British Journal of Oral and Maxillofacial Surgery(2003)41, 376–379© 2003 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.

doi:10.1016/S0266-4356(03)00171-2, available online at www.sciencedirect.com

Alveolar distraction before insertion of dental implants in the posteriormandible

A. Garcia-Garcia,∗, † M. Somoza-Martin,‡ P. Gandara-Vila,‡ N. Saulacic,§ J. M. Gandara-Rey¶∗Head of Section, Department of Maxillofacial Surgery, Complejo Hospitalario Universitario de Santiago; †Professorof Maxillofacial Surgery; ‡Assistant Professor, Oral Surgery Unit; §Postgraduate Student, Oral Surgery Unit;¶Professor of Oral Medicine, School of Dentistry, University of Santiago de Compostela,Santiago de Compostela, Spain

SUMMARY.We investigated the efficacy of alveolar distraction for reducing crown height:implant length ratioin the posterior mandible. Ten alveolar distractions were done in seven patients. The pre-distraction ratio ofrequired crown height to bone height available for implantation was in all cases ≥1. Two implants were placed ineach distracted area (total 20 implants). Before distraction, the mean (SD) predicted crown height was 12.8 (2.1)mm; mean bone height available for implantation was 7.8 (1.5) mm. After distraction and insertion of implants,mean crown height was 8.1 (1.9) mm, and mean implant length was 11.3 (1.9) mm. Before distraction, the meanrequired crown height:available bone height ratio was 1.7 (0.3); after distraction and insertion of implants, themean crown:implant ratio was 0.7 (0.2) (P > 0.0005). Alveolar distraction is effective for increasing the height ofthe alveolar ridge in the posterior mandibular region, and should be considered when the height of the predictedcrown that is required is greater than or equal to the maximum height of bone available for implantation.© 2003 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.

Keywords: Preprosthetic surgery; Bone augmentation; Osteodistraction

INTRODUCTION

One of the most common problems in oral implantologyis insufficient bone height between the alveolar ridgeand the dental canal, as a result of mandibular atrophyfrom edentulism. The edentulous mandible atrophiesprogressively, losing up to 50% of its original volume,1

and in severe cases this atrophy affects both the alve-olar ridge and the mandibular basal bone.2 Ulm et al.3

reported that the mandible loses 60% of its bone vol-ume during progressive atrophy, and that most is lost inthe early stage of the process. The areas showing mostloss are the molar and premolar regions (the posteriormandible). Insufficient bone height often means that thecrown height:implant length ratio is too great,4,5 whichis likely to reduce the implant’s useful lifespan, becauseof the leverage effect (degree of force acting on the im-plant site). It has been suggested that the length of thecrown should be no more than 50% of total length of theprosthesis.4

Transpositioning of the mandibular nerve is one op-tion to allow insertion of long and stable implants in themolar regions. However, problems with paraesthesia ofthe mental nerve have been reported.6 Another technique

is to place short implants above the mandibular canal.7

However, these implants are anchored only in the superiorcortex,which compromises their load-bearing capacity.4,5

Insertion of implants lingual to the nerve canal, throughbothsuperior and inferior cortex, hasalsobeendescribed.8

Neither of these techniques resolves the problemof exces-sive length of the crown. Another approach is autologousbone grafting, but such grafts are reabsorbed to a variableextent.9,10 An additional operation is also required to ob-tain the bone for grafting, and in some cases sufficientbone may not be available.

In recent years, another technique has gained increas-ing acceptance, namely alveolar distraction, which allowsthe height of the alveolar ridge to be increased so that im-plants can have shorter crowns. A key early figure in boneand soft-tissue distraction was Ilizarov,11 who initiallyused it in long bones. Subsequently, distraction techniqueshavebeenapplied to facial bonesandsoft tissues,12–14andmore specifically to the alveolar ridge, for which a numberof specially designed distractors are now available.15–20

In thepresent studywe investigated theefficacyof alve-olar distraction to increase the available height of bonein patients requiring implants in the posterior mandibularregion.

376

Alveolar distraction before insertion of dental implants 377

PATIENTS AND METHODS

Seven patients (5 men and 2 women; mean age (SD) 43(7) years) were studied. All patients had unilateral (n =4) or bilateral (n = 3) partial edentulism in the poste-rior mandible, with varying degrees of alveolar atrophy.None of the patients had teeth missing from the anteriormandible, or teeth remaining posterior to the edentuloussites. A total of 10 alveolar distractions were done, and20 implants inserted (16 International Team for Implan-tology Straumann, Switzerland, and 4 Frialoc, Friadent,Germany). In all cases opposing teeth were present in theupper jaw.

Investigations before distraction

The distance between the alveolar ridge and the dentalcanal wasmeasured by computed tomography (CT) (Den-tascan, Siemens, Somatom AR SP, Erlangen, Germany)(Fig. 1). The height of bone available for implantationwas estimated as this distance minus 1 mm (to ensure theintegrity of the dental canal). The required crown height(without distraction) was measured with the aid of plastercasts mounted on a Dentatus articulator (Hägersten, Swe-den) (Fig. 2). Both measurements were made by a personwho was unaware that distraction was under considera-tion. The required crown height:bone height ratio avail-able for implantation was calculated (Index A). Alveolardistraction was limited to those patients in whom index Awas≥1 (all those cases in the present study).

Surgical technique and alveolar distraction

In all patientsweusedLeadSystemdistractors (Leibinger,Germany), following the procedure described by Chin.21

Fig. 1 Preoperative measurement by computed tomography of boneheight (B) between the dental canal (A) and the alveolar border.

Fig. 2 Preoperative plaster casts of a patient who had alveolardistraction in the posterior section of the mandible. The casts aremounted on a Dentatus articulator for measurement of crown height.

We made an incision in the mucosa at the level of thealveolar crest, raised a vestibular mucoperiosteal flap,and left the lingual mucoperiosteum adhering to thebone (Fig. 3). One week after fitting the distractor, we

Fig. 3 Insertion of a Lead System distractor. (A) Threaded rod; (B)transport plate anchored to the mobile bone segment; (C) base platefixed to basal bone.

378 British Journal of Oral and Maxillofacial Surgery

started distraction at a rate of 0.5mm every 12 hoursfor 5 days, with the aim of increasing the height of thealveolar ridge by 5mm. Once this had been achieved,the distractor was left in place for 3 months to ensurebony consolidation, then removed to allow insertion ofimplants. The prothesis was constructed 3 months af-ter implantation. Follow-up ranged from 6 months to2 years.

Follow-up after implantation

Wemeasured the height of the crown the length of the im-plant in each case. Crown height was measured by thesame person as before operation, again unaware of thetreatment that had been used. The crown:implant lengthratio was calculated (Index B).

Results are expressed as means (SD).

RESULTS

The mean predicted height of crown required (as esti-mated before distraction) was 12.8 (2.1) mm. The meanavailable height of bone was 7.8 (1.5) mm. After dis-traction and implantation, the mean height of the crownwas 8.1 (1.9) mm, while the length of the implant was11.3 (1.9) mm. The mean ratio of predicted crown heightto bone available before distraction was 1.7 (0.3) (In-dex A), and the mean ratio of crown height to lengthof implant after distraction was 0.7 (0.1) (Index B).These two means differed significantly (P < 0.0005)(Fig. 4).

3.0

2.5

2.0

1.5

1.0

0.5

0.0

A

B

20 20N

Fig. 4 Box plots showing: A= ratio of predicted crown height toavailable bone height before distraction (Index A), and B= ratio ofactual crown height to actual implant length after distraction (Index B).Each plot shows the median, quartiles, and range (excluding outliers).

DISCUSSION

We used two measurements of available bone. Beforedistraction we used CT to measure the height availablebetween the alveolar ridge and the dental canal. Thismeasurement is obtained routinely in all patients who arebeing considered for dental implants. After distraction,however, we used panoramic radiography to calculateimplant length (total bone height minus 1mm), becauseof the high cost of a second CT and the higher dose ofradiation it would entail. We consider that the two mea-surements are objective, subject to minimal error, andperfectly comparable.

We consider that alveolar distraction is an attractiveoption for this type of cases of this type, the advantagesof which include the lack of any need for an additionaloperation as in autologous bone grafting and minimalrisk of nerve damage compared with displacement of thedental nerve. It is also easy to achieve a crown:implantratio of less than 1, as alveolar distraction acts both toreduce crown height and to permit increased implantlength. However, the technique is not without drawbacks,such as the discomfort caused by the distractor, whichmay interfere with eating.

In addition, as with any other technique, alveolar dis-traction may have complications.22,23

The Lead System distractor that we used is an in-traosseous distractor (in contrast to juxtaosseous distrac-tors, which are fitted over the vestibular surface of themandible). We have used intraosseous distractors becausethey can be adapted to the posterior region of the body ofthe mandible, where space is limited (particularly whenopposing teeth are present, as in all the cases treated byus). They are also considerably cheaper than juxtaosseousdistractors.

In conclusion, alveolar distraction in the posteriormandible is indicated in cases in which the ratio of pre-dicted required crown height:available bone height isgreater than or equal to 1, with the aim of achieving a ratioof crown:implant length of less than 1. Full evaluation ofthe effectiveness of alveolar distraction in the 20 implantsstudied by us will require long-term follow-up. However,good results have been obtained in animal models 1 yearpost-operatively.24

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The Authors

A. Garcia-Garcia MD, PhDHead of Section, Department of Maxillofacial SurgeryComplejo Hospitalario Universitario de SantiagoProfessor of Maxillofacial SurgeryM. Somoza-Martin DDSAssistant ProfessorOral Surgery UnitP. Gandara-Vila DDSAssistant ProfessorOral Surgery UnitN. Saulacic DDS, MScPostgraduate StudentOral Surgery UnitJ. M. Gandara-Rey MD, PhD, DDSProfessor of Oral Medicine, School of DentistryUniversity of Santiago de CompostelaSantiago de Compostela, Spain

Correspondence and requests for offprints to: Dr Abel Garcıa GarcıaMD, PhD, Head of Section, Professor of Maxillofacial Surgery,Facultad de Odontologıa, Entrerrios s/n, Santiago de Compostela,Spain.; E-mail: ciabelgg@usc.es

Accepted 12 August 2003