The recovery time for dental implants is similar to physiological healing of bone tissue. The studies of titanium implants have shown that the process of healing can be divided in three phases: osteophilic, osteoconductive and osteoadaptive (1, 2). The success of therapy is surgically, esthetically and functionally predictable only if there is an adequate amount of bone and gingival tissue (3). The amount of crestal bone loss during the first year may affect the sulcus depth and environment for the longevity of the implant (4).
Radiographic analyses have shown that the micro threaded design was superior at minimizing marginal bone loss during stress-free healing and under functional loading. The use of rough-surfaced micro threaded implants is recommended to maintain crestal bone levels (5-8). A rough surface and micro threads at the implant neck not only reduce crestal bone loss but also help with early biomechanical adaptation against loading compared to the machined neck design (8). Some authors have reported greater marginal bone loss with conventional platforms than with platform switching (9-14). This appeared more evident with increasing the extent of implant-abutment mismatching (14).
Implant surgery in posterior regions of upper and lower jaws is not difficult in cases with a satisfactory bone volume of the alveolar process. However, in cases of alveolar atrophy the anatomical limitations with the maxillary sinus cavity and the alveolar nerve canal, the situation becomes more problematic and has to be solved by using different kinds of graft techniques. However, most cases can be successfully solved with the techniques that are available today. (15). According to Sbordone et al, the use of particulate chin bone grafts in sinus lift procedures does not seem to yield optimal outcomes. Milled iliac crest and chin bone tends to remodel around the implant apices, leading to bulging within the sinuses. Grafting sinuses with either chin or iliac crest bone blocks yields the highest implant success rates and stable sinus floors (16). Regarding remodeling in augmented sinus areas, the behavior of the autologous bone from the iliac crest and the xenogenic material was ultimately very similar at the implant apex, even though for bovine bone material the resorption was much slower than that of the autogenous graft. The behavior of autologous bone from the chin seemed similar to that of xenogenic material, probably because of the dense cortical composition of such grafts. The differences between immediate and delayed procedures of implantation, with regard to marginal bone, showed a lesser resorption process of the former as compared with the latter (17). The short-term sinus grafting procedure for dental implant placement performed with freeze-dried allogeneic bone showed an outcome close to that reported for autogenous bone. Performing maxillary sinus augmentation with dry-preserved bone allogeneic materials in block form could be considered even when the residual floor thickness is less than 3 mm (18). Clinicians who plan a fixed prosthesis supported by dental implants placed in the maxillary sinus, with or without bone volume augmentation, should consider the negative remodeling encountered in the autogenous particulate materials, both in the apical and marginal peri-implant aspects. Implants placed in native areas beneath the sinus did not exhibit such behavior; therefore, the procedure seems to be more reliable. Nevertheless, the survival of these implants is quite similar to those placed in augmented areas (19).
Implant placement in the anterior region of the mandible is still the most common indication, especially when using four implants. The bone availability varies depending on the degree of atrophy. Implant placement in the posterior mandible is more often unilaterally in order to avoid a partial denture, or bilaterally after long periods of edentulousness (20). At the maxilla, the front part of alveolar crest to the second premolar is conditionally favorable region for implantation. An unfavorable region for implantation is the posterior maxilla, including the maxillary tuberosity (21). When installing implants in front region of the maxilla the greatest attention should be paid to the esthetics of the prosthesis (20). Insufficient bone in vestibular-oral dimension is a common problem in treating missing front teeth with implants (3).
The aim of this study was to evaluate crestal bone resorption around dental implants in different regions of maxilla and mandible after one year of functional loading.
Materials and methods
This study has been approved by the Ethics Committee of the School of Dentistry Sarajevo (University of Sarajevo). All the subjects gave their informed consent.
This study was conducted at the Department of Prosthodontics, School of Dentistry Sarajevo (University of Sarajevo), from January 2010 to December 2013.
Inclusion selection criteria were: age > 18 years; both sexes; patients without contraindications for implant placement; patients who gave their informed consent to participate in the study; patients without indications for bone augmentation; completely edentulous or partially dentate patients; sufficient height of the alveolar bone for placement of dental implants of diameter 3.5 x 10 mm and 4.0 x 8 mm.
Exclusion selection criteria were: disease of oral soft tissue; disease and defects of the maxilla and mandible; poor oral hygiene; alcohol consumption; drug addiction; systemic diseases which affect bone metabolism and oral mucosa and impossibility of dental implant placement according the manufacturer’s instructions for any reason.
Forty two patients, 23 males and 19 females, were included in this study. The mean age of patients was 56, ranging in age from 18 to 81 years. Among male patients, 78.3% were partially dentate, while 21.7% were totally edentulous. 94.7% females were partially dentate, only 5.3% were totally edentulous.
A total of 161 implants type Bredent blueSKY® were inserted according to a two-stage surgical protocol. Thirty six implants of diameter 3.5 x 10 mm were inserted in the maxilla and 12 in the mandible. Fifty two implants of diameter 4.0 x 8 mm were inserted in the maxilla and 61 in the mandible. The implants were placed into the mandible and maxilla according to a strict surgical protocol following the manufacturer’s instructions.
After using SKY pilot drill, the Twist-Drill was used to determine depth and direction of the implant. The depth of the drilled hole exceeds the implant length by approx. 0.5 mm. The cylindrical core of the implant was prepared, depending on the bone quality, with the D3-4 for soft and medium hard bones, and with D1-2 drills for hard bone. The depth of the drilled hole exceeded the implant length by approx. 0.5 mm. Finally, the conic-cylindrical preparation of the coronal cavity took place. After healing phase of three months without functional loading, a gingiva former was inserted. After 14 days, the gingiva former was removed and impressions were taken. The time placement of prosthetic restorations on the implants was four months after surgery. All the implants were used as abutments of individual crowns and bridges.
Dental panoramic radiographs were made before surgery, immediately after surgery and after 12 months of functional loading, using Ortopantomograph type Kodak 8000 c, XJAM530. Panoramic images were calibrated using CliniView (version 5.2 Instrumentation Imaging). The measurements were performed using software Kodak dental software 18.104.22.168.
Crestal bone resorption was measured mesially and distally for each implant from the coronal portion of the abutment to the detectable margin of the alveolar bone, immediately after implant placement (point A) and after a year of functional loading (point B) (Figure 1, Figure 2).
Table 1 shows a description of patients regarding gender and smoking habits.
Table 2 shows the frequency of inserted implants in the anterior and posterior region of the mandible and maxilla on the right and left side.
No statistically significant differences in distal as well as in mesial bone losses were found between implant sites on left and right sides of both jaws, for both implant diameters, as reported in Tables 3 and 4.
* Analysis of variance (ANOVA)
* Analysis of variance (ANOVA)
Table 5 shows statistically significant differences in mean crestal bone loss around dental implants with diameter of 3.5 mm between maxilla front, maxilla posterior, mandible front and mandible posterior. Statistically significant differences were found between maxilla front, maxilla posterior, mandible front and mandible posterior at implant sites regarding distal and mesial bone losses as shown by analysis of variance (ANOVA).
* Analysis of variance (ANOVA)
The highest mean of bone resorption was measured in mandible front distally (M = 0.91), and the mandible front mesially (M = 0.96).
The mean of distal and mesial resorption at implant diameter of 4.0 x 8 mm between regions of the mandible front, mandible lateral and the maxilla lateral were not tested by ANOVA due to insufficient number of cases in the mandible front (n = 1).
Table 6 shows the differences in mean crestal bone loss around dental implants with different diameters. Student′s t-test showed no statistically significant differences in marginal bone loss.
Marginal bone loss is evaluated by means of radiography and is directly associated with the long-term success of implant treatments (22). The most observed loss occurring in mesial or distal sides is considered as the final implant bone loss (23). According to Albrektsson et al, marginal bone level changes in the first year after implant insertion should be less than 1-1.5 mm and the ongoing annual bone loss should be less than 0.2 mm (24). According to some other authors, the critical values of bone loss following one year after implantation have been proposed to be less than 1.5 mm with the mean 0.1 mm annual rate in the following years (25-27). In this study, the measured mean mesial and distal bone loss of the implants was less than the mentioned critical value, be considered a success.
Rasouli Ghahroudi et al. (22) found no significant differences regarding bone loss occurring at the distal and mesial sides of the mandibular and maxillary implants or the maximum bone loss, taking place at these sides between the upper and lower implants. After 1-year loading the mean distal bone loss of mandibular and maxillary implants were 0.759 mm (standard error: 0.088) and 0.615 mm (SE: 0.097), and the mean mesial bone loss of mandibular and maxillary implants was also 0.701 mm (SE: 0.088) and 0.627 mm (SE: 0.097), respectively (22). Hobo et al (28) reported the mean bone loss of 1-1.5 mm for the first year of implant placement. Johansson and Ekfeldt (29) showed a mean bone loss amounting to 0.4 mm at the first year. Jang et al. (30) found bone loss of 0.7 mm after the first year. Mesial crestal resorption ranged from 0.4 mm to 1.2 mm and distal crestal resorption ranged from 0.3 mm to 1.3 mm (30). Hürzeler et al. (31) found bone loss of 0.40 mm (± 0.12 mm) within one year.
Several factors influence implant prognosis and can attribute to implant failure: length and diameter of the implant, implant location, implant designs, bone quality, implant surface and the general health of the patient, functional loading (5-14, 32-37). In the present study, the patients with systemic diseases have been excluded and implant prognosis was based on the different implant diameters. The mean marginal bone loss which was measured around dental implants of diameter 4.0 x 8 mm was less than around dental implants of diameter 3.5 x 10 mm, but the differences between these groups were not statistically significant.
Karoussis et al. (35) evaluated and compared the 10-year survival and complication rates of hollow screw, hollow cylinder and angulated hollow cylinder (AHC) ITI® Dental Implants. Complications occurred at 10% of hollow screw implants, while at hollow cylinder implants, the prevalence of peri-implantitis in 10 years was almost three times higher (29%). Angulated hollow cylinder implants presented a complication rate of 12%. Danza et al. (37) reported that crestal bone maintenance around conventionally and immediately loaded modified diameter implants was similar, with slight significant differences in mandible where a lower marginal bone loss was observed.
In this study, we found no significant different bone loss between maxillary and mandibular implants regarding sites. This finding is in agreement with the results obtained in some studies (22, 38, 39). On the contrary, Penarrocha et al (40) and Pham et al. (41) showed more bone loss for maxillary implants compared to mandibular implants.
This study showed more bone loss for anterior implants compared to the posterior ones, which is contrary to the results of Boronat et al. (23). Some authors found no significant differences regarding implants placed at anterior and posterior regions (22, 42).
The assessment of crestal bone loss around implants is necessary for evaluating implant success. This study showed more crestal bone loss for anterior implants compared to the posterior ones, but there was no significantly different crestal bone loss between maxillary and mandibular implants regarding sites, after one year of functional loading.