Minimal Intervention Minimally Invasive Dentistry Health And Social Care Essay

Dentistry has very much shifted from an invasive to a more conservative approach over the years. This is due to an extended understanding of the nature of the disease and its process and discovering more effective methods of treatment instead of the traditional “cut, drill and fill” technique. Hence, the concept of minimally invasive and minimal intervention dentistry is now gaining popularity in modern dentistry.

Minimal intervention is a modern medical approach to the treatment of caries focusing on prevention and detection of dental diseases at the earliest stage to avoid invasive treatment.

When surgical intervention is necessary, minimally invasive techniques are being used widely to conserve as much tooth structure as possible and reduce risk of tooth fracture and pulpal problems.

The minimally interventive approach involves reduction of cariogenic bacteria. It uses preventive measures such as topical fluorides, fissure sealants and patient education on oral hygiene. Early lesions are remineralised by non-interventive management, such as fluoride ions in saliva. The surgery carried out if necessary is minimally invasive and uses adhesive materials such as glass ionomer cements and adhesive composite systems. Innovative, modified cavity designs are used with possibly no drilling such as ART techniques.

The resurgence of air abrasive technology with newer restorative materials has given a new dimension to “minimally invasive dentistry.” The micro-mechanical bonding of the restoration to the tooth structure through maximum preservation of healthy tooth structure negates the need to follow conventional G.V. Black cavity design parameters.

Firstly, the difference between minimal intervention dentistry and minimally invasive dentistry need to be pointed out. Minimal intervention can be defined as a philosophy of professional dental care, with emphasis on early detection and earliest possible cure of the carious disease. This is followed by minimally invasive dentistry, which is the conservation of healthy tooth structure by using techniques that are patient friendly and cause minimal damage to the dental tissue and focuses on repair of irreversible damages caused by the disease and remineralisation.1

The concept of minimally invasive treatment emerged in dentistry in the early 1970s. One of the early examples of this is the application of diamine silver fluoride, which arrests the carious process and prevents the formation of any new caries. The silver ions in the diamine silver fluoride kill pathogenic organisms. Application is simple, cost effective and does not require any complex training to carry out.2 Several other examples are the development of preventive resin restorations (PRR) that were introduced in the 1980s, atraumatic restorative treatment (ART) which is the treatment of caries using only hand instruments and restoring with an adhesive filling material such as glass ionomer cement, and Carisolv in the 1990s which is a chemo-mechanical method that is efficient at removing carious dentine.3

The fundamental components of minimally invasive dentistry are the risk assessment of the disease; paying particular attention on early detection and prevention of caries, remineralisation of the enamel and dentine, use of a wide range of restorative materials and techniques that cause minimal intervention and resorting to surgery only if absolutely necessary.

The following definition can be used to summarise the different aspects of minimally invasive dentistry: “the maintenance and monitoring of oral health through continuous care, comprising comprehensive preventive management, a longitudinal approach to risk assessment and diagnosis of chronic disease, and a minimally interventive approach to any necessary operative intervention”.4

Minimally invasive dentistry is not only restricted to the management of caries. The concept can be used in various dental applications such as the treatment of periodontal conditions, wear of teeth through erosion and attrition and management of chronic oral mucosal diseases such as xerostomia.

The patient is very much involved in this type of approach to preserve and maintain their dentition and oral health. The patient takes responsibility for the daily care of their mouth and to control and prevent the risk of developing disease or progression of existing disease to the best of their ability. To do this, patients must have a good understanding of the disease process and know what to do to maintain good oral health and should be consistently motivated by members of the dental team.

(REWORD FULLY)Minimal intervention suggests remineralisation of any enamel margin that is not yet cavitated as well as remineralisation of the lesion floor to avoid irritation of the pulp. Demineralised enamel around the margin of the lesion will be restored during the stabilisation phase of treatment aimed at elimination of the disease through application of fluoride. The floor of the lesion will be remineralised through the placement of a glass-ionomer cement for the restoration and this, at the same time will seal the margins against microleakage.14

The minimally invasive approach has been described by Tyas and co-workers as follows:

Early caries diagnosis

The classification of caries depth and progression using radiographs

An assessment of individual caries risk

Reduction in cariogenic bacteria, in order to decrease the risk of further demineralisation

The arresting of active lesions

The remineralisation and monitoring of non-cavitated arrested lesions

The placement of restorations with minimal cavity designs

Repair rather than replacement of defective restorations

Assessment of disease management outcomes at regular intervals13

Patient Motivation (CUT & EDIT COMPLETELYYYYYY)

Preventive care is the foundation for minimally invasive dentistry.

Preventive care is an essential factor of the minimal invasion technique, but is reliant on the patient carrying out effective oral hygiene techniques. The motivation for this is most likely to stem from educating the patient about the carious process so that they understand the importance of maintaining good oral health. The most active method of doing this is likely to be actual demonstration of the carious process to patients as such stimulation is likely to show them the full effects, and encourage them to take part in preventive care on their own. An important factor to take into account is that each patient will have a different caries risk and assessment of this risk is necessary before treatment can take place. Caries risk is much more significant if there has been previous history of caries risk. In fact the best way of addressing treatment, in my opinion is to use the risk score assessment method, treatment by this method ensures that management of the disease is specialist to the patient, so that the results are the most successful. A risk score is worked out and used to manage the disease in a specialised way based on the individual patient. Several different caries treatment techniques will be discussed.

Firstly, Caries Management by Risk Assessment (CAMBRA), developed by Featherstone in university of San Francisco, ‘This tool provides not only the assessment mechanism but also a set of interventions tailored to the disease level predicted.’- haven’t changed words around!!

Secondly, the technique of DIAGNOdent is lesion specific and detect lesions Some types of caries detection tools are lesion-specific and detect lesions at their earliest stages.

DIAGNOdent is very useful in detecting demineralisation on certain surfaces, particularly the occlusal surfaces of teeth.

Prevention stems from patient motivation to carry out effective oral hygiene techniques at home and maintain good oral health.

Educating patients about dental caries in addition to talking about cavities is an important factor in motivating the patient as when they have a better understanding of the carious process they are more inclined to maintain good oral health to prevent such disease.

The ability to demonstrate the caries process to patients might be the best motivational tool.

If patients could see the process actually happening before cavitation occurs, they might be more likely to practice appropriate oral hygiene methods at home.

It is first necessary to assess the patient’s caries risk.

One of the most important predictors of caries risk is the history of caries.

Featherstone and colleagues at the University of California, San Francisco have developed and tested a caries assessment tool called. This tool provides not only the assessment mechanism but also a set of interventions tailored to the disease level predicted.

Some types of caries detection tools are lesion-specific and detect lesions at their earliest stages.

DIAGNOdent is very useful in detecting demineralisation on certain surfaces, particularly the occlusal surfaces of teeth.

DIFOTI which stands for “digital imaging fibre optic transillumination” uses visable light between and through the teeth to see shadows that might be indicative of caries or other defects in the tooth structure.

Quantitative light-induced fluorescence (QLF) scans the entire surface of the tooth and detects caries lesions at their earliest phases. By superimposing the lesion at two separate stages, it can assess the status of remineralisation. This is an example of psychological effect of caries management by risk assessment and early detection.

A technology such as QLF allows the patient and practitioner to work together to achieve remineralisation. This empowers the patient and shows them the important of their role combined with professional recommendations in reversing the process before its cavitation stage. (Motivation is key hence patient more likely to follow and successful outcome).

An increase in patient awareness of treating disease has developed a new kind of dentistry.

Only at such an early stage can the patients’ focus shift from restorative dentistry to disease management.15

GV Black’s Approach(REWORD & REARRANGE ORDER)

In 1895, G.V Black introduced the concept of ‘extension for prevention’. The principle of extension for prevention is that not only must the lesion be included in the outline, but any adjacent areas not at present carious but likely to do so in the near future should also be included to reduce the risk of subsequent carious recurrence near the cavity margin.

The principles of cavity design, as described by G.V. Black underpinned operative dentistry for almost a century. As a consequence of adhesive techniques and new understanding of carious process, Black’s principles have been revisited. Eg: Black’s concept of ‘extension for prevention’ has been replaced by ‘prevention of extention’.17

The preparation of a retentive lock or key in the occlusal aspect of posterior teeth in order to prevent displacement of non-adhesive amalgam restorations result in substantial loss of tooth structure, weakening the tooth.

The purely surgical approach to caries control as taught by Black is now recognised as being too invasive and destructive. It is inefficient as it does not eliminate the cause of the disease and also leads to a continuing process of replacement dentistry, enlarging the cavity further. The restoration is subjected to an increasingly heavy load and the tooth gets weaker.

The cavity designs proposed by Black required geometric precision with sharp line angles, flat floors and removal of all signs of demineralised tooth structure.

The fundamental problem with Black’s classification is that it proposes a cavity design regardless of the size and extent of the lesion. Therefore, there will be a standard amount of tooth structure removed whether it is involved with the disease or not. This results in the cavity preparation being larger that it needs to be. Also extension for prevention increases the areas for access of microbes, resulting in even more tooth structure being removed to remove the secondary caries.18

New Cavity Classification

The concept of minimal intervention cavity designs is now being used as a replacement to the traditional Black’s classification. The new classification will identify both the position of a lesion on the exposed crown of a tooth and the extent to which it has progressed. It is not needed to specify a particular design for the cavity that needs to be prepared.

(Table 1: Mount GJ, 2009)

The above table shows a new cavity classification that has been developed by Graham Mount which takes into account the changes in caries activity so is classified by size as well as site:

Site 1 lesions are similar to pit and fissure class I restorations and other defects on smooth enamel surfaces.

Site 2 lesions are those at contact areas between any pair of teeth.

Site 3 lesions are those originating close to the gingival margin including exposed root surfaces. 13, 14

As the size of the lesion extends so does the complexity of the restoration. The sizes that can be identified are as follows:

Size 0 – the initial lesion at any site that has not yet had surface cavitation so may be possible to heal it.

Size 1 – the smallest minimal lesion requiring operative intervention.

Size 2 – a moderate sized cavity. There is still adequate sound tooth structure to maintain integrity of the remaining crown.

Size 3 – cavity needs to be modified and enlarged to provide some protection for the remaining crown from the occlusal load.

Size 4 – cavity is now extensive following loss of a cusp from a posterior tooth or an incisial edge from an anterior.14

Cavity preparation

One of the most important aims of minimally invasive techniques is to preserve as much sound tissue as possible. The smaller the cavity preparation, the better the performance of the restoration placed within it.

It is important to excavate only the irreparable, diseased enamel and dentine, keeping the cavity as small as possible. The cavity walls have to be modified in order to restore the cavities with a suitable adhesive material that can strengthen and support the remaining tooth structure, promote remineralisation and ideally have antibacterial activity. Any remaining bacteria need to be sealed off so that their nutrient supply is cut off and the carious process is arrested.

When carrying out the stages of caries removal, it is imperative to follow a minimally invasive approach, and for this to be successful a good knowledge of the chemistry and handling of dental materials is essential. There are many different approaches for proximal cavity preparation, with focus on preserving as much tooth substance as possible.5 Several techniques will be discussed as followed.

Sonic Techniques

The sonic oscillating, SONICflex system is used in minimally interventive occlusoproximal preparations. It was developed to cut small proximal cavities and used a high frequent oscillating preparation instruments in an air-driven oscillating handpiece. Damage to adjacent teeth is minimised by the use of safe-sided diamond coated, round ended preparation tips. SONICflex can be used in situations where access is difficult, such as proximal sections. The SONICflex PrepGold and SONICflex PrepCeram instruments are designed for minimally interventive gold and ceramic inlay preparations.

Figure 1 – preparation with SONICflex Prep Ceram (Wilson NHF, 2007)

Figure 2 – Preparation with SONICflex Prep Gold (Wilson NHF, 2007)

Sonic instrumentation allows proximal beveling with limited risk of damage to the adjacent tooth surfaces.4

Air Abrasion & Bioactive Glasses

The air abrasion technology was developed by Dr Robert Black in 1945 and was successfully introduced in 1951 with the Airdent air abrasion unit by S.S. White. Air abrasion can be described as a pseudo-mechanical, non-rotary method of cutting hard dental tissue where the tooth surface is bombarded with high velocity desiccated abrasive particles, transferring kinetic energy to the tooth surface, which is micro-chipped away. (REWORD) Studies have shown that bonding of enamel and dentine surfaces that have been prepared with air abrasion are much better than those prepared with conventional carbide burs or acid etching.6

Air abrasion produces no heat, vibration, pressure, pain or noise and extent of hard tissue damage is far less than that accomplished using rotary instruments, therefore making air-abraded hard tissue surface more favourable to adhesive bonding.

It works by using a stream of aluminium oxide particles produced from compressed air. The abrasive particles strike the tooth with high velocity and removes a small amount of the tooth structure. Efficiency of removal is relative to the hardness of the tissue or material being removed and the operating parameters of the air abrasion device. (REWORD) A number of parameters such as air pressure, operating distance, powder flow rate, particle size, diameter of the nozzle tip and time of exposure vary the amount of hard tissue removal and depth of penetration. The safety for clinical use of alumina was supported by the fact that the particles are large enough to exceed the upper limit for respirable airborne pollutants.4

Air pressure usually varies from 40 to 160 psi and most common particle sizes are 27 or 50 micrometres in diameter. A high powder flow rate will allow more particles to abrade the tooth faster. Operating distances from the tooth range from 0.5 to 2 mm.

Applications of air abrasion include caries removal, removal of superficial enamel defects, detection of pits and fissures, removal of pit and fissure surface stain, preparation of tooth structure for the placement of composites and ceramics, surface preparations of abfractions and abrasions, removal of existing restorations and as an adjunct to the conventional handpiece bur.7

Air polishing is an alternative type of air abrasion that removes plaque and surface stains effectively by using sodium bicarbonate powder instead of alumina.

Advantages of air abrasion include majority of patients do not need local anaesthetic, discomfort can be managed by reducing air pressure and patients are less anxious with the sound of air abrasion compared to a turbine drill.

Air abrasion has a large number of indications but several contraindications are that it cannot be used to remove large amalgam restorations and is not efficient for removal of gross caries because it does not cut substances that are soft. It also produces a round cavity that is not suitable for preparations requiring sharp margins.13

Bioactive glass particles are recognised for their bone inductive properties and there is evidence that shows that bioglass particles can interact with dentine through the formation of a hydroxyl carbonate apatite layer which can provide an effective interactive seal. Bioglass particles can be used for extrinsic stain removal, desensitisation of exposed cervical dentine, removal of selective demineralised enamel and composite removal. They have the ability of discriminating incipient lesions from sound enamel, treating them selectively and minimally.

Chemomechanical Treatment

Chemomechanical treatment is a gel-based dentine caries removal system and remains the least interventive approach to the removal of carious dentine. Carisolv gel is used with this system and has the advantages of limiting the need for anesthesia, preserves dental tissues, reduces the use of rotary instruments and is effective in controlling patient anxiety.

Carisolv gel is applied into the cavity and subsequently the carious tissue is removed using specially designed hand instruments. The Carisolv hand instruments scrape away the material dissolved by the gel, hence preserving remineralisable layers of dentine and underlying sound dentine.

Carisolv gel consists of a 0.1% hypochlorite-based alkaline gel with amino acids. The mechanism of the gel is that it dissolves infected dentine that has undergone proteolytic breakdown of collagen, causing further collapse of the collagen network for easy removal with hand instruments. The gel has no detrimental effect on healthy, hard dental tissue.

Indications include the treatment of anxious patients, root caries and deep lesions of caries.4

Chemomechanical methods of caries removal is considered to be less painful compared to the use of rotary instruments.8 It is a well-accepted method by patients, despite the prolonged time taken to carry out the treatment. It is a self-limiting technique only removing infected dentine so it is not possible to cut away too much of the tooth structure.13

Polymer Cutting Instruments

Metal and diamond burs are not able to discriminate between infected and healthy dentine. Polymer instruments have been designed to differentiate between these two structures as it is able to remove softened dentine but cannot cut the hard, healthy dentine. These instruments have the potential to prepare selected cavities without the need for local anaesthesia.9

Sound enamel has a Knoop hardness of approximately 400 and for dentine is 70-90. Carious dentine has a much lower Knoop hardness between 0-30. This allows a cutting instrument with a Knoop hardness of around 50 to be developed, which is halfway between carious and sound dentine.

The polymer instrument remains largely intact when removing carious dentine but when it hits sound dentine, it is visably worn away therefore cannot remove or damage the sound dentine. This also means that it does not operatively expose vital odontoblasts and therefore has a limited capacity to cause pain and discomfort. Consequently, it may be possible to complete caries removal without having to use local anaesthesia.10

Stepwise Excavation & Atraumatic Restoration Technique (ART)

Stepwise excavation and ART are modern applications of the minimally invasive approach of managing deep cavitated carious lesions. Both techniques use simple hand instruments such as excavators to remove the necrotic caries-infected dentine and also some caries-affected dentine.5 The reasons for using hand instruments instead of electric rotating handpieces is that it requires minimal cavity preparation that conserves sound tooth tissues and cause less trauma to teeth. Also, the need for local anaesthesia is reduced as the patient will not have to endure as much pain.

The stepwise excavation technique involves at different intervals. Carious tissue was removed and a thin layer of calcium hydroxide was placed followed by a temporary restoration. The calcium hydroxide’s primary purpose is to act as a protective seal of exposed dentine surface. It is a strong alkali so stimulates secondary dentine formation in very deep cavities.

No final excavation is performed in the first visit. Re-entry and final excavation is made at a later date. There are several variations to the stepwise excavation technique such as Magnusson and Sundell placed a zinc oxide-eugenol cement temporary restoration and carried out the final excavation four to six weeks later. In 1962, Law and Lewis placed calcium hydroxide and an amalgam restoration and re-entry was made six months later. More recently developed ART techniques restore the cavity with chemically adhesive GIC which forms a better seal, instead of the traditional amalgam and also releases fluoride which prevents and arrests caries.5

When the restoration is removed, arrested caries-affected dentine which is darker and harder is exposed and tertiary dentine is also deposited.

In the excavation procedure, all the undermining enamel has to be removed to allow easy access to the carious dentine along the enamel-dentine junction. 1 mm of carious dentine is left behind on the pulpal wall and re-entry takes place after a year and the final excavation is carried out.

By removing infected dental tissue in deep cavities, excavation is at a very close level to the pulp. By using the stepwise excavation, pulpal exposure is avoided and any pulpal complications are minimised.11

(Figure 3: Bjorndal L, 2008)

Figure 3 show the less invasive stepwise excavation procedure. The red zones indicate where plaque is found. A closed lesion environment before first excacation (a) and after (b) followed by application of calcium hydroxide material and a provisional restoration(c). During the treatment interval the demineralized dentine has clinically changed into signs of slow lesion progress, seen by a darker demineralized dentin (d). After final excavation (e) the permanent restoration is made (f).11

Restorative Materials

At present there are several restorative materials that are compatible with a minimal interventive philosophy such as resin composites, giomers, ormocers, compomers, resin-modified and traditional glass-ionomer cements. The use of adhesive techniques such as resin composites removes the need of occlusal keys and undercuts, therefore conserving more tooth substance.13

Amalgam (REWORD)

Amalgam is one of the oldest direct restorative materials still in use. It is an alloy of several metals including silver, tin, copper, zinc and a small amount of mercury. Amalgam is not compatible with the minimal intervention philosophy despite its proven durability. It requires an undercut to retain the restoration macro-mechanically; hence more tooth structure is removed or damaged, ultimately weakening the remaining tissue. Consequently amalgam is not recommended for the initial management of lesions of caries and where a minimally interventive approach is indicated.(REWORD)

It is possible for the amalgam to be bonded to teeth with dentine adhesive systems, reducing the need for undercuts. These are called bonded amalgam restorations.

Modern techniques for cavity preparation such as air abrasion are not well suited for the removal of amalgam and there is concern for the levels of mercury released when amalgam is abraded. Air abrasion of amalgam for one minute released mercury vapour four times in excess of the OSHA standard.12

Resin Composites (REWORD COMPLETELY)

Resin composites are glass filler particles in a resin matrix. Composites for anterior and posterior teeth require different properties. Materials with a higher filler: resin ratio are recommended for posterior restorations, whereas materials with more resin matrix are used for anterior restorations. This is because materials with a higher filler: resin ratio tend to be stronger, more wear resistant and shrink less when cured. A high concentration of filler particles makes the material more opaque and is more difficult to finish. On the other hand, materials with a higher filler: resin particle ratios are more easily finished and translucent so better suited for anterior teeth restorations. However they shrink more when cured.

All resin systems contract on curing. The concept of ‘soft-start’ polymerisation has been shown to produce better marginal adaptation which may lead to reduced interfacial leakage. Also the net overall shrinkage is less.

Composite restorative materials follow the minimally invasive concept as they can be used in conjunction with a dental adhesive system with minimal tooth preparation. Another advantage is that light-curing provides command cure which allows for immediate finishing and polishing. The restoration, if placed correctly in suitably prepared teeth, seals the tooth restorative interface, reducing interfacial leakage. It is possible to add material to cured increments, which allows for incremental build-up and further additions at a later date.

Disadvantages include shrinkage typically 2-3% which can disrupt the marginal adaptation of the restoration. Bonding to dentine still remains problematic and water absorption with surface and marginal staining may occur after some years.

Flowable composites are used in the repair of marginal defects in restorations and as a liner. They have a low filler: resin ratio and suffer relatively large percentage shrinkage when they are cured, but have the advantage of easy of adaptation to preparations.

Compomers

Compomers are made predominately from resin composite with the addition of a polyacid-modified molecule, which makes the material more hydrophilic. Compomers are initially light-cured, but subsequently absorb water, allowing for an acid-base reaction to set the polyacid-modified molecule.

Initially the material shrinks due to polymerisation contraction but expands subsequently as water is absorbed. Compomers are easy to handle and release fluoride. they are resin-made so a dentine bonding agent is required. Properties are similar to composites but wear and fracture resistance are less than for composite.

Glass-Ionomer Cements (GICs) and resin-modifed GIC (RMGICs)

GICs are used for cervical restorations, fissure sealants and proximal lesions in anterior teeth. RMGICs are indicated for bonded-base restorations, temporary restorations especially between appointments in endodontic therapy. They are also used in high caries risk patients and atraumatic restoration treatments. GICs not indicated for definitive restorations in adult dentitions expect for the treatment of root caries.

The advantages include self-adhesion to the tooth tissue through bio reacting with the tooth surface and the release of fluoride and other ions. They perform well in low-stress areas. It can also be rechargeable, therefore taking up fluoride from the environment.20

The disadvantages of GICs include poor fracture strength and wear rates. They are also quite difficult to handle but this can be overcome by adding resin to create resin-modified glass ionomer cements which is easier to place and has improved aesthetics. Traditional GICs are more opaque and less aesthetic than RMGICs and also cause more marginal chipping. Exogenous stain build-up is common with traditional GICs.20

Giomers

Giomers are a relatively new type of restorative material. The name ‘giomer’ is a hybrid of the words ‘glass ionomer’ and ‘composite’. They have properties of both glass ionomers such as fluoride release and recharge, and of resin composites such as aesthetics and biocompatibility. Therefore the material combines advantages of both materials. The material is composed of prereacted glass-ionomer particles within a resin matrix.

Ormocers

Ormocer stands for Organically Modified Ceramic. It is a three dimensionally cross-linked copolymer. Their chemistry is based on a polyvinylsiloxane backbone. Ormocers are fully polymerised materials. Ormocers undergoes 1.97% volume shrinkage which is lowest value recorded so far for a resin based filling material.

Due to their cross-linking and chemical nature, Ormocers ensure that it is a highly biocompatible filling material. Their advantages compared to conventional composites are outstanding biocompatibility, minimal shrinkage, resistance to masticatory loading and aesthetics resembling natural teeth.

Examples of minimally invasive procedures

Sealants

A Dental sealant is a thin protective covering made of resin that is applied to the chewing surfaces of posterior teeth to prevent the formation of cavities. It is a primary preventive procedure. If the sealant is placed properly it does not require any cutting of the tooth structure. Placement of sealants in suspect teeth within six months of tooth eruption can be very effective in preventing the need for restorations in the future.16

Ceramic Inlays & Onlays

Inlays and onlays can be easily placed, predictable, long-lasting and minimally invasive. They preserve a large amount of tooth structure compared to crowns. It is possible to save tooth structure by doing inlay-supported bridges instead of full coverage bridges which often fail since decay occurs along the margins of the crown. An inlay reduces the chances of this occurring.19

Veneers

Veneers are very thin tooth coloured material made of either porcelain, ceramic or composite bonding material. They are used to treat stained, discoloured, damaged or crooked teeth. Veneers are a less invasive method compared to crowns which are considered very invasive as a lot of tooth structure has to removed for their placement.

Porcelain veneers are stronger and more durable than composite veneers. Also composite veneers are more prone to staining and do not last as long and require regular replacement. However, they are cheaper than porcelain veneers and are less destructive to the tooth and can be placed directly on the tooth in one visit. Porcelain veneers need the tooth reshaping therefore removing more tooth structure and being more invasive.