Evaluation of the amount of bone loss on CAD/CAM(milled framework) support two implant Telescopic mandibular overdenture attachments by splinting and Non splinting of two different impression materials (Vinyl Polyether Silicone and additional silic

Introduction

Edentulism has a very detrimental effect on individuals . It has been observed to result in functional, psychological, and social limitations and affects the quality of life and general health.⁽¹⁾

Edentulism is a challenging problem for the healthcare providers, for going of this problem as a literature review, main responsible factors for teeth loss Dental caries and periodontal diseases. ⁽²⁾  

Negative impact of teeth loss will affect esthetics also functional activity, prosthetic rehabilitation is the best choice to solve this problems for restoring vertical dimension also esthetics and function, either treating traditionally by conventional complete den-tures or by implant supported prostheses. ⁽³⁾  

Retention, stability and support, improved by implant supported -overdentures which have many functions as two implant overdentures have been agreed to be the basic standard restorative solution for the edentulous mandible overcoming the problems associated with conventional dentures. ⁽⁴⁾  

Implant overdentures can be divided according to the type of retention systems to bar splinting or solitary attachments⁽⁵⁾  Also the number, distribution, of implants and placement sits depending  on many factors, which include the  anatomical condition and the economic status of patients.  

From the biomechanical view, overdenture prosthetic option considering the best restorative option as they allow for a proper physiological force distribution and gentle impact on the mucosa also residual ridge preservation. ⁽⁶⁾

Excessive functional loads on implants, leads to crestal bone loss leading to implant faliure This may result from biomechanical response of implant to stress.⁽⁷⁾

Impressions is a critical part of the process of constructing a well-fitting prosthesis; it is imperative that it copies the exact topography of the recorded site and translates it accura-tely to its cast. To achieve this, the impression material must be both accurate and stable ^(8,9)

Accuracy of impression plays an essential role in prosthesis-implant fit.⁽⁹⁾ Although there are many studies comparing different impression materials and techniques, but there is still no consensus ^(10-14).

Materials and methods

Twenty completely edentulous patients were selected from the outpatient clinic of the Prosthodontic department, Faculty of dentistry, Minia University according to the following inclusion criteria:

1. Highly motivated completely edentulous patient with aged range from 50 to 60 years old.
2. According to American Society of Anesthesiologists (ASA) Classifications which illustrate the types of patients free from any systemic diseases that will hinder or affect the survival rate of the implant. or affect implant surgery: patients Selected were (ASA. type. 1) and (ASA. type. 2),
3. Well-developed ridge with adequate amount of keratinized mucosa.
4. patients with adequate inter arch space.
5. patients with normal facial symmetry and normal muscle tone.
6. Angle’s Class I skeletal relationship

The following patients were excluded from the study:

1. severly atrophied ridges
2. Young aged patients
3. (ASA. type. 3) & (ASA. type. 4) having a systematic disease that may affect the survival rate of the implant.
4. Angle’s Class II and III skeletal relationship
5. Irradiated patient or patient undergoing chemotherapy
6. D1&D4 bone densities

Upper and lower Complete dentures were constructed for all patients, the lower denture was duplicated, radiographic markers inserted into canine region to be used as a radiographic stent and later as a surgical stent.

Each patient received two mandibular root form implants with standardized diameter of 3.5 mm. and 13mm length, placed at the canine region.  then they were divided randomly into two main groups (I & II) and two subgroups (A & B):

Group (I):  Divided into two subgroups Group (I.A):  5 patient receive two implants with on CAD/CAM (milled) two implant supported Telescopic mandibular overdenture attachments opposing maxillary complete denture with final impression technique made by Vinyl Polyether Silioxaine (VPES) with splinting technique.

Group (I.B): 5 patient receive two implants with on CAD/CAM (milled) two implant supported Telescopic mandibular overdenture attachments opposing maxi-llary complete denture with final impression technique made by polyvinyl silicone with splinting technique.

Group (II):  Divided into two subgroups Group (II.A): 5 patient receive two implants with on CAD/CAM (milled) two implant supported Telescopic mandibular overdenture attachments opposing maxi-llary complete denture with final impression technique made by Vinyl Polyether Silioxaine (VPES) without splinting.

Group (II.B):  5 patient receive two implants with on CAD/CAM (milled) two implant supported Telescopic mandibular overdenture attachments opposing maxillary complete denture with final impression technique made by polyvinyl silicone without splinting.

After ensuring Osseointegration the implants, its uncovered, multi-unit abutm-ents heights 1.2 were screwed in the implants hex (fig. 1) all patients recalled after seven days for primary impression making which poured to making a study model upon which a customized open tray technique.

The digital images were analyzed to evaluate the level of marginal bone height mesial and distal to the implant. To 

btain an actual measurement the option calibration was used. The screen length of the implant was measured and calibrated to the actual length of the implant. The contact between the implant platform and the abutment base was selected as reference point.
Bone height was measured as a distance between the reference point and the highest point of bone crest in contact with the implant. 
Measurments of marginal bone loss were divided into four intervals (1st interval 0-3 months, 2nd interval 0-6, 3rd interval 0-9 &4th interval 0-12).
Marginal bone loss at 1st interval was measured by subtracting the bone height after one month from bone height at loading time.

Results
Data were presented as means and standard deviation (SD) values. One Way-ANOVA was used to study the bone loss after different follow up intervals, different splinting techniques and the effect of different impression materials used within each group. Tukey’s post-hoc test was used for pair-wise comparison between the means when ANOVA test was significant. 
Statistical analysis was performed with IBM® SPSS® (SPSS Inc., IBM Corporation, NY, USA) Statistics Version 
23 for Windows. 
The success rate of the placed implants during the follow up was 100% (i.e. No implant was lost or showed signs of failure). 
The two bone height readings recorded for each implant (Mesial and distal aspects) were pooled for further statistical analysis as the statistical analysis for all the implants in all groups showed no significant difference. 
the readings were pooled for further statistical analysis. The mean bone loss values recorded for different study groups 
are shown in (Table 1)

Discussion
The original implant position must be reproduced in an accurate working cast by means of an impression technique which differ from splinting and non-splinting techniques This plays an essential role in the prosthesis implant adaptation conse-quent of crestal bone loss(9,10) . Several authors have reported that addition silicones are very accurate impression materials and should be used for implant-level impressions (10,11)
.
In addition, condensation silicone had been described as the worst material for implant transfer impressions and may be considered contraindicated (12)
.
The objective of this study was to compare two different impression materials (Vinyl Polyether Silicone and additional silicone) by splinting and non-splinting grouping on amount of marginal bone loss of two implant-retained Bar mandibular overdenture Polyvinyl siloxane produced accurate casts in this study in less chair time, as a 
dimensionally stable material, characterrized by its rigidity for proper splinting of transfer copings without micromovment, in agreement with other studies (13)
.
One of the drawbacks when the impression copings are rigidly splinted with autopolymerizing acrylic resin and making 
impression with additional silicone they seem to be susceptible to shrinkage lead to difficulty in determining the passive fit.
However, if polymerization shrinkage occurs, it will be noticeable and the resin should be sectioned and joined again with
small amounts of acrylic resin, all of that’s process surely affect passive fit of jeg than affect passive fit of prosthesis and affect amount of bone loss if prosthesis non passive ⁽¹²⁾.