Our objective was to compare survival and peri-implant bone levels of immediately nonocclusally vs early loaded implants in partially edentulous patients up to 12 months after implant placement. Eighty patients (inclusion criteria: general good health, good oral hygiene, 30–65 years old; exclusion criteria: head and neck irradiation/cancer, pregnancy, uncontrolled diabetes, substance abuse, bruxism, lack of opposing occluding dentition, smokers >10 cigarettes/day, need for bone augmentation procedures) were selected in 5 Italian study centers and randomized into 2 groups: 40 patients in the immediately loaded group (minimal insertion torque 30 Ncm) and 40 patients in the early loaded group. Immediately loaded implants were provided with nonoccluding temporary restorations. Final restorations were provided 2 months later. Early loaded implants were provided with a definitive restoration after 2 months. Peri-implant bone resorption was evaluated radiographically with software (ImageJ 1.42). No dropout occurred. Both groups gradually lost peri-implant bone. After 12 months, patients of both groups lost an average of 0.4 mm of peri-implant bone. There were no statistically significant differences (evaluated with t test) between the 2 loading strategies for peri-implant bone level changes at 2 (P = .6730), 6 (P = .6613) and 12 (P = .5957) months or for survival rates (100% in both groups). If adequate primary stability is achieved, immediate loading of dental implants can provide similar success rates, survival rates, and peri-implant bone resorption as compared with early loading, as evaluated in the present study.
According to the Branemark protocol,1 a stress-free healing period is an essential prerequisite for controlled implant integration. Osseointegrated dental implant procedures have traditionally followed a 2-stage protocol.2 This approach envisages the implant being submerged and left to heal for a period of 3–4 months in mandibles and 6–8 months in maxillae; this is to ensure protection from bacterial infection and to minimize loading forces and related movement during the initial healing period. Following a 4–6-month healing period, a second surgical procedure is performed to expose the implants.
In 1990, findings were published of the first longitudinal clinical trial that suggested implants could be loaded immediately or early in the mandibles of selected patients.3 Several studies have revealed that good clinical outcomes could be achieved with 1-stage implants4 or 1-stage protocols with 2-piece implant systems.5
Several authors have argued that immediate loading is possible using fixed superstructures6,7 or bar-retained overdentures, thereby preventing implant movement with a rigid splint. Chiapasco et al8 and Gatti et al9 demonstrated that the success rates for immediately loaded mandibular implants using U-shaped Dolder bars are similar to that obtained in cases of delayed loading. Recent clinical7,8 and experimental10 results have encouraged a progressive shortening of the healing period, and immediate loading has been proposed.
Nowadays, immediate and early loading of dental implants are techniques that are gradually gaining in popularity. Such procedures are highly appreciated by the patients, whose treatment period is drastically reduced, and who can resume a normal life with minimal discomfort.
A systematic Cochrane review evaluating the efficacy of immediately and early loaded implants vs conventionally loaded implants concluded that, in carefully selected cases, such procedures can be successful11 ; however, not all trials showed predictably high success rates.12,13 This suggests that, although such procedures are likely to be technique sensitive, it is possible to load oral implants immediately in selected cases.
A recent split-mouth designed clinical study revealed significantly higher failure rates in single, immediately loaded implants than in single, conventionally loaded implants.13 Failed implants had been inserted with 20 Ncm insertion torque, and the authors demonstrated a strong correlation between implant failure and insertion torque.
These and other studies support the hypothesis that primary implant stability and lack of micromovement at the bone-implant interface is a determining factor in achieving high success rates.
Micromovement at the bone-implant interface is deleterious in terms of bone healing, but it has been shown that micromovement of between approximately 30 and 150 μm did not negatively affect bone healing.14 It is possible to splint implants together in order to reduce micromovement and obtain cross-arch stabilization.
To reduce the risk of failure in cases of immediately loaded implants, various clinical protocols have been proposed, including underpreparation techniques at the implant site to achieve high primary stability15; the use of temporary, nonocclusal restoration during the first 2 months of healing16; and progressive loading of the prosthesis.
The purpose of this multicenter randomized clinical study was to compare the survival and success rates of immediately and early loaded implants in partially edentulous patients. This paper presents preliminary 12-month results. Immediate loading was defined as the seating of provisional restoration immediately after implant placement that would not be in occlusal contact for about 2 months; early loading was defined as loading of both mandibular and maxillary implants subsequent to a 2-month healing period.
aterials and M ethods
For this study 80 partially dentate patients were selected, who required 2 implants for rehabilitation. In 1 patient, randomized to the immediately loaded group, 3 implants were placed. All patients were followed up for 12 months. The study protocol was explained in detail to each patient, and informed written consent was obtained. For patients with multiple edentulous areas to be restored, the operator was free at the screening visit to select 1 area to be included in the trial. Patients were randomized into 2 groups: the test group (immediate loading) and the control group (early loading). Patient recruitment, implant placement, and follow-up were carried out by a single expert operator in 5 study centers in Italy.
Patient inclusion was based on the following criteria:
Age between 30 and 65 years
Good oral hygiene
Good general health
Signed, informed consent
Patients were excluded from the study if any one of the following criteria was present:
Patient had undergone in the past 12 months radiation therapy to the head and neck area
Poor oral hygiene and motivation
Substance and alcohol abuse
Treatment with bisphosphonate drugs
Lack of opposing occluding dentition at the proposed implant site
Severe bruxism or clenching
Active infection or severe inflammation at the proposed implant site
Need for bone augmentation procedures including sinus augmentation
Smoking more than 10 cigarettes a day
During the first visit, the patient's oral hygiene and periodontal health were assessed. In particular, periodontal screening and recording (PSR) was performed. Patients with a PSR reading of up to 3 were treated by a dental hygienist and reviewed after 30 days for a plaque index evaluation17 . Where the plaque index was up to 2, patients were excluded from the study.
Immediate postextractive implants were included in the study if the implants could be placed with a final insertion torque of 30 Ncm. In such cases, the osteotomy did not follow the tooth socket but an ideal prosthetically driven position. The gap between one of the bone walls and the surface of the implant did not exceed 1.5 mm.
Patients enrolled were randomly assigned to 1 of the 2 treatment groups.
Local anesthesia was obtained using articaine with adrenaline 1:100 000 (Septanest, Septodont, Saint-Maur-des-Fossés, Cedex, France). Implants were placed using a flapless or flapped technique. Full-thickness crestal flaps were elevated with a slight extension to reduce patient discomfort to a minimum. If teeth were to be extracted, extractions were performed as atraumatically as possible to preserve the buccal alveolar bone using periotomes and small levers. Extraction sockets were carefully cleaned of any granulation tissue. Implant sites were prepared according to the manufacturer's instructions. Implants were placed at the crestal level in the healed edentulous ridge.
During the initial osteotomy, bone quality was assessed at the preparatory site on the basis of resistance to drilling with a 2-mm twist drill. Bone was classified as either D1, D2, D3, or D4 and respective values were recorded.18 In this study, tapered self-tapping implants were used (JDEvolution, JDentalCare, Modena, Italy).
Implants were placed using a 1-stage (nonsubmerged) surgical protocol. The diameters of implants used were 4.3 and 5 mm; their lengths were 10, 11.5, and 13 mm (see Table 1). The choice of implant diameter and length was left to the surgeon's discretion. Final insertion torque was measured with a calibrated torque wrench (JDTorque, JDentalCare, Modena, Italy) and its value was recorded.
During the protocol formulation phase it was decided that implants should attain insertion torque of at least 20 Ncm to be included in the study. Implants that attained an insertion torque of less than 30 Ncm were excluded from the immediate loading group.
Interrupted sutures were placed using a synthetic monofilament thread (Vycril, Ethicon, Johnson & Johnson, Cornelia, Ga) and were removed after 10 days.
All patients were instructed to rinse their mouth with 0.2% chlorhexidine mouth rinse twice a day, commencing 3 days prior to the intervention and thereafter for a 2-week period. All patients were asked to adopt a diet based on soft food for 48 hours postoperatively and to avoid chewing hard food at the rehabilitated sites for a 6-week period. They were recommended to brush implant sites with particular delicacy. Antibiotics and analgesics were administered to all patients: amoxicillin 2 g 1 hour prior to surgery and 1 g bid for 6 days, and ibuprofen 400 mg bid for 4 days. Patients allergic to penicillin were given clarithromycin 500 mg 1 hour before the intervention and 250 mg bid for 6 days.
In the test group, titanium abutments were placed immediately following the surgical phase. A provisional restoration, manufactured prior to the intervention, was relined in situ with acrylic resin, refined, and polished (Figures 1–6). The absence of centric or eccentric contacts was verified by interposing 200-μm articulating paper.
In the control group, a healing abutment was connected to the implants.
The definitive prostheses were delivered 2 months after surgery. An impression with pickup impression copings was made using addition silicone (Elite Implant Impression Material; Zhermack, Badia Polesine, Italy). For both groups, definitive restorations were cemented with full occlusal contacts (Figures 7–9).
Patients were recalled at 2 weeks and at 2, 6, and 12 months after surgery. Periapical radiographs were performed prior and subsequently to implant insertion and postoperatively at 2, 6, and 12 months.
Criteria used in this study to assess the outcome were peri-implant marginal bone level; implant failure (any mobility or infection that required implant removal); and biologic or prosthetic complications. Changes in peri-implant marginal bone level were evaluated on intraoral radiographs performed using paralleling technique. Periapical X rays were taken at implant placement and thereafter at 2, 6, and 12 months. Radiographs were scanned, digitized in JPG format, converted to TIFF format with a 600-dpi resolution, and stored in a personal computer.
The peri-implant marginal bone levels were measured using Image J 1.42 software (National Institute of Mental Health, Rockville, Md). Each image was calibrated twice, the first time using the known length of the radiograph's side (40 × 30 mm), the second time using the known length of the fixture. To facilitate measurement and fix the major axis in a vertical direction, the images were rotated slightly using the software program. Where necessary, contrast between bone and implant was increased with an image-enhancement procedure.
Readings of mesial and distal bone levels adjacent to each implant were made to the nearest 0.01 mm. The vertical distance was measured between the coronal margin of the implant collar (taken as the reference point) and the most coronal bone-to-implant contact.
An increase in the vertical distance between the reference point and the most coronal bone-to-implant contact for consecutive radiographs was considered indicative of peri-implant marginal bone resorption. Bone loss was calculated by clinicians at each follow-up visit for each implant, any variations from the baseline values being recorded.
Criteria applied to gauge the successful outcome of each implant were the absence of:
clinically detectable mobility
pain, paresthesia, or neuropathies
crestal bone loss in excess of 1.5 mm by the end of the first year of functional loading
All data were analyzed in compliance with a preestablished plan, the patient being the statistical unit of analysis. The data were analyzed by a biostatistician with expertise in dentistry. The group to which patients had been assigned was undisclosed. All statistical comparisons were carried out to a .05 level of significance.
This trial initially selected 88 patients, but only 80 were included, 8 patients being excluded on the grounds of insufficient oral hygiene. All patients enrolled in the trial agreed to participate and signed the consent form. They were randomized into 2 groups: 40 to the test group and 40 to the control group. All patients were treated in compliance with the trial protocol and no patients dropped out of the study. All implants were successfully seated with a torque of more than 30 Ncm.
The follow-up study focused on the period between implant placement and 12 months thereafter. Patient distribution among the various centers is shown in Table 2.
Chief patient characteristics are presented in Table 3. Patients were generally healthy, though 3 patients suffered from diabetes. One of these was included in the test group, the other 2 in the control group.
Eighty-one implants were placed in the immediately loaded group and eighty in the early loaded group. The lengths and diameters of the inserted implants are presented in Table 1, whereas the bone quality and the insertion torque are given in Table 4.
In the test group, 62 implants were placed in the lower jaw and 19 in the upper jaw. In the control group, 58 implants were placed in the lower jaw and 22 in the upper jaw. Insertion torque values varied from 30 to 100 Ncm in the control group and from 55 to 95 Ncm in the test group. The mean values were 58.93 and 77.06 respectively.
As can be seen, the 2 study groups were comparable at baseline. Marginal peri-implant bone loss was statistically significant in both groups (P = .001) at 2, 6, and 12 months (Table 5). Measurements from postoperative radiographs were analyzed with t test in order to verify any differences between test and control group at baseline: there were no significant baseline imbalances between the 2 groups (P = .1322).
After 2 months, patients in the immediately loaded group lost an average of 0.214 mm peri-implant bone, compared with 0.249 mm for those in the early loaded group (Table 5). After 6 months, patients in the immediately loaded group lost an average of 0.382 mm of peri-implant bone, compared with 0.324 mm for those in the early loaded group (Table 5). After 12 months, patients in the immediately loaded group lost an average of 0.421 mm of peri-implant bone, compared with 0.467 mm for those in the early loaded group. There were no statistically significant differences between the 2 loading strategies for peri-implant bone level changes at 2 (P = .6730), 6 (P = .6613), and 12 (P = .5957) months. Mean and standard deviation for bone level changes are given in Table 5.
No implant failed within a 12-month period. No surgical or prosthetic complications were observed in any of the patients. All treated patients were accounted for without exception.
The aim of this study was to compare survival and peri-implant bone resorption of immediate nonocclusal vs early loading implants in partially edentulous patients up to 12 months after placement.
The clinical success of dental implant therapy is based on the anchorage in the bone tissue of the implant's endosseous component. Osseointegration is a complex biological phenomenon determined by a series of events such as angiogenesis, recruitment and migration of osteogenic cells to the implant, and bone-matrix deposition. It has been demonstrated that the presence of movement at the implant-bone interface can lead to the formation of a soft-tissue interface that encapsulates the implant, causing its failure.19
To minimize the risk of soft-tissue encapsulation, it has been recommended that the implants should be kept load free by submerging them during the healing period.2 This approach presupposed a 2-phase technique: in this way implant sites are preserved from infection during the bone-healing phase. Clearly, the traditional approach requires longer treatment periods (4–6 months) as well as a second surgical intervention to expose the implants.
By contrast, immediate or early loading of the implants entails several advantages for the patient. Immediate loading protocols are aimed at simplifying implant therapy, reducing costs, and eliminating the use of removable prostheses. This is achieved by reducing the number of surgical interventions and visits required prior to delivery of the final prosthesis.
Henry and Rosenberg suggest that both the clinical performance and the prognosis of immediate loading compare favorably with traditional methods.20 Other clinical trials have shown that immediately and early loaded implants achieve high success rates.21
Immediate and early loading increased stress during bone healing. Movement at the bone-implant interface promotes the transformation of mesenchymal cells into fibroblast and causes fibrous encapsulation at the implant site. Bone tissue trophicity can be maintained with mechanical stimulation; conversely, the bone segment became atrophic where mechanical loading did not take place. Thus, the mechanical stimulation of bone tissue, as in the case of immediate loading, can also activate mesenchymal cells and promote the recruitment of the osteogenic cells.22 It has been observed that small strains not only improve bone-fracture healing, but may be essential to the healing process itself, whereas the absence of strain is known to impair the bone-healing process.23
The formation of new bone tissue is most intense at 2 months after implant placement, when more than 30% of osteons are in an active remodeling state. Submitting the bone to loading stimulus while it is undergoing its maximum remodeling activity may well help the bone to adapt more readily to loading stress rather than when remodeling activity has abated, as would be the case where a dental implant remains unloaded for 3 to 6 months.24 Microstrain may thus exert a benign influence during the healing period subsequent to implant placement. Osteoporosis research confirms that it leads to increased bone density,25 and similar findings have been reported in dental implantology.26
Immediate and early loading procedures can be successful only when micromovement at the bone-implant interface remains below a certain threshold during the healing phase. Micromovement is known to cause fibrous encapsulation of the implant only if it is above 150 μm.27
The results of this trial are encouraging: none of the implants were lost over a 12-month period. It should be emphasized that the immediately loaded implants were not submitted to direct occlusion for 2 months, although they were used during chewing. Other clinical trials confirm the absence of significant clinical differences in the survival of immediately and early loaded implants.28
It is not early or immediate loading that prevents osseointegration; rather, excess micromovement during the healing phase interferes with the process of bone repair. In this study protocol, micromovement was reduced to a minimum by splinting implants together.
All implants achieved high primary stability at placement, and this appears to be the key factor in obtaining the high survival and success rates.
This study evaluated survival rates up to 12 months from implant placement. This follow-up period is brief, but takes account of the fact that implant failure due to mechanical overloading occurs early on in the healing period.29 Marginal bone loss was in the range of 0.42–0.46 mm and was identical for both study groups at 12 months.
lt can be concluded that immediate loading of dental implants can be successful if clinical guidelines are adhered to. These include underpreparation of the implant site, particularly where the bone is soft; the use of active implants to achieve high primary stability; the achievement of high insertion torques (>30 Ncm); and close control of loading. Some authors also advocate the use of new implant surfaces to reduce healing time.30 Other authors report that their trials selected patients so as to exclude risk factors from mechanical overloading (eg, bruxism, occlusal instability).
To the best of the authors' knowledge, only 1 published randomized clinical trial (RCT) has compared immediate loading with early loading in partially edentulous patients.28 However, very little bone-level data is available. A recent Cochrane review11 was able to include only 2 RCTs15,31 in a meta-analysis comparing bone-level changes in patients with immediate vs conventionally loaded implants.
If adequate primary stability is achieved, immediate loading of dental implants can provide similar success rates, survival rates. and peri-implant bone resorption as compared with early loading. Treatment goals were achieved with both of the loading protocols used; however, immediate nonocclusal loading achieved these goals faster and with higher patient satisfaction.