This clinical study aimed to clinically and radiographically compare the implant survival rate and peri-implant tissue response between immediate and delayed loading protocols for unsplinted implant retained mandibular overdentures. Twenty patients were enrolled to participate in this study. Each subject was randomly assigned to 1 of 2 treatment groups: test group patients' implants (n = 10), which were immediately loaded, and control group patients' implants (n = 10), which were conventionally loaded. Locator abutments were torqued to 15 Ncm at delivery. Attachments were picked up intraorally immediately after implant placement for the test group and at 3 months for the control group, and 3-lb retention inserts were placed. Marginal bone levels based on cone beam computed tomography fixed reference points were recorded at baseline and 12 months. Modified plaque index, gingival index, and implant stability quotients were recorded at baseline, 3 months, and 12 months. After 12 months, implant survival rate was 100% in both groups. Marginal bone levels, keratinized mucosa, modified plaque index, and gingival index were significantly different among the groups at 3- and 12-month intervals, whereas no significant differences were found in implant stability quotients between the groups. The fact that implant survival rate was 100% in both treatment groups suggests that, within the limitations of this study, immediate loading protocol for unsplinted implant retained mandibular complete overdenture is as predictable, safe, and successful as the delayed loading protocol. Implementing the immediate loading protocol for mandibular implant retained overdentures could shorten treatment time, which could lead to better patient's satisfaction.

Complete edentulism creates many challenges, which often affect the quality of life and health of those involved. In most industrialized countries, the number of edentulous people positively correlates with mean age.1  Being edentulous for a prolonged period results in an atrophic alveolar ridge, which in turn creates a challenge for oral rehabilitation for those patients with removable prostheses. Moreover, patients with prolonged edentulism report difficulty eating many types of food and subsequently have poor nutritional habits.1,2 

The predictability of dental implants has changed prosthetic rehabilitation of mandibular edentulous patients. Dental implants in the anterior mandible have shown a high survival rate as proven by longitudinal clinical studies.35  Recent evidence suggests that the use of dental implants to retain mandibular overdentures significantly improved not only clinical outcomes, but also quality of life. Further, there was no significant difference in long-term cost compared with conventional dentures.5  Thus, implant retained mandibular overdentures were considered the standard of care in the treatment of mandibular edentulism in cases where an implant supported fixed prosthesis is not the treatment of choice.3 

Since their introduction, dental implants have been investigated for osseointegration healing time, using various loading protocols based on clinical situations and bone quality. Branemark's initial recommendation called for a healing period of 4–6 months before loading mandibular implants.6  Gallucci et al7  published consensus statements and clinical recommendations for implant loading protocols. Immediate loading was defined as the implant-supported restoration is placed within 48 hours of implant placement and is functionally in occlusal contact with the opposing dentition.7 

Current studies showed high survival rates of threaded and microtextured implants that used with a minimum diameter of 3 mm for the support of overdenture prostheses in early or conventional loading protocols.810  The overall cumulative survival rate after 10–27 years of follow-up in these studies was 92.6%.810 

Schimmel et al11  listed criteria for immediate loading: insertion torque (≥30 Ncm), implant stability quotient (ISQ) value (≥60), 2 or more implants in the mandible, or 4 or more implants in the maxilla.11  Also, splinting of implants and the type of attachment system had no effect on 12-month implant survival rate compared with unsplinted implants.11 

Conventional treatment with implant-retained overdentures (IODs) suggested that attachments be installed no earlier than 3 months after implant placement.12  During the initial phase of healing, patients were sometimes instructed not to wear the removable dentures for several weeks to avoid premature loading of the implants, which is believed to impair the osseointegration process.12  Additionally, several appointments for adjustments and/or soft relining of the treatment dentures are often required during this healing period. These restrictions and frequent appointments are, at best, inconvenient for the patient.

Survival and success of dental implants are dependent on many factors including, but not limited to implant surface, quality of bone, implant stability during healing, and loading protocol. Research suggested that implants with enhanced surface microtopography can achieve secondary stability at earlier healing times.13,14  Several clinical studies on different implant systems showed that the loading time in complete mandibular implant retained overdentures can be safely shortened without compromising the osseointegration process and implant success rate.1521 

Since their introduction in 2001, Locator attachments (Zest Anchors Inc, Escondido, Calif) have been used successfully.1517,22,23  Delayed or early loading of implant-retained mandibular overdentures (IOD) showed equivalent success rates when the IODs opposed maxillary complete dentures.1518  Several studies on immediate functional loaded and splinted implant-supported overdentures have reported high success rates.21,2432  However, there is a lack of comparative studies in the literature on immediately loading of two unsplinted implant retained mandibular overdentures with Locator type attachments.1517,27,3335 

Romanos et al36  suggested that immediate functional loading of dental implants improved bone regeneration and enhances bone remodeling at the bone–implant interface and that new-bone formation can be achieved and bone resorption controlled. Such a mechanism promotes healing and reduces treatment time.36,37 

Several studies validated the use of the Osstell (Gothenburg, Sweden) instrument in evaluating implant primary stability in determining the loading protocol.3842  Resonance frequency analysis (RFA) was emerging as a valuable tool for the implant surgeon to determine the viability of a particular implant by providing a relatively unobtrusive method for assessing the stability of the newly placed implant. On the other hand, RFA measurements may be applied as a predictor of implant success for immediately loaded implants. Both intraoperatively and postoperatively, RFA was considered a noninvasive technique that can be used repeatedly for quantitative stability measurements and RFAs can be assessed for any implant system.43,44 

The torque of a dental implant is measured in Newton centimeters (Ncm).45  Insertion torque is the continuous measurement of torque while the implant is being placed. The torque increases if the size of the osteotomy decreases or if the bone quality increases. Additional factors that affect the torque are the sharpness of the implant-cutting tip, the surface properties of the implant, lubrication of the preparation provided by blood, and the design of the implant.45 

The primary aim of this study was to compare the survival of implants immediately loaded with mandibular overdentures using two Locator attachments vs implants with delayed loading. The secondary aim was to clinically and radiographically compare the peri-implant tissue response around implants immediately loaded with mandibular complete overdentures to implants and overdentures with delayed loading.

This study was a single site, randomized, controlled, and prospective clinical study. The methodology was reviewed by an independent statistician. Twenty edentulous patients were enrolled from the clinics of the University of Kentucky, College of Dentistry. Ten subjects per group is reasonable for a pilot study, providing an 89% probability of estimating the true mean for bone quality and implant stability to within half a standard deviation in each group. These means, along with the observed standard deviations and within-subject correlations that we obtained, will prove essential for designing the larger, confirmatory study that constitutes the next phase of this research. This study received Institutional Review Board approval (IRB#12-0931-F1V) and was conducted in accordance with the Helsinki Declaration of 1975, as revised in 2000. Each subject provided signed informed consent before participation.

Each subject was randomly assigned to one of the treatment groups: the test group (n = 10) received immediately loaded, unsplinted implant retained mandibular complete overdentures (20 implants). The control group (n = 10) received delayed loaded, unsplinted implant retained mandibular complete overdentures (20 implants).

Subjects

To be included in the study, all subjects must have demonstrated an understanding of the study and willingness to participate as evidenced by voluntary written informed consent. The minimum age was at least 22 years old. Subjects also had to demonstrate that they were willing, able, and likely to comply with all study procedures and restrictions. Moreover, all subjects were competent in written and spoken English and able to follow directions. They had to be in satisfactory general health with no clinically significant and relevant abnormalities of medical history, and subjects must have expressed interest in receiving a 2-implant retained mandibular complete overdenture, as well as be available for the follow-up examinations.

Subjects were excluded from the study if they were pregnant or breastfeeding or could not undergo oral surgery procedures for any reason. Subjects were excluded if they were undergoing chemotherapy or radiation, uncontrolled diabetes, had seriously impaired cardiovascular or pulmonary function, had immune-compromised diseases, kidney, or liver disease, or had a history of severe multiple allergies.

Instrumentation/procedures

All participants received new maxillary and mandibular complete dentures before implant placement. Two implants were inserted under local anesthesia, using 2% Lidocaine HCL with 1:100,000 epinephrine (Dentsply Sirona, New York, NY) following the routine administration of prophylactic antibiotic medications 1 hour before the surgical procedure. Based on penicillin allergy, 2 g amoxicillin or 600 mg clindamycin was administered. A modified crestal incision was made, and full-thickness flaps were conservatively reflected to the mucogingival junction to reduce the possibility of postsurgical swelling and to allow surgical access to the implant sites. The implant positions were predetermined with a clear duplicate of the mandibular dentures used as positioning guides and adjusted at the canine areas to allow for introduction of pilot drills and guiding pins. Two osteotomies at the sites of the mandibular canines were prepared according to the protocols specified by BioHorizons (Birmingham, Ala). For both test and control groups, tapered internal laser lock 3.8- × 12-mm implants were inserted, and peak insertion torque was measured immediately with a minimum of 35 Ncm. ISQ measurements were recorded by using resonance frequency analysis (RFA) using Osstell mentor (Osstell, Baltimore, Md). Using the manufacturers' guidelines, Smartpegs type 4 (Osstell) were attached to the implant platform and the mean of 2 consecutive ISQ values, recorded from the facial aspect and then from the distal or mesial aspect, was calculated. Locator abutments (Zest Dental Solutions, Carlsbad, Calif) were connected to the implant fixtures with 15 Ncm torque in the test group, and cover screws were placed into implant fixtures in the control group. The flap was sutured with 4-0 Vicryl (Ethicon-coated Vycril synthetic absorbable, Ethicon Inc, Blue Ash, Ohio) sutures to achieve tension-free primary closure. The complete dentures were modified by creating a space in the intaglio surface for the metal housing of the attachment to have no contacts between the metal housing and the denture base. The attachments were picked up intraorally with Quick-Up autopolymerizing resin (Voco, Indian Land, SC). A cone beam computerized tomography (CBCT) scan was made immediately after implant placement for research purposes for both groups (i-CAT Cone Beam 3D Imaging with settings: diameter 16 cm, height 6 cm, mandible/resolution 0.3 mm, voxel 8.9 seconds/mAs = 18.54/KVp = 120, acquisition time 8.9 seconds, Henry Schein Dental, Albany, NY). For the control group, the Locator abutments were placed, and intraoral attachment pick up was performed 3 months following implant placement (Figures 1 and 2).

Figures 1 and 2

Figure 1. Treatment protocol for test group. (a) Preoperative edentulous ridge. (b) Locator abutments delivered immediately after implant placement and 3-0 Vicryl interrupted sutures to secure the flaps. (c) Three-month follow-up visit to evaluate healing. (d) Locator attachments picked up into the intaglio surface of the mandibular denture and medium attachments were used for immediate function. Figure 2. Treatment protocol for control group. (a) Preoperative edentulous ridge. (b) Cover screws placed and flap secured with 3-0 Vicryl interrupted sutures. (c) Locator abutments delivered at 3 months. (d) Locator attachments picked up into the intaglio surface of the mandibular denture and medium attachments were used for immediate function.

Figures 1 and 2

Figure 1. Treatment protocol for test group. (a) Preoperative edentulous ridge. (b) Locator abutments delivered immediately after implant placement and 3-0 Vicryl interrupted sutures to secure the flaps. (c) Three-month follow-up visit to evaluate healing. (d) Locator attachments picked up into the intaglio surface of the mandibular denture and medium attachments were used for immediate function. Figure 2. Treatment protocol for control group. (a) Preoperative edentulous ridge. (b) Cover screws placed and flap secured with 3-0 Vicryl interrupted sutures. (c) Locator abutments delivered at 3 months. (d) Locator attachments picked up into the intaglio surface of the mandibular denture and medium attachments were used for immediate function.

Close modal

Postoperative care

The recommendation for postoperative care included amoxicillin, 1 500-mg tablet every 8 hours for 10 days, and analgesics, mainly ibuprofen, up to 600 mg every 6–8 hours as needed. If the patient was allergic to penicillin, 300 mg clindamycin twice a day was prescribed instead. Sutures were removed 2 weeks after surgery. Patients were advised to clean the surgical area gently by rinsing with 0.12% chlorhexidine gluconate twice daily for 2 weeks. Follow-up evaluations were done at 2 weeks, 3 months, and 12 months.

Measurement

The following outcome measures were evaluated.

Implant Survival Rate

A “surviving implant” is when the implant remains in the jaw and is stable and when the subject's treatment is functionally successful even though all the individual success criteria, as defined by Smith and Zarb, are not fulfilled46: (1) does not cause allergic, toxic, or gross infectious reactions either locally or systematically; (2) offers anchorage to a functional prosthesis; (3) does not show any signs of fracture or bending; (4) does not show any mobility when individually tested by tapping or rocking with a hand instrument; and (5) does not show any signs of continuous radiolucency on an intraoral radiograph using a paralleling technique strictly perpendicular to the implant-bone interface.

Implant Stability Evaluated by Osstell

All implant stability values were recorded at the time of implant placement and at 3 and 12 months. ISQ has a nonlinear correlation to micro mobility, whereas micro mobility decreases more than 50% from 60 to 70 ISQ.

Implant Insertion Torque

The insertion torque for every implant was recorded at the time of surgery. Values recorded were 35 Ncm and higher.

Peri-implant 4-Dimentional Marginal Bone Loss

CBCT was made at implant installation as baseline and at 12 months postoperatively to evaluate bone changes around the implant (Figures 3 and 4)

Figure 3

Cone beam computerized tomography for control group made immediately after implant placement at baseline and at 12-month follow-up visit to measure the crestal bone changes around the platform of each implant at 4 sites (mesial [M], distal [D], buccal [B], and lingual [L]). (a) B and L crestal bone level measured from the most inferior point of the mandible at the implant site at baseline. (b) M and D crestal bone level measured from the most inferior point of the mandible at the implant site at baseline. (c) B and L crestal bone level measured from the most inferior point of the mandible at the implant site at 12 months. (d) M and D crestal bone level measured from the most inferior point of the mandible at the implant site at 12 months.

Figure 3

Cone beam computerized tomography for control group made immediately after implant placement at baseline and at 12-month follow-up visit to measure the crestal bone changes around the platform of each implant at 4 sites (mesial [M], distal [D], buccal [B], and lingual [L]). (a) B and L crestal bone level measured from the most inferior point of the mandible at the implant site at baseline. (b) M and D crestal bone level measured from the most inferior point of the mandible at the implant site at baseline. (c) B and L crestal bone level measured from the most inferior point of the mandible at the implant site at 12 months. (d) M and D crestal bone level measured from the most inferior point of the mandible at the implant site at 12 months.

Close modal
Figure 4

Cone beam computerized tomography for test group made immediately after implant placement at baseline and at 12-month follow-up visit to measure the crestal bone changes around the platform of each implant at 4 sites (mesial [M], distal [D], buccal [B], and lingual [L]). (a) B and L crestal bone level measured from the most inferior point of the mandible at the implant site at baseline. (b) M and D crestal bone level measured from the most inferior point of the mandible at the implant site at baseline. (c) B and L crestal bone level measured from the most inferior point of the mandible at the implant site at 12 months. (d) M and D crestal bone level measured from the most inferior point of the mandible at the implant site at 12 months.

Figure 4

Cone beam computerized tomography for test group made immediately after implant placement at baseline and at 12-month follow-up visit to measure the crestal bone changes around the platform of each implant at 4 sites (mesial [M], distal [D], buccal [B], and lingual [L]). (a) B and L crestal bone level measured from the most inferior point of the mandible at the implant site at baseline. (b) M and D crestal bone level measured from the most inferior point of the mandible at the implant site at baseline. (c) B and L crestal bone level measured from the most inferior point of the mandible at the implant site at 12 months. (d) M and D crestal bone level measured from the most inferior point of the mandible at the implant site at 12 months.

Close modal

Keratinized Mucosa

The zone of keratinized mucosa (KM) was measured using a UNC 15 Periodontal probe (Hu-Friedy Manufacturing Co, Chicago, Ill) at the time of implant placement and 3 and 12 months.

Modified Gingival Index and Plaque Index

The gingival index (GI) has been modified and adapted (mGI) for application around oral implants (Tables 1 and 2). However, soft tissue texture and color around implants depend on the normal appearance of the recipient tissues before implant placement and may be influenced by the material characteristics of the implant surface. Furthermore, difficulties in recording mucosal inflammation have been reported, such as nonkeratinized peri-implant mucosa normally appearing redder than keratinized tissue.47,48 

Table 1

mGI* scores around implants as described by Mombelli et al49  and Apse et al50 

mGI* scores around implants as described by Mombelli et al49 and Apse et al50
mGI* scores around implants as described by Mombelli et al49 and Apse et al50
Table 2

mPI scores around implants as described by Mombelli et al49  and Lindquist et al

mPI scores around implants as described by Mombelli et al49 and Lindquist et al
mPI scores around implants as described by Mombelli et al49 and Lindquist et al

Mombelli et al49  modified the original plaque index introduced by Silness and Loe to assess biofilm formation in the marginal area around ITI implants (mPI) (Institut Straumann, Waldenburg, Switzerland). Aspe et al50  assessed oral hygiene levels according to a 3-point scale and reported a significant relationship between oral hygiene and peri-implant bone resorption over an observation period of 6 years.

The results were analyzed and reviewed by an independent statistician. The statistician suggested for this pilot study that 10 subjects per group was reasonable. The results of this pilot study can be used for power calculation for a phase 2 randomized controlled clinical study on immediate loading implant retained overdenture with longer follow-up. Although there was a small sample size and a short period of follow-up for this pilot study, the results presented are clinically relevant.

KM

Independent-samples t-tests were conducted to compare KM measurements between the treatment and control group at each of the three time intervals (baseline and 3 and 12 months). At baseline, there was a significant difference in the KM measurements for the treatment group (M = 5.45 mm, SD = 0.826) and control group (M = 4.80 mm, SD = ±0.951; P = .027). At 3 months, there was not a significant difference in the measurements for the treatment group (M = 5.00 mm, SD = ±1.085) and control group (M = 4.20 mm, SD = ±1.508; P = .071). At 12 months, there was a significant difference in the KM measurements for the treatment group (M = 5.06 mm, SD = ±0.873) and control group (M = 3.70 mm, SD = ±1.809; P = .007; Table 3).

Table 3

Comparisons of keratinized mucosa measurements between groups at each time point

Comparisons of keratinized mucosa measurements between groups at each time point
Comparisons of keratinized mucosa measurements between groups at each time point

For both the control and treatment groups, no significant differences were found between baseline, 3 months, and 12 months as determined by 1-way analysis of variance (ANOVA) [control group: F(2,58) 3.233, P = .047; and treatment group F(2,56) 1.317, P = .277]. Because there were no significant differences overall, no post hoc comparisons were calculated (Table 4; Figure 5).

Table 4

Comparisons of keratinized mucosa measurements overtime within groups at each time point

Comparisons of keratinized mucosa measurements overtime within groups at each time point
Comparisons of keratinized mucosa measurements overtime within groups at each time point
Figures 5–7

Figure 5. Chart showing comparison between mean keratinized mucosa measurements at baseline, 3 months, and 1 year. Figure 6. Chart showing comparison between mean crestal bone loss around buccal (site B), distal (site D), lingual (site L), and mesial (site M) surfaces of implants in the test and control groups. Figure 7. Chart showing comparison between mean Osstell ISQ values of the test and control groups.

Figures 5–7

Figure 5. Chart showing comparison between mean keratinized mucosa measurements at baseline, 3 months, and 1 year. Figure 6. Chart showing comparison between mean crestal bone loss around buccal (site B), distal (site D), lingual (site L), and mesial (site M) surfaces of implants in the test and control groups. Figure 7. Chart showing comparison between mean Osstell ISQ values of the test and control groups.

Close modal

A 2-way repeated-measure ANOVA was used to test the interaction between group and time; the interaction was not statistically significant [F(2,35) 2.326, P = .113], illustrating that changes in the KM measurements over time for the treatment group were not significantly different than the changes over time for the control group.

Bone level measurements

Independent-samples t-tests were conducted to compare bone level measurements between treatment and control groups. Reference points used for crestal bone changes were the inferior point of the mandible to the platform of each implant. At baseline, there was a significant difference in the bone level measurements from the reference point for the treatment group (M = 26.71 mm, SD = ±3.54) and control group (M = 24.17 mm, SD = ±4.37; P < .0001). At 12 months, there was a significant difference in the bone level measurements from the reference point for the treatment group (M = 25.86 mm, SD = 3.46) and control group (M = 22.84 mm, SD = ±4.82; P < .0001). There was also a significant difference in change in bone level measurements from baseline to 12 months for the treatment group (M = −0.65 mm, SD = ±1.69) and control group (M = −1.33 mm, SD = ±1.473; P = .009; Table 5; Figure 6).

Table 5

Comparisons of crestal bone level changes between groups

Comparisons of crestal bone level changes between groups
Comparisons of crestal bone level changes between groups

Osstell results

Independent-samples t-tests were conducted to compare Osstell measurements between the treatment and control group at each of the 3 time points. At baseline, there was a significant difference in the RFA measurements for the treatment group (M = 79.88, ISQ, SD = 3.44) and control group (M = 74.45, ISQ, SD = 6.66; P < .020). At 3 months, there was a significant difference in the RFA measurements for the treatment group (M = 80.08, ISQ, SD = 3.08) and control group (M = 74.73, ISQ, SD = 6.77; P = .004). At 12 months, there was a significant difference in the Osstell measurements for the treatment group (M = 79.56, ISQ, SD = 3.35) and control group (M = 76.33, ISQ, SD = 5.60; P = .040; Table 6; Figure 7).

Table 6

Comparisons of Osstell measurements between groups at each time point

Comparisons of Osstell measurements between groups at each time point
Comparisons of Osstell measurements between groups at each time point

For the control group, there was no significant difference between baseline, 3 months, and 12 months, with an increase in ISQ after loading, as determined by 1-way ANOVA [F(2,58) 0.517, P = .60]; thus, no post hoc comparisons were calculated. For the treatment group, there was no significant difference between baseline, 3 months, and 12 months as determined by 1-way ANOVA [F(2,56) 0.12; P = .85). No post hoc comparisons were calculated (Table 7).

Table 7

Comparisons of Osstell measurements over time within groups at each time point

Comparisons of Osstell measurements over time within groups at each time point
Comparisons of Osstell measurements over time within groups at each time point

A 2-way repeated-measures ANOVA was used to test the changes intragroup over time. The interaction was not significant [F(2,35) 0.847; P = .438], demonstrating that the changes in the Osstell measurements for the treatment group and control group were not significantly different over time.

In summary, ISQ, measured using Osstell RFA, showed that, at baseline, there was a significant difference in the ISQ measurements for the treatment group (M = 79.88, SD = ±3.437) and control group [M = 74.45, SD = ±6.657; t(38) = 3.238; P = .020].

At 3 months, there was a significant difference in the ISQ measurements for the treatment group (M = 80.08, SD = ±3.083) and control group [M = 74.73, SD = 6.770; t(36) =3.080; P = .004]. At 12 months, there was a significant difference in the measurements for the treatment group (M = 79.56, SD = ±3.351) and control group [M = 76.33, SD = ±5.601; t(36) = 2.127; P = .040]. At baseline, there was a significant difference in the gingiva measurements for the treatment group (M = 5.45, SD = 0.826) and control group [M = 4.80, SD = 0.951; t(38) = 2.308; P = .027].

Implant survival rate

After 12 months, implant survival rate was 100% for both immediate load and delayed load groups.

Modified plaque index and gingival index

At 12 months, the modified gingival index was higher in the control group than the test group, with no significant difference between groups. The modified plaque index was higher in the test group than the control group, with no significant difference between groups.

Complications

Throughout the course of the study, 2 patients had fractured mandibular dentures that needed repair. Two additional patients developed gingival recession due to lack of keratinized mucosa and bone loss along the facial aspects of the implants, which necessitated further surgical intervention using soft tissue grafting (free gingival graft) around implants.

Several subjects required frequent follow-up visits for damaged locator attachments or for locator abutments replacement with shorter or longer heights following complete healing (Table 8).

Table 8

Complications/modifications and number of subjects*

Complications/modifications and number of subjects*
Complications/modifications and number of subjects*

The purpose of this investigation was to clinically and radiographically compare the implant success rate and peri-implant tissue response between the immediate loading protocol and delay loading protocol for unsplinted implant retained mandibular overdenture, using the following metrics: marginal bone levels, modified plaque index, gingival index, and ISQ, and success rate.

Bone level changes were measured at 4 sites (mesial, buccal, distal, and lingual) around the implants. There was a significant difference in change of the bone level measurements from baseline to 12 months for the treatment groups, indicating that immediate loading implant retained overdenture maintained more crestal bone compared with delayed load implant retained overdenture. This difference of crestal bone loss around the neck of implants could be due to the immediate bone response over time to healing and reorganization along with functional stresses.36,5153 

Although many host factors cannot be controlled by the operator in general, the choice of the implant design and surface in conjunction with the surgical techniques are operator dependent and can affect implant stability. Primary stability is an important prerequisite in achieving osseointegration and considered a useful predictor for successful osseointegration.54 

Endosseous implant stability is the capacity of the implant to withstand loading in axial, lateral, and rotational directions. Achievement of initial primary stability depends on quality of bone, surgical technique, implant design, and prosthetic design.55  The strengths of this study were based on these fundamental factors that used to maintain stability of the studied implants.

Bone quality was classified into 4 categories, ranging from dense to spongy bone. Implants placed in dense bone (types 1 and 2) show better initial stability than those placed in poorer quality bone (types 3 and 4).56  Therefore, this may be considered a main strength factor to have an equivalent success rate between immediate and delayed loading groups because all implants placed in this study were in type 1 symphysis bone.

Dental implants with laser-ablated coronal microgrooves reduce peri-implant crestal bone loss (CBL). However, laser microgrooves appear to inhibit apical migration of crevicular epithelium and to promote true attachment of peri-implant gingiva. The formation of an interface between connective tissue and the implant collar that is more like that of a natural tooth will improve the long-term performance of dental implants.57  In this study, we used Laser-Lok BioHorizons implants that are characterized by only surface treatment shown to attract a true physical connective tissue attachment onto the surface of dental implants.58  The implants used in this study were tapered to provide excellent primary stability, maximum bone maintenance, and soft tissue attachment for optimal esthetics. The tapered implant achieved these benefits from its anatomically tapered dental implant body, aggressive buttress threads, and advanced Laser-Lok surface technology. These implants have a deep 1.5-mm internal hex connection with a lead-in tapered bevel to create a rigid connection and a stable biologic seal. Moreover, implants with textured surfaces achieve better anchorage in bone tissue compared with implants with machined surfaces.59 

Generally, in all bone quality, reducing the diameter of implant osteotomy by 5% will increase in torque value by 15%–20%, and this will improve bone density to optimize primary implant stability.60  Rough surfaces provide more favorable conditions for stabilizing the fibrin clot that forms on the surface of a freshly inserted implant for better osseointegration. Rough implants tend to yield higher bone-to-implant contact (BIC) values than machined ones.61 

A reduction in abutment diameter (ie, platform switch [PS]) resulted in the translation of less stress to the crestal bone in the microthread implants.62 

The microthreaded design was found to be more effective in reducing shear stress under off-axis loading, which dominates in the oral cavity. However, higher peak compressive stress and strain around the microthreaded implant were found to be localized in a smaller bone volume. The biomechanical rationale of the microthreaded design may reduce the risks of marginal bone loss caused by overloading.63,64 

Although the design of this study was to test using unsplinted implants to retain mandibular complete overdenture with resilient attachments for locator abutments, which were considered not rigid for the immediate loading protocol, we used several surgical and restorative techniques along with the implant design to maximize primary stability of implants that were controlled by the operator, such as undersizing the osteotomy, tapered implant design, widened crestal portion, threaded implant design, buttress thread design, platform switch design, and rough surface. Patient compliance was another important factor in this study. All patients were instructed to stay on soft food for 6 weeks after surgery, as this is the most critical time for osseointegration to be established. Quality of life and patient satisfaction were not measured in this study. This is another limitation of this pilot study. The mean marginal bone loss values observed for both groups at 12 months remain below the normal range of values reported in the literature (1.5–2 mm in the first year).6568  The number of disconnecting and reconnecting Locator abutments to measure ISQ for this research purpose along with raising the flap for implant placement may influence the rate of crestal bone loss around the neck of the implants, and this is one of the limitations of the study. A recent study by Rodriguez et al69  found that implants with a PS design are associated with less CBL during the healing process and as their abutments are disconnected than are non–platform-switched (NPS) implants with a comparable number of disconnections and reconnections.69 

During the period of the study, 1 patient in the test group did not complete the follow-up appointments at 3 and 12 months. There was no significant difference in implant success between the 2 groups in the current study. These finding agrees with previous studies15,52  where there was a 100% success rate when unsplinted implants with Locator attachments were placed in the mandibles to retain an overdenture using the immediate loading protocol.

A systematic review conducted by Zygogiannis et al53  found that studies demonstrated similar outcomes between conventional and immediate loading protocols in cases of mandibular implant overdentures including ball attachments, O-rings, bar attachments, and unsplinted implants.

Forty implants were inserted in this study, with >35-Ncm torque in both immediate and conventional loading groups. All had >64 ISQ values, which is required for successful immediate loading procedures and indicates a high degree of primary stability. Although preliminary, these findings provide a platform for future clinical research. Larger cohorts and long-term follow-up are recommended.

Study limitations

The limitations of this study were the short-term clinical trial and follow-up period of only 1 year. Bias was due to the nature of the study with the inability to blind study examiners. The free-handed implant placement technique was used, along with raising flaps for implant installations. Moreover, there was a small sample size for this pilot study. Future research investigations can increase the sample size with long-term follow-up data. A future phase 2 research study sample size can be selected based on the results of this pilot study. It can be estimated that a sample size of 41 patients per group (anticipated 10% dropouts) will be necessary to provide 90% power with a type I error of .05, for a difference of 0.4 mm (SD = 0.53 mm) in peri-implant vertical bone loss between groups, which would be statistically significant.

The computer-guided surgery technique is a more accurate and reliable tool to be considered for future studies. This technique can be done with or without raising a flap for implant installation. The flapless technique may preserve more crestal bone around the neck of the implants. Future research should consider the differences between these techniques for long-term results.

Immediate loading the unsplinted implant in different bone qualities (ie, in maxillary edentulous patients) is another project for future research.

Patient satisfaction and quality of life are important and were not measured in this pilot study. Oral health, as related to quality of life (OHRQoL), can be used in the future to establish new prosthetic rehabilitation strategies. The Oral Health Impact Profile (OHIP) questionnaire is a valid and reliable instrument for assessment of OHRQoL. Future research considering patient satisfaction can be assessed using the Oral Health Impact Profile in Edentulous Adults questionnaire.

Moreover, this study was conducted at a single-site university setting. Multicenter studies may be needed to verify the validity of this pilot study results.

An independent statistician reviewed the conclusions and suggested a longer healing time with a larger sample size. Immediately loaded implants retaining mandibular overdentures using Locator attachments showed higher stability and less bone and soft tissue loss after 12-month follow-up and could be considered an alternative treatment modality. Implementing the immediate loading protocol for the mandibular implant retained overdentures using Locator attachments would shorten the treatment time, which could lead to better patient satisfaction. More research is needed to verify these pilot study results.

Abbreviations

    Abbreviations
     
  • B

    buccal

  •  
  • BIC

    bone to implant contact

  •  
  • BIV

    bone–implant volume

  •  
  • CBCT

    cone beam computerized tomography

  •  
  • D

    distal

  •  
  • GI

    gingival index

  •  
  • IOD

    implant-retained overdenture

  •  
  • ISQ

    implant stability quotients

  •  
  • ITI

    International Team of Implantologists

  •  
  • KM

    keratinized mucosa

  •  
  • L

    lingual

  •  
  • M

    mesial

  •  
  • NPS

    non–platform switch

  •  
  • PI

    plaque index

  •  
  • PS

    platform switch

  •  
  • RFA

    resonance frequency analysis

This study was partially funded by BioHorizons. The authors thank Dominique Zephyr for performing statistical analysis and reviewing the methodology, results, and conclusions.

The authors declare no conflicts of interest.

1
Tallgren
A.
The continuing reduction of the residual alveolar ridges in complete denture wearers: a mixed-longitudinal study covering 25 years. 1972
.
J Prosthet Dent
.
2003
;
89
:
427
435
.
2
Kapur
KK,
Soman
SD.
Masticatory performance and efficiency in denture wearers, 1964
.
J Prosthet Dent
.
2004
;
92
:
107
111
.
3
Feine
JS,
Carlsson
GE,
Awad
MA,
et al.
The McGill consensus statement on overdentures. Mandibular two-implant overdentures as first choice standard of care for edentulous patients. Montreal, Quebec, May 24-25, 2002
.
Int J Oral Maxillofac Implants
.
2002
;
17
:
601
602
.
4
Balshi
TJ,
Wolfinger
GJ,
Stein
BE,
Balshi
SF.
A long-term retrospective analysis of survival rates of implants in the mandible
.
Int J Oral Maxillofac Implants
.
2015
;
30
:
1348
1354
.
5
Melilli
D,
Rallo
A,
Cassaro
A.
Implant overdentures: recommendations and analysis of the clinical benefits
.
Minerva Stomatol
.
2011
;
60
:
251
269
.
6
Payne
AG,
Tawse-Smith
A,
Kumara
R,
Thomson
WM.
One-year prospective evaluation of the early loading of unsplinted conical Branemark fixtures with mandibular overdentures immediately following surgery
.
Clin Implant Dent Relat Res
.
2001
;
3
:
9
19
.
7
Gallucci
GO,
Benic
GI,
Eckert
SE,
et al.
Consensus statements and clinical recommendations for implant loading protocols
.
Int J Oral Maxillofac Implants
.
2014
;
29
:
287
290
.
8
Rutkunas
V,
Mizutani
H,
Puriene
A.
Conventional and early loading of two-implant supported mandibular overdentures. A systematic review
.
Stomatologija
.
2008
;
10
:
51
61
.
9
Turkyilmaz
I,
Tozum
TF,
Tumer
C,
Ozbek
EN. A
2-year clinical report of patients treated with two loading protocols for mandibular overdentures: early versus conventional loading
.
J Periodontol
.
2006
;
77
:
1998
2004
.
10
Turkyilmaz
I,
Tumer
C.
Early versus late loading of unsplinted TiUnite surface implants supporting mandibular overdentures: a 2-year report from a prospective study
.
J Oral Rehabil
.
2007
;
34
:
773
780
.
11
Schimmel
M,
Srinivasan
M,
Herrmann
FR,
Müller
F.
Loading protocols for implant-supported overdentures in the edentulous jaw: a systematic review and meta-analysis
.
Int J Oral Maxillofac Implants
.
2014
;
29
:
271
286
.
12
Adell
R.
Tissue integrated prostheses in clinical dentistry
.
Int Dent J
.
1985
;
35
:
259
265
.
13
Goiato
MC,
Pellizzer
EP,
Barao
VA,
et al.
Clinical viability for immediate loading of dental implants: part II: treatment alternatives
.
J Craniofac Surg
.
2009
;
20
:
2143
2149
.
14
Romanos
GE,
Testori
T,
Degidi
M,
Piattelli
A.
Histologic and histomorphometric findings from retrieved, immediately occlusally loaded implants in humans
.
J Periodontol
.
2005
;
76
:
1823
1832
.
15
Schincaglia
GP,
Rubin
S,
Thacker
S,
Dhingra
A,
Trombelli
L,
Ioannidou
E.
Marginal bone response around immediate- and delayed-loading implants supporting a locator-retained mandibular overdenture: a randomized controlled study
.
Int J Oral Maxillofac Implants
.
2016
;
31
:
448
458
.
16
Elsyad
MA,
Elsaih
EA,
Khairallah
AS.
Marginal bone resorption around immediate and delayed loaded implants supporting a locator-retained mandibular overdenture. A 1-year randomized controlled trial
.
J Oral Rehabil
.
2014
;
41
:
608
618
.
17
Al-Dharrab
A.
Three-year prospective evaluation of immediately loaded mandibular implant overdentures retained with locator attachments
.
J Contemp Dent Pract
.
2017
;
18
:
842
850
.
18
Alsabeeha
N,
Atieh
M,
Payne
AG.
Loading protocols for mandibular implant overdentures: a systematic review with meta-analysis
.
Clin Implant Dent Relat Res
.
2010
;
12
:
e28
e38
.
19
Attard
NJ,
Zarb
GA.
Immediate and early implant loading protocols: a literature review of clinical studies
.
J Prosthet Dent
.
2005
;
94
:
242
258
.
20
Kawai
Y,
Taylor
JA.
Effect of loading time on the success of complete mandibular titanium implant retained overdentures: a systematic review
.
Clin Oral Implants Res
.
2007
;
18
:
399
408
.
21
Ormianer
Z,
Garg
AK,
Palti
A.
Immediate loading of implant overdentures using modified loading protocol
.
Implant Dent
.
2006
;
15
:
35
40
.
22
Trakas
T,
Michalakis
K,
Kang
K,
Hirayama
H.
Attachment systems for implant retained overdentures: a literature review
.
Implant Dent
.
2006
;
15
:
24
34
.
23
Evtimovska
E,
Masri
R,
Driscoll
CF,
Romberg
E.
The change in retentive values of locator attachments and hader clips over time
.
J Prosthodont
.
2009
;
18
:
479
483
.
24
Attard
NJ,
David
LA,
Zarb
GA.
Immediate loading of implants with mandibular overdentures: one-year clinical results of a prospective study
.
Int J Prosthodont
.
2005
;
18
:
463
470
.
25
Castellon
P,
Blatz
MB,
Block
MS,
Finger
IM,
Rogers
B.
Immediate loading of dental implants in the edentulous mandible
.
J Am Dent Assoc
.
2004
;
135
:
1543
1549
26
Chiapasco
M,
Gatti
C.
Implant-retained mandibular overdentures with immediate loading: a 3- to 8-year prospective study on 328 implants
.
Clin Implant Dent Relat Res
.
2003
;
5
:
29
38
.
27
da Silva
RJ,
Issa
JP,
Semprini
M,
et al.
Clinical feasibility of mandibular implant overdenture retainers submitted to immediate load
.
Gerodontology
.
2011
;
28
:
227
232
.
28
Lozada
JL,
Ardah
AJ,
Rungcharassaeng
K,
Kan
JY,
Kleinman
A.
Immediate functional load of mandibular implant overdentures: a surgical and prosthodontic rationale of 2 implant modalities
.
J Oral Implantol
.
2004
;
30
:
297
306
.
29
Martinez-Gonzalez
JM,
Barona-Dorado
C,
Cano-Sanchez
J,
Fernandez-Caliz
F,
Sanchez-Turrion
A.
Evaluation of 80 implants subjected to immediate loading in edentulous mandibles after two years of follow-up
.
Med Oral Patol Oral Cir Bucal
.
2006
;
11
:
E165
E170
.
30
Sadowsky
SJ.
Immediate load on the edentulous mandible: treatment planning considerations
.
J Prosthodont
.
2010
;
19
:
647
653
.
31
Stoker
GT,
Wismeijer
D.
Immediate loading of two implants with a mandibular implant-retained overdenture: a new treatment protocol
.
Clin Implant Dent Relat Res
.
2011
;
13
:
255
261
.
32
Tarnow
DP,
Emtiaz
S,
Classi
A.
Immediate loading of threaded implants at stage 1 surgery in edentulous arches: ten consecutive case reports with 1- to 5-year data
.
Int J Oral Maxillofac Implants
.
1997
;
12
:
319
324
.
33
Akca
K,
Akkocaoglu
M,
Comert
A,
Tekdemir
I,
Cehreli
MC.
Bone strains around immediately loaded implants supporting mandibular overdentures in human cadavers
.
Int J Oral Maxillofac Implants
.
2007
;
22
:
101
109
.
34
Andreiotelli
M,
Att
W,
Strub
JR.
Prosthodontic complications with implant overdentures: a systematic literature review
.
Int J Prosthodont
.
2010
;
23
:
195
203
.
35
Ma
S,
Payne
AG.
Marginal bone loss with mandibular two-implant overdentures using different loading protocols: a systematic literature review
.
Int J Prosthodont
.
2010
;
23
:
117
126
.
36
Romanos
GE.
Wound healing in immediately loaded implants
.
Periodontol 2000
.
2015
;
68
:
153
167
.
37
Schenk
RK,
Buser
D.
Osseointegration: a reality
.
Periodontol 2000
.
1998
;
17
:
22
35
.
38
Balshi
SF,
Allen
FD,
Wolfinger
GJ,
Balshi
TJ.
A resonance frequency analysis assessment of maxillary and mandibular immediately loaded implants
.
Int J Oral Maxillofac Implants
.
2005
;
20
:
584
594
.
39
Han
J,
Lulic
M,
Lang
NP.
Factors influencing resonance frequency analysis assessed by Osstell mentor during implant tissue integration: II. Implant surface modifications and implant diameter
.
Clin Oral Implants Res
.
2010
;
21
:
605
611
.
40
Rodrigo
D,
Aracil
L,
Martin
C,
Sanz
M.
Diagnosis of implant stability and its impact on implant survival: a prospective case series study
.
Clin Oral Implants Res
.
2010
;
21
:
255
261
.
41
Sim
CP,
Lang
NP.
Factors influencing resonance frequency analysis assessed by Osstell mentor during implant tissue integration: I. Instrument positioning, bone structure, implant length
.
Clin Oral Implants Res
.
2010
;
21
:
598
604
.
42
Sul
YT,
Jonsson
J,
Yoon
GS,
Johansson
C.
Resonance frequency measurements in vivo and related surface properties of magnesium-incorporated, micropatterned and magnesium-incorporated TiUnite, Osseotite, SLA and TiOblast implants
.
Clin Oral Implants Res
.
2009
;
20
:
1146
1155
.
43
Shokri
M,
Daraeighadikolaei
A.
Measurement of primary and secondary stability of dental implants by resonance frequency analysis method in mandible
.
Int J Dent
.
2013
;
2013
:
506968
.
44
Sennerby
L,
Meredith
N.
Implant stability measurements using resonance frequency analysis: biological and biomechanical aspects and clinical implications
.
Periodontol 2000
.
2008
;
47
:
51
66
.
45
Barikani
H,
Rashtak
S,
Akbari
S,
Fard
MK,
Rokn
A.
The effect of shape, length and diameter of implants on primary stability based on resonance frequency analysis
.
Dent Res J (Isfahan)
.
2014
;
11
:
87
91
.
46
Smith
DE,
Zarb
GA.
Criteria for success of osseointegrated endosseous implants
.
J Prosthet Dent
.
1989
;
62
:
567
572
.
47
Salvi
GE,
Lang
NP.
Diagnostic parameters for monitoring peri-implant conditions
.
Int J Oral Maxillofac Implants
.
2004
;
19
:
116
127
.
48
Loe
H.
The gingival index, the plaque index and the retention index systems
.
J Periodontol
.
1967
;
38
:
610
616
.
49
Mombelli
A,
van Oosten
MA,
Schurch
E
Jr,
Land
NP.
The microbiota associated with successful or failing osseointegrated titanium implants
.
Oral Microbiol Immunol
.
1987
;
2
:
145
151
.
50
Apse
P,
Zarb
GA,
Schmitt
A,
Lewis
DW.
The longitudinal effectiveness of osseointegrated dental implants. The Toronto Study: peri-implant mucosal response
.
Int J Perio Rest Dent
.
1991
;
11
:
94
111
.
51
Albrektsson
T,
Zarb
GA.
Current interpretations of the osseointegrated response: clinical significance
.
Int J Prosthodont
.
1993
;
6
:
95
105
.
52
Elsyad
MA,
Al-Mahdy
YF,
Fouad
MM.
Marginal bone loss adjacent to conventional and immediate loaded two implants supporting a ball-retained mandibular overdenture: a 3-year randomized clinical trial
.
Clin Oral Implants Res
.
2012
;
23
:
496
503
.
53
Zygogiannis
K,
Wismeijer
D,
Aartman
IH,
Osman
RB.
A systematic review on immediate loading of implants used to support overdentures opposed by conventional prostheses: factors that might influence clinical outcomes
.
Int J Oral Maxillofac Implants
.
2016
;
31
:
63
72
.
54
Meredith
N,
Alleyne
D,
Cawley
P.
Quantitative determination of the stability of the implant-tissue interface using resonance frequency analysis
.
Clin Oral Implants Res
.
1996
;
7
:
261
267
.
55
Brink
J,
Meraw
SJ,
Sarment
DP.
Influence of implant diameter on surrounding bone
.
Clin Oral Implants Res
.
2007
;
18
:
563
568
.
56
Turkyilmaz
I,
Tumer
C,
Ozbek
EN,
Tozum
TF.
Relations between the bone density values from computerized tomography, and implant stability parameters: a clinical study of 230 regular platform implants
.
J Clin Periodontol
.
2007
;
34
:
716
722
.
57
Ketabi
M,
Deporter
D.
The effects of laser microgrooves on hard and soft tissue attachment to implant collar surfaces: a literature review and interpretation
.
Int J Perio Rest Dent
.
2013
;
33
:
e145
e152
.
58
Nevins
M,
Nevins
ML,
Camelo
M,
Boyesen
JL,
Kim
DM.
Human histologic evidence of a connective tissue attachment to a dental implant
.
Int J Perio Rest Dent
.
2008
;
28
:
111
121
.
59
Trisi
P,
Rebaudi
A.
Progressive bone adaptation of titanium implants during and after orthodontic load in humans
.
Int J Perio Rest Dent
.
2002
;
22
:
31
43
.
60
Beer
A,
Gahleitner
A,
Holm
A,
Birkfellner
W,
Homolka
P.
Adapted preparation technique for screw-type implants: explorative in vitro pilot study in a porcine bone model
.
Clin Oral Implants Res
.
2007
;
18
:
103
107
.
61
Mustafa
K,
Wroblewski
J,
Hultenby
K,
Silva Lopez
B,
Arvidson
K.
Effects of titanium surfaces blasted with TiO2 particles on the initial attachment of cells derived from human mandibular bone: a scanning electron microscopic and histomorphometric analysis
.
Clin Oral Implants Res
.
2000
;
11
:
116
128
.
62
Schrotenboer
J,
Tsao
YP,
Kinariwala
V,
Wang
HL.
Effect of microthreads and platform switching on crestal bone stress levels: a finite element analysis
.
J Periodontol
.
2008
;
79
:
2166
2172
.
63
Al-Thobity
AM,
Kutkut
A,
Almas
K.
Microthreaded implants and crestal bone loss: a systematic review
.
J Oral Implantol
.
2017
;
43
:
157
166
.
64
Hudieb
MI,
Wakabayashi
N,
Kasugai
S.
Magnitude and direction of mechanical stress at the osseointegrated interface of the microthread implant
.
J Periodontol
.
2011
;
82
:
1061
1070
.
65
Albrektsson
T,
Zarb
G,
Worthington
P,
Eriksson
AR.
The long-term efficacy of currently used dental implants: a review and proposed criteria of success
.
Int J Oral Maxillofac Implants
.
1986
;
1
:
11
25
.
66
Zarb
GA,
Albrektsson
T.
Consensus report: towards optimized treatment outcomes for dental implants
.
J Prosthet Dent
.
1998
;
80
:
641
.
67
Roos
J,
Sennerby
L,
Lekholm
U,
Jemt
T,
Gröndahl
K,
Albrektsson
T.
A qualitative and quantitative method for evaluating implant success: a 5-year retrospective analysis of the Brånemark implant
.
Int J Oral Maxillofac Implants
.
1997
;
12
:
504
514
.
68
Albrektsson
T,
Zarb
GA.
Current interpretations of the osseointegrated response: clinical significance
.
Int J Prosthodont
.
1993
;
6
:
95
105
.
69
Rodrıguez
X,
Vela
X,
Mendez
V,
Segala
M,
Calvo-Guirado
JL,
Tarnow
DP.
The effect of abutment dis/reconnections on peri-implant bone resorption: a radiologic study of platform-switched and non-platform switched implants placed in animals
.
Clin Oral Implants Res
.
2013
;
24
:
305
311
.