Pattern of transmission of laser light through carious molar teeth

AIMS: The aims of this study were to investigate the pattern of transmission of laser light through carious human molar teeth, and to examine the effect on light transmission of reactions to caries in the dentine. METHODOLOGY: Sectioned carious human molars were examined whilst illuminated from their external surfaces by a helium-neon laser probe of 0.5 mm diameter. The pattern of light transmission was observed and selected specimens were photographed. The passage of light through the surrounding dentine toward the pulp space was investigated by confocal microscopy. Further carious and restored teeth were illuminated from three buccal and three lingual sites to establish the probability of light being able to reach the coronal pulp space. RESULTS: For all 31 teeth examined, it was possible to illuminate the pulp space from a position on the buccal side. The presence of intracoronal restorations did not necessarily prevent light transmission to the pulp. Confocal microscopy demonstrated conduction of light within dystrophic deposits of irregular secondary dentine. CONCLUSIONS: The presence of carious lesions or restorations in molar teeth does not necessarily interfere with transmission of laser light to the pulp space. Light is conducted within irregular secondary dentine. With appropriate probe placement, assessments of pulp health in diseased posterior teeth may be possible using laser Doppler flowmetry.     

Coronal fractures in posterior teeth

Coronal fractures of posterior teeth are not rare in clinical practice. Most of the time they constitute a restorational problem for the clinician, since they usually end below the free gingival crest. Two hundred coronal fractures of posterior teeth were examined in this study, with respect to several factors. Some of the factors were the sex and age of the patient, type and location of the tooth, and vitality of the pulp. The results showed that frequency of fractures is not influenced by the sex or age of the patient, the type or location of the tooth, or the vitality of the pulp. Factors that significantly affect the appearance of a fracture include caries, restored surfaces, and tooth morphology. Lingual cusps fracture more often than buccal cusps, fractures ended more frequently above or at the gingival crest in teeth with vital pulps, and in nonvital teeth fractures ended more frequently below the crest. Conservative cavity designs for tooth restorations and conservative access to the root canals for endodontic treatment will decrease the frequency of tooth or restoration fracture.     

Possible application of transmitted laser light for the assessment of human pulpal vitality

Abstract The purpose of this study was to determine whether use of transmitted laser light would enable a better assessment of human pulpal vitality than back-scattered light does (LDF: laser Doppler flowmetry). The experiments were carried out on ten upper central incisors in six subjects aged 23–28 years; five of the teeth were vital with no restoration, and five were non-vital. For use with transmitted laser light, the fibers within the probe of a conventional LDF apparatus were used, one for transmitting light onto the buccal surface, the other for receiving it at the palatal surface of the same tooth. For LDF, the probe was fixed at the buccal surface. Blood flow was measured at three different locations on each experimental tooth: the incisal third, the center and the cervical third of the tooth crown. In non-vital teeth, 1) output signals with transmitted laser light all registered zero, and no oscillation could be seen in recordings from any location on the tooth, but 2) LDF signals were above zero, there were regular oscillations related to heart rate, and passive increases in blood flow (corresponding to blood pressure increases) were recorded from both the center and the cervical third of the tooth, indicating that LDF registered blood flow of non-pulpal origin. In vital teeth, LDF signals were significantly higher than in non-vital teeth at each location on the tooth. At the central site on vital teeth, the output signals for transmitted laser light were about twice those seen with LDF, and passive blood flow changes corresponding to blood pressure increases were more clearly observed. These results indicated that transmitted laser light would be useful for the assessment of tooth pulp vitality both because the blood flow signals did not include flow of non-pulpal origin, and because its output signals and response to blood flow changes were clear and could easily be monitored.     

Effect of pulp protection technique on the clinical performance of amalgam restorations: three-year results

This study evaluated the influence of the pulp protection technique on clinical performance of amalgam restorations after three years, with particular reference to post-operative sensitivity and secondary caries. One hundred and twenty (120) Class II amalgam restorations (68 premolars, 52 molars; 78 MOD, 42 OD/MO) were placed in 30 participants (four restorations per participant). The restorations were divided into four groups according to the pulp protection technique used: copal varnish; 2% neutral sodium fluoride; adhesive resin and no pulp protection. The parameters evaluated were post-operative sensitivity, staining of the dental structure, tooth vitality, partial or total loss of the restoration and secondary caries. One hundred and eight (108) restorations were available for evaluation after three years. No partial or total loss of restorations had occurred; all teeth were vital, no tooth structure staining or secondary caries was detected in any of the restored teeth. Post-operative sensitivity was observed only in two restorations at baseline and at seven-days. The three-year clinical performance of teeth restored with a high copper dispersed phase amalgam was not affected by the choice of pulp protection technique.     

Pulpal blood flow recorded from exposed dentine with a laser Doppler flow meter using red or infrared light

ObjectiveTo determine the percentage of the blood flow signal that is derived from dental pulp when recording from exposed dentine in a human premolar.DesignRecordings were made from 7 healthy teeth in 5 subjects (aged 22–33 yr.) with a laser Doppler flow meter (Periflux 4001) using either a red (635 nm) or an infrared (780 nm) laser. After exposing dentine above the buccal pulpal horn (cavity diam. 1.6 mm, depth 3 mm) and isolating the crown with opaque rubber dam, blood flow was recorded alternately with infrared or red light from the exposed dentine under four conditions: before and after injecting local anaesthetic (3% Mepivacaine without vasoconstrictor) (LA) over the apex of the root of the tooth; after exposing the pulp by cutting a buccal, class V cavity in the tooth; and after sectioning the coronal pulp transversely through the exposure.ResultsThere was no significant change in mean blood flow recorded with either light source when the tooth was anaesthetized or when the pulp was exposed. After the pulp had been sectioned, the blood flow recorded with infrared light fell by 67.8% and with red light, by 68.4%. The difference between these effects was not significant.ConclusionsWhen recording blood flow from exposed coronal dentine with either infrared or red light in a tooth isolated with opaque rubber dam, about 68% to the signal was contributed by the pulp. The signal:noise ratio was better with infrared than red light, and when recording from dentine than enamel.     

Pulpal anaesthesia for mandibular permanent first molar teeth: a double-blind randomized cross-over trial comparing buccal and buccal plus lingual infiltration injections in volunteers

AIM: To compare the efficacy of buccal and buccal plus lingual infiltration anaesthesia for permanent mandibular first molars. METHODOLOGY: Thirty one healthy adult volunteers received each of the following methods of anaesthesia for a mandibular first molar tooth in a randomised order, 1) Buccal infiltration of 1.8 mL and needle penetration lingually. 2) Buccal infiltration of 0.9 mL, plus lingual infiltration of 0.9 mL. Two percent lidocaine with 1:100,000 epinephrine was used. Electrical pulp testing was performed before, and every 2 minutes for 30 minutes after injection. A successful outcome was recorded as the absence of pulp sensation on two or more consecutive maximal pulp tester stimulations (80 microA). Injection discomfort was assessed using visual analogue scales. Data were compared with McNemar and Wilcoxon Signed Ranks tests. RESULTS: Buccal infiltration was successful in 38.7% of cases compared to 32.3% after combined infiltrations; the difference was not significant (P = 0.63). Buccal infiltration produced more episodes of no response to maximum stimulation than buccal and lingual infiltrations (129 and 114 respectively), this difference was not significant (P = 0.11). Peak anaesthetic effect occurred around 10-14 minutes after injection. There was no difference in injection discomfort between buccal injections of 0.9 mL and 1.8 mL of solution (P = 0.90). Lingual injection was more uncomfortable than lingual penetration (P = O.O02). CONCLUSIONS: Buccal and buccal plus lingual infiltrations did not differ in their efficacy in producing anaesthesia of permanent first molar teeth.     

Laser light transmission in teeth: a study of the patterns in different species

AIM: The aim of this study was to investigate the pattern of light transmission through teeth of different species and to examine laser light propagation within enamel from various animal sources. METHODOLOGY: Sectioned teeth from five species--pig, horse, sheep, cat and rat--were evaluated. Samples were illuminated individually by a helium-neon laser light from the buccal surface using a probe 0.5 mm in diameter placed at varying angles between 60 and 120 degrees C. The pattern of light transmission was observed macroscopically. Further evaluation of laser light transmission in enamel was achieved using confocal microscopy. RESULTS: In each species, light was transmitted through the tooth to the pulp, but in the cat and the rat, light was also transmitted to the far side of the tooth. Despite the different patterns of enamel in the species, light was transmitted through enamel to dentine. CONCLUSION: Light from a laser Doppler probe appeared to reach the dental pulp in all the species: however, in the mammals with smaller teeth, light may also have been able to reach the periodontium and thus the reflected signal may not be entirely of pulpal origin.     

An ex vivo study of the effects of retained coronal dentine on the strength of teeth restored with composite core and different post and core systems

AIM: To investigate the fracture resistance and fracture patterns of teeth restored with composite cores supported by different pre-fabricated post systems and different heights of remaining coronal dentine. METHODOLOGY: Four groups of 30 single rooted teeth were used. Each group was divided into three subgroups of 10 teeth each and restored with carbon fibre, glass fibre, or Radix titanium posts luted with dual cure resin cement. The control group A had no retained coronal dentine. Groups B, C and D had 2, 3 and 4 mm of retained buccal and lingual coronal dentine, respectively. Teeth were tested to failure using an Instron Universal Testing Machine. Subsequently, the fracture mode of specimens was recorded. RESULTS: Teeth with retained dentine were more resistant to fracture (P = 0.001). Tooth fracture resistance was not significantly different between groups B, C and D. Within group A, titanium posts were associated with higher fracture resistance than fibre posts. Within the other groups, tooth fracture resistance was not related to post material. Within groups C and D, fracture resistance of teeth restored with carbon fibre posts was significantly higher than those restored with glass fibre posts. The dominant fracture mode in group A was core and vertical oblique root fracture whilst a combination of core, coronal dentine and root fracture occurred in the other groups. CONCLUSIONS: Fracture resistance of teeth increased with the presence of retained coronal dentine. The use of glass and carbon fibre posts did not improve the fracture resistance or the fracture pattern of teeth when compared with metal titanium posts regardless of the presence of retained coronal dentine. The dominant fracture pattern of teeth was not related to the amount of retained dentine if it was >2 mm high.     

Class IV preparations for fractured anterior teeth restored with composite resin restorations

Pediatric dentists play a major role in treating most of the anterior teeth fractures due to the fact that most patients who suffer such traumatic injuries are between the ages of seven and fourteen. Several techniques has been developed to restore the fractured incisors to the original shape and color, these include full-coverage of the traumatized tooth, or restoring the incisors with a resin. The purpose of this study is to find the ideal combination of tooth preparation and restorative material, namely, to determine if stair step chamfer preparations provide more retention in class IV restorations than the plain chamfer preparation technique when restored with a combination of a hybrid composite resin and a microfilled composite resin. This was done by comparing the shear strength values between the buccal stair-step chamfer preparation, and a modification on it (buccal and lingual stair-step chamfer preparation) and the plain chamfer preparation techniques in class IV restorations on anterior incisors using different composite resin materials. The Instron machine was used to test shear strength. One hundred and two bovine incisor teeth were freshly harvested from the slaughterhouse. The teeth were prepared and restored according to the following six groups; Plain Chamfer preparation with Tetric Ceram Composite, Plain Chamfer preparation with Renamel Composite, buccal stair-step chamfer preparation with Tetric Ceram composite, buccal stair-step chamfer preparation with Renamel composite, Buccal and lingual stair-step preparation with Tetric Ceram Composite, Buccal and lingual stair-step chamfer preparation with renamel composite. All samples were fractured using the Instron testing machine then the surface area were measured using Image-J software. Shear strength for every sample was calculated using the load numeric result from the Instron machine and the measured surface area. The Two-Factorial (AB) Analysis of Variance For Independent Samples showed that the buccal stair-step chamfer preparation showed significantly higher shear strength and fracture resistance than plain chamfer or the buccal and lingual stair-step chamfer preparation. The combination of Renamel Hybrid and Renamel Microfill composite materials showed better results than the Tetric Ceram composite when used with all three preparation techniques, but did not show a statistical significance. It was concluded that buccal stair-step preparation technique provided the ideal preparation technique with bonded composite resins in fractured anterior teeth. Only 7% of the entire sample size had an adhesion failure versus 93% that had cohesion failure. There was no significant difference in shear strength, between the restorative materials used, in conjunction with all the preparation techniques.     

An in vitro investigation into the effects of retained coronal dentine on the strength of a tooth restored with a cemented post and partial core restoration

AIM: This study aimed to examine the fracture resistance of teeth restored with cast post and partial cores supported by different heights of coronal tooth structure. METHODOLOGY: Four specimen groups were prepared. Group A was the control and consisted of 10 single-rooted teeth restored with post and cores cemented in dowel channels with no retained coronal dentine.The test groups, B, C and D differed in the amount of retained buccal coronal dentine having 3, 4 and 5 mm, respectively. All groups were tested to failure using an Instron Universal Testing Machine, Model 1195. The mode of failure for representative specimens for each group was recorded photographically. RESULTS: Specimens in group B where the remaining dentine core was 3 mm in height fractured at a higher force than specimens in the control group (P = 0.0239). There were no statistically significant differences in the forces required to fracture teeth with retained buccal coronal dentine cores of 4 and 5 mm when compared to the control. There was no statistically significant difference between forces required to fracture groups B and C or groups B and D. CONCLUSION: In this in vitro study, 3 mm of retained coronal buccal dentine improved fracture resistance of teeth restored with partial post and cores when compared to teeth without retained coronal dentine.     

Argon laser curing of fluoride-releasing pit and fissure sealant: in vitro caries development

The purpose of this study was to compare the effect of argon laser polymerization of a visible-light-cured, fluoride-releasing pit and fissure sealant on caries development in vitro. A total of twelve caries-free premolar and molar teeth was selected, and underwent a fluoride-free prophylaxis and soft tissue debridement. Cavity preparations were placed in buccal and lingual surfaces. Lingual cavity preparations were filled with the fluoride-releasing sealant (UltraSealXTplus, Ultradent) and visible light cured per the manufacturer's recommendation. Buccal preparations were filled with the fluoride-releasing sealant and argon laser cured (231 mW, 12 J/cm2 for 10 seconds). Following sealant placement, the teeth were sectioned into buccal and lingual halves. An acid-resistant varnish was placed leaving a 1 mm rim of exposed surface enamel adjacent to the sealant. The specimens were then thermocycled in synthetic saliva (500 cycles, 5 to 50 degrees C). In vitro caries lesions were formed (2.2 mM Ca, 2.2 mM PO4, 50 mM acetic acid, 5 ppm fluoride, pH 3.95). Longitudinal sections (five sections per tooth half) were obtained and evaluated by polarized light microscopy for mean outer surface lesion depths and frequency of wall lesions. Mean primary surface (outer) lesion depth was significantly decreased (ANOVA, DMR, P < .05) for the fluoride-releasing sealant with argon laser polymerization (152 +/- 16 um) when compared with visible light curing (211 +/- 23 um). Likewise, wall lesion frequency was substantially reduced for the argon laser polymerized sealants (17 percent) when compared with that for the visible light polymerized sealants (24 percent, ANOVA, DMR, P < .05). Argon laser polymerization of a fluoride-releasing pit and fissure sealant improved caries resistance markedly in the surface enamel adjacent to the sealant material. Argon laser curing enhanced the caries protective ability of the sealant along the enamel-resin cavosurface, as noted by a decrease in wall lesion frequency. Argon laser polymerization provides further caries protection against a cariogenic challenge over that afforded by fluoride-releasing sealants. Caries development around a sealant material may be hampered by the combination of fluoride release from the sealant and argon laser polymerization.     

Histological comparison of pulpal inflammation in primary teeth with occlusal or proximal caries

Objective.  A number of clinical and histological studies have investigated caries-related changes in the primary tooth pulp, but the effect of caries site, as a clinical variable, has not been previously considered. This study sought to compare inflammatory changes within the pulp of primary molars according to the location of the caries lesion (occlusal or proximal).
Methods.  Eighty-three primary molars were extracted under general anaesthesia for caries and/or orthodontic reasons, and were split immediately after removal and fixed in 10% formalin. Teeth were then decalcified, sectioned, and stained with haematoxylin and eosin for histological examination using light microscopy. Caries depth was measured using a graticle, and the site of the caries lesion noted as occlusal or proximal. Samples were further classified into one of five subgroups according to the observed degree of pulpal inflammation.
Results.  Key findings were that where caries depth was less than 50% of the total dentine thickness, there were no significant differences in inflammatory status according to caries site. In contrast, marked inflammatory changes were significantly more likely throughout the coronal pulp of teeth with proximal caries compared to teeth with occlusal caries where caries depth was equal to, or greater than, 50% of the total dentine thickness ( P  = 0.017, Fisher's exact test).
Conclusion.  Primary teeth with proximal carious lesions extending more than 50% through the dentine thickness appear to have more extensive inflammatory pulpal changes than teeth with occlusal caries of a similar depth. This finding has clinical implications and may help inform treatment decisions in the management of primary teeth with deep carious lesions.     

Caries outcomes after orthodontic treatment with fixed appliances: do lingual brackets make a difference?

van der Veen MH, Attin R, Schwestka‐Polly R, Wiechmann D. Caries outcomes after orthodontic treatment with fixed appliances: do lingual brackets make a difference? Eur J Oral Sci 2010; 118: 298–303.©2010 The Authors. Journal compilation © 2010 Eur J Oral Sci Orthodontic treatment with fixed appliances is considered a risk factor for the development of white spot caries lesions (WSL). Traditionally, brackets are bonded to the buccal surfaces. Lingual brackets are developing rapidly and have become more readily available. Buccal surfaces are considered to be more caries prone than lingual surfaces. Furthermore, lingual brackets are shaped to fit the morphology of the teeth and seal almost the entire surface. In the present study we tested the hypothesis that lingual brackets result in a lower caries incidence than buccal brackets. We tested this hypothesis using a split‐mouth design where subjects were allocated randomly to a group receiving either buccal or lingual brackets on the maxillary teeth and the alternative bracket type in the mandible. The results indicate that buccal surfaces are more prone to WSL development, especially when WSL existed before treatment. The number of WSL that developed or progressed on buccal surfaces was 4.8 times higher than the number of WSL that developed or progressed on lingual surfaces. When measured using quantitative light‐induced fluorescence (QLF), the increase in integrated fluorescence loss was 10.6 times higher buccally than lingually. We conclude that lingual brackets make a difference when caries lesion incidence is concerned.     

Pulp size in molars: underestimation on radiographs

The aim was to determine whether radiographs provide a clinically useful indication of pulp size in diseased/restored human first molar teeth, and to investigate accessibility of pulp tissue for diagnostic testing using laser Doppler flowmetry (LDF). Extracted teeth of known age were collected. Restorative materials were removed and teeth with evidence of pulp exposures excluded. Fifty-six teeth were radiographed from buccal and mesial aspects, and then their crowns were sectioned axiobuccolingually and photographed. Images were digitally scanned and measurements made of the total pulp area (above a line across the most superior part of the pulpal floor) and the pulp area in the clinical crown (superior to a line between the amelocemental junctions). The pulp width at the cervix and the highest point of the pulp were also recorded. Data were analysed using Pearson correlations. Pulp areas within the clinical crowns were significantly larger than indicated by radiographs, by 23% in the case of the clinically attainable buccal view (P < 0.05). Pulps may be more accessible to flowmeter testing than they appear. Absence of pulp tissues in the crown was recorded in equal numbers of teeth on radiographs and sections, but with agreement for only one tooth. Sixteen per cent of the teeth had no pulp area in the clinical crown when sectioned, but might still be suitable for testing using LDF.     

Quantitative microradiography of intact and worn human coronal dentine

The mineral content of the incisai part of the coronal dentine of intact and worn teeth per unit volume was determined by means of quantitative contact microradiography. In the buccal to lingual direction, a zonated pattern of mineralization was evident. In the intact teeth, the highest values for the mineral content were at the central streak between the incisal tip of the dentine and the pulp horn (50 per cent). A narrow zone of dentine adjacent to the central streak contained about 45 per cent minerals and the bulk of dentine about 48 per cent, whereas the mineral content of the mantle dentine averaged 42 per cent. Only small variations in the degree of mineralization were found in this area of the coronal dentine between teeth at various age levels.In the worn teeth, an increase in the mineral content of the incisai dentine was evident at all levels between the exposed surface and the pulp horn. Centrally in the worn dentine, the increase was about 4 per cent whereas laterally the increase averaged 2 per cent.     

Argon laser irradiation and fluoride treatment effects on caries-like enamel lesion formation in primary teeth: an in vitro study

PURPOSE: To evaluate topical acidulated phosphate fluoride (APF) and low fluence argon laser (Ar) treatment effects on in vitro caries formation in primary tooth enamel. METHODS: 20 extracted or exfoliated primary teeth with sound buccal and lingual surfaces underwent soft tissue debridement and a fluoride-free prophylaxis. Treatment groups were: (1) Control [n=5]; (2) Ar [231mW, 10 seconds, 11.5J/cm2; n=5], (3) 1.23% APF for 4 minutes before Ar [n=5]; (4) Ar before APF [n=5]. Buccal and lingual enamel surfaces were treated, and then rinsed in deionized,distilled water (24 hours). An acid-resistant coating was applied leaving buccal and lingual sound enamel windows exposed. In vitro enamel caries was created (2.2 mM calcium, 2.2 mM phosphate, 5.0 mM fluoride, pH 3.90, 10 days). Following longitudinal sectioning, two lesions per primary tooth (10 lesions total) with each group were evaluated for lesion depth (polarized light, water imbibition) and compared (ANOVA, Duncan's Multiple Range). RESULTS: Argon laser irradiation alone provided a 41% reduction in lesion depth (176 +/- 21 microm, P< 0.05) when compared with that for the no treatment controls (297 +/- 31 microm). The combination of argon laser irradiation with APF treatment resulted in lesion depth decreases of slightly over 50% (140 +/- 23 microm for APF before ArTx; 124 +/- 17 microm for ArTx before APF, P< 0.05) compared with control lesion depths, and 20 to 30% over that for argon laser treatment alone (P< 0.05). There was no statistical difference in lesion depth regardless of whether fluoride treatment occurred before or after laser irradiation (P> 0.05).     

The radiographic assessment of pulp size: validity and clinical implications

A study was performed to determine if the radiographic appearances of the coronal pulp spaces provide a reliable indication of pulp size in maxillary incisors. The use of student and staff assessor groups showed that length of clinical experience did not influence assessments of the size of the coronal pulp. A measuring grid, superimposed over a duplicate set of films, decreased the students' perception of the size of the coronal pulp. The presence of small carious lesions or restorations did not affect the assessments for either of the film types viewed. The data were pooled to give a mean radiographic size for each tooth, and the teeth were sectioned. Analysis of the results demonstrated the value of carefully viewing incisor crowns shown on pre-operative periapical radiographs. Sectioning of the teeth suggested that very little dentine may remain to protect the pulp after routine crown preparations. Even the very conservative preparations sometimes necessary when providing veneers might be considered a hazard to the pulp, as they may expose large areas of the dentine of an immature tooth.     

Articaine infiltration for anesthesia of mandibular first molars

A randomized, controlled trial of 31 healthy volunteers compared 4% articaine with 1:100,000 epinephrine buccal infiltration to buccal plus lingual infiltration of the same dose of drug in achieving pulpal anesthesia of mandibular first molar teeth. Data were compared with efficacy of an inferior alveolar nerve block using 2% lidocaine 1:80,000 epinephrine in a cohort of 27 of the volunteers. Anesthesia was determined using electronic pulp testing. Buccal and buccal plus lingual infiltrations of articaine with epinephrine did not differ in efficacy in obtaining pulpal anesthesia for mandibular permanent first molars (p = 0.17). Efficacy of 4% articaine with epinephrine infiltrations for first molar pulp anesthesia was similar to that of an IANB using lidocaine with epinephrine over a 30-minute study period (96 and 80 episodes of no response to maximal stimulation respectively, p = 0.097). Subjective tooth numbness was more common after IANB than buccal infiltration (p = 0.005). The discomfort of buccal infiltration with articaine was volume dependent (p = 0.017) and similar to that of an IANB.     

Importance of mini-dumbbell specimen to access tensile strength of restored dentine: historical background and the future perspective in dentistry

OBJECTIVES: The development of adhesive resins to dentine enables resin restorations to be more durable. Several bond strength measurement techniques for measuring adhesion have been proposed. A standardised method is needed which produced higher and more consistent bond strength values which allow bond stability and the bonding mechanism to be studied. Our aim was to investigate mainly the adhesives and not the substrate. DATA SOURCES: This review is based on the literature on an adhesive, 4-META/MMA-TBB resin and conditioners to modify dentine substrates. The latter is a very important topic for developing our understanding of the bonding to dentine. The objective of the review is to explain the efficacy of the mini-dumbbell specimen in measuring the tensile strength of resin to dentine and to analyze the resin to dentine interface. Both the adhesive and the substrate control the quality of hybridized dentine. CONCLUSIONS: By creating an impermeable acid resistant barrier to both biological and chemical stimuli between the exposed dentine and the restored tooth surface we are able to protect exposed dentine from caries (infection) at the same time as protecting the pulp and preventing toothache. This barrier also helps maintain tooth vitality and for the purposes of this article is termed 'artificial enamel'. Microleakage free restorations are possible through the introduction of this 'impermeable artificial enamel' barrier.     

Pattern of transmission of laser light in teeth

This study examined the transmission of helium neon laser light in 20 dog and human teeth. The effect of probe position and angulation was observed both macroscopically and at a microscopic level using con-focal microscopy. In all teeth in both species, laser light was transmitted through teeth to the pulpal surface with the light following the path of the enamel prisms and dentinal tubules. Probe angulation did not affect the pattern of light transmission, nor did probe position; however, the position of the probe on the tooth surface determined which section of the pulp was illuminated. Enamel and dentine together are able to collect and distribute light within the tooth, with both enamel prisms and dentinal tubules acting as optical fibres.