Complete-arch fixed reconstruction by means of guided surgery and immediate loading: a retrospective clinical study on 12 patients with 1 year of follow-up

A retrospective evaluation was conducted on the customized records of patients that were treated with guided implant surgery during the period from January 2014 to December 2017, in a private dental clinic in Baden-Baden, Germany (Henriette Lerner Dental Clinic).

Patients were included according to the following criteria.

Inclusion criteria:

Exclusion criteria:

The analyzed records included patient-related information (gender, age at surgery, systemic health, smoking habit) details about the inserted implants (type, position, length, and diameter) and the prosthetic rehabilitation (single crown, fixed partial prosthesis, fixed full arch) including the dates of delivery. In addition, the analyzed data included all information about any implant failure or complication that occurred during the intervention, after the surgery, and at each follow-up visit. According to the inclusion and exclusion criteria, only patients treated with guided implant surgery and immediate loading by means of complete-arch fixed reconstruction without artificial gum were considered eligible and thus enrolled in the study. A necessary condition for enrollment in the present study was also the patient’s willingness to present him/herself at a final control visit. All other patients (i.e., patients treated with dental implants to restore partially or totally edentulous jaws, without the aid of guided surgery; or patients treated with guided implant surgery but restored with fixed full-arch maxillary prostheses with artificial gum) were excluded from this study. The principles highlighted in the Helsinki Declaration on experimentation on human subjects were strictly followed. This retrospective study received ethical approval from the Institutional Review Board of the Goethe University of Frankfurt, Germany (number: 182/19). All patients were fully informed on the nature of this retrospective study, read and signed a written consent form for inclusion, and for the analysis of their records, that was approved by the University. In addition, the authors obtained written consent for publication from the patients enrolled in this retrospective study.

A complete clinical, photographic, and radiographic dataset was acquired for each patient. In particular, photographs of the initial situation were taken (Fig. 1a, b, c, d, e) accompanied by two-dimensional (panoramic) radiographs (Fig. 1f), periodontal probing and three-dimensional radiographs (CBCT of both arches). General impressions were taken, and stone casts were obtained for the study of the case (Fig. 1g, h). Starting from the photographic data, a digital smile-design software was used for a first evaluation of the length and width of the teeth. The information taken from this analysis was used for the preparation of a diagnostic wax-up on the stone cast models (Fig. 2a, b, c). Finally, the initial situation, the diagnostic wax-up (and therefore the ideal morphology of the teeth) and the situation after virtual extractions were then scanned with a desktop scanner (Deluxe®, Open Technologies srl, Brescia, Italy), in order to have all the. STL files available for upload in the guided surgery software (Fig. 2d).

In a guided surgery software, the. STL files with the ideal teeth morphology, derived from the scan of the diagnostic wax-up, were imported and superimposed on the bone anatomy, obtained from the CBCT. Then, the surgeon (H.L.) and the dental technician (U.H.) were able to plan the placement of the implants in the correct position, depth, and inclination, guided by the prosthetic wax-up, in a prosthetically-driven manner (Fig. 3a, b, c, d). Care was taken to try to engage the fixtures as much as possible in the residual bone, exceeding the apex of fresh extraction sockets at least 3–4 mm, by choosing appropriate implant length. At the same time, care was taken to position the implants in the palatal portion of the sockets, ideally at a distance of 2–3 mm from the residual buccal bone walls, and at a proper inclination. Ideally the axis of the implants had to be in the center of the teeth, to achive a perfect prosthetic plan. The same procedure was repeated in both maxilla and mandible. After the planning was successfully completed and carefully controlled, the models of the situation were 3D printed in the laboratory with a desktop printer and the implant analogues were inserted in these models (Fig. 4a, b). These models not only included the correct position of the planned implants, but also the mucosa and the residual teeth, which had not been removed in the planning, in order to facilitate the superimposition in the guided surgery software and to stabilize the surgical guide during the intervention (these hopeless teeth had to be removed at the end of the intervention). Based on the virtual planning, surgical guides were then printed, and the sleeves were manually inserted in (Fig. 4c, d). In the lower jaw, since the sleeves of the central incisors touched each other, two different guides were 3D printed. Finally, before surgery, provisional full-arch restorations were prepared for immediate loading and aesthetics. A burn-out framework based on the prosthetic project and virtual implant position was milled (Fig. 5a, b). This led to a metal structure on which resin composite (Nexco®, Ivoclar Vivadent, Schaan, Liechtestein) was manually stratified, in order to obtain a highly aesthetic temporary full-arch prosthesis for immediate loading (Fig. 5c). This prosthesis had to be seated on temporary abutments immediately after implant placement.

The implants used in this study (Esthetic Line-EL®, C-Tech, Bologna, Italy) were conical, with a Morse-taper hexed connection and an acid-etched surface. In details, these implants incorporate three different threading profiles, designed to adapt to the different bone structures that occurr along the depth of the fixture. In the coronal portion, in fact, microgrooving is present, whereas in the intermediate portion, the fixtures present a double lead thread, to facilitate insertion and to increase primary stability, particularly in soft bone. In the apical portion, these implants are endowed with aggressive apical threading which is particularly indicated to stabilize the fixture in post-extraction sockets, in the case of immediate placement after extraction; however, a rounded apex protects such anatomical structures as the maxillary sinus membrane and inferior alveolar nerve. Further characteristics of these implants are a beveled shoulder, to facilitate bone growth in the case of subcrestal placement in post-extraction sockets; a Morse-taper hexed connection, to reduce screw loosening and micromovements of the abutment; and a concave aesthetic concept with platform switching, for better soft-tissue healing. The presence of one connection for all implant diameters facilitates the prosthetic treatment, by offering a large range of tissue-shaping possibilities. The fixtures used in this study were available in different lengths (8,9,10,11,12,13, and 14 mm) and diameters (3.8, 4.3, 5.1, 6, and 7 mm).

After this, flapless surgery could start with the atraumatic extraction of all hopeless teeth (with the exception of the ones used to stabilize the guide; those teeth had to be removed after the removal of the guide). During extraction, care was taken not to damage the alveoli and particularly the delicate maxillary buccal bone wall (Fig. 6a, b). After the digital planning, the surgical template was positioned, the fit was carefully checked (Fig. 6c), and the guided surgery started with the preparation of all implant sites, using drills of incremental diameter, and ended with the placement of all planned implants, through the guide (Fig. 6d, e). After implant placement, the surgeon could verify the positioning as well as the soft-tissue status and proceed with simultaneos minor/major grafting procedures, where needed. The need for grafting procedures obviously forced the clinician to raise a full-thickness flap, but this procedure was limited exclusively to the area or areas that required bone augmentation; in all other cases and in all other areas, a flapless surgery was carried out. After the surgery was completed, the temporary fixed full-arch provisional in resin with metal framework was carefully adapted and relined on temporary abutments, removed, accurately polished, and then delivered to the patient (Fig. 7a). This fixed full-arch temporary was cemented and a panoramic radiograph was taken (Fig. 7b). Six months after surgery, when the period of provisionalization ended, the clinician recalled the patient and took two different impressions: (i) generic alginate impressions with the provisional prostheses in position; and (ii) precision impression with polyether open tray over multi-unit intermediary abutments, to avoid damaging the peri-implant structures (Fig. 8a, b). These two impressions were sent to the dental laboratory, where plaster casts were poured and scanned with the same aforementioned desktop scanner. These models were then overlapped in a computer-assisted-design (CAD) software, in order to have a guide for modeling the final restorations and performing aesthetic modifications (Fig. 9a). All these modifications, however, were done manually, on 3D-printed models (Fig. 9b, c). Then the final shapes were scanned again. At this point, the dental technician could proceed to design, in a CAD software (Exocad®, Darmstadt, Germany), the final individual, customized abutments (which had to be cemented extraorally on selected titanium bases) and the final restorations (Fig. 10a, b, c). Both the individual, customized abutments and the final restorations were full-ceramic and milled in zirconia with a powerful milling machine (M1 WET Heavy Metal®, Zirkonzhan, Bolzano, Italy), in order to improve the aesthetic outcome. The restorations had to be single crowns (in the frontal area, for a better biological response, with physiological auto-detersion, and to allow for excellent oral hygiene maneuvers, such as the passage of dental floss) and fixed partial prostheses (in the posterior areas, to improve the functional response). At the delivery of the final restorations, the customized abutments were screwed in the correct position: the margins were positioned subgingivally, in accordance with the original surgical and prosthetic plan (Fig. 10d) and all restorations were placed. The marginal adaptation was checked clinically using magnifying glasses (Zeiss 4.5x®, Zeiss, Oberkochen, Germany) and the occlusion was carefully evaluated using articulating papers (Bausch Articulating Paper®, Bausch Inc., Nashua, NH, USA) as well as digital devices (Tekscan®, Boston, MA, USA) prior to cementation. Clinical pictures (Fig. 11a, b) and a panoramic radiograph (Fig. 11c) were taken, along with a digital analysis of the occlusion (Fig. 11d).

The outcome measures for the present study were implant stability at placement, implant survival, complications, prosthetic success, marginal bone remodeling, soft-tissue stability, and patient satisfaction.

Implant stability was measured at placement. Insertion torque (IT) and resonance frequence analysis (RFA) were used as methods for measuring implant stability, as previously described [32, 33]. IT was measured before the removal of the surgical guide. Since all implants were placed using the implant motor, a standard IT of 50 Ncm was set at placement. If the machine-driven insertion was discontinued because of high IT (> 50 Ncm), the implant insertion was completed manually, through the guide, with a dedicated wrench. Conversely, if the final IT was < 45 Ncm, the full procedure was guided by the implant motor. The IT was considered poor when < 35 Ncm. Finally, RFA was used to confirm the stability of each implant, immediately after implant placement, after the removal of the guide. For each implant, the average value from 4 different measurements (buccal, palatal, mesial, and distal) was obtained. The stability of the fixture was considered acceptable with an implant stability quotient (iSQ) ranging from 55 to 85, low with an iSQ < 55. Regardless of the stability value that emerged, all implants were subjected to immediate functional loading, splinted through a temporary full-arch restoration.

An implant was classified as “surviving” if still functioning regularly at the 1-year follow-up control. Conversely, in all cases in which the implant failed and had to be removed, it was classified as “failed.” The reasons for implant failure were:

The assessment of immediate operative/ post-operative, biologic, and prosthetic complications included identification of any problem or complication that had affected the guided implant procedures and the implant-supported restorations, from the initial surgery until the end of the 1-year follow-up period. Complications were divided into immediate operative / post-operative (related to the guided surgery procedure), biologic, and prosthetic. Biologic and prosthetic complications could be early or late, according to when they occurred: a complication was defined as early if it occurred no later than the third month after implant placement; conversely, a complication was late if it occurred more than 3 months from implant placement.

(1) mechanical complications, i.e., complications that occurred on pre-formed components and part of the implant system, such as unscrewing of the connecting screw and loss of connection between the implant and the abutment (abutment screw loosening), fracture of the connecting screw (abutment screw fracture), or fracture of the prosthetic abutment;

(2) technical complications, i.e., complications on prosthetic parts designed and built by the dental technician, such as customized zirconia individual abutments and prosthetic restorations (whether temporary or definitive). Among these complications were fracture of the individual abutments as well as fracture or chipping of the prosthetic restorations.

An implant-supported prosthetic restoration was considered successful if it did not present any failure or complication, either of a biological or a prosthetic nature, throughout the entire course of the study, i.e., from the moment of placement with the immediate functional load of the temporary restoration, until replacement with the definitive restoration, and for the whole period in which the definitive restoration remained in situ, from delivery up to the 1-year follow-up control. The possible complications that could occur were the aforementioned procedural, biological, and prosthetic complications, which could affect the implants and/or the prosthetic structure.

The soft-tissue stability was verified from clinical photographs, taken at the placement of the definitive restoration and at the 1-year follow-up, with the same digital camera (d7100®, Nikon, Tokyo, Japan) under the same settings (distance 0.6 m, f 22). Only the area of the smile, from the first right premolar to the first left premolar was investigated. The authors compared the stability of the tissues on these frontal pictures, focusing their attention on the stability of the papillae and the soft-tissue contours, using a novel index modified from Furhauser [34].

At the 1-year follow-up control, each patient was asked to fill out a patient satisfaction questionnaire consisting of 4 different questions. The questions read as follows:

For each question, the patient could give 5 possible replies: a) very satisfied; b) satisfied; c) neither satisfied nor dissatisfied; d) dissatisfied; e) very dissatisfied.

A total of 12 patients (5 males and 7 females, mean age 50.0 ± 13.8 years, median age 54.5 years, CI 95% 42.2–57.9 years) were enrolled in the present retrospective clinical study; 110 implants (65 of them post-extractive) were installed, immediately loaded by means of a provisional fixed full arch. After 6 months of provisionalization, then, 72 fixed prosthetic restorations (53 single crowns, 17 bridges, and 2 fixed full arches) were delivered, in order to prosthetically reconstruct the complete arch. The distribution of patients is summarized in Table 1. The patients’ groups were homogeneous in distribution according to gender (p = 0.563) and age class (p = 0.738), whereas most of the patients were systemically healthy (p = 0.049, with only 2 patients with diabetes mellitus and 2 others with auto-immune diseases) and non-smokers (p = 0.008, with only 3 smoking patients). The distribution of the implants is summarized in Table 2. Most of the implants were placed in the maxilla (p < 0.001), but the distribution of the fixtures was homogeneous per position (p = 0.735). However, the distribution of the fixtures was non-homogeneous per length (p < 0.001, with most of the placed fixtures being 11 or 13 mm in lenght) and per diameter (p = 0.001, most of the installed fixtures being 4.3, 5.1, and 6 mm in diameter). Finally, the distribution of the prosthetic restorations is summarized in Table 3. Most of the 72 fixed restorations (45) were delivered in the maxilla, versus only 27 delivered in the mandible, and there was a statistically significant difference in the number of restorations between maxilla and mandible (p = 0.033), with the groups that were considered non-homogeneous. Similarly, most of the restorations delivered in this retrospective clinical study were single-crown (53) or short-span restorations (17); thus there was a statistically significant difference in the distribution of the restorations, per type (p < 0.001).

The mean implant stability at placement, as measured by IT and RFA (iSQ), is summarized in Table 4.

Two implants failed and had to be removed, in the same 57-year-old diabetic female patient. The patient was a light smoker. These implants were lost in the posterior maxilla because they failed to osseointegrate 1 month after surgery and before the final restorations were delivered. Thus, the 1-year implant-based survival rate was 98.2% (108/110 surviving implants). Considering the patient as a statistical unit, with one patient experiencing implant failure and therefore categorized as failure, the 1-year patient-based survival rate was 91.6% (11/12 patients not having any implant failure).

During guided surgery procedures, no complications were reported. All surgical guides showed an excellent fit and were sufficiently resistant not to break during the insertion of the fixtures. All implants were sufficiently stable at the removal of the guides and they appeared to be in the planned position, without any evident mistake or aberrant positioning. The immediate provisional fixed full arch was easily adapted on the fixture after implant placement. In addition, over the 1-year follow-up period, no major biological complications affected the surviving (108/110) implants. Two patients had peri-implant mucosal inflammation with bleeding on probing around two post-extraction implants after 3 months, but the improved oral hygiene reduced the inflammation. No peri-implantitis occurred, nor progressive marginal bone resorption. The incidence of biologic complications amounted to 1.8% (2/108 implants). No issues were registered with the provisional restorations. With regard to the final implant-supported fixed restorations, only two single crowns underwent abutment screw loosening; these abutments were re-screwed and no further loosening was reported. The incidence of mechanical complications was therefore 1.8% (2/108) implants. No technical complications were reported.

Considering the implant failures that occurred and the different biologic and prosthetic complications that were encountered, the 1-year prosthetic success of this study amounted to 66.6% (8/12 prostheses did not undergo any failure or complication).

The photographic analysis revealed little or no differences between the pictures taken at the delivery of the final restorations and those at the 1-year controls. A certain degree of maturation of soft tissues was also evidenced, with growth of inter-implant papillae and adequate stability of soft-tissue contours.

The results of the patient satisfaction questionnarie are summarized in Table 5. The great majority of patients were satisfied with the treatment received (Fig. 12a, b, c, d, e) and no patients reported being dissatisfied when answering the 4 questions asked in the questionnaire.