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Table of Contents
ORIGINAL ARTICLE
Year : 2021  |  Volume : 11  |  Issue : 1  |  Page : 36-43

Randomize clinical trial of the effect of machined and rough surface of implant collar on crestal bone level and surrounding soft tissue


1 Department of Prosthontics, Post Graduate Institute of Dental Sciences, Rohtak, Haryana, India
2 Department of Oral Medicine and Radology, Post Graduate Institute of Dental Sciences, Rohtak, Haryana, India

Date of Submission11-Oct-2020
Date of Decision20-May-2021
Date of Acceptance21-May-2021
Date of Web Publication10-Jun-2021

Correspondence Address:
Dr. Anshul Chugh
Department of Prosthontics, Post Graduate Institute of Dental Sciences, Rohtak, Haryana
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jdi.jdi_26_20

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   Abstract 

Statement of Problem: The importance of implant collar/neck in crestal bone area triggered the need to understand the influence of its design/surface topography on surrounding hard and soft tissues.
Purpose: This study analyzed the effect of machined and rough surface of implant collar on bone level at crestal region and surrounding soft tissues in maxillary and mandibular anterior region.
Materials and Methods: The clinical study was conducted on 20 participants (15 males and 5 females) based on the inclusion and exclusion parameters. Participants were broadly divided into two groups with 10 dental implants in Group R (implant with rough collar design) and Group M (implant with machined collar design). The participants were evaluated at baseline (within 1 week after implant placement), 3 months, and 6 months for crestal bone level and soft tissue parameters (pink esthetic score [PES]).
Results: All implants showed clinically acceptable bone loss at interval of 6 months, i.e., 0.68 and 0.74 on mesial and distal aspect of R group implants, respectively, and 1.15 and 0.83 at mesial and distal aspect of R group implants, respectively. And also, the PES of all implants observed was above the clinical acceptability level, i.e., 6.15 and 6.05 for R and M groups implants, respectively.
Conclusion: It can be concluded from the present study that there is no significant difference statistically in bone level at crestal region and soft tissues parameters in two different implant collar designs used in the study although the loss of bone observed was higher in machined group in comparison to rough group of implants and the PES observed was also more in R group in comparison to M group.

Keywords: Crestal bone loss, implant collar design, soft tissue parameter


How to cite this article:
Chugh A, Rani S, Gupta A. Randomize clinical trial of the effect of machined and rough surface of implant collar on crestal bone level and surrounding soft tissue. J Dent Implant 2021;11:36-43

How to cite this URL:
Chugh A, Rani S, Gupta A. Randomize clinical trial of the effect of machined and rough surface of implant collar on crestal bone level and surrounding soft tissue. J Dent Implant [serial online] 2021 [cited 2021 Nov 29];11:36-43. Available from: https://www.jdionline.org/text.asp?2021/11/1/36/318068




   Introduction Top


Dental implant has changed the treatment modality for missing tooth replacement. Although the replacement of missing tooth with dental implants has a long history, nowadays, it has become very common due to increase in success rate and predictable outcome of the treatment. For the success of dental implant, integration between implants and hard and soft tissues is highly accountable. On basis of current literature, implant collar designs are one of the most likely causes of implant bone loss.[1] Crest module attaches the prosthetic part of implant to the implant body. It can be parallel, convergent or divergent depending on its shape and can be rough and machined surface. Its design makes it compatible with surrounding soft and hard tissues.[2]

Bone resorption occurs mainly in the neck region of implant and can be initiated by overloading of the implant-bone interface, surgical trauma, and bacterial infection. Previous studies tried to decrease loss of bone at crestal region by increasing contact area of bone to implant surface and thus decreasing overload at crest of alveolar bone.[3],[4] To increase the contact area of the implant-bone interface, researchers have worked on changing in the design of fixture, characteristics of implant surface and shape, and surface characterization at the collar region.

  1. The crest module design can help to improve osseointegration and provide bone-implant stability through bone stimulation decrease of bone overload. The attachment of connective tissues also varies according to the surface characterization of implant. The presence of microgrooves leads to perpendicularly oriented fibers of connective tissue to the implant surface. These connective tissue fibers provide a seal to prevent ingress of fibroblasts and connective tissue cells apically and decrease the loss of marginal bone. Alomrani, et al.(2005)[5] studied the effect of machined titanium coronal collar on marginal bone placed at different height in relative to crestal bone and concluded that in implant system having machined collar of around 1.8mm, bone loss was observed more as compared to the sandblasted and acid-etched (SLA) surface implant. And with each type of implant when the top of implant was placed above the alveolar crest, bone loss observed was comparatively less. Koodaryan and Hafezeqoran[6] conducted a systematic review and meta-analysis to compare dental implants with different collar surfaces, evaluating marginal bone loss and survival rates of implants and concluded that Rough and rough-surfaced microthreaded implants are considered a predictable treatment for preserving early marginal bone loss.


It should be always be remembered that implant only replicates the natural tooth, the lack of periodontal ligament and cementum, less vascularity and fibroblast, parallel orientation of supracrestal connective tissue make the implant more susceptible to microbial infection.[7]

Various other possible factors considered responsible for marginal bone loss such as, surgical trauma, biological width, periosteal reflection, microgap, for which crest module also plays some role.[8]

The location and size of microgap affects the marginal bone by establishing the bone implant contact at least at a radiological distance of 2mm from the microgap.[9]

Crest module is said to have a biological width influence, surgical influence, a prosthetic influence, loading profile considerations, and hence, the design of this part of an implant is important for overall success of the implant.

Keeping in view the above literature, the study was planned to analyze and compare the bone level at crestal region and soft tissue parameters like distal papilla, mesial papilla, facial mucosa curvature, height of facial mucosa, root contour, color and texture of surrounding soft tissues of dental implants with rough and machined collar designs.


   Materials and Methods Top


Study setting

The present study was conducted involving the participants selected from the out-patient Department of Prosthodontics and Crown and Bridge, PGIDS, Rohtak. Ethical clearance was obtained from Ethical Committee of Post Graduate Institute of Dental Sciences, Rohtak, Haryana. Participants were evaluated based on chief complaints requiring replacement of missing maxillary and mandibular anterior teeth.

Study population

A total of 55 participants were evaluated based on the chief complaint requiring replacement of maxillary anterior teeth. After meticulous clinical and radiographic examination only 20 participants were selected for placement of implants based on the inclusion and exclusion criteria.

Inclusion criteria

  1. Participants who consented to participate in the study and will also be available for follow-up
  2. Participants with maintainable oral hygiene and nonsmokers
  3. Participants who presented with partially edentulous maxilla and mandible
  4. Participants with adequate buccolingual, mesiodistal, and interocclusal space at the site of implant placement
  5. Participants having adequate quantity and quality of bone at the site of implant placement.


Exclusion criteria

  1. Participants with the presence of infection around site of implant placement
  2. Participants with a history of bleeding disorder or on anticoagulant drugs
  3. Participants with immune-compromised state or debilitating disease
  4. Participants with parafunctional habits and periodontal diseases
  5. Participants with any other systemic diseases such as diabetes, recent history of myocardial infarction
  6. Participants with any dental or medical conditions that would interfere with the soft tissue and bone healing.


The participants were divided into two groups randomly, i.e., Group M and Group R. Group M will receive implant having machined collar and Group R will receive implant having rough collar design. Ten participants in Group M and 10 in Group R were included for placement of implant.

Preoperative analysis

The preoperative evaluation included a careful clinical and radiographic criteria [Figure 1]. Low dose cone beam computed tomography (CS9300, Carestream Health) was used to assess the height and thickness of bone crest for implant placement. A template was made for radiographic assessment. Diagnostic wax-up was done on plaster model keeping in view the patient's prosthetic needs. Other investigations such as complete hemogram and blood sugar were done.
Figure 1: Preoperative evaluation

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Implant design

The implants (Tuff TT Noris, Nesher, Israel) in both groups were identical in macrodesign (screw shape), type of abutment connection, and surface characteristics but had implant neck of different designs; one set had a machined surface and the other had Resorbable Blast Media (RBM) treated surface to induce the sub-micro-topography, i.e., rough surface. The material used for RBM process is calcium phosphate, which is a highly resorbable and biocompatible material [Figure 2] and [Figure 3].
Figure 2: (a) Rough Implant design. (b) Smooth Implant design

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Figure 3: Placed implant in anterior region

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Surgical and prosthetic phase

All surgical procedures were carried out under local anesthesia, using lignocaine with adrenaline (1: 100,000). A midcrestal incision followed by with two lateral vertical incisions. Osteotomy procedure was initiated with pilot drill taking all precautions to avoid overheating. Osteotomy preparation was done as per manufacturer's protocol at the osteotomy site approximating the cervical collar of dental implant with the crestal bone margin. Reasons for using this method were to avoid undue early stresses on implant during healing period, to minimize infection risk at the site, and also, to prevent apical growth of mucosal epithelium.[10] At the end, cover screw was placed. A 3-0 black braided silk was used for interrupted suture [Figure 4].
Figure 4: Prosthesis delivered

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Implant placement was evaluated after 3 months in mandibular anterior and 6 months in maxillary anteriors after placement of implant. Final impression with impression coping in place was made with multiple mix technique utilizing polyvinyl siloxane putty and light body impression material (AFFINIS, COLTENE) using a stock tray of suitable size. The final cast was prepared by attaching implant analog over the impression coping. Porcelain fused to metal prosthesis was fabricated over the master cast. The cementation of prosthesis was done with luting Cement Type I glass ionomer (GC Corporation Tokyo). Occlusion was analyzed with articulating paper (NORDIN) [Figure 5]. The patients were instructed to maintain Oral hygiene patient and taught about maintenance of implant.
Figure 5: Measurements done using software

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Radiographic analysis of bone at crestal region

All implants were radiographically evaluated at interval of 3 months for 6 months after placement of implant. The intraoral periapical radiograph was obtained with paralleling technique and digitalized. To obtain a reproducible data, the definition of reference points is most important. The first thread of implant was taken as a reference line as being static, clearly noticeable on all radiographs. Level of bone was taken at the spot of contact of implant to bone. The measurements were made with the help of digimizer image analysis, MedCalc Software, Version 4.3.5.0 (Medcalc software Ltd, Ostend, Belgium). Before interpretation, calibration of image was done geometrically depending on length of implant, so that the actual distance can recorded. Measurements were recorded at interval of 3 months for a period of 6 months on the mesial and distal side of implants by dropping perpendiculars from the reference line to the bone level.

Assessment of soft tissue

All the patients were assessed for soft tissue using pink esthetic score (PES). The PES comprises of following variables:

The facial soft tissue curvature line, which is referred as emergence line of crown of the implant from the soft tissues, was evaluated as score 2 if similar, score 1if slightly different, and score 0 if clearly different compared to contralateral natural tooth (control) and thus, gave information regarding the natural harmonious appearance.

The height of the facial mucosa around implant was measured by comparing the height of facial mucosa to the contralateral tooth, if vertical level found similar (score 2), a slight variation of ≤1 mm (score 1), and variation ≥1 mm (score 0).

The index also calculated three other specific soft tissue parameters that were scored as one variable: the presence, partial presence, or absence of root eminences on the facial aspect, also the color and texture of mucosa. The color and texture of mucosa reflect if there any inflammatory reaction or not, that can adversely affect the appearance of anterior implant restoration.

For scoring of this variable, all the three parameters should be almost similar to the contralateral tooth/control tooth to get the score 2. Score 1 if two parameters are similar to identical, and a score 0 if none or only single parameter is similar to the control. These five described parameters (5 × 2) add up under optimum conditions to make a score of 10. The clinical acceptability level was set at 6 [Table 1]. The measurements were recorded after cementation of prosthesis to implant. Mesial papilla, distal papilla, curvature of facial mucosa, level of facial mucosa, and root convexity/soft tissue color and texture at facial aspect of implant site were analyzed using standardized clinical photograph. Photographs were taken 2 weeks after cementation of prosthesis at each implant site and at the contra-lateral tooth to facilitate a direct objective assessment related to PES index.
Table 1: Pink esthetic score variables

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   Results Top


Statistical analysis

  • Data obtained was compiled on a MS Office Excel Sheet (v 2010) and was subjected to statistical analysis using Statistical package for social sciences (SPSS v 21.0, IBM, Armonk, NY: IBM Corp.). Descriptive statistics such as mean age, frequency, and percentage of the participants overall and group-wise has been depicted
  • Comparison of bone at crestal region was done mesially and distally to the implant at different time intervals. Other variables such as MP, DP, CFM, HFM, RCCT, and TOTAL out of 10 between the groups have been done using Mann–Whitney U-test (since data did not follow a normal distribution as per Kolmogorov–Smirnov test). Intragroup comparison of the variables like in each of the two groups across time has been done using Friedman's test followed by Wilcoxon signed-rank test [Table 2] and [Table 3].
  • For the statistical tests, P < 0.05 was considered to be significant statistically, keeping α error at 5% and β error at 20%, thus giving a power to the study as 80%
  • The present study showed that there was a statistically highly significant difference in the bone level on mesial aspect between all time intervals (P < 0.01) with the mean value highest at baseline followed by 3 months and least at 6 months
  • The mean crestal bone level on mesial aspect of implant at 3 months was recorded to be 2.80 and 2.57 in Groups R and M, respectively, with P > 0.05 indicating that decrease in crestal bone level at 3 months is more in Group M than Group R but the difference is clinically nonsignificant. Similarly, the mean crestal bone level on mesial aspect of implant at 6 months was recorded to be 2.12 and 1.42 in Groups R and M, respectively, with P > 0.05 indicating that decrease in crestal bone level at 6 months is more in Group M than Group R [Figure 4] and [Table 4].
  • The mean of mesial papilla was recorded to be 1.17 and 1.0 for Groups R and M, respectively, indicating that mesial papilla fill was more in R group as compared to M group. The mean of distal papilla was recorded to be 1.42 and 1.50 for Groups R and M, respectively, indicating that distal papilla fill was more in M group as compared to R group. The mean of curvature of facial mucosa was recorded to be 1.00 and 1.10 for Groups R and M, respectively, indicating that curvature of facial mucosa was good in M group as compared to R group. The mean of height of facial mucosa was recorded to be 1.17 and 1.10 for Groups R and M, respectively, indicating that height of facial mucosa was near to natural tooth in R group as compared to M group. The mean of root convexity, soft tissue color, and texture at the implant site was recorded to be 1.00 and 0.60 for Groups R and M, respectively, showing better result in R group as compared to M group. The mean of PES was recorded to be 6.15 and 6.01 for Groups R and M, respectively [Table 1].
Table 2: Comparison of soft tissue variables between the two groups after cementation of prosthesis

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Table 3: Comparison of crestal bone level measurements on distal aspect of implants between two groups at different time intervals

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Table 4: Comparison of crestal bone level measurements on mesial aspect of implants between two groups at different time intervals

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   Discussion Top


Dental implant has become a treatment of choice nowadays in most of situations of missing teeth. The implants have revolutionized the treatment modality in restorative dentistry. This treatment option has proved to be successful as it is more similar to natural tooth. The extent of loss of bone at crestal region in initial year of implant placement depicts the success rate of implant. Early crestal bone loss is usually highest during the first year after implant placement ranging from 0.9 to 1.6mm. In the subsequent years, it is averaged 0.05-0.13mm.[6],[11] Ferracane et al. described that the success criteria for implant include an acceptable bone loss of 1.5 mm within the 1st year of implant service, but subsequent resorption should be <0.2 mm annually to ensure that adequate bone remains to provide stability to the implant.[12] An implant should be able to osseointegrate in the bone of host, to bear occlusal forces while in function, and to support the prosthesis. Loss of Bone around the implant decreases its longevity. Loss of bone in an implant begins from the collar region and it progresses apically. Different causes for loss of bone during initial year of a functioning implant are implanting collar design and shape, surgical trauma, presence of microgap, biological width reformation, peri-implantitis, occlusal overload, and feasible causes of marginal loss of bone could be a local infection/inflammation and pressure acting on the marginal bone around the collar of implant. Multiple types of dental implants with different surface topography are being used for rehabilitation of patient. Collar surface design is a critical factor in controlling the loss of bone at the margin around an implant, so it needs to be evaluated and compared. Over the last two decades many improvements have taken place within the surface characterization of implant and design to increase the favorable outcome of implants.[13]

At present, evidence is lacking in the literature regarding ideal implant collar configurations that limit the loss of bone at margin around the implant. The specific aims of the present study were to compare the loss of bone at margin around implants with machined and rough surface collar design and also the various soft tissue parameters such as mesial papilla, distal papilla, facial mucosa curvature, height of facial mucosa, root convexity, soft tissue color, and texture.

The present study evaluated two types of implants, R group had collar surface with microthreads and blasted with calcium phosphate; Group M has a machined surface with microthread similar to the R group implant but without blasting of phosphate media. Difference in marginal bone loss was nonsignificant (P > 0.05), although bone loss was higher in Group M in comparison to R group. In 1998 Norton MR conducted a study and observed a great difference in bone loss after modification of implant surface from machined titanium collar to roughened surface. But he was not able to conclude whether microthread or the TiOblast surface was responsible for maintenance of marginal bone.

Based on the results of present study, we can say that microthreads have important role for the maintenance of marginal bone and the blasting media also has positive effect on marginal bone. Our results support previous studies such as Meriç et al.,[3] Shin and Han,[14] Lee et al.,[15] Negri et al.,[16] and Alormani et al.[5] implant (test) with sandblasted, large grit, dual acid-etched surface (SLA) were placed at crestal level and implant with machined collar (control) were placed supracrestally. All these findings are also in accordance with studies done by Goswami MM[4], Shapoff CA, Lahey B, Wasserlauf PA and Kim DM[17] and G Meric, et al.[3] and shin YK et.al.[5] Although implant placement level in the present study was not similar to this study, the results of the present study were in accordance to the study by Alormani et al.

According to Shapoff CA, Lahey B, Wasserlauf PA and Kim DM.[17] Laser Lok collar resulted in less crestal bone loss after 3 year of restoration than the commonly accepted 1.5mm -2mm. It was observed that difference in crestal bone level after 6 months of implant placement between the two groups was found to be nonsignificant (P > 0.05). There was more crestal bone loss on mesial and distal aspect at 3 months and 6 months in implant with machined collar as compared to that in implant with rough collar as depicted in tables. Similarly, Goswami MM in 2009[4] conducted a study and observed overall average crestal bone loss of 0.62 mm with smooth collar implant and 0.59 mm with rough collar implant after 6 months of implant placement. At this stage, the difference was statistically nonsignificant (P > 0.05). However, after 1 year of implant loading, the overall average bone loss of 1.53 with smooth collar implant and 1.42 mm with rough collar implant was observed, the difference found at this stage between the two groups was statistically significant (P < 0.05). Our results were in accordance with study by Goswami till the period of 6 months. Hence, it is possible that extension of the present study to 1 year or more the difference in crestal bone level may show significant results (P < 0.05).

In a recent study by Gultekin et al.[18] short collar implant with identical geometries was divided into two groups: M group with machined collar design and L group with laser microtextured collar group. Evaluation of implant was done after 3 years of follow-up for marginal bone loss, probing depth, and implant success. All implants showed clinically acceptable marginal bone loss, although bone loss was lower in the L group (0.49 mm) as compared to the M group (1.38 mm) at 3 years (p <0.01). During follow-up a significantly shallower probing depth was found for the implants in the L group. The present study support above studies in marginal bone loss difference around the rough and machined collar design in long run.

Currently, evidences are lacking in the literature regarding ideal implant collar configurations that limit the loss of marginal bone around the implant. The specific aims of this study were to compare the loss of marginal bone around implants with machined and rough surface collar design and also the various soft tissue parameters such as mesial papilla, distal papilla, curvature of facial mucosa, height of facial mucosa, root convexity, soft tissue color, and texture. Shows the mean of PES that was recorded to be 6.15and 6.01 for group R and M respectively. The mean values are above the clinical acceptability level. Under optimal conditions the parameters adds to a score of 10 but the threshold of clinical acceptability was set at 6 by Belser UC, Grutter L, Vailati F, Bornstein MM, Weber HP, Buser D.[18]

Placement of implant at the crestal bone level was also kept same in both the groups. Along with this PFS, evaluation was also done in both groups.


   Conclusion Top


It can be concluded from the present study that there is no statistically significant difference in crestal bone level and soft tissues parameters in two different implant collar designs used in the study, although the bone loss observed was higher in machined group as compared to rough group of implants and the PES observed was also higher in R group as compared to M group. Further, the longer time period study is required to find the hard tissue changes after loading of implants.

Merits of the study

  1. Implant placement was done in a specified/predetermined maxillary and mandibular anterior region
  2. IOPA-X-rays used for the assessment of bone level were standardized by using occlusal putty zig. The putty zig was used for taking further IOPA at different time intervals
  3. IOPA X-rays were obtained by using paralleling technique to minimize distortion.
  4. A single implant system was used throughout the study
  5. In the present study, all participants participated until the end of the study Both soft and hard tissue assessment criteria were included in the present study.


Limitations of the study

  1. IOPA radiographs were processed manually. Although the precautions were taken to standardize the temperature and concentration of processing solution, the difference in density and contrast due to processing in the follow-up radiographs is possible
  2. Small sample size
  3. Short follow-up time period
  4. Bone levels on buccal and lingual aspect were not included in study.


Acknowledgments

The authors thank Dr. S.C Narula for helping in evaluation of radiographs by digimizer.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

1.
Guarnieri R, Serra M, Bava L, Grande M, Farronato D, Iorio-Siciliano V. The impact of a laser-microtextured collar on crestal bone level and clinical parameters under various placement and loading protocols. Int J Oral Maxillofac Implants 2014;29:354-63.  Back to cited text no. 1
    
2.
Aparna IN, Dhanasekar B, Lingeshwar D, Gupta L. Implant crest module: A biomechanical consideration. Indian J of Dent Res 2012;23:257-63.  Back to cited text no. 2
    
3.
Meriç G, Erkmen E, Kurt A, Eser A, Özden AU. Biomechanical comparison of two different collar structured implants supporting 3-unit fixed partial denture: A 3-D FEM study. Acta Odontol Scand 2012;70:61-71.  Back to cited text no. 3
    
4.
Goswami MM. “Comparison of crestal bone loss along two implant crest module designs.” Med J Armed Forces India 2009;65:319-22.  Back to cited text no. 4
    
5.
Alomrani AN, Hermann JS, Jones AA, Buser D, Schoolfield J, Cochran DL. The effect of a machined collar on coronal hard tissue around titanium implants: A radiographic study in the canine mandible. Int J Oral Maxillofac Implants 2005;20:677-86.   Back to cited text no. 5
    
6.
Koodaryan R, Hafezeqoran A. Evaluation of implant collar surfaces for marginal bone loss: A systematic review and meta-analysis. Biomed Res Int 2016;2016:4987526.  Back to cited text no. 6
    
7.
Costa C, Peixinho N, Silva JP, Carvalho S. Study and characterization of the crest module design: A 3D finite element analysis. J Prosthet Dent 2015;113:541-7.  Back to cited text no. 7
    
8.
Pozzi A, Tallarico M, Moy PK. Three-year post-loading results of a randomised, controlled, split-mouth trial comparing implants with different prosthetic interfaces and design in partially posterior edentulous mandibles. Eur J Oral Implantol 2014;7:47-61.  Back to cited text no. 8
    
9.
Shen WL, Chen CS, Hsu ML. Influence of implant collar design on stress and strain distribution in the crestal compact bone: A three-dimensional finite element analysis. Int J Oral Maxillofac Implants 2010;25:901-10.  Back to cited text no. 9
    
10.
Rajpal J, Gupta KK, Tandon P, Srivastava A, Chandra C. Assessment of hard and soft tissue changes around Implants: A clinico-radiographic in vivo study. J Dent Implant 2014;4:126-34.  Back to cited text no. 10
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11.
Norton MR. Marginal bone levels at single tooth implants with a conical fixture design. The influence of surface macro- and microstructure. Clin Oral Implants Res 1998;9:91-9.  Back to cited text no. 11
    
12.
Ferracane JL. Clinical factors concerning implants. In: Ferracane JL, editor. Materials in Dentistry-Principles and Applications. 2nd ed. Lippincott Williams & Wilkins; Philadelphia: 2001. p. 318–9.  Back to cited text no. 12
    
13.
Abrahamsson I, Berglundh T. Effects of different implant surfaces and designs on marginal bone-level alterations: A review. Clin Oral Implants Res 2009;20 Suppl 4:207-15.  Back to cited text no. 13
    
14.
Shin SY, Han DH. Influence of a microgrooved collar design on soft and hard tissue healing of immediate implantation in fresh extraction sites in dogs. Clin Oral Implants Res 2010;21:804-14.  Back to cited text no. 14
    
15.
Lee DW, Choi YS, Park KH, Kim CS, Moon IS. Effect of microthread on the maintenance of marginal bone level: A 3-year prospective study. Clin Oral Impl 2007;18:465-70.  Back to cited text no. 15
    
16.
Bruno N, Guirado JL, de Val JE, Ruiz RA, Fernãndez MP, Dorado CB. “Peri-implant tissue reactions to immediate nonocclusal loaded implants with different collar design: An experimental study in dogs.” Clin Oral Implants Res 2014;25:e54-63.  Back to cited text no. 16
    
17.
Shapoff CA, Lahey B, Wasserlauf PA, Kim DM. Radiographic analysis of crestal bone levels around Laser-Lok collar dental implants. Int J Periodontics Restorative Dent 2010;30:129-37.  Back to cited text no. 17
    
18.
Gultekin BA, Sirali A, Gultekin P, Yalcin S, Mijiritsky E. Does the Laser-Microtextured Short Implant Collar Design Reduce Marginal Bone Loss in Comparison with a Machined Collar? Biomed Res Int 2016;2016:9695389.  Back to cited text no. 18
    


    Figures

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

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



 

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