Introduction
It has been estimated that by the year 2035, more than 20% of the U.S. population will be 65 or older.1 Marcus et al documented a close relationship between age and complete edentulism.2 While the standard therapeutic option for rehabilitating complete edentulism has been the conventional denture, in a large number of cases this does not satisfy patient expectations.3 Problems related to the lack of stability of mandibular dentures often have a
negative effect on patients’ quality of life.4
A valid alternative to conventional mandibular dentures is the use of implant overdentures, which are more stable, functionally efficient, and comfortable.5-7 However, patients who have worn complete dentures for several years often develop a severe degree of alveolar atrophy that makes placement of standard-sized implants impossible unless regenerative procedures are also employed. Such procedures typically require multiple invasive surgeries. This often discourages patients from receiving treatment. Elderly patients in particular may have economic and/or psychological issues impeding treatment acceptance.8 They also often develop chronic systemic diseases (such as diabetes, osteoporosis, cardiovascular disease, etc.) requiring specific medications that may be contraindications for surgeries.9
The possibility of shortening treatment time and having implants placed with less invasive surgery thus represents a valuable opportunity for these patients.10,11 The use of small-diameter implants (also known as mini or narrow-diameter implants) offers one way to achieve this. Rootform implants with a diameter of less than 3mm were first introduced in the early 1990s as a transitional measure, supporting provisional prostheses while standard-diameter implants healed.12,13 However, the immediately loaded small-diameter implants themselves often osseointegrated,14,15 suggesting that they might be used to support definitive restorations.16-18 In 1997, the Food and Drug Administration cleared their long-term use.
The smaller diameter offers several advantages. Placement is simpler, less invasive, and more cost-effective as compared to standard-diameter implants. Small-diameter implants can be used to rehabilitate atrophic edentulous mandibles with a single surgery, enabling treatment to be complete in one day.19-21 The present study was undertaken to evaluate the ability of narrow-diameter implants to support mandibular overdentures and improve the quality of life for patients in a clinical practice.
Materials and Methods
Between December 2012 and September 2014, ten consecutive edentulous patients who were experiencing significant discomfort due to unstable mandibular dentures were enrolled in the study. The main inclusion factors were insufficient posterior bone height (less than 7mm)
and inadequate ridge thickness (less than 5mm) in the intraforaminal region. Neither smoking nor severe systemic disorders were exclusion criteria.
Each patient received a complete intraoral examination and a cone-beam computed tomographic (CBCT) scan. Bone quality was categorized as one of four types according to Lekholm and Zarb.22 Impressions were made, and interarch relationships were recorded in order to mount study casts in an articulator. If possible, the existing complete mandibular dentures were to be re-used by picking up the attachment housings (denture caps) chairside.
Twenty-four hours before surgery, each patient was instructed to start systemic antibiotic prophylaxis (amoxicillin 1g twice a day for six days) and rinse with mouthwash (0.20% chlorhexidine). Local anesthesia was induced with articaine 4% with adrenaline (1:100,000) in the vestibular and lingual areas and adrenaline (1:50,000) on the incision line.
The implants were 2.4mm or 2.9mm in diameter and 10mm, 12mm, or 14mm in length. When the crest was wider than 4mm, and there was an adequate band of keratinized tissue, a flapless approach was preferred. Either two or four narrow-diameter implants (ZEST LOCATOR® Overdenture Implant (LODI) System, distributed by BIOMET 3i, Palm Beach Gardens, Florida) were inserted in the intraforaminal area. All implants were inserted with a minimum distance between the implants of 10mm. They were placed in the mandible, at least 7mm anterior to the mental foramen to avoid the mesial loop of the mental nerve.23
All osteotomies were prepared using a piezoelectric surgical unit first and then following the drilling protocol suggested by the manufacturer, taking care to underprepare the diameter by at least 0.5mm. The implants were inserted using the motor unit. Final seating was achieved using a calibrated torque hand ratchet to a final insertion torque between 30 and 70Ncm. LOCATOR® Abutments were connected to the implants and torqued to 30Ncm, following the manufacturer’s
protocol. The cuff height of the abutment (2.5mm or 4mm in height) was chosen depending upon the mucosal thickness and available interarch space.
The attachment housings (denture caps) were picked up in the denture with autopolymerizing acrylic resin. The patient was asked to close and was guided into centric occlusion, holding the position until complete setting of the resin. The occlusion was adjusted, and the patient’s function with the denture was assessed. The denture was then removed, adjusted, polished, and returned to the patient’s mouth.
Patients were instructed to consume a liquid diet for the first week. After that, no limitation or restriction in the diet was required.
Patients were checked once a month in the first three months and then once every six months. At the follow-up visits, peri-implant health was checked for bleeding on probing or any sign of inflammation. Radiographs were taken to evaluate bone loss. Implants were considered to be successful if they were stable, with no signs of mucositis, and if the bone levels were stable.
One month after delivery of the prosthesis, patients were asked to complete a standardized evaluation form assessing the efficacy of overdentures retained by narrow-diameter implants. Questions assessed such areas as eating and speaking ability, facial appearance, and satisfaction during daily social life.
Figures 1-12 illustrate typical use of LODIs to treat a patient who presented with a severely resorbed edentulous mandible.
Results
The ten patients (two males and eight females) ranged in age from 65 to 80. Because of the investigators’ initial lack of experience with the LODI system, the first two patients received four narrow-diameter implants to minimize the risk of failure due to overloading. After that, only two narrow-diameter implants were placed in each patient. A total of 24 mandibular narrow-diameter implants were thus inserted.
The bone quality in six patients was judged to be Type 1, in three patients it was Type 2, and in one patient it was Type 3. Insertion torque for 14 of the implants was between 50 and 70Ncm. For the other ten implants, the insertion torque was between 30 and 49Ncm (Table 1).
For all ten patients, it was possible to use their existing dentures. No signs or symptoms of postoperative complications were observed.
After an average follow-up period of 15.2 months (range: 3 to 27 months), the success rate was 100%. All ten patients replied that they were “very satisfied” with the degree of improvement in their dentures’ stability and mastication force. The full results of the patient responses are shown in Table 2.
Discussion
The use of narrow-diameter implants can overcome a number of impediments to implant-supported overdentures, such as anatomical limitations, psychological resistance, and other contraindications for surgery.24 Shatkin et al, in their retrospective analysis of 2,514 mini implants placed over a five-year period and supporting both fixed and removable prostheses, found a cumulative survival diameter implants, the authors attributed the difference to the learning curve for the procedure and concluded that the mini implant survival rate improved with experience.
Tu et al showed how denture fracture could be avoided by including a lingual cast-metal reinforcement in a new mandibular denture. If the patient preferred to use his or her existing denture, the authors stated that a metal framework should be incorporated into the overdenture,
and the denture should be relined.25
A literature review published by Klein et al in 2014 included ten articles about narrow (<3.0mm) diameter implants that were followed for between 12 and 96 months.26 In these studies, the implants were placed using both flapped and flapless techniques. In most of the studies, the implants were loaded immediately, in both edentulous arches in lateral incisor positions. Survival rates ranging from 90.9% to 100% were reported.
Similar conclusions were reached by Griffitts et al in a study including 116 mini implants. The final success rate of 97.4% was comparable to standard sized implants.27 Ertugrul and co-workers compared the stress resistance of a narrow-diameter implant to that of a Brånemark standard root-form implant. They found that although the narrow-diameter implants were less stable under the same in vitro conditions, they were advantageous because they could be inserted in ridges with suboptimal bone quantity, using minimally invasive surgery and simpler protocols, and resulting in less morbidity and comparable patient satisfaction.28
When placing narrow-diameter implants, a flapless surgery is preferred whenever possible. Flapless insertion minimizes complications such as swelling, pain, and postoperative discomfort.29 Several authors have reported success rates for flapless implant insertion that are comparable to conventional techniques,30 with a lower incidence of inflammation and earlier reepithelialization.31 When the amount of available bone is limited, however, flap elevation facilitates implant placement, optimizing bone exposure and reducing the risk of implant fenestration.
All the patients recruited in the present study accepted treatment with LODIs to improve their function and comfort. The results regarding their satisfaction with the functional and aesthetic results were similar to those reported by other authors.32-34
Clinical Relevance
Within the limitations of this study, the use of immediately loaded LODIs to support mandibular overdentures appeared to be a valuable option for treating edentulous patients with severe mandibular atrophy. The use of narrow-diameter implants can simplify the treatment of challenging cases such as those in which severe bone atrophy is present. Such implants can be placed with minimally invasive surgical procedures and can enable patients to be rehabilitated with immediately loaded implant-retained, tissue-supported overdentures in a single visit. Providing patients with an immediate improvement in comfort and function can improve their quality of life and social relationships, leading to an increase of implant-treatment acceptance by the elderly population.