Atrophy of the jaws is the main guide in the decision process of immediate fixed restorations which dictates the number of implants, angulation, and diameter/length of the implant. According to the current literature, especially in the case of severely resorbed alveolar ridges, placement of a narrow or tilted implant is a suitable and feasible treatment alternative to avoid additional surgical invasive procedures [1, 5, 10, 11, 16]. In previous papers, the use of implants with narrow diameters of 3.3 to 3.5 mm and Ti-Zr alloy are well documented in all indications including load-bearing posterior regions with promising success rates [12, 17,18,19]. However, the data of NDIs used in the treatment of fixed full-arch prosthesis was inadequate in the literature.
Peri-implant bone level changes of implants supporting immediate fixed full-arch prosthesis were reported by some researchers. Crespi et al. reported mean 1.10 ± 0.45 mm MBL for axial maxillary implants (n = 48 implants) and 1.11 ± 0.32 mm MBL for tilted maxillary implants (n = 48 implants) at the 36-month evaluation . In the mandible, the mean peri-implant MBL of 1.06 ± 0.41 mm for axial implants (n = 40) and 1.12 ± 0.35 mm for tilted implants (n = 40) was found at 36 months’ follow-up in the same study. In a study of Malo et al., the average peri-implant bone loss in the mandible was 1.7 mm ± 0.6 mm at 5 years while it was 1.6 ± 0.4 mm in the maxilla at 3 years .
Patzelt et al. evaluated 13 (487 initially identified) papers which met inclusion criteria in their systematic review. A number of 4804 implants was evaluated and the mean MBL (12 months) of maxilla, mandible and combined were 1.0 ± 0.5 mm, 0.8 ± 0.4 mm, and 0.9 ± 0.5 mm, respectively and the mean MBL (24 months) of the maxilla, mandible, and combined were 0.8 ± 0.4 mm, 1.0 ± 0.4 mm, and 0.9 ± 0.4 mm, respectively. The bone loss in axial implants (12 months) of the maxilla, mandible, and combined were 0.8 ± 0.3 mm, 0.9 ± 0.5 mm, and 0.8 ± 0.4 mm, respectively. The bone loss in axial implants (24 months) of maxilla, mandible and combined were 0.8 ± 0.4 mm, 1.0 ± 0.4 mm, and 0.9 ± 0.4 mm, respectively. The bone loss in tilted implants (12 months) of the maxilla, mandible, and combined were 0.7 ± 0.4 mm, 0.8 ± 0.5 mm, and 0.8 ± 0.4 mm, respectively. The bone loss in tilted implants (24 months) of the maxilla, mandible, and combined were 0.9 ± 0.4 mm, 0.9 ± 0.4 mm, and 0.9 ± 0.4 mm respectively. They reported no significant differences between maxillary versus mandibular arches and axially versus tilted implants . Also, Menini et al. evaluated the outcomes of axial and tilted implants supporting fixed full-arch dentures for the immediate rehabilitation of edentulous maxilla, after at least 1 year of function in their meta-analysis. The MBL was obtained from 6 studies and the mean MBL was 0.75 mm (tilted, 0.77 mm; axial, 0.73 mm) which was not statistically significant .
In the present study, the mean MBL was 0.51 ± 0.51 mm and 0.73 ± 0.66 mm at 1 and 2 years, respectively. In the maxilla, MBL resulted in 0.41 ± 0.38 mm in 1 year and 0.43 ± 0.32 mm in the second year while it was 0.63 ± 0.60 mm and 0.90 ± 0.74 mm in the mandible respectively. The difference in mean MBL between mandible and maxilla was significant in one (p = 0.009) and 2 years’ (p = 0.032) follow-up. This result is not in accordance with the systematic review of Patzelt et al. in which the majority of the evaluated studies consisted of the rehabilitation with 4 implants . The significance of MBL in the present study was interpreted as the more than half of the cases in maxilla was rehabilitated with six implants while it was with 4 implants in mandible mostly. Also, the mean MBL of tilted and axial implants was 0.61 ± 0.63 mm and 0.45 ± 0.41 mm respectively at 1 year. In the second year, MBL of tilted and axial implants was 0.90 ± 0.75 mm and 0.61 ± 0.57 mm respectively. By means of angulation, tilted implants tended to be associated with a greater bone loss but this was not significant at one (p = 0.072) and second (p = 0.181) years. The mean MBL changes (maxilla as well as mandible) of the present study are consistent with the literature in terms of angulation in 2 years’ follow-up [3, 20, 23,24,25,26].
Immediate loading protocol of the dental implants for the rehabilitation of edentulous jaws has been proven with similar survival and success rates with early and conventional loading. By means of MBL, survival and success rates for immediate loading would provide the same outcome as conventional protocols [3, 4, 13, 15]. In the present study, 130 of 179 implants were immediately loaded on the same day and the only implant which failed in the mandible was an immediately loaded implant that resulted in 98.5% CRS in 2 years. At 1 and 2 years, the mean MBL was recorded as 0.53 ± 0.53 mm and 0.67 ± 0.56 mm respectively which was not significantly different from conventional loaded implants in both 1 (p = 0.522) and 2 (p = 0.099) years and was in accordance with the literature [3, 4, 13, 14].
No consensus has been reached on the most advantageous number of implants to be used to support a fixed dental prosthesis . Malò and colleagues presented the first data following the rehabilitation with four immediately loaded implants in 2005 . The successful results of implant and prosthesis survival/success rates and marginal bone-level changes of this concept were reported in literature. Some researchers reported that six implants could be considered a predictable and cost- and time-effective option for the immediate restoration of the edentulous maxilla [29,30,31]. Tallarico et al. reported similar MBL and CSR in the maxilla which was rehabilitated with 4 or 6 implants in their 5 years’ follow-up study . Along with all these recent articles, in 1995, P.-I. Brånemark et al. reported the same survival rates with 4 and 6 six implants in edentulous patients while 4 implant scenarios had higher complications . In the present study, patients were mostly rehabilitated with 4 implants in the mandible. In the maxilla, there was an even distribution with 4 and 6 implant-supported solutions. The mean MBL of implants in which the rehabilitation was done with 4 implants was 0.63 ± 0.59 mm (n = 80 [24 maxilla/56 mandible]) while it was 0.35 ± 0.33 mm (n = 54 [42 maxilla/12 mandible]) in 6 implant-supported prosthesis at 1 year. Even though cumulative survival and success rates were not affected from the variability of the number of implants, MBL in four implant-supported rehabilitations was greater in 1 year (p = 0.0060). This result is in accordance with Branemark et al. and Tallarico et al. [32, 33].
The smallest implant diameter for full-arch rehabilitations is 3.3 mm in the literature [19, 32, 34]. In the study of Tallarico et al., four 3.3-mm-diameter implants of total 200 implants were included while Malo et al. placed NDIs only in the anterior region of the maxilla. However, both studies did not mention about the MBL and CSRs of 3.3-mm implants specifically. Piano et al. evaluated twenty-one patients with a total of immediately loaded 84 (74 of 4.1 mm/10 of 3.3 mm) implants (Straumann Bone Level SLActive implants) with the 2-year period. Implant and prosthetic survival rates of 100% were achieved. The mean MBL of 0.34 mm ± 0.45 mm in 2 years was reported. Also, similar marginal bone loss of NDIs and regular-diameter implants was reported (p = 0.67) .The present study was conducted with the combination of Roxolid Bone Level Tapered NDIs (3.3 mm) and 4.1-mm and 4.8-mm implants. The NDIs (3.3 mm) achieved 0.63 mm (n = 58/Sd 0.44 mm) MBL at 1-year data and such result was not significantly different from 4.1 (0.46 mm MBL) and 4.8 (0.32 mm MBL) mm diameter implants. The MBL of NDIs was 1.02 ± 0.74 mm in the second year. The difference between narrow and regular diameter (4.1 mm) was significant in the second year which was clinically acceptable.
In the present study, one implant was lost in the mandible in the provisional prosthesis period which resulted in implant survival as 99.4% for all implants and 98.5% for NDIs at 2 years’ follow-up. According to the implant CSR, many papers in the literature reported clinically acceptable CSRs for tilted and axial implants either in the mandible or the maxilla in the 1- to 5-year period [3, 4, 6, 10, 20, 21, 23,24,25, 28, 29, 34,35,36,37,38]. Moreover, Patzelt et al. (1 year: 98.6 ± 1.3%, 97.5 ± 1.2% for the maxilla and 99.3 ± 0.7% for the mandible, 2 years: 99.1 ± 1.1%, 98.2 ± 1.1% for the maxilla; and 99.7 ± 0.6% for the mandible) and Soto-Peñaloza et al. (2 years: 99.8%) reported clinically acceptable CSR values for tilted and axial implants either in the mandible or in the maxilla [5, 39]. The CSR of the implants in the present study are consistent with CSR values of implants in the literature.
Out of one lost implant, another 3 implants (2 in the mandible and one in the maxilla) in 3 patients presented biological complications that showed > 4-mm peri-implant pocket, > 2-mm marginal bone loss (MBL), and bleeding on probing. The success rate of all implants in the present study was 98.3% in 2 years. According to the implant success rate, Butura et al. (3 years: 99.66% for the mandible), Graves et al. (16 months: 97.48% for the maxilla), Galindo and Butura (1 year: 99.86% for the mandible), Malo et al. (5 years: 98.1% and up to 10 years: 94.8% for the mandible), Rosen and Gynther (up to 10 years: 97% for the maxilla), Krekmanov et al. (5 years: 100% in mandibula (tilted and axial implants), 98% for tilted implants and 93% for axial implants in the maxilla), Tallarico et al. (up to 7 years: 98.2%), and Degidi et al. (3 years: 97.8% for axial implants and 99.2% for tilted implants in the maxilla) reported clinically acceptable implant success rate values for tilted and axial implants either in the mandible or in the maxilla [11, 26, 35, 40,41,42,43,44]. The success rate of the implants achieved in the present study is accordance with the literature.
Different materials were used in the studies to fabricate immediate fixed provisional prostheses. Some authors used a full-arch acrylic provisional prosthesis reinforced with a titanium or metal framework or with titanium cylinders, while the other authors used all-acrylic prostheses [22, 26, 31, 45, 46]. In the present study, a number of 29 screw-retained fixed provisional all-acrylic prostheses without metal framework were incorporated on the same day. There are many prosthetic mechanical complications such as the fracture of the provisional acrylic prosthesis [39, 47], loosening of prosthetic components [24, 43], and the detachment of an element of the prosthesis [47,48,49]. In the present study, the fracture of the provisional prosthesis was recorded in 4 patients (14,3%). The incidence of fracture of the provisional prostheses in the present study was 16,1% (5 prostheses) of the total cases. Tooth detachment of the provisional fixed acrylic prosthesis was recorded in two prostheses in two patients, while the screw loosening occurred only in a provisional prosthesis.
In the current study, titanium or chrome-cobalt alloy and ceramic or composite resin were used as a framework and as a veneering material, respectively. Prosthetic CSR was reported between 98.9 and 100% in the literature up to 10 years in the literature [5, 10, 20, 23, 34, 40, 43, 50]. Prosthetic survival in the present study was 100% in 2 years which was similar to those previously reported studies.
Mutually protected occlusion with anterior guidance was used in cases of opposing natural dentition, or tooth and/or implant-supported fixed partial prosthesis as previously described . In all cases of the present study, all fabricated definitive prostheses opposed natural dentition or fixed prosthesis supported by tooth and/or implant not removable prosthesis.