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Article

Clinical and Radiographic Follow-Up of Full-Arch Implant Prosthetic Rehabilitations: Retrospective Clinical Study at 6-Year Follow-Up

by
Matteo Nagni
1,2,
Filippo Pirani
1,2,
Bianca D’Orto
1,2,*,
Francesco Ferrini
1,2 and
Paolo Cappare
1,2,†
1
Dental School, Vita-Salute San Raffaele University, 20132 Milan, Italy
2
Department of Dentistry, IRCCS San Raffaele Hospital, 20132 Milan, Italy
*
Author to whom correspondence should be addressed.
†
Dedicated to the memory of author Paolo Cappare, who passed away during the preparation of this manuscript.
Appl. Sci. 2023, 13(20), 11143; https://doi.org/10.3390/app132011143
Submission received: 23 March 2023 / Revised: 24 May 2023 / Accepted: 28 May 2023 / Published: 10 October 2023
(This article belongs to the Special Issue Esthetic and Oral Rehabilitation: Novel Techniques, Materials and Applications)
Versions Notes

Abstract

:
Aim: the aim of this retrospective clinical study was to evaluate clinically and radiographically full-arch implant prosthetic rehabilitations supported by six axial implants or four implants placed according to the All-on-Four protocol. Materials and methods: Patients in need of immediately loaded full-arch implant prosthetic rehabilitations of one or both arches were considered. Follow-up visits were performed one week after surgery, at 3 and 6 months and then once a year for the next 6 years to record implant survival, peri-implant parameters, marginal bone loss, bone cortical thickness and possible muscular, articular and prosthetic complications. A satisfaction evaluation questionnaire was also made available to all patients at the end of the follow-up period. Results: A total of 30 patients with total edentulism of one or both arches or need for avulsion of residual impaired teeth were enrolled for this study and underwent implant prosthetic rehabilitation on four or six implants. The overall implant survival rate at the six-year follow-up was 98.09%. Statistical analysis revealed a significant association between implant site and higher plaque and bleeding index in the posterior site. The extent of keratinized tissue was statistically superior in anteriorly located implants. Statistical analysis showed a significant difference between the values of bone-marginal levels as a function of time. The vestibular and palatal/lingual bone cortices were preserved, with an increasing trend in the apical direction. Regarding muscular and articular complications, the results of this study showed statistically significant differences between the mean values recorded in male and female subjects, while the most frequently encountered problems during the clinical evaluation were the presence of joint clicks and pain in the masseter muscles. Two of the patients examined showed problems with mandibular latero-deviation and prosthetic fracture. Conclusion: within the limitations of the present study, immediate implant-retained prosthetic rehabilitations supported by six axial implants or four fixtures placed according to the All-on-Four method could represent a valid therapeutic alternative to provide edentulous patients with restoration of masticatory function and aesthetics and promote their acceptance.

1. Introduction

Although many procedures are aimed at preserving teeth for as long as possible, poor oral hygiene, periodontal disease, destructive caries lesions and other issues may result in edentulism. The increase in life expectancy of the individual and the consequent growth in the number of totally edentulous individuals with functional and aesthetic needs, especially in cases where more traditional removable prosthetic solutions are not well tolerated, leads to an increased demand for the stabilization of prosthetic restorations by means of implant fixtures [1,2,3,4,5,6].
Following the loss of dental elements, what ensues is progressive involution in terms of contraction of the upper jaw and in terms of expansion in the mandible [7,8,9].
The consequence, in a transverse direction, is the alteration of inter-maxillary skeletal relationships, with the development, even in previously normal-occluded subjects, of a third skeletal class. In the vertical direction, bone loss results in an increase in the inter-arch distance, which causes a progressive reduction in vertical dimension directly proportional to the degree of atrophy [10,11].
The senescent appearance of the patient is further emphasized by the loss of tissue trophism, mainly due to the loss of support of the orbicularis muscle of the lip and the labial and perioral soft tissues. The downward prominence of the nasal pyramid causes an exacerbation of the peri-oral and nose-to-lip furrows, with progressive reduction of the nasolabial filter [12,13].
From the point of view of the noble structures, the following changes can be seen in the case of bone atrophy in the anterior upper jaw: the nasopalatine canal and the foramen of the same name tend to move closer to the margin of the crest [14]; in the posterior region there is the process of pneumatization of the maxillary sinus and distalization of the greater palatine nerve, closer to the palatal margin of the bone crest [15]; in the anterior mandible, the mental foramen and the corresponding nerve trend towards superficialization [16], as occurs in the posterior region with the inferior alveolar nerve [17].
In relation to soft tissues, as hard tissues act as spinner expanders, it follows that the process of bone atrophy is associated with a reduction in the proportion of keratinized mucosa [18,19].
Furthermore, when tooth loss occurs, alveolar ridge resorption [20,21] could bring a significant bone atrophy that increases more in the posterior region than in the anterior, also associated with an important bone density decrease [22].
To achieve the necessary bone volume for axial implant placement, several procedures have been suggested to regenerate height and width (e.g., bone osteogenesis distraction, guided bone regeneration (GBR) with or without membrane or titanium mesh, bone blocks, bone substitutes) [23,24].
Given possible complications related to these surgical procedures, dental implants placed in basal bone by exploiting fixture tilting could be considered a viable therapeutic alternative [25,26,27].
Although several therapeutic alternatives have been proposed as a solution to the reported problems, in case of low bone height of the posterior sectors and superficializing of the nerve–vessel structures, rehabilitation by means of the All-on-Four protocol could be considered the best choice to exploit the basal bone [28,29], thus avoiding more invasive procedures [30,31,32,33,34,35,36].
The aim of this retrospective clinical study was to evaluate clinically and radiographically full-arch implant prosthetic rehabilitations supported by six axial implants or four implants placed according to the All-on-Four protocol. In detail, implant survival, peri-implant parameters, marginal bone loss and cortical bone thickness were considered, investigating possible muscular, articular and prosthetic complications and the degree of patient satisfaction with the performed work.
The null hypothesis was that there were no implant failures, there was no correlation between plaque, bleeding, keratinized mucosa amount and implant placement site (anterior or posterior), there was a time-dependent variation of marginal bone levels (the thickness of the bony cortical areas progressively increased in the apical direction), there were no statistically significant differences between males and females concerning maximum opening of the oral cavity, there was no prevalence among one or more specific articular or muscular pains/issues and there was no satisfaction from patient′s side in response to the treatment.

2. Materials and Methods

2.1. Patients’ Selection

This retrospective clinical trial was performed at the Department of Dentistry, IRCCS San Raffaele Hospital, Milan, Italy. The ethics committee approval number is 190/INT/2021.
The study was conducted in accordance with the tenets of the Declaration of Helsinki and followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guidelines for cohort studies (http://www.strobe-statement.org, accessed on 20 April 2023).
Patients with total edentulism or impaired residual dentition undergoing full-arch implant prosthetic rehabilitation were considered.
Medical records from May 2015 to January 2017 were analyzed to assess parameters at a minimum follow-up of six years.
The eligibility criteria were as follows: age > eighteen years old, edentulism of both arches or severe impairment of residual teeth, requiring fixed prosthetic rehabilitation, absence of systemic diseases that may represent a contraindication to the implant placement, adequate residual bone height for the insertion of 4 or 6 fixtures in basal bone (with no requirement for bone regeneration procedures), ability to practice home hygiene maintenance and compliance with follow-up checks and professional oral hygiene sessions.
Exclusion criteria were age < eighteen years old, smokers of more than 10 cigarettes/day, uncontrolled systemic diseases, oral or intravenous bisphosphonate therapy, head and neck radiotherapy within less than one year, severe malocclusion, severe parafunction and inability to adhere to home and professional hygiene maintenance protocols.
All diagnoses were made clinically and radiographically. The radiographic examination was conducted at first level with panoramic radiography and at second level with cone beam computed tomography (CBCT) to identify residual bone height and width.
Blood tests were prescribed about one month before surgery to check patient′s general health and to identify possible signs of uncompensated systemic diseases.
A written informed consent for implant prosthetic rehabilitation was obtained from all patients prior to the beginning of the study and the local ethical committee approved the study. Professional oral hygiene was provided before surgery.

2.2. Surgical Protocol

2.2.1. Pre-Surgical Protocol

All patients were administered 2 g amoxicillin (Zimox, Pfizer Italia, Latina, Italy) one hour before surgery. Anesthesia was administered by local infiltration of lidocaine 20 mg/mL with adrenaline at a concentration of 1:50,000 (Ecocain, Molteni Dental, Firenze, Italy). After preparation of the patient, povidone and chlorhexidine rinses were performed [37].

2.2.2. Surgical Protocol

A full-thickness linear incision was made in the palatal direction; subsequently, mesial and distal release incisions were made to release the flap.
The presence of keratinized tissue was preserved on both sides of the horizontal incision to simplify suturing procedures and to allow a biological seal to be achieved at the soft-tissue implant interface. Surgical dissection was performed according to cleavage plans and full-thickness incisions were made.
The implant sites were prepared according to the recommendations of the manufacturer of the implants employed (CSR implant system, Sweden & Martina, Due Carrare, Padova, Italy), i.e., with standard drills following the palatal wall as a guide, and the apical portion of the implant site was prepared at least 4 mm beyond the apex. After finishing the implant site preparation process, the implants were placed (CSR, Sweden & Martina, Due Carrare, Padova, Italy). The fixtures inserted were made of grade 4 titanium, had a cylindrical shaped body with tapered apex and 4 cutting chambers to increase anti-rotational capabilities. They also featured a new type of connection based on a double conometric system, a 0.8 mm machined neck and a 0.3 mm bevel for the platform change technology.
Four to six implants were placed in all patients. When necessary, the distal implants were tilted to avoid damaging the noble structures, never exceeding a 30-degree inclination. When necessary, crestal leveling was performed with a bone scraper to achieve homogeneous sub-crestal positioning and bone remodeling was performed at the level of the inclined implants. Finally, the 2 anterior implants were placed axially. In cases where reduced bone density was present, primary stability was achieved by sub-preparation of the implant site. All implants were placed with a minimum torque of at least 40 N/cm and by positioning the coronal margin of the implant apically 0.5 mm from the vestibular bone crest. In cases where inclined implants were present, offsetting any disparallelism was achieved with the use of 17/30 degree pre-angled abutments. These angles were chosen to guide the access holes of the prosthetic screws in an occlusal or palatal position. The soft tissues were sutured tension-free with 4-0 non-resorbable suture threads.

2.2.3. Post-Surgical Protocol

After surgery, a low-level laser therapy protocol with a 645 nm diode laser was performed to reduce tissue inflammation and to improve the tissue healing phase (Diode Laser, 645 nm, 0.6 Watt) (EGG Laser, DMT, Lissone, Italy). After the post-surgical visit, occlusal balancing was made and, after 3 months, a control recording was made to verify functional adaptation.
An orthopantomography was performed to confirm the correct positioning of the implant fixtures. Immediately after the surgical procedure, the patients were instructed to avoid traumatic phenomena induced by brushing. As a non-steroidal anti-inflammatory medication, patients were prescribed ibuprofen (Brufen 600 mg, Abbott Laboratories, Chicago, IL, USA), a chlorhexidine digluconate 0.2% mouthwash to be used for 2 weeks after surgery and amoxicillin (Zimox 1 g, Pfizer Italia, Latina, Italy), to be taken twice daily for 1 week. Patients were also instructed to follow a cold diet for 24 h after surgery and a soft diet for 2 months.

2.3. Prosthetic Protocol

Prior to surgery, all patients had their vertical dimension recorded by means of facial landmarks. Preliminary alginate impressions were taken to allow immediate loading. Immediately after surgery, provisional acrylic resin prostheses were relined intra-orally using self-curing polyurethane resin (Voco, Fort Mill, SC, USA). Within 24 h, the prostheses were placed with a torque spanner applying a torque of 15 N/cm.
Intra-oral digital radiographies (DIGORA 2.5 Soredex software, Tuusula, Finland) were performed to assess the marginal adaptation of the prosthetic structure.
Static and dynamic occlusion and contacts in centric relation were verified and modified using an articulating chart (Bausch 40 μm articulating chart, Nashua, NH, USA). Centric and lateral contacts were limited to the inter-canine area and the passivity of the prosthesis was verified. Finally, a temporary material (Fermit, Ivoclar Vivadent, Naturno, Bolzano, Italy) was used to cover the screw access holes.
After a period of about four months, necessary for the tissues to fully heal, definitive prosthetic procedures were begun using digital methods.
The scan bodies (Sweden & Martina, Due Carrare, Padua, Italy), which replace the traditional impression coping, were joined in the same way as for traditional prosthetic techniques. The intra-oral scanner used for all patients was a Carestream CS 3600 (Version 3.1.0 Acquisition Software, Carestream Dental LLC, Atlanta, GA, USA). The Carestream system operates using the principle of structured light, transforming the three-dimensional geometry of the dental arches into a virtual model.
The light source was initially held parallel to the occlusal plane, starting from the distal implant elements on the left side and moving towards the anterior implants of the contralateral quadrant; the source was then moved behind the distal implants on the left side, tilting it towards the palatal/lingual side. The occlusal plane was crossed towards the buccal side and the scanner was moved again from the scan starting point of the left side to the anterior implant of the right side, trying to keep it orthogonal to the occlusal plane. Subsequently, the image obtained was carefully analyzed and the incomplete areas were completed by further passes of the scanner. The same scanning procedure was performed on the contralateral side. Next, the operator scanned both the soft tissue and the provisional prosthesis with the analogues in place and then the scans were matched to each patient. The antagonist arch was scanned with the same procedure, followed by a scan of the buccal aspect of the patient′s teeth in maximum intercuspation and the resulting 3D scans were exported in the standard tessellation format (.stl).
The model of the provisional prosthesis, with implant analogues in place, was subsequently acquired extra-orally through the use of a laboratory scanner (Neway, Open Technologies, Rezzato, Italy) to verify the accuracy and precision of the intra-oral scan. In cases where differences were noted between the intra-oral and extra-oral scans, the restoration would be performed using the extra-oral scan as reference. All scanner scans were processed in the laboratory and returned after post-processing. The virtual images were evaluated for accuracy of detail and correct occlusal relationship.
Once the virtual model was completed, with dental implants in place, the digital framework was fabricated using CAD Ultimate software (Exocad Software, Darmstadt, Germany). Subsequently, the titanium framework was machined and, at the same time, the prototype model was used to realize the final restoration. The final prosthesis was made based on the provisional prosthesis but with greater attention to aesthetic, functional and soft tissue details. Following the aesthetic assessment, the prosthetic restoration was finalized. The aesthetic tooth restoration material (Nacera Hybrid, Doceram Medical Ceramics GmbH, Dortmund, Germany) and soft tissue were added on top of the meso-structure.
Subsequently, the prosthesis was cemented with the titanium mono-structure, using a self-adhesive composite cement (RelyX Unicem, 3M, St. Paul, MN, USA).
All prostheses were placed and screwed onto the dental implants and the Sheffield test was performed to check the accuracy of the structure. The marginal fit of the final prosthetic frameworks screwed onto the implants was checked by intra-oral digital radiographic examination; articulating paper (Bausch Articulating Paper, Nashua, NH, USA) was used to check the occlusion.
Specifically, static occlusion consisted of central contacts established on all masticatory units, while dynamic occlusion included canine and premolar guidance. The screw access holes were covered with temporary resin (Fermit, Ivoclar Vivadent, Naturno, Bolzano, Italy).
The results of the impression techniques were analyzed according to the following criteria:
  • Accurate imprinting in the implant areas;
  • Absence of voids in the lingual, buccal and occlusal areas;
  • Correct reproduction from the vestibule to the mucogingival junction.
Impressions that did not meet the criteria were discarded and the entire procedure was repeated.

2.4. Follow-Up

Follow-up visits were performed one week after surgery, at 3 and 6 months and then once a year for the next 6 years; any complications were recorded. Intra-oral X-rays were taken at 3, 6 and 12 months and once a year during the follow-up period to evaluate peri-implant marginal bone levels. At the end of the follow-up period, the patient underwent a cone beam CT scan on a Hyperion X5 3D/2D unit (MyRay, Cefla s.c., Imola, Bologna, Italy), with automatic exposure settings (MRT Technology, Suzhou, China), 4–15 mA and 16.8 s exposure time, to evaluate the thickness of the vestibular, palatal and lingual bone cortical areas. The clinical muscle and joint assessments were evaluated during the same time frame, i.e., at the end of the evaluation period.
Professional oral hygiene sessions were carried out every 4 months after the surgical–prosthetic procedure and, six years after implant placement, peri-implant parameters were measured.
At the end of the follow-up period, patients were given a questionnaire to assess their degree of satisfaction with the implant prosthetic protocol applied.

2.5. Clinical Outcomes

2.5.1. Implant Survival Rate

Implant survival was defined as the absence of implant mobility, peri-implant infection and/or marginal bone loss leading to removal of the fixture. Implant success was established as implant survival associated with less than 1.5 mm marginal bone loss after 1 year of loading and no more than 0.2 mm loss between each follow-up appointment.

2.5.2. Peri-Implant Health Status

The criteria taken into account to assess the health status of the peri-implant soft tissue were: mucosal suppuration, presence of bleeding, plaque index, pain and pocket depth at probing.
The clinical parameters measured at the peri-implant level were:
  • Plaque index;
  • Bleeding on probing (BoP);
  • Keratinized gingiva width (KTW);
  • Vestibular probing;
  • Mesial probing;
  • Palatal/lingual probing;
  • Distal probing.
All were surveyed by one clinician, using a PCP11 millimeter periodontal probe (Hu-Friedy Tuttlingen-Möhringen, Frankfurt, Germany), while a second clinician recorded the results.
In order to evaluate the possible correlation between implant site and plaque and bleeding index, the implants were divided into two categories based on the position of insertion in the arch; in particular, implants placed in zones 4, 5 and 6 were considered posterior implants or in the diathoric position, while implants placed in the other zones were considered anterior implants or in the anterior position.

2.5.3. Marginal Bone Loss

Bone level measurements were taken mesially and distally to each implant, using the implant–abutment junction as a reference point. To adjust for dimensional distortion and magnification on the radiographs, the actual implant dimensions were compared with the implant dimensions measured on the radiograph. A blind operator measured the changes in marginal bone height over time and the presence of voids at the prosthesis–implant connection by interactively marking the reference points and measured lines on the screen using specific software (DIGORA 2.5 Soredex Software, Tuusula, Finland). Calibration was obtained through the implant height. Mesial, distal and mean bone losses were calculated.

2.6. Evaluation of Bone Cortical

The thickness of cortical bone was evaluated by means of three-dimensional cross-sectional examination, using the calibration and measurement tools intrinsic to the software in use (MyRay v.10.1.0, Cefla s.c., Imola, Bologna, Italy). The measurement of horizontal bone thicknesses, both vestibular and palatal, was calculated at 1, 3 and 5 mm apical to the implant neck. The measurements were performed by three different operators and the final value was calculated by averaging the values taken by the three operators. Mean and standard deviation were classified according to implant placement site (maxillary or mandibular).

2.7. Clinical Muscular and Articular Assessment

The clinical muscle and joint assessment were performed according to the criteria of the European Academy of Craniomandibular Disorders (Eacd). Specifically, the following were assessed:
-
Maximum oral cavity opening (in millimeters), divided into men and women;
-
Pain in the masseter muscles (Yes/No);
-
Pain in the temporalis muscles (Yes/No);
-
Pain in the internal pterygoid muscles (Yes/No);
-
Presence of mandibular latero-deviation (Yes/No);
-
Presence of joint clicks (Yes/No);
-
Chipping/fracture of the prosthesis (Yes/No).

2.8. Degree of Patient Satisfaction

At the end of the follow-up period, all patients were given a form with 12 items (questions) to which they had to give a score from 0 to 100, according to their experience (Table 1).

2.9. Statistical Analysis

Dedicated software (SPSS 25.0, SPSS Inc., Chicago, IL, USA) was used to evaluate the presence of any association between implant site and plaque index, between implant site and bleeding index and between implant site and keratinized gingiva width; the Chi-square test was conducted.
The same dedicated software was also adopted to calculate and compare, by means of the multivariate analysis of variance MANOVA, the changes in marginal bone loss occurring over time at specific intervals. The statistical significance value was set at p = 0.05.

3. Results

According to the inclusion and exclusion criteria, 30 patients (13 females, 17 males) with total edentulism of one or both arches or need for avulsion of residual impaired teeth and subjected to implant prosthetic full-arch rehabilitation at a minimum follow-up of 6 years were enrolled for this study. The mean age was 66.5 years (range: 54–79).
Based on the grade of bone atrophy in the posterior region, patients received full-arch rehabilitation (of one or both jaws) with six axial implants or, if the residual posterior bone height was insufficient, All-on-Four rehabilitation (Table 2).

3.1. Implants Survival Rate

A total of 262 implants were placed, of which 132 in the maxilla and 130 in the mandible (Table 3).
Implant removal was needed in three patients, specifically in four cases in the upper jaw and one in the mandible. The overall implant survival rate was 98.09% and the null hypothesis was rejected. The lost implants were repositioned and immediately loaded. Although in the case of early failure there was a lack of osseointegration of the implant, the possible causes of late failure were associated with comorbidities developed by the respective patients during the follow-up period (increased number of cigarettes/day, decompensation of diabetic disease) and non-compliance with oral hygiene protocols for a period longer than three years (Table 4).

3.2. Peri-Implant Health Status

Regarding parameters measured at the peri-implant level, the frequencies and percentages inherent to the plaque index and bleeding index were recorded (Table 5).
The Chi-square test revealed a significant association between implant site and plaque index (χ2 = 8.33, p = 0.003); a positive association was found between plaque index and implant site in the diathoric position.
The Chi-square test also revealed a significant association between implant site and bleeding index (χ2 = 16.63, p < 0.001); a positive association was found between plaque index and implant site in the diathoric position. The null hypothesis was rejected.
In addition, probes of the four sectors and the width of the keratinized tissue were recorded (Table 6).
The Chi-square test revealed a significant association (χ2 = 7.03, p = 0.006) between a KTW value ≥ 2 and the anterior implant location. The null hypothesis was rejected.

3.3. Marginal Bone Loss

Concerning marginal bone loss, the values recorded were summarized according to measures obtained during follow-up and averaged for each group (Table 7).
To test the hypothesis of a time-dependent variation of marginal bone levels, a MANOVA (repeated measures ANOVA) test was performed with the within factor (time) alone. The test showed a significant difference between the values of bone-marginal levels as a function of time, F (1, 45) = 2229.18, p < 0.001. The null hypothesis was assessed.

3.4. Evaluation of Cortical Bone

The values for horizontal bone thicknesses, measured at 1, 3 and 5 mm apically at the implant neck, respectively, at the mandibular and maxillary level, are shown below (Table 8).
At the maxillary level, the thickness of the bony cortical progressively increased in the apical direction, increasing at the vestibular level from an average value of 1.11 mm to 3.62 mm and at the lingual level from an average value of 1.61 mm to 3.62 mm. Similarly, in the mandibular bone there was a progression of bone thickness in the apical direction, both at the vestibular level (from 1.24 mm to 1.65 mm) and at the lingual level (from 2.12 mm to 4.14 mm). The null hypothesis was assessed.

3.5. Clinical Muscular and Articular Assessment

The values of the maximum opening of the oral cavity are reported, broken down by gender, in Table 9, while the data concerning the presence/absence of pain in the masseter, temporalis and pterygoid muscles are summarized in Table 10.
The values inherent in the presence or absence of mandibular latero-deviation, joint clicks and chipping/fractures of the prosthesis are summarized in Table 11.
The maximum opening of the oral cavity showed statistically significant differences between the mean values recorded in the 17 male subjects (48.7 mm ± 2.8) and in the 13 female subjects (43.0 mm ± 5.1), while the most frequently reported problems during the clinical evaluation were the presence of joint clicks (13.3%) and pain in the masseter muscles (13.3%). Two of the patients examined showed problems with mandibular latero-deviation and prosthetic fracture. The null hypothesis was rejected.

3.6. Degree of Patient Satisfaction

The degree of patient satisfaction has been schematised in the following table (Table 12).
Regarding the evaluation questionnaire, the average results obtained for each individual item were extremely high. All patients showed high levels of general satisfaction with the rehabilitation performed (mean evaluation 95.2% ± 6.73) and high levels of satisfaction with the functional result obtained (mean evaluation 96.24 ± 5.12). Regarding satisfaction with the aesthetic results obtained (mean evaluation 94.97 ± 7.34), only one patient gave a score of less than 50/100, as he was not particularly satisfied with the aesthetics of the final prosthesis. A high level of pain during the surgical procedures was reported by only one patient, while post-operative pain was, on average, the lowest (mean rating 82.49 ± 16.88). The patients were extremely satisfied with the time required for the surgical procedure to be performed and for the final artefact to be delivered, considering the time required to be absolutely justified (mean evaluation 92.17 ± 15.12). Only one patient complained of continuous postponements and delays. The same patient was the only one who claimed to have developed problems with bruxism at night and to have experienced for the first few months following the definitive prosthesis chewing difficulties that forced him to considerably decrease his chewing speed and to pay attention to the positioning of his tongue when chewing food, due to the repeated traumas to which he was subjected. All patients under review stated that they would undergo the treatment performed again should it be necessary in the future (mean rating 97.38 ± 7.31) and that they would recommend the treatment to friends and relatives (mean rating 96.87 ± 8.26). The null hypothesis was rejected.

4. Discussion

In this retrospective clinical study, full-arch implant prosthetic rehabilitations supported by six axial implants or four implants placed according to the All-on-Four protocol were analyzed clinically and radiographically to assess implant survival rate, peri-implant parameters, marginal bone loss, bone cortical thickness, possible muscular, articular and prosthetic complications and patient satisfaction with the procedure.
The overall implant survival rate at the six-year follow-up was 98.09%. Similar results have been reported by other authors. Caramel et al., in their retrospective clinical study of full-arch rehabilitations, found a 5-year implant survival rate of 97.9% [38].
Carosi et al., when evaluating immediate loading rehabilitations with a reduced number of implants, reported a 4-year implant survival rate of 96.9% [39], while Romanos et al. reported a survival rate of 97.5% at a longer follow-up [40].
Concerning peri-implant parameters, the plaque index, the bleeding index and the thickness of the keratinized component of the mucosa were evaluated.
The Chi-square test revealed a significant association between implant site and plaque index and between implant site and bleeding index and a positive relationship was identified between both parameters and implant site in the diathoric position.
In their study, Carosi et al. evaluated bleeding and plaque index; BoP was detected around 6 implants (3.7%) and 16 implants showed a superficial amount of plaque resulting in a plaque score of 10% [41].
Menini et al., when analyzing plaque accumulation and peri-implant soft tissue inflammation in patients with immediately loaded implants supporting fixed full-arch prostheses, recorded a mean PI and BOP of 61.7% and 21.1%, respectively, in congruence with the results of this study [42].
As reported by several authors, and in accordance with the protocol adopted in the present study, home and professional hygiene maintenance could be significant in reducing plaque, bleeding and consequently any peri-implant complications, having a favorable impact on the tested parameters [43,44,45].
Concerning the width of keratinized tissue, the Chi-square test revealed a significant association between a KTW value ≥ 2 and the anterior implant site.
As pointed out by Schrott et al., the proportion of keratinized mucosa on peri-implant soft tissue could influence health and stability around implants; in the case of a thickness of less than 2 mm it could favor lingual plaque accumulation and bleeding [46].
Similar results were obtained by other authors, who stated that the lack of keratinized mucosa around the dental implants was significantly associated with more plaque accumulation, mucosal recession, inter-proximal bone level ≥ 3 mm and peri-implantitis [47].
Regarding this concept, the literature might illustrate conflicting results; the presence of more than 2 mm of KM width, although it might be associated with mucosal recession, might not affect other peri-implant parameters [48,49].
Regarding marginal bone loss, the results obtained are similar to those of other authors.
Cucchi et al., in their prospective clinical study, evaluated crestal bone loss around tilted and straight implants supporting immediate-loading full-arch rehabilitations and reported that the crestal bone level was 0.5 ± 0.4 mm for straight implants and 0.6 ± 0.4 mm for tilted implants (p > 0.05). Straight and tilted implants seemed to have similar behavior after immediate loading rehabilitations. After functional loading, straight and tilted implants did not differ significantly in clinical outcome [50].
Fan et al., in their retrospective clinical study of immediate rehabilitation of the edentulous and potential edentulous jaws with implant-supported full-arch prostheses, found that the average marginal bone loss at 1 and 5 years was (0.7 ± 0.2) mm and (1.1 ± 0.3) mm [51].
Malò et al., evaluating full-arch prostheses with the All-on-Four method in the mandible, reported an average marginal bone loss of 1.72 mm and 2.32 mm at 10 and 15 years, respectively; higher values, i.e., greater than 3 mm, were associated with smoking (OR = 2.72), previous failure of a contiguous implant or biological complication. Similar results were also obtained in the upper jaw [52,53].
To test the hypothesis of a time-dependent variation of marginal bone levels, a MANOVA (repeated measures ANOVA) test was performed with the within factor (time) alone. The test showed a significant difference between the values of bone marginal levels as a function of time, F (1, 45) = 2229.18, p < 0.001.
In agreement with the statistical analysis, Krennmair et al., in their prospective clinical study, evaluated clinical and radiographic outcome mandibular full-arch fixed prostheses supported on four implants with either axial or tilted distal implants, reporting a marginal bone loss at years 1, 2, and 3 of 1.11 ± 0.4 mm, 1.26 ± 0.42 mm and 1.40 ± 0.41 mm, respectively, representing a significant (p < 0.001) continuing time-dependent annual reduction [54].
In addition to the assessment of marginal bone loss obtained with intra-oral radiographs, the aid of cone beam CT enabled the thickness of the bony cortical to be assessed to highlight any dehiscence. In agreement with the results obtained, both at the maxillary and the mandibular levels, the thickness of the bony cortical progressively increased in the apical direction.
Our results agree with those of Sugiura et al., who reported that avoiding cantilever loading during the healing period prevented implant micromovements from adversely affecting implant stability, thus allowing the preservation of cortical bone in full-arch rehabilitations [55].
Furthermore, as suggested by several authors, implant planning with second-level examinations, coupled with exploitation of the basal bone with placement of the fixtures in the vestibulo-palatal or vestibulo-lingual direction (in order to avoid fenestrations or leakage at the thinner vestibular wall) could promote implant stability over time [56,57].
Concerning muscular and articular complications, the results of this study showed statistically significant differences between the mean values recorded in male and female subjects, while the most frequently encountered problems during the clinical evaluation were the presence of joint clicks and pain in the masseter muscles. Two of the patients examined showed problems with mandibular latero-deviation and prosthetic fracture.
Edentulous patients rehabilitated with implant-supported fixed prostheses demonstrated a greater degree of muscular activity during clenching and chewing [24]; in addition, as reported by Muller et al., an improvement in masseter muscle activity and maximum bite force could also be recorded [58].
Precisely, an increase in the activity of the masseter muscles more than the temporalis [57] could justify a greater incidence of pain in these muscles.
With regard to prosthetic complications, Cercadillo-Ibarguren et al., in their retrospective clinical study in which they described the clinical outcomes and complications related to provisional prostheses after full-arch implant-supported rehabilitation by means of an immediate loading protocol, reported that fracture of the provisional prosthesis was the more common finding [59].
In contrast, Francetti et al. reported the detachment of an element of the definitive prosthesis as the most frequent prosthetic complication of rehabilitations with a reduced number of implants [60].
Cavalli et al., in their 5-year follow-up, in accordance with the results obtained in this study, recorded the following prosthetic complications (reported in order of incidence): fracture or detachment of one or multiple acrylic teeth in temporary prosthesis, definitive and minor acrylic fractures in the temporary and definitive prosthesis [61].
In relation to the degree of satisfaction, as reported by several authors, patients reported an improvement in their starting conditions from a functional and aesthetic point of view and considered the timing of both the surgical intervention and the prosthesis phases to be appropriate [62,63,64,65].

5. Conclusions

Within the limitations of the present study, immediate implant-retained prosthetic rehabilitations supported by six axial implants or four fixtures placed according to the All-on-Four method could represent a valid therapeutic alternative to provide edentulous patients with restoration of masticatory function and aesthetics and promote acceptance.
At the six-year follow-up, implant survival could be considered high and marginal bone loss increasing in relation to time within normal ranges, periodontal parameters and the proportion of keratinized mucosa could be related with the implant placement site. The most frequently reported problems during the clinical evaluation were the presence of joint clicks and pain in the masseter muscles. Patient satisfaction was high.
Further studies may be necessary to obtain a broader spectrum evaluation in terms of both sample size and length of follow-up.

Author Contributions

Conceptualization, M.N. and F.P.; methodology, P.C., B.D. and F.F.; validation, F.F.; supervision, F.F., M.N. and P.C.; resources, B.D.; data curation, F.F. and M.N.; writing—review and editing, F.F. and B.D. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

The study was conducted in accordance with the Declaration of Helsinki and approved by the Institutional Review Ethics Committee of Vita-Salute San Raffaele University n.188/INT/2021, Dental School Department of Dentistry IRCCS San Raffaele Hospital, Milan, 20132, Italy.

Informed Consent Statement

Informed consent was obtained from all subjects involved in the study.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Table 1. Assessment questionnaire submitted to patients to evaluate their level of satisfaction.
Table 1. Assessment questionnaire submitted to patients to evaluate their level of satisfaction.
ItemScoreScoring Scale
1. Are you satisfied with the treatment performed?…………..(0 = not at all satisfied; 100 = very satisfied)
2. Are you satisfied with the functional result obtained?…………..(0 = not at all satisfied; 100 = very satisfied)
3. Are you satisfied with the aesthetic result obtained?…………..(0 = not at all satisfied; 100 = very satisfied)
4. Did you experience pain during the surgical procedures?…………..(0 = much pain; 100 = no pain)
5. Did you experience any pain in the days following surgery?…………..(0 = much pain; 100 = no pain)
6. Do you think the time required for treatment is justified?…………..(0 = absolutely no; 100 = absolutely yes)
7. Was the treatment performed as planned?…………..(0 = absolutely no; 100 = absolutely yes)
8. Did you develop bruxism (teeth grinding) problems as a result of the treatment?…………..(0 = absolutely no; 100 = absolutely yes)
9. Did you develop chewing problems as a result of the treatment?…………..(0 = absolutely no; 100 = absolutely yes)
10. Did you encounter any problems not listed above as a result of the treatment?If yes, please provide a brief description.…………..(0 = absolutely no; 100 = absolutely yes)
11. Would you undergo treatment again?…………..(0 = absolutely no; 100 = absolutely yes)
12. Would you recommend this treatment to friends and relatives?…………..(0 = absolutely no; 100 = absolutely yes)
Table 2. Patients’ classification according to gender and number of implants placed in the maxilla and mandible and the total number of fixtures for each.
Table 2. Patients’ classification according to gender and number of implants placed in the maxilla and mandible and the total number of fixtures for each.
PatientGenderN° Maxillary ImplantsN° Mandible Implants
Implants		Total Implants Placed
1male6410
2female448
3female448
4male4410
5male4610
6female4610
7male448
8male6410
9female448
10male448
11male448
12male6612
13female4410
14female448
15male448
16male4610
17female448
18male448
19female448
20female6410
21male448
22female6612
23male4410
24male4410
25male6612
26female448
27female448
28female448
29male448
30male448
Table 3. Number, diameter and length of dental implants.
Table 3. Number, diameter and length of dental implants.
Number, Diameter and Length of Dental Implants
length 9 mmlength 11 mmlength 13 mmlength 15 mm
n = 262diameter 3.3 mm9311713
diameter 3.8 mm49546128
Table 4. Implant failure before 6 months (early failure), after osseointegration period (after 6 months/late failure) and possible comorbidities which could be associated with implant loss.
Table 4. Implant failure before 6 months (early failure), after osseointegration period (after 6 months/late failure) and possible comorbidities which could be associated with implant loss.
Implants SiteEarly FailureLate FailureComorbidity
Patient 1 Maxilla11Smokers more than 10 cigarettes/day
Patient 2Mandible/1Uncompensated diabetes
Patient 3Maxilla 11Non-compliance with oral hygiene program
Table 5. Values recorded in relation to plaque index and BoP.
Table 5. Values recorded in relation to plaque index and BoP.
Yes (%)No (%)
Plaque Index111 (58.4%) 79 (41.6%)
BoP110 (57.9%) 80 (42.1%)
Table 6. Mean and standard deviation concerning width of keratinized tissue.
Table 6. Mean and standard deviation concerning width of keratinized tissue.
Average ± St. Deviation
KTW (mm)2.19 ± 1.19
Vestibular probing (mm)1.46 ± 0.60
Mesial probing (mm)1.37 ± 0.59
Palatal/lingual probing (mm)1.29 ± 0.50
Distal probing (mm)1.41 ± 0.54
Table 7. Average marginal bone loss for each group during the follow-up.
Table 7. Average marginal bone loss for each group during the follow-up.
Marginal Bone Loss
6 months (mm)0.66 ± 0.48
1 year (mm)0.72 ± 0.61
2 years (mm)0.80 ± 0.61
3 years (mm)0.84 ± 0.77
4 years (mm)0.86 ± 0.85
5 years (mm)0.97 ± 1.01
6 years (mm)1.00 ± 0.91
Table 8. Average ± standard deviation related horizontal bone thicknesses, measured at 1, 3 and 5 mm apical to the implant neck, respectively, divided according to implant placement site (maxilla or mandible).
Table 8. Average ± standard deviation related horizontal bone thicknesses, measured at 1, 3 and 5 mm apical to the implant neck, respectively, divided according to implant placement site (maxilla or mandible).
MaxillaMandible
Vestibular thickness at 1 mm1.11 ± 0.771.24 ± 0.56
Vestibular thickness at 3 mm1.55 ± 0.981.39 ± 1.11
Vestibular thickness at 5 mm1.78 ± 0.911.65 ± 1.03
Palatal/lingual thickness at 1 mm1.61 ± 0.772.12 ± 1.17
Palatal/lingual thickness at 3 mm2.77 ± 1.322.59 ± 1.88
Palatal/lingual thickness at 5 mm3.62 ± 1.314.14 ± 2.19
Table 9. Maximum mouth-opening values found in men and women.
Table 9. Maximum mouth-opening values found in men and women.
No. PatientsAverage ± St. Dev.
Males1748.7 ± 2.8
Females1343.0 ± 5.1
Table 10. Patients who reported masticatory muscle pain and frequency following implant prosthetic rehabilitation.
Table 10. Patients who reported masticatory muscle pain and frequency following implant prosthetic rehabilitation.
Pain Frequency (%)
Masseters4 (13.3%)
Temporals3 (10%)
Pterygoids3 (10%)
Table 11. Patients who reported other complaints following implant prosthetic rehabilitation.
Table 11. Patients who reported other complaints following implant prosthetic rehabilitation.
Pain Frequency (%)
Latero-deviation2 (6.7%)
Joint clicks4 (13.3%)
Chipping/prosthetic fractures2 (6.7%)
Table 12. Results obtained from filling in the satisfaction questionnaire.
Table 12. Results obtained from filling in the satisfaction questionnaire.
Average ± St. Dev.
Item (1)95.20 ± 6.73
Item (2)96.24 ± 5.12
Item (3)94.97 ± 7.34
Item (4)93.29 ± 12.65
Item (5)82.49 ± 16.88
Item (6)92.17 ± 15.12
Item (7)96.04 ± 11.98
Item (8)96.92 ± 4.27
Item (9)94.56 ± 12.83
Item (10)96.41 ± 10.46
Item (11)97.38 ± 7.31
Item (12)96.87 ± 8.26
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MDPI and ACS Style

Nagni, M.; Pirani, F.; D’Orto, B.; Ferrini, F.; Cappare, P. Clinical and Radiographic Follow-Up of Full-Arch Implant Prosthetic Rehabilitations: Retrospective Clinical Study at 6-Year Follow-Up. Appl. Sci. 2023, 13, 11143. https://doi.org/10.3390/app132011143

AMA Style

Nagni M, Pirani F, D’Orto B, Ferrini F, Cappare P. Clinical and Radiographic Follow-Up of Full-Arch Implant Prosthetic Rehabilitations: Retrospective Clinical Study at 6-Year Follow-Up. Applied Sciences. 2023; 13(20):11143. https://doi.org/10.3390/app132011143

Chicago/Turabian Style

Nagni, Matteo, Filippo Pirani, Bianca D’Orto, Francesco Ferrini, and Paolo Cappare. 2023. "Clinical and Radiographic Follow-Up of Full-Arch Implant Prosthetic Rehabilitations: Retrospective Clinical Study at 6-Year Follow-Up" Applied Sciences 13, no. 20: 11143. https://doi.org/10.3390/app132011143

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