Per-Olof Glantz

Technical failures and some related clinical complications in extensive fixed prosthodontics: An epidemiological study of long-term clinical quality

Three hundred and sixteen fixed partial dentures made in 1975-1976 by 112 general practitioners in Malmö, Sweden, were selected for a questionnaire study of the technical failure rates after 6-7 years. Cariologic, periodontal, endodontic, and esthetic complications were also identified, as were those appearing in the stomatognathic system. The total material consisted of three groups with an approximately equal number of reconstructions. One group consisted of fixed partial dentures with distal abutment teeth, another was formed of fixed prostheses with single cantilever pontic/pontics, and a third consisted of double cantilever pontics. Excluding the 26 reconstructions, which had been made for patients who died (24) or emigrated (2) during the observation period, data was obtained for 97% of the selected restorations. The results showed high rates of cariologic (18-31%), endodontic (5-23%), periodontal (7-12%), esthetic (10-16%), and technical (8-34%) complications. Differences were noted between the groups. For all types of technical failures (fractures and loss of retention) higher frequencies were related to the extent of cantilevering. Direct relationships were found between the technical failure rate and the time in service, the sum of all cantilever extension pontics in the reconstructions, and the state of the pulps of the distal abutments. No relationship was found between the technical failure rate and the status of the dentition in the opposing jaw. The clinical significance of the results obtained is discussed.

On cantilever loading of vital and non-vital teeth An experimental clinical study

Three healthy subjects with neighboring or contralateral vital and root-filled teeth requiring crown therapy were selected as test persons. All teeth had optimal alveolar bone support. The root-filled teeth were furnished with individual cast posts and cores, and veneer crowns were made on both the vital and non-vital teeth. Buccal extension bars were then soldered to the occlusal surfaces of these crowns, and weights were applied in different positions along the bars until the test persons experienced pain. The experiments were repeated under local anesthesia. The results showed that non-vital teeth had mean pain threshold levels that, on cantilever loading, were more than twice as high as those of their neighboring or contralateral vital teeth. The positions of the centers of rotational deformations of the loaded teeth, which were assumed to be mainly rotational, were calculated and found to be located inside the peripheries of the crowns for the vital teeth but extracoronally in markedly more peripheral positions for the non-vital teeth.

Characterization of oral in vivo films formed on different types of solid surfaces

Studies were made of oral films formed in vivo, which had been allowed to form on fused silica and Ge-prisms during periods between 2 s and 2 h using a variety of physico-chemical methods. To produce surfaces of different qualities the silica and Ge-prisms had either been detergent-washed, glow discharge treated or covered with polydimethylsiloxane. The following simultaneous analytical techniques were performed on the adsorbed films: a. internal reflection infrared spectroscopy, b. ellipsometry, c. contact potential measurements, d. contact angle measurements, e. scanning electron microscopy and f. energy-dispersive x-ray analysis. The results of these studies show that the formation of oral films proceeds at high speed and is of a certain qualitative selectivity. The formed films were found to be stable over long periods of time, and only showed patches of adhering micro-organisms on some of the prisms which had been exposed in the oral cavity for 2 h.

Status of Mercury and Selenium in Dental Personnel: Impact of Amalgam Work and Own Fillings

Urinary mercury (U-Hg) and plasma mercury (P-Hg) levels were higher in 244 dental personnel than in 81 matched referents (U-Hg: 1.8 and 1.1 mumol/mol creatinine, respectively; p less than .001; P-Hg: 6.7 and 6.2 nmol/l, respectively; p = .03). The amalgam in the mouth influenced mercury levels in whole blood (B-Hg), plasma, and urine. The association was nonlinear: the more amalgam, the larger the relative increase in mercury levels. The number of amalgam surfaces accounted for more of the variance in blood and urine mercury levels than did the number of fillings (e.g., U-Hg: 44% and 36%, respectively). The estimated increases in mercury level with rising amalgam load were 3.0%, 2.0%, and 0.8% per filled surface for U-Hg, P-Hg, and B-Hg, respectively (p less than .0001 in all cases). The impact of occupational exposure on U-Hg in the dental personnel corresponded to approximately 19 amalgam surfaces. Ceramo metallic restorations were associated with higher (31%) U-Hg.

A novel sensor for bite force determinations

OBJECTIVES The clinical usefulness, accuracy and precision of a novel bite force sensor based on force sensing resistors were tested in six subjects wearing maxillary removable partial dentures retained by conical crowns. METHODS The surfaces of the sensor were manufactured in a silicone material that had mechanical properties similar to those of tough foodstuffs. In two separate series of standardized bite force tests, submaximum force levels were recorded with the sensor and with a strain gaged bite fork. Subjects were assisted in the loading tests with visual feedback instrumentation. Reliability estimates for the bite force sensor were calculated in order to show their reproducibility. Strain gages attached to the prostheses were used to determine the pattern of force distribution during loading tests. The bite force results obtained with the new bite force sensor and with the bite fork were analyzed with ANOVA and Scheffés tests. The strain patterns registered with strain gages were analyzed with F-test. RESULTS The bite force sensor and the bite fork transducer showed no statistically significant differences in respect of intra-individual bite force levels (range 50-300N). The bite forces registered with the new sensor were dependent on the loading position (p<0.05), sex (p<0.05) and test subject (p<0.05). The reliability of the new sensor for submaximum bite forces was calculated to be 93%. Strain gage results showed that the new sensor generated strain patterns of less variance (p<0.05) than the bite fork and therefore allowed for higher precision during biting tests. SIGNIFICANCE The presented instrument has such clinical merits, as to favor its use in experimental clinical studies on the biomechanics of prosthetic appliances.

Clinical Adhesiveness of Selected Dental Materials: An in-vivo study

An investigation was conducted to determine the clinical adhesiveness of some commonly used dental materials. Contact angle measurement data, obtained under clinical conditions, were used to calculate the in vivo-critical surface tensions for enamel, gold, stainless steel, and a resin polymer. The results of this study showed that the adhesive properties of the artificial surfaces studied were considerably modified in the oral environment. Thus, after two hours these solids with diverse original surface chemistries were observed to produce in vivo-critical surface tensions common to those recorded for enamel. The observed changes were attributed to be absorbed biofilm (acquired pellicle), which forms on all solid surfaces in the oral cavity.

The adhesiveness of teeth

Abstract In a laboratory study of the wettability of plane surfaces of enamel, dentine, and some common restorative dental materials as judged from contact angles the following observations were made: Surfaces of enamel and dentine are normally covered by a low-energy material (or materials), which originate from the organic phase of these tooth substances. Aqueous solutions of certain metal fluorides reduce, and aqueous solutions of lactic acid increase, the wettability of enamel and dentine. Pretreatment with aqueous solutions of stannous fluoride decreases the effect of lactic acid solutions on them. Apart from poly (methylmethacrylate), the restorative dental materials tested (Ag-amalgam, phosphate cement, silicate cement, dental porcelain, stainless steel, and CoCr alloy) have virtually hydrophilic surfaces. Judging from a comparison with a previously published clinical study of plaque adhesion the changes measured are of clinical significance.

On functional strain in fixed mandibular reconstructions I. An in vitro study

Six linear strain gauges and one rosette strain gauge were used on three different types of models prepared from one partially dentate subject, to study loading deformation in a six-unit fixed mandibular bridge. The bridge was mounted on each of the models on an adjustable articulator and loaded in a universal testing machine at loading levels ranging from 0 to 491 N. The results showed considerable differences between the three types of model, with regard to both the magnitude of the recorded strains for the individual gauges and the calculated direction of the principal strains under the rosette gauges. The findings indicate that the mechanical properties and the design of the supporting structures have a major influence on the functional deformation of fixed dental appliances.

Quality of fixed prosthodontics after 15 years

Interviews and/or clinical examinations by means of the California Dental Association quality evaluation system were carried out in a group of persons who had received extensive restorative treatments with fixed partial dentures 15 years before this study. The studied group consisted of 77 persons who agreed to participate from an original group of 150 persons selected at random from the Swedish Dental Insurance System records. Of the original group 20 had died, 17 were not traceable or not able to participate for medical reasons, and 36 declined to participate. Thirty-two per cent of the recorded reconstructions had been lost, and 8% partially lost during the 15-year period. Thirty-five per cent of the reconstructions were rated as Satisfactory, whereas the remaining ones had mixed clinical quality ratings. Failures and Not Acceptable quality ratings were found to be caused mainly by fractures, loss of retention, and/or dental caries.

Quality of extensive fixed prosthodontics after five years

A group of 150 patients who had received extensive restorative treatment 5 years prior to this study was selected at random from the Swedish Dental Insurance System records in Malmo. Of the 133 respondents to a questionnaire, 109 participated in a clinical evaluation of 891 restorations including 498 crowns, 232 pontics, 6 removable partial dentures, and 155 adjacent or opposing metallic restorations. The clinical evaluation was performed by two trained examiners by means of the CDA quality evaluation for dental care. Ninety percent of the crowns and pontics, 80% of the adjacent or opposing metallic restorations, and all six partial dentures were rated satisfactory. Twenty-three percent of the crowns, 49% of the pontics, 17% of the adjacent or opposing restorations, and half the partial dentures rated in the range of excellence. Not acceptable ratings for crowns included 3.4% T ratings and 6.6% V ratings. For pontics, the corresponding percents were 9.5% and 0.4%, respectively. T ratings were in most cases indicative of overcontouring, whereas V ratings for crowns were usually given because of secondary caries. Marginal periodontitis was mainly associated with not acceptable ratings but was also observed in connection with satisfactory restorations. Only 2% of the restorations had been lost during the 5-year period after insertion.