Clinical Investigation of an Immediate Load Protocol Using Axial and Tilted Implants to Treat Patients with Failing Dentition or Complete Edentulism

Clinical Investigation of an Immediate Load Protocol Using Axial and Tilted Implants - Featured Image

Preliminary Results of a Multicenter Cohort Study

Abstract

Objective: This clinical investigation evaluated a specific surgical/prosthetic protocol for full-arch fixed dental restorations supported by immediate loaded axial and axial and tilted implants in a multicenter cohort study. Evaluation was based on a comparison of the survival rates of axial and tilted implants, as well as the overall prosthetic survival rate.

Materials and Methods: From 2013 to 2019, 38 patients (22 males and 16 females) were recruited and treated with tapered internal dental implants. Provisional fixed-dental prostheses  were  screw-retained  over  axial or axial and tilted implants within a  24-  to  48-hour period after surgery. Follow-ups  were  scheduled  at  6, 12, and 24 months and annually  for  up  to  four  years, and radiographic evaluations of peri-implant bone level changes were conducted.

Results: The 38 patients were followed up for an average of 43 months. Eight patients received both upper and lower implant rehabilitations, resulting in 42 restorations. A total of 210 implants were placed (i.e., 118 maxillary implants; 92 mandibular implants) and 64% of the fixtures were evaluated at the six-year recall. Cumulative survival rates were 97.96% for implants (i.e., 98.96% axial implants and 94.94% tilted implants) and 96.95% for prosthetics. At the two-year evaluation, no significant difference in marginal bone loss was found between tilted and axial implants placed in either jaw

Conclusion: Mid-study results confirmed that immediate loading of axial and tilted implants following the studied protocol provides a viable treatment modality for the rehabilitation of edentulous arches and terminal dentition.

Key Words: immediate loading, axial implants, straight implants, tilted implants, failing dentition, edentulous

«Full arch immediate restorations over tilted and axial implants reported high percentage of survival rates, in line with rehabilitations supported solely by conventionally placed fixtures.»

Introduction

Elderly patients commonly present with failing dentition or complete edentulism. Many of these patients wear either complete dentures or old failing restorations, and/or exhibit periodontally compromised teeth, as well as complain about chewing ability, overall esthetics, functional loss, decreased motor control of the tongue, reduced bite force, and diminished oral sensory function.1,2 With greater frequency and in growing numbers, patients with failing dentition are consulting clinicians for alternatives to wearing removable dentures. Currently, a treatment of choice for these types of patients is the use of a fixed prosthesis anchored to an endosseous implant, an option that significantly improves their quality of life (Figs 1 & 2).3,4

However, post-extraction edentulous patients or long-time full denture patients often present with minimal posterior bone support. Additionally, anatomical structures (e.g., the maxillary sinuses and mandibular nerves) may prevent implant placement in the posterior regions (Fig 3). To face these limitations, clinicians have different therapeutic options (e.g., long distal cantilever,5 short implants,6,7 sinus lift,8 bone regeneration,9 or implants placed in specific anatomical areas such as the pterygoid region,10 the tuber,11,12 or the zygoma).13,14 Each of these procedures requires surgical and prosthetic expertise and has its own specific limitations, risks, and complications, which can reduce patients’ acceptance.

Clinical15-17 and experimental studies18-20 have shown several surgical and prosthetic advantages in tilting posterior implants, representing a viable alternative to grafting. Partial21 or total immediate restorations over tilted and axial implants22,23 reported high percentages of survival rates, in line with rehabilitations supported solely by conventionally placed fixtures.24,25

During the last decades materials and techniques have improved continuously and immediate loading has proved to be a predictable and reliable procedure, especially for full-arch rehabilitations.23,24 Earlier studies on immediate loading have included a high number of dental implants,25,26 specifically when applied in the maxilla, which typically exhibits poor bone density. Recent reports have shown good outcomes with the use of only four implants (i.e., two axial and two tilted).27,28 However, at this point, the ideal number of dental implants and their distribution supporting immediate fixed full-arch restorations is not reported in the literature and no clear up-to-date guidelines are present for immediate loading applications.

This study’s aims were to evaluate the clinical outcomes and levels of patient satisfaction with immediately loaded full-arch fixed prostheses utilizing a particular surgical/prosthetic protocol supported solely by axial implants or by a combination of axial and tilted implants in both jaws and to compare the outcome of tilted versus axial fixtures in the same patients for a period of up to six years. The null hypothesis was that there would be no difference in survival rate and marginal bone level change between axial and tilted implants, and no difference in prosthetic survival rate between rehabilitations supported only by axial implants or by a combination of axial and tilted implants.

Figure 1: The dentolabial analysis highlighted a low smile, thin upper lip, inappropriate occlusal planes, and a smile width of 10 teeth.

Figure 2: Intraoral analysis showing the removable appliance in the anterior upper arch, dental disproportions, and gingival asymmetries.

Figure 3: Full-mouth periapical x-ray images illustrate that potentially edentulous patients or patients with failing dentition require a thorough multidisciplinary approach due to the complexity of clinical and psychological issues. Note the moderate horizontal bone resorption, short roots, several significant areas of decay, and periapical lesions on the remaining teeth.

Study Specifics

Study Design

This was a retrospective multicenter controlled clinical study evaluating a specific surgical/prosthetic protocol (TeethXpress, BioHorizons; Birmingham, AL); survival rate, marginal bone levels, peri-implant tissue conditions, and prosthetic complications of axial and tilted implants were compared after six years of function.

Inclusion criteria: They were as follows:

  • male and female subjects older than 18 years who were physically and psychologically able to undergo implant surgery and restorative procedures29
  • signed an informed consent to participate in the study.
  • completely edentulous (mandible and/or maxilla)
  • with failing dentition and/or the presence of teeth with unfavorable long-term prognosis requiring dental implants (mandible and/or maxilla)
  • adequate bone volume for implant placement (i.e., at least 8 mm long and 7 mm wide)
  • smokers (i.e., grouped as non-smoker, light smoker of ≤ 10 cigarettes/day, or heavy smoker of ≥ 11 cigarettes/day).

Exclusion criteria: They were as follows:

  • presence of active infection or inflammation in the future implant placement area
  • hematologic diseases
  • uncontrolled diabetes
  • metabolic disease affecting bone or disease of the immune system
  • radiation therapy in the head or neck region in the previous five years
  • poor oral hygiene and motivation.

Outcome measures: Tested at each follow-up visit, the primary outcome measure of success was prosthesis functionality (i.e., the prosthesis functioned without any mobility, stability, and pain issues, even at the loss of one or more implants).

Secondary outcome measures were as follow:

  1. Implant survival (i.e., the implant was in function and stable with no evidence of peri-implant radiolucency, no suppuration or pain at the implant site, or ongoing pathologic processes).30
  2. Biological and prosthetic complications (e.g., peri-implant mucositis, peri-implantitis, fistulas or abscesses, or any mechanical or prosthetic complications such as fracture of the implant and prosthetic components).31,32
  3. Marginal bone level change: Periapical radiographs were performed at six and 12 months, and yearly thereafter. An evaluator-blinded assessment of the marginal bone level was made using image analysis software (UTHSCSA Image Tool version 3.00 for Windows, University of Texas Health Science Center; San Antonio, TX). The implant platform (i.e., the horizontal interface between the implant and the abutment) was used as the reference for each measurement and the linear distance between the platform and the most coronal bone-to-implant contact was Mesial and distal values were averaged to establish a single value for each implant. Bone loss around tilted and axial implants was compared using paired student’s t-test. Analysis of variance was used to compare bone level changes over time. The level of significance was p = .05; a marginal bone loss of 2 mm was considered a parameter of success.
  4. Peri-implant tissue parameters: Six and 12 months after implant placement digital impressions of the study jaws were taken and digital calipers were used to evaluate the stability of the soft tissues around the implants.
  5. Complications and adverse effects were recorded and reported.

Implant type: Tapered internal implants (Laser-Lok, BioHorizons); operators were free to choose diameter and lengths according to their preferences and to use them straight or tilted according to each patient’s anatomical scenario.

Abutment type: Multi-unit abutment system (BioHorizons).

Data collection and follow-up: During the first month patients were scheduled for weekly control visits for tissue healing assessment and prosthetic functionality. At the delivery of the prostheses, each implant was probed all around and these measurements were checked yearly. Periapical radiographs were taken at baseline, six months, 12 months, and yearly thereafter for up to five years. Acting in an assessor-blinded manner, a biostatistician with experience in implant dentistry created a database for the analysis of all data. During each follow-up visit, the prosthetic structure’s mobility and occlusion were checked and any complications were recorded. At the one-year followup visit and annually thereafter, the prostheses were unscrewed, and each implant was tested for stability, its ability to withstand pressure and probed.

Figure 4: View of the first set of reinforced provisional restorations relined, polished, and cemented on natural, hopeless teeth. The primary objective was to deliver a fixed prosthesis on natural dentition that met the patient’s needs and expectations (i.e., comfort, improved overall esthetics, and function as compared to the initial situation).

Figures 5a & 5b: This therapeutic phase allowed the clinician to remove the most compromised teeth and to reduce hard and soft tissue inflammation. Note the health of gingival tissues at the one-month followup appointment. The primary retention of the abutments and the patient’s low biomechanics risk aided in avoiding complications during this first phase of treatment.

Study Protocol Phases

Pre-Surgical

After being screened for eligibility and informed consent, prospective participants were given a pre-surgical evaluation (Figs 1 & 2). Arch size, bone volume, inter arch relation, and distance were evaluated preoperatively by means of a clinical examination and analysis of panoramic radiographs, periapical radiographs, computerized tomography scans, lateral view radiographs of the skull, and articulator-mounted study models (Fig 3).

Before surgery, a resin transfer plate was realized as a duplicate of the patient’s tested denture or based on an esthetic try-in for partially edentulous patients (Figs 4-5b), with a secure stop on the palatal vault or on the retromolar triangle. An opening at the level of the occlusal surface was made to use the plate as a surgical guide.33

Surgical

Chlorhexidine mouthwash (Curasept, Curaden Healthcare SRL; Milan, Italy) was prescribed to patients, starting three days before surgery and then daily for 15 days. All surgeries were performed under local anesthesia and intravenous sedation.

Implant number, diameter, length, and positioning were planned based on clinical and radiographic analysis, as well as the final prosthetic restoration. Other factors (e.g., age, gender, opposing dentition, and facial morphotype) also were considered. The final decision, determined intra-operatively, was primarily based on bone quality and quantity, and the implant’s primary stability.

After local anesthesia, the remaining teeth were extracted and sockets were thoroughly debrided. A midcrestal incision was made, dividing the available keratinized gingiva in half while always making sure to exclude the retromolar triangle or the maxillary tuberosity. A full-thickness flap was elevated; direct visualization of the mental nerve was made, and the anterior loop was estimated with an atraumatic periodontal probe gently placed into the canal. In the upper jaw, the vestibular bony wall was exposed to allow the clinician a direct understanding of sinus morphology during the drilling phase. Where necessary, crest regularization was performed with bony forceps and rotating instruments before stabilizing the resin transfer plate using the palatal vault or the retromolar area.

For the rehabilitation of the mandible, if the remaining bone height was more than 9 mm, four to six implants were placed axially and symmetrically along the alveolar crest. In case of atrophic posterior ridges with less than 7 mm height from the mandibular canal, straight interforaminal implants or two axial and two posterior tilted implants were inserted. Similar considerations for the maxilla were treated with four to six straight implants in the presence of full bone (i.e., 9 mm or more) or with four axial and two tilted dental implants or two axial and two tilted implants in case of reduced bone height (i.e., less than 7 mm relative to sinus floor) and bone availability between maxillary anterior sinus walls. (Note: Implants are considered tilted when they are placed with a mesiodistal inclination ranging between 20° and 40° relative to the occlusal plane.) Bone quality was evaluated based on Lekholm and Zarb classification,34 and tapered internal implants were placed following manufacturer’s instructions to optimize primary stability.

Wherever necessary, peri-implant bone regeneration was performed using a combination of autogenous bone and bone substitute mixed in equal proportion and covered by a resorbable membrane. In the case of post-extraction sockets, the gaps were filled with a mixture of autogenous bone and bone substitute without the use of any membrane. Multi-unit abutments were screw-retained and tightened at 30 Ncm to straight and tilted implants.

Immediate provisional restoration: Titanium cylinders were positioned over the abutments and isolated with a rubber dam. The surgical guide in patient’s mouth was checked for stability. Sutures made with Gore Tex 5/0 (WL Gore & Associates; Flagstaff, AZ) were fixed to the surgical guide using composite (Protemp 4, 3M ESPE; Pioltello, Milan, Italy).33 After five minutes, the titanium cylinders and guide were removed, and healing abutments were placed.

Implant analogs were screwed on the impression copings and the stone was removed from the study model in the area corresponding to implant placement. The entire complex—surgical guide, titanium cylinders, and analogs—was positioned once again over the study model. New stone was placed to secure implant analogs, converting the study model into the final master cast.33 A screw-retained metal reinforced provisional was made and positioned in the patient’s mouth the same day or within 24 hours after surgery. The immediate restoration typically contained no more than 12 teeth. Full occlusal contacts in centric occlusion were maintained for all teeth, and canine or group guidances were created, with moderate inclination, avoiding nonworking interferences (Figs 6a-11d).

Final restoration: After six months of loading, in the absence of pain and inflammation (Figs 12a-12b), patients received the final restoration. Titanium and zirconium-oxide frameworks were made with computer-aided design/computeraided manufacture (CAD/CAM) technology. Porcelain veneer, acrylic resin, composite dental materials were used to restore the teeth according to patient desires (Figs 12c-18c).

Figure 6a
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Figure 6b
b
Figure 6c
c

Figures 6a-6c: Note the cone-beam computed tomography (CBTC) evaluation at the nine-month follow-up and the horizontal volume in the occlusal image.

Figure 7: Upper arch esthetic try in based on the information based on the information derived from the first provisional’s esthetic and functional analysis without flanges in position. At this stage, any modifications can be evaluated, discussed, and performed by the laboratory. Once accepted by the patient, the esthetic try in will be duplicated in the surgical guide.

Figure 8a
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Figure 8b
b
Figure 8c
c
Figure 8d
d
Figure 8e
e
Figure 8f
f

Figures 8a-8f: Placement of the two axial implants in the fresh extraction site of #42 and healed ridge of #32 and the two tilted distal implants, following esthetic and structural evaluation of the prosthesis, obtained a primary stability of 50 Ncm. Thanks to the appropriate color-coded carrier, the two straight MUAs and the two tilted ones were positioned, then tightened to 30 Ncm.

Figure 9a
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Figure 9b
b
Figure 9c
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Figure 9d
d
Figure 9e
e

Figures 9a-9e: On the same surgical day as the lower arch, due to a significant bone defect in the anterior right maxilla, it was necessary to recreate the appropriate volume by means of a ramus block graft for augmentation.

Figures 10a & 10b: At this stage, the template is used as a custom tray to transfer, through the dual composite, the exact position of the multi-unit abutments (MUA) on the master model mounted in an articulator. Note the occlusal gear, verified in centric relation (CR) at the correct vertical dimension using the pattern resin.

Figure 11a
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Figure 11b
b
Figure 11c
c
Figure 11d
d

Figures 11a-11d: Placement of the tilted implant in #15. Note the quantity of regenerated bone. Surgery was concluded with two straight implants and a tilted distal one. Views of the provisional restoration’s dentolabial analysis. The provisional restoration characteristics to obtain are accuracy, strength, and passive fit.

Figure 12a
a
Figure 12b
b
Figure 12c
c
Figure 12d
d

Figures 12a-12d: Osseointegration is complete and hard and soft tissues are stable. Note the implant disposition in the arches resulting in an ideal AP Spread. At this point a digital impression was detected (iTero Element Intraoral Scanner, Align Technology; San Jose, CA) utilizing dedicated Scan Strategy and Scan Bodies (Toothless, Simbiosi SRL; Empoli Firenze, Italy). The scanning plan to execute this digital impression was:

  • Upper Provisional Restoration Scan
  • Lower Provisional Restoration Scan
  • Bite Registration
  • Upper Scan Bodies Scan
  • Lower Scan Bodies
  • Upper and Lower Provisional Restoration Chairside Scan

Figure 13: During the computer-aided design (CAD) phase, the technician worked on a digital prosthesis, resulting from the merging of all of the different scans. The first step was to digitally project and produce an aluminum bar to test the impression accuracy by checking the bar’s passive fit.

Figure 14: The second step of the CAD phase was to project a prototype to test in the patient’s mouth before finalizing the restoration.

Figure 15a
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Figure 15b
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Figure 15c
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Figures 15a-15c: The use of a prototype as part of a completely digital workflow reduces the number of clinical steps required for definitive restoration, because it enables simultaneous checking of accuracy, occlusal, esthetic parameter, and peri-implant soft tissue characteristics. Note how in this case it was helpful to determine whether or not to use the artificial pink component, including in this decision the patient perspective as well.

Figure 16a
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Figure 16b
b
Figure 16c
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Figures 16a-16c: Once the patient has accepted the test drive prototype, the laboratory technician, using CAD technology, can finalize the details of the final restoration.

Figure 17a
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Figure 17b
b
Figure 17c
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Figures 17a-17c: View of the two titanium bars produced. The zirconia restorations will be cemented on top of these two bars.

Figure 18a
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Figure 18b
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Figure 18c
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Figures 18a-18c: Final monolithic zirconia cemented on titanium bar restoration. The correct occlusal compensation curves have been restored. The presence of the pink artificial component made it possible to restore the correct dental proportions and consequently the white and pink esthetic balance. The final prosthesis was delivered eighteen months after the first consultation, respecting the case’s esthetic, functional, and structural goals. Thanks to a coordinated and accurate workflow, the patient’s needs and wants were met, resulting in a prosthesis well integrated into the smile.

Results

The study included 38 patients (22 males and 16 females; mean age 67.41 years) for a total of 42 full-arch fixed-dental rehabilitations (21 maxillae and 21 mandibles) (Table 1). Six patients were smokers (21.3%), showing an average daily consumption of 15 cigarettes. From 2013 to 2019, a total of 210 implants were placed and all of them were immediately loaded; 166 dental implants were placed axially to the bone crest, while 44 were tilted mesiodistally between 20° and 40° according to the type of rehabilitation and anatomical conditions. In one case, considered an exception, only one posterior implant was tilted less than 20° due to asymmetrical anatomic bone conditions. Ninety-eight implants were positioned in fresh extraction sockets or in what remained of the socket after bone crest regularization; 20 of them were tilted implants and from these fixtures, 13 engaged the extraction site only in the most coronal part, while seven passed through those sites only with their bodies. Only 12 implants needed buccal bone regeneration to cover the exposed threads.

Table 1. Patient Distribution by Gender and Age

Gender Restoration Location Ages
40-50
Ages
51-60
Ages
61-70
Ages
71-80
Ages
81-90
male (N=22) maxilla (N=12)
mandible (N=10)
1
0
1
1
4
4
6
5
0
0
female (N=16) maxilla (N=9)
mandible (N=11)
0
1
0
2
4
4
5
3
0
1
Total (N=38) Total (N=42) 2 4 16 19 1

Eleven maxillary arches and eight mandibles were treated with the use of 38 tilted implants in addition to 47 conventional dental implants, while 15 arches (i.e., nine maxillae and six mandibles) were rehabilitated with a total of 109 axial implants (i.e., 61 in the upper jaw and 48 in the lower jaw) (Table 2).

Provisional restorations always consisted of acrylic resin prosthesis reinforced with a metal framework with or without reduced distal cantilevers, while final rehabilitations varied according to patient’s desires and clinician’s suggestions. Fortytwo prostheses (100%) were based on a CAD/CAM rehabilitation with a titanium or zirconia framework; 9 of them (21.4%) were veneered with ceramic, 9 with composite teeth (21.4%), 9 with acrylic resin teeth (21.4%), 4 (9.5%) were partially monolithic zirconia rehabilitations, 6 (14.2%) were fully monolithic zirconia rehabilitations, and 3 (7.14%) were a fully monolithic translucent zirconia on titanium bars. All prostheses were screw-retained on the multi-unit abutment system. Unilateral or bilateral distal cantilevers were present according to the extension of the opposing dentition.

Table 2. Overview of Each Patient’s Rehabilitation

Patient Gender Arch Position, Axial Implants Position, Tilted Implants Failures Final Prosthesis Final Opposing Dentition
M mandibular 24, 22, 20, 25, 27, 29 -- 0 hybrid titanium with acrylic resin teeth fixed dental prosthesis (FDP) with ceramic teeth
M mandibular 22, 21, 19, 27, 28, 30 -- 0 hybrid titanium with ceramic teeth hybrid titanium with ceramic teeth
M maxillary 3, 4, 5, 6, 11, 13, 14 -- 0 hybrid titanium with ceramic teeth hybrid titanium with ceramic teeth
M mandibular 22, 21, 18, 27, 29, 30 -- 0 partially monolithic zirconia hybrid zirconia with ceramic teeth
M maxillary 8, 9 5, 12 0 full monolithic zirconia hybrid zirconia with ceramic teeth
F maxillary 3, 6, 7, 9, 12, 14 -- 0 hybrid titanium with acrylic resin teeth natural teeth and removable dental prosthesis (RDP)
M mandibular 24, 22, 21, 25, 27, 28 -- 0 hybrid titanium with acrylic resin teeth denture
M maxillary 3, 6, 8, 9, 12, 14 -- 0 partially monolithic zirconia natural teeth
F mandibular 24, 22, 20, 25, 27, 30 -- 0 hybrid titanium with ceramic teeth hybrid zirconia with ceramic teeth
M maxillary 3, 5, 6, 11, 12, 14 -- 0 hybrid titanium with ceramic teeth FDP with resin teeth
M mandibular 23, 21, 20, 26, 28, 29 -- 0 hybrid titanium with composite teeth hybrid titanium with composite teeth
M maxillary 5, 6, 7, 10, 12, 14 -- 0 hybrid titanium with composite teeth hybrid titanium with composite teeth
M maxillary 3, 4, 6, 11, 13, 14 -- 0 partially monolithic zirconia natural teeth
M mandibular 23, 26 20, 29 0 hybrid titanium with ceramic teeth natural teeth and implants
M maxillary 5, 7, 10, 12 3, 14 0 hybrid titanium with composite teeth FDP with ceramic teeth
M mandibular 22, 19, 27, 28, 29, 30 -- 0 hybrid titanium with ceramic teeth FDP with ceramic teeth
M mandibular 24, 26 20, 29 0 hybrid titanium with acrylic resin teeth hybrid titanium with acrylic resin teeth
M maxillary 7, 10 4, 13 0 hybrid titanium with acrylic resin teeth hybrid titanium with acrylic resin teeth
F mandibular 23, 26 20, 29 0 partially monolithic zirconia hybrid titanium with composite teeth
F maxillary 7, 10 4, 13 0 hybrid titanium with composite teeth hybrid titanium with composite teeth
M maxillary 5, 7, 10, 12 3, 14 0 full monolithic zirconia natural teeth and implants
F mandibular 23, 26, 27 20, 29 0 hybrid titanium with acrylic resin teeth natural teeth
F maxillary 6, 8, 10, 11 3, 14 0 Hybrid titanium with acrylic resin teeth natural teeth
F maxillary 4, 8, 9, 13 -- 4 denture denture
F mandibular 24, 25 20, 29 0 hybrid titanium with acrylic resin teeth denture
M mandibular 23, 26 20, 29 0 hybrid titanium with acrylic resin teeth denture
F maxillary 8, 9 5, 12 0 full monolithic zirconia on titanium bars natural teeth
F maxillary 4, 6, 7, 10, 11, 13 -- 0 hybrid zirconia with ceramic teeth natural teeth
M mandibular 4, 5, 6, 10, 11 13 0 full monolithic zirconia zirconia crowns on natural teeth and implants
M mandibular 23, 21, 19, 26, 28, 30 -- 0 partially monolithic zirconia natural teeth and implants
F mandibular 22, 27 20, 29 0 hybrid titanium with composite teeth hybrid titanium with composite teeth
F maxillary 6, 11 4, 13 0 hybrid titanium with composite teeth hybrid titanium with composite teeth
M maxillary 7, 9 4, 13 0 partially monolithic zirconia natural teeth
F mandibular 23, 26 20, 29 0 hybrid titanium with composite teeth FDP with ceramic teeth
F maxillary 8, 9 4, 13 0 hybrid titanium with composite teeth denture
F mandibular 23, 26 20, 29 0 full monolithic zirconia on titanium bars FDP with ceramic teeth
F mandibular 22, 23, 26 20, 29 0 hybrid titanium with acrylic resin teeth denture
F maxillary 7, 10 4, 13 0 hybrid zirconia with ceramic teeth natural teeth and implants
M maxillary 4, 7, 10, 14 -- 0 hybrid titanium with composite teeth natural teeth and implants
M maxillary 4, 7, 10, 12, 14 -- 0 hybrid titanium with composite teeth natural teeth and RDP
F mandibular 29, 26, 23 20 0 monolithic zirconia natural teeth
F mandibular 29, 26, 23, 20   0 hybrid zirconia with ceramic teeth natural teeth
Total:   166 44 4    

Complications and Implant Loss

One fixed provisional restoration failed (3.33%) two months after the surgery due to the loss of the four implants supporting it. Breaking of esthetic veneering of the temporary prostheses occurred in two cases after two months of loading (5.5% of cases), while no fracture of a final prostheses or any screw loosening has been reported.

Four immediate loaded implants failed in one single patient before the six-month follow-up (Table 3). This patient was a heavy smoker (i.e., 30 cigarettes a day) and was wearing a reinforced prosthesis in acrylic resin with extremely compromised anatomic conditions. The implants were extracted and the patient was finalized with full removable dentures.

Survival Rates

The mid-study patient follow-up period ranged from 18 to 62 months with a mean observation time of 54 months. All patients and implants were seen for the one-year follow-up. At the 24-month follow-up, 29 arches and 171 implants (84%) were examined. Twenty-three arches and 139 implants (69%) were summoned for the third-year recall. At the fourth-, fifth-, and sixth-year recalls, 10 and eight arches, as well as 89 (46%) and 48 (26%) implants, respectively, were examined. After an observation time of up to six years, a 97.96% implant (n = 210) and 96.77% prosthetic (n = 42) cumulative survival rate was observed. Implant survival was 97.44% in the mandible and 98.93% in the maxilla. Four implants (two straight and two tilted) belonging to a single patient rehabilitation were lost, with an overall axial implant survival rate of 98.82% (n = 164) and an overall tilted implant survival rate of 94.85% (n = 44).

Bone Loss

After one-year follow-up, peri-implant bone loss was evaluated for all patients and all 42 restorations. In the mandible, this parameter averaged 1.3 1 0.11 mm for axial and 1.35 1 0.12 mm for tilted implants, while in the upper jaw, it was 1.37 1 0.14 mm for axial and 1.42 1 0.14 for tilted implants. The difference in peri-implant bone loss was not significant between both groups (p > .05). When bone loss around mandibular implants was compared with the corresponding maxillary implants, no significant differences were found for axial and tilted fixtures at each time frame even though slightly higher mean values were registered for the upper jaw. There were no significant differences between mesial and distal sides for axial and tilted implants in both arches, as well as no relationship regarding smoking habits or baseline periodontal condition with bone loss tendency.

Table 3. Cumulative Survival Rates for Axial and Tilted Implants

Patient Gender Age at Surgery (years) Time of Failure of Function (months) Implant Position Implant Diameter/Length (mm) Insertion Torque Bone Quality Smoking (number of cigarettes/day) Reason for Failure
F 74 2 7 3.6 x 10.5 35 D3 Y/30 mobility
F 74 2 10 3.6 x 10.5 35 D3 Y/30 mobility
F 74 2 4 3.6 x 10.5 35 D3 Y/30 mobility
F 74 2 13 3.6 x 10.5 35 D3 Y/30 mobility

Comparable Studies Investigating Different Implant Systems and Their Outcomes

This study’s primary aim was to evaluate the outcomes for immediate implant-supported fixed-dental rehabilitations for patients with terminal dentition or complete edentulism. A total of 42 arches were treated with screw-retained immediate and final restorations supported by only axial dental implants or with a combination of axial and tilted implants, achieving an overall implant survival rate of 97.96%. This result is in line with similar reports on immediate rehabilitations,23,35,36 as well as longterm clinical studies with a delayed loading protocol.37-39

To help determine the effectiveness of this study’s technique method as a viable treatment approach, the authors compared their study’s results with those of other clinical studies investigating different implant systems and loading protocols to achieve similar results in the maxilla and/or mandible. The measures of comparison were as follow:

Use of axial dental implants as sole support: Looking at restorations supported only by axial dental implants, Kinsel and Liss40 reported retrospective data for 43 patients and 344 immediately loaded single-stage implants (Straumann Dental Implant System, Straumann Group; Basel, Switzerland) (39 maxillary arches and 17 mandibles). Fifteen out of 261 implants placed in the maxilla failed for an implant survival rate of 94.3%, while only one of the 83 implants placed in the mandible failed, resulting in a 98.3% survival rate. A five-year retrospective study by Degidi and colleagues21 showed an overall implant survival rate of 98% with 388 maxillary implants placed in 43 patients, while Bergkvist and colleagues reported 97.5% cumulative survival rate at 32 months for 153 maxillary implants.22

Use of axial and tilted implants: Analyzing dental literature, survival rates for axial and tilted implant rehabilitations are comparable with the outcomes of the present investigation. Following a precise clinical protocol, Malo and colleagues reported a 98.5% implant survival rate for 867 mandibular dental implants followed up for 10 years,19 while Agliardi and colleagues showed 98.36% in the maxilla and 99.73% in the mandible up to 60 months of loading.41 Agliardi and colleagues reported 100% success rate with the use of two axial and four tilted dental implants for the treatment of 20 maxillary arches.42 In a systematic review, Del Fabbro and colleagues analyzed 470 immediate rehabilitations supported by a total of 1992 implants (1026 axial and 966 tilted) with no differences in terms of success between maxilla and mandible, and between axial and tilted implants in both arches.43

Implant primary stability: Implant primary stability is still considered a fundamental prerequisite for immediate loading application.44,45 In this study, more than one-third of the implants were positioned in fresh extraction sockets and none of them failed. A careful socket debridement46 and the underpreparation of the surgical site guaranteed a high level of primary stability for the implants.

Type and number of implants used: Clinical studies with different types of loading protocol evidenced excellent outcomes also with a reduced number of implants.38,47 In 1995, Branemark and colleagues reported no significant differences between six and four axial implants38 and recent works evidenced encouraging results with immediate function on six straight implants 22 or two axial and two tilted implants.41,42

The present authors used between four to six dental implants for fixed full-arch restorations based on the type of prosthetic solution, bone quality and quantity, and patient characteristics (i.e., face morphotype, dietary habits, masticatory muscles, biomechanics, and anatomic bone conditions). Following general guidelines, six implants were favored in case of second molar occlusion in upper arch, while four straight dental implants were used with occlusion limited to the first molars in the lower arch. In some cases, dental implants in post-extraction socket or with large peri-implant regeneration were preferred over short implants or fixtures in not-ideal position to guarantee benefit for the prosthetic design. Insufficient or limited bone conditions in posterior areas of the maxilla or mandibular sometimes resulted in the placement of four/six implants, of which the two terminal ones were generally tilted in a mesiodistal direction of up to 40°.

Tilting of implants brings surgical and prosthetic advantages and also allows the placement of longer implants compared with the straight insertion. Decreased long-term survival rate has been reported for implants shorter than 7 mm when compared with longer fixtures.2,3 Shorter implants were found to be associated with increased failure rate40,48-51 and, according to the publication of Kinsel and Liss,40 reduced implant length (less than 10 mm) was the sole significant predictor of failure during his immediate loading procedures. Also, Schnitman and colleagues52 attributed the failure of two of three immediately loaded implants to fixture length (7-mm implants), bone quality, and inability to get cortical engagement. In the posterior area of both arches, the authors gave preference to longer implants (more than 10 mm) positioned in native bone and getting multicortical anchorage instead of shorter implants or dental implants placed with simultaneous sinus membrane elevation. The determination of whether to use tilted implants up to 40° or axial dental implants was based on the amount of residual bone to implant spatial distribution and prosthetic cantilever.

Bone loss: Observed marginal peri-implant bone loss showed no difference between axial or tilted implants after the first year of loading, which is in line with other publications investigating different implant systems.41,53,54 Differences also were not related to jawbone, post-extraction sites, or native bone and implants treated with bone grafts. According to the authors, filling the gaps between implant surface and socket with a combination of autogenous bone and allograft contributed to the reduction of the buccal bone collapse and the consequent maintenance of hard and soft tissue architecture.55,56 Analyzing data, only a limited number of fixtures had their platform in extraction socket or in what remained of the socket after crestal bone regularization. As a consequence, the intermediate and apical part of the socket remained intact and they are usually characterized by moderate or null dimensional changes.57 Therefore, fixtures were placed close to the palatal or lingual side of the socket.

Provisional restoration procedures: Provisional restorations were either delivered the same day or within 24 hours of surgery, giving the dental technician time to create a metal framework to reinforce the prosthesis. Loading was distributed all along the occlusal surface, and canine or group guidances were created, with moderate inclination, avoiding nonworking interferences. This concept was applied for every patient, independently of his/her characteristics (i.e., dietary habits, muscle activity, face morphotype, or type of opposing dentition). Comparable clinical studies preferred limited occlusal contacts, mostly from canine to canine, with the absence of contacts at the posterior cantilever.41,42,58,59 Provisional restoration fractures were of minor concern compared with other investigations.22,58,59 One possible explanation for this might be related to the general presence of a metal framework that gives the provisional extreme strength. Furthermore, it is seen as a planning phase advantage30 that the occlusal concept could be thoroughly evaluated before the surgical implant procedure and transferred to the provisional restorations.

«A total of 42 arches were treated with screw-retained immediate and final restorations supported by only axial dental implants or with a combination of axial and tilted implants, achieving an overall implant survival rate of 97.96%.»

Summary

Immediate fixed full-arch rehabilitations using a combination of tilted and axial implants or with axial implants alone proved to be a reliable technique, with advantages for both patients and clinicians. The TeethXpress patient solution provided a predictable result from diagnosis to delivery of the final prostheses. Within the limitations of this study, the promising mid-study outcomes obtained seem to confirm this method as a viable treatment approach for the immediate rehabilitation of total arches.

Acknowledgement

The authors thank Laura Morselli, and Luca and Matteo Dondi for the laboratory work shown in this article.

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