Journal of Dental Implants

ORIGINAL COMPARATIVE STUDY
Year
: 2018  |  Volume : 8  |  Issue : 2  |  Page : 54--60

The effect of using prefabricated bars on marginal bone loss around tilted or axially placed and immediately loaded implants for retaining mandibular overdentures


Elsayed Abdallah Abdel-Khalek, Ahmed Khalifa Khalifa, Nesreen Elmekawy 
 Department of Prosthodontics, Faculty of Dentistry, Mansoura University, Mansoura, Egypt

Correspondence Address:
Dr. Nesreen Elmekawy
1 Mecka Street from Gyhan Street, Mansoura
Egypt

Abstract

Objectives: The goal of this study was to evaluate the effect of using prefabricated stress-free implant bar (SFI-Bar) on marginal bone loss around tilted or axially placed and immediately loaded two implants for retaining mandibular overdentures. Materials and Methods: Thirty patients with a mean age of 56.5 years were chosen. Patients were divided into two groups as follows: Group (AB) (n = 15): Patients received two axially implants connected by SFI-Bars for retaining mandibular overdentures. Group (TB) (n = 15): Patients received two mesially tilted implants connected by SFI-Bars for retaining mandibular overdentures. For each patient, two dental implants (3.8 mm × 12 mm) were bilaterally inserted in the canine regions. Implants were immediately loaded with SFI-Bar system overdentures. Digital periapical radiographs were scheduled at implant placement (baseline) and subsequently after every 12 months up to 36 months to measure peri-implant bone loss (PiBL). The recorded data were subjected to statistical analysis. Results: Both groups showed insignificant PiBL at 12 and 24 months, while at 36 months, patients in Group TB showed significantly higher marginal PiBL than that with Group AB. Conclusions: Prefabricated SFI-Bar retained mandibular overdentures could offer an alternative attachment for two angulated, immediately loaded implants with predictable radiographic outcomes.



How to cite this article:
Abdel-Khalek EA, Khalifa AK, Elmekawy N. The effect of using prefabricated bars on marginal bone loss around tilted or axially placed and immediately loaded implants for retaining mandibular overdentures.J Dent Implant 2018;8:54-60


How to cite this URL:
Abdel-Khalek EA, Khalifa AK, Elmekawy N. The effect of using prefabricated bars on marginal bone loss around tilted or axially placed and immediately loaded implants for retaining mandibular overdentures. J Dent Implant [serial online] 2018 [cited 2019 Aug 21 ];8:54-60
Available from: http://www.jdionline.org/text.asp?2018/8/2/54/247582


Full Text

 Introduction



Rehabilitating edentulous patients with residual ridge resorption has been improved tremendously because of modern implant dentistry.[1],[2],[3] Moreover, implant overdentures, are notarized as a cost-effective and reliable treatment option for total edentulism.[1],[2] The York consensus statement in 2009 confirmed that the treatment with mandibular two implant-supported overdentures is considered as the standard of care for edentulous patients.[1]

Excellent results have been reported for immediately loaded implants supporting overdentures and revealed predictable outcomes.[4] This concept permits far less invasive protocol and has been proposed to reduce treatment time, avoid complications, and reduce overall cost.[4],[5],[6] However, different attachment systems for implant overdentures are available including splinting bars, ball attachment, double crowns, or stud-type such as locators and magnets.[7] Bar attachments and double crowns were reported to offer advantages in elderly patients with manual limitations and in cases with atrophic jaws.[8]

The primary goal of using bar joint attachment, with implant-retained overdentures, is to allow free rotation of the denture base around the supporting implants to minimize the bending moments.[9],[10],[11] The optimal forces transmission among the implants through the splinting effect is documented to be the most favorable biomechanical condition that maintain the initial primary stability and preserve the long-term success of the osseointegrating implants.[5],[12],[13]

Unfortunately, the laboratory processed conventional bars may be subjected to impaired fabrication conditions such as making the impression procedures during wound bleeding or a swollen mucosa, inaccuracies of the master cast, or metal casting artifacts.[14] With the exception of rigid splinting, the tilted implants are a poor candidate for immediate loading that horizontal stress rather than axial loading adversely affect the clinical success of implant overdentures.[5],[13] However, with modern planning for implant placement; the clinician may be obligated to angulate the implant fixtures because of the anatomical limitations such as compromised ridge contour.[14],[15],[16],[17] The alternative option is maintaining the axially placed implants with subsequent use of delayed loading protocol with the invasive grafting procedures.[5],[18]

Stress-Free Implant Bar (SFI-Bar) is a prefabricated attachment system that passively connects two or more implants with no soldered or laser welded joints.[6],[14],[19],[20] When the immediate loading protocol is adopted, and despite the advantages produced by individual attachments, SFI-Bar combines the advantages of both bars and studs attachment systems.[15] In this type of bars, all parts can be processed chairside, and no impression taking is necessary. The possibility of convenient cleaning with minimal plaque adhesion on the highly polished prefabricated attachments is another advantage.[16]

Concerning the angulation of the implants, it was advocated that SFI-Bar adaptor permits 30° for the tilted implants and allows fabrication of a passive-fit bar and clip system.[19],[20] The presence of Bar-Abutment joint in the SFI-Bar design can dramatically alters the direction and magnitude of forces, on the implants with direct clinical effect on the peri-implant marginal bone.[14],[21] Monitoring marginal bone height, and its changes over time, around the implants in standardized and serial radiographs are considered to be an important parameter for the implants success.[22],[23]

According to the authors' knowledge about SFI-Bar studies, the effect of offset loads transferred via the denture base to the implant fixtures and surrounding bone is not sufficiently reported in the literature. Thus, the goal of this study was to evaluate the effect of using prefabricated SFI-Bar on peri-implant bone loss (PiBL) around immediately loaded bilateral axially or 15° mesially-tilted two implants retaining mandibular overdentures.

 Materials and Methods



Study setup and patient selection

This study was performed, on 30 patients (22 men and 8 women) who were fully edentulous with a mean age of 56.5 years (range: 48–64 years). The study was carried out on patients already treated with complete dentures that were fulfilled all conventional prosthodontics criteria,[3] from January 2013 to May 2017, in the Department of Removable Prosthodontics, Mansoura University, Egypt. All dentures were assessed using modified Kapur's method according to Olshan et al.[24] Clinically, well-fitting dentures were defined having sum score ≥6 for retention and stability of both maxillary and mandibular dentures.

All patients had been complaining from instability and poor retention of their mandibular dentures. After explanation of all study procedures, patients who were expressed interesting in participating in the study were asked to sign informed written consents, i.e., “Informed consent was obtained from all individual participants included in the study.” The study protocol and objectives were revised and approved by the Dental Research Ethical Committee of the faculty of dentistry, Mansoura University.

The selected patients had the following criteria: mandibular atrophied ridge with at least 15 mm of estimated anterior bone height measured on the panoramic radiograph (Orthophos XG Plus, Sirona Dental System, Germany). A minimum of 14 mm vertical space from the ridge crest at the proposed implant sites to the incisal edge of the artificial teeth. Adequate bone quality with higher bone density (D2 or D3) should be radiographically diagnosed to ensure primary implant stability. Patients must be free from any tempro-mandibular disorders or neuromuscular diseases.

Patients were excluded when they exhibited the following criteria (based on history and clinical examinations): health conditions that precluded surgical treatment, local bony defects at the planned implant areas such as previous tumors, chronic bone diseases, administered steroid therapy or bisphosphonates, habits such as alcohol or drug abuse, heavy smoking (>10 cigarettes per day), poorly controlled diabetes, radiotherapy to head or neck region, and high parafunctional habits such as clenching or bruxism.

Presurgical procedures

All participants were examined and their dentures were clinically assessed. The available restorative space was evaluated using Boley gauge through measuring the distance from the fitting surfaces of mandibular dentures to their incisal edges. A mucosally-supported stereolithographic surgical guide was fabricated for flapless implant placement in each patient using cone-beam computerized tomography scans and prototyping technology by following the dual-scan method.[25]

During virtual planning procedures, each implant was placed axially at least 5 mm away from the anterior wall of the mental nerve loops bilaterally or tilted mesially at 15° from the vertical axis. Patients were randomly divided into two equal groups as follows: Group (AB) (n = 15): Where each patient received two axially parallel implants connected by SFI-Bars for retaining mandibular overdentures [Figure 1]a. Group (TB) (n = 15): Where each patient received two 15° mesially tilted implants connected by SFI-Bars for retaining mandibular overdentures [Figure 1]b.{Figure 1}

Surgical procedures

Patients administered 2 g of prophylactic amoxicillin/clavulanate potassium antibiotic (Augmentin, GlaxoSmithKline, Egypt) as a single dose 1 h before surgery. Local anesthesia solution of 1:100,000 mepivacaine with epinephrine was infiltrated to the anterior mandible. Two implant fixtures (12 mm length with 3.8 mm diameter) were placed in the canine regions bilaterally (BioHorizons implant systems Inc., USA) by using flapless surgical protocol.[25] After using tissue punch and sequential drilling for preparing the implant bed, osteotomy sites were irrigated by copious amounts of sterile normal saline as recommended by the manufacturer. Each implant was placed at 30 rpm insertion speed with 75 Ncm torque as recommended. A manual torque of at least 45 Ncm was applied with a torque wrench, and then the initial stability of implant stability quotient (ISO) ≥60 was verified by using the resonance frequency analysis (Osstell ISQ, Gothenburg, Sweden), according to West and Oates.[13]

Prosthetic procedures

The two implants were connected by SFI-Bars (C+M, Biel/Bienne, Switzerland) and immediately loaded by the mandibular denture in the same appointment as follows: SFI-Bar implant adapters of 3 mm gingival height were screwed into the implants at 20 Ncm torque. According to the manufacturer's guidelines, the bar was directly adapted and mounted on the adapters based on the proper length of the hollow tube and its ball joints at each end [Figure 2].[6]{Figure 2}

After assembling the bar by screwing the ball joints, the intaglio surface of the existing mandibular denture was perforated lingual to the artificial teeth, extending from canine to canine. Lingual denture perforation exposed the bar assembly and allowed denture seating over SFI-Bar without interferences. A single T-clip (all titanium Grade IV with nylon insert) was snapped on the middle of the bar followed by blocking out space under the bar by baseplate wax (Cavex, Holland). Bar clips were picked up using auto polymerized acrylic resin while the patient closed his/her mouth on maximal intercuspal position. A minimum thickness of 2 mm of acrylic resin was maintained to ensure denture base strength. After trimming the excess resin and polishing, the denture was immediately re-inserted. The occlusal relation was verified and refined if needed. Patients were instructed not to remove dentures for 48 h; and they were limited to a soft diet for 4 weeks. Postoperative prophylactic antibiotic and 0.2% chlorhexidine mouthwash were administrated and continued for 3–5 days postoperatively. The patients were seen 1 day after surgery and then follow-up visits for radiographic assessment were arranged.

Evaluation peri-implant bone loss

Follow-up visits were scheduled for the 1st week after surgery for postinsertion adjustments and checking the occlusion. The patients were scheduled annually up to 3 years after implant placement. The denture base–ridge relation was assessed at each recall appointment for possible relining procedures. Digital periapical radiographs were performed using the long cone paralleling technique aided with customized film aiming device (XCP holder; Dentsply, USA).[22] Time intervals were scheduled at immediate implant placement (baseline) and subsequently after every 12 months up to 36 months. Radiographic measurements were interpreted on the radiograph by using software (Corel Draw v12.iso, Corel Corp., Canada) at ×400. After applying a distortion coefficient to correct dimensional distortion in the radiographic image, the distance from the implant shoulder to the most coronal point of bone-implant contact was measured mesially and distally [Figure 3]. The data were recorded, and PiBL was calculated by subtracting bone levels at each time interval from the baseline value.[22] Mean values of bone loss at the right and left implants were recorded as PiBL for each patient. The collected data were tabulated for statistical analysis.{Figure 3}

Data analysis

Data were entered and statistically analyzed using the Statistical Package for Social Sciences (SPSS) version 20 (SPSS IBM Inc., England). Quantitative data were described as mean and standard deviation after testing normality by Kolmogorov–Smirnov test. Student t-test was used for comparison between two groups. Pearson correlation coefficient used for parametric correlation between continuous variables.-“P ≤ 0.05” was considered to be statistically significant. All tests were two-tailed.

 Results



[Table 1] compares PiBL between AB and TB at different time intervals. There were the insignificant difference in PiBL between AB and TB at 12 and 24 months. At 36 months, the PiBL in TB (0.35 ± 0.04) was significantly higher than AB (0.30 ± 0.06) (P = 0.01).{Table 1}

On comparing PiBL of the mesial aspect of both groups, PiBL in TB recorded a significant increase at 12 and 36 months (0.19 ± 0.01 and 0.28 ± 0.03, respectively) in comparison to AB (0.17 ± 0.01 and 0.24 ± 0.05, respectively) while at 24 months. AB showed a statistically significant higher PiBL (P = 0.001) as shown in [Table 2].{Table 2}

Comparing PiBl on the distal aspect of both groups, [Table 2] shows a statistically nonsignificant difference between groups at 12 months. However, the recorded PiBL at 24 and 36 months was 0.35 ± 0.05 and 0.42 ± 0.04, respectively, for TB and was 0.30 ± 0.06 and 0.36 ± 0.08, respectively, for AB with a significantly higher PiBL in TB group (P = 0.04 and P = 0.02, respectively).

The present study showed a statistically significant weak positive correlation between the PiBL and time of measurements for either AB group (r = 0.46) or TB group (r = 0.56) that was presented in [Table 3] and [Figure 4].{Table 3}{Figure 4}

In relation to time of measurement, linear regression analysis for prediction of PiBL in each group revealed a statistically significant predictor of 17.6% and 19% (where R2 = 0.176 and 0.19) for AB and TB, respectively. At a certain time, a predictable PiBL for each group could be calculated by the following equation:

Predictable PiBL for Group AB = 0.17 + (0.04 multiplied by Time of measurement [in months])Predictable PiBL for Group TB = 0.13 + (0.06 multiplied by Time of measurement [in months]).

 Discussion



Bar attachments had been highly recommended for the immediate rehabilitation of edentulous mandibles, particularly when discrepancies in angulations of implants exist.[5],[12] Several researchers proposed that rigid splinting of tilted implants would counteract the bending effects of lateral forces on the implant attachments and thus optimize the treatment outcome through the cross-arch stability.[7],[8],[9],[10],[11],[12]

Placing tilted implants is considered a less invasive alternative solution to ridge augmentation.[14] From a biomechanical point of view, implants should be placed in line to the direction of the occlusal loading. Therefore, tilted implants could theoretically receive accentuated nonaxial forces that result in the higher moment with damaged bone-implant contact as a result from torsional forces to the surrounding bone.[18],[21] However, residual ridge reduction in anterior mandibular regions often preclude placement of axial standard implants.[17] In the last few years, a chair-side SFI-Bar was introduced for an immediate loading protocol that permits the elimination of intermediate laboratory errors and offers time-saving during fitting the bar.[6],[14],[20]

In the current study, the authors tried to control potential confounding factors that would have negative impacts on the implants supporting the mandibular overdentures.[11] The use of opposing maxillary denture with the standardized occlusal scheme and proper functional adaptation of the prosthesis to eliminate the higher magnitude of stresses induced by opposing natural dentition or by a fixed prosthesis.[21],[26]

An implant length of 12 mm inserted in D2 or D3 bone quality were used in the current study to ensure primary stability that is a prerequisite for immediate loading protocol as stated by Chrcanovic et al.[11] Standardized intra-oral periapical radiographs are used in the study instead of panoramic imaging because of the reported accuracy of long cone paralleling technique parallel cone technique for evaluating PiBL with the advantage of minimal radiation dose.[22],[24]

The present study revealed that PiBL in TB group was not significantly different from AB group during the 1st and 2nd years with less PiBL in TB group, which agreed with Lehmann et al.[17] This lack of significance may be explained by the relatively long implants (>10 mm) used in the study and cross arch splinting effect of the bar.[18] At the 3rd follow-up year, the study recorded statistically significant differences in PiBL between both groups that may be a result of the accumulated biomechanical effect of functional forces on the tilted implants.[27]

In a systematic review, Monje et al.[18] found no statistical differences for tilted implants compared to straight implants in the short and medium terms; however, tilted implants lost more PiBL. In this line, Chrcanovic et al.[11] and, Wentaschek et al.[28] systematically reviewed the changes in bone loss around axially versus tilted implants with no or small differences were reported, primarily in favor of axial implants.

The current study observed a significant increased PiBL at the mesial aspect of group AB compared to group TB after the second follow-up year. This increase may be attributed to the difficulty in cleaning the gap formed at the angle between the undersurface of the bar and the bar abutments. Therefore, accumulation of plaque and pathogenic microflora favor the narrower inaccessible right angle of axially placed implants rather than a cleansable obtuse angle formed at the tilted implants. This explanation could be confirmed by the mucosal hyperplasia observed in the first 18 months following the placement of the denture in the study of Wright et al.[10] Additionally, it was reported that these sites have been associated with increased plaque accumulation and presence of microflora that results in increased probing depth and subsequent PiBL.[11]

The nonsignificant difference in PiBL at distal aspect between both groups was recorded during the 1st year. This result may be attributed to the possibility of convenient cleansing at the distal aspect of the implants that permits better plaque control.[16] However, after 2nd and, 3rd years, increased PiBL measured on the distal aspect in TB group may be explained by soft-tissue impingement at the distal aspect of the mesially inclined implant because of free denture rotation as described in the 3 years study performed by Wright et al.[10]

Moreover, horizontal denture movements in conjunction with the presence of free joint between the bar tube and the abutments may decrease the effectiveness of splinting action with SFI-Bars and increase the horizontal forces on the tilted implants in a similar response to individual attachments under function.[6],[10],[11],[18] The findings of previous experimental study[29] and animal study.[30] reported that the areas of concentrated tensile stresses are associated with more bone loss at the opposite side of the implant inclinations.

PiBL in the present study correlated positively with increased follow-up time, especially for tilted implants. This observation could be due to the continued resorption of the residual ridge under the prosthesis, thus may exacerbate the unfavorable loading direction and induces greater bone loss around nonaxial implants.[10],[11]

Despite the frequent postinsertion care and adjustments provided to the patients during follow-up visits in this study, unavoidable ridge resorption could occur by posterior loading and downward rotation of the denture base around the anteriorly placed hinged bar.[9]

In general, there was a significant difference between study groups, means of PiBL recorded for both AB and TB groups lied within the normal range of acceptable criteria for implant success. The majority of bone loss occurred during the 1st year in accordance with short-term and medium-term systematic reviews done by Sannino and Barlattani.[5] PiBL measurements did not exceed 0.2 mm annually after the 1st year of function.[23]

The present study recorded PiBL smaller than the study of Marzola et al.[26] who reported an average marginal bone loss of 0.7 mm for two immediately loaded unsplinted implants after a 1-year follow-up period. After 24 weeks of follow-up, Tözüm et al.[31] observed 0.14 mm bone loss around two individual immediately loaded implants compared to 0.22 mm bone loss for delayed loaded implants. This explained the role of SFI-Bars and their effectiveness in better splinting of implants in comparison to individual attachments under functional loading.

The present study included some limitations. First, the study assessed the implants only in mesiodistal direction, whereas buccolingual direction might be of equal importance for treatment outcomes. Second, the reduced number of published similar studies makes drawing a definitive conclusion a questionable. Third, the current study does not report on soft-tissue conditions around the implants. Fourth, the reported outcomes in short-term follow-up may be changed with further clinical long-term observations.

Further studies are needed to investigate the effect of different implant inclinations on this type of chair-side prefabricated bars. The continuing need for regular recall may be a matter of importance for mandibular SFI-Bars retained overdentures that may be proved by future long-term clinical studies.

 Conclusions



According to the present results and within the limitations of this 3-year study, it could be concluded that;

SFI-Bar could offer an alternative attachment for angulated and immediately loaded implants to retain mandibular overdentures with predictable radiographic outcomesPlacing dental implants axially and perpendicular to the occlusal plane, whenever possible, should be planned for mandibular overdentures retained by SFI-BarsFurther long-term prospective clinical trials are needed to investigate the clinical and prosthetic outcomes of this treatment option.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

References

1Thomason JM, Feine J, Exley C, Moynihan P, Müller F, Naert I, et al. Mandibular two implant-supported overdentures as the first choice standard of care for edentulous patients – The york consensus statement. Br Dent J 2009;207:185-6.
2Sadowsky SJ. Mandibular implant-retained overdentures: A literature review. J Prosthet Dent 2001;86:468-73.
3Zarb G, Hobkirk J, Eckert S, Jacob R, editors. Prosthodontic Treatment for Edentulous Patients: Complete Dentures and Implant-Supported Prostheses. 13th ed. St. Louis: Elsevier Mosby; 2013. p. 269.
4Stoker GT, Wismeijer D. Immediate loading of two implants with a mandibular implant-retained overdenture: A new treatment protocol. Clin Implant Dent Relat Res 2011;13:255-61.
5Sannino G, Barlattani A. Straight versus angulated abutments on tilted implants in immediate fixed rehabilitation of the edentulous mandible: A 3-year retrospective comparative study. Int J Prosthodont 2016;29:219-26.
6Kim HY, Kim RJ, Qadeer S, Jeong CM, Shin SW, Huh JB, et al. Immediate loading on mandibular edentulous patient with SFI bar® overdenture. J Adv Prosthodont 2011;3:47-50.
7Zitzmann NU, Rohner U, Weiger R, Krastl G. When to choose which retention element to use for removable dental prostheses. Int J Prosthodont 2009;22:161-7.
8Stoumpis C, Kohal RJ. To splint or not to splint oral implants in the implant-supported overdenture therapy? A systematic literature review. J Oral Rehabil 2011;38:857-69.
9Wright PS, Watson RM. Effect of prefabricated bar design with implant-stabilized prostheses on ridge resorption: A clinical report. Int J Oral Maxillofac Implants 1998;13:77-81.
10Wright PS, Watson RM, Heath MR. The effects of prefabricated bar design on the success of overdentures stabilized by implants. Int J Oral Maxillofac Implants 1995;10:79-87.
11Chrcanovic BR, Albrektsson T, Wennerberg A. Tilted versus axially placed dental implants: A meta-analysis. J Dent 2015;43:149-70.
12de Almeida EO, Rocha EP, Assunção WG, Júnior AC, Anchieta RB. Cortical bone stress distribution in mandibles with different configurations restored with prefabricated bar-prosthesis protocol: A three-dimensional finite-element analysis. J Prosthodont 2011;20:29-34.
13West JD, Oates TW. Identification of stability changes for immediately placed dental implants. Int J Oral Maxillofac Implants 2007;22:623-30.
14Albrecht D, Ramierez A, Kremer U, Katsoulis J, Mericske-Stern R, Enkling N. Space requirement of a prefabricated Bar on two interforaminal implants: A prospective clinical study. Clin Oral Implants Res 2015;26:143-8.
15Sugiura T, Yamamoto K, Horita S, Murakami K, Tsutsumi S, Kirita T, et al. Effects of implant tilting and the loading direction on the displacement and micromotion of immediately loaded implants: An in vitro experiment and finite element analysis. J Periodontal Implant Sci 2017;47:251-62.
16Abd El-Dayem MA, Assad AS, Eldin Sanad ME, Mahmoud Mogahed SA. Comparison of prefabricated and custom-made bars used for implant-retained mandibular complete overdentures. Implant Dent 2009;18:501-11.
17Lehmann KM, Kämmerer PW, Karbach J, Scheller H, Al-Nawas B, Wagner W, et al. Long-term effect of overdenture bar design on peri-implant tissues. Int J Oral Maxillofac Implants 2013;28:1126-31.
18Monje A, Chan HL, Suarez F, Galindo-Moreno P, Wang HL. Marginal bone loss around tilted implants in comparison to straight implants: A meta-analysis. Int J Oral Maxillofac Implants 2012;27:1576-83.
19Wei L, Ma Q, Qin X, Pan S.In vitro cyclic dislodging test on retentive force of two types of female parts of SFI-bar. Int J Prosthodont 2016;29:293-5.
20Ha SR, Kim SH, Song SI, Hong ST, Kim GY. Implant-supported overdenture with prefabricated bar attachment system in mandibular edentulous patient. J Adv Prosthodont 2012;4:254-8.
21Zygogiannis 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.
22Hegazy S, Elmekawy N, Emera RM. Peri-implant outcomes with laser vs. nanosurface treatment of early loaded implant-retaining mandibular overdentures. Int J Oral Maxillofac Implants 2016;31:424-30.
23Albrektsson 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.
24Olshan AM, Ross NM, Mankodi S, Melita S. A modified Kapur scale for evaluating denture retention and stability: Methodology study. Am J Dent 1992;5:88-90.
25D'haese J, De Bruyn H. Effect of smoking habits on accuracy of implant placement using mucosally supported stereolithographic surgical guides. Clin Implant Dent Relat Res 2013;15:402-11.
26Marzola R, Scotti R, Fazi G, Schincaglia GP. Immediate loading of two implants supporting a ball attachment-retained mandibular overdenture: A prospective clinical study. Clin Implant Dent Relat Res 2007;9:136-43.
27Kobayashi M, Srinivasan M, Ammann P, Perriard J, Ohkubo C, Müller F, et al. Effects of in vitro cyclic dislodging on retentive force and removal torque of three overdenture attachment systems. Clin Oral Implants Res 2014;25:426-34.
28Wentaschek S, Lehmann KM, Scheller H, Weibrich G, Behneke N. Polygonal area of prosthesis support with straight and tilted dental implants in edentulous maxillae. Int J Prosthodont 2016;29:245-52.
29Watanabe F, Hata Y, Komatsu S, Ramos TC, Fukuda H. Finite element analysis of the influence of implant inclination, loading position, and load direction on stress distribution. Odontology 2003;91:31-6.
30Barbier L, Schepers E. Adaptive bone remodeling around oral implants under axial and nonaxial loading conditions in the dog mandible. Int J Oral Maxillofac Implants 1997;12:215-23.
31Tözüm TF, Turkyilmaz I, Yamalik N, Karabulut E, Eratalay K. Analysis of the potential association of implant stability, laboratory, and image-based measures used to assess osteotomy sites: Early versus delayed loading. J Periodontol 2007;78:1675-82.