Bone Healing at Non-submerged Implants Installed With Different Insertion Torques. A Split Mouth Histomorphometric Randomized Controlled Trial.
Phase: NA
Conditions: Edentulous; Alveolar Process, Atrophy
Sponsor: ARDEC Academy

 
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TITLE: Bone healing at non-submerged implants installed with different 
insertion torques. A split mouth histomorphometric randomized 
controlled trial. 
 
AUTHORS: Yoshiyuki Amari, DDS*, Adriano Piattelli, MD, DDS, DrHC, DrHC**, Karol Alí 
Apaza Alccayhuaman DDS***, Natalia Fortich Mesa, DDS, MSc§, Mauro Ferri, DDS#, 
Giovanna Iezzi, DDS, PhD##, Daniele Botticelli, BMBD, PhD° 
* Research affiliate at ARDEC Academy, Ariminum Odontologica, Rimini, Italy; 
** Full Professor, Department of Medical, Oral and Biotechnological Sciences, University 
of Chieti-Pescara, Chieti, Italy; Chair of Biomaterials Engineering, Catholic University of 
San Antonio of Murcia (UCAM), Murcia, Spain; 
*** Research affiliate at ARDEC Academy, Ariminum Odontologica, Rimini, Italy; 
§ Docente con Función de Coordinación en Investigación, Programa de Odontología, 
Corporación Universitaria Rafael Nuñez, Cartagena de Indias, Colombia; 
# Docente Auxiliar II, Facultad ciencias de la salud, Programa de Odontología, 
Universidad Rafael Núñez, Cartagena de Indias, Colombia; 
## Associate Professor, Department of Medical, Oral and Biotechnological Sciences, 
University of Chieti-Pescara, Chieti, Italy;  
° Private Practice, Principal Researcher at ARDEC Academy, Ariminum Odontologica, 
Rimini, Italy  
Corresponding author: 
Karol Ali Apaza Alccayhuaman 
Viale Giovanni Pascoli 67, 47923 Rimini (RN), Italy 
Tel.: +39-0541-393444, Fax: +39-0541-397044, E-mail: caroline7_k@hotmail.com 
 
Cartagena 20th April 2017 

 
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ABSTRACT 
Objectives: to evaluate histomorphometrically the healing at implants installed with 
standard or very low insertion torque values. 
Material and methods: Twelve volunteer patients will be recruited, and two screw-shaped 
titanium devices will be installed in the distal segments of the mandible using insertion 
torque values of either <10 Ncm or ~30 Ncm. The implants will be left to heal in a non-
submerged fashion. After 8 weeks, biopsies will be retrieved and ground sections will be 
prepared for histological evaluation. 
 
 
INTRODUCTION 
Very high insertion torque values have been recommended when immediate loading is 
applied to implants.1 However, it has been shown that similar clinical outcomes may be 
achieved even with insertion torque values ≤15 Ncm when implants are splinted together.2 
Nevertheless, in a consensus conference, insertion torque values comprised between 20 
and 45 Ncm were recommended for implants immediately loaded with single crowns.3 
Moreover, in animal experiments, the highest rate of osseointegration was observed when 
insertion torque of 30-35 Ncm were applied.4-6 
Different insertion torque values have been tested both in human 7-9 and in animals 
studies.1,4-6,10-12 A systematic review with meta-analyses summarized data from both 
animal and human studies and two groups were identified based on the insertion toque 
values: >25 Ncm or <30 Ncm. 13 No differences were found between the two groups in 
terms of implant survival rate or marginal bone loss. Nevertheless, in a randomized clinical 
study,7 after 12 months of healing, implants installed with torque ≥50 Ncm presented 
higher marginal bone loss compared to implants with torque included between 20-50 Ncm. 
Very low insertion torques have been also tested both in animals and humans. After 4 
months of healing, in an experimental study in dogs,5 an osseointegration >55% was 

 
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obtained at implant installed with torque close to 0 Ncm. In a clinical study,8 eleven 
implants were installed with a torque <10 Ncm. After 4 to 6 months, a reversal torque of 35 
Ncm was applied and all implants showed a good stability. 
However, it has to be considered that implants presenting a rotational instability during 
implant installation resulted in a lower survival rate compared to implants installed with 
higher insertion torque.14,15  
Due to the contradictory outcomes on the influence of the torque on osseointegration and 
a lack of histological data in humans, there is a need of more evidences that may support 
the clinicians in the decision making when an unintentional low insertion torque occur at 
implants during the daily practice. 
Hence, the aim of the present study was to evaluate histomorphometrically the healing at 
implants installed with standard or very low insertion torque values. 
 
MATERIALS & METHODS  
Patient selection 
The Declaration of Helsinki on medical protocols and ethics will be followed. The protocol 
has the approval of the Ethical Committee of the Corporación Universitaria Rafael Núñez, 
Cartagena de Indias, Colombia with protocol #04-2014 on October 8, 2014. All treatments 
will be performed in that institution starting from November 2016. All surgical procedures 
and possible complication will be clearly explained to each participant and a written 
informed consent was signed by all patients. The study will be reported according to the 
CONSORT guidelines. 
For sample calculation, data from a dog experiment were used 5 and a sample of 12 
subjects was calculated for matched pairs considering a difference in bone-to-implant 
contact of 10% being clinically relevant. A power of 0.8 and α=0.05 were used. 
 

 
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The following inclusion criteria will be required:  
(i) 
presence of at least two edentulous zone in the posterior segment of the 
mandible 
(ii) 
≥ 25 years of age 
(iii) 
smoking ≤ 10 cigarettes per day 
(iv) 
Good general health 
(v) 
No contraindication for oral surgical procedures. 
(vi) 
Not being pregnant.  
The following exclusion criteria will be adopted:  
(i) 
Presence of systemic disorders 
(ii) 
Chemotherapy or radiotherapy;  
(iii) 
Smokers >10 cigarettes per day 
(iv) 
Previous bone augmentation procedures in the region. 
 
Device 
Customized solid titanium screw-shaped devices will be used (Sweden & Martina, Due 
Carrare, Padua, Italy). The devices have an intraosseous portion with a moderately rough 
surface16 (ZirTi® surface, Sweden & Martina, Due Carrare, Padua, Italy). The intraosseous 
portions will be 4 mm long, with a diameter of 2.65 mm at the apical aspect and 3 mm at 
the coronal margin. A polished neck 2.4 mm long junction represents the transmucosal 
portion of the implant. 
 
Randomization  
Each patient will receive two mini-implants, installed in recipient sites prepared either to 
reach torque of <10 Ncm or ~30 Ncm. The two recipient sites will be selected prior the 
surgery, while the type of site preparation will be randomly decided. The randomization will 

 
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be performed electronically (randomization.com) by a researcher neither involved in the 
selection of the patients nor in installation of the devices (DB). Sealed opaque envelopes 
will be prepared and opened at the time of surgery by an author not involved in the surgery 
(DB). Surgeon and patients will be blinded. 
The histological slides will be coded so that the assessor will be blinded about the type of 
site preparation when the histological slides will be evaluated. 
 
Clinical procedures 
The surgical procedures will be performed by an expert surgeon. After the injection of local 
anesthesia, small crestal and releasing incisions will be performed in the distal segments 
of the mandible, and small full-thickness muco-periosteal flaps will be elevated. The test 
sites (<10 Ncm) will be over-prepared with drills of larger diameter compared to those used 
at the standard sites (~30 Ncm). All site preparations will be performed deeper compared 
to the length of the implant so that the implant apex cannot reach the bottom of the 
osteotomy. This, in turn, means that the final torque will be produced by the lateral 
pressure against the bone walls, as described in a previous animal experiment.4 The mini-
implants will be subsequently installed and the final insertion torque will be measured with 
wrench calibrated on a newton-meter (Newton; Leader Italia, Cinisello Balsamo, MI, Italy). 
A cover screw will be placed on the top of the mini-implants, and the flaps will be sutured 
allowing a non-submerged healing. 
 
Maintenance 
Antibiotics (amoxicillin 875 mg/clavulanic acid 125 mg twice a day for 6 days) and non-
steroidal anti-inflammatory drugs as needed (Ibuprofen 400 mg) will be prescribed. Mouth 
rinses with 0.12% chlorhexidine three times a day for 10 days will be also recommended.  

 
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After 7 days, the sutures will be removed, and the patients will be recalled every 2 weeks 
after surgery. 
 
Biopsies 
After 8 weeks of healing the patients will be recalled to the clinic for biopsies retrieval. Full-
thickness flaps will be elevated and biopsies including the mini-implants will be retrieved 
using the trephine in an eccentric position to reduce the size of the donor site and obtain 
sufficient hard tissue at least at one side of the biopsies. 17 
 
Histological preparation of the biopsies 
The biopsies will be washed in saline solution and immediately stored in 10% buffered 
formalin. The histological process will be performed in the Histology Laboratory for Hard 
Tissues at the University of Chieti-Pescara, Italy. All biopsies will be first dehydrated in an 
ascending series of alcohol and subsequently embedded in resin (Technovit® 7200 VLC; 
Kulzer, Wehrheim, Germany).  After polymerization, the biopsies will be sectioned 
following the longitudinal axis using a precision diamond disk. Specimens of ~150 microns 
of width will be obtained that will be afterwards ground to ~30 µm of width. A staining with 
acid fuchsine and toluidine blue will be applied. 
 
Histomorphometric evaluation 
The histomorphometric evaluations will be performed twice by an expert examiner, and 
mean values will be used. The examiner will be blinded, and no indications will be reported 
on the histological slides that may allow the identification of groups. All histological 
analyses will be performed in ARDEC facilities (Ariminum Odontologica, Rimini, Italy) 
using an Eclipse Ci microscope (Nikon Corporation, Tokyo, Japan) that will be coupled 
with a digital video camera (Digital Sight DS-2Mv, Nikon Corporation, Tokyo, Japan). The 

 
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measurements will be taken using the software NIS-Elements D 4.10 (Laboratory Imaging, 
Nikon Corporation, Tokyo, Japan). The percentages of new bone, pre-existing (old) bone, 
soft tissue (marrow spaces, Haversian canals, BMUs canals), bone debris/ clot remnants, 
and marrow spaces (soft tissue) will be evaluated both in contact with the implant surface 
and surrounding the implant to a distance of 0.4 mm from the surface. All measurements 
will be performed at x200 magnification from the most coronal contact of bone to the 
implant surface (B) to the apical extension of the tissues (A). The total mineralized bone 
will be assessed as sum of new and old bone. For the morphometrical measurements of 
the tissues surrounding the implant surface (tissue density), a point counting procedure will 
be adopted, using a lattice with squares of 50 microns superimposed over the histological 
image, at a magnification of x200. 
Outcomes measures  
Primary outcome: New bone in contact with the implant surface 
Description: The percentages of new bone will be evaluated both in contact with the 
implant surface 
Timeframe: After 8 weeks of healing 
Secondary outcome: Bone density around the implant surface 
Description: The total mineralized bone will be assessed as sum of new and old bone 
Timeframe: After 8 weeks of healing  
Other pre-specified outcomes: pre-existing (old) bone, soft tissue (marrow spaces, 
Haversian canals, BMUs canals), bone debris/ clot remnants, and marrow spaces (soft 
tissue) 
Description: The percentages of pre-existing (old) bone, soft tissue (marrow spaces, 
Haversian canals, BMUs canals), bone debris/ clot remnants, and marrow spaces (soft 
tissue) will be evaluated all in contact with the implant surface 
Timeframe: After 8 weeks of healing. 

 
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Data analysis 
The primary variable will be new bone in contact with the implant surface. New bone (bone 
density) around the implant surface will be the secondary variable. 
Mean values and standard deviations as well as 25th, 50th (median), and 75th percentiles 
will be calculated for each outcome variable. Means, standard deviations and 95% 
confidence intervals of the differences between test and control sites will be calculated for 
each variable analyzed. 
A Wilcoxon test will be used to analyze differences between sonic and drill groups. The 
level of significance will be set at α 0.05. 
 
 
ACKNOWLEDGEMENTS 
This study will be economically supported by Sweden & Martina, Due Carrare, Padua, 
Italy, by ARDEC Academy, Ariminum Odontologica Srl, Rimini, Italia. 
DISCLOSURE: The Authors claim to have no financial interest, either directly or 
indirectly, in the products or information listed in the article.  
 
 

 
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