Annotation to the seminars 8-9 Topic: Pin-like constructions of dental prostheses.

Transcription

1 Annotation to the seminars 8-9 Topic: Pin-like constructions of dental prostheses. Pin-like constructions of dentures contain a pin (post) as one of main constructional elements. All variety of dental pin-like constructions can be classified on base of the following features (fig. 1): Fig. 1. Classification of pin-like constructions, used in dentistry According to post topography; According to principles of connection between post and crown; According to technology of pin-construction fabrication; According to constructional material, used for post production. According to topography they distinguish intracanal and parapulpal pins. Intracanal posts are located in root canal of the tooth, and parapulpal pins in hard tissues out of the pulp chamber. According to principle of connection between intracanal post with artificial crown pin-like constructions are divided into pinned teeth and cast custom post-and-cores. In pinned teeth intracanal post with artificial crown is a single constructions (fig. 2a). Cast custom post-and-core is a construction, which consists of post and core, similar to a prepared tooth shape. Artificial core is used for its future covering with an artificial crown (fig. 2b; 2c; 2d). According to fabrication technology pin-like constructions are classified into cast custom post-andcores (fig. 2b) and cast custom post-and-cores, manufactured with the use of prefabricated posts (fig. 2c; 2d). According to constructional material, used for prefabricated posts, they are divided into metallic posts (fig. 2c) and fiberglass posts (fig. 2d). а b c d Fig. 2. Types of pin-like constructions: a pinned tooth; b cast custom post-and-core; c post-and-core with the use of prefabricated post; d post-and-core with the use of prefabricated fiberglass post PARAPULPAL PINS Parapulpal pins are special cylinder metallic pins with or without notches on the surface, secured in the hard tooth tissues and used for stronger fixation of direct restorations in II and IV class cavities. Parapulpal pins are made from titan, stainless steel or gold alloys. For anterior teeth they manufacture titan pins, covered by silanized adhesive system with opaque facing, similar to dentine colour. Such pins are not showing under restorative material, and their tooth-coloured facing makes chemical connection with composite, providing stabile connection and necessary esthetics. Pin diameter varies from 0,35 mm till 1 mm, the diameter of 0,7-0,8 mm is mostly used. As a rule, pin length is 5 mm (fig. 3a).

2 а b C Fig. 3. Parapulpal pins (a) and their clinical application (b) during restoration with the use of silver amalgam (c) Optimal area for insertion of a parapulpal pin is gingival area of a tooth (fig. 3b). Fig. 4. Parapulpal pin positioning Pin should be positioned in the middle between pulp and periodont (fig. 4). Optimal distance from tooth edge is 1-1,5 mm and at least 0,5 mm away from enamel-dentinous junction. There should be at least 0,5 mm space between pin and pulp chamber. Before making a channel for the pin a small deepening should be done in the place of supposed pin location, with a round bur of 0,5-0,6 mm diameter. Creation of the channel is made with a special broach from carbon steel in low speed. Intradentinal part of the pin should be at least 2 mm. Optimal rate between intradentinal and supradentinal parts of the pin is 1:1. Pin should end 1,5-2 mm away from occlusal surface. It is not recommended to apply intrapulpal pins in direct restorations during restoration of devitalized teeth. In such cases intracanal posts should be used. 1 2 Fig. 5. Application of parapulpal pins in indirect restorations: 1 additional retentive element of a pinlay; 2 additional retentive element of cast custom postand-core (a), preventing rotation of the main intracanal post (b) As adhesive systems appear in dentistry, creation of additional retentive elements for better fixation of fillings is no longer needed. Parapulpal pins in prosthodontic dentistry are applied as additional retentive elements for fixation of pinlays (fig. 5.1), splinting constructions and cast custom post-and-cores (fig. 5.2a). PINNED TEETH Pinned tooth is a fixed denture, restoring defect of a crown with the help of artificial crown, connected to a pin, which secures the whole construction in root canal. Application of pin-like constructions of dentures began in XVII century. One of first dental prostheses is a wooden pinned tooth (fig. 6.1) made in Japan during empire of Tokugava Ieyasu (1603). The founder of scientific dentistry, French dentist Pierre Fauchard ( ) in his work «Le chirurgien-dentiste, ou Traite des dents» (1728) made a detailed description of pinned teeth construction while restoration of tooth tissues defect and partial teeth loss (fig. 6.2).

3 In 1895 american dentist C.M. Richmond, ( ), offered a pinned tooth construction which contained soldered golden cap, post and metallic platform for ceramic facing (fig. 5.3). In 1899 F.Е. Logan offered to use ceramic crown with an incremented post for restoration of destroyed natural crown. Pinned teeth were manufactured industrially and issued as sets of teeth of different sizes (fig. 6.4). In 1911 american dentist W.C. Davis offered to use a pin-like construction, including prefabricated posts and prefabricated porcelain crowns (fig. 6.5). Crowns had standard blind perforations, corresponding to posts diameter. After preparation of the root, post was fit and fixated in the root canal. After that a crown of an appropriate colour was selected, grinded according to supragingival part of the root and fixated with the post and root with the help of cements. 4 5 Fig. 6. History of pin-like constructions application in prosthodontic restoration of hard tooth tissues: 1 wooden pinned tooth, made in the times of Tokugava Ieyasu; 2 construction of pinned tooth by Pierre Fauchard; 3 construction of pinned tooth byy Richmond; 4 construction of pinned tooth by Logan; 5 construction of pinned tooth by Davis Nowadays pinned teeth have limitated application in dentistry, because indications for these constructions depend on group belonging of teeth and conditions of their supragingival part. Besides, in pinned teeth there is no possibility of changing the artificial crown and keeping the same post in canal. In clinic pinned teeth are used as provisory dentures while cast custom post-and-cores are manufactured. In such cases chair-side technique of making simple pinned teeth in a single appointment is used (fig. 7). Chair-side making of a pinned tooth in a single appointment supposes preparation of supragingival part of tooth, removing affected tissues (fig. 7.1) and forming supragingival plato (fig. 7.2). Then removal of a root filling is done. It s important to keep necessary rate between post length and the length of root canal. Length of the post which is introduced into the root canal, should make 2/3 of root length and shouldn t be less than vertical size of the crown. 4 Fig. 7. Sequence of chair-side fabrication of simple pinned tooth Preparation of canal should begin with opening of the orifice with a round bur, Gates Glidden or Largo. Then removing of filling material and shaping of root canal begins (fig. 7.2), which should be performed under radiographic control. Post is made from orthodontic wire of chrome-nickel steel (1C18Ni9Т) 0,8-1,2 mm diameter. Wire cross-section should correspond to the diameter of prepared canal. The post end is sharpened and fit into

4 the root canal (fig. 7.3). The wire part which is above the root, is bent as a loop or flattened with a hammer. It is necessary to prepare the post in such a way that it wouldn t disturb occlusion of teeth. There should be gap between the end of the post and antagonist tooth for the plastic layer. In some cases prefabricated metallic posts can be used (fig. 8.2). When appropriate plastic tooth (by size and colour) is selected from the set, it is grinded according to the supragingival platform of the tooth. Lingual surface of the plastic tooth is grinded with a cutter, to prepare space for self-curing polymer between artificial tooth and post. After that a small amount of selfcuring polymer Акрилоксид is mixed. In a dough-like stage polymer is placed onto supragingival part of the post and plastic tooth, and artificial tooth is matched with the post. After polymerization artificial tooth with the post is recovered from the oral cavity (fig. 8.2), processed, polished and fixated in the root canal with a temporary luting agent (fig. 8.3). Artificial crown in simple pinned tooth can be made from standard prefabricated polycarbonate patterns, self-curing plastic with the help of free moulding method or with the use of celluloide caps (watch topic Provisory dentures ). Fig. 8. Fabrication of simple pinned tooth for tooth 2.1 with a traumatic defect, with the use of prefabricated metallic post and standard plastic for removable dentures: 1 clinical view before treatment; 2 simple pinned tooth; 3 simple pinned tooth after temporary fixation POST AND CORE Nowadays post and cores together with a facing construction (metallic, plastic, ceramic or metalceramic crowns) are widely spread in dentistry. The construction consisting of 2 parts (post and core and the covering crown) has advantages comparing to pin-retained artificial teeth. Post and cores can be used for restoration of frontal and posterior teeth, partially or fully destroyed crowns. And the facing construction can be replaced if necessary without removal of post and core out of the root. CAST CUSTOM POST AND CORES CCPC are manufactured with the technology of metal alloys casting. Modelling can be carried out by direct method (modeling of CCPC in the oral cavity) or indirect method (on gypsum model, cast with a precise impression from elastomeric impression materials). Constructional metal alloys which can be used for casting of post and cores are presented in the table 1. Table 1 Constructional metal alloys, used for CCPC fabrication Noble alloys Highly noble alloys contain minimum 75% gold Noble alloys contain 25-75% (weight ratio) of gold or platinum group metals. Common mass of gold, platinum group metls and silver should make at least 70% of alloy mass. Base alloys Alloys on base of cobalt are the alloys with cobalt as main element, and other elements of the alloy are chrome (at least 25%), nickel and molybdenum (at least 4%). Common mass of Co, Ni and Cr should make at least 85% of the alloy

5 Noble metals alloys on base of palladium the alloys which have palladium as main element (palladiumcopper-gallium alloy or palladium-silver alloy). Noble metals alloys on base of silver the alloys which have silver as main element, and another component of the alloy is palladium Alloys on base of nickel are the alloys with nickel as main element, and other elements of the alloy are chrome (at least 20%) and molybdenum (at least 4%). Common mass of Ni and Cr should make at least 85% of the alloy On the fig. 9 the indications for cast custom post and cores are presented. Fig. 9. indications for cast custom post and cores use during fabrication of artificial crowns: 1 to strengthen devitalized teeth; 2 tooth destruction within the half of clinical crown height; 3 full destruction of the crown; 4 full destruction of the crown with subgingival destruction of the root. Sequence of CCPC fabrication by direct method is presented on the fig. 10. Clinical stages of post and core fabrication include: examination of a patient and if necessary initial preparing him for prosthodontics; preparation of tooth stump and root canal (fig. 10.2); modeling of post (10.3) and core (10.4); setting and fixation of cast custom post and core in the root canal (fig. 10.5); fabrication and fixation of facing artificial crown (fig. 10.6) Fig. 10. Sequence of cast custom post and core fabrication by direct method

6 Examination of a patient is carried out by general methodic with the use of special methods. X-ray examination is important, it allows to evaluate previously done endodontic treatment, periapical tissues condition, number and topography of root canals. Preparation of tooth stump is started with removal of soft dentine, thin walls and edges of the crown with the use of diamond burs and finishing cups. To prevent secondary caries and to achieve strong connection of tooth surface with the core its necessary to grind affected hard tissues of the tooth till healthy tissues. A smooth, fine surface of the stump is made, for a better fitting with cast post-and-core. It is recommended to make a bevel of to prevent root fracture complications resulting from mastication pressure onto the cast post-and-core (specially side loads, causing riving action of the post) (fig. 11). Fig. 11. Preparation of supragingival part of the tooth and root canal for making cast custom post-and-core Preparation of root canal includes largening of an orifice and removal of filling material along 1/2- - 2/3 of root length. When calculating the depth of root canal preparation, you should consider that post length must overcome the height of core and covering artificial crown (fig. 11). Widening of root canal is done with the use of broaches, giving to a canal taper and save the maximal thickness of canal walls (not less than 1 mm), so as it could withstand masticatory pressure. Modelling of post-and-core is made with wax or ashless resins. In direct method of post-and-core making the modelling wax Lavaks is used (fig. 12.1). A stick of podelling wax is warmed up over the torch flame and stretched out repeating the shape of root canal (fig. 12.2). Then again wax is heated over the flame and inserted into canal with a slight pressure. Excess of wax stick is cut away according to the heigh of artificial core. After that modelling of core is started. Shape of the modelled core should be same as the shape of natural tooth stump after its preparation for the corresponding artificial crown. After modelling work is done, a warm metal wire pin of 0,5-0,6 mm thickness is inserted into wax for 2-3 mm. The postand-core should be cooled down with a water spray and recovered out of the canal with the help of the wire pin, along tooth axis. 1 2 Fig. 12. Modelling wax Lavaks If modelling is performed with ashless resins, the modelling resin is applied onto standard ashless polymer pin which was previously selected and tried into the canal (fig. 13.1). Standard pin with the resin

7 is put into the canal, saving its position until the end of setting time of the resin (till 2-3 min). Then pin is recovered from the canal and the modelling quality is evaluated. If marginal pores are noticed, a new portion of resin should be prepared and the surface relief of the pin should be corrected. After the post is modelled, we proceed to the modelling of the core (fig. 13.2). Resin is applied portion by portion onto supragingival part of the post until artificial core receives necessary shape. Each new portion of resin connects easily with the set material, creating a monolith model. On the final steps of modelling work, the core is given final shape (fig. 13.3) by processing with a cutter out of the oral cavity and correcting details in the oral cavity using carbide burs for turbine handpieces. Using of water-cooling prevents brining of metal blades of the bur by plastic. Fig. 13. Modelling of post-and-core with the use of ashless resin Sequence of indirect method of CCPC fabrication. Is represented on the fig. 14. Fig. 14.Sequence of cast custom post-and-core fabrication by indirect method of wax modelling In the indirect method of modeling custom post-and-core, after preparation of supragingival part of the tooth and root canals (fig. 14a) doctor receives 2-layered 1-step impression with the use of elastomer materials (fig. 14b). To make an impression it is logic to use ashless plastic pins, which reinforce the intracanal impression and prevent their deformation during making a model. Same pins can be used on the step of modeling, to make introduction of polymer into root canals more convenient. In dental laboratory the impression (fig. 14c) allows to make a model from dental stone (14d; 14e). Isolation is done to prevent connection of plastic with stone model. On the stone model technician provides modeling works with the use of ashless plastics (fig. 14f). When modelling work is over the post-and-core

8 is removed from the model and given to the foundry for changing of plastic into constructional metal alloy (fig. 14g). The final steps of cast custom post-and-core fabrication is its setting and fixation with the help of luting agents (fig. 14h). Indirect method of modeling post-and-core allows to produce not only entire (fig. 15.1), but complicated sectional post-and-cores as well with the maximal use of all canal surface of multirooted teeth (fig. 15.2; 15.3). Fig. 15. Desing of cast custom post-and-cores in multirooted teeth: 1 post-and-core with main and additional posts; 2 sectional post-and-core, containing 2 or 3 parts; 3 sectional post-and-core with a lock post On the fig. 16 there are shown some steps of sectional post-and-core fabrication for tooth 2.6, consisting of 3 parts Fig. 16. some steps of sectional post-and-core fabrication for tooth 2.6, consisting of 3 parts: 1 silicone impression; 2 stone model; 3 sectional post-and-core with 3 parts; 4 post-and-core, all in one out of the oral cavity; 5 setting of separate parts of post-and-core on stone model; 6 cast post-and-core for 2.6, fit on the stone model all parts collected together CORE BUILD-UP WITH THE USE OF PREFABRICATED POSTS Tooth restoration system with the use of prefabricated posts includes three basic elements: prefabricated post; restorative material for crown or stump of the tooth; luting agent for post fixation. Prefabricated posts are made in fabric from metals and their alloys (titanium, stainless steel, brass with gold galvanization) and from fiberglass (nonmetallic, fiberglass). Prefabricated post should correspond to the following requirements: biocompatability;

9 good retention towards restorative material; posts should have various sizes for optimal adaptation to the canal volume (diameter, length etc.); manufacturer should supply kit with various work tools, to provide post adaptation to prosthetic tissues. Metallic prefabricated posts Metallic prefabricated posts are classified on base of post shape (fig. 17) and its retention type in canal. Shape of the post can be cylinder (fig. 17.1), taper (fig. 17.2) and cylinder-conical combining both shapes (fig. 17.3). Fig. 17. Shapes of prefabricated posts: 1 cylinder; 2 conical; 3 combined (cylinder and conical) Post retention in root canal is provided by surface of the post and luting agent, used for its fixation. 1 2 Fig. 18. Methods of retention of prefabricated metallic post in root canal: 1 passive; 2 active Posts, which are surrounded by luting agent all along and don t make any other types of retention, are called passive (fig. 18.1). Posts, which are incremented into dentine with the help of serrated surface, besides luting agent fixation, are called active (fig. 18.2). So called passive posts may have flat surface with transversal notches (fig. 19.1), spiked surface for mechanical connection with luting agent (fig. 19.2) or steps relief (fig. 19.3). Active posts have notches, which allow penetration of post into dentine of root canal (fig. 19.4) Fig. 19. Types of prefabricated posts according to their retention method in root canal: 1 passive post with smooth surface and transversal notches; 2 passive serrated post; 3 passive post with steps relief; 4 active post for penetration of post into root dentine

10 1 2 Fig. 20. Stresses which are observed in optically active models, during usage of active (1) and passive (2) posts One of disadvantages of active prefabricated posts is their high aggressiveness towards tooth tissues. During screwing of serrated post into dentinal walls there appear internal tensions, which may conduce cracks in dentine and fracture of root. On the fig. 20 there are presented tensions, observed in the models, made from optically active material, during usage of active (1) and passive(2) posts (N. V. Getman, 2004). Prefabricated metallic posts are used in dental clinics to reinforce devitalized teeth, in direct restorations with the use of filling materials and to build-up artificial core for further covering it by crown (fig. 21). Fig. 21. Indications for use of prefabricated metallic posts: 1 to reinforce devitalized teeth; 2 for direct restorations with the use of filling materials; 3 to build-up artificial core for further covering it by crown To build-up artificial core for the artificial crown amalgam can be used, as well as composite materials, some types of glass-ionomer cements, reinforced with metal. For metal posts fixation, zinc-phosphate cements, GIC and composite cements can be used. On the fig. 22 there is presented sequence of composite build-up making with the use of prefabricated post Fig. 22. sequence of composite build-up making with the use of prefabricated post: 1 defect of a crown part of a tooth; 2 root canal preparation with the help of calibrated broaches, corresponding to the prefabricated post size; 3 preparation

11 of a platform in dentine by front cutter; 4 filling of a root canal with luting agent; 5 introduction of an active post into root canal with the use of special tools; 6 building-up an artificial core with the use of filling material and shaping it as a prepared tooth stump; 7 covering with a restorative crown. On the fig. 23 there is shown a sequence of a core build-up making with the use of prefabricated passive post and filling material Fig. 23. sequence of a core build-up making with the use of prefabricated metallic passive post and filling: 1 defect of a tooth crown; 2 preparation of root canal with the help of calibrated broaches, corresponding to the prefabricated post size; 3 prefabricated metallic post: 4 filling of a root canal with luting agent and fixation of post; 5 building-up an artificial core with the use of filling material and shaping it as a prepared tooth stump; 6 covering with a restorative crown Fiberglass prefabricated posts Fig. 24. Prefabricated fiberglass posts and calibrated root broaches Prefabricated fiberglass posts appeared in 90 s and keep developing and gaining popularity up till nowadays, their shape and composition are improved. Convenience in work is provided by calibrated broaches which are supplied together with fiberglass posts (fig. 24). Fig. 25. Microscope structure of fiberglass post (Camillo D Arcangelo, 2005) Table 2 Comparative characteristic of elasticity modulus of hard tooth tissues and several constructional materials, used for manufacture of posts Fiberglass posts are manufactured from glass fibers (fig. 25.2), which are horizontally located and dipped into polymer matrix (Bis-GMA) (fig. 25.1). Weight rate of fibers and matrix varies within fiber posts of different manufacturers. Optimal combination of glass fibers and matrix which which is similar to tooth structure and at the same time which strength is similar to metal is till 75% fiberglass and 25% composite (till 40%). Fiberglass posts have unique physical properties. The bending breaking point of these posts is 560 МPа.

12 The force of 160 kg should be applied to break a fiber post of 1 mm diameter. Elasticity modulus corresponds to the one of hard tooth tissues. In the table 2 there are shown elasticity modulus indexes of hard tooth tissues and several constructional materials, used for manufacture of posts. Indications for application of fiberglass posts are same as for metallic prefabricated posts. Advantages of fiberglass posts: - biocompatible with tooth tissues; - decrease stress and riving loads onto root walls; - create monolithic structure with tooth tissues and composite luting agent; - allow to restore tooth stump or perform restoration at a single appointment; - are not prone to corrosion and discoloration; - good esthetic result of the restoration; - can be easily removed out of the root canal if necessary. Steps of making a core build-up with the use of fiberglass post are shown on the fig. 26. Preparation of root canal is started with a removal of filling material in the orifice with a round bur (fig. 26.1) or Gates Glidden. Further preparation of 2/3 of the canal is made with a drillbur (fig. 26.2). Widening of root canal is made with a special broach, supplied together with the prefabricated fiber post of the needed size (fig. 26.3). A fiber post of same marking as the used broach (fig. 26.5) is fit into the prepared root canal (fig. 26.4). Necessary length of the post is measured and the excess is cut off out of the oral cavity with a diamond disc (fig. 26.6). Preparation of luting agent and its inserting into canal is done according to manufacturer s instructions. Universal self-etching self-adhesive luting agents with automixing system and double polymerization mechanism are most conveninent to use (RelyX U200 Automix). A little quantity of luting agent is inserted into root canal (additional placing of cement onto post surface is possible) and fixation in the root canal is performed. After removal of cement excess the artificial core build-up is done with the help of special composite materials. The work is finished with processing of artificial core with abrasive instruments and shaping it as a prepared stump of a tooth (fig. 26.7). Chairside technique of artificial core build-up with the use of fiber post and filling materials allows to make impression in same appointment and proceed to fabrication of artificial crown. Fixation of crown on the build-up is the final of prosthodontics treatment (fig. 26.8). 4

13 Fig. 26. Sequence of core build-up with the use of fiberglass post