Dr Juan Blanco
email: jblanco@blancoramos.net

Antonio Liñares

Javier Pérez#

Fernando Muñoz

HISTOMETRIC STUDY IN THE BEAGLE DOG

Keywords: extraction, immediate implant, immediate loading, ridge alterations Immediate implants, immediate loading, ridge alterations, flapless surgery

Objective: To assess the effect of immediate loading on ridge alterations following implants placed into fresh extraction sockets in a dog model.

Material and Methods:

Six Beagle dogs were used. Four implants were placed into post-extraction sockets in the lower jaw immediately after removal of premolar 3 and 4.

In the control side, two implants remained without occlusal loading, and in the test side received an immediate prosthesis with occlusal contacts (involved implant sites).

Extraction sockets without implants were used as test in non-involved implant sites.

Three months later the dogs were sacrificed.

Results: Vertical distance from implant shoulder to Bone Crest (BC) was similar for both groups. BC at the buccal aspect was located 3.66 mm apical to the shoulder in the test group and 4.11 mm in the control group. This difference was not statistically significant. Buccal bone resorption was more pronounced in the premolar 3 area than in the premolar 4 area. In edentulous sites the buccal bone crest was located 0.97 mm apical to the lingual counterpart.

Conclusion:

Immediate implant placement with or without immediate loading does not prevent the amount of bone resorption that occurs following tooth extraction without immediate implant placement.

Deleted: Four implants were placed in the lower jaw (two per side) in 6 beagle dogs, immediately after tooth extraction (Pm3, Pm4). Flapless immediate implant placement was performed in one hemimandible (control). The same procedure was done in the contralateral side and immediate prosthesis was connected with occlusal contacts (test). After 3 months the dogs were sacrificed, and samples were processed to assess ridge alterations with histometric Deleted: analysis The distance from the shoulder to the first bone-to-implant contact was similar in both groups. The mean first bone-implant contact at the buccal aspect was located in relation to the SLA level at 1.2 mm for the test group and 1.7mm for the unloaded group. This difference was not statistically significant. The amount of buccal bone resorption was more pronounced in the premolar 3 area than in the premolar 4 Deleted: Buccal bone resorption do always occur following tooth extraction.

Deleted: aspects as

Deleted: There is an increasing interest in immediate implant placement and immediate loading protocols, but from a biological point of view there are some aspects (osseointegration process, bone resorption, etc.) that are necessary to be clarified before recommending such technique in a daily practice. We present the results of an experimental study in the beagle dog, where we have compared flapless immediate implant placement and immediate loading versus no loading. ¶ (Araújo & Lindhe 2005[START_REF] Johnson | A study of the dimensional changes occurring in the maxilla after tooth extraction. Part I. Normal healing[END_REF][START_REF] Johnson | A study of the dimensional changes occurring in the maxilla following tooth extraction[END_REF][START_REF] Pietrokovski | Alveolar ridge resorption following tooth extraction[END_REF][START_REF] Schropp | Bone healing and soft tissue contour changes following single-tooth extraction: a clinical and radiographic 12month prospective study[END_REF]. [START_REF] Schropp | Bone healing and soft tissue contour changes following single-tooth extraction: a clinical and radiographic 12month prospective study[END_REF], in a prospective clinical study, showed that about 50% of the bucco-lingual width of the alveolar bone was lost 12 months following single tooth extraction. An important finding was that two-thirds of this loss occurred within the first 3 months. [START_REF] Paolantonio | Immediate implantation in fresh extraction sockets. A controlled clinical and histological study in man[END_REF] suggested that the placement of implants into post-extraction sockets could maintain the original shape of the alveolar ridge. Moreover, the survival rates of implants placed into post-extraction sites are similar to those implants placed in healed sites [START_REF] Chen | Clinical and esthetic outcomes of implants places in postextraction sites[END_REF].

However, experimental models have shown that following immediate implant placement a process of bone resorption occurs, mainly on the buccal aspect (Araújo et al. 2005, Araújo et al. 2006[START_REF] Blanco | Ridge alterations following immediate implant placement in the dog: flap versus flapless surgery[END_REF]. The amount of resorption in the preclinical models of immediate implants is inconsistent, and it may be affected by implant location (Caneva et al. 2010a), implant diameter (Caneva et al. 2010b), implant surface [START_REF] Vignoletti | Early healing of implants placed into fresh extraction sockets: an experimental study in the beagle dog. II: ridge alterations[END_REF], socket dimension and thickness of the buccal bone plate (Araújo et al 2006), and the surgical approach [START_REF] Blanco | Ridge alterations following immediate implant placement in the dog: flap versus flapless surgery[END_REF], Caneva et al 2010c).

On the other hand, experimental studies evaluating the hard tissue healing of immediate implants in humans [START_REF] Botticelli | Hard tissue alterations following immediate implant placement in extraction sites[END_REF][START_REF] Sanz | A prospective, randomized-controlled clinical trial to evaluate bone preservation using implants with different geometry placed into extraction sockets in the maxilla[END_REF]) have shown a similar amount of horizontal bone resorption to that observed at sockets that heal spontaneously after tooth extraction [START_REF] Schropp | Bone healing and soft tissue contour changes following single-tooth extraction: a clinical and radiographic 12month prospective study[END_REF].

Deleted: ¶ ¶ ¶ ¶ ¶ ¶ ¶ ¶ ¶ Deleted:
Following tooth extraction a process of bone resorption occurs in the alveolar ridge leading to dimensional alterations that may affect treatment strategy to restore the missing teeth. Clinical and radiographic studies [START_REF] Johnson | A study of the dimensional changes occurring in the maxilla after tooth extraction. Part I. Normal healing[END_REF][START_REF] Johnson | A study of the dimensional changes occurring in the maxilla following tooth extraction[END_REF][START_REF] Pietrokovski | Alveolar ridge resorption following tooth extraction[END_REF][START_REF] Camargo | Influence of bioactive glass on changes in alveolar process dimensions after exodontias[END_REF][START_REF] Schropp | Bone healing and soft tissue contour changes following single-tooth extraction: a clinical and radiographic 12month prospective study[END_REF] Some authors have suggested that certain loads may increase the amount of mineralized bone at the bone-to-implant interface and in the peri-implant bone area [START_REF] Wehrbein | Bone-to-implant contact of orthodontic implants in humans subjected to horizontal loading[END_REF][START_REF] Gotfredsen | Bone reactions adjacent to titanium implants subjected to static load of different duration. A study in the dog (III)[END_REF]. Immediate implant loading may stimulate bone formation and thus may influence early stages of osseointegration [START_REF] Romanos | Histologic and histomorphometric evaluation of peri-implant bone subjected to immediate loading: an experimental study with Macaca fascicularis[END_REF][START_REF] Romanos | Bone-implant interface around titanium implants under different loading conditions: a histomorphometrical analysis in the Macaca fascicularis monkey[END_REF].

Moreover, immediately loaded implants present similar survival rates to implants loaded in a delayed protocol [START_REF] Esposito | Interventions for replacing missing teeth: different times for loading dental implants[END_REF].

The combination of immediate implant placement and loading shows slightly lower survival rates to those of immediate loading of implants placed in healed sites.

However, the bimodal approach showed favorable marginal bone changes after 1 year [START_REF] Atieh | Immediate restoration/loading of immediately placed single implants: is it an effective bimodal approach?[END_REF].

A recently published minipig study showed that the amount of bone resorption was similar in immediate implants with immediate loading as immediate implants with delayed loading, in non-splinted implants [START_REF] Liñares | Effect of immediate or delayed loading following immediate placement of implants with a modified surface[END_REF].

The objective of the present investigation was to assess the effect of immediate loading on ridge alterations following implants placed into fresh extraction sockets in a dog model.

Material and methods

Once approval from the Ethics Committee of the University of Santiago had been given, this research was carried out using 6 beagle dogs.

Experimental study

Surgical procedure

The experimental model used in this study was recently reported [START_REF] Blanco | Flapless immediate implant placement with or without immediate loading. A histomorphometric study in beagle dog[END_REF].

Six beagle dogs, about 2 years old and 20 kg of weight, were enrolled in the study.

During surgical procedures, the animals were premedicated with acepromacine (0.05 mg/Kg intramuscularly) and morphine (0.2 mg/Kg intravenously). Immediately after, they were induced general anesthesia by injection of propofol (2 mg/Kg intravenously).

Isofluorane (1.5-2%) and O 2 (100%) were used as inhalated anaesthetics.

In total, 24 implants were placed in 6 dogs. All implants were 8 mmlong, 3.3mm flush with the buccal bone crest. In order to achieve this, the buccal soft tissue height

was measured with a periodontal probe immediately before implant installation and having in mind that the smooth surface of the implant had a height of 2.8 mm (Fig. 1c).

Before implant placement, the socket diameter was measured with a periodontal probe.

The mean bucco-lingual width was 3.5 ± 0.3 mm and 3.9 mm ± 0.3 for the premolar 3 and 4 respectively. Thus, after implant placement a small gap < 1 mm was present between the inner part of the socket and the implant surface. No grafting procedures nor suturing were performed.

After implant installation the experimental groups were randomly selected. Two implants of one side (test group) received an immediate loading restoration by means of provisional abutments for bridges (Straumann® Dental Implant System, Basel, Switzerland). The provisional prosthesis splinted the implants by an acrylic stent that remained with occlusal contacts with the antagonist teeth. The occlusion was checked again at sacrifice. Short healing caps (1.5 mm height) were connected to the the implants in the contralateral side (control group) aiming a non-submerged healing approach without loading (Fig. 1 h & i).

The mesial sockets of premolar 3 and 4 were left to heal without implant placement and served as test in non-involved implant sites. The second mandibular premolars in both quadrants were not involved in the surgical procedures and were used as controls in non-involved implant sites.

During the first week after surgery, the animals received Amoxicillin (500 mg, twice daily) orally and Meloxicam (0.1 mg/Kg, once a day) orally. Throughout the experiment, the animals were fed a pellet diet. They were placed on a plaque control regimen that included tooth and implant cleaning three times per week with the use of toothbrush and dentifrice.

After three months of healing, the animals were euthanized with an overdose of sodium pentobarbital through the cephalic veins and a histometric analysis was performed to evaluate the main variables on each group:

Histological preparation

The mandibles were removed and block biopsies of each implant were dissected using an oscillating saw [START_REF] Donath | Preparation of Histological Sections (by the Cutting-Grinding Technique for Hard Tissue and other Material not Suitable to be Sectioned by Routine Methods) -Equipment and Methodological Performance[END_REF]). The samples were fixed 1 week in 10% formol. Next, the samples were dehydrated in different graded ethanol series (70-100%), and infiltrated with 4 different graded mixtures of ethanol and infiltrating resine, glicometacrilate (Technovit 7200®, VLC -Heraus Kulzer GMBH, Werheim, Germany) with 1% of Benzoyle Peroxide (BPO®: Heraus Kulzer GMBH, Werheim, Germany).

The last infiltration was performed with pure infiltrating resine under vacuum. The samples were then polymerized, first under low intensity UV light for 4 h, followed by a polymerization under high intensity UV light for 12 h and finally by keeping the samples heated for 24 h to assure complete polymerization.

The samples were glued to a sample holder. Longitudinal sections in bucco-lingual direction of 200 microns were cut with a band saw and mechanically polished (Exakt Apparatebau, Norderstedt, Germany) using 1200 and 4000 grit silicon carbide papers (Struers, Copenhagen, Denmark) until a samples thickness of 70 µm was obtained and all sections were stained with Levai Laczko tintion for histometric analysis.

Histometric analysis.

Formatted: Font: Bold The samples on the permanent ports were observed using the Olympus® SZX9 microscope (Olympus, Tokyo, Japan). By means of the Olympus® DP12 digital camera (Olyumpus, Tokyo, Japan), the images were captured and transferred to the computer.

With the Microimage® program, the points of interest were identified from the digital histological images in order to measure the distances, which were expressed in millimeters.

Implant site

A line was traced along the digital image parallel to the implants longitudinal axis. The following marks were then marked on both the vestibular and lingual side of each implant: (Fig. -S -BC: Distance from the implant shoulder to the bone crest.

-S -IC: Distance from the implant shoulder to the most coronal bone implant contact.

-BCb-BCl:Vertical distance between buccal and lingual bone crest.

Tooth site

Formatted: Font: Italic At tooth sites (premolar 2), the following marks were identified at the buccal and lingual side (Fig. 2b):

• CEJ: cemento-enamel junction

• BC: bone crest (buccal/lingual)

• GM: gingival margin

From each point, a perpendicular line was traced towards a parallel line along the tooth longitudinal axis and the following measurements (expressed in millimeters) were taken:

• GM-BC: distance from the gingival margin to bone crest

• GM-CEJ: distance from the gingival margin to cemento-enamel junction

• CEJ-BC: distance from the cemento-enamel junction to the bone crest.

Edentulous site

At the edentulous sites, the height of the cortical bone walls was determined in the The statistical analysis was performed using the Sigma-Stat statistics program.

Statistical analysis

Descriptive statistics were taken for each of the variables and groups (mean values and standard deviation).

To compare the implant groups in each variable for test and control and implant position (premolar 3 or 4), the Student´s t-test for paired observations was used.

The dog was used as unit for analysis (n=6), using average results across similarly treated implants in the same dog and then compared. P-values <0.05 were considered statistically significant.

Results

Clinical observations

In total 24 implants were immediately placed following tooth extraction, 12 of them were immediately loaded and the other 12 remained without loading in a nonsubmerged healing approach. At the end of the experimental period, none of the implants and prosthesis was lost. At the time of sacrifice all restorations were still in service and the occlusal contacts remained in the provisional bridge, however, all restorations showed abrasion of the occlusal aspects.

Histological observations

Implant sites

The histological study showed that the buccal and lingual mucosa in each implant of both groups was covered by a keratinized oral epithelium that continued from the periimplant marginal mucosa with the barrier epithelium facing to the implants. Apical to this epithelium was an area of fibre rich connective tissue, with fibres orientated parallel to the implant surface.

Tooth sites

The GM was located coronal to the CEJ at the buccal and lingual aspect of each tooth.

The bone wall was markedly wider at the lingual than at the buccal aspect of the teeth.

The buccal BC was located at a longer distance from the CEJ than the corresponding lingual BC.

Edentulous sites

The mucosa covering the healed socket was lined by an oral epithelium that harboured a well-keratinized surface layer. The underlying, connective tissue was characterized by its densely packed collagen fibres and lack of infiltrates of inflammatory cells. A newly formed hard-tissue bridge covered the entrance of the extraction socket. This marginal ridge was mainly made up of woven bone, although small areas of lamellar bone could also be observed. The newly formed hard-tissue bridge extended a varying distance into the extraction socket. Apical of the bridge, the edentulous region was comprised of cancellous bone dominated by its bone marrow. The marginal termination of the original buccal bone wall was located apical of its lingual counterpart.

Histometric results.

Implant sites (Table 1) (Fig. 3 &4)

Distance between S and BC

No significant differences were found between groups. Considering that the implant neck is 2.8 mm long, the bone crest was at the buccal aspect roughly 0.86 mm apical to Deleted: on Deleted: In the immediate loading group, this was 3.66 ± 0.44 mm (buccal) and 2.28 ± 0.55 mm (lingual). In the unloaded group this was 4.11 ± 1.04 mm (buccal) and 2.77 ± 0.72 mm (lingual).

Deleted: in terms of S-BC distance.

Deleted: . the SLA border and 0.50 mm coronal at the lingual one in the test group. In the control group the bone crest was located 1.3 mm apical to the SLA border at the buccal and at the same level of the SLA border on the lingual aspect.

Deleted

Distance between S and IC

No significant differences were found between groups. The most coronal bone-toimplant contact was located 1.27 mm apical to the SLA surface, and 0.30 mm at the lingual aspect. Again, these distances were similar in the unloaded group, 1.70 mm at the buccal and 0.37 mm at the lingual aspect.

Vertical distance between buccal and lingual bone plate at implant sites.

The mean vertical distance between buccal and lingual bone crest was similar in both groups. The difference was not statistically significant. The buccal bone crest was always located apical to the lingual counterpart.

Distance from the implant shoulder (S) to the most coronal bone-to-implant contact (S-IC) and to the bone crest (S-BC) comparing implants from premolar 3 region with implants from premolar4 region. (Table 2 & Fig. 5)

The mean S-IC (buccal) distance in all implants of the premolar 3 region was 4.67 ±0.83 mm and 3.87 ± 0.34 mm in the premolar 4. This difference was statistically significant (p=0.026). In the lingual aspect the difference was not significant. The mean S-BC (buccal) distance in the premolar 3 region was 4.4 ± 0.82 mm and 3.33 ± 0.33 mm in the premolar 4. This difference was statistically significant (p=0.004). Again there was no difference between premolar 3 and 4 in the lingual aspect. The mean distance between the GM and the BC was 3.02 ± 0.38 mm (buccal) and 2.57 ± 0.34 mm (lingual), while the corresponding distance between GM and CEJ was 2.24 ± 0.34 mm (buccal) and 1.98 ± 0.39 mm (lingual). The BC was located on the average of 0.77 ± 0.19 (buccal) and 0.53 ± 0.07 mm (lingual) apical to the CEJ.

Tooth sites (

Edentulous sites

The mean vertical distance between the buccal and lingual bone crest was 0.97 ± 0.63 mm. The buccal bone crest always remained apical to the lingual counterpart.

Discussion

The present investigation was designed to assess the impact of immediate implant placement and loading in terms of ridge alterations in the beagle dog model. This experimental model confirms the results shown in similar animal models of immediate implant placement (Araújo et al. 2005, 2006b[START_REF] Blanco | Ridge alterations following immediate implant placement in the dog: flap versus flapless surgery[END_REF][START_REF] Vignoletti | Early healing of implants placed into fresh extraction sockets: an experimental study in the beagle dog. II: ridge alterations[END_REF], Caneva et al. 2010a& b, Liñares et al. 2011). This means that a process of bone resorption occurs after tooth extraction, even when an implant is placed immediately in a post-extraction socket. The present study has also evaluated the potential effect of immediate loading in immediate implant placement. No differences were found between the immediate loading group and the unloaded group. These means that the immediate loading protocol did not affect the process of ridge alterations of implants placed immediately after tooth extraction, and this is in agreement with a recently published minipig study [START_REF] Liñares | Effect of immediate or delayed loading following immediate placement of implants with a modified surface[END_REF]. The amount of buccal bone resorption showed in that study (0.7 mm test and 0.8 mm control) is similar to the results of the present investigation (0.8 mm test and 1.3 mm control). Several preclinical investigations have shown higher amounts of buccal bone resorption. Araújo et al. (2005) in a similar model but without loading showed 2.6 mm of buccal bone resorption after 3 months of healing of immediately placed implants. In another study, the same group showed at 2 months of healing, 2.1 mm of buccal bone resorption (Araújo et al. 2006b). This difference may be due to the fact of raising a flap in those studies, but probably more to the size of the implant, since they used a 4.1 mm Straumann implant and the present study a 3.3 mm implant with the same characteristics. In fact, a recently published study in the Labrador dog showed almost double bone resorption with a 5 mm implant compared to a 3.3 mm implant (Caneva et al. 2010b). In the present study, the resorption process was more pronounced at the buccal aspect and in the premolar 3 area. The mean distance from SLA border to bone crest at buccal in the premolar 3 area was three times longer than in the premolar 4 region. The bone crest in premolar 3 was located 1.6 mm apical to the coronal level of the rough surface, and in the premolar 4 area the bone crest was situated 0.5 mm apical to the same landmark. This is in agreement with the results of a similar study by [START_REF] Vignoletti | Early healing of implants placed into fresh extraction sockets: an experimental study in the beagle dog. II: ridge alterations[END_REF], who showed that with a 3.25 mm diameter implant the amount of buccal bone resorption was significantly higher in the premolar 3 area in comparison with the premolar 4 area. Moreover, Araújo et al. 2006a in a similar model but using 2 different socket sizes found more bone resorption in the socket of reduced diameter in comparison with the bigger one. In the premolar area the mean distance from shoulder to first bone-to-implant contact was 2 mm, however in the molar area was 0.8 mm. This may be due not only to the size of the socket but also to the thickness of the buccal bone plate. The authors stated that the thinner a bone wall, and the closer the implant is placed to this wall, the higher the risk of compromised healing and occurrence of bone dehiscence. However, it should be considered that the presence of an adjacent tooth to an implant may counteract the bone resorption process following tooth extraction. The implant in the premolar 4 area had an adjacent tooth (molar 1), but the implant in the premolar 3 area did not. Therefore this situation could have an impact on the final results.

Thus from this study and previous animal models it seems that the size of the socket, thickness of the buccal bone plate and implant diameter may play an important role in terms of buccal bone resoption after immediate implant placement.

A small intrabony defect was detected in most of the implants at the end of the experiment, since the distance from implant shoulder to bone crest was shorter than the distance from shoulder to the first bone-to-implant contact. It is unclear if after longer healing periods these defects tend to disappear after a process of bone remodelling.

On the other hand, the present investigation found that the mean vertical distance between the buccal and lingual bone crest was 0.97 mm at edentulous sites. At implant sites, this distance was longer, 1.38 mm in the test group and 1.34 mm in the control.

Thus, almost 0.5 mm more buccal bone resorption was found in the implant sites than in the edentulous sites. Araújo et al. (2005) showed in a similar study the amount of bone resorption following extraction of premolars 3 and 4 with or without immediate implant placement. After 3 months of healing, the amount of buccal bone height reduction (in comparison with lingual bone alteration) was similar at implant sites and edentulous sites. The vertical distance between the buccal and lingual bone crest was 2.2 mm in edentulous sites and 2.4 mm in implant sites. Thus, the amount of buccal bone resorption in the edentulous sites showed by Araújo was more than double to the observed in the present investigation. This could be explained by the surgical approach performed in the Araújo study (raising a flap) in comparison to this study (flapless approach). It must be emphasized that this surgical trauma (flap elevation), implying the separation of the periostium and its disconnection from the underlying bone surface, will cause vascular damage and an acute inflammatory response, which in turn will mediate the resorption of the exposed bone surface [START_REF] Wilderman | Repair after a periosteal retention procedure[END_REF][START_REF] Staffileno | Histologic study of cellular mobilization and repair following a periosteal retention operation via split thickness mucogingival flap surgery[END_REF][START_REF] Wood | Buccal bone resorption do always occur following tooth extraction with or without immediate implant placement and with or without immediate loading to those implants[END_REF]. Recently, two experimental studies in the beagle dog have evaluated the impact of elevating a flap for tooth extraction on the dimensional alterations of the ridge. The use of a bone graft, filling the buccal void that may result after implant installation into fresh extraction sockets, could prevent bone resorption, however conflicting data exists on this issue (Araújo et al. 2011, Hsu et al. in press).

In summary, it can be concluded due to the results of the present study that immediately loaded implants placed into fresh extraction sockets, do not prevent bone resorption that mainly occurs at the buccal bone plate in the normal remodelling process. The distance from the shoulder to the first bone-to-implant contact was similar in both groups. The mean first bone-implant contact at the buccal aspect was located in relation to the SLA level at 1.2 mm for the test group and 1.7mm for the unloaded group. This difference was not statistically significant. The amount of buccal bone resorption was more pronounced in the premolar 3 area than in the premolar 4 area. In edentulous sites the buccal bone crest was located 0.97 mm apical to the lingual counterpart.

F

Formatted

  study: There is an increasing interest in immediate implant placement and immediate loading protocols. From a biological point of view, ridge alterations and alveolar bone resorption must be clarified before recommending such technique in daily practice. The present study shows the results in terms of ridge alterations following flapless immediate implant placement with or without immediate loading. Principal findings: In this animal model, ridge alterations did always occur irrespective of the loading protocol applied to the immediately placed implants. Practical implications: Buccal bone resorption did always occur and this may compromise the aesthetic outcome of post-extraction implant placement in the anterior area.

  The resorption process may be more pronounced in implant sites than in extraction sites. Deleted: at different degrees Deleted: ¶ Introduction Several experimental and human studies have shown that alveolar bone dimensions are reduced following tooth extraction

  have shown important reductions in the height and width of the alveolar crest following tooth extraction (single or multiple).

  indiameter with Standard neck height (2.8mm), Straumann Dental Implant System(Institute Straumann, Basel, Switzerland). All the implants had a sand-blasted and acid etched surface (SLA). The implants were placed into fresh extraction sockets, and bone augmentation procedures were not attempted The lower premolars 3 and 4 were carefully removed, separating the roots by means of tooth hemisectioning with the use of a fissure bur, and extracting them individually with elevators and forceps (Fig.1 a & b). After the extraction, immediate implants were placed into the center of the distal socket of each tooth (Fig.1 d-g). Four implants were placed in each dog (2 in each hemimandible) according to the manufacturer protocol(Straumann® Dental Implant System, Basel, Switzerland). The implants were placed so that the marginal level of the sand blasted and acid etched (SLA) -coated surface was

Deleted:

  The implant was positioned in the center of the socket.

  2 a) S: Implant shoulder PM: Peri-implant mucosa margin IC: Most coronal contact point of the bone with the implant BC: Bone crest From each point, a perpendicular line was traced towards a parallel line along the implants longitudinal axis and the following measures (expressed in millimeters) were taken:

Formatted:

  Space Before: 6 pt Formatted: Font: Italic, English (U.K.) Formatted: Indent: Left: 36 pt, No bullets or numbering Formatted: Font: Italic Formatted: No bullets or numbering Deleted: ¶ Deleted: subsequently Deleted: made Deleted: <#>SLA: Marginal border of the SLA-coated surface that was located 2.8 mm. apical of S. ¶ Deleted: l Deleted: BIC Deleted: First Deleted: BIC Deleted: first Deleted: <#>PM -BIC: Distance from the peri-implant margin mucosa to the first bone to-implant contact, that is, the length of the biologic width. ¶

  following way according to Araujo & Lindhe (2005) (Fig. 2c): a line parallel to the long axis of the center of the socket was drawn (C-C) to separate the buccal and lingual compartments. Subsequently, horizontal lines (LC and BC) perpendicular to C-C were drawn to connect the most coronal portions of the buccal and lingual bone crest to C-C. The vertical distance between the buccal and lingual intersections with C-C was measured and expressed in mm (LC-BC).

Formatted

Formatted

  Deleted: bone resorption was more pronounced at the buccal than at lingual Deleted: occurred Deleted: in the extraction sites without implants.

  [START_REF] Fickl | Tissue alterations after tooth extraction with and without surgical trauma: a volumetric study in the beagle dog[END_REF] compared alveolar bone healing following tooth extraction with or without flap elevation. Plaster casts were taken before, 2 and 4 months after the extractions. Volumetric bone changes were analyzed with specially designed software. The results showed an increase of 0.7 mm of volumetric shrinkage of both hard and soft tissues in the flap with respect to the flapless group. Later,[START_REF] Araújo | Ridge alterations following tooth extraction with and without flap elevation: an experimental study in the dog[END_REF] in a similar experimental model but with longer follow-up (6 months), showed that the resorption of the alveolar crest was not influenced by the technique for tooth extraction (flap or flapless). Recently, an experimental study in the Labrador dog(Caneva et al. 2010c), showed no difference in terms of bone resorption for postextraction implants with flapless or flap approach. Thus, it seems that in shorter healing periods the impact of flap elevation may have an effect on early bone resorption, but in longer healing periods the amount of resorption may be equal when performing tooth extraction with or without flap elevation.

  Figure 3.

Figure 4 .

 4 Figure 4.

Figure 5 .

 5 Figure 5.

They were provided by the School of Veterinary Studies at the University of Cordoba, and were installed in the Animal

		Deleted: in humans have shown that
	were performed according to the Spanish Government Guide and the European	the amount of horizontal resorption is similar in immediate implant placement
		(Botticelli et al. 2004, Sanz et al. 2010)
	Community Guide for animal care.	and sockets that heal spontaneously after tooth extraction (Schropp et al. 2003). ¶
		Deleted: with
	F o r
		Deleted: in press
	P	Formatted: Font: Not Italic
	e e r	Formatted: Adjust space between Latin and Asian text, Adjust space between Asian text and numbers Deleted: to assess dimensional changes of the alveolar ridge after tooth extraction
		alone and immediate implant placement
	R	with or without immediate loading. Deleted: The objective of this study was to assess in the beagle dog model the
	e v i e	influence of flapless immediate implant placement and loading on ridge alterations of the alveolar bone Deleted: .
	Experimentation Service facility at the Veterinary Teaching Hospital Rof Codina of w
	Lugo. The animals were maintained in individual kennels in a 12:12 light/dark cycle
	(lights on at 07:00 h) and 22 ± 2°C, with regular chow and tap water. All experiments

Table 3 )

 3 Deleted: border,

	Deleted: on
	Deleted: aspect
	Deleted: unloaded
	Deleted: on
	Deleted: BIC
	Deleted: in terms of S-IC distance
	Deleted: In the immediate loading
	group, this was 4.07 ± 0.67 mm (buccal)
	and 3.10 ± 0.29 mm (lingual). In the
	unloaded group this was 4.50 ± 0.78 mm
	(buccal) and 3.17 ± 0.33 mm (lingual).
	This implies that in the immediate
	loading group, on the buccal aspect,
	Deleted: the first
	Deleted: on
	Deleted: on
	Deleted: on
	Deleted: No significant differences
	were found between groups. ¶
	¶
	Distance between PM and BIC (biologic
	width) ¶
	In the immediate loading group, this was
	3.93 ± 0.64 mm at the buccal and 2.95 ±
	0.37 mm at the lingual aspect. In the
	unloaded group, this was 4.01 ± 0.65 mm
	at the buccal and 2.64 ± 0.53 mm at the
	lingual aspect, with no significant
	differences between groups. ¶
	Deleted: the
	Deleted: bone crest
	Deleted: the
	Deleted: e
	Deleted: 1.38 ± 0.51 mm in the test
	group and 1.34 ± 0.87 mm in the control.
	This difference
	Deleted: first
	Deleted: BIC
	Deleted: BIC

Table 2 .

 2 Results of histometric measurements in mm (mean and SD) describing the

	Deleted: buccal vertical bone
	resorption in both groups but in the flap
	group 0.7 mm more bone loss was found
	than in the flapless group.

Table 3 .

 3 Results of histometric measurements in mm (mean and SD) describing the distance between landmarks in tooth sites.

	GM-CEJ	CEJ-BC	GM-BC
	Buccal	Lingual	Buccal	Lingual	Buccal	Lingual
						Formatted Table
	2.24±0.34 1.98±0.39 0.77±0.19 0.53±0.07 3.02±0.38	2.57±0.34
						Deleted: the
						Deleted: h sites. ¶
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GM-CEJ, distance from the gingival margin to cemento-enamel junction. CEJ-BC, distance from the cemento-enamel junction to the bone crest. GM-BC, distance from the gingival margin to bone crest.

Journal of Clinical Periodontology -PROOFJournal of Clinical Periodontology -PROOF

This study was supported by Straumann Company (Straumann, Basel, Switzerland).