklar (A, B) yaratishga imkon beradigan koronali rekonstruksiya.
Grooves and boxes are also of great importance in helping to ascertain a single insertion axis for the restoration. Restorations with more than one insertion axis have a poorer prognosis. A single-path insertion means that the restoration has only one way to be seated or removed from the preparation (Fig3-13). These alternatives are important as we are often faced with limited preparation options. Fig3-13 Different insertion situations. Crown with adequate angulation and a single insertion axis(A). Crown with increased angulation and multiple insertion axis(B). Crown with increased angulation, additional grooves, and a single insertion axis(C).
Considering that diverse forces of varying magnitude and direction are present in the oral cavity, it is necessary for the restoration to be resistant enough to withstand these forces so that there are no fractures, deformations or displacement. The tooth should be prepared in a manner that allows for a restoration of sufficient thickness that is able to withstand masticatory forces. The tooth reduction required for good structural stability will depend on the restorative material of choice. The structural stability is regarded as the minimum material thickness oftherestorationtoresisttheaction of mastication loads without deforming.35 For metal restorations, a reduction permitting an occlusal thickness of 1.0 mm ought to be sufficient to receive and transmit the occlusal loads to other dental structures. When the metal is combined with porcelain in a metal-ceramic crown, this reduction should be 1.3 to 2.0 mm to achieve adequate strength for porcelain. For all-ceramic restorations, there must be enough room for 1.5 to 2.0 mm of material. An inadequate thickness or an excessive occlusal load may cause deformation or at least tensions, which may result in dislodgement (Fig3-14). Fig 3-14 Adequate amount of reduction in accordance with the material. Metal crown (A), Metal-ceramic crown(B). All-ceramic crown(C). The teeth should be uniformly reduced to ensure a restoration with suitable shape and esthetics. The uniform reduction eases the job of the laboratory technician to create esthetic restorations with a color and translucency that resemble the natural tooth. Uniform reduction also promotes the production of a restoration with normal contours.23 However, lack of proper tissue reduction can lead to disfigurement or weakness of the restoration due to lack of material. The attempt to correct inadequate reduction leads to an overcontoured restoration, causing biological damage (Fig3-15). Fig-3-15 Inadequate reduction causing marginal overcontouring. The occlusal thickness must be carefully checked in the centric contention areas of the cusps (lower vestibular and upper palatal) and in the fossae, where the incidence of forces is higher. It is important to note that the occlusal reduction should follow the existing anatomy, including pits and fissures, and reproduce the main ridges, allowing an appropriate occlusal morphology of the restoration (Fig3-16). Fig-3-16 Inadequate reduction, without considering the anatomy(A). Inadequate reduction, talking the anatomy into account(B).
These walls also play an important role in transmitting the masticatory forces to the cervical regions of the preparations. The angles of the preparations should be rounded to increase the strength of the ceramic restorations and to facilitate laboratory manufacturing steps and the adjustment of the metal restorations (Fig3-17). Fig-3-17 Preparation with rounded anles. Acute angles on the prepared surfaces act as stress concentration regions.41 Rounding these angles increases the strength of all-ceramiccrowns. Full-metal and metal-ceramic crowns do not show increased resistance, but models and wax patterns without entrapped bubbles can be made with greater ease. The presence of bubbles in the infrastructure may hamper complete seating of the restoration if not detected and removed. Moreover, if present, they are easier to detect and remove when the angles of the preparations are rounded. 23 Oluklar va qutilar, shuningdek, tiklash uchun bitta o'qni aniqlashga yordam berishda katta ahamiyatga ega. Bir nechta kiritish o'qi bo'lgan restavratsiya yomon prognozga ega. Bitta yo'lli qo'shimchani tiklash restavratsiyaning o'tirish yoki uni tayyorlashdan olib tashlashning yagona yo'li borligini anglatadi (3-13-rasm). Ushbu alternativalar juda muhimdir, chunki biz ko'pincha cheklangan tayyorgarlik variantlariga duch kelamiz. Shakl3-13 Turli xil qo'shilish holatlari. Kerakli burchakka va bitta qo'shma o'qga (A) ega bo'lgan toj. Burchakning ko'payishi va ko'p sonli o'qi (B) bilan toj. Kuchli burchakka, qo'shimcha oluklarga va bitta kiritish o'qiga (C) ega bo'lgan toj. Qarshilik Og'iz bo'shlig'ida har xil kattalik va yo'nalishdagi turli xil kuchlar mavjudligini hisobga olib, tiklash uchun bu kuchlarga bardosh beradigan darajada chidamli bo'lish kerak, shunda yoriqlar, deformatsiyalar va siljishlar bo'lmaydi. Tish chaynash kuchlariga bardosh beradigan etarlicha qalinlikni tiklashga imkon beradigan tarzda tayyorlanishi kerak. Yaxshi tizimli barqarorlik uchun zarur bo'lgan tishlarni kamaytirish tanlangan restorativ materialga bog'liq bo'ladi. Strukturaviy barqarorlik, ularni qayta tiklashga qarshilikning minimal qalinligi sifatida qabul qilinadi deformatsiyasiz mastitatsiya yuklarining deformatsiyasi.35 Metall restavratsiya qilish uchun okklyuzion qalinligi 1,0 mm bo'lgan pasayish okluzal yuklarni qabul qilish va boshqa stomatologik tuzilmalarga etkazish uchun etarli bo'lishi kerak. Metall-keramika tojida metall chinni bilan birlashtirilganda, chinni uchun etarli quvvatga erishish uchun bu pasayish 1,3 dan 2,0 mm gacha bo'lishi kerak. Butun keramikani tiklash uchun 1,5 dan 2,0 mm gacha bo'lgan materiallar uchun etarli joy bo'lishi kerak. Etarli bo'lmagan qalinlik yoki ortiqcha okklyuzion yuk deformatsiyani yoki hech bo'lmaganda taranglikni keltirib chiqarishi mumkin, bu esa joy almashinishiga olib kelishi mumkin (3-14 rasm). Shakl 3-14 Materiallarga muvofiq etarli miqdorda kamayish. Metall toj (A), metall keramika toj (B). Butun seramika toj (C). Tegishli shakli va estetikasi bilan tiklanishni ta'minlash uchun tishlarni bir tekis qisqartirish kerak. Bir xil pasayish tabiiy tishga o'xshash rang va shaffoflik bilan estetik tiklanishlarni yaratish bo'yicha laboratoriya texnikining ishini engillashtiradi. Yagona pasayish, shuningdek, normal konturlar bilan tiklanishni ishlab chiqarishga yordam beradi.23 Ammo to'qimalarning to'g'ri qisqarishining etishmasligi moddiy etishmovchilik tufayli tiklanishning yomonlashishiga yoki zaifligiga olib kelishi mumkin. Noto'g'ri pasayishni to'g'rilashga urinish biologik zarar etkazadigan haddan tashqari konturni tiklashga olib keladi (3-15-rasm). Shakl-3-15 Noto'g'ri pasayish cheklangan ortiqcha konturni keltirib chiqaradi. Okklyuzion qalinligi kustlarning markazlashtirilgan tortishish joylarida (pastki vestibulyar va yuqori palatal) va kuchlar paydo bo'lish darajasi yuqori bo'lgan fossalarda ehtiyotkorlik bilan tekshirilishi kerak. Shuni ta'kidlash kerakki, okklyuzion qisqarish mavjud anatomiyani, shu jumladan chuqur va yoriqlarni kuzatib borishi va tiklanishning tegishli okluzal morfologiyasiga imkon beradigan asosiy tizmalarni ko'paytirishi kerak (3-rasm). Shakl-3-16 Anatomiyani (A) hisobga olmasdan etarli darajada kamayish. Noto'g'ri qisqartirish, anatomiyani hisobga olish (B).
Ushbu devorlar, shuningdek, chaynash kuchlarini tayyorgarlikning bo'yin qismlariga etkazishda muhim rol o'ynaydi. Keramika tiklanishining mustahkamligini oshirish va laboratoriyada ishlab chiqarish bosqichlarini osonlashtirish va metallarning tiklanishini sozlash uchun preparatlarning burchaklari yumaloq bo'lishi kerak (3-17-rasm). Shakl-3-17 Dumaloq to'piq bilan tayyorlash. Tayyorlangan yuzalardagi keskin burchaklar stress kontsentratsiyasi mintaqalari vazifasini bajaradi.41 Ushbu burchaklarni yaxlitlash barcha keramik tojlarning kuchini oshiradi. To'liq metall va metall keramika tojlari yuqori qarshilik ko'rsatmaydi, ammo tuzoqqa solingan pufakchalarsiz modellar va mum naqshlari osonroq bajarilishi mumkin. Infrastrukturada pufakchalar mavjudligi aniqlanmasa va olib tashlanmasa, tiklanishning to'liq joylanishiga xalaqit berishi mumkin. Bundan tashqari, agar mavjud bo'lsa, preparatlarning burchaklari yumaloq bo'lganda ularni aniqlash va olib tashlash osonroq bo'ladi. 23 BIOLOGICAL PRINCIPLES PRESERVATION OF THE PULPAL TISSUE The objectives of rehabilitation are to avoid major damage, to minimize postoperative sensitivity, and to preserve pulp vitality before restoring the shape and function of the tooth.13-51 The dental pulp is a unique tissue. Its importance in the longevity and longterm prognosis of the tooth is often ignored. It is the only tissue that is located in a chamber that provides mechanical and biological protection. If this structure loses its integrity, the threat to pulpal tissue increases due to the presence of caries, cracks, fractures, and marginal maladjustment, which serve as a pathway for the penetration of microorganisms and their toxins.66 The reaction of the pulp tissue to the tooth preparation for direct and indirect restorations is the subject of constant concern during the restorative treatment.68 The thickness of the dentin remaining after tooth preparation has been shown to be a critical factor in protecting the pulp from the aggression caused by the preparation.39 Studies consider a range of 1 to 2 mm of remaining dentin to be sufficient to prevent damage to the pulp 44-57-58(Fig3-18). Fig3-18 The dental structure remaining after the preparation of the tooth is very important with regard to pulpal protection. During the preparation of a tooth for subsequent placement of a full crown, about 30,000 to 40,000 tubules per mm2 of dentin are exposed, which renders a total of about 1 to 2 million exposed dentinal tubules20 (Table 3-1) (Figs3-19 and3-20). Table3-1 Relationship between distance from the pulp and the number and diameter of dentin tubules....... Fig-3-19 Schematic drawing of the tubular structure. The main factors that can compromise the pulp vitality are: •Inappropriate cavity preparation; Evolution of the carious process; •Trauma; •Restorativ ematerials. Paradoxically, the proper treatment to repair the tooth can cause damage to the dental pulp. Cavity preparation is a common cause of pulp inflammation because it promotes heat and dehydration, particularly when approximating the pulp. Preparation at high speed is less harmful to the pulp than preparation at low speed due to the decrease of vibration and heat generation, but even when air/water spray is used to cool the area, some degree of pulp irritation will occur.58 During preparation, worn diamond burs require more pressure from the clinician. This excessive pressure generates more heat on the tooth surface and may cause pulp damage (Fig3-21). The pulp tissue should not undergo temperature increases of greater than 5°C, since this could lead to inflammatory reactions and even irreversible damage to the pulp.67 A temperature increase of 5.6°C in the dental pulp can result in a 15% incidence of necrosis, especially in less voluminous dental elements where pulp necrosis occurs more frequently.16 Fig3-21 Photomicrograph of diamond burs for preparation. New bur, appropriate for use(A,B). Used bur, inappropriate for use(C,D). PRESERVATION OF THE PERIODONTIUM The dental-periodontal relationship is an ongoing subject of research, in particular the junction between the teeth and the gingiva12 (Fig3-22), where the interrelationship between periodontics and prosthodontics is more pronounced because it is an area that is relevant to the work of both periodontist and prosthodontist, The preparation procedure occurs in this area, as does the gingival retraction and impression.Moreover, it is the preferred location of most of the preparation finish line, and therefore the region of restoration adaptation. The periodontium forms the basis for esthetics, function, and comfort of the dentition. A healthy periodontium is a prerequisite for all prosthetic rehabilitations. The interaction between periodontics and restorative dentistry occurs on several fronts: location of the restoration margins, contours of the prosthetic crowns, and response of the gingival tissues to the preparation procedure.42 To control biofilm, the restoration margins of the preparations must have regular ends and be positioned in areas with better access. This leads to a better periodontal outcome.36 A deeper location of the restoration margins into the gingival sulcus results in more intense inflammatory responses.26'40 Some authors have reported the presence of restorations with subgingival margins as one of the main risk factors for periodontitis50'55 (Fig3-23). The positioning of the gingival level of the cervical finish line of the preparation has been thoroughly discussed. Various authors have suggestions regarding the positioning at three different levels-supragingival, gingival, and subgingival-depending on the clinical situation. The finish line should end in enamel wherever possible. Fig-3-22.The dentogingival junction comprises the space between the cementoenamel junction and the border of the marginal gingiva. When handled improperly, it can lead toinflammation (A,B).------------------------------------------------------------------------------------------- BIOLOGIK PRINSIPLAR PULPAL TKRASHNING XAVFI Reabilitatsiya vazifalari katta zararlardan saqlanish, operatsiyadan keyingi sezgirlikni minimallashtirish va tishning shakli va funktsiyasini tiklashdan oldin pulpa hayotiyligini saqlab qolishdir. Tish pulpasi noyob to'qimadir. Tishning uzoq umr ko'rishida va uzoq muddatli prognozida uning ahamiyati ko'pincha e'tiborga olinmaydi. Bu mexanik va biologik himoyani ta'minlaydigan kamerada joylashgan yagona to'qimadir. Agar bu struktura yaxlitligini yo'qotsa, mikroorganizmlar va ularning toksinlari kirib boradigan yo'l bo'lib xizmat qiladigan karies, yoriqlar, yoriqlar va chekka notekisliklar mavjudligi sababli pulpa to'qimalariga tahdid kuchayadi.66 Pulpa to'qimalarining tishni to'g'ridan-to'g'ri va bilvosita tiklashga tayyorlanishiga reaktsiyasi restorativ davolanish paytida doimiy tashvishga soladi. Tish tayyorlangandan keyin qolgan dentinning qalinligi pulpani preparat tomonidan yuzaga kelgan tajovuzdan himoya qilishda hal qiluvchi omil ekanligi ko'rsatilgan. pulpa 44-57-58 (3-18-rasm). Shakl3-18 Tish tayyorlangandan keyin qolgan tish tuzilishi pulpa himoyasi jihatidan juda muhimdir.
(3-19 va 3-20-rasmlar). Jadval3-1 Pulpadan masofa va dentin tubulalarining soni va diametri o'rtasidagi bog'liqlik ....... Shakl-3-19 Naychali konstruktsiyani sxematik chizish. Pulpa hayotiyligini buzishi mumkin bo'lgan asosiy omillar: • Kovakni noto'g'ri tayyorlash; Carious jarayonining rivojlanishi; • Shikastlanish; • Qayta tiklanadigan materiallar. Paradoksal ravishda tishni tiklash uchun to'g'ri davolash tish pulpasiga zarar etkazishi mumkin. Bo'shliqqa tayyorgarlik pulpa yallig'lanishining keng tarqalgan sababidir, chunki u issiqlik va suvsizlanishga yordam beradi, ayniqsa pulpa yaqinlashganda. Vibratsiyaning pasayishi va issiqlik hosil bo'lishi sababli yuqori tezlikda tayyorgarlik pulpa uchun past tezlikda tayyorlanishga qaraganda zararli emas, ammo bu joyni sovutish uchun havo / suv purkagichidan foydalanganda ham pulpa tirnash xususiyati paydo bo'ladi.58 Tayyorgarlik paytida eskirgan olmos burmalar klinisyandan ko'proq bosim talab qiladi. Ushbu haddan tashqari bosim tish yuzasida ko'proq issiqlik hosil qiladi va pulpa shikastlanishiga olib kelishi mumkin (3-21-rasm). Pulpa to'qimasi haroratni 5 ° C dan yuqori ko'tarilmasligi kerak, chunki bu yallig'lanish reaktsiyalariga olib keladi va hatto pulpaga qaytarilmas zarar etkazishi mumkin.67 Tish pulpasida haroratning 5,6 ° S ga ko'tarilishi 15% kasallanishiga olib kelishi mumkin. nekroz, ayniqsa pulpa nekrozi tez-tez uchraydigan unchalik katta bo'lmagan tish elementlarida Shakl 3-21 Tayyorlash uchun olmos burmalarining fotomikrografiyasi. Yangi bur, foydalanishga yaroqli (A, B). Ishlatilgan bur, ishlatishga yaroqsiz (C, D). PERIODONTIUMNI QO'LLASH Dental-periodontal munosabatlar doimiy ravishda olib borilayotgan tadqiqot mavzusidir, xususan tish va gingiva12 orasidagi bog'lanish (3-22-rasm), bu erda periodontika va prostodontiya o'rtasidagi o'zaro bog'liqlik yanada aniqroq bo'ladi, chunki bu ish uchun mos bo'lgan sohadir. ham periodontist, ham prostodontist, bu erda gingival retraktsiya va taassurot kabi tayyorgarlik jarayoni ham sodir bo'ladi.Bundan tashqari, bu tayyorlanish chizig'ining aksariyat qismida eng maqbul joy va shuning uchun tiklanish moslashuvi mintaqasi. Periodontium estetikasi, funktsiyasi va tish tishining qulayligi uchun asos bo'lib xizmat qiladi. Sog'lom periodontium barcha protezlarni tiklash uchun zaruriy shartdir. Periodontika va restorativ stomatologiya o'rtasidagi o'zaro bog'liqlik bir necha jabhada sodir bo'ladi: tiklanish chekkalarining joylashishi, protez tojlari konturlari va gingival to'qimalarning tayyorgarlik jarayoniga munosabati.42 Biofilmni boshqarish uchun preparatlarni qayta tiklash chekkalari muntazam uchlarga ega bo'lishi va kirish imkoniyati yaxshiroq bo'lgan joylarda joylashishi kerak. Bu yaxshiroq periodontal natijaga olib keladi.36 Tiklanish chegaralarining gingival sulkusga chuqurroq joylashishi yanada kuchli yallig'lanish reaktsiyalariga olib keladi.26'40 Ba'zi mualliflar periodontit 50'55 uchun asosiy xavf omillaridan biri sifatida subgingival chekkalari bilan restavratsiya mavjudligini xabar berishgan (3-23-rasm). Preparatning bo'yin tugatish chizig'ining gingival darajasining joylashuvi yaxshilab muhokama qilindi. Turli xil mualliflar klinik holatga qarab uch xil darajadagi supragingival, gingival va subgingival darajadagi joylashuvga oid takliflariga ega. Finiş chizig'i iloji boricha emal bilan tugashi kerak. Shakl-3-22. Dentogingival birikma sementoenamel birikmasi va chekka tish go'shti chegarasi orasidagi bo'shliqni o'z ichiga oladi. Noto'g'ri ishlov berilganda, u yallig'lanishni keltirib chiqarishi mumkin (A, B). -------------------------------------------------------------- Download 35.66 Kb. Do'stlaringiz bilan baham: 
|