The document discusses post-core-crown restorations. It provides a historical background and summarizes key findings from studies on post length, diameter, form and failure rates. Threaded posts have the highest retention but also highest risk of root fracture. Parallel-sided posts have less retention but distribute stresses more evenly. At least 4mm of gutta-percha should remain at the apex. Post length is generally recommended to be 3/4 of the root length. Proper post diameter is 1/3 the root width or less.

1. Post-Core Crown Heading to a further clinical longevity of teeth

2. Post-Core Crown Historical Background Various methods of restoring pulpless teeth have been reported for more than 200 years. In 1747, Pierre Fauchard described the process by which roots of maxillary anterior teeth were used for the restoration of single teeth and the replacement of multiple teeth Posts were fabricated of gold or silver and held in the root canal space with a heat-softened called “mastic.”

3. Porcelain pivot crowns were described in the early 1800s by a well-known dentist of Paris, Dubois de Chemant One of the best representations of a pivoted tooth appears in Dental Physiology and Surgery , written by Sir John Tomes in 1849 5 Tomes’s post length and diameter conform closely to today’s principles in fabricating posts. Post-Core Crown Historical Background

4. POST AND CORE PLACEMENT TECHNIQUES 1. Post length 2. Post diameter 3. Anatomic/structural limitations 4. Type of post and core that will be used (prefabricated post and restorative material core or anatomically customized cast post and core) 5. Root selection in multirooted teeth 6. Type of definitive restoration being placed and its effect on core form and tooth reduction depths

5. Clinical failure rate of posts & cores Mean values 8years = 9% clinical failure Loss of retention & tooth fracture are the most common causes of post & core failures

6. Clinical Failure Rate of Posts and Cores Mean values † 6 yr 9 (196 of 2,220 9 (72 of 788) 1–69 mo Torbjörner, 1995 14 (8 of 56) 4–0 y Wallerstedt, 1984 8 (39 of 516) 1–10 y Mentink, 1993 11 (17 of 154) 3 y Hatzikyriakos, 1992 7 (9 of 138) 10 y or more Weine, 1991 9 (9 of 96) 5 y 9 Bergman, 1989 9 (36 of 420) 1–25 y Sorenson, 1984 12 (6 of 52) 5 y Turner, 1982 % Clinical Failure Study Length Lead Author

7. Clinical Failure Rate of Posts and Cores Tapered posts are the least retentive , threaded posts the most retentive & Parallel is intermediate

8. Post form & root fracture Threaded posts produce undesirable levels of stresses Henery Tapered threaded posts increase the root fracture by 20 times as parallel threaded posts Deutch Split threaded posts do not reduce stress associated with threaded pins Thoresteinsson posts designed for cementation produced less stress than threaded posts.

9. Clinical Failure of Posts and Cores Post form & root fracture When parallel-sided cemented posts have been compared with tapered cemented posts, stress testing results have generally favored parallel-sided posts. parallel-sided posts distribute stress more evenly to the root Henery

10. Post Form and Tooth Fracture Clinical Data (% of Post and Cores Studied That Failed via Tooth Fracture) Threaded Posts 7% Mean Parallel-Sided Posts 1% Mean Tapered Posts 3% Mean 5 Studies (Sorensons,Ross,Wallestedt,Linde & Morfis)

11. Post form & root fracture A parallel post ensures the greatest retention of the post within the canal, and is perhaps utilized with only the slightest loss of tooth structure to the internal wall of the canal. A smooth-surfaced post, although less retentive than either serrated or threaded post surfaces, transmits the least amount of force to the root structure. While both smooth and serrated posts are passive, in that they simply lie within the post space after being cemented, threaded posts actively engage the internal walls of the root canal as they are screwed in, and, while being the most retentive by far, produce such a force on the brittle root structure that they are contraindicated in most situations.

12. Post Selection The best design for a post to decrease the risk of failure is the narrowest & longest smooth, parallel post that one can fit into the post space .

13. Post-Core Crown The use of a post and core does not strengthen the tooth prior to restoration with a crown; rather, it may contribute to the weakening of the tooth structure, as the forces placed upon the future prosthetic crown and core are now transmitted along virtually the entire length of the brittle, endodontically treated tooth.

14. Do posts Improve Long-Term Clinical Prognosis Both laboratory & clinical data failed to provide definitive support for the concept that post strengthen endodontically treated tooth

15. Clinical failure rate of posts & cores Mean values 8years = 9% clinical failure

16. Types of post & core failures (of 100 failures Turner found ) Loosening (59 ) Apical Abscess (42 ) Dental Caries (19 )

17. When 4mm gutta-percha left 1 of 89 specimen showed leakage When 2mm gutta-percha left 32 of 89 specimen showed leakage (MJattison) Post apical end 2 studies found when 4mm gutta-percha left no leakage (Portell) When less than 3mm gutta-percha left significantly higher frequency of periapical radiolucencies (Kvist) When 4mm gutta-percha left no leakage (Raiden)

18. Post apical end 4-5 mm gutta-percha should be left

19. Basically, it is important to leave at least 5 mm of gutta percha at the apex of the root canal, because it is within the apical 5 mm of the root canal that 95% of lateral accessory canals split off from the main canal and anastomose with the exterior surface of the root. Should these lateral canals not be blocked with the gutta percha and the cement used to place the gutta percha, the chances of microleakage and percolation of microbes is drastically increased, thereby increasing the likelihood of an endodontic failure . Post apical end

20. the largest ideal diameter for a post is the diameter of the root at the most apical portion of the post space .

22. Tapered posts are the least retentive and threaded posts the most retentive in laboratory studies. Most of the clinical data support the laboratory findings.

23. Post Form and Tooth Fracture laboratory tests generally indicate that all types of threaded posts produce the greatest potential for root fracture When comparing tapered and parallel cemented posts, the results generally favor the parallel cemented posts.

24. WHAT IS THE PROPER LENGTH FOR A POST ? A wide range of recommendations have been made regarding post length, which includes the following: (1) the post length should equal the incisocervical or occlusocervical dimension of the 2) The post should be longer than the crown (3) the post should be one and one-third the crown length (4) the post should be half the root length (5) the post should be two-thirds the root length (6) the post should be four-fifths the root length (7) the post should be terminated halfway between the crestal bone and root apex (8) the post should be as long as possible without disturbing the apical

25. WHAT IS THE PROPER LENGTH FOR A POST ? Johnson and Sakumura determined that posts that were three quarters or more of the root length were up to 30% more retentive than posts half of the root length or equal to the crown length.86 Leary et al. indicated that posts with a length at least three-quarters of the root offered the greatest rigidity and least root bending.

26. WHAT IS THE PROPER LENGTH FOR A POST ? Abou-Rass . proposed a post length guideline for maxillary and mandibular molars based on the incidence of lateral root perforations occurring when post preparations were made in 150 extracted teeth.90 They determined that molar posts should not be extended more than 7 mm apical to the root canal orifice.

27. WHAT IS THE PROPER LENGTH FOR A POST ? When teeth have diminished bone support, stresses increase dramatically and are concentrated in the dentin near the post apex. A recent study established a relationship between post length and alveolar bone level. To minimize stress in the dentin and in the post, the post should extend more than 4 mm apical to the bone.

28. WHAT IS THE PROPER LENGTH FOR A POST ? Reasonable clinical guidelines for length include the following : (1) Make the post approximately three-quarters the length of the root when treating long-rooted teeth ; (2) when average root length is encountered, then post length is dictated by retaining 5 mm of apical gutta-percha and extending the post to the gutta-percha (3) whenever possible, posts should extend at least 4 mm apical to the bone crest to decrease dentin stress. (4) molar posts should not be extended more than 7 mm into the root canal apical to the base of the pulp chamber

29. WHAT IS THE PROPER POST DIAMETER post diameter is to not exceed one-third the root Diameter (Based on measuring the root dimensions of 1,500 teeth Each millimeter of increase (beyond one-third the root diameter) causes a sixfold increase in the potential for root fracture.)

30. WHAT IS THE PROPER POST DIAMETER Instruments used to prepare posts should be related in size to root dimensions to avoid excessive post diameters that lead to root perforation Safe instrument diameters to use are 0.6 to 0.7 mm for small teeth such as mandibular incisors and 1 to 1.2 mm for large diameter roots such as the maxillary central incisor. Molar posts longer than 7 mm have an increased chance of perforations and therefore should be avoided even when using instruments of an appropriate diameter.

31. Mechanical Aspect of PCR Stressing capability of posts. Retention of posts. Posts & Restorative materials. Anatomical Aspect of PCR Foundation Anatomy of the root . Radiographs. Inclinations. Anatomical anomalies

32. Mechanico-Anatomical Aspect of Posts Maxillary Centrals favorable for posts (Anitrotational required). Maxillary Laterals tapered post only indicated. Maxillary Cuspid Ideal for posts tapered post & sided parallel (Anitrotational required). Maxillary first Premolars is not advisable to mechanically widen the canal ( use smallest post ) U-shaped parallel can be used. Maxillary first Premolars is favorable for posts sided parallel is most indicated & tapered post are least indicated. Maxillary 1 st & 2 nd Molar, palatal root is favorable for posts sided parallel is most indicated , it is unadvisable for the buccal roots Maxillary 3 rd Molar has unpredictable root study carefully before.

33. Mechanico-Anatomical Aspect of posts Mandibular Centrals only the smallest tapered post (Anitrotational required) Mandibular Laterals the same as centrals with better accommodation. Mandibular Cuspid one of the most suitable for posts prime indication for tapered post. (Anitrotational required). Mandibular first Premolars much more suitable for posts, sided parallel is most indicated Mandibular 2 nd Premolars is more stronger favorable for posts (Anitrotational is not required) Mandibular 1 st & 2 nd Molar, the distal root is favorable for posts, be careful of sided parallel or not because of perforation tendency. Mandibular 3 rd Molar has unpredictable root study carefully before.

34. POST AND CORE PLACEMENT TECHNIQUES

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