1. Introduction
Modern dental implantology requires solutions that reduce morbidity and treatment time. At the same time, challenging situations, such as vertical bone atrophy, demand advanced technology and designs, surgical efficiency, and intelligent prosthetic solutions.
Maxillary atrophy is a frequently encountered condition that makes implant-supported oral rehabilitation difficult. This deficiency is directly related to tooth loss time and/or severity [
1]. It can lead to the proximity of the bone defect to critical anatomical structures, making it impossible to place implants with conventional lengths without prior bone grafting [
2].
The anatomical limitations that make it difficult to place implants in the maxillary bone include the maxillary sinus pneumatization [
3], nasal fossa, inferior alveolar nerve, mental nerve, and mandibular fovea. Bone atrophy and proximity to these regions require prior surgical procedures to allow the placement of regular-size implants such as bone grafts, distraction osteogenesis, and inferior alveolar nerve transposition [
1,
4,
5,
6]. However, these treatments offer increased morbidity, edema, treatment time, cost, and risk of paresthesia [
1,
7,
8,
9,
10,
11]. Short and extra-short implants have been developed to address these disadvantages as a viable treatment alternative [
12,
13].
Oral rehabilitation with short and extra-short implants in atrophic areas is a treatment option with less complexity, trauma, cost, and treatment time [
1,
5]. However, attention must be paid to the technique used to place these implants, as they offer a smaller bone-to-implant contact area. Therefore, factors such as bone density, quality and quantity, implant surface characteristics, surgical technique, prosthesis mechanical conditions, tissue biotype, and occlusal balance must be meticulously planned and adjusted during the treatment [
5,
14,
15].
Studies evaluating prosthetic aspects associated with implant size are still limited. Misch et al. (2006) [
16] concluded that the length of the implant does not seem to be the most critical factor in the distribution of loads at the bone–implant interface. For these authors, the diameter of the implant, increase in the crown-to-implant ratio (C/I), increase in the chewing forces, and lateral tensions are important factors for the distribution of loads and could lead to possible implant failures. Anitua et al. (2014) [
4], Anitua et al. (2015) [
17], and Di Fiore et al. (2019) [
18] also indicated that implants without a positive crown-to-implant ratio are more susceptible to failure as they influence the increase in marginal bone loss (MBL).
However, since the short implants are two-piece, the occlusal adjustment could affect the intensity of stress transmitted to the marginal bone and proximity to the microgap, in addition to repeated abutment tightening/loosening [
19]. These associated or isolated factors can influence marginal bone loss and promote the inflammation and accumulation of microorganisms in short implants, including occlusal maladjustment [
12].
In the literature, some authors [
5,
10,
20] compared regular-size implants with short implants; however, few observed the behavior of extra-short implants in regions of extreme atrophy. Thus, there is much to be explored regarding the mechanical and biological mechanism of implants with reduced sizes [
5].
Recently, the Neodent company launched a new model of short and extra-short implants with important changes to their design. Different classifications [
6,
21] were proposed for short (≤6 mm) and extra-short (≤5 mm) implants [
22]. In this study, we consider short (≥8.5 mm ≤6 mm) and extra-short (<6 mm) implants.
In this way, this study aimed to assess clinical and radiographic outcomes, including implant survival, marginal bone loss, and patient satisfaction, in individuals with severe bone atrophy treated using a newly developed system of short and extra-short implants.
2. Materials and Methods
2.1. Study Design
This clinical study was previously approved by the Research Ethics Committee of the Universidade Tuiutí do Paraná (Curitiba, Brazil no. 5.793.029).
The inclusion criteria were patients who had received Short® system implants (Neodent, Curitiba, Brazil) with prostheses installed at least six months before the data collection at Faculdade ILAPEO (Curitiba, Brazil), patients with periapical radiography performed at the time of prosthesis installation, and patients with good systemic health.
Patients with no periapical radiography at the time of prosthesis installation, a lack of follow-up visits, the presence of systemic diseases that could affect tissue response, uncontrolled diabetes, the use of bisphosphonates or proton inhibitors (PPI), a history of radiotherapy treatment, and autoimmune diseases were excluded.
After analyzing the medical records, participants were selected and invited to participate. All patients signed the informed consent form before any study procedure. Twelve patients were selected, one of whom did not attend appointments and was therefore excluded. Thus, 11 adult patients of both sexes with partial or total maxillary edentulism were included. These patients received 44 implants, 37 short implants (≤8.5 mm and ≥6 mm), and 7 extra-short implants (<6 mm) and were rehabilitated with total or partial implant-supported prostheses (temporary and/or metal-ceramic). The patient follow-up was carried out at a minimum of six months and a maximum of 24 months after the procedure. All patients were on a maintenance program with appointments every six months.
2.2. Surgical Procedures
Short® implant (Neodent, Curitiba, Brazil) was placed under local anesthesia (4% Articaine with 1:100,000 epinephrine) and with adequate bone bed preparation according to the manufacturer’s recommendations. All patients received the same brand and implant model with variations in the implant length and diameter according to the patient’s needs. Only one operator was responsible for all treatments. The patients were also given post-operatory and oral hygiene orientations. Patients with parafunction were also oriented to search for treatment and use an occlusal splint. However, the study team did not deliver the treatment.
After implant placement, the suture was performed, and an X-ray was taken. Patients were instructed to return between 7 and 14 days after surgery to remove the sutures.
The loading protocol (delayed or immediate) was selected according to each patient’s needs and the manufacturer’s instructions (IFU). At the surgeon’s discretion, immediate loading was applied when primary stability reached at least 35 N.cm and the patient presented physiological occlusion.
All patients received a temporary or final prosthesis per the clinician’s definition. After the prosthesis installation, a radiographic examination was performed to confirm the adaptation of the prosthetic work.
2.3. Clinical Analysis
The following variables (a and b) were extracted from the patient’s medical records and (c) clinically collected during the follow-up visit:
- (a)
Variables related to the patient: sex, age, systemic conditions, smoking, signs of parafunction, history of diseases, regularity of follow-up visits, and follow-up time.
- (b)
Variables related to the implant treatment: type and size of implants, need for grafts, bone type, type of implant load, and abutments.
- (c)
Outcome variables: mechanical complications (wear and fractures of prostheses; abutments and implants; and screw loosening, replacement, and loss), biological complications (presence of biofilm, bleeding on probing, suppuration, gingival recession, hyperplasia, bone loss), implant condition (pain, mobility), crown-to-implant ratio, and patient satisfaction.
The data described in item C were obtained according to the following steps: removal of the restorative material from the screw holes; assessment of prosthesis screw tightness; prosthesis removal; evaluation of the presence of plaque; assessment of abutment tightness; examination of the condition of the implants and peri-implant tissues; periapical radiography performed to check the peri-implant bone condition (presence or not of bone loss); and a questionnaire about satisfaction with the treatment performed.
After collecting clinical data, patients received prophylaxis, instructions in effective oral hygiene, guidance on a regular maintenance protocol every six months, and, if necessary, the prostheses were reinstalled with occlusal adjustments.
2.4. Peri-Implant Soft Tissue Analysis
The presence of visible plaque (VP) in the abutments and prosthesis was evaluated with Score 0 indicating absence of plaque and Score 1 indicating its presence. Bleeding on probing (BP) [
23] and probing depth (PD) were assessed at six different sites: mesio-buccal, buccal, disto-buccal, mesio-lingual, lingual, and disto-lingual.
The height of the keratinized mucosa (KM) was evaluated measuring the distance from the gingival margin to the mucogingival line in all implants in the mesiobuccal, buccal, and distobuccal positions. The measurements were classified as 0, >0 <2, and ≥2 mm. The gingival phenotype was classified as thick or thin through the visual analysis of the millimeter probe transparency in the peri-implant sulcus.
The appearance of the peri-implant mucosa was visually evaluated concerning the presence or absence of hyperplasia, with Score 0 being assigned for its absence and Score 1 for its presence. Gingival recession was also assessed visually by identifying the exposure of the abutment transmucosal or implant threads, then assigning Score 0 for the absence of recession and Score 1 for the presence of recession. Suppuration was assessed by applying digital pressure to the peri-implant tissues, with Score 0 indicating its absence and Score 1 indicating its presence.
All analyses were performed by a single experienced operator calibrated in all measurements.
2.5. Analysis of the Implant and Prostheses Survival and Success Rates
To evaluate the implant success, the absence of peri-implant infection, continuous radiolucency around the implant, bone loss in the first year < 1.5 mm, and annual bone loss < 0.2 mm were radiographically analyzed [
24]. Furthermore, pain, mobility, and percussion tests were also performed using a clinical mirror handle and prosthetic installation screwdriver, according to the criteria of Albrektsson et al. (1986) [
25]. The bone type was collected from clinical follow-up records according to the classification of Lekholm and Zarb (1985) [
26].
The prosthesis was considered successful when it was functional without presenting more than four complications that could be resolved. Complications included prosthesis, implant, and abutment wear, chips, and fractures and screw loosening, replacement, and loss. The loss of the abutment and abutment screw torque was evaluated with a counterclockwise force of 10N.
The crown-to-implant ratio (C/I) was split into two groups (C/I < 2 and C/I ≥ 2) and was analyzed and correlated with marginal bone loss (MBL), prosthesis design and material over time. The clinical C/I was calculated according to below [
4,
17,
18]:
2.6. Radiographic Assessment
Intraoral radiographs were taken at the time of prosthesis installation (T0) and follow-up visit (T1) using the Heliodent X-ray device (Sirona, Bensheim, Germany), with a CMOS sensor (Xios Supreme, Sirona, Bensheim, Germany). The periapical parallelism technique was used with an XCP-DS positioner (Dentsply Rinn, Elgin, IL, USA) to obtain radiography with standardized distance. After image calibration using the implant diameter as a reference, linear mesial and distal peri-implant bone height measurements were performed using the Sidexis 4 Software (Sirona). A reference line was drawn on the implant platform in the calibrated image. The measurement was obtained from the most apical point of the radiolucent image (at the bone/implant interface) to the implant platform reference line for implants with bone level below the implant platform line (
Figure 1A). In implants with bone level above the implant platform, the measurement was performed from the highest point of the alveolar crest to the implant platform line (
Figure 1B).
2.7. Assessment of Patient Satisfaction
Patient satisfaction with the treatment performed was assessed through a questionnaire applied as a visual analogue scale (VAS), with gradations from 0 to 10, with 0 being “totally dissatisfied” and 10 being “totally satisfied” [
27].
2.8. Statistical Analysis
Descriptive data analysis was carried out with estimates of the mean, median, standard deviation, and 25% and 75% percentile of quantitative variables and simple and relative frequencies of qualitative variables.
All analyses were conducted in the R 4.1.0 environment [
28].
4. Discussion
With the evolution of implant dentistry, modifications in the implant design were proposed to meet the specificities of the treatment and allow oral rehabilitation with lower cost, morbidity, and surgical time [
4,
17,
29,
30]. However, the ideal definition of regular, short, and extra-short implants is still inconclusive in the literature. Previous studies [
10,
31] considered regular implants to be ≤11 mm, short implants to be <7 mm, and extra-short implants to be ≤6.5 mm. In this study, short implants were considered to be 8.0 mm and extra-short implants were considered to be 4.0 and 5.5 mm in length.
Several authors have concluded that reduced-size implants offer an effective solution for patients with severe maxillary atrophy, achieving high long-term survival rates between 92% and 99% [
1,
15,
32,
33,
34]. These results corroborate those of the present clinical study, where the implant survival was 100%. Randomized clinical trials (RCTs) evaluating and comparing the behavior of short implants in atrophic areas and long implants in grafted areas in the posterior region of the mandible for one year [
29], three years [
30], and five years [
20] of follow-up showed similar results between both treatments, suggesting that treatment with short implants is a feasible alternative to bone graft associated with conventional implants and is associated with shorter treatment time, morbidity, and cost.
Although there is a fear to subject short implants to immediate loading, in the present study, immediate loading proved reliable, with 100% of implant success and survival with a mean of 13.45 months of follow-up. A prospective study [
35] reported that four of five short implants (7 mm) placed with immediate loading were lost. However, the literature has limited information about the influence of immediate loading on the survival of short and extra-short implants. Recently, Thomé et al. (2024) [
36] reported a 12-month follow-up of two clinical cases with short/extra-short implants in an atrophic posterior mandible, rehabilitated by digital workflow three months after surgery. These cases proved to be a successful treatment alternative.
The high implant survival and success rates in this pilot study can be justified by the abutment/implant interface, with a smooth “one piece” transmucosal collar positioned far from the bone crest to optimize the adaptation of the peri-implant biological space. The smooth surface of the gingival portion allows for more favorable results and minimizes loss of the peri-implant bone crest compared to other prosthetic interface designs [
1,
15,
37]. Since this prosthesis implant interface is at the gingival level, it reduces the presence of bacteria near the implant–bone contact.
A factor that strongly contributed to the implant success rate was the inclusion of patients in a peri-implant follow-up program [
38]. Findings suggest that a history of periodontal disease may be a possible risk factor for peri-implant diseases [
39]. In this clinical study, 63.64% of patients who received the implants had a history of periodontal disease. However, regularity in follow-up visits was 100%. Lombardo et al. (2020) [
21] compared patients with and without a history of periodontal disease in which 326 short and extra-short implants were posterior bimaxillary placed and restored with single-unit prostheses in a 3-year follow-up and concluded that periodontal disease did not appear to negatively influence the peri-implant conditions. When patients’ satisfaction was evaluated, only 36.36% of the patients reported low satisfaction regarding cleaning the prostheses (36.36%), especially when implant-supported. For this reason, it becomes even more essential to guarantee theparticipants maintenance in peri-implant follow-up programs.
When evaluating implant survival, it is necessary to consider peri-implant conditions as stability at the level of the marginal bone crest, since implants with a progressive loss of the bone crest may fail [
40]. Previous studies [
4,
9,
22] stated that the highest occlusal load is concentrated in the cervical region of the implant. In this way, bone stress is present around the implant collar and the first few millimeters (5 mm), regardless of the length of the implant. According to results obtained in this pilot study, short implants showed a tendency towards more apical marginal bone loss in the distal and mesial measurement compared to extra-short implants. Studies have shown similar values for marginal bone loss and high survival rates in conventional (8 mm), short (6 mm), and extra-short (4 mm) implants after a 2-year follow-up period [
34] and after three years of functional load [
1].
The mean mesial C/I ratio was 2.11 and 2.16 in distal. Tang et al. [
41] reported a mean clinical C/I ratio of 1.16. The difference from our study can be related to implant size since Tang′s study analyzed only implants with lengths of 8 and 6.5 mm, and ours considered extra-short implants, which can enhance the C/I ratio. The correlation between the C/I ratio and marginal bone loss is controversial. Different studies found no correlation between the C/I ratio and bone loss [
42,
43,
44]; Hingsammer et al. [
45] reported that a C/I ratio higher than 1.16 increases the risk of bone loss; and Tang et al. [
41] found an inverse correlation between the C/I ratio and bone loss. Malchiodi et al. [
46] reported that excessive bone loss can occur only when the clinical C/I ratio exceeds 3.4. The clinical C/I ratio found in our research is less than this threshold. In this way, our study showed a high C/I ratio, 100% implant survival, and marginal bone loss according to the expected, suggesting that short and extra-short implants are an alternative to rehabilitating posterior regions with atrophic alveoli despite their high C/I ratio.
Regarding the soft tissue conditions, the probing depth found in this study varied between 1.76 mm to 2.43 mm for short implants and 1.29 mm to 2.71 mm for extra-short implants. These results are similar to the 2.31 mm reported by Han et al. [
47] in one year of post-loading follow-up. Another study showed a 23.9% bleeding on probing in non-diabetic patients, comparable to the bleeding on probing in most of the regions analyzed in this study [
48]. In general, our study showed healthy soft tissue around short and extra-short implants.
All mechanical complications found were related to the patients with bruxism. Besides the orientation for occlusal splint use, the patients did not treat the parafunction. It is well-known that overload associated with bruxism can lead to dental wear, screw/implant loosening, screw/implant fracture, and loss of retention [
49]. In addition, according to the literature, short implants are associated with higher rates of prosthetic complications compared to conventional implants [
50]. As the mechanical complications reported in this study occurred in patients with bruxism, it can be concluded that they are unrelated to the new implant system.
Patients with systemic conditions and smoking habits were not excluded in this study. These characteristics can be confounding in the peri-implant tissue evaluation. The literature has already correlated a smoking habit with higher scores of bleeding index, mean peri-implant probing depth, and peri-implant mucosal inflammation [
51]. However, our results showed a good peri-implant tissue, and we believe these confounding did not influence the results due to patient adherence to the maintenance program.
Although this study presents limitations related to sample size and inequality between the number of short and extra-short implants evaluated, we can conclude that these implants showed excellent performance and are an alternative to the rehabilitation of atrophic jaws. Future randomized clinical studies are needed to confirm these results.