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ORIGINAL ARTICLE
Year : 2022  |  Volume : 12  |  Issue : 1  |  Page : 38-44

Comparative evaluation of bone density changes around root-form, threaded collar, two-piece endosseous implants at three different levels as influenced by early loading and conventional loading protocols using cone-beam computed tomography: An in vivo study


1 Department of Prosthodontics and Crown and Bridge, ITS-CDSR, Muradnagar, Uttar Pradesh, India
2 Department of Oral Medicine and Radiology, Divya Jyoti (DJ) Dental College, Modinagar, Uttar Pradesh, India

Date of Submission01-Oct-2021
Date of Acceptance27-Feb-2022
Date of Web Publication16-Jun-2022

Correspondence Address:
Dr. Shuja Mohammed Khan
Senior Lecturer, Department of Prosthodontics Including Crown & Bridge, Maxillofacial Prosthodontics & Oral Implantology, I.T.S Centre for Dental Studies and Research, Muradnagar, Ghaziabad - 201 206, Uttar Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jdi.jdi_21_21

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   Abstract 

Background: Understanding the changes in bone density after insertion of dental implants and their relation to immediate/early loading is essential to achieving improvements in their survival rate. Histological investigations of the bone bed in humans are limited, which in turn hampers opportunities to deepen knowledge about the remodeling process around dental implants.
Purpose: The aim of this pilot study was to comparatively evaluate the bone density changes around root-form, threaded collar, two-piece endosseous implants at three different levels as influenced by early and conventional protocols using cone-beam computed tomography (CBCT).
Methodology: Twenty implants were placed in 20 patients who were randomly assigned to two groups. Group A (n = 10 implants, 10 patients) received conventional loading protocol and Group B (n = 10 implants, 10 patients) followed early loading protocol following implant placement. Bone density changes were evaluated and compared as influenced by early and conventional protocols using CBCT (gray values).The gray values were measured at the apical level, middle region of radiological implant length, and at the crestal level. The measurements were made immediately (T0) and 36 weeks (T1) post implant placement.
Results: Intergroup comparison of bone density changes was done between Group A (conventional loading) and Group B (early loading) from immediate post implant placement to 36 weeks post implant placement follow-up. From immediate post implant placement to follow-up, significant difference was seen in bone density of Group A and Group B at apical and middle levels as P < 0.05, but at crestal level, no significant difference was seen.
Conclusion: Under the conditions of this study, early loading significantly densified more bone as compared to conventional loading. Further studies are required to determine CBCT gray values and its correlation with computed tomography Hounsfield units for quantification of the bone.

Keywords: Bone density, cone-beam computed tomography, conventional loading, early loading, gray levels


How to cite this article:
Khan SM, Kumar M, Issar G, Dhillon M, Poduval T S, Tyagi S. Comparative evaluation of bone density changes around root-form, threaded collar, two-piece endosseous implants at three different levels as influenced by early loading and conventional loading protocols using cone-beam computed tomography: An in vivo study. J Dent Implant 2022;12:38-44

How to cite this URL:
Khan SM, Kumar M, Issar G, Dhillon M, Poduval T S, Tyagi S. Comparative evaluation of bone density changes around root-form, threaded collar, two-piece endosseous implants at three different levels as influenced by early loading and conventional loading protocols using cone-beam computed tomography: An in vivo study. J Dent Implant [serial online] 2022 [cited 2022 Jul 7];12:38-44. Available from: https://www.jdionline.org/text.asp?2022/12/1/38/347663


   Introduction Top


The clinical application of the concept of osseointegration introduced in the mid-sixties soon showed predictable long-term success.[1] Nowadays, the use of implants is even popular in the replacement of a single missing tooth.[2] In several studies, immediate or early loading of dental implants has shown a high implant success rate and improvement in bone formation around the implants.[3],[4] Regardless of protocol, i.e., delayed or immediate loading, the development of osseointegration as defined by Albrektsson et al. is a major factor determining clinical success after implant placement.[5]

A large body of scientific evidence of varying quality has demonstrated that successful outcomes can be achieved with different clinical treatment protocols for a wide range of indications. Loading protocols for dental implants have been a central focus of discussion in the field since the origin of osseointegration.

The insertion of implants according to traditional protocols includes a prolonged period of healing time, especially if the treatment involves tooth extraction and healing before implant surgery. The use of immediate ⁄ early-loaded implants has obvious advantages because patients can be rehabilitated with functional crowns for immediate function and esthetics.[6]

Frost[7] reported on the cellular reaction of bone to different microstrain levels. These four zones include the acute disuse window, the adapted window, the mild overload zone, and the pathologic overload zone. When bone has an ideal strain (50–1500 microstrain), it remains organized, mineralized, and the ideal load-bearing bone (adapted window). Bone remains in a steady state, and this may be considered the homeostatic window of health. The histologic description of this bone is primarily lamellar or load-bearing bone. This is the range of strain ideally desired around an endosteal implant, once a stress equilibrium has been established.

The ideal goal of a radiographic examination is to achieve as much information as possible about the jawbone while minimizing the radiation burden to the patient according to the ALARA principle (as low as reasonably achievable) and the costs.

There have been several approaches to study bone reaction and healing around dental implants. These studies are mostly based on experimental and histological investigations on animals.[8],[9] The lack of histological investigations in humans makes understanding of the healing processes of the bone around dental implants difficult. One possible approach is to follow up the change in bone density based on the Hounsfield units of computed tomography (CT) or the gray levels of cone-beam computed tomography (CBCT). The frequent exposure of the patients to CT increases the risk of overdoses of radiation, which is the main reason for the limitation of the use of CT for monitoring the change in bone density.

Conventional loading protocol provides successful outcome in most of the situations. However, the literature reveals that the clinical and histological studies of early loading protocol is a useful and viable option beside the classic conventional loading protocol. As there is an increase in esthetic and clinical demands, this study is an attempt to follow and compare the changes in bone density around endosseous intraoral implants following early loading versus conventional loading protocols dental implants using CBCT.


   Methodology Top


Clinical data and sample size

This study was conducted in the Department of Prosthodontics and Crown and Bridge of I. T. S. Centre for Dental Studies and Research, Delhi-Meerut Road, Ghaziabad, from November 2018 to October 2020. A total of 30 patients were initially recruited from the outpatient department of our institute. Seven patients did not fulfill the inclusion criteria and three patients refused to participate in the study. Twenty male patients of mean age 35.1 ± 6.8 years (range: 26–45 years) participated in the study. The study was approved by the Institutional Ethical Committee and was conducted according to the principles outlined in the Helsinki Declaration for biomedical research involving human subjects. The clinical trial was not registered. Written informed consent was obtained from the patients before their inclusion in the study.

The selection criteria included mandibular first molar/premolar monoedentulous site; tooth extraction at least 6 months before implant surgery; nongrafted implant site; Type 2 or 3 bone quality according to the Lekholm and Zarb classification;[10] adequate space with buccolingual width of minimum 6 mm and mesiodistal width of minimum 8 mm; interocclusal distance >6 mm, and wherein primary stability with minimum torque of 20–45 Ncm was achieved following implant placement. Any systemic illness that contraindicates surgery; uncontrolled diabetes mellitus; bisphosphonate therapy; history of radiotherapy in the maxillofacial region within the last 12 months; smoking; parafunctional habits; poor oral hygiene with full-mouth plaque score and full-mouth bleeding score ≥25%; periodontally compromised patients with attachment loss ≥3 mm; and/or radiographic bone loss ≥30% of root length in ≥30% of sites and those who refused to return for follow-up were excluded from this study.

A sample size of 10 implants per group was determined (statistical power = 80%; confidence level = 95%), considering the mean crestal bone level difference between two groups as 7.2, standard deviation of 5.4, and 20% follow-up loss. Therefore, one implant per patient was placed by randomly distributing patients into two separate groups.

For the treatment allocation, numbered sealed envelopes were used. Group A (n = 10 implants, 10 patients) received conventional loading protocol and Group B (n = 10 implants, 10 patients) followed early loading protocol post implant placement.

Surgical implant placement

Standard surgical protocol was followed for implant placement in the mandibular posterior edentulous site. Strict asepsis was maintained during the surgery. Lignocaine hydrochloride 2% with adrenaline (1:100,000) was used for infiltration. Custom-made surgical guides were used for implant placement. Full-thickness mucoperiosteal flap was elevated following mid-crestal incision and the osteotomy was done under copious normal saline irrigation. The bone level tapered implants (Touareg-S, Adin Dental Implant System Ltd., Afula, Israel) with aluminum oxide-blasted/acid-etched surface of 10 mm–11.5 mm length with a diameter of 3.75 mm were placed. Implant placement was done flush with the bone crest in accordance to the clinical protocol following the manufacturer's instructions. Only those implants which achieve primary stability with a minimum torque of 35 Ncm were included in the study. Submerged healing was followed in Group A and nonsubmerged healing was followed in Group B. All the patients were prescribed amoxicillin/clavulanic acid 625 mg orally every 8 h for 7 days, starting 1 h before surgery, diclofenac sodium 50 mg orally every 8 h for 3 days, and 0.12% chlorhexidine mouth rinse three times daily for 7 days.

Prosthetic phase

The first/baseline CBCT was taken immediately post implant placement to assess bone density changes around the implants.

Suture removal was done after 7 days of implant placement in Group B patients (early loading protocol). An abutment was placed followed by an abutment level alginate impression. Provisional crowns were fabricated using CAD-CAM milled PMMA and were cemented on the 8th day of post implant placement using RelyX™ temporary cement.

Second stage surgery was performed after 8 weeks of implant placement. Healing abutment/gingival former was placed at a torque of 20 Ncm for 7–10 days in Group A patients (Conventional Loading protocol). Rigid fixation of implant at the time of definitive prosthetic loading was assessed using clinical criteria proposed by Albrektsson et al.[5]

For both the groups, an implant level impression was obtained. A perforated custom tray was fabricated and tray adhesive was applied on it. Polyether impression material was used for making impression in a custom-made acrylic tray. Implant analog was screwed onto the impression post, gingival mask (Gingitech, Ivoclar Vivadent Inc., USA) was applied and cast poured in die stone (Type IV), (Ultrarock, Kalabhai Dental Pvt. Ltd., Mumbai, India). Facebow record was transferred to semi-adjustable articulator (Hanau Wide-Vue Semi-Adjustable Articulator, Whip Mix Corporation, USA). Abutment was modified according to the height required for the prostheses.

For both Group A and Group B patients, metal-ceramic crowns were fabricated following implant-protected occlusion guidelines. After making occlusal adjustments, cementation was done using conventional glass-ionomer cement. The second CBCT was done 36 weeks post implant placement to assess bone density changes at three different levels.

Radiological evaluation of bone density changes

In our study, Newtom Giano (CEFLA S. C. – CEFLA DENTAL GROUP, Italy) CBCT unit was used. For standardization, the orientation beam was used to align the jaw bone parallel to the reference surface. The tube voltage was 85 kVp–90 kVp and the tube current was 10 mA with exposure time of 12 s. Field of view (FOV) selected for each CBCT was 5 cm × 5 cm. Interactive CBCT image processing software NNT (CEFLA S. C. – CEFLA DENTAL GROUP, Italy) was used to measure the gray values.

Bone density changes were evaluated and compared at three different levels as influenced by early and conventional protocols using CBCT (gray values). The gray values were measured at the apical level, middle region of radiological implant length, and at the crestal level. A coronal view along the middle of the implant was used to measure the gray values in the three regions mesially and distally, while a sagittal view along the middle of the implant was used to measure the gray values buccally and lingually [Figure 1]. As the titanium artifact at the bone–implant interface was within 0.5 mm for all the CBCT data, the values were registered at a distance of 2 mm from the implant in a spot diameter of 2 mm.[2] The CBCT scans were conducted at two time intervals, i.e., immediately post implant placement [Figure 2] and [Figure 3] and at 36 weeks of post implant placement [Figure 4] and [Figure 5].
Figure 1: Orientation of cone-beam computed tomography scan

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Figure 2: Gray value readings on lingual aspect at crestal, middle, and apical regions (post implant placement)

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Figure 3: Gray value readings on distal aspect at crestal, middle, and apical regions (post implant placement)

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Figure 4: Gray value readings on lingual aspect at crestal, middle, and apical regions (36-week follow-up)

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Figure 5: Gray value readings on distal aspect at crestal, middle, and apical regions (36-week follow-up)

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Statistical analysis

The data were entered in Microsoft Excel format and were analyzed using IBM SPSS Statistics for Windows, version 22 (IBM Corp., Armonk, N.Y., USA). Independent t-test was used for inferential statistics. The results were shown as mean ± standard error (SE). Level of statistical significance was set at P < 0.05.


   Results Top


Descriptive analysis of bone density in Group A (conventional loading) and Group B (early loading) showing mean, SD, and SE mean at apical level, middle region of radiological implant length, and at the crestal level using CBCT immediately and at 36 weeks of post implant placement (follow-up) is represented in [Table 1] and [Table 2]. Intergroup comparison of bone density changes was done between Group A (conventional loading) and Group B (early loading) from immediate post implant placement to 36 weeks post implant placement follow-up. From immediate post implant placement to follow-up, significant difference was seen in bone density of Group A and Group B at apical and middle levels as P < 0.05, but at crestal level, no significant difference was seen [Table 3]. Intra-observer reliability in measurement of bone density changes. No significant differences were seen in mean bone density when recorded at two time intervals by the same examiner on apical, middle, and crestal levels as P > 0.05 [Table 4].
Table 1: Descriptive analysis of bone density in Group A (conventional loading) showing mean, standard deviation, and standard error mean at apical level, middle region of radiological implant length, and at the crestal level using cone-beam computed tomography immediately and at 36 weeks of post implant placement (follow-up)

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Table 2: Descriptive analysis of bone density in Group B (early loading) showing mean, standard deviation, and standard error mean at apical level, middle region of radiological implant length, and at the crestal level using cone-beam computed tomography immediately and at 36 weeks of post implant placement (follow-up)

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Table 3: Intergroup comparison of bone density changes from immediate post implant placement to 36 weeks post implant placement follow-up

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Table 4: Intra-observer reliability in measurement of bone density changes

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   Discussion Top


The available bone, i.e., the width, height, length, and angulation of the edentulous area, plays an important role in the treatment planning. Sufficient quantity of bone is the primary condition for the use of endosteal implants. In addition, available bone is also described in density, which reflects the hardness of the bone. When a tooth is lost, the alveolar bone starts to lose dimension.

Our inclusion criteria included partially edentulous sites in mandibular posterior region which predominantly had D2/D3 type of bone. As females are more to hormonal changes leading to imbalance in bone metabolism (osteoporosis, pregnancy, and postmenopausal osteopenia), male patients between 26 and 45 years with well-rounded cortical bone which does not require osteoplasty were selected. Patients with any systemic disease which contraindicated surgery, temporomandibular joint disorders, history of radiation therapy in maxillofacial area, positive medical history of immunosuppressive drugs, habit of tobacco abuse in any form, occlusal anomalies, and parafunctional habits were excluded from the study.

The use of immediate ⁄ early-loaded implants has obvious advantages because patients can be rehabilitated with functional crowns for immediate function and esthetics.[6] Zhu et al.[11] concluded that although early implant loading is convenient and comfortable for patients, this method still cannot achieve the same clinical outcomes as the conventional loading method. Since early loading of dental implants has gained widespread popularity because of its advantages in shortening treatment duration and improving esthetics and patient acceptance, our study aimed to follow early loading versus conventional loading protocols and compare the changes in bone density around endosseous intraoral implants using CBCT.

In all our cases, implants were primarily torqued using calibrated torque wrench with torque ranging 35 Ncm–50 Ncm. Osteoplasty was not done in any of the cases in this study. Goyal observed that if bone width is increased by osteoplasty, very valuable cortical crestal part of bone is lost and implant lies in underlying trabecular bone which is less dense and offers less bone to implant contact, thus less primary stability and an increased prosthetic space.[12]

In our study, Newtom Giano (CEFLA S. C. – CEFLA DENTAL GROUP, Italy) CBCT unit was used. For standardization, the orientation beam was used to align the jaw bone parallel to the reference surface. The tube voltage was 85 kVp–90 kVp and the tube current was 10 mA with exposure time of 12 s. FOV selected for each CBCT was 5 cm × 5 cm. Interactive CT/CBCT image processing software NNT (CEFLA S. C. – CEFLA DENTAL GROUP, Italy) was used to measure the gray values. Bone density changes were evaluated and compared at three different levels as influenced by early and conventional protocols using CBCT (gray values). The gray values were measured at the apical level, middle region of radiological implant length, and at the crestal level. A coronal view along the middle of the implant was used to measure the gray values in the three regions mesially and distally, while a sagittal view along the middle of the implant was used to measure the gray values buccally and lingually. As the titanium artifact at the bone–implant interface was within 0.5 mm for the all CBCT data, the values were registered at a distance of 2 mm from the implant in a spot diameter of 2 mm.[2] The CBCT scans were conducted at two time intervals, i.e., immediately post implant placement and at 36 weeks of post implant placement.

In our study, one implant failed in the early loading group (n = 10) and one patient did not turn up for follow-up in the conventional loading group (n = 10). The results showed a significant increase in the grayscale values from post implant placement to 36 weeks post implant placement in both conventional and early loading protocols.

In the conventional loading group, at apical level, the mean bone density was found to be 1222.94 ± 339.60 immediately post implant placement, and 1239 ± 415.48 at 36-week follow-up. At middle level, the mean bone density was found to be 1074.275 ± 369.80 immediately post implant placement, and 1145.08 ± 381.46 at 36-week follow-up. At crestal level, the mean bone density was found to be 991.668 ± 322.09 immediately post implant placement, and 1239.60 ± 280.688 at 36-week follow-up. Maximum increase in bone density changes was seen at crestal region followed by middle and apical regions.

In the early loading group, at apical level, the mean bone density was found to be 1144.53 ± 220.22 immediately post implant placement, and 1462.84 ± 236.54 at 36-week follow-up. At middle level, the mean bone density was found to be 1129.423 ± 276.04 immediately post implant placement, and 1338.00 ± 314.02 at 36-week follow-up. At crestal level, the mean bone density was found to be 1069.63 ± 178.62 immediately post implant placement, and 1369.80 ± 222.51 at 36-week follow-up. Maximum increase in bone density changes was seen at apical region followed by crestal and middle regions Both the loading groups revealed a statistically significant difference at apical and middle levels. But at crestal level, no statistically significant difference was seen.

The reason of increase in the bone density gray levels attributes to the mechanical adaptation of alveolar bone to strain. The adapted window, also referred to as physiologic loading zone (50–1500 microstrains), represents an equilibrium of modeling and remodeling, and bone conditions are maintained at this level.[8] Bone remains in a steady state, and this may be considered the homeostatic window of health. The histologic description of this bone is primarily lamellar or load-bearing bone. This is the range of strain ideally desired around an endosteal implant. Therefore, bone increases in density if an increase in stress occurs within physiologic limits.

Furthermore, permissible micromotion at the implant–tissue interface should be between the threshold of 50–150 microns during the post implantation healing phase.[13] We ensured this by selecting optimum implant design, loading protocol, occlusal material, occlusal contacts, and diet.

Compared with a tooth, the direct bone interface with an implant is not as resilient. No cortical lining is present around the implant, which indicates that the forces are not dissipated ideally around the interface. Instead, the energy imparted by an occlusal force is not dissipated away from the crestal region but rather transmits a higher intensity force to the crestal contiguous bone interface.[14]

The amount of bone strain at the bone–implant interface is directly related to the amount of stress applied through the implant prosthesis. As the maximum stresses are concentrated in the crestal region, this region is more subjected to remodeling during the healing phase of post implant placement. Hence, no significant difference was seen in the gray values at the crestal region between the conventional and early loading groups.

The study conducted revealed that the bone densified more when the implants were loaded following early loading protocol within physiologic limit. Thus, the surgical protocol, healing, treatment planning, and loading protocols are the determining factors for implant placement.


   Conclusion Top


In the present study, statistically significant differences were observed at apical and middle bone levels between conventional and early loading protocols. The reason of increase in the bone density gray levels attributes to the mechanical adaptation to strain within the physiological limit. As the maximum stresses are concentrated in the crestal region, this region is more subjected to remodeling during the healing phase of post implant placement. Hence, no significant differences were seen in the gray values at the crestal region between the conventional and early loading groups. Early loading protocol may be considered a good option to form a loading-bearing bone for better stress distribution in the 1st year of post implant placement. Furthermore, we need more studies on the CBCT gray values and its correlation with CT Hounsfield units for quantification of the bone.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

1.
Lindquist LW, Carlsson GE, Jemt T. A prospective 15-year follow-up study of mandibular fixed prostheses supported by osseointegrated implants. Clinical results and marginal bone loss. Clin Oral Implants Res 1996;7:329-36.  Back to cited text no. 1
    
2.
Belser U, Schmit B, Higginbottom F, Buser D. Outcome analysis of implant restorations located in the anterior maxilla: A review of the literature. Int J Oral 2004;19: 30-42.  Back to cited text no. 2
    
3.
Cochran DL, Buser D, ten Bruggenkate CM, Weingart D, Taylor TM, Bernard JP, et al. The use of reduced healing times on ITI implants with a sandblasted and acid-etched (SLA) surface: Early results from clinical trials on ITI SLA implants. Clin Oral Implants Res 2002;13:144-53.  Back to cited text no. 3
    
4.
Stavropoulos A, Nyengaard JR, Lang NP, Karring T. Immediate loading of single SLA implants: Drilling vs. osteotomes for the preparation of the implant site. Clin Oral Implants Res 2008;19:55-65.  Back to cited text no. 4
    
5.
Brånemark PI, Zarb GA, Albreksson T. Tissue-integrated prostheses. osseointegration in clinical dentistry. Plastic & Reconstructive Surgery 1986;77:496-7.  Back to cited text no. 5
    
6.
Ostman PO. Immediate/early loading of dental implants. Clinical documentation and presentation of a treatment concept. Periodontol 2000 2008;47:90-112.  Back to cited text no. 6
    
7.
Frost HM: Bone's Mechanostat: a 2003 Update, The Anatomical Record Part A 275A:1081-1101, 2003.  Back to cited text no. 7
    
8.
Barone A, Ricci M, Calvo-Guirado JL, Covani U. Bone remodelling after regenerative procedures around implants placed in fresh extraction sockets: An experimental study in Beagle dogs. Clin Oral Implants Res 2011;22:1131-7.  Back to cited text no. 8
    
9.
Mano T, Ishikawa K, Harada K, Umeda H, Ueyama Y. Comparison of apatite-coated titanium prepared by blast coating and flame spray methods – Evaluation using simulated body fluid and initial histological study. Dent Mater J 2011;30:431-7.  Back to cited text no. 9
    
10.
Lekholm U, Zarb GA. Patient selection and preparation. In: Branemark PI, Zarb GA, Albrektsson T, editors. Tissue Integrated Prostheses: Osseointegration in Clinical Dentistry. Chicago: Quintessence Publishing Company; 1985. p. 199-209.  Back to cited text no. 10
    
11.
Zhu Y, Zheng X, Zeng G, Xu Y, Qu X, Zhu M, et al. Clinical efficacy of early loading versus conventional loading of dental implants. Sci Rep 2015;5:15995.  Back to cited text no. 11
    
12.
Goyal S, Iyer S. Bone manipulation techniques. Int J Clin Implant Dent 2009;1:22-31.  Back to cited text no. 12
    
13.
Szmukler-Moncler S, Salama H, Reingewirtz Y, Dubruille JH. Timing of loading and effect of micromotion on bone-dental implant interface: Review of experimental literature. J Biomed Mater Res 1998;43:192-203.  Back to cited text no. 13
    
14.
Misch CE. Dental Implant Prosthetics 2nd ed. St. Louis: Elsevier Mosby; 2015. P 18.  Back to cited text no. 14
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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