Subcrestal Placement of PRAMA Implants With Convergent Neck Incorporating Ultrathin Threaded Microsurface: A Randomized Controlled Clinical Trial
Phase: NA
Conditions: Edentulism, Dental Implantation, Endosseous, Marginal Bone Loss, Periimplant Bone Loss
Sponsor: ARDEC Academy

 
 
 
 
 
STUDY PROTOCOL 
 
Subcrestal placement of PRAMA implants with convergent neck 
incorporating Ultrathin Threaded Microsurface: A randomized 
controlled clinical trial 
 
ClinicalTrials.gov Identifier (NCT Number): NCTXXXXXXXX 
Document Date: June 2024 
 
 
 
 
 
 
 

Subcrestal placement of PRAMA implants with convergent neck 
incorporating Ultrathin Threaded Microsurface. A randomized 
controlled clinical trial. 
 
Gianfranco Cesaretti, Karol Apaza Alccayhuaman,  Daniele Botticelli, Tomaso 
Mainetti, Franco Bengazi 
 
Introduction 
Subcrestal implant placement has been indicated as a method capable of better 
maintaining the volume and height of hard and soft tissues compared to implants 
placed at the level of the alveolar bone crest (Hermann et al. 2001, Novaes et al. 
2009; Barros et al. 2010; Degidi et al. 2011; Huang et al. 2012). A systematic review 
with meta-analysis concluded that platform-switching implants placed subcrestally 
show less marginal bone level change compared to crestally placed implants (Valles 
et al. 2018). In an experimental study in dogs (Cesaretti et al. 2014), similar results 
were reported, with the bone crest and coronal bone contact with the implant in a 
more coronal position in the subcrestal group compared to the crestal group. 
However, when the data were related to the original bone level, subcrestal implants 
showed more loss of buccal marginal bone and greater soft tissue recession than 
crestal implants. 
In that experiment, the neck surface was polished, and this configuration may have 
influenced the results. These findings are consistent with a clinical study in which 

two implants with a 2.8 mm polished neck were placed in eleven patients (Hämmerle 
et al. 1996). One implant was placed with the rough margin at the bone crest level, 
while the other was placed with that margin 1 mm subcrestally. Greater bone loss 
was observed in the subcrestal implants. Again, the neck surface was polished, 
suggesting that surface treatment of the neck might be necessary. 
The characteristics of the abutment surface may influence marginal bone level if the 
implant is placed subcrestally. In a dog experiment (Welander et al. 2009), the rough 
margin of the implant was placed 2 mm subcrestally. Abutments with standard or 
rough surfaces were applied to the control and test sites, respectively. After four 
months of healing, the marginal bone level was more coronal in the subcrestal 
implant compared to the crestal ones. About 40% of the test implants exhibited bone 
apposition coronal to the abutment/fixture junction. Two-piece implants were used in 
this experiment. In another dog study (Hermann et al. 2011), bone and soft tissue 
levels were evaluated in one-piece non-submerged implants and two-piece 
submerged or non-submerged implants. One-piece implants with a rough neck 
surface exhibited more coronal peri-implant mucosa and less marginal bone loss 
compared to implants with a polished surface. Furthermore, conical abutments with 
a convergent transmucosal morphology showed less marginal bone loss compared 
to divergent configurations (Agustín-Panadero et al. 2019). Conical abutments 
applied with the platform-switching concept have shown circular fibers that could 
contribute to the long-term stabilization of marginal peri-implant soft and hard tissues 
(Rodríguez et al. 2016). Moreover, an in vitro study (Doyle et al. 2009) showed that 
unidimensional surface patterns favor cell migration and phenotype expression. 

The effect of subcrestal implant positioning on hard and soft tissues remains 
controversial, and using an implant that incorporates three features—one-piece 
design, convergent (conical) neck, and micro-threads across the entire surface—
could provide important clinical insights. Therefore, the aim of this RCT is to compare 
longitudinal changes in peri-implant hard and soft tissue levels around one-piece 
implants with conical necks and micro-threads placed juxtacrestally or subcrestally. 
 
Materials and Methods 
The protocol will be submitted for approval to the Ethics Committee of the local 
research center, and the Declaration of Helsinki on medical protocols and ethics will 
be applied. Patients will be informed about procedures and possible complications 
and asked to sign informed consent. The study will follow the CONSORT checklist 
(http://www.consort-statement.org/). This RCT will be registered at ClinicalTrials.gov 
to obtain an identification number xxxxxxx. 
 
Study Population 
In this parallel randomized controlled trial, patient recruitment, surgeries, and follow-
ups will be carried out at the University of Medical Sciences of Havana. 
Inclusion criteria: 1. Edentulous area allowing placement of two implants in the 
posterior maxilla or mandible (premolars and molars); 2. Alveolar bone height 
allowing insertion of implants at least 6 mm deep (minimum total of 10 mm); 3. Need 
for implant-supported prosthetic restoration; 4. ≥21 years old; 5. Good general health 
without contraindications for oral surgical procedures; 6. Not pregnant; 7. Patients 

who agree to participate and sign informed consent. 
 
Exclusion criteria: 1. Presence of uncontrolled systemic disease; 2. History of 
chemotherapy or radiotherapy; 3. Smokers declaring >10 cigarettes per day; 4. 
Previous bone regeneration procedures at the target site. 
 
Implants Used 
The PRAMA implant, 6 mm in length and 3.8 mm in diameter (Sweden & Martina, 
Due Carrare, Padua, Italy), is a one-piece implant (Agustín-Panadero et al. 2019) 
with a ZirTi surface (Caneva et al. 2016). The neck has three different configurations: 
short type (1.8 mm high with hyperbolic convergent coronal portion), standard type 
(0.80 mm cylindrical portion and 2.00 mm convergent portion), and long type (0.80 
mm cylindrical portion and 3.00 mm convergent portion). The entire neck surface 
contains parallel micro-threads (Ultrathin Threaded Microsurface - UTM). 
 
Study Design 
This is a parallel randomized controlled trial. Two implants per patient will be used 
to restore edentulous posterior ridges of the maxilla or mandible with 2- or 3-unit 
bridges. Three patient groups will be included, each receiving randomly assigned 
implants with short (short group), standard (standard group), or long necks (long 
group). Implants will be placed with the coronal margin of the rough surface at the 
bone crest for the short group; 1 mm below the crest for the standard group; and 2 
mm below the crest for the long group. 
Additionally, one of the implant-supported crowns will have a false root shape 

apically, while the other will have a traditional shape adapted to the mucosal margin. 
 
Sample Size 
Sample size was calculated based on a preclinical experimental study in dogs that 
showed statistically significant differences in soft and hard tissue levels using six 
animals (Cesaretti et al. 2015). Given the parallel design and potential dropouts, 30 
patients will be included, ten per group (n=10). 
 
Randomization and Allocation Concealment 
Randomization will be conducted electronically by one author not involved in surgical 
procedures (DB). Assignments will be sealed in opaque envelopes opened at the 
clinic. Treatment allocation will be revealed to the surgeon after flap elevation and 
before site preparation. The distribution of differently shaped crowns will also be 
randomized and concealed as described above, and operators will only know at the 
time of prosthesis delivery. 
 
Clinical Procedures 
Clinical procedures will be performed by an experienced clinician (MCM). All 
surgeries will be performed applying a digital workflow. Both implants will be placed 
according to random assignment (see study design). Healing screws of sufficient 
length will be applied to ensure non-submerged healing. Sutures will be placed to 
adapt the flaps around the healing screw. Sutures will be removed after 
approximately 1 week. After three months of healing, digital impressions will be 
taken, and customized 2- or 3-unit zirconia bridges will be provided. Except for 

complications, antibiotics will not be prescribed. 
Maintenance 
After surgery, patients may take analgesics if needed. 0.12% chlorhexidine mouth 
rinses will be used three times daily until suture removal (7-10 days). Patients will be 
enrolled in a maintenance program throughout the study. They will be followed for at 
least 3 years, and data will be reported annually. 
 
Clinical and Radiographic Evaluations 
At prosthesis installation (Baseline), probing depth will be recorded. Clinical 
photographs, standardized intraoral radiographs, CBCT, and digital impressions will 
be taken. 
-After 6 months, plaque index, bleeding on probing, and probing depth will be 
assessed. Clinical photos, intraoral radiographs, and digital impressions will be 
repeated. 
-Annually: plaque index, bleeding on probing, and probing depth will be evaluated. 
Clinical photos, intraoral radiographs, CBCT, and digital impressions will be 
collected. 
 
Calibration for Measurements and Blinding Procedures 
Radiographic image analysis will be performed by an experienced evaluator blinded 
to treatment groups, although implant types may be recognizable in images. For 3D 
image analysis, the evaluator will be blinded to treatment allocation. 
 
Imaging Analysis 

Bone tissue levels will be evaluated on intraoral radiographs and CBCT images. 
Peri-implant volumes will be assessed using 3D images obtained from digital 
impressions. 
 
Interventional Study Model 
Parallel Assignment (with a split-mouth design within subjects) 
Number of Arms 
3 
Arm Descriptions and Interventions 
Short Neck Implant (Crestal Placement) 
Arm Type: Experimental 
One-piece PRAMA implant with a 1.8 mm short convergent neck placed at the bone 
crest. 
Intervention: Device: Short Neck PRAMA Implant – Crestal Placement 
Standard Neck Implant (1 mm Subcrestal Placement) 
Arm Type: Experimental 
One-piece PRAMA implant with a 0.8 mm cylindrical and 2.0 mm convergent neck 
placed 1 mm below the bone crest. 
Intervention: Device: Standard Neck PRAMA Implant – 1 mm Subcrestal Placement 
Long Neck Implant (2 mm Subcrestal Placement) 
Arm Type: Experimental 
One-piece PRAMA implant with a 0.8 mm cylindrical and 3.0 mm convergent neck 
placed 2 mm below the bone crest. 
Intervention: Device: Long Neck PRAMA Implant – 2 mm Subcrestal Placement 

Outcome Measures 
Type 
Outcome Title 
Description 
Time Frame 
Primary 
Change in Peri-
Implant 
Bone 
Height Over Time 
Vertical changes 
in marginal bone 
levels 
at 
each 
implant site using 
radiographs, 
CBCT, and scans. 
Baseline, 
6 
months, annually 
up to 3 years 
Secondary 
Volumetric 
Change in Peri-
Implant Tissues 
3D 
volumetric 
changes 
measured through 
digital 
scan 
overlays. 
Baseline, 
6 
months, annually 
up to 3 years 
Secondary 
Effect of Crown 
Emergence 
Profile on Peri-
Implant 
Tissue 
Volume 
Comparison 
of 
tissue 
volume 
changes between 
two 
crown 
emergence 
profiles. 
6 
months, 
annually up to 3 
years 
Secondary 
Changes 
in 
Clinical 
Parameters 
Probing 
depth, 
plaque index, and 
bleeding 
on 
probing. 
6 
months, 
annually up to 3 
years 
 

Statistical Analysis 
Data distribution for each parameter and group will be assessed using the Shapiro–
Wilk test. Depending on the results of the normality assessment, group comparisons 
will be performed using either one-way ANOVA (for normally distributed data) or the 
Kruskal–Wallis test (for non-normally distributed data). 
Post-hoc pairwise comparisons will be conducted using the Tukey HSD test 
(following ANOVA) or the Mann–Whitney U test with Bonferroni correction (following 
Kruskal–Wallis). A corrected p value < 0.05 will be considered statistically significant. 
 
 

Referencias 
Agustín-Panadero R, Martínez-Martínez N, Fernandez-Estevan L, Faus-López J, Solá-Ruíz 
MF. Influence of Transmucosal Area Morphology on Peri-Implant Bone Loss in Tissue-Level 
Implants. Int J Oral Maxillofac Implants. 2019;(34):947–952. doi:10.11607/jomi.7329 
Barros, R.R., Novaes, A.B. Jr., Muglia, V.A., Iezzi, G. & Piattelli, A. (2010) Influence of 
interimplant distances and placement depth on peri-implant bone remodeling of adjacent 
and immediately loaded Morse cone connection implants: a histomorphometric study in 
dogs. Clinical Oral Implants Research 21: 371-378. 
Caneva M, Lang NP, Calvo Guirado JL, Spriano S, Iezzi G, Botticelli D. Bone healing at 
bicortically installed implants with different surface configurations. An experimental study in 
rabbits. Clin Oral Implants Res. 2015;26(3):293-299. doi:10.1111/clr.12475 
Cesaretti G, Lang NP, Salata LA, Schweikert MT, Gutierrez Hernandez ME, Botticelli D. 
(2015) Sub-crestal positioning of implants results in higher bony crest resorption: an 
experimental study in dogs. Clinical Oral Implants Research 26:1355-1360. 
Degidi, M., Perrotti, V., Shibli, J.A., Novaes, A.B., Piattelli, A. & Iezzi, G. (2011) Equicrestal 
and subcrestal dental implants: a histologic and histomorphometric evaluation of nine 
retrieved human implants. Journal of Periodontology 82: 708-715.  
Doyle AD, Wang FW, Matsumoto K, Yamada KM. One-dimensional topography underlies 
three-dimensional 
fibrillar 
cell 
migration. 
J 
Cell 
Biol. 
2009;184(4):481-490. 
doi:10.1083/jcb.200810041. 
Hämmerle, C.H., Brägger, U., Bürgin, W. & Lang, N.P. (1996) The effect of subcrestal 
placement of the polished surface of ITI implants on marginal soft and hard tissues. Clinical 
Oral Implants Research 7: 111-119. 
Hermann JS, Jones AA, Bakaeen LG, Buser D, Schoolfield JD, Cochran DL. Influence of a 
machined collar on crestal bone changes around titanium implants: a histometric study in 
the canine mandible. J Periodontol. 2011;82(9):1329-1338. doi:10.1902/jop.2011.090728. 

Hermann, J.S., Buser, D., Schenk, R.K., Schoolfield J.D. & Cochran, D.L. (2001) Biologic 
Width around one- and two-piece titanium implants. Clinical Oral Implants Research 12: 
559-571. 
Huang, B., Meng, H., Piao, M., Xu, L., Zhang, L. & Zhu. W. (2012) Influence of placement 
depth on bone remodeling around tapered internal connection implant: a clinical and 
radiographic study in dogs. Journal of Periodontology 83: 1164-1171. 
Novaes, A.B. Jr., Barros, R.R., Muglia, V.A. & Borges, G.J. (2009) Influence of interimplant 
distances and placement depth on papilla formation and crestal resorption: a clinical and 
radiographic study in dogs. Journal of Oral Implantology 35: 18-27. 
Rodríguez X, Navajas A, Vela X, Fortuño A, Jimenez J, Nevins M. Arrangement of Peri-
implant Connective Tissue Fibers Around Platform-Switching Implants with Conical 
Abutments and Its Relationship to the Underlying Bone: A Human Histologic Study. Int J 
Periodontics Restorative Dent. 2016;36(4):533-540. doi:10.11607/prd.2580 
Valles C, Rodríguez-Ciurana X, Clementini M, Baglivo M, Paniagua B, Nart J. Influence of 
subcrestal implant placement compared with equicrestal position on the peri-implant hard 
and soft tissues around platform-switched implants: a systematic review and meta-analysis. 
Clin Oral Investig. 2018 Mar;22(2):555-570. 
Welander, M., Abrahamsson, I. & Berglundh, T. (2009) Subcrestal placement of two-part 
implants. Clinical Oral Implants Research 20: 226-231.