Geographic distribution of porcelain veneer preparation depth with various clinical techniques

STATEMENT OF PROBLEM: Various clinical techniques have been advocated for uniform reduction of the tooth surface before a porcelain veneer restoration. Often these techniques do not produce a consistently uniform labial reduction. PURPOSE: The purpose of this study was to identify the degree of inconsistency on a geographic scale in the depth of labial reduction for porcelain veneers, resulting from the use of 3 clinical techniques. The technique of co-ordinate metrology was used to map the variations in the depth of the preparation. MATERIAL AND METHODS: A single operator using 3 techniques (dimples as depth guides, freehand, or depth grooves as depth guides) prepared 90 noncarious, unrestored extracted teeth to receive porcelain veneers (n=30). Impressions of the prepared and unprepared teeth were scanned with a co-ordinate measuring machine. In-house software was used to color-code the plotted images on the basis of the depth of preparation. Profile measurements were also made along the mid-labial sagital plane at the mid-labial, incisal, and cervical regions, as well as along the mesial proximal and distal proximal areas along the mid-labial horizontal plane. The ideal depth range for the labial reduction was chosen to be 0.4 to 0.6 mm. One-way analysis of variance and the Bonferroni test were performed to determine the significance (P<.05) in the difference between the means of reductions achieved with the 3 techniques. RESULTS: There was no statistically significant difference in the mean percentage area prepared to the ideal depth range (0.4 mm-0.6 mm), between dimple (44.59%), freehand (36.35%), and depth groove (38.43%) techniques. The difference in the mean percentage area of reduction greater than 0.6 mm between dimple (12.98%), freehand (29.66%), and dimple and depth groove (37.32%) techniques were statistically significant (P=.0000), but not between freehand and depth groove techniques. With the profile measurements it was seen that there were statistically significant differences in the mean depth between dimple (0.45 mm) and depth groove (0.63 mm), and freehand (0.51 mm) and depth groove in the mid-buccal (P<.0004) and cervical (dimple = 0.48 mm, freehand = 0.52 mm, depth groove = 0.63 mm) (P<.0005) regions. There was statistically significant difference (P<.0000) in the mean depth between the dimple (0.39 mm) and freehand (0.30 mm), dimple and depth groove (0.50 mm), and freehand and depth groove techniques in the incisal area. In the mesial proximal region statistically significant difference (P<.0034) in the mean depth was found between the dimple (0.52 mm) and freehand (0.68 mm), and dimple and depth groove (0.64 mm) techniques only. In the distal proximal region, there was no statistically significant difference in the mean depth between dimple (0.55 mm), freehand (0.66 mm), and depth groove (0.64 mm) techniques. CONCLUSION: The use of dimple technique showed a trend to greater consistency and fidelity in labial reduction to a depth of 0.4 to 0.6 mm. The 3 techniques for veneer preparations studied were associated with varying degrees of inconsistency in the distribution of depth of preparation within a tooth and between teeth in the same technique group.     

A comparison of the depths produced using three different tooth preparation techniques

STATEMENT OF PROBLEM: Inadequate preparation of teeth for metal ceramic crowns can significantly influence the ultimate form and longevity of the definitive restoration, as well as adversely affect the supporting tissues. PURPOSE: The purpose of the study was to determine the effect that 3 different tooth preparation techniques had on an operator's ability to appropriately and consistently prepare teeth for metal ceramic crowns. MATERIAL AND METHODS: Thirty typodont maxillary central incisor teeth were mounted individually and randomly allocated to 3 equal groups (A, B, and C). One operator was asked to prepare each tooth for a metal ceramic crown. A freehand approach was used to prepare the teeth in Group A, which acted as a control. Groups B and C were prepared with the assistance of a silicone index and a suitable depth gauge bur, respectively. A silicone index of the unprepared tooth, into which contrasting silicone was injected to occupy the space created by tooth preparation, was sectioned in the midline. Images of the sectioned index were captured with an optical microscope (resolution +/- 0.02 mm), which was attached to a personal computer. A calibrated image analysis program was used to measure the depth of preparation (in millimeters) at 5 points (labial cervical, mid-labial, incisal, mid-palatal, and palatal cervical) on 2 occasions. These results were pooled and averaged to give a mean labial and palatal preparation depth (in millimeters) and incisal edge reduction. The data were analyzed by use of a 1-way analysis of variance and Scheffe's post hoc statistical test (P<.05). RESULTS: The mean depths of labial and palatal preparation for Groups A, B, and C were 1.28 and 0.47 mm; 1.46 and 0.56 mm; and 1.45 and 0.63 mm, respectively. The difference between the groups' labial preparation depth was not significant (P=.06), but the difference for palatal preparation depth was significant (P=.01). The mean incisal reduction was 3.00 mm for Group A, 2.74 mm for Group B, and 2.13 mm for Group C (P=.00). CONCLUSION: Within the limitations of this study, it was concluded that preparation of teeth for metal ceramic crowns without the use of devices to help gauge reduction depth can result in insufficient labial reduction and incisal overreduction.     

Tooth preparation techniques for porcelain laminate veneers

OBJECTIVE: The purpose of this study was to determine the effect that two guides to tooth preparation had on an operator's ability to appropriately and consistently prepare teeth for porcelain laminate veneers. STUDY DESIGN: In-vitro study. MATERIALS AND METHODS: Thirty typodont central incisor teeth were randomly allocated into three groups and a general dental practitioner was asked to prepare the teeth for porcelain laminate veneers. Group A were prepared freehand while Groups B and C were prepared with the assistance of a silicone index and depth preparation bur respectively. Images of the prepared teeth were used to calculate the mean labial depth of preparation and incisal reduction of teeth in each group. RESULTS: The mean labial reduction for Groups A, B and C was 0.37 mm (SD 0.13), 0.62 mm (SD 0.17) and 0.61 mm (SD 0.15) and the mean incisal reduction for Groups A, B and C was 1.0 mm (SD 0.28), 1.0 mm (SD 0.38) and 1.03 mm (SD 0.26) respectively. CONCLUSION: It is suggested that consideration be given to the use of a silicone index or depth gauge bur when teeth are prepared for porcelain laminate veneers.     

Evaluation of three different tooth preparation techniques for metal ceramic crowns by comparing preparation depths: An in vitro study

Aim:

To determine the effect of three different tooth preparation techniques had on operator''s ability to appropriately and consistently prepare teeth for metal ceramic crowns.

Materials and Methods:

Ninety maxillary left central incisor typodont teeth were allocated to three equal groups (A, B and C) of thirty and mounted in standard working model one at a time. A freehand approach was used to prepare the teeth in Group A, which acted as a control. Groups B and C were prepared with the assistance of silicon index and suitable depth gauge burs, respectively. A silicon index of unprepared teeth, into which contrasting colored silicon injected to occupy the space created by tooth preparation, was sectioned in the midline. Images of sectioned index were captured with optical microscope attached to a personal computer. A calibrated image analysis software was used to measure the depth of preparation (in millimeters) at five points (labial-cervical, mid-labial, incisal, mid-palatal and palatal cervical) on two occasions. These results were pooled and averaged to give a mean labial, incisal and palatal preparation depths in mm. The data were analyzed by one-way analysis of variance and Scheffe''s post-hoc statistical test.

Results:

The mean depth of labial and incisal preparation for Groups A, B and C was 1.23 and 1.72 mm, 1.45 and 1.96 mm, 1.47 and 1.95 mm, respectively. The difference between the groups’ labial preparation depth was significant as well as the difference between groups’ incisal preparation depth. The mean palatal preparation was 0.46 mm for Group A, 0.54 mm for Group B and 0.59 mm for Group C.

Conclusion:

Teeth preparation for metal ceramic crowns without any assistance can lead to under-preparation of labial and incisal surface.

Clinical Significance:

Whenever possible, considerable importance should be given to the use of index or depth gauge burs for preparing teeth for receiving metal ceramic crowns.Key Words: Comparison, depth gauge bur, experimental, in vitro, silicon index     

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.     

The effects of tooth preparation on pressure measured in the pulp chamber: a laboratory study

PURPOSE: The purpose of this study was to determine pressure changes in the pulp space during tooth preparation with either diamond or tungsten carbide burs in a high-speed dental handpiece in the laboratory. MATERIALS AND METHODS: Twenty premolar teeth were collected and randomly assigned to two groups: group 1 received preparation with diamond burs and group 2 with tungsten carbide burs. The teeth were mounted on a pressure transducer and the pulp chambers were filled with saline. A 0.1-mm thickness of tooth tissue was removed from the proximal surface of each tooth, alternating dry and wet cutting, until the pulp chamber was exposed. Pressure and temperature changes were recorded during tooth preparation. RESULTS: At 0 to 1 mm of remaining dentin depth dry cutting with diamond and tungsten carbide burs generated a mean positive pulpal pressure of 12 kPa and 6 kPa, respectively. Wet cutting under the same conditions produced 0.6 kPa and 0.15 kPa, respectively. The difference between wet and dry cutting was highly significant (P < 0.001). Diamond burs produced significantly higher pressure increases than carbide burs at all levels for both wet and dry techniques (P < 0.05). When cutting farther than 2 mm from the pulp, tooth preparation created a mean 0.09-kPa pressure increase, which was not influenced by either coolant use or bur type. The temperature change was minimal during wet cutting and only minor temperature increases were recorded during dry cutting. CONCLUSION: From this laboratory study it is concluded that significant pressure changes occur in the pulp chamber during tooth preparation of extracted teeth when the remaining dentin thickness is less than 2 mm.     

A cognitive systematic approach to analyzing preparation design for a difficult space management case

There are at least two different techniques for preparing teeth prior to bonded porcelain restorations. The first involves using depth cutters guided by the existing tooth structure. A more recently developed approach integrates an additive wax-up that represents the final volume of the teeth, with indices used to guide the preparation design. This article illustrates in detail a clinical case that was prepared by combining the earlier simplified depth cutter approach with recontouring and preparation design principles determined clinically by the dentist. The same case was prepared in the laboratory on plastic models, using labial and incisal reduction preparation guides fabricated from a diagnostic wax-up. This combination of techniques will simplify preparation design for difficult space management cases and facilitate predictable and repeatable results that meet current esthetic standards while staying conservative and preserving tooth structure.     

Cutting efficiency of three diamond bur grit sizes

BACKGROUND: Tooth preparation requires safe, efficient and rapid cutting, and diamond burs routinely are used for extracoronal preparation and gross tooth reduction. Coarser-grit diamond burs often are used for gross tooth reduction, with tooth surface finishes being sacrificed for the presumed greater cutting rates, or CRs, of the coarser diamond burs. The authors compared the CRs of medium-, coarse- and super-coarse-grit diamond burs. METHODS: The authors used a self-contained dental treatment system with digitally controlled handpiece speed, torque and water flow rate to cut a machinable glass ceramic cutting substrate with medium-, coarse- and super-coarse-grit diamond burs from the same manufacturer under a load of 147.5 grams (0.9 kilonewton at the bur tip) and a coolant flow rate of 22 milliliters per minute. They made three cuts through 13-millimeter bars of the cutting substrate with six diamond burs of each grit size. They determined CRs as the transection time per millimeter and analyzed CR data by one-way analysis of variance and post hoc Scheffé tests. RESULTS: The authors found no statistically significant difference in CR (P > .05) between the three diamond bur grit sizes for the first (13 mm) cuts. When they compared the three cuts (39 mm total cut length), they found no difference (P > .05) between CRs for coarse- and super-coarse-grit diamond burs, but they did find that the super-coarse-grit diamond burs cut faster than the medium-grit diamond burs (P < .01). CONCLUSION: Differences in CR for the three diamond bur grit sizes are due to the greater decrease in CR for the medium-grit diamond burs (50 percent) compared with the CRs of the coarse- and super-coarse-grit diamond burs (35 percent and 25 percent, respectively) over the total cutting period. CLINICAL IMPLICATIONS: Coarser-grit diamond burs may be useful for extensive gross tooth preparations, but dental professionals should be aware of the associated effects of the coarser grit on surface finish, heat generation and enamel damage.     

An evaluation of polymer rotary instruments' ability to remove healthy, non-carious dentine

The aim of this study was to confirm that Smartprep burs do not cut non-carious, healthy dentine. Twenty non-carious extracted molars were trimmed with a diamond bur to remove enamel and to create a flat dentine surface. A new Smartprep bur (RA # 4) was applied to each tooth for 30 seconds. As a control, a new number three round stainless steel bur was applied to each tooth. The mean dentine loss was 4.25 mg (range 1.4 - 9 mg) for Smartprep burs and 12.21 mg (range 7.6 - 16.5 mg) for stainless steel burs. The Smartprep burs remove significantly less dentine than stainless steel burs.     

A customized metal guide for controllable modification of anterior teeth contour prior to minimally invasive preparation

ObjectiveOptimal tooth reduction is a key requirement for aesthetics, function, and the longevity of fixed restorations. Research has demonstrated that controlled and conservative tooth preparation is crucial for the long-term success of adhesive restorations. Different techniques of fabricating reduction guides have been previously reported in literature. The present technical note describes the fabrication technique and clinical application of a customized metal preparation reduction guide.Material and methodPatient presented with tilted maxillary left central incisor. The flared-out part of the tooth was modified prior to veneer restoration preparation. Resin pattern reduction guide was fabricated on the diagnostic cast with a window on the tilted mesial portion of the tooth. After intraoral evaluation, resin pattern guide was casted. Metal reduction guide was place intraorally and reduction was provided on the exposed surface of the tooth. After the removal of the tilted portion, a harmonious arch form allowed the clinician to provide adequate evaluation and preparation for veneer restorations.ResultsThe device demonstrated good practical value, allowing for selective and controlled reduction of tooth structure, and definitive protection of adjacent tooth surfaces from iatrogenic damage. The clinical outcome successfully addressed the patient’s restorative and aesthetic needs, and the veneer was stable 2 years postoperatively.ConclusionUse of a metal guide assists clinicians to provide a more predictable reduction of a desired tooth surface, while decreasing the risk of compromising the other/adjacent tooth surfaces.     

瓷贴面美容性修复四环素牙的临床应用

目的：探讨一种较理想修复四环素牙的方法。方法：应用瓷贴面修复中度四环素牙114颗。唇面均匀磨除0．5mm，终止线位于龈下0．5mm。在耐火代型上制作瓷贴面，粘结面用氢氟酸超声酸蚀30秒。用Cerinate烤瓷贴面专用粘结剂粘固。结果：114个贴面经3年观察，总成功率95．6％。结论：瓷贴面具有脱落率低，美观，耐磨损，抗着色及对牙龈组织无刺激等优点，是修复四环素牙的一种较理想方法。     

牙釉质、牙本质与Vita饰面瓷的半透性比较

目的:比较天然牙牙釉质和牙本质与Vita饰面瓷的半透性差异。方法:制备0.8mm的牙釉质切片和1.0mm牙本质切片各32例,制作厚度1.0mm的Vita釉瓷EN1、EN2,透明瓷T4、Window,体瓷A1、A2、A3、A3.5、A4、B2、C2、D2试件,每组各3个。用PR-650光谱扫描色度仪分别测量牙体组织切片和瓷片试件的透射率、反射率,计算透射系数。采用SPSS12.0软件包计算牙釉质和牙本质透射系数的95%可信区间,使用SNK法对不同色相和饱和度的体瓷的透射系数进行两两比较。结果:牙釉质的透射系数范围为0.0817～0.1009mm-1,高于2种釉瓷的透射系数(分别为0.0507mm-1和0.0408mm-1)。牙本质的透射系数范围为0.0418～0.0482mm-1,高于体瓷的透射系数(0.016mm-1～0.027mm-1)。随着饱和度的增大,体瓷试件的透射系数下降(P<0.05)。结论:Vita饰面瓷与牙体组织的透射性能有明显差异,尤其以釉瓷和牙釉质的差别最大。     

Periodontal healing after mandibular third molar surgery--A comparison of distolingual alveolectomy and tooth division techniques

The purpose of this study was to compare the periodontal healing of mandibular second molars after the removal of impacted mandibular third molars using distolingual alveolectomy and tooth division techniques. A total of 120 consecutive healthy patients who presented with bilaterally impacted mandibular third molars were included in this study. The same operator removed the impacted third molars on both sides in all patients. The third molar on one side was removed by distolingual alveolectomy using a chisel, whereas the contralateral tooth was removed by the tooth division technique using burs. Attachment level, periodontal pocket depth and bone healing distal to the mandibular second molars were assessed at 7 days, 3 months and 6 months after surgery. The results showed better periodontal healing and bone healing when distolingual alveolectomy was employed, especially in the removal of deeply impacted mandibular third molars.     

Removal of porcelain veneers aided by a fluorescing luting cement

PURPOSE: Porcelain veneers are a safe and effective treatment modality for selected teeth that have poor esthetics. However, removal of porcelain veneers that have failed may be time-consuming and involve considerable removal of sound tooth structure adjacent to the veneer. The aim of this study was to evaluate a novel method of porcelain laminate veneer removal by incorporating a fluorescent dye into the luting cement that allows the practitioner to visualize the cement on the tooth and remove the veneer without causing residual damage to the adjacent tooth substance. MATERIALS AND METHODS: Porcelain veneers were luted on extracted teeth with a luting cement modified with a fluorescing agent. Faculty teaching staff and final year dental undergraduates were asked to remove the veneers with the aid of a curing light to render the luting cement visible by fluorescing. They were then asked to compare the removal of comparable veneers without this visual aid and to complete a standard questionnaire. The depth of cure of the conventional and modified cements was measured using a penetrometer. RESULTS: Results of the questionnaire indicated that the operators found removing the veneer cemented with the modified (fluorescing) cement considerably easier than removing the veneer cemented with the conventional cement. Microscopy indicated that more damage was caused to the underlying tooth during removal of conventionally cemented veneers. The incorporation of the dye into the cement reduced the depth of cure from 4.238 mm (SD = 0.025) to 3.761 mm (SD = 0.096).     

Postoperative tomographic assessment of veneer bone grafting with implant placement in the maxillary anterior region

Various ridge augmentation and sinus lift procedures were performed in severely resorbed alveolar crests of a maxilla to provide some volume for implant treatment. It was reported that the outcome of maxillary sinus lift procedures was evaluated with conventional tomography or computerized tomography, and that grafted bone around implants markedly progressed in resorption, particularly at the implant apex. However, veneer bone grafting with implant placement has not been evaluated after treatment with imaging techniques. Therefore, the purpose of this study was to assess veneer bone grafting after maxillary anterior implant treatment. Seven patients with a mean age of 24 years, with implants placed in the maxillary anterior region with or without autogenous veneer bone grafting were postoperatively examined using conventional tomography. On tomograms, the ratio of bone-to-implant contact and the area of bone were measured in labial bones with bone grafts, and they were compared with the values without bone grafts. In cases with bone grafting, the average ratio of bone-to-implant contact was 63.6%, whereas 81.8% was formed in cases without bone grafting. The average area of bone was 12.9 mm and 23.4 mm in patients with and without bone grafting, respectively. No significant difference was found between the implants with and without bone grafts. Resorbed labial bone was observed in the maxillary anterior region with and without veneer bone grafting.     

Removal of Porcelain Veneers Aided by a Fluorescing Luting Cement

Purpose: Porcelain veneers are a safe and effective treatment modality for selected teeth that have poor esthetics. However, removal of porcelain veneers that have failed may be time‐consuming and involve considerable removal of sound tooth structure adjacent to the veneer. The aim of this study was to evaluate a novel method of porcelain laminate veneer removal by incorporating a fluorescent dye into the luting cement that allows the practitioner to visualize the cement on the tooth and remove the veneer without causing residual damage to the adjacent tooth substance. Materials and Methods: Porcelain veneers were luted on extracted teeth with a luting cement modified with a fluorescing agent. Faculty teaching staff and final year dental undergraduates were asked to remove the veneers with the aid of a curing light to render the luting cement visible by fluorescing. They were then asked to compare the removal of comparable veneers without this visual aid and to complete a standard questionnaire. The depth of cure of the conventional and modified cements was measured using a penetrometer. Results: Results of the questionnaire indicated that the operators found removing the veneer cemented with the modified (fluorescing) cement considerably easier than removing the veneer cemented with the conventional cement. Microscopy indicated that more damage was caused to the underlying tooth during removal of conventionally cemented veneers. The incorporation of the dye into the cement reduced the depth of cure from 4.238 mm (SD = 0.025) to 3.761 mm (SD = 0.096). CLINICAL SIGNIFICANCE The fluorescent cement was considered to be superior to conventional cements in its ease of visibility, and as a consequence, veneers cemented with the fluorescing cement are easier to remove. The fluorescing dye significantly reduced the depth of cure, but this may not be clinically significant, because of the small thickness of cement employed when luting adhesive restorations. The use of such fluorescing materials may not be restricted to a luting cement for veneers but may also be incorporated into bases and lining materials so they can be visualized on removal of tooth‐colored restorations, to prevent further tooth destruction.     

Cutting effectiveness of carbide burs following multiple steam autoclaving cycles

New carbide burs that are placed on a bur block can be subjected to multiple steam autoclaving cycles prior to their first use. The decision to discard a bur before or during cavity preparation is a subjective one based on operator expectations and experience. This study examined the durability of carbide burs after multiple autoclaving cycles by judging not only their initial sharpness but also their ability to maintain sharpness throughout a cavity preparation. Five experienced operators were given a set of No. 330 carbide burs that had been separated into five blind categories: those not autoclaved at all and those that had been autoclaved one, two, five, or 10 times. Each operator judged the cutting effectiveness of each bur by making an initial plunge cut through the enamel of a freshly extracted tooth. After the initial plunge cut, each operator used the same set of burs to complete an occlusal cavity preparation in molar models fabricated from composite restorative material. Each operator was asked to examine the burs for any visual deterioration and to rate the cutting ability of each bur. The burs were also examined for wear under a scanning electron microscope. Based on the results, this study concluded that up to 10 autoclaving cycles did not significantly affect the perception of either initial sharpness or the bur's effectiveness while completing the preparation.     

Effect of cutting instruments on permeability and morphology of the dentin surface.

There are major differences in morphological detail after cutting the dentin surface among the methods commonly used to prepare dental cavities. The purpose of this study was to compare dentin permeability and the morphology of the dentin surfaces prepared with diamond and carbide steel burs after etching with 6% citric acid. Twenty-four freshly extracted human third molars were sectioned, mounted on plexiglass, and connected to the dentin-permeability measuring apparatus. The permeability of dentin was measured by fluid filtration and expressed as hydraulic conductance. There were two study groups of 12 teeth. Each tooth had one occlusal cavity preparation prepared but utilized three depths: the original was prepared just into the dentin, the second 0.5 mm deeper than the first, and the third 0.5 mm deeper than the second. One group had the first cavity prepared with a diamond, the second deepened using a steel bur, then the third depth was made by use of the diamond. The other group had the first cavity preparation prepared with a steel bur, deepened 0.5 mm again using a diamond, then deepened again using a steel bur. Dentin permeability was measured after cavity preparation, then after 2 minutes of acid etching. Analysis of variance and Duncan's multiple range test were used to establish whether differences were significant at the 0.05 confidence level. Prepared and acid-etched surfaces were characterized using a scanning electron microscope to identify any differences between the two groups. After acid etching with 6% citric acid, the permeability of dentin cavities prepared with diamond burs was significantly less than the permeability of cavities prepared with carbide steel burs. After etching, there were differences in the appearance of the dentin surfaces prepared with diamonds and steel burs. Dentin bonding agents may have their effectiveness reduced when placed following cavity preparation by use of a diamond.     

A technique of measurement of the depth of the vestibular fornix in the mandibular anterior region.

A radiographic method of measurement of the depth of labial vestibule in the mandibular anterior region has been described. Contrast medium was applied to the lip and mucobuccal fold and radiopaque marker attached to the labial surface of each tooth. The head was positioned in a craniostat and a posterior-anterior radiograph exposed. The radiopaque boundaries of the vestibule showed on the radiograph so that they could be measured. Statistical analysis showed a recording error of 0.6 mm and an observation error of 0.29 mm, which are within the range of error acceptable for this type of recording technique.