Surgical Extrusion for the Clinical Crown Lengthening: a 12-months Prospective Clinical Study
Phase: NA
Conditions: Tooth Decay
Sponsor: Universitat Internacional de Catalunya

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
TITLE OF THE STUDY: Surgical extrusion for the clinical 
crown lengthening: a 12-months prospective clinical study 
 
RESEARCH ETHICAL COMMITTEE APROVAL DATE: 
15 March 2018 
 
 
 
 
 
 
 
 
 
 
 

 
 
 
PROTOCOL 
 
1. Scientific background: 
 
Long-term survival rates of restorations after endodontic treatment range between 81% 
and 100%. Outcome predictors for the restored tooth with a prosthetic crown mainly 
include cavity wall integrity and the presence of 1.5 to 2 mm of ferrule (360 degrees 
sound dentin collar). In some clinical situations, the aforementioned requirements 
cannot be achieved, especially in deep carious lesions, cervical perforations, crown-root 
fractures, and failed crowns with preexisting subgingival margins. In such cases, ferrule 
should not be provided at the expense of the remaining tooth structure since it may 
provoke a biologic width invasion and, consequently, a chronic gingival inflammation 
and a loss soft tissue and bone. 
 
Three treatment options aim to obtain adequate ferrule while respecting the biologic 
width: surgical crown lengthening, rapid orthodontic extrusion and surgical extrusion. 
Surgical crown lengthening involves the removal of hard and soft tissue for the 
exposure of sufficient supragingival tooth structure. Rapid orthodontic extrusion, which 
is a less invasive treatment, allows the preservation of periodontal tissues. However, it 
is necessary to consider the patient’s willingness to wear orthodontic appliances, which 
increases the cost and time of the therapy. Surgical extrusion consists in atraumatic 
luxation of the tooth to enable its coronal reposition. Several authors have reported 
survival rates higher than 95% on surgical extrusiosion. However, little prospective 
studies are available in relation to the periodontal changes after SE.  
 
2. Objectives: 
2.1. Main objectives 
• Evaluate the success rate after at least 12 months of the surgical 
extrusion. 
• Evaluate the soft tissue rebound (STR) after at least 12 months of the 
surgical extrusion. 
 
 

 
 
 
2.1. Secondary objectives 
Evaluate the following periodontal and radiographic parameters: 
 
• Gingival papillae shape and height (Jemt index).  
• Bleeding on probing (mm). 
• Plaque index (Turesky index). 
• Gingival index (Silness & Löe index).  
• Clinical attachment level (mm). 
• Tooth mobility (Miller classification). 
• Crown-root ratio (mm). 
• Periapical healing (Rud score). 
• Root resorption. 
• Marginal bone loss. 
• Patient satisfaction. 
 
3. Hypotheses 
 
Null hypothesis (H0):   
Ho1: Surgical extrusion is not a predictable treatment for the restoration of single 
rooted teeth. 
Ho2: Surgical extrusion of single rooted teeth results in an unfavorable aesthetic 
outcome. 
 
Alternative hypothesis (H1):  
H11: Surgical extrusion is a predictable treatment for the restoration of single 
rooted teeth. 
H12: Surgical extrusion of single rooted teeth results in a favorable aesthetic 
outcome. 
 
4. Study design 
This is an interventional, monocentric, single-group, prospective clinical study. 
 
 

 
 
 
5. Methods 
 
5.1 Study population 
This prospective study comprises 14 consecutive patients in whom 15 single-rooted 
teeth were surgically extruded at the Department of Endodontics at International 
University of Catalonia, St Cugat del Vallès, Barcelona, Spain. The sample was 
recruited according to the following inclusion and exclusion criteria:  
 
Inclusion criteria: 
• Systemically and periodontally healthy, non-smoking patients. 
• Single-rooted, straight teeth with insufficient ferrule, which require restorative 
treatment. 
• Teeth with a favorable crown-root ratio. 
Exclusion Criteria: 
• Severe systemic disease patients (American Society of Anesthesiologists 
classification 1 or 2). 
• Multi-rooted, curved and/or short teeth. 
• Teeth with an uncontrolled periodontal pathology. 
• Pregnant women. 
• Teeth with types II or III mobility. 
All included patients signed an informed consent, and the study was approved by the 
Ethics Committee of Investigation of the Universitat Internacional de Catalunya (END - 
ECL – 2017 - 02). 
 
5.2 Treatment plan 
5.2.1 Pre-surgical assessment (Visit 1) 
On the first appointment, patient's medical and dental history was reviewed. Patients 
age, sex and tooth number were recorded. A pre-operative cast model of each extruded 
 Also, patient’s biotype (De 
tooth was taken and digitally scanned to assess the STR. 
Rouck) was registered based on the transparency of the periodontal probe through the 
gingival margin while probing the buccal sulcus, as follows: 
 

 
 
 
• 0: Both upper central incisors have thin biotype. 
• 1: One of the two upper central incisors has a thin biotype. 
• 2: Both upper central incisors have thick biotype. 
 
A) Clinical parameters 
 •
Percussion: assessed with a mirror handle in a vertical direction. 
 •
Palpation: assessed by a gentle finger pressure on both buccal and palatal soft 
tissue around the transplant. 
• Periodontal variables, using an standardized manual periodontal probe PCP-
UNC 15 (Hu-Friedy®, Rockwell St, Chicago, IL): 
o Periodontal probing depths (PPD): measured at 6 sites per tooth. Defined 
as the distance, in millimeters, from the gingival margin to the bottom of 
the probable pocket.  
o Gingival recession: measured at 6 sites per tooth. Defined as the 
distance, in millimeters, from the cementoenamel junction (CEJ) to the 
gingival margin.  
o Clinical attachment level (CAL): calculated indirectly as the sum of the 
previously recorded PPD and gingival recession, representing the 
distance between the CEJ and the bottom of the pocket on all present 
teeth. 
o Bleeding on probing (BoP): recorded dichotomously, at six sites, as 
present or absent within 15 seconds after the direct assessment of PPD, at 
six aspects of each tooth. 
 
• Tooth mobility (Miller classification): measured using two dental mirror 
handles. 
 
o Grade 0: Normal (physiologic) movement when force is applied. 
o Grade 1: Mobility greater than physiologic. 
o Grade 2: Tooth can be moved up to 1mm or more in a lateral 
direction (buccolingual or mesiodistal). Inability to move the tooth 
in a vertical direction (apicocoronally). 

 
 
 
o Grade 3: Tooth can be moved 1mm or more in a lateral direction 
(buccolingually or mesiodistally). Ability to move the tooth in a 
vertical direction. 
 
• Gingival papillae shape and height (Jemt index): based on the distance from the 
highest curvature of the marginal buccal gingiva to the contact point of the 
transplanted tooth with the following index scores: 
 
o 0 No papilla is present. 
o 1 Less than half of the height of the papilla is present. 
o 2 Half or more of the height of the papilla is present but does not extend 
all the way up to the contact point between the teeth. 
o 3 The papilla fills up the entire proximal space and is in good harmony 
with the adjacent papillae. There is optimal soft tissue contour. 
o The papilla is hyperplastic and covers too much of the transplanted or 
adjacent tooth. The soft tissue contour is more or less irregular. 
 
• Bleeding on probing (mm): recorded dichotomously as present or absent 
within 15 seconds after the assessment of PPD, at six aspects of each 
transplant. 
 
• Plaque index (Turesky index): visually measured as follows: 
o 0: No plaque present 
o 1: Separate flecks of plaque at the cervical margin. 
o 2: A thin continuous back of plaque (up to 1 mm) at the cervical 
margin. 
o 3: A band of plaque wider than 1 mm but covering less than one-
third of the surface. 
o 4: Plaque covering at least one-third but less than two-thirds of the 
surface. 
o 5: Plaque covering more than two-thirds of the surface. 
 

 
 
 
• Gingival index (Silness & Löe index): the scores of the four areas of the tooth 
can be summed and divided by four to give the GI for the tooth. 
o Score 0 = Normal gingiva. 
o Score 1 = Mild inflammation - slight change in color, slight edema. 
No bleeding on probing. 
o Score 2 = Moderate inflammation - redness, edema, glazing. 
Bleeding on probing. 
Score 3 = Severe inflammation - marked redness and edema, 
ulceration. Tendency toward spontaneous bleeding. 
 
B) 2D radiographic parameters 
Standardized digital bitewings and periapical radiographs with paralleling technique 
(Kodak RVG 6100; Carestream Health, Rochester, NY) and a selective CBCT scan (CS 
9300; Carestream Health, set at 8.0 mA and 84 kV, with a 12-second exposure time and 
the smallest possible field of view (5 x 5 cm) were taken to assess root anatomy as well 
as the following radiographic parameters:  
 
 •
Preoperative periapical lesion, recorded dichotomously as present or absent from 
the periapical radiography. 
 
• Crown-root ratio (mm): measured on the periapical radiograph, and scored as 
follows: 
o 
Good: crown-root ratio < 1. 
 
o 
Just: crown-root ratio = 1.   
o 
Unfavorable: crown-root ratio > 1. 
 
• Marginal bone loss: based on the bone crest aspect on the bitewing radiograph, as 
follows: 
o Initial: < 25% of marginal bone loss. 
o Moderate: between 25% - 50% of marginal bone loss.  
o Severe: > 50% of marginal bone loss. 

 
 
 
5.2.2 Surgical extrusion (Visit 2) 
The principal investigator performed all the procedures following the modified 
technique described by Kahnberg. Under local anesthesia and after having removed the 
caries lesion, each tooth was gently luxated with thin elevators, which were placed no 
more than 1mm within the gingival margin to avoid damaging the cervical PDL cells. 
Subsequently, teeth were coronally positioned using thin forceps to expose sufficient 
supracrestal tooth structure and splinted for 4 weeks with a retainer. Post surgery, the 
patients were prescribed analgesics and antibiotics for 1 week, and instructed to rinse 
daily with 0.12% clorhexidine and follow a soft diet for 2 weeks.  
 
5.2.3 Endodontic therapy (Visit 3) 
All the root canal treatment and retreatments were completed one month after the 
surgery. 
 
5.2.4 Restorative treatment (Visit 4) 
The biologic width of each tooth was left to reestablish itself for 2 months, after which 
the same operator (ML) restored the teeth with a composite build-up and a fiber glass-
reinforced epoxy post (Exacto, Angelus, Londria, PR, Brazil) (if required) and in the 
same appointment all the teeth were prepared for single crowns with horizontal 
 
preparations. 
 
 
5.2.5 Post-surgical assessment (Visit 5) 
cast model was taken for the 
Patients were recalled at 12 months post-surgery, when a 
post-operative digital scanning, and the following clinical and radiographic parameters 
 
were recorded:
 
A) Clinical parameters 
 
 •
Percussion. 
 •
Palpation. 
 •
Periodontal probing depths. 
 •
Gingival recession. 

 
 
 
 •
Clinical attachment level. 
 •
Bleeding on probing. 
• Tooth mobility. 
• Gingival papillae shape and height. 
• Bleeding on probing. 
• Plaque index.  
• Gingival index. 
• Soft tissue rebound (STR): measured in mm by superposing both pre-operative 
and post-operative scanned models of each patient using surgical planning 
software (Blue Sky Plan, Blue Sky Bio, Libertyville, IL, USA). Soft tissue 
rebound was measured by calculating the difference between the lowest point of 
the gingival margin of the pre-operative model and the lowest point of the 
 
gingival margin of the post-operative model.
 
B) Radiographic parameters 
 
• Periapical healing (Rud score): based on any radiolucency surrounding the 
apical third of the root, as follows: 
 
o Complete: Reestablishment of the periodontal space and the hard lamina 
around the apex. 
o Incomplete (scar tissue): Decrease or alteration of the apical lesion with 
at least one of the following characteristics: the periphery of the 
radiolucency is irregular and may be demarcated by a compact bony 
margin; the radiolucency is located asymmetrically around the apex. 
o Uncertain: Radiolucency greater than twice the width of the periodontal 
space and surrounded by tissue resembling a hard lamina. Lesion with 
circular or semicircular periphery and located symmetrically around the 
apex. 
o Unsatisfactory: Increase or maintenance of the size of the lesion. 
 
 

 
 
 
• Root resorption: based on the aspect of the transplant periodontal ligament, as 
follows: 
 
o Absence of root resorption: complete PDL healing with normal width of 
the PDL space around the whole root. 
o Inflammatory root resorption: radiolucency is observed all along the 
external root surface of the dentin. 
o Replacement resorption: resorption lacunae are filled with bone and the 
PDL space is missing. 
 
• Crown-root ratio (mm). 
• Marginal bone loss. 
 
C) Patient’s satisfaction 
 
Each patient filled in a questionnaire based on a 10-cm visual analogue scale to assess 
their degree of satisfaction regarding the surgical procedure and the esthetic outcome; 0 
indicated a complete satisfaction while 10 was entirely unsatisfactory. 
 
5.2 Success assessment 
The following criteria were evaluated to establish the success of the treatment:  
 •
Normal function of the extruded tooth with physiologic mobility without pain or 
discomfort. 
 •
Healthy periodontal tissue surrounding the extruded tooth with periodontal 
pockets < 4 mm. 
 •
Normal appearance of the PDL around the extruded tooth with no signs of any 
progressive root resorption or marginal bone loss > 25%. 
 
 
 
 
 

 
 
 
STATISTIC ANALYSIS PLAN (SAP) 
 
The sample size was calculated based on the STR variation, using as a reference the 
study of Arora et al., in which the mean STR reported at 6 months was 0.77 ± 0.58 mm 
after the crown lengthening. This measure corresponds to a large effect size (d=1.3).  In 
the present study the sample size was calculated using one sample t-test, considering a 
relevant STR of 0.5 mm at 12 months and a dropout of 15%. Thus, the final sample 
consisted in 15 patients, for a power of 80%, and considering an effect size of d = 0.85. 
 
The data contained in the follow-ups were entered into a database (Excel, Microsoft 
Corporation) for data analysis and preparation for the final report. All the variables were 
analyzed using a descriptive method (mean, %). Besides, Chi2 test was used to find a 
statistical relation between pre-operative and post-operative marginal bone loss of the 
extruded teeth.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
 
 
INFORMED CONSENT FORM (ICF) 
 
This study aims to evaluate the clinic and radiographic outcomes of the surgical 
extrusion at one year. This procedure involves the extrusion (separation) of the tooth 
with respect to the bone in a vertical direction, in order to expose sufficient tooth 
structure to restore the tooth. Subsequently, the tooth is stabilized with a wire attached 
to the adjacent teeth for 2 – 4 weeks. Then, the root canal treatment / retreatment is 
performed, after which the tooth is restored with a prosthetic crown. 
 
We have requested your participation in a research study. Before deciding whether to 
agree to participate, it is important that you understand the reasons for the research, how 
your information will be used, what the study will consist of, and the possible benefits, 
risks, and discomforts that may result.  
 
VOLUNTARY PARTICIPATION 
Participation in a trial is a voluntary and personal decision. In the case of not wanting to 
participate or wanting to leave the study, the quality of the care you will receive will not 
be affected and the usual protocols will be followed. If you choose to participate, the 
Patient Information Sheet and the Informed Consent will be given to you to sign all 
sheets of both documents.  
 
If the Principal Investigator considers that the study may harm your health, he or she 
will invite you to abandon it, and will give you the pertinent explanations. 
Finally, once your participation has ended, you must follow the procedures indicated by 
the doctor to guarantee your safety. 
The immediate benefit of participating in the study is your contribution to scientific 
knowledge and development, without being able to guarantee an immediate benefit for 
you. 
 
Me, Mr./Mrs.:……………………………………………………………………….. 
 

 
 
 
I have received verbal information about the study and have read the attached written 
information, of which I have received a copy. I have understood what has been 
explained to me. 
I have been able to comment on the study and ask questions of the responsible 
professional. 
I give my consent to take part in the study and I assume that my participation is 
completely voluntary. 
I understand that I can withdraw at any time without affecting my future medical care. 
 
By signing this informed consent form, I give my consent so that my personal data can 
be used as described in this consent form, which complies with the provisions of 
Organic Law 15/1999, of December 13, Protection of Personal Data. 
 
 
 
Signature of the patient 
 
 
 
 
Date of the signature 
DNI 
 
 
 
STATEMENT OF THE INVESTIGATOR OR INVESTIGATOR 
 
The patient who signs this consent form has received, from the professional, detailed 
information in oral and written form of the process and nature of this research study, 
and has had the opportunity to ask any questions regarding the nature, the risks and 
benefits of participating in this study. 
 
 
Signature of the investigator  
 
                     Date of the signature 
Name: