Complications, Risk Factors, and Failures of Immediate Functional Loading of Implants Placed in the Completely Edentulous Maxillae

A Report of 3 Consecutive Cases

Abstract

Purpose: 

The aim of this article was to document the failure of immediate functional loading of implants placed in 3 consecutive completely edentulous maxillae to analyze the possible causes, risk factors, and how to avoid the complications that occur due to this procedure.

Materials and Methods: 

Six implants with standardized length and diameter were placed in 3 consecutive patients with completely edentulous maxillae in the canine, premolar, and molar region bilaterally and flaplessly using computer-guided surgical guides. Screw-retained conversion maxillary prostheses were delivered immediately after the surgery.

Results: 

Patients complained from severe to moderate pain. For the first and second patients (P1 and P2), 4 implants per patient were lost during the second week after implant surgery, whereas 5 implants were lost during the third week after implant surgery for the third patient (P3).

Conclusion: 

This high failure rate presented in this report may be explained by 1 or more of the following reasons: poor maxillary bone quality, nonaxial loading of the implants, nonrigid splinting material, high forces delivered from the opposing dentition, and/or patients with para-functional habits.

The ideal goal for modern dentistry is to restore the patient to the normal facial contour, function, esthetics, speech, health, and comfort.¹ Clinical studies on humans and animals have shown that immediately loaded implants develop bone at the implant surface and are able to tolerate occlusal forces.^1,2 The immediate functional loading of maxillary implants have been advocated by many authors and have proven high success rates in many studies as reported by Mozatti et al,³ Tealdo et al,⁴ Malchiodi et al,⁵ Collaert and De Bruyn,⁶ and Romanos et al.⁷

In a retrospective study performed by Strietzel et al,⁸ implant survival in cases treated with immediately loaded implants in the edentulous maxilla or mandible by fixed prostheses was found to be 99.6%. Whereas in another study performed by Testori et al,⁹ the success rate of immediate occlusal loading of tilted implants for the rehabilitation of the atrophic edentulous maxilla was as high as 98.8%.

Even though these high success results are reported, the devastating complications and failures still occur. Several common primary factors in maxillary implant failure scenarios were identified in a study performed by Parel and Phillips.¹⁰ A preliminary protocol was suggested for both treatment planning and profiling patients aimed at reducing immediate loading implant failures in the maxilla and enhance success.¹⁰

Computer-based guiding systems for dental implant placement provide safer, faster, and minimally invasive surgery by integrating the patient's anatomy for future rehabilitation and to construct a precise surgical template and prosthesis, which is connected at the time of implant placement as reported by Balshi et al¹¹ and Rocci et al.¹² Generally, the planning for implant placement is performed using a preoperative CT scan for the patient. These systems can be divided into static surgical guides and navigators as explained by Vercruyssen et al.¹³ Lee et al¹⁴ and Avrampou et al¹⁵ also agreed that stereolithiographic (STL) file data are able to accurately fabricate an STL model and surgical guide for implant surgery.

Materials and Methods

The 3 male patients (P1, P2, and P3) presented in this report were selected from the outpatient clinic of the Department of Prosthodontics and Implantology, Cairo University. The 3 patients aged 54, 66, and 61 years, respectively, presented with completely edentulous maxillae with adequate zone of keratinized attached mucosa over the crest of the upper ridge, showing normal maxillo-mandibular relationship (Class I Angle classification) and systemically free from any medical conditions. P1, P2, and P3 were completely edentulous during at least the past 2 years and most teeth were extracted due to unrestorable extensive carious lesions and inability to maintain good oral hygiene measures. P1 was the only smoker out of these 3 patients and who was asked to sign a consent form including smoking cessation throughout the whole period of treatment. Preliminary clinical and radiographic examinations revealed adequate bone quality and quantity in the maxillae. All the 3 patients had satisfactory screw-retained fixed mandibular prostheses supported by 4 successfully osseointegrated implants.

The presurgical preparation required the construction of conventional maxillary complete dentures (Fig. 1, A). The finished maxillary dentures were duplicated to obtain radio-opaque scan guides. Duplication was performed using a mixture of amalgam powder and transparent self-cured acrylic resin powder with a ratio of 1 g of amalgam powder to every 6 g of acrylic resin (Fig. 1, B). The patients' maxillae were radiographed using cone beam computed tomographic (CBCT) scanning machine (Sanora 3D; Soredex, Helsinki, Finland). During imaging, the patients were instructed to wear their scan guides and to stabilize it in place by biting on an occlusal index constructed for each patient, separating the mandibular teeth from the guide. DICOM files obtained from the CT scan were loaded into the Mimics software (Mimics; Materialise HQ, Leuven, Belgium) whereby coronal and sagittal reformatting and panoramic views were obtained (Fig. 2, A). The desired implant sites were identified through the radiolucent channels previously prepared in the radiographic guide at the prosthetic teeth centers. The bone volumes at each of the 6 potential sites were evaluated for sufficient bone height, width, and density (Fig. 2, B). For each patient, 6 implants were to be planned in the lateral incisor/canine region, the first premolar, and the first molar region according to the available bone height and width. All implants were with standardized diameter (3.7 mm) and height (13 mm) for the 4 anterior implants and 10 mm for the 2 posterior implants. The implants used in this study are coated with soluble blast media surface texture and hydroxyl-apatite plasma spray coating. The implants have a 1-mm smooth collar, followed by 1.2 mm height of mini-threads on its coronal aspect (Quadrapule 0.2 mm apart lead threads), and finally a threaded fixture body (double 0.4 mm apart lead threads). The virtual STL files of the implants were imported into the MIMICS software and then virtual planning was performed at the proposed implant sites (Fig. 2, C).

Fig. 1: A, Finished and polished maxillary denture. B, The scan appliances with cutting holes in the proposed implant sites.

Fig. 2: A, The software interface showing the axial, coronal, sagittal, and 3D views. B, Bone height, width, and density measurements at the proposed implant sites. C, Virtual implant planning performed at the proposed implant sites. D, 3D reconstruction of the final edited mask being performed. E, “Split” and “Boolean operation” being done. F, The final virtual guide of the 3 cases.

The base of the radiographic guide was separated from the bone and teeth using the segmentation process. The created mask of the base was grown to a 3D object (Fig. 2, D) and then united with the supra bony portion of the implant model using the “Boolean operation” tool (Fig. 2, E). The resultant object is the 3D virtual guide that was exported as an STL file for 3D printing machine (Invision Si2) to build the guide from a photo-curable resin material (Fig. 2, E). Metallic sleeves were fitted into the designed holes of the fabricated guide.

Implant Installation

Before starting the surgical procedure, the peri-oral region of the patient was wiped by betadine antiseptic solution, the surgical instruments were autoclaved, and the computer-guided surgery guide was disinfected with a suitable disinfectant (Cidex Activated Dialdehyde Solution; J. and J. Medical). At the time of surgery, infiltration anesthesia was injected at each implant site. The guide was fixed in place using 3 fixation screws (Fig. 3, A). Osteotomies were then prepared using the classical drilling sequence (pilot, intermediate, and final drills) and were irrigated with sterile saline after each drill (Fig. 3, B). For every drill, a specially designed “drill guide” was used. The outer diameter of the drill guide fitted accurately within the metal sleeves fixed into the guide, whereas the inner diameter of the drill guide was 2.5, 3, and 3.5 for the 2.3, 2.8, and 3.4 drills, respectively. This difference in diameter should allow for penetration of the saline irrigant with the pumping motion of the drill. The implants were then unpacked and inserted manually through the guide till manual tightening met resistance, and further tightening was completed with a ratchet using a depth controlling implant driver. The primary stability of each implant was checked to be 30 N·cm using a Torque wrench and then the guide was retrieved (Fig. 3, C).

Fig. 3: A, The fabricated surgical guide with the metal sleeves was checked for proper extension and stability and fixed in place using 3 fixation screws. B, Osteotomy performed using the classical drilling sequence. C, Implants after being surgically installed and guide retrieval. D, Temporary titanium abutments screwed over each Implant. E, A pick-up impression was then done using the patient's complete denture after holes were done opposing to each implant site. F, Flanges of the complete denture were removed, and the conversion prosthesis was then finished and polished.

Temporary titanium abutments were screwed over each implant (Fig. 3, D), and holes were done at each corresponding implant sites in the maxillary denture. A mix of chair side hard lining resin (Bosworth Co.) was applied into the holes while the denture was seated in place to connect the abutments to the prosthesis (Fig. 3, E). The abutments were unscrewed to remove the prosthesis with the picked up temporary abutments to which implant analogs were attached. The prosthesis was modified by cutting off the buccal, labial, and palatal flanges as well as the denture base distal to the first molar and then finished and polished (Fig. 3, F). The screw-retained provisional restorations were delivered 24 hours after implant surgery and torqued to 30 N·cm (Fig. 4). The occlusion was checked in both centric and eccentric positions following the mutually protected occlusal scheme. The patients were instructed to follow strict oral hygiene measures, a soft diet protocol for the first 8 weeks, and to cessate smoking during the whole treatment and follow-up period. Postoperative CT scans were also performed to ensure proper placement of the implants in their preplanned sites (Fig. 5). The patients were recalled 24 hours after prosthesis delivery and on a weekly basis for a periodic check-up. The patients were also instructed to immediately report the outbreak of any complication.

Fig. 4: The screw-retained provisional restorations were delivered 24 hours after implant surgery for the 3 cases (P1, P2, and P3).

Fig. 5: CT scans were performed to ensure proper placement of the implants in the preplanned sites.

Results

During the second week after implant surgery, patients (P1, P2, and P3) complained from severe to moderate pain on function. On clinical examination, peri-implantitis and slight swelling were noticed under the prosthesis. The prostheses for all 3 cases were found to be slightly clinically mobile, and the prostheses were retrieved with some of the implants attached to the titanium abutments in the provisional restoration (Fig. 6). Pain on palpation and percussion as well as clinical implant mobility were noted on some of the remaining implants when intraoral examination was performed. There was no sign of active infection, exudate, or facial swelling for all the 3 cases, indicating that the prime causative factor for failure is “stress-induced bone loss”¹⁶ (bone loss from traumatic occlusion, off axis loading, overloading, and so on).

Fig. 6: The failed Implants and provisional restorations 2 to 3 weeks after surgery.

For P1 and P2, a total of 4 implants were lost per patient during the second week of implant surgery while 5 implants were lost during the third week after implant surgery for P3. P3 also presented with a midline fracture in his provisional restoration.

Discussion

The immediate functional loading of maxillary implants have been advocated by many authors and have proven high success rates in many studies as reported by Mozatti et al,³ Tealdo et al,⁴ Malchiodi et al,⁵ and Romanos et al.⁷ Nevertheless, complications and failures still occur even in these studies reporting high success rates. The main purpose of this article was to pinpoint, highlight, and focus on the possible causes of immediately loaded maxillary implant failures and to present the possible risk factors that can help clinicians avoid future failures and complications.

In this study, special attention has been given to proper patient selection with sufficient bone height and width to accommodate implants with adequate height and diameter (3.7 mm diameter and 13 mm for the 4 anterior implants and 10 mm for the 2 posterior implants), adequate number of implants (6 implants), proper implant location (lateral incisor/canine region, the first premolar and the first molar region), favorable dental arch form, satisfactory implant distribution and anteroposterior (AP) spread, the elimination of horizontal or vertical offset loads or cantilevers, and finally, the utilization of a suitable occlusal scheme concept (mutually protected occlusion).

Even though all these factors were optimally fulfilled, a disturbing high failure rate of 72.2% and devastating clinical complications occurred. The following is a thorough analysis and possible explanations to this alarming high failure rate of the 3 cases presented in this study:

1. Poor maxillary bone quality is one of the major reasons of failure in the 3 cases presented in this study. Most of the CT numbers at the failure sites for P1, P2, and P3 ranged from 150 to 350, that is, D4 bone according to the CBCT software. Worth to mention, the values obtained from CBCT images are not absolute values, unlike the Hounsfield units obtained by medical multi-slice CT (MSCT)¹⁷ and that CBCT does not give exact and reliable information about bone quality¹⁸ hence giving a false idea of the bone density at the proposed implant sites. Whenever feasible, MSCT should be performed to accurately evaluate the bone quality at the proposed implant sites if immediate loading is to be performed especially in the compromised maxillae. It must also be strictly stressed that immediate loading should be avoided in D4 and D5 bone, that is, bone less than 350 HU.
2. In nonaxial loading of the implants, implants were preoperatively planned in the canine region with AP inclination >20 degrees to the occlusal plane in P3 due to the nature of maxillary arch anatomy. In such cases, immediate loading should be considered highly risky due to the nonaxially transmitted forces to the bone-implant interface, thus jeopardizing with the implants' prognosis. Bone augmentation procedures to improve the implant inclination could have been done as agreed upon by Misch¹⁹ to overcome this problem.
3. In nonrigid splinting, acrylic resin of the conversion prostheses was used to splint the immediately loaded implants in P1, P2, and P3. Acrylic resin flexes with biting force and thus transmits unfavorable shear forces to the bone-implant interface. This flexing occurs due to the inevitably excessively thinned acrylic resin (inadequate bulk) at certain areas of the provisional restoration, the poor mechanical properties of acrylic resin, and the poor bond between the acrylic resin and temporary titanium abutments. To overcome this problem, constructing implant-supported superstructures with a rigid material, such as metal alloys, zirconia, or dental composites with high mechanical properties, is a primary prerequisite if immediate loading is to be performed in the edentulous maxilla as also agreed upon by Nikellis et al²⁰ and van Steenberghe et al.²¹
4. High forces were delivered from the opposing implant supported screw–retained mandibular prostheses in P1, P2, and P3. These forces are 4 times greater than natural teeth due to the loss of periodontal proprioception.²² An acrylic resin stabilization splint should have been constructed to overcome this problem as it contributes to optimally distribute and vertically redirect forces generated by opposing dentition as reported by Perel.²³ Otherwise, conventional loading protocol should have been followed to avoid the risk of overload.
5. P1 and P3 had para-functional habits that passed unnoticed during the initial step of diagnosis. Moreover, P3 in this study presented with a midline fracture in his maxillary screw-retained provisional restoration denoting excessive biting forces and/or para-functional habits. Therefore, thorough clinical and functional examination of the TMJ and muscles of mastication should have been performed before implant surgery, especially with male patients due to their stronger muscle nature. In a study performed by Parel and Phillips,¹⁰ the authors reported that men experienced primary implant failure 3 times more than women possibly due to the generally stronger occlusal forces generated by the male musculature. They also stated that depending on data obtained from patient's interview is not reliable as most patients deny having a para-functional habit because they are unaware of it.
6. The surgical protocol advocated in this study using computer-guided surgical guides might have partially contributed to the failure of implants in this study. The slight difference in diameter between the drill guide and the metal sleeves should have allowed for penetration of the irrigation saline solution to the osteotomies with the pumping motion of the drill. However, the use of external irrigation in these cases might have not allowed the saline irrigant to adequately reach the bone interface, possibly leading to heat generation during drilling. This thermal surgical trauma might have caused bone damage and/or microfracture of bone during implant placement leading to osteonecrosis and possible fibrous and granulation tissue encapsulation around the implants. The use of internal irrigation might have allowed for better saline penetration to the osteotomies hence avoiding any possibility for overheating of the surgical bed. Table 1 summarizes the reasons of failure for each of the 3 cases (P1, P2, and P3) presented in this report.

Table 1: Summary of the Risk Factors and Causes of Failure for P1, P2, and P3

Summary

Primary Risk Factors

If 1 or more of the following factors are present, immediate functional loading of the maxillary implants should be strictly contraindicated:

1. Opposing dentition: patients with a complete set of natural dentition or restored with a long-term fixed implant supported full arch prosthesis.
2. Poor bone density: proper preoperative evaluation of the bone quality using MSCT at the proposed implant should be performed if immediate loading is to be planned. Immediate loading should not be performed in bone quality less than 350 HU, that is, D4 or D5 bone.
3. Nonaxial loading of implants: angulation of occlusal load (between the occlusal plane and implant body) >20 degrees should not be performed in immediately loaded implants to avoid nonaxial forces to be transmitted to the bone-implant interface.
4. Nonrigid splinting material: rigid splinting of the implants with a material having strong mechanical properties is a very important factor for the success of immediate loading.
5. Para-functional habits: it is strictly contraindicated to perform immediate loading of implants in patients with bruxing and/or para-functional habits.
6. Possible thermal surgical injury to the osteotomy site preparations associated with the use of computer-guided surgical guides.

Secondary Risk Factors

If 2 or more of the following factors are present, immediate functional loading of the maxillary implants should be strictly contraindicated:

1. Systemic and local infections/pathology: presence of any systemic or local infections is a strong limiting factor if immediate loading is to be planned also as recommended by Parel and Phillips.¹⁰
2. Cantilevers: it should be strictly eliminated to avoid force transmission beyond the physiological threshold that bone can withstand in immediately loaded implants. Studies by Rubo and Souza²⁴ and Suedam et al²⁵ reported that in cantilevered prostheses, the most distal implants represent the fulcrum, thus creating a class I lever, therefore, are subjected to compression forces, while intermediary abutments suffer tension.
3. Inappropriate implant distribution with limited AP spread: limited bone availability or unfavorable arch form can lead to inadequate implant distribution that in turn leads to unfavorable force distribution and overloading to the bone-implant interface of immediately loaded implants.
4. 4.Compromised implant number: if 6 or less implants are to be placed and immediately loaded in the maxilla, all other primary and secondary risk factors should be optimum to ensure predictable success.
5. Inadequate implant length and diameter: if the implant length or diameter were compromised due to inadequate bone availability, a modification in the implant number, design, and/or arrangement can be done if immediate loading should be performed. Misch¹ reported that the most effective method to increase the surface area of implant support is by increasing the number of implants used to support prosthesis.
6. Uncooperative patients: patient cooperation is an important factor when selecting candidates for immediate loading as their compliance with instructions, such as smoking cessation, oral hygiene measures, and soft diet, can have a potentially significant role in the occurrence of early failures.

Conclusion

The immediate functional loading in the maxillae still requires further research and clinical studies to propose comprehensive guidelines for success to accurately evaluate all the possible causes of failure and risk factors and how to overcome them.

Disclosure

The authors claim to have no financial interest, either directly or indirectly, in the products or information listed in the article.