This article provides clinicians with 3 main factors that relate to long-term success. Long term in this article represents the lifespan of the patient, often requiring more than 40 years of function on the implant restoration. Literature is reviewed and used to provide evidence for these recommendations. Cases are presented to demonstrate these critical factors.
Key points
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Takeaway: Long-term follow-up of implants must consider decades of functional stability. Patients should be able to maintain hygiene as they age, grafts placed must maintain their form and volume over time, and clinicians should realize that thin bone over an implant most likely will resorb resulting in long-term adverse situations.
Introduction
Patients receive implants for many reasons including but not limited to replacement of missing teeth secondary to agenesis, when traumatized teeth become nonrestorable secondary to resorption or fracture, or when their past dental treatments fail resulting in loss of teeth. The resultant implant placement and restorative care should consider a long-term solution, which may extend to the lifetime of the patient. For example, a 25-year-old patient has implants to replace lateral incisors. Thirty years later she is 55 years old, with a projected lifespan into her 90s. For patients in their 40s requiring replacement of failed anterior teeth secondary to blunt trauma when they were teenagers, their expected lifespan will require more than 40 years of function on their implants. For patients in their 60s a full-arch restoration needs to be successful while they age and may lose their ability to be maintained by the dentist because of difficulty with transportation, mobility, and general health concerns. Long-term is over the lifespan of the patient; it is patient derived and exists while the patient ages. Depending on the age of the patient, considering the patient’s lifespan, some implants may require more than 70 years of function and stability.
This author, after evaluating failed implants, with observation of multiple patients with more than 25 years of follow-up to 40 years, recommends 3 main factors for “long-term” success. There are certainly other factors to be considered.
Factors Associated with Long-Term Success
- 1.
The final restoration must be hygienic. The final restoration should be engineered to withstand the forces of chewing and mastication. Clinicians should fabricate and design the restorations to be self-hygienic. Patients need to be able to clean their teeth effectively at home especially as they age.
- 2.
Grafts need to last over time. The implants should be placed into grafts that have low resorption profiles.
- 3.
Thin bone resorbs. Clinicians should place implants into ridges with at least 2 mm of bone on the facial aspect or augment the site to achieve this width to protect the implant. The implants should be placed with the final restoration planned so they can be navigated to an intended optimal position, , resulting in 2 mm of bone labial to the implants. Thick gingiva aids in long-term preservation of the underlying bone.
Surgeons need to follow their cases to confirm that everything is going according to plan, including maintenance.
Make the restorations self-hygienic: patients need to clean at home as they age
Over time patient records in the form of paper, outdated computer files, or legibility can be lost or hard to find. The treating doctor may retire or stop working due to personal reasons, with their records taken on by a new doctor. The new doctor may or may not store these older records in a location easy to access. Thus, follow-up of patients receiving implants can become less predictive over time for very practical reasons.
As the patient ages maintenance visits with a hygienist may decrease, due to lack of scheduling by a new doctor, records lost, or simply that as the patient ages they find it hard to mobilize with transportation to a doctor’s office. Patients may not be available for office recall due to physical mobility issues, medical problems, or finances. The prostheses placed need to be easy to clean by the patient because routine maintenance decreases over time.
Long-term reports over 10 years are scarce. Technical complications resulting in the need for prosthesis repair were seen in 100% of full-arch prostheses after 10 years of function. Most prosthetic complications are reversible and do not affect the overall implant/prosthesis survival rate.
Biological complications
Biological complications illustrate the need for effective hygiene to decrease the incidence of peri-implant disease including bone loss. The total incidence of biological complications increases as time elapses, ranging from 9% early, to 50% at 5 years, and 90% at 10 years. , , , The incidence of biological complications was found to increase with age and smoking. ,
Peri-implantitis and bone loss
Marginal bone loss on full-arch maxillary restorations after 5 years was seen in 50% of implants. , , When the prostheses had a minimal flange, peri-implantitis was found in 12%. Peri-implantitis was greater in patients whose restoration had a flange preventing easy hygiene access with 57% of implants with peri-implant mucositis. When the prostheses are removed every year for cleaning, hygiene issues were less because of the high level of dentist maintenance but still present.
When there was limited access for hygiene marginal bone loss ranged from 1.4 to 2.8 mm after 5 years. , , At 10 years the average marginal bone loss was 1.8. When the prostheses had less flange and had access for the patients to clean their implants, the 6-year bone loss was 1.39 mm.
When reviewing clinical follow-up reports it is clear that the traditional hybrid style design with limited access to the implants was associated with a higher incidence of peri-implant disease. Patients older than 60 years had a 3.24 times greater risk of developing peri-implant disease compared with younger patients. Age and difficulty accessing the implants due to prosthesis design were a long-term problem.
In a 12- to 15-year follow-up report, different surfaced implants resulted in bone loss ranging from 16% to 29% in patients with at least one implant with greater than 2-mm bone loss after the first year in function. In the review by Jemt and Johansson using the traditional Branemark design with the intaglio surface clearly off the ridge for easy hygiene access, only 1.3% of implants showed greater than 3.0-mm accumulated bone loss after 15 years. Jemt and Johansson commented that when there was greater than 2 mm marginal bone loss in more than 16% of implants, they anticipated further bone loss over time.
Hygiene/maintenance
Hygiene maintenance has been reported to be a major problem over time with full-arch prostheses with limited access to the implants with more than 30% of patients with peri-implant mucositis and 10.4% with peri-implantitis. , When the recall program was effective the soft tissue indices indicated improved soft tissue health around the implants. , ,
Soft tissue recession was found in 20.8% of implants with the hybrid prosthesis design with a flange. Difficulty with hygiene maintenance was reported by 64.5% of patients with maxillary full-arch hybrid-style prostheses. Plaque coverage on the intaglio surface exceeded 50% with biofilm present in more than 60% of the prostheses surfaces. , , , , , ,
Prostheses that were retained by using telescope copings had low complication rates after 15 years of function; this was presumed to be secondary to ease of maintenance and hygiene access to the implants. Maintenance visits were limited to minor interventions. Overdentures or fixed/removable prostheses that can be removed to allow for implant cleaning result in less peri-implant disease.
The patient who is treatment planned for an implant-supported full-arch restoration will need determination of the location of the planned final teeth positions. Implant positioning can be determined resulting in a restoration that can be maintained because the implants are accessible for daily hygiene by the patient ( Table 1 ).
| Biological Complications | Range |
|---|---|
| Total incidence | 6% to 9% early At 5 y 49.6% 90% at 10 y |
| Bone loss | After 3 y 0.38 mm; after 6 y 1.39 mm; 5–10 y 1.18–2.8 mm |
| Hygiene/maintenance | Hygiene related and included 38.2% of patients Difficulty with hygiene maintenance 64.5% of patients |
| Peri-implant mucositis | 11.8% to 57% of patients |
| Plaque on intaglio surface | The percentage of plaque coverage was more than 50% |
| Biofilm | 62% of the intaglio prosthesis surface covered by biofilm |
| Soft tissue recession | 11% to 45.5% of implants |
The surgeon and restorative dentist have to decide on the form of the final prosthesis.
- 1.
The restoration can be a set of teeth with no pink flange material. This restoration is used when the patient is missing teeth and has a small amount of alveolar bone loss ( Figs. 1 and 2 ).
Fig. 1 ( A ) Frontal view of the dentition on a 60-year-old man presenting with desire for a full fixed maxillary prosthesis with natural-appearing teeth. ( B ) Computerized planning showing planned placement of implants for a full-arch prosthesis with implants placed under the crowns allowing for a natural emergence profile with no plans for a flange. ( C ) Posterior implants were placed using the anterior teeth to stabilize guide stent. The anterior teeth were removed and the implants in the lateral incisor locations were placed. ( D ) A frontal view of the immediate provisional prosthesis that was screw retained, 4 weeks after implant placement. ( E ) Frontal view of the restoration 14 years after implant restoration showing no peri-implant mucositis and no evidence of hard tissue loss. The patient can clean using floss and a toothbrush.( Prosthetics by LSU Department of Prosthodontics under supervision of Dr Marco Brindis.)
Fig. 2 ( A ) A frontal view showing a 48-year-old man with multiple missing maxillary teeth, desiring a fixed maxillary reconstruction. His ridge palpates with thick bone across the arch. ( B ) A denture was duplicated to provide the locations for implants. The duplicated denture had guide holes made to allow for placement of the implants under the crowns of the teeth. Implants were placed in the premolar sites, the canine sites, and the central incisor sites. No flange was used for this patient. The planned prosthesis was a porcelain fused to metal restoration simulating the appearance of natural teeth. ( C ) After implant placement small bone irregularities were grafted using high-temperature-processed xenograft. ( D ) The implants were exposed and implant-level impressions made. Custom anatomic abutments were cast simulating teeth preparations. A provisional was used to develop the soft tissue contours. ( E ) Final procelain-fused-to -metal prostheses in place. Normal tooth contours were used to allow for proper contour development. ( F ) Frontal view of the restoration, with 26 years’ follow-up, showing excellent gingival health with no mucositis and no evidence of bone loss. One posterior crown had a small porcelain fracture that was repaired.( Prosthetics by Dr Steven Locascio.) - 2.
The restoration can be a set of teeth with minimal pink material with the implants clearly accessible for probing and hygiene.
- 3.
The restoration requires a flange for paranasal support resulting in the need for a removable prosthesis to allow for implant maintenance ( Fig. 3 ).
Fig. 3 Thirty-six-year follow-up of an 89-year-old man with a bar clip, removable prosthesis. He can remove the teeth and easily clean the bar. The implants have retained their bone volume over the 36 years of follow-up.( Prosthetics by Dr Israel Finger.)
What are the solutions?
For some reason, clinicians do not treatment plan full-arch implant-borne prostheses the same way they treatment plan a single implant-supported tooth. When a single implant is planned the clinician preserves the bone, re-creates the bone, and re-creates the alveolar height and width for optimal implant positioning and a natural emergence of the crown. This approach allows for proper embrasures to be developed and follows all the principles that dentists learn to allow for functional restorations that can be maintained by the patient throughout their life. Effective maintenance will decrease plaque, which will reduce peri-implant inflammation, which should result in improved long-term prognosis.
A full-arch restoration can be planned to allow for implant placement under the crowns similar to single teeth. The bone can be preserved and not removed. The restoration can be designed for normal use of floss and tooth brushing, with normal oral prophylaxis procedures by hygienists. Full-arch rehabilitation on teeth follows the same treatment planning procedures that are used for single tooth implant restorations.
If we assume that plaque and lack of maintenance play a significant role in the development of marginal bone loss from peri-implantitis, then the ideal restoration must be designed to allow the patient to clean their implants easily. If the smile line is high then implants can be placed with the restoration replacing teeth without the need for replacement of gingiva. If paranasal support is necessary then a fixed-removable prosthesis can be made to allow the patient to remove it for implant maintenance. For long-term success plaque management must be considered.
How is a full-arch prosthesis designed to result in creation of natural-appearing teeth emerging from the gingiva, with minimal need for pink prosthetic material? The restorative dentist fabricates a new denture or a virtual setup that positions normal-shaped teeth in their correct position. From this a navigation method is chosen, and the virtual plan is merged with the cone beam scan, allowing for implant positioning on the computer. Either dynamic navigation or a static guide is used to guide implant placement. The virtual setup can be used to mill a provisional, which can be converted at surgery or within a few days if scanning the implants is used after their placement. It is time that we eliminate the procedures and prosthetics that prevent long-term maintenance on prostheses.
Grafts should last over time
Patients often present with insufficient horizontal and vertical bone to support dental implant placement in an ideal position. The goals of horizontal ridge reconstruction are to augment the thin ridge with a material that will be present for a long time. Long time is the lifespan of the patient ( Figs. 4–7 ).
To reconstruct bone deficiency, augmentation methods have historically included movement of the bone by ridge splitting or interpositional osteotomies, or by onlaying grafting materials. The material for the onlay should be easy to handle, work at least 95% of the time, and cause minimal morbidity. Materials to consider include synthetic hydroxylapatite (HA), high-temperature (HT)-processed xenograft, low-temperature-processed xenograft, allograft, or autogenous bone.
Bovine xenografts are either dried at room temperature or processed to remove organic materials at HTs ranging from 600°C to 1200°C. Removal of the animal’s organic species-specific material is accomplished by either solvent extraction or heat treatment, with copious washing resulting in a clean anorganic material. To decrease resorption by increasing crystallinity approaching synthetic sintered HA, HT xenografts are processed at HTs.
HT processing of the bone harvested from the bovine femoral cancellous bone results in a macroporous particle with high crystallinity, a decrease of surface porosity, and an anorganic ceramic-type graft that has minimal resorption after being placed onto bone. Grafts that are not heat processed have resorption profiles that vary. ,
Why use HT processed xenograft as a graft material? What prior history is available to support its use to augment a ridge and then support implants during function over time?
In the 1970s and the early 1980s edentulous patients often needed restoration of ridge form to support and stabilize dentures. Because of the morbidity associated with bone grafting and osteotomies of the jaws used to increase the volume of the ridge, a synthetic material, HA, was developed in particulate form to be used within a tunnel on an edentulous ridge. This history can provide us with information that is relevant to augmentation of the ridge for implant placement.
Frame and colleagues showed in a dog study that bone ingrowth into the augmented ridge was greater with cancellous particles. Bone can form within the nonresorbable ceramic augmentation. Animal studies indicated fibrous tissue was predominant peripherally within the augmentation when HA was used alone as the augmentation material. Bone formation within the augmentation occurred early when autogenous bone was combined with the HA particles. This dog ridge augmentation study demonstrated that the use of autogenous bone combined with HA particles resulted in bone formation through the HA augmentation, compared with the use of HA particles alone. When HA particles were used alone for ridge augmentation, bone did form 2 to 3 mm into the HA augmentation, at the interface of the HA, and underlying cortical bone.
Chao and Poon reported histologic evaluation on 2 specimens taken from patients who had HA augmentation. Both specimens, one 5 months and the second 1 year postgrafting, showed bone formation into the augmentation. Page and Laskin confirmed this observation. A human biopsy of a mandibular augmentation using HA and autogenous bone showed bone within the augmentation and a stable interface of the native bone to the augmentation. A 9-year post-HA augmentation sample showed no observable resorption of the augmentation, and bone formation had occurred within the augmentation.
HA ridge augmentations were stable over time but unfortunately did not necessarily result in improved denture retention and stability. When dental implants were introduced, the use of implants in the edentulous ridges provided patients with excellent denture stability. Patients who had had previous ridge augmentation with HA had implants placed successfully either within the augmentation or after the augmentation had been removed. After 35 years patients can be seen to have successful implant overdenture function, with the posterior HA augmentation still present (see Fig. 4 ). These patients provide evidence that there is a potential long-term augmentation method that can provide ridge bulk for implant support over time.
The crystallinity of HT-processed xenograft is very close to the crystallinity of synthetic HA. Bone formation within the adjacent bone graft interface is necessary to support implant placement and to stabilize the graft. , ,
The clinical need is for an augmentation to maintain its dimension over time with bone within the graft to support implant integration. Pelegrine and colleagues’ retrospective study evaluated the response of a ridge augmentation procedure taking into consideration the amount of cancellous bone in the recipient site. In the presence of a site with cortical bone without cancellous bone, allografts and xenografts did poorly. When the patient had cancellous bone in the recipient site the grafts did well. This finding implies blood supply and cell availability must be considered when planning for ridge augmentation.
Autogenous bone covered with low-temperature-processed xenograft covered by a collagen membrane was reported in a clinical series, , involving patients with ridge width between 4 and 6 mm. Implants were placed at the time of the augmentation. Collagen membrane exposure occurred in 13% and was associated with smokers. Implants were deemed successful based on periodontal parameters and marginal bone loss. The average width gain was 5.03 mm with bone loss of 1.03 mm (20%) after 1 year. Longer follow-up was not reported.
The placement approach for augmentation of the ridge will be either open with a flap or the use of a tunnel approach. The stuby by Mercier and colleagues, using a tunnel approach for HA particulate ridge augmentation, reports vertical stability of HA-augmented edentulous ridges. Patients were followed an average of 5.3 years; 73% had no appreciable decrease in ridge augmentation. If there was incisional or other related early problems ridge augmentation was compromised.
Xuan and colleagues’ dog study evaluated bone formation through xenograft blocks of bone comparing an open with a tunnel approach. Their hypothesis was that new bone formation would be greater with the tunneling procedure than with the flap procedure, because the former is minimally invasive and provides more blood supply to the graft because the overlying mucosa was not incised. The mean percentage of newly formed bone within the block was 15.3% ± 6.6% in the flap group and 46.6% ± 23.4% in the tunneling group. In a technique article, tunneling was used to augment narrow ridges using xenograft combined with platelet-derived growth factor. The author claims 5 mm of ridge augmentation. The article did not differentiate between different sites, and the measurement methods were not clearly described. Block and colleagues have reported the use of tunneling for ridge augmentation with consistent results.
Stability of the graft particles during the initial revascularization phase and fibrous tissue ingrowth may be important to maintain graft bulk and form during the early healing phase. Hellem and colleagues used Tisseel, a version of a fibrin glue product, to maintain the fibrin clot’s integrity by preventing lysis of the coagulum due to a protease inhibitor, during the first 3 to 4 weeks of graft healing. Narrow ridges were augmented with autogenous bone combined with low-temperature-dried xenograft with Tisseel to maintain augmentation form. After the graft had healed, implants were placed with a high success rate, with maintenance of the graft. The investigators did not evaluate graft thickness over time.
What were the results?
When a xenograft is heated the crystallinity of the calcium phosphate matrix of bone increases; this results in a significantly lower resorption rate of the material. Microporosity or surface grain morphology is decreased but not eliminated when the xenograft is heated. The ramifications of the change in surface porosity are not clear. The macroporosity of heat-treated cancellous xenograft does not change when heat processed. ,
What is the evidence for bone formation within HT-processed cancellous xenograft particles? The particulate form of the material should be cancellous to promote bone formation within the augmentation and within the particles. Hing and colleagues have published a series of studies indicating that in animals, porous HT-processed xenografts had bone ingrowth into HT-processed porous xenograft-implanted graft from 10 days to 5 weeks. Hing and colleagues further characterized HT-processed porous xenograft (Endobon, Biomet Fr, France). The heat treatment did not convert the bone to pure HA. There were retained carbonate, magnesium, and sodium ions. The microstructure had variations in density and had retained traces of the intraosseous network of osteocyte lacunae. The pore structure was complex. The investigators further determined that the rate of bone ingrowth into the porous particles was related to pore connectivity. The bone ingrowth strengthened the resultant composite graft because of the volume of bone ingrowth. Further studies confirmed that the interconnectivity between porous particles was critical for bone ingrowth in the early periods but less important over time.
Microporosity or surface roughness has been shown to have a positive effect on cell attachment to the graft particles. Cells have an affinity to micropores through filopodia extensions during the early period of cellular attachment. With 14 to 30 days seeded cells covered macropores of the graft material. The microporosity of the graft materials was found to play a role in the early attachment but did not affect long-term attachment.
Heat treatment of bovine xenografts will affect osteoconductivity; this may be related to the surface morphology. When heated to 820°C, the surface composition of the particles was smoother than unheated materials. The higher temperature (1200°C)-treated graft particles had smoother surface morphology and less osteoconductivity than the nonheated or 820°C bone. Bone did form on all materials at different amounts depending on temperature treatment.
Based on this discussion and literature review, it can be concluded that HT-processed xenografts have a high crystallinity approaching sintered synthetic HA. This high crystallinity results in minimal resorption over time. The porous macrostructure will have a positive effect on bone ingrowth into the particles. Even though the HT processing decreases microsurface porosity, the residual surface morphology can still have a positive osteoconductivity characteristic.
When placed in a host site with good vascularity and perhaps through a tunnel preserving soft tissue blood supply, there is a high potential for graft healing with bone within a portion of the graft adjacent to the native bone.
Surgical technique
When an open method is chosen a crestal incision is made with vertical release incisions posteriorly. A full-thickness flap is elevated. The HT-treated xenograft is placed over the narrow ridge and is covered with a resorbable membrane.
A tunnel approach can be used to place the graft. After the subperiosteal tunnel is developed the particulate graft is placed. Since 2020 serum from L-PRF (platelet-rich fibrin) has been used to hydrate the grafts to provide antibiotics and growth factors because the serum was patient derived. No membranes are used, and no bone perforations are made. The grafts are compacted firmly with no other materials used.
A period of nine months is preferred before implant placement, which is performed with either static or dynamic guidance with minimal or no elevation of the buccal or facial gingiva. Four to 6 months are allowed for implant integration. The restorations are then fabricated. Patients return for their routine yearly visit. Typically cone beam scans are taken after 1 year and up to 40 years, with no radiographs taken unless indicated between biyearly examinations.
With 2- to 40-year follow-up, the immediate postgraft augmentation gain was measured to be 5.85 ± 2.45 mm. The longest time follow-up width of the augmentation was 5.13 ± 2.37 mm; this represents 84% augmentation stability or a 16% loss in ridge width over time.
Thin bone resorbs over time
Facial bone thickness: Hard and soft tissue deficiencies around implants can have multiple sources that can result in progressive tissue loss. These sources can include systemic patient factors, iatrogenic factors involving placement and grafting issues, trauma, local disease states including periodontal disease and caries, and hygiene issues.
The facial bone thickness may be an important prognosticator for future bone thickness around an implant. When the facial bone thickness is 1 mm or less, progressive bone resorption can occur with accompanying vertical bone changes. In contrast, sites with thicker bone have less progressive bone thickness loss. When placing an implant into a fresh extraction site the implant placement should result with 2 mm of facial wall thickness, and if necessary a gap of this dimension should be grafted to maintain the thick wall morphology. ,
A systematic review showed that during healing, when the facial bone is thin, it may compromise the health of the bone around the implant, resulting in bone loss. The investigators concluded that implants placed into thin bone are more prone to bone loss and gingival recession ( Fig. 8 ).
