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Basic and Clinical Research

A Comparative Study Between Early Occlusal Loading at 1 and 6 Weeks in Implant-Retained Mandibular Overdentures

Gadallah, Asma A. BDS, MDSc, DDSc*; Youssef, Hana'a G. BDS, MDSc, DDSc; Shawky, Yasser M. BDS, MDSc, DDSc

Author Information
doi: 10.1097/ID.0b013e31824eeaa5
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Abstract

Mandibular overdentures retained by two implants have been demonstrated to be a simplified and a successful treatment option for the completely edentulous patients. This is as a result of the positive outcomes of clinical studies using different loading protocols.1,2

The early loading protocol was defined in a consensus report as the placement of a denture in functional occlusion at least 48 hours after implant placement but not later than 3 months afterward.3 Outcomes from both retrospective and prospective clinical studies demonstrated that successful osseointegration occurred when implants were early loaded with overdentures.4–6

Two unsplinted implants can be successfully loaded with mandibular overdentures as early as 6 weeks after surgery.7,8 Evaluation of a shorter healing period was performed to identify the minimum safe interval between implant placement and functional loading for an overdenture treatment concept.9–12

The precise timing of early loading is loosely defined because it includes an extended timeframe during which the bone response around dental implants may vary during the healing period. Hence, studies on comparative evaluation of treatment outcomes for implant overdentures using early loading protocols at different healing times are required. Such data would enable edentulous patients to benefit as soon as possible from the expected implant-associated improvement in the quality of their lives. The aim of this study was to compare the efficacy of early occlusal loading at 1 week versus 6 weeks in mandibular overdentures retained by two implants.

Materials and Methods

Patient Sample

Twelve edentulous male patients were considered for this clinical trial. The inclusion criteria were that patients should be between 45 and 60 years old with healthy mucosa, sufficient interarch space (at least 12 mm), and sufficient residual anterior bone height and width allowing the placement of two implants with a diameter of 3.8 mm and length of 14 mm.

Exclusion criteria were patients with systemic disease compromising implant surgery, a history of smoking or a night-time bruxism with dentures; poor oral hygiene and motivation, psychiatric problems or unrealistic expectations, acute infection in the area intended for implant placement, with need for bone-augmentation procedure; who had previously bone-grafted jaws or previously irradiated jaws.

Patients accepted enrollment in this study after being explained about its protocol and objectives, and they all signed an informed consent to be recruited in this trial. They were asked to participate in the study without previous knowledge of which treatment they were going to receive. They were assigned equally to receive implants early loaded after 1 or 6 weeks. Preliminary screening was performed on intraoral radiographs, panoramic radiographs, or computed tomography scans.

Surgical and Prosthetic Procedures

New maxillary and mandibular complete dentures were fabricated. Preliminary impressions were taken with a stock tray using alginate (Cavex, CA37, Haarlem, the Netherlands). Secondary impressions were taken with a custom-made tray using medium body rubber base impression material (Coltene/Whaledent AG Feldweisenstrasse 20, Altstatten, Switzerland).

Record blocks were fabricated and jaw relations were recorded. Shallow cusp acrylic resin teeth (Vitapans, Vita Zahnfabrik, Bad Säckingen, Germany) were used, and the functional masticatory concept was a lingualized occlusion. Trial dentures were verified intraorally for aesthetics and function.

Dentures processed were then duplicated into transparent heat-cured acrylic resin to construct radiographic stents with radiopaque markers. The radiographic stent modified to be used as a surgical stents. Prophylactic antibiotic coverage and mouth rinse were given before the operation.

Using a flapless technique, bone preparation was done using three drills at increasing diameter. Two nonsubmerged implants (SwissPlus, Zimmer Dental Company, Germany) (with diameters of 3.7 and 14 mm) were inserted interforaminally in the canine region. Healing abutments were connected. The patient's existing mandibular dentures were relieved over implant sites with generous relief in both abutment positions. All participants were permitted to use their mandibular dentures immediately postoperatively. A soft diet for the first 1 week and a strict regimen of removal at night was agreed to by the participants. Corticosteroids, anti-inflammatory drugs were given after the surgery. Oral hygiene instructions were commenced postoperatively and reinforced at recall appointments.

Study Design

A manually generated randomization list was used to create two groups with equal numbers of patients. Only one of the investigators, not involved in the selection and treatment of the patients, was aware of the randomization sequence and had access to the randomization list stored in a password-protected portable computer.

The randomized codes were enclosed in sequentially numbered, identical, opaque, sealed envelopes. After implant installation, the envelope containing the randomization code was opened, the time of loading is identified and patients were randomly divided into the following two groups

  • Group I: Implants were loaded 1 week after surgery.
  • Group II: Implants were loaded 6 weeks after surgery.

Prosthetic Loading

One week after surgery in group I, 6 weeks in group II, ball abutments were connected and each mandibular denture was relined to include the matrices. A functional reline impression was used in all cases. The labial periphery of each mandibular implant overdenture was reduced in both housing areas to minimize the possibility of irritation leading to periabutment or periimplant mucosal enlargement. Then the nylon caps were picked up using indirect pick up technique. All prosthetic procedures were performed by the same prosthodontist who was not blind to the type of loading used.

Follow-Up Assessments

After denture delivery, patients were recalled at first day and at 3, 6, 9, and 12 months after loading for clinical and radiographic examination. The clinical and radiographic results were assessed by two independent, blinded examiners. Each examiner performed several independent measurements at the same time for reduction of inter- and intraobserver errors.

Clinical Evaluation

  1. Modified plaque index (mPLI)13: score 0, no plaque detected; score 1, plaque recognizable only by running a probe across the smooth marginal surface of the implant; score 2, plaque visible to the naked eye; and score 3, abundance of soft matter.
  2. Modified bleeding index13: score 0, no bleeding when a periodontal probe is passed along the gingival margin adjacent to the implant; score 1, isolated bleeding spot visible; score 2, blood forms a confluent red line on margin; and score 3, heavy or profuse bleeding.
  3. Periodontal pocket depth measurement: probing depth (PD) at the mesial, distal, buccal, and lingual/palatal aspect of each implant, by means of a periodontal probe (XP23/U*NC 15, Hu-Friedy, Chicago, IL) and rounded off to the nearest millimeter.14

Radiographic Evaluation

Periapical x-rays were taken using long cone paralleling technique with periapical film holder and individually constructed radiographic acrylic templates. Radiographs were scanned (HP Scanjet 3c/t, Hewlett Packard, Cernusco sul Naviglio, Milan, Italy), digitized in JPG, converted to TIFF format with a 600 dpi resolution, and stored in a personal computer.

Marginal bone height measurements

Periimplant marginal bone levels were measured using linear measurements system supplied by the direct digital radiography software. Measurements of the mesial and distal bone crest level adjacent to each implant were made to the nearest 0.01 mm.

Bone density measurements

Bone density measurements were done using linear analysis of bone density mesial and distal to the implants supplied by direct digital radiography software that detect and trace changes in gray levels. For determining the value of bone density, three lines were made mesial and distal to each implant. The first line extended from the first flute of the implant to the apex of the implant passing just tangential to the flutes. The second line was drawn 1 mm apart equal to the other two lines were made parallel to the first line, and the same procedure was repeated for the third line being 1 mm apart. Bone density along each of the three lines was recorded and expressed by pixels then the mean value of the three readings was calculated for further evaluation.

Results

No patient dropped out or was excluded from the trial, and all were followed up to 12 months after implant placement. All the implants in this study showed successful osseointegration. Implant mobility was not observed clinically during the evaluation period, which was confirmed by radiographs showing no periimplant radiolucency around any of the evaluated implants, denoting rigid fixation. Percussion was performed and the stability of the implant was always maintained.

Statistical Analysis

Statistical analysis of the obtained data was done using SPSS version 8 software program at a level of significance P < 0.05.

Results of Clinical Evaluation

The mean mPLI for the 3-month examination in group I and II was 1.04 and 1.08, respectively, whereas the mean modified sulcus bleeding index (mSBI) was 0.66 in group I and 0.64 in group II. The mean mPLI scores decreased for the 6, 9, and 12 month examinations in both groups, with values of 1.03, 0.98, and 0.94, respectively, in group I and with values of 1.06, 1.02, and 0.98 in group II, whereas mSBI scores were with mean values of 0.48, 0.34, and 0.26, respectively, in group I and 0.49, 0.37, and 0.26 in group II. The decrease of the means of both mPLI and mSBI score at the 1-year examination in comparison with the mean value at the 3-month examination was statistically insignificant (P > 0.05).

At the 3-month examination, the mean periodontal pocket depth measurement (PD) was 4.3 mm. At the 6-, 9-, and 12-month examinations, the mean PD measurements decreased slightly, with values of 4.46, 4.31, and 4.27 mm, respectively, in group I, whereas in group II was 4.5, 4.42, and 4.34 mm. The decrease of the mean PD measurements at the 1-year examination was statistically insignificant (P > 0.05).

Results of Radiographic Evaluation

Results of marginal bone height

The results of marginal bone heights in both groups are summarized in Tables 1 and 2 and Figures 1 and 2. Statistical analysis of the changes in mean values of marginal bone height measurements at both mesial and distal sides revealed that the difference between the two groups was statistically insignificant throughout the different time intervals of the follow-up period (P > 0.05).

Table 1
Table 1:
Comparison Between Mesial Marginal Bone Height (mm) in Group I and II
Table 2
Table 2:
Comparison Between Distal Marginal Bone Height (mm) in Group I and II
Fig. 1
Fig. 1:
Mesial marginal bone height (mm) at different follow-up periods in groups I and II.
Fig. 2
Fig. 2:
Distal marginal bone height (mm) at different follow-up periods in group I and group II.

Results of bone density

The results of marginal bone density in both groups are summarized in Tables 3 and 4 and Figures 3 and 4. Statistical analysis of the changes in mesial and distal periimplant bone density revealed that the difference between the two groups was statistically insignificant from the time of denture insertion till the end of the study (P > 0.05).

Table 3
Table 3:
Comparison Between Mesial Bone Density Expressed by Pixels in Group I and II
Table 4
Table 4:
Comparison Between Mesial Bone Density Expressed by Pixels in Group I and II
Fig. 3
Fig. 3:
Mesial bone density expressed in pixels at different follow-up periods in group I and group II.
Fig. 4
Fig. 4:
Distal bone density expressed in pixels at different follow-up periods in group I and group II.

Discussion

Delayed loading protocol allows for a period of undisturbed healing after implant placement, to minimize the risk of healing complications. In recent years, shorter loading times have become more common, especially due to increasing patient demands.

This study provides support for early loading with mandibular overdentures and evaluates whether marginal periimplant bone and soft tissues behaved in a different way between 1 and 6 weeks loading time.

Most of studies compared between conventional loading and early loading at 6 weeks.7,8,15 Few studies evaluated early loading protocol at 29,16 or 3 weeks.17

Loading after 1 week has been evaluated in a study of 26 patients who were provided with two nonsubmerged implants to support an overdenture. In the test group, the implants were loaded with overdentures after 1 week and after 3 months in the control group. All patients were followed up for 2 years. No implants were lost and there were no differences in marginal bone loss or implant stability between the two groups.18

Early loading of two unsplinted implants with an overdenture does not negatively affect periimplant clinical parameters or marginal bone conditions when compared with implants subjected to 12 weeks of healing before loading.2,15,19 The clinical evidence shows that early loading can be predictable, with implant survival rates comparable with the conventional delayed loading protocol.20,21 However, it has been noted that patients need to be carefully selected to maximize the potential success of the procedure.22–24

This study was planned on the basis that proper osseointegration of the implants is of paramount importance. Therefore, all factors that could affect osseointegration either systemically or locally were considered from the beginning, during patient selection, implants selection, insertion, construction of overdentures, and regular dentures maintenance. The selected patients had no history of debilitating disease to avoid the adverse effect on the healing process of bone and soft tissue.22 All implants used were placed in the anterior mandible, where bone density is high compared with other regions. High bone density results in high primary stability, which is considered as one important determinant of success.25,26

All dental implants inserted in this study were considered clinically and radiographically successful according to the implant quality health scale established by Misch et al,27 as there is no pain or tenderness upon function, no exudates or clinical mobility and the radiographic bone loss from initial surgery was less than 2 mm.

In this study, dental implants were clinically evaluated using periodontal indices and pocket depth measurement and it was found that, the clinical findings are in agreement with previous studies on the effect of implant overdentures on periimplant soft tissues.28,29 On the other hand, it was suggested that periodontal indices alone do not define implant success or failure and must be related to other factors such as pain or exudates. In addition, the PDs around implants may be of little diagnostic value, unless accompanied by signs as radiographic radiolucencies or symptoms as pain.27

Concerning the effects of the different groups although there was a slightly higher plaque and bleeding indices with deeper PDs in the second group, but the statistical analysis of the clinical results showed insignificant differences between the two groups. The slightly higher clinical parameters of the second group may be attributed to the subjective nature of the probing pressures and periodontal indices.27

The marginal bone loss figures for this study were accepted as criteria for success on the basis of implant quality scale of Pisa Consensus report as the average loss of bone height adjacent to each fixture was less than 2 mm at the end of this 1-year follow-up study.27,30,31

The bone height results were in agreement with the findings obtained in previous follow-up studies using either early loading or conventional loading in mandibular overdentures,2,32–36 Raghoebar et al37 reported 0.41 mm marginal bone loss for implant overdenture 1 year after placement. Payne et al9 reported 0.35 mm marginal bone loss after 1 year.

Sennerby and Gottlow1 reviewed the literature on the clinical outcome of early loading of dental implants based on studies published up to 2005. They found six comparative studies and reported that none of these revealed any significant difference in survival or marginal bone loss after 1 to 5 years.

The acceptable range of periimplant bone loss in this study may be attributed to several factors where the opposing occlusion was restricted to complete dentures, which may have helped to reduce stresses, load reduction, and distribution was carried out by selecting the lingualized occlusal scheme and maximum coverage of the edentulous alveolar ridge.

The increase in periimplant bone density is considered to be a physiologic response to functional loads.38–40 Moreover, occlusal adjustment, reduction of cusps inclines, and maximum coverage of the edentulous ridge contribute to load reduction and distribution that may enhance the structural orientation of bone trabeculae and increase the bone density around the implant.41

Regarding the effects of the different groups, no statistically significant differences were observed in marginal bone heights and density measurements for implants loaded 1 or 6 weeks after surgery, indicating that it is possible to early load dental implants using unsplinted prosthodontics designs with overdentures.

Conclusion

Early loading of unsplinted implants at 1 week with mandibular implant overdentures produces equal outcomes as 6 weeks loading.

Disclosure

The authors claim to have no financial interest, directly or indirectly, in any entity that is commercially related to the products mentioned in this article.

References

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Keywords:

dental implants; mandibular overdenture; early loading; radiographic evaluation; clinical evaluation

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