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PubMed2002

Stress distribution of inlay-anchored adhesive fixed partial dentures: a finite element analysis of the influence of restorative materials and abutment preparation design.

STATEMENT OF PROBLEM: Indirect composite or ceramic fixed partial dentures (FPDs) have become an alternative to conventional metal-ceramic adhesive fixed partial dentures (AFPDs). Little information about the adequate restorative material and tooth preparation design for inlay-anchored AFPDs is available to the clinician. PURPOSE: The purposes of this simulation study were: (1) to use 2-dimensional finite element modeling to simulate stresses at the surface and interface of 3-unit posterior AFPDs made with 6 different restorative materials, and (2) to investigate the influence of 3 different abutment preparation configurations on the stress distribution within the tooth/restoration complex. MATERIAL AND METHODS: A mesio-distal cross-section of a 3-unit AFPD was digitized and used to create 2-dimensional models of the periodontal membrane, supporting bone, different restorative materials (gold, alumina, zirconia, glass-ceramic, composite, and fiber-reinforced composite), and different abutment preparation configurations (interproximal slots vs. 2-surface [MO, DO] vs. 3-surface [MOD]). A simulated 50-N vertical occlusal load was applied to the standardized pontic element. The principal stress within the restorative materials, stresses at the tooth/restoration interface, and surface tangential stresses at the level of the pontic were calculated in MPa from the postprocessing files and compared to each other. RESULTS: All materials and tooth preparation design exhibited a similar stress pattern, with a definite compressive area at the occlusal side of the pontic, a tensile zone at the gingival portion of the pontic, and tensile stress peaks in the abutment/pontic connection areas. Among isotropic materials, standard non-reinforced composites exhibited better stress transfer and reduced tensile stresses at the adhesive interface than ceramics and gold. Optimized placement of the glass fibers within the composite resulted in similar stress distribution when tested in 2-surface abutment preparation configuration. There was no detectable influence of preparation design on the behavior of the pontic area. Among all 3 preparation designs, only the DO design exhibited almost pure compression at the interface. CONCLUSION: Within the limitations of this simulation experiment, the composite materials tested demonstrated a resilient component that favored stress transfer within the tooth/restoration complex. Their clinical use, however, may be contraindicated due to insufficient strength and fracture toughness. The addition of extremely tough fibers to composites represents the most promising combination. Clinical trials are required to ensure that veneering composite can survive under clinical conditions.

Cementation↗
PubMedDate not supplied

An in vitro study of dentin exposure during resin-bonded fixed partial denture preparation.

OBJECTIVES: The aim of this in vitro study was to investigate whether dentin is exposed during tooth preparation for resin-bonded fixed partial dentures and, if so, to quantify the amount of dentin exposure. METHOD AND MATERIALS: Twenty extracted premolars were prepared in the following manner: The palatolingual and proximal axial surfaces were reduced by 0.50 mm. Mesial and distal grooves, 1.00 mm in depth, and mesial and distal occlusal rest seats, measuring 2.00 mm buccolingually x 1.50 mm mesiodistally x 1.00 mm deep, were prepared. The specimens were stained with a modified van Gieson's stain to identify dentin exposure, mounted on a jig to allow standardization, and photographed after 30-degree rotation to create a panoramic image of each tooth. The image was modified and analyzed to measure the percentage of the preparation area that exhibited dentin exposure. RESULTS: Dentin exposure was noted in all specimens. The mean area of dentin exposure was 11.06 mm2 (16.15% of the preparation area). The minimum and maximum areas of dentin exposure were 4.07 mm2 (7.03%) and 19.73 mm2 (27.28%), respectively. CONCLUSION: Dentin is exposed during resin-bonded fixed partial denture preparation if current tooth preparation guidelines are followed, despite the commonly made recommendation that the preparation remain within enamel. The region of the grooves consistently exhibited exposed dentin; exposure at the cervical margin was variable.

Bicuspid↗
PubMed1983

A mathematical treatise on the fit of crown castings.

A mathematical analysis was given to calculate the marginal cement thickness, Dm, of a cemented crown casting as a function of the minimum cement film thickness, F; the width, W, of the base of the tapered region; the width, W', at the bevel (if present) of the tooth preparation; the taper angle, theta; the marginal angle, beta; and the compensatory expansion, X, of the metal investment system: Dm = [F/sin theta - 0.5(X - 1) (W cot theta - W' cot beta)] sin beta. The elevation of the cemented casting, delta H, above the tooth preparation may also be obtained from this equation by substituting beta = 90 degrees, in which case Dm = delta H. The effect of the preparation of a chamfer margin or bevel on the marginal film thickness may be calculated from this equation. An additional analysis showed that the minimum marginal cement thickness, Dm = F, can be obtained for a shoulder preparation and X values of common metal-investment systems by applying a spacer of appropriate thickness on the entire occlusal and axial walls of the die. This renders the preparation of bevels superfluous. The thickness of the spacer should allow for the cement film thickness, roughness of the tooth and casting surfaces, dimensional inaccuracies of the die, and distortions of the wax pattern. If the spacer is thicker than required, a minimum value of Dm is still obtained for preparations without bevels. If the horizontal part of the die shoulder is covered as well with the spacer, a greater spacer thickness is required to obtain a minimum value of Dm than if the spacer extends to the end of the axial walls. In this case the spacer thickness should be greater on the occlusal die wall than on other regions of the die for values of X smaller than 1. The spacer should also be thicker in the occlusal region if restriction of the investment setting expansion by the wax pattern occurs mainly in this region.

Cementation↗
PubMed2001

Microleakage of three sealants following conventional, bur, and air-abrasion preparation of pits and fissures.

OBJECTIVES: The aim of this study was to compare the microleakage of a filled sealant with a drying agent (UltraSeal XT plus), a filled sealant (Prismashield) and an unfilled sealant (Delton), after conventional, bur, and air-abrasion tooth preparation techniques. SETTING: The study was completed in a clinical setting at the Simulated Practice Environment Clinic, School of Dentistry, University of Western Ontario, London, Ontario, Canada. SAMPLE AND METHODS: One hundred and eighty extracted teeth were cleaned and divided randomly into three groups. Group 1 was prepared using acid etch only. Group 2 was prepared with a 1/4 round bur in a low-speed handpiece followed by acid etching. Group 3 was prepared with high speed (120PSI) microabrasion using 27 microm alpha-alumina particles in a Midwest Airtouch unit. The teeth in each group were randomly assigned to one of the three subgroups according to the sealant applied. Subgroup A was sealed with a filled sealant with drying agent, B with a filled sealant only, and C with an unfilled sealant. All teeth were stored in artificial saliva for 7 days at 37 degrees C. After this, the teeth were coated with nail varnish 1 mm from the sealant and immersed in 1% methylene blue dye for 48 h at 37 degrees C. Each tooth was sectioned at four locations buccolingually and a total of 665 sections were ranked (0-3) for microleakage. Statistical analysis was completed using the Chi-squared test and Fisher's exact test. RESULTS: UltraSeal XT plus, the filled sealant with drying agent, showed significantly less microleakage than the other two sealants (P < 0.05). Delton, the unfilled sealant, showed significantly less microleakage than Prismashield, the filled sealant (P < 0.05). Air abrasion with acid etch showed significantly less microleakage than either bur with acid etch or acid etch alone. There was however, no significant difference between the bur and acid etch tooth preparations (P < 0.05). CONCLUSIONS: UltraSeal XT plus was the most effective sealant for preventing microleakage in this study. The most successful method of preparation was air abrasion with acid etch.

Acid Etching, Dental↗
PubMedDate not supplied

Dentin exposure and decay incidence when removable partial denture rest seats are prepared in tooth structure.

Prosthodontists surveyed preferred inverted V-shaped canine cingulum ledge rest seats located at the junction of the middle and cervical thirds of the lingual surface. Most respondents indicated that they preferred a ledge depth of at least 1.0 mm and indicated that their preparations usually did not extend into dentin. When the respondents evaluated various ledge depths, the mean depth of those judged adequate was 0.74 mm, which was less than the respondent and textbook recommendations. Premolar occlusal rest seats judged adequate generally met textbook size guidelines. The mean clinical incidence of dentin exposure with cingulum ledges and occlusal rest seats was 61%, close to the 55% exposure rate found on extracted teeth. Dentin Detector Gel effectively identified clinical dentin exposure but tooth sensitivity was not a good indicator of dentin exposure. Seventy-one of the 107 rest seats studied for incidence of caries and decalcification had exposed dentin but only two of the 71 had lesions. Ten of the 107 had small enamel fractures, primarily occurring on cingulum ledges.

Attitude of Health Personnel↗
PubMed1975

A study of temperature changes during removal of amalgam restorations.

Because tooth preparation is only one of several potent causes of trauma to the pulp during clinical procedures, the objective should be to increase the chance of pulp survival by reducing this trauma wheneve- possible. In case of tooth preparation, this study shows that there is far less potential for pulpal damage when water is used as a coolant.

Dental Amalgam↗
PubMedDate not supplied

The effect of recementation on crown retention.

PURPOSE: The object of this study was to evaluate retention of complete cast crowns cemented with different luting cements and to determine whether recemented castings are as retentive as when initially placed. MATERIALS AND METHODS: Thirty standardized Rexillium III complete crowns were made on extracted human molar teeth prepared with a modified milling machine using conventional laboratory techniques. The crowns were randomly assigned into three groups according to the luting cement used: zinc phosphate (Fleck's, Mizzy), adhesive resin (Panavia-EX, J. Morita), and glassionomer (Ketac-Cem, Aplicap, ESPE-Premier Sales). Retention was evaluated by measuring the tensile force required to dislodge the crowns from tooth preparations with an Instron testing machine after thermocycling (1,500 cycles between 5 degrees C and 55 degrees C with 1-minute dwell times). Subsequently, the tooth preparations were scraped clean and polished with flour of pumice (prophylaxis paste), and the fitting surfaces of the artificial crowns were ultrasonically cleaned and air abraded using 50-micron aluminum oxide powder prior to recementation. Results were subjected to two-way analysis of variance and Tukey's Studentized Range test. RESULTS: The analysis showed the highest mean retention for cast crowns cemented with Panavia-EX cement (314 N), but the difference was not statistically significantly different from crowns cemented with glass-ionomer cement (307 N). However, crowns cemented with zinc phosphate cement (233 N) had significantly lower values (P < 0.05). Restorations recemented with zinc phosphate had significantly lower retention (190 N) than their initial cementation (P < 0.05). CONCLUSIONS: Panavia-EX and glass-ionomer cements yielded the highest initial and recementation retentive strength, with values almost 32% higher than those obtained with zinc phosphate cement during the initial cementation and 59% higher than zinc phosphate for recementation. Zinc phosphate cement exhibited significantly lower retention for the initial and second trial of cementation.

Analysis of Variance↗
PubMed1991

Maintaining and enhancing gingival architecture in fixed prosthodontics.

The long-term success of fixed prosthodontic restorations is greatly dependent upon the health and stability of the surrounding periodontal structures. This article deals with the interrelationship between fixed prosthodontic procedures and the stability and health of the periodontium. The commonly encountered problem of alterations in gingival architecture is examined in relation to tooth preparation as well as soft tissue preparation. In addition, the ability of the provisional restoration to guide soft tissue form is discussed as well as the role of the final restoration in providing long-term tissue maintenance. Key factors such as margin placement, tissue damage during tooth preparation, the role of the provisional restoration, tissue injury during impression procedures, crown contour, pontic design, and embrasure design are covered in detail.

Crowns↗
PubMed1993

Clinical factors affecting adhesive fixed partial dentures: a 6-year study.

One hundred forty-one adhesive fixed partial dentures were placed under controlled conditions for a 6-year longitudinal study. The influence of location (anterior/posterior, maxilla/mandible), tooth preparation techniques (retentive/less invasive), and four different methods of metal conditioning (sandblasting/electrolytic etching and/or pyrolytic/tribochemical silane coating) on the survival rate was investigated. Failures (23 of 24) were caused by loss of adhesion at the metal-cement interface. The retentive tooth preparation reduced the risk of failure to almost one twentieth, but the intraoral location did not influence survival time. The effect of silane-coating on longevity was extremely positive and was not reflected by successful retainers.

Chi-Square Distribution↗
PubMedDate not supplied

Bonded porcelain veneer masking of dark tetracycline dentinal stains.

Resin-bonded porcelain veneer restorations can attractively mask dark dentinal tooth discoloration caused by tetracycline staining. When placing these restorations, special attention must be given to tooth preparation, handling of the porcelain, and veneer thickness. When treating adolescent patients whose occlusal development is not as yet completed, there are additional special considerations. This case report describes the placement of 6 resin-bonded porcelain veneer restorations in an adolescent patient to conceal dark tetracycline staining. Emphasis is placed on proper tooth preparation and meticulous handling of the soft tissue. The learning objective of this article is to familiarize the reader with the techniques of implementation and the special considerations in treating adolescent patients.

Adolescent↗
PubMed2005

[Microflora on mucosa under different pontics of fixed partial bridge].

OBJECTIVE: To investigate the influence of three pontic types on alveolar ridge mucosal microecosystem. METHODS: Sixty patients ready to accept three unit metal ceramic bridges were selected. The bacterial type and the cultivable flora were counted and the proportions of bacteria detected on the top of alveolar ridge mucosal contact area before tooth preparation and three months after bridge insertion. RESULTS: Type and CFU of bacteria on the alveolar ridge mucosa under modified base-type pontics and modified ridge lap pontics increased significantly (P < 0.05); while there was no significant change under the ovata pontics (P > 0.05). Before tooth preparation and 3 months after fixed prosthesis insertion, the percentages of oral Streptococci and Neisseriae changed significantly (P < 0.05). CONCLUSIONS: The ovata pontic had less influence on mucosal microecosystem than the other two pontics and is the appropriate pontic design for clinical dentist.

Adult↗
PubMed2001

Effect of groove placement on the retention/resistance of resin-bonded retainers for maxillary and mandibular second molars.

STATEMENT OF PROBLEM: Lack of retention/resistance form in the clinical preparation of teeth for resin-bonded retainers may lead to clinical failure. PURPOSE: This study investigated the effect of proximal grooves on the retention/resistance of cast resin-bonded retainers for maxillary and mandibular second molar teeth. MATERIAL AND METHODS: Two ivorine teeth (a maxillary and a mandibular second molar) were prepared for resin-bonded retainers. Twenty metal replicas of the prepared teeth were made (10 for each tooth morphotype). Resin-bonded retainers 0.5 mm thick were made for the 40 replicas and luted with Panavia EX cement. Forces for dislodgment of the retainers were applied along the long axes of the teeth. Forces recorded at the time of dislodgment were analyzed with 2-way analysis of variance and the post hoc Scheffé test. RESULTS: Grooves resulted in substantial increases in debonding forces for maxillary molars (P<.001). The effect of grooves on mandibular second molars was not significant (P=.13). CONCLUSION: Grooves placed in tooth preparations of maxillary molar teeth for resin-bonded retainers had a significant effect on retention/resistance. The effect of grooves on mandibular second molars was less pronounced.

Analysis of Variance↗
PubMed1995

A clinical evaluation of porcelain inlays.

Sparse data are available concerning the survival rate of porcelain inlays or onlays to inform the dentist and address the expectations of patients. A total of 25 posterior porcelain inlays were inserted by two dentists at a private Danish clinic; the time elapsed since cementation was 20 to 57 months (average 40.4 months). Tooth preparations for MOD porcelain inlays were completed for 13 premolars and 12 molars but most did not include cuspal coverage. All inlays were constructed at the same commercial dental laboratory and according to the manufacturer's recommendations; they were etched and treated with silane before they were cemented. The cementation included etching of cavosurface enamel and treatment of the dentin with a dentinal bonding system. A thin layer of composite resin luting agent was applied to the tooth preparation before the porcelain inlays were cemented. The first 10 porcelain inlays were cemented with a light-curing composite resin cement and the remaining 11 with a dual-curing composite resin cement. Twelve of the 25 porcelain inlays failed and were replaced during the observation period. Ten failures were due to a fracture of the inlay, one was caused by secondary caries, and the final failure was attributed to a marginal gap between the inlay and proximal tooth surface. Porcelain inlays cemented with light-curing composite resin exhibited more failures (p = 0.05) than those cemented with dual-curing composite resin. In addition, more failures (p = 0.07) were recorded among inlays inserted in molars than among those in premolars.

Acid Etching, Dental↗
PubMed1999

The safety and efficacy of treatment with air abrasion technology.

AIMS: To evaluate patient and operator exposure to respirable particulates following the use of air abrasion in tooth preparation, and to compare the microleakage of pit and fissure sealants after conventional, bur and air abrasion preparation of the pits and fissures. METHODS: To examine air abrasion safety, sampling data were collected using a physical model of the upper torso of a patient. Previously extracted bovine incisors were prepared using an air abrasion instrument. Patient and operator exposure samples were collected. The variables examined included the size of the alumina oxide particles, the speed of particle delivery and the method of dust collection. To assess the efficacy of air abrasion, 36 extracted human molars were divided into three groups. The groups were prepared by conventional acid etching, opening the pits and fissures with a round bur, or by air abrasion. To simulate oral conditions, sealed teeth were immersed in artificial saliva and thermocycled. Teeth were immersed in a 1% solution of methylene blue and sectioned to assess the microleakage associated with each sealant. CONCLUSIONS: (1) Dust from the KCP 1000 is insufficient to be a health hazard to patients or operators, (2) chair-side suction can be used as an alternative to the KCP 1000 suction, (3) superior sealants were obtained when tooth surfaces were prepared by a bur, compared to air abrasion and conventionally prepared surfaces, and (4) air abrasion tooth surfaces demonstrated less microleakage than conventionally prepared tooth surfaces.

Aerosols↗
PubMed2000

Marginal fit of nickel-chromium copings before and after internal adjustments with duplicated stone dies and disclosing agent.

STATEMENT OF PROBLEM: Despite careful procedures, master stone dies may be damaged during laboratory procedures. The dentist routinely adjusts castings because the marginal fit of casting is not as accurate as on the dies. PURPOSE: This study evaluated the technique of internal adjustment of castings with use of duplicated stone dies and a disclosing agent to improve marginal fit discrepancy. MATERIAL AND METHODS: Thirty-two nickel-chromium copings were fabricated and simulated standard clinical and laboratory procedures with 2 variables: tooth preparation convergence angles of 6 and 18 degrees, with or without internal relief. Master stone dies and their duplicates were selected for coping construction and internal adjustment, respectively. A specimen positioning device was coupled with a Toolmakers microscope to allow reproducibility of measurements. Each coping was evaluated at 8 locations of its marginal perimeter, before and after internal adjustment. RESULTS: Marginal fit discrepancy of copings were significantly reduced with an internal adjustment technique (mean > 52%) for all experimental groups. Tooth preparations with greater convergence and internally relieved castings recorded a better marginal fit. CONCLUSION: The casting internal adjustment technique with use of duplicated stone dies and a disclosing agent substantially reduced marginal fit discrepancy.

Analysis of Variance↗
PubMedDate not supplied

Longevity of low- and high-copper amalgams analyzed by preparation class, tooth site, patient age, and operator.

The purpose of this study was to compare the long-term survivals of two low-copper and three high-copper amalgam alloys, and to analyze four clinical factors for their possible effects on the restoration survivals. Some 1476 polished restorations were placed in hospital patients by a large number of operators and assessed over periods of up to 10 years. There were no significant survival differences found among the high-copper alloys and one low-copper alloy, and their survivals were significantly better than for the other low-copper alloy. These results could not have been reliably predicted from the different compositions and creep values of the alloys. A significant effect on restoration survivals was also found with different operators.

Adolescent↗