Jan Lindhe. Clinical Periodontology

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IMPLANTS IN THE LOAD CARRYING PART OF THE DENTITION • 957

Fig. 41-38. Eight months following the combined ante-

rior sinus floor elevation and lateral bone augmenta-

tion procedure, the site is reopened and three implants

are inserted.

Fig. 41-39. In order to increase the amount of kerati-

nized mucosa on the vestibular aspect of the implants,

the flap is repositioned accordingly. The resulting defi-

ciency on the palatal aspect is compensated for by

means of a connective tissue being part of the partial

thickness flap.

Fig. 41-40. Three months after implant placement, fa-Fig. 41-41. The corresponding radiograph confirms suc-

vorable peri-implant soft tissue conditions have been

cessful osseointegration of the three implants that are

re-established.

mostly located in augmented bone.

Fig. 41-42. In a case of implant shoulder location corn-

Fig. 41-43. Clinical view of the final three-unit metal-ce-

patible with cementation, respective solid abutments

ramic implant suprastructure, featuring a flat and con-

are selected and tightened to 35 Ncm with a calibratedtinuous emergence profile and adequate access for in-

torque wrench.

terimplant oral hygiene.

' CHAPTER 41

Fig. 41-44. The 4-year follow-up radiograph confirms

stable conditions at the osseointegrated interface.

MULTIPLE-UNIT TOOTH-BOUND

POSTERIOR IMPLANT

RESTORATIONS

Number, size and distribution of implants

When it comes to implant therapy in extended poste-

rior edentulous segments confined mesially and dis-

tally by remaining teeth, the question about optimal

number, size and distribution of implants has to be

raised again. Among the key parameters to be ad-

dressed during the decision-making process are the

mesio-distal dimension of the edentulous segment,

the

precise alveolar bone crest volume (including bone

height and crest width in an oro-facial direction), the

opposing dentition (premolars or molars), interarch

distance and specific occlusal parameters, as well as

the periodontal, endodontic and structural conditions

of the neighboring teeth.

One feasible approach consists of segmenting the

edentulous space in premolar-size units of approxi-

mately 7 mm of mesio-distal diameter at the level of

the

occlusal plane, and of approximately 5 mm at the

prospective implant shoulder. As on posterior loca-

tions clinicians increasingly prefer a rather superficial

implant shoulder location or in many instances even

supramucosal one, the respective measurements can

carried out at the crest level of study casts. It is

important during this process to anticipate a minimal

distance between implant shoulders of approximately

2 mm, and between a natural tooth and an implant of

about 1.5 mm (to be measured at the interproximal soft

tissue level). Again, the treatment objective, i.e. a long-

lasting implant-supported FPD, should be predict-

ably

reached on the one hand with optimal efficacy

and on

the other hand with a minimum of invasive

ness and

cost. The still existing controversy of whether

each

missing occlusal unit should be replaced by one

implant or whether a minimal number of implants

should be used, has already been addressed earlier in

this chapter.

Fig. 41-45. Schematic representation of a tooth-bound

posterior edentulous segment, restored by two im-

plants and a three-unit FPD with a central pontic.

Fig. 41-46. If a given tooth-bound edentulous space

only permits the insertion of two adjacent implants, a

minimal interimplant distance of 2 mm and a minimal

implant-to-tooth distance of 1.5 mm (at the interproxi

mal soft tissue level) should be respected.

In the case of three missing occlusal units and in the

absence of other particular restrictive conditions such

as limited local bone volume, the authors recommend

the insertion of a mesial and a distal implant to sup-

port a three-unit FPD with a central pontic (Fig. 41-45).

This approach permits the fabrication of three metal-

ceramic elements featuring a mesio-distal diameter of

about 7 mm each. Based on an average implant shoul

der dimension of approximately 5 mm, one can antici-

pate a gradually increasing, harmonious emergence

profile from the implant shoulder to the occlusal sur-

face. In order to satisfy the remaining important di-

mensional conditions, i.e. respecting the minimal dis-

tance between adjacent implants and in between teeth

and implants, one needs to dispose of a minimal total

mesio-distal gap distance of 21-22 mm (Fig. 41-47).

In the case of two missing occlusal units, one should

try as a general rule to select the largest possible

implant diameters with respect to the total mesio-dis-

tal distance of the given tooth-bound edentulous seg-

ment. Decisive parameters are again interimplant dis-

tance and space between implants and adjacent teeth,

as well as oro-facial crest width at the two prospective

implant sites. For a total gap diameter of about 14-15

IMPLANTS IN THE LOAD CARRYING PART OF THE DENTITION • 959

Fig. 41-47. In the case of three missing occlusal units,

an implant-supported FPD with a central pontic (ap-

proximately 7 mm in width) may be considered as a vi-

able solution.

Fig. 41-49. Vestibular aspect of a metal-ceramic restora

tion supported by two screw-type implants. Due to an

excess of mesio-distal space, the implants have been

separated by approximately 4 mm. Instead of a tradi-

tional pontic, a root imitation has been performed close

to the distal implant, providing an adequate guide for

interdental brush in view of an efficient plaque con

trol

at the marginal area of the implant restoration.

Fig. 41-48. In the presence of a mesio-distal gap width

of approximately 17 mm, one may consider the combi-

nation of a standard and an increased-diameter ("wide

neck

) implant. The same minimal interimplant and

implant-to-tooth distances have to be respected.

Fig. 41-50. With respect to cleansibility, the respective

prosthesis design is clearly visible on the postoperative

radiograph.

Fig. 41-51. The corresponding master model visualizes

the different dimensions and distances involved in this

individual case.

Fig. 41-52. On an oblique view the vestibular axial pro-

file of the implant restoration becomes visible. Soft tis-

sue (cheek and tongue) support and harmony with ad-

jacent teeth are of paramount importance.

mm, two standard-size implants are most suitable nation of one standard and one wide-diameter/wide-

(Fig. 41-46),

while for one of 17 to 18 mm the combi- platform implant is considered adequate (Fig. 41-48).

960 • CHAPTER

Fig. 41-53. Buccal view of an extended edentulous right

mandibular tooth-bound gap treated with an implant

restoration. In the pontic area a design favoring the effi-

cacy of an interdental brush close to the implant mar-

gins has been applied.

Fig. 41-55. Occlusal view of the completed 4-unit im-

plant-borne fixed porcelain-fused-to-metal prosthesis.

Table 41.5. Splinting of multiple adjacent posterior

implants

Parameters to consider:

• access for oral hygiene

• marginal adaptation/"passive fit"

• technical simplicity/ease of eventual

reinterventions

• "overload" of the osseointegrated interface

• "rotational forces" on implant components

• screw-loosening/fatigue fractures

It goes without saying that the latter choice requires

also the respective oro-facial bone volume.

These are just frequently encountered clinical ex-

amples, but in the function of other morphology and

dimensions of edentulous tooth-bound segments, ad-

ditional approaches and implant combinations may be

envisioned. Two such particular clinical situations are

presented in Figs. 41-49 to 41-52 and Figs. 41-53 to 41-

55. In the first case, the gap diameter required the two

adjacent implants to be spaced wider than the

Fig. 41-54. The related radiograph illustrates the chosen

design in the pontic area in terms of access to and effi-

cacy of interproximal plaque control.

normally advocated interproximal 2 mm. The labora-

tory technician compensated for this excess of space

with a root-imitation pontic which in turn provided an

excellent guide facilitating the use of an interdental

brush (Fig. 41-49). In the second case, only the place-

ment of three standard-size implants was possible due

to a restricted bone volume in oro-facial direction.

Again, the technician could optimally distribute the

different restoration volumes but still comply with

basic prerequisites such as a flat axial emergence pro-

file and optimal access for the patient's oral hygiene (

Figs. 41-53, 41-54).

Splinted versus single-unit restorations of

multiple adjacent posterior implants

Another persisting controversial issue relates to the

question whether multiple adjacent implants in the

load carrying part of the dentition should support

splinted or segmented single-unit restorations (Table

41-5). There still appears to be a confrontation between

rather "biological" considerations versus more "me-

chanical" thinking.

Generally speaking, the biologically oriented con-

siderations, insisting on easy access for oral hygiene

and optimal marginal adaptation, represent probably

the more scientifically-based point of view. Clinicians

advocating splinting of multiple adjacent implants do

so primarily for mechanical reasons. They hypothe-

size that this approach decreases forces and force mo-

ments at the level of the suprastructures and the vari-

ous underlying implant components, and that rela-

tively frequent mechanical complications such as

screw-loosening and fractures may be significantly

reduced or prevented by this measure. The related

literature does not at present provide a clear answer, as

randomized long-term clinical trials addressing this

particular parameter are still scarce. Some more

general reports do exist, however, addressing mainly

IMPLANTS IN THE LOAD CARRYING PART OF THE DENTITION •

961

Fig. 41-56. The implant shoulder-abutment complex of

the three left maxillary posterior implants has been pre

pared with fine-grain diamond burrs under abundant

water cooling in order to facilitate the configuration of

the related suprastructure. Particular emphasis was

given to margins following closely the scalloped course

of the soft tissue.

Fig. 41-57. In a case of reduced-diameter implants,

splinting of adjacent units may reduce the risk for tech

nical complications. A metal framework try-in prior to

the application of the ceramic veneering may help to

detect and eliminate an eventual non-passive fit at an

early stage.

Fig. 41-58. The vestibular view of the final metal-ce-

ramic restoration illustrates the impact on esthetics of a

metal margin. This aspect should be discussed with the

patient before treatment. In case of a high smile line,

one may consider an increased sink depth during im-

plant surgery

type and frequency of mechanical complications

(

Goodacre et al. 1999).

Among the frequently forwarded arguments to

plead

the case of splinting are reduced-diameter (Figs.

41-56

to 41-59) or short (i.e. less than 8 mm) implants,

implants inserted in low-density bone, implants

placed

in augmented or grafted (e.g. after anterior sinus floor

elevation) bone, or implant restorations in the posterior

segments of patients with verified nota

ble occlusal

parafunctions or bruxism. One should be

aware,

however, that the majority of these arguments

are

primarily based on clinical opinions and eventually

common sense, and that to date they are lacking

formal scientific evidence. In fact, there is increased

indication, derived from prospective multicenter

studies (although not addressing this parameter in

particular), that splinting does not appear to be a

prerequisite for preventing excessive crestal bone re-

sorption or even loss of osseointegration. Nowadays,

Fig. 41-59. On the 1-year follow-up radiograph an ac

ceptable marginal fidelity can be assessed.

the authors would seriously reconsider their respec-

tive choice related to the suprastructure design pre-

sented in Figs. 41-60 and 41-61. Definitely, in the pres

ence of standard-size (i.e. addressing both diameter

and length) implants, which are placed in normal

density original (non-augmented or grafted) bone,

single-unit restorations are recommended as they

comply better with the various parameters that are

important from a more biological point of view, as

demonstrated by the clinical example presented in

Figs. 41-62 and 41-63.

POSTERIOR SINGLE-TOOTH

REPLACEMENT

At the time when most implant systems had basically

only one "standard" dimension at disposition, this

962 • CHAPTER

Fig. 41-60. Occlusal view of a right maxillary posterior

three-unit implant restoration featuring premolar-sized

segments.

Fig. 41-61. The corresponding follow-up radiograph

confirms acceptable peri-implant conditions.

Fig. 41-62. Occlusal view of three independent, implant

supported fixed metal-ceramic restorations in the

right

posterior mandible.

corresponded to approximately 4–5 mm at the im-

plant shoulder and thus was optimally suited for

premolar-size restorations, featuring a continuously

increasing (towards coronally) flat axial emergence

profile and a mesio-distal diameter of about 7–8 mm

at the occlusal surface. Clinicians were not infre-

quently faced with posterior single-tooth sites, how-

ever, that did not comply with these dimensions, for

example in the case of missing first molars or after the

loss of persisting deciduous (primary) second molars.

As a consequence, the resulting implant restorations

featured either unfavorable excessive interproximal

overcontour or wide open embrasures. The first situ-

ation was difficult to clean, while the second led to

undesired food retention (impaction). Nowadays

most

of the leading implant manufacturers offer wide

body/wide-platform implants designed for the re-

placement of multirooted teeth (Fig. 41-3).

Premolar-size single-tooth restorations

When it comes to posterior single-tooth gaps that

dimensionally correspond to an average premolar,

Fig. 41-63. As confirmed by the follow-up radiograph,

an increased (more molar-like) dimension has been

given to the most distal restoration, despite the fact

that a standard-sized implant had to be used for re-

stricted bone volume reasons.

standard-size screw-form implants are well suited.

The respective implant dimensions which include

both the intrabony part and the implant shoulder,

offer the additional advantage of being mostly com-

patible with a limited bone volume in oro-facial direc-

tion. Whenever feasible, a straightforward low-main-

tenance restorative design is advocated, which nor-

mally consists of a cementable porcelain-fused-to-

metal crown with vestibular and oral axial contours

that are in harmony with the adjacent teeth and thus

provide adequate guidance for cheek and tongue

(

Figs. 41-64 to 41-66).

Molar-size single-tooth restorations

If a given posterior single-tooth gap corresponds

rather to the mesio-distal dimension of a molar, it is

recommended, for the reasons quoted in the previous

paragraph, that the insertion of a wide-neck implant

is planned (Bahat & Handelsman 1996). This ap-

proach, however, also requires the respective bone

volume in an oro-facial direction. If this is not the case,

the presurgical site analysis, eventually in the form of

IMPLANTS IN THE LOAD CARRYING PART OF THE DENTITION • 963

Fig. 41-64. Occlusal view of a single-tooth implant res

toration replacing a missing mandibular right second

premolar.

a bone-mapping, should identify whether it is possible

to have an implant placement in combination with a

lateral bone augmentation procedure according to a

simultaneous approach. If the local bone anatomy

requires a bone augmentation according to a staged

protocol, one has to carefully ponder and discuss with

the patient if this additional effort, risk and ultimately

also cost can be justified by an anticipated implant

restoration featuring close-to-ideal axial contours and

embrasures.

A clinical example demonstrating the potential of

increased-diameter implants for the optimal replace-

ment of a single missing mandibular molar is given in

Figs. 41-67 and 41-68.

Fig. 41-65. The 5-year radiographic follow-up displays

favorable bony conditions around this 12 mm solid

screw implant.

Fig. 41-66. On the oblique view one can notice that an

axial contour similar to that present on the adjacent

natural teeth has been applied to facilitate oral hygiene

and to assure adequate soft tissue (cheek and tongue)

guidance and support.

Fig. 41-67. In a case of the replacement of a single miss

ing molar, ideally the use of an implant with corre-

sponding dimensions is recommended to permit a res-

toration featuring optimal subjective comfort and clean-

sibility.

Fig. 41-68. On the 1-year radiographic follow-up a di-

ameter-increased ("wide neck") implant can be noted

which is essential for a suprastructure design without

extremely open interdental embrasures, which would

be prone to food retention and oral parafunctions.

964 • CHAPTER 41

Fig. 41-69. Clinical aspect of a single-tooth implant res

toration in the mandibular right premolar area.

Fig. 41-70. The related 2-year follow-up radiograph

shows a so-called unfavorable relationship between the

height of the suprastructure and the length of the sup

porting implant. The placement of a longer implant

was not possible due to the limited local bone condi-

tions.

Fig. 41-71. Oblique view of a molar single-tooth im

plant restoration in the left mandible.

Sites with limited vertical bone volume

Quite frequently the clinician is confronted with pos-

terior single-tooth gaps that present all of the major

prerequisites for successful implant therapy listed ear

lier in this chapter, with the exception of sufficient

vertical bone height for the insertion of an implant

featuring what is broadly accepted as an adequate

length of the implant itself and in relation to the

prospective length of the suprastructure. The question

that arises is whether there is a minimal implant

length required in the context of posterior single-tooth

restorations and whether the ratio between implant

length and suprastructure length has an influence on

crestal bone resorption and ultimately on the longev-

ity of the entire implant-suprastructure complex. The

Fig. 41-72. A short diameter-increased screw implant

supporting a long molar-sized suprastructure is dis-

played on the 1-year follow-up radiograph. Note that a

normal level of the first bone-to-implant contact has

been maintained.

analysis of the respective implant data collected at the

University of Geneva School of Dental Medicine in the

frame of a prospective multicenter study from 1989 to

2002, permitted the conclusion that shorter implants

(

6-8 mm) did not show more average crestal bone

resorption than longer implants (10-12 mm), and that

a so-called unfavorable ratio between implant length

and suprastructure height did not lead to more pro-

nounced crestal bone resorption (Bernard et al. 1995a,

Bernard & Belser 2002). This data is corroborated by

other recently published reports (ten Bruggenkate et

al. 1998, Bischof et al. 2001, Deporter et al. 2001).

Two examples of respective clinical anecdotal-type

evidence, one premolar-size and one molar-size sin-

gle-tooth restoration, are presented in Figs. 41-69 and

41-70 and Figs. 41-71 and 41-72.

IMPLANTS IN THE LOAD CARRYING PART OF THE DENTITION • 965

Table 41.6. Indications for screw-retained posterior

fixed implant restorations

Parameters to consider:

•

implant shoulder location incompatible with a cemented

suprastructure, i.e. inaccessible for meticulous excess

cement removal (> 2 mm submucosally)

•

reduced intermaxillary distance (< 5 mm)

•

foreseeable need for reintervention at the respective

implant site

•

extended implant-supported rehabilitations, involving

numerous implants

•

high overall level of complexity (e.g. non-parallel implants)

CLINICAL APPLICATIONS

Screw-retained implant restorations

For many years there was a strong tendency to design

most of the fixed implant restorations as screw-re-

tained suprastructures. Retrievability, and by this

maintaining the possibility for modification, exten-

sion or eventually repair of the prosthesis, was the

main rationale for this strategy. One should be aware,

however, that this approach also encompasses notable

specific inconveniences: colonization of the inner

compartments of the implant-abutment-suprastruc-

ture complex with mostly anaerobic microorganisms,

risk for loosening or fracture of screws, increased

technical complexity and related costs, possible inter

ference with structural parameters (weakening of the

metal-ceramic design) and esthetics, as well as a

higher maintenance profile" (Sutter et al. 1993, Wie

1995, Hebei & Gajjar 1997, Keller et al. 1998). As far as

the microbial colonization is concerned, it remains

unknown to date whether and under which condi-

tions this may have an adverse effect on the longevity

of osseointegrated implants.

For these reasons there exists currently a distinct

trend towards cementable fixed implant restorations

in the load carrying part of the dentition.

The main indications for screw-retention are listed

in Table 41-6.

Transocclusal screw-retention

If for one of the aforementioned reasons a transoc-

clusally screw-retained suprastructure is adopted,

several parameters should be taken into considera-

tion. First, the screw-access channel should be centred

on the occlusal surface in order not to interfere too

much with the area to be occupied by the cuspids.

A typical clinical example documenting an indica-

tion for a screw-retained posterior single-tooth resto-

ration is given in Figs. 41-73 to 41-75. A reduced inter

arch distance has led to a deeper than usual implant

shoulder location which in turn is neither accessible

for well-controlled excess cement removal nor in

reach

Fig. 41-73. Left lateral view showing the intermaxillary

relationship of a young patient in centric occlusion.

The missing maxillary second premolar has been re-

placed by a single-tooth, screw-retained implant resto

ration. Screw-retention was chosen for two reasons:

limited interocclusal distance and implant shoulder lo

cation incompatible with cementation.

Fig. 41-74. 1-year follow-up radiograph of the de

scribed 8 mm solid screw implant.

Fig. 41-75. Ideally, the screw-access channel should be

located in the center of the occlusal surface. This re-

duces both the risk for interference with an appropriate

metal-ceramic design in general, and the risk for porce

lain fractures in particular.

966 • CHAPTER 41

Fig. 41-76. Occlusal view of a mandibular master

model comprising two posterior implant analogues

and a prepared natural second premolar abutment.

Note the proximity of the mesial implant and the sec

ond premolar on the one hand, and the distinct lingual

position of the two implants on the other.

Fig. 41-78. The related 3-year follow-up radiograph

documents an only minimal distance between implant

shoulder and occlusal surface. Under such conditions,

a slight reduction of the alveolar ridge prior to implant

placement would have provided more vertical leeway

for compensating the lingual implant position and ulti

mately for covering the occlusal screw.

for the patient's routine oral hygiene. In order to bene

fit from their superior surface quality characteristics

and marginal precision, prefabricated machined cast-

on components have been used for the respective

suprastructure fabrication. Ideally, the screw-access

channel occupies a restricted area in the centre of the

occlusal table, and the distance from the head of the

screw to the occlusal surface should be sufficient for a

subsequent composite cover-restoration (Fig. 41-75).

Furthermore, the principles of the metal-ceramic

technology require a well-defined space for develop-

ing an adequate metal support for a uniform thickness

of the overlaying stratification of porcelain. Even in a

case of a well-centred occlusal perforation, the latter

occupies close to half of the mesio-distal and oro-facial

diameter of the occlusal table, and thereby signifi-

cantly weakens the overall mechanical resistance of

Fig. 41-77. The clinical view of the completed transoc

clusally screw-retained three-unit implant-supported

FPD demonstrates that the lingual implant position did

not allow for a suprastructure that is in line with the

adjacent teeth. Furthermore, the screws are reaching

the occlusal surface, leaving no space for an esthetic

coverage with composite resin.

the structure. If the screw-access channel is not cen-

tered, however, additional problems are created in the

sense of both weakening the restoration and interfer-

ing with esthetical criteria. Under such circumstances

one should consider, for example, the use of angled

abutments as currently offered by most of the leading

implant systems.

Another key parameter represents the interarch

distance, or more specifically, the distance between the

implant shoulder and the plane of occlusion. Accord-

ing to our experience this distance should be at least

equal to 5 mm. This is minimal and does not permit —

for esthetic reasons — the occlusal screw to be sub-

sequently covered with a composite resin restoration.

In this context 6-7 mm are clearly more adequate.

A combination of several well-known problems,

which are frequently encountered after implant place

ment in the posterior mandible, are shown in Figs.

41-76 to 41-78. Two implants have been inserted to

restore a distally shortened arch with a three-unit FPD.

Owing to the local bone anatomy, the implants were

placed in a more lingual position than the original

teeth (Fig. 41-76). The — for these particular circum-

stances — too superficial implant shoulder location did

not provide sufficient distance to gradually correct the

discrepancy between the actual implant shoulder po-

sition and the ideal occlusal location. Furthermore, the

necessity to keep the screw-access in the center of the

occlusal table, and the insufficient room for composite

screw-head coverage, ultimately led to a considerable

compromise (Fig. 41-77). The final radiograph (Fig.

41-78) clearly shows that the presurgical bone volume

would have permitted a vertical reduction of the eden

tulous bone crest to be performed prior to implant

insertion. By this token the suboptimal implant posi-

tion could have been partially corrected by the im-

plant restoration, and the occlusal screw covered by

composite resin, or a screw-retained restoration even-