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Pasqualini U, Pasqualini ME. Treatise of Implant Dentistry: The Italian Tribute to Modern Implantology. Carimate (IT): Ariesdue; 2009 Oct.

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Treatise of Implant Dentistry: The Italian Tribute to Modern Implantology.

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Chapter XIIIIMMEDIATE FIXED TEMPORARY PROSTHESES AND DEFINITIVE PROSTHESES ON IMPLANTS

Introduction

All two-step implants require a consolidation period that forces patients to remain edentulous or endure the discomforts (and risks) of wearing temporary removable prostheses (1, 2).

Other types of implants, such as soldered needles and self-tapping, bicortical, rapid and MUM screws, can instead immediately offer the aesthetic and functional advantages of fixed and immediate temporary prostheses (3–7). With the exception of very particular cases, patients are always discharged with temporary fixed prostheses for cosmetic reasons, with no harm to the supporting implants. In any case, the procedures should be performed respecting the static and dynamic occlusal principles that are crucial for the stability of natural teeth, in addition to the occlusal static principles applicable to the “emerging” implants that have been discussed. In this section we will briefly examine these principles, which have been extensively described, demonstrated and discussed in Le patologie occlusali. Eziopatogenesi e terapia, which is recommended to readers who would like to learn more about this science, as it is the cornerstone of dentistry as a whole, including implantology.

Constructing fixed temporary prostheses

Temporary prostheses on implants, as on natural teeth, can be traumatic if they fail to respect static and dynamic occlusal balance. We will summarize basic and crucial recommendations for temporary or fixed implant and prosthetic rehabilitation.

Front single-tooth implant1

The replacement of a single front tooth represents the most “classic” implant indication. The immediate loading of front single-tooth implants requires comprehensive knowledge of occlusal physiology, which can be summed up based on two indications.

  1. No front tooth, including canines, should have static contacts with the opposite teeth. These contacts are pathological due to the different loading direction with respect to the root inclination.
  2. Premolars and molars are the only teeth that can safely withstand static occlusal force, since they distribute the load along the main axis of the roots.

The purpose of the practical examples that follow is to give the reader insight into these aspects. Patients who have lost or are about to lose one or more front teeth due to occlusal trauma frequently ask for temporary prosthetic rehabilitation, as in the case of the typical patient shown in the following illustrations. Replacing the tooth that is about to be expelled with a single-tooth implant and crown placed without previous occlusal rebalancing of both arches would subject the new restoration to the selfsame expulsive causes, thus slating the implant for failure.

Those who are unaware of the importance of occlusal balance would likely attribute failure to the fact the single-tooth implant was not splinted to the adjacent teeth or, as too often happens, to the fact that submerged implants were not been employed, and/or to microbial causes.

The following series of photographs (Figs. 1–24) shows that, after removal of the premature distal contacts leading to expulsion of the central incisor by traumatic mandible translation, it was possible to replace the tooth with a single-tooth implant with an emerging abutment. Despite the scarce residual bone crest, this permitted immediate temporary loading and subsequent placement of a single definitive gold-porcelain crown, which proved its validity at the regular checkups performed over the next twenty years (1984–2004).

Fig. 1. Left upper central incisor in the expulsive phase (1984).

Fig. 1

Left upper central incisor in the expulsive phase (1984).

Fig. 2. Radiographic validation.

Fig. 2

Radiographic validation.

Fig. 3. Premature contacts in centric occlusion after condylar repositioning in hinge axis.

Fig. 3

Premature contacts in centric occlusion after condylar repositioning in hinge axis.

Fig. 4. The arrows point the premature contacts caused by malocclusion due to previous extractions.

Fig. 4

The arrows point the premature contacts caused by malocclusion due to previous extractions.

Fig. 5. The premature contacts in centric occlusion prevent swallowing, and the mandible shifts forward in order to find acentric contacts that will allows a tongue positioning suitable for peristaltic movements.

Fig. 5

The premature contacts in centric occlusion prevent swallowing, and the mandible shifts forward in order to find acentric contacts that will allows a tongue positioning suitable for peristaltic movements.

Fig. 6. Mandible translation causes pathological contact of the incisor with subsequent mobilization and expulsion.

Fig. 6

Mandible translation causes pathological contact of the incisor with subsequent mobilization and expulsion.

Fig. 7. In order to obtain correct occlusal balance, selective grinding is required before any oral implant rehabilitation.

Fig. 7

In order to obtain correct occlusal balance, selective grinding is required before any oral implant rehabilitation.

Fig. 8. Surgical phase: note the bone lesion.

Fig. 8

Surgical phase: note the bone lesion.

Fig. 9. X-ray image of the Garbaccio bicortical screw placed according to the longer axis of the available bone.

Fig. 9

X-ray image of the Garbaccio bicortical screw placed according to the longer axis of the available bone.

Fig. 10. Rendering of the surgical screw insertion path.

Fig. 10

Rendering of the surgical screw insertion path.

Fig. 11. To increase implant retention we placed a stabilizing needle with a divergent and palatal axis with respect to the adjacent tooth (1984).

Fig. 11

To increase implant retention we placed a stabilizing needle with a divergent and palatal axis with respect to the adjacent tooth (1984).

Fig. 12. The bone defect is filled with non-resorbable hydroxyapatite granules (to prevent cosmetic problems in the area).

Fig. 12

The bone defect is filled with non-resorbable hydroxyapatite granules (to prevent cosmetic problems in the area).

Fig. 13. Lyophilized dura mater free “graft” to reduce possible bone resorption in the area of the repositioning flap schisis.

Fig. 13

Lyophilized dura mater free “graft” to reduce possible bone resorption in the area of the repositioning flap schisis.

Fig. 14. Suture.

Fig. 14

Suture.

Fig. 15. Radiographic checkup: the arrow at the bottom points to the coronal welding of a small titanium bar, placed for prosthetic reasons (to increase the volume of the external abutment).

Fig. 15

Radiographic checkup: the arrow at the bottom points to the coronal welding of a small titanium bar, placed for prosthetic reasons (to increase the volume of the external abutment).

Fig. 16. Immediate temporary crown after surgery (1984).

Fig. 16

Immediate temporary crown after surgery (1984).

Fig. 17. Temporary crown and healthy stippled mucosa at one month.

Fig. 17

Temporary crown and healthy stippled mucosa at one month.

Fig. 18. Definitive gold-porcelain crown (1985).

Fig. 18

Definitive gold-porcelain crown (1985).

Fig. 19. Checkup X-ray (1985).

Fig. 19

Checkup X-ray (1985).

Fig. 20. Traction test with 5 orthodontic elastics: note the ischemic finger, demonstrating the great pressure applied.

Fig. 20

Traction test with 5 orthodontic elastics: note the ischemic finger, demonstrating the great pressure applied.

Fig. 21. Checkup after 16 years (2000).

Fig. 21

Checkup after 16 years (2000).

Fig. 22. Clinical appearance (2000).

Fig. 22

Clinical appearance (2000).

Fig. 23. Another checkup (2004).

Fig. 23

Another checkup (2004).

Fig. 24. Radiographic validation after 20 years (2004).

Fig. 24

Radiographic validation after 20 years (2004).

The importance of dynamic occlusal balance

The second part of Le patologie occlusali. Eziopatogenesi e terapia is devoted to the physiology of dynamic balance and the pathological consequences of its absence.

The 430 pages that the book devotes to the topic can be summed up in a single rule, which we will supplement with significant practical examples in order to demonstrate the importance of this knowledge in virtually every branch of dentistry, particularly implantology.

▮

Like the other front teeth, canines should have no static contact with the opposite teeth. However, they can easily withstand dynamic contacts, protecting - during their lateral movements - all the other teeth in the arches from any pathological contact. This function is thus known as “canine disclusion.”

Due to lack of space we cannot expand on the “non-existence of the condylar guide,” the disclusive physiology of the “maximum moment” of the canines, their peculiar bone stabilization in the juga alveolaria, and the reason for the thicker enamel layer that protects the surface of their dynamic disclusion path during Bennett movements. This demonstration will thus rely on the sole evidence of the examples presented here, which must be examined carefully.

Clinical example

A young woman with congenital agenesis of the upper lateral incisors, orthodontically treated with distalization of both canines to create the space for two single implants in order to replace the missing teeth (Figs. 25–43) (8).

Fig. 25. Agenesis of the lateral incisors in a young patient (1986).

Fig. 25

Agenesis of the lateral incisors in a young patient (1986).

Fig. 26. X-ray of two quick screws.

Fig. 26

X-ray of two quick screws.

Fig. 27. The two single-tooth implants were placed during flapless surgery (1986).

Fig. 27

The two single-tooth implants were placed during flapless surgery (1986).

Fig. 28. The two definitive gold-porcelain crowns.

Fig. 28

The two definitive gold-porcelain crowns.

Fig. 29. Three years later the single-tooth left implant appears compromised and some papillae are bleeding (arrow).

Fig. 29

Three years later the single-tooth left implant appears compromised and some papillae are bleeding (arrow).

Fig. 30. The radiographic checkup shows resorption of the peri-implant bone around the threads.

Fig. 30

The radiographic checkup shows resorption of the peri-implant bone around the threads.

Fig. 31. Manual condyle repositioning in the hinge axis, which immediately reveals the presence of instable distal contacts.

Fig. 31

Manual condyle repositioning in the hinge axis, which immediately reveals the presence of instable distal contacts.

Fig. 32. The arrow points to trauma of the left single-tooth implant following translation in static occlusion.

Fig. 32

The arrow points to trauma of the left single-tooth implant following translation in static occlusion.

Fig. 33. The trauma (arrows) is also worsened by the loss of canine disclusion (dynamic trauma).

Fig. 33

The trauma (arrows) is also worsened by the loss of canine disclusion (dynamic trauma).

Fig. 34. The occlusal plane of the upper arch shows good amalgam fillings made by a colleague.

Fig. 34

The occlusal plane of the upper arch shows good amalgam fillings made by a colleague.

Fig. 35. Occlusal check with the aid of the Pasqualini stopper.

Fig. 35

Occlusal check with the aid of the Pasqualini stopper.

Fig. 36. The premature contact marked on the occlusal surface of an amalgam filling must be removed immediately to restore both the centric and dynamic balance.

Fig. 36

The premature contact marked on the occlusal surface of an amalgam filling must be removed immediately to restore both the centric and dynamic balance.

Fig. 37. The pathological situation before restoration of the occlusal balance.

Fig. 37

The pathological situation before restoration of the occlusal balance.

Fig. 38. The new morphology of the peri-implant mucosa, healed “simply” after occlusal balance was restored.

Fig. 38

The new morphology of the peri-implant mucosa, healed “simply” after occlusal balance was restored.

Fig. 39. Check of canine disclusion.

Fig. 39

Check of canine disclusion.

Fig. 40. Replacement of the old crown (1989).

Fig. 40

Replacement of the old crown (1989).

Fig. 41. The new crown shaped according to the morphology of the healed epithelium (1989).

Fig. 41

The new crown shaped according to the morphology of the healed epithelium (1989).

Fig. 42. Canine disclusion.

Fig. 42

Canine disclusion.

Fig. 43. The X-ray taken after one year (1990) underscore the remarkable neoformation of peri-implant tissue.

Fig. 43

The X-ray taken after one year (1990) underscore the remarkable neoformation of peri-implant tissue. Note: compare to the X-ray in Figure 30.

After the flapless insertion of two bicortical screws, two temporary crowns were placed immediately, following careful check of the absence of premature static contacts with the antagonist teeth.

After healing of the periodontal soft tissues, the temporary resin crowns were replaced by two single porcelain ones, made respecting the same occlusal principles (static and dynamic). The young woman was observed three years later, as she was worried about the sudden mobility of the left implant and the severe gingival irritation of the area.

The X-rays showed the different osseointegration pattern between the stable right implant and the left mobile one, where an initial peri-implant bone resorption was detected. The different superficial appearance of the related mucosae was also apparent. The lateral leftward movement showed the loss of canine disclusion with premature contact on the compromised single-tooth implant, while the contralateral canine exhibited physiological disclusion. The patient reported that the trouble with the left implant started immediately after placement of an amalgam filling on a molar by her dentist (who also referred her to us). With the aid of a Pasqualini stopper, we detected a single premature contact - on the “beautiful” filling made by our colleague! Removing it sufficed to re-establish centric occlusion of the mandible, and it solved the translation that had shifted it forward and prevented left disclusion.

At the one-month checkup the patient showed complete healing of the soft tissue inflammation above the implant, which had regained its complete original stability. Since the previous dynamic trauma displaced the crown and created a diastema, the former was replaced and the occlusion checked. Comparison of the two X-rays (Figs. 30, 43), taken at the time of implant involvement and after crown replacement, is fascinating, showing the remarkable recovery of the peri-implant bone tissue one year after occlusal rebalancing.

Single-tooth implants on canines

The next photographs show that single-tooth implants on canines require strict observance of the same occlusal principles (Figs. 44–68), the only difference being that on the immediate temporary prostheses both static and dynamic contacts must be excluded as a precautionary measure, as they can be harmful during integrating osteogenesis.

Fig. 44. Loss (iatrogenic) of the canine of this very young patient (1987).

Fig. 44

Loss (iatrogenic) of the canine of this very young patient (1987).

Fig. 45. The lack of canine disclusion determines severe dynamic premature contacts.

Fig. 45

The lack of canine disclusion determines severe dynamic premature contacts.

Fig. 46. The temporary “spider” wore by the patient strictly for cosmetic reasons (1987) and with no dynamic function.

Fig. 46

The temporary “spider” wore by the patient strictly for cosmetic reasons (1987) and with no dynamic function.

Fig. 47. The X-ray shows the post-extraction socket area.

Fig. 47

The X-ray shows the post-extraction socket area.

Fig. 48. Flap incision.

Fig. 48

Flap incision.

Fig. 49. The flap detachment shows bone loss along the juga alveolaria of premolar and incisor (horizontal atrophy) caused by the lack of canine disclusion, and unquestionably not due to bacterial infection.

Fig. 49

The flap detachment shows bone loss along the juga alveolaria of premolar and incisor (horizontal atrophy) caused by the lack of canine disclusion, and unquestionably not due to bacterial infection.

Fig. 50. Two surgical phases.

Fig. 50

Two surgical phases.

Fig. 51. Use of the self-centering drill.

Fig. 51

Use of the self-centering drill.

Fig. 52. The 3.1-mm MUM implant before insertion in the surgical tunnel.

Fig. 52

The 3.1-mm MUM implant before insertion in the surgical tunnel.

Fig. 53. Implant correctly placed up to contact and penetration of the deep cortical bone.

Fig. 53

Implant correctly placed up to contact and penetration of the deep cortical bone.

Fig. 54. The radiographic checkup shows successful bicorticalism and the use of a 1.1-mm self-centering drill for the subsequent placement of a stabilizing needle.

Fig. 54

The radiographic checkup shows successful bicorticalism and the use of a 1.1-mm self-centering drill for the subsequent placement of a stabilizing needle.

Fig. 55. Insertion of the stabilizing needle (personal technique).

Fig. 55

Insertion of the stabilizing needle (personal technique).

Fig. 56. Intraoral soldering.

Fig. 56

Intraoral soldering.

Fig. 57. Radiographic checkup: note the bicorticalism of the two implants.

Fig. 57

Radiographic checkup: note the bicorticalism of the two implants.

Fig. 58. The single-tooth implant.

Fig. 58

The single-tooth implant. Note the soldering mark and the loss of bone tissue on the premolar (arrow).

Fig. 59. Immediate temporary crown upon completion of surgery.

Fig. 59

Immediate temporary crown upon completion of surgery. Since this tooth is a canine, it requires al least 2 months of “resting” after complete osseointegration before it can regaining its physiological disclusion function.

Fig. 60. Healing of the soft tissues at 60 days indicates complete osteogenesis.

Fig. 60

Healing of the soft tissues at 60 days indicates complete osteogenesis.

Fig. 61. The subgingival preparation of the implant abutment and impression taking.

Fig. 61

The subgingival preparation of the implant abutment and impression taking.

Fig. 62. Perfect healing of the peri-implant mucosa “despite” the presence of a bifurcation.

Fig. 62

Perfect healing of the peri-implant mucosa “despite” the presence of a bifurcation.

Fig. 63. Definitive gold-porcelain crown immediately after placement.

Fig. 63

Definitive gold-porcelain crown immediately after placement.

Fig. 64. Radiographic checkup (1987).

Fig. 64

Radiographic checkup (1987).

Fig. 65. Correct disclusion and the absence of dynamic premature contacts.

Fig. 65

Correct disclusion and the absence of dynamic premature contacts.

Fig. 66. Palatal view.

Fig. 66

Palatal view.

Fig. 67. The same canine 21 years later (2008).

Fig. 67

The same canine 21 years later (2008).

Fig. 68. The X-ray shows only mild initial conical resorption (2008).

Fig. 68

The X-ray shows only mild initial conical resorption (2008).

The temporary periodontal involvement of the other teeth of the arch, due to the absence of canine disclusion, will be offset by their quick return to normality after physiological disclusion is restored with the definitive gold-porcelain crown placed on the single-tooth implant after osteogenesis of the integrating tissue has been completed.

Close attention should be paid to the next case, which we consider very interesting from an educational standpoint. It demonstrates that even crowns on single-tooth implants in the canine area must bear the dynamic contact during disclusion. Vascular fragility, marginal gingival hypertrophy and the evident horizontal bone atrophy affecting the adjacent teeth disappeared a few weeks after the crown was cemented on the canine and disclusion was restored. The crown has been in service for many years, and is perfectly functional and stable.

Single-tooth implant in the lower front area

The next case shows the favorable evolution of a single-tooth implant replacing a lower lateral incisor, consisting of a single 2.6 mm MUM implant without balancing needles, as no other solutions were feasible due to the narrowness of the available space (Figs. 69–93). The photographs show the absence of peri-implant gaps, which can instead be noted next to the root of the natural central incisor, where the pathological widening of the periodontal space was appreciable (1991).

Fig. 69. Loss of the right lower lateral incisor (1991).

Fig. 69

Loss of the right lower lateral incisor (1991).

Fig. 70. The X-ray highlights a pathological increase of the periodontal space of the central incisor adjacent to the edentulous area (arrows).

Fig. 70

The X-ray highlights a pathological increase of the periodontal space of the central incisor adjacent to the edentulous area (arrows).

Fig. 71. The arrows point to enamel abrasion, sign of dynamic trauma due to displacement of the lower canine.

Fig. 71

The arrows point to enamel abrasion, sign of dynamic trauma due to displacement of the lower canine.

Fig. 72. Flap detachment and preparation of a surgical tunnel in a very thin bone.

Fig. 72

Flap detachment and preparation of a surgical tunnel in a very thin bone.

Fig. 73. Placement of a 2-mm MUM implant at the neck.

Fig. 73

Placement of a 2-mm MUM implant at the neck. Note (arrow) the transparency of the labial bone. In this case, flapless surgery would have been difficult and would probably have culminated in failure.

Fig. 74. Cut and preparation of the abutment.

Fig. 74

Cut and preparation of the abutment.

Fig. 75. X-ray (1991).

Fig. 75

X-ray (1991).

Fig. 76. Suture and immediate temporary crown.

Fig. 76

Suture and immediate temporary crown.

Fig. 77. Check of the disclusion.

Fig. 77

Check of the disclusion. The arrow points to a dynamic premature contact that will be removed later.

Fig. 78. The temporary crown and mucosal healing.

Fig. 78

The temporary crown and mucosal healing.

Fig. 79. Before placement of the definitive crown.

Fig. 79

Before placement of the definitive crown.

Fig. 80. Definitive gold-porcelain crown (1991).

Fig. 80

Definitive gold-porcelain crown (1991).

Fig. 81. Interdental contact points are crucial, since placement of a stabilizing needle is unfeasible due to reduced space.

Fig. 81

Interdental contact points are crucial, since placement of a stabilizing needle is unfeasible due to reduced space.

Fig. 82. Occlusal contact marking with articulating paper, to check for the presence of premature contacts in centric occlusion.

Fig. 82

Occlusal contact marking with articulating paper, to check for the presence of premature contacts in centric occlusion.

Fig. 83. The two black dots (arrows) indicate the corrections to make on the incisal margins, both on the artificial crown and the natural tooth.

Fig. 83

The two black dots (arrows) indicate the corrections to make on the incisal margins, both on the artificial crown and the natural tooth.

Fig. 84. The correction.

Fig. 84

The correction.

Fig. 85. Canine disclusion (arrow) indicates the presence of a premature dynamic contact.

Fig. 85

Canine disclusion (arrow) indicates the presence of a premature dynamic contact.

Fig. 86. Use of “Red Indicator” dry self-molding varnish.

Fig. 86

Use of “Red Indicator” dry self-molding varnish.

Fig. 87. Lateral movement to the right.

Fig. 87

Lateral movement to the right.

Fig. 88. The small premature contact (arrow) must be removed immediately to avoid implant damage.

Fig. 88

The small premature contact (arrow) must be removed immediately to avoid implant damage.

Fig. 89. Disclusion in the incisor area is now free from premature contacts.

Fig. 89

Disclusion in the incisor area is now free from premature contacts.

Fig. 90. Lateral movement toward left.

Fig. 90

Lateral movement toward left.

Fig. 91. The same case at a later checkup (1993).

Fig. 91

The same case at a later checkup (1993).

Fig. 92. The X-ray shows healing of the periodontal damage along the root of the adjacent incisor, and the good osseointegration of the MUM implant.

Fig. 92

The X-ray shows healing of the periodontal damage along the root of the adjacent incisor, and the good osseointegration of the MUM implant.

Fig. 93. Close-up of the healthy appearance of the mucosa (1993).

Fig. 93

Close-up of the healthy appearance of the mucosa (1993).

The placement of a provisional crown on a single-tooth implant with no lateral stabilization, such as the one in question, could have been risky, but the crown was splinted to the adjacent teeth - which were still stable - via contact areas that acted as natural “welds.” The temporary crown on the single-tooth implant was also checked for the presence of pathological contacts, both static and dynamic; the same precautions were taken when shaping the definitive porcelain crown that was later cemented to the implant abutment.

However, the cementation caused a slight height increase due to the incompressibility of fluid cements, which can happen on occasion. This was subsequently eliminated along with premature dynamic contacts on the contiguous lateral incisor (9).

Follow-up X-rays taken two years later demonstrate the resolution of periodontal disease along the whole root of the natural incisor and perfect osseointegration of the MUM implant.

What we have said so far about the immediate loading of front upper and lower implants - single or multiple - is of little value if static occlusion is not borne by the distal teeth, molars and premolars, in occlusal balance.

In the absence of molars and premolars or when they are present but the antagonist tooth is missing, we usually observe mobile and compromised front teeth that are often still in place for purely cosmetic reasons. In such cases, we proceed as follows:

  1. we initially place the distal implants without extracting the mobile front teeth;
  2. after 2–3 weeks, when the surgical wounds of the mucosae have reached a satisfactory level of initial healing, we extract the front teeth and replace them with at least four implants, which are temporarily splinted using one or more bars soldered to the distal implants. We then take impressions of the whole arch, and one or two days later we place a temporary bridge fixed with definitive cement, carefully checking the load distribution along the whole length, making sure that it has no harmful effects on the supporting implants.

In exceptional cases, when the patient can endure the placement of all the distal and frontal implants in a single session, we immediately take the impression and place a temporary prosthesis, avoiding multiple surgeries in two or three sessions (10–12).

Implant-anchored definitive prostheses

Prostheses on implants should be manufactured following the same principles adopted for traditional ones: The crown borders should end below the gingival border of the implants, with intermediate pontics fashioned with a “flute beak” shape, and interdental spaces as similar as possible to those found between natural teeth.

The introduction of “flute beak” pontics contributed to the elimination of both of the old “vaulted” pontics and “hygienic” ones, which are now generally constructed as a “flute beak” and are perfectly functional, with no discomfort for the patient. The implant abutments should be made to permit placement of definitive crowns, manufactured with the classic protective profile of the gingival sulcus of the natural abutments. The fact that crowns on implants also end below the gingival margin serves both cosmetic and hygienic purposes, since this feature assures food removal from the critical impaction area, and avoid its penetration if there are steps or undercuts above the gum.

The intermediate pontics should also be constructed with the self-cleaning “flute beak” profile. The interdental spaces of the prosthetic pontic should not be too wide, not only because they are poorly tolerated by the patient but also because they are hygienically inadequate, since the tongue - expanding during deglutition - should be able to perform cleaning and massaging action without pushing the food bolus below the pontic (13–15).

The wide interdental spaces proposed in some publications represent a prosthetic throwback because, in the name of a wrongful concept of mechanical cleaning, they deprive the patient of the natural cleaning action exerted by cheeks and tongue, forcing him/her to resort to specific devices such as waterpicks, interdental brushes, electric toothbrushes and so on.

Furthermore, we avoid the free-end saddle bridges that are suggested by these publications (16–30) to overcome the intrinsic limitations of the type of implants they recommend. In fact, all such extensions are kept ridiculously below the occlusal plane and thus have a reduced masticatory function. These kinds of extensions are subject to modifications, which are required when the implants need to be placed in areas that do not coincide with the original sites of the missing teeth. These are all consequences of the use of a single type of implant that does not always permit implant placement in the site corresponding to the natural tooth that was lost (31).

Impression taking with implant abutments

Since there is no difference between the shape of prostheses on implants and those on natural abutments (except for the fact that titanium is not caries-susceptible and can thus be undercut) the impression-taking technique is the same. The old method - which used aluminum transfers for natural abutments and pre-made transfers for implants, and was the best available at a time when impressions were taken using copper rings and Kerr thermoplastic paste - has now been surpassed, in terms of precision, by modern impression techniques using retraction cords (also used for implant abutments) and elastomeric impression materials, polyethers, silicones, etc.

We have been using the latter technique alone for many years, and it is always employed after parallelism of the natural and implant abutments has been achieved. We must point out that, unlike natural abutments consisting of dentine, which is more fragile, implant abutments can be reduced more in size due to the higher resistance and incorruptibility of titanium. Nevertheless, it is not always possible to give the implant abutments an optimal inclination, since they are inserted in relation to the slope of the available bone crest and not based on future prosthetic needs.

All abutments are prepared by taking care that the drill tip will always reach the subgingival space, even around the implant abutments. Due to the tenacious apposition of the mucosa on the titanium abutment surface, a few drops of local anesthetic are almost always injected.

Following insertion of the retraction cord to create a gingival sulcus, which is indispensable for each type of preparation, we take impressions of both the implants and natural abutments.

The antagonist dental arch impression is taken with quick-setting alginate, wrapped in a disinfectant-soaked paper towel and sent to the laboratory in sealed plastic bags. The wax-bite occlusal registration, taken by manual manipulation of the patient’s mandible in centric relation, is extremely important. We have already mentioned Le patologie occlusali. Eziopatogenesi e terapia, but would like to emphasize the importance of respecting and/or restoring static and dynamic occlusal harmony for both natural and artificial teeth, as it is fundamental for the long life of any implant.

Cementation of implant abutments

Implant abutments should never be fixed with temporary cement because of possible imbalance in the event of partial decementation, nor with definitive oxyphosphate cement since the adhesion between gold and/or crown metal and titanium is not stable. Our protocol always calls for strong resin cement to fit the titanium abutments securely to the crowns, as once it is polymerized it will prevent decementation. The use of fluid resin cements is indispensable in order to avoid height increases, which are very difficult to adjust. As soon as a change in height is detected, the bridge must immediately be removed and cleaned, and the entire procedure must be repeated from scratch.

For bridges or mixed prostheses supported by implants or natural abutments, we prefer concomitant cementation of the crowns on natural teeth with oxyphosphate, using glass ionomer cement for the crown placed on titanium abutments2.

The dental assistants (preferably two) should be used to working together, coordinating the different preparation times of the two materials (personal technique). It is also advisable to remove excess resin cement from the crowns immediately, because once it hardens it will require finishing that is not only difficult to perform but also imprecise.

Gold-resin versus gold-porcelain prostheses

At every conference and hands-on course, there is a participant who asks the germane question of whether the prostheses should be made of gold-resin or gold-porcelain. The answer invariably depends on the teacher’s opinion and experience. Both solutions (gold-resin and gold-porcelain) have valid indications, but just as many serious contraindications.

The reasons for using porcelain crowns have to do with better aesthetics, longer life and the absence of occlusal surface damage caused by abrasion or overbrushing. In turn, the contraindications are represented by the risk of fractures of the porcelain or of the metal framework, which always have serious consequences.

Gold-resin prostheses are preferred because of the lower risk of fracture, better “occlusal cushioning” and progressive (and, according to many authors, desirable) compensatory abrasion.

Currently we are seeing the comeback of composite resins, which have been improved in strength and resistance to fracture.

Prostheses on single-tooth implants

The definitive prosthesis on single-tooth implants should always be made with single porcelain crowns. The choice of porcelain is justified by the following considerations.

Since single-tooth implants replace single dental elements between natural teeth, they must resemble the contiguous teeth from a cosmetic standpoint. No material can surpass the aesthetics, functionality, duration and fracture resistance of single porcelain crowns.

Le patologie occlusali. Eziopatogenesi e terapia clarified that even single porcelain crowns must comply with the same static and dynamic principles of the teeth they are replacing, which are often lost due to occlusal imbalance disharmony. It would be inexcusable if the crowns on single implants replicated the same pathological conditions that caused expulsion of the natural teeth or caused new ones.

Furthermore, single porcelain crowns on central and lateral incisors (upper and lower) must be free of lateral premature dynamic contacts, and possibly protrusive ones, the sole exception being canines, as they are the only teeth in the arch that can withstand them, due to their position of “maximum movement” (see detail in Figs. 25–93).

Like incisors, the canines must be free of static contacts, but they should be able to disclude all the remaining teeth of both arches during lateral movements.

In presence of Class II or III, or ectopic canines, disclusion is impossible. In this case, the teeth should be checked to be sure that they are not subject to premature static contacts, since (preventive) orthodontic correction, which would theoretically be ideal, is not always possible.

The single crowns on premolars and molars, which naturally have static contacts in centric occlusion, should always be protected by canine disclusion, which should prevent dynamic interference. Therefore, they must be checked to be sure that there are no premature dynamic contacts, which must be corrected using articulating paper and “Red Indicator” dry self-molding varnish, as described in Le patologie occlusali. Eziopatogenesi e terapia.

After cementation, it is crucial to verify that there are no pathological premature contacts.

Partial prosthesis

When partial prostheses are placed between sectors composed of sound natural teeth in occlusal balance, they should be manufactured in gold-porcelain or resin with gold occlusal surfaces, in order to match the elasticity and occlusal hardness of the other sectors.

In the case of lower prostheses including the canine, it is advisable to manufacture at least the canine in gold-porcelain, which can easily be soldered to other parts of the gold-resin prosthesis. The reason is that the labial resin surface would be subject to abrasion, preventing the tooth’s disclusive function3.

Complete fixed prostheses

No rule can be advocated with respect to the choice of porcelain versus gold-resin for manufacturing complete fixed prostheses, since their advantages and disadvantages are compensated by their respective features.

What we propose to “smart” patients with fewer aesthetic requirements is a canine-canine (or premolar-premolar) porcelain prosthesis joined with a gold-resin prosthesis with gold occlusal surfaces on the distal teeth, an option that offers excellent functional and cost benefits. We never propose fixed porcelain works if there the antagonist teeth are made of resin.

For the long-term success of both types of prosthesis (porcelain and resin), knowledge of occlusal principles is crucial. These principles can be summarized as follows:

  1. concomitant static and centric contacts only on the teeth distal to the canines;
  2. dynamic contacts only on the canines;
  3. all front teeth, canines included, must always be free of pathological static contacts.

Complete fixed prostheses on implants in place of dentures

For completely edentulous patients with sufficiently wide ridges, both in the front and distal areas (at least up to the first molar), fixed rehabilitation is theoretically always possible. However, some fundamental rules must be respected in order to avoid mistakes that could thwart rehabilitation efforts.

  1. In each arch, all surgery should be completed in a single session, to immediately provide the patients with a temporary prosthesis (fixed, if possible) in occlusal balance.
  2. The bone height should be checked with X-rays and/or CT, followed by assessment of the width by means of occlusal and bucco-palato-lingual probing. Targeted tomographic analysis and calipers are very useful for this, also making it possible to establish implant diameters in advance.

The measurements are very useful both for flapless surgery as well as open surgery. Some areas that are seemingly suited for implant placement may instead be too thin to permit insertion. This unfortunate situation is even more embarrassing when it occurs suddenly, thwarting and/or complicating the work that has already been done. These problems can be almost always solved with needles or MUM implants, balanced by means of the intraoral solder. The safest thing to do is to splint all the implants temporarily with welded bars, in order to achieve uniform load distribution until placement of the definitive prosthesis.

Another rule is never to attempt total rehabilitation of the upper arch if there are still good front teeth in the mandible. In these cases, permanent rehabilitation of the complete lower arch is required first, in order to avoid imbalance and expulsion of the upper prosthesis due to the presence of the front teeth.

If the remaining lower teeth are still anchored to partial removable prostheses, the absence of mucosal resilience should be carefully assessed, as it will force contact with the more stable front teeth, sustaining the aforementioned imbalance.

We must again stress the need for preventive rehabilitation of the lower arch with a stable prosthesis. Otherwise, the patient will soon render even the most resistant prosthesis on implants unstable (destroying it), for the same reasons that led to mobilization and loss of the front teeth in the first place4. This will be followed by failure of the complete prosthesis on the residual teeth or instability of the complete denture, which he/she cannot tolerate. The patient will thus end up asking to have it replaced with a more stable one on implants.

Implant-anchored removable dentures

So far we have examined the indications and contraindications for replacing upper and lower dentures with implant-supported complete fixed prostheses. At this point, we will deal with the rehabilitation of edentulous atrophic distal areas, where the successful anchoring of dentures to a few implants friction-fitted Dolder and Ackerman bars or telescopic prostheses is still possible (21–25).

Removable dentures on implants make it possible to eliminate the palate from the upper prosthesis and manufacture less bulky lower dentures, thus making them more stable and functional.

Any reference to partial removable prostheses goes beyond the scope of this chapter. When they are connected to implants, they can cause nothing but damage, even if the most “inventive” connection systems are used.

We will deal exclusively with complete removable dentures anchored to a few supporting implants. The patient will still be able to remove them, but after they are anchored by “snapping” them onto the implants or bars he/she will immediately perceive the positive difference compared to common dentures.

Manufacturing technique for removable dentures. Advantages and problems

We must premise this section by noting that only two-step implants (after completion of the osseointegration phase) permit the placement of removable dentures and can withstand loading.

Considering that this type of prostheses can be placed only on completely edentulous subjects, the patients should be advised that they will not be able to wear them until the two-step implants are fully consolidated5,6.

Osseointegration time varies according to the type of implants employed; it is directly proportional to their immediate post-surgical stabilization and inversely proportional to the need for a later stabilization by including osteogenesis. The two steps needed for the implants are due to the fact that only a few patients are willing to endure - while toothless - both the time required for their osseointegration and the shorter time needed for the mucosae to heal. Therefore, we are forced to place implants with screwable abutments that do not interfere with the base of the temporary dentures, which must be put back into the oral cavity after surgery, after they have been relieved in the areas above the implants and the sutures.

Postoperative swallowing and mucosal edema following anesthesia will make the dentures unstable. Due to local pain, they are worn primarily for cosmetic reasons, at least during the first week. Unfortunately, as the pain caused by pressure subsides, the patient begins to use them for chewing, applying adhesives that break the suture and displace the mucosa detached for surgery. Healing, which would otherwise be very fast, is thus prolonged and often occurs by second intention.

After an initial healing phase, during which the mucosa adheres to the periosteum, relining and adjustments of the old denture are required, but below the relining material the mucosa may exert excessive pressure on buried implants, leading to mobilization and failure.

Troubleshooting

Most professionals opt for submerged implants because they consider them trauma-free and due to the fact that the implants achieve consolidation without any problems. We have just examined the causes of failures, due chiefly to the fact that after denture relining the implant site is no longer detectable with any level of certainty. This means that the prosthesis can be relieved only marginally, which can lead to unpleasant consequences.

We advise patients to refrain from using adhesives until suture removal and, even then, only after our approval. The waiting period required for definitive osseointegration is not risk-free when the upper denture is not stable on the remaining edentulous areas (especially the retromolar trigones) and the hard palate, and if the denture is not strongly relieved by the implants.

A final piece of advice: do not use the old denture unless strictly necessary. It is best to manufacture a new denture with optimal occlusal balance.

Removable lower prostheses

When the front sector of the mandible still has good height and cancellous bone above the basal one, implant placement does not require precautions other than those recommended for manufacturing upper removable dentures. Very often, however, we need to rehabilitate atrophic mandibles that are very low and are reduced to the basal bone.

Such mandibles make any kind of effective removable rehabilitation almost impossible. The conditions of these patients are truly compromised, and professionals are forced to deal with very complex situations. Several pre-prosthetic surgeries have been designed to provide edentulous ridges, vestibular fornices and/or the sublingual area with higher retentive possibilities (28–34).

With the two-step implants we achieve good results by following these precautions.

  1. We always employ two-step implants that are specifically designed for this purpose and have variable lengths and threads. Their diameters are always suitable for the rehabilitation of sufficiently wide atrophic crests.
  2. Incision of the mucosa is followed by minimal flap detachment, without lingual or buccal extension, which is sufficient to visualize the occlusal crest surface. This approach prevents laceration of the small capillaries coming from the periosteum, which would affect the already severely reduced venous and lymphatic flow.
  3. The insertion tunnel is carefully prepared.
  4. The implants designed for compact bone have large threads in order to bear the load, compensating reduced height with increased width The threads are very sharp, but could nevertheless impact the tunnel walls. Therefore, this surgery requires a great deal of caution and patience, with the sequential use of tappers with progressively larger thread diameters up to the final dimensions of the definitive implant, which will be screwed in manually without using tappers. Following insertion, the healing screw is put in place and the mucosa is sutured, making sure that the upper part of the screw protrudes only slightly from the mucosa or is completely submerged. Stress protection is achieved by following the same rules outlined for the upper implants, relieving the denture only well above the implants.
  5. Implants designed for the compact bone can be loaded after three months without the risk of mobilization. Once the healing screws have been removed, and the abutments placed and parallelized, the supporting bars for denture retention are added.

Conclusions

The numerous details sketched out here may seem excessive, but we are convinced that they are necessary for the success of these types of removable denture. Indeed, when well executed these dentures allow patients to enjoy stable, effective, and long-lasting artificial dentition (Figs. 94–100, 101–107, 108–113).

Fig. 94. Case of severe atrophy of the upper maxilla.

Fig. 94

Case of severe atrophy of the upper maxilla.

Fig. 95. Surgical phase in the placement of two-step implants.

Fig. 95

Surgical phase in the placement of two-step implants.

Fig. 96. Healing of the mucosae and bone tissue at 6 months.

Fig. 96

Healing of the mucosae and bone tissue at 6 months.

Fig. 97. Dolder bar screwed to the implants.

Fig. 97

Dolder bar screwed to the implants.

Fig. 98. The finished definitive overdenture.

Fig. 98

The finished definitive overdenture.

Fig. 99. Palatal view.

Fig. 99

Palatal view.

Fig. 100. The final radiography.

Fig. 100

The final radiography.

Fig. 101. Lower edentulism treated with 4 two-step implants.

Fig. 101

Lower edentulism treated with 4 two-step implants.

Fig. 102. The screwed bar.

Fig. 102

The screwed bar.

Fig. 103. The overdenture.

Fig. 103

The overdenture.

Fig. 104. The same case, upper maxilla; it was also treated with two-step implants and a bar.

Fig. 104

The same case, upper maxilla; it was also treated with two-step implants and a bar.

Fig. 105. The two prostheses anchored to the bars.

Fig. 105

The two prostheses anchored to the bars.

Fig. 106. View of the upper overdenture without the palate.

Fig. 106

View of the upper overdenture without the palate.

Fig. 107. Radiography of the finished case.

Fig. 107

Radiography of the finished case.

Fig. 108. Another case successfully treated with two-step implants.

Fig. 108

Another case successfully treated with two-step implants.

Fig. 109. Close-up of the resin block of the positioning transfers with Duralay.

Fig. 109

Close-up of the resin block of the positioning transfers with Duralay.

Fig. 110. The impression.

Fig. 110

The impression.

Fig. 111. The two screwed bars.

Fig. 111

The two screwed bars.

Fig. 112. Finished case.

Fig. 112

Finished case.

Fig. 113. The final radiography.

Fig. 113

The final radiography.

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Footnotes

1

In order to avoid repetitions and made the chapter easier to follow, the term “single-tooth implant” is used broadly to indicate the replacement of a single tooth both with a single implant or with several implants joined to form a single prosthetic abutment (screw stabilized with one or more needles, tripods made of needles, two screws).

2

A single type of cement (i.e. glass ionomer) can also be used both on natural and titanium abutments.

3

Zirconia-porcelain prosthetic elements have recently been used successfully, with excellent cosmetic results.

4

Too often attributed to microbial causes and/or lack of hygiene.

5

The term “consolidation time” is easier for patients to understand than “osseointegration time”.

6

This “temporary disability” can be overcome using mini-implants placed in between the two-step implants (26, 27), allowing the patient to wear a rather stable temporary prosthesis.

Figs. 25–43 are from Pasqualini U. Eziopatogenesi e terapia. Milan: Masson; 1993. Le patologie occlusali; pp. 401–56.

Figs. 45, 58, 62–65 are from Pasqualini, op. cit., pp. 391–92.

© copyright 2009 Azienda Pubblica di Servizi alla Persona “Suor Agnese”.

All rights reserved. No part of this book covered by the copyrights hereon may be reproduced, stored, communicated or copied in any form or by any means - graphic, electronic, or mechanical including photocopying, taping, or information storage and retrieval systems - without written consent from Marco E. Pasqualini (tel. +39.02.799651).

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