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Treatment Planning: Force Factors Related to Patient Conditions chapter6 Presented by:Dr.Ali Beygi Supervised by: Dr. Mansour Rismanchian And Dr.saied.

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Presentation on theme: "Treatment Planning: Force Factors Related to Patient Conditions chapter6 Presented by:Dr.Ali Beygi Supervised by: Dr. Mansour Rismanchian And Dr.saied."— Presentation transcript:

1 Treatment Planning: Force Factors Related to Patient Conditions chapter6 Presented by:Dr.Ali Beygi Supervised by: Dr. Mansour Rismanchian And Dr.saied Nosouhian Dental of implantology Dental implants research center Isfahan university of mediacal science 1

2 Treatment Planning: Force Factors Related to Patient Conditions chapter6 2

3 Biomechanical stress : significant risk factor in implant dentistry. dental force factor : risk of stress-related complications Different patient : different amounts of force in magnitude, duration, type, and direction several factors may multiply or increase the effect of these other conditions The initial implant survival, loading survival, marginal crestal bone loss, incidence of abutment or prosthetic screw loosening, and unretained restorations, porcelain fracture, and component fracture are all influenced by the force factors. 3

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5 NORMAL BITE FORCE The greatest natural forces exerted against teeth, and thus against implants, occur during mastication primarily perpendicular to the occlusal plane in the posterior regions, are of short duration, occur only during brief periods of the day, and range from 5 to 44 lb for natural teeth. time of chewing forces on the teeth is about 9 minutes each day The perioral musculature and tongue exert a more constant, yet lighter horizontal force on the teeth or on implants.These forces reach 3 to 5 psi during swallowing A person swallows 25 times per hour while awake and 10 times per hour while sleeping, for a total of 480 times each day. 5

6 natural forces against teeth are primarily in their long axis, less than 30 psi, and for less than 30 minutes for all normal forces of deglutition and mastication (Box 6-2) Forces of mastication placed on implant-supported bridges have been measured in a similar range as natural teeth. 6

7 The maximum bite force differs from mastication force, varies widely among individuals, and depends on the state of the dentition and masticatory musculature More recent studies indicate normal maximum vertical biting forces on teeth or implants can range from 45 to 550 psi The forces on the chewing side and the opposite side appear very similar in amplitude there are conditions that increase our risks of occlusal overload on the implant prosthesis. Most noteworthy are the parafunctional forces of bruxism and clenching 7

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9 PARAFUNCTION are characterized by repeated or sustained occlusion The lack of rigid fixation during healing is often a result of parafunction on soft tissue- borne prostheses overlying the submerged implant The most common cause of both early and late implant failure after successful surgical fixation is the result of parafunction. complications occur with greater frequency in the maxilla, because of a decrease in bone density and an increase in the moment of force 9

10 Nadler has classified the causes of parafunction or nonfunctional tooth contact into the following six categories: 1. Local 2. Systemic 3. Psychological 4. Occupational 5. Involuntary 6. Voluntary 10

11 Local factors include tooth form or occlusion, soft tissue changes such as ulcerations or pericoronitis. Systemic factors include cerebral palsy, epilepsy, and drug-related dyskinesia Psychological causes occur with the greatest frequency and include the release of emotional tension or anxiety Occupational factors concern professionals such as dentists, athletes, and precision workers, as well as the seamstress or musician who develops altered oral habits involuntary movement that provokes bracing of the jaws, such as during lifting of heavy objects or sudden stops while driving Voluntary causes include chewing gum or pencils, bracing the telephone between the head and shoulder, and pipe smoking. 11

12 Bruxism Bruxism is the most common oral habit. horizontal, nonfunctional, significant excess forces Bruxism may affect the teeth, muscles, joints, bone, implants, and prostheses. These forces may occur while the patient is awake or asleep and may generate increased force on the system several hours per day A study on bruxing patients with implants showed 80% of sleep bruxism occurred during light sleep stages but did not cause arousal. rarely have muscle tenderness when they are awake; and are usually unaware of their oral habit. In other words, nocturnal bruxism is sometimes difficult to diagnose." 12

13 The maximum biting force of bruxing patients is greater than average. Fortunately, the bite force does not continue to increase in most bruxing patients. When muscles do not vary their exercise regimen, their size and function adjust to the dynamics of the situation. As a result, the higher bite forces and muscle size usually do not continue in an unending spiral. 13

14 Diagnosis Bruxism does not necessarily represent a contraindication for implants, but it does dramatically influence treatment planning. The symptoms of this disorder, which may be ascertained by a dental history, may include repeated headaches, a history of fractured teeth or restorations, repeated uncemented restorations, and jaw discomfort upon awakening. A lack of these symptoms does not negate bruxism as a possibility. 14

15 The signs of bruxism include an increase in size of the temporal and masseter muscles (these muscles and the external pterygoid may be tender), deviation of the lower jaw on opening, limited occlusal opening, increased mobility of teeth, cervical abfraction of teeth, fracture of teeth or restorations, and uncemented crowns or fixed prostheses. However, the best and easiest way to diagnose bruxism is to evaluate the wearing of teeth Not only is this the easiest method to determine bruxism in an individual patient, it also allows the disorder to be classified as absent, mild, moderate, or severe (Figures 6-1 to 6-3). 15

16 No anterior wear patterns in the teeth signify an absence of bruxism. Mild bruxism has slight wearing of anterior teeth but is not a cosmetic compromise. Moderate bruxism has obvious anterior incisal wear facets but no posterior occlusal wear pattern. Severe bruxism has absent incisal guidance from excessive wear, and posterior wearing of the teeth is obvious. 16

17 Nonfunctional wear facets on the incisal edges may occur on both natural or replacement teeth, especially in the mandible and maxillary canines, and there may be notching of the cingulum in the maxillary anterior teeth. Isolated anterior wear is not much of a concern if all posterior teeth contacts can be eliminated in excursions. Tooth wear is most significant when found in the posterior regions and changes the intensity of bruxism from the moderate to the severe category. Posterior wear patterns are more difficult to manage, because this usually is related to a loss of anterior guidance in excursions; once the posterior teeth contact in excursive jaw positions, greater forces are generated 17

18 With incisal guidance and an absence of posterior contact, two thirds of The masseter and temporalis do not contract and, as a consequence, the bite force is dramatically reduced. posterior teeth contact the bite forces in excursions = during posterior biting. In severe bruxism, the occlusal plane, the anterior incisal guidance, or both may need modification Bruxing patients often repeat mandibular movements, which are different from border movements of the mandible and are in one particular direction( "pathway of destruction). As a result, the occlusal wear is very specific and primarily on one side of the arch, or even on only a few teeth (Figure 6-4). 18

19 This engram pattern usually remains after treatment. Establishment of incisive guidance on teeth severely affected by an engram bruxing pattern: complications on these teeth The most common complications on teeth restored in this "pathway of destruction" are porcelain fracture, uncemented prostheses, and root fracture. When implants support the crowns in the pathway of destruction the implant may fail, fracture, or have crestal bone loss, abutment screw loosening, porcelain fracture, or unretained restorations. 19

20 Bruxism changes normal masticatory forces magnitude (higher bite forces), duration (hours rather than minutes), direction (lateral rather than vertical), type (shear rather than compression), and magnification (four to seven times normal). anterior teeth wear + eruption overall occlusal vertical dimension remains unchanged. In addition, the alveolar process may follow the eruption of the tooth. As such, when the anterior teeth are restored for esthetics (or to obtain an incisal guidance), the reduced crown height cannot be increased merely by increasing the height of the crown to an average dimension. 20

21 Instead, the following guidelines are suggested: 1.Determine the position of the maxillary incisor edge of the anterior teeth acceptable (if eruption occurred as they wore) or need greater coronal length to correct related incisal wear. 2. Determine the desired occlusal vertical dimension. facial measurements, closest speaking space, physiologic rest position, speech, and esthetics. 21

22 The accelerated occlusal wear may cause a loss of occlusal vertical dimension (OVD). The OVD is rarely decreased when incisal guidance is still present, as the posterior teeth maintain the dimension and the anterior teeth have time to erupt because the forces are less and the wear rate is slower. 3. Evaluate and restore the position of the lower anterior teeth where necessary. In the past, several authors have stated that a reconstruction begins with the lower anterior teeth. The mandibular arch cannot be restored until the maxillary anterior teeth and occlusal vertical dimension are established. 22

23 Incisal guidance must be greater than the condylar disc assembly (the angle of the eminential) so the posterior teeth will separate during mandibular excursions. In patients with moderate to severe bruxism, the height of the vertical overjet and the angle of incisal guidance should not be extreme, as the amount of the force on the anterior abutments, cement seals, and porcelain is directly related to these conditions (Figure 6-5). In patients with severe bruxism, the intensity of the force should be reduced, because the duration of the force is increased. 23

24 When anterior tooth wear is accompanied by tooth eruption and maintenance of the occlusal vertical dimension, alveolar bone and cervical regions should be reduced and crown lengthening should be performed on the teeth before their restoration. most often necessary in the mandibular anterior region but may be observed in any region of the mouth after long-term severe bruxism endodontic therapy may be required to allow proper anterior tooth preparation. when the vertical dimension has been reduced Crown lengthening and associated procedures are not necessary : The restoration restores the occlusal vertical dimension and reestablishes anterior incisal guidance. 24

25 4. Determination of posterior plan of occlusion. This may be accomplished by using first the maxillary arch or the posterior mandibular arch. it is best if the same bilateral posterior quadrants are addressed at the same time, so that the posterior plane may be parallel to the horizontal plane. The maxillary posterior region is most often determined first in the completely edentulous patient. 25

26 Fatigue Fractures The increase in duration of the force fatigue curve number of cycles and the intensity 26

27 A bruxing patient is at greater risk of fatigue fractures for two reasons: magnitude of the forces increases over time as the muscles become stronger number of cycles increase on the prosthetic components. incisal guidance - higher forces with posterior contact during excursions, 27

28 No long-term prosthetic result is expected in patients with severe bruxism. the treatment plan is altered in an attempt to minimize the negative effect on the longevity of the implant, bone, and final restoration. 28

29 elements able to reduce stress 29

30 Occlusal Guards bruxism and occlusal disharmony Premature and posterior contacts during mandibular excursions increase stress conditions elimination of eccentric contacts recovery of periodontal ligament health and muscle activity within 1 to 4 weeks No study demonstrates an increase in parafunction after occlusal adjustment. 30

31 night guard as a useful diagnostic tool Michigan night guard even occlusal contacts in centric relation occlusion posterior disocclusion with anterior guidance. may be fabricated with 0.5 to 1 mm colored acrylic resin on the occlusal surface. After 4 weeks of nocturnal wear, if the patient wears this device for an additional month or more, the influence of occlusion on the bruxism may be directly observed. the colored acrylic is still intact : the nocturnal parafunction has been reduced or eliminated occlusal reconstruction or modification may proceed 31

32 If the colored acrylic on the night guard is ground through, an occlusal adjustment will have little influence on decreasing this parafunctional habit. The night guard is still indicated to relieve stresses during nocturnal parafunction, but the treatment plan should account for the greater forces 32

33 If the opposing arch is a soft tissue-supported removable prosthesis, the effects of the nocturnal habit may be minimized if the patient removes the prosthesis at night. night guard and fixed prosthesis : in order to transfer the weakest link of the system to the removable acrylic device 33

34 Unlike teeth, implants do not extrude in the absence of occlusal contacts in partially edentulous patients, the maxillary night guard can be relieved around the implant crowns so the remaining natural teeth bear the entire load. When the restoration is in the mandible, the occluding surfaces of the maxillary night guard are relieved over the implant crowns so no occlusal force is transmitted to the implants (Figure 6-8). 34

35 A mandibular posterior cantilever on a full-arch implant prosthesis may also be taken out of occlusion with a maxillary night guard. implant supported fixed prosthesis in posterior maxilla opposing mandibular teeth: a soft reline material is placed around the implant crowns When full-arch implant restorations are opposing each other, the night guard provides solely anterior contacts during centric occlusion and mandibular excursions. Thus the parafunctional force is reduced on the anterior teeth/implants and eliminated in the posterior regions. 35

36 Treatment Planning The implant treatment plan is modified primarily in two ways when implants are inserted in the posterior region: (1) additional implants that are wider in diameter (2) the anterior teeth may be modified to recreate the proper incisal guidance and avoid posterior interferences during excursions (opposing natural teeth or an implant or tooth supported fixed prosthesis) 36

37 (1) the elimination of posterior contacts effect of angled forces during bruxism (2) the presence of posterior contacts during excursions almost all fibers of the masseter, temporalis, and the external pterygoid muscles contract place higher forces on the anterior teeth/implants in the absence of posterior contacts : forces applied on the anterior implant-teeth system are reduced by as much as two thirds 37

38 Clenching constant force, Without any lateral movement habitual clenching position does not necessarily correspond to centric occlusion The jaw may be positioned in any direction before the static load; therefore a bruxing and clenching combination may exist The clench position most often is in the same repeated position and rarely changes from one period to another The direction of load may be vertical or horizontal are similar to bruxism in amount and duration ; however, several clinical conditions differ in clenching. 38

39 Diagnosis the signs for clenching are often less obvious The forces generated during clenching are directed more vertically to the plane of occlusion, at least in the posterior regions of the mouth Wearing : usually not evident ; therefore clenching often escapes notice during the intraoral examination Many of the clinical signs of clenching often resemble bruxism 39

40 clinical signs of clenching Tooth mobility muscle tenderness or hypertrophy deviation during occlusal opening limited opening stress lines in enamel cervical abfraction material fatigue (enamel, enamel pits, porcelain and implant components) 40

41 All these conditions may also be found in the bruxing patient. enamel wear has such a strong correlation to bruxism that it is the primary and often the only factor needed to evaluate or bruxism The clenching patient has the "sneaky disease of force." 41

42 Hyperactive muscles are not always tender tender muscles in the absence of trauma or disease is a sign of excess use or incoordination among muscle groups The lateral pterygoid muscle is more often overused by the bruxing or clenching patient but is difficult to palpate The ipsilateral medial pterygoid muscle : antagonist to the lateral pterygoid in hyperfunction and, when tender, provides a good indicator of overuse of the lateral pterygoid 42

43 Muscle evaluation for clenching also includes : deviation during opening the jaw, limited opening, and tmj tenderness Deviation to one side during opening indicates a muscle imbalance on the same side 43

44 Limited opening : muscular imbalance or degenerative joint disease normal opening : at least 40 mm from the maxillary incisal edge to the mandibular incisal edge in an Angle's Class I patient ( taking into consideration an overjet or overlap) horizontal overjet or overlap value in millimeters is subtracted from the 40-mm minimum opening measurement The range of opening without regard for overlap or overjet 38 to 65 mm for men 36 to 60 mm for women, from incisal edge to edge. 44

45 Increased mobility : force beyond physiologic limits, bone loss, or their combination The rigid implant may receive more occlusal force when surrounded by mobile teeth Fremitus is often present in the clenching patient is symptomatic of local excess occlusal loads. To evaluate this condition, the dentist's finger barely contacts the facial surface of one tooth at a time and feels for vibrations while the patient taps the teeth together. 45

46 Cervical erosion is primarily a sign of parafunctional clenching or bruxism (Figure 6-10) Black analyzed the eight most popular theories for gingival ditching of the teeth, finding all inconclusive. 46

47 Other signs of enamel or occlusal material fatigue include occlusal invaginations or pits, stress lines in enamel, stress lines in alloy restorations or acrylic (lines of Luder), and material fracture (Figures 6-11 and 6-12). Fremitus can be noticed clinically on many cervically eroded, nonmobile teeth 47

48 A common clinical finding of clenching is a scalloped border of the tongue (Figure 6-13). The tongue is often braced against the lingual surfaces of the maxillary teeth during clenching, exerting lateral pressures and resulting in the scalloped border. This braced tongue position may also be accompanied by an intraoral vacuum, which permits a clench to extend for a considerable time, often during sleep. 48

49 Fatigue Fractures clenching creep fracture of components Creep: increasing deformation related to constant load This condition may also occur in bone, which may result with implant mobility and failure 49

50 clenching versus bruxism Clenching affects the treatment plan in a fashion similar to bruxism. vertical forces are less detrimental than horizontal forces, and alteration of the anterior occlusal scheme is not as critical as with the bruxing patient. Night guards are also less effective. a hard acrylic shell and softer, resilient liner night guard, which is slightly relieved over the implants, is often beneficial to a clenching patient. 50

51 parafunction in a patient wearing a soft tissue supported prosthesis over a submerged implant premature loading micromovement of the implant body compromise osteointegration. pressure necrosis causes soft tissue dehiscence over the implant. prosthesis over the implant should be generously relieved during the healing period whenever parafunction is noted. 51

52 6-mm diameter hole through the metal substructure should be prepared (Figure 6-17). 52

53 Prosthetic Considerations progressive bone-loading techniques produce load-bearing bone Anterior implants submitted to lateral parafunction forces require further treatment considerations: Additional implants are indicated, preferably of greater diamete The excursions are canine guided if natural, healthy canines are present. Mutually protected occlusion : implants are in the canine position or if this tooth is restored as a pontic centric vertical contacts aligned with the long axis of the implant narrow posterior occlusal tables to prevent inadvertent lateral forces and to decrease the occlusal forces Enamoplasty of the cusp tips of the opposing natural teeth : direction of vertical force Clenching increases the risk of mechanical failure, such as porcelain fracture, uncemented restoration, abutment screw fracture, implant body fracture, and crestal bone loss (Figure 6-18). 53

54 TONGUE THRUST AND SIZE A force of approximately 41 to 709 g/cm2 on the anterior and lateral areas of the palate has been recorded during swallowing Six different types of tongue thrust anterior, intermediate, posterior, and either unilateral or bilateral may be in most any combination A common question is which came first, the aberrant tongue position or the misalignment of teeth 54

55 force of tongue thrust : lesser intensity than in other parafunctional forces horizontal in nature and can increase stress at the permucosal site of the implant. most critical for one-stage surgical approaches : implants are in an elevated position at initial placement and the implant interface is in an early healing phase. The tongue thrust may also contribute to incision line opening, which may compromise both the hard and soft tissues If the teeth exhibit increased mobility, the implant prosthesis may be subject to increased occlusal loads Evaluation of anterior tongue trust the patient is unable to swallow while the lower lip is withdrawn. 55

56 Evaluation of posterior tongue thrust The posterior tongue thrust may occur in patients wearing a maxillary denture opposing a Kennedy Class 1 mandibular arch, without a mandibular prosthesis replacing the posterior 56

57 lateral tongue thrust :complaint of inadequate room for the tongue once the mandibular implants are restored A prosthetic mistake is to reduce the width of the lingual contour of the mandibular teeth (often increases the occurrence of tongue biting ) The lingual cusp of the restored mandibular posterior teeth should follow the curve of Wilson and include proper horizontal overjet to protect the tongue during function 57

58 loss of teeth (Even in the absence of tongue thrust) tongue size increase This patient complains of inadequate room for the tongue and may bite it during function usually short-lived the patient eventually adapts to the new intraoral condition (Figure 6-22). 58

59 CROWN HEIGHT SPACE Definition ideal CHS needed for a fixed implant prosthesis : mm Includes : biological width, abutment height for cement retention or prosthesis screw fixation, occlusal material strength, esthetics, and hygiene considerations around the abutment crowns Removable prostheses often require greater than 12 mm denture teeth, acrylic resin base strength, attachments, bars, and oral hygiene considerations. 59

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61 Biomechanic Consequences of Excessive Crown Height Space Mechanical complication rates for implant prostheses are often the highest of all complications reported in the literature Implant body fracture may result from fatigue loading of the implant,but occurs at less incidence than most complications. Crestal bone loss,often occurs before implant body fracture Porcelain and occlusal material fracture Clips or attachment fractures Fracture of the framework or substructure 61

62 Force magnifiers situations or devices that increase the amount of force applied and include a screw, pulley, incline plane, and a lever CHS is a vertical cantilever when any lateral or cantilevered load is applied and, therefore, is also a force magnifier Direction of forces vertical contilevered or lateral forces ( direct relationship to the CH ) 62

63 Bidez and Misch evaluated the effect of a cantilever on an implant and its relation to crown height. 63

64 A cantilevered force may be in any direction: facial, lingual, mesial, or distal. Forces cantilevered to the facial and lingual direction are often called offset loads. edentulous ridge resorption : more lingual implant facial cantilevered restoration An angled load to a crown will also magnify the force applied to the implant. A 12-degree force to the implant will be increased by 20%. This increase in force is further magnified by the crown height( as in Maxillary anterior teeth that are usually at an angle of 12 degrees or more to the occlusal) 64

65 Most forces applied to the osteointegrated implant body are concentrated in the crestal 7 to 9 mm of bone, regardless of implant design and bone density. Therefore implant body height is not an effective method to counter the effects of crown height. The implant does not rotate away from the force in relation to implant length. Instead, it captures the force at the crest of the ridge. 65

66 The greater the CHS, the greater number of implants usually required for the prosthesis, especially in the presence of other force factors. 66

67 crestal bone loss CHS increases screw loosening, crestal bone loss, implant fracture, and implant failure 67

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69 Excessive CHS greater than 15 mm causes may include long term edentulism,genetics, trauma, and implant failure Treatment of excessive CHS before implant placement includes orthodontic and surgical methods. Orthodontics in partially edentulous patients is the method of choice, as other surgical or prosthetic methods are usually more costly and have greater risks of complications 69

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71 surgical techniques block onlay bone grafts particulate bone grafts with titanium mesh or barrier membranes Interpositional bone grafts, distraction osteogenesis 71

72 surgical techniques A staged approach to reconstruction of the jaws is often preferred Distraction osteogenesis has several advantages Vertical bone gains are not limited by factors such as graft size or expansion of the existing soft tissue volume There is no donor site morbidity Distraction osteogenesis requires patient compliance, and bone volume gains are unidirectional secondary bone augmentation procedures are often required for dental implant placernent. surgical techniques 72

73 Misch presented a unique approach combining vertical distraction and horizontal onlay bone grafting to reconstruct the deficiency threedimensionally. Osseous distraction is performed first to vertically increase the ridge and expand the soft tissue volume. Secondarily an onlay bone graft is used to complete the repair of the defect (Figure 6-29) 73

74 In case of excessive CHS, bone augmentation may be preferred to prosthetic replacement. reduce the CHS improve implant biomechanics Augmentation wider body implants with the associated benefit of increased surface area. when restoring excessive CHS gingival colored prosthetic materials (pink porcelain or acrylic resin) removable restoration In the maxilla, a vertical loss of bone results in a more palatal ridge position. As a consequence, implants are often inserted more palatal than the natural tooth position. 74

75 removable prosthesis does not require embrasures for hygiene. may be removed during sleep to decrease the effects of an increase in CHS on nocturnal parafunction. may improve the lip and facial support, which is deficient because of the advanced bone loss. may have sufficient bulk of acrylic resin to decrease the risk of prosthesis fracture 75

76 A rigid overdenture : identical requirements to a fixed prosthesis, because it is rigid during function. Misch describes the "hidden cantilever" beyond the cantilevered bar with a rigid implant overdenture. When the overdenture has no movement during function, the cantilever does not stop at the end of the cantilevered substructure but ends at the last occlusal contact position on the prosthesis, often the distal of a second molar The position and type of overdenture attachments may render an overdenture rigid during function :when three anterior implants are splinted together and a Hader dip is used to retain the prosthesis if the Hader clips are placed at angle to the midline angles to the midline limited movement rigid overdenture 76

77 Misch suggests the prosthesis movement, not the individual attachment movement, should be evaluated. The ideal CHS for a fixed prosthesis is between 8 and 12 mm 3 mm of soft tissue, 2 mm of occlusal material thickness, and a 5-mm or greater abutment height. a CHS greater than 12 mm may be of concern in fixed restorations. 77

78 The greater impact force on implants combined with the increased crown height, creates increased moment forces on implants and risks of component and material fracture. These problems are especially noted when associated with less favorable biomechanics on cantilevered sections of fixed restorations a CHS greater than 15 mm means a large amount of metal must be used in the substructure of a traditional fixed restoration to keep porcelain to its ideal 2-mm thickness (figure 6-31). 78

79 Controlling surface porosities of metal substructures after casting as their different parts cool at different rates becomes increasingly difficult. when the casting is reinserted into the oven to bake the porcelain, and the heat is within the casting at different rates, so the porcelain cools in different regions at different rates. risk of porcelain fracture considerable weight of the prosthesis (approaching 3 oz of alloy) Noble metals must be used to control alloy's heat expansion or corrosion; increases the costs Proposed methods to produce hollow frames to alleviate these problems, including the use of special custom trays to achieve a passive fit will double or triple the labor costs." 79

80 An alternative method of fabricating fixed prostheses in situations of CHS of 15 mm or greater is the fixed complete denture or hybrid prosthesis, with a smaller metal framework, denture teeth, and acrylic resin to join these elements together (figure 6-32). 80

81 The reduced metal framework compared with a porcelain-to-metal fixed prosthesis exhibits fewer dimensional changes and may more accurately fit the abutments, which is important for a screw-retained restoration. less expensive, is highly esthetic (premade denture teeth), easily replaces teeth and soft tissue in appearance, and is easier to repair if fracture occurs. Because resin acts as an intermediary between the teeth and metal substructure, the impact force during dynamic occlusal loading may also be reduced. hybrid prosthesis is often indicated for implant restorations with a large CHS 81

82 On occasion, under contoured interproximal areas are designed by the laboratory in such restorations to assist oral hygiene and have been referred to as "high water" restorations. This is an excellent method in the mandible; however, it results in food entrapment, affects air flow patterns, and may contribute to speech problems in the anterior maxilla. 82

83 stress reducing options 1. Shorten cantilever length 2. Minimize offset loads to the buccal or lingual 3. Increase the number of implants 4. Increase the diameters of implants 5. Design implants to maximize the surface area of Implants 6. Fabricate removable restorations that are less retentive and incorporate soft tissue support 7. Remove the removable restoration during sleeping hours to reduce the noxious effects of nocturnal Parafunction 8. Splint implants together, whether they support a fixed or removable prosthesis 1. Shorten cantilever length 2. Minimize offset loads to the buccal or lingual 3. Increase the number of implants 4. Increase the diameters of implants 5. Design implants to maximize the surface area of Implants 6. Fabricate removable restorations that are less retentive and incorporate soft tissue support 7. Remove the removable restoration during sleeping hours to reduce the noxious effects of nocturnal Parafunction 8. Splint implants together, whether they support a fixed or removable prosthesis 83

84 the greater the crown height, the shorter the prosthetic cantilever should extend In CHS greater than 15 mrn, no cantilever should be considered, unless all other force factors are minimal. The occlusal contact intensity should be reduced on any offset load from the implant support system. Occlusal contacts in centric relation occlusion may even be eliminated on the most posterior aspect of a cantilever. In this way, a parafunction load may be reduced, as the most cantilevered portion of the prosthesis is only loaded during functional activity (such as chewing). 84

85 diagnosis and treatment of bruxism and clenching are in some ways different. Bruxism and clenching are the most critical factors to evaluate in any implant reconstruction. No long-term success will be obtained with severe parafunction of bruxism or clenching. This does not mean that patients with moderate and severe parafunction cannot be treated with implants. 85

86 MASTICATORY DYNAMICS Masticatory muscle dynamics amount of force exerted on the implant system patient size,gender, age, and skeletal arch position, muscle mass, exercise, diet, state of the dentition, physical status In general, the forces recorded in women are 20 lb less than those in men. The brachiocephalic, with may generate three times the bite force compared with a regular head shapea 86

87 The skeletal Class III patient is primarily a vertical chewer and generates vertical forces with little excursive movement. However, some patients appear "pseudo- Class III" as a result of anterior bone resorption or loss of posterior support and collapse of the vertical dimension with an anterior rotation of the mandible. These patients do exhibit lateral excursive movements when the incisal edge position is restored to its initial position 87

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89 Arch position ( position in arch ) Maximum bite forces in the anterior incisor region correspond approximately 35 to 50 psi; canine region : psi molar area : psi bone loss 89

90 The anterior biting force is decreased in the absence of posterior tooth contact and greater in the presence of posterior occlusion or eccentric contacts. mechanical properties of a Class III lever function Greater contraction of large masticatory muscles implants in the posterior regions should often be of greater diameter, especially in the presence of additional force factors 90

91 the edentulous bone density is inversely related to the amount of force generally applied in that arch position T he posterior maxilla is the most at-risk arch position, followed by the posterior mandible, then the anterior maxilla. The most ideal region is the mandibular anterior. 91

92 OPPOSING ARCH Natural teeth transmit greater impact forces than soft tissue-borne complete dentures the maximum occlusal force of patients with complete dentures is limited and may range from 5 to 26 psi A complete implant fixed prosthesis does not benefit from proprioception as do natural teeth, and patients bite with a force four times greater than with natural teeth. Thus, the highest forces are created with implant prostheses 92

93 premature contacts in occlusal patterns or during parafunction on the implant prostheses do not alter the pathway of closure, as occlusal awareness is decreased with implant prostheses when compared with natural teeth. Partial denture patients may record forces intermediate between that of natural teeth and complete dentures, depending on the location and condition of the remaining teeth, muscles, and joints. In the partially edentulous patient with implant-supported fixed prostheses, force ranges are more similar to those of natural dentition, but lack of proprioception may magnify the load amount during parafunctional activity 93

94 Rarely should the opposing arch be maintained in a traditional denture to decrease the stress to the implant arch. Instead, the implant arch should be designed to compensate for the higher stresses expected from an implant-supported opposing arch (Figure 6-38). 94

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