Metal-ceramic bond: how to improve?

Metal-ceramic restorations include the positive features of metal (strength, durability and stability) and ceramics (esthetics). The strong bond on the metal-ceramic interface is the basic prerequisite for the durability of the metal-ceramic restoration. The heating of metal construction results in the diffusion of certain atoms (tracers) on the surface. There they react with atmospheric oxygen creating in oxides which remain on the cast surface, because the reversible diffusion is prevented. Atoms of silica in ceramic are bound with these oxides as a result of which a metal-tracer-ceramic compound is formed and a chemical bond is realised. In addition to forming an oxide layer, the oxidation heat treatment (OHT) is applied for all alloys in order to remove the entrapped gas and eliminate surface contaminants. Surface metal preparation before porcelain application may also affect the bond strength of metal and ceramics. Roughened surface by sandblasting enables mechanical interlocking and an increased surface for bonding metal and ceramics. Applying a bonding agent may improve the quality of the bond of certain metal-ceramic restorations. Due to the continued oxidation of titanium and creation of a non-adherent oxide layer, the bond strength between titanium and ceramics is weak, which is attempted to be resolved by firing in an argon atmosphere.

Failures in fabrication and treatment using ceramic crowns.

Dental ceramics is a constituent prosthodontic material with excellent aesthetic properties. It is stable, does not change shape, color or size, and is biotolerant. Treatment with ceramic restorations is a standard procedure in modern fixed prosthodontics. Because of its multiphase structure and the thermal processes it undergoes during the making of a fixed prosthodontic replacement, ceramics is highly sensitive to small failures in fabrication. These failures can develop into cracks that can ultimately cause fracture of restorations in use. This is why each phase of restoration in a dental practice and a dental laboratory requires professional skill. Selection of a definite ceramic system for a specific clinical case is more important than with other constituent materials. Patient selection, oral hygiene, masticatory force, as well as proper maintenance of instruments and devices for the fabrication of ceramic replacements are all important.

Jaw elevator silent periods in complete denture wearers and dentate individuals.

Functional meaning and underlying mechanisms of jaw elevator silent period (SP) have still not been completely understood. Since complete denture wearers (CDWs) have no periodontal receptors in their jaws, the aim was to examine SPs in CDWs and to compare it with dentate individuals (DIs). Thirty six DIs (skeletal/occlusal Class I) and 24 eugnath CDWs participated. EMG signals were registered using the EMGA-1 apparatus from the left and the right side anterior temporalis (ATM) and masseter muscles (MM). Ten registrations of an open-close-clench (OCC) cycle were obtained for each individual. DIs had the average latency between 12.5 and 12.9 ms and always one single short inhibitory pause (IP) with complete inhibition of motoneurons (20.1-21.1 ms). On the other hand, in CDWs various types of SPs emerged: single or single prolonged SPs, double SPs, SPs with three IPs, periods of depressed muscle activity following the first, or the second IP, SPs with relative inhibition of motoneurons or even in several registrations the SP was missing. Unless more than one IP emerged, complete duration of inhibitory pauses (CDIP) was measured. CDIP varied from 37.17 to 42.49 ms. Average latencies were from 16.22 to 16.76 ms. Based on the results of this study it is obvious that both, the duration and the latencies were significantly longer in CDWs than in DIs (p<0.05), which can be explained by different mechanisms responsible for the muscle reflex behaviour.

Temporomandibular disorders and bruxism. Part I.

Correct functioning of the entire stomatognathic system is achieved by a compatible relationship of all its parts. Four determinants, by their mutual harmonious activity, dictate the function of the entire system: the teeth, periodontium with supporting structure, muscles, temporomandibular joint (TMJ) and CNS. In such a complex system a disorder of any integrative part causes disturbances also in other parts of the system. Changed functions can arise through organic disorder, and also iatrogenically by inadequate conservative, prosthetic, surgical or orthodontic therapy. For this reason it is often difficult to recognise the primary cause. The first responses of the system to the disorder are adaptive mechanisms which occur within one or more integrative parts, and depending on their intensity and duration symptoms grow more prominent. Tissue response can be ortho- or parafunctional. Attempts are made to exclude psychoemotional influences and the obstacle eliminated by either abrasion, clenching or grinding of the teeth. If the obstacle is not eliminated by abrasion, the cause of such functional disorder becomes the trigger for parafunctional activity. From a review of the relevant literature it can be concluded that parafunctional activity is caused by changed occlusion, with determined psychological habits of the patient and specific tissue response of the stomatognathic system. Therefore, therapy of these disorders is made more difficult and includes a multidisciplinary approach.

Diagnostic methods for detection of signs and symptoms of temporomandibular disorders. Part II.

Temporomandibular disorders (TMD) is a term which includes numerous clinical symptoms that affect the teeth and their supportive apparatus, masticatory muscles and jaw joints. They are frequently the cause of orofacial painful conditions. Etiology of dysfunction is complex and the role and importance of certain etiological factors are inadequately defined. This study includes a review of the literature and presentation of a diagnostic protocol for the detection of signs and symptoms of TMD. Optoelectronic pantography enables the application of relatively uncomplicated methods for more precise and simpler diagnosis of the above disorder, at the same time recording the results in its software and storing them, which can be extremely important during the choice of therapeutic procedure and the control of therapy efficacy.

Expression of contact allergy in undergoing prosthodontic therapy patients with oral diseases.

AIM: Contact allergy is a postponed reaction of hypersensitivity where a localised cutaneous or mucosal lesion occurs due to a recurrent contact with an allergen. Placement of a fixed or removable prosthetic replacement into the oral cavity causes corrosive processes on the surface of the restoration and discharge of ions, which as haptens can induce allergic reactions. The purpose of this study was to examine occurrence of allergies to basic and auxiliary restorative dental materials in patients with lichen, stomatitis and stomatopyrosis by means of an epicutaneous allergy test. METHODS: The study included 32 patients with a fixed and/or removable replacement and 7 patients with one of the mentioned diagnoses, but without any replacement. Testing was conducted using a standard method (patch test), and hypersensitivity to 13 most common allergens in prosthodontics was examined. RESULTS: The research results revealed higher frequency of positive allergic reactions in persons with the mentioned diseases and with a restoration. Patients with lichen indicated positive patch test in the majority of cases. The allergens of nickel, cobalt and chromium demonstrated the highest score of positive results, and negative score was found for dibutylphthalate and HH mix. Stomatopyrosis was more common in persons with hypersensitivity to chromium. A lower incidence of positive allergic reactions to epoxide resins was found in female than in male subjects. CONCLUSIONS: The epicutaneous (patch) test performed in the subjects examined in this study, showed that the majority of positive reactions was caused by mixes of nickel, cobalt and chromium; however, unwanted reactions also to other auxiliary materials used in dental practice should also be considered.

Screening of fixed prosthodontic dentures after five years of use in relation to material and construction.

The aim of this study was to screen patients with fixed prosthodontic appliances that were in oral cavity for a period of 5 years or more and to assess clinically and radiologically root caries, gingival recession, pocket formation, alveolar ridge resorption, as well as gingival (GI) and plaque index (PI). The aim also was to find out the differences between materials and constructions, between abutment and non-abutment teeth, and to find out the need for replacement. A total of 260 patients and their orthopantomograms were examined, with a total of 2,265 teeth, 610 being bridge abutments and 246 being crowns. The most frequent were metal+ acrylic veneer crowns or bridges. Root caries was found under the abutments in 10-20%; however abutments with ceramic crowns had the lowest percentage of caries (p < 0.01). Alveolar ridge resorption, pocket formation deeper than 3 mm and gingival recession of various degree was found in 50% of the cases, again with the lowest percentage of ceramic-fused-to-metal appliances (p < 0.01). Pocket depth was registered in significantly higher percentage in metal-acrylic veneer appliances compared to natural teeth (p < 0.01), while there was no significant difference between metal-ceramic appliances and natural teeth (p > 0.05). Although the worst findings were recorded for metal- + acrylic veneer crowns for PI, no significant difference existed between crowns of different material or non-abutment teeth (p > 0.05). There was statistically significant difference between abutments with metal + acrylic veneer crowns, full metal crowns, metal ceramic crowns and non-abutments for GI scores. Higher percentage of scores 0 and 1 was recorded for metal ceramic crowns and non-abutments and significantly higher percentage of scores 2 and 3 was recorded for metal + acrylic veneer crowns and full metallic crowns. Almost 50% of metal-ceramic abutments had no pathologic findings. Almost 30% of the patients needed replacement, or even some abutments to be extracted and therefore a new prosthodontic appliance.

Some periodontological parameters in patients with oesophagogastric passage insufficiency.

The aim of this study was to examine the state of oral hygiene (OHI), the presence of tooth calculus and the condition of the gingiva on the group of 101 patient with oesophagogastric passage insufficiency. The control was group of 78 examines without clinical signs of oesophagogastric disease. The plaque was visualised by plaque revelator and recorded on each tooth. The calculus and condition of gingiva was determined according to the modified instruction of WHO, 1987. Both parameters were determined for each sextant of upper and lower jaw. The results of the OHI on the patients with oesophagogastric passage insufficiency (0.3, SD 0.126) was statistically different (p < 0.01) in comparison with control group (0.51, SD 0.25). Pathological changes of gingiva were more prominent in patient with insufficiency and that difference was statistically significant (p < 0.05). Calculus was more evident in control group but statistically insignificant (p < 0.1). The data show that insufficiency of oesophagogastric passage can cause pathological changes of gingiva while the lower OHI and less prominent calculus could be explained probably by better oral hygiene of patients because of bad taste in mouths.