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The Endo-Distractor for preimplant mandibular regeneration
Received: 6 July 2008 Accepted: 29 September 2008 Available online 8 January 2009
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Original article L’Endo-distractor pour la reconstruction pre´implantaire de la mandibule 1, 2 C. Krenkel *, I. Grunert 1 Clinic of Oral and Maxillofacial Surgery, Paracelsus Medical School, Federal Medical Center Salzburg, Landeskrankenhaus Salzburg, Muellner Hauptstrasse 48, 5020 Salzburg, Austria 2 Dental School, Department of Prosthetic Dentistry, Medical University Innsbruck, Innsbruck,
The Endo-Distractor for preimplant mandibular regeneration
Austria
Summary Objective. A simple practical device for a new technique of vertical distraction osteogenesis was developed. The Endo-Distractor KrenkelW was originally intended for the anterior regeneration of highly atrophic mandibles. The Endo-Distractor features several novelties. Placement is made intraosseously in the basal cortical bone. The distraction screw length may be adapted to the depth of chin soft tissues. The quality of anchorage in the basal cortical bone guarantees the stability of the distraction vector. The endobuccal emergence is that of an artificial crown, and does not cause any patient discomfort. The device can easily be removed without secondary surgery. All kinds of implants may be placed after the retention time. This study’s objective was to evaluate the use of the Endo-Distractor KrenkelW in edentulous patients with highly atrophic mandibles. Material and method. This new device was used on 18 patients, between January 2000 and September 2004, who were then followed-up for at least 36 months. Mandibular atrophy was measured with a lateral cephalogram, then classified according to Atwood’s modified classification. The studied criteria included the amplitude of distraction, its duration, the distractor’s lingual tilt, the number and outcome of implants, and complications. Results. The sex ratio was 17 female for one male patient. The mean patient age was 56 years (43 to 66 years). The mean distraction amplitude was 11.3 mm (8 to 14 mm). The mean retention time was 186.8 days (37 to 309 days). The distractor’s mean lingual tilt was 4.38 (0 to 238). Two mandibular fractures occurred 6 weeks after placing the Endo-Distractor. The first one was treated medically, and the second one required removing the Endo-Distractor and osteosynthesis. An average of four interforaminal implants were placed for a total of 24 Bra˚nemarkW and 51 StraumannW implants. Four implants were lost in a patient due to infection. All other
Re´sume´ Objectif. Un appareillage simple a e´te´ cre´e´ pour une nouvelle technique de distraction alve´olaire. Le syste`me Endo-Distractor KrenkelW a e´te´ conc¸u pour reconstruire le secteur ante´rieur de mandibules tre`s atrophiques. L’Endo-Distractor pre´sente plusieurs particularite´s novatrices. L’implantation se fait au travers de l’os cortical basal. La longueur de la tige d’activation est adaptable en fonction de l’e´paisseur des parties molles mentonnie`res. La qualite´ de l’ancrage dans l’os cortical basal garantit la stabilite´ du vecteur de distraction. L’e´mergence endobuccale est celle d’une couronne dentaire classique, elle n’occasionne aucun inconfort. L’appareillage peut eˆtre facilement de´pose´ sans geste chirurgical secondaire. Des implants de tous types peuvent eˆtre adapte´s apre`s la contention. Cette e´tude avait pour but d’e´valuer l’Endo-Distractor chez des patients e´dente´s avec une mandibule tre`s atrophique. Mate´riel et me´thode. Ce nouveau syste`me a e´te´ utilise´ sur 18 patients de janvier 2000 a` septembre 2003, puis suivi pendant au moins 36 mois. L’atrophie mandibulaire a e´te´ mesure´e sur des te´le´radiographies de profil, puis classe´e selon la classification d’Atwood modifie´e. Les crite`res e´tudie´s ont e´te´ l’amplitude de distraction, la dure´e de contention, le degre´ de bascule linguale du distracteur, le nombre et le devenir des implants dentaires mis en place et les complications. Re´sultats. Le sex-ratio e´tait de 17 femmes pour un homme. L’aˆge moyen e´tait de 56 ans (de 43 a` 66 ans). L’amplitude moyenne de distraction e´tait de 11,3 mm (de 8 a` 14 mm) obtenue en 19,4 jours en moyenne (de 13 a` 28 jours). Le temps moyen de consolidation e´tait de 186,8 jours (de 37 a` 309 jours). La bascule linguale moyenne du distracteur e´tait de 4,38 (de 0 a` 238). Deux fractures mandibulaires sont survenues six semaines apre`s la mise en place du distracteur. L’une a e´te´ traite´e me´dicalement, la seconde a ne´cessite´ la de´pose de l’Endo-Distractor et une oste´osynthe`se.
* Corresponding author. e-mail : [email protected]
17 0035-1768/$ - see front matter ß 2008 Elsevier Masson SAS. All rights reserved. 10.1016/j.stomax.2008.09.014 Rev Stomatol Chir Maxillofac 2009;110:17-26
C. Krenkel, I. Grunert
implants were osseointegrated. No bone loss was detected at followup after functional loading. Discussion. These results show that alveolar distraction is possible on severely atrophic mandibles. The quality of bone and gum reconstruction is satisfactory both for functional and esthetic results. Surgical difficulty and rate of complications were lower than with conventional distraction techniques. ß 2008 Elsevier Masson SAS. All rights reserved. Keywords: Bone regeneration, Biomedical engineering, Distraction osteogenesis, Dental implants
Rev Stomatol Chir Maxillofac 2009;110:17-26
En moyenne, quatre implants interforaminaux par patient ont e´te´ mis en place, soit un total de 24 implants BranemackW et 51 implants StraumannW. Quatre implants ont duˆ eˆtre remplace´s chez un patient a` cause d’une infection. Tous les autres implants ont e´te´ parfaitement inte´gre´s. Aucune perte osseuse n’a e´te´ de´cele´e apre`s la mise en charge fonctionnelle. Discussion. Ces re´sultats montrent que la distraction alve´olaire est possible sur des mandibules tre`s atrophiques. La qualite´ de la reconstruction osseuse et gingivale aboutit a` un re´sultat esthe´tique et fonctionnel satisfaisant. Les difficulte´s chirurgicales et le taux de complications sont moins importants qu’avec les techniques de distraction classique. ß 2008 Elsevier Masson SAS. Tous droits re´serve´s. Mots cle´s : Re´ge´ne´ration osseuse, Bio-inge´nierie, Distraction osseuse, Implants dentaires
Introduction Several surgical procedures have been commonly used for the treatment of severe mandibular alveolar ridge atrophy. A longitudinal study [1] reported that dental implants were successfully placed in highly atrophic mandibles, down to a ridge height of 5 to 8 mm. A subsequent study [2] showed this treatment concept to be associated with severe complications. In the past decade a new technique was developed for the regeneration of the alveolar ridge by callus distraction, based on the concept of distraction osteogenesis. Early experiments with this concept were reported by an orthopedic research group investigating limb lengthening [3,4]. In the early 1990s, the concept of distraction osteogenesis was introduced in oral and maxillofacial surgery for the treatment of micrognathism in young children [5]. In 1994, preprosthetic alveolar ridge augmentation was attempted according to Ilizarov’s callus distraction technique with intraoral appliances. All of these distraction devices present disadvantages. Some of them use bulky intraoral rods, which compromise patient comfort and esthetics, particularly in the anterior mandible. They can be subject to lingual tilting during the distraction time, due to muscle pull. Many of these devices are anchored by two miniplates which have to be removed in a second procedure. The Endo-Distraction technique was developed as an alternative to the Groningen Distraction Device to avoid these disadvantages. A special device was designed (fig. 1). It is anchored in the center of the bony arch and the osteotomized alveolar 18
segment. It gradually separates the bony segments to a selected distance in the chosen direction (fig. 2a, b). This simple technique features two novelties: the distraction screw is anchored in a tap hole in the cortical bone of the basal segment, and the extralength of the distraction screw is placed in a sterile soft tissue pocket deep in the chin. The right-hand threaded distraction screw is guided in a tap hole in the mandibular body into a left-hand thread hollow screw, which is secured in the osteotomized transport segment. Winding the distraction screw counterclockwise does not unscrew the left-hand threaded hollow screw during distraction. The gap between the hollow screw and the distraction screw is sealed with a watertight silicon seal to keep saliva out.
Figure 1. The Endo-Distraction Device System. The distraction screw is placed inside a hollow screw, which rests on top of the distraction screw shoulder. A silicon seal inside the hollow screw prevents exposure of the bone to saliva.
The Endo-Distractor for preimplant mandibular regeneration
Figure 2. a: Endo-Distraction Device before distraction with the new concept of placing the extralength of the distraction screw through the bone in the soft tissue; b: Endo-Distraction Device at the end of the distraction period. Note that the original extralength is visible between the osteotomized bone segments.
We present the evaluation of 18 patients treated with this newly developed distraction device.
Material and methods Eighteen patients between 43 and 66 years of age were treated between January 2000 and September 2003 and prospectively followed-up until April 2007. The mean patient age was 56 years. The sex ratio was 17 female versus one male patient. All patients were severe bruxers. Mandibular atrophy was graded with a modified Atwood classification [6]. The six main classes were subdivided into five intermediate stages (table I). Mandibular atrophy was evaluated by preoperative lateral transcranial X-rays. Bone distraction, retention time, degree of distractor tilting, number and follow-up of implants, and complications were analyzed. Patients were evaluated clinically and by orthopantomography and cephalograms at the end of the distraction period and before placing dental implants.
Surgical procedure Surgery was performed under general anesthesia because of the risk of bleeding in the floor of the mouth. This also Table 1
Distribution of the 18 patients according to the modified Atwood classification. Modified Atwood classification (total = 18) Class Number
3–4 1
4 3
4–5 4
5 5
5–6 2
6 3
facilitated access for hemostasis in case of bleeding and the maintenance of strictly sterile conditions during surgery. A supraperiosteal dissection of the osteotomy segment preserved vascularization. The mental nerves were identified before extending the osteotomy laterally. A vertical bone volume of at least 8 mm was necessary to obtain segments at least 4 mm high to prevent fractures. The osteotomy was made parallel to the lower edge of the mandible (mandibular plane). The lower jaw was usually distracted at an angle of approximately 908 with the mandibular plane to match the normal tooth position. Compensatory tilt of 108 was possible in Angle class II or III occlusion. Depending on the planned direction, one or two parallel tap holes (Ø = 2.0 mm) were drilled in the body of the basal segment for the long right-hand threaded distraction screws. In the transport segment, one or two larger parallel tap holes (Ø = 3.2 mm) were drilled for the left-hand threaded hollow screw. The bone hole for the distraction screw (Ø = 2.7 mm) and the hollow screw (Ø = 4.0 mm) were tapped. The distraction screw was inserted into the bony arch subjacent to the superficial transport segment. It could reach down to 12 mm below the bone into the soft tissues of the chin (fig. 3a). This determined the amount of bone gained by distraction. The square end of the distraction screw rose 5 mm above the alveolar crest for screwdriver use. A ringshaped shoulder on the distraction screw prevented upward slippage through the hollow screw during distraction. When the long distraction screw was gradually unscrewed, it raised the osteotomy segment creating a chamber for callus formation (fig. 3b). The combination of the right-hand thread of the distraction screw and the left-hand thread of the hollow screw firmly secured the hollow screw, while the distraction screw was progressively unscrewed during distraction. 19
C. Krenkel, I. Grunert
Rev Stomatol Chir Maxillofac 2009;110:17-26
Figure 3. a: position of the Endo-Distraction Device. Note the gap at the osteotomy line before distraction. The extralength of the distraction screw is buried in a sterile soft tissue pocket; b: end of distraction. Note the newly formed callus between the osteotomized segments during retention.
Figure 4. Patient-controlled intraoral distraction with a simple screwdriver.
After osteotomy a primary gap of approximately 2–3 mm initiated juvenile callus formation. The Endo-Distraction Device was protected and secured with a cover screw for an initial retention time of approximately 1 week. Distraction began after the initial retention time and soft tissue healing. The end of the distraction screw is squareheaded for easy and controlled handling of the screwdriver by the patient in front of a mirror. A 3608 counterclockwise rotation of the screw raised the segment by 1 mm. The patient or a relative should strictly follow the distraction protocol and the surgeon’s instructions ‘‘at home’’. Weekly check-ups with the dentist are mandatory (fig. 4). The number and range of daily distraction should be increased, as the thickness and stretchability of the newly formed distraction callus increase. An initial distraction of 0.25 mm 20
once a day for the first 6 days is enough for a ‘‘soft start’’. This ensures safe osteogenesis without pain or fresh bleeding within the osteotomy gap. The daily distraction range should not exceed one tenth of the actual distraction gap. Extensions should be increased to 2 mm 0.25 mm a day for the next 6 days, followed by 3 mm 0.25 mm for another 4 to 8 days. Thus, a distraction of 11 to 15 mm is achieved within 16 to 20 days. At the end of distraction, the Endo-Distraction Device is secured with the cover screw during a latency period of 3 to 4 months. Retrieving the device is not very painful, because the screws are not firmly osseointegrated and are easily unscrewed (fig. 5a, b).
Implant placement and prosthodontic rehabilitation The newly developed technique is not limited to a specific dental implant design. Four long cylindrical implants with threads in the basal bone should be used. A simple customized stainless steel bar without extensions and a soft lining for the temporary denture should be used to enhance both healing and patient rehabilitation so as to obtain primary implant stability. The temporary bar is removed after 4 months and replaced by the final restoration. Titanium bar-retained overdentures or, more recently, customized gold bars and dentures retained with a galvanoforming procedure are used for standardized prosthodontic management. Additional 10–15 mm solid distal extensions guide the force applied to the interforaminal implants, thus preventing
The Endo-Distractor for preimplant mandibular regeneration
Figure 5. a: simple removal of the hollow screw with its characteristic left-hand thread; b: easy unscrewing of the nonosseointegrated threaded distraction screw with the right-hand thread leaving behind a tiny hole in the mucosa, which heals like an extraction socket.
Results
Figure 6. Lateral transcranial X-rays of a 53-year-old woman before and after distraction osteogenesis and implant placement. Note the ideal structure of the newly formed bone with a cortical layer and cancellous bone matching the original alveolar bone.
pressure on the distal mucosa. Repeated shaving of the denture in the molar region provides free space at the base of the denture for mucosal tissue and for vertical bone regeneration during functional loading (figs. 6 and 7).
The results are summarized in table II. The mean distraction range was 11.3 mm (min: 8 mm, max: 14 mm) achieved in an average of 19.4 (13 to 27) days. The mean retention time was 186.8 days (37 to 309 days). The mean tilting angle throughout the retention time was 4.48 (range: +2 to 238). Five patients presented with distractor anchorage loosening. This appeared 2 weeks after distraction osteogenesis was initiated and was due to a technical flaw during surgery for case No. 3, (weakening of the cortical layer of the osteotomy segment). The four other patients (cases No. 7, 8, 13, 14) presented with anchorage loosening, months after surgery, temporary denture in place. An average of four implants were placed interforaminally (total: 24 Bra˚nemarkW fixtures and 51 StraumannW implants). Four implants were lost during healing in one patient and were replaced by four standard implants in a second procedure. All other dental implants were osseointegrated without any visible signs of bone loss after loading. Two patients presented with an infection of the operative site. Bone fracture occurred in two patients, approximately 6 weeks after surgery. One of them underwent revision with internal miniplate fixation and removal of the Endo-Distraction Device. During revision, a ‘‘tumor-like’’ bulky calcified callus was detected, bridging the fracture ends with almost no mobility. The second case was managed by conservative 21
C. Krenkel, I. Grunert
Rev Stomatol Chir Maxillofac 2009;110:17-26
Figure 7. The case of a 51-year-old woman before and after treatment step by step. a: previous conventional rehabilitation with full dentures was unsatisfactory because of the severe atrophy of the alveolar ridge; b: X-ray performed after the placement of two Endo-Distraction Devices with an initial gap between the osteotomized segments; c: orthopantomography during the retention time, 8 weeks after surgery with juvenile callus formation before visible calcification; d: the intraoral aspect at the end of the retention time. Four months later, four interforaminal implants were placed and connected by a temporary bridge; e: the final restoration with a customized titanium bar and distal extensions; f: posttreatment X-rays with fully functional implants connected by a bar; g and h: comparison of the pre- and postoperative aspects.
22
The Endo-Distractor for preimplant mandibular regeneration
Table 2
Descriptive data (N = 18). Patient No. Age Modified Date of (gender) (years) Atwood surgery Classes
Implant Prosthetic Comments on Distraction Distraction Retention Tilting placed treatment osteotomy, angle amplitude time time distraction, (in days) (degrees) (in mm) (in days) implantation, (minus = prosthodontic lingual) treatment 4 Br 4 Br 4 Br
Yes Yes Yes
4 Str
Yes
–1.5
4 Br 4 Str
Yes
286
–1
4 Br
Yes
11 11 14 8 13 11 13.5 11 11 10
309 204 231 171 260 240 218 178 229 248
0 –4 –6.5 –6 –2 +2 –3 –2 –4 –7
4 Str 4 Br 4 Str 4 Str 3 Str 4 Str 4 Str 4 Str 4 Str 4 Str
Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes
13 12
263 202
–1 +1.5
4 Str 4 Str
Yes Yes
1 (f) 2 (f) 3 (f)
43 51 49
4.5 5.0 5.0
26.01.00 16 12.07.00 21 02.08.00 21 + 24
10 10 11
86 69 76
4 (f)
60
5.5
24.08.00 25
13
57
5 (f)
46
4.0
29.09.00 20
10
37
6 (f)
64
5.5
29.01.01
14
11
7 (f) 8 (f) 9 (f) 10 (f) 11 (f) 12 (f) 13 (f) 14 (f) 15 (f) 16 (f)
57 53 65 60 56 46 54 66 63 57
3.5 4.0 4.5 6.0 6.0 4.5 4.5 4.0 6.0 5.0
29.01.01 17.04.01 21.05.01 06.09.01 12.12.01 01.02.02 11.04.02 31.10.02 07.02.03 03.04.03
16 22 27 16 28 16 19 20 15 23
17 (f) 18 (m)
59 60
5.0 5.0
11.06.03 19 05.09.03 13
treatment with antibiotics and soft-food diet. An extralarge bone volume was detected at the fracture site in this patient at follow-up in 2007, because the fracture callus was superimposed on the distraction callus.
Discussion The Endo-Distraction Device was designed for preimplant mandibular regeneration Rehabilitation of edentulous patients requires that the alveolar ridge in the interforaminal region be restored for subsequent implant placement and fully implant-supported overdentures. Distraction is intended to rebuild the alveolar ridge to a sufficient height and width compatible with Atwood class 2 in an appropriate direction to restore the
–8 –4.5 –2
–23
Anchorage loosening of 2 Endo-Distraction Devices – replaced by 3 Endo-Distraction Devices Infection, osteomyelitis, guided bone regeneration (GBR) Infection, loss of 4 Br implants, bone grafting, another 4 Str implants placed Mandibular fracture, surgical treatment Anchorage loosening Anchorage loosening
Anchorage loosening Anchorage loosening Mandibular fracture Conservative treatment
sagittal interalveolar relation to normal. This reconstruction provides normal conditions with enough gum, and normal vestibulum and lingual folds (Fig. 7d). This ensures optimal oral hygiene for the implants in the interforaminal region. Unlike conventional techniques using short implants and long abutments, callus distraction rebuilds the alveolar ridge to an adequate height for the accommodation of long implants with short abutments; it minimizes the risk of abutment, implant fractures, or periimplantitis with a risk of jaw fracture. Since the regenerated alveolar crest provides a natural support for the lower lip, the patient’s features are restored to normal, with normal sensibility, normal tongue function, normal mastication, and restored facial esthetics. An argument often raised against bone reconstruction of edentulous atrophic mandibles is that, in nearly all cases it is not necessary for dental implants. But the limits of this 23
C. Krenkel, I. Grunert
‘‘conservative’’ approach was demonstrated by requiring emergency surgery in two patients with mandibular fractures secondary to implant placement, as outpatient. Other authors also reported fractures related to short dental implants in highly atrophic mandibles [2]. Chiapasco et al.’s studies [7–9] provided evidence that distraction osteogenesis was a reliable technique and the best method for vertical bone augmentation, superior to sandwich osteotomy and guided bone regeneration (GBR). The vertical bone gain obtained by distraction may reach 15 mm. It is obtained in a more ‘‘physiological’’ way than with vertical GBR, without need for bone grafting and features less morbidity. Another benefit is the progressive distraction of the surrounding soft tissue with a very low risk of wound dehiscence and bone exposure. The main indication for this technique is a mandible with severe Atwood class 4 to 6 atrophy [10]. The need for this technique in rather young edentulous women between 43 and 66 years of age came as a surprise. A similar gender distribution was reported in a recent study by the University of Amsterdam [11]. Early tooth loss appears to be caused by periodontal problems with associated bruxism and jaw contraction worsened by immunological disorders and endocrine factors. Two factors are responsible for highly atrophic edentulous mandibles: early tooth loss due to periodontal compromise, and insufficient dentures with poor function and destruction of the alveolar process. We preferred the Atwood classification for mandible atrophy because, unlike the metric Cawood and Howell classification [12], the Atwood classification discriminates between various types of alveolar atrophy. However, these are not easily classified because of the various mandible sizes. Therefore, templates using various magnifications are necessary. In the past decade many authors presented various devices for distraction in the interforaminal region. Conventional devices usually require two miniplates in connection with a threaded distraction rod outside the bone. The total length of this distraction rod determines the distraction amplitude. During early distraction with this conventional technique, the threaded rod projects far into the oral cavity. This may cause patient discomfort and be a limit to this technique. The open space between the oral cavity and the osteotomy gap may induce other complications, i.e. infections, osteomyelitis, or even spontaneous mandibular fractures [13]. Distraction devices secured with plates require secondary surgery for removal, with repeated dissection of the mental muscles. This may jeopardize the esthetic outcome and leave the patient with a ‘‘witch’s chin’’ in the worst case. Lingual tilting of the proximal bone fragment, due to 24
Rev Stomatol Chir Maxillofac 2009;110:17-26
genioglossus or orbicularis oris muscle pull, is a common complication of conventional devices, even of bidirectional devices. It requires secondary bone grafting before implant placement [14]. New approaches based on novel principles were considered when it was understood that no modification of conventional distraction devices with plates would eliminate the inherent problems. A solution was the Endo-Distraction Device, which offers benefits for both patients and surgeons. Minimal tilting of the distraction device during retention is one of these benefits. The amount of tilting was assessed by lateral transcranial radiographs with the distraction screw postoperatively and at the end of the retention period (latency period). The expected tilting angle of less than 58 is accounted for in the treatment plan by routinely adding 58 to achieve the best distraction vector. For one of our patients, the 238 tilt was due to severe infection. Tilting was negligible in all other patients. The Endo-Distraction Device comes in a single shape and size for all types of mandibles, all directions and all distances of distraction. This gives maximum flexibility for planning both the distraction vector and the callus distraction width. Another advantage of the technique is that secondary surgery for removal is unnecessary, since the threaded distraction screw and the threaded hollow screw are visible in the oral cavity and the retrieval instruments can be easily used. If two Endo-Distraction Devices are used, these should be absolutely parallel. This can be achieved by using the specially designed surgical instrument set (special surgical divider and instruments) and a step-by-step surgical technique. Endo-Distraction with a single device is much easier. It can be performed with a slimmer surgical instrument set and causes fewer complications. The theoretical concern of permanent rotating movements around the single distraction screw due to the lack of gum elasticity proved to be unfounded. The single Endo-Distraction Device is the first choice for vertical augmentation. A smaller device is under development for small single-tooth defects. The Endo-Distraction Device is planned and managed like a conventional dental implant with, for example, 3D-navigation systems and drilling templates based on CT scans. Problems and complications were noted during the learning curve. The two severe infections may have several explanations. The procedure was performed on a site where strictly sterile conditions are essential. The intraoperative communication between the oral cavity and the submental fat pad, which is very sensitive to salivary infections, is a major source of
The Endo-Distractor for preimplant mandibular regeneration
complications. Perfect preoperative oral hygiene, oral mouth rinsing with chlorhexidine, and rinsing of the tap holes with BetadineW as well as treating with systemic antibiotics for 3 days are mandatory to prevent these infections. Jaw clenching with early temporary dentures on top of the distraction device may overload the system. This may have induced anchorage loosening for the device reported in five patients. For four of these patients, this was associated with extremely long retention times of more than 6 months. Anchorage loosening did not have serious consequences for the patients other than shrinkage of the distraction callus by approximately 25%. Because of these complications, temporary dentures are no longer recommended during the retention time. Instead, dental implants should be placed within 3 to 4 months after surgery. Patients are given instructions not to wear the upper dentures during the night to prevent damage from occlusal overload. The daytime absence of the lower dentures during the retention time does not compromise the patient esthetically, because the regenerated ridge prevents the lower lip from slipping backward. Long threaded dental implants were initially used like positioning screws after a short retention time. Successful in the first three cases, the short retention time caused severe problems due to infections in the next two cases. These were thought to be attributable to the mobility of the implants in the newly formed bone, which was still of poor quality, approximately 2 months after surgery. As a result, implant placement was postponed, until orthopantomography showed clear evidence of calcification, and retention times were extended to 6 months. Individual intrinsic factors determine the retention time needed for optimal calcification, the key for stable implant placement and immediate loading with temporary dentures. Postmenopausal hormonal status, malnutrition, malabsorption, avitaminosis, and calcium metabolism disorders may all be responsible for poor bone growth and may increase the healing time. Therefore, dental implants should be placed neither too early (1–2 months) nor too late (9 months), because this may cause infection or anchorage loosening of the device. These problems can be avoided with the new concept of placing four long implants anchored in the basal segment, as positioning screws, approximately 4 months after surgery and connecting them with a temporary bar and temporary prosthesis. Special attention should be paid to blood supply, especially in the proximal segment, to prevent necrosis and infection. This means that the terminal branches of the sublingual arteries should be preserved during dissection. The dissection
technique was accordingly modified from a subperiosteal to a supraperiosteal approach after case No. 5. The two cases of mandibular fractures, 4 to 6 weeks after surgery, were due to nocturnal bruxism. The distraction callus formation showed that osteosynthesis, as performed in one patient, was not necessary. Conservative treatment is sufficient in such cases. Acknowledgements The authors would like to thank Mr Georg Lixl for the technical assistance during the production of the prototypes for patenting. They are indebted to Dr Holm for his technical assistance and thank Dr Christian Weismann from the Radiology Department, Paracelsus Medical School of Salzburg, for the CT and ultrasound follow-ups.
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Original article L’Endo-distractor pour la reconstruction pre´implantaire de la mandibule 1, 2 C. Krenkel *, I. Grunert 1 Clinic of Oral and Maxillofacial Surgery, Paracelsus Medical School, Federal Medical Center Salzburg, Landeskrankenhaus Salzburg, Muellner Hauptstrasse 48, 5020 Salzburg, Austria 2 Dental School, Department of Prosthetic Dentistry, Medical University Innsbruck, Innsbruck,
The Endo-Distractor for preimplant mandibular regeneration
Austria
Summary Objective. A simple practical device for a new technique of vertical distraction osteogenesis was developed. The Endo-Distractor KrenkelW was originally intended for the anterior regeneration of highly atrophic mandibles. The Endo-Distractor features several novelties. Placement is made intraosseously in the basal cortical bone. The distraction screw length may be adapted to the depth of chin soft tissues. The quality of anchorage in the basal cortical bone guarantees the stability of the distraction vector. The endobuccal emergence is that of an artificial crown, and does not cause any patient discomfort. The device can easily be removed without secondary surgery. All kinds of implants may be placed after the retention time. This study’s objective was to evaluate the use of the Endo-Distractor KrenkelW in edentulous patients with highly atrophic mandibles. Material and method. This new device was used on 18 patients, between January 2000 and September 2004, who were then followed-up for at least 36 months. Mandibular atrophy was measured with a lateral cephalogram, then classified according to Atwood’s modified classification. The studied criteria included the amplitude of distraction, its duration, the distractor’s lingual tilt, the number and outcome of implants, and complications. Results. The sex ratio was 17 female for one male patient. The mean patient age was 56 years (43 to 66 years). The mean distraction amplitude was 11.3 mm (8 to 14 mm). The mean retention time was 186.8 days (37 to 309 days). The distractor’s mean lingual tilt was 4.38 (0 to 238). Two mandibular fractures occurred 6 weeks after placing the Endo-Distractor. The first one was treated medically, and the second one required removing the Endo-Distractor and osteosynthesis. An average of four interforaminal implants were placed for a total of 24 Bra˚nemarkW and 51 StraumannW implants. Four implants were lost in a patient due to infection. All other
Re´sume´ Objectif. Un appareillage simple a e´te´ cre´e´ pour une nouvelle technique de distraction alve´olaire. Le syste`me Endo-Distractor KrenkelW a e´te´ conc¸u pour reconstruire le secteur ante´rieur de mandibules tre`s atrophiques. L’Endo-Distractor pre´sente plusieurs particularite´s novatrices. L’implantation se fait au travers de l’os cortical basal. La longueur de la tige d’activation est adaptable en fonction de l’e´paisseur des parties molles mentonnie`res. La qualite´ de l’ancrage dans l’os cortical basal garantit la stabilite´ du vecteur de distraction. L’e´mergence endobuccale est celle d’une couronne dentaire classique, elle n’occasionne aucun inconfort. L’appareillage peut eˆtre facilement de´pose´ sans geste chirurgical secondaire. Des implants de tous types peuvent eˆtre adapte´s apre`s la contention. Cette e´tude avait pour but d’e´valuer l’Endo-Distractor chez des patients e´dente´s avec une mandibule tre`s atrophique. Mate´riel et me´thode. Ce nouveau syste`me a e´te´ utilise´ sur 18 patients de janvier 2000 a` septembre 2003, puis suivi pendant au moins 36 mois. L’atrophie mandibulaire a e´te´ mesure´e sur des te´le´radiographies de profil, puis classe´e selon la classification d’Atwood modifie´e. Les crite`res e´tudie´s ont e´te´ l’amplitude de distraction, la dure´e de contention, le degre´ de bascule linguale du distracteur, le nombre et le devenir des implants dentaires mis en place et les complications. Re´sultats. Le sex-ratio e´tait de 17 femmes pour un homme. L’aˆge moyen e´tait de 56 ans (de 43 a` 66 ans). L’amplitude moyenne de distraction e´tait de 11,3 mm (de 8 a` 14 mm) obtenue en 19,4 jours en moyenne (de 13 a` 28 jours). Le temps moyen de consolidation e´tait de 186,8 jours (de 37 a` 309 jours). La bascule linguale moyenne du distracteur e´tait de 4,38 (de 0 a` 238). Deux fractures mandibulaires sont survenues six semaines apre`s la mise en place du distracteur. L’une a e´te´ traite´e me´dicalement, la seconde a ne´cessite´ la de´pose de l’Endo-Distractor et une oste´osynthe`se.
* Corresponding author. e-mail : [email protected]
17 0035-1768/$ - see front matter ß 2008 Elsevier Masson SAS. All rights reserved. 10.1016/j.stomax.2008.09.014 Rev Stomatol Chir Maxillofac 2009;110:17-26
C. Krenkel, I. Grunert
implants were osseointegrated. No bone loss was detected at followup after functional loading. Discussion. These results show that alveolar distraction is possible on severely atrophic mandibles. The quality of bone and gum reconstruction is satisfactory both for functional and esthetic results. Surgical difficulty and rate of complications were lower than with conventional distraction techniques. ß 2008 Elsevier Masson SAS. All rights reserved. Keywords: Bone regeneration, Biomedical engineering, Distraction osteogenesis, Dental implants
Rev Stomatol Chir Maxillofac 2009;110:17-26
En moyenne, quatre implants interforaminaux par patient ont e´te´ mis en place, soit un total de 24 implants BranemackW et 51 implants StraumannW. Quatre implants ont duˆ eˆtre remplace´s chez un patient a` cause d’une infection. Tous les autres implants ont e´te´ parfaitement inte´gre´s. Aucune perte osseuse n’a e´te´ de´cele´e apre`s la mise en charge fonctionnelle. Discussion. Ces re´sultats montrent que la distraction alve´olaire est possible sur des mandibules tre`s atrophiques. La qualite´ de la reconstruction osseuse et gingivale aboutit a` un re´sultat esthe´tique et fonctionnel satisfaisant. Les difficulte´s chirurgicales et le taux de complications sont moins importants qu’avec les techniques de distraction classique. ß 2008 Elsevier Masson SAS. Tous droits re´serve´s. Mots cle´s : Re´ge´ne´ration osseuse, Bio-inge´nierie, Distraction osseuse, Implants dentaires
Introduction Several surgical procedures have been commonly used for the treatment of severe mandibular alveolar ridge atrophy. A longitudinal study [1] reported that dental implants were successfully placed in highly atrophic mandibles, down to a ridge height of 5 to 8 mm. A subsequent study [2] showed this treatment concept to be associated with severe complications. In the past decade a new technique was developed for the regeneration of the alveolar ridge by callus distraction, based on the concept of distraction osteogenesis. Early experiments with this concept were reported by an orthopedic research group investigating limb lengthening [3,4]. In the early 1990s, the concept of distraction osteogenesis was introduced in oral and maxillofacial surgery for the treatment of micrognathism in young children [5]. In 1994, preprosthetic alveolar ridge augmentation was attempted according to Ilizarov’s callus distraction technique with intraoral appliances. All of these distraction devices present disadvantages. Some of them use bulky intraoral rods, which compromise patient comfort and esthetics, particularly in the anterior mandible. They can be subject to lingual tilting during the distraction time, due to muscle pull. Many of these devices are anchored by two miniplates which have to be removed in a second procedure. The Endo-Distraction technique was developed as an alternative to the Groningen Distraction Device to avoid these disadvantages. A special device was designed (fig. 1). It is anchored in the center of the bony arch and the osteotomized alveolar 18
segment. It gradually separates the bony segments to a selected distance in the chosen direction (fig. 2a, b). This simple technique features two novelties: the distraction screw is anchored in a tap hole in the cortical bone of the basal segment, and the extralength of the distraction screw is placed in a sterile soft tissue pocket deep in the chin. The right-hand threaded distraction screw is guided in a tap hole in the mandibular body into a left-hand thread hollow screw, which is secured in the osteotomized transport segment. Winding the distraction screw counterclockwise does not unscrew the left-hand threaded hollow screw during distraction. The gap between the hollow screw and the distraction screw is sealed with a watertight silicon seal to keep saliva out.
Figure 1. The Endo-Distraction Device System. The distraction screw is placed inside a hollow screw, which rests on top of the distraction screw shoulder. A silicon seal inside the hollow screw prevents exposure of the bone to saliva.
The Endo-Distractor for preimplant mandibular regeneration
Figure 2. a: Endo-Distraction Device before distraction with the new concept of placing the extralength of the distraction screw through the bone in the soft tissue; b: Endo-Distraction Device at the end of the distraction period. Note that the original extralength is visible between the osteotomized bone segments.
We present the evaluation of 18 patients treated with this newly developed distraction device.
Material and methods Eighteen patients between 43 and 66 years of age were treated between January 2000 and September 2003 and prospectively followed-up until April 2007. The mean patient age was 56 years. The sex ratio was 17 female versus one male patient. All patients were severe bruxers. Mandibular atrophy was graded with a modified Atwood classification [6]. The six main classes were subdivided into five intermediate stages (table I). Mandibular atrophy was evaluated by preoperative lateral transcranial X-rays. Bone distraction, retention time, degree of distractor tilting, number and follow-up of implants, and complications were analyzed. Patients were evaluated clinically and by orthopantomography and cephalograms at the end of the distraction period and before placing dental implants.
Surgical procedure Surgery was performed under general anesthesia because of the risk of bleeding in the floor of the mouth. This also Table 1
Distribution of the 18 patients according to the modified Atwood classification. Modified Atwood classification (total = 18) Class Number
3–4 1
4 3
4–5 4
5 5
5–6 2
6 3
facilitated access for hemostasis in case of bleeding and the maintenance of strictly sterile conditions during surgery. A supraperiosteal dissection of the osteotomy segment preserved vascularization. The mental nerves were identified before extending the osteotomy laterally. A vertical bone volume of at least 8 mm was necessary to obtain segments at least 4 mm high to prevent fractures. The osteotomy was made parallel to the lower edge of the mandible (mandibular plane). The lower jaw was usually distracted at an angle of approximately 908 with the mandibular plane to match the normal tooth position. Compensatory tilt of 108 was possible in Angle class II or III occlusion. Depending on the planned direction, one or two parallel tap holes (Ø = 2.0 mm) were drilled in the body of the basal segment for the long right-hand threaded distraction screws. In the transport segment, one or two larger parallel tap holes (Ø = 3.2 mm) were drilled for the left-hand threaded hollow screw. The bone hole for the distraction screw (Ø = 2.7 mm) and the hollow screw (Ø = 4.0 mm) were tapped. The distraction screw was inserted into the bony arch subjacent to the superficial transport segment. It could reach down to 12 mm below the bone into the soft tissues of the chin (fig. 3a). This determined the amount of bone gained by distraction. The square end of the distraction screw rose 5 mm above the alveolar crest for screwdriver use. A ringshaped shoulder on the distraction screw prevented upward slippage through the hollow screw during distraction. When the long distraction screw was gradually unscrewed, it raised the osteotomy segment creating a chamber for callus formation (fig. 3b). The combination of the right-hand thread of the distraction screw and the left-hand thread of the hollow screw firmly secured the hollow screw, while the distraction screw was progressively unscrewed during distraction. 19
C. Krenkel, I. Grunert
Rev Stomatol Chir Maxillofac 2009;110:17-26
Figure 3. a: position of the Endo-Distraction Device. Note the gap at the osteotomy line before distraction. The extralength of the distraction screw is buried in a sterile soft tissue pocket; b: end of distraction. Note the newly formed callus between the osteotomized segments during retention.
Figure 4. Patient-controlled intraoral distraction with a simple screwdriver.
After osteotomy a primary gap of approximately 2–3 mm initiated juvenile callus formation. The Endo-Distraction Device was protected and secured with a cover screw for an initial retention time of approximately 1 week. Distraction began after the initial retention time and soft tissue healing. The end of the distraction screw is squareheaded for easy and controlled handling of the screwdriver by the patient in front of a mirror. A 3608 counterclockwise rotation of the screw raised the segment by 1 mm. The patient or a relative should strictly follow the distraction protocol and the surgeon’s instructions ‘‘at home’’. Weekly check-ups with the dentist are mandatory (fig. 4). The number and range of daily distraction should be increased, as the thickness and stretchability of the newly formed distraction callus increase. An initial distraction of 0.25 mm 20
once a day for the first 6 days is enough for a ‘‘soft start’’. This ensures safe osteogenesis without pain or fresh bleeding within the osteotomy gap. The daily distraction range should not exceed one tenth of the actual distraction gap. Extensions should be increased to 2 mm 0.25 mm a day for the next 6 days, followed by 3 mm 0.25 mm for another 4 to 8 days. Thus, a distraction of 11 to 15 mm is achieved within 16 to 20 days. At the end of distraction, the Endo-Distraction Device is secured with the cover screw during a latency period of 3 to 4 months. Retrieving the device is not very painful, because the screws are not firmly osseointegrated and are easily unscrewed (fig. 5a, b).
Implant placement and prosthodontic rehabilitation The newly developed technique is not limited to a specific dental implant design. Four long cylindrical implants with threads in the basal bone should be used. A simple customized stainless steel bar without extensions and a soft lining for the temporary denture should be used to enhance both healing and patient rehabilitation so as to obtain primary implant stability. The temporary bar is removed after 4 months and replaced by the final restoration. Titanium bar-retained overdentures or, more recently, customized gold bars and dentures retained with a galvanoforming procedure are used for standardized prosthodontic management. Additional 10–15 mm solid distal extensions guide the force applied to the interforaminal implants, thus preventing
The Endo-Distractor for preimplant mandibular regeneration
Figure 5. a: simple removal of the hollow screw with its characteristic left-hand thread; b: easy unscrewing of the nonosseointegrated threaded distraction screw with the right-hand thread leaving behind a tiny hole in the mucosa, which heals like an extraction socket.
Results
Figure 6. Lateral transcranial X-rays of a 53-year-old woman before and after distraction osteogenesis and implant placement. Note the ideal structure of the newly formed bone with a cortical layer and cancellous bone matching the original alveolar bone.
pressure on the distal mucosa. Repeated shaving of the denture in the molar region provides free space at the base of the denture for mucosal tissue and for vertical bone regeneration during functional loading (figs. 6 and 7).
The results are summarized in table II. The mean distraction range was 11.3 mm (min: 8 mm, max: 14 mm) achieved in an average of 19.4 (13 to 27) days. The mean retention time was 186.8 days (37 to 309 days). The mean tilting angle throughout the retention time was 4.48 (range: +2 to 238). Five patients presented with distractor anchorage loosening. This appeared 2 weeks after distraction osteogenesis was initiated and was due to a technical flaw during surgery for case No. 3, (weakening of the cortical layer of the osteotomy segment). The four other patients (cases No. 7, 8, 13, 14) presented with anchorage loosening, months after surgery, temporary denture in place. An average of four implants were placed interforaminally (total: 24 Bra˚nemarkW fixtures and 51 StraumannW implants). Four implants were lost during healing in one patient and were replaced by four standard implants in a second procedure. All other dental implants were osseointegrated without any visible signs of bone loss after loading. Two patients presented with an infection of the operative site. Bone fracture occurred in two patients, approximately 6 weeks after surgery. One of them underwent revision with internal miniplate fixation and removal of the Endo-Distraction Device. During revision, a ‘‘tumor-like’’ bulky calcified callus was detected, bridging the fracture ends with almost no mobility. The second case was managed by conservative 21
C. Krenkel, I. Grunert
Rev Stomatol Chir Maxillofac 2009;110:17-26
Figure 7. The case of a 51-year-old woman before and after treatment step by step. a: previous conventional rehabilitation with full dentures was unsatisfactory because of the severe atrophy of the alveolar ridge; b: X-ray performed after the placement of two Endo-Distraction Devices with an initial gap between the osteotomized segments; c: orthopantomography during the retention time, 8 weeks after surgery with juvenile callus formation before visible calcification; d: the intraoral aspect at the end of the retention time. Four months later, four interforaminal implants were placed and connected by a temporary bridge; e: the final restoration with a customized titanium bar and distal extensions; f: posttreatment X-rays with fully functional implants connected by a bar; g and h: comparison of the pre- and postoperative aspects.
22
The Endo-Distractor for preimplant mandibular regeneration
Table 2
Descriptive data (N = 18). Patient No. Age Modified Date of (gender) (years) Atwood surgery Classes
Implant Prosthetic Comments on Distraction Distraction Retention Tilting placed treatment osteotomy, angle amplitude time time distraction, (in days) (degrees) (in mm) (in days) implantation, (minus = prosthodontic lingual) treatment 4 Br 4 Br 4 Br
Yes Yes Yes
4 Str
Yes
–1.5
4 Br 4 Str
Yes
286
–1
4 Br
Yes
11 11 14 8 13 11 13.5 11 11 10
309 204 231 171 260 240 218 178 229 248
0 –4 –6.5 –6 –2 +2 –3 –2 –4 –7
4 Str 4 Br 4 Str 4 Str 3 Str 4 Str 4 Str 4 Str 4 Str 4 Str
Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes
13 12
263 202
–1 +1.5
4 Str 4 Str
Yes Yes
1 (f) 2 (f) 3 (f)
43 51 49
4.5 5.0 5.0
26.01.00 16 12.07.00 21 02.08.00 21 + 24
10 10 11
86 69 76
4 (f)
60
5.5
24.08.00 25
13
57
5 (f)
46
4.0
29.09.00 20
10
37
6 (f)
64
5.5
29.01.01
14
11
7 (f) 8 (f) 9 (f) 10 (f) 11 (f) 12 (f) 13 (f) 14 (f) 15 (f) 16 (f)
57 53 65 60 56 46 54 66 63 57
3.5 4.0 4.5 6.0 6.0 4.5 4.5 4.0 6.0 5.0
29.01.01 17.04.01 21.05.01 06.09.01 12.12.01 01.02.02 11.04.02 31.10.02 07.02.03 03.04.03
16 22 27 16 28 16 19 20 15 23
17 (f) 18 (m)
59 60
5.0 5.0
11.06.03 19 05.09.03 13
treatment with antibiotics and soft-food diet. An extralarge bone volume was detected at the fracture site in this patient at follow-up in 2007, because the fracture callus was superimposed on the distraction callus.
Discussion The Endo-Distraction Device was designed for preimplant mandibular regeneration Rehabilitation of edentulous patients requires that the alveolar ridge in the interforaminal region be restored for subsequent implant placement and fully implant-supported overdentures. Distraction is intended to rebuild the alveolar ridge to a sufficient height and width compatible with Atwood class 2 in an appropriate direction to restore the
–8 –4.5 –2
–23
Anchorage loosening of 2 Endo-Distraction Devices – replaced by 3 Endo-Distraction Devices Infection, osteomyelitis, guided bone regeneration (GBR) Infection, loss of 4 Br implants, bone grafting, another 4 Str implants placed Mandibular fracture, surgical treatment Anchorage loosening Anchorage loosening
Anchorage loosening Anchorage loosening Mandibular fracture Conservative treatment
sagittal interalveolar relation to normal. This reconstruction provides normal conditions with enough gum, and normal vestibulum and lingual folds (Fig. 7d). This ensures optimal oral hygiene for the implants in the interforaminal region. Unlike conventional techniques using short implants and long abutments, callus distraction rebuilds the alveolar ridge to an adequate height for the accommodation of long implants with short abutments; it minimizes the risk of abutment, implant fractures, or periimplantitis with a risk of jaw fracture. Since the regenerated alveolar crest provides a natural support for the lower lip, the patient’s features are restored to normal, with normal sensibility, normal tongue function, normal mastication, and restored facial esthetics. An argument often raised against bone reconstruction of edentulous atrophic mandibles is that, in nearly all cases it is not necessary for dental implants. But the limits of this 23
C. Krenkel, I. Grunert
‘‘conservative’’ approach was demonstrated by requiring emergency surgery in two patients with mandibular fractures secondary to implant placement, as outpatient. Other authors also reported fractures related to short dental implants in highly atrophic mandibles [2]. Chiapasco et al.’s studies [7–9] provided evidence that distraction osteogenesis was a reliable technique and the best method for vertical bone augmentation, superior to sandwich osteotomy and guided bone regeneration (GBR). The vertical bone gain obtained by distraction may reach 15 mm. It is obtained in a more ‘‘physiological’’ way than with vertical GBR, without need for bone grafting and features less morbidity. Another benefit is the progressive distraction of the surrounding soft tissue with a very low risk of wound dehiscence and bone exposure. The main indication for this technique is a mandible with severe Atwood class 4 to 6 atrophy [10]. The need for this technique in rather young edentulous women between 43 and 66 years of age came as a surprise. A similar gender distribution was reported in a recent study by the University of Amsterdam [11]. Early tooth loss appears to be caused by periodontal problems with associated bruxism and jaw contraction worsened by immunological disorders and endocrine factors. Two factors are responsible for highly atrophic edentulous mandibles: early tooth loss due to periodontal compromise, and insufficient dentures with poor function and destruction of the alveolar process. We preferred the Atwood classification for mandible atrophy because, unlike the metric Cawood and Howell classification [12], the Atwood classification discriminates between various types of alveolar atrophy. However, these are not easily classified because of the various mandible sizes. Therefore, templates using various magnifications are necessary. In the past decade many authors presented various devices for distraction in the interforaminal region. Conventional devices usually require two miniplates in connection with a threaded distraction rod outside the bone. The total length of this distraction rod determines the distraction amplitude. During early distraction with this conventional technique, the threaded rod projects far into the oral cavity. This may cause patient discomfort and be a limit to this technique. The open space between the oral cavity and the osteotomy gap may induce other complications, i.e. infections, osteomyelitis, or even spontaneous mandibular fractures [13]. Distraction devices secured with plates require secondary surgery for removal, with repeated dissection of the mental muscles. This may jeopardize the esthetic outcome and leave the patient with a ‘‘witch’s chin’’ in the worst case. Lingual tilting of the proximal bone fragment, due to 24
Rev Stomatol Chir Maxillofac 2009;110:17-26
genioglossus or orbicularis oris muscle pull, is a common complication of conventional devices, even of bidirectional devices. It requires secondary bone grafting before implant placement [14]. New approaches based on novel principles were considered when it was understood that no modification of conventional distraction devices with plates would eliminate the inherent problems. A solution was the Endo-Distraction Device, which offers benefits for both patients and surgeons. Minimal tilting of the distraction device during retention is one of these benefits. The amount of tilting was assessed by lateral transcranial radiographs with the distraction screw postoperatively and at the end of the retention period (latency period). The expected tilting angle of less than 58 is accounted for in the treatment plan by routinely adding 58 to achieve the best distraction vector. For one of our patients, the 238 tilt was due to severe infection. Tilting was negligible in all other patients. The Endo-Distraction Device comes in a single shape and size for all types of mandibles, all directions and all distances of distraction. This gives maximum flexibility for planning both the distraction vector and the callus distraction width. Another advantage of the technique is that secondary surgery for removal is unnecessary, since the threaded distraction screw and the threaded hollow screw are visible in the oral cavity and the retrieval instruments can be easily used. If two Endo-Distraction Devices are used, these should be absolutely parallel. This can be achieved by using the specially designed surgical instrument set (special surgical divider and instruments) and a step-by-step surgical technique. Endo-Distraction with a single device is much easier. It can be performed with a slimmer surgical instrument set and causes fewer complications. The theoretical concern of permanent rotating movements around the single distraction screw due to the lack of gum elasticity proved to be unfounded. The single Endo-Distraction Device is the first choice for vertical augmentation. A smaller device is under development for small single-tooth defects. The Endo-Distraction Device is planned and managed like a conventional dental implant with, for example, 3D-navigation systems and drilling templates based on CT scans. Problems and complications were noted during the learning curve. The two severe infections may have several explanations. The procedure was performed on a site where strictly sterile conditions are essential. The intraoperative communication between the oral cavity and the submental fat pad, which is very sensitive to salivary infections, is a major source of
The Endo-Distractor for preimplant mandibular regeneration
complications. Perfect preoperative oral hygiene, oral mouth rinsing with chlorhexidine, and rinsing of the tap holes with BetadineW as well as treating with systemic antibiotics for 3 days are mandatory to prevent these infections. Jaw clenching with early temporary dentures on top of the distraction device may overload the system. This may have induced anchorage loosening for the device reported in five patients. For four of these patients, this was associated with extremely long retention times of more than 6 months. Anchorage loosening did not have serious consequences for the patients other than shrinkage of the distraction callus by approximately 25%. Because of these complications, temporary dentures are no longer recommended during the retention time. Instead, dental implants should be placed within 3 to 4 months after surgery. Patients are given instructions not to wear the upper dentures during the night to prevent damage from occlusal overload. The daytime absence of the lower dentures during the retention time does not compromise the patient esthetically, because the regenerated ridge prevents the lower lip from slipping backward. Long threaded dental implants were initially used like positioning screws after a short retention time. Successful in the first three cases, the short retention time caused severe problems due to infections in the next two cases. These were thought to be attributable to the mobility of the implants in the newly formed bone, which was still of poor quality, approximately 2 months after surgery. As a result, implant placement was postponed, until orthopantomography showed clear evidence of calcification, and retention times were extended to 6 months. Individual intrinsic factors determine the retention time needed for optimal calcification, the key for stable implant placement and immediate loading with temporary dentures. Postmenopausal hormonal status, malnutrition, malabsorption, avitaminosis, and calcium metabolism disorders may all be responsible for poor bone growth and may increase the healing time. Therefore, dental implants should be placed neither too early (1–2 months) nor too late (9 months), because this may cause infection or anchorage loosening of the device. These problems can be avoided with the new concept of placing four long implants anchored in the basal segment, as positioning screws, approximately 4 months after surgery and connecting them with a temporary bar and temporary prosthesis. Special attention should be paid to blood supply, especially in the proximal segment, to prevent necrosis and infection. This means that the terminal branches of the sublingual arteries should be preserved during dissection. The dissection
technique was accordingly modified from a subperiosteal to a supraperiosteal approach after case No. 5. The two cases of mandibular fractures, 4 to 6 weeks after surgery, were due to nocturnal bruxism. The distraction callus formation showed that osteosynthesis, as performed in one patient, was not necessary. Conservative treatment is sufficient in such cases. Acknowledgements The authors would like to thank Mr Georg Lixl for the technical assistance during the production of the prototypes for patenting. They are indebted to Dr Holm for his technical assistance and thank Dr Christian Weismann from the Radiology Department, Paracelsus Medical School of Salzburg, for the CT and ultrasound follow-ups.
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