CASE R E P O R T

Implant Treatment of Posterior Mandibular Sextants Henry Martinez, DDS;* Mithridade Davarpanah, MD, DDS;? Renato Celletti, DDS;' Patrick Missika, DDS5

ABSTRACT In mandibular posterior sextants an insufficient bone quality or volume may contraindicate implant placement. Crestal bone resorption, supra-eruption of teeth, and minimal bone coronal to the mandibular canal are the principal reasons for not plac- ing dental implants. The available prosthetic space is also a major factor in determining surgical and prosthetic treatment, Various surgical approaches are used to create adequate bone volume in the posterior mandible, thereby allowing the possibil- ity for implant placement. The therapeutic choice is made depending upon residual bone volume and available prosthetic space. The risks and disadvantages of the various techniques must be seriously evaluated and explained to the patient.

KEY WORDS: bone quality, bone volume, implant, mandibular sectors, posterior edentulous area

atisfactory long-term success rates have been reported S for the implant treatment of various types of edentu- lou~ness.l-~ In the posterior mandibular sextants an insufficient quality or volume of bone may contraindi- cate implant Pronounced alveolar resorption or a coronal positioning of the mandibular canal are the major causes of insufficient residual bone v ~ l u m e . ~ In some instances, multiple short implants (< 10 mm of bone) of standard diameter (3.75 or 4.00 mm) are a treatment possibility (Figure 1). There are various sur- gical approaches to recreate an adequate bone volume for the placement of dental implant^.^"'^ The available interarch distance also is a major factor in determining the treatment plan. This article presents a case series of patients treated according to a prosthetically driven surgical protocol. The protocol is based on determining a correct diagnosis of the patients' occlusion, interoc-

clusal space, and remaining alveolar ridge height and width. The residual alveolar anatomy determines whether standard implants can be placed or ridge aug- mentation is necessary. The patients in this series were treated with standard implants, periodontal crown lengthening procedures, guided bone regeneration, or onlay autologous grafts.

Table 1 presents a diagnostic classification system for evaluating varying anatomic, surgical, and prosthetic situations encountered prior to implant p1a~ement.I~ For example, evaluation of the available prosthetic space and the residual bone volume determines the surgical and prosthetic therapeutic choices (Figure 2; Table 1). Supra-eruption frequently is encountered in non- restored postereior areas.14 The arrangement of the interarch space with correction of the occlusal plane must be considered before the definitive prosthetic treatment is achieved.16

*Clinical Assistant Professor, Department of Oral Surgery, Faculty of Odontology, University of Paris VII, Paris, France. +Private Practice, Paris, and Clinical Assistant Professor, Department of Periodontology, Pitie Salpetriere Hospital, Paris, France. 'Private Practice, Rome, and Clinical Assistant Professor, Department of Prosthodontics, Univer- sity of G. d'Annunzio, Chieti, Italy; $Private Practice, Paris, and Pro- fessor and Chairman of Irnplantology, Department of Oral Surgery, University of Paris VII, Paris, France.

Reprint requests: Mithridade Davarpanah, MD, DDS, 174, rue de courcelles, 75017 Paris, France.

01999 B.C. Decker Inc.

CASE STUDIES

Case 1

A 55-year-old female patient had worn a removable partial denture for more than 15 years. She desired fixed restorations. The partial denture maintained an adequate prosthetic space. The clinical and radiologic diagnosis revealed sufficient bone width and height to allow placement of short standard fixtures (7 mm). A

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106 Clinical Implant Dentistry and Related Research, Volume I , Number 2, 1999

two-stage surgical approach allowed placement of five commercially pure machined titanium implants (Nobel Biocare, Paris, France) fixtures (four, 7 mm long and one, 15 mm long) in front of the mental foramen. Stan- dard abutments (3 mm height) were placed at second- stage surgery. Final ceramic screwed type restorations were placed (see Figure 1).

Case 2

A 60-year-old female patient was missing teeth in the lower right posterior sextant and consulted regarding the possibility of placing dental implants. The diagno- sis confirmed Class I occlusion and sufficient bone width to place a wide diameter implant in the molar area. The maxillary molars had over-erupted because the patient did not wear a removable partial denture. Implants (Implant Innovations, Palm Beach Gardens, Florida) were placed in the lower right sextant. The distal implant in the molar position was a 5-mm diam- eter implant. Gold UCLA abutments were used to fab-

ricate three splinted cemented crowns. The maxillary prosthetic treatment involved crown lengthening before restoring the teeth with ceramic fixed crowns (Figure 3).

Case 3

A 45-year-old female presented for implant treatment. She did not want to wear a removable denture. The computed tomography (CT) scan revealed a knife edge alveolar ridge with insufficient bone height in the lower left sextant. The maxillary left posterior teeth had supra- erupted slightly. The surgery in the mandible consisted of a cranial “J” autogenous graft. The control CT scan performed 7 months after graft placement revealed sat- isfactory bone healing. Three standard implants were placed in the left lower sextant. The implants were uncovered at 4 months and three splinted screw-type crowns were placed. The prosthetic treatment in the maxilla consisted of reshaping the crowns on the second premolar and the two molars (Figure 4).

Figure 1. A, Clinical view of a posterior partially edentulous mandible with advanced resorption. B, CT scan coronal cut. Note the lim- ited bone height. C, Clinical view of the final prosthetic rehabilitation supported by multiple standard implants. (Photograph provided by Dr. J.-P. Bresand, private practice, Paris, France.) D, Follow-up radiograph 10 years after prosthetic rehabilitation. Note the stable marginal conditions around the 7 mm implants.

Implants in Posterior Mandible 107

TABLE 1. M a n d i b u l a r Surg ica l T r e a t m e n t a n d Maxi l la ry P r o s t h e t i c T r e a t m e n t of t h e P o s t e r i o r S e c t o r s

Bone Volume

Prosthetic Space Limited 8-10 mm

Reduced Prosthetic treatment Coronoplasty if mild over-eruption of teeth Crown lengthening and fixed prosthesis if

pronounced over-eruption

Multiple standard short implants Wide diameter implants

Surgical treatment

Adequate

Increased

Prosthetic treatment

Surgical treatment Preservation of prosthetic space

Multiple standard short implants Wide diameter implants

Prosthetic treatment Preservation of prosthetic space if curve

Fixed prosthesis if curve of Spee is altered

Multiple standard short implants Wide diameter implants Supracrestal GBR (1-3 mm)

of Spee is normal

Surgical treatment

Insufficient < 8 mm

Prosthetic treatment Coronoplasty if mild over-eruption of teeth Crown lengthening and fixed prosthesis if

pronounced over-eruption

Multiple standard short implants Wide diameter short implants Transposition of inferior alveolar nerve

Preservation of prosthetic space

Multiple standard short implants Wide diameter short implants Supracrestal GBR (1 to 3 mm) Transposition of inferior alveolar nerve

Preservation of prosthetic space if curve of

Fixed prosthesis if curve of Spee is altered

Autogenous bone graft (onlay graft) Supracrestal GBR (3-5 mm)

Surgical treatment

Prosthetic treatment

Surgical treat ment

Prosthetic treatment

Spee is normal

Surgical treatment

Case 4

A 60-year-old male with unilateral edentulism con- sulted for fixed restoration in the lower right sextant. The clinical and radiographic diagnosis revealed a thin alveolar ridge. Treatment consisted of GBR with a tita- nium-reinforced ePTFE membrane. The membrane was stabilized with two fEation screws. The partial den- ture was not worn during the 9 month healing interval. The patient was seen every month during this period. Membrane exposure did not occur. After membrane removal, the newly regenerated tissue allowed for place- ment of three standard implants (Figures 5A-H).

DISCUSSION

Implant treatment of the posterior mandibular sextants often is complex, because the bone and prosthetic condi- tions frequently are inappropriate. The bone is less dense in the posterior region than in the anterior region of the mandible. The use of short implants (< 8.5 mm) of stan- dard diameter (3.75 or 4.00 mm) may be considered.

Many publications have shown higher failures rate at medium- and long-term using short implant^.^>^^ Nev- ertheless, Bernard et a1 report good results at 3 years with short implants in the posterior sextants.28

In the presence of a wide crest (> 8mm), the use of wide diameter implants may be considered.12 Indeed, short implants of wide diameter offer an anchorage sur- face that is superior to that of the standard implants.12 The decrease of length is compensated by the increase of diameter of the implant and is translated clinically into better primary stability of the implant (bicortical anchor- age). This approach often avoids the use of major surgical techniques (GTR, bone grafts, displacement of the dental nerve). The short-term results obtained with wide diam- eter implants are satisfactory (90 to 97% from 1 to 4 years).12>18,29,30 Nevertheless, some clinicians observe, at short-term, greater crestal bone loss than is reported with the standard implant.18,31 Renouard et a1 suggested this loss may be associated with the presence of an extremely dense cortical bone.31 These authors propose a modified,

108 Clinical Implant Dentistry and Related Research, Volume 1, Number 2, 1999

Figure 2. Depiction of posterior mandibular sectors with A, adequated prosthetic space; B, reduced prosthetic space; and C, increased prosthetic space. Left, limit bone volume. Right, insufficient bone volume.

less traumatic drilling process for the cortical bone. According to Sendax, there exists a critical diameter for an implant beyond which the necrosis threshold may be exceeded (personal communication) .32 An increase of cervical stresses leading to ischemia may explain this hypothesis. The formation of a biologic space after the second surgical intervention may explain the bone loss around wide implants without smooth collars. Indeed, the initial bone loss (about 1 mm) may go beyond the second thread because the first thread ends at the base of the external hexagon.

Stella et a1 described a radiographic technique that permits placements of implants lateral to the mandibular canal, using a precise surgical guide.32 The mandibular canal is located beforehand with the dental scanner.

However, the authors reported a high risk of inferior alveolar nerve damage (54%) when the implants are placed more than 20 mm distal to the mental foramen. According to Sethi, mandibular anatomy rarely allows the practitioner to by-pass the mandibular canal with- out risk of nerve damage.33

Autogenous bone grafts are indicated in the pres- ence of a large bone volume and large prosthetic space; they also allow treatment of the thin alveolar crests. The use of bone grafts in edentulous areas poses the prob- lem of sufficient soft tissue coverage. According to

Figure 3. A, Clinical view of three UCLA abutments (top); buccal view of the final crowns (bottom) (Photograph provided by Dr. P. Raygot, private practice, Paris, France.) B, Radiographic view of the three implants at 2 years. The implant diameters from mesial to distal are 3.75 mm, 4.00 mm, and 5.00 mm.

Implants in Posterior Mandible 109

Tulasne et a1 this technique exerts large constraints on the patient.l' Pulling on the soft tissues to cover the graft may eliminate the buccal space, which may be reconstructed later by gingival or cutaneous grafts. The manipulation of the soft tissues is less demanding when enlarging a thin crest of good height with the aid of a bone graft.33 Resorption of the bone graft may occur during the first 6 to 12 months of healing.3s It is advis- able to avoid the wearing of a removable prosthesis during the duration of bone healing (5-7 mo).

An increase of the height of the alveolar crest may be achieved by the technique of GBR. However, clinical

studies are limited.13722>23 Simion et a1 report a bone gain of 4 mm. Tinti et a1 obtained supracrestal tissue regeneration of more than 4 mm. The amount of regenerated tissue depends upon barrier stability and of the total time of h e a l i ~ ~ g . ' ~ > ~ ~ The use of autogenous bone was recommended. However, the number of cases reported was limited (6 cases and 14 sites), and the resistance and the stability of this newly formed bone has not been demonstrated. In 1998, Simion et a1 con- firmed the results obtained by Tinti.23 They reported an average tissue gain of 3 mm for 22 sites treated by GBR and demineralized bone, and a gain of 5 mm for 30

Figure 4. A, CT scan oblique cuts showing insufficient bone for implant placement. B, Note the thin ridge after flap elevation (Zefr); clinical view after placement and fixation of a cortical onlay graft (right). (Photograph provided by Dr. J.-F. Tulasne, private practice, Paris, France.) C, Radio- graphic CT scan control showing adequate bone after 6 months of heal-

, ing. D, Follow-up radiograph 1 year after implant placement. E, Clinical view of the final prosthetic rehabilitation. (Photograph provided by Dr. G. Audi, private practice, Paris, France.)

110 Clinical Implant Dentistry and Related Research, Volume I, Number 2, 1999

Figure 5. A, CT scan oblique cut showing an advance buccolingual ridge resorption. B, Occlusal view of a very thin ridge. C, Clinical view after placement of a GORE-TEX membrane (W.L. Gore, Flagstone, Arizona) stabilized with two futation screws. D, Periapical radiograph taken after membrane placement. E, Clinical view of the soft tissue after 9 months of healing (no removable partial denture was given to the patient) (left); appearance after flap elevation with the membrane in place (right). F, Clinical view of the crestal bone regeneration. Note the considerable amount of bony regeneration. G, Periapical x-ray after placement of three implants. H, Radiographic view 1 year after implant loading. Note the bone loss in the medial implant.

sites treated with GBR associated with autogenous bone.23 The results obtained with the technique of supracrestal regeneration are controversial. The com- plications related to membrane placement must be considered when applying these methods.

Transpositioning of the inferior alveolar nerve may be indicated in the posterior mandibular sectors. It is an intervention that presents an extremely high risk of pro- longed or permanent nerve damage.33 Transitory prob- lems related to sensitivity progressively disappeared when the manipulation of the dental nerve was delicately per- f ~ r m e d . ~ The sequellae (anesthesia, paresthesia, or dyses- thesia) are frequent and the reversibility of these prob- lems is unpredictable.26 Kan et a1 report post-surgical alteration of lip or chin sensitivity in 52% of 15 patients (21 sites)?5 Rosenquist presented a 94% normalization rate of sensitivity in 72 sites examined at 18 months, and considers this return of sensitivity to be Total nor- malization was obtained respectively in 21% of the patients at 1 week, and in 77% of the patients at 6 months.36 The risk of mandibular fructure also is increased in patients presenting with pronounced bone resorption or bone that is Dao and Mellor pub- lished a critical review of the literature regarding neu- rosensitive disturbances associated with the use of dental implants?8 For these authors, the large variation of the neurosensitive alterations (0 to 100%) reported in the lit- erature has not been evaluated sufficiently. All of the patients having undergone transpositioning of the infe- rior alveolar nerve show transitory sensitivity distur- bances, and 16% of the individuals have long-term sen- sory alterations. The major disadvantage of this technique is the risk of definitive loss of the lip or chin sensitivity in case of nerve trunk section. This high-risk therapeutic option should not be considered as a routine solution.

CONCLUSION

Bone and prosthetic management of the mandibular posterior sextants require precise diagnosis and treat- ment planning. The therapeutic choice depends on residual bone volume and the available prosthetic space. A multidisciplinary approach to treatment often is necessary when there is an altered prosthetic space and a diminished bone volume. The displacement of the dental nerve presents the risk of serious nerve dan- age, and the risks and disadvantages of all of the different techniques must be seriously evaluated and explained to the patient.

Implants in Posterior Mandible 11 1

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