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 »  Home  »  Dental Implant 1  »  Immediate Loading of Implant-Fixed Mandibular Prostheses
Immediate Loading of Implant-Fixed Mandibular Prostheses
A Prospective 18-Month Follow-Up Clinical Study - Preliminary Report

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Lino Esteve Colomina, MD, DDS
Private Practice, Alicante, Spain.


Until now it has been thought that a stress-free period was essential for the rigid anchoring of implants to bone. Adell et al.1 and Brånemark et al.,2 after an empirical review of a large number of clinical series, proposed a stress-free waiting period of 3 to 6 months. Similarly, experimental studies showed that immediately loaded implants could not obtain direct boneimplant contact, developing instead a fibrous interface.3 However, the immediate loading protocol used with overdentures on four interforaminal implants, as described by Ledermann, 4 has been successfully practiced for more than 20 years, using several implant designs.5–8 With regard to fixed prostheses, the preloading healing period has recently been questioned by several authors who have achieved similar success rates with immediately and traditionally loaded implants,9–14 reaching the conclusion that a waiting period is not an absolute necessity, but rather a “therapeutic reserve,” as defined by Henry and Rosenberg in 1994.10 Even immediately loaded single implants have given totally satisfactory results, both in experimental15 and clinical16 studies. The latest experimental work reinforces the thesis that failure to obtain direct boneimplant contact is not caused by immediate loading but by micromotion at the interface that exceeds a certain level.17–20 This level is yet to be determined, but according to Brunski21 is about 100 mm.
Although there is growing scientific evidence that implants can be immediately loaded in certain cases, the indications for immediate loading have yet to be sufficiently specified because the main factors involved are not completely understood. Given the importance to patients of safely receiving their prostheses immediately after surgery, it is vital to undertake clinical research to redefine the timing of loading and to establish reliable immediate loading protocols that can be put into general use. This paper supports the case for immediate functional loading; we present our preliminary results from a systematic application of immediate loading to fixed mandibular prostheses.

MATERIAL AND METHODS.
Between February 1999 and September 2000, 13 fixed mandibular prostheses were immediately loaded. These were the hybrid type (11 total and 2 partial) with 61 implants from four different manufacturers: 13 Klöckner (Klöckner SA, Barcelona, Spain), 17 Astra (Astra Tech, Mölndal, Sweden), 5 ITIStraumann (Straumann Institute, Waldenburg, Switzerland), and 26 Eckermann (Eckermann Laboratorium, Orihuela, Spain). The protocol was to load transitional fixed prostheses within 2 weeks of inserting the implants.

Patients.
The patients were consecutively enrolled in the prospective longitudinal trial. The selection was made using the basic criteria of an absence of risk factors such as heavy smoking, bruxism, or general ill health. Patients with lesions in the area to be implanted or with defects that needed to be treated with regenerative techniques were also rejected. The average age was 57.5 years (range, 41–74 years). Five of the 13 patients had natural teeth, fixed prostheses, or removable partial prostheses with the presence of the anterior tooth as an antagonist. The eight remaining patients were full upperdenture wearers.
All of the implants in this series were placed into bone of a density of from I to III, according to the classification systems currently in use. They required an insertion torque .25 N (the approximate maximum force of the operator’s fingers when the insertions were performed manually). With regard to the number of implants, two fixed prostheses were placed on four implants, seven prostheses were placed on five implants, one partial prosthesis was placed on four implants, and the other partial prothesis was placed on two implants. The minimum length of the implants was 10 mm, and the maximum length was 16 mm.
In six patients, the removal of residual dentition and the installation of implants were done simultaneously. In two patients, these two operations were separated by 2 months. The other five patients already had the surgical zone edentulous .12 months.

Surgical Procedure.
After infiltration of local anaesthetics, a full thickness midcrestal incision was made in the edentulous anterior mandible or, in the cases where residual teeth had to be removed at the same time, a sulcular incision was used. The mucoperiosteal flaps were raised, and the mental neurovascular bundles were identified. At that point, the extractions of the remaining teeth were carefully made, and the alveoli were thoroughly debrided until any residual soft tissues were eliminated. To optimize the ridge width for receiving the implants, the exposed bone crest was flattened by performing a horizontal osteotomy with a round bur at a low speed and under copious sterile saline irrigation. Implant recipient sites were prepared, and the implants were inserted according to each manufacturer’s instructions. The abutments were immediately connected in the case of Astra and ITI implants, and the flaps were then repositioned and sutured.
Immediately after having sutured the surgical wound and while under local anaesthesia, an interocclusal registration was taken using a customized baseplate. Transfer copings were then connected, and an impression was taken with a polyether rubber material (Impregum, Espe Dental AG, Munich, Germany) using either a custom-made tray in the case of simultaneous extractions or the preexisting or prefabricated denture in edentulous cases.
The healing caps were screwed in, and the patient was then dismissed after having received detailed instructions on postoperative wound hygiene and the use of a 0.2% chlorhexidine gel (Perio-Kin, Laboratories Kin, Barcelona, Spain). Oral antibiotics were prescribed for 2 days preoperatively and, with NSAIDs, were maintained for 1 week after surgery.

Immediate Transitional Prosthesis.
In the laboratory, the working cast incorporating implant analogues was transferred to the previously mounted articulator. At this point, two different methods of fabricating an immediate fixed prosthesis were used: either the direct transformation of the full denture worn by the patient or the conventional procedure. The former, based on the “conversion prosthesis” reported since 1985 by Balshi and Wolfinger26 was performed as follows: the preexisting prosthesis was modified by trimming the lingual anterior flange, thus allowing it to be used first as a surgical template and then as an impression tray. After lingual reduction was made, modified copings could be accommodated without interfering with the placement of the denture in its correct position. Then, two techniques were tried to fix the copings to the altered denture to provide the laboratory with an exact register of their relative positions: either a small amount of autopolymerizing resin (Duralay, Reliance Dental, Worth, IL) or the rubber impression material. In 24 hours, the laboratory was able to return the denture converted into a hybrid-type fixed prosthesis, highly polished and including metallic copings on the implants as well as wire reinforcement.
The conventional procedure uses a transparent acrylic surgical template and a custom impression tray. After subsequent sessions for intermaxillary registrations and try-in, the final installation of the transitional prosthesis take place in about 10 days.
In both cases, the prostheses were carefully checked clinically and radiographically to verify their correct fit on the implant shoulders. In the case of a misfit, the prosthesis was separated into two or more parts that were again rigidly connected with resin. If an increased friction or force requirement was noticed when tightening the screws, the coping inner faces were polished to better accommodate the screws.
All of the prostheses had two distal extensions from 5 to 15 mm according to clinical necessities. These transitional prostheses were substituted by the definitive ones in about 6 months (range, 4–14 months).

Follow-Up Visits and Parameters Recorded.
On the day of installation of the transitional prosthesis, a Panoramic x-ray as well as standardized periapical x-rays were taken using XCP holders (Dentsply International Inc., York, PA). These formed the baseline. After having the prostheses installed, the patients were examined after a week to take the sutures out and evaluate the postoperative condition. Subsequent visits were scheduled at 2 weeks and 2 months to check occlusal function and to reinforce oral hygiene procedures (Fig. 6). The next visit was at 4 months and was the moment when the transitional prosthesis was unscrewed for the first time since its installation, allowing individual clinical examination of each implant. After this visit, the fabrication of the final prosthesis could begin. Parallel x-rays were repeated at the moment of the placement of the final prosthesis. Afterwards, a standard maintenance protocol was instituted.
The following parameters were recorded:
  • Implant stability, assessed by percussion and clinical mobility of the implant, using the handles of two dental mirrors
  • Marginal bone loss, measured on parallel x-rays using a 7-X magnifying glass graded in tenths of millimeters. Measurements were taken to the nearest 0.1 mm on the mesial and distal sides using the implant shoulder level as a reference point.