CONNECTORS AND SOLDERS IN FIXED DENTAL PROSTHESIS

Connectors in fixed prosthodontics,the portion of the fixed partial denture that unites the retainers and pontic . Rigid connectors are the portion of fixed partial denture that joins the individual retainer and pontic together as complete restoration.

1. CONNECTORS AND OTHER SOLDER JOINTS Dr Athira Krishna K Senior lecturer Department of prosthodontics Sree anjaneya institute of dental sciences

2. INTRODUCTION Connectors in fixed prosthodontics,the portion of the fixed partial denture that unites the retainers and pontic . Rigid connectors are the portion of fixed partial denture that joins the individual retainer and pontic together as complete restoration.

3. TYPE OF CONNECTORS 1. Rigid connector- They are the ideal choice of connectors for F.P.D’s. They provide maximum rigidity and accurately transfer occlusal forces to abutment teeth . 2. Non rigid connector- They are usually used for pier abutments due to differences in physiologic tooth movement and difference in arch position of abutment. It provides a scope for flexing of mandible during opening and closing movements but it is technically sensitive.

4. pier abutments A frequent clinical situation, either in the maxillary or mandibular arch, is of a missing first premolar and first molar, resulting in fixed partial denture design in which the canine and the second molar act as terminal abutments and second premolar act as a pier abutment. It has been postulated that the tendency of terminal abutments to intrude during function results in a unbalanced movements, where the pier abutment act as a fulcrum. These movements will eventually result in debonding of the less retentive terminal retainer. In order to overcome this potential risk, utilization of non rigid connectors has been advised.

5. The movement in a non-rigid connector is enough to prevent the transfer of stress from segment being loaded to the rest of the FPD. The most commonly used non rigid connector consists of a T-shaped key that is attached to the pontic and a dovetail key way placed within the retainer

6. CLASSIFICATION OF CONNECTORS: 1 . RIGID CONNECTOR: A: cast connector B: soldered connector C: welded connector 2. NON RIGID CONNECTOR: A:dovetail or key-key ways- precision attachment. Semi-precision attachment . B: split pontic C: cross-pin and wing

7. Connectors for provisional restorations: - The connectors for provisional restorations should be carefully fabricated due to the low strength of the material usually used. They should be slightly overcontoured for increasing strength. Decrease the sharpness at the junction this relieves the stress concentration which may lead to fatigue failure of restoration. Use high strength materials such cast metals, heat-processed resin fiber reinforced.

8. RIGID CONNECTORS: A cast ,soldered ,or fused union between the retainers and pontic . Rigid connections in metal can be made by the following : 1. casting 2. soldering 3. welding

9. PRINCIPLES OF CONNECTOR DESIGN The connector design determines the success of F.P.D to a certain extent. The factors to be observed while fabricating a connector are: - • Type of connector -Rigid connector -Non-rigid connector. • Size of connector • Shape of connector

10. SIZE OF CONNECTOR The size of connector is important in maintaining the periodontal health of the abutment teeth. The recommended occusogingival height of connector is, ideally 3-4 mm. It should be sufficiently large to prevent distortion /fracture during function. It should not be too large which interfere with effective plaque control.

11. SHAPE OF CONNECTOR Connector’s should have a concave shape mesiodistally (appear as meniscus) and Convex buccolingually . In cross section it appears as ellipse. For effective functioning the long axis of ellipse should be parallel to direction of force, this leads to encroachment of gingival embrasure, so usually the long axis of ellipse is placed perpendicular to long axis of force. It should be highly polished. For anterior teeth connector should be placed lingual and use of large connector /inappropriately shaped connector result in display of metal leading to esthetic failure of F.P.D

12. CLASSIFICATION OF CONNECTORS Rigid connectors- i . Cast connectors ii. Soldered connectors iii. Welded connectors iv. Loop connectors Non rigid connectors i . Key & keyway (dovetail) ii. Split pontic iii. Cross pin and wing

13. RIGID CONNECTORS

14. CAST CONNECTORS They are commonly used type of connector, simple in processing. They are usually indicated for 3-unit F.P.D, full veneer preparations. Contraindications: - 1. F.P.D’s more than 3 units 2. Partial veneer F.P.D’s

15. Preparation: - Cast connectors are prepared by waxing the interproximal area before reflowing the margins and investing the pattern. There should be 1 mm of gap between connector and gingiva.

16. Disadvantages: - 1. Difficulty in reflowing proximal margins. 2. Access for proximal margins impeded so removal of patterns from die is difficult. 3. Simple in fabrication but difficult in seating. 4. No opportunity to verify fit of individual retainers in mouth.

17. LOOP CONNECTOR: A simple solution to a complex prosthodontic dilemma In a loop connector fixed partial denture, the connector consists of a loop on the lingual aspect of the prosthesis that connects adjacent retainers and/or pontic . The loop may be cast from sprue wax that is circular in cross section or shaped from platinum-gold-palladium ( Pt -Au- Pd ) alloy wire.

18. SOLDERED CONNECTORS Soldering - is joining of 2 metal parts using a filler metal with melting point <4500 C Brazing - is joining of 2 metal parts using a filler metal with melting point >4500C But for theoretical purposes brazing is regarded as soldering. The most common connector after cast connectors are soldered connectors. They are commonly indicated for F.P.D’s more than 3 units; when F.P.D’s with cast connectors are exhibiting high marginal discrepancy, repair of fractured connectors.

19. Hong So Yang et al (1999): - studied the stress levels in the teeth and supporting structures of F.P.D and alteration of stress with addition of multiple abutments (finite element analysis study) They found that – 1. Increased number of abutments did not solve the mechanical problems of long span F.P.D. 2. High stress concentration was found at connector (215.8-298.9 kg /cm 2) 3. The connector material should nave high yield strength and rigidity. 4. Connectors in long span FPD’s should be of greater dimensions.

20. NON RIGID CONNECTORS

21. NON RIGID CONNECTORS: Non rigid connectors are indicated to relieve the stress which is associated with pier abutments. It relieves stress at midspan on long pontics and tilted abutment cases. Non rigid connectors are indicated when it is not possible to prepare two abutments for an FPD with a common path of placement. In the mandibular arch,non rigid connectors are indicated when a complex FPD consists of anterior and posterior segments . Non rigid connectors are fabricated through incorporation of prefabricated inserts in the wax pattern or through custom milling procedures after the first casting have been obtained. The second part is then custom fitted to the milled retainer and cast. They are often made with prefabricated plastic patterns. the retainers are then cast separately and fitted to each other in metal.

22. TYPES OF NON RIGID CONNECTORS: 1 . dovetail (key – keyways) 2. splitpontic ( connectors inside the pontic ) 3. cross pin and wing

23. The indications for the use of non rigid connector in fixed prosthodontics • The existence of pier abutment, which promote a fulcrum‑like situation that can cause the weakest of the terminal abutments to fail and may cause the intrusion of the pier abutment • The existence of the malaligned abutment, where parallel preparation might result in devitalization . Such situation can be solved by the use of intracoronal attachments as connectors • The presence of mobile teeth, which need to be splinted together with fixed prosthesis • Long‑span FPDs which can be distort due to shrinkage and pull of porcelain on thin sections of framework and thus , affect the fitting of the prosthesis on the teeth.

24. Contraindication for non- rigid connector • If the abutment presents significant mobility • If the span between the abutments is longer than one tooth, because the stresses transferred to the abutment tooth under soldered retainer would be destructive • If the posterior retainer and pontic are opposed by a removable partial denture or an edentulous ridge while the two anterior retainers are opposed by natural dentition.

25. Advantages of non rigid connectors they , transmit shear stresses to supporting bone rather than concentring them in connectors. It minimizes mesiodistal torquing of abutments and allow them to move independently . Disadvantage of non rigid connectors are: ( 1) More tooth reduction of pier abutment (2 ) Increased laboratory time and expense. ( 3) In the absence of occlusal stability some, key have been observed to lift off from their keyway

26. DOVETAIL:precision & semiprecision When a fixed partial denture is fabricated with a non rigid connector, it is necessary to align the path of insertion of the key way with that of the distal abutment. This technique is best suited for relieving stress at midspan on long pontics . Precision attachments are small interlocking devices to connect prosthesis and abutments

27. Precision attachment can be described as a retainer used in fixed and removable partial denture construction consisting of a metal receptacle and a closely fitting part, the former is usually contained within the normal or expanded contours of the crown of the abutment tooth, and the latter is attached to a pontic or to the denture frame work . First component or matrix is a metal receptacle or keyway, which is positioned within the normal clinical contours of a cast restoration placed on the attachment or the second component of patrix , is attached to the removable partial denture. They are designed to replace occlusal rest, bracing arm, and retaining arm of the conventional clasp retained partial denture.

28. Indications  Movable joints in fixed movable bridge work.  As stress breaker in free end saddles and bridges.  Intracoronal attachments as effective direct retainers for removable partial dentures.  As a connector for sectional dentures.  Sections of a fixed prosthesis may be connected with intra coronal attachments .  To lock a connector joining saddles in the opposite side of the arch.  As contingency devices for the extension or conversion of existing dentures.  Where fixed dentures are contraindicated due to periodontal condition.  In the esthetic zone where extracoronal direct retainer adversely affects the esthetics

29. ADVANTAGES  Cross arch load transfer/force transmission and prosthesis stabilization may also be improved with attachments particularly when rigid precision attachments are used.  Lateral forces in the abutment during the insertion and removal are Eliminated Precision attachments provide better vertical support and better stimulation to the underlying tissue through intermittent vertical massage  In case of distal extension base, removable partial denture prosthesis attachment positioned between the abutment and extension bases ,as these attachments permit vertical, horizontal/rotational movement of the denture bases during function relative to the abutment.

30. Semi precision attachment Semi precision attachment (laboratory-made or custom-made types): components usually originate as prefabricated or manufactured patterns (made of plastic, nylon , or wax) or hand waxed.

31. According to their relationship to the abutment teeth Intracoronal /internal attachment: If the attachment resides within the body/normal contours of the abutment teeth. Extracoronal /external attachment: If the attachment resides outside the normal clinical contours of the abutment crown/teeth. Radicular/ intraradicular stud type attachments: These attachments are connected to a root preparation. The female or male is soldered or cast to a root cap coping.

32. SPLIT PONTIC: This is an attachment that is placed entirely within the pontic . It is particularly useful in tilted abutment cases where the use of a conventional dovetail would necessitate the preparation of a very drastic box in the distal aspect of the pier abutment. splits the pontic and acts as a stress breaker .

33. CROSS – PIN AND WING: The cross pin and wing are the working elements of a two piece pontic system that allows the two segments to be rigidly fixed after the retainers have been cemented on their respective abutment preparations. The design is used primarily to accommodate abutment teeth with disparate long axes. The path of insertion of each tooth preparation is made to parallel the long axis of that tooth. The distal retainer and wing are cemented first. The retainer- pontic segment is seated last. .

34. The retainer with the wing is cemented first, followed by the retainer- pontic segment. The pin is seated in the hole with a punch and mallet. A tapered pin is driven through the pontic , the wing, and back out through the pontic . Completed cross-pin and wing fixed partial denture

35. Designing of connectors The size, shape and position of the connectors will all determine the influence the success of the fixed partial denture. Connectors must be sufficiently large to prevent distortion or fracture of the bridge during function. But too large and bulky connectors will interfere with effective plaque control and lead to periodontal problems over time. Hence adequate access must be made to be available for the access of the oral hygiene aids cervical to the connector. Inciso-cervically bulky connectors will adversely affect this access . Large and inappropriately shaped connectors will also lead to metal exposure and compromised aesthetics of the restoration .

36. Hygiene considerations : Mesio -distally the connectors must produce a smooth transition from one component to the other. Tissue surface of the connectors must be highly polished and curved facio-lingually to facilitate cleansing and to thereby prevent plaque accumulation. The connectors should occupy the normal anatomic inter-proximal contact areas because encroaching into the buccal , lingual, incisal and gingival embrasures can result in restricted accessto the plaque control measures. Too large, bulky connection will interfere with efficient plaque control measures . Hence, inciso-cervically connectors should not be bulky.

37. Biologic considerations The pulp size and crown height are the limiting factors for the placement of non-rigid connectors as the pre-fabricated patterns require the preparation of box in the retainers. Since ideal thickness of the box in difficult to achieve, a 3 to 4 mm vertical height of the box is considered adequate and recommended by most of the manufacturers of the plastic patterns. However to improve the aesthetics without compromising on the hygiene considerations , connectors in the anterior region are placed slightly towards the lingual side.

38. Mechanical considerations: The bucco -lingual cross section of the connector must have an elliptical shape. This is considered to be the strongest shape for the connection if the major axis of the ellipse parallels the direction of the applied force. This might not be possible to achieve in all cases due to anatomical factors. Due to space constraints, most of the connectors have their greatest dimension perpendicular to the direction of the applied force which thereby results in a weak connection.

39. Aesthetic considerations Large inappropriately designed connectors will lead to metal exposure and compromised aesthetics. Connectors should occupy the normal anatomic inter-proximal contact areas. Slight lingual placement can improve the aesthetics

40. connector failure The main causes of connector failure:- - Improper design - Weak framework - Incomplete flow /crystallization of the soldered joints. - Porosities can result in either soldered/ cast connectors that may lead to failures.

41. CONCLUSION Every part of the prosthesis has its own role in the long-term success. The connector also plays a vital role in the success of the prosthesis. The design features of the connector are to be kept in mind while fabricating the prosthesis

42. solders

43. soldering Soldering is the process of joining metal using an intermediate metal alloy whose melting temperature is lower than that of the solidus temperature of the metal to be joined . Metal to be joined is parent metal and metal used for joining parent metal is solder or filler metal . The parts to be joined are not melted during soldering , but must be thoroughly wetted by liquefied solder/ filler metal .

44. brazing Soldering is similar to brazing. Solder melt at temperature below 840 degree F(450 degreee C) and in brazing filler materials melt at temperature above this point . Soldering operation at or above 450 degree C is generally termed brazing.

45. welding Welding is the process of joining two pieces of similar metals without addition of another metal . Welding has a very limited use in prosthodontics. It is usually used to join flat surfaces like bands and brackets, in pedodontics to weld bands and other appliances, in prosthodontics to join wrought wire clasps and repair of broken metal partial dentures. .

46. Commonly used dental solders are: - 1 ) Gold solders- Composition: - Gold –49-73%-corrosion resistance Silver –17.5 –9%- flow Copper –23-12.5% Tin-4.5-2.5 % Zinc –6.0- 3.0% Fusion temperature of gold solders –780-8300c They are commonly used with gold alloys

47. 2) Silver solder: - Composition – Silver Copper Zinc&cadmium-decrease the fusion temperature. Fusion temperature is 600-7500 c They are commonly used for base metal alloys

48. Soldering Investment Composition of soldering investment is similar to routinely used gypsum and phosphate-bonded investment. But the refractory component used is fused quartz. It shows least thermal expansion.-<0.1% at temp >7000 c.

49. FLUX A flux is a powerful reducing agent. Its purpose is to facilitate “wetting” of the parent metal by the molten solder by preventing oxidation and by dissolving and removing surface oxides that form during the soldering operation . ANTIFLUX An antiflux acts to limit the flow of solder on clean metal surfaces. A layer of graphite (C), whitening (ZnO2), or rouge (Fe2O3) can be applied over the parent metal/alloy, where appropriate, for this purpose.

50. Flux is placed on the surfaces to be soldered before they are heated. Fluxes may provide surface protection , reduce oxides, or dissolve oxides. Flux is displaced by solder, which then can form an interface with and bond to the surface being soldered. Soldering fluxes for noble metals are based on borate compounds. They form low-fusing glasses that protect the metal surface, and they also reduce oxides such as copper oxide. They often are too fluid for preceramic soldering. Fluorides are used on base metal alloys to dissolve the stable oxides of chromium, cobalt, and nickel. In addition toacting as solvents, these fluxes also serve a protective role

51. Antiflux is a material used to outline the area to be soldered in order to restrict the flow of solder. The most common antiflux is the mark of a soft graphite pencil, which works best on surfaces that do not have a high polish. Polishing rouge (iron oxide) suspended in chloroform can also be painted around the area of the solder joint to prevent undesired spread of the solder.

52. Soldering Flux (Flow) They are used to provide a clean surface for soldering and increase wetting of solder they are available as powder, liquid and pastes. Types of fluxes: - 1. Surface protective – cover metal surface and prevent access to oxygen. 2. Reducing agent –reduces any oxides present 3. Solvent –dissolves and carry away any surface oxides present.

53. Commonly used soldering fluxes are Borax Flux: - (Na2 B4 O7) it is commonly used for pre soldering, as they are too fluid in nature. They have type I and II function. They are used with noble metal alloys due to high affinity for copper Composition; - Borax glass – 55% Boric acid –35% Silica-10% Fluoride Flux: - They are used with base metal alloys. They are available as powder, liquid and pastes. They dissolve Co,Cr,Ni oxides Composition: - Borate Fluoride.

54. Soldering Antiflux They limit spread of solder to unwanted areas. Commonly used antifluxes are: Graphite –economical & evaporates at high temperature. Iron oxide (rouge) +turpentine –it is painted on casting with small bristle brush.

55. APPLICATION OF SOLDERING IN PROSTHODONTICS: 1 . Assemble long span fixed partial dentures. 2. Joining wrought wire clasps arms to cast partial dentures framework. 3. Joining precision attachments. 4. Joining sections of metal superstructure for implant supported restorations etc. 5. To overcome distortion in multiunit cast fixed prostheses,. 6. Repair of perforated crown and bridges. 7. Develop contacts points in crown. 8. Cutting and rejoining of ill fitted distorted bridge.

56. Dental solder should be: Corrosion resistant. Restorations, such as fixed partial dentures, which are permanently placed in the mouth, require the use of a solder of high fineness to resist corrosion. The minimum fineness that should be used is 580 fine, and a higher number would be better for preventing tarnish and discoloration . Lower fusing than alloy. The solder should possess a fusion temperature that is about 60°C (100 to 150°F) below that of the metal being soldered. Nonpitting . Pitting in solder is not desirable. More pitting occurs when there is an increased amount of base metal in the solder, which may vaporize when the gap between the components is too narrow or when the solder is overheated.

57. Strong. Solder should be as strong as the alloy with which it is used. The hardness of the solder decreases as the fineness (gold content) increases . Free-flowing. The solder should flow freely. Silver in the solder tends to make it adhere to metal and to flow more freely. Copper, on the other hand, makes it more sluggish. Solders that melt at higher temperatures have a lower surface tension and flow easily through narrow gaps. Low-fusing solders flow poorly through narrow gaps. Same color . The color of the solder should match that of the alloy being soldered.

58. The soldering procedures to be considered are: Gold alloy fixed partial denture soldering Adding proximal contact Repairing casting voids Breaking solder joints Preveneer metal-ceramic alloy soldering ( presolder ) Postveneer metal-ceramic alloy soldering ( postsolder )

59. SOLDERING TECHNIQUES 1 . Indexing/connecting 2. Investment 3. Joint configuration 4. Gap width 5. Assembly heating/cooling

60. Indexing/connecting For soldering three-unit posterior fixed partial dentures An index of the relationship of the fixed partial denture components in the patient’s mouth. This provides for the most accurate relationship between the retainers and between each retainer and its abutment tooth. The index must accurately maintain that relationship until the parts of the fixed partial denture have been embedded in soldering investment.

61. If the fixed partial denture will not completely seat after routine adjustments have been made, a thin (0.009-inch or 0.23- mm) separating disk (Ultra disks, Dedeco ) is used to cut through one connector, and then the separate pieces of the fixed partial denture are tried back in the mouth. Harper and Nicholls compared the 3D distortion caused by various indexing media. They concluded that ZOE bite registration paste was the most accurate indexing method, plaster and Duralay resin were less accurate sticky wax least accurate .

62. The provisional restoration is removed from the patient’s mouth, and it is confirmed that there are no traces of temporary cement left on the tooth preparations. The single retainer is tried in first, then the retainer- pontic combination The occlusion is adjusted with green stones or other appropriate abrasives .

63. T he two surfaces to be soldered are parallel piece of utility wax ,solder joint area strip of boxing wax is wrapped around the index.

64. Facial and lingual notches are carved in the investment. Flux is placed in the solder joint area. Solder is placed into the lingual notch. The flame is directed against the facial side of the investment and into the facial notch when the block is hot enough for soldering.

65. Soldering The invested castings should be preheated to ensure even heating. If the castings are not preheated, the uneven heat distribution that will occur when the blowpipe is applied to a cold block may produce distortion of the finished joint . Two or three 2 × 3–mm pieces of solder, covered with flux, are wedged into the lingual embrasure of the joint area . They will be melted by the heat of the castings. Quenching shortly after soldering will produce thermal stresses that will result in distortion, The investment is removed after placing it in water.

66. The invested fixed partial denture is allowed to bench cool for 5 minutes and is then quenched, distortion should be minimized. This allows time for the gold and solder to respond to an ordering heat treatment, which will increase hardness and strength while reducing elongation. If it is too bulky, it can be trimmed down with a carborundum disk . The fixed partial denture is ready to be finished and tried in the patient’s mouth.

67. Adding Proximal Contacts The addition of solder to a proximal contact area is done to build up a contour that may be deficient for any number of reasons. It can easily be done freehand on a single restoration. A fixed partial denture must be invested before the addition.

68. Repairing Casting Voids There are some deficiencies in casting that can be repaired by soldering. Blowholes ( ie , voidsextending all the way through a casting on an axial surface) and pits that do not extend all the way through are candidates for solder repairs . Solder should not be used to repair : Deficient margins. It is impossible to get an acceptably adapted margin by adding solder. Occlusal holes. Holes in the occlusal surface cannot be successfully soldered because of the risk of solder running over the entire surface. Aside from the technique difficulties, the presence of a hole on the occlusal surface of a crown is usually symptomatic of inadequate occlusal reduction in the preparation.

69. Heat Source It is needed to melt the filler metal. Different type of heat source used are: - 1 ) Flame 2) Oven 3) Infrared light.

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