300 volume 1 • issue 3 July / September 2011 • Abstract
The mechanical properties of zirconium are optimum, comparatively with the other ceramic materials. Initial and fracture resistance, as well as its resistance to flexion, the white, opaque colour, permitting several shades, the special biological properties, largely recommend large-scale utilization of zirconium in prosthetic restorations.
Zirconium crowns and bridges were realized in 129 patients (81 women and 48 boys), with ages between 15 and 57 years, along 4 years.
The working method applied in the laboratory made use of the CAD-CAM system, followed by scanning on a Dental Wings scanner and a CAM burring system from Wieland 917, 18.
In a few cases, repeated evaluations demonstrated ac-cidents and complications, such as skeletal fractures, ce-ramic chipping, decementation, etc.
Key words::zirconium, clinical evaluation, bio-mechani-cal advantages
Introduction of zirconium (zirconium diox-ide, ZrO2) as a dental material generated a spe-cial interest for the dental community from the very beginning of its application. Zirconium is largely employed for prostheses (at the level of the bony skeleton), as due to its special proper-ties, namely: chemical and dimensional stabil-ity, high mechanical resistance, its Young modu-lus (210 GPa) being compatible with that of the steel alloys (193 GPa). The mechanical proper-ties of zirconium are among the highest, com-paratively with the other ceramic materials (1-4). The initial and fracture resistance of zirco-nium derives from the physical property of the zirconium partially stabilized by final transfor-mation and strengthening (5-8). In vitro studies demonstrated a bending strength of 900-1200 MPa/m2. On the other side, it is opaque-white in colour, permitting further colouring (5 shades are possible), with the great advantage, in the aesthetic zones, of covering the teeth
reconsti-CLINICAL EVALUATION OF CERAMIC PROSTHETIC RESTORATIONS
ON A ZIRCONIUM STRUCTURE AFTER 4 YEARS
Delia Cristina Bahrim1, Andreea Munteanu2, Sava Nazira3, Carmen Stadoleanu4
1. Ph.D. in medicine
2. preparator, Apollonia University, Iasi 3. stomatologist, Apollonia University, Iasi 4. prof. univ. dr., Apollonia University, Iasi E-mail [email protected]
tuted with metallic radicular pivots or devital-ized teeth modified in colour, and the capacity of stopping colour transmission from the odontal substrate (9-12). Last but not least, it possesses special biological properties, the gingival con-tour remains integer in contact with it, maintain-ing a similar texture and colour with the gmaintain-ingiva of the natural tooth (13-16).
MATERIALS AND METHOD
Zirconium crowns and bridges were inserted in 129 patients ( 81 women, 48 men), with ages ranging between 15 and 57 years, over a period of 4 years.
The working method applied in the labora-tory made use of the CAD-CAM system, fol-lowed by scanning on a Dental Wings scanner and a CAM burring system from Wieland 917, 18. 646 ceramic elements of zirconium were in-serted, mostly on teeth, but also on implants. In both cases, they occurred as singular elements (covering crowns) and dental bridges (from 3 to 6 elements).
Year Crowns on teeth
Elements in dental bridges on
teeth
Crowns on implants
Dental bridges on implants
2007 15 26 --- ---
2008 118 149 3 ---
2009 51 58 11 ---
2010 75 49 30 ---
2011 22 16 12 11
281 298 56 11
The number of crowns on natural teeth repre-sents 83.4% , comparatively with the individual crowns on implants – 16.6%.
As to the number of elements from the dental bridges on the teeth, a clear ratio of 96.4% was
Prosthetic Dentistry
International Journal of Medical Dentistry 301
recorded, comparatively with those occurring on implants – of 3.6%.
Configuration of the singular elements was based on the aesthetic requirements of the pa-tients, as well as on the clinical status. Some-times, the solution was to consider them to-gether, in other cases they were individualized, especially in the frontal zone, if the pillar teeth had sufficient coronary volume, so that not to compromise retention. The dental bridges had 1, 2 or 3 intermediates.
Evaluation of the dental bridges was made on 48 patients, to whom the prosthesis was applied for solving intercalate edentation. Out of these 48, 45 had dental bridges on pillar teeth, 2 had them on both teeth and implants (no mixed sup-port) and only 1 had them exclusively on im-plants.
The bridges had an amplitude equivalent to minim 3 elements, up to maximum 7 elements, and 1, 2 or 3 intermediates.
The distribution on the arch, in the frontal and lateral zone, was also considered. In the opinion of the authors, the dental bridges present on ca-nines, considered as anterior pillar teeth laying towards the lateral zone, belonged to it.
In this way, there were 72 bridges in the lat-eral zone and only 8 in the frontal one. In the dental bridges from implants,1 occured in the frontal zone and 2 in the lateral one.
Out of the group of 129 patients, in whom 646 ceramic elements on zirconium had been made, over a 4 year interval, there have been selected,
for statistical purposes, only the patients who came to periodical controls, examined within 18-48 months from the moment of cementation.
The experimental group was made up of 71 patients (50 women and 21 men, according to the distribution on sexes), hospitalized from 18 to 48 months, taken over form a larger group, with dental works made in 2007, 2008 and 2009. 321 elements of zirconium, both singular and in dental bridges, were built up, as follows:
129 crowns on teeth ->83in frontal ares -> maxillary 83 -> mandibula 0
->46in lateral area -> maxillary 32 -> mandibula 14 51 dental bridges (with 192 elements) ->5in frontal area ->4 maxillary ->1 mandibula ->46in lateral area->26maxillary
->20 mandibula
Equally important is the distribution of the zirconium elements as a function of the faceted
ceramics: ZenoTec from Wieland and VITA VM9
from Vita Zahnfabrik.
321->109elements were faceted with ZenoTec ceramics ->212elements were faceted with VITA VM9 ceramics
RESULTS AND DISCUSSION
Distribution on arch Complications Type of
work Frontal zone
Lateral zone
Skeletal fracture
Ceramic chipping
Deceme ntation
Others
Zenotec ceramics– 109 elements 45 singular
elements
39 6 - 4 - 4
20 dental
bridges
1 19 - 1 - -
64 elements 3 61 - - - -
VITA VM9 ceramics– 212 elements 84 singular
elements
44 40 - 2 2 1
31 dental
bridges
4 27 2 1 - -
128 elements
14 114 - - - -
During the observation period of the 71 hos-pitalized patients, 2 of the 51 bridges were lost through skeletal fracture at connecting level.
The first bridge, made up of 4 elements with 2 intermediates, placed in the lateral mandibular area, got fractured after 3 months. The main
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cause of connector’s fracture was traumatic oc-clusion, once the antagonistic tooth was a termi-nal one, acting in a cuspid-cuspid (and not punc-tiform) manner on the surface, at the joint between the bridge body and the covering crown, so that occlusion was performed exclu-sively on that unilateral hemiarch.
The solution was to give up the classical den-tal bridge treatment, maintaining the zirconium crowns on the pillar teeth; also, at the level of the edented gap, 2 implants – corresponding to the absent teeth – were inserted.
The second bridge, occurring in the lateral maxillary area, was formed of 6 elements: 3 pil-lar teeth, 2 bridge bodies and an intermediate. The fracture was produced at the level of the mezial connector of the bigger bridge body, a month after final cementing. The cause was the erroneous selection of such a treatment, the pa-tient rejecting the implant variant for the larger edented gap.
Chippings and detachments of the ceramic facets were observed, especially with Zanotec. The most severe complication occurred in a pa-tient with 4 crowns on the maxillary incisives, 6 weeks after cementing. The cause was exclu-sively technical, related to the deficient zirco-nium structure, which induced ceramic fissur-ing. The solution was to wholly re-construct the work, which required a medical control each year, for 42 months of utilization.
Some other minor incidents (chippings) were registered in 4 singular elements and 2 elements from the dental bridges, treated by finishing and polishing, while the dental bridge was corrected in the laboratory. One chipping was caused by a home accident, in a central incisive.
Some complications had biological causes:
– Detachment of the glass fiber pillar - >
recemented;
– Crown fracture in 2 pillar teeth -> reconsti-tuted;
– IOS decementation – radicular fracture, loss of tooth;
– periapical cyst – eliminated through rezection, without affecting the work; – palatinal gingival inflammation in the
maxillary incisives, versus the zirconium crowns – local treatment applied.
Decementation was also observed in 2 singu-lar elements. Apparently, decementation oc-curred more frequently in the cases dealt with in 2010. When the 24 months of monitoring are over, a final conclusion will be drawn. The as-sumption is that the problem is related to the internal surface of the caps and to the way in which retention is assured, possibly involved being also the type of cementum.
CONCLUSIONS
• The higher the number of patients, of zir-conium elements and the longer the hospi-talization period, the higher the success ratio will be.
• The most recent results registered in the field are highly encouraging the zirconium bridges, comparatively with the classical metalo-ceramic ones.
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