Marginal Adaptation and Fracture Resistance of Lithium Disilicate Laminate Veneers on Teeth with Different Preparation Depths

The purpose of this study was to evaluate the marginal adaptation and fracture load of ceramic laminate veneers on teeth with different preparation depths. A total of 75 extracted intact human maxillary central incisors were prepared with three different preparation depths (P) and assigned to the following five groups (n = 15): P1 (0.3-mm depth of preparation; preparation entirely in enamel); P2 (0.5-mm depth of preparation; preparation in enamel and dentin complex); P3 (1-mm depth of preparation; preparation entirely in dentin); P4 (no preparation, only surface roughening); and P5 (unrestored, intact teeth as control). A total of 60 lithium disilicate laminate veneers were fabricated. The marginal adaptation of the veneers was evaluated by light microscope and scanning electron microscope after cementation with resin cement. Finally, the veneers were loaded until fracture at a 90-degree angle to the lingual surface of the tooth. Statistical analyses were performed using analysis of variance and Tukey multiple range test. There was a significant difference between the marginal gap value of the distocervical measurement points of P1 and P2 and the distal measurement points of P3 and P4 (P = .33 and P = .017, respectively). The highest fracture resistance values were observed in the P5 group (mean: 389.55 ± 22 N) and the P2 group (mean: 322.86 ± 79.38 N), and the lowest values were observed in the P3 group (mean: 219.21 ± 60.74 N). The marginal adaptation of the laminate veneer restorations was not related to the depth of preparation. Mean fracture resistance of laminate veneers with 0.5-mm preparation depth was greater than that of the 0.3-mm and 1-mm preparation depth laminate veneers and those with no preparation.

A comparison of the efficacy of potassium nitrate and Gluma desensitizer in the reduction of hypersensitivity in teeth with full-crown preparations

AIM

The aim of this clinical investigation was to compare the efficacy of Gluma Desensitizer and potassium nitrate desensitizing agents on the reduction of hypersensitivity of teeth prepared for full coverage crowns.

METHODS AND MATERIALS

This study included 75 vital teeth in 25 patients in need of fixed prosthesis treatment. After completing routine examinations, hypersensitivity of the teeth was measured using an air sensitivity test. The measurement of sensitivity was using a Visual Analog Scale (VAS) before preparation, after preparation, before using desensitizers, after using desensitizers, and before cementation. Each tooth was randomly put into one of the three groups of 25 teeth according to the desensitizing agent used (potassium nitrate, Gluma, and the control). In each patient potassium nitrate was used on one of the abutments and Gluma was used on the other abutment and on the third abutment (the control) no substance was used.

RESULTS

Both desensitizers decreased dentinal hypersensitivity in vital teeth prepared for full-coverage crowns, but potassium nitrate was more effective when applied before cementation. In 88% of the teeth to which Gluma was applied a vascular pain (with pulse) was present.

CONCLUSION

The results of this investigation suggest the application of potassium nitrate to dentin in full crown preparations prior to cementation reduces post-operative sensitivity.

CLINICAL SIGNIFICANCE

Clinical experiments show the preparation of vital teeth for full coverage crowns can cause sharp, transient pain as a result of dentinal hypersensitivity in the majority of cases. Several different substances and methods have been suggested for reducing such hypersensitivity including costly laser treatments. However, the findings of this study indicate the use of desensitizer substances such as potassium nitrate can reduce tooth hypersensitivity efficiently with less expense.

Effect of remaining coronal structure on the resistance to fracture of crowned endodontically treated maxillary first premolars

OBJECTIVE

Endodontically treated maxillary first premolars present a restorative challenge. The objective of the present study was to assess the resistance to fracture of crowned endodontically treated maxillary first premolars under simulated occlusal load, while preserving various degrees of remaining coronal structure.

METHODS AND MATERIALS

The study consisted of 50 intact maxillary first premolars with bifurcated roots and similar root diameter and length, randomly divided into 5 equal experimental groups. All dowels were luted with Flexi-Flow titanium-reinforced composite resin cement. TiCore titanium-reinforced composite resin was used to fabricate the core. Complete cast crowns were fabricated and cemented with zinc phosphate cement. Forces at fracture and mode of failure were recorded.

RESULTS

Statistically significant differences (P < .05) were found among mean failure forces for all tested groups in their resistance to fracture under load with the Kruskal-Wallias test and among all combinations of the 5 groups (Z = -1.56/-2.34; P > .05) with the Mann-Whitney test. This indicates that crowned maxillary first premolars with varying degrees of remaining coronal structure differ significantly in their resistance to fracture under occlusal load. There was increased protection against fracture under occlusal loads with more remaining tooth structure.

CONCLUSIONS

Within the limitations of this study, remaining coronal structure influenced the fracture resistance of crowned endodontically treated maxillary first premolars. Preservation of tooth structure is important for its protection against fracture under occlusal loads and may influence the tooth prognosis.

Cervicofacial and mediastinal emphysema after crown preparation: a rare complication

Cervicofacial emphysema is a well-known complication associated with the use of a high-speed air turbine. However, retropharyngeal emphysema or pneumomediastinum in the absence of severe trauma is rare. Immediate recognition of this phenomenon is essential to avoid life-threatening complications such as potential airway obstruction or venous air embolism. This article reports a case of gas diffusion into the mediastinum after dental preparatory treatment for a single-tooth crown. Pneumomediastinum should be considered whenever there are anamnestic data for retrosternal chest pain accompanied by dysphagia, dysphonia, or dyspnea caused by cervicofacial emphysema after dental treatment.

Surgical Emphysema Following a Restorative Procedure: A Case Report

Surgical emphysema is a rare complication following a restorative procedure, despite the use of air-driven handpieces. Although most cases resolve spontaneously, it should be correctly managed to avoid potentially life-threatening situations, such as pneumomediastinum and pneumothorax.

CLINICAL RELEVANCE

Surgical emphysema, although rare, can occur following certain dental procedures. It should be avoidable but, when it occurs, appropriate management is essential.

Dentin exposure in tooth preparations for porcelain veneers: a pilot study

STATEMENT OF PROBLEM

The various clinical techniques available for even reduction of a tooth surface to receive a porcelain veneer restoration do not produce a consistently even conservative reduction. In addition, it is not known which technique is most conservative of enamel.

PURPOSE

The purpose of this pilot study was to assess the effectiveness of 3 clinical techniques, namely, dimple, depth groove, and freehand, in producing an intraenamel preparation. The relation between overpreparation beyond the commonly accepted depth of preparation of 0.5 mm and dentin exposure was also examined.

MATERIAL AND METHODS

A single operator prepared 3 groups of 5 extracted maxillary central incisors to a depth of 0.5 mm using dimple, depth-groove, and freehand methods of tooth preparation. The prepared teeth were scanned using an x-ray microtomography scanner. The reconstructed images were studied using software that provided a volume-rendering routine so that, by choosing suitable x-ray linear attenuation coefficient thresholds, enamel (2.78 cm(-1) at 40 keV) and dentin (1.63 cm(-1) at 40 keV) surfaces could be viewed. The percentage area of enamel conserved was analyzed from these images. Coordinate metrology was used to produce color-coded images depicting the depth of preparation. The Kruskal-Wallis test was used to determine the statistical significance (alpha=.05) in the difference between the mean percentage area of enamel conserved in the 3 technique groups. The coordinate metrology and x-ray microtomography images were visually compared to study the correlation between overpreparation and dentin exposure.

RESULTS

The Kruskal-Wallis test did not demonstrate significant difference (P=.07) between the 3 techniques in conserving enamel. However, the dimple technique showed a greater trend to retaining a larger mean percentage area of enamel (77.5% +/- 14.2) compared to depth-groove (50.1% +/- 17.5) and freehand (76.8% +/- 24.4) techniques. Preparation depth in the range of 0.4 to 0.6 mm was largely seen to be intraenamel, except in the cervical region.

CONCLUSION

Within the limitations of this pilot study, the 3 different techniques tested did not differ significantly in conserving enamel.

Subcutaneous cervicofacial emphysema and pneumo-mediastinum: a rare complication after a crown preparation

Subcutaneous cervicofacial emphysema and pneumo-mediastinum are relatively rare complications from different dental procedures (including oral surgery and restorative treatment). Many cases go unrecognized or are misdiagnosed. While the majority of cases resolve spontaneously, some can lead to life-threatening complications that require emergency intervention. This article presents a case report of subcutaneous and mediastinal emphysema following a routine restorative dental procedure. The differential diagnosis and management of this condition is discussed.

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.

Comparison of using calcium hydroxide or a dentine primer for reducing dentinal pain following crown preparation: a randomized clinical trial with an observation time up to 30 months1

The purpose of this study was to evaluate effect of a calcium hydroxide suspension [Ca(OH)2] or glutaraldehyde based dentine primer (GDP) to reduce tooth sensitivity after full crown preparation. Thirty-six patients were treated with Ca(OH)(2) on one tooth and with GDP on another. Patients completed a questionnaire regarding sensitivity during crown preparation, when the not-anaesthetized abutments were irritated [cotton pellet (20 degrees C)]. The teeth were tested before (T(0)) and after using the desensitizer (T(1)), again after 7 days (T(2)), 6 months (T(3)) and 30 months (T(4)). The results were registered on a visual analogue scale [0 (no pain)-100 (severe pain)]. The changes of tooth sensitivity between different testing times were analysed. The median and the (interquartile range) for the different time intervals for Ca(OH)(2) were DeltaT(0)-T(1): 5 (6-17), DeltaT(0)-T(2): 17 (14-32), and for GDP, DeltaT(0)-T(1): 9 (7-18) DeltaT(0)-T(2): 18 (16-33), the decreases in sensitivity were lower for DeltaT(0)-T(1) than for DeltaT(0)-T(2) for both desensitizers (P < 0.001). There was no statistical difference (P > 0.05) between the agents (DeltaT(0)-T(1), DeltaT(0)-T(2), DeltaT(3)-T(4)). Both substances might be useful in reducing tooth sensitivity after crown preparation, but no differences in the efficacy were found when comparing the materials.

[Gingival risks of fixed prostheses at the Institute of Odontology and Stomatology of Dakar (I.O.S.)]

The realisation of a bridgework involves a direct action on the gingival marginal edge. It is submitted to peremptoriness of execution that one of the objectives is to respect the periodontium with a great rigour. In the opposite case it can become a greater aggression agent, source of prosthetic failures we carried out this report in order to evaluate in the framework of a pedagogic operational programme of crown and bridge prosthesis, the superficial periodontal risks linked to the preparation of the abutment teeth and to the prosthetic chain. We examined a randomised sample of 50 patients chosen from the Dakar LOS prosthetic consultation. On the periodontium initially sound we noted inflammatory lesions of the superficial periodontium from the beginning to the end of the treatment we used the Russel periodontal index. The whole individual scores summarised on a collective chart have been submitted to the statistical analysis of the independence by using the chi-square test. The population consulting in bridge work at the Dakar LOS is relatively young, 33 years in a average with a sex ratio of 1.17 and it shows a moderate (60% of the cases) and severe periodontal seizure (40% of the cases) dealing significantly with the type of prosthesis and the axial and occlusal morphology of the prosthesis pieces. This study shows that prosthesis rehabilitation in the frame work of a clinical training at the Dakar I.O.S. includes relatively high risks of periodontium aggression that we would minimise by setting more correctly the indications of the bridge work and by bringing more rigour to the record and the postpone of the patients occlusion in the laboratory conception of the prosthesis pieces.

Influence of timing of coronal preparation on retention of cemented cast posts and cores

PURPOSE

This study investigated the effect of coronal preparation by high-speed handpiece on the retention of cemented cast posts and cores.

MATERIALS AND METHODS

Cast posts and cores were fabricated for 90 extracted single-rooted human teeth cemented with zinc-phosphate cement and randomly divided into six groups of 15 specimens each. The six groups were matched randomly two by two, such that one of each of the matched groups was subjected to a 4-minute period of high-speed preparation of the cores. Castings from the first pair (1 and 2) were subjected to an axially directed removal force using a universal testing machine 15 minutes from the start of cement mixing; castings from the second (3 and 4) and third (5 and 6) pairs were tested at 1 hour and 24 hours, respectively, having been stored in water at 37 degrees C for the waiting periods. The forces required for dislodgment of posts from their prepared spaces were recorded. Data were statistically analyzed using two- and one-way ANOVA and the Student's t test.

RESULTS

The results showed increased mean retentive strengths of posts as the time to testing increased for both unprepared and prepared groups. Significantly higher mean retentive strengths of posts were recorded for unprepared compared to prepared groups tested at 15 minutes and 1 hour after cementation.

CONCLUSION

High-speed preparation had a significant negative effect on the retentive strengths of posts tested at 15 minutes and 1 hour after cementation, but not on those tested at 24 hours.

Dentin permeability and eugenol diffusion after full crown preparation

PURPOSE

To compare teeth prepared to receive a metallic versus a metal-ceramic crown with respect to (1) in vitro dentin permeability before and after using a desensitizing agent and (2) pulpal eugenol concentration after sealing a temporary crown with a zinc oxide-eugenol based cement.

MATERIALS AND METHODS

The roots of 20 human mandibular molars were separated and the crowns were prepared to receive a metallic crown. The hydraulic conductance was recorded before and after using Protect dentin desensitizer. The crowns were then further reduced to receive a metal-ceramic crown and the hydraulic conductance was recorded under the same conditions, on deeper dentin, before and after using the desensitizing agent. Twenty additional teeth were prepared: 10 to receive a metallic crown and 10 teeth to receive a metal-ceramic crown. A tube filled with 1 mL phosphate buffered saline (PBS) was sealed to the cementoenamel junction. A temporary crown was sealed onto the preparation with Temp Bond. The amount of eugenol that diffused across dentin into PBS was spectrofluorimetrically measured at Day 1 and Day 7. The crown preparations were vertically sectioned and the dentin remaining thickness was recorded.

RESULTS

The hydraulic conductance of teeth prepared for a metal-ceramic crown was twice as high as teeth prepared for a metallic crown (P < 0.001). The desensitizing agent reduced the hydraulic conductance in both groups (P< 0.001). The two groups showed the same hydraulic conductance after using Protect (ns). No significant difference was found in the amount of eugenol diffusion between the two groups of teeth although eugenol diffusion decreased with time (P < 0.01). No correlation was found between eugenol diffusion and remaining dentin thickness.

[Hemodynamics in the pulp of abutment teeth after their preparation for metal-ceramic denture restoration at various degree of lateral wall convergence]

Reaction of the pulp to degree-by-degree changes (from 3 to 18 degrees) in inclination of lateral walls of abutment teeth during preparation for cermet dentures was studied by the functional diagnosis methods (electroodontodiagnosis, rheodentography) in 50 patients with intact abutment teeth. Changes in dental pulp electric conductivity and hemodynamics depended on the inclination angle formed during preparation. The optimal safe angle of the lateral wall inclination was determined to be 3-12 degrees. Increase of the angle (> 12 degrees) can lead to traumatic pulpitis.

Has tooth structure been replaced?

In my opinion, there is an obvious trend in the dental literature and in continuing education courses to promote overcutting teeth when preparing them for restorations. There are many reasons for overcutting. Some feel that there is a more optimum esthetic potential when the teeth are prepared more deeply, which is a debatable view. Others are using all-ceramic crowns or polymer crowns when other types of less radical crowns could be used. There also is a significant tendency to prepare teeth for crowns instead of for onlays or inlays, thereby removing more tooth structure than is necessary. High-speed dental air rotor or electric handpieces can cause inadvertent removal of more tooth structure than is necessary. Using large burs can overcut tooth structure, and teeth should be reversed.

Clinical evaluation of a new resin composite crown system to eliminate postoperative sensitivity

This study evaluated the long-term clinical performance of a new resin composite restorative system with a 4-META dentin-bonding agent to seal complete crown preparations prior to temporization and after permanent luting with a companion resin cement. Complete-coverage crown preparations were completed on 33 vital teeth and 5 nonvital teeth (control). The new restorative material demonstrated satisfactory clinical performance for the 3-year test period. The dentin-bonding agent and its companion resin cement successfully eliminated postoperative hypersensitivity in 100% of the prepared vital teeth over the 3-year term, suggesting excellent seal of dentinal tubules exposed by the complete-crown preparations.

In vitro permeability and scanning electron microscopy study of acid-etched and ground enamel surfaces protected with dental adhesive coating

Clinical procedures, such as acid etching and reshaping of the teeth supporting removable partial dentures by grinding off some enamel surface, increase the permeability of dental enamel. Teeth take several months in vivo to partially recover from such damage. In the meantime, the tooth is more susceptible to carious decay. To prevent this the ground or etched enamel should be effectively protected. Using electron paramagnetic resonance (EPR) and a two-chamber diffusion cell the authors studied the influence of adhesive resin applied to the ground and acid-etched enamel surfaces on the diffusion of spin label TMAPO (2,2,6-6 tetramethyl-4-acetamido-piperidine-1-oxyl) molecules through the enamel. The enamel permeability was measured in samples exposed to 1-min etching with 37% phosphoric acid, in samples etched for 5 min, and in samples ground with a diamond bur. Next, all the treated enamel surfaces were coated with Scotchbond Multi-Purpose Plus(R) dental adhesive system and the permeability measurements repeated. Scanning electron microscopy (SEM) was used to study the porosity of enamel surfaces. The adhesive resin film covering the etched or ground enamel surfaces was found to decrease significantly the diffusion through dental enamel. This finding confirms the clinical value of dental adhesives used to protect ground or accidentally acid-etched enamel surfaces. SEM analysis showed that adhesive resin covers the porous surface of the acid-etched and ground enamel tightly.

Coronal leakage along apical root fillings after immediate and delayed post space preparation

The seal provided by a full-length root canal filling may be compromised by post space preparation. Eighty human mandibular premolars each with a single canal were obturated with laterally condensed gutta-percha cones and a sealer. Immediate post space preparation was carried out on half the number of teeth and delayed post space preparation on the remaining 40 teeth. Leakage along the apical root fillings was determined using a fluid transport device under a head space pressure of 30 kPa (0.3 atm). More leakage was found after delayed preparation than after immediate preparation (P = 0.0059).

Tooth structure loss apical to preparations for fixed partial dentures when using self-limiting burs

STATEMENT OF PROBLEM

Burs with guide pins may be used to limit the depth of tooth preparation for fixed partial dentures. The effects of guide pins on tooth structure apical to the finish line after tooth preparation for fixed partial dentures has not been recorded.

PURPOSE

This in vitro study recorded loss of tooth structure within 1.0 mm apical to the finish line of teeth prepared with straight cylinder and tapered cylinder self-limiting burs and one conventional bur.

MATERIAL AND METHODS

Forty-five extracted human teeth were randomly divided into three groups. The facial surface of each tooth was prepared with two types of diamond burs with guide pins and a conventional diamond for the control. The surface was profiled before and after tooth preparation. Profiled surfaces were analyzed and the groups were compared using analysis of variance and the Tukey-Kramer HSD test (alpha = 0.05).

RESULTS

No significant difference was recorded between the control group and the group prepared with a round-ended tapered cylinder self-limiting pin. However, there was a statistically significant difference between the control and cylindrical pin groups, and between the two groups prepared with self-limiting diamonds.

CONCLUSION

This study revealed abrasion apical to the finish line of the preparation in all groups. The cylindrical guide pin group exhibited the greatest loss of tooth surface.

Enamel subsurface damage due to tooth preparation with diamonds

In clinical tooth preparation with diamond burs, sharp diamond particles indent and scratch the enamel, causing material removal. Such operations may produce subsurface damage in enamel. However, little information is available on the mechanisms and the extent of subsurface damage in enamel produced during clinical tooth preparation. The aim of this study, therefore, was to investigate the mechanisms of subsurface damage produced in enamel during tooth preparation by means of diamond burs, and to examine the dependence of such damage on enamel rod orientation, diamond particle size, and removal rate. Subsurface damage was evaluated by a bonded-interface technique. Tooth preparation was carried out on two enamel rod orientations, with four clinical diamond burs (coarse, medium, fine, and superfine) used in a dental handpiece. The results of this study showed that subsurface damage in enamel took the form of median-type cracks and distributed microcracks, extending preferentially along the boundaries between the enamel rods. Microcracks within individual enamel rods were also observed. The median-type cracks were significantly longer in the direction parallel to the enamel rods than perpendicular to the rods. Preparation with the coarse diamond bur produced cracks as deep as 84 +/- 30 microns in enamel. Finishing with fine diamond burs was effective in crack removal. The crack lengths in enamel were not significantly different when the removal rate was varied. Based on these results, it is concluded that subsurface damage in enamel induced by tooth preparation takes the form of median-type cracks as well as inter- and intra-rod microcracks, and that the lengths of these cracks are sensitive to diamond particle size and enamel rod orientation, but insensitive to removal rate.

The response of human premolars to cyclic loading

The aim of the study was to obtain data on the dynamic strength of both intact and prepared premolars for partial veneer crowns. Cyclic loading was performed in a modified Amslers high-frequency pulsator with varying force (between 400 and 1400 N). The greatest dynamic strength was exhibited by the intact samples. The greater the load the fewer the cycles necessary to fracture the tooth. A statically significant difference was found (P < 0.05) between the magnitude of cyclic loads and the different types of specimens tested.

Tooth preparation and pulp degeneration

Conscious attention must be directed toward providing atraumatic tooth preparations for crowns, and to constructing adequate provisional restorations. If meticulous care is not taken, pulpal damage or death can occur. Patients should be warned that pulpal death and endodontic therapy can result from crown placement.

Fractures of posterior teeth: a review and analysis of associated factors

PURPOSE OF STUDY

To examine factors which may predispose to tooth fracture, and to assess the compressive strengths of foods and sweets which are associated with tooth fracture in vivo.

POPULATION STUDIED

Consecutive dental patients presenting with one or more fractured posterior teeth at the surgeries of three general dental practitioners, over a four-month period.

METHOD

A pro forma was designed to elicit information on the factors associated with tooth fracture and the nature and extent of such fractures. Three general dental practitioners were requested to complete a pro forma for each patient presenting with a fractured posterior tooth over a four-month period. Foods and sweets considered to be associated with tooth fracture were identified and their compressive strengths tested.

FINDINGS

A total of 129 cases of fractured posterior teeth were recorded, of which 48% occurred in the mandibular arch and 52% in the maxillary arch. In the mandible, 75% of tooth fractures occurred in molars while in the maxillary arch 50% occurred in molars. In 57% of cases assessed, no identifiable causative item was noted. Forty-five per cent of fractures were in teeth which had been restored on three or more surfaces. Compressive forces of 0.16KN to 2.2KN were obtained for food items implicated in tooth fractures.

CONCLUSION

As mesio-occlusodistal restorations were identified as a major predisposing factor to tooth fracture in this study, with mandibular first molar teeth particularly affected, placement of cuspal coverage restorations may be considered to be a justifiable preventative measure in teeth identified as being at risk.

Tooth sensitivity associated with the use of luting cements

Luting Cements are still a source of frustration to the dentist. None of the cements currently available satisfies everyone, including the patient. The problems encountered when trying to obtain adhesion to a wet substance such as dentin are well-known (Christensen, 1994). The cause of postcementation sensitivity continues to a perplexing problem.