Jan Lindhe. Clinical Periodontology

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IMPLANTS IN THE LOAD CARRYING PART OF THE DENTITION • 947

Fig. 41-4. Occlusal view of the mandible of a 22-year

old male patient. All premolars are congenitally miss

ing, the remainder of the dentition is intact.

Fig. 41-5. Final view after insertion of four implants, re

stored with cemented metal-ceramic suprastructures.

Fig. 41-6. Bilaterally distally shortened dental arch in

the mandible of a 66-year-old female patient.

cal advantage, as it contributes to the reduction of the

lever effect and resulting bending moments acting on

the junction between implant and suprastructure.

This is clinically relevant, as one should be aware of

the existence of an increasing body of evidence report-

ing technical complications, such as loosening/frac-

ture of screws or fracture of components/veneers,

related to implant-supported prosthetic suprastruc-

tures (Lundgren & Laurell 1994, Wie 1995, Hebel &

Gajjar 1997, Rangert et al. 1997, Bosse & Taylor 1998,

Glantz & Nilner 1998, Taylor 1998, Bragger 1999, Goo

dacre et al. 1999, Isidor 1999, Keith 1999, Schwarz 2000,

Johnson & Persson 2001). Besides mechanical type of

complications, a number of other conditions that are

rather biological in nature, like for example peri-im-

plantitis, are reported in the recent literature (Elle-

gaard et al. 1997a,b, Ellen 1998, Lang et al. 2000, Brag

ger et al. 2001, Quirynen et al. 2001, 2002). As these are

addressed in detail in another chapter, we will only

focus on aspects related to fixed posterior implant

restoration design and maintenance.

It is the aim of this chapter to present clinically

oriented guidelines and procedures for implant ther-

apy of various types of edentulism located in the load

carrying part of the dentition, addressing primarily the

partially dentate patient and mainly focusing on fixed

implant-supported prostheses.

Fig. 41-7. Four implants have been inserted to lengthen

the arch bilaterally to the region of the first molars.

Fig. 41-8. Five premolar-sized metal-ceramic elements

were used to restore the four implants.

Indications for implant restorations in the

load carrying part of the dentition

When it comes to partial edentulism in the posterior

segments of the jaws, implants are increasingly used

to either preserve sound mineralized tooth structure

to avoid removable partial dentures (RPDs) and

high-

risk conventional fixed partial dentures (FPDs).

This

includes situations with missing teeth in other-

wise

intact dentitions (Figs. 41-4, 41-5), the distally

shortened dental arch (Figs. 41-6 to 41-8), extended

948 • CHAPTER 41

Table 41-1. Indications for posterior implants

•

Replacement of missing teeth in intact dentitions (e.g.

congenitally missing premolars), i.e. preservation of tooth

structure

•

Avoidance of removable partial dentures (RPDs)

•

Increase of the number of abutments:

•

reduction of the prosthetic risk

•

application of the principle of segmenting

•

ease of eventual reinterventions

•

Maintenance of pre-existing crowns and FPDs

•

Following prosthetic complications and failures

Table 41.2. Impact of dental implants related to the

treatment of posterior partial edentulism

•

Favorable overall long-term results

•

Preservation of mineralized tooth structure

•

"Mechanical" advantages:

•

commercially pure (c.p.) titanium (biocompatibility,

mechanical properties, no risk for caries)

•

reproducible, prefabricated ("machined") primary,

secondary and tertiary components and auxiliary parts

•

Simplified clinical and laboratory protocols

Table 41.3. "High risk" conventional fixed partial

dentures (FPDs)

•

Long-span fixed partial bridges

•

Cantilever units (mainly distal extensions)

•

Missing "strategic" tooth abutments

•

Structurally/periodontally/endodontically compromised tooth

abutments

•

Reduced inter-arch distance

•

Presence of occlusal parafunctions/bruxism

edentulous segments, missing "strategic" tooth abut-

ments and structurally, endodontically or periodon-

tally compromised potential abutment teeth (Table

41-1).

The rapid advance in terms of the broad utilization

of dental implants is not exclusively based on the

associated favorable long-term reports for this treat-

ment modality. Other parameters such as purely "me-

chanical" advantages and the availability of prefabri-

cated components and auxiliary parts, which in turn

contribute notably to the simplification of the treat-

ment, had a significant impact on current concepts

and strategies as well (Table 41-2). Furthermore, clini-

cal decision making based on prosthetically oriented

risk assessment (Table 41-3), frequently leads to the

need for an increased number of abutments. The ob-

jective is to reduce the overall risk associated with a

given prosthetic solution on the one hand, and to

implement the principle of segmenting on the other.

A representative clinical example is given in Figs. 41-9

and 41-10. Instead of a conventional five-unit FPD,

replacing the missing maxillary left first and second

premolars as well as the absent first molar, three im-

plants have been inserted. This approach allowed the

avoidance of a long span bridge, a full coverage prepa

ration of the second molar and an associated surgical

crown lengthening procedure. The additional cost re-

lated to the three implants was justified by an overall

reduced prosthodontic risk. The question about ade-

quate number, size and distribution of implants will

be addressed later in this chapter. Prosthetically ori-

ented risk assessment comprises the comprehensive

evaluation of potential natural abutment teeth, in-

cluding their structural, restorative, periodontal and

endodontic status. As often several well-documented

treatment modalities are possible to replace missing

posterior teeth, this objective evaluation is of primary

importance and represents an ever increasing chal-

lenge to the clinician. This is illustrated by a maxillary

posterior segment where both the first premolar and

the first molar were missing (Figs 41-11 to 41-14). The

insertion of a five-unit tooth-borne FPD was discarded

because of its too invasive nature related to the intact

canine, and owing to a slightly questionable status of

the endodontically treated second premolar in view of

its eventual use as so-called "peer-abutment". Finally,

an implant has been placed at the site of the missing

first premolar and subsequently restored with a sin-

gle-unit restoration. As the proximity of the maxillary

sinus at the location of the missing first molar would

have required a grafting procedure to make an im-

plant installation possible, a three-unit tooth sup-

ported FPD was — after having duly discussed the

respective advantages and shortcomings with the pa-

tient — ultimately chosen. Having attributed to the

moderately compromised second premolar a "strate-

gic value" by using it as abutment of a short span

bridge, there was still a difficulty in consistently es-

tablishing clinical treatment plans that were fully

based on scientific evidence.

Still under the influence of the high level of predict-

ability and longevity reported for implant therapy, the

clinician is currently not only pondering implant-

borne restorations versus conventional FPDs, but in-

creasingly implant versus maintaining a compro-

mised tooth (Figs. 41-15, 41-16). In this particular clini

cal case, the evaluation focused on whether or not it

was objectively opportune to restore the structurally

compromised root of a maxillary second premolar.

This would have required — after elimination of the

decayed dentin — a surgical crown lengthening proce-

dure to create access to the margin, which in turn

would have included the risk for an adverse effect (

furcation proximity of the adjacent first molar) on the

neighboring teeth. Furthermore, a three-unit FPD was

out of the question for obvious reasons. Based on this

rationale and in the context of a more comprehensive

analysis of the situation, it was finally decided to

extract a

per se

treatable root and to replace it by an

IMPLANTS IN THE LOAD CARRYING PART OF THE DENTITION • 949

Fig. 41-9. Maxillary occlusal view displaying natural

Fig. 41-10. A similar restorative design has been chosen

and implant abutments prior to the insertion of an ex-for both natural and implant-supported metal-ceramic

tended porcelain-fused-to-metal restoration. In order to

suprastructures.

avoid a high-risk long-span FPD, three implants have been added in the left

posterior segment.

Fig. 41-11. Preoperative radiograph of the left maxilla,

revealing two missing dental elements. One should

note

in particular an intact canine, a structurally re

duced

second premolar and an extended recessus of

the sinus

in the area of the missing first molar.

Fig. 41-13. The postoperative radiograph documents

that

an endodontic revision has been performed on the

second premolar prior to its restoration with an adhe-

sive carbon-fibre-post based build-up and a metal-ce-

ramic crown (bridge retainer).

Fig. 41-12. Vestibular view of the prosthetic rehabilita-

tion of the maxillary left quadrant: an implant-sup-

ported single-tooth restoration on the site of the first

premolar, and a three-unit tooth-borne FPD to replace

the missing first molar.

Fig. 41-14. An identical prosthetic design has been ap

plied for both the implant-supported and the tooth-

supported restoration.

950 • CHAPTER 41

Fig. 41-15. Ad hoc radiograph of the upper right poste

rior sextant. One notes the presence of a structurally

compromised second premolar. The treatment of that

particular root would require build-up and crown-

lengthening (margin exposure, creation of an adequate

ferrule) which in turn would negatively affect the adja-

cent teeth.

Fig. 41-16. The postoperative radiograph documents

that the root of the second premolar has been replaced

by a single-tooth implant restoration. In particular, the

pre-existing metal-ceramic crown on the first molar

could be maintained by this approach.

Table 41.4. Controversial issues related to posterior

implant restorations

•

Adequate number, size (length/diameter), configuration and

distribution of implants

•

Cemented versus screw-retained (

transocclusal/transverse

screw-retention)

•

Single units versus splinted adjacent implant restorations

•

Longest possible versus shorter implants

•

Impact of implant axis

•

Optimal implant shoulder sink depth

•

Minimal ratio between implant length and suprastructure

height

•

Combination of natural teeth and implants in the same

restoration

•

Design of the optimal abutment-to-implant connection

•

Implant-specific occlusal concepts, including occluding

restorative materials, non-axial loading, type of guidance

during mandibular excursions

•

Healing times prior to functional loading

(

immediate/early/delayed)

•

Significance of offset/staggered implant positioning

implant. One should never forget, however, that this

trend to consider, under certain circumstances, an

implant as a better solution than treating "acrobati-

cally" a severely compromised tooth, calls for well

defined evidence-based respective criteria and repre-

sents a non-negligible ethical responsibility for the

clinician.

Controversial issues

Despite the ever-growing body of scientific evidence

indicating that implant therapy in the partially eden-

tulous patient is an overall highly predictable treat-

ment modality, several conceptional issues remain

controversial to date (Table 41-4). These controversial

issues include open questions addressing adequate

number, size and distribution of implants for optimal

therapy of a given type and configuration of partial

edentulism, as well as parameters related to occlusion

and occlusal materials, to implant axis, to the minimal

acceptable ratio between suprastructure height and

implant length, and – last but not least – related to

questions focusing more specifically on the mechani-

cal aspects and requirements of posterior implant

prosthodontics. Among these, the kind of connection

between implant and abutment have to be mentioned

in particular. Most of these questions will be discussed

in the remainder of this chapter, at length where pos-

sible and appropriate, or more superficially when solid

information is missing or when the topic is more

adequately covered by other authors in this book.

RESTORATION OF THE DISTALLY

SHORTENED ARCH WITH FIXED

IMPLANT-SUPPORTED

PROSTHESES

As pointed out earlier in this chapter, from 1989 to

2002 the distally shortened arch represented the most

frequent indication for the use of implants at the Uni-

versity of Geneva School of Dental Medicine. In fact,

out of a total of 3638 implants, almost 1500 were

placed in distally shortened arches, with close to 1000

implants inserted in the mandible and about 500 in the

posterior maxilla (Fig. 41-1). Implants were primarily

used when premolars were also missing. Whenever

possible, the adopted treatment strategy consisted of

IMPLANTS IN THE LOAD CARRYING PART OF THE DENTITION • 951

Fig. 41-17. Schematic representation of the distally

shortened dental arch. One therapeutic option consists

of replacing each missing occlusal unit up to the first

molar area with an implant.

Fig. 41-18. An alternative option would be the replace

ment of the three missing occlusal units by two im-

plants to support a three-unit suprastructure with a

central pontic.

Fig. 41-19. In a case of an inadequate bone volume in

the area of the missing first premolar, the placement of

two distal implants may be considered, leading to a

three-unit suprastructure with a mesial cantilever.

Fig. 41-20. In a case of an inadequate bone volume in

the area of the missing first molar, the placement of

two mesial implants may be considered, leading to a

three-unit suprastructure with a distal cantilever.

restoring the shortened dental arch to the region of the

first molars. Occasionally, implant therapy was re-

stricted to the premolar area, according to the princi-

ples of the well-established premolar occlusion con-

cept, or extended to the second molar area if an an-

tagonistic contact had to be established for an oppos-

ing natural second molar.

Number, size and distribution of implants

Although it is still unclear to date how many implants

of which dimension at which localization are required

to optimally rehabilitate a given edentulous segment in

the load carrying part of the dentition, a number of

different respective recommendations and related

strategies are currently in use, mostly derived from

traditional prosthodontic experience and attitudes,

and

based on so-called clinical experience and com

mon

sense rather than on solid scientific evidence. In

defense of the situation one should be aware, however,

that it is often difficult to design and carry out ran-

domized clinical trials evaluating exclusively and

Fig. 41-21. In a case of inadequate bone volume in the

area of the two missing premolars, the placement of a

distal implant may be considered, leading to a four-

unit suprastructure with a mixed (tooth and implant)

support.

without interference one specific parameter of con-

ceptual relevance.

In a situation where the canine is the most distal

remaining tooth of a dental arch, at least five different

options can be taken into consideration if one plans to

952 •

CHAPTER 41

Fig. 41-22. (a) Occlusal view of a cemented three-unit metal-ceramic FPD, supported by a mesial and a distal im

plant. (b) The corresponding 3-year follow-up radiograph confirms stable conditions at the implant to bone inter

face of the two 12 mm solid screw implants.

replace the missing teeth up to the first molar area

(

Figs. 41-17 to 41-21). These include the replacement

each missing occlusal unit by one implant (Fig.

41-

17), a mesial and a distal implant to support a

three-

unit FPD with a central pontic (Fig. 41-18), two

distal

implants to permit the insertion of a three-unit

FPD

with a mesial cantilever (Fig. 41-19), two mesial

implants to sustain a three-unit FPD with a distal

cantilever (Fig. 41-20) and, finally, only one distally

inserted implant in view of a four-unit FPD combining

implant and natural tooth support (Fig. 41-21).

As far as the recommendation to use premolar-

sized units for implant-borne posterior FPDs is con-

cerned, it has proven its practical validity in more than

ten years of clinical experience (Buser et al. 1997,

Bernard & Belser 2002). In fact, a crown featuring a

mesio-distal diameter of 7-8 mm at its occlusal surface

allows the optimal generation of a harmonious axial

profile, gradually emerging from the standard im-

plant shoulder

4-5 mm on average) to the maxi-

mum circumference. In addition, the width of the

occlusal table is confined, limiting thereby the risk for

unfavorable bending moments to the implant-abut-

ment-suprastructure complex (Belser et al. 2000).

Based on an increasing body of scientific evidence,

most clinicians' first choice represents the mesial and

distal implant and the respective FPD with the central

pontic (Figs. 41-22a,b). Prospective long-term mul-

ticenter data (Buser et al. 1997, Bernard & Belser 2002)

have confirmed the efficacy and predictability of this

specific modality. In fact, it permits the defined treat-

ment objective with a minimal number of implants

and associated costs. Although presently still lacking

formal evidence at the level of prospectively docu-

mented, randomized clinical trials, it appears from

clinical experience that the use of two implants to

support a four-unit FPD with two central pontics (

Figs. 41-23, 41-24) may be adequate in certain clinical

situations. Clinicians tend to use this approach in the

presence of favorable bone conditions, permitting

standard-size or wide-diameter implants with appro-

priate length (i.e. 8 mm or more).

If the alveolar bone crest dimension is also suffi

cient in an oro-facial direction, the utilization of wide-

diameter/wide-platform implants is preferred. Due

their increased dimensions a more adapted supras

tructure volume and improved axial emergence pro-

file of the implant restoration – when compared to a

so-called premolar unit – can be achieved in the molar

area (Figs. 41-25, 41-28). By this token the intercuspa

tion with an opposing natural molar is facilitated as

well.

Implant restorations with cantilever units

There is strong evidence in the relevant dental litera-

ture that cantilever units – in particular distal exten-

sions – of conventional tooth-borne FPDs are associ-

ated with a significantly higher complication rate

when compared to FPDs featuring a mesial and a

distal abutment and a central pontic. Respective fail-

ure rates could be attributed to decisive factors such

as non-vital abutment teeth as well as specific occlusal

conditions such as a reduced interarch distance

and/or occlusal parafunctions (Glantz & Nilner 1998).

These authors concluded in their review of the current

relevant literature that risks were lower for mechani-

cal failures with cantilevered implant-borne recon-

structions than with comparable conventional fixed

situations. The risks, however, do exist. As loss of

retention, which was one of the frequent complica-

tions encountered on conventional cantilevered pros-

theses, can easily be prevented when it comes to im-

plant-supported restorations of this type, the latter

seem to be a viable alternative in cases where the local

alveolar bone crest conditions do not allow the inser-

tion of an implant at the most favorable location. In

such situations the clinician has to ponder whether a

bone augmentation procedure can be objectively jus-

tified or if the risk for complications of a more simple,

straightforward approach can be considered low.

The 6-year clinical and radiographic follow-up of a

three-unit FPD featuring a mesial cantilever is pre-

sented in Figs. 41-29 and 41-30.

IMPLANTS IN THE LOAD CARRYING PART OF THE DENTITION • 953

Fig. 41-23. Occlusal view of a cemented four-unit metal-

ceramic FPD supported by a mesial and a distal im

plant.

Fig. 41-24. The related 2-year follow-up radiograph

documents that at the distal site a 10 mm solid screw

implant with an increased diameter ("wide body im-

plant") has been used.

Fig. 41-25. Occlusal view of a bilaterally distally short-

ened mandibular arch. Two implants have been placed

on either side to restore the arch to the area of the first

molars. The two distal implants feature an increased di-

ameter, better suited for the replacement of a missing

molar.

Fig. 41-26. The master model comprises color-coded

aluminum laboratory analogues at the implant sites, fa-

cilitating the technician's work in view of the supra-

structure fabrication. This is in contrast to the site of

the

prepared natural abutment.

Fig. 41-27. Once the metal-ceramic restorations are com-

pleted, no noticeable design difference between im

plant-

supported and tooth-supported suprastructures is

apparent.

Fig. 41-28. The respective clinical view confirms an ac-

ceptable integration of the four implant restorations in

the existing natural dentition.

954 • CHAPTER 41

Fig. 41-29. Six-year clinical follow-up view of a

mandibular three-unit FPD supported by two distal im

plants.

Combination of implant and natural tooth

support

There is general agreement that, from a purely scien

tific point of view, the combination of implants and

natural teeth to support a common FPD is feasible.

Clinical studies reporting prospectively documented

long-term data did not show adverse effects of splint

ing teeth to implants (Olsson et al. 1995, Gunne et al.

1997, 1999, Hosny et al. 2000, Lindh et al. 2001, Naert

et al. 2001a,b, Tangerud et al. 2002). The issue of con

necting implants and teeth by means of rigid or non-

rigid connectors, however, remains controversial to

date, but intrusion of natural roots has been reported

in the literature as a potential hazard of non-rigid

connection (Sheets & Earthman 1993). Most of the

recently published respective literature reviews con-

clude with the general clinical recommendation that

one should avoid, whenever possible, the direct com-

bination of implants and teeth as it may frequently

lead to a more complicated type of prosthesis. If there

no viable alternative available, a rigid type of con-

nection is preferred to prevent an eventual intrusion

of the involved abutment teeth (Lundgren & Laurell

1994, Gross & Laufer 1997).

Furthermore, it has been demonstrated that despite

the fundamental difference between an osseointe-

grated implant and a tooth surrounded by a periodon

tal ligament, the assumption that when these two

structures are combined, the entire occlusal load will

ultimately go to the implant and hence create an un-

favorable "cantilever-type" situation, is not valid from

a scientific point of view (Richter, Isidor, Bragger). In

fact, under normal function, such as during mastica-

tion, the tooth abutment is similarly load-bearing.

This may change, however, during severe occlusal

parafunctions, like nocturnal bruxism.

Fig. 41-30. The 6-year radiograph displays stable bony

conditions around the two implants supporting a ce

mented suprastructure with a premolar-sized mesial

cantilever unit.

Sites with extended horizontal bone volume

deficiencies and/or anterior sinus floor

proximity

It is not infrequent that distally shortened dental

arches do not feature an adequate local bone volume

at the prospective implant sites. This may refer to bone

height, bone width, alveolar bone crest axis or to the

vicinity of noble structures such as the mandibular

alveolar nerve canal or the anterior part of the maxil-

lary sinus. Often a combination of several of the men-

tioned limitations is encountered. As implant inser-

tion is clearly a three-dimensional surgical and re-

storative procedure on the one hand, and as "restora-

tion-driven" rather than "bone-driven" implant

placement is widely recommended on the other hand,

meticulous presurgical site analysis - based on the

envisioned treatment objective - is of primary impor-

tance. In order to keep the treatment as easy and

finally also as cost-effective as possible, one should

comprehensively evaluate whether a minor deviation

from the ideal implant position could be considered

acceptable, i.e. not leading to a compromise which

might adversely affect predictability, longevity

and/or

subjective comfort. This approach may still

permit in

some cases a professionally defendable re

sult, but

without a complexity of treatment that would

difficult to bear by some patients.

Advanced invasive procedures like lateral bone

augmentation, anterior sinus floor elevation, alveolar

ridge splitting or distraction osteogenesis, require a

high level of skills and respective experience and

hence should only be deployed if the relation between

benefit and risk/cost is soundly balanced (Buser et al.

1993, 1995, 1996, 1999, 2002, Chiapasco et al. 1999,

2001a, Simion et al. 2001, von Arx et al. 2001a,b,

Zitzmann et al. 2001).

In this specific context, a complex implant treat-

ment of a 67-year-old male patient whose most distal

remaining tooth in the left maxilla was an endodonti-

cally treated canine, is shown in Figs. 41-31 to 41-44.

Preoperative diagnosis revealed the necessity to per-

IMPLANTS IN THE LOAD CARRYING PART OF THE DENTITION • 955

form — according to a staged approach — first a com

bined lateral bone augmentation procedure and ante-

rior sinus floor elevation and, after a six months'

healing period, the insertion of implants. For the sinus

floor elevation the so-called "trap-door" technique

was

used and the created space grafted with auto

genous

bone chips and BioOss®. The lateral bone

augmentation comprised the fixation of a large block

graft in the area of the first premolar. After application

of an ePTFE barrier membrane, primary wound clo-

sure was achieved by sectioning of the periosteum of

the respective muco-periosteal flap. This often leads

to a lack of attached keratinized mucosa on the ves-

tibular aspect of the surgical site, which has to be

subsequently corrected, most conveniently at the mo

ment of implant placement. When it comes to sites that

have been previously grafted, the majority of sur-

geons advocate inserting one implant per missing

occlusal unit. This attitude appears to be based more

on the reflection that the overall heaviness of the

approach would largely justify this additional secu-

rity and/or on the hypothesis that augmented bone

may not have exactly the same "load-bearing" capac-

ity as the pre-existing bone, than on irrefutable scien

tific evidence. Accordingly, three adjacent screw-type

implants — the most distal one an increased-diameter

titanium screw — had been placed and subsequently

restored by a three-unit splinted metal-ceramic FPD

(

Figs. 41-38 to 41-44).

Results from a recently published longitudinal

clinical study (Buser et al. 2002) on 40 consecutively

Fig. 41-31. Initial radiograph of the maxillary left poste

rior segment of a 67-year-old male patient. The

canine

represents the most distal remaining tooth

element.

Note the marked extension of the anterior

recessus of

the sinus.

enrolled patients, who were first treated with a lateral

bone augmentation procedure and subsequently, in a

second stage, received implants inserted in the pre-

viously augmented area. In the totality of treated sites

implants could finally be placed as planned, and at the

5-year clinical and radiographic follow-up examina-

tion a 97% success rate was revealed. It was thus

concluded that lateral bone augmentation is indeed a

predictable procedure and that implants sub-

sequently inserted in augmented sites do have similar

success rates to implants placed in comparable non-

augmented sites.

956 • CHAPTER

Fig. 41-32. After elevation of a mucoperiosteal flap, anFig. 41-33. In view of an anterior sinus floor elevation

insufficient horizontal bone volume in the region of the

procedure, the first step for a respective osteotomy is

premolars becomes apparent.

performed. Attention is given not to perforate the

Schneiderian membrane.

Fig. 41-34. After the so-called "hinge-door" procedure

Fig. 41-35. The lateral bone augmentation procedure is

in the region of the maxillary sinus, an autogenous

completed by adding a combination of autogenous

bone block graft, harvested from the patient's retromo-bone chips, bone slurry and BioOss®.

lar area, is positioned and then immobilized by a fixation screw at the location of the missing first

premolar.

Fig. 41-36. Prior to flap repositioning and suturing, a

barrier membrane is applied.

Fig. 41-37. One month after primary wound closure

and uneventful healing, the involved soft tissues have

recovered their normal appearance.