rezumat teza de doctorat - limba engleza.doc.doc

UNIVERSITY OF AGRICULTURAL SCIENCES AND VETERINARY MEDICINE OF BANAT TIMISOARA

FACULTY OF VETERINARY MEDICINE

RECONSTRUCTION TECHNIQUES IN STOMATOLOGICAL AFFECTIONS OF

DOMESTIC CARNIVORES

thesis to obtain the title doctor in veterinary medicine

COORDINATOR: PROF. DR. IGNA CORNEL

PHD STUDENT:

SABĂU MARIUS

2009

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SUMMARY

INTRODUCTION

Dental pathology on dog include various types of traumatic and degenerative affections associated with alimentary diet or trauma, frequently finalized with hard dental structures destructions or even with the loss of teeth. Secondary to these, may appear manducation problems and changes of temporo-mandibular joints biomechanics, with consequences in alimentary behavior of the dog.

These problems impose the use of advanced reconstruction techniques from human dentistry – implantotherapy – a treatment modality accepted and preferred in case of partially or totally edentulous patients. The use of implants in dentistry has extended, a large diversity of designs and surface microstructures being in use.

Various studies were conducted to optimize the contact between alveolar bone and dental implant and create a biomedical interface. The literature mentions an adhesive interface between bone and titanium and titanium alloy implants with sandblasted, acid etched, electrochemical deposals, hidroxyapatite or titanium plasma sprayed surfaces.

Locally, the collaboration between Discipline of Prosthetics from the Faculty of Dentistry and Discipline of Metal Processing from the Faculty of Mechanics was materialized in conception and achieving endooseous screw type dental implants for oral rehabilitations, improvement of titanium and titanium alloy implants stability by sandblasting, license for shaping thread part of implants apparatus by electroerosion and diamonded disk cutting.

In the area of osteoinductive nanomaterials applied on metallic surfaces we can remind the Institute of Research and Technological Design Bucharest and ISIM Timisoara, concerning porous ceramic materials deposals on metallic structures and hidroxyapatite deposals on titanium structures. Also, research and production activities in biomaterials, acid etched and hidroxyapatite coated titanium implants are carried on by SC. Poneti SRL, Bucharest.

All these new directions of research, outline this study, encountering on one side the request for prosthetic restorations on dogs and on the other side the request to elaborate autochthonous dental implants.

Approaching these aspects is made from the point of view of the veterinarian and does not look at dogs as experimental models for the introduction of human use new types of dental implants, but as a patient.

The objective of this study is underlying reconstructive techniques for dental affections on dogs, using oral implants with osteointegrative interface and metaloceramic crowns for partially edentulous patients and reinforced composite reconstructions with endodontic dowels for patients with dental fractures.

I. BIBLIOGRAPHICAL STUDY

The bibliographical part of this paper contains 75 pages, grouped in seven chapters, include morphology and anatomy elements for domestic carnivores dentition, a brief description of the main dental pathology that conclude with hard dental tissue breakage or even the loss of teeth and therapy elements for these problems, illustrated with 30 figures.

The therapy part include main extractions techniques, endodontic treatment and dental reconstruction, dental implantology elements, osteointegration principles for dental implants and considerations regarding biomaterials used in oral implantology.

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Dental medicine aspects were approached to open the veterinarian practitioner to the diversity of dental pathology of domestic carnivores and to list their usual treatment techniques.

II. ORIGINAL CONTRIBUTIONS

This part of the paper contains 120 pages grouped in seven chapters, including 99 figures, 82 tables and 25 graphics.

1. SCREW TYPE EXPERIMENTAL DENTAL IMPLANTMODELS ELABORATION

We have considered necessary to begin a potential innovative study with technological transfer possibility to obtain autochthon endosseous dental implants with similar design and properties to those used in human dentistry, but on lower production costs and with proper size for the canine patients.

Purposes of the study: Designing the experimental dental implants. Applying computed simulation tests to evaluate bone-implant interface resistance by

finite element method for optimal shape configuration of the implants.

1.1 Designing the experimental dental implants

Materials and methods

Design of new types of dental implants takes count of the dental medicine principles as well as the local production possibilities.

Also, other aspects were considered: the used materials, implant type, surgical type of insertion, prosthetic restoration stages, and dimensions.

The implants must be conceived so they can be used in canine model and to allow further prosthetic loading for functional and aesthetic dental rehabilitation.

To establish the intra-osseous part of the implants we considered necessary to study the roots dimensions from 30 mesocephalic dog skulls, measuring especially the mandibulary and maxillary premolars. We selected these parts of arcades to be future edentulous, respectively the support for dental implants. The data was used to establish the dimensions for the osseous part of the implants.

Results and discussions

Following this study we have determined that the average lengths of dental roots are between 8,9 mm and 16,2 mm and the average values of the root dimensions are between 4,8-11,6 mm proximally and between 3,7-5,2 mm distally. Also, we have observed that the proximal diameters, in vestibular-oral way are lower that the ones in mesial-distal way, the roots being flattened in vestibulo-palatinal direction, respectively in vestibulo-lingual direction, especially on the 4th upper premolar. We have concluded that dental roots have conoidal shape with flattened proximal part.

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From the literature results that titanium and his alloys have optimal mechanical properties for oral implants and their oxides are very stable in physiological conditions. These aspects recommended titanium alloys for the proposed implants production.

From the multitude of implants made till present, we have chosen endooseous, one stage dental implants because they substitute very well a dental root in tridimensional way and are close to their natural shape.

Regarding surgical type of insertion, we can differentiate screw on implants, implants with preliminary tapping, self-tapping implants, cylinder implants and blade implants. The practice demonstrated that screw type dental implants inserted in medium and lower density bone tissue are better to be self-tapping and those inserted in high density bone must be with preliminary tapping.

Concerning the number of surgical stages we can differentiate one-stage dental implants that necessitate a single surgical intervention and two-stage dental implants that necessitate two interventions.

Considering that the maxillary and mandibulary bone support of the future implantation sites are characterized by all the density degrees described above, we have designed both self-tapping and with preliminary tapping implants.

Technologically speaking, for the production of screw-type, one-stage dental implants we have considered as economically for the small serial production the cutting process.

We choosed to design both self-tapping and with preliminary taping dental implants, one-stage, with a 3,5 mm and 3 mm diameter and with three different lengths of the thread part (8, 10, 12 mm).

Conclusions

The dental implants that we designed are screw type, one-stage implants and copy the dental root morphology.

The lengths of the threaded parts were established in accordance with the results from the study made on natural teeth of dog skulls (8, 10, 12 mm lengths and 3,5 mm diameters for cylindrical screw type implants, respectively 3,5 mm proximal diameter and 3 mm distal diameter for conoidal screw type implants), so they will be easy to adapt on canine maxilllary and mandibulary bone support.

Because we wanted to insert the implants in both maxillary and mandibulary bone we designed self-tapping implants and implants with preliminary tapping.

1.2. Computed simulation tests to evaluate bone-implant interface resistance by finite element method for optimal shape configuration of the implants

The finite elements method plays an important role in the solution of engineering problems and can be applied to simulate different biomechanical systems – in our case the alveolar bone – dental implant ensemble. This type of analysis was generally accepted as complementary instrument to understand mechanical reactions in different biological investigations.

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The principle of finite elements method consist in the replacement of the real structure with an ensemble of interconnected individual elements (finite elements) that have determined dimensions. By the analyze of the phenomenon that took place on each finite element, as an integrative part of the structure, the reaction of hole system can be recomposed.

Using Solidworks software, geometrical tridimensional models of the implant and surrounding bone were created and than transferred to Ansys numerical analysis software.

With these models and data from the literature regarding mechanical and material characteristics different loading situations, similarly to oclusal forces, were simulated.

Von Misses stress values and their distribution at the bone-implant interface were determined at the moment of oclusal loading and graphic illustrated by a colored spectrum, each color corresponding to a value of stress.


A stress concentration was observed at the level of implant’s necks and in the cortical area of the alveolar bone. Stress values decreased in the area of cancellous bone. The implant acted like a rigid structure. The analysis of the numerical models confirmed the fact that in cervical area of the alveolar bone and in the implant material there is a major stress accumulation. Mesial and distal to the implant the stress distribution was symmetrical. On compression, the maximum value of stress was observed also in the cervical area of the implants and decreased to the apical part of implant.

Analyzing the level of stress peaks it can be observed that titanium has enough strength reserve not to exceed the supportable values that could generate fissure and breakdown of the components.

Following the observations obtained with computed simulation we have observed that conoid dental implant assure a more homogeneous distribution of stress, respectively a lower concentration at cervical region.

Our results may be compared with other author’s results that used finite element analysis to evaluate the geometry of implants and periimplantary stress distribution with Solidworks and Ansys software. They observed the same tendency to stress accumulation around cervical part of the implants.

Conclussions

The finite element method allows the alveolar bone-implant ensemble analysis in conditions similar to oclusal forces, the results being useful for an optimal configuration of the implants.

Both types of implants are submitted to increased stress in the cervical region.The conical dental implant assures a more uniform distribution of stress around the

threaded part of the implant and a lower concentration around the cervical regions. Titanium alloy has enough strength resistance not to exceed the supportable values that

could fissure and break the implant.

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2. THE ACHIEVEMENT OF EXPERIMENTAL DENTAL IMPLANTS

The objectives of this stage was the finite product – dental implants obtaining, and accuracy of production checking for the cutting process. Also we tested the mechanical strength of the implants to different solicitations and tried to improve the osteointegrative properties by various types of surface changes of the threaded part.

2.1. Prototypes fabrication


The fabrication of screw type dental implants was made in Biomechanics and Intelligent Prosthetics Laboratory of Polytechnic University Timisoara on SL 10 CNC automatic turrete lathe with numerical command.

The materials used were 4 mm diameter titanium alloy - TiAl6V4 calibrated rods. The implants were polished on the extraosseous part with natural leather disks activated

wits chrome oxide.After finishing prototypes production those were measured individually to check the

reproductibility of the cutting process.


Both types of implants were made with the three length variants (8, 10, 12 mm).The roughness obtained on the threaded parts had values between 42 and 58 μm and

between 0,4 – 0,8 μm on the rest of the implant.The dimensions of dental implants resulted from the cutting process with automatic turrete

lathe with numerical command respected all the specification described in the design chapter.The precision of this lathe is high because of the numerical command equipment that

controls the production by software and so the human error almost does not exist. The cutting process used for dental implants prototypes and further small series obtaining

for animal model tests represents the optimum economical alternative because powder metallurgy and metal casting involve technological costs justified for large series.

ConclusionsThe cutting process with on automatic turrete lathe with numerical command is an adequate

method to produce small series of screw-type dental implants.Automatic turrete lathe with numerical command minimize production errors that intervene

when classical lathe is used, the resulted implants reproducing all the characteristics described for his type.

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2.2. Mechanical testing of experimental models on tensile, compression, torsion and shock breakage solicitations


Mechanical testing of the dental implants was made at CIDUCOS Laboratory of Polytechnic University.

Tensile, compression and bending tests were made on the same equipment - MULTITEST 5-I device and torsion tests were made on VORTEX – X device.


In both types of implants the critical cross-section corresponded to 2,5 mm.A very important aspect on these implants is intermittent solicitations values which must

not exceed the fatigue breakage strength σo and torsion τ0. These strengths are lower that mechanical traction strength.

If fatigue strength is exceeded, the implant will brake after a wile, without deformation because of the internal atomic bonds destruction.

The fractures of the implants are rigid and appear at the place where a stress concentration that acts multiaxial. The medium value of the force at pulsatile bending breakage, after five determinations, was 183, 98 N for cylindrical implant and 214,63 N for conical implant.

Corresponding to these forces the pulsatile bending breakage strength values are between 610-695 N. These two values are placed in the admissible interval (525 - 1080). The pulsatile torsion strength value is 307 N for cylindrical implant and 395 N for conical implant. Also these values are in the admissible interval.

On both implants, the breakage appeared at the end of the threaded part (cervical part of the implants) where the bending moment has maximum value.

Similar values for mechanical strengths of titanium alloys are described in the literature, our results being comparable with other authors.

Conclusions

All the values obtained on strength mechanical tests of the dental implants are placed in the admissible values interval.

These data sustain the results obtained on computed simulation tests.TiAl6V4 titanium alloy has enough strength not to exceed the supportable values that could

generate fissures in case of oclusal forces, his mechanical properties being superior to pure titanium.

2.3. Improvings of the threaded part of dental implants

To assure a better integration of the dental implants in the bone structure, the literature cite threaded part modifications. Frequently, surface treatments consist in acid etching, titanium and hidroxyapatite plasma spraying, electrochemical deposition of tricalcium phosfate etc., which increase the contact surface of the implant with bone.

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To increase the surface contacts of the threaded part, we used different procedures of surface treatments: acid etching, electrochemical deposition of calcium and phosphorus ions, titanium oxide and hidroxyapatite plasma spraying.

2.3.1. Acid etching This method consisted in sinking the threaded part into an phpsphoric acid bathe and pass

through the implants a stream with different values of voltage and amperage.

2.3.2. Electrochemical deposition of calcium and phosphorus Preliminary preparation was made by chemical polish into a fluorhidric, sulfuric, azotic

acids and water mix and than chemical passivation.Deposition of calcium and phosphorus ions was made by sinking into electrolitic solution

with a Ca/P =1,7 ratio.

2.3.3. Titanium oxide and hidroxyapatite plasma deposition Was made on Metcoschultzer plasma jet device.


Electrochemical deposition assure a thinner layer and a more uniform distribution on the implant’s surface, that respects the thread profile in comparison with the plasma jet deposition method. By sinking the implants into electrolytic solution, the level of depositions can be controlled better, the purpose of this method being only the thread parts modification.

These findings are valid for acid etching that is also a electrochemical method which tries to combine the favorable qualities of rough surfaces with those of micro-roughness in one type of surface that has a higher contact with bone.

Because of the osteoconductive properties of hidroxyapatite, explained by the net this material puts at osteoblasts and osteocites disposition, these implants have higher tolerance in less favorable conditions (micromovements).

Similarly to hidroxyapatite implants, the ones with electrochemical deposals have a positive effect on periimplantary osteogenesys process.

An increase of contact surface but without osteoconductive properties was observed on titanium plasma sprayed dental implants.

Conclusions

Al these methods fulfill the challenge to increase the contact surface with the bone.The electrochemical method assures a better control of the deposition on the threaded part

of the implant.

3. SURGICAL EDENTATION. CREATING THE BONE SUPPORT NECESSARY FOR IMPLANTATION

The objective of this part of the study was to create the partially edentulous animal model, which has mandibulary and maxillary bone support to insert the dental implants. We prepared for the implantation the premolar region.

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On 30 common breed dogs, ages between 1 and 4 years, weighted between 16-24 kg, clinically healthy, premolars extractions (106, 107, 108, 206, 207, 208, 307, 308, 407 and 408) were made under general anesthesia associated with regional analgesia of the infraorbitary and mandibular nerve.

Before surgery, the teeth were scaled (if needed) and the oral cavity was rinsed with clorhexidine solution.

The extraction technique includes several stages as described in the bibliographical chapter for pluriradicular teeth.

Postoperatively, we administrated amoxicillin (Synulox) for five days associated with local treatment with clorhexidine, in order to prevent septic complications.

Radiographic exam was performed for eventually root remnants alveolar bone fragments observation.

After 10 days the sutures were removed. Three months after surgery radiographic exam was performed again to confirm the existence of a suitable bone support for implant insertion.


The extractions evolved without any complications. The upper 4th premolars (108, 208) were extracted with difficulty because of their large vestibular roots and strong periodontal ligaments.

The surgical wounds healed uneventfully, without septic complications, fistulas and dehiscence.

After conventional and digital radiographic exam performed immediate after surgery, a normal alveolar contour without bone fragments or root remnants was observed. At three months postoperatively the radiographic exam showed into the dental alveoli a calcified bone tissue with a density similar to the contiguous bone.

Our observations could be compared with the ones cited by the literature.

Conclussions

Surgical edentation according to the techniques accepted by the veterinary dentistry assures the prerequisites for a healing without complications.

At three months after extractions we have radiographic confirmation of a satisfactory bone support for implantation.

4. DENTAL IMPLANTS INSERTION AND THEIR PERIODICAL CLINICAL AND RADIOGRAPHIC EVALUATION FOR OSTEOINTEGRATION

At these phase we benefit of experimental created animal model, at 90 after extractions, to insert the dental implants.

The objective of this phase of the study is to evaluate the osteointegration process by periodical clinical and radiographic exams.


The implants insertion was made under general anesthesia combined with infraorbitar and mandibular nerve analgesia and the distribution was in conformity to roots dimensions determined in subchapter 1.1.

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After surgery the prevention for septic conditions was made with oral administration of Stomorgyl 10 and local administration of Germostop bucal.

The diet consisted in semisolid dog food for all the integration period.The periodical evaluation was made by the following parameters evaluation made at three

and six months: morphological aspect of periimplantary gingiva, Periotest index, gingival bleeding index, periimplantary probing depth index, modified plaque index and by conventional and digital radiographic examination.


The clinical exam of periimplantary soft tissues revealed postoperatively the presence of an mild regional edema (which does not put tension on sutures), the presence of blood clots on incision and on cervical parts of the implants. We have observed that periimplanary gingival tissue does not copy the cervical parts of the implants and is slightly elliptic.

In the next seven days, the edema decreased gradually, tha blood clots disappeared and on the incision and cervical area a scar tissue has formed.

We considered that the healing of periimplantary soft tissue is accomplished after 14 days from surgery.

The crestal incision presented as a linear scar tissue with a slightly depression. The granulation tissue filled the remaining gaps around the cervical parts of the implants and covered it with epithelium. The sutures that did not fall till 14 days were removed.

Along with the other parameters evaluation, the periimplantary gingival tissue was observed. At both three and six months we did not observed gingival tissue changes. The cervical gingival had a healthy aspect, without contour, volume or color changes and without spontaneous bleeding tendency.

Exception from these findings were the individuals with no. 4 from experimental group 4 and no. 5 from experimental group 2 at which we have observed gingival changes. The cervical gingiva showed signs of chronic inflammation with detachment from the implants necks and with retraction on vestibular part, spontaneous bleeding tendency and alimentary debris accumulation.

Periotest values were between -8 and -1 reflecting a good and very good stability on all experimental groups. We have observed that on implants with surface changes the periotest values were lower than the ones without, which indicate a better primary stability. The early osteointegration of implants with modified surfaces was due to the increase of contact surface.

Exception from these results are individuals with no. 5 from experimental group 2 and no. 4 from experimental group 4, which as result of abnormal behavior (cage bars biting), oversolicitated the implants. At these individuals the Periotest values are in accepted range concerning osteointegration but without the possibility of functional loading. At six months, a stability aggravation was observed more obvious on the mesial and central implants of individual no.5 and on all three implants of individual no. 4.

Although the distal implant has an acceptable stability, we considered this patient as being compromised for prosthetic rehabilitation of the edentulous area.

Gingival bleeding index evaluation is made for periimplantary soft tissue status evaluation because it represents a barrier between oral environment and the threaded part of the implant. In case of healthy periimplant soft tissues, the success chances of osteointegration are increasing.

In most of the cases, the bleeding was absent or like isolated spots, which indicates a good/satisfactory health status of the periimplantary soft tissues.

On dog no. 5 from experimental group 2 we observed at mesial and central implants a gingival contour alteration and a spontaneous bleeding tendency. On probing around the distal implant of this individual the bleeding was like isolated spots.

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The advantage of one-stage dental implants in comparison with two-stage dental implants is that the firsts doesn’t need a second intervention that could determine a periimplantar inflammatory process and complications because of the unsealed gingivo-implant space.

The average values of periimplantary pobing depths are between 1 and 3,5 mm and represents a healthy/satisfactory periimplantary tissue. The absence of periimplantary pockets larger then 6 mm demonstrates that the tissues tolerate well the presence of the implants.

Exception from these results are the same individuals described above at which we obtained values over 6 mm, being in correlation with the morphological aspect of the gingival, respectively with his retraction on the vestibular part. Because of this retraction the measurements were made having as landmark the bottom of gingivo-implantary sulcus and the border of implants’cervix.

This lack of attachment on surrounding tissues positively correlates with the absence of stability (increased Periotest values).

Although the modified plaque index does not have an objective value, it can be considered as an indicator of oral hygiene in oral implantology.

The values are between 1 and 4, being correlated with the semisolid diet and with the lack of oral hygiene.

Radiographic we have observed a homogenously dense periimplant bone tissue, without lucencies or resorbtion areas over the threaded part. The images present an alveolar bone loss in the case of mesial and central implant of dog no. 5, respectively on all three implants of dog no.4. The resorbtion areas are mostly vertical. At six months we have also observed an horizontal bone tissue resorbtion, especially near the cervical parts.

To increase her objective value, the radiographic interpretation must be correlated with the others parameters. There is a positive correlation of radiographic images with Periotest values, gingival bleeding index and periimplantary probing depth.

Conclusions

Quantitative-objective evaluation of dental implants osteointegration can be accomplished based on mobility index, periimplantary bleeding index, periimplantary probing depth and radiographic aspect appreciation.

The modified plaque index is subjective, having only a guiding value regarding the quality of oral hygiene, not being necessarily positive correlated with periimplant tissue health status.

The results obtained at clinical evaluation are in correlation with the radiographical findings.

In about 94,75%, the implants can be considered integrated, the rest of them being considered failure – independent to the surgical act or maintenance conditions (behavioral problems being responsible for the failure).

On three months after implantation we have observed a better stability of modified surface implants, especially on those with hidroxyapatite and Ca-P deposals.

The early superior stability of hidroxyapatite and Ca-P implants, confirmed data from literature regarding the osteoinductive properties of these implants.

The six months evaluation confirms a good integration of all implants, small differences between groups regarding Periotest values and similar values for the soft tissues assessment.

After six months, most of the implants (94,75%) are integrated and can be functionally loaded.

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5. DENTAL RECONSTRUCTION WITH METALO-CERAMIC CROWNS FIXED ON DENTAL IMPLANTS

The objective was to finalize the morphological and functional rehabilitation of the dental arcades by metalo-ceramic crowns appliance on the integrated dental implants. The purpose of the reconstruction was a normal occlusion and manducation obtainance.


On two dogs from eache experimental group, under general anesthesia (Propofol Lipuro 1% - self-dosage), two step impressions (putty-wash) were made using Spofa Dental products: Stomaflex Solid for preliminary impression - putty (condesation curing silicone impression material, very high viscosity) and Stomaflex Creme - wash (condensation curing silicone impression material, low viscosity, light bodied material).

Based on these impressions, plaster models were obtained. After that, metallic caps were molded and coated with ceramic material (Vita Ceramics). The metalo-ceramic crowns were manufactured for the reconstruction of the upper premolars (107, 108, 207, and 208) and lower premolars (307, 407).

The crowns were fixed on the implants using a glass-ionomer luting cement (Kavitan Cem). Each crown was fixed on one dental implant with the exception of those for the reconstruction of 108 and 208, that were fixed on two implants (representing the two main roots)

The mobility was determined with Periotest® (Siemens) immediate after fixing crowns on the implants and two months later. The reading values are between -8 and +50 and (Periotest, 2007)

In this two months interval all the dogs were feded with dry food (granulated) according to producer’s specifications concerning quantity.


Using Stomaflex Solid and Stomaflex Creme we have obtained very good details of the regions that needed reconstruction.

Plaster models based on these silicone impressions represent precise copies of edentulous regions with dental implants inserted.

Periotest values obtained immediate after fixing the crowns on the implants were between -4 and +2, meaning a good initial stability (the accepted degree of mobility for dental implants is placed between -8 and +1.

The Periotest values obtained after two months are similar to those found immediate after cementation (values placed between -4 and -1).

Concerning crowns for reconstruction of upper 4th premolars (108 and 208), most of the Periotest values were negative (between -4 and -2), which can be explained by the fact that each one of these were fixed on two implants.

Conclusions

Metalo-ceramic crowns represent a physionomical and high resistance method for premolars reconstruction in dogs.

Silicone materials from the synthetic elastomers group (Stomaflex Solid şi Stomaflex Crema) facilitate a good detail obtainance of implanted edentulous regions.

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Crowns cementation on dental implants offers a good stability in the condition of dry, granulated alimentary diet.

6. HISTOLOGICAL EVALUATION OF THE OSTEOINTEGRATION PROCESS

The objective of these stage is histological confirmation of osteointegration on one side and osteoconductivity evaluation of different roughness surfaces on the other side.


From one individual of each experimental group bone-implant specimens were excised, dehydrated and then preinfiltrated, infiltrated and embedded using Technovit 9100 New Kit.

The samples were sectioned using Leica SP1600 diamonded disk saw microtome.The sections were submitted for polymer extraction, stained using the hematoxilin –eosin

method and then examined with Olympus CX41 optic microscope.


Analyzing the sections, a normal density periimplantary bone tissue with bone marrow spaces was observed. The screw threads are filled with mineralized bone tissue and there are no signs of inflammatory or foreign body reactions. The presence of osteons near by screws’ threads suggests a bone remodeling process.

On cylindrical implant, lateral to his surface and parallel with his border, a dense fibrous connective tissue can be observed but only around coronal part. This connective tissue seems to be continuous with the bone. The spaces between threads are filled with both lamellar and cancellous bone and bone.

The bondage between hidroxyapatite layer and titanium alloy is intimate on all surface. It can be observed that the HA and titanium oxide layer have variable thickness. Unlike plasma sprayed surfaces, the electrochemical obtained ones are almost indistinguishable on the sections, only an increased contact surface being observed.

Bone – implant contact is increase in case of rough surfaces. HA and plasma sprayed titanium oxide markedly increase contact surface in comparison with mechanical obtained surfaces and positively influence the osteointegration process.

Conclusions

The histological evaluation made at six months after implants insertion confirms an direct contact of those with alveolar bone and the presence of newly-formed bone tissue around them.

Histological aspects does not reveal major differences of the bone tissue at bone-implant interface with the specification that rough surfaces increase the contact areas.

7. „IN VITRO” COMPARATIVE EVALUATION OF DENTAL RECONSTRUCTIONS WITH OR WITHOUT REINFORCEMENTS

Dental fractures with extensive loss of dental tissue, especially on teeth under increased occlusal forces, involve reinforced restoratives. The oclusal stress in case of carnassial teeth is the result of compression and shearing forces.

The objective of this study was the comparative evaluation of the resistance to compression on reinforced composite restoratives with and without endodontic dowels.

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For this study we have used 40 upper 4th premolars taken from 20 mesocephalic dog skulls, grouped as following: Group 1 – teeth without restoratives (n=8); Group 2 – teeth with self-cure composite restoratives, without endodontic dowels (n=8); Group 3 – teeth with photo-cure composite restoratives, without endodontic dowels (n=8); Group 4 – teeth with self-cure composite restoratives, with endodontic dowels (n=8); Group 5 – teeth with photo-cure composite restoratives, with endodontic dowels (n=8).

On all teeth, except group one, coronal fractures were simulated using a dental micromotor with diamonded disk. The tips of the principal cusps were removed and thereby opening of the pulp chamber was created.

Endodontic treatment was performed on all the teeth with simulated crown fractures. On groups two and three, the cavities were prepared in a retentive form, acid etched and

then self-cured composite (Evicrol – Spofa Dental – group two) and photo-cured composite (Opticor – Spofa Dental – group three) restoratives were made.

On groups four and five, after removing excess root filling material, gold plated screw posts were inserted into vestibular root canals . Self-cured composite (group 4) and photo-cured composite (group 5) restoratives were then performed, preserving as much as possible the tooth morphology.

The mechanical test of the restoratives was made at C.I.D.U.C.O.S Laboratory of Polytechnic University on Multitest 5-I device. To simplify positioning in testing device, the teeth roots were integrated in acrylic material - Duracryl, SpofaDental.


Following the axial compression mechanical tests more values were obtained, corresponding to the three moments on dental structure or reconstruction breakage: mesial cusp fracture, distal cusp fracture, crown or reconstruction fracture.

It can be observed that composite reconstructions without reinforcements had lower resistance that natural teeth and reinforced restoratives.

We have also determined that after the two main cusps breakage, as result of compression force increase, the lateral coronal wall will brake and the composite detaches from the palatinal part of the tooth.

In case of reinforced restoratives, after the two main cusps breakage, the crown fractures on mesio-distal sagittal plane, corresponding to the main roots, in which the endodontic dowels are inserted. The composite material changes his aspect but does not detach himself from the crown.

There were not significant resistance differences between self-cure and foto-cure composites.

On natural teeth, without restoratives, the forces were similar to those obtained for the reinforced restoratives. The aspect of the fractured crown is similar with the one observed on reinforced restoratives, meaning a fracture line on the sagittal plane corresponding to the long axes of the main roots.

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Conclusions

Compression resistance of reinforced composite restoratives in similar to natural teeth resistance.

Composite restoratives without reinforcements have lower compression resistance that the ones with because of the thinning of dental crown in retentive purpose, which predispose to fracture.

Speaking of the same type of reconstruction, we didn’t observed differences between self-cure and foto-cure composites.

FINAL CONCLUSIONS

Autochthon dental implants achievement, easy to adapt on canine bone support, is the first step to internal development of these advanced technique of dental reconstruction and represent an timely approach in veterinary dentistry.

Surface changes of the threaded parts of implants, speaking of increased roughness and osteoconductivity, reflects positively on the osteointegrative properties of those.

Following clinical and radiographical exams corroboration, we have determined a high percent (94,25%) of experimental dental implants osteointegration, confirmed by histological exam of bone-dental implant interfaces.

Dental reconstruction with metalo-ceramic crowns fixed on dental implants complete and finalize dental and oral rehabilitation, aesthetically and functionally speaking.

Partial dental reconstructions using composite materials and endodontic pins represent a reliable technique in the limited destructions of dental tissues condition.

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