screwretainedvscementretainedprosthesis-230912073015-e50c6d82.pptx

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1. Screw vs cement retained prosthesis

2. Contents Introduction Screw retained prosthesis Advantages Disadvantages Screw loosening Cement retained prosthesis One piece abutment Two piece abutment

3. Screw versus cement retained prosthesis Ease of fabrication and cost Passivity of the framework Retention Occlusion Esthetics Delivery Retrievability

4. Summary Conclusion References and Bibliography

5. Introduction

6. Screw retained implant prosthesis: Screw-retained prostheses have a well-documented history of successful application in completely edentulous patients. As noted in the literature, “Screw-retained implant restorations have an advantage of predictable retrievability but demand precise placement of the implant. Screw retained versus cement retained prosthesis

7. However, with the increase in treatment of partially edentulous patients, new restorative concepts have evolved in the field of implant Prosthodontics. In screw-retained restorations, the fastening screw provides a solid joint between the restoration and the implant abutment which can be easily retrivable . Screw retained versus cement retained prosthesis

8. Advantages • Easily Retrievable • Low profile retention • Limited crown height space • No cement in soft tissue peri implant area • Retention even for small dimensions

9. Disadvantages Disadvantages: • Screw loosening under final prosthesis • Fracture • Device not sealed (bacterial growth) • Non passive castings • Increased risk of porcelain fracture • Less esthetic restorations • Access difficult • Increased cost

10. Potential Problems of Screw Retained Prosthesis • Chronic screw loosening • Costly • Time consuming Chronic Screw Loosening The screw loosens only if outside forces trying to separate the parts are greater than the force keeping them together.

11. Implant Screw Mechanics: To understand how screws can be safely kept tight, one must understand why screws become loose. When two parts are tightened together by a screw, this unit is called a screw joint . The screw loosens only if outside forces trying to separate the parts are greater than the force keeping them together. Forces attempting to disengage the parts are called joint separating forces. The forces keeping the parts together are called as clamping forces.

12. Methods to limit loosening include: • Preloading the screw • Use of a mechanical torque wrench • Accurate framework • Proper component fit • Sufficient number of implants Screw retained versus cement retained prosthesis 12

13. Cement retained prosthesis

14. Cement retained implant restorations: Cement-retained prostheses have become, the restoration of choice for the treatment of implant patients. This evolution started after a modification of the abutment, i.e. fabrication of customized abutments to overcome esthetic and angulation problems.

15. Lewis and coworkers in 1988 were the first to describe a new technique for the fabrication of implant-supported restorations made directly on Brånemark System implants (Nobel Biocare , Göteborg , Sweden), without the use of traditional transmucosal abutment cylinders, so as to overcome limited interocclusal space problems.

16. In 1989, Lewis and associates described the fabrication of telescopic crowns on customized abutments made from UCLA abutments to solve problems with implant angulation .

17. Currently, there are numerous pre-machined cement-retained abutments, as well as preparable titanium and ceramic abutments. These abutments can be further modified in the mouth to accommodate soft tissue changes.

18. Two broad categories of abutments are used for cement retained restorations. A single unit abutment (one piece abutment) Two piece abutment.

19. One piece abutment for cement retention: The one piece abutment for cement is often the abutment of choice for single unit restorations.

20. Advantages of one piece abutment: No torque wrench needed. Stronger. No screw loosening. Easy complete seating. No need to retighten under restoration. Less expensive. Thicker walls to allow great freedom of preparation.

21. Disadvantages: Only for single abutments. Limited flexibility for angulation correction. Weaker for fracture. Not retrievable.

22. Two piece abutment for cement retention: two-piece abutment refers to an abutment system where the abutment and implant coonection screw are separate components.

23. Advantages of Cement Retained Prosthesis Passive Casting Axial loading Esthetics and hygiene Occlusal material fracture Access Fatigue Progressive loading Abutment crown crevice Cost and time

24. Disadvantages: Screw loosening. Abutment loosening under restoration. Torque and counter torque devices needed for preload. Proper seating with radiograph must be checked. Thinner walls limits freedom of preparation.

25. Screw Vs Cement implant restorations:

26. The factors that are influenced by different methods of fixation of the prostheses to the implants are: Ease of fabrication and cost Passivity of the framework Retention Occlusion Esthetics Delivery Retrievability

27. Ease of fabrication and cost: The fabrication of cement-retained prostheses is easier than that for screw-retained prostheses. The components used for this type of restoration are less expensive and does not require special training for technician. The screw retained restorations for same incidence is not simple as it is technique-sensitive and demanding.

28. Passivity of frame work: The possible complications of non-passively fitting frameworks can be categorized into 2 groups: Biologic complications: increased transfer of load to the bone, bone loss, and development of micro flora at the gap between the implant and the abutment. Prosthetic complications: loosening or fracture of the fastening screw.

29. The fabrication of implant-supported restorations requires many clinical and laboratory procedures that must be very precise. Each stage in the fabrication procedure can incorporate a small error, which will contribute to a positional distortion of the prosthesis.

30. Possible distortion can occur during the impression procedure, during fabrication of the master cast, during fabrication of wax patterns, during investing and casting procedures, during firing of the porcelain, or during delivery of the prosthesis.

31. A truly passive screw retained dental restoration is virtually impossible to fabricate. Screwed restorations may create permanent strain on implants that can be 2to3 times greater than that of cemented prosthesis.  A passive fit is easier to accomplish in cemented restorations due to die spacers.

32. The die spacer creates an approximately 40 μm cement space, which compensates for laboratory distortions and permits a more passive casting. If the laboratory is utilizing CAD/CAM technology, the cement space can be adjusted based on the substructure.

33. Occlusal material fracture: Occlusal material fracture is more common with implants than natural teeth because of lack of periodontal stress relief with implants. A decreased incidence of porcelain or acrylic fracture of prosthesis has been observed with cement retained restorations compared with screw retained restorations.

34. In screw retained restorations, screw holes may increase stress concentration to the restoring material and more often leads to unsupported porcelain.

35. Accessibility: Access is more challenging in the posterior regions of mouth for insertion of screw retained restorations. The manipulation of small screws and screw drivers is far more time consuming and challenging than the preparation and cementation of restoration.

36. Fatigue: A long term complication of screw retained prosthesis is fatigue failure of screw components. The narrow diameter of prosthesis screws reduces its long term strength. Cemented prosthesis have no small diameter components such complications were not observed.

37. Abutment –Crown crevice: A screw retained prosthesis does not seal the abutment to crown interface or margin, which harbors bacteria in the crevice. The crevice may act as endotoxin pump, encouraging the proliferation of microorganisms in the sulcular region. A cemented crown seals the crown abutment connection and prevents bacterial penetration.

38. Retention: Retention certainly influences the lack of complications as well as the longevity of implant prostheses. The factors that influence retention of the cement retained restorations are surface area and height, roughness of the surface, and type of cement.

39. Roughness of surface: Roughness of axial walls offers greater retention to cemented prosthesis. Implant abutments can be roughened by using diamond bur or air borne particle abrasion.

40. Path of insertion: In ideal conditions the path of insertion of restoration should be slightly different from direction of occlusal load. If the fixed partial denture path of insertion is identical to direction of occlusal force then grater tensile forces were placed on the cement. So, ideal suggestion is that the path of insertion should be about 10 degrees divergent from the axial load of implant during occlusion to prevent dislodgement.

41. Type of cement: The cements used in fixed prosthodontics are either definitive or provisional. The definitive cements are used to increase retention and provide good marginal seal for the restorations. Provisional cements are used primarily for interim restorations to facilitate their removal. As no risk of decay for the abutments, provisional cements can also be used for the cementation of implant restorations, for easy retrivability .

42. Zinc phosphate cements have excellent properties for definitive implant restorative cement, have adequate working time and excess material can be removed without scratching the surface of abutment.

43. For screw-retained restorations, retention is obtained by the fastening screw, which connects the implant with the abutment and the abutment with the prosthesis. The screws most commonly used are the gold and the titanium. Retention is obtained by the friction resistance developed between the internal threads of the implant and those of the fastening screws.

44. In the case of titanium abutment screws, there can be slight damage of both the implant and the fastening screw threads, which results in their joining. This phenomenon is called galling. Gold abutment screws have a smaller coefficient of friction, allowing them to be tightened more effectively than the titanium without risking galling between the threads.

45. Occlusion: Occlusion is another factor affecting the selection of the restoration type-screw- or cement-retained. The bucco -lingual dimension of maxillary premolars and maxillary 1 st and 2 nd molars would be 9mm and 11mm. The occlusal table for above mentioned teeth is 4.5mm & 5-6mm. The heads of fastening screws have a diameter of 3mm, thus requiring screw access hole diameter of 3mm.

46. Esthetics: Esthetics is another factor to consider when deciding between screw-retained and cement-retained crowns. In anterior screw-retained crowns, the implant is placed lingually to allow screw emergence through the cingulum area.

47. An implant for an anterior cemented restoration is placed under the incisal edge. An angulated abutment is then used, which eliminates the ridge lap and replicates a more natural emergence profile.

48. In posterior screw-retained restorations, the access hole will exit through the central fossa of the prosthetic tooth. The cement retained crown obviously has no entrance cavity. Allowing the forces of occlusion to be distributed along the axial inclination, congruent with the long axis of the tooth, is easier.

49. Delivery: For screw retained restorations, only a radiographic examination is required to verify the precise fit of the prosthesis. However for cemented restorations, there is need for careful removal of cement remnants in addition with radiographic examination. The removal of cement residues is critical for peri -implant health.

50. Retrivability : The main advantage of screw retained prosthesis is retrievability . The crown is not only recoverable, but no damage occurs upon removal of the crown. In screw retained prosthesis, the access hole is covered with composite. To retrieve the screw retained prosthesis, the dentist must remove occlusal obturation , underlying cotton pellet and coping screw.

51. Once the prosthesis is reinserted, the screws may need to be changed and torqued . The main disadvantage of cemented prostheses is the difficulty of their retrievability . Although retrieval is needed less often because of the dramatically increased survival rates for dental implants, the need for future removal of FPDs should not be overlooked. For this provisional luting cements are being used.

52. Summary

53. Conclusion: It is to be stated that the decision to screw or cement retain abutments remain an individual choice for dentists. Clinicians should be aware of the limitations and is advantages of each type of prosthesis so as to select the one that is most appropriate for a given clinical situation.

54. Bibliography and references: Carl E. Misch ; Contemporary implant dentistry; 3 rd Edition.  Charles A. Babbush ; Dental implants art & science; 2 nd Edition.  Michalakis K.X, Hirayama .H; Cement retained versus screw retained implant restorations- A critical review; Int J Oral Maxillofacial implants 2003; 18; 719-728.  

55. W.Chee , Screw versus cemented implant supported Restoration, British dental journal volume 201 no. 8 Oct 21 2006 501 Hebel KS, Gajjar RC. Cementretained versus screw-retained implant restorations: achieving optimal occlusion and esthetics in implant dentistry.JPD 1997;77(1):20-35 Sanath shetty,Principles of screw‑retained and cement‑retained fixed implant prosthesis: A critical review;Journal of Interdisciplinary dentistry,2014

56. Giblin J; A Rationale for the successful retention of implant supported restorations- to screw or cement; Australian dental practice; 2009; 136-146. Roberta,Cement retained versus screw retained dental prostheses:A literature review;Dental press Implantology,April,2013