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Barium in teeth advances study of weaning among Neanderthals, early humans

By Peter Reuell

Harvard Staff Writer

Monday, June 3, 2013

Image by Ian Harrowell, Christine Austin, and Manish Arora

Molar tooth model with the cut face showing color-coded barium patterns merging with a microscopic map of growth lines, which have been accentuated to reflect their ringlike nature.

Did a shift in the way infants were weaned give early humans an evolutionary advantage over their Neanderthal cousins? Scientists have long speculated that a change to earlier weaning played a key role in human development, but they have been stymied in efforts to prove such theories by the lack of an accurate record for comparing weaning ages in both species.

Now, Harvard scientists say they’ve discovered such a record, and that it was right in front of researchers all along — in teeth.

Tanya Smith, an associate professor of human evolutionary biology, and Katie Hinde, an assistant professor of human evolutionary biology, worked with colleagues at the Icahn School of Medicine at Mount Sinai in New York and Westmead Hospital in Australia to demonstrate that the levels of barium in teeth correspond with increases in breast-feeding, and fall as infants are weaned. Importantly, the researchers say, the barium levels survive in fossils that are thousands of years old, meaning the test can show how breast-feeding behavior changed among Neanderthals and early humans. The work was described in a paper published May 22 in Nature.

“There’s an ongoing debate about whether Neanderthal and contemporary Homo sapiens would have practiced different behaviors in terms of their breast-feeding,” Smith said. “People have speculated that an early weaning process in modern humans may have been part of their evolutionary advantage. We don’t have the data to answer that question yet, but we now have the method to be able to start collecting that data.

“It’s clear that there are developmental differences between Neanderthals and modern humans — we’ve amassed good evidence for that in the fossil record,” she continued. “What we haven’t been able to do is make a direct comparison using a biomarker like first reproduction age, or life span, or weaning age. That’s why this is so exciting, because now we can get at one of these ‘life history’ variables directly.”

To get at weaning age, researchers took advantage of the unique way teeth grow.

Like trees, teeth grow in regular layers that are created as various minerals — such as calcium — oxygen, and small amounts of metals are deposited in tooth enamel and dentine. Using sophisticated analytical chemistry and microscopic records of daily growth, researchers were able to show that while barium levels in teeth are initially low because very little of the metal passes through the placenta, levels increase dramatically as breast-feeding begins, then fall off as infants begin to supplement their diet with other foods.

To show that barium levels correlate with breast-feeding, researchers first analyzed data from humans and monkeys who had known dietary histories.

As part of a study conducted by the University of California at Berkeley’s Center for the Health Assessment of Mothers and Children of Salinas, participants provided naturally shed baby teeth along with precise records of infant diet, including the duration of breast-feeding and timing of formula introduction. Macaque teeth, milk, and dietary histories were provided through a long-term lactation study conducted by Harvard’s Comparative Lactation Lab and the California National Primate Research Center. Researchers also analyzed the first molar tooth of a juvenile Neanderthal from Belgium to assess weaning patterns in a Middle Paleolithic hominin.

“We can see when the barium shows up in the tooth after birth, and we see it increase over time, because an infant will take more milk as they get bigger and more active, and then you see it drop off in this beautiful, inverted U-shaped function,” Hinde said. “This is a game-changer in many ways, because this will allow us to go to museum collections and look at this as a proxy for how much milk different infants got from their mothers and what their weaning process was like. We can now look at that within species, but we can also look at that among species.  That will tell us about the evolution of how mothers invest in their young.”

The potential for important insights doesn’t end there.

“There’s also a human health component to this,” Smith said. “People intuitively understand that breast-feeding is important for normal development. We can use this data to study the breast-feeding histories of adults and that could predict later health outcomes.”

Perhaps most importantly, she said, the technique will allow scientists to begin to answer questions of how changes in lifestyle may have contributed to modern humans’ evolutionary advantage over Neanderthals.

“This can give us a window into one aspect of life that may have separated modern humans from Neanderthals,” she said. “This topic has been debated for a long time in the scientific community. What does it mean that human and Neanderthal cranial development was different? What does it mean that their dental development was different? We haven’t been able to get at these questions in the fossil record, but now we can actually get at a real developmental benchmark. That’s why this is so exciting.”

We all need some sun exposure; it's our primary source of vitamin D, which helps us absorb calcium for stronger, healthier bones. But it doesn't take much time in the sun for most people to get the vitamin D they need, and repeated unprotected exposure to the sun's ultraviolet rays can cause skin damage, eye damage, immune system suppression, and skin cancer. Even people in their twenties can develop skin cancer.

 Most kids rack up a lot of their lifetime sun exposure before age 18, so it's important that parents teach their children how to enjoy fun in the sun safely. With the right precautions, you can greatly reduce your child's chance of developing skin cancer.

 Facts About Sun Exposure

 The sun radiates light to the earth, and part of that light consists of invisible ultraviolet (UV) rays. When these rays reach the skin, they cause tanning, burning, and other skin damage.

 Sunlight contains three types of ultraviolet rays: UVA, UVB, and UVC.

1.UVA rays cause skin aging and wrinkling and contribute to skin cancer, such as melanoma. Because UVA rays pass effortlessly through the ozone layer (the protective layer of atmosphere, or shield, surrounding the earth), they make up the majority of our sun exposure. Beware of tanning beds because they use UVA rays as well as UVB rays. A UVA tan does not help protect the skin from further sun damage; it merely produces color and a false sense of protection from the sun.

2.UVB rays are also dangerous, causing sunburns, cataracts (clouding of the eye lens), and effects on the immune system. They also contribute to skin cancer. Melanoma, the most dangerous form of skin cancer, is thought to be associated with severe UVB sunburns that occur before the age of 20. Most UVB rays are absorbed by the ozone layer, but enough of these rays pass through to cause serious damage.

3.UVC rays are the most dangerous, but fortunately, these rays are blocked by the ozone layer and don't reach the earth.

 What's important is to protect your family from exposure to UVA and UVB, the rays that cause skin damage.

 Melanin: The Body's First Line of Defense

 UV rays react with a chemical called melanin that's found in skin. Melanin is the first defense against the sun because it absorbs dangerous UV rays before they do serious skin damage. Melanin is found in different concentrations and colors, resulting in different skin colors. The lighter someone's natural skin color, the less melanin it has to absorb UV rays and protect itself. The darker a person's natural skin color, the more melanin it has to protect itself. (But both dark- and light-skinned kids need protection from UV rays because any tanning or burning causes skin damage.)

 Also, anyone with a fair complexion — lighter skin and eye color — is more likely to have freckles because there's less melanin in the skin. Although freckles are harmless, being outside in the sun may help cause them or make them darker.

 As the melanin increases in response to sun exposure, the skin tans. But even that "healthy" tan may be a sign of sun damage. The risk of damage increases with the amount and intensity of exposure. Those who are chronically exposed to the sun, such as farmers, boaters, and sunbathers, are at much greater risk. A sunburn develops when the amount of UV exposure is greater than what can be protected against by the skin's melanin.

 Unprotected sun exposure is even more dangerous for kids with:

•moles on their skin (or whose parents have a tendency to develop moles)

•very fair skin and hair

•a family history of skin cancer, including melanoma

 You should be especially careful about sun protection if your child has one or more of these high-risk characteristics.

 Also, not all sunlight is "equal" in UV concentration. The intensity of the sun's rays depends upon the time of year, as well as the altitude and latitude of your location. UV rays are strongest during summer. Remember that the timing of this season varies by location; if you travel to a foreign country during its summer season, you'll need to pack the strongest sun protection you can find.

 Extra protection is also required near the equator, where the sun is strongest, and at high altitudes, where the air and cloud cover are thinner, allowing more damaging UV rays to get through the atmosphere. Even during winter months, if your family goes skiing in the mountains, be sure to apply plenty of sunscreen; UV rays reflect off both snow and water, increasing the probability of sunburn.

 With the right precautions, kids can safely play in the sun. Here are the most effective strategies:

 Avoid the Strongest Rays of the Day

 First, seek shade when the sun is at its highest overhead and therefore strongest (usually 10 a.m. until 4 p.m. in the northern hemisphere). If kids must be in the sun between these hours, be sure to apply and reapply protective sunscreen — even if they're just playing in the backyard. Most sun damage occurs as a result of incidental exposure during day-to-day activities, not at the beach.

 Even on cloudy, cool, or overcast days, UV rays travel through the clouds and reflect off sand, water, and even concrete. Clouds and pollution don't filter out UV rays, and they can give a false sense of protection. This "invisible sun" can cause unexpected sunburn and skin damage. Often, kids are unaware that they're developing a sunburn on cooler or windy days because the temperature or breeze keeps skin feeling cool on the surface.

 Make sure your kids don't use tanning beds at any time, even to "prepare" for a trip to a warm climate. Both UVA and UVA/UVB tanning beds produce sunburn. And there is an increase in the risk of melanoma in people who have used tanning beds before the age of 35.

 Cover Up

 One of the best ways to protect your family from the sun is to cover up and shield skin from UV rays. Ensure that clothes will screen out harmful UV rays by placing your hand inside the garments and making sure you can't see it through them.

 Because infants have thinner skin and underdeveloped melanin, their skin burns more easily than that of older kids. But sunscreen should not be applied to babies under 6 months of age, so they absolutely must be kept out of the sun whenever possible. If your infant must be in the sun, dress him or her in clothing that covers the body, including hats with wide brims to shadow the face. Use an umbrella to create shade.

 Even older kids need to escape the sun. For all-day outdoor affairs, bring along a wide umbrella or a pop-up tent to play in. If it's not too hot outside and won't make kids even more uncomfortable, have them wear light long-sleeved shirts and/or long pants. Before heading to the beach or park, call ahead to find out if certain areas offer rentals of umbrellas, tents, and other sun-protective gear.

 Use Sunscreen Consistently

 Lots of good sunscreens are available for kids, including formulations for sensitive skin, brands with fun scents like watermelon, long-lasting waterproof and sweat-proof versions, and easy-application varieties in spray bottles.

 What matters most in a sunscreen is the degree of protection from UV rays it provides. When faced with the overwhelming sea of sunscreen choices at drugstores, concentrate on the SPF (sun protection factor) numbers on the labels.

 For kids age 6 months and older, select an SPF of 30 or higher to prevent both sunburn and tanning. Choose a sunscreen that states on the label that it protects against both UVA and UVB rays (referred to as "broad-spectrum" sunscreen). In general, sunscreens provide better protections against UVB rays than UVA rays, making signs of skin aging a risk even with consistent use of sunscreen. To avoid possible skin allergy, don't use sunscreens with PABA; if your child has sensitive skin, look for a product with the active ingredient titanium dioxide (a chemical-free block).

 To get a tanned appearance, teens might try self-tanning lotions. These offer an alternative to ultraviolet exposure, but only minimal (or no) protection from UV light.

 For sunscreen to do its job, it must be applied correctly. Be sure to:

•Apply sunscreen whenever kids will be in the sun.

•Apply sunscreen about 15 to 30 minutes before kids go outside so that a good layer of protection can form. Don't forget about lips, hands, ears, feet, shoulders, and behind the neck. Lift up bathing suit straps and apply sunscreen underneath them (in case the straps shift as a child moves).

•Don't try to stretch out a bottle of sunscreen; apply it generously.

•Reapply sunscreen often, approximately every 2 hours, as recommended by the American Academy of Dermatology. Reapply after a child has been sweating or swimming.

•Apply a waterproof sunscreen if kids will be around water or swimming. Water reflects and intensifies the sun's rays, so kids need protection that lasts. Waterproof sunscreens may last up to 80 minutes in the water, and some are also sweat- and rub-proof. But regardless of the waterproof label, be sure to reapply sunscreen when kids come out of the water.

 Keep in mind that every child needs extra sun protection. The American Academy of Dermatology recommends that all kids — regardless of their skin tone — wear sunscreen with an SPF of 30 or higher. Although dark skin has more protective melanin and tans more easily than it burns, remember that tanning is also a sign of sun damage. Dark-skinned kids also can develop painful sunburns.

 Use Protective Eyewear for Kids

 Sun exposure damages the eyes as well as the skin. Even 1 day in the sun can result in a burned cornea (the outermost, clear membrane layer of the eye). Cumulative exposure can lead to cataracts (clouding of the eye lens, which leads to blurred vision) later in life. The best way to protect eyes is to wear sunglasses.

 Not all sunglasses provide the same level of ultraviolet protection; darkened plastic or glass lenses without special UV filters just trick the eyes into a false sense of safety. Purchase sunglasses with labels ensuring that they provide 100% UV protection.

 But not all kids enjoy wearing sunglasses, especially the first few times. To encourage them to wear them, let kids select a style they like — many manufacturers make fun, multicolored frames or ones embossed with cartoon characters. And don't forget that kids want to be like grown-ups. If you wear sunglasses regularly, your kids may be willing to follow your example. Providing sunglasses early in childhood will encourage the habit of wearing them in the future.

 Double-Check Medications

 Some medications increase the skin's sensitivity to UV rays. As a result, even kids with skin that tends not to burn easily can develop a severe sunburn in just minutes when taking certain medications. Fair-skinned kids, of course, are even more vulnerable.

 Ask your doctor or pharmacist if any prescription (especially antibiotics and acne medications) and over-the-counter medications your child is taking can increase sun sensitivity. If so, always take extra sun precautions. The best protection is simply covering up or staying indoors; even sunscreen can't always protect skin from sun sensitivity caused by medications.

 If Your Child Gets a Sunburn

 A sunburn can sneak up on kids, especially after a long day at the beach or park. Often, they seem fine during the day but then gradually develop an "after-burn" later that evening that can be painful and hot and even make them feel sick.

 When kids get sunburned, they usually experience pain and a sensation of heat — symptoms that tend to become more severe several hours after sun exposure. Some also develop chills. Because the sun has dried their skin, it can become itchy and tight. Sunburned skin begins to peel about a week after the sunburn. Encourage your child not to scratch or peel off loose skin because skin underneath the sunburn is vulnerable to infection.

 If your child does get a sunburn, these tips may help:

•Have your child take a cool (not cold) bath, or gently apply cool, wet compresses to the skin to help alleviate pain and heat.

•To ease discomfort, apply pure aloe vera gel (available in most pharmacies) to any sunburned areas.

•Give your child an anti-inflammatory medication like ibuprofen or use acetaminophen to lessen the pain and itching. (Do not, however, give aspirin to children or teens.) Over-the-counter diphenhydramine may also help reduce itching and swelling.

•Apply topical moisturizing cream to rehydrate the skin and treat itching. For the more seriously sunburned areas, apply a thin layer of 1% hydrocortisone cream to help with pain. (Do not use petroleum-based products, because they prevent excess heat and sweat from escaping. Also, avoid first-aid products that contain benzocaine, which may cause skin irritation or allergy.)

 If the sunburn is severe and blisters develop, call your doctor. Until you can see your doctor, tell your child not to scratch, pop, or squeeze the blisters, which can become easily infected and can result in scarring. Keep your child in the shade until the sunburn is healed. Any additional sun exposure will only increase the severity of the burn and increase pain.

 Be Sun Safe Yourself

 Don't forget: Be a good role model by consistently wearing sunscreen with SPF 30 or greater, using sunglasses, and limiting your time in the sun. These preventive behaviors not only reduce your risk of sun damage, but teach your kids good sun sense.

 Reviewed by: Kate M. Cronan, MD

 Date reviewed: August 2010

 Note: All information on KidsHealth® is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor.

 © 1995-2013 The Nemours Foundation. All rights reserved.

 By John S. Casko, DDS, MS, PhD Based on: Zachrisson BU, Nyogaard L, Mobarak K. Dental Health Assesed More Than 10 Years After Interproximal Enamel Reduction of Mandibular Anterior Teeth. Am J Orthodontics Dentofacial Orhtop 2007; 131 (Feburary): 162-169 

When you have patients with crowded mandibular anterior teeth, do you sometimes use interproximal reduction or enamel stripping to resolve the crowding and avoid extractions? I suspect many orthodontists do. If you do use interproximal stripping or enamel reduction, what are the long term dental and periodontal effects of using this procedure? A recent study addresses this question.

Authors evaluated 61 patients who had undergone interproximal enamel reduction of the mandibular anterior teeth an average of 12.5 years after treatment. The procedure for enamel reduction used at the time these patients were treated consisted of reducing the interproximal enamel with fine- or medium- grit, safe sided diamond disk at mdium speed with the contra- angle handpiece. Air-cooling was usd during the procedure. Polishing after stripping with a diamond disk was done with fine sand disks. Topical fluoride agents were not applied to the ground tooth surfaces, but all patients were routinely instructed to use diluted sodium fluoride mouth rinses once daily. Sixteen dental students were used as a control group to compare the long-term dental and periodontal results of stripping.

The results of this study were very encouraging. No new carious lesions were detected. Premature adults had some minor labial gingival recession. There was no evidence of root pathology, and 59 of 61 patients reported no increased sensitivity due to temperature variations. Additionally, the overall irregularity index at the long-term follow-up period was only 0.67.

I believe the results of this study provide great news particularly for the treatment of adult patients with full class II malocclusions and a large anteroposterior skeletal discrepancy. For these patients with the maxillary premolars extracted, it is necessary to attract the maxillary canines the entire width of the maxillary first premolar space. If the mandibular canines are retracted to any degree for instance after the extraction of mandibular first premolars, it then becomes necessary to retract the maxillary canines a greater distance than the full maxillary first premolar space, which creates an extremely difficult if not impossible treatment problem. Therefore, avoiding the retraction of the mandibular canines becomes an important goal of treatment. If the patient has small maxillary lateral incisors, this can often be accomplished by the extraction of one mandibular incisor.

However, if the patient does not have small maxillary lateral incisors and protrusion of the mandibular anterior teeth is not appropriate, interproximal reduction of the mandibular anterior teeth becomes the only alternative to avoid extracting mandibular premolars. It is, therefore, nice to know this procedure can be safely applied with no long-term negative dental or periodontal effects.

 

Take Home Pearl:

An association exists between static occlusion and dynamic occlusion in untreated subjects. Background:

During orthodontic finishing, orthodontists typically assess 2 aspects of a patient’s occlusion- static occlusion and dynamic occlusion. A goal for orthodontists is to achieve a Class I molar and canine relationship in static occlusion. It is typical that orthodontists are taught to achieve canine guidance in protrusive position. But, is there any association between static occlusion and dynamic occlusion? Objective:

To determine which type of dynamic occlusion is associated with which type of static occlusion. Design/Participants:

Descriptive analysis of 94 dental students between the ages of 21 and 30 years. Methods:

None of the subjects had received previous orthodontics treatment, and all subjects had a fully permanent dentition. Each of these subjects was classified initially with respect to their static occlusion (Class I, Class II, or Class III). Then, the subjects were asked to move their mandible 0.5 mm right and left to determine which teeth contacted. Then they moved 3 mm right and left to determine which teeth were in contact. Finally, they were asked to move their mandible anteriorly in order to determine which teeth contacted in protrusive position. Results:

The resuts of this study showed that, in static occlusion, 49 subjects had a Class I relationship, 27 subjects had a Class II relationship, and 18 subjects had a Class III occlusion. When the authors evaluated the dynamic occlusion approximately 24% had bilateral group function at 0.5 mm lateral guidance, and 18% had mixed canine guidance and group function. However, at the 3 mm position, the guidance pattern changed predominately to canine guidance. Fifty percent of subjects at that position had bilateral canine guidance. The authors compared the static and dynamic occlusion, and they found an association between Class I and bilateral canine protected occlusion at the 0.5 mm lateral excursion. However, at the 3 mm lateral guidance, only 50% of the Class I and 11% of the Class III subjects had bilateral canine protected occlusion. On the other hand, 70% of the subjects with Class II relationships had bilateral canine protected occlusion at 3 mm. Conclusions:

The authors conclude that there is an association between static occlusion and dynamic occlusion, and that at the 3 mm lateral excursion; bilateral canine protected occlusion was only predominant in subjects with a Class II relationship. Reviewer’s Comments:

subjects finish with a slight Class II molar and canine position, they do have better canine guidance in lateral occlusion.

This was an interesting comparison. Although we as orthodontists typically try to achieve a Class I relationship for our patients, often, if Reviewer:

Vincent G. Kokich, Sr, DDS, MSD